ANNUAL

REVIEWS Further
Quick links to online content

Ann.Rev. Pharmacol. Toxicol. 1986. 26:371-99

Copyright 1986 by Annual Reviews Inc. All rights reserved

COMPARATIVE TOXICOLOGY AND

by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

MECHANISM OF ACTION OF
POL YCHLORINATED
DIBENZO-P-DIOXINS AND
DIBENZOFURANS

S. H. Safe
Department of Physiology and Pharmacology, College of Veterinary Medicine, Texas
A&M University, College Station, Texas 77843

INTRODUCTION

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated di

benzofurans (PCDFs) are members of a chemical family (polyhalogenated
aromatics) that also includes the polychlorinated biphenyls, naphthalenes,
azobenzenes, and azoxybenzenes, and the polybrominated biphenyls. In con
trast to the polychlorinated biphenyls and naphthalenes and the polybrominated
biphenyls, the PCDDs and PCDFs are not primary industrial products. PCDFs
are found as by-products 1 ppm) in commercial polychlorinated biphenyls
and naphthalenes and are probably derived from dibenzofuran impurities in the
industrial hydrocarbons that are subsequently chlorinated ( 1 -3). There is also
circumstantial evidence that the effects of heat or arcing may produce PCDFs
from polychlorinated biphenyls during use (4). This is evidenced by the
relatively high levels of PCDFs (ca 100 ppm) detected in the polychlorinated
biphenyl-containing heat transfer fluids that were the toxic agents in the Yusho
disasters in Japan and Taiwan (3,5,6). PCDDs and PCDFs are also found as
impurities in chlorinated phenols and their derived products (3, 7, 8), and it is
apparent that the combustion of chlorinated aromatics and diverse types of
chemical, industrial, and municipal waste results in the formation and release of
these toxic chemicals into the environment (9-14). The potential for the

371
0362-1642/86/0415-0371$02.00
 372 SAFE

formation of PCDDs and PCDFs from nonindustrial sources, i.e. energy

derived combustion and forest fires, led to the "trace chemistries of fire"
hypothesis, which speculated that the origins of PCDDs and PCDFs in the
environment were nonanthropogenic ( 1 5 , 16). However, analysis of aquatic
sediment cores from the Saginaw River and Bay and from Lake Huron does not
support the trace chemistries of fire hypothesis ( 1 7 , 1 8). The PCDD and PCDF
congener composition of dated sediment cores demonstrates that the con
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

centrations of these compounds in sediments have greatly increased since the

Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

1 940s and that "this historical increase is similar to trends for the production,
use, and disposal of chlorinated organic compounds" (17, 1 8).
Human exposure to PCDDs and PCDFs has occurred via three major path
ways: occupational, accidental, and environmental. Industrial workers en
gaged in the manufacture or use of polychlorinated biphenyls, chlorinated
phenols, and their derived products are exposed to PCDDs and/or PCDFs in
combination with their associated major commercial product ( 1 9-21 ) . Acci
dents in which PCDDs have been released into the workplace or into the
environment (e. g. the Seveso accident in Italy) have also resulted in human
exposure to mixtures of the industrial chemicals and their PCDD/PCDF toxic
contaminants (22-24). The Yusho poisoning in Japan and Taiwan involved the
exposure of several thousand individuals to PCBs and their PCDF contaminants
(5 , 6, 25-27). The uptake of environmental residues of PCDDs and PCDFs into
higher trophic levels of the food chain is only now being investigated, and trace
levels (parts per trillion) have been detected in fish, wildlife, and human tissues
( 1 9 , 28-32). In common with accidental and industrial exposures to PCDDs
and PCDFs, exposure levels to these toxins represent only a small fraction of
the total bioavailable lipophilic environmental pollutants. 2 , 3,7 ,8-
Tetrachlorodibenzo-p-dioxin (TCDD) is the major by-product formed from
2,4,5-trichlorophenol and its derived products; this highly toxic compound has
been the focus of most biologic and toxic studies on the PCDDs. However, all
other human and environmental exposures to PCDDs and PCDFs involve a
complex mixture of isomers and congeners in combination with other chem
icals.
The scientific, regulatory, and media attention focused on PCDDs, PCDFs,
and particularly 2,3,7 ,8-TCDD has continued unabated; moreover, with the
recent identification of trace levels of these toxins in human tissue, domestic
animals, the environment, and toxic chemical waste dumpsites, the scientific
and societal concern about this class of compounds will no doubt continue. It is
apparent from the scientific literature that one member of this class of com
pounds, namely 2,3,7 ,8-TCDD , ranks with benzo[a]pyrene as one of the most
thoroughly studied toxins. Unfortunately, the biologic and toxic effects of the
remaining 74 PCDD and 1 35 PCDF congeners have not been thoroughly
 PCDDs AND PCDFs-SARs 373

investigated, and the interactive effects of these compounds or their activities in

combination with polychlorinated biphenyls and chlorinated phenols have also
not been addressed. This article (a) briefly reviews the species-dependent toxic
and biologic effects of PCDDs and PCDFs, (b) demonstrates the parallel modes
of action of PCDDs and PCDFs and endogenous cellular hormones, (c) summa
rizes the data that support the proposed receptor-mediated mechanism of
action, including the structure-activity relationships (SARs) that have been
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

developed for both PCDD and PCDF congeners, and (d) discusses the few
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

interactive studies published.

TOXIC AND BIOLOGIC EFFECTS OF PCDDs AND PCDFs

Several review articles (33-45) have summarized the toxic and biologic effects
elicited by PCDDs, PCDFs, and related toxic halogenated aryl hydrocarbons.
The toxic effects resulting from exposure to this group of chemicals are
dependent on a number of factors which include the dose of the toxin, and the
age, strain, species, and sex of the animals used. The complete spectrum of
toxicity is not usually observed in any single animal species; however, the
limited data available indicate that the toxic PCDDs, PCDFs, and related
compounds elicit the same qualitative pattern of responses within each species.
The differences in species susceptibility to this group of chemicals are illus
trated by the LDso values for 2,3,7,8-TCDD, which vary over 5000-fold (33,
34) from the highly sensitive guinea pig to the resistant hamster [LDsos (j.Lg/kg);
guinea pig (0.6--2.0), rat (22-45), chicken (25-50), monkey (70), rabbit (115),
dog ( l 00-200), mouse (114-284), bullfrog (> 1000), hamster (1157-5051)].
The quantitative differences in the toxicity of PCDF congeners have recently
been demonstrated (47) for a series of ten congeners (see structure-activity
section, below). The 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) EDso val
ues for thymic atrophy and body weight loss in the rat were 0.21 and 1.04
j.Lmol/kg; the 1,2,4,7,8-PeCDF isomer elicited the same toxic effects, but the
EDso values were 220 and 47 times higher, respectively (47). The toxic
responses observed in several animal species by PCDDs and PCDFs include
dermal toxicity, teratogenicity, reproductive problems, body weight loss,
hepatotoxicity, gastric lesions, lymphoid involution, immunotoxicity, and
carcinogenicity. The two most characteristic toxic effects observed in all
laboratory animals are lymphoid involution and/or immunotoxicity and body
weight loss. Chloracne and related dermal lesions are the most frequently noted
signs of PCDD and PCDF toxicosis in humans; dermal lesions are also observed
in rhesus monkeys, hairless mice, and rabbits that have been exposed to this
group of toxins. In contrast, rats, most strains of mice, guinea pigs, and
hamsters do not develop chloracne and related dermal toxic lesions after
 374 SAFE

r:'Y
Figure 1 Structure of the polychlorinated dibenzofurans and dibenzo-p-dioxins.
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

exposure to 2,3,7,8-TCDD. Poland & Knutson (38) have noted that many of
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

the observed toxic lesions are either hyperplastic/metaplastic or hypoplastic,

and primarily affect epithelial tissues. The mechanisms by which PCDDs and
PCDFs elicit this diverse group of species-dependent toxicities remain un
explained although several hypotheses have been advanced and are discussed in
this review.
PCDDs and PCDFs cause diverse biological responses in mammals and
mammalian cells in culture including the highly characteristic induction of
microsomal benzo[a]pyrene hydroxylase (aryl hydrocarbon hydroxylase,
AHH) and several related cytochrome P-450-dependent monooxygenases (37,
38, 44, 47-53). In the rat, these activities are associated with the preferential
induction of cytochrome P-450c, P-450d, and P-450a, with the former isozyme
responsible for most of the induced monooxygenase enzyme activities (54). In
the mouse, 2,3,7,8-TCDD induces cytochromes PI-450 and P3-450 (55-57),
and the former isozyme exhibits antigenic and enzymatic similarities with the
rat cytochrome P-450c (58). 2,3,7,8-TCDD induces two cytochrome P-450
isozymes (forms 4 and 6) in the rabbit, and their inducibility is highly tissue
specific (59, 60). 2,3,7,8-TCDD and related compounds also induce glu
tathione S-transferases (61) and glucuronosyl transferase (62, 63) and several
other enzymes including DT-diaphorase (64), ornithine decarboxylase (65),
8-aminolevulinic acid synthetase (48), epidermal transglutaminase (66),
and hepatic DNA polymerase B (67). Detailed summaries of these and
other biochemical effects of 2,3,7,8-TCDD have recently been reviewed
(38, 42).
The remarkably broad spectrum of biologic and toxic responses observed in
animals exposed to 2,3,7,8-TCDD and related toxic halogenated aromatics has
stimulated research on the mechanism or mechanisms of action of these chem
icals. Unlike many toxins, the most active halogenated aryl hydrocarbons do
not appear to require metabolic activation into presumed "toxic" intermediates
that alkylate specific cellular acceptors (e. g. DNA, RNA, and protein) or
initiate cellular lipoperoxidation. On the contrary, the most toxic halogenated
aryl hydrocarbons are highly resistant to oxidative metabolic degradation and
exhibit minimal metabolically mediated alkylation of cellular macromolecules
(68-70); moreover limited data suggest that PCDD and PCDF metabolites are
much less toxic than their parent hydrocarbons (71). Many of the effects of this
 PCDDs AND PCDFs-SARs 375

class of environmental toxins are comparable to those associated with modula

tion of several hormone-mediated responses. For example, there are many
similarities between animals that exhibit thyroid dysfunction and those treated
with toxic halogenated aryl hydrocarbons. Daily injections of the active thyroid
honnone, triiodothyronine (T 3) to male mice treated with a lethal dose (200
j.Lg/kg) of 2,3,7,8-TCDD did increase their mean surival times; however, all the
animals in the 2,3,7,8-TCDD and 2,3,7,8-TCDD + T3"treated groups died
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

(43). More recent studies (7 1 , 72) have demonstrated that thyroid hormones
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

may play a more important role in modulating the toxicity of 2,3,7,8-TCDD;

radiothyroidectomy protected rats against 2,3,7,8-TCDD-mediated T-cell im
munotoxicity (as measured by the spleen anti-SRBC plaque-forming cell
assay), mortality, and body weight loss (73). Like the glucocorticoids, PCDDs,
PCDFs, and related toxic halogenated aryl hydrocarbons cause lymphoid
involution (33,34,37,38,40,41,74,75), are teratogens in mice (76-&0),and
induce cytochrome P-450-dependent monooxygenases (37, 38, 44, 46-54).
However the mechanisms of action of glucocorticoids and 2,3,7,8-TCDD are
not directly linked since the latter compound is toxic to adrenalectomized rats,
does not bind to the glucocorticoid receptor, and does not induce tyrosine
aminotransferase (43) or the dexamethasone-induced cytochrome P-450 iso
zyme (8 1). Other adrenal steroids resemble the toxic halogenated aryl hydro
carbons since they also induce several hepatic drug-metabolizing enzymes,
including monooxygenases and glucuronosyl transferases (81-84).
It has been proposed that 2,3,7,8-TCDD and related toxic isostereomers, like
the steroid hormones, elicit their responses via the initial noncovalent interac
tion with a cytosolic receptor protein in target tissues (37, 38, 75). The
synthesis of radiolabelled eH]-2,3,7 ,8-TCDD with high specific activity (52 . 5
Cilmmol) resulted i n the identification o f a specific binding protein i n hepatic
cytosol of responsive C57BLl6J mice, whereas minimal binding activity was
observed in nonresponsive DBA/2J hepatic cytosol (85). The role of this Ah
receptor protein in the mechanism of action of toxic halogenated aryl hydrocar
bon has been thoroughly investigated and satisfies most of the specific criteria
that support a receptor mediated cellular process. These criteria include: (a) the
existence of a finite number of binding or receptor sites and therefore saturable
binding, (b) high affinity ligand binding that is commensurate with the usually
low levels of circulating hormones, (c) stereoselective binding capacity for the
receptor, (d) tissue or organ response specificity for the receptor ligand, and (e)
a correlation between binding affinities, receptor occupancy, and the magni
tude of the response. This review focuses on research that supports the role of
the Ah receptor in the mechanism of action of PCDDs and PCDFs and high
lights the detailed structure activity relationships (SARs) that have been de
veloped for this group of environmental and industrial toxins.
 376 SAFE

PCDD AND PCDF ACTIVITIES: EVIDENCE THAT

SUPPORTS THE ROLE OF THE CYTOSOLIC Ah
RECEPTOR PROTEIN
High Affinity Saturable Binfling
The saturable binding of [3H]-2, 3 , 7 ,8-TCDD with hepatic and extrahepatic
cytosolic receptor protein from several species has been demonstrated using the
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

following receptor assay procedures: charcoal/dextran absorption, protamine

Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

sulfate precipitation, hydroxylapatite absorption, isoelectric focusing in

polyacrylamide gels, gel permeation chromatography, sucrose density gradient
centrifugation, and gel permeation high performance liquid chromatography
(85-1 10). Scatchard plot analysis of [3H]-2,3 ,7,8-TCDD specific binding to
hepatic cytosolic receptor protin gives dissociation consants (Ko) that are
dependent on a number of factors including the animal species and strain, the
receptor binding assay used, and the age of the animal. The KD values for
responsive C57BLl6 mice and rats vary from 0. 27-3.0 nM (85, 95) and
0 . 1 3- 1 .2 nM (9 1 , 95 , 1 02), respectively, and the value for cynomolgus
monkeys was approximately 3 nM (108). The concentration of hepatic cytosol
ic receptor was also highly variable, but the upper limit for most studies was less
than 1 10 fmol/mg cytosolic protein (85, 9 1 , 95). One study demonstrated that
hepatic receptor levels in the rat varied with age and that these levels were
endocrine independent since hepatic receptor levels were virtually unaltered by
orchiectomy, ovariectomy, adrenalectomy, or hyposectomy ( 1 06). This
observation was consistent with the inactivity of several steroid hormones as
competitive ligands for this receptor protein (85 , 86, 89, 99 , 102).
Since certain polycyclic aromatic hydrocarbons resemble 2,3,7,8-TCDD in
their mode of induction of AHH and related cytochrome P-450 isozymes in
responsive strains of mice and mammalian cells in cultures, it is not surprising
that many of these compounds competitively displace [3H]-2,3,7,8-TCDD
from the receptor protein. Moreover, [3H]-3-methylcholanthrene, benzo[a]py
rene, and dibenzo[a,h]anthracene, three active AHH inducers, exhibit satur
able binding with the rat hepatic receptor protein and the ligand-receptor
complex sediments at 8-9 S under low ionic strength conditions using the
sucrose density gradient technique (97, 105). The radioactive binding peaks
were eliminated after competition with a 200-fold molar excess of 2 , 3 , 7 ,8-
TCDD. Similar results were also observed with responsive C57BLl6 mouse
hepatic cytosol. However, eH]-benzo[a]pyrene unexpectedly does not yield a
radiolabelled ligand-receptor binding peak that is eliminated after competition
with a 200-fold molar excess of unlabelled 2,3,7 ,8-TCDD.

Tissue/Organ, Strain, and Cell Culture Response Specificity

The 2,3,7,8-TCDD receptor levels in several organs and tissues in Sprague
Dawley rats, C57BLl6J and DBN2J mice have been reported (96, 103, 1 04,
 PCDDs AND PCDFs-SARs 377

106). The cytosolic Ah receptor concentrations (fmol/mg cytosolic protein) in

the C57BLl6J mice and Sprague-Dawley rat organs and tissues were: liver, 32
1.5 and 39 1.9; lung, 23 6.4 and 47 4.3; kidney, 10 0.4 and 1.2
0.9; intestine, 8 2.3 and 15 1. 7; thymus, 8 2.2 and 54 3.9 (The Ah
receptor was not detectable in the adrenals, heart, brain, skeletal muscle, and
testis). Although the Ah receptor was not detected in the cytosol of DBAl 2J
mice, 18 hr after administration of eH]-2,3,7,8-TCDD to these animals levels
of the receptor-ligand complex could be measured in nuclear protein extracts
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

from liver (5. 4 0.3 fmoVmg), lung (7.4 0.3 fmol/mg), and kidney (4.7
0.1 fmol/mg). The appearance of hepatic nuclear radiolabeled ligand-receptor
protein complexes and the elimination of this radioactivity by preinjection with
a large excess of unlabeled 2,3,7,8-TCDD has been reported by several groups
(89, 91, 96, 99, 102, 106); however, Mason & Okey (96) demonstrated that
lung, liver, and kidney nuclear Ah receptor levels were higher in the responsive
C57BLl6J mice than in the nonresponsive DBA/2J strain. This observation is
consistent with the fact that 2,3,7 ,8-TCDD and other toxic halogenated aryl
hydrocarbons elicit biologic and toxic responses in both strains of mice but at
different dose levels. Unfortunately there are insufficient data available to
correlate tissue/organ receptor levels with the magnitude of specific responses
in these target sites.
The criteria for receptor response specificity are supported by numerous
studies with genetically inbred responsive and nonresponsive strains of mice
and with some mammalian cells in culture. For example, there is an excellent
rank order correlation between the maximum AHH inducibility in several
inbred strains of mice and FI hybrids and the number of Ah receptor molecules
per liver cell (109). Nebert and co-workers have also shown a linear correlation
(r:= 0.99) between the amount of 2,3,7,8-TCDD-receptor complex appearing
in hepatic nuclei of C57BL/6 and DBAI2 mice and the percentage of maximally
induced cytochrome PI-450 mRNA (104). Hudson and co-workers have
demonstrated that for several human squamous cell carcinoma lines, the rela
tive amount of receptor measured in each cell line correlated well with the
7-ethoxycoumarin O-deethylase inducibility in these cells by 2,3,7,8-TCDD
(110).
These data that support the receptor-mediated response specificity are in
contrast to data in several other studies with animals and cell cultures. Hepatic
2,3,7,8-TCDD receptor levels in guinea pigs, rats, mice, hamsters, and nonhu
man primates vary less than tenfold (10-100 fmoVmg cytosolic protein) and
exhibit comparable KD values for [3H]-2,3,7,8-TCDD binding (93); these
levels show no correlation between their maximal hepatic AHH inducibility or
susceptibility to the toxic effects of 2,3,7,8-TCDD and related halogenated aryl
hydrocarbons (93, 97, 108). For several mammalian cells in culture there is no
correlation between receptor levels and their AHH inducibility (98, 99, 111-
113). Recent studies by Whitlock and co-workers indicate "that transcription of
 378 SAFE

the cytochrome PI-450 gene is under both positive and negative control by at
least two trans-acting regulatory factors" (113). The factors that control
cytochrome P 1-450 in variant mouse heptoma cells may also play a role in some
animal species and requires further investigation. It is apparent that response
specificity to Ah receptor ligands is a highly complex process that depends not
only on receptor levels but also on many other factors, an observation not
unique to the Ah receptor protein (113, 114).
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

Structure-Activity Relationships

RECEPTOR BINDING AFFINITIES OF PCDDs AND PCDFs: SUBSTITUTION

EFFECTS Poland, Glover & Kende first reported the relative binding affinities
of 23 halogenated dibenzo-p-dioxins and dibenzofurans using the dextran
charcoal receptor assay and [3H]-2,3,7,8-TCDD as the competing radioligand
(85). This study included 10 PCDD congeners and 7 PCDF congeners that
differed only with respect to their degree of chlorination and substitution
pattern. Table 1 summarizes results from a more recent study of the effects of
structure on the receptor binding affinities of 14 PCDDs and 14 PCDFs using rat
hepatic cytosol and the sucrose density gradient assay procedure (47, 51; G.
Mason, J. Pikorska-Pilszczynska, B. Keys & S. Safe, unpublished results).
2,3,7,8-TCDD and 1,2,3,7,8-pentachlorodibenzo-p-dioxin were the most avid
PCDD competitive binding ligands for displacement of [3H]-2,3,7,8-TCDD
from the receptor protein, and their ECso values were 1.0 x 10-8 and 7.9 x
10-8 M, respectively. Inspection of these data clearly demonstrated the im
portance of the lateral CI substituents in facilitating the interaction between the
PCDD ligands and the cytosolic receptor protein. The relative receptor binding
EC50 values for a series of tetrachloro isomers were 2,3,7,8- > 2,3,6,7- >
1,3,7,8- > 1,2,3,4-, in the order of decreasing number of lateral substituents.
The fivefold difference in the receptor binding activities of the 2,3,6,7- and
1,3,7,8-TCDD isomers illustrates a more subtle structural feature that affects
binding. The increased affinity of the former compound must be due to the
receptor binding site preference for a vicinal 6,7- (or, 1,2) group over a meta
1 ,3-dichloro functionality. The data also illustrate that the degree of chlorina
tion of non-lateral sites is an important structural determinant for interaction
with the receptor protein. The 2,3,7,8-tetra-, 1,2,3,7,8-penta-, 1,2,3,4,7,8-
hexa-, and 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxins all contain four later
al CI substituents; however, there is a marked decrease in their receptor binding
avidities with increasing CI substitution at the nonlateral 1, 4, 6, and 9
positions. The stepwise addition of CI groups at 1, 4, 6, and 9 would result in
several structural changes in the more highly chlorinated PCDDs including
increased molecular size and volume, increased lipophilicity, a possible de
crease in PCDD coplanarity associated with steric crowding, and decreased
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

Table 1 The effects of structure on the rat hepatic cytosolic receptor binding affinities and AHHfEROD induction potencies of PCDDs and PCDFs

In Vitro EC50 (M) In Vitro EC5 0 (M)

Receptor Receptor
PCDD Binding AHH EROD PCDF Binding AHH EROD

2,3,7,8- 1.0 x 10-8 7.2 X 10-11 1.9 X 10-10 2,3,4,7,8- 1.5 x 10-8 2.6 X 10-10 1.3 X 10-10
1,2,3,7,8- 7.9 x 10-8 1.1 X 10-8 1.7 X 10-8 2,3,4,7- 2.5 x 10-8 1.8 X 10-8 1.5 X 10-8
2,3,6,7- 1.6 x 10-7 6.1 X 10-8 1 . 1 X 10-8 2,3,7,8- 4.1 x 10-8 3.9 x 10-10 2.0 X 10-10
0
2,3,6- 2.2 x 10-7 2,3,4,6,7,8- 4.7 x 10-8 6.9 X 10- 10 5.8 X 10-1
1,2,3,4,7,8- 2.8 x 10-7 2.1 X 10-9 4. 1 X 10-9 1 , 2,3,7,8- 7.5 x 10-8 2.5 X 10-9 3.1 X 10-8
1,3,7,8- 7.9 x 10-7 5.9 X 10-7 3.2 X 10-7 1 , 2,3 ,7- 1.1 x 10-7 2.7 X 10-5 6.3 X 10-5
1,2,4,7,8- 1.1 x 10-6 2.1 X 10-8 1.1 X 10-8 1 ,3 ,4,7,8- 2.0 x 10-7 1.6 X 10-9 1.4 X 10-9 ?S
ti
1 ,2,3,4- 1.3 x 10-6 3.7 X 10-6 2.4 X 10-6 2,3 ,4,7,9- 2.0 x 10-7 7.9 X 10-9 5.8 X 10-9 ti
X 10-7 1.4 2.0 10-7 4.1 X 10-8 3.8 X 10-8
'"
2,3,7- 7. 1 x 10-8 3.6 X 10-7 2,3 ,4,8- x
0 >
2,8- 3.2 x 10-6 >1.0 x 10 -4 >1.0 x 10-4 1 , 2,3,4,7,8- 2.3 x 10-7 3.6 X 10- 10 3.8 X 10-1 Z
1 ,2,3,4,7- 6.4 x 10-6 6.6 X 10-7 8.2 X 10-7 1 , 2,3,6,7,8- 2.7 x 10-7 1.5 X 10-9 1.2 X 10-9 ti
"0
1 , 2,4- 1.3 x 10 -5 4.8 x 10-5 2.2 X 10-6 1 , 2,3,7,9- 4.0 x 10-7 8.6 X 10-8 8.6 X 10-8 n
OCDD >1.0 x 10-5 3.1 X 10-7 7.0 X 10-7 1 , 2,4,7,8- 1.3 x 10-6 1.1 X 10-7 1.5 X 10-7 ti
:" >Tj
1- >1.0 x 10-4 >1.0 10-4 > 1.0 X 10-4 1 , 2 ,4,6,8- 3.1 10 6 1.0 10-5 1.2 X 10-5
1>
x x x

iI:'
'"

W
--.J
\0
 380 SAFE

+++

-
I
Q-- -:- - OJ
9
-
I 1 +++

-
- <,'> -
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

Figure 2 The differential effects of chlorine substituents at different positions in the dibenzo-p
dioxin and dibenzofuran rings on the relative receptor binding affinities of PCDD and PCDF
congeners.

aromatic ring electron density(due to the additional electronegative CI groups).

One or more of these changes may be related to the decrease in binding affinities
of the more highly chlorinated 2,3,7,8-substituted PCDDs. Figure 2 summa
rizes the differential effects of Cl substituents on the affinities of PCDDs for the
cytosolic receptor protein and illustrates the importance of lateral chloro
groups. It has also been suggested that the other critical structural factors that
contribute to the high binding affinities of 2,3,7,8-TCDD include the planar
ring structure and an ideal ligand area, 3 x 10 A (37, 38).
The direct binding of radiolabelled 2,3,7,8-tetrachlorodibenzofuran(TCDF)
and other PCDFs to the Ah receptor protein has not been demonstrated.
However, the competitive binding affinities of three 2,3,7,8-substituted com
pounds demonstrated their relatively high binding affinities for the receptor
protein (85). The development of new procedures for the synthesis of PCDFs
(115) has resulted in the preparation of over 40 congeners that have been used to
develop detailed SARs for this series of halogenated aryl hydrocarbons (47,
51). The dibenzofuran ring system possesses a single axis of symmetry(Figure
2); therefore there are four geometrically different positions on each aromatic
ring, namely C-1 (or C-9), C-2 (or C-8), C-3 (or C-7), and C-4 (or C-6). A
complete SAR for PCDFs as ligands for the receptor protein must distinguish
between the djfferential contributions of all four positions on the dibenzofuran
ring. (See Table 1 for compounds selected for this study.) Inspection of these
d a t a confirms that the m o st active congener s, 2,3,4,7,8-penta
chlorodibenzofuran(PeCDF, 1.5 X 1O-8M), 2,3,7,8-TCDF(4.1 x 1O-8M),
2,3,4,6,7,8-hexachlorodibenzofuran (HCDF, 4.7 X 10-:-8 M), and 1,2,3,7,8-
:
PeCDF (7.5 X 10-8 M) were all fully substituted in their lateral 2, 3, 7, and 8
positions. Moreover, a comparison of the receptor binding ECso values for the
2,3,4,7,8-, 1,2,4,7,8-, and 1,2,4,6,8-PeCDF isomers demonstrates the im
portance of lateral chloro substituents since there is a decrease in receptor
binding affinities with decreasing lateral substitution. Two pairs of PCDF
isomers, namely 1,3,4,7,8- and 1,2,4,7,8-PeCDF, 2,3,4,7- and 2,3,4,8-
TCDF, differ only with respect to their substitution of C-2(or C-8) and C-3 (or
 PCDDs AND PCDFs-SARs 381

C-7). In both cases the C-3 (or C-7) substituted compounds were 6.5-8 times
more active than the corresponding C-2 (or C-8) isomers as competitive ligands
for the rat hepatic cytosolic receptor protein. A comparison of the relative
binding affinities of a series of C- l (or C-9) and C-4 (or C-6) isomer pairs
illustrates the higher binding activities of the isomer that retains the C-4 (or C-6)
substituent. For example the ECso values for the 2,3,4,7-, 2,3,4,7,8-,
2,3,4,7,9-, and 2,3,4,6,7,8-substituted PCDFs were 2.5 x 10-8 M, 1.5 X
10- 8 M, 2.0 X 10-7, and 4.7 x 10-8 M whereas the values for the correspond
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

ing C-l (or C-9) isomers (i.e. 1,2,3,7-TCDF, 1,2,3,7,8-, and 1,2,3,7,9-
PeCDF, and 1,2,3,6,7,8-HCDF) were 1.1 x 10-7 M, 7.5 X 10-8 M, 3.4 X
10-7 M, and 2.7 x 10-7 M, respectively.
Figure 3 illustrates an overlay of 2,3,7,8-TCDD and 2,3,4,7,8-PeCDF, the
two most active PCDD and PCDF ligands for the Ah receptor. The molecular
areas and volumes of the dibenzofuran and dibenzo-p-dioxin ring systems are
similar, but the spatial orientations of their substituents exhibit marked dif
ferences. The C-3 (or C-7) substituents occupy a position between the lateral
2,3 (or 7,8) groups in 2,3,7,8-TCDD and clearly occupy the dominant lateral
position in the dibenzofuran ring system. The spatial orientations of the C-4
(and C-6) and C-2 (and C-8) substituents are comparable and exhibit less
overlap with the lateral positions of 2,3,7,8-TCDD; the C- l (or C-9) PCDF
substituents exhibit the least overlap with the lateral positions of 2,3,7,8-
TCDD. These observations on the molecular orientations of the dibenzofuran
Cl substituents are consistent with the observed SARs for PCDF receptor
binding affinities and illustrate the stereospecific nature of the receptor protein
ligand interactions.

RECEPTOR BINDING AFFINITIES OF PCDDs AND PCDFs: A QSAR ANALY

SIS The receptor binding avidities of PCDDs and PCDFs summarized in

Table 1 and in other studies (37, 38, 47, 51) not only demonstrate the im
portance of Cl substitution patterns on ligand-receptor protein complex forma
tion but also show that substituents are important structural determinants for
these interactions. For example, the receptor binding ECso values for 2,3,7-
trichlorodibenzo-p-dioxin is 7.1 X 10-8 M; replacement of the 7-Cl substituent
with H gives 2,3-dichlorodibenzo-p-dioxin, which exhibits a greatly di
minished receptor binding ECso value (> 10-5 M). It is clear that these
substituent effects at this lateral C-7 position must be related to differences in
their physicochemical characteristics which in turn influence ligand-receptor
avidities. A series of substituted PCDD, PCDF, and polychlorinated biphenyl
analogs have been synthesized (Figure 4) as probes for delineating the effects of
substituent structure on ligand-receptor binding affinities (116-118). Each
series of analogs contains a variable substituent group at a single lateral
position, and it is apparent that substituent structure has a remarkable effect on
 382 SAFE
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

O-PCDD D-PCDF
Figure 3 Overlay of 2,3,7,8-TCDD and 2,3,4,7,8-PeCDF structures.

the receptor binding avidities of these compounds. For example the ECso value
for 7-trifluoromethyl-2,3-dichlorodibenzo-p-dioxin (1.95 X 10-8 M) was
1000 times lower than the value for 7-amino-2,3-dichlorodibenzo-p-dioxin
(2.88 x 10 5 M). The effects of different substituents on the activity of a series
-

of analogs can be analyzed quantitatively by correlating the differences in a

biological effect (e.g. receptor binding) with known substituent physicochem
ical parameters (116-119), such as lipophilicity (1T), electronegativity (0"),
hydrogen bonding capacity (HB), and substituent width (AB5)' Multiparameter
linear regression analysis of the receptor binding data for sixteen 7-substituted-
2,3-dichlorodibenzo-p-dioxins gave the following equation (1):

log (lIEC5o) = 1 .241T + 6.11 1.

(n = 14, s = 0.29, r = 0.950),

where 1T is the substituent lipophilicity, s is the standard deviation, and r is the

correlation coefficient. The only substituents treated as outliers for the deriva
tion of this equation were the bulky C6HS and t-C4H9 groups, which possess van
der Waals volumes of 48.5 and 41.8 cm3 /mol, respectively. This suggests that
substituent molecular volumes are also important structural determinants for
determining ligand affinities for the receptor protein binding site. Previous
studies with the 4' -substituted-2,3,4,5-tetrachlorobiphenyls indicated that the
maximum molecular volume for lateral substituents was < 35 cm3 /mol (118).
However it is apparent that if substituent molecular volume requirements are
satisfied, the the receptor binding affinities of these analogs are directly related
to the lipophilicity of the 7-substituents.
The competitive receptor binding affinities of a series of thirteen 8-
substituted-2,3,4-trichlorodibenzofurans and ten 8-substituted -2,3-dichlorodi
benzofurans (Figure 4) have also been determined, and the competi-
 PCDDs AND PCDFs-SARs 383

X I()Y I()Y0 CI

O CI CI

CI CI
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

CI
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

X=CF3 , Br, I, CI, F, OH, CH3, X=H, OH, CH3, F, OCH3, COCH3, eN,
OCH3, N02, CN, NH2 ( )
CI, CH2CH3, Br, I, CH CH3 2' CF3

X CI X CI

O CI oyci
CI

X=t-C4Hg, F, Br, I, i-C3H7' X=CI, Br , CF3, I, F, CH3, i-C3H7'

CI, CH3, OCH3, OH, H C2 Hs, t-C4Hg, H, OCH3, OH, CH2Br

Figure 4 Structures of substituted PCDDS, PCDFs, and polychlorinated biphenyls used for
QSAR studies.

tive displacement binding data results have been analyzed by multiparameter

linear regression analysis to give Equations 2 and 3, respectively_

log (lIECso) = l . 091T + 5.77 2.

log ( l/ECso) = LlO1T + 5_19 3_

For the 8-substituted-2,3,4-trichlorodibenzofurans, both the t-C4H9 and i-C3 H

7
were outliers, whereas only the t-C4H9 substituent was not included in the
derivation of Equation 3. Analysis of the collective data for 33 substituted
polychlorinated dibenzofurans and dibenzo-p-dioxins (Figure 5) has demon
strated the excellent linear correlation between the log ( l/ECso) receptor bind
ing data and lipophilicity ( 1T)_ Moreover the slopes and intercepts for Equations
1-3 were not significantly different. These data are consistent with a receptor
protein that binds the PCDDs and PCDFs at a common binding site(s) on the
protein; this site must accommodate the molecular area and volume encum
bered by these ligands, and the QSAR results are consistent with a binding site
that is highly hydrophobic_
The effects of substituent structure on the rat hepatic cytosolic receptor
binding affinities of 4-substituted-2,3,4,5-tetrachlorobiphenyls have also been
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

w
00
-I'>

en
>
"T:I
7r S tIl

r 8

7
L;:

7r
t-C4Hg
0I i-C3H7
L;: 6
0 CsHs

:1

":.
I r<'l '0
0I
r<'l N

N I r<'l 41
I x t-C4Hg N
x I t-C4Hg
I 5 6 X 6
<XI

0

g U
10 0
10
u U
UJ UJ
UJ
0>
.34
I
.3
I
5
I
5

0 1 2 0 1 2
r -I 0 2
I

err-
1T 'if
Figure 5 Correlation between receptor binding avidities for the substituted PCDDs and PCDFs vs the substituent lipophilicity (1T) values_
 PCDDs AND PCDFs-SARs 385

reported (118). Multiparameter linear regression analysis of the results of these

analogs gave Equation 4, which suggests that substituent lipophilicity,
electronegativity (0") and hydrogen bonding capacity (HB) are factors that
influence receptor-ligand affinities:

log ( lI ECso) = 1.390" + 1.311T + 1.12 HB + 4.20 4.

The bulky t-C4H9 and C6HS substituents were also treated as outliers for the
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

derivation of Equation 4. These results demonstrate that substituent molecular

volumes play a role in ligand-receptor interactions for the substituted PCBs,
PCDDs, and PCDFs. However, the data analysis for the former group of
analogs suggests that the critical 4 '-substituent for the PCBs interacts with both
polar and hydrophobic regions of the receptor binding site. The differences
between Equations 1-3 and Equation 4 are somewhat paradoxical since
molecular overlap of the four sets of substituted ligands does not indicate that
there are major differences in their spatial orientation (Figure 4). Therefore it is
likely that the differences observed for the substituted PCBs are due to the free
rotation about the Ph-Ph bond and a limited population of the coplanar conform
ers. Chlorinated biphenylenes that possess a fixed coplanar ring structure
exhibit binding affinities comparable to those of 2,3,7,8-TCDD and related
isostereomers; this emphasizes the importance of a planar ring system. It is also
possible that the receptor binding sites for the substituted PCBs and PCDDs/
PCDF are not identical, a problem currently being investigated in my labora
tory.

AHH INDUCTION ACTIVITIES OF PCDDs AND PCDFs The in vivo and in vitro
SARs for PCDDs and PCDFs as inducers of hepatic and extrahepatic AHH have
been reported by several groups (37, 38, 47-49, 51-53). The most active
PCDDs were substituted in their 2,3,7, and 8 position; inspection of the data in
Table 1 indicates that there were comparable SARs for PCDDs as ligands for
the receptor protein and as AHH inducers; however, there is not a linear
correlation between these two bioassays. SARs for several PCDF congeners as
in vitro AHH inducers were comparable to those already discussed for receptor
binding. Moreover, for the PCDFs summarized in Table 1 a comparison of in
vitro ECso values for AHH induction in rat hepatoma H-4-U E cells and in vivo
EDsos for AHH induction in male Wistar rats showed a linear correlation
between these two values. Like the PCDD congeners, however, there was not a
strong correlation between AHH induction potencies and receptor binding
avidities for the PCDF congeners. A comparison of the AHH and EROD
induction potencies of t 7-substituted-2,3-dichlorodibenzo-p-dioxins with
their rat hepatic cytosolic receptor binding avidities also showed that there was
not a linear correlation between the two in vitro activities for this series of
 386 SAFE

analogs ( 1 1 6). Multiple parameter linear regression analysis of the AHH

induction results for these compounds gave the following equation:

log ( l IECSO)AHH = 1 . 60 11' - 0.33(ABs)2 + 5.85 5.

Like the receptor binding avidities for these substituted PCDDs, their AHH
induction potencies were dependent on substituent lipophilicity; however, a
second parameter, STERIMOL (ABs) has also been included in the derivation
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

of this equation. The STERIMOL parameter (119) is a measure of the max

imum width of the substituents (compared to H) from the axis connecting the
7 -substituent to the rest of the molecule and has previously been used in QSAR
studies that involve the interaction of substituted organic ligands and macro
molecules. The dependence of AHH induction activities by the substituted
PCDDs on both ABs and 11' suggests that substituent-dependent effects such as
conformational changes in the ligand-receptor complex occur after the initial
receptor-ligand binding process.
The AHH and EROD induction EC50 values for the 8-substituted-2,3-di- and
2,3 ,4-trichlorodibenzofurans in rat hepatoma H-4-II E cells were also subjected
to multiple parameter linear regression analysis to give Equations 6 and 7,
respectively (117).

log ( lIECSO)AHH = 0.8011' + 0.87ABs - 0. 35(ABsf + 4. 63 6.

log ( l /ECso)AHH =
O .761T + 1 . 1 1 ABs + 2 . 23 O'p + 6 . 78 7.

Both Equations 5 and 6 showed that AHH induction potencies for the 8-
substituted-2,3-dichlorobenzofurans and 2,3-dichlorodibenzo-p-dioxins were
dependent on substituent and B5 p arameters . The correlation for the more
highly chlorinated set of analogs, the 8-substituted-2 , 3 ,4-trichlorodibenzo
furans, also includes a Hammett substituent parameter (O'p); presumably the
requirement for 0'p must be due to the effects of the C-4 chlorine group, which
constitutes the only structural difference between the two sets of substituted
PCDP analogs .
Equations 8-10 were developed from the AHH and EROD induction data for
the 8-substituted-2,3-dichlorodibenzo-p-dioxins, -2,3-dichlorodibenzofurans,
and -2,3,4-trichlorodibenzofurans , respectively .

log ( lIECSO)EROD = 0.99 log ( lIEC:;o)AHH - 0 . 07 8.

log ( lIECsokROD = 0.90 log ( lIECSO)AHH + 0.83 9.

log ( l IECSO)EROD = 0.92 log (1/ECsO)AHH + 0 . 2811' + 0 . 27 10.

 PCDDs AND PCDFs-SARs 387

For a total of twenty-five 7-substituted-2,3-dichlorodibenzo-p-dioxins and

8-substituted-2,3-dichlorodibenzofurans and fifteen 4' -substituted-2,3,4,5-
tetrachlorobiphenyls there was a linear correlation between the ECso values for
AHH and EROD induction, and the slopes for these equations were not
significantly different from that of equation one. These data suggest that both
ethoxyresorufin and benzo[a]pyrene are catalyzed by the same cytochrome
P-450 isozyme(s). In contrast, Equation 10 required a 'IT term to correlate the
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

effects of the substituted 2,3,4-trichlorodibenzofurans; the rationale for these

Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

differences between the two sets of substituted PCDF analogs is unknown.

OTHER BIOLOGIC EFFECTS OF PCDDs AND PCDFs: STRUCTURE-ACTIVITY

RELATIONSHIPS PCDDs and PCDFs elicit a broad spectrum of species

dependent biologic effects, but because pure standards have been unavailable
few studies report qualitative or quantitative SARs for these compounds. The
SARs for PCDDs as inducers of ALA synthetase were comparable to the effects
of structure on, their activities as AHH inducers (48). Knutson & Poland have
used cultured XB cells derived from a mouse teratoma as an in vitro model for
halogenated aryl hydrocarbon toxicity (120). 2,3,7,8-TCDD and related toxic
isostereomers produce a dose-dependent keratinization response which in part
resembles the in vivo dermal toxicity that develops in some animals after
exposure to these toxins. The most active PCDD congeners in this in vitro assay
possessed three or four lateral substituents, and the SARs were similar to those
reported for their receptor binding affinities. 2,3,7,8-TCDD causes comparable
dermal toxicity in cultures of newborn foreskin keratinocytes (121).
Several human squamous cell carcinoma (SeC) lines have been utilized as
model systems for investigating the mechanism of action of toxic halogenated
aryl hydrocarbons (110, 122). SCC cells possess variable Ah receptor levels,
and the relative amount of receptor in several cell lines correlates with the
maximal 7-ethoxycoumarin O-deethylase inducibility in these cell lines.
2,3,7,8-TCDD causes down-regulation of the epidermal growth factor (EGF)
receptor in the SCC-12F cell line, and this effect is dose- and structure
dependent. Both 2,3,7,8-TCDD and 2,3,7,8-tetrabromodibenzofuran, which
exhibit a high affinity for the Ah receptor, decrease EGF receptor binding,
whereas 2,7-dichlorodibenzo-p-dioxin is inactive (123). Comparable results
have been observed in keratinocyte strains derived from normal neonatal
foreskin; the authors report that 2,3,7,8-TCDD acts (in part) through the Ah
receptor in epidermal basal cells to enhance terminal differentiation (123).
2,3,7,8-TCDD also down-regulates EGF receptor activity in hepatic plasma
membranes in several animal species and cultured mouse hepatoma cells (124,
125); however, structure-activity effects in the rat do not necessarily support the
role of the Ah receptor in mediating this process (125).
 388 SAFE

TOXICOLOGY OF PCDDs AND PCDFs: STRUCTURE-ACTIVITY RELATIONSHIPS

The doseresponse acute toxicities of nine PCDD isomers and congeners in the
guinea pig and responsive mouse have been reported (33, 34, 126). The
relative LD50 values in both species were highly dependent on the number of
lateral CI substituents and the degree of substitution; their rank order of toxic
potencies was similar to their in vitro receptor binding and AHH induction
activities as discussed above. A comparative study (127) of the toxicity of
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

2,3,7,8- TCDF, 2,3,7,8-tetrabromodibenzofuran, and 2,3,4,7,8-penta

Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

chlorodibenzofuran in guinea pigs, mice, and rhesus monkeys confirms that

these compounds elicit the characteristic broad spectrum of toxic effects
observed for 2,3,7,8-TCDD and related isostereomers.
Poland & Glover (75) reported the effects of several PCDD congeners and
other toxic halogenated aryl hydrocarbons on genetically inbred strains of mice.
Although dose-response studies were carried out only with 2,3,7,8-TCDD, the
relative toxicities (i. e. thymic atrophy) of these compounds correlated with
their in vitro binding and induction activities. The dose-response toxicities
(thymic atrophy and body weight loss) of the PCDFs listed in Table I have been
determined in the immature male Wistar rat (47). Inspection of the ED50 data
for the toxic effects showed that the potencies of these congeners were struc
ture-dependent and that the in vivo SARs for toxicity were identical to those
observed for their in vitro AHH induction potencies. Figure 6 summarizes a plot
of the -log ED50 values for thymic atrophy and body weight loss in immature
male Wistar rats vs their in vitro AHH induction activities. The linear correla
tion constant (r) and slope for the plots of the reciprocal log values for AHH
induction vs body weight loss were 0.96 and 1.30 (slope), respectively, and
values of 0. 88 (r) and 1.16 (slope) were obtained for the comparable plot of the
reciprocal log values for AHH induction vs thymic atrophy. The linear correla
tion was observed only for those compounds that do not contain vicinal
unsubstituted carbon atoms and are not significantly metabolized. For example,
the toxicity of 1,2,3,7- or 2,3,4,8-TCDF in the rat was lower than predicted by
the in vitro AHH (or EROD) induction data (not shown) owing to in vivo
metabolism. Current research in my laboratory (S. H. Safe, unpublished
results) indicates that for several PCDD isomers and congeners there is a linear
correlation between -log EC50 (AHH induction) and -log ED50 (thymic
atrophy and body weight loss in the rat). These results suggest that the rat
hepatoma cell monooxygenase induction bioassay may serve as a short-term
test system for predicting the toxicities of PCDDs, PCDFs, and related haloge
nated aryl hydrocarbons.
Poland and co-workers have investigated the effects of 2,3,7,8-TCDD,
several PCDD congeners, and related halogenated aryl hydrocarbons in the skin
of inbred HRS/J hairless mice segregating for the hr locus (128, 129). The
homozygous hrlhr hairless and heterozygous hrl+ haired mice exhibit identical
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

2,3,4,7,8- F2,3,7,8-TCOol
lOr
',2,3,4,7,8-....... I
'e-PCOF mix
2,3,4,6,7,8- ......
1,2,3,4, 7,8- = , 3,7,8-T COO
[!=2 I
e 10
9f- ___ 1,2.3,6,7,8" '\.
1,2,3,7,8-
PCDF mix .. e-2,3,4,7,8-
-.e
_

_ 2,3,7,8-

e_2,3,4,6,7,8-
_-2,3,4,7,9- 9 1,2,3,6,7,8--e

U
:5 8 1 e-1,3,4,7,8-
e
e-1,2,3,6,7,8-

2,3,7,8- -e-2,3.4,7,9-
lIJ
1,2,3,7,9-_e 8
F 7 .-1,2,4,7,8- e - 1,3,4,7,8-
.!.
U
'C lIJ
,7,9 -
go 7 1,2,4,7. 8- _1-1,2,3
:J: 6 I
:J:
-0

6
5f-
:J:

go
:J:

5 '"

-'---
o
2 3 4 5 6 7 8
Body WI. Loss Hog ED501 ?5
2 3 4 5 6 7 8 Sil
Thymic Atrophy HogED501
1>
Figure 6 A plot of the -log ECso values for in vitro AHH induction vs the -log EDso values for thymic atrophy (right) and body weight loss (left) in the male :;:Q
'"
Wistar rat for several PCDF congeners and 2,3,7,8-TCDD,

\;J
00
\0
 390 SAFE

genetics except for one allele at the hr locus. Topical application of 2,3,7,8-
TCDD to the dorsal skin of hairless mice resulted in epidermal hyperplasia,
sebaceous gland metaplsia, and hyperkeratosis, but these histological lesions
are not observed in hrl+ haired mice. The development of a graded epidermal
response by several PCDD congeners, 2,3,7,8-TCDF, and related toxic aryl
hydrocarbons was structure-dependent and correlated with rank order of recep
tor binding affinities for these compounds ( 1 28) . For example, the total dose
(nmol/mouse) required to produce a 2+ response was 0.36, 1 .76, 1 .2 > 360 and
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

> 360 for 2 , 3 , 7 , S-TCDD, 1 ,2,3 ,6,7,8-HCDF, 2 , 3 ,7 , 8-TCDD , 1 ,3 ,6,8-

TCDD, and 2,7-DCDD , respectively. These results are consistent with the
involvement of both the Ah and hr loci in the development of murine epidermal
lesions after exposure to PCDDs, PCDFs, and related toxins . 2,3,7,8-TCDD
can also act as a potent tumor promoter in HRS/J mice, and the results of this
study confirm the segregation of the activity with the Ah and hr loci. A
qualitative structure-activity study also suggests a possible role for the Ah
receptor in mediating the tumor promotion activities of the toxic halogenated
aryl hydrocarbons ( 1 30) .
The SARs for PCDDs and PCDFs clearly support an Ah receptor-mediated
mechanism of action for these compounds; comparable studies have been
reported for other classes of halogenated aryl hydrocarbons . It is assumed that
the persistent effects elicited by these toxins are related to a sustained receptor
ligand occupancy of nuclear binding sites, but this has not yet been demon
strated experimentally . The identity and role of any endogenous ligand(s) for
the Ah receptor have not been determined; however, lumichrome, a riboflavin
metabolite, does bind to the receptor ( 1 3 1) .

Genetic Evidence
Pharmacogenetic studies with genetically inbred strains of mice typefied by the
Ah-responsive C57BLl6 and nonresponsive DBA/2 mice have provided strong
evidence in support of the role of the Ah receptor in mediating the biologic and
toxic effects of toxic halogenated aryl hydrocarbons. Nonresponsive DBA/2
mice contain relatively low levels of hepatic or extrahepatic cytosolic or nuclear
Ah receptor 1 fmoVmg cytosolic protein) , whereas much higher levels of the
receptor are detected in responsive strains of mice. The EDso for 2,3,7,8-
TCDD mediated hepatic microsomal AHH induction in C57B 1/6J mice was 1
nmol/kg whereas this value is at least tenfold higher in DBAl2J mice. In genetic
crosses and backcrosses between C57BLl6J and DBA/2J mice the trait or
responsiveness to AHH induction is inherited in a simple autosomal mode (50,
1 32-1 34). The responsive backcross animals also had detectable hepatic recep
tor levels (85 , 89, 97 , 1 03 , 1 09). The segregation of the toxicity of PCDDs and
PCDFs with the Ah locus has been determined primarily with 2,3,7,8-TCDD
using both responsive and nonresponsive genetically inbred mice and their
 PCDDs AND PCDFs-SARs 391

crosses and backcrosses. The results illustrate that several toxic effects includ
ing teratogenicity, porphyria and hepatotoxicity, immunotoxicity, and body
weight loss segregate with the Ah locus (75-80, 1 35-1 39) . Dermal toxic
lesions appear to be dependent on the interaction between the Ah and hr locus as
previously noted ( 1 28-1 30). It has also been suggested that additional genetic
loci may also be involved in the hepatotoxic effects of 2,3 ,7,8-TCDD, however
this observation requires further substantiation ( 1 40).
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

PCDDs , PCDFs , AND RELATED

COMPOUNDS-INTERACTIVE EFFECTS

Although the SARs and toxicology of PCDDs and PCDFs have been ex
tensively studied the interactive effects of PCDD/PCDF mixtures and related
compounds are not well understood. 2,3,7 ,8-TCDD can act as a tumor promot
er for several initiators in the rodent liver ( 4 1 ) , mouse skin ( 30), and
C3H/lOTII2 cells ( 142), and as a cocarcinogen causing 3-methylcholanthrene
initiated subcutaneous tumors in nonresponsive DBA/2 mice ( 1 43). In contrast,
2 , 3 ,7 , 8-TCDD exhibits anticarcinogen activity in female CD- l mice ( 1 44) .
These effects are related to the agent's induction of drug-metabolizing enzymes
that alter rates of metabolic activation of polynuclear aromatic hydrocarbon
initiators. Several studies (5 1 , 5 3 , 1 20, 145 , 146) report the application of in
vitro bioassays as short-term tests for assessing the potential toxicity of PCDD/
PCDF mixtures; a comparison of the in vitro AHH induction activity of a
reconstituted mixture of PCDFs identified in Yusho patients ( 147) and the
toxicity of this mixture (Figure 6) suggest that the effects of the individual
PCDFs in this mixture are additive ( 148) . In contrast, the immunotoxicity and
AHH induction activity of 2 , 3 ,7 , 8-TCDD in C57BL/6 mice were decreased by
coadministering a nontoxic or noninducing dose of 2,3 ,7 ,8-TCDF 00 j.Lg/kg)
( 149). A rational explanation for the antagonistic effects of 2,3,7,8-TCDF is
not apparent.
Birnbaum and co-workers (77) have reported that treatment of pregnant mice
with a combination of 2 , 3 , 7 ,8-TCDD (3 j.Lg/kg) and a nontoxic dose of
2 , 3 ,3' ,4,4' ,5-hexachlorobiphenyl (20 j.Lg/kg) resulted in a tenfold increase in
incidence in cleft palate compared to those animals receiving only 2 , 3 ,7 , 8-
TCDD. A second PCB congener, 2,2' ,4,4' ,5,5' -hexachlorobiphenyl , at dose
levels of 50 or 25 mg/kg in combination with 2 , 3 ,7 ,8-TCDD (3 j.Lg/kg), did not
effect the teratogenic potency of the latter compound. Although 2,3,3' ,4,4' ,5-
hexachlorbiphenyl is less toxic than 2 , 3 ,7,8-TCDD, this monortho coplanar
PCB congener elicits several receptor-mediated biologic and toxic effects (74).
It is conceivable that the interactive effects of 2 , 3 , 3 ' ,4,4' ,5-hexachlorobi
phenyl and 2 , 3 , 7 ,8-TCDD may be additive if the dose-response curve for
the former compound is steep and if the 20 mg/kg dose level is just
 392 SAFE

below the minimum observable teratogenic dose. Current research in my

laboratory has demonstrated that administration of several compounds, includ
ing several polychlorinated biphenyl congeners , increase hepatic 2 , 3,7 ,8-
TCDO receptor levels in rats and C57BLl6 mice. Pretreatment of rats and mice
with these receptor modulators followed by administration of 2,3,7,8-TCDD
results in markedly increased hepatic AHH and EROD induction activities.
Both positive and negative modulators and antagonists of the hepatic and
extrahepatic cytosolic receptor protein are currently being investigated as
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

probes for delineating the mechanism of action of PCDDs and PCDFs and the
role of the receptor protein in mediating these effects. These interactive studies
will also be_ important for assessing the effects of polyhalogenated aromatic
environmental pollutant mixtures and their potential human health impact.

ACKNOWLEDGMENTS

The author gratefully acknowledges the financial assistance of the National

Institutes of Health (EC-03554), the Environmental Protection Agency, and the
Texas Agricultural Experiment Station. The collaboration of G. Mason, M. A.
Denomme, K. Homonko, L. Safe, B. Keys, S. Bandiera, T. Sawyer, M.
Romkes, J. Piskorska-Pliszczynska, B. Zmudzka, and T. Fujita are gratefully
acknowledged.

Literature Cited

1 . Bowes, G. W . , Mulvihill, M. J . , Sim 1984. Causal agents o f Yusho. Am. J.

oneit, B. R. T. , Burlingame, A. L . , Ind. Med. 5:45-58
Risebrough, R. W. 1 975. Identification 6. Masuda, Y . , Yoshimura, H. 1984. Poly
of chlorinated dibenzofurans in Amer chlorinated biphenyls and dibenzofurans
ican polychlorinated biphenyls. Nature in patients with Yusho and their toxicolo
256:305-7 gical significance. Am. J. Ind. Med.
2. Vos, J. G . , Koeman, J. H . , Van der 5:3 1-44
Maas, H. L. , Ten Noever de Brauw, M . 7. National Research Council of Canada.
c . , de Vos, R. H. 1 970. Identification 1 978a. Phenoxy Herbicides-Their Ef
and toxicological evaluation of chlori fects on Environmental Quality, Ottawa
nated dibenzofuran and chlorinated nap NRCC Publication No. 1 6075 , 440
thalene in two commercial polychlorin pp.
ated biphenyls. Food Cosmet. Toxicol. 8. Firestone, D. 1977. Determination of
8 : 625-33 . polychlorodibenzo-p-dioxins and poly
3. Rappe, C. , Buser, H. R. 1980. Chemical chlorodibenzofurans in commercial gela
properties and analytical methods. In tins by gas liquid chromatography. J.
Halogenated Biphenyls, Terphenyls, Agric. Food. Chem. 25: 1 274-80
Napthalenes, Dibenzodioxins and Re 9. Rappe, c., Marklund, S . , Buser, H. R . ,
lated Products, ed. R . D . Kimbrough, Bosshardt, H . P. 1978. Formation of
pp. 41-76. Amsterdam: Elsevier. 406 polychlorinated dibenzo-p-dioxins heat
pp. ing chlorophenates. Chemosphere 7:
4 . Morita, M . , Nakagawa, J . , Rappe, C. 269-8 1
1978. Polychlorinated dibenzofuran 10. Ballschmiter, K. , Zoller, W . , Scholz, C.
(PCDF) formation from PCB mixture by H., Nottrodt, A. 1983. Occurrence and
heat and oxygen. Bull. Environ. Contam. absence of polychlorodibenzofurans and
Toxicol. 19:665-70 polychlorodibenzodioxins in fly ash from
5. Kunita, N . , Kashimoto, T . , Miyata, H . , municipai incinerators. Chemosphere 12:
Fukushima, S . , Hori, ' S . , Obana, H. 585-94
 PCDDs AND PCDFs-SARs 393

1 1 . Buser, H. R . , Bosshardt, H. P . , Rappe, sarcoma pathology in U . S . chemical

C. 1978. Identification of polychlori workers . In Biological Mechanisms oj
nated dibenzo-p-dioxin isomers found in Dioxin Action, ed. A. Poland, R. D .
fly ash. Chemosphere. 7 : 1 65-72 Kimbrough, p p . 461-70. Banbury Re
1 2 . Buser, H. R. 1 979. Formation of polych port 1 8 , Cold Spring Harbor Laboratory.
lorinated dibenzofurans (PCDFs) and di 500 pp.
benzo-p-dioxins (PCDDs) from the 22. Fara, G., Del Corono, G., Bonetti, F . ,
pyrolysis of chlorobenzenes. Chemo Caramaschi, F . , Dardanoni, L . , et al.
sphere 8:41 5-24 Chloracne after release of TCDD at
1 3 . Olie, K . , Vermeulen, P. L . , Hutzinger, Sevesco, Italy. In Chlorinated Dioxins
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

O. 1977. Chlorodibenzo-p-dioxins and and Related Compounds: Impact on the

Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

chlorodibenzofurans are trace com Environment, ed. O. Hutzinger, R. Frei,

ponents of fly ash and flue gas of some E. Merian, F. Pocchiari, pp. 545-59.
municipal incinerators in The Nether Oxford: Pergamon 658 pp.
lands. Chemosphere 6:455-59. 23. Kimbrough, R. D. , Falk, H . , Stehr, P. ,
1 4 . Rappe, C . , Marklund, S . , Bergqvist, P. Fries, G. 1984. Health implications of
A . , Hansson, M. 1 983. Polychlorinated 2,3,7,8-tetrachlorodibenzo-p-dioxin
dioxins, dibenzofurans and other poly (TCDD) contamination of residential
nuclear aromatics formed during in soil. J. Toxicol. Environ . Health 14:47-
cineration and PCB fires. In Chlorinated 93
Dioxins and Dibenzojurans in the Total 24. Zack, J . , Gaffey, W. 1983. A mortality
Environment, ed. G. Choudhary, L. H. study of workers employed at the Mon
Keith, C. Rappe, pp. 99-124. Boston: santo Company plant in Nitro, West Vir
Butterworth ginia. In Human and Environmental
1 5 . Bumb, R. R . , Crummett, W. B . , Cutie, Risks ojChlorinated Dioxins and Related
S . S . , Gledhill, J. R . , Hummel, R. H . , et Compounds, ed. R. Tucker, A. Young,
al. 1980. Trace chemistries of fife: A A. Gray, pp. 575-9 1 . New York: Ple
source of chlorinated dioxins. Science num. 823 pp.
2 1 0:385-90 25 . Masuda, Y . , Kuroki , H . , Yamaryo, T . ,
1 6. Crummett, W. B . , Townsend, D . I. Haraguchi, K . , Kuratsune, M . , Hsu, S
1 984. The trace chemistries of fire: re T. 1982. Comparison of causal agents in
view and update. Chemosphere 1 3:777- Taiwan and Fukuoka Japan polychlori
88 nated biphenyl poisoning. Chemosphere
1 7 . Czuczwa, 1 . M . , McVeety, B . D . , Hites, 2:1 99-206
R. A. 1984. Environmental fate of com 26. Hsu, S-T . , Ma, C-L, Kwo-Hsiung, S . ,
bustion-generated polychlorinated di Wu, S-S . , Hsu, N . H-M . , Yeh, CoCo
oxins and furans. Environ . Sci. Technol. 1 984. Discovery and epidemiology of
1 8:444-50 PCB poisoning in Taiwan. Amer. J. Ind.
1 8 . Czuczwa, J. M . , McVeety, B. D . , Hites, Med. 5:7 1-79
R. A . 1 984. Polychlorinated dibenzo-p 27. Kashimoto, T . , Miyata, H . , Shiriji, K . ,
dioxins and dibenzofurans in sediments Tung, T . , Hsu, S-T . , et al. 1 98 1 . Role of
from Siskiwit Lake, Isle Royale. Science polychlorinated dibenzofuran in Yusho
226:568-69 (PCB Poisoning). Arch. Environ. Health
19. Rappe, C . , Bergquist, P. A . , Hansson, 36:321-26
M . , Kjeller, L-O . , Lindstrom, G . , et al. 28 . Norstrom, R. J. , Hallet, D. J . , Simon,
1 984. In Biological Mechanisms of Di M . , Mulvihill, M. J. 1982. Analysis of
oxin Action, ed . A . Poland, R. D . Kim great lakes herring gull eggs for tetrachlo
brough, pp. 1 7-25 . Banbury Report 1 8 , rodibenzo-p-dioxins. In Chlorinated Di
Cold Spring Harbor Laboratory. 500 pp. oxins and Related Compounds. Impact
20. Lathrop, G . D . , Wolfe, W. D . , on the Environment, ed. O. Hutzinger,
Albanese, R. A . , Moynahan, P . 1984. R. W. Frei, E. Merian, F. Pocchiari, pp.
An epidemiologic investigation of health 1 73-8 1 . Oxford: Pergamon 658 pp.
effects in Air Force personnel following 29. Van Den Berg, M . , otie, K . , Hutzinger,
exposure to herbicides. In Mechanisms of O. 1985. Polychlorinated dibenzofurans
Dioxin Action, ed. A . Poland, R. D . (PCDFs): environmental occurrence,
Kimbrough, p p . 471-74. Banbury Re physical, chemical and biological proper
port 1 8 , Cold Spring Harbor Laboratory. ties. Toxicol. Environ. Chem. 9 : 1 7 1-217
500 pp. 30. Rappe, c., Buser, H . R . , Stalling, D . L. ,
2 1 . Fingerhut, M . A., Halperin, W. E., Hon Smith, L. M . , Dougherty, R. C. 1 98 1 .
char, P. A . , Smith, A. B . , Groth, D. H . , Identification of polychlorinated cli
Russell, W . O . 1984. A n evaluation of benzofurans in environmental samples.
reports of dioxin exposure and soft tissue Nature 292:524-26
 394 SAFE

3 1 . Tieman, T. 0 . , Taylor, M. L . , Garrett, J. and related chemicals in animals. Phar

H., Van Ness, G. F . , Soleh, J. G., et al. mac. Ther. 1 9 : 1 95-209
1 985. Sources and fate of polychlori 43. Neal, R. A . , Beatty, P. W . , Gasiewicz,
nated dibenzo-p-dioxins, dibenzofurans T. A. 1979. Studies on the mechanisms
and related compounds in human en of toxicity of 2,3,7,8-tetrachlorodiben
vironments. Environ . Health Persp. zo-p-dioxin (TCDD). Ann. N. Y. Acad.
59: 145- 1 58 Sci. 320:204- 1 3
32. Stalling, D. L . , Smith, L. M . , Petty, J. 44. Poland, A . 1984. Reflections o n the
D . , Hogan, J . W., Johnson, J. L. , et al. mechanism of action of halogenated
1 983. Residues of polychlorinated di aromatic hydrocarbons. In Biological
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

benzo-p-dioxins and dibenzofurans in Mechanisms ofDioxin Action, ed . A. Po

Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

Laurentian Great Lakes fish. In Human land, R. D. Kimbrough, pp. 109- 1 7 .

and Environmental Risks of Chlorinated Banbury Report 1 8 , Cold Spring Harbor
Dioxins and Related Compounds. ed. R. Laboratory. 450 pp.
E. Tucker, A. L. Young , A. P. Gray, pp. 45. McConnell, E. E. 1984. Clinicopatho
22 1-40. New York: Plenum. 823 pp. logic concepts of dibenzo-p-dioxin in
33. Kociba, R . J. , Schwetz, B. A. 1982. toxication. In Biological Mechanisms of
Toxicity of 2 , 3 ,7 ,8-tetrachlorodibenzo Dioxin Action, ed. A . Poland, R . D.
p-dioxin (TCDD). Drug Metabolism Re Kimbrough, pp. 27-37. Banbury Report
views 1 3 :387-406 1 8 , Cold Spring Harbor Laboratory. 450
34. Kociba, R. J . , Schwetz, B . A. 1982. A pp.
review of the toxicity of 2 , 3 ,7,- 46. Kociba, R. 1984. Evaluation of the
8-tetrachlorodibenzo-p-dioxin (TCDD) carcinogenic and mutagenic potential of
with a comparison of the toxicity of other 2 , 3 ,7,8-TCDD and other chlorinated di
chlorinated dioxin isomers. Assoc. Food oxins. In Biological Mechanisms of Di
Drug Officials Quart. Bull. 46: 1 68- oxin Action. ed. A. Poland, R. D. Kim
88 brough, pp. 73-84. Banbury Report 1 8 ,
35. Lowrance, W. W . , ed. 1984. Public Cold Spring Harbor Laboratory. 450
Health Risks of the Dioxins. New York: pp.
Rockefeller University Press. 389 pp. 47. Mason, G . , Sawyer, T . , Keys, B . , Ban
36. National Research Council of Canada. diera, S . , Romkes, M . , et al. 1985.
1 98 1 . Polychlorinated dibenzo-p-dio Polychlorinated dibenzofurans (PCDFs):
xins: Criteria for Their Effects on Man in vivo and in vitro quantitative structure
and his Environment. NRCC Publication activity relationships (QSAR). Toxicol.
No. 1 8574. 25 1 pp. 37: 1 - 1 2
37. Poland, A . , Greenlee, W . F. , Kende, A. 48. Poland, A . , Glover, E. 1973. Chlori
S . 1979. Studies on the mechanism of nated dibenzo-p-dioxins: Potent inducers
action of the chlorinated dibenzo-p of &-aminolevulinic acid synthetase and
dioxins and relted compounds. Ann. N. Y. aryl hydrocarbon hydroxylase II. A study
Acad. Sci. 30: 2 1 4-30 of the structure activity relationship.
38. Poland, A . , Knutson, J. C. 1982. Mol. Pharmacol. 9:737-47
2 , 3 ,7,8-Tetrachlorodibenzo-p-dioxin 49. Yoshihara. S . . Nagata, K. , Yoshimura,
and related halogenated aromatic hydro H . , Kuroki, H . , Masuda, Y. 1 98 1 . In
carbons: examination of the mechanisms ductive effect on hepatic enzymes and
of toxicity. Ann. Rev. Pharmacol. Tox acute toxicity of individual polychlori
icol. 22:5 1 7-24 nated dibenzofuran congeners in rats.
39. Reggiani, G. 1 98 3 . Toxicology of TCDD Toxieol. Appl. Pharmacol. 59:580-88
and related compounds: Observations in 50. Poland, A. P. , Glover, E . , Robinson, J.
man. Chemosphere 1 2:463-75 R., Neber!, D. W . 1 974. Genetic expres
40. Poiger, H . , Schlatter, C. 1983. Animal sion of aryl hydrocarbon hydroxylase
toxicology of chlorinated dibenzo-p activity. Induction of monooxygenase
dioxins. Chemosphere 1 2:453-62 activities and cytochrome P-450 forma
4 1 . McConnell. E. E. 1980. Acute and tion by 2,3,7 ,8-tetrachlorodibenzo-p
chronic toxicity, carcinogenesis , repro dioxin in mice generally "nonresponsive "
duction teratogenesis and mutagenesis in to other aromatic hydrocarbons. J. Bioi.
animals. In Halogenated Biphenyls, Ter Chern. 249:5599-606
phenyls. Naphthalenes. Dibenzodioxins 51. Bandiera, S . , Sawyer, T. , Romkes, M . ,
and Related Products. ed. R. D. Kim Zmudzka, B . , Safe , L. , e t a ! . 1984.
brough, pp. 1 09-50. Amsterdam: Else Polychlorinated dibenzofurans (PCDFs):
vier. 406 pp. effects of structure on binding to the
42 . Matsumura, F. 1 983. Biochemical as 2 , 3 ,7 ,8-TCDD cytosolic receptor pro
pects of action mechanisms of 2,3,7,- tein, AHH induction and toxicity. Tox
8-tetrachlorodibenzo-p-dioxin (TCDD) ieol. 32: 1 3 1-44
 PCDDs AND PCDFs-SARs 395

52. Nagayama, J . , Kuroki, H . , Masuda, Y . , 62. Owens, I. S. 1977 . Genetic regulation of

Kuratsune, M . 1983. A comparative VDP-glucuronosyltransferase induction
study of polychlorinated dibenzofurans, by polycyclic aromatic hydrocarbons in
polychlorinated biphenyls and 2,3,7,8- mice. 1. Bioi. Chem. 252:2827-33 I
tetrachlorodibenzo-p-dioxin on aryl hy 63. Thunberg , T., Ahlborg , V. G . , Wahl
drocarbon hydroxylase inducing potency strom, B. 1984. Comparison between the
in rats. Arch. Toxicol. 53: 177-84 effects of 2,3,7 ,8-tetrachlorodibenzo-p
53. Bradlaw, J. A . , Casterline, J. L. 1979. dioxin and six other compounds on vita
Induction of enzyme activity in cell cul min A storage, the VDP-glucuronosyl
ture: a rapid screen for detection of planar transferase and the aryl hydrocarbon hy
polychlorinated organic compounds. 1. droxylase activity in the rat liver. Arch.
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

Assoc. Off. Anal. Chem. 62:904--16 Toxicol. 55: 16-19

Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

54. Goldstein, J. A . , Linko, P. 1984. Differ 64. Beatty , P. W., Neal, R. A. 1976. Induc
ential induction of 2,3, 7 ,8-tetrachlorodi tion of DT-diaphorase by 2,3, 7,8-
benzo-p-dioxin-inducible fonns of cy tetrachlorodibenzo-p-dioxin (TCDD).
tochrome P-450 in extrahepatic versus Biochem. Biophys. Res. Commun.
hepatic tissues. Mol. Pharmacol. 25: 68: 197-204
185-91 65. Nebert, D. W., Jensen, N . , Perry, J . ,
55. Tukey, R . H., Negishi, M . , Nebert, D. Oka, T . 1980. Associations between
W. 1982. Quantitation of hepatic cyto ornithine decarboxylase E,C.-4. 1 . 1 . 17
chrome P,-450 mRNA with the use of induction and the Ah locus in mice
cloned DNA probe: effects of various P- treated with polycyclic aromatic com
450 inducers in C57BLl6N and DBA/2N pounds. 1. Bioi. Chem. 255:6836-
mice. Mol. Pharmacol. 22:779-86 42
56. Tukey, R. H. , Nebert, D. W. 1984. 66. Puhvel, S. M . , Ertl , D. C . , Lynberg, C.
Regulation of mouse cytochrome P3-450 A. 1984. Increased epidennal transgluta
by the Ah receptor studies with P3"450 minase activity following 2 ,3,7,8-tetra
DNA clone. Biochem. 23:6003-8 chlorodibenzo-p-dioxin: In vivo and in
57. Kimura, S . , Gonzalez, F. J . , Nebert, D. vitro studies in mouse skin. Toxicol.
W. 1984. The murine Ah locus. Com Appl. Pharmacol . 73:42-47
parison of the complete cytochrome PI- 67. Kurl, R. N . , Lund, J . , Poellinger, L. ,
450 and P3"450 DNA nucleotide and ami Gustafsson, J-A. 1982. Differential ef
no acid sequences. 1. Bioi. Chem. fects of 2,3,7 ,8-tetrachlorodibenzo-p
259: 1 0705- 13 dioxin on nuclear RNA polymerase activ
58. Thomas, P. E., Reedy, J., Reik, L. M . , ity in the rat liver and thymus. Biochem.
Ryan, D. E . , Koop, D. R . , Levin, W . Phannacol. 3 1 :2459-62
1984. Vse of monoclonal antibodies 68. Sawahata, T . , Olson, J. R . , Neal, R . A .
probes against rat hepatic cytochromes 1982. Identification of metabolites of
P-450c and P-450d to detected im 2,3,7,8-tetrachlorodibenzo-p-dioxin
munochemically related isozymes in liv (TCDD) fonned on incubation with iso
er microsomes from different species. lated rat hepatocytes. Biochem. Biophys.
Arch. Biochem. Biophys . 235:239- Res. Commun. 105:34 1-46
53 69. Poland, A . , Glover, E. 1979. An es
5 9 . Serabjit-Singh, C. J . , Albro, P. W . , timate of the maximum in vivo covalent
Robertson, I. G. C . , Philpot, R . M. binding of 2,3,7 ,8-tetrachlorodibenzo-p
1983. Interaction between xenobiotics dioxin to rat liver protein, ribosomal
that increase or decrease the levels of RNA and DNA. Cancer Res. 39:3341-
cytochrome P-450 isozymes in rabbit 44
lung and liver. J. Bioi. Chem. 258: 70. Weber, H . , Poiger, H . , Schlatter, C .
12827-34 1982. Fate of 2,3,7,8-tetrachlorodiben
60. Liem, H. H., Muller-Eberhard, V . , zo-p-dioxin metabolites from dogs and
Johnson , E. F . 1980. Differential induc rats . Xenobiatica 12:353-57
tion of 2,3,7 ,8-tetrachlorodibenzo-p 71. Weber, H . , Poiger, H . , Schlatter , C .
dioxin of multiple-fonns of rabbit micro 1982. Acute oral toxicity o f TCDD
somal cytochrome P-450: evidence or metabolites in male guinea pigs. Toxicol.
tissue specificity . Mol. Pharmacol. 18: Lett . 14: 177-82
565-70 72. Rozman, K . , Rozman , T . , Greim. H .
6 1 . Baars, A. J . , Jansen, M . , Breimer, D. D . 1984. Effect o f thyroidectomy and thy- .
1978. The influence o f phenobarbital, 3 - roxine on 2,3 ,7,8-tetrachlorodibenzo-p
methylcholanthrene and 2,3,7 ,8-tetra dioxin (TCDD) induced toxicity. Tox
chlorodibenzo-p-dioxin on glutathione S icol. Appl. Pharmacol. 72:372-76
transferase activity of rat liver cytosol. 73. pazdernik, T. L . , Rozman, K. L. Effect
Biochem. Pharmacal. 27:2487-94 of thyroidectomy and thyroxine on
 396 SAFE

2,3,7 ,8-tetrachlorodibenzo-p-dioxin - in monkey during late gestation. Biochem.

duced immunotoxicity. Life Sci. 36: J. 225 : 1 83-88
695-703 85. Poland, A. P. , Glover, E . , Kende, A. S .
74. Safe , S. 1984. Polychlorinated biphenyls 1 976. Stereospecific, high affinity bind
(PCBs) and polybrominated biphenyls ing of 2,3,7 ,8-tetrachlorodibenzo-p
(PBBs): biochemistry, toxicology and dioxin by hepatic cytosol. Evidence that
mechanism of action. CRC Crit. Rev. the binding species is the receptor for the
Toxicol. 1 3 : 3 1 9-95 induction of aryl hydrocarbon hydroxy
75. Poland, A. , Glover, E. 1980. 2,3,7,8- lase. J. Bioi. Chem . 25 1 :4936-46
Tetrachlorodibenzo-p-dioxin: Segrega 86. Greenlee, W. F. , Poland, A. P. 1979.
tion of toxicity with the Ah locus. Mol. Nuclear uptake of 2,3 ,7 ,8-tetrachlorodi
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

Pharmacol. 17:86-94 benzo-p-dioxin in C57BU6J and DBA!

76. Pratt, R. M . , Dencker, L., Diewert, V. 2J mice. J. Bioi. Chem. 254:9814-21
M. 1984. 2,3,7,8-Tetrachlorodibenzo-p 87. Carlstedt-Duke, J., Elfstrom, G.,
dioxin-induced cleft palate in the mouse: Snochowski , M . , Hogberg, B . , Gustafs
evidence for alterations in palatal shelf son, J-A. 1978. Detection of the 2,3,7,8-
fusion. Teratogenesis Carcin. and Mu tetrachlorodibenzo-p-dioxin (TCDD) re
tagen 4:427-36 ceptor in rat liver by isoelectric focusing
77. Birnbaum, L. S . , Weber, H . , Harris, M . in polyacrylamide gels Toxicol. Lett.
W . , Lamb, J . C . , McKinney, J. D . 1985. 2:365-73
Toxic interaction of specific polychlori 88. Hannah, R. R . , Neber!, D. W . , Eisen, H.
nated biphenyls and 2,3,7,8-tetrachloro J . 198 1 . Regulatory gene product of the
dibenzo-p-dioxin: increased incidence of Ah complex. Comparison of 2,3 ,7,8-
cleft palate in mice. Toxicol. Appl. Phar tetrachlorodibenzo-p-dioxin and 3-meth
macol. 77:292-302 yIcholanthrene binding to several moiet
78. Weber, H . , Lamb, J. C . , Harris, M . W. , ies in mouse liver cytoco!. J. Bioi. Chem.
Moore, J. A. 1984. Teratogenicity of 256:4584-90
2,3,7,8-tetrachlorodibenzofuran (TCDF) 89. Okey, A. B . , Bondy, G. P . , Mason, M .
in mice. Toxicol. Lett. 20:1 83-88 E . , Kahl, G. F. , Eisen, H. J . , eta!. 1979.
79. Hassoun, E. , d'Argy, R . , Dencker, L. Regulatory gene products of the Ah re
1984. Teratogenicity of 2,3,7,8- ceptor complex and evidence for its nu
tetrachlorodibenzofuran in the mouse. J. clear translocation. J. Bioi. Chem.
Toxicol. Environ. Health 14:337-5 1 254: 1 1636-48
80. Hassoun, E . , d'Argy, R. , Dencker, L. , 90. Gasiewicz, T. A . , Neal, R. A. 1982. The
Lundin, L. G . , Borwell, P. 1984. Ter examination and quantitation of tissue
atogenicity of 2,3,7,8-tetrachlorodiben cytosolic receptors for 2,3,7 ,8-tetrachlo
zofuran in BXD recombinant inbred rodibenzo-p-dioxin using hydroxyapa
strains. Toxicol. Lett. 23:37-42 tite . Anal. Biochem. , 1 24: I -l l
81. Scheutz, E. G . , Wrighton, S. A . , Bar 9 1 . Gasiewicz, T. A . , Rucci, G. 1984. Ex
wick, J. L . , Guzelian, P. S. 1984. Induc amination and rapid analysis of hepatic
tion of cytochrome P-450 by glucocorti cytosolic receptors for 2,3,7 ,8-tetrachlo
eoids in rat liver. J. Bioi. Chem. 259: rodibenzo-p-dioxin using gel permeation
1 999-2006 high performance liquid chromatogra
82. Lax, R. E . , Baumann, P . , Schriefers, H . phy. Biochem. Biophys. Acta 798:37-
1984. Changes in the activities o f micro 45
somal enzymes involved in hepatic 92. Carlstedt-Duke, J. M. B. 1979. Tissue
steroid metabolism in the ' rat after ad distribution of the receptor for 2,3,7,8-
ministration of androgenic, estrogenic tetrachlorodibenzo-p-dioxin in the rat.
and progestational anabolic and catatoxic Cancer Res. 39: 3 172-76
steroids. Biochem. J. 33:1 235-41 93. Gasiewicz, T. A. Evidence for a
83. Rumbaugh, R. C . , McCoy, Z. , Lucier, homologous nature of Ah receptors
G. W. 1984. Correlation of hepatic cyto among . mammalian species 1984. In
solie androgen binding proteins with an Mechanisms ojDioxin Action, ed. A . Po
drogen induction of hepatic microsomal land, R. D. Kimbrough, pp. 1 61-75.
ethylmorphine N-demethylase in the rat. Banbury Report 18, Cold Spring Harbor
J. Steroid Biochem. 2 1 :243-54 Laboratory. 500 pp.
84. Leakey, J. A . , Althaus, Z. R . , Bailey, J. 94. Kahl, G. F . , Friederici, D. E . , Bigelow,
R. , Slikker, W. 19 85. Dexamethasone S. W. , Okey, A. B . , Neber!, D. W.
increased UDP-glucuronosyl transferase Ontogenetic expression of regulatory and
activity towards bilirubin, oestradiol and structural gene products associated with
testosterone in foetal liver from rhesus the Ah locus . Comparison of rat , mouse,
 PCDDs AND PCDFs-SARs 397

rabbit and Sigmoden hispedies. Devel. Biochem. Biophys. Res. Commun. 1 1 8:

Pharmacal. Ther. 1 : 1 37-52 1 83--90
95. Okey, A. B . , Vella, L. M. 1982. Binding 105 . Okey, A. B . , Dube, A. W. , Vella, L. M.
of 3-methylcholanthrene and 2,3,7,8- 1984. Binding ofbenzo[a]pyrene and di
tetrachlorodibenzo-p-dioxin to a com benz[a,h]anthracene to the Ah receptor in
mon Ah receptor site in mouse and rat mouse and rat hepatic cytosols. Cancer
hepatic cytosols. Eur. J. Biochem. Res. 44: 1426--32
1 27:39--47 106. Carlstedt-Duke, J. M. B . , Elfstrom, G . ,
96. Mason, M. E . , Okey, A. B. 1982. Hogberg, B . , Gustafsson, J. A. 1979.
Cytosolic and nuclear binding of 2,3,7,8- Ontogeny of the rat hepatic receptor for
2,3,7,B-tetrachlorodibenzo-p-dioxin and
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

tetrachlorodibenzo-p-dioxin to the Ah re
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

ceptor in extrahepatic tissues of rats and its endocrine independence. Cancer Res.
mice. Eur. J. Biochem. 123:209-- 1 5 39:4653--5 6
9 7 . Okey, A. B . , Mason, M. E . , Vella, L . 107. Poellinger, L . , Lund, J., Gillner, M . ,
M . 1983. The A h receptor: species and Hansson, L. A . , Gustaffson, J. A. 1984.
tissue variation in binding of 2,3,7,B Physiochemical characterization of spe
tetrachlorodibenzo-p-dioxin and carcino cific and nonspecific polyaromatic
genic aromatic hydrocarbons. In Ex hydrocarbon binders in rat and mouse
trahepatic Drug Metabolism and Chemi liver cytosol. J. Bioi. Chem. 258: 1 3535-
cal Carcinogenesis, ed. J. Rydstrom, M. 42
Bengtsson, pp. 389--93. Amsterdam: 108. Okey, A. B . , Vella, L. M . , Iverson, F.
Elsevier 1984. Ah receptor in primate liver: bind
98. Miller, A. G . , Israel, D . , Whitlock, J. P. ing of 2,3,7 ,8-tetrachlorodibenzo-p
1983. Biochemical and genetic analysis dioxin and carcinogenic polycyclic
of variant mouse hepatoma cells de aromatic hydrocarbons. Can. J. Physial.
fective in the induction of benzo[a] Pharmacal. 62: 1292-95
pyrene metabolizing enzyme activity. 109. Nebert, D. W . , Eisen, H. J . , Hankinson,
J. Bioi . Chem. 258:3523-27 O. 1984. The Ah receptor: binding
99. Okey, A. B . , Bondy, G. P. , Mason, M. specificity only for foreign chemicals.
E . , Nebert, D. W . , Forster-Gibson, C. Biachem. Pharmacal. 33:917-24
J., et al. 1980. Temperature-dependent 1 1 0. Hudson, L. G . , Shaikh, R . , Toscano, W.
cytosol-to-nucleus translocation of the A., Greenlee, W. F. 1983. Induction of
Ah receptor for 2,3,7,8-tetrachlorodi 7 -ethoxycoumarin O-deethylase activity
benzo-p-dioxin in continuous cell culture in - '.lltured human epithelial cells by
lines. J. Bioi. Chem. 255 : 1 1415--22 ,,:,3,7,8 - tetrachlorodibenzo - p - dioxin
100. Carlstedt-Duke, J. M. B . , Harnemu, U. (TCDD): evidence for a TCDD receptor.
B . , Hogbert, B . , Gustafsson, J. A. 19B I . Biochem. Biaphys. Res. Cammun . 1 15:
Interaction of hepatic receptor protein for 6 1 1-17
2,3,7,8-tetrachlorodibenzo-p-dioxin I l l . Jones, P. B . C., Miller, A. G., Israel, D.
with DNA. Biochem. Biophys. Acta I . , Galeazzi , D. R., Whitlock, J. P.
672: 1 3 1--41 1984. Biochemical and genetic analysis
101. Whitlock, J . P . , Galeazzi, R. 1984. of variant mouse hepatoma cells which
2 , 3 ,7,8-Tetrachlorodibenzo-p-dioxin re overtranscribe the cytochrome P ,-450
ceptors in wild type and variant mouse gene in response to 2,3,7,8-tetrachloro
hepatoma cells; nuclear location and dibenzo-p-dioxin. J. Bioi. Chem. 259:
strength of nuclear binding. J. Bioi. 12357-63
Chem. 259:980--85 1 1 2. Israel, D. I . , Whitlock, J. P. 1984. Regu
102. Poellinger, L . , Kurl, R. N . , Lund, J . , lation of cytochrome P,-450 gene
Gillner, M. , Carlstedt-Duke, J. M. B . , et transcription by 2,3,7,8-tetrachlorodi
al. 1982. High affinity binding of benzo-p-dioxin in wild type and variant
2,3, 7 ,8tetrachlorodibenzo-p-dioxin in mouse hepatoma cells. J. Bioi. Chem.
cell nuclei from rat liver. Biochem. Bio 254:5400--2
phys. Acta 7 14:5 16--23 1 1 3. Jones, P. B . C . , Galeazzi, D. R . , Fisher,
1 03 . Gasiewicz, T. A. and Rucci, G. 1984. J. M . , Whitlock, 1. P. 1985. The control
Cytosolic receptor for 2,3,7,8-tetrachlo of cytochrome P ,-450 gene expression by
rodibenzo-p-dioxin. Mol. Pharmacal. dioxin. Science 227: 1499--1 502
26:90--98 1 14. Ringold, G. M. 1985. Steroid hormone
104. Gasiewicz, T. A . , Ness, W. C . , Rucci, regulation of gene expression. Ann. Rev.
G. 1984. Ontogeny of the cytosolic re Pharmacal. Taxical. 25:529-66
ceptor for 2,3,7 ,8-tetrachlorodibenzo-p 1 15. Safe, S . , Safe, L. 1984. Synthesis and
dioxin in rat liver, lung and thymus. characterization of twenty-two poly-
 398 SAFE

chlorinated dibenzofurans. 1. Agric. pig, mouse and hamster. Prac. Natl.

Food Chern. 32:68-72 Acad. Sci. U.S.A. 8 1 :7407-1 1
1 1 6. Denomme, M. A . , Homonko, K. , Fujita, 1 26. McConnell, E. E . , Moore, J. A . , Hase
T . , Sawyer, T . , Safe, S. 1985. The man, J. K . , Harris, M. W. 1978. The
effects of substituents on the cytosolic comparative toxicity of chlorinated di
receptor binding avidities and AHH in benzo-p-dioxin in mice and guinea pigs.
duction potencies of 7-substituted-2,3- Toxical. Appl. Pharmacal. 44:335-56
dichlorodibenzo-p-dioxins-QSAR anal 1 27 . Moore, J. A . , McConnell, E. E . , Dal
ysis. Mol. Pharmacol. 27:656-61 gard, D. N . , Harris, M. W. 1979. Com
1 17 . Denomme, M. A . , Homonko , K . , Fujita, parative toxicity of three halogenated di
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

T . , Sawyer, T . , Safe, S. 1986. Sub benzofurans in guinea pigs, mice and

rhesus monkeys. Ann. N. Y. Acad. Sci.
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

stituted polychlorinated dibenzofuran re

ceptor binding affinities and AHA induc 30: 1 5 1-63
tion potencies-a QSAR analysis. Chem. 1 28 . Knutson, J. C . , Poland, A. 1 982. Re
BioI. Interact. In press sponse of murine epidermis to 2 , 3 ,7 ,8-
! l8. Bandiera, S . , Sawyer, T . , Campbell, M . tetrachlorodibenzo-p-dioxin. Interaction
A . , Fujita, T. , Safe, S . 1983 . Competi of Ah and hr loci. Cell 30:225-234
tive binding to the cytosolic 2,3 ,7,8- 1 29 . Poland, A . , Knutson, J. C . , Glover, E.
TCDD receptor: effects of structure on 1 984. Histologic changes produced by
the affinities of substituted halogenated 2 , 3 ,7,8-tetrachlorodibenzo-p-dioxin in
biphenyls-a QSAR approach. Biochem. the skin of mice carrying mutations that
Pharmacol. 32:3803- 1 3 affect integument. 1. Invest. Derm.
1 1 9. Verloop, A. 1 983. The STERIMOL 83:454-59
approach: further development of the 130. Poland, A . , Palen, D . , Glover. 1982.
method and new applications. In Pesti Tumour promotion by TCDD in skin of
cide Chemistry, Human Welfare and the HRS/J hairless mice. Nature 300:27 1-73
Enviranment, ed. J. Miyamoto, P. C. 1 3 \ . Kurl, R. N. and Villee, C. A. 1 985. A
Kearney, pp . 334-44. Oxford: Pergamon metabolite of riboflavin binds to the
120. Knutson, J. C . , Poland, A. 1980. 2 ,3,7,8 - tetrachlorodibenzo - p - dioxin
Keratinization of mouse teratoma cell (TCDD) receptor. Pharmacol. 30:241-
line XB produced by 2,3,7,8- 44
tetrachlorodibenzo-p-dioxin: an in vitro 1 32 . Poland, A . , Glover, E. 1975. Genetic
model of toxicity. Cell 22:27-36 expression of aryl hydrocarbon hydroxy
121. Milstone, L. M . , LaVigne, J. F. 1984. lase by 2 , 3 ,7 ,8-tetrachlorodibenzo-p
2 , 3 ,7,8-Tetrachlorodibenzo-p-dioxin in dioxin: Evidence for a receptor mutation
ducers hyperplasia in confluent cultures in genetically non-responsive mice. Mal.
of keratoinocytes . 1. Invest. Dermatol. Pharmacal. I I :389-98
82:532-34 1 3 3 . Nebert, D. W . , Robinson, J. R . , Niwa,
1 22. Hudson, L. G . , Toscano, W. A . , Green A . , Kumaki, K . , Poland, A . P. 1975.
lee, W. F. 1985. Regulation of epidermal Genetic expression of aryl hydrocarbon
growth factor binding in a human kera hydroxylase activity in the mouse. 1.
tinocyte cell line by 2,3,7 ,8-tetrachloro Cell. Physiol. 85:393-14
dibenzo-p-dioxin. Taxical. Appl. Phrma 134. Niwa, A . , Kumaki, K . , Nebert, D. W.
col. 77:251-59 1 975 . Induction of aryl hydrocarbon hy
1 23 . Osborne, R . , Greenlee , W. F. 1985 . droxylase in various cell cultures by
2 , 3 ,7,8-Tetrachlorodibenzo-p-dioxin 2 , 3 ,7,8 - tetrachlorodibenzo - p - dioxin.
(TCDD) enhances terminal differentia Mol. Pharmacal. 1 l :399-08
tion of cultured human epidermal cells. 1 3 5 . Jones, K. G . , Sweeney, G . D . 1980.
Toxicol. Appl. Pharmacol. 77:434-43 Dependence of the porphyrogenic effect
124. Karenlampi, S. 0., Eisen, H. J . , Hankin of 2,3,7 ,8-tetrachlorodibenzo-p-dioxin
son, 0 . , Nebert, D. W. 1983 . Effects of upon inheritance of aryl hydrocarbon
cytochrome Pt-450 inducers on the cell hydroxylase responsiveness. Taxical.
surface receptors for epidermal growth Appl. Pharmacal. 53:42-49
factor, phorbol 1 2 , 1 3-dibutyrate or in 136. Nagarkatti , P. , Sweeney, G. D . , Gaul
sulin of cultured mouse hepatoma cells. die, J . , Clark, D. A. 1 984. Sensitivity to
1. Bial. Chem. 258 : 1 0378-83 suppression of cytotoxic T cell genera
125. Madhukar, B. V . , Brewster, D. W . , tion by 2,3,7 ,8-tetrachlorodibenzo-p
Matsumura, F. 1984. Effects o f i n vivo dioxin (TCDD) is dependent on the Ah
administered 2,3,7 ,8-tetrachlorodiben genotype of the murine host. Taxicol.
zo-p-dioxin on receptor binding of Appl. Pharmacal. 72: 1 69-76
epidermal growth factor in the hepatic 1 37. Clark, D. A . , Sweeney, G. D . , Safe, S . ,
plasma membrane of rat, guinea Hancock, E . , Kilburn, D . G . , Gauldie, J .
 PCDDs AND PCDFs-SARs 399

1983. Cellular and genetic basis for 1978. 2,3,7,8-Tetrachlorodibenzo-p

suppression of cytotoxic T cell genera dioxin as cocarcinogen causing 3-
tion by haloaromatic hydrocarbons. Im methylcholanthrene-initiated subcuta
munopharmacol. 6: 143-53 neous tumors in mice genetically nonre
138. Vecchi, A . , Sironi, M . , Canegrati, M . sponsive at Ah locus. Cancer Res. 38:
A . , Recchia, M . , Garattini, S . 1983 . Im 2777-83
munosuppressive effects of 2,3 ,7,8- 144. DiGiovanni , J . , Berry, D. L. , Gleason,
tetrachlorodibenzo-p-dioxin in strains of G. L. , Kishore , G. S . , Siaga, T. J. 1980.
mice with different susceptibility to in Time-dependent inhibition by 2,3,7,-
duction of aryl hydrocarbon hydroxylase. 8-tetrachlorodibenzo-p-dioxin of skin
Taxicol. Appl. Pharmacal. 68:434-41 tumorigenesis with polycyclic hydrocar
by Stanford University - Main Campus - Lane Medical Library on 03/30/13. For personal use only.

1 39. Vecchi , A., Mantovani , A., Sironi, M . , bons. Cancer Res. 40:1 580-87
Annu. Rev. Pharmacol. Toxicol. 1986.26:371-399. Downloaded from www.annualreviews.org

Luini, W . , Spreafico, F. , Garattini, S . 145. Sawyer, T. , Bandiera, S . , Safe , S . ,

1 980. The effect of acute administration Hutzinger, 0 . , Olic, K . 1983. Bioanaly
of 2,3,7 ,8-tetrachlorodibenzo-p-dioxin sis of polychlorinated dibenzofuran and
(TCDD) on humoral antibody production dibenzo-p-dioxin mixtures in fly ash.
and cell-mediated activities in mice. Chemasphere 12:529-35
Arch. Toxicol. 4: 1 63-65 146. Gierthy, J. F . , Crane, D . , Frenkel, G. D .
140. Greig, J. B . , Francis, J. E . , Kay, S. J. E . , 1 984. Application o f a n i n vitro
Lovell, D. P . , Smith, A. G. 1984. In keratinization assay to extracts of soot
complete correlation of 2,3 ,7 ,8-tetra from a fire in a polychlorinated biphenyl
chlorodibenzo-p-dioxin hepatotoxicity containing transformer. Fund. Appl.
with Ah phenotype in mice. Toxico Taxieal. 4: 1036-41
L.App/. PharmacoL. 74: 1 7-25 147. Bandiera, S . , Farrell, K., Mason, G . ,
141 . Pitot, H. c . , Goldsworthy, T. , Camp Kelley, M . , Romkes, M . , e t al. 1984.
bell, H . A . , Poland, A. 1980. Quantita Comparative toxicities of the polychlo
tive evaluation of the promotion of rinated dibenzofuran (PCDF) and bi
2 , 3 ,7 ,8-tetrachlorodibenzo-p-dioxin of phenyl (PCB) mixtures which persist in
hepatocarcinogenesis from diethylnitro Yusho victims. Chemosphere 1 3:507-12
samine. Cancer Res. 40:3616-20 148. Sawyer, T . , Safe , S . 1985. In vitro AHH
142. Abernethy, D. J . , Greenlee, W. E , induction by polychlorinated biphenyl
Huband, J . C . , Boreiko, C . J . 1985. and dibenzofuran mixtures: additive
2,3,7,8 - Tetrachlorodibenzo - p - dioxin effects. Chemosphere 14:79-84
(TCDD) promotes the transformation of 149. Rizzardini , M . , Romano, M . , Tursi, F . ,
C3H1IOTl/2 cells. Carcin . 6:65 1-53 Salmona, M . , Vecchi, A . , e t al. 1983 .
143. Kouri, R. E. , Rude, T. H . , loglekar, R . , Toxicological evaluation of urban waste
Dansette, P . M . , Jerina, D. M . , e t al. emissions. Chemosphere 12:559-64