Pharmacologic evidence to support clinical decision making for peripartum methadone treatment

RATIONALE

Limited pharmacological data are available to guide methadone treatment during pregnancy and postpartum.

OBJECTIVES

Study goals were to (1) characterize changes in methadone dose across childbearing, (2) determine enantiomer-specific methadone withdrawal kinetics from steady state during late pregnancy, (3) assess enantiomer-specific changes in methadone level/dose (L/D) ratios across childbearing, and (4) explore relationships between CYP2B6, CYP2C19, and CYP3A4 single-nucleotide polymorphisms and maternal dose, plasma concentration, and L/D.

METHODS

Methadone dose changes and timed plasma samples were obtained for women on methadone (n = 25) followed prospectively from third trimester of pregnancy to 3 months postpartum.

RESULTS

Participants were primarily white, Medicaid insured, and multiparous. All women increased their dose from first to end of second trimester (mean peak increase = 23 mg/day); 71 % of women increased from second trimester to delivery (mean peak increase = 19 mg/day). Half took a higher dose 3 months postpartum than at delivery despite significantly larger clearance during late pregnancy. Third trimester enantiomer-specific methadone half-lives (range R-methadone 14.7-24.9 h; S-methadone, 8.02-18.9 h) were about half of those reported in non-pregnant populations. In three women with weekly 24-h methadone levels after delivery, L/D increased within 1-2 weeks after delivery. Women with the CYP2B6 Q172 variant GT genotype have consistently higher L/D values for S-methadone across both pregnancy and postpartum.

CONCLUSIONS

Most women require increases in methadone dose across pregnancy. Given the shorter half-life and larger clearances during pregnancy, many pregnant women may benefit from split methadone dosing. L/D increases quickly after delivery and doses should be lowered rapidly after delivery.

Phase I trial of pemetrexed in combination with cetuximab and concurrent radiotherapy in patients with head and neck cancer

BACKGROUND

We studied the combination of pemetrexed, a multi-targeted antifolate, and cetuximab, an mAb against the epidermal growth factor receptor, with radiotherapy in poor prognosis head and neck cancer.

PATIENTS AND METHODS

Patients received pemetrexed on days 1, 22, and 43 on a dose-escalation scheme with starting level (0) 350 mg/m(2) (level -1, 200 mg/m(2); level +1, 500 mg/m(2)) with concurrent radiotherapy (2 Gy/day) and cetuximab in two separate cohorts, not previously irradiated (A) and previously irradiated (B), who received 70 and 60-66 Gy, respectively. Genetic polymorphisms of thymidylate synthase and methylenetetrahydrofolate reductase were evaluated.

RESULTS

Thirty-two patients were enrolled. The maximum tolerated dose of pemetrexed was 500 mg/m(2) in cohort A and 350 mg/m(2) in cohort B. Prophylactic antibiotics were required. In cohort A, two dose-limiting toxicities (DLTs) occurred (febrile neutropenia), one each at levels 0 and +1. In cohort B, two DLTs occurred at level +1 (febrile neutropenia; death from perforated duodenal ulcer and sepsis). Grade 3 mucositis was common. No association of gene polymorphisms with toxicity or efficacy was evident.

CONCLUSION

The addition of pemetrexed 500 mg/m(2) to cetuximab and radiotherapy is recommended for further study in not previously irradiated patients.

Association of metabolic gene polymorphisms with alcohol consumption in controls

The objectives were to study the association between metabolic genes involved in alcohol metabolism (CYP2E1 RsaI, CYP2E1 DraI, ADH1C, NQO1) and alcohol consumption in a large sample of healthy controls. Healthy subjects were selected from the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens (GSEC). Subjects with information on both alcohol consumption and at least one of the studied polymorphisms were included in the analysis (n=2224). Information on the amount of alcohol consumption was available for a subset of subjects (n=844). None of the studied genes was significantly associated with drinking habits. A significant heterogeneity with age was observed when studying the association between CYP2E1 RsaI and alcohol drinking. CYP2E1 RsaI polymorphism was significantly associated with being a never drinker at older ages (odds ratio [OR] 2.4, 95% confidence interval [CI] 1.2-4.8; at ages above 68 years), while the association was reversed at ages below 47 years (OR 0.5, 95% CI 0.2-1.4). For subjects with detailed information on alcohol intake, no association between alcohol quantity and polymorphisms in metabolic genes was observed; subjects carrying the NQO1 polymorphism tended to drink more than subjects carrying the wild-type alleles. Therefore, no significant association between CYP2E1 RsaI, CYP2E1 DraI, ADH1C, NQO1 polymorphisms and alcohol consumption was observed in healthy controls.

Prediction of response to alkylator-based chemotherapy in metastatic melanoma (MM) using gene expression and promoter methylation signatures

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Background: Temozolomide and dacarbazine (TMZ and DTIC) remain the mainstay of alkylator-based chemotherapy for MM, despite response rates of 10–15% and the absence of any impact on survival. Classification of patients according to responsiveness can guide the individualization of therapy and inform approaches to abrogate mechanisms of chemotherapy resistance. Epigenetic mechanisms play an important role in regulation of genes associated with resistance and were evaluated in tandem with gene expression profiling in biological samples from MM patients (pts) to refine our understanding of the epigenomic-genomic-phenotypic interplay. Methods: We examined promoter methylation and gene expression in tumor tissues of 21 pts with MM treated with TMZ or DTIC, using high throughput technologies (Illumina Inc). The cases were divided into responder (R) and non-responder (NR) groups based on clinical response. The data were analyzed using Prediction Analysis of Microarrays (PAM) from BRB array tools. Results: Differential promoter methylation analysis revealed that 63.6% of promoter sites were hypomethylated in tumors obtained from R pts (p<0.0001). PAM analysis of gene expression data revealed that a classifier set consisting of 82 genes was able to predict NRs from Rs with 83% sensitivity and 89% specificity. Promoter methylation profiling did not independently correlate with R status. A simultaneous analysis of the promoter methylation and gene expression values first stratified into 3 data-driven categories and then combined into a 3 by 3 matrix allowed us to identify a common gene expression/methylation signature of 15 genes that classified both NR and R groups accurately 100% of the time. Conclusions: Gene expression signatures independently predict response to chemotherapy in MM, however promoter methylation profiling alone does not. Analysis of combined gene expression and promoter methylation in a well- annotated clinical data set dichotomized according to response identified a highly predictive signature. The findings from this study are qualified by the relatively small sample size and are currently being validated in an expanded sample set. Supported in part by the ECOG Paul Carbone, MD, Fellowship Award.

No significant financial relationships to disclose.

TS and MTHFR gene polymorphisms in patients (pts) with recurrent or metastatic squamous cell carcinoma of the head or neck (SCCHN) treated with pemetrexed (P) and bevacizumab (B)

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Background: P inhibits multiple enzymes in folate metabolism. We examined polymorphisms in thymidylate synthase (TS) and methylenetetrahydrofolate reductase (MTHFR) in patients with SCCHN treated in a phase II clinical trial with P and B (ASCO 2008; A6069). Methods: All pts were treated with P 500 mg/m2 and B 15 mg/kg, given IV every 21 days until progression. Primary endpoint was time to progression (TTP). DNA was isolated from whole blood samples using commercially available kits. Polymorphisms examined were MTHFR (C677T, A1298C and G1793A) and TS (TS2R3R, TSG2RG and TSmut6). The MTHFR SNPs were detected using TaqMan based SNP genotyping kits from Applied Biosystems, run on the ABI Prism 7700 Sequence Detection systems v 1.7 (Foster City, CA). The TS promoter repeat and promoter SNP polymorphisms and the 3’ untranslated region 6 bp deletion polymorphism were determined using published methods to detect PCR product size and RFLP-PCR assays respectively. Results: 22 pts were genotyped from 34 enrolled. There was no significant difference in characteristics between pts with and without genotype data. For the MTHFR polymorphism C677T, there was a trend towards decreased disease control rate (DCR) (CR/PR/SD) (p = 0.058, Jonckheere-Terpstra trend test) and worse TTP (p = 0.04) transitioning from variant CC to CT to TT; comparing TT genotype versus CT and CC combined, pts with TT had inferior DCR (p = 0.03) and TTP (p = 0.0003); homozygotes with TT had a median TTP of 2.6 months (mo) 95% CI (1.4, NA) versus 5.6 mo (4.2, 11.4) for pts with CT or CC variants. For the MTHFR A1298C SNP, there was no significant difference in DCR between variants, median TTP for homozygotes pts with AA was 4.1 mo (2.6, NA) vs. 6.7 mo (5.1, NA) in pts with AC or CC variants (p = 0.084); median overall survival for AA was 10.2 mo (7.6, NA) and for AC or CC 17.6 mo (17, NA) (p = 0.045). The MTHFR G1793A and TS polymorphisms did not impact DCR, TTP or overall survival. There was no association between any polymorphism and the incidence of grade >2 toxicities. Conclusions: Polymorphisms in MTHFR are potentially associated with antitumor efficacy of P-based therapy in recurrent or metastatic SCCHN. These results warrant validation in larger studies with P in SCCHN.

No significant financial relationships to disclose.

Meta- and pooled analysis of GSTT1 and lung cancer: a HuGE-GSEC review

Lung cancer is the most common malignancy in the Western world, and the main risk factor is tobacco smoking. Polymorphisms in metabolic genes may modulate the risk associated with environmental factors. The glutathione S-transferase theta 1 gene (GSTT1) is a particularly attractive candidate for lung cancer susceptibility because of its involvement in the metabolism of polycyclic aromatic hydrocarbons found in tobacco smoke and of other chemicals, pesticides, and industrial solvents. The frequency of the GSTT1 null genotype is lower among Caucasians (10-20%) than among Asians (50-60%). The authors present a meta- and a pooled analysis of case-control, genotype-based studies that examined the association between GSTT1 and lung cancer (34 studies, 7,629 cases and 10,087 controls for the meta-analysis; 34 studies, 7,044 cases and 10,000 controls for the pooled analysis). No association was observed between GSTT1 deletion and lung cancer for Caucasians (odds ratio (OR) = 0.99, 95% confidence interval (CI): 0.87, 1.12); for Asians, a positive association was found (OR = 1.28, 95% CI: 1.10, 1.49). In the pooled analysis, the odds ratios were not significant for either Asians (OR = 0.97, 95% CI: 0.83, 1.13) or Caucasians (OR = 1.09, 95% CI: 0.99, 1.21). No significant interaction was observed between GSTT1 and smoking on lung cancer, whereas GSTT1 appeared to modulate occupational-related lung cancer.

Evaluation of flurbiprofen urinary ratios as in vivo indices for CYP2C9 activity

AIMS

We investigated flurbiprofen pharmacokinetics in 12 volunteers to develop a phenotypic trait measure that correlates with the fractional clearance to 4'-hydroxyflurbiprofen. The effect of the CYP2C9 inhibitor fluconazole on flurbiprofen metabolism was also evaluated.

METHODS

Flurbiprofen pharmacokinetics were evaluated before and after the first and seventh doses of fluconazole. The urinary recovery ratio was calculated as FLRR = 4'-OHF/[4'-OHF + F(tot)] and the urinary metabolic ratio was calculated as FLMR = 4'-OHF/F(tot), where 4'-OHF and F(tot) represent total (conjugated and unconjugated) amounts recovered in urine.

RESULTS

There was a statistically significant relationship between the 4'-OHF formation clearance (4OHCLf) and both the 8-h FLRR and the 8-h FLMR with and without administration of fluconazole. The flurbiprofen apparent oral clearance (CL/F) was decreased by 53% [90% confidence interval (CI) -58, -48] and 64% (90% CI -69, -59), respectively, after administration of one and seven doses of fluconazole when compared with administration of flurbiprofen alone; similarly, the 4OHCLf decreased by 69% (90% CI -74, -64) and 78% (90% CI -83, -73), the 8-h FLRR decreased by 35% (90% CI -41, -29) and 40% (90% CI -46, -35) and the 8-h FLMR decreased by 61% (90% CI -65, -58) and 67% (90% CI -70, -63). The magnitude of decrease in CL/F and 4OHCLf was greater after seven doses compared with after one dose of fluconazole (P < 0.005).

CONCLUSIONS

This study provides strong evidence that both the 8-h FLRR and the 8-h FLMR are suitable phenotypic indices for CYP2C9 activity.

Polymorphisms in CYP1A1, GSTM1, GSTT1 and lung cancer below the age of 45 years

BACKGROUND

A genetic component of early-onset lung cancer has been suggested. The role of metabolic gene polymorphisms has never been studied in young lung cancer cases. Phase 1 and Phase 2 gene polymorphisms are involved in tobacco carcinogens' metabolism and therefore in lung cancer risk.

METHODS

The effect of metabolic gene polymorphisms on lung cancer at young ages was studied by pooling data from the Genetic Susceptibility to Environmental Carcinogens (GSEC) database. All primary lung cancer cases of both sexes who were Caucasian and </=45 years of age at diagnosis, and the corresponding controls were selected. We obtained 261 cases and 1452 controls.

RESULTS

There was a marginally significant association between lung cancer and GSTT1 null genotype (OR=1.2; 95% CI:1.0-1.6), and a significant association between lung cancer and the homozygous CYP1A1 Msp1 variant allele (CYP1A1*2A and *2B) genotype (OR=4.7 95% CI:1.2-19.0). When data were stratified by smoking status, the association between CYP1A1 genotype and lung cancer was confined to never smokers.

CONCLUSIONS

These results suggest that metabolic genetic factors play a role in lung cancer developing at young ages.

Metabolic gene polymorphism frequencies in control populations

Using the International Project on Genetic Susceptibility to Environmental Carcinogens (GSEC) database containing information on over 15,000 control (noncancer) subjects, the allele and genotype frequencies for many of the more commonly studied metabolic genes (CYP1A1, CYP2E1, CYP2D6, GSTM1, GSTT1, NAT2, GSTP, and EPHX) in the human population were determined. Major and significant differences in these frequencies were observed between Caucasians (n = 12,525), Asians (n = 2,136), and Africans and African Americans (n = 996), and some, but much less, heterogeneity was observed within Caucasian populations from different countries. No differences in allele frequencies were seen by age, sex, or type of controls (hospital patients versus population controls). No examples of linkage disequilibrium between the different loci were detected based on comparison of observed and expected frequencies for combinations of specific alleles.

In vivo modulation of CYP enzymes by quinidine and rifampin

BACKGROUND

The metabolism of drugs and other xenobiotics is mediated by enzymes whose activities can be modulated by different compounds. The activities of these modulators have the potential to be used to optimize drug action, prevent toxicity, or identify the enzymes involved in a reaction. This approach requires that selective agents be used for specific enzymes. However, selectivity of action has been poorly characterized in vivo.

METHODS

This study investigated the effect of 3 and 28 days of treatment with quinidine (200 mg daily) and rifampin (INN, rifampicin) (600 mg daily) on the activities of four cytochrome P450 enzymes and N-acetyltransferase in 28 healthy young male volunteers divided into three groups with a cocktail of drug probes used, including caffeine, mephenytoin, debrisoquin (INN, debrisoquine), and dapsone.

RESULTS

Quinidine selectively and almost completely inhibited the activity of CYP2D6 from day 3 through day 28 without affecting any other enzymes. Rifampin showed evidence of time-dependent induction of the activities of all measured oxidative routes of metabolism but decreased the acetylation ratio in fast acetylators. The quinidine/rifampin combination resulted in selective CYP2D6 inhibition and induction of all other enzymes evaluated over this time period, suggesting that predictable complex interactions occur with the drug combination.

CONCLUSIONS

These observations illustrate the value of simultaneous assessment of the effect of modulators on the activities of multiple specific enzymes with the drug cocktail approach.

Cigarette smoking, N-acetyltransferase 2 acetylation status, and bladder cancer risk: a case-series meta-analysis of a gene-environment interaction

Tobacco use is an established cause of bladder cancer. The ability to detoxify aromatic amines, which are present in tobacco and are potent bladder carcinogens, is compromised in persons with the N-acetyltransferase 2 slow acetylation polymorphism. The relationship of cigarette smoking with bladder cancer risk therefore has been hypothesized to be stronger among slow acetylators. The few studies to formally explore such a possibility have produced inconsistent results, however. To assess this potential gene-environment interaction in as many bladder cancer studies as possible and to summarize results, we conducted a meta-analysis using data from 16 bladder cancer studies conducted in the general population (n = 1999 cases), Most had been conducted in European countries. Because control subjects were unavailable for a number of these studies, we used a case-series design, which can be used to assess multiplicative gene-environment interaction without inclusion of control subjects. A case-series interaction odds ratio (OR) > 1.0 indicates that the relationship of cigarette smoking and bladder cancer risk is stronger among slow acetylators as compared with rapid acetylators. We observed an interaction between smoking and N-acetyltransferase 2 slow acetylation (OR, 1.3; 95% confidence interval, 1.0-1.6) that was somewhat stronger when analyses were restricted to studies conducted in Europe (OR, 1.5; confidence interval, 1.1-1.9), a pooling that included nearly 80% of the collected data. Using the predominantly male European study population and assuming a 2.5-fold elevation in bladder cancer risk from smoking, we estimated that the population attributable risk percent was 35% for slow acetylators who had ever smoked and 13% for rapid acetylators who had ever smoked. These results suggest that the relationship of smoking and bladder cancer is stronger among slow acetylators than among rapid acetylators.

Quantification of G protein mRNA using reverse transcription and competitive PCR with a colorimetric microplate assay

This paper reports an assay for the quantification of levels of specific mRNA for the alpha subunits of the inhibitory G proteins G alpha i-1, G alpha i-2, and G alpha i-3. The assay employs reverse transcription and competitive polymerase chain reaction (PCR) coupled to enzyme-linked oligonucleotide sorbent assay for differential detection and quantification of PCR products. The assay was conducted with conventional thermal block PCR cyclers as well as rapid air microcapillary cyclers. The detection stage consists of three steps using synthetic oligonucleotides, commercially available reagents and a conventional 96-well plate absorbance reader at settings of 450 and 630 nm. The assay is: (1) rapid, requiring about 3 h for quantification of PCR products; (2) safe, being non-radiometric; (3) relatively simple; (4) highly sensitive, being capable of detecting less than 10 initial copies of target cDNA; (5) precise, resolving two-fold differences in initial copy numbers of specific sequences as low as 10(-20) mol; (6) linear over a 3 log range, with two-fold differences in the quantity of cDNA producing consistent reductions in quantity of specific cDNA detected; and (7) reproducible, intra-assay and inter-assay coefficients of variation being 11.9 and 14.7%, respectively.

All-trans-retinoic acid modulation of drug-metabolizing enzyme activities: investigation with selective metabolic drug probes

PURPOSE

All-trans-retinoic acid (ATRA) is a retinoid analogue that has been shown to be effective in acute promyelocytic leukemia. It is currently being investigated for efficacy in the treatment and prevention of various types of cancer. One of the factors limiting its use is the observed increase in ATRA clearance and elimination which occurs shortly after treatment is started, leading to reduced levels of drug in the body and loss of effectiveness. ATRA efficacy may be enhanced if this autoinduction of metabolism can be overcome, for example through the inhibition of the activity of the induced specific metabolizing enzyme(s). This requires the identification of this induced enzyme(s) and development of approaches to selectively inhibit its activity.

METHODS

In the course of a phase II evaluation of ATRA in prostate cancer, we investigated the activities of five specific cytochrome P450 (CYP) (CYPs 1A2, 2C19, 2D6, 2E1 and 3A4) and N-acetyltransferase enzymes using a newly developed five-drug cocktail involving caffeine, mephenytoin, debrisoquine, chlorzoxazone and dapsone respectively. Enzyme activities were assessed in 17 patients with hormone-refractory prostate cancer before the initiation of ATRA therapy, after 14 days of continuous ATRA administration and 7 days after cessation of drug therapy.

RESULTS

After 14 days of ATRA therapy, the activities of CYP2E1 (chlorzoxazone hydroxylase) and N-acetyltransferase (in fast acetylators only) were increased by 83% and 29% (P < 0.05), respectively. Both activities returned to baseline by 7 days after cessation of therapy and the profiles were similar to the changes seen in the clearance of ATRA itself. There were no changes in the activities of any of the other enzymes investigated.

CONCLUSION

This study shows that ATRA selectively modulates the activities of specific metabolizing enzymes and that this approach may be useful in identifying enzymes that can be explored in an attempt to mitigate ATRA autoinduction through selective modulation of enzyme activities. Further investigations are required to determine whether the elevated enzymes are also responsible for the increased clearance and elimination of ATRA.

Clonal analysis of human recurrent superficial bladder cancer by immunohistochemistry of P53 and retinoblastoma proteins

PURPOSE

To investigate the clonal origin of malignant cells in recurrent superficial bladder cancer.

MATERIALS AND METHODS

We compared the protein expression of p53 and retinoblastoma (Rb) by immunohistochemistry using antibody P1801 and PMG3-245, respectively, in 13 patients at the time of primary superficial bladder cancer resection (6 Ta and 7 T1) and their 15 corresponding recurrences of disease. Mutations in p53 and Rb were inferred on the basis of immunoperoxidase staining.

RESULTS

At the time of initial tumor resection, a p53 mutation was observed in 5 patients (39%) and an Rb mutation was observed in 3 (23%). The p53/Rb mutation status of recurrent bladder cancers completely matched their corresponding primary bladder cancer.

CONCLUSIONS

The chance that recurrent bladder cancer originated from independent clones in this study was extremely small (p < 10(-6)). This result strongly supports the monoclonal origin of recurrent superficial bladder cancer.

Association of low CYP3A activity with p53 mutation and CYP2D6 activity with Rb mutation in human bladder cancer

p53 and Rb gene mutations are intermediate biomarkers useful for the prediction of neoplastic progression in bladder cancers. Previously, we have shown that low CYP3A activity, measured by dapsone N-hydroxylation, and high CYP2D6 activity, assessed by debrisoquine 4-hydroxylation, were significant susceptibility risk factors in developing aggressive bladder cancer. However, no information is available about the relationship between drug/xenobiotic metabolizing enzyme activities and p53/Rb mutations that may suggest mechanisms of bladder carcinogenesis. We evaluated in vivo CYP3A activity by the dapsone recovery ratio (DPRR), CYP2D6 activity by the debrisoquine recovery ratio (DBRR), CYP2C19 activity by the mephenytoin R/S ratio (RSR), N-acetyltransferase activity by the monoacetyl dapsone to dapsone ratio and glutathione-S-transferase M1 (GSTM1) genotype by PCR. In immunohistochemical studies of bladder tumor tissue, over expression of p53 protein was detected with antibody pAb1801 and loss of Rb protein expression was evaluated with antibody PMG3-245 in patients with transitional cell carcinoma of the bladder. Low CYP3A activity was significantly associated with over expression of or mutated p53 protein (P < 0.05). High CYP2D6 activity (within the extensive metabolizer group) was significantly associated with loss of expression of or mutated Rb protein (P < 0.05). Positive p53 staining also predicted aggressive bladder cancer histopathology (P < 0.05, odds ratio 2.9), and the lowest tertile of DPRR predicted p53 positivity (P < 0.01, odds ratio 3.9 comparing means of lower tertile versus upper tertile of DPRR). These selective associations are consistent with the hypothesis that an environmental pro-carcinogen fails to be detoxified by CYP3A which may preferentially induce p53 mutations, whereas, an alternative pro-carcinogen that may be activated by CYP2D6, may selectively induce Rb mutations.

CYP2D6 mRNA expression in circulating peripheral blood mononuclear cells correlates with in vivo debrisoquine hydroxylase activity in extensive metabolizers

Extensive metabolizers of drugs which are oxidized by cytochrome P450s show wide interindividual variability in drug metabolism. Elucidation of the relationship between specific P450 isozyme mRNA expression and variability in metabolism of specific drugs could improve understanding of the molecular mechanism involved. In this study, a novel non-radiometric reverse transcription polymerase chain reaction based assay was used to quantify CYP2D6 mRNA levels in peripheral blood mononuclear cells in twelve human volunteers who were phenotyped as extensive metabolizers of debrisoquine. We report a significant correlation (r=0.724, p= 0.008) between CYP2D6 mRNA levels in circulating peripheral blood mononuclear cells and the in vivo debrisoquine recovery ratio. This suggests that interindividual variability in extensive metabolizers could be related, in part, to differences in gene expression. Circulating peripheral blood mononuclear cells can provide an accessible ex vivo measure of this phenomenon.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related compounds as antioestrogens: characterization and mechanism of action

In the female Sprague-Dawley rat uterus 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds exhibited a broad spectrum of antioestrogenic responses. For example 2,3,7,8-TCDD inhibited the 17 beta-oestradiol-induced uterine wet weight increase, peroxidase activity, oestrogen and progesterone receptor levels, epidermal growth factor (EGF) receptor binding, and EGF receptor and c-fos protooncogene mRNA levels. The aryl hydrocarbon (Ah) receptor was identified in the rat uterus and the antioestrogenic activities of TCDD and related compounds were structure-dependent. In parallel studies, the effects of TCDD as an antioestrogen in MCF-7 human breast cancer cells was also investigated. TCDD inhibited the 17 beta-oestradiol-induced proliferation of these cells and the secretion of the 34-, 52- and 160-kDa proteins. Treatment of MCF-7 cells with 1 nM [3H]-17 beta-oestradiol resulted in a rapid accumulation of nuclear oestrogen receptor (ER) complexes. Pretreatment of the cells with TCDD caused a rapid decrease in nuclear ER binding activity and immunoreactive protein; moreover, the structure-dependent potencies of TCDD and related compounds as antioestrogens were similar to their Ah receptor binding affinities. TCDD also caused a decrease in nuclear ER levels in wild-type Ah-responsive Hepa 1c1c7 cells but was inactive in Ah non-responsive mutant Hepa 1c1c7 cells. Moreover, in the wild-type cells, both actinomycin D and cycloheximide blocked the effects of TCDD. 6-Methyl-1,3,8-trichlorodibenzofuran (MCDF) has previously been characterized as a TCDD antagonist in rodents and in transformed rodent cell lines. However, like TCDD, MCDF also exhibited a broad spectrum of antioestrogenic activities in both the female Sprague-Dawley rat uterus and MCF-7 cells. MCDF is relatively non-toxic compared to TCDD and is being investigated as a compound which may be clinically useful for the treatment of mammary cancer.

Cloning and expression of complementary DNAs for multiple members of the human cytochrome P450IIC subfamily

The present study characterizes the profile of cDNAs from the human P450IIC subfamily in a library from one individual, and it describes three new members of this subfamily (IIC17, IIC18, and IIC19) isolated from two human cDNA libraries. cDNA libraries were constructed from two human livers which differed phenotypically in the hepatic content of P450 HLx (IIC8). The library from the phenotypically low HLx individual was screened by using a cDNA for rat liver P450IIC13 and an oligonucleotide probe for human IIC8. One clone, 245c, was isolated which clearly represents a new member of the human P450IIC subfamily (IIC17). This clone lacked the first 358 nucleotides at the N-terminus but was only 91% homologous in its nucleic acid sequence to IIC9 and 79% homologous to IIC8. Near-full-length clones for IIC9 were also isolated from this library, but no clones for IIC8 were found. Northern blots indicated that the mRNA for IIC8 was low or absent in this individual. A second cDNA library (from a liver phenotypically high in HLx) was then screened. Eighty-three essentially full-length (greater than 1.8 kb) clones belonging to the IIC subfamily were isolated from this library. These include full-length clones for two additional new members of the IIC subfamily. Clones 29c and 6b appear to be allelic variants (IIC18), differing by one nucleotide (one amino acid change) in the coding region. Clone 11a represents a full-length clone for a third new P450 (IIC19).(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-dependent induction of aryl hydrocarbon hydroxylase in human breast cancer cell lines and characterization of the Ah receptor

The structure-dependent induction of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase by 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran, and 1,2,4,7,8-pentachlorodibenzo-p-dioxin was determined in the MCF-7, T47-D, and MDA-MB-231 human breast cancer cell lines. Both the MCF-7 and T47-D cells were responsive to the induction effects of the halogenated aryl hydrocarbons and the structure-induction relationships were comparable to the reported structure-activity (induction, receptor binding, and toxicity) relationships observed in rodents and rodent cells in culture. The induction of ethoxyresorufin O-deethylase in the T47-D cells was the most sensitive aryl hydrocarbon (Ah) receptor-mediated response in both cell lines and this enzyme activity was more inducible than aryl hydrocarbon hydroxylase. In contrast, the three congeners were inactive as monooxygenase enzyme inducers in the MDA-MB-231 cells. Despite the differential Ah responsiveness of the cell lines, incubation of the cells with [3H]-2,3,7,8-tetrachlorodibenzo-p-dioxin followed by extraction of the nuclei with high salt and velocity sedimentation analysis of the extracts showed that specifically bound nuclear Ah receptor complexes were present in the three cell lines. The sedimentation coefficients (and levels) for the nuclear receptors were 6.6 S (32.1 fmol/mg protein/mg DNA), 6.9 S (61.6 fmol/mg protein/mg DNA), and 7.4 S (38.2 fmol/mg protein/mg DNA) in the T47-D, MCF-7, and MDA-MB-231 cell lines, respectively. Cytosolic receptor was also detected in the MCF-7 and MDA-MB-231 cells. Thus, despite the differences in Ah responsiveness of the T47-D and MDA-MB-231 cells, comparable levels of nuclear receptor were detected in both cell lines. Furthermore, the elution profiles of the nuclear receptors from DNA-Sepharose columns by using a salt gradient were similar and this suggested that defects in the DNA-binding activity of MDA-MB-231 nuclear receptor complexes were not major factors associated with their failure to respond to 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds.

Comparative activities of 2,3,7,8-tetrachlorodibenzo-p-dioxin and progesterone as antiestrogens in the female rat uterus

The comparative antiestrogenic effects of progesterone and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on cytosolic and nuclear estrogen (ERc and ERn, respectively) and progesterone (PRc and PRn, respectively) receptor levels were determined in female Long Evans rats. Estradiol treatment typically increases ER and PR levels in target cells or tissues and these proteins have been proposed as markers of estrogen action. 2,3,7,8-TCDD causes a dose-dependent decrease in uterine ERc, ERn, PRc, and PRn levels which persist up to 7 days. Progesterone treatment caused significant decreases in uterine ERc, ERn, and PRn levels; however, after 7 days, the effects of the hormone on receptor levels were diminished. The effects of 2,3,7,8-TCDD and progesterone on hepatic ER and PR levels were comparable to those observed in the uterus. Treatment of the rats with estradiol (5 micrograms/kg), estradiol (5 micrograms/kg) plus progesterone (1 mg/animal), or 2,3,7,8-TCDD (80 micrograms/kg) showed that both progesterone and 2,3,7,8-TCDD significantly antagonized the estradiol-mediated increases in uterine (and hepatic) ERc, ERn, PRc, and PRn levels and for 2,3,7,8-TCDD the decreased receptor levels persisted for up to 7 days. In vitro studies with freshly isolated uterine strips demonstrated that both 2,3,7,8-TCDD and progesterone antagonized the estradiol-mediated increases in ER and PR levels. Previous studies suggest that the antiestrogenic activity of progesterone is due, in part, to the induction of proteins which are involved in decreasing ERn levels in target cells. Moreover in the uterine strip assay procedure, it was previously shown and reproduced in this study that the decrease in uterine ERn by progesterone was inhibited by both protein and RNA synthesis inhibitors over a 4-hr incubation period. In contrast, the 2,3,7,8-TCDD-mediated decrease in uterine ERn was inhibited only by actinomycin D and not by cycloheximide or puromycin. These in vitro studies thus confirm that both progesterone and 2,3,7,8-TCDD exhibit comparable antiestrogenic effects in vivo and in vitro; however, the results suggest that these effects are expressed through different mechanisms.

Quantitative structure-activity relationships: analysis of interactions of 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2-substituted analogues with rat, mouse, guinea pig, and hamster cytosolic receptor

The competitive receptor binding affinities of thirteen 2-substituted 3,7,8-trichlorodibenzo-p-dioxins to hepatic cytosol from rat, mouse, guinea pig, and hamster were determined with [3H]-2,3,7,8-tetrachlorodibenzo-p-dioxin as the radioligand. Multiple parameter linear regression analysis of the binding data from the four species gave the following equations: pEC50 (rat) = 7.196 + 0.600 pi - 0.255 delta Es - 1.683 HB pEC50 (mouse) = 6.365 + 1.641 pi + 1.206 sigma 0 pEC50 (hamster) = 7.416 + 1.026 pi + 0.509 delta Es + 0.748 sigma 0 pEC50 (guinea pig) = 6.892 + 1.035 pi where pi, delta Es, HB, sigma 0, and Vw are physicochemical parameters for substituent lipophilicity, steric effect, hydrogen bonding capacity, electronegativity, and van der Waals volume (relative to H), respectively. These equations demonstrate that there are important species differences in the receptor protein binding site interactions with the substituted analogues. These data, coupled with the known species differences in the molecular properties of the receptor proteins, are evidence for a heterologous nature of the receptor between mammalian species. Multiple parameter linear regression analysis of the relative aryl hydrocarbon hydroxylase (AHH) induction potencies of these analogues in rat hepatoma H-4-II E-cells in culture gave the following equation. The correlation pEC50 (AHH induction) = 3.208 + 0.950 pEC50 (rat binding) - 0.955 delta B5 between receptor binding and AHH induction was dependent on a steric parameter (delta B5, STERIMOL) and the results suggest that an additional substituent-dependent process (e.g., an activation step) may be required after initial ligand-receptor binding for the ultimate expression of the receptor-mediated response (i.e., AHH induction).

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on hepatic and uterine estrogen receptor levels in rats

Administration of a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 20 or 80 micrograms/kg) resulted in significantly decreased hepatic and uterine estrogen receptor (ER) levels in 25-day-old female Long-Evans rats. By contrast, estradiol (5 and 15 micrograms/kg) administration increased hepatic and uterine ER levels, while a combination of 2,3,7,8-TCDD plus estradiol resulted in uterine and hepatic ER levels which were similar or lower than those observed after treatment with only 2,3,7,8-TCDD. In addition, 2,3,7,8-TCDD significantly decreased the effects of estradiol on uterine wet weight increase. Competitive binding studies showed that estradiol did not bind to the aryl hydrocarbon (Ah) receptor and that 2,3,7,8-TCDD did not bind to the ER. The effects of structure on the activity of polychlorinated dibenzo-p-dioxin congeners on their activity to down-regulate hepatic and uterine ER levels were determined by using 2,3,7,8-TCDD, 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 1,3,7,8-TCDD, and 1,2,4,7,8-PeCDD. Both 2,3,7,8-TCDD and 1,2,3,7,8-PeCDD exhibit high affinities for the Ah receptor and at dose levels of 80 micrograms/kg the hepatic ER levels were decreased 42 and 41%, respectively, and uterine ER levels were decreased 53 and 49%, respectively. 1,3,7,8-TCDD and 1,2,4,7,8-PeCDD bind less avidly to the Ah receptor and at dose levels of 400 micrograms/kg these compounds decreased hepatic ER levels 36 and 40%, respectively, and uterine ER levels 21 and 24%, respectively. These results support a role for the Ah receptor in the down-regulation of uterine and hepatic ER levels in the female rat by 2,3,7,8-TCDD and this effect may be associated with the decrease in spontaneous mammary and uterine tumors observed in female rats treated with 2,3,7,8-TCDD.

Polychlorinated dibenzofurans (PCDFs): correlation between in vivo and in vitro structure-activity relationships

Fifteen polychlorinated dibenzofuran (PCDF) congeners were administered in a dose-response fashion to immature male Wistar rats and ED50 values for body weight loss, thymic atrophy and the induction of the hepatic microsomal cytochrome P-448-dependent monooxygenases, aryl hydrocarbon hydroxylase (AHH) and 4-chlorobiphenyl hydroxylase were determined. There was an excellent correlation between the in vivo quantitative structure-activity relationships for these PCDFs and their in vitro activities as AHH inducers in rat hepatoma H-4-II E cells and as ligands for the 2,3,7,8-TCDD receptor protein. A comparison of isomers which differ at all 4 positions in the dibenzofuran ring system indicated that chlorine substitution at each position contributed differentially to the overall molecular activity [C-3 (or C-7) greater than C-2 (or C-8) greater than C-4 (or C-6) greater than C-1 (or C-9)]. There was also an excellent linear correlation between a plot of the -log ED50 for body weight loss vs. -log EC50 for in vitro AHH induction (correlation coefficient, r = 0.96) and -log ED50 for thymic atrophy vs. -log EC50 for in vitro AHH induction (correlation coefficient, r = 0.88). Since body weight loss and thymic atrophy in the rat are representative toxic responses to PCDFs and related toxic halogenated aryl hydrocarbons, the correlations noted above support the use of the in vitro AHH induction assay as a short term quantitative test system for this class of toxic halogenated aryl hydrocarbons.

Effects of structure on binding to the 2,3,7,8-TCDD receptor protein and AHH induction--halogenated biphenyls

The quantitative structure-activity relationships (QSARs) for polychlorinated biphenyl (PCB) congeners have been determined by comparing the EC50 values for three in vitro test systems, namely, aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) induction in rat hepatoma H-4-II-E cells and competitive binding avidities to the rat cytosolic receptor protein (using 2,3,7,8-tetrachlorodibenzo-p-dioxin as a radioligand). For several PCB congeners that are in vivo inducers of rat hepatic microsomal AHH, there was a linear correlation between the -log EC50 values for receptor and the -log EC50 values for AHH (or EROD) induction; moreover, a comparable linear relationship was observed between the -log EC50 values for AHH and EROD induction. Previous in vivo studies have shown that the most active PCB congeners 3,3',4,4'-tetra-, 3,4,4',5-tetra-, 3,3',4,4',5-penta-, and 3,3',4,4',5,5'-hexachlorobiphenyl, cause many of the biologic and toxic effects reported for the highly toxic halogenated aryl hydrocarbon, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Moreover, the monoortho-substituted homologs of the four coplanar PCBs also elicit comparable in vivo biologic and toxic responses. It was evident from the QSARs for PCBs that there was an excellent correspondence between the in vivo and in vitro potencies of the individual PCB congeners. The effects of substituents on both receptor binding and AHH/EROD induction was determined for a series of 4'-substituted (X)-2,3,4,5-tetrachlorobiphenyls (where X = H, Cl, Br, I, OH, OCH3, NO2, COCH3, F, CF3, CH3, C2H5, i-C3H7, n-C4H9 and t-C4H9). Not unexpectedly, there was a linear relationship between the -log EC50 values for AHH and EROD induction, and these results confirm that both enzymatic oxidations are catalyzed by the same cytochrome P-450 isozyme(s). The effects of substituent structure on receptor binding for 12 substituents was subjected to multiple regression analysis which correlates the relative binding affinities of the compounds with the physical chemical characteristics of the substituents. The analysis gave the following equation: log (1/EC50) = 1.53 sigma + 1.47 pi + 1.09 HB + 4.08 for n = 12, s = 0.18, r = 0.978; where n is the number of substituents, s is the standard deviation, r is the correlation coefficient, and sigma = electronegativity, pi = hydrophobicity (log P) and HB = hydrogen bonding capacity for the substituent groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Polychlorinated dibenzofurans (PCDFs): effects of structure on binding to the 2,3,7,8-TCDD cytosolic receptor protein, AHH induction and toxicity

The effects of structure on the activity of 26 polychlorinated dibenzofurans (PCDFs) as competitive ligands for the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) rat hepatic cytosolic receptor protein were determined in a dose-response fashion. The ED50 values for these compounds varied 100 000-fold and the most active PCDFs were substituted in the 2,3,7 and 8 lateral positions; the ED50 for the most active PCDF, 2,3,4,7,8-pentachlorodibenzofuran was 1.5 X 10(-8) M which was only slightly less active than 2,3,7,8-TCDD (1.0 X 10(-8) M). A comparison of the binding affinities of several isomer pairs also indicated the relative importance of chlorine substitution at C-4 (or C-6) compared to C-1 (or C-9). Moreover, for some isomers it is apparent that C-4 (or C-6) substituents are more active than lateral substituents for facilitating ligand binding to the receptor protein. This is illustrated by the relative binding potencies of the following isomer pairs: 1,2,4,6,7-/1,2,4,7,8 = 19.2; 2,6,7-/2,3,8- = 2.2; 1,3,6-/1,3,8- = 19. Most of the PCDF structure-activity effects noted above were also observed for the induction of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) in rat hepatoma H-4-II-E cells in culture. The most active compounds were also substituted in the lateral 2,3,7 and 8 positions and a comparison of C-4 (or C-6) vs. C-1 (or C-9) substituted PCDFs confirmed the higher induction potencies for most of the former group of compounds. The in vitro quantitative structure-activity data were complemented by in vivo studies which determined the relative activities of selected PCDFs as inducers of hepatic microsomal cytochrome P-448 dependent monooxygenases and their effects on body weight gain and thymus weights in immature male Wistar rats. The results indicated that for 2 series of isomers, namely the 2,3,4,7,8-, 1,2,4,7,8- and 1,2,4,7,9-pentachlorodibenzofurans and the 2,3,7,8-, 2,3,4,8- and 1,2,4,8-tetrachlorodibenzofurans, their biologic and toxic potencies were dependent on one major structural factor, the number of lateral chloro substituents. These results support the proposed role of the cytosolic receptor protein in mediating the biologic and toxic effects of the PCDFs.