Expression of xenobiotic metabolizing enzymes in breast cancer

Ultra-Fast Portable and Wearable Sensing Design for Continuous and Wide-Spectrum Molecular Analysis and Diagnostics

The design and characterization of spatiotemporal nano-/micro-structural arrangement that enable real-time and wide-spectrum molecular analysis is reported and demonestrated in new horizons of biomedical applications, such as wearable-spectrometry, ultra-fast and onsite biopsy-decision-making for intraoperative surgical oncology, chiral-drug identification, etc. The spatiotemporal sesning arrangement is achieved by scalable, binder-free, functionalized hybrid spin-sensitive (<↑| or <↓|) graphene-ink printed sensing layers on free-standing films made of porous, fibrous, and naturally helical cellulose networks in hierarchically stacked geometrical configuration (HSGC). The HSGC operates according to a time-space-resolved architecture that modulate the mass-transfer rate for separation, eluation and detection of each individual compound within a mixture of the like, hereby providing a mass spectrogram. The HSGC could be used for a wide range of applictions, including fast and real-time spectrogram generator of volatile organic compounds during liquid-biopsy, without the need of any immunochemistry-staining and complex power-hungry cryogenic machines; and wearable spectrometry that provide spectral signature of molecular profiles emiited from skin in the course of various dietry conditions.

Regulation of cardiovascular biology by microsomal epoxide hydrolase

Microsomal epoxide hydrolase/epoxide hydrolase 1 (mEH/EPHX1) works in conjunction with cytochromes P450 to metabolize a variety of compounds, including xenobiotics, pharmaceuticals and endogenous lipids. mEH has been most widely studied for its role in metabolism of xenobiotic and pharmaceutical compounds where it converts hydrophobic and reactive epoxides to hydrophilic diols that are more readily excreted. Inhibition or genetic disruption of mEH can be deleterious in the face of many industrial, environmental or pharmaceutical exposures and EPHX1 polymorphisms are associated with the development of exposure-related cancers. The role of mEH in endogenous epoxy-fatty acid (EpFA) metabolism has been less well studied. In vitro, mEH metabolizes most EpFAs at a far slower rate than soluble epoxide hydrolase (sEH) and has thus been generally considered to exert a minor role in EpFA metabolism in vivo. Indeed, sEH inhibitors or sEH-deficiency increase EpFA levels and are protective in animal models of cardiovascular disease. Recently, however, mEH was found to have a previously unrecognized and substantial role in EpFA metabolism in vivo. While few studies have examined the role of mEH in cardiovascular homeostasis, there is now substantial evidence that mEH can regulate cardiovascular function through regulation of EpFA metabolism. The discovery of a prominent role for mEH in epoxyeicosatrienoic acid (EET) metabolism, in particular, suggests that additional studies on the role of mEH in cardiovascular biology are warranted.

The Multifaceted Role of Epoxide Hydrolases in Human Health and Disease

Epoxide hydrolases (EHs) are key enzymes involved in the detoxification of xenobiotics and biotransformation of endogenous epoxides. They catalyze the hydrolysis of highly reactive epoxides to less reactive diols. EHs thereby orchestrate crucial signaling pathways for cell homeostasis. The EH family comprises 5 proteins and 2 candidate members, for which the corresponding genes are not yet identified. Although the first EHs were identified more than 30 years ago, the full spectrum of their substrates and associated biological functions remain partly unknown. The two best-known EHs are EPHX1 and EPHX2. Their wide expression pattern and multiple functions led to the development of specific inhibitors. This review summarizes the most important points regarding the current knowledge on this protein family and highlights the particularities of each EH. These different enzymes can be distinguished by their expression pattern, spectrum of associated substrates, sub-cellular localization, and enzymatic characteristics. We also reevaluated the pathogenicity of previously reported variants in genes that encode EHs and are involved in multiple disorders, in light of large datasets that were made available due to the broad development of next generation sequencing. Although association studies underline the pleiotropic and crucial role of EHs, no data on high-effect variants are confirmed to date.

Proteomic Analysis Reveals that EPHX1 Contributes to 5-Fluorouracil Resistance in a Human Hepatocellular Carcinoma Cell Line

PURPOSE

The extensive drug resistance of hepatocellular carcinoma (HCC) has become a major cause of chemotherapy failure. A deeper understanding of the drug resistance mechanism of tumor cells is very significant for improving the clinical prognosis of patients with HCC.

EXPERIMENTAL DESIGN

In this study, proteomic studies on the composition of 5-fluorouracil (5-Fu) resistant Bel/5Fu cell line and its parent Bel7402 cell line by using an ionic liquid assisted proteins extraction method with the advantage of extracting plasma membrane proteins to a wider extent are performed. Then the expression level and function of differentially expressed plasma membrane proteins are verified.

RESULTS

In total, 25 plasma membrane proteins are shown differentially expressed in Bel/5Fu compared with Bel7402. Western blot analysis results further confirmed that the EPHX1 PLIN2 RAB27B SLC4A2 are upregulated in Bel/5Fu cells in accordance with the proteomics data. Moreover, cell viability assay and clonogenic survival assay results demonstrated that EPHX1 is closely related to the chemoresistance of Bel/5Fu to 5-Fu.

CONCLUSIONS AND CLINICAL RELEVANCE

Plasma membrane protein EPHX1 is closely related to the chemotherapy resistance of Bel/5Fu cells and can be used as a new drug target to improve the clinical prognosis of patients with HCC.

Cytochrome P450 3A4, 3A5, and 2C8 expression in breast, prostate, lung, endometrial, and ovarian tumors: relevance for resistance to taxanes

Enzymes of the cytochrome P450 (CYP) subfamily 3A and 2C play a major role in the metabolism of taxane anticancer agents. While their function in hepatic metabolism of taxanes is well established, expression of these enzymes in solid tumors may play a role in the in situ metabolism of drugs as well, potentially affecting the intrinsic taxane susceptibility of these tumors. This article reviews the available literature on intratumoral expression of docetaxel- and paclitaxel-metabolizing enzymes in mammary, prostate, lung, endometrial, and ovarian tumors. Furthermore, the clinical implications of the intratumoral expression of these enzymes are reviewed and the potential of concomitant treatment with protease inhibitors (PIs) as a method to inhibit CYP3A4-mediated metabolism is discussed.

Pathway-Structured Predictive Model for Cancer Survival Prediction: A Two-Stage Approach

Heterogeneity in terms of tumor characteristics, prognosis, and survival among cancer patients has been a persistent problem for many decades. Currently, prognosis and outcome predictions are made based on clinical factors and/or by incorporating molecular profiling data. However, inaccurate prognosis and prediction may result by using only clinical or molecular information directly. One of the main shortcomings of past studies is the failure to incorporate prior biological information into the predictive model, given strong evidence of the pathway-based genetic nature of cancer, i.e., the potential for oncogenes to be grouped into pathways based on biological functions such as cell survival, proliferation, and metastatic dissemination. To address this problem, we propose a two-stage approach to incorporate pathway information into the prognostic modeling using large-scale gene expression data. In the first stage, we fit all predictors within each pathway using the penalized Cox model and Bayesian hierarchical Cox model. In the second stage, we combine the cross-validated prognostic scores of all pathways obtained in the first stage as new predictors to build an integrated prognostic model for prediction. We apply the proposed method to analyze two independent breast and ovarian cancer datasets from The Cancer Genome Atlas (TCGA), predicting overall survival using large-scale gene expression profiling data. The results from both datasets show that the proposed approach not only improves survival prediction compared with the alternative analyses that ignore the pathway information, but also identifies significant biological pathways.

Microsomal epoxide hydrolase 1 (EPHX1): Gene, structure, function, and role in human disease

Microsomal epoxide hydrolase (EPHX1) is an evolutionarily highly conserved biotransformation enzyme for converting epoxides to diols. Notably, the enzyme is able to either detoxify or bioactivate a wide range of substrates. Mutations and polymorphic variants in the EPHX1 gene have been associated with susceptibility to several human diseases including cancer. This review summarizes the key knowledge concerning EPHX1 gene and protein structure, expression pattern and regulation, and substrate specificity. The relevance of EPHX1 for human pathology is especially discussed.

Discovery of microarray-identified genes associated with ovarian cancer progression

Ovarian cancer is the most lethal cancer of female reproductive system. There is a consistent and urgent need to better understand its mechanism. In this study, we retrieved 186 genes that were dysregulated by at least 4-fold in 594 ovarian serous cystadenocarcinomas in comparison with eight normal ovaries, according to The Cancer Genome Atlas Ovarian Statistics data deposited in Oncomine database. DAVID analysis of these genes enriched two biological processes indicating that the cell cycle and microtubules might play critical roles in ovarian cancer progression. Among these 186 genes, 46 were dysregulated by at least 10-fold and their expression was further confirmed by the Bonome Ovarian Statistics data deposited in Oncomine, which covered 185 cases of ovarian carcinomas and 10 cases of normal ovarian surface epithelium. Six genes, including aldehyde dehydrogenase 1 family, member A2 (ALDH1A2), alcohol dehydrogenase 1B (class I), β polypeptide (ADH1B), NEL-like 2 (chicken) (NELL2), hemoglobin, β (HBB), ATP-binding cassette, sub-family A (ABC1), member 8 (ABCA8) and hemoglobin, α1 (HBA1) were identified to be downregulated by at least 10-fold in 779 ovarian cancers compared with 18 normal controls. Using mRNA expression profiles retrieved from microarrays deposited in the Gene Expression Omnibus Profiles database, RT-qPCR measurement and bioinformatics analysis, we further indicated that high expression of HBB might predict a poorer 5-year survival, high expression of ALDH1A2 and ABCA8 might predict a poor outcome; while ALDH1A2, ADH1B, HBB and ABCA8, in particular the former two genes, might be associated with drug resistance, and ALDH1A2 and NELL2 might contribute to invasiveness and metastasis in ovarian cancer. This study thus contributes to our understanding of the mechanism of ovarian cancer progression and development, and the six identified genes may be potential therapeutic targets and biomarkers for diagnosis and prognosis.

Complementary and alternative medicine: a survey of its use in pediatric oncology

Background. The use of complementary and alternative medicine (CAM) is high among children and youths with chronic illnesses, including cancer. The objective of this study was to assess prevalence and patterns of CAM use among pediatric oncology outpatients in two academic clinics in Canada. Procedure. A survey was developed to ask patients (or their parents/guardians) presenting to oncology clinics at the Stollery Children's Hospital in Edmonton and the Children's Hospital of Eastern Ontario (CHEO) in Ottawa about current or previous use of CAM products and practices. Results. Of the 137 families approached, 129 completed the survey. Overall CAM use was 60.5% and was not significantly different between the two hospitals. The most commonly reported reason for not using CAM was lack of knowledge about it. The most common CAM products ever used were multivitamins (86.5%), vitamin C (43.2%), cold remedies (28.4%), teething remedies (27.5%), and calcium (23.0%). The most common CAM practices ever used were faith healing (51.0%), massage (46.8%), chiropractic (27.7%), and relaxation (25.5%). Many patients (40.8%) used CAM products at the same time as prescription drugs. Conclusion. CAM use was high among patients at two academic pediatric oncology clinics. Although most respondents felt that their CAM use was helpful, many were not discussing it with their physicians.

Antiproliferative effect of the Ginkgo biloba extract is associated with the enhancement of cytochrome P450 1B1 expression in estrogen receptor-negative breast cancer cells

Ginkgo biloba is a dioecious tree and its extract is a complex mixture that has been used for thousands of years to treat a variety of ailments in traditional Chinese medicine. The aim of this study was to present our observations on the inhibitory effects of different Ginkgo biloba extracts on human breast cancer cell proliferation and growth. Our results demonstrated that treatment of MCF-7 and MDA-MB-231 human breast cancer cells with Ginkgo biloba leaves and ginkgo fruit extract inhibited cell proliferation. It was also observed that this inhibition was accompanied by the enhancement of cytochrome P450 (CYP) 1B1 expression in MDA-MB-231 cells. In addition, treatment with ginkgo fruit extract resulted in a higher CYP1B1 expression in MDA-MB-231 cells compared to treatment with the Ginkgo biloba leaves extract. Our results suggested that the inhibitory effects of the Ginkgo biloba extract on estrogen receptor-negative breast cancer proliferation and the induction of CYP1B1 expression may be exerted through an alternative pathway, independent of the estrogen receptor or the aryl hydrocarbon receptor pathway.

Biomedical importance of indoles

The indole nucleus is an important element of many natural and synthetic molecules with significant biological activity. This review covers some of the relevant and recent achievements in the biological, chemical and pharmacological activity of important indole derivatives in the areas of drug discovery and analysis.

The comparison of cytotoxicity of the anticancer drugs doxorubicin and ellipticine to human neuroblastoma cells

Ellipticine is an antineoplastic agent, whose mode of action is based mainly on DNA intercalation, inhibition of topoisomerase II and formation of covalent DNA adducts mediated by cytochromes P450 and peroxidases. Here, the cytotoxicity of ellipticine to human neuroblastoma derived cell lines IMR-32 and UKF-NB-4 was investigated. Treatment of neuroblastoma cells with ellipticine was compared with that of these cancer cells with doxorubicin. The toxicity of ellipticine was essentially the same as that of doxorubicin to UKF-NB-4 cells, but doxorubicin is much more effective to inhibit the growth of the IMR-32 cell line than ellipticine. Hypoxic conditions used for the cell cultivation resulted in a decrease in ellipticine and/or doxorubicin toxicity to IMR-32 and UKF-NB-4 neuroblastoma cells.

Profiling the expression of cytochrome P450 in breast cancer

AIMS

The cytochrome P450s (P450) are key oxidative enzymes that metabolize many carcinogens and anticancer drugs. Thus, these enzymes influence tumour development, tumour response to therapy and are putative tumour biomarkers. The aim was to define the P450 expression profile in breast cancer and establish the significance of P450 expression in this tumour type.

METHODS AND RESULTS

A tissue microarray containing 170 breast cancers of no special type was immunostained for a panel of 21 P450s. The highest percentage of strong immunopositivity in breast cancers was seen for CYP4X1 (50.8%), CYP2S1 (37.5%) and CYP2U1 (32.2%), while CYP2J (98.6%) and CYP3A43 (70.7%) were the P450s that most frequently displayed no immunoreactivity. CYP4V2 (P = 0.01), CYP4X1 (P = 0.01) and CYP4Z1 (P = 0.01) showed correlations with tumour grade. CYP1B1 (P = 0.001), CYP3A5 (P = 0.001) and CYP51 (P = 0.005) showed the most significant correlations with oestrogen receptor status. Correlations with survival were identified for CYP2S1 (P = 0.03), CYP3A4 (P = 0.025), CYP4V2 (P = 0.026) and CYP26A1 (P = 0.03), although none of these P450s was an independent marker of prognosis.

CONCLUSIONS

This study has defined the expression profile of cytochrome P450s in breast cancer and may offer their potential application as biomarkers to aid decisions regarding optimal adjuvant hormonal therapy.

Tissue-specific induction of the carcinogen-inducible cytochrome P450 isoforms in the gastrointestinal tract

Gastrointestinal tissues are directly exposed to dietary xenobiotics. In spite of this, modulation of cytochrome P450 (CYP) enzymes in the gastrointestinal tract is not well established. CYP induction could facilitate transformation of chemical agents to potentially toxic or carcinogenic metabolites. This might also determine drug efficacy, burden of foreign chemicals on tissues or bioavailability of certain therapeutic agents. In order to assess the induction of the CYP subfamilies 1A1/2, 2B1/2, 2E1 and 3A2 in the gastrointestinal tract, male Wistar rats were treated with phenobarbital/β-naphthoflavone (PB/NF), cyclohexanol/albendazole (CH/ABZ) or toluene (TL). Microsomal fractions were prepared from tissue samples of the esophagus, the stomach, the duodenum, the colon and the liver. Western blot and enzymatic activity analyses revealed an increase in the expression and activity of CYP1A1/2 and CYP3A2 isoenzymes in the esophageal, duodenal and colonic microsomes from animals treated with PB/NF. CYP1A1/2 and CYP3A2 were induced in hepatic and duodenum microsomes by treatment with CH/ABZ. Our results demonstrate differential induction of CYP along the gastrointestinal tract by known CYP hepatic inducers, being the treatment with PB/NF the best induction system of the CYPs.

Targeting cytochrome P450 enzymes: a new approach in anti-cancer drug development

Cytochrome P450s (CYPs) represent a large class of heme-containing enzymes that catalyze the metabolism of multitudes of substrates both endogenous and exogenous. Until recently, however, CYPs have been largely overlooked in cancer drug development, acknowledged only for their role in phase I metabolism of chemotherapeutics. The first successful strategy targeting CYP enzymes in cancer therapy was the development of potent inhibitors of CYP19 (aromatase) for the treatment of breast cancer. Aromatase inhibitors ushered in a new era in hormone ablation therapy for estrogen dependent cancers, and have paved the way for similar strategies (i.e., inhibition of CYP17) that combat androgen dependent prostate cancer. Identification of CYPs involved in the inactivation of anti-cancer metabolites of vitamin D(3) and vitamin A has triggered development of agents that target these enzymes as well. The discovery of the over-expression of exogenous metabolizing CYPs, such as CYP1B1, in cancer cells has roused interest in the development of inhibitors for chemoprevention and of prodrugs designed to be activated by CYPs only in cancer cells. Finally, the expression of CYPs within tumors has been utilized in the development of bioreductive molecules that are activated by CYPs only under hypoxic conditions. This review offers the first comprehensive analysis of strategies in drug development that either inhibit or exploit CYP enzymes for the treatment of cancer.

Expression of xenobiotic and steroid hormone metabolizing enzymes in human breast carcinomas

The potential to metabolize endogenous and exogenous substances may influence breast cancer development and tumor growth. Therefore, the authors investigated the protein expression of Glutathione S-transferase (GST) isoforms and cytochrome P450 (CYP) known to be involved in the metabolism of steroid hormones and endogenous as well as exogenous carcinogens in breast cancer tissue to obtain new information on their possible role in tumor progression. Expression of GST pi, mu, alpha and CYP1A1/2, 1A2, 3A4/5, 1B1, 2E1 was assessed by immunohistochemistry for primary breast carcinomas of 393 patients from the German GENICA breast cancer collection. The percentages of positive tumors were 50.1 and 44.5% for GST mu and CYP2E1, and ranged from 13 to 24.7% for CYP1A2, GST pi, CYP1A1/2, CYP3A4/5, CYP1B1. GST alpha was expressed in 1.8% of tumors. The authors observed the following associations between strong protein expression and histopathological characteristics: GST expression was associated with a better tumor differentiation (GST mu, p = 0.018) and with reduced lymph node metastasis (GST pi, p = 0.02). In addition, GST mu expression was associated with a positive estrogen receptor and progesterone receptor status (p < 0.001). CYP3A4/5 expression was associated with a positive nodal status (p = 0.018). Expression of CYP1B1 was associated with poor tumor differentiation (p = 0.049). Our results demonstrate that the majority of breast carcinomas expressed xenobiotic and drug metabolizing enzymes. They particularly suggest that GST mu and pi expression may indicate a better prognosis and that strong CYP3A4/5 and CYP1B1 expression may be key features of nonfavourable prognosis.

Increased CYP3A4 copy number in TONG/HCC cells but not in DNA from other humans

Two recent screens for copy-number variations in the entire human genome found 12.4 gene copy number variations per person, including 2.5% of individuals with gains between 7q21.1 and 7q22.1, the chromosomal location of CYP3A4. CYP3A4 is involved in the metabolism of approximately 50% of all drugs, including many cancer chemotherapeutic agents. CYP3A4 gene copy was determined in DNA from 143 individuals: normal human livers, primary and secondary liver tumors, human hepatic cell lines, and immortalized cell lines representing eight ethnically diverse populations. CYP3A4 gene copy was normal in all but one sample, a primary human hepatocellular carcinoma cell line (TONG/HCC). Southern blots of TONG/HCC DNA revealed an approximate 10-fold increase in CYP3A and a corresponding increase in CYP3A mRNA expression and catalytic activity. Fluorescent in situ hybridization of TONG/HCC revealed specific amplification of the CYP3A4 gene on chromosome 7q21 but no amplification of the MDR1 gene that localizes 11.9 Mb upstream of CYP3A4. High resolution analysis of DNA copy number by comparative genomic hybridization confirmed amplification at 7q21.3-7q22. The amplicon spanned 1.7 Mb and contained 30 known genes, including the entire CYP3A locus. To determine whether CYP3A4 expression affected chemotherapeutic toxicity, LLC-PK1 cells were transduced with adenoviruses expressing CYP3A4 and P450 reductase. CYP3A4 conferred resistance to taxol, vinblastine and topotecan. These studies demonstrate that CYP3A4 copy number differences do not contribute to the normal variation in CYP3A4 expression. Tumors with increased CYP3A copy number (via amplification or increased chromosome 7q) would be expected to show reduced cytotoxicity to some chemotherapeutic drugs and potentially an increase in the outgrowth of drug resistant tumors.

Pharmacogenetics and regulation of human cytochrome P450 1B1: implications in hormone-mediated tumor metabolism and a novel target for therapeutic intervention

Several of the hormone-mediated cancers (breast, endometrial, ovarian, and prostate) represent major cancers in both incidence and mortality rates. The etiology of these cancers is in large part modulated by the hormones estrogen and testosterone. As advanced disease develops, the common treatment for these cancers is chemotherapy. Thus, genes that can alter tissue response to hormones and alter clinical response to chemotherapy are of major interest. The cytochrome P450 1B1 (CYP1B1) may be involved in disease progression and modulate the treatment in the above hormone-mediated cancers. This review will focus on the pharmacogenetics of CYP1B1 in relation to hormone-mediated cancers and provide an assessment of cancer risk based on CYP1B1 polymorphisms and expression. In addition, it will provide a summary of CYP1B1 gene regulation and expression in normal and neoplastic tissue.

Expression of the steroid and xenobiotic receptor and its possible target gene, organic anion transporting polypeptide-A, in human breast carcinoma

Steroid and xenobiotic receptor (SXR) or human pregnane X receptor (hPXR) has been shown to play an important role in the regulation of genes related to xenobiotic detoxification, such as cytochrome P450 3A4 and multidrug resistance gene 1. Cytochrome P450 enzymes, conjugation enzymes, and transporters are all considered to be involved in the resistance of breast carcinoma to chemotherapeutic or endocrine agents. However, the expression of SXR/hPXR proteins and that of its target genes and their biological or clinical significance have not been examined in human breast carcinomas. Therefore, we first examined SXR/hPXR expression in 60 breast carcinomas using immunohistochemistry and quantitative reverse transcription-PCR. We then searched for possible SXR/hPXR target genes using microarray analysis of carcinoma cells captured by laser microscissors. SXR/hPXR was detected in carcinoma tissues but not in nonneoplastic and stromal cells of breast tumors. A significant positive correlation was detected between the SXR/hPXR labeling index and both the histologic grade and the lymph node status of the carcinoma cases. Furthermore, in estrogen receptor-positive cases, SXR/hPXR expression was also positively correlated with expression of the cell proliferation marker, Ki-67. Microarray analysis showed that organic anion transporting polypeptide-A (OATP-A) was most closely correlated with SXR/hPXR gene expression, and both OATP-A mRNA and protein were significantly associated with SXR/hPXR in both breast carcinoma tissues and its cell lines. These results suggest that SXR/hPXR and its target gene, such as OATP-A, may play important roles in the biology of human breast cancers.

Profiling cytochrome P450 expression in ovarian cancer: identification of prognostic markers

PURPOSE

The cytochromes P450 are a multigene family of enzymes with a central role in the oxidative metabolism of a wide range of xenobiotics, including anticancer drugs and biologically active endogenous compounds. The purpose of this study was to define the cytochrome P450 profile of ovarian cancer and identify novel therapeutic targets and establish the prognostic significance of expression of individual cytochrome P450s in this type of cancer.

EXPERIMENTAL DESIGN

Immunohistochemistry for a panel of 23 cytochrome P450s and cytochrome P450 reductase was done on an ovarian cancer tissue microarray consisting of 99 primary epithelial ovarian cancers, 22 peritoneal metastasis, and 13 normal ovarian samples. The intensity of immunoreactivity in each sample was established by light microscopy.

RESULTS

In primary ovarian cancer, several P450s (CYP1B1, CYP2A/2B, CYP2F1, CYP2R1, CYP2U1, CYP3A5, CYP3A7, CYP3A43, CYP4Z1, CYP26A1, and CYP51) were present at a significantly higher level of intensity compared with normal ovary. P450 expression was also detected in ovarian cancer metastasis and CYP2S1 and P450 reductase both showed significantly increased expression in metastasis compared with primary ovarian cancer. The presence of low/negative CYP2A/2B (log rank = 7.06, P = 0.008) or positive CYP4Z1 (log rank = 6.19, P = 0.01) immunoreactivity in primary ovarian cancer were each associated with poor prognosis. Both CYP2A/2B and CYP4Z1 were also independent markers of prognosis.

CONCLUSIONS

The expression profile of individual P450s has been established in ovarian cancer. Several P450s show increased expression in ovarian cancer and this provides the basis for developing P450-based therapeutics in ovarian cancer. Expression of CYP2A/2B or CYP4Z1 in primary ovarian cancer were independent markers of prognosis.

Mammalian peroxidases activate anticancer drug ellipticine to intermediates forming deoxyguanosine adducts in DNA identical to those foundin vivo and generated from 12-hydroxyellipticine and 13-hydroxyellipticine

Ellipticine is a potent antineoplastic agent, whose mode of action is considered to be based mainly on DNA intercalation, inhibition of topoisomerase II and cytochrome P450-mediated formation of covalent DNA adducts. This is the first report on the molecular mechanism of ellipticine oxidation by peroxidases (human myeloperoxidase, human and ovine cyclooxygenases, bovine lactoperoxidase, horseradish peroxidase) to species forming ellipticine-DNA adducts. Using NMR spectroscopy, the structures of 2 ellipticine metabolites were identified; the major product is the ellipticine dimer, in which the 2 ellipticine skeletons are connected via N(6) of the pyrrole ring of one ellipticine molecule and C9 in the second one. The minor metabolite is ellipticine N(2)-oxide. Using (32)P-postlabeling and [(3)H]-labeled ellipticine, we showed that ellipticine binds covalently to DNA after its activation by peroxidases. The DNA adduct pattern induced by ellipticine consisted of a cluster of up to 4 adducts. The 2 adducts are indistinguishable from the 2 major adducts generated between deoxyguanosine in DNA and either 13-hydroxy- or 12-hydroxyellipticine or in rats treated with ellipticine, or if ellipticine was activated with human hepatic and renal microsomes. The results presented here are the first characterization of the peroxidase-mediated oxidative metabolites of ellipticine and we have proposed species, 2 carbenium ions, ellipticine-13-ylium and ellipticine-12-ylium, as reactive species generating 2 major DNA adducts seen in vivo in rats treated with ellipticine. The study forms the basis to further predict the susceptibility of human cancers to ellipticine.

Cytochrome P450 expression in rat gastric epithelium with intestinal metaplasia induced by high dietary NaCl levels

Drug metabolizing enzymes like cytochrome P450 (CYP) play an important role in determining the susceptibility of organs or tissue to the toxic effects of drugs or other xenobiotics. There is some evidence indicating that individual isoforms of CYPs are over-expressed in different types of malignant tumors including that of oesophagus, pancreas, breast, lung, colon and stomach. Nevertheless, it is not clear if this change in expression is previous or after the appearance of malignancy. This is important in order to clarify the possible role of xenobiotics in the development of gastric cancer. On the other hand, it has been reported that a high salt ingestion leads to histological changes in rat stomach mucosa including enhanced cell proliferation, lipid peroxidation and intestinal metaplasia. The aim of this study is to explore the expression and activity of CYP families involved in the metabolism of carcinogens in normal rat stomach mucosa and intestinal metaplasia induced by high NaCl ingestion. Male Wistar rats were exposed to diets containing different NaCl concentrations (0.6% control group, 6%, 12%, 18% and 24%) for 12 weeks and histological changes as well as CYP modulation were monitored in gastric mucosa. Chronic gastritis, regenerative hyperplasia and focal metaplasia were noted in animals receiving the 12%, 18% and 24% NaCl diets. In the same groups, induction of CYP1A1 and CYP3A2 was produced, mainly in areas of metaplasia. The expression of xenobiotic metabolizing enzymes in the gastric mucosa might contribute to chemical activation in the stomach, metabolizing both exogenous and endogenous compounds implicated in the development of gastric cancer.

The Anticancer Drug Ellipticine Forms Covalent DNA Adducts, Mediated by Human Cytochromes P450, through Metabolism to 13-Hydroxyellipticine and Ellipticine N2-Oxide

Ellipticine is an antineoplastic agent, the mode of action of which is considered to be based on DNA intercalation and inhibition of topoisomerase II. We found that ellipticine also forms the cytochrome P450 (CYP)-mediated covalent DNA adducts. We now identified the ellipticine metabolites formed by human CYPs and elucidated the metabolites responsible for DNA binding. The 7-hydroxyellipticine, 9-hydroxyellipticine, 12-hydroxyellipticine, 13-hydroxyellipticine, and ellipticine N(2)-oxide are generated by hepatic microsomes from eight human donors. The role of specific CYPs in the oxidation of ellipticine and the role of the ellipticine metabolites in the formation of DNA adducts were investigated by correlating the levels of metabolites formed in each microsomal sample with CYP activities and with the levels of the ellipticine-derived deoxyguanosine adducts in DNA. On the basis of this analysis, formation of 9-hydroxyellipticine and 7-hydroxyellipticine was attributable to CYP1A1/2, whereas production of 13-hydroxyellipticine and ellipticine N(2)-oxide, the metabolites responsible for formation of two major DNA adducts, was attributable to CYP3A4. Using recombinant human enzymes, oxidation of ellipticine to 9-hydroxyellipticine and 7-hydroxyellipticine by CYP1A1/2 and to 13-hydroxyellipticine and N(2)-oxide by CYP3A4 was corroborated. Homologue modeling and docking of ellipticine to the CYP3A4 active center was used to explain the predominance of ellipticine oxidation by CYP3A4 to 13-hydroxyellipticine and N(2)-oxide.

CYP3A4, CYP2C9 and CYP2B6 expression and ifosfamide turnover in breast cancer tissue microsomes

Ifosfamide is a prodrug that requires bioactivation by cytochrome P450 for antitumour activity. Up to now, little is known, to what extent in addition to the liver the ifosfamide metabolism may occur intratumorally. For this purpose, we investigated the expression of CYP3A4, CYP2C9 and CYP2B6 in breast cancer tissue using Western Blotting. Ifosfamide turnover was determined by detection of metabolites of the ifosfamide 4-hydroxylation and N-dechloroethylation in tumour microsomal incubations using HPLC/UV and LC/MS. The results demonstrate that all mammary tumours (n=11) reveal CYP3A4 expression; contents varied from 0.5 to 63 pmol mg(protein)(-1). CYP2C9 (n=9) was present in all tested breast tumour samples, too, while CYP2B6 (n=10) protein could not be detected. All measured breast cancer microsomes (n=4) showed an ifosfamide N-dechloroethylation capacity in the range from 0.04 to 0.21 pmol min(-1) mg(protein)(-1), while metabolites of the 4-hydroxylation could not be determined. In conclusion, the detected presence of CYP3A4 and CYP2C9 in breast tumours offers the possibility of intratumoral turnover of ifosfamide. For the first time in the literature, we could demonstrate a turnover of ifosfamide by microsomal preparations from human breast cancer tissue. A calculated modulation of intratumoral ifosfamide turnover could considerably influence its therapeutic efficiency.

Expression of CYP3A4 in human breast tumour and non-tumour tissues

Cytochrome P450 3A4 (CYP3A4), a member of multigene superfamily of enzymes, plays a major role in the activation of procarcinogens such as polycyclic hydrocarbon dihydrodiols, aflatoxins and heterocyclic amines as well as of several drugs including tamoxifen which is used in breast cancer therapy. Using immunohistochemistry, the cellular distribution and the level of expression of CYP3A4 was assessed in breast tumour and surrounding tumour free (control) breast tissue in 25 pairs of samples obtained from females with infiltrating ductal carcinoma. Cells staining with the CYP3A4 antibody showed only cytoplasmic positivity with varying intensities in 100% (25/25) of tumours and 68% (17/25) of normal breast tissues. Cytoplasmic staining was present in invasive ductal carcinoma cells but not in tumour stroma. CYP3A4 was detected in normal epithelium and myoepithelium. Only focal staining was noted in some of the non-epithelial cells (e.g. endothelial cells) in normal breast tissues. When CYP3A4 staining was assessed semiquantitatively the mean staining score values of CYP3A4 were found to be significantly higher in tumours compared to that of normal breast tissues. These results show that CYP3A4 protein is expressed in both tumour and normal breast tissue with an increased expression in tumours.

DNA adduct formation by the anticancer drug ellipticine in rats determined by 32P postlabeling

Ellipticine is a potent antineoplastic agent whose mode of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts in vitro and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (CYP). Here, we investigated the capacity of ellipticine to form DNA adducts in vivo. Male Wistar rats were treated with ellipticine, and DNA from various organs was analyzed by (32)P postlabeling. Ellipticine-specific DNA adduct patterns, similar to those found in vitro, were detected in most test organs. Only DNA of testes was free of the ellipticine-DNA adducts. The highest level of DNA adducts was found in liver (19.7 adducts per 10(7) nucleotides), followed by spleen, lung, kidney, heart and brain. One major and one minor ellipticine-DNA adducts were found in DNA of all these organs of rats exposed to ellipticine. Besides these, 2 or 3 additional adducts were detected in DNA of liver, kidney, lung and heart. The predominant adduct formed in rat tissues in vivo was identical to the deoxyguanosine adduct generated in DNA by ellipticine in vitro as shown by cochromatography in 2 independent systems. Correlation studies showed that the formation of this major DNA adduct in vivo is mediated by CYP3A1- and CYP1A-dependent reactions. The results presented here are the first report showing the formation of CYP-mediated covalent DNA adducts by ellipticine in vivo and confirm the formation of covalent DNA adducts as a new mode of ellipticine action.

Immunohistochemical demonstration of the expression of CYP2E1 in human breast tumour and non-tumour tissues

Environmental chemicals are one of the risk factors in breast cancer genesis. Cytochrome P450 2E1 (CYP2E1), a member of multigene superfamily of enzymes, plays a major role in the activation of some of these chemicals such as tobacco-derived N-nitrosamines. Using immunohistochemistry, the cellular distribution and the level of expression of CYP2E1 was assessed in breast tumour and surrounding tumour free (control) breast tissue in 25 pairs of samples obtained from females with infiltrating ductal carcinoma. Cells staining with the CYP2E1 antibody showed only cytoplasmic positivity with varying intensities in 100% (25/25) of tumours and 96% (24/25) of normal breast tissues. Cytoplasmic staining was present in invasive ductal carcinoma cells but not in tumour stroma. CYP2E1 was detected in normal epithelial, myoepithelial and to a lesser degree in some of the non-epithelial cells (e.g. endothelial cells). No positive staining was detected in other non-epithelial cells such as fibroblasts in normal breast tissues. When CYP2E1 staining was assessed semiquantitatively the mean staining score values of CYP2E1 was found to be significantly higher in tumours compared to that of normal breast tissues. These results show that CYP2E1 protein is expressed in both tumour and normal breast tissue with an increased expression in breast tumours.

Prognostic significance of glutathione S-transferase-pi in invasive breast cancer

Glutathione S-transferase pi (GST-pi), a Phase II detoxification enzyme, has recently been implicated in protection against apoptosis. Expression of GST-pi and Bcl-2 protein, an established apoptosis marker, was analyzed by immunohistochemistry in 116 cases of infiltrative ductal breast carcinomas in Singapore women. The markers were correlated with apoptosis detected by the TUNEL method and clinico-pathological parameters. There were 67 (58%) GST-pi-positive breast tumors and 43 (37%) Bcl-2-positive tumors. In a large proportion of GST-pi-positive/Bcl-2-positive tumors, there was a distinct accumulation of the GST-pi enzyme within the nucleus of cancer cells when examined by double immunofluorescence labeling under confocal microscopy. GST-pi immunoreactivity was not significantly correlated with any of the traditional histologic factors known to influence prognosis, whereas Bcl-2 overexpression was associated with reduced size of primary tumor (P =.021) and positive estrogen receptor status (P =.001). Univariate analysis revealed that GST-pi-positive, Bcl-2-positive, and lower histological grade tumors had decreased levels of apoptosis (P =.024, P =.011, and P =.029, respectively). However, multivariate analysis showed that histological grade and Bcl-2, but not GST-pi, immunoreactivity were correlated with apoptotic status. The Kaplan-Meier disease-free survival curves showed a significant difference between GST-pi-positive and GST-pi-negative breast cancer cases (P =.002). Disease-free survival in patients with GST-pi-positive tumors was also worse than that in patients with GST-pi-negative tumors in the group who had adjuvant chemotherapy (P =.04). In patients who were lymph node positive, GST-pi immunopositivity was found to influence disease-free survival. Recurrence of tumors was also significantly affected by GST-pi immunoreactivity (relative risk of 8.1). The findings indicate that GST-pi-positive tumors are more aggressive and have a poorer prognosis than do corresponding GST-pi-negative breast cancers.

Decreased hepatic drug metabolising enzyme activity in rats with nitrosamine-induced tumours

N-Methyl N-benzyl nitrosamine (MBNA), which requires P450-dependant activation to be mutagenic, has been shown to produce squamous cell carcinoma of rat oesophagus. The aim of this study was to determine the effects of tumour induction on hepatic cytochrome P450 (CYP) and phase II enzyme activity. Female Wistar rats were given MBNA (2.5 mg/kg) by gavage, twice weekly for 12 weeks. At the end of 12 weeks they were sacrificed; livers and oesophagi were removed. The activity of hepatic CYP and phase II enzymes was determined by incubation of liver microsomes with appropriate CYP substrates. All rats receiving MBNA developed oesophageal lesions. Hepatic CYP1A2 activity (phenacetin 5 microM) in tumour-bearing rats was significantly decreased to 53% of the controls (p <0.05). CYP2E1 (p-nitrophenol hydroxylase), CYP2D (debrisoquine hydroxylase) and CYP3A (quinine hydroxylase) activity was significantly (p <0.05) reduced. Microsomal UDP-glucuronosyl transferase activity was also found to be markedly decreased while glutathione-S-transferase activity remained almost unchanged. Alteration of the activities of drug metabolising enzymes in rats with chemically induced tumours could be an important factor in determining resistance or susceptibility to xenobiotics and antitumour drugs.

Covalent binding of the anticancer drug ellipticine to DNA in V79 cells transfected with human cytochrome P450 enzymes

Ellipticine is a potent antineoplastic agent whose mechanism of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Recently, we found that ellipticine also forms covalent DNA adducts and that the formation of the major adduct is dependent on the activation of ellipticine by cytochrome P450 (CYP). We examined a panel of genetically engineered V79 cell lines including the parental line V79MZ and recombinant cells expressing the human CYP enzymes CYP1A1, CYP1A2 or CYP3A4 for their ability to activate ellipticine. The extent of activation was determined by analysing DNA adducts by 32P-postlabelling. Ellipticine was found to be toxic to all V79 cell lines with IC(50) values ranging from 0.25 to 0.40 microM. The nuclease P1 version of the 32P-postlabelling assay yielded a similar pattern of ellipticine-DNA adducts with two major adducts in all cells, the formation of only one of which was dependent on CYP activity. This pattern is identical to that detected in DNA reacted with ellipticine and the reconstituted CYP enzyme system in vitro as confirmed by HPLC of the isolated adducts. Total adduct levels ranged from 2 to 337 adducts per 10(8) nucleotides, in the parental line and in V79 expressing CYP3A4, respectively. As in vitro, human CYP1A2 and CYP1A1 were less active. The results presented here are the first report showing the formation of CYP-mediated covalent DNA adducts by ellipticine in cells in culture, and confirm the formation of covalent DNA adducts as a new mechanism of ellipticine action.

The organochlorine pesticide residues and antioxidant enzyme activities in human breast tumors: is there any association?

The levels of some organochlorine pesticides (OCP)s (hexachlorobenzene, HCB, alpha-hexachlorocyclohexane, alpha-HCH, beta-HCH, gamma-HCH, heptachlorepoxide, HE, bis (4-chlorophenyl)-1,1-dichloroethene, p.p'DDE, bis (4-chlorophenyl)-1,1,1-trichloroethane, p.p' DDT and total DDT (E-DDT) and antioxidant enzyme activities namely Cu, Zn superoxide dismutase (SOD), catalase (CAT), selenium-dependent glutathione peroxidase (Se-GSH-Px), total glutathione peroxidase (T-GSH-Px), selenium independent glutathione peroxidase (GSH-Px II), glutathione reductase (GRd), level of reduced glutathione (GSH) and lipid peroxidation (LP), glutathione S-transferase (GST) activity toward several substrates including 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), ethacrynic acid (EAA), 1,2-epoxy-3-(p-nitrophenoxy)-propane (ENPP) were measured in tumor and surrounding tumor free tissues of 24 female breast cancer patients and was evaluated whether there exist any association between the levels of OCPs and antioxidants. The mean levels of GSH, alpha-BHC, gamma-BHC and HE, and activities of SOD, Se-GSH-Px, T-GSH-Px, GSH-Px II,GRd, GST CDNB, and GST DCNB were significantly higher in tumors than in controls. In tumors, significant correlations were noted between: SOD and y-BHC; Se-GSH-Px and gamma-BHC; T-GSH-Px and gamma-BHC; GSH-Px II and alpha-BHC, gamma-BHC; GSH and alpha-BHC, gamma-BHC, HE; GRd and alpha-BHC; CDNB GST and alpha-BHC, gamma-BHC. These results show that free-radical mediated oxidative stress is, at least partly, associated with some of these OCP residues in human breast tumors.

The anticancer agent ellipticine on activation by cytochrome P450 forms covalent DNA adducts

Ellipticine is a potent antitumor agent whose mechanism of action is considered to be based mainly on DNA intercalation and/or inhibition of topoisomerase II. Using [3H]-labeled ellipticine, we observed substantial microsome (cytochrome P450)-dependent binding of ellipticine to DNA. In rat, rabbit, minipig, and human microsomes, in reconstituted systems with isolated cytochromes P450 and in Supersomes containing recombinantly expressed human cytochromes P450, we could show that ellipticine forms a covalent DNA adduct detected by [32P]-postlabeling. The most potent human enzyme is CYP3A4, followed by CYP1A1, CYP1A2, CYP1B1, and CYP2C9. Another minor adduct is formed independent of enzymatic activation. The [32P]-postlabeling analysis of DNA modified by activated ellipticine confirms the covalent binding to DNA as an important type of DNA modification. The DNA adduct formation we describe is a novel mechanism for the ellipticine action and might in part explain its tumor specificity.

The expression of cytochrome P450 enzymes in human breast tumours and normal breast tissue

Environmental chemicals are one of the risk factors in breast cancer genesis. Cytochrome P450 (CYP) enzymes play a major role in the activation of these chemicals. Using highly specific and sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. the expression profile of all major xenobiotic metabolizing CYP forms was screened in breast tumour and surrounding tumour free (control) breast tissue in a series of 20 sample pairs obtained from females with infiltrating ductal carcinoma. The levels of CYPIAI mRNA were very low in both tumour and normal tissue. CYP1B1, CYP2B6, CYP2C, CYP2D6, CYP2E1, CYP4B1, and CYP11A1 expressions were positive in both tumours and control tissue. CYP2A6, CYP2A7, CYP2A13, CYP2F1, CYP3A4, CYP3A5. and CYP3A7 mRNAs were expressed neither in tumours nor in control tissue. These results show that several CYPs. responsible for the activation of a quite large number of procarcinogens and genotoxic estrogen metabolites. are expressed in breast tissue with a lack of qualitative differences in CYP expression at mRNA level between breast tumours and surrounding normal breast.

Distribution of microsomal epoxide hydrolase in humans: an immunohistochemical study in normal tissues, and benign and malignant tumours

Microsomal epoxide hydrolase is a biotransformation enzyme which is involved in the hydrolysis of various epoxides and epoxide intermediates. In the present study, its distribution was investigated in both normal human tissues and human tumours of different histogenetic origin using immunohistochemical techniques. In normal tissue, epithelial cells were more often and more intensely immunostained than mesenchymal cells. The main epithelial cell types expressing microsomal epoxide hydrolase were hepatocytes, acinus cells of the pancreas, and cells of salivary and adrenal glands. Immunostained cells of mesenchymal origin included monocytes, fibrocytes, fibroblasts, vessel endothelium, muscle cells, and cells of the reproductive system. Three patterns of expression were observed in tumour tissues: (1) moderate or strong in hepatocellular carcinomas, tumours of the adrenal gland, and theca-fibromas of the ovary; (2) inhomogeneous staining pattern of variable intensity in breast cancer, lung cancer, colorectal carcinomas, carcinoid tumours, and some tumours of mesenchymal origin; and (3) no expression in malignant melanomas, malignant lymphomas, and renal carcinomas. These data indicate that microsomal epoxide hydrolase expression is not restricted to tissue of any particular histogenetic origin. Nonetheless, immunohistochemical identification of microsomal epoxide hydrolase may be helpful in some well-defined histological settings, for example, confirmation of hepatocellular carcinoma.

Microsomal epoxide hydrolase expression as a predictor of tamoxifen response in primary breast cancer: a retrospective exploratory study with long-term follow-up

PURPOSE

It has been suggested that estrogen receptor-independent high-affinity binding sites for antiestrogens could limit their local bioavailability and response. Microsomal epoxide hydrolase (mEH) was recently shown to be a component of the antiestrogen binding site complex. We investigated whether mEH expression in primary breast tumors is related to disease outcome and to the efficacy of tamoxifen treatment.

PATIENTS AND METHODS

Expression of mEH was semiquantitatively assessed by immunohistochemistry in sections prepared from archival paraffin blocks of primary breast cancers from 179 patients with a mean follow-up time of 81 months.

RESULTS

Expression of mEH was correlated with poor disease outcome in all patients (P: < .01; n = 179) and in patients receiving tamoxifen (P: < .01; n = 78), but not in patients not treated with tamoxifen. Moreover, mEH was an independent prognostic factor by Cox regression analysis.

CONCLUSION

The results of this first exploratory study suggest that mEH expression in primary breast cancer could be of predictive value for response to tamoxifen treatment and/or may be a novel independent prognostic factor for survival. The results are in agreement with the model that mEH participates in an estrogen receptor-independent tamoxifen- binding complex.

The role of cytochrome P450 in tumour development and progression and its potential in therapy

The cytochromes P450 (P450) are a large group of constitutive and inducible haem-containing enzymes, which have a central role in the oxidative metabolism of a diverse range of xenobiotics. Many P450 substrates are carcinogenic, while other substrates are anti-cancer drugs; the P450s thus have various potentially important roles in tumour biology. Several P450 genes are polymorphic and are associated with the increased risk of cancer development in specific tissues. Individual P450s, especially CYP1B1, are overexpressed in different types of tumours. The increased expression of P450s in tumours is highly significant and is important for understanding tumour development and progression. The tumour-specific expression of P450 provides the basis for the development of novel diagnostic and therapeutic strategies.

Polymorphisms in P450 CYP1B1 affect the conversion of estradiol to the potentially carcinogenic metabolite 4-hydroxyestradiol

Most drug metabolizing cytochrome P450s (P450) are predominantly expressed in the liver. In contrast, human CYP1B1 is an extrahepatic P450 which is overexpressed in many tumours and has been strongly implicated in the activation of carcinogens. Rare allelic variants of the CYP1B1 gene which encode an inactive protein have been identified. However, four polymorphisms which most likely do not abolish functionality have been described. In this report, we have characterized the functional consequences of these. A CYP1B1 cDNA, identical to a cDNA published previously, served as a template to introduce allelic changes either separately or in combination. The resulting effects on CYP1B1 activity were determined in membranes isolated from Escherichia coli which coexpressed CYP1B1 together with P450 reductase. None of the allelic changes affected the CYP1B1 expression level. The allelic changes Arg48 to Gly, Ala19 to Ser and Asn453 to Ser had little influence on the Vmax and the Km of the CYP1B1 mediated 2- and 4-hydroxylation of estradiol. In contrast, the Km of these metabolic pathways was increased at least three-fold by the allelic change Va432 to Leu or by simultaneously changing Val432 to Leu and Asn453 to Ser. However, these alterations had little effect on the kinetic parameters of other CYP1B1 mediated reactions such as the epoxidation of (-)-trans-(7R,8R)-benzo[a]pyrene 7,8-dihydrodiol as determined by (r-7,t-8,t-9,c-10)-benzo[a]pyrene tetraol formation, or such as the O-dealkylation of ethoxyresorufin and the 1'-hydroxylation of bufuralol. Molecular modelling suggests that amino acid residue 432 of CYP1B1 may be involved in the interaction between CYP1B1 and P450 reductase. Since 4-hydroxyestradiol has been implicated in hormonal carcinogenesis and CYP1B1 is expressed in target tissues, the data presented demonstrate that polymorphisms in CYP1B1 have the potential to affect disease susceptibility.

Enhancement of chemotherapy and radiotherapy of murine tumours by AQ4N, a bioreductively activated anti-tumour agent

AQ4 (1,4-Bis-[[2-(dimethylamino-N-oxide)ethyl]amino]5,8-dihydroxyanthrace ne-9, 10-dione) is a prodrug designed to be excluded from cell nuclei until bioreduced in hypoxic cells to AQ4, a DNA intercalator and topoisomerase II poison. Thus, AQ4N is a highly selective bioreductive drug that is activated in, and is preferentially toxic to, hypoxic cells in tumours. Five murine tumours (MAC16, MAC26, NT, SCCVII and RIF-1) have been used to investigate the anti-tumour effects of AQ4N. In only one tumour (MAC16) was AQ4N shown to be active as a single agent. However, when combined with methods to increase the hypoxic tumour fraction in RIF-1 (by physical clamping) and MAC26 tumours (using hydralazine) there was a substantial enhancement in anti-tumour effect. Notably, RIF-1 tumours treated with AQ4N (250 mg kg(-1)) followed 15 min later by physically occluding the blood supply to the tumour for 90 min, resulted in a 13-fold increase in growth delay. When combined with radiation or chemotherapy, AQ4N substantially increased the effectiveness of these modalities in a range of in vivo model systems. AQ4N potentiates the action of radiation in both a drug and radiation dose-dependent manner. Further the enhancement observed is schedule-independent with AQ4N giving similar effects when given at any time within 16 h before or after the radiation treatment. In combination with chemotherapy it is shown that AQ4N potentiates the activity of cyclophosphamide, cisplatin and thiotepa. Both the chemotherapeutic drugs and AQ4N are given at doses which individually are close to their estimated maximum tolerated dose (data not included) which provides indirect evidence that in the combination chemotherapy experiments there is some tumour selectivity in the enhanced action of the drugs.

Metabolism and pharmacokinetics of oxazaphosphorines

The 2 most commonly used oxazaphosphorines are cyclophosphamide and ifosfamide, although other bifunctional mustard analogues continue to be investigated. The pharmacology of these agents is determined by their metabolism, since the parent drug is relatively inactive. For cyclophosphamide, elimination of the parent compound is by activation to the 4-hydroxy metabolite, although other minor pathways of inactivation also play a role. Ifosfamide is inactivated to a greater degree by dechloroethylation reactions. More robust assay methods for the 4-hydroxy metabolites may reveal more about the clinical pharmacology of these drugs, but at present the best pharmacodynamic data indicate an inverse relationship between plasma concentration of parent drug and either toxicity or antitumour effect. The metabolism of cyclophosphamide is of particular relevance in the application of high dose chemotherapy. The activation pathway of metabolism is saturable, such that at higher doses (greater than 2 to 4 g/m2) a greater proportion of the drug is eliminated as inactive metabolites. However, both cyclophosphamide and ifosfamide also act to induce their own metabolism. Since most high dose regimens require a continuous infusion or divided doses over several days, saturation of metabolism may be compensated for, in part, by auto-induction. Although a quantitative distinction may be made between the cytochrome P450 isoforms responsible for the activating 4-hydroxylation reaction and those which mediate the dechloroethylation reactions, selective induction of the activation pathway, or inhibition of the inactivating pathway, has not been demonstrated clinically. Mathematical models to describe and predict the relative contributions of saturation and autoinduction to the net activation of cyclophosphamide have been developed. However, these require careful validation and may not be applicable outside the exact regimen in which they were derived. A further complication is the chiral nature of these 2 drugs, with some suggestion that one enantiomer may have a favourable profile of metabolism over the other. That the oxazaphosphorines continue to be the subject of intensive investigation over 30 years after their introduction into clinical practice is partly because of their antitumour activity. Further advances in analytical and molecular pharmacological techniques may further optimise their use and allow rational design of more selective analogues.

Divergent mechanisms for loss of Ah-responsiveness in benzo[a]pyrene- and adriamycinR-resistant MCF-7 cells

The intracellular aryl hydrocarbon receptor (AhR) mediates signal transduction by environmental pollutants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo[a]pyrene by functioning as a ligand-activated transcription factor. We have investigated AhR signaling in sublines of the human breast cancer cell line MCF-7 selected for resistance to AdriamycinR (AdrR) and benzo[a]pyrene (BP(R)). Previously we reported that AdrR cells have a loss of estrogen receptor (ER) expression and are Ah-nonresponsive. Here we show that AhR mRNA and protein are expressed at normal levels in AdrR cells, and the activated AhR complex is functionally capable of binding a xenobiotic responsive element. In MCF-7 cells AhR was depleted to 15% of normal levels after 4 hr TCDD treatment; however, 45% of AhR remained in AdrR cells during this time course. In BP(R) cells AhR mRNA levels were found to be decreased relative to wild-type cells, which led to decreased AhR protein levels and DNA-binding activity. Cellular ER content has been shown to correlate with Ah-responsiveness in human breast cancer cell lines. BP(R) cells were found to be ER-positive, although chronic (BP(R) cells) and acute (24 hr) exposure to benzo[a]pyrene led to significantly lower ER protein levels in MCF-7 cells. We conclude that loss of Ah-responsiveness occurs by different mechanisms in xenobiotic-resistant MCF-7 sublines: AhR mRNA is down-regulated in BP(R) cells, whereas AdrR cells are deficient in AhR signaling by a mechanism unrelated to AhR expression and activity.

Merits and limitations of recombinant models for the study of human P450-mediated drug metabolism and toxicity: an intralaboratory comparison

A wide variety of pharmacological and toxicological properties of drugs are determined by cytochrome P450-mediated metabolism. Characterization of these pathways and of the P450 isoenzymes involved constitutes an essential part of drug development. Similarly, because P450s are catalyzing the toxication and detoxication of environmental pollutants, an understanding of these reactions facilitates risk assessment in environmental toxicology. Recently, a variety of recombinant expression systems has been employed to study the role of human P450s in these reactions. These include insect, bacterial, yeast, and mammalian models. As these were developed and characterized by different laboratories, evaluation of their merits and limitations is inherently difficult. To resolve this problem, we have established and characterized the latter three systems and present the key results here. In general, the catalytic properties of P450 isozymes in the various models were rather similar. However, taking technical considerations into account as well as the high level of functional expression of P450s achieved in bacteria make this system ideally suited for drug metabolism research, including the generation of milligram quantities of metabolites for structural determinations. For toxicological studies, however, expression of P450s in mammalian cells was most appropriate. This is exemplified here by studies into the role of human P450s in the activation and inactivation of chemotherapeutic drugs.

Cytochrome P450 CYP3A in human renal cell cancer

Renal cell cancer is the main malignant tumour of the kidney and has an increasing incidence. This type of tumour has a poor prognosis and shows intrinsic resistance to several anti-cancer drugs. The CYP3A P450 family, which consists of three closely related forms, is involved in the oxidative activation and deactivation of a variety of carcinogens and several anti-cancer drugs. In this study the presence and cellular localization of CYP3A has been investigated using a combination of immunohistochemistry, immunoblotting and reverse transcriptase polymerase chain reaction (RT-PCR) in renal cell cancer and corresponding normal kidney. CYP3A was consistently expressed in both renal call cancer and in normal kidney. In renal cell cancer, CYP3A was localized to tumour cells and in normal kidney the predominant cellular localization of CYP3A was to proximal tubular epithelial cells. RT-PCR showed that both CYP3A5 mRNA and CYP3A7 mRNA were consistently present in both tumour and normal samples, while CYP3A4 mRNA was present in 65% of tumours and 90% of normal samples. This study indicates that individual members of the CYP3A family are expressed in renal cell cancer. The presence of CYP3A in renal cell cancer might be important in the metabolic potentiation as well as the detoxification of chemotherapeutic agents used to renal cancer.

Glutathione S-transferase M1 null genotype: lack of association with tumour characteristics and survival in advanced breast cancer

BACKGROUND

Glutathione S-transferase (GST)M1, a member of the mu class GST gene family, has been shown to be polymorphic because of a partial gene deletion. This results in a failure to express the GSTM1 gene in 50-60% of individuals. Several studies have demonstrated a possible link with the GSTM1-null genotype and susceptibility to cancer. Furthermore, a GSTM1 isoenzyme has been positively associated with protective effect against mutagenic drugs, such as alkylating agents and anthracyclines.

OBJECTIVES

To determine whether GSTM1 polymorphisms are associated with tumour characteristics and survival in advanced breast cancer patients, and whether it may constitute a prognostic factor.

METHODS

We genotyped 92 patients receiving primary chemotherapy, which included cyclophosphamide, doxorubicine and 5-fluorouracil. The relationships between allelism at GSTM1 and clinicopathological parameters including age, menopausal status, tumour size, grade hormone receptors, involved nodes and p53 gene mutations were analysed. Of the patients with GSTM1-positive genotype, tissue samples obtained before and after treatment were available from 28 cases, allowing RNA extraction and GSTM1 expression by reverse transcription polymerase chain reaction. Relationships with clinical response to chemotherapy, and disease-free and overall survival were also evaluated. The data obtained was analysed using logistic regression to estimate the odds ratio and 95% confidence interval.

RESULTS

Of 92 patients, 57.6% (n = 53) were classified as heritably GSTM1-deficient, and 42.4% (n = 39) were of the GSTM1-positive genotype. There were no statistically significant relationships between GSTM1-null genotype and the clinicopathological parameters analysed. No relationship was observed between GSTM1 RNA expression and objective clinical response to chemotherapy. Objective clinical response to chemotherapy was related only to clinical tumour size (P = 0.0177) and to the absence of intraductal carcinoma (P = 0.0013). GSTM1-null genotype had no effect on disease-free or overall survival. The absence of hormone receptors (P = 0.002), the presence of a mutated p53 gene (P = 0.0098) and lack of response to primary chemotherapy (P = 0.0086) were the only factors associated with reduced disease-free or overall survival.

CONCLUSIONS

GSTM1-null genotype alone had no effect on tumour characteristics and outcome of patients with advanced breast cancers. The lack of correlation of GSTM1 genotype with clinical tumour features, clinical response to chemotherapy and survival exclude a role for GSTM1 polymorphism as a prognostic factor in advanced breast cancer.

Involvement of human cytochromes P450 (CYP) in the reductive metabolism of AQ4N, a hypoxia activated anthraquinone di-N-oxide prodrug

PURPOSE

To establish the role of the human cytochromes P450 (CYPs) in the reductive metabolism of the novel anthraquinone di-N-oxide prodrug AQ4N.

METHODS AND MATERIALS

Metabolism of AQ4N was conducted in a panel of 17 human phenotyped liver microsomes. AQ4N and metabolites were detected by reverse phase isocratic HPLC. CYP inhibitors and Spearman rank correlation were used to determine the significance of AQ4N metabolism versus specific CYP activity and/or expression.

RESULTS

Anaerobic metabolism of AQ4N to the 2-electron reduction product, AQM, and the 4-electron reduced tertiary amine, AQ4, occurred in all 17 human liver microsome preparations. The range (+/- SE) for total AQ4N turnover was 14.26 +/- 1.43 nmol/incubate (highest) to 3.65 +/- 1.05 nmol/incubate (lowest). Metabolism was not detected in the absence of NADPH or microsomes. In aerobic incubates, AQM was less than 4% of anaerobic values whereas AQ4 was undetectable. CYP-mediated metabolism of AQ4N was inhibited completely by ketoconazole (KET) and carbon monoxide (CO), two global inhibitors of CYP-mediated metabolism. AQ4N metabolism correlated significantly with probes for CYP 3A, specifically benzoxylresorufin O-dealkylation [r(s) = 0.70,p <0.01] and tamoxifen N-demethylation (r(s) = 0.85, p < 0.01), but not with probes for CYPs 2C, 2D, and 1A. CYP 3A involvement was confirmed by the use of the CYP 3A specific inhibitor, triacetyloleandomycin (TAO), which repressed the formation of AQM to 13% of the uninhibited value and abolished completely the formation of AQ4. Alpha-naphthoflavone (ANF), an inhibitor of CYP 2C and 1A, had no significant effect on AQ4N metabolism.

CONCLUSIONS

These data suggest that the human CYP 3A enzymes can contribute to the reductive metabolism of AQ4N. CYP 3A enzymes are highly expressed in a broad spectrum of human cancers. The results show that AQ4N requires anaerobic conditions for CYP 3A-mediated reduction and hence this subfamily of enzymes is likely to selectively activate AQ4N in hypoxic tumors.

Enhanced expression of cytochrome P450 in stomach cancer

The cytochromes P450 have a central role in the oxidative activation and detoxification of a wide range of xenobiotics, including many carcinogens and several anti-cancer drugs. Thus the cytochrome P450 enzyme system has important roles in both tumour development and influencing the response of tumours to chemotherapy. Stomach cancer is one of the commonest tumours of the alimentary tract and environmental factors, including dietary factors, have been implicated in the development of this tumour. This type of tumour has a poor prognosis and responds poorly to current therapies. In this study, the presence and cellular localization of several major forms of P450, CYP1A, CYP2E1 and CYP3A have been investigated in stomach cancer and compared with their expression in normal stomach. There was enhanced expression of CYP1A and CYP3A in stomach cancer with CYP1A present in 51% and CYP3A present in 28% of cases. In contrast, no P450 was identified in normal stomach. The presence of CYP1A and CYP3A in stomach cancer provides further evidence for the enhanced expression of specific forms of cytochrome P450 in tumours and may be important therapeutically for the development of anti-cancer drugs that are activated by these forms of P450.

Synovial sarcoma: immunohistochemical expression of P-glycoprotein and glutathione S transferase-pi and clinical drug resistance

Our purpose was to study the role of the expression of P-glycoprotein (Pgp) and glutathione S transferase-pi (GST-pi) in predicting the response to chemotherapy, relapse-free interval, and survival of patients with synovial sarcoma (SS). Thirty-seven cases of primary SS, without regional lymph node or distant metastases, were studied. There were 17 females and 20 males, ranging in age from 7 to 81 years (median, 31 years) with tumors located in the lower extremity (n = 24) upper extremity (n = 5) and trunchus (n = 8). The cases were retrospectively studied without knowledge of clinical course to compare the immunohistochemical expression of Pgp and GST-pi, flow cytometry parameters (ploidy and % of cells in S+G2 phases), and PCNA and Ki-67 labeling of primary tumors before any therapy, with that observed in local recurrences and metastases after chemotherapy. The relationship of the aforementioned parameters with clinicopathological features (gender, age, and histo-blood group of the patients, size, location, histological subtype. TNM stage, and clinical response to chemotherapy of the tumors) was also evaluated. Results revealed that Pgp and GST-pi were expressed in 29.7% and 40.5% of the cases, respectively. In 48.6% of the tumors there was expression of a least one of the drug resistance markers. The markers were coexpressed in 25.0% of the tumors. The prevalence of Pgp expression was lower, but not significantly, in stage I-II (17.6%) than in stage III (40.0%) tumors, and also in cases without clinical progression (16.7%), than in cases with (36.0%). No such differences were observed for GST-pi expression. Pgp and GST-pi expressions were significantly associated with biphasic SS and were particularly noticeable in solid/glandular areas of biphasic SS. The expression of the drug resistance markers was not significantly associated with gender, age, and histo-blood group of the patients, dimension, location, and proliferative activity of the tumors; it was also not significantly related to relapse-free interval and survival of the patients. The expression of Pgp and GST-pi was not significantly associated either to response to chemotherapy or influenced by chemotherapy. We conclude that Pgp and GST-pi expressions are not good predictors response to of the chemotherapy in patients with localized SS. Other drug resistance mechanisms may be active in SS.