Studies on the relationship between estrogen receptor content, glutathione S-transferase pi expression, and induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin and drug resistance in human breast cancer cells

Estrogen- and estrogen receptor (ER)-mediated cisplatin chemoresistance in cancer

Cisplatin is a platinum-based chemotherapeutic drug used in the standard treatment of various solid cancers including testicular, bladder, head and neck, cervical and ovarian cancer. Although successful clinical responses are observed in patients following initial cisplatin treatment, resistance to cisplatin ultimately develops in most patients, leading to therapeutic failure. Multiple molecular mechanisms contributing to cisplatin resistance in cancer cells have been identified to date. In this review, we discuss the effect of estrogen, estrogen receptors (ERs) and estrogen-related receptors (ERRs) on cisplatin resistance in various cancer types. We highlight that estrogen treatment or increased expression of ERs or ERRs are generally associated with higher cisplatin resistance in cancer in vitro, mostly due to decreased caspase activity, increased anti-apoptotic protein levels such as BCL-2, higher drug efflux and higher levels of antioxidant enzymes. Targeted inhibition of ERs or estrogen production in combination with cisplatin treatment thus can be a useful strategy to overcome chemoresistance in certain cancer types. Estrogen levels and ER status can also be considered to identify cancer patients with a high potential of therapy response against cisplatin. A better mechanistic understanding of the involvement of estrogen, ERs and ERRs in the development of cisplatin resistance is needed to improve the management of cancer treatment.

Differential effects of metal ions on TCDD-induced cytotoxicity and cytochrome P4501A1 gene expression in a zebrafish liver (ZFL) cell-line

Trace metal ions and trace organic compounds are common co-contaminants in the environment that pose risks to human health. We evaluated the effects of four metal ions (As(3+), Cu(2+), Hg(2+), and Zn(2+)) on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced cytotoxicity and the expression of the cytochrome P4501A1 gene (cyp1a1) in the zebrafish liver (ZFL) cell line. A metal accumulation study showed that Cu and Zn did not accumulate in ZFL cells. However, As and Hg did accumulate, which resulted in the inhibition of TCDD-mediated induction of cyp1a1 mRNA and protein expression, and 7-ethoxyresorufin O-deethylase activity. A luciferase assay showed that both As(3+) and Hg(2+) inhibited the TCDD-induced activity of gene constructs containing either synthetic 3XRE or a distal cyp1a1 promoter region, implying that the decreased levels of TCDD-induced cyp1a1 were due to transcriptional effects. A proteomic study showed that the toxic effects of As(3+) might be due to changes in cellular metabolic processes, the cellular stimulation response and the cellular redox state in ZFL cells.

Toxic effect on tissues and differentially expressed genes in hepatopancreas identified by suppression subtractive hybridization of freshwater pearl mussel (Hyriopsis cumingii) following microcystin-LR challenge

Microcystins are a family of potent hepatotoxins produced by freshwater cyanobacteria and can cause animal intoxications and human diseases. In this study, the effect of microcystin-LR (MC-LR) on the tissues of freshwater pearl mussel (Hyriopsis cumingii) was evaluated and differentially expressed genes in the hepatopancreas of the mussel exposed to MC-LR were identified. HPLC analysis of cell extracts from various tissues of the mussel indicated that the hepatopancreas had the highest MC-LR levels (55.78 ± 6.73 μg g⁻¹ DW) after 15-day exposure. The MC-LR concentration in gill or muscle was an order of magnitude less than in hepatopancreas or gonad. Subtractive cDNA library was constructed by suppression subtractive hybridization (SSH), and ∼400 positive clones were sequenced, from which 98 high quality sequences were obtained by BLAST analysis. The screening identified numerous genes involved in apoptosis, signal transduction, cytoskeletal remodel, innate immunity, material and energy metabolism, translation and transcription which were extensively discussed. The results of this study add large amount of information to the mussel genome data, and for the first time present the basic data on toxicity effect of MC-LR on mussel.

Evidence for the association of synaptotagmin with glutathione S-transferases: implications for a novel function in human breast cancer

OBJECTIVE

To analyze the pattern of changes in GSTs in cancerous and adjacent non-cancerous tissues obtained from breast cancer patients undergoing surgery.

DESIGN AND METHODS

Cytosolic GST purification, assay of GST, protein expression levels, and GST-synaptotagmin association were analyzed using standard biochemical techniques like GSH-affinity purification, spectrophotometry, SDS-PAGE, Western blots, and matrix-assisted laser desorption and ionization-time of flight (MALDI-TOF).

RESULTS

GST activity in cancerous tissues (0.26 U/mg protein) was significantly higher (P < 0.05) as compared to those from adjacent non-cancerous tissues (0.14 U/mg protein) of breast cancer patients. Further analysis of GST subunits on SDS-PAGE and Western blots using class-specific GST antibodies revealed significant elevation in GST-pi levels in cancer tissues with no appreciable changes in GST-alpha and GST-mu. Along with the elevation of GST-pi levels, high molecular weight proteins (approximately 70 kDa) cross reacting with GST antibodies were detected only in surgically resected tumor biopsies but not in the non-cancerous tissues adjacent to the tumor. Based on MALDI-TOF analysis, the high molecular weight band was identified as synaptotagmin V bound to GST-M1 with 47% sequence coverage after processing on an MS-FIT search engine.

CONCLUSIONS

Our results suggest a novel putative functional role for the GST-synaptotagmin complex in human breast cancers. As this association of GST M1-synaptotagmin was not seen in adjacent non-cancerous tissues, this can be used as a marker for breast cancers.

Tumoral drug metabolism: overview and its implications for cancer therapy

Drug-metabolizing enzymes (DME) in tumors are capable of biotransforming a variety of xenobiotics, including antineoplastics, resulting in either their activation or detoxification. Many studies have reported the presence of DME in tumors; however, heterogeneous detection methodology and patient cohorts have not generated consistent, firm data. Nevertheless, various gene therapy approaches and oral prodrugs have been devised, taking advantage of tumoral DME. With the need to target and individualize anticancer therapies, tumoral processes such as drug metabolism must be considered as both a potential mechanism of resistance to therapy and a potential means of achieving optimal therapy. This review discusses cytotoxic drug metabolism by tumors, through addressing the classes of the individual DME, their relevant substrates, and their distribution in specific malignancies. The limitations of preclinical models relative to the clinical setting and lack of data on the changes of DME with disease progression and host response will be discussed. The therapeutic implications of tumoral drug metabolism will be addressed-in particular, the role of DME in predicting therapeutic response, the activation of prodrugs, and the potential for modulation of their activity for gain are considered, with relevant clinical examples. The contribution of tumoral drug metabolism to cancer therapy can only be truly ascertained through large-scale prospective studies and supported by new technologies for tumor sampling and genetic analysis such as microarrays. Only then can efforts be concentrated in the design of better prodrugs or combination therapy to improve drug efficacy and individualize therapy.

The dioxin TCDD protects against aflatoxin-induced mutation in female rats, but not in male rats

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmental contaminant and a potent carcinogen in laboratory rodents. When combined with other environmental toxins, it has been shown to increase the (geno)toxicity of some compounds. In this study, the effect of TCDD on the mutagenicity of aflatoxin-B1 (AFB1) was examined in the rat liver using a lacI transgenic rodent mutation assay. AFB1 induces GC-->TA transversions. Since TCDD is known to have a differential effect in male and female rodents, both sexes were studied. The data showed that a 6-week pre-exposure to TCDD had no significant effect on the frequency of aflatoxin-induced mutation in the liver of male rats. However, the TCDD treatment completely prevented the aflatoxin-induced transversion mutations in female animals.

Effect of phenobarbital on the induction of glutathione S-transferases in rat testis

Glutathione S-transferases are a family of multifunctional proteins involved in intracellular transport processes and drug detoxication. In rats, these enzymes are dimeric proteins, and exist as cytosolic and microsomal proteins. The affinity purified rat testicular glutathione S-transferases are comprised of four subunits, Yc of alpha class, Yb and Ybeta of mu class and Ydelta of pi class. On chromatofocusing, they were resolved into six anionic and four cationic isozymes. The cationic isozymes were found to be abundant. All these isozymes on electrophoresis were found to contain heteromers except for two isozymes. The expression of individual subunits and their activity was elevated on treatment with multiple doses of phenobarbital in rat testis. Among all of these, according to the immunological studies, Ydelta, a pi class glutathione S-transferase, was induced predominantly in response to phenobarbital.

Inhibition of cellular enzymes by equine catechol estrogens in human breast cancer cells: specificity for glutathione S-transferase P1-1

Glutathione S-transferases (GSTs) are a family of detoxification isozymes that protect cells by conjugating GSH to a variety of toxic compounds, and they may also play a role in the regulation of both cellular proliferation and apoptosis. We have previously shown that human GST P1-1, which is the most widely distributed extrahepatic isozyme, could be inactivated by the catechol estrogen metabolite 4-hydroxyequilenin (4-OHEN) in vitro [Chang, M., Shin, Y. G., van Breemen, R. B., Blond, S. Y., and Bolton, J. L. (2001) Biochemistry 40, 4811-4820]. In the present study, we found that 4-OHEN and another catechol estrogen, 4,17beta-hydroxyequilenin (4,17beta-OHEN), significantly decreased GSH levels and the activity of GST within minutes in both estrogen receptor (ER) negative (MDA-MB-231) and ER positive (S30) human breast cancer cells. In addition, 4-OHEN caused significant decreases in GST activity in nontransformed human breast epithelial cells (MCF-10A) but not in the human hepatoma HepG2 cells, which lack GST P1-1. We also showed that GSH partially protected the inactivation of GST P1-1 by 4-OHEN in vitro, and depletion of cellular GSH enhanced the 4-OHEN-induced inhibition of GST activity. In addition, 4-OHEN GSH conjugates contributed about 27% of the inactivation of GST P1-1 by 4-OEHN in vitro. Our in vitro kinetic inhibition experiments with 4-OHEN showed that GST P1-1 had a lower K(i) value (20.8 microM) compared to glyceraldehyde-3-phosphate dehydrogenase (GAPDH, 52.4 microM), P450 reductase (PR, 77.4 microM), pyruvate kinase (PK, 159 microM), glutathione reductase (GR, 230 microM), superoxide dismutase (SOD, 448 microM), catalase (562 microM), GST M1-1 (620 microM), thioredoxin reductase (TR, 694 microM), and glutathione peroxidase (GPX, 1410 microM). In contrast to the significant inhibition of total GST activity in these human breast cancer cells, 4-OHEN only slightly inhibited the cellular GAPDH activity, and other cellular enzymes including PR, PK, GR, SOD, catalase, TR, and GPX were resistant to 4-OHEN-induced inhibition. These data suggest that GST P1-1 may be a preferred protein target for equine catechol estrogens in vivo.

How shall we apply the new biology to diagnostics in surgical pathology?

Molecular technology plays an ever-increasing role in academic pathology and frequent claims are made that these technical developments will revolutionize diagnostic histopathology. In reviewing the role and potential utility of molecular genetics in the clinical practice of tumour pathology, it is evident that claims have outweighed facts, at least to date, and while molecular data have helped to clarify specific small areas of tumour classification and have facilitated the diagnosis of certain relatively rare tumours (especially on limited tissue), the overall impact on cancer management has been small. In particular, molecular markers of prognosis or tumour response have yet to impact substantially on the role of conventional light microscopic examination. We believe that these shortcomings have more to do with the generally different goals of basic medical science and clinical practice. In order to optimize the benefit to patients of modern molecular pathology, these techniques need to be rigorously appraised in the clinical setting and properly analysed in terms of cost-benefit. This requires close collaboration between the basic research community and histopathologists. Suggestions that 'H&E' pathology will be superceded in the near future are both premature and unrealistic.