Activities of benzphetamine N-demethylase and aryl hydrocarbon hydroxylase in cells isolated from gamma-glutamyl transpeptidase-positive foci and surrounding liver.

The levels of two cytochrome P-450-linked enzymes of xenobiotic metabolism, benzphetamine N-demethylase and aryl hydrocarbon hydroxylase, were determined in cells isolated from gamma-glutamyl transpeptidase (GGT)-positive foci and in cells from surrounding liver obtained from carcinogen-treated inbred F344 rats. Rat liver foci were initiated with diethylnitrosamine (CAS: 55-18-5) and promoted with sodium phenobarbital [(PB) CAS: 64038-21-7] for 4 1/2 or 12 months. The levels of both enzymes were relatively low in the GGT-positive hepatocytes, while the GGT-negative hepatocytes from the surrounding liver had elevated levels of both enzymes comparable to levels seen in rats treated with PB alone. After 12 months of promotion the PB was removed from the diet and the activities of both enzymes fell below the control levels in the GGT-positive hepatocytes and returned to the control levels in the surrounding GGT-negative hepatocytes. Therefore, the cells in the GGT-positive foci contained low levels of these two cytochrome P-450 enzymes in relation to the levels in GGT-negative cells. These levels were responsive to phenobarbital induction, although the induced levels in the GGT-positive cells were much lower than the induced levels in GGT-negative hepatocytes. The liver surrounding the foci responded to phenobarbital induction to the same degree as did the liver of noninitiated rats.

Application of quantitative stereology to the evaluation of phenotypically heterogeneous enzyme-altered foci in the rat liver.

Quantitative stereologic relationships are applied in this report to the evaluation of F344 rat liver foci where the tissue sections exhibit congruent enzyme-altered areas of the several different phenotypes as well as enzyme-altered areas within a larger area of another enzyme alteration, that is, a "focus within a focus.' Quantitation of both the numbers and volume occupied by each of the phenotypes of the enzyme-altered foci was accomplished by the unique logic described in this report. The application of this logic to four representative experimental protocols with the use of three phenotypic markers demonstrated all possible congruent phenotypes as well as a small number of "foci within foci.' The variance of the quantitation of the experimental data was shown to depend on the number of focal transections identified in the sections, the number of sections examined, and the distribution of phenotypic alterations among foci.

Growth of carcinogen-altered rat hepatocytes in the liver of syngeneic recipients promoted with phenobarbital.

An improved transplantation system for the study of carcinogen-altered hepatocytes is described. This system, which is based on that reported by Laishes and Farber (Cancer Res., 61: 507-512, 1978), involves the transfer of hepatocytes from male F344 animals to syngeneic adult hosts. Unlike the earlier protocol, the recipient rats were fed phenobarbital (PB) rather than the DNA-reactive agent, 2-acetylaminofluorene. gamma-Glutamyl transpeptidase (GGT)-positive hepatocytes were induced in the donor animals by one of three different hepatocarcinogenic treatment regimens. The recipient rats received 0.05% PB in the diet for 3 wk prior to the cell transfer and were maintained on the PB diet for 2 to 7 mo. Hepatocytes from a male F344 donor rat that had received a 70% hepatectomy and 30 mg of diethylnitrosamine per kg and had been maintained on 0.05% PB for 12 mo formed GGT-positive colonies and hepatocellular carcinomas in both male and female recipients. No GGT-positive colonies were formed when 0.05% PB was omitted from the diet of the recipients. A 70% partial hepatectomy of the recipients at the time of cell transfer was also essential for the development of colonies and tumors. The mean volume of the colonies was 5 times larger in female recipients than in males, occupying 38% of the total liver volume in the females. GGT-positive foci arose in recipient livers that had received hepatocytes from either a male F344 donor rat treated according to the Solt and Farber [Nature (Lond.), 263: 701-703, 1976] selection protocol or a male F344 donor rat that received a 70% hepatectomy and 30 mg of diethylnitrosamine per kg and was maintained on 0.05% PB for 5 mo. The recipient animals were treated with PB which the initial experiments showed was essential for the development of foci. The number and volume of the foci in the recipient varied according to the treatment regimen that the donor rat received. This system provides a method for analyzing the growth regulation of altered foci at various stages of neoplastic development during hepatocarcinogenesis in the rat in the absence of DNA-reactive selection agents.

Inhibition of gamma-glutamyl transpeptidase activity by acivicin in vivo protects the kidney from cisplatin-induced toxicity.

Cisplatin [cis-dichlorodiammineplatinum(II)] is a widely used chemotherapeutic drug that is toxic to the proximal tubule cells of the kidney. gamma-Glutamyl transpeptidase (GGT) is localized to the luminal surface of the renal proximal tubules. GGT catalyzes the initial step in the metabolism of glutathione-conjugated drugs to mercapturic acids, some of which are severely nephrotoxic. We proposed that the nephrotoxicity of cisplatin was dependent on the cleavage of a cisplatin-glutathione conjugate by GGT. To test this hypothesis, renal GGT activity was blocked in male Sprague-Dawley rats by acivicin, a non-competitive inhibitor of GGT. Treatment with cisplatin alone caused extensive acute necrosis of the proximal tubules, but the proximal tubule cells appeared normal in rats treated with acivicin prior to cisplatin. Blood urea nitrogen and serum creatinine levels confirmed the protective effect of acivicin. Glutathione is a physiological substrate for GGT. Administration of an 83-fold excess of glutathione 30 min prior to cisplatin also inhibited cisplatin-induced nephrotoxicity. These data provide important new evidence that a large bolus of glutathione blocks the nephrotoxicity of cisplatin by competitively inhibiting GGT. These results indicate that cisplatin is conjugated to glutathione in vivo. The platinum-glutathione conjugate is nontoxic until metabolized by the proximal tubule cells. Formation of the nephrotoxic derivative of cisplatin requires GGT activity.

Human ovarian tumors express gamma-glutamyl transpeptidase.

Gamma-glutamyl transpeptidase (GGT) is a cell surface enzyme that initiates the cleavage of extracellular glutathione, thereby providing the cell with the amino acids necessary for increased synthesis of glutathione. GGT is induced in ovarian tumor cell lines selected in vitro for resistance to cisplatin. No study has examined GGT expression in primary human ovarian tumors. We analyzed frozen sections of 80 normal human ovaries and 56 ovarian tumors for expression of GGT. Histochemical staining showed that GGT was not expressed in the cells of the follicle or surface germinal epithelium of the normal ovary. GGT was expressed in some epithelial inclusion glands and occasionally in a small subset of stromal cells. Granulosa-stromal cell tumors were largely GGT-negative. In contrast, GGT-positive neoplastic cells were observed in 33 of 45 common epithelial ovarian tumors. None of the patients had been treated with chemotherapy. Some of the tumors had only rare GGT-positive cells, while others consisted almost entirely of GGT-positive cells. Among the low malignant potential and invasive tumors, at least one-half of the cells were GGT-positive in 6 of 9 serous borderline tumors (2 with mucinous foci), 0 of 1 borderline mucinous tumor, 3 of 12 serous papillary carcinomas, 2 of 3 mucinous carcinomas, 1 of 2 endometrioid carcinomas, 2 of 2 clear cell carcinomas, 0 of 2 transitional cell carcinomas, and 4 of 5 undifferentiated carcinomas. There was no correlation between the stage of the tumor and GGT expression, indicating that a GGT-negative tumor does not become GGT-positive as it progresses to a more widely disseminated lesion. In addition, there was no correlation between serum levels of CA 125 and GGT expression. These data show that GGT is expressed in many common ovarian epithelial neoplasms. We are currently following the response of these patients to chemotherapy to determine if expression of GGT serves as a marker for identifying neoplasms with enhanced resistance to platinum-based therapy.

Immunohistochemical detection of gamma-glutamyl transpeptidase in normal human tissue.

We developed a new, highly specific antibody that localizes gamma-glutamyl transpeptidase (GGT) in formalin-fixed sections of human tissue. The specificity of the antibody, GGT129, is demonstrated by immunostained Western blots of whole cell homogenate from five different tissues. The utility of the antibody is shown by a comprehensive study of GGT expression in normal human tissue. This study reveals GGT expression for the first time in a number of tissues, including glands in the endocervix, endometrium, and adrenals. Strong immunoreactivity was observed on the surface of renal proximal tubule cells, hepatic bile canaliculi, and capillary endothelial cells within the nervous system. Secretory or absorptive cells in sweat glands, prostate, salivary gland ducts, bile ducts, pancreatic acini, intestinal crypts, and testicular tubules were also GGT-positive. Small bands of positively stained stromal cells and GGT-positive histiocytes were seen in some tissues. Analysis of human fetal tissue shows that the developmental expression of GGT differs in humans and rodents. These findings form the basis for further work on GGT induction in tumors and the effect of GGT expression on the response of tumors to chemotherapy.

Altered expression of gamma-glutamyl transpeptidase in human tumors.

Elevated levels of gamma-glutamyl transpeptidase (GGT) activity and intracellular glutathione in tumor cells have been correlated with resistance to several classes of chemotherapeutic drugs. In this study, the first comprehensive analysis of GGT expression in human malignant neoplasms, 451 tumors were immunostained with an antibody directed against a c-terminus peptide of the human GGT protein. Analysis of the immunostaining revealed that GGT was expressed in 22 of 44 lung carcinomas and 16 of 22 ovarian surface epithelial carcinomas, although normal pulmonary and ovarian epithelium are GGT-negative. The tumor samples were obtained from patients before the start of therapy; therefore, GGT was not induced by radiation or chemotherapy. There was no GGT expression in mesotheliomas, Hodgkin's disease, non-Hodgkin's lymphomas, melanomas, basal cell carcinomas, and most soft tissue sarcomas, all of which are derived from GGT-negative cells. Carcinomas arising from some GGT-positive epithelium retained their GGT-positive phenotype. These included renal cell carcinomas, hepatocellular and cholangiocarcinomas, and carcinomas of the prostate and thyroid whereas both pancreatic adenocarcinomas and infiltrating carcinomas of the breast showed a wide range of GGT expression. Further studies are underway to determine whether expression of GGT plays a role in the inherent resistance of some tumors to alkylating agents and other classes of chemotherapeutic drugs.

Automated immunohistochemical assay for estrogen receptor status in breast cancer using monoclonal antibody CC4-5 on the Ventana ES.

Determination of breast cancer estrogen receptor (ER) status as a predictor of tumor response to adjuvant endocrine therapy remains a mainstay of breast cancer management. Recent second generation anti-ER antibodies and new epitope retrieval methods have produced paraffin-based immunohistochemical results that correlate closely with the dextran-coated charcoal (DCC) assay and appear to represent a superior method of ER assay. The authors determined the ER status of 103 invasive breast cancers by paraffin-based, automated immunohistochemistry on the Ventana ES using a new monoclonal antibody, CC4-5, and compared the results to those of parallel DCC biochemical analysis and manual immunohistochemical analysis using anti-ER monoclonal antibody ER1D5. The specificity of the CC4-5 antibody for ER protein was confirmed by Western blot analysis. Sixty of 103 cases were positive for ER by CC4-5 automated immunohistochemistry. With a ligand binding assay threshold value of 20 fmol/mg protein, there were 50 positive cases by biochemical assay. The biochemical results corresponded to an 88% rate of agreement with automated CC4-5 staining. Analysis of discordant cases revealed that the majority of CC4-5 immunopositive only cases (8 of 11) were strongly positive, stroma rich tumors, suggesting that corresponding biochemical measurements were diluted by non representative stromal tissue. There was only one immunonegative, biochemically positive case (27 fmol/mg protein). Semiquantitation of CC4-5 staining using percent positive tumor cells or weighted average staining intensity (HSCORE) showed moderate to good correlation with quantitative DCC results (r = 0.64 and 0.62, P < .0001). ER1D5 was not suitable for use on the Ventana ES, most likely due to temperature constraints of the instrument. By manual ER1D5 staining, 40 of 79 examined cases were positive corresponding to a 99% rate of agreement with automated CC4-5 staining. Semiquantitation of ER1D5 staining by percent positive tumor cells and weighted average staining intensity (HSCORE) showed excellent correlation with semiquantitation of automated CC4-5 results (r = 0.90 and 0.88, P < .0001). Automated immunohistochemistry using the Ventana ES and monoclonal antibody CC4-5 is a reliable method for determining breast cancer ER status. As with other immunohistochemical methods, direct correlation with morphology precludes errors due to tissue sampling, allowing for accurate analysis of stroma-rich or partially necrotic tumors and small neoplasms that otherwise would yield insufficient tumor tissue for biochemical analysis.

gamma-Glutamyl transpeptidase, a glutathionase: its expression and function in carcinogenesis.

gamma-Glutamyl transpeptidase (GGT) is found throughout the plant and animal kingdoms. It is a cell surface glycoprotein that cleaves gamma-glutamyl amide bonds. The most abundant physiologic substrates for the enzyme are glutathione and glutathione-conjugated compounds. GGT initiates the cleavage of extracellular glutathione into its constituent amino acids which can then be transported into the cell. It also catalyzes the initial step in the conversion of glutathione-conjugated compounds to mercapturic acids. GGT is expressed at high levels in many human tumors and in many carcinogen-induced tumors in animals. These observations have lead an increased focus on the role of the enzyme in the development and treatment of tumors. This chapter begins with an overview of the structure and function of GGT in normal tissues. A summary of its expression in neoplastic tissues and the ways in which GGT effects the response of tumors to chemotherapy follows. The chapter concludes with a discussion of strategies for using GGT to activate and target chemotherapy drugs to tumors as a means of improving treatment for common human malignancies.

Association between expression of glutathione-associated enzymes and response to platinum-based chemotherapy in head and neck cancer.

We examined the correlation between response to platinum-based chemotherapy and expression of glutathione S-transferase (GST), gamma-GGT (both by immunohistochemistry) and gamma-GCS (by in situ hybridization) in 51 patients with head and neck cancer, who received a total of 56 courses of chemotherapy. The overall response rate for the 56 chemotherapy treatment courses was 48%. The overall response rate (CR, PR) for patients with low GST scores was 88% (21 of 24), while among the patients with high GST scores, the overall response rate was 19% (6 of 32, P = 0.001). Patients with a low GST score were 4.7 times more likely to respond to chemotherapy than patients with high GST scores. GST scores corresponded to response in 84% of cases. Among 33 patients treated with chemotherapy for relapsed disease, the overall response rate for patients with low GST score was 70% (7 of 10), while among the patients with high GST scores, the overall response rate was 8.7% (2 of 23), P < 0.001). In contrast, both gamma-GCS and gamma-GGT showed a range of expression in these samples, but there was no significant correlation with treatment response. We conclude that GST expression correlates well with response to platinum based chemotherapy in head and neck cancer.

Genetic determinants of hepatocarcinogenesis in the B6C3F1 mouse.

The B6C3F1 mouse is highly susceptible to the induction of liver tumors because of the contribution of a specific gene, an allele of the Hcs (Hepatocarcinogen sensitivity) locus, inherited from its C3H inbred parent. This gene affects the rate of growth of preneoplastic hepatic lesions and results in the more rapid appearance of hepatic neoplasms in mice carrying the C3H allele in comparison to mice homozygous for the resistant C57BL/6 allele. The Hcs locus also acts synergistically with at least one class of chemical tumor promoters, the halogenated aromatic hydrocarbons. Because of this genetic promotion of hepatocarcinogenesis, B6C3F1 mice are more sensitive to liver tumor induction by both genotoxic and non-genotoxic carcinogens.

Optimizing chemotherapy: concomitant medication lists.

Identifying sources of variability in the response to cancer chemotherapy requires knowledge of all variables, including concomitant medications, that can alter the metabolism and pharmacokinetics of chemotherapy. This study investigated the accuracy of the lists of concomitant medications in the charts of cancer patients. Information collated from a questionnaire, patient interview, and the patient's medical chart was used to obtain validated medication lists. Patients took an average of 4.8 prescription drugs, 1.6 nonprescription drugs, and 1.6 other remedies within the 3 days prior to chemotherapy. Of the concomitant drugs actually taken, the medical records did not report 24% of prescription drugs, 84% of nonprescription drugs, and 83% of other remedies. Electronic medical records (EMRs) were more complete than paper charts, but even these omitted >75% of nonprescription drugs and other remedies. Potential drug interactions were noted in this study. This study documents the extent and complexity of the concomitant drugs taken by patients undergoing chemotherapy and the deficiencies in recording this information in medical charts.

Expression of gamma-glutamyl transpeptidase provides tumor cells with a selective growth advantage at physiologic concentrations of cyst(e)ine.

Cells from the GGT-negative mouse hepatoma cell line, Hepa 1-6, were transfected with a human GGT cDNA and stably transformed clones were isolated. In standard tissue culture medium the GGT-positive cells and GGT-negative controls grew equally well. However, when the cysteine concentration of the medium was reduced to physiologic levels the GGT-positive cells had a growth advantage. Further investigation revealed that the medium of the GGT-negative Hepa 1-6 cells contained glutathione that had been excreted by the cells, but no glutathione was present in the medium of the GGT-positive cells. We have previously shown that expression of GGT enables cells to use extracellular glutathione as a source of cysteine (Hanigan and Ricketts, Biochem., 32:6302, 1993). These new data reveal that physiologic levels of cysteine can be limiting for cell growth and expression of GGT can provide the cells with a selective growth advantage. These data explain the observation that cells transfected with GGT grow at the same rate as the GGT-negative controls in tissue culture medium which contains a high level of cysteine, but the GGT-positive cells grow more rapidly than the GGT-negative cells when transplanted into animals (Warren et al., Proc. Soc. Exp. Biol. Med., 202:9, 1993). GGT-positive tumor cells have a selective growth advantage in vivo in comparison to GGT-negative tumor cells because they are able to use serum glutathione as a secondary source of cysteine thereby overcoming the growth restriction imposed by serum levels of cysteine.

Extracellular glutathione is a source of cysteine for cells that express gamma-glutamyl transpeptidase.

We show that gamma-glutamyl transpeptidase (GGT) is a glutathionase that enables cells to use extracellular glutathione as a source of cysteine. We transfected NIH/3T3 mouse fibroblasts with a plasmid containing cDNA for human GGT, and obtained stably transformed cell lines that expressed GGT in its proper orientation on the outer surface of the cell. NIH/3T3 fibroblasts require cysteine for growth and are unable to use extracellular glutathione as a source of cysteine. We demonstrate GGT-positive fibroblasts are able to grow in cysteine-free medium supplemented with glutathione. Cysteine derived from the cleavage of extracellular glutathione can be used to maintain intracellular levels of glutathione. GGT-positive NIH/3T3 cells were able to replenish intracellular glutathione when incubated in cysteine-free medium containing glutathione. GGT-negative cells could not. Therefore, GGT is a glutathionase that provides the cell with access to a secondary source of cysteine.

Cisplatin nephrotoxicity: inhibition of gamma-glutamyl transpeptidase blocks the nephrotoxicity of cisplatin without reducing platinum concentrations in the kidney.

OBJECTIVE: Inhibition of gamma-glutamyl transpeptidase activity by acivicin or a large bolus of intravenous glutathione blocks the nephrotoxicity of cisplatin. The purpose of this study was to determine whether these compounds inhibit nephrotoxicity by reducing the amount of platinum retained by the kidney. STUDY DESIGN: The platinum concentration in urine and kidney of cisplatin-treated rats was determined by graphite furnace atomic absorption spectroscopy. Tissues from three experimental groups of rats were analyzed. The first group was treated with a nephrotoxic dose of cisplatin. The second group was treated with acivicin before cisplatin. The third group received a bolus of glutathione before cisplatin. Urine collected for 3 hours after the injection of cisplatin and kidney tissue from animals 5 days after treatment were analyzed for platinum content. RESULTS: Urine from animals pretreated with acivicin had the same concentration of platinum as that of control animals treated with cisplatin alone. Analysis of kidney tissue, blood urea nitrogen and serum creatinine 5 days after treatment showed that pretreatment with acivicin or glutathione blocked the nephrotoxicity of cisplatin. However, these agents did not alter the concentration of platinum in the kidney. CONCLUSIONS: The data in this study reveal that pretreatment with acivicin or glutathione does not block the uptake of platinum into the kidney nor do these agents reduce the concentration of platinum retained by the kidney. The mechanism by which these agents may inhibit the nephrotoxicity of cisplatin is discussed.

Partial hepatectomy is a promoter of hepatocarcinogenesis in C57BL/6J male mice but not in C3H/HeJ male mice.

We have shown previously that the difference between C57BL/6J and C3H/HeJ male mice in their susceptibilities to chemically-induced liver tumors results predominantly from an allelic difference at the Hepatocarcinogen sensitivity (Hcs) locus. This locus modulates the rate of growth of preneoplastic liver lesions and may also play a role in the turnover of normal hepatocytes in the adult liver. To define further the growth regulatory pathway of which the Hcs gene is a component, we asked whether the expression of the Hcs gene would modulate the response of preneoplastic liver lesions to the physiologic growth stimulus generated by a two-thirds hepatectomy. Twelve-day-old male and female C57BL/6J and C3H/HeJ mice were injected with 0.5 mumols N-ethyl-N-nitrosourea/g body weight. At six weeks of age half the animals received a two-thirds hepatectomy. Groups of animals were killed between 14 and 44 weeks of age for analysis of glucose-6-phosphatase (G6Pase)-deficient foci and hepatic tumors. The partial hepatectomy induced a regenerative response that caused both the G6Pase-deficient foci and the surrounding, histochemically normal hepatocytes to undergo several rapid rounds of division. As a result, the G6Pase-deficient foci were larger in the hepatectomized animals than in the sham operated controls. The foci in the non-hepatectomized C57BL/6J male mice grew more slowly than in the C3H/HeJ male mice [volume doubling time (Td) = 2.9 +/- 0.1 weeks and 2.0 +/- 0.6 weeks, respectively]. Following partial hepatectomy, the G6Pase-deficient foci in the C57BL/6J male mice maintained a significantly higher growth rate (Td = 2.2 +/- 0.3 weeks) than the foci in the sham operated C57BL/6J male mice. The partial hepatectomy did not have any long term effect on the growth rate of the G6Pase-deficient foci in the C3H/HeJ male mice nor in female mice of either strain. At 32 weeks of age, the mean liver tumor multiplicity for hepatectomized C57BL/6J male mice was approximately 5.3-fold greater than that for sham operated animals. In contrast, a two-thirds hepatectomy resulted in a 60% reduction in the number of liver tumors in C3H/HeJ male mice relative to sham operated mice. These data demonstrate that partial hepatectomy can act as a promoter of hepatocarcinogenesis in C57BL/6J male mice but not C3H/HeJ male mice. We propose that the Hcs gene and partial hepatectomy may promote hepatocarcinogenesis through the same pathway of growth regulation.

Models of hepatocarcinogenesis in the rat--contrasts and comparisons.

A variety of approaches for the induction of altered hepatic foci, hyperplastic nodules, and hepatocellular carcinomas in rat liver have been developed. These protocols, aided by the appearance of preneoplastic lesions during the carcinogenic process, have proven to be very useful for examining many of the characteristics of events involved in rat hepatocarcinogenesis. A number of models have demonstrated distinct steps or stages in the progression of the carcinogenic process. These protocols are currently employed in the classification and distinction of agents effecting hepatocarcinogenesis at one or more of its stages. This review presents an overview of the present-day multistage hepatocarcinogenesis model systems in the rat, with contrasts and comparisons of these systems. The potential uses of the model systems in the identification of complete carcinogens, initiating agents, and promoting agents devoid of initiating action are discussed.

Gamma-glutamyl transpeptidase immunoreactivity in benign and malignant breast tissue.

GGT 129, a polyclonal antibody directed against gamma-glutamyl transpeptidase (GGT), was used to study GGT expression in formalin-fixed paraffin-embedded tissues from normal breast, 24 benign lesions, 27 in situ carcinomas or atypical hyperplasias, and 79 infiltrating mammary carcinomas. Epithelium of the ducts and ductules in normal breast tissue showed immunoreactivity along the apical surface. There was a strong correlation (P < 0.01) between the histologic classification of the tissue and GGT expression. All of the benign breast lesions stained positive for GGT. Among in situ carcinomas and atypical hyperplasias, 5/27 (19%) were negative for GGT while 22/27 were immunopositive. Infiltrating carcinomas showed the greatest deviation from normal tissue with 23/79 (29%) negative for GGT. GGT expression in benign and malignant breast tissue was not correlated with the age of the patient, suggesting that menopausal status does not influence expression of GGT. Correlation of GGT immunoreactivity with tubule formation, nuclear pleomorphism, mitoses, grade, size of tumor, lymph node status, and ER/PR status was performed for 69 cases of infiltrating ductal adenocarcinoma. There were no statistically significant relationships between the level of GGT immunoreactivity and any of the parameters. The loss of GGT in some of the cases is evidence that this enzyme is not required for mammary tumor development or maintenance. However, as GGT is a component of the pathways that metabolize glutathione and glutathione-conjugates, the difference in levels of the enzyme in invasive breast cancers may be one explanation for the variation in chemotherapy response that has been observed in patients treated for advanced mammary cancer.

Expression of gamma-glutamyl transpeptidase in stage III and IV ovarian surface epithelial carcinomas does not alter response to primary cisplatin-based chemotherapy.

OBJECTIVE: Gamma-glutamyl transpeptidase activity has been shown to be essential for the nephrotoxicity of cisplatin. The purpose of this study was to determine whether expression of gamma-glutamyl transpeptidase in ovarian carcinomas is necessary for the antitumor effect of cisplatin. STUDY DESIGN: Tumor tissue from 18 patients with stage III or IV ovarian serous papillary carcinoma or poorly differentiated adenocarcinoma was analyzed for expression of gamma-glutamyl transpeptidase by histochemical or immunohistochemical staining. Response to cisplatin-based combination chemotherapy was evaluated on the basis of clinical response, progression-free interval, and survival. RESULTS: Gamma-glutamyl transpeptidase expression in the tumors ranged from 0% to 100% of the tumor cells gamma-glutamyl transpeptidase positive. Patient survival ranged from 15 months to 9 years. Twelve of the 18 patients had a complete response to the initial course of cisplatin-based combination chemotherapy. There was no statistically significant correlation between either response or time to relapse and gamma-glutamyl transpeptidase expression. However, there was a correlation between high levels of gamma-glutamyl transpeptidase in the tumor and acute ototoxicity in patients treated with cisplatin. Expression of high levels of gamma-glutamyl transpeptidase in the tumor was also found to be associated with shorter patient survival, suggesting that gamma-glutamyl transpeptidase might have a role in resistance to drugs used in second- and third-line therapy. CONCLUSIONS: Expression of gamma-glutamyl transpeptidase in ovarian serous papillary or poorly differentiated adenocarcinomas is not necessary for the antitumor activity of cisplatin. A correlation was found between high levels of gamma-glutamyl transpeptidase in the tumor and both increased ototoxicity from cisplatin and decreased patient survival. These data suggest that administering an inhibitor of gamma-glutamyl transpeptidase activity to block the nephrotoxicity of cisplatin would not interfere with its therapeutic effect.