gamma-Glutamyl transpeptidase mediation of tumor glutathione utilization in vivo

A γ-Glutamyl Transpeptidase (GGT)-Triggered Charge Reversal Drug-Delivery System for Cervical Cancer Treatment: In Vitro and In Vivo Investigation

Neutral/negatively charged nanoparticles are beneficial to reduce plasma protein adsorption and prolong their blood circulation time, while positively charged nanoparticles easily transverse the blood vessel endothelium into a tumor and easily penetrate the depth of the tumor via transcytosis. Γ-Glutamyl transpeptidase (GGT) is overexpressed on the external surface of endothelial cells of tumor blood vessels and metabolically active tumor cells. Nanocarriers modified by molecules containing γ-glutamyl moieties (such as glutathione, G-SH) can maintain a neutral/negative charge in the blood, as well as can be easily hydrolyzed by the GGT enzymes to expose the cationic surface at the tumor site, thus achieving good tumor accumulation via charge reversal. In this study, DSPE-PEG2000-GSH (DPG) was synthesized and used as a stabilizer to generate paclitaxel (PTX) nanosuspensions for the treatment of Hela cervical cancer (GGT-positive). The obtained drug-delivery system (PTX-DPG nanoparticles) was 164.6 ± 3.1 nm in diameter with a zeta potential of -9.85 ± 1.03 mV and a high drug-loaded content of 41.45 ± 0.7%. PTX-DPG NPs maintained their negative surface charge in a low concentration of GGT enzyme (0.05 U/mL), whereas they showed a significant charge-reversal property in the high-concentration solution of GGT enzyme (10 U/mL). After intravenous administration, PTX-DPG NPs mainly accumulated more in the tumor than in the liver, achieved good tumor-targetability, and significantly improved anti-tumor efficacy (68.48% vs. 24.07%, tumor inhibition rate, p < 0.05 in contrast to free PTX). This kind of GGT-triggered charge-reversal nanoparticle is promising to be a novel anti-tumor agent for the effective treatment of such GGT-positive cancers as cervical cancer.

Sodium-glucose cotransporter 2 (SGLT2) inhibitors and non-small cell lung cancer survival

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a relatively new class of antidiabetic drugs with demonstrated renal and cardiovascular disease benefit. This study evaluates the role of SGLT2 inhibitors on the survival of non-small cell lung cancer (NSCLC) patients.

METHODS

We used National Surveillance, Epidemiology and End Results (SEER)-Medicare linked data. Twenty four thousand nine hundred fifteen NSCLC patients newly diagnosed between 2014 and 2017 with pre-exiting diabetes and aged 66 years or older were included and followed to the end of 2019. Information on SGLT2 inhibitors use was extracted from the Medicare Part D file.

RESULTS

SGLT2 inhibitor use was associated with significantly reduced mortality risk after adjusting for potential confounders (HR = 0.68, 95% CI = 0.60-0.77) with stronger association for longer duration of use (HR = 0.54, 85% CI = 0.44-0.68). Further, we found that SGLT2 inhibitor use was associated with a significant reduced risk of mortality regardless of patients' demographic, tumour characteristics and cancer treatments.

CONCLUSION

Our large SEER-Medicare linked data study indicates that SGLT2 inhibitors use was associated with improved overall survival of NSCLC patients with pre-existing diabetes. Further studies are needed to confirm our findings and elucidate the possible mechanisms behind the association.

Design and evaluation of novel analogs of 2-amino-4-boronobutanoic acid (ABBA) as inhibitors of human gamma-glutamyl transpeptidase

Inhibitors of gamma-glutamyl transpeptidase (GGT1, aka gamma-glutamyl transferase) are needed for the treatment of cancer, cardiovascular illness and other diseases. Compounds that inhibit GGT1 have been evaluated in the clinic, but no inhibitor has successfully demonstrated specific and systemic GGT1 inhibition. All have severe side effects. L-2-amino-4‑boronobutanoic acid (l-ABBA), a glutamate analog, is the most potent GGT1 inhibitor in vitro. In this study, we have solved the crystal structure of human GGT1 (hGGT1) with ABBA bound in the active site. The structure was interrogated to identify interactions between the enzyme and the inhibitor. Based on these data, a series of novel ABBA analogs were designed and synthesized. Their inhibitory activity against the hydrolysis and transpeptidation activities of hGGT1 were determined. The lead compounds were crystalized with hGGT1 and the structures solved. The kinetic data and structures of the complexes provide new insights into the critical role of protein structure dynamics in developing compounds for inhibition of hGGT1.

Characteristics of peripheral blood Gamma-glutamyl transferase in different liver diseases

Gamma-glutamyl transferase (GGT) is a marker of oxidative stress and cholestasis. Because of its low specificity, clinicians usually ignore its diagnostic value.To compare and analyze the clinical features of GGT in primary biliary cholangitis (PBC), drug-induced liver injury (DILI), alcoholic liver disease (ALD), and non-alcoholic fatty liver disease (NAFLD) from the perspective of different causes instead of the severity of the disease.We observed the distribution characteristics and the rate of abnormality of GGT in the above 4 diseases. The relationship between GGT and alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), total serum bilirubin, triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol, high-density lipoprotein cholesterol was analyzed using Spearman correlation.The highest level of GGT was up to 1000.00 to 2000.00 U/L in PBC and DILI, and the highest level of GGT was more than 2000.00 U/L in ALD, yet the difference was not statistically significant (P > .05). The highest level of GGT was only about 200.00 U/L in NAFLD and was the lowest in 4 liver diseases. Also, GGT was positively correlated with ALP, TC in PBC and DILI. Also, in ALD, GGT was positively correlated with ALT, AST, ALP, TG, and TC. In NAFLD, GGT was positively correlated with ALT, AST, and TG.The abnormal GGT in PBC and cholestasis DILI was associated with cholestasis; in ALD, it was associated with oxidative stress and cholestasis, and in NAFLD, it was associated with oxidative stress. GGT levels had different characteristics in different liver diseases, which were closely related to the pathogenesis of liver diseases.

Application of glutathione depletion in cancer therapy: Enhanced ROS-based therapy, ferroptosis, and chemotherapy

Glutathione (GSH) is an important member of cellular antioxidative system. In cancer cells, a high level of GSH is indispensable to scavenge excessive reactive oxygen species (ROS) and detoxify xenobiotics, which make it a potential target for cancer therapy. Plenty of studies have shown that loss of intracellular GSH makes cancer cells more susceptible to oxidative stress and chemotherapeutic agents. GSH depletion has been proved to improve the therapeutic efficacy of ROS-based therapy (photodynamic therapy, sonodynamic therapy, and chemodynamic therapy), ferroptosis, and chemotherapy. In this review, various strategies for GSH depletion used in cancer therapy are comprehensively summarized and discussed. First, the functions of GSH in cancer cells are analyzed to elucidate the necessity of GSH depletion in cancer therapy. Then, the synthesis and metabolism of GSH are briefly introduced to bring up some crucial targets for GSH modulation. Finally, different approaches to GSH depletion in the literature are classified and discussed in detail according to their mechanisms. Particularly, functional materials with GSH-consuming ability based on nanotechnology are elaborated due to their unique advantages and potentials. This review presents the ingenious application of GSH-depleting strategy in cancer therapy for improving the outcomes of various therapeutic regimens, which may provide useful guidance for designing intelligent drug delivery system.

Alanine Aminotransferase and Gamma-Glutamyl Transpeptidase Predict Histologic Improvement in Pediatric Nonalcoholic Steatohepatitis

BACKGROUND AND AIMS

Predictive, noninvasive tools are needed to monitor key features of nonalcoholic fatty liver disease (NAFLD) in children that relate to improvement in liver histology. The purpose of this study was to evaluate the relationship between liver chemistries and liver histology using data from the CyNCh (Cysteamine Bitartrate Delayed-Release for the Treatment of NAFLD in Children) clinical trial.

APPROACH AND RESULTS

This study included 146 children. Improvement in liver histology, defined as decrease in nonalcoholic fatty liver disease (NAFLD) Activity Score ≥2 points without worsening of fibrosis, occurred in 43 participants (30%). There were 46 participants with borderline zone 1 nonalcoholic steatohepatitis (NASH) at baseline, with resolution in 28% (12 of 46). Multivariate models were constructed using baseline and change in alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transferase (GGT) at 52 weeks, for improvement in (1) liver histology primary outcome, (2) borderline zone 1 NASH, and (3) fibrosis. For improvement in histology, the model (P < 0.0001) retained baseline and change in GGT (area under the receiver operating characteristic [AUROC], 0.79; 95% confidence interval [CI], 0.71-0.87). For borderline zone 1 NASH, the model (P = 0.0004) retained baseline and change in ALT (AUROC, 0.80; 95% CI, 0.67-0.93). For fibrosis, the model (P < 0.001) retained baseline and change in ALT (AUROC, 0.80; 95% CI, 0.67-0.93). Additional clinical parameters were added to the models using Akaike's information criterion selection, and significantly boosted performance: improvement in histology with AUROC of 0.89 (95% CI, 0.82-0.95), borderline zone 1 NASH with AUROC of 0.91 (95% CI, 0.83-0.99), and fibrosis with AUROC of 0.89 (95% CI, 0.82-0.94). Models were validated using data from the TONIC (Treatment of Nonalcoholic Fatty Liver Disease in Children) trial.

CONCLUSIONS

In children with NAFLD, dynamic changes in serum ALT and GGT are associated with change in liver histology and appear to be powerful indicators of histological response.

Preoperative serum markers for individual patient prognosis in stage I-III colon cancer

Carcinoembryonic antigen (CEA) remains the only recommended biomarker for follow-up care of colorectal cancer (CRC), but besides CEA, several other serological parameters have been proposed as prognostic markers for CRC. The present retrospective analysis investigates a comprehensive set of serum markers with regard to cancer-specific survival (CSS) and disease-free survival (DFS). A total of 472 patients with colon cancer underwent surgery for curative intent between January 1988 and June 2007. Preoperative serum was analyzed for the following parameters: albumin, alkaline phosphatase (aP), beta-human chorionic gonadotropin (βhCG), bilirubin, cancer antigen 125 (CA 125), cancer antigen 19-9 (CA 19-9), CA 72-4, CEA, C-reactive protein (CRP), cytokeratin-19 soluble fragment (CYFRA 21-1), ferritin, gamma-glutamyltransferase (γGT), glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), hemoglobin, haptoglobin, interleukin-6, interleukin-8, creatinine, lactate dehydrogenase (LDH), serum amyloid A (SAA), and 25-hydroxyvitamin D. After a median follow-up period of 5.9 years, the overall 3- and 5-year CSS was 91.7 and 84.9 % and DFS rates were 82.7 % (3 years) and 77.6 % (5 years). Multivariate analyses confirmed preoperative CEA as an independent prognostic factor with regard to CSS and DFS. CA 19-9 and γGT also provided prognostic value for CSS and DFS, respectively. Younger age was negatively associated with DFS. According to UICC stage, CEA provided significant prognostic value with regard to CSS and DFS, while CA 19-9 was only prognostic for CSS. Combined analysis is able to identify patients with favorable prognosis. In addition to tumor baseline parameters, preoperative CEA could be confirmed as prognostic marker in colon cancer. CA 19-9 and γGT also provide additional prognostic value with regard to survival and recurrence in stage III and stage I disease, respectively. The combined use of CEA together with CA 19-9 and γGT improve risk-adapted post-op surveillance.

Gamma-glutamyl transpeptidase: redox regulation and drug resistance

The expression of gamma-glutamyl transpeptidase (GGT) is essential to maintaining cysteine levels in the body. GGT is a cell surface enzyme that hydrolyzes the gamma-glutamyl bond of extracellular reduced and oxidized glutathione, initiating their cleavage into glutamate, cysteine (cystine), and glycine. GGT is normally expressed on the apical surface of ducts and glands, salvaging the amino acids from glutathione in the ductal fluids. GGT in tumors is expressed over the entire cell membrane and provides tumors with access to additional cysteine and cystine from reduced and oxidized glutathione in the blood and interstitial fluid. Cysteine is rate-limiting for glutathione synthesis in cells under oxidative stress. The induction of GGT is observed in tumors with elevated levels of intracellular glutathione. Studies in models of hepatocarcinogenesis show that GGT expression in foci of preneoplastic hepatocytes provides a selective advantage to the cells during tumor promotion with agents that deplete intracellular glutathione. Similarly, expression of GGT in tumors enables cells to maintain elevated levels of intracellular glutathione and to rapidly replenish glutathione during treatment with prooxidant anticancer therapy. In the clinic, the expression of GGT in tumors is correlated with drug resistance. The inhibitors of GGT block GGT-positive tumors from accessing the cysteine in extracellular glutathione. They also inhibit GGT activity in the kidney, which results in the excretion of GSH in the urine and a rapid decrease in blood cysteine levels, leading to depletion of intracellular GSH in both GGT-positive and GGT-negative tumors. GGT inhibitors are being developed for clinical use to sensitize tumors to chemotherapy.

Glutathione S-conjugates as prodrugs to target drug-resistant tumors

Living organisms are continuously exposed to xenobiotics. The major phase of enzymatic detoxification in many species is the conjugation of activated xenobiotics to reduced glutathione (GSH) catalyzed by the glutathione-S-transferase (GST). It has been reported that some compounds, once transformed into glutathione S-conjugates, enter the mercapturic acid pathway whose end products are highly reactive and toxic for the cell responsible for their production. The cytotoxicity of these GSH conjugates depends essentially on GST and gamma-glutamyl transferases (γGT), the enzymes which initiate the mercapturic acid synthesis pathway. Numerous studies support the view that the expression of GST and γGT in cancer cells represents an important factor in the appearance of a more aggressive and resistant phenotype. High levels of tumor GST and γGT expression were employed to selectively target tumor with GST- or γGT-activated drugs. This strategy, explored over the last two decades, has recently been successful using GST-activated nitrogen mustard (TLK286) and γGT-activated arsenic-based (GSAO and Darinaparsin) prodrugs confirming the potential of GSH-conjugates as anticancer drugs.

Synergistic effect of gamma glutamyltransferase and obesity on metabolic syndrome, independent of hepatic steatosis

PURPOSE

Both obesity and gamma glutamyltransferase (GGT) are individually considered to be closely associated with metabolic syndrome (MetS). Whether the 2 factors synergistically associate with MetS is not yet confirmed. The purpose of this study was to investigate whether obesity and GGT are interactively associated with MetS.

METHODS

A cross-sectional study of 7390 adults (age 32-62 years old) was conducted from 2009 to 2010.

RESULTS

Our results showed that greater serum GGT quartiles were positively associated with all MetS components and fatty liver (P < .001). The odds ratio of MetS increased significantly along with quartiles of GGT and obesity. In comparison with subjects with normal body mass index and first quartile GGT, the odds ratio of MetS in obese groups with 1st, 2nd, 3rd, and 4th quartile GGT were 6.8, 14.5, 20.3, and 45.2, respectively, and it remained tenable after adjustment for fatty liver. The synergy index of GGT and obesity on MetS is 2.2 (95% confidence interval, 1.9-2.6).

CONCLUSIONS

Serum GGT level in combination with obesity can be a simple but useful tool for risk stratification of developing MetS. Obese individuals with high-normal GGT levels require close monitoring for high risk of MetS.

Exploratory clinical trial of (4S)-4-(3-[18F]fluoropropyl)-L-glutamate for imaging xC- transporter using positron emission tomography in patients with non-small cell lung or breast cancer

PURPOSE

(4S)-4-(3-[(18)F]fluoropropyl)-l-glutamate (BAY 94-9392, alias [(18)F]FSPG) is a new tracer to image x(C)(-) transporter activity with positron emission tomography (PET). We aimed to explore the tumor detection rate of [(18)F]FSPG in patients relative to 2-[(18)F]fluoro-2-deoxyglucose ([(18)F]FDG). The correlation of [(18)F]FSPG uptake with immunohistochemical expression of x(C)(-) transporter and CD44, which stabilizes the xCT subunit of system x(C)(-), was also analyzed.

EXPERIMENTAL DESIGN

Patients with non-small cell lung cancer (NSCLC, n = 10) or breast cancer (n = 5) who had a positive [(18)F]FDG uptake were included in this exploratory study. PET images were acquired following injection of approximately 300 MBq [(18)F]FSPG. Immunohistochemistry was done using xCT- and CD44-specific antibody.

RESULTS

[(18)F]FSPG PET showed high uptake in the kidney and pancreas with rapid blood clearance. [(18)F]FSPG identified all 10 NSCLC and three of the five breast cancer lesions that were confirmed by pathology. [(18)F]FSPG detected 59 of 67 (88%) [(18)F]FDG lesions in NSCLC, and 30 of 73 (41%) in breast cancer. Seven lesions were additionally detected only on [(18)F]FSPG in NSCLC. The tumor-to-blood pool standardized uptake value (SUV) ratio was not significantly different from that of [(18)F]FDG in NSCLC; however, in breast cancer, it was significantly lower (P < 0.05). The maximum SUV of [(18)F]FSPG correlated significantly with the intensity of immunohistochemical staining of x(C)(-) transporter and CD44 (P < 0.01).

CONCLUSIONS

[(18)F]FSPG seems to be a promising tracer with a relatively high cancer detection rate in patients with NSCLC. [(18)F]FSPG PET may assess x(C)(-) transporter activity in patients with cancer.

Gamma-glutamyltransferase and cancer incidence: the Ohsaki cohort study

Background

Although experimental studies have shown that gamma-glutamyltransferase (GGT) has a role in tumor progression, epidemiologic evidence for a relationship between GGT and cancer incidence is limited. The present study investigated the association between GGT and cancer incidence and assessed the role of alcohol consumption in this association.

Methods

We examined a cohort of 15 031 Japanese adults aged 40 to 79 years who attended a health checkup in 1995 and were free of cancer at that time. GGT was measured using the Szasz method. The participants were then followed from 1 January 1996 until 31 December 2005, and cancer incidence was recorded by using the Miyagi Regional Cancer Registry. Hazard ratios (HRs) and 95% confidence intervals (CIs) were computed for each quartile of GGT and compared. The lowest quartile (GGT <13.0 IU/ml) was used as the reference category.

Results

We documented 1505 cancers. Among participants in the highest quartile (GGT ≥31.0 IU/ml), the multivariate HR for any cancer was 1.28 (95% CI, 1.08–1.53; P for trend, <0.001), the HR for colorectal cancer was significantly greater than unity, and the HRs for esophageal, pancreatic, and breast cancers were greater than unity but not significantly so. This positive trend was observed only in current drinkers.

Conclusions

Our findings suggest that there is a positive relationship between GGT and cancer incidence only for alcohol-related cancers in current drinkers and that the positive association of GGT with cancer incidence largely reflects alcohol consumption.

The prognostic role of gamma-glutamyltransferase activity in non-diabetic ST-elevation myocardial infarction

In patients with acute coronary syndrome, gamma-glutamyltransferase activity (GGT) proved to be an independent predictor of the development of major adverse cardiac events at early and long terms. No data are available on GGT in ST-elevation myocardial infarction (STEMI). We assessed, in 337 consecutive STEMI patients without previously known diabetes submitted to mechanical revascularization, the prognostic role of GGT for in-Intensive Cardiac Care Unit mortality, together with the relation(s) between GGT and acute glucose dysmetabolism (admission glycemia, peak glycemia, insulin resistance as indicated by the Homeostatic Model Assessment HOMA index). At logistic regression analysis, GGT was an independent predictor for in-ICU mortality (OR 1.01 (95% CI 1.003-1.013) p = 0.002), when adjusted for BMI and for major bleedings [(OR 1.005 (95% CI 1.001-1.009) p = 0.029]. At linear regression analyses, GGT was significantly correlated with admission glycemia (r = 0.172; p = 0.002), uric acid (r = 0.146; p = 0.011), insulin (r = 0.171; p = 0.002) and age (r = -0.129; p = 0.020). We document that in STEMI patients without previously known diabetes submitted to mechanical revascularization, GGT values are an independent predictor of early mortality. The significant correlation between GGT and acute glucose dysmetabolism (as indicated by admission glycemia and insulin-resistance) can account, at least in part, for the prognostic role of GGT.

Glutathione in cancer cell death

Glutathione (L-γ-glutamyl-L-cysteinyl-glycine; GSH) in cancer cells is particularly relevant in the regulation of carcinogenic mechanisms; sensitivity against cytotoxic drugs, ionizing radiations, and some cytokines; DNA synthesis; and cell proliferation and death. The intracellular thiol redox state (controlled by GSH) is one of the endogenous effectors involved in regulating the mitochondrial permeability transition pore complex and, in consequence, thiol oxidation can be a causal factor in the mitochondrion-based mechanism that leads to cell death. Nevertheless GSH depletion is a common feature not only of apoptosis but also of other types of cell death. Indeed rates of GSH synthesis and fluxes regulate its levels in cellular compartments, and potentially influence switches among different mechanisms of death. How changes in gene expression, post-translational modifications of proteins, and signaling cascades are implicated will be discussed. Furthermore, this review will finally analyze whether GSH depletion may facilitate cancer cell death under in vivo conditions, and how this can be applied to cancer therapy.

Intertissue flow of glutathione (GSH) as a tumor growth-promoting mechanism: interleukin 6 induces GSH release from hepatocytes in metastatic B16 melanoma-bearing mice

B16 melanoma F10 (B16-F10) cells with high glutathione (GSH) content show high metastatic activity in vivo. An intertissue flow of GSH, where the liver is the main reservoir, can increase GSH content in metastatic cells and promote their growth. We have studied here possible tumor-derived molecular signals that could activate GSH release from hepatocytes. GSH efflux increases in hepatocytes isolated from mice bearing liver or lung metastases, thus suggesting a systemic mechanism. Fractionation of serum-free conditioned medium from cultured B16-F10 cells and monoclonal antibody-induced neutralization techniques facilitated identification of interleukin (IL)-6 as a tumor-derived molecule promoting GSH efflux in hepatocytes. IL-6 activates GSH release through a methionine-sensitive/organic anion transporter polypeptide 1- and multidrug resistance protein 1-independent channel located on the sinusoidal site of hepatocytes. Specific siRNAs were used to knock down key factors in the main signaling pathways activated by IL-6, which revealed a STAT3-dependent mechanism. Our results show that IL-6 (mainly of tumor origin in B16-F10-bearing mice) may facilitate GSH release from hepatocytes and its interorgan transport to metastatic growing foci.

A direct spectrophotometric gamma-glutamyltransferase inhibitor screening assay targeting the hydrolysis-only mode

Gamma-glutamyltransferase (GGT, E.C. 2.3.2.2) catalyzes the hydrolysis and transpeptidation of extracellular glutathione. Due to its central role in maintaining mammalian glutathione homeostasis, GGT is now believed to be a valuable drug target for a variety of life-threatening diseases, such as cancer. Unfortunately, however, effective tools for screening GGT inhibitors are still lacking. We report here the synthesis and evaluation of an alpha-phenylthio-containing glutathione peptide mimic that eliminates thiophenol upon GGT-catalyzed hydrolysis of the gamma-glutamyl peptide bond. The concurrent, real-time spectrophotometric quantification of the released thiophenol using Ellman's reagent creates a GGT assay format that is simple, robust, and highly sensitive. The versatility of the assay has been demonstrated by its application to the kinetic characterization of equine kidney GGT, and enzyme inhibition assays. The ability of the glutathione mimic to behave as an excellent donor substrate (exhibiting Michaelis-Menten kinetics with a K(m) of 11.3+/-0.5 microM and a k(cat) of 90.1+/-0.8 nmol mg(-1)min(-1)), coupled to the assay's ability to study the hydrolysis-only mode of the GGT-catalyzed reaction, make our approach amenable to high-throughput drug screening platforms.

Glutathione in Cancer Biology and Therapy

The glutathione (GSH) content of cancer cells is particularly relevant in regulating mutagenic mechanisms, DNA synthesis, growth, and multidrug and radiation resistance. In malignant tumors, as compared with normal tissues, that resistance associates in most cases with higher GSH levels within these cancer cells. Thus, approaches to cancer treatment based on modulation of GSH should control possible growth-associated changes in GSH content and synthesis in these cells. Despite the potential benefits for cancer therapy of a selective GSH-depleting strategy, such a methodology has remained elusive up to now. Metastatic spread, not primary tumor burden, is the leading cause of cancer death. For patient prognosis to improve, new systemic therapies capable of effectively inhibiting the outgrowth of seeded tumor cells are needed. Interaction of metastatic cells with the vascular endothelium activates local release of proinflammatory cytokines, which act as signals promoting cancer cell adhesion, extravasation, and proliferation. Recent work shows that a high percentage of metastatic cells with high GSH levels survive the combined nitrosative and oxidative stresses elicited by the vascular endothelium and possibly by macrophages and granulocytes. ?-Glutamyl transpeptidase overexpression and an inter-organ flow of GSH (where the liver plays a central role), by increasing cysteine availability for tumor GSH synthesis, function in combination as a metastatic-growth promoting mechanism. The present review focuses on an analysis of links among GSH, adaptive responses to stress, molecular mechanisms of invasive cancer cell survival and death, and sensitization of metastatic cells to therapy. Experimental evidence shows that acceleration of GSH efflux facilitates selective GSH depletion in metastatic cells.

Bcl-2 and glutathione depletion sensitizes B16 melanoma to combination therapy and eliminates metastatic disease

PURPOSE

Advanced melanoma resists all current therapies, and metastases in the liver are particularly problematic. Prevalent resistance factors include elevated glutathione (GSH) and increased expression of bcl-2 in melanoma cells. GSH has pleiotropic effects promoting cell growth and broad resistance to therapy, whereas Bcl-2 inhibits the activation of apoptosis and contributes to elevation of GSH. This study determined the in vivo efficacy of combination therapies administered while GSH and Bcl-2 were individually and simultaneously decreased in metastatic melanoma lesions.

EXPERIMENTAL DESIGN

Highly metastatic murine B16 melanoma (B16M-F10) cells have elevated levels of both GSH and Bcl-2. B16M-F10 cells were injected i.v. to establish metastatic lesions in vivo. GSH was decreased using an L-glutamine--enriched diet and administration of verapamil and acivicin, whereas Bcl-2 was reduced using oligodeoxynucleotide G3139. Paclitaxel, X-rays, tumor necrosis factor-alpha, and IFN-gamma were administered as a combination therapy.

RESULTS

Metastatic cells were isolated from liver to confirm the depletion of GSH and Bcl-2 in vivo. Reduction of Bcl-2 and GSH, combined with partial therapies, decreased the number and volume of invasive B16M-F10 foci in liver by up to 99% (P<0.01). The full combination of paclitaxel, X-rays, and cytokines eliminated B16M-F10 cells from liver and all other systemic disease, leading to long-term survival (>120 days) without recurrence in 90% of mice receiving the full therapy. Toxicity was manageable; the mice recovered quickly, and hematology and clinical chemistry data were representative of accepted clinical toxicities.

CONCLUSIONS

Our results suggest a new strategy to induce regression of late-stage metastatic melanoma.

Gamma-glutamyltransferase, redox regulation and cancer drug resistance

Gamma-glutamyltransferase, a key enzyme of GSH metabolism, can modulate crucial redox-sensitive functions, such as antioxidant/antitoxic defences and cellular proliferative/apoptotic balance, with potential implications in tumour progression and drug resistance. Recent studies have elucidated the mechanisms of GGT involvement in various pathological processes suggesting its potential role as therapeutic target and diagnostic/prognostic marker.

Gamma glutamyl transferase and metabolic syndrome, cardiovascular disease, and mortality risk: the Framingham Heart Study

OBJECTIVE

To determine whether serum gamma-glutamyl transferase (GGT) predicts cardiovascular disease (CVD) morbidity and mortality, accounting for temporal changes in known CVD risk factors and C-reactive protein (CRP).

METHODS AND RESULTS

In 3451 Framingham Study participants (mean age 44 years, 52% women) we examined the relations of GGT with CVD risk factors, and prospectively determined the risk of new-onset metabolic syndrome, incident CVD, and death. GGT was positively associated with body mass index, blood pressure, LDL cholesterol, triglycerides, and blood glucose in cross-sectional analysis (P<0.005). On follow-up (mean 19 years), 968 participants developed metabolic syndrome, 535 developed incident CVD, and 362 died. The risk of metabolic syndrome increased with higher GGT (multivariable-adjusted hazard ratio [HR] per SD increment log-GGT, 1.26 [95%CI; 1.18 to 1.35]). Adjusting for established CVD risk factors (as time-dependent covariates updated quadriennially) and baseline CRP, a 1-SD increase in log-GGT conferred a 13% increase in CVD risk (P=0.007) and 26% increased risk of death (P<0.001). Individuals in the highest GGT quartile experienced a 67% increase in CVD incidence (multivariable-adjusted HR 1.67, 95%CI; 1.25 to 2.22).

CONCLUSIONS

An increase in serum GGT predicts onset of metabolic syndrome, incident CVD, and death suggesting that GGT is a marker of metabolic and cardiovascular risk.

Influence of the level of γ-glutamyltranspeptidase activity on the response of poorly and moderately differentiated rhabdomyosarcoma cell lines to all-trans-retinoic acid

Differentiation therapy with retinoic acid has been considered a potential approach for treating rhabdomyosarcoma. Analysis of retinoids as differentiating agents for rhabdomyosarcoma is, however, rendered incomplete by the fact that some rhabdomyosarcoma cell lines are retinoic acid resistant. Therefore, the aim of the present work was to study the effect of all-trans-retinoic acid on two rat tumour cell lines, derived from the same rhabdomyosarcoma tumour model (i.e. the moderately differentiated low metastatic F21 cell line and the poorly differentiated high metastatic S4MH cell line), to discover how degree of differentiation and glutathione metabolism influence response to this retinoic acid derivative. We observed that whereas in the S4MH cell line all-trans-retinoic acid induced a significant inhibition of tumorigenic potential, in F21 cells all-trans-retinoic acid enhanced tumour growth and only at a higher dose was there a slight antiproliferative effect. These effects were in consonance with the activity level of gamma-glutamyltranspeptidase, which was significantly increased in F21 cells, but not in S4MH cells, in response to the all-trans-retinoic acid-induced increase in reactive oxygen species. The pro-tumour effect observed in F21 cells was reversed by adding buthionine sulphoximide, a specific cellular glutathione-depleting agent, to the all-trans-retinoic acid treatment. This combination produced a decrease in gamma-glutamyltranspeptidase activity, and an increase in oxidative stress and apoptosis. Our findings suggest that the response to all-trans-retinoic-acid of the tumour cell lines studied is influenced by the strong relationship between intracellular glutathione content, gamma-glutamyltranspeptidase activity and degree of differentiation of the rhabdomyosarcoma cell line, and that this relationship should be taken into account when identifying 'retinoid-sensitive' tumours.

Expression of gamma-glutamyltransferase in cancer cells and its significance in drug resistance

The expression of gamma-glutamyltransferase (GGT), a cell surface enzyme involved in cellular glutathione homeostasis, is often significantly increased in human tumors, and its role in tumor progression, invasion and drug resistance has been repeatedly suggested. As GGT participates in the metabolism of cellular glutathione, its activity has been mostly regarded as a factor in reconsitution of cellular antioxidant/antitoxic defences. On this basis, an involvement of GGT expression in resistance of cancer cells to cytotoxic drugs (in particular, cisplatin and other electrophilic agents) has been envisaged. Mechanistic aspects of GGT involvement in antitumor pharmacology deserve however further investigations. Recent evidence points to a more complex role of GGT in modulation of redox equilibria, with effects acting both intracellularly and in the extracellular microenvironment. Indications exist that the protective effects of GGT may be independent of intracellular glutathione, and derive rather from processes taking place at extracellular level and involving reactions of electrophilic drugs with thiol metabolites originating from GGT-mediated cleavage of extracellular glutathione. Although expression of GGT cannot be regarded as a general mechanism of resistance, the involvement of this enzyme in modulation of redox metabolism is expected to have impact in cellular response to several cytotoxic agents. The present commentary is a survey of data concerning the role of GGT in tumor cell biology and the mechanisms of its potential involvement in tumor drug resistance.

Bcl-2 and Mn-SOD antisense oligodeoxynucleotides and a glutamine-enriched diet facilitate elimination of highly resistant B16 melanoma cells by tumor necrosis factor-alpha and chemotherapy

Mitochondrial glutathione (mtGSH) depletion increases sensitivity of Bcl-2-overexpressing B16 melanoma (B16M)-F10 cells (high metastatic potential) to tumor necrosis factor-alpha (TNF-alpha)-induced oxidative stress and death in vitro. In vivo, mtGSH depletion in B16M-F10 cells was achieved by feeding mice (where the B16M-F10 grew as a solid tumor in the footpad) with an L-glutamine (L-Gln)-enriched diet, which promoted in the tumor cells an increase in glutaminase activity, accumulation of cytosolic L-glutamate, and competitive inhibition of GSH transport into mitochondria. L-Gln-adapted B16M-F10 cells, isolated using anti-Met-72 monoclonal antibodies and flow cytometry-coupled cell sorting, were injected into the portal vein to produce hepatic metastases. In l-Gln-adapted invasive (iB16M-Gln+) cells, isolated from the liver by the same methodology and treated with TNF-alpha and an antisense Bcl-2 oligodeoxynucleotide, viability decreased to approximately 12%. iB16M-Gln+ cell death associated with increased generation of O2*- and H2O2, opening of the mitochondrial permeability transition pore complex, and release of proapoptotic molecular signals. Activation of cell death mechanisms was prevented by GSH ester-induced mtGSH replenishment. The oxidative stress-resistant survivors showed an adaptive response that includes overexpression of manganese-containing superoxide dismutase (Mn-SOD) and catalase activities. By treating iB16M-Gln+ cells with a double anti- antisense therapy (Bcl-2 and SOD2 antisense oligodeoxynucleotides) and TNF-alpha, metastatic cell survival decreased to approximately 1%. Chemotherapy (taxol plus daunorubicin) easily removed this minimum percentage of survivors. This contribution identifies critical molecules that can be sequentially targeted to facilitate elimination of highly resistant metastatic cells.

Acceleration of glutathione efflux and inhibition of gamma-glutamyltranspeptidase sensitize metastatic B16 melanoma cells to endothelium-induced cytotoxicity

Highly metastatic B16 melanoma (B16M)-F10 cells, as compared with the low metastatic B16M-F1 line, have higher GSH content and preferentially overexpress BCL-2. In addition to its anti-apoptotic properties, BCL-2 inhibits efflux of GSH from B16M-F10 cells and thereby may facilitate metastatic cell resistance against endothelium-induced oxidative/nitrosative stress. Thus, we investigated in B16M-F10 cells which molecular mechanisms channel GSH release and whether their modulation may influence metastatic activity. GSH efflux was abolished in multidrug resistance protein 1 knock-out (MRP-/-1) B16M-F10 transfected with the Bcl-2 gene or in MRP-/-1 B16M-F10 cells incubated with l-methionine, which indicates that GSH release from B16M-F10 cells is channeled through MRP1 and a BCL-2-dependent system (likely related to an l-methionine-sensitive GSH carrier previously detected in hepatocytes). The BCL-2-dependent system was identified as the cystic fibrosis transmembrane conductance regulator, since monoclonal antibodies against this ion channel or H-89 (a protein kinase A-selective inhibitor)-induced inhibition of cystic fibrosis transmembrane conductance regulator gene expression completely blocked the BCL-2-sensitive GSH release. By using a perifusion system that mimics in vivo conditions, we found that GSH depletion in metastatic cells can be achieved by using Bcl-2 antisense oligodeoxynucleotide- and verapamil (an MRP1 activator)-induced acceleration of GSH efflux, in combination with acivicin-induced inhibition of gamma-glutamyltranspeptidase (which limits GSH synthesis by preventing cysteine generation from extracellular GSH). When applied under in vivo conditions, this strategy increased tumor cytotoxicity (up to approximately 90%) during B16M-F10 cell adhesion to the hepatic sinusoidal endothelium.

Effect of cacao liquor extract on tumor marker enzymes during chemical hepatocarcinogenesis in rats

This study investigated the effect of cacao liquor extract (CLE) on tumor marker enzymes--alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (GGT), glutathione-S-transferase (GST), and glutathione reductase (GR) activities--in plasma and/or liver of hepatocarcinogenic rats, which were induced with diethylnitrosamine and 2-acetylaminofluorene. Twenty-nine male Sprague-Dawley rats (weighing 150-330 g) were divided into four groups (n = 6-8): normal control group (N), normal group + CLE (NE), cancer group (C), and cancer group + CLE (CE). Analysis of variance showed significant differences (P<.05) in the specific activities of ALP, GGT, and GST between the C and N groups. However, GR activity for the C group was not significantly different compared with the N group. In the CE group, the specific activities of ALP, GGT, GST, and GR were significantly lower (P<.05) compared with the C group. The findings showed that CLE could lower the activity of tumor marker enzymes of rats during hepatocarcinogenesis. Based on the results obtained, polyphenol compounds present in the cacao liquor, extracted by using ethanol, have the potential in decreasing the severity of hepatocarcinogenesis.

Inhibition of gamma-glutamyl transpeptidase activity decreases intracellular cysteine levels in cervical carcinoma

PURPOSE

To determine whether gamma-glutamyl transpeptidase (gamma-GT) is involved in the maintenance of elevated cysteine levels in cervical carcinoma.

METHODS

Four cervical carcinoma cell lines were tested in vitro for cysteine accumulation and gamma-GT levels. The highest and lowest gamma-GT-expressing cell lines were used in in vivo experiments to determine the effect of gamma-GT inhibition on cysteine levels.

RESULTS

Treatment of a series of cervical carcinoma cell lines with acivicin decreased intracellular cysteine concentrations. Cysteine depletion was evident in Me180 cells which had the greatest levels of gamma-GT activity, and had a more pronounced cysteine decrease in medium with glutathione and cysteine concentrations simulating the in vivo situation. Also investigated were the effects of inhibition of gamma-GT activity on intracellular cysteine levels in xenografts grown in severe combined immunodeficient (SCID) mice. With the use of 35 mg/kg of acivicin, gamma-GT activity decreased to basal levels of detection in both tumour types and significant decreases in cysteine levels were seen in the high gamma-GT-expressing tumours (Me180). Thus, inhibition of gamma-GT activity may have therapeutic potential in high-expressing cancers.

CONCLUSIONS

In tumours and cell lines with elevated levels of gamma-GT activity, inhibition of this enzyme led to decreases of cysteine levels.

Characterization of sequence-dependent synergy between ZD1839 ("Iressa") and oxaliplatin

ZD1839 ("Iressa"), a selective epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), is currently undergoing preclinical and clinical evaluation in several solid tumors. The present study aimed to assess the effect of ZD1839 in combination with oxaliplatin in the colon cancer cell lines HT-29 and LoVo. For in vitro chemosensitivity testing, cells were treated with serial dilutions of each drug sequentially at a fixed ratio of doses that corresponded to 1/20, 1/10, 1/5, 1/2, 1, 1.5 and 2 times the individual IC(50) values. Oxaliplatin followed by ZD1839 produced a synergistic effect. In contrast, oxaliplatin following ZD1839 exhibited an additive effect at best. Mass spectrometry examination revealed that ZD1839 modestly enhanced cellular oxaliplatin accumulation and platinum-DNA (Pt-DNA) adducts (P>0.05). In additional studies, high-performance liquid chromatography revealed that oxaliplatin had no effect on ZD1839 accumulation. In contrast, ZD1839 markedly inhibited removal of Pt-DNA adducts (P<0.05). With oxaliplatin treatment (1 day) followed by ZD1839 (1 day), then incubation with drug-free medium (1 day), 90% of Pt-DNA adducts remained. Apoptosis examination revealed that oxaliplatin-induced apoptosis was prolonged by sequential oxaliplatin followed by ZD1839 treatment compared with oxaliplatin alone. Further experiments revealed that ZD1839 decreased cellular gamma-glutamyltransferase activity.

CONCLUSIONS

The above observations provide a mechanistic explanation for the synergy of oxaliplatin followed by ZD1839, and suggest that this treatment combination warrants further preclinical and clinical investigation.

Is the expression of γ-glutamyl transpeptidase messenger RNA an indicator of biological behavior in recurrent hepatocellular carcinoma?

AIM: To investigate the correlation between gamma-glutamyl transpeptidase (γ-GTP) expression in the primary HCC and post-resection recurrence and its biological behaviors.

METHODS: Forty consecutive patients having curative resection for HCC were included in this study. The primers for reverse -transcription polymerase chain reaction (RT-PCR) were corresponding to the 5’-noncoding human γ-GTP mRNA of fetal liver (type A), HepG2 cells (type B), and placenta (type C). Both the cancer and non-cancerous tissues of the resected liver were analyzed. The correlations between the expression of γ-GTP and the clinicopathological variables and outcomes (recurrence and survival) were studied.

RESULTS: Those with type B γ-GTP mRNA in cancer had significant higher recurrence rate than those without it (63.6% vs 14.3%). Both those with type B in cancer and in non -cancer died significantly more than those without it (45.5% vs 0% and 53.6% vs 0%, respectively). By multivariate analysis, the significant predictors of recurrence included high serum AFP (P = 0.0108), vascular permeation (P = 0.0084), and type B γ-GTP mRNA in non-cancerous liver (P = 0.0107). The significant predictors of post-recurrence death included high serum AFP (P = 0.0141), vascular permeation ( P = 0.0130), and daughter nodules (P = 0.0053). As to the manifestations (recurrent number 2, recurrent extent 2 segments, extra-hepatic metastasis, and death) in recurrent patients, there were no statistical significant differences between those with type B in the primary tumor and those without it. The difference between those with type B in non-cancerous liver and those without it also was not significant.

CONCLUSION: Patients of HCC with type B γ-GTP mRNA both in cancer and in non-cancerous tissue had a worse outcome, earlier recurrence, and more post-recurrence death.

Glutathione conjugates and their synthetic derivatives as inhibitors of glutathione-dependent enzymes involved in cancer and drug resistance

Alterations in levels of glutathione (GSH) and glutathione-dependent enzymes have been implicated in cancer and multidrug resistance of tumor cells. The activity of a number of these, the multidrug resistance-associated protein 1, glutathione S-transferase, DNA-dependent protein kinase, glyoxalase I, and gamma-glutamyl transpeptidase, can be inhibited by GSH-conjugates and synthetic analogs thereof. In this review we focus on the function of these enzymes and carriers in cancer and anti-cancer drug resistance, in relation to their inhibition by GSH-conjugate analogs.

The expression of gamma-glutamyltransferase in rat colon carcinoma cells is distinctly regulated during differentiation and oxidative stress

Gamma glutamyltransferase (GGT) is a plasma membrane bound enzyme that initiates the degradation of glutathione. The presence of several promoters in the rat GGT gene indicates strict control and regulation of its expression. The aim of this study was to investigate whether the GGT gene was regulated differently after butyrate-induced differentiation and oxidative stress exposure of rat colon carcinoma cells and whether the regulation was related to the glutathione level. The activity of GGT was upregulated in a time-and-dose dependent manner after both butyrate and menadione incubations. The presence of antioxidants blocked the menadione but not the butyrate mediated induction of the enzyme. The level of intracellular glutathione was reduced after menadione, but not after butyrate incubations. Depletion of glutathione alone did not alter GGT activity. Reactive oxygen species (ROS) were not produced after incubations with butyrate, while menadione incubations produced ROS. The multiple GGT mRNA transcripts (mRNA I-V) that originate from the five distinct promoters were all present in the cell line. Incubations with butyrate enhanced mRNA II and IV transcripts whereas a reduction in mRNA IV-1 was noted during menadione incubations. The level of total GGT mRNA (I-V) was not altered when related to the amount of total beta-actin mRNA. We conclude that GGT activity can be upregulated by at least two distinct mechanisms during differentiation and oxidative stress. Apparently, the regulation of the enzyme is not directly linked to the intracellular level of glutathione.

gamma-Glutamyl transpeptidase overexpression increases metastatic growth of B16 melanoma cells in the mouse liver

B16 melanoma (B16M) cells with high glutathione (GSH) content show rapid proliferation in vitro and high metastatic activity in the liver in vivo. gamma-Glutamyl transpeptidase (GGT)-mediated extracellular GSH cleavage and intracellular GSH synthesis were studied in vitro in B16M cells with high (F10) and low (F1) metastatic potential. GGT activity was modified by transfection with the human GGT gene (B16MF1/Tet-GGT cells) or by acivicin-induced inhibition. B16MF1/Tet-GGT and B16MF10 cells exhibited higher GSH content (35 +/- 6 and 40 +/- 5 nmol/10(6) cells, respectively) and GGT activity (89 +/- 9 and 37 +/- 7 mU/10(6) cells, respectively) as compared (P <.05) with B16MF1 cells (10 +/- 3 nmol GSH and 4 mU GGT/10(6) cells). Metastasis (number of foci/100 mm(3) of liver) increased in B16MF1 cells pretreated with GSH ester ( approximately 3-fold, P <.01), and decreased in B16MF1/Tet-GGT and B16MF10 cells pretreated with the GSH synthesis inhibitor L-buthionine (S,R)-sulphoximine ( approximately 5-fold and 2-fold, respectively, P <.01). Liver, kidney, brain, lung, and erythrocyte GSH content in B16MF1/Tet-GGT- or B16MF10-bearing mice decreased as compared with B16MF1- and non-tumor-bearing mice. Organic anion transporting polypeptide 1-independent sinusoidal GSH efflux from hepatocytes increased in B16MF1/Tet-GGT- or B16MF10-bearing mice ( approximately 2-fold, P <.01) as compared with non-tumor-bearing mice. Our results indicate that tumor GGT activity and an intertissue flow of GSH can regulate GSH content of melanoma cells and their metastatic growth in the liver.

Expression of urokinase-type plasminogen activator in an experimental model of hepatocarcinoma

Hepatocellular carcinoma (HCC) is the most common primary malignant tumor of the liver. Molecular genetic analyses have clarified that accumulation of genome changes provides important steps in carcinogenesis. Urokinase type plasminogen activator (uPA) forms part of an important enzymatic system that degraded the extracellular matrix in process of invasion and metastasis. In order to study the kinetics of uPA cellular expression during this process, we used specific polyclonal antibodies against uPA in an immunohistochemistry assay in liver sections from a HCC in rats. The neoplastic transformation induced with this model was preceded by the appearance of numerous hyperplastic nodules during early stages, after time lesions progressed to well-differentiated HCC. The morphological changes of premalignant and malignant lesions were associated with a progressive increment of uPA expression, which reached its peak at 5 and 6 months after the administration of the carcinogenic drugs. Of the enzymatic markers analyzed, the gamma glutamyl transpeptidase showed correlationship with the histological findings. Our results suggest that the increase in the uPA expression should not only be considered as the hallmark of metastasis, but may also be related to early events in the neoplastic transformation and with the proliferation of vessels and biliary ducts.

Human germ cell tumours: expression of gamma-glutamyl transpeptidase and sensitivity to cisplatin

Previous studies have shown that the enzyme-glutamyl transpeptidase (GGT) is essential for the nephrotoxicity of cisplatin. This study was designed to determine whether GGT activity is necessary for the therapeutic effect of the drug. The relationship between GGT expression and clinical response to platinum-based chemotherapy was examined in 41 human germ cell tumours. Sections of formalin-fixed, paraffin-embedded tumours were immunohistochemically stained with an antibody directed against human GGT. There was no expression of GGT in any of the 17 seminomas or four dysgerminomas; whereas, 12/12 ovarian yolk sac tumours and 4/4 embryonal carcinomas of the testis were GGT-positive. In stage I tumours fewer tumour cells expressed GGT than in later stage tumours. In four germ cell tumours of mixed histology, the seminomatous and dysgerminoma areas were GGT-negative while the areas of the tumour with yolk sac or embryonal histology contained GGT-positive tumour cells. The patients with seminomas or dysgerminomas who were treated with cisplatin-based chemotherapy, all had a complete response despite the absence of GGT expression in these tumours. Fifteen of the 16 patients with yolk sac or embryonal carcinomas received cisplatin-based chemotherapy following surgery. Twelve had a complete response, while three failed to respond to platinum-based therapy. There was no correlation between the level of GGT-expression and response to therapy in this group. Three of the four patients with tumours of mixed histology were treated with cisplatin-based therapy, and had a complete response. Therefore, expression of GGT is not necessary for the therapeutic effect of cisplatin in germ cell tumours. The results from this study suggest that systemic inhibition of GGT would inhibit the nephrotoxic side-effect of cisplatin without interfering with its activity towards germ cell tumours.

Gamma-glutamyl transpeptidase accelerates tumor growth and increases the resistance of tumors to cisplatin in vivo

We have shown previously that gamma-glutamyl transpeptidase (GGT) activity is essential for the nephrotoxicity of cisplatin. In this study we asked whether GGT activity was necessary for the antitumor activity of cisplatin. GGT was transfected into PC3 cells, a human prostate tumor cell line. Two independent GGT-positive cell lines were isolated and characterized. GGT cleaves extracellular glutathione providing the cells with access to additional cysteine. Expression of GGT had no effect on the growth rate of the cells in vitro where the culture medium contains high levels of cysteine. However, when the cells were injected into nude mice the GGT-positive tumors grew at more than twice the rate of the GGT-negative tumors. Weekly treatment with cisplatin was toxic to both GGT-positive and -negative tumors. The GGT-positive tumors were significantly more resistant to the toxicity of cisplatin than the GGT-negative tumors. Therefore, expression of GGT is required for the nephrotoxicity of cisplatin, but diminishes the tumor toxicity of the drug. These results indicate that the nephrotoxicity and the tumor toxicity of cisplatin are via two distinct pathways.

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.

Elevation of glutathione and related enzyme activities in high-grade and metastatic extremity soft tissue sarcoma

BACKGROUND

Glutathione is a free radical scavenger implicated in the chemoresistance of certain tumors. As treatment with chemotherapy has added little to improved survival in adult soft tissue sarcoma and little is known concerning the mechanisms of chemoresistance in sarcoma, we studied concentrations of glutathione (nmol/mg protein) and activities of gamma-glutamylcysteine synthetase (GCS; nmol/mg protein/h) and gamma-glutamyl transpeptidase (GGTP; U/mg protein) in extremity soft tissue sarcoma.

METHODS AND RESULTS

Tumor specimens (n = 65) were frozen in liquid nitrogen at the time of resection. Fourteen low-grade tumors, 40 high-grade tumors, and 11 pulmonary metastases were analyzed. Glutathione concentrations and GGTP activity were significantly lower in low-grade (3.97 +/- 0.7 nmol/mg protein and 1.07 +/- 0.2 U/mg protein) than in high-grade (8.98 +/- 1.2 nmol/mg protein, p < 0.001; 2.10 +/- 0.4 U/mg protein, p < 0.002) tumors and pulmonary metastases (10.05 +/- 1.8 nmol/mg protein, p < 0.008; 3.14 +/- 2.8 U/mg protein, p < 0.04). While GCS activity was lower in low-grade (0.81 +/- 0.3 nmol/mg protein/h) than high-grade (1.49 +/- 0.5 nmol/mg protein/h) tumors and pulmonary metastases (1.03 +/- 0.2 nmol/mg protein/h), these differences were not significant. In those patients with a high-grade tumor presenting with a local recurrence, glutathione levels were higher in those patients who had received preoperative doxorubicin-based chemotherapy (9.25 +/- 1.7 nmol/mg protein; n = 7) than in those who had no preoperative chemotherapy (4.71 +/- 3.1 nmol/mg protein; n = 4, p = 0.08).

CONCLUSIONS

In extremity soft tissue sarcoma, glutathione concentration and GGTP activity are significantly elevated in patients with high-grade and metastatic sarcomas. In addition, there is a trend for increased glutathione levels in tumors previously exposed to doxorubicin-based chemotherapy. Glutathione may play a role in soft tissue sarcoma chemoresistance.

Altered glutathione metabolism in oxaliplatin resistant ovarian carcinoma cells

Elevation of glutathione (GSH) is commonly observed in cellular resistance to a number of anticancer agents. Most frequently reported change in GSH metabolism that is associated with the elevated GSH levels is increased mRNA expression and activity of gamma-glutamyl cysteine synthetase (gamma GCS), the first enzyme of the GSH biosynthetic pathway. We have isolated sublines of the A2780 ovarian carcinoma cell line (C10 and C25) that are 8- and 12-fold resistant to oxaliplatin by repeatedly exposing the cells to increasing concentrations of the platinum agent. The GSH levels in C10 and C25 cell sublines are 3.1- and 3.8-fold higher than the parent A2780 cell line. The mRNA levels and activities for gamma GCS and that for gamma-glutamyl transpeptidase (gamma GT), the GSH salvage pathway enzyme, were measured in these cells. The mRNA for gamma GT and gamma GCS were measured by RT-PCR, with quantitation of the PCR product by HPLC; mRNA levels are expressed as ratios to beta-actin mRNA, used as an endogenous standard. GSH and gamma GCS activity were measured by HPLC assays and gamma GT activity by a colorimetric assay. The increase in GSH in C10 and C25 was associated with an elevation in gamma GT mRNA (2.5- and 8-fold) and gamma GT activity (2.7- and 2.8-fold). No changes were observed in gamma GCS mRNA levels or activity. The data indicate that alterations in GSH metabolism leading to elevations in cellular GSH in A2780 ovarian carcinoma cells selected for low levels of resistance to oxaliplatin are mediated by gamma GT, the "salvage' pathway, rather than an increase in GSH biosynthesis.