Association between glutathione-S-transferase GSTP1 genotypes, GSTP1 over-expression, and outcome in epithelial ovarian cancer

Glutathione S-Transferase M3 Is Associated with Glycolysis in Intrinsic Temozolomide-Resistant Glioblastoma Multiforme Cells

Glioblastoma multiforme (GBM) is a malignant primary brain tumor. The 5-year relative survival rate of patients with GBM remains <30% on average despite aggressive treatments, and secondary therapy fails in 90% of patients. In chemotherapeutic failure, detoxification proteins are crucial to the activity of chemotherapy drugs. Usually, glutathione S-transferase (GST) superfamily members act as detoxification enzymes by activating xenobiotic metabolites through conjugation with glutathione in healthy cells. However, some overexpressed GSTs not only increase GST activity but also trigger chemotherapy resistance and tumorigenesis-related signaling transductions. Whether GSTM3 is involved in GBM chemoresistance remains unclear. In the current study, we found that T98G, a GBM cell line with pre-existing temozolomide (TMZ) resistance, has high glycolysis and GSTM3 expression. GSTM3 knockdown in T98G decreased glycolysis ability through lactate dehydrogenase A activity reduction. Moreover, it increased TMZ toxicity and decreased invasion ability. Furthermore, we provide next-generation sequencing-based identification of significantly changed messenger RNAs of T98G cells with GSTM3 knockdown for further research. GSTM3 was downregulated in intrinsic TMZ-resistant T98G with a change in the expression levels of some essential glycolysis-related genes. Thus, GSTM3 was associated with glycolysis in chemotherapeutic resistance in T98G cells. Our findings provide new insight into the GSTM3 mechanism in recurring GBM.

FBX8 degrades GSTP1 through ubiquitination to suppress colorectal cancer progression

F-box only protein 8 (FBX8), as a critical component of the SKP1-CUL1-F-box (SCF) E3 ubiquitin ligases, has been associated with several malignancies through interacting with a member of proteins. However, the substrates of FBX8 for destruction in the progression of colorectal carcinoma (CRC) need to be explored. Here, we show that loss of FBX8 accelerates chemical-induced colon tumorigenesis. FBX8 directly targets GSTP1 for ubiquitin-mediated proteasome degradation in CRC. GSTP1 promotes the proliferation, invasion, and metastasis of CRC cells. Furthermore, GSTP1 is upregulated in CRC tissue samples and predicts poor prognosis of CRC patients. The inactivation of FBX8 negatively correlated with increased levels and stability of GSTP1 in clinical CRC tissues and FBX8 knockout transgenic mice. These findings identify a novel ubiquitination pathway as FBX8-GSTP1 axis that regulates the progression of CRC, which might be a potential prognostic biomarker for CRC patients.

Protective and therapeutic potential of ginger (Zingiber officinale) extract and [6]-gingerol in cancer: A comprehensive review

Natural dietary agents have attracted considerable attention due to their role in promoting health and reducing the risk of diseases including cancer. Ginger, one of the most ancient known spices, contains bioactive compounds with several health benefits. [6]-Gingerol constitutes the most pharmacologically active among such compounds. The aim of the present work was to review the literature pertaining to the use of ginger extract and [6]-gingerol against tumorigenic and oxidative and inflammatory processes associated with cancer, along with the underlying mechanisms of action involved in signaling pathways. This will shed some light on the protective or therapeutic role of ginger derivatives in oxidative and inflammatory regulations during metabolic disturbance and on the antiproliferative and anticancer properties. Data collected from experimental (in vitro or in vivo) and clinical studies discussed in this review indicate that ginger extract and [6]-gingerol exert their action through important mediators and pathways of cell signaling, including Bax/Bcl2, p38/MAPK, Nrf2, p65/NF-κB, TNF-α, ERK1/2, SAPK/JNK, ROS/NF-κB/COX-2, caspases-3, -9, and p53. This suggests that ginger derivatives, in the form of an extract or isolated compounds, exhibit relevant antiproliferative, antitumor, invasive, and anti-inflammatory activities.

A computational framework for complex disease stratification from multiple large-scale datasets

BACKGROUND

Multilevel data integration is becoming a major area of research in systems biology. Within this area, multi-'omics datasets on complex diseases are becoming more readily available and there is a need to set standards and good practices for integrated analysis of biological, clinical and environmental data. We present a framework to plan and generate single and multi-'omics signatures of disease states.

METHODS

The framework is divided into four major steps: dataset subsetting, feature filtering, 'omics-based clustering and biomarker identification.

RESULTS

We illustrate the usefulness of this framework by identifying potential patient clusters based on integrated multi-'omics signatures in a publicly available ovarian cystadenocarcinoma dataset. The analysis generated a higher number of stable and clinically relevant clusters than previously reported, and enabled the generation of predictive models of patient outcomes.

CONCLUSIONS

This framework will help health researchers plan and perform multi-'omics big data analyses to generate hypotheses and make sense of their rich, diverse and ever growing datasets, to enable implementation of translational P4 medicine.

Genetic variants as ovarian cancer first-line treatment hallmarks: A systematic review and meta-analysis

BACKGROUND

The potential predictive value of genetic polymorphisms in ovarian cancer first-line treatment is inconsistently reported. We aimed to review ovarian cancer pharmacogenetic studies to update and summarize the available data and to provide directions for further research.

METHODS

A systematic review followed by a meta-analysis was conducted on cohort studies assessing the involvement of genetic polymorphisms in ovarian cancer first-line treatment response retrieved through a MEDLINE database search by November 2016. Studies were pooled and summary estimates and 95% confidence intervals (CI) were calculated using random or fixed-effects models as appropriate.

RESULTS

One hundred and forty-two studies gathering 106871 patients were included. Combined data suggested that GSTM1-null genotype patients have a lower risk of death compared to GSTM1-wt carriers, specifically in advanced stages (hazard ratio (HR), 0.68; 95% CI, 0.48-0.97) and when submitted to platinum-based chemotherapy (aHR, 0.61; 95% CI, 0.39-0.94). ERCC1 rs11615 and rs3212886 might have also a significant impact in treatment outcome (aHR, 0.67; 95% CI, 0.51-0.89; aHR, 1.28; 95% CI, 1.01-1.63, respectively). Moreover, ERCC2 rs13181 and rs1799793 showed a distinct ethnic behavior (Asians: aHR, 1.41; 95% CI, 0.80-2.49; aHR, 1.07; 95% CI, 0.62-1.86; Caucasians: aHR, 0.10; 95% CI, 0.01-0.96; aHR, 0.18; 95% CI, 0.05-0.68, respectively).

CONCLUSION(S)

The definition of integrative predictive models should encompass genetic information, especially regarding GSTM1 homozygous deletion. Justifying additional pharmacogenetic investigation are variants in ERCC1 and ERCC2, which highlight the DNA Repair ability to ovarian cancer prognosis. Further knowledge could aid to understand platinum-treatment failure and to tailor chemotherapy strategies.

Glutathione S-transferase A1 mediates nicotine-induced lung cancer cell metastasis by promoting epithelial-mesenchymal transition

The present study aimed to investigate the effect of glutathione S-transferase A1 (GSTA1) on lung cancer cell viability, invasion and adhesion in the presence of nicotine in vitro. Furthermore, the effect of GSTA1 on the epithelial-mesenchymal transition (EMT), a process strongly associated with lung cancer metastasis, was examined. Human lung carcinoma A549 cells were treated with various concentrations of nicotine (0.01, 0.1, 1 and 10 µM) and levels of GSTA1 mRNA and protein were measured by reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. To knock down GSTA1 expression, GSTA1-small interfering RNA was transfected into A549 cells. Cell viability, invasion and adhesion abilities were determined by MTT, Transwell-Matrigel invasion and cell adhesion assays, respectively. The expression of the epithelial cell markers E-cadherin and keratin, and the mesenchymal cell markers vimentin and N-cadherin in A549 cells were examined by western blot analysis. The current study indicated that the expression of GSTA1 was increased in A549 cells following nicotine treatment. GSTA1 suppression inhibited the viability, invasion and adhesion of lung cancer cells. In addition, the increase in lung cancer cell viability, invasion and adhesion by nicotine was suppressed following GSTA1 knockdown. Furthermore, GSTA1 affected the expression of EMT markers in nicotine-treated or untreated lung cancer cells. Thus the present study demonstrates that GSTA1 promotes lung cancer cell invasion and adhesion and mediates the effect of nicotine on lung cancer cell metastasis in vitro. Furthermore, the results demonstrated that GSTA1 exerts its effect on lung cancer cell metastasis by promoting the EMT.

Effects of Ginger Phenylpropanoids and Quercetin on Nrf2-ARE Pathway in Human BJ Fibroblasts and HaCaT Keratinocytes

Quercetin and phenylpropanoids are well known chemoprotective compounds identified in many plants. This study was aimed at determining their effects on activation of Nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant response element (Nrf2-ARE) signalling pathway and expression of its important downstream effector phase II detoxification enzyme glutathione-S-transferase P1 (GSTP1) in BJ foreskin fibroblasts and skin HaCaT keratinocytes. Cell lines and their corresponding Nrf2-ARE luciferase reporter cells were treated by ginger phenylpropanoids and quercetin for 10 h and the level of Nrf2 activity was subsequently determined. Both, ginger phenylpropanoids and quercetin, significantly increased the level of Nrf2 activity. Subsequent western blot analyses of proteins showed the increased expression level of glutathione-S-transferase P1 (GSTP1) in BJ cells but not in HaCaT cells. Such phenomenon of unresponsive downstream target expression in HaCaT cells was consistent with previous studies showing a constitutive expression of their GSTP1. Thus, while both ginger phenylpropanoids and quercetin have the property of increasing the level of Nrf2 both in HaCaT and in BJ cells, their effects on its downstream signalling were mediated only in BJ cells.

Glutathione S-transferase P1 gene rs4147581 polymorphism predicts overall survival of patients with hepatocellular carcinoma: evidence from an enlarged study

As the most important detoxifying enzymes in liver, glutathione S-transferases (GSTs) can protect hepatocytes against carcinogens. We conducted a large cohort study to investigate the prognostic value of single nucleotide polymorphisms (SNPs) in seven encoding genes of GSTs for hepatocellular carcinoma (HCC). Twelve SNPs were genotyped and correlated with overall survival in 469 HCC patients. The median follow-up time of all patients was 21 (range 3-60) months, and the median survival time was 22 months. By the end of the study, 135 (28.8 %) patients were alive. Only rs4147581 in GSTP1 gene exhibited a significant association with survival of HCC patients (P = 0.006), with its mutant allele bearing a significantly lower risk of death (hazard ratio, 0.71; 95 % confidence interval 0.53-0.90), compared with the homozygous wide-type. A longer median survival time in patients with rs4147581 mutant allele was noticed than those homozygous wide-type (P = 0.03), and there was a marked adverse effect on survival conferred by smoking exposure in these patients. Conclusively, our findings provide supporting evidence for a contributory role of GSTP1 rs4147581 polymorphism in predicting the prognosis of HCC.

Thiazolides promote apoptosis in colorectal tumor cells via MAP kinase-induced Bim and Puma activation

While many anticancer therapies aim to target the death of tumor cells, sophisticated resistance mechanisms in the tumor cells prevent cell death induction. In particular enzymes of the glutathion-S-transferase (GST) family represent a well-known detoxification mechanism, which limit the effect of chemotherapeutic drugs in tumor cells. Specifically, GST of the class P1 (GSTP1-1) is overexpressed in colorectal tumor cells and renders them resistant to various drugs. Thus, GSTP1-1 has become an important therapeutic target. We have recently shown that thiazolides, a novel class of anti-infectious drugs, induce apoptosis in colorectal tumor cells in a GSTP1-1-dependent manner, thereby bypassing this GSTP1-1-mediated drug resistance. In this study we investigated in detail the underlying mechanism of thiazolide-induced apoptosis induction in colorectal tumor cells. Thiazolides induce the activation of p38 and Jun kinase, which is required for thiazolide-induced cell death. Activation of these MAP kinases results in increased expression of the pro-apoptotic Bcl-2 homologs Bim and Puma, which inducibly bind and sequester Mcl-1 and Bcl-x_L leading to the induction of the mitochondrial apoptosis pathway. Of interest, while an increase in intracellular glutathione levels resulted in increased resistance to cisplatin, it sensitized colorectal tumor cells to thiazolide-induced apoptosis by promoting increased Jun kinase activation and Bim induction. Thus, thiazolides may represent an interesting novel class of anti-tumor agents by specifically targeting tumor resistance mechanisms, such as GSTP1-1.

Polymorphisms of glutathione S-transferase genes and survival of resected hepatocellular carcinoma patients

AIM: To investigate the effects of single nucleotide polymorphisms (SNPs) in glutathione S-transferase (GST) genes on survival of hepatocellular carcinoma (HCC) patients.

METHODS: Twelve tagging SNPs in GST genes (including GSTA1, GSTA4, GSTM2, GSTM3, GSTO1, GSTO2 and GSTP1) were genotyped using Sequenom MassARRAY iPLEX genotyping method in a cohort of 214 Chinese patients with resected HCC. The Cox proportional hazards model and log-rank test were performed to determine the SNPs related to outcome. Additionally, stratified analysis was performed at each level of the demographic and clinical variables. An SNP-gene expression association model was further established to investigate the correlation between SNP and gene expression.

RESULTS: Two SNPs (GSTO2: rs7085725 and GSTP1: rs4147581) were significantly associated with overall survival in HCC patients (P = 0.035 and 0.042, respectively). In stratified analysis, they were more significantly associated with overall survival in patients with younger age, male gender and cirrhosis. We further investigated cumulative effects of these two SNPs on overall survival in HCC patients. Compared with the patients carrying no unfavorable genotypes, those carrying 2 unfavorable genotypes had a 1.70-fold increased risk of death (P < 0.001). The cumulative effects were more significant in those patients with younger age, male gender and cirrhosis (HR = 2.00, 1.94 and 1.97, respectively; all P < 0.001). Additionally, we found that heavy smoking resulted in a significantly worse overall survival in those patients carrying variant alleles of rs7085725 (HR = 2.07, 95%CI: 1.13-3.76, P = 0.018). The distributions of GSTO2: rs7085725 and GSTP1: rs4147581 genotypes were associated with altered gene expression and contributed to influences on overall survival.

CONCLUSION: Our study provides the first evidence that GSTO2 and GSTP1 gene polymorphisms may serve as independent prognostic markers for HCC patients.

[Structure and functions of glutathione transferases]

Data about classification, nomenclature, structure, substrate specificity and role of many glutathione transferase's isoenzymes in cell functions have been summarised. The enzyme has been discovered more than 50 years ago. This family of proteins is updated continuously. It has very different composition and will have demand for system analysis for many years.

Expression of P-glycoprotein, multidrug resistance-associated protein, glutathione-S-transferase pi and p53 in canine transmissible venereal tumor

The overexpression of proteins P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP1), mutant p53, and the enzyme glutathione-S-transferase (GSTpi) are related to resistance to chemotherapy in neoplasms. This study evaluated the expression of these markers by immunohistochemistry in two groups of canine TVT, without history of prior chemotherapy (TVT1, n=9) and in TVTs presented unsatisfactory clinical response to vincristine sulfate (TVT2, n=5). The percentage of specimens positively stained for P-gp, MRP1, GSTpi and p53 were, respectively 88.8%, 0%, 44.5% and 22.2% in TVT1 and 80%, 0%, 80% and 0% in TVT2. In TVT1, one specimen presented positive expression for three markers and four specimens for two markers. In TVT2, three specimens expressed P-gp and GSTpi. In conclusion, the canine TVTs studied expressed the four markers evaluated, but just P-gp and GSTpi were significantly expressed, mainly at cytoplasm and cytoplasm and nuclei, respectively, either before chemotherapy as after vincristine sulfate exposure. Future studies are needed to demonstrate the function of these two markers in conferring multidrug resistance (MDR) or predict the response to chemotherapy in canine TVT.

Predictive potential of glutathione S-transferase polymorphisms for prognosis of osteosarcoma patients on chemotherapy

OBJECTIVE

To evaluate the predictive value of glutathione S-transferase (GST) gene polymorphisms for the prognosis of osteosarcoma patients receiving chemotherapy.

METHODS

A total of 159 patients were included in our study between January 2005 and December 2007., with follow-up until January 2012. Genotyping was based upon the duplex polymerase-chain-reaction with the PCR-CTPP method.

RESULTS

At the time of diagnosis, 15.4% of the patients presented with metastasis, while 22.3% developed metastasis during follow-up. At the time of final analysis on January 2012, the median follow-up was 45.5 months. Patients with null GSTM1 and GSTT1 had a higher event free survival rate than non-null genotype, but no significant association was found between the two genotypes and prognosis of osteosarcoma. Individuals with GSTP1 Val/Val genotype tended to live shorter than with the IIe/IIe genotype, and we found a significantly higher risk of death from osteosarcoma (adjusted HR=2.35, 95% CI=1.13-4.85).

CONCLUSION

The GSTP1 gene polymorphism may have an important role in the prognosis of osteosarcoma patients with chemotherapy. Further analyses with larger samples and more genes encoding metabolizing and DNA repair enzymes are warranted.

Assessment of glutathione S-transferaseM1 (GSTM1) and its polymorphisms GSTM1 null in the response to treatment with chemotherapy in advanced ovarian carcinoma

OBJECTIVE

To assess if the genotype of the glutathione S-transferase M1 (GSTM1) enzyme and its GSTM1 null polymorphism can influence the response to chemotherapeutic treatment of advanced ovarian cancer.

METHODS

Case-control study of 112 patients with advanced ovarian cancer submitted to chemotherapy during the period from January 1995 to December 2005. The tissue to study the GSTM1 genotype and its deletion came from surgical staging to treat ovarian cancer. The PCR product generates two distinct genotypes, characterized as positive and null. The response to chemotherapy was evaluated using the World Health Organization (WHO) criteria. Patients were classified as having: a) no response, b) a response.

RESULTS

The presence of GSTM1 or its GSTM1 null polymorphism did not influence the preoperative chemotherapy response. Among the patients who did respond, 88.9% presented with positive GSTM1 and 11.1% with null GSTM1. Among the patients that did not respond, 85.71% presented with positive GSTM1 and 14.29% with null GSTM1 (p = 0.825). GSTM1 and its GSTM1 null polymorphism had no influence on the postoperative response to chemotherapy. Among the patients who did respond, 80.65% presented with positive GSTM1 and 19.35% with null GSTM1. Among the patients who did not respond, 87.50% presented with positive GSTM1 and 12.5% with the null polymorphism (p = 0.553).

CONCLUSION

No difference was observed in the response to treatment with chemotherapy in patients with advanced ovarian cancer, as to the GSTM1 genotype compared to its GSTM1 null polymorphism.

Predicting adverse drug reactions using publicly available PubChem BioAssay data

Adverse drug reactions (ADRs) can have severe consequences, and therefore the ability to predict ADRs prior to market introduction of a drug is desirable. Computational approaches applied to preclinical data could be one way to inform drug labeling and marketing with respect to potential ADRs. Based on the premise that some of the molecular actors of ADRs involve interactions that are detectable in large, and increasingly public, compound screening campaigns, we generated logistic regression models that correlate postmarketing ADRs with screening data from the PubChem BioAssay database. These models analyze ADRs at the level of organ systems, using the system organ classes (SOCs). Of the 19 SOCs under consideration, nine were found to be significantly correlated with preclinical screening data. With regard to six of the eight established drugs for which we could retropredict SOC-specific ADRs, prior knowledge was found that supports these predictions. We conclude this paper by predicting that SOC-specific ADRs will be associated with three unapproved or recently introduced drugs.

Translational medicine and reliability of single-nucleotide polymorphism studies: can we believe in SNP reports or not?

BACKGROUND

The number of genetic association studies is increasing exponentially. Nonetheless, genetic association reports are prone to potential biases which may influence the reported outcome.

AIM

We hypothesized that positive outcome for a determined polymorphism might be over-reported across genetic association studies analysing a small number of polymorphisms, when compared to studies analysing the same polymorphism together with a high number of other polymorphisms.

METHODS

We systematically reviewed published reports on the association of glutathione s-transferase (GST) single-nucleotide polymorphisms (SNPs) and cancer outcome.

RESULT

We identified 79 eligible trials. Most of the studies examined the GSTM1, theGSTP1 Ile105Val mutation, and GSTT1polymorphisms (n = 54, 57 and 46, respectively). Studies analysing one to three polymorphisms (n = 39) were significantly more likely to present positive outcomes, compared to studies examining more than 3 polymorphisms (n=40) p = 0.004; this was particularly evident for studies analysing the GSTM1polymorphism (p =0.001). We found no significant associations between journal impact factor, number of citations, and probability of publishing positive studies or studies with 1-3 polymorphisms examined.

CONCLUSIONS

We propose a new subtype of publication bias in genetic association studies. Positive results for genetic association studies analysing a small number of polymorphisms (n = 1-3) should be evaluated extremely cautiously, because a very large number of such studies are inconclusive and statistically under-powered. Indeed, publication of misleading reports may affect harmfully medical decision-making and use of resources, both in clinical and pharmacological development setting.

Serine phosphorylation of glutathione S-transferase P1 (GSTP1) by PKCα enhances GSTP1-dependent cisplatin metabolism and resistance in human glioma cells

Recently, we reported that the human GSTP1 is phosphorylated and functionally activated by the PKC class of serine/threonine kinases. In this study, we investigated the contribution of this post-translational modification of GSTP1 to tumor cisplatin resistance. Using two malignant glioma cell lines, MGR1 and MGR3, the ability of PKCα-phosphorylated GSTP1 to catalyze the conjugation of cisplatin to glutathione was assessed and correlated with cisplatin sensitivity and cisplatin-induced DNA interstrand cross-links and apoptosis of the cells. The results showed PKCα activation and associated phosphorylation of GSTP1 to correlate significantly with increased glutathionylplatinum formation, decreased DNA interstrand cross-link formation and increased cisplatin resistance. Following PKC activation, the IC(50) of cisplatin increased from 13.63μM to 36.49μM in MGR1 and from 20.75μM to 38.45μM in MGR3. In both cell lines, siRNA-mediated GSTP1 or PKCα transcriptional suppression similarly decreased cisplatin IC(50) and was associated with decreased intracellular levels of glutathionylplatinum metabolite. Combined inhibition/transcriptional suppression of both PKCα and GSTP1 was synergistic in enhancing cisplatin sensitivity. Although, cisplatin-induced apoptosis was associated with the translocation of Bax to mitochondria, release of cytochrome c and caspase-3/7 activation, the levels of relocalized Bax and cytochrome c were significantly greater following GSTP1 knockdown. These results support a mechanism of cisplatin resistance mediated by the PKCα-dependent serine phosphorylation of GSTP1 and its associated increased cisplatin metabolism, and suggest the potential of simultaneous targeting of GSTP1 and PKCα to improve the efficacy of cisplatin therapy.

Glutathione-S-transferase P1, T1 and M1 genetic polymorphisms in neoadjuvant-treated locally advanced gastric cancer: GSTM1-present genotype is associated with better prognosis in completely resected patients

OBJECTIVE

Neoadjuvant chemotherapy in gastric cancer is now standard in the Western world; however, only 30-40% of the patients respond to induction therapy. Pretherapeutic predictors of response and prognosis would be of utmost interest to individualize treatment. Glutathione-S-transferase enzymes detoxify therapeutic drugs such as platin derivates and may influence outcome of the treated patients. Therefore, glutathione-S-transferase (GST) polymorphisms were assessed as predictive markers in cisplatinum-based neoadjuvant-treated gastric cancer.

MATERIALS AND METHODS

DNA was isolated from 139 patients with locally advanced gastric cancer (cT3/4 anyN cM0) before chemotherapy. Multiplex polymerase chain reaction was used for GSTT1 and GSTM1 genes, and allelic discrimination assay with the TaqMan system for the GSTP1 gene.

RESULTS

One hundred ten patients could be analyzed for GSTT1 (T-:23; T+87), 112 for GSTM1 (M-:52; M+:60) and 132 for GSTP1 (Ile/Ile: 55; Ile/Val: 59; Val/Val: 18). There was no significant correlation between any of the GSTT1, GSTM1, or GSTP1 genotypes and patients' characteristics or histopathological data; only the GSTM1+ genotype was associated with the non-intestinal subtype of the Lauren classification (p=0.045). GSTT1, GSTM1, and GSTP1 genotypes were not correlated with response to chemotherapy (p=0.57, p=0.38, p=0.33). In R0 resected patients, we found an improved survival for patients with the GSTM1-present genotype compared to patients with the GSTM1-null genotype (p=0.017). Moreover, the GSTM1-present genotype showed a significantly better tumor-related (p=0.017) and disease-free survival (p=0.029).

CONCLUSION

None of the common GST polymorphisms predicts response in our study, but the GSTM1+ genotype was associated with a better prognosis in completely resected patients. Further investigations on chemotherapy-associated gene polymorphisms are warranted.

Drug metabolism by tumours: its nature, relevance and therapeutic implications

Drug-metabolising enzymes (DMEs) are present in tumours and are capable of biotransforming a variety of antineoplastics. Tumoural drug metabolism is both a potential mechanism of resistance and a means of achieving optimal therapy. This review addresses the classes of DMEs, their cytotoxic substrates and distribution in specific malignancies. The limitations of preclinical and clinical studies are highlighted. Their role in predicting therapeutic response, the activation of prodrugs and the potential for their modulation for gain is also addressed. The contribution of tumoural DMEs to cancer therapy can only be ascertained through large prospective studies and supported by new technologies. Only then can efforts be concentrated in the design of better prodrugs or combination therapy to optimise individual therapy.

Epithelial ovarian cancer and low malignant potential (LMP) tumors associated with a lower incidence of second primary breast cancer

OBJECTIVES

Differences in the clinical characteristics of ovarian tumors of low malignant potential (LMP) and ovarian cancer have suggested divergences in tumor biology. The aim of this population-based study was to compare the risk of a second primary breast cancer after a history of either an LMP tumor or an epithelial ovarian cancer.

METHODS

Breast cancers were evaluated among 3297 women with a history of LMP tumors, and 45,986 women with a history of epithelial ovarian cancer, within the Surveillance, Epidemiology, and End Results (SEER) Program. The expected incidence of breast cancer was then determined as a function of year, age, race, and geographic location, and combined with the observed incidence to derive the standardized incidence ratio (SIR).

RESULTS

Forty-one (1.2%) patients with an LMP history were diagnosed with breast cancer, where 56.8 cases were expected, for an SIR of 0.72 [95% confidence interval (CI) 0.52-0.98]. Similarly, 734 patients (1.6%) with a history of ovarian cancer were diagnosed with breast cancer, where 809 were expected, for an SIR of 0.91 (95% CI 0.84-0.98). Overall, LMP patients were younger and had a shorter time between diagnoses. LMP patients also had a significantly lower relative risk of developing second primary breast cancers.

CONCLUSION

Patients with a history of having either an LMP tumor or an epithelial ovarian cancer have a less than expected risk of subsequent breast cancer. Patients with LMP tumors are at lower risk than patients with a history of ovarian cancer for the development of these second malignancies.

The role of glutathione-S-transferase polymorphisms in ovarian cancer survival

Resistance to chemotherapy represents one of the most important causes of treatment failure in patients with ovarian cancer. Common polymorphisms in the glutathione-S-transferase (GSTM1, GSTP1 and GSTT1) family have been implicated in chemoresistence and ovarian cancer survival. In this study, we have analysed Australian women diagnosed with primary invasive epithelial ovarian cancer between 1985 and 1997, using DNA extracted from peripheral blood and archival uninvolved (normal) tissues. GSTP1 genotypes were determined using ABI Prism 7700 Sequence Detection System methodology (n=448) and GSTT1 and GSTM1 genotypes using PCR-agarose methodology (n=239). We observed a significant survival advantage among carriers of GSTP1 Ile105Val GG/GA genotype (HR 0.77, 95% confidence interval (CI) 0.61-0.99,p=0.04) and a non-significant survival advantage among women who were homozygous for the GSTM1 and GSTT1 deletion variants. There was also evidence of an additive effect, with a stronger survival benefit in women carrying three low function GST genotypes (GSTM1 null, GSTT1 null and GSTP1 GA/GG) (HR 0.47, 95% CI 0.22-1.02). The results of this study, the largest to date, are consistent with a number of previous smaller studies which have also observed that reduced GST function was associated with better survival outcomes in patients with ovarian cancer.

Association of GSTP1 polymorphism and survival for esophageal cancer

PURPOSE

Activity of glutathione S-transferase (GST) is associated with detoxification of xenobiotics and the maintenance of cell viability. Genetically variant GSTs produce different enzymatic activities. The clinical significance of this variation is still puzzling. We investigated whether genetic polymorphisms of GST including GSTP1, GSTM1, and GSTT1 affect survival among esophageal cancer patients.

EXPERIMENTAL DESIGN

From 1996 to 2002, 233 patients with pathologically proven esophageal cancer were recruited from the Department of Surgery, National Taiwan University Hospital. GST genotypes, including GSTT1, GSTM1, and GSTP1, were determined by PCR or PCR-RFLP. The influence of the genetic polymorphisms on patient survival was estimated using the method of Kaplan-Meier survival function and Cox proportional hazards models.

RESULTS

The mean survival times (months) of the GSTP1 Ile/Ile, Ile/Val, and Val/Val were 11, 10, and 7, respectively (P < 0.05). The more the patients carried GSTP1 variant Val alleles, the poorer the survival rate (adjusted hazard ratio, 1.36; 95% confidence interval, 1.01-1.84; Ptrend = 0.045). In contrast, no association of GSTT1 or GSTM1 genotypes with survival rate was noted.

CONCLUSION

The presence of the GSTP1 variant allele (Val) is associated with a poorer prognosis of esophageal cancer.

Malignant ascites increases the antioxidant ability of human ovarian (SKOV-3) and gastric adenocarcinoma (KATO-III) cells

OBJECTIVES

The antioxidant status of cancer cells is an important factor in tumor invasion and metastases. This study investigated whether metastatic cancer cells derive beneficial antioxidant protection from ascitic fluid and are rendered resistant to oxidative stress in the form of a chemically generated free radical insult.

METHODS

Human gastric carcinoma (KATO-III) and ovarian adenocarcinoma (SKOV-3) cell lines were cultured and incubated for 24 h with (1) M199 medium; (2) M199 + 20% fetal calf serum (FCS); (3) malignant ascites. All cells were exposed to a hydroxyl radical-generating system for 1 h. Cellular lipid peroxidation was assessed by measuring malondialdehyde (MDA) in cell suspensions. Glutathione (GSH) levels in cell pellet were measured in SKOV-3 cells after 0, 24, 48, and 72 h of incubation with buthionine sulphoximine (BSO). CD44 gene expression of cancer cells was analyzed by Northern blotting.

RESULTS

The results showed that the cancer cells were rendered resistant to oxidative stress and with upregulated CD44 gene expression by components of malignant ascites.

CONCLUSIONS

These findings suggest that malignant ascites increases the antioxidant ability of cancer cells and the potential of adhesion and invasion. Thus, determination of the nature of these putative tumor-protective components of ascites may provide targets for therapeutic intervention.

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.