Associations of GSTM1 and GSTT1 polymorphisms with pancreatic cancer risk: evidence from a meta-analysis

Transcriptomic analysis of pancreatic adenocarcinoma specimens obtained from Black and White patients

In pancreatic cancer clinical trials, Black patients are under-represented while having higher morbidity and mortality rates as compared to other racial groups. Multiple factors, including socioeconomic and lifestyle factors may contribute to this disparity, but genomic contributions remain unclear. In an exploratory project to identify genes that may contribute to differences in survival between Black (n = 8) and White (n = 20) patients with pancreatic cancer, transcriptomic sequencing of over 24,900 genes was performed in human pancreatic tumor and non-tumor tissue obtained from Black and White patients. Over 4,400 genes were differentially expressed in tumor and non-tumor tissue, irrespective of race. To validate these results, the expression of four genes (AGR2, POSTN, TFF1, and CP) reported to be up-regulated in pancreatic tumor tissue as compared to non-tumor tissue were confirmed using quantitative PCR. Transcriptomic analysis that compared pancreatic tumor tissue from Black and White patients revealed differential expression in 1,200 genes, while a comparison of the non-tumor and tumor gene expression differences within each race revealed over 1,500 tumor-specific differentially expressed genes in pancreatic tumor and non-tumor tissue from Black patients. We identified TSPAN8 as a potential tumor-specific gene significantly overexpressed in pancreatic tumor tissue in Black patients as compared to White patients. Using Ingenuity Pathway Analysis software to compare the race-associated gene expression profiles, over 40 canonical pathways were identified to be potentially impacted by the gene expression differences between the races. Heightened expression of TSPAN8 was associated with poor overall survival, suggesting TSPAN8 as one potential genetic factor contributing to the differential outcomes in Black patients with pancreatic cancer, supporting the potential utility of larger genomic studies to further explore the role of TSPAN8 in pancreatic cancer.

An Overview of Genetic Changes and Risk of Pancreatic Ductal Adenocarcinoma

The pancreatic carcinoma is a leading cause of death in cancer carriers worldwide. The early diagnostic is difficult due to late stage during diagnosis, lack of characteristic symptoms and also multifactor basis. In cancer development take part both, environmental and genetic factors, alone or in conjunction with each other. The nonspecific biomarkers of cancers are a reason for the search for more accurate factors which allow for fast and personalized diagnostics. Some of cancers have identified molecular (metabolic, biochemical or genetic) markers but in most cases the only clue is patient`s interview and abnormal levels of organ functions markers. Possible genetic basis of cancer suggests to widen studies on connection between environmental factors with both, nuclear and mitochondrial, genes changes.

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.

Association between X-ray repair cross-complementation group 1 rs25487 polymorphism and pancreatic cancer risk

Previous published studies suggested that genetic polymorphisms in DNA repair genes could modify the DNA repair capacity and could be associated with pancreatic cancer risk. However, previous studies on the association between X-ray repair cross-complementation group 1 (XRCC1) rs25487 (Arg399Gln) polymorphism and pancreatic cancer risk reported inconsistent results. To obtain a more precise estimation of the association between XRCC1 rs25487 polymorphism and pancreatic cancer risk, we performed a meta-analysis of previous published studies by calculating the pooled odds ratio (OR) with a 95% confidence interval (95% CI). Eight individual studies with 5,542 subjects from six publications were finally included into this meta-analysis. The meta-analysis of total eight studies showed that there was no association between XRCC1 rs25487 polymorphism and pancreatic cancer risk in total population under all four genetic models (Gln versus Arg: OR = 1.10, 95% CI 0.95-1.28, P = 0.199; GlnGln versus ArgArg: OR = 1.15, 95% CI 0.93-1.41, P = 0.191; GlnGln/ArgGln versus ArgArg: OR = 1.10, 95% CI 0.97-1.25, P = 0.127; GlnGln versus ArgArg/ArgGln: OR = 1.12, 95% CI 0.92-1.36, P = 0.253). Subgroup analysis showed that there was no association between XRCC1 rs25487 polymorphism and pancreatic cancer risk in Caucasians, but XRCC1 rs25487 polymorphism was associated with pancreatic cancer risk in Asians (GlnGln/ArgGln versus ArgArg: OR = 1.24, 95% CI 1.01-1.53, P = 0.040). Therefore, the meta-analysis suggests that XRCC1 rs25487 polymorphism is associated with pancreatic cancer risk in Asians. Further studies with more participants are needed to provide a more precise estimation on the association above.

Glutathione S-transferase T1 null genotype is associated with oral cancer susceptibility in Asian populations

Though there are many studies assessing the association between glutathione S-transferase T1 (GSTT1) null genotype and oral cancer risk, the association between GSTT1 null genotype and oral cancer in Asian populations is still inconclusive. We performed a meta-analysis of 19 studies including 2,845 cases and 4,295 controls to derive a more precise estimation of the relationship. The pooled odds ratio (OR) with its corresponding 95 % confidence interval (95 % CI) was used to assess the relationship. Meta-analysis of those 19 studies suggested that there was an association between GSTT1 null genotype and elevated risk of oral cancer risk (OR = 1.25, 95 % CI = 1.00-1.56, P = 0.047). Sensitivity analysis by omitting one study at a time showed that the significance of the corresponding pooled ORs was materially altered frequently, indicating that the pooled ORs were not statistically stable. In addition, there was no obvious risk of publication bias in the meta-analysis. Therefore, the present meta-analysis suggests that the GSTT1 null genotype is a risk allele for oral cancer development in Asian populations, but more studies with large sample and well-matched controls are needed to further confirm the finding from the meta-analysis.