Tiva T. VanCleave

Examination of polymorphic glutathione S-transferase (GST) genes, tobacco smoking and prostate cancer risk among Men of African Descent: A case-control study

BackgroundPolymorphisms in glutathione S-transferase (GST) genes may influence response to oxidative stress and modify prostate cancer (PCA) susceptibility. These enzymes generally detoxify endogenous and exogenous agents, but also participate in the activation and inactivation of oxidative metabolites that may contribute to PCA development. Genetic variations within selected GST genes may influence PCA risk following exposure to carcinogen compounds found in cigarette smoke and decreased the ability to detoxify them. Thus, we evaluated the effects of polymorphic GSTs (M1, T1, and P1) alone and combined with cigarette smoking on PCA susceptibility.MethodsIn order to evaluate the effects of GST polymorphisms in relation to PCA risk, we used TaqMan allelic discrimination assays along with a multi-faceted statistical strategy involving conventional and advanced statistical methodologies (e.g., Multifactor Dimensionality Reduction and Interaction Graphs). Genetic profiles collected from 873 men of African-descent (208 cases and 665 controls) were utilized to systematically evaluate the single and joint modifying effects of GSTM1 and GSTT1 gene deletions, GSTP1 105 Val and cigarette smoking on PCA risk.ResultsWe observed a moderately significant association between risk among men possessing at least one variant GSTP1 105 Val allele (OR = 1.56; 95%CI = 0.95-2.58; p = 0.049), which was confirmed by MDR permutation testing (p = 0.001). We did not observe any significant single gene effects among GSTM1 (OR = 1.08; 95%CI = 0.65-1.82; p = 0.718) and GSTT1 (OR = 1.15; 95%CI = 0.66-2.02; p = 0.622) on PCA risk among all subjects. Although the GSTM1-GSTP1 pairwise combination was selected as the best two factor LR and MDR models (p = 0.01), assessment of the hierarchical entropy graph suggested that the observed synergistic effect was primarily driven by the GSTP1 Val marker. Notably, the GSTM1-GSTP1 axis did not provide additional information gain when compared to either loci alone based on a hierarchical entropy algorithm and graph. Smoking status did not significantly modify the relationship between the GST SNPs and PCA.ConclusionA moderately significant association was observed between PCA risk and men possessing at least one variant GSTP1 105 Val allele (p = 0.049) among men of African descent. We also observed a 2.1-fold increase in PCA risk associated with men possessing the GSTP1 (Val/Val) and GSTM1 (*1/*1 + *1/*0) alleles. MDR analysis validated these findings; detecting GSTP1 105 Val (p = 0.001) as the best single factor for predicting PCA risk. Our findings emphasize the importance of utilizing a combination of traditional and advanced statistical tools to identify and validate single gene and multi-locus interactions in relation to cancer susceptibility.

Interaction Among Variant Vascular Endothelial Growth Factor (VEGF) and Its Receptor in Relation to Prostate Cancer Risk

Prostate cancer (PCa) incidence and mortality are disproportionately high among African‐American (AA) men. Its detection and perhaps its disparities could be improved through the identification of genetic susceptibility biomarkers within essential biological pathways. Interactions among highly variant genes, central to angiogenesis, may modulate susceptibility for prostate cancer, as previous demonstrated. This study evaluates the interplay among three highly variant genes (i.e., IL‐10, TGFβR‐1, VEGF), their receptors and their influence on PCa within a case‐control study consisting of an under‐served population.

Multi-institutional prostate cancer study of genetic susceptibility in populations of African descent

Prostate cancer disparities have been reported in men of African descent who show the highest incidence, mortality, compared with other ethnic groups. Few studies have explored the genetic and environmental factors for prostate cancer in men of African ancestry. The glutathione-S-transferases family conjugates carcinogens before their excretion and is expressed in prostate tissue. This study addressed the role of GSTM1 and GSTT1 deletions on prostate cancer risk in populations of African descent. This multi-institutional case-control study gathered data from the Genetic Susceptibility to Environmental Carcinogens (GSEC) database, the African-Caribbean Cancer Consortium (AC3) and Men of African Descent and Carcinoma of the Prostate Consortium (MADCaP). The analysis included 10 studies (1715 cases and 2363 controls), five in African-Americans, three in African-Caribbean and two in African men. Both the GSTM1 and the GSTT1 deletions showed significant inverse associations with prostate cancer [odds ratio (OR): 0.90, 95% confidence interval (CI) 0.83-0.97 and OR 0.88, 95% CI: 0.82-0.96, respectively]. The association was restricted to Caribbean and African populations. A significant positive association was observed between GSTM1 deletion and prostate cancer in smokers in African-American studies (OR: 1.28, 95% CI: 1.01-1.56), whereas a reduced risk was observed in never-smokers (OR: 0.66, 95% CI: 0.46-0.95). The risk of prostate cancer increased across quartiles of pack-years among subjects carrying the deletion of GSTM1 but not among subjects carrying a functional GSTM1. Gene-environment interaction between smoking and GSTM1 may be involved in the etiology of prostate cancer in populations of African descent.

No Association between Variant DNA Repair Genes and Prostate Cancer Risk among Men of African descent

Recent reports hypothesize that multiple variant DNA repair gene interactions influence cancer susceptibility. However, studies identifying high‐risk cancer‐related genes use single gene approaches that lack the statistical rigor to model higher order interactions.

8q24 sequence variants in relation to prostate cancer risk among men of African descent: A case-control study

BackgroundHuman chromosome 8q24 has been implicated in prostate tumorigenesis.MethodsConsequently, we evaluated seven 8q24 sequence variants relative to prostate cancer (PCA) in a case-control study involving men of African descent. Genetic alterations were detected in germ-line DNA from 195 incident PCA cases and 531 controls using TaqMan polymerase chain reaction (PCR).ResultsInheritance of the 8q24 rs16901979 T allele corresponded to a 2.5-fold increase in the risk of developing PCA for our test group. These findings were validated using multifactor dimensionality reduction (MDR) and permutation testing (p = 0.038). The remaining 8q24 targets were not significantly related to PCA outcomes.ConclusionsAlthough compelling evidence suggests that the 8q24 rs16901979 locus may serve as an effective PCA predictor, our findings require additional evaluation in larger studies.

No Association Between Variant N-acetyltransferase Genes, Cigarette Smoking and Prostate Cancer Susceptibility Among Men of African Descent

Objective We evaluated the individual and combination effects of NAT1, NAT2 and tobacco smoking in a case-control study of 219 incident prostate cancer (PCa) cases and 555 disease-free men. Methods Allelic discriminations for 15 NAT1 and NAT2 loci were detected in germ-line DNA samples using Taqman polymerase chain reaction (PCR) assays. Single gene, gene-gene and gene-smoking interactions were analyzed using logistic regression models and multi-factor dimensionality reduction (MDR) adjusted for age and subpopulation stratification. MDR involves a rigorous algorithm that has ample statistical power to assess and visualize gene-gene and gene-environment interactions using relatively small samples sizes (i.e., 200 cases and 200 controls). Results Despite the relatively high prevalence of NAT1*10/*10 (40.1%), NAT2 slow (30.6%), and NAT2 very slow acetylator genotypes (10.1%) among our study participants, these putative risk factors did not individually or jointly increase PCa risk among all subjects or a subset analysis restricted to tobacco smokers. Conclusion Our data do not support the use of N-acetyltransferase genetic susceptibilities as PCa risk factors among men of African descent; however, subsequent studies in larger sample populations are needed to confirm this finding.

IRAK4 and TLR3 Sequence Variants may Alter Breast Cancer Risk among African-American Women

Mounting evidence suggests that imbalances in immune regulation contribute to cell transformation. Women of African descent are an understudied group at high risk for developing aggressive breast cancer (BrCa). Therefore, we examined the role of 16 innate immune single nucleotide polymorphisms (SNPs) in relation to BrCa susceptibility among 174 African-American women in Atlanta, GA, USA. SNPs were examined in germ-line DNA collected from 102 BrCa patients and 72 women with benign nodules using SNPstream methodology. Inheritance of the TLR3 rs10025405 GG genotype was associated with an 82% decrease in BrCa risk. In contrast, individuals who possessed at least one IRAK4 rs4251545 T allele had a 1.68- to 4.99-fold increase in the risk of developing BrCa relative to those with the referent genotype (OR = 4.99; 95% CI = 1.00, 25.00; p = 0.0605). However, the IRAK4 rs4251545 locus was only significant under the additive genetic model (p trend = 0.0406). In silico predictions suggest IRAK4 rs4251545 SNP falls within a transcription enhancer/silencer region of the gene and codes for an Ala428Thr amino acid change. This missense mutation introduces a potential phosphorylation site in the extreme carboxy terminus (XCT) of the IRAK4 kinase domain. Preliminary molecular modeling predicts that this SNP stabilizes two alpha helices within the XCT on the surface of the IRAK4 kinase domain and increases the size of the groove between them. Our in silico results, combined with previous reports noting the presence of IRAK4 and XCT fragments in mouse and human serum, suggest the possibility that the XCT subdomain of IRAK4 possesses biological function. These findings require further evaluation and validation in larger populations, additional molecular modeling as well as functional studies to explore the role of IRAK4 and its XCT in cell transformation and innate immunity.

Impact of Gentamicin Concentration and Exposure Time on Intracellular Yersinia pestis

The study of intracellular bacterial pathogens in cell culture hinges on inhibiting extracellular growth of the bacteria in cell culture media. Aminoglycosides, like gentamicin, were originally thought to poorly penetrate eukaryotic cells, and thus, while inhibiting extracellular bacteria, these antibiotics had limited effect on inhibiting the growth of intracellular bacteria. This property led to the development of the antibiotic protection assay to study intracellular pathogens in vitro. More recent studies have demonstrated that aminoglycosides slowly penetrate eukaryotic cells and can even reach intracellular concentrations that inhibit intracellular bacteria. Therefore, important considerations, such as antibiotic concentration, incubation time, and cell type need to be made when designing the antibiotic protection assay to avoid potential false positive/negative observations. Yersinia pestis, which causes the human disease known as the plague, is a facultative intracellular pathogen that can infect and replicate in macrophages. Y. pestis is sensitive to gentamicin and this antibiotic is often employed in the antibiotic protection assay to study the Y. pestis intracellular life cycle. However, a large variety of gentamicin concentrations and incubation periods have been reported in the Y. pestis literature without a clear characterization of the potential influences that variations in the gentamicin protection assay could have on intracellular growth of this pathogen. This raised concerns that variations in the gentamicin protection assay could influence phenotypes and reproducibility of data. To provide a better understanding of the potential consequences that variations in the gentamicin protection assay could have on Y. pestis, we systematically examined the impact of multiple variables of the gentamicin protection assay on Y. pestis intracellular survival in macrophages. We found that prolonged incubation periods with low concentrations of gentamicin, or short incubation periods with higher concentrations of the antibiotic, have a dramatic impact on intracellular growth. Furthermore, the degree of sensitivity of intracellular Y. pestis to gentamicin was also cell type dependent. These data highlight the importance to empirically establish cell type specific gentamicin protection assays to avoid potential artificial data in Y. pestis intracellular studies.

Abstract 926: Oxidative Stress Response Sequence Variants as Predictors of Prostate Cancer Risk and Aggressive Disease among men of European and African Descent

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Background: Prostate cancer (PCA) has the second incidence and mortality rates among cancers affecting U.S. men. Furthermore, men of African descent (MAD) are at increased risk to develop PCA, be diagnosed with more aggressive cases, and less likely to survive 5-years following diagnosis when compared to men of European descent (EA). Unfortunately, mechanisms contributing to PCA etiology and disparities are poorly characterized. Identification of genetic and environmental factors contributing to PCA development and disease aggressiveness are essential to reducing its incidence, disparity and mortality. Research Goal & Objective: With the ultimate goal of improving clinical management, we systematically evaluated the relationship between oxidative stress-related (OSR) susceptibility factors and PCA outcomes among a case control population of 3,200 men. Hypothesis: We hypothesized individuals inheriting variant OSR loci linked with reduced antioxidation, oxidative DNA damage repair, and apoptotic potential have an increased risk of developing PCA and aggressive disease. Materials and Methods: In order to evaluate the effects of OSR sequence variants on PCA we used SNP profile data collected from 2277 EA participants of the Cancer Genetic Markers of Susceptibility project (1176 cases, 1101 controls) and 923 MAD (224 cases, 699 controls). We evaluated the independent effects of 205 variant OSR genes in relation to PCA risk and aggressive disease using logistic regression and multi-factor dimensionality reduction (MDR) modeling. Results: Among EA, inheritance of at least one minor OSR loci involved in antioxidation [NOS2A\_rs2274894, TXNDC5 rs2743993, TXNRD2\_rs5746847), DNA repair (OGG1\_rs12570, XRCC1\_rs1799778), and apoptosis [BNIP3L\_rs7813520, CASP3\_rs4647693, CDK9\_rs3217751, MAPK1\_rs743409, MSRA (rs6997224, rs17151728), RASSF5\_rs11589, TGFB2\_rs1891467, TNFAIP8\_rs1112247] associated with PCA risk and aggressive disease (p<0.046). We also identified three additional apoptotic variants (i.e., BCL2L11\_rs3789068, CASP9\_rs1052576, NFKB1\_rs230528) associated with PCA risk (p<0.043) among MAD. MDR with permutation testing will be used to determine which loci remain significant after controlling for multiple comparisons. Conclusions: Our findings suggest that variations in genes involved OSR may play a role in prostate carcinogenesis among EA and MAD. Population attributable risk calculations may allow us to discern whether OSR markers may help to explain prostate cancer incidence disparities among MAD. Further analysis of gene-gene and gene-environment interactions in OSR susceptibility markers will allow us to better characterize a panel capable of predicting PCA risk and disease progression in high-risk subgroups. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 926.

Abstract 931: Innate immunity-related sequence variants (TOLLIP, TLR2) as predictors of prostate cancer risk among men of African descent

Emerging genome-wide association studies suggest genome variation plays a rather important, yet largely uncharacterized, role in dissecting the genetic underpinnings of prostate cancer (PCa) health disparities. Moreover, recent advances in molecular and genetic studies demonstrate a relationship between chronic/recurrent inflammation and complex diseases. In terms of prostate cancer, it is speculated that chronic or recurrent inflammation, attributed to persistent exposure to pathogens may alter the tissue microenvironment that favors tumor growth. Despite the fact that men of African descent suffer disproportionately from PCa and may have a natural selection advantage toward inheriting innate immunity signaling loci linked with pro-inflammatory response, it remains to be determined whether variant innate immunity-related alleles will explain the higher PCa risk and disease severity in this sub-group. With the ultimate goal of understanding the genetic underpinnings of PCa health disparities, we set out to systematically evaluate the impact of innate immunity-related single nucleotide polymorphisms (SNPs) in relation to PCA risk among 3,200 men of African and European descent. We hypothesized that individuals inheriting high-risk innate immunity loci (linked with elevated pro-inflammatory response) will have an increased risk of developing PCa relative to those with the referent genotypes. In order to evaluate the effects of innate immunity sequence variants on PCa we used SNP profile data collected from 2277 European participants of the Cancer Genetic Markers of Susceptibility (CGEMS) project (1176 cases, 1101 controls) and 923 men of African descent (224 cases, 699 controls). Using a case-control study design, we evaluated the independent effects of 19 variant innate immunity genes (e.g., TLR 1-4, CD14, IRAK2, IRF3, TOLLIP) in relation to PCa risk using logistic regression and multi-factor dimensionality reduction (MDR) modeling. Inheritance of at least one minor TOLLIP rs5743899G (p = 0.002) and the TLR-2 rs4696480A allele (linked with enhanced cytokine production) was significantly associated with a 2.1-4.5 fold increase prostate cancer susceptibility among men of African descent. Notably, the TOLLIP marker remained significant even after adjusting for multiple comparisons following MDR with permutation testing (p = 0.01). These markers were not associated with PCa among European participants. In summary, variations in genes involved in the innate immunity signaling may play a role in PCa risk among men of African Descent in the current study. However, these findings require validation in larger and ethnically diverse sub-populations. Such efforts will help to identify and validate new genetic fingerprints with the capacity to unravel the genetic contributions of prostate cancer incidence and mortality disparities among high-risk subgroups. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 931.