We are conducting translational research to develop new agents and/or therapeutic maneuvers that appear to have antitumor activity in prostate cancer (CaP), and to develop molecular profiles of patients with CaP to tailor an individualized treatment plan. We are extensively involved in the efforts to understand the biology of CaP and to correlate biological variables associated with CaP and response to therapy. We reported the first confirmation of the therapeutic efficacy of flutamide withdrawal and the enhanced activity of simultaneous adrenal suppression. It has been hypothesized that the clinical improvement associated with flutamide is a result of the presence of a mutation within the ligand-binding domain of the androgen receptor. We have analyzed candidate genes at the genomic level for genetic variations that may predispose individuals to increased risk of prostate cancer. Biomarker discovery for CaP is an ongoing effort in our laboratory and we have focused on the identification of single nucleotide polymorphisms (SNPs) involved in CaP progression. We use a candidate gene approach which uses a panel of 96 SNPs (identified from prior studies and published literature) from over thirty genes and using DNA samples from subjects with metastatic disease or without biochemical recurrence for over 5 years after treatment. Constitutional DNA from men who were biochemical recurrence free after treatment of their CaP identified from the San Antonio center for Biomarkers Of risk for prostate cancer (SABOR) are being provided by our research collaborator, Dr. Robin Leach. These samples are compared to the constitutional DNA from men with documented metastatic prostate cancer identified from patients treated at the NCI. Only one SNP, rs7311358 in the SLC01B3 gene, showed statistically significant results after adjusting for age and multiple testing. For men under the age of 60, there was an increased risk of metastatic disease with an odds ratio of 12.25 (p=0.002). Future experiments will saturate the polymorphic markers around this gene to identify more important SNPs and give focus for biochemical and molecular biological testing. The organic anion transporter OATP1B3, encoded by SLCO1B3, is involved in the transport of steroid hormones. We have shown that prostate cancer overexpresses OATP1B3 compared to normal or benign hyperplastic tissue, and the common SLCO1B3 GG/AA haplotype is associated with impaired testosterone transport and improved survival in patients with CaP. We found that a polymorphism in this transporter increases testosterone import is associated with a shorter time to androgen independence in patients with CaP who are treated with ADT. We are currently ascertaining whether OATP1B3-mediated hormone uptake is significant over diffusion using an MDCK transwell model that is transduced with a tet-inducible SLCO1B3 expression system. We are also currently harvesting tumors from castrated and uncastrated mouse xenograft models to determine if SLCO1B3 expression is related to intratumoral testosterone concentrations and the expression of androgen-receptor-mediated genes. Finally, we are currently conducting a drug screen to identify potential OATP1B3 inhibitors that may have clinical utility in the prostate cancer setting. Our preliminary data indicate quite strongly that OATP1B3 is significantly involved in tumoral androgen accumulation, and this uptake may be a driver of progression in castration resistant prostate cancer. Moreover, our data demonstrate that OATP1B3-dependent uptake can be targeted by specific inhibitors. OATP1B3 is expressed de novo in prostate cancer as two isoforms: liver-type (lt) and cancer type (ct). Studies are underway to characterize the molecular expression of each type and how they are differentially modulated in castration sensitive tumors (LNCaP and 22Rv1) versus castration resistant tumors (PC3 and DU145). The Prostate Cancer Prevention Trial (PCPT) investigated the prevention of prostate cancer using the steroid 5 alpha-reductase inhibitor finasteride over a 7-year treatment period. Through a longstanding collaboration, we have access to the tissue samples of 18,800 men enrolled in this study. The overall goals of this project are: a) to better understand associations between important androgen regulatory gene polymorphisms and CaP risk;and b) to evaluate the effects of these polymorphisms and serum hormone concentrations on the use of finasteride as a chemopreventive agent for CaP. Our focus is on hormone-related factors that are associated with cancer risk, which may help explain the findings of the PCPT (i.e., decreased overall occurrence of adenocarcinoma, but increased prevalence of high-grade disease in the finasteride treatment arm). We hypothesized that men with polymorphisms within genes that positively impact androgen levels will have a higher risk of developing CaP and high-grade disease than those with the wild-type alleles. Long-term exposure to finasteride may select for somatic alterations and increase serum levels of testosterone and potentially harmful testosterone breakdown products. Evaluation of whether the polymorphic variations in the AR, SRD5A2 and HSD3B2 genes are associated with the risk of biopsy-detected CaP in the PCPT is underway. We identified, by laser-capture microdissection and direct nucleotide sequencing, somatic alterations in AR and HSD3B2 that may have been selected for by long-term exposure to finasteride. We are also determining whether prostate cancer somatic mutations of these genes differ with regard to their prevalence between the placebo and finasteride arms, and among PIA, HGPIN, prostate cancer and normal epithelium. These findings will help define a pharmacogenomic profile to identify men that are most likely to benefit from treatment with 5 alpha-reductase inhibitors. We found that finasteride concentrations and genes involved in regulating its metabolism and target enzyme are associated with prostate cancer risk. We also found that AR CAG repeats are not associated with TMPRSS2:ETS formation in prostate cancer. Furthermore, we investigated racial disparities in the association between variants on 8q24 and prostate cancer and demonstrated that recent studies implicate SNPs within the 8q24 region as a risk factor for CaP. New developments suggest that 8q24 encodes regulators of the nearby MYC gene, a known oncogene. We performed meta-analyses, stratified by race, of seven SNPs and one microsatellite marker previously identified as risk loci on the 8q24 region of the genome. We reviewed the literature examining the possible associations between these polymorphisms and clinicopathological features of CaP. The results of the meta-analyses indicate that rs6983267, rs1447295, rs6983561, rs7837688, rs16901979, and DG8S737 are significantly associated with a higher risk for CaP for at least one race, whereas the variants rs13254738 and rs7000448 are not. The degree of association and frequency of the causative allele varied among men of different races. Though several studies have demonstrated an association between certain 8q24 SNPs and clinicopathological features of the disease, review of this topic revealed conflicting results.
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