The purpose of this project is to perform translational research to develop new agents, and/or therapeutic maneuvers, that appear to have antitumor activity in prostate cancer, and to develop molecular profiles of patients with prostate cancer to tailor an individualized treatment plan. To achieve this goal, we have become extensively involved in the efforts to understand the biology of prostate cancer. Currently, we are attempting to correlate biological variables associated with prostate cancer and response to therapy. One early achievement by the Molecular Pharmacology Section was to report the first confirmation of the therapeutic efficacy of flutamide withdrawal, as well as 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 remain interested in analyzing candidate genes at the genomic level for genetic variations that may predispose individuals to increased risk of prostate cancer. We have completed the analysis of genes involved in the natural production of endostatin (COL18A1, no statistical difference), a gene directly involved in the synthesis of testosterone from cholesterol (CYP17, the results suggest that the polymorphism is associated with overall survival in patients with androgen independent prostate cancer), a gene involved in the toxic metabolic breakdown of testosterone (CYP1B1, an association with decreased survival was observed), drug metabolism (CYP3A4 &5, the studied genetic variants are unlikely to have an important functional significance to phenotypic CYP3A activity in patients with cancer), and a gene involved in cellular transport and conjugation (UGT1A9, functional variants are rare in Caucasians and likely to be clinically insignificant in irinotecan regimens). The organic anion transporter OATP1B3, encoded by SLCO1B3, is involved in the transport of steroid hormones. However, its role in testosterone uptake and progression of prostate cancer is unknown. SLCO1B3 genotype was assessed in the NCI-60 panel of tumor cells by sequencing, while testosterone transport was analyzed in Cos-7 cells transfected with wild-type (WT), 334G and 699A SLCO1B3 variants. OATP1B3 expression in prostatic tissues was examined by fluorescence microscopy and the relationship between SLCO1B3 haplotypes and survival was examined in patients. Our recent study showed that prostate cancer over-expresses 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 prostate cancer. We examined the association between this SLCO1B3 polymorphism and time from ADT to androgen independence, ADT to prostate-specific antigen (PSA) nadir and PSA nadir to androgen independence in 68 Caucasian patients with advanced prostate cancer who were treated with ADT with metastatic disease (D2) or biochemical failure with no metastatic disease (D0). When examined separately, patients in the individual stages tended to have a shorter time to androgen independence with the T allele in the D0 (P = 0.11) and D2 (P = 0.18) groups. Combining these groups and stratifying by stage yielded a statistically significant shorter time to androgen independence with the T allele (P = 0.048). Thus, a polymorphism in a transporter that increases testosterone import is associated with a shorter time to androgen independence in patients with prostate cancer who are treated with ADT. Based on this evidence, we conducted a study to determine whether patients with advanced prostate cancer carrying a polymorphism that codes for a more active testosterone transporter have less durable responses ADT than patients not carrying this polymorphism. We examined the association between this SLCO1B3 polymorphism and time from ADT to androgen independence, ADT to prostate-specific antigen (PSA) nadir and PSA nadir to androgen independence in 68 Caucasian patients with advanced prostate cancer who were treated with ADT with metastatic disease (D2) or biochemical failure with no metastatic disease (D0). When examined separately, patients in the individual stages tended to have a shorter time to androgen independence with the T allele in the D0 (p=0.11) and D2 (p=0.18) groups. Combining these groups and stratifying by stage yielded a statistically significant shorter time to androgen independence with the T allele (p=0.048). Our findings demonstrate that a polymorphism in a transporter that increases testosterone import is associated with a shorter time to androgen independence in patients with prostate cancer who are treated with ADT. We are currently examining the changes in gene and protein expression of OATP1B3 due to hypoxia and androgen deprivation and characterizing the androgen transport properties. Furthermore, the analysis of other genes (SRD5A1&2, LOX, CYP19, ER) which have shown preliminary evidence that suggests that they may play important roles are ongoing and at various stages of completion. Other polymorphic containing genes of interest have been recently identified after screening the DNA from patients with prostate cancer against a gene chip designed to screen genes involved in metabolism and drug transport. These important genes will be added to the ongoing goal of a molecular fingerprint of prostate cancer. Some of the overall goals of this project are: (a) to better understand associations between important androgen regulatory gene polymorphisms and prostate cancer risk and (b) to evaluate the effects of these polymorphisms and serum hormone concentrations on the use of finasteride as a chemopreventive agent for prostate cancer. The recently completed Prostate Cancer Prevention Trial (PCPT) investigated the prevention of prostate cancer using the steroid 5 alpha-reductase inhibitor finasteride over a seven year treatment period. Through a longstanding collaboration we have access to tissue samples of the 18,800 men enrolled in this study. We are currently focusing on hormone-related factors that are associated with prostate 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 hypothesize that men with polymorphisms within genes that positively impact androgen levels will have a higher risk of developing prostate cancer and high grade disease than those with the wild-type alleles. In addition, long-term exposure to finasteride may select for somatic alterations and increase serum levels of testosterone and potentially harmful testosterone breakdown products. The evaluation of whether the polymorphic variations in the AR, SRD5A2 and HSD3B2 genes are associated with the risk of biopsy-detected prostate cancer in the PCPT are underway. We are identifying by laser-capture microdissection and direct nucleotide sequencing somatic alterations in the AR and HSD3B2 that may have been selected for by long-term exposure to finasteride. Furthermore, we are 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.
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