We are conducting 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 are 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 are interested in analyzing candidate genes at the genomic level for genetic variations that may predispose individuals to increased risk of prostate cancer. We 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 and 5, the 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. Our recent study showed 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 prostate cancer. 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 to ADT than patients not carrying this polymorphism. We examined the association between this SLCO1B3 polymorphism in Caucasian patients with advanced prostate cancer who were treated with ADT with metastatic disease (D2) or biochemical failure with no metastatic disease (D0). We found 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 recently completed a study on 321 primary tissue samples from 21 normal and cancerous patients that examined the expression of 3 family members implicated in cancer: OATP1B3, OATP1B1 and OATP2B1. The results showed that OATP2B1 is more ubiquitously expressed in all tissues than OATP1B1 and OATP1B3. OATP1B3 was also expressed in fewer normal tissue types;however, it was expressed in 50% of cancerous samples and there was a trend of increasing OATP1B3 expression with a higher Gleason score. This supports previous data suggesting a role for OATP1B3 in advancing prostate cancer. Further experiments from quantitative PCR and Western blot suggest that hypoxia elements in the OATP1B3 promoter are activated under tumor conditions and explain the increased expression in tumor cells. In addition, transport studies in Xenopus oocytes showed that optimal transport occurs at low androgen levels such as those seen in patients after androgen deprivation therapy. In summary, upon examining the expression of OATP1B3, OATP1B1 and OATP2B1 in primary tissue samples, there appear to be several cancers for which these may be progression or cancer biomarkers, especially in prostate cancer progression, and warrant further study. Furthermore, we are currently determining the polymorphisms of other genes (SRD5A1 and 2, LOX, CYP19, ER, VEGFR2) and their association with prostate cancer risk and/or progression. We found that both ERalpha SNPs [PvuII T greater than C(rs2234693) and XbaI A greater than G(rs9340799) transitions] were associated with increases in prostate cancer risk [OR(95%CI) greater than or equal to 2.3 (1.3-4.2);P less than or equal to 0.032], and the association with the ERalpha PvuII T greater than C also improved in those men who were greater than 70 years old [OR(95%CI) greater than or equal to 2.9 (1.3-4.2);P=0.0073]. This study implicates ERalpha polymorphisms in the risk of developing prostate cancer, especially in older men. In another study, we evaluated polymorphisms in the VEGFR2 gene (V297I and H472Q) and found that inheritance patterns within VEGFR2 are related to the risk of developing prostate cancer as well as prognosis of men with CRPC. Furthermore, these polymorphisms vary by race, suggesting a differential outcome across ethnic populations. These studies are currently underway and will yield exciting results as we continue to investigate the relationship between genetic polymorphisms and their association with prostate cancer risk and/or disease progression. Recently, other polymorphic-containing genes of interest were identified after screening 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 our goal of developing a molecular fingerprint of 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 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 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. We are focusing 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 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. 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 is underway. We are identifying, 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. 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.
Showing the most recent 10 out of 52 publications
