Polymorphisms of the androgen transporting gene SLCO2B1 and response to abiraterone acetate in mCRPC patients

174 Background: Abiraterone Acetate (AA), an effective treatment for metastatic castration resistant prostate cancer (mCRPC), is highly variable in its effectiveness and it is well known that form of primary and acquired resistance to this agent, exist. This resistance may partly depend on the increased capacity of CRPC cells to synthesize testosterone and dihydrotestosterone from weak adrenal androgens (i.e. DHEA, DHEA-S) or de novo from cholesterol, in response to a chronic exposition to a low-testosterone environment. The organic anion-transporting polypeptides (OATPs) encoded by SLCO genes, mediate the cellular uptake of many compounds, including adrenal androgens. We hypothesized that germ-line variants of the androgen transporter gene SLCO2B1 (solute carrier organic anion transporter family member 2B1), altering the ability of the prostate cancer cell to stock adrenal precursors, may influence the response to AA of mCRPC patients. Methods: Three single nucleotide polymorphisms (SNPs), exonic SNP rs12422149 and intronic SNPs rs1789693 and rs1077858, were genotyped in a cohort of 21 consecutive patients with mCRPC who were treated with AA at the Sant’Andrea Hospital of Rome, Italy. The SNPs were detected in blood samples using pyrosequencing technique. The median TTBP (Time to Biochemical Progression), PFS (Progression Free Survival) and OS (Overall Survival) was estimated using the Kaplan-Meier method, with 95% CI. To test the association between SNPs and TTBP, PFS and OS the log-rank test was used. Results: The intronic polymorphism of SLCO2B1 rs1077858A > G was associated with TTBP (p = 0.03) and PFS (p = 0.04) of mCRPC patients on AA therapy. Patients carrying the SLCO2B1 rs1077858 risk genotype (GG) exhibited a TTBP that was 8 months shorter than that of patients with the major allele of SNP rs1077858 (AA or GA) (TTBP: A/A+G/A = 12 (95% CI: 12-NA) vs G/G = 4 (95% CI: NA) months). Patients carrying genotype GG of SNP rs1077858 also showed an 11 months shorter PFS on AA therapy than patients with AA or GA genotype (PFS: GG = 5.1 (95% CI:NA) vs AA+GA = 16.7 (95%CI:14.9-NA) months). Conclusions: Genetic variants of SLCO2B1 may function as pharmacogenomic determinants of resistance to AA in mCRPC.