Effect of generation 2.5 antisense inhibitor of androgen receptor on MDV3100-resistant prostate cancer cell growth in vitro and in vivo.

Abstract

94 Background: MDV3100 is a potent androgen receptor (AR) antagonist with activity in castration resistant prostate cancer (CRPC); however, progression to MDV3100-resistant (MDV-R) CRPC frequently occurs with rising serum PSA levels, implicating AR full length or variants in disease progression. We studied the activity of Generation 2.5 antisense oligonucleotide (ASO) targeting the AR full length (ARfl) and splice variants in MDV-R CRPC models. Methods: and Results: ThreeASOs targeting exon 1, intron 1, or exon 8 were designed to suppress ARfl and known AR splice variants. We generated by selection MDV-R LNCaP-derived sub-lines that uniformly expressed high levels of both ARfl and AR-V7 compared to CRPC LNCaP cell lines. MDV-3100 induced time- and dose-dependent increases in ARfl and AR-V7 protein levels; ARfl levels were ~20-fold higher than AR-V7. All 3 AR-ASO decreased ARfl and PSA expression. Exon 1 ASO decreased expression of both ARfl and AR-V7 in MDV-R-LNCaP cells; in contrast, exon 8 ASO decreased ARfl without reducing AR-V7 levels. Exon 1 ASO also most potently suppressed ARfl and splice variants in M12 cells stably overexpressing AR splice variants AR-V7 and AR-V567es. Despite these differential effects on ARfl and splice variant knockdown, the AR ASO similarly inhibited cell growth and induced apoptosis and G1 cell cycle arrest in LNCaP-derived CRPC and MDV-R cell lines. In 22RV-1 cells (which express endogenous ARfl and AR-V7), exon 1 ASO more potently suppressed ARfl and AR-V7 levels, AR transcriptional activity and AR-regulated gene expression compared to exon 8 ASO, but inhibition of cell growth did not differ significantly. Exon 1 ASO was evaluated in vivo in MDV-R49F CRPC LNCaP xenografts; mean tumor volume and serum PSA levels decreased significantly by 40% and 50%, respectively, compared to controls. Conclusions: While MDV-3100 induces both ARfl and AR-V7 levels, the biologic consequences appear cell line dependent and mainly driven by ARfl. AR-ASO knockdown of ARfl and its splice variants suppresses MDV-R LNCaP tumor growth, providing pre-clinical proof of principle to support clinical evaluation in post-AR pathway inhibitor CRPC.