Use of antisense oligonucleotides targeting the antiapoptotic gene, clusterin/testosterone-repressed prostate message 2, to enhance androgen sensitivity and chemosensitivity in prostate cancer

Background: Androgen resistance develops, in part, from upregulation of ant iapoptotic genes after androgen withdrawal. Identification and targeting of genes mediating androgen-independent (AI) progression may lead to developm ent of novel therapies that delay hormone-refractory prostate cancer. Clust erin is a cell survival gene, that increases after androgen ablation. Here, we review clusterin's functional role in apoptosis and the ability of anti sense oligonucleotides (ASOs) against clusterin to enhance apoptosis in pro state cancer xenograft models. Results: Immunostaining of radical prostatectomy specimens confirm that clu sterin is highly expressed in 80% prostate cancer cells after neoadjuvant h ormone therapy, but is low or absent (< 20%) in untreated specimens. Cluste rin levels increase > 10 fold in regressing Shionogi tumors after castratio n. Pretreatment of mice bearing androgen-dependent Shionogi tumors with cal cium antagonists inhibited castration-induced apoptosis, tumor regression, and clusterin gene upregulation, illustrating that clusterin is an apoptosi s-associated gene and not an androgen-repressed gene. Clusterin ASOs reduce d clusterin levels in a Close-dependent and sequence-specific manner. Adjuv ant treatment with murine clusterin ASOs after castration of mice bearing S hionogi tumors decreased clusterin levels by 70% and resulted in earlier on set and more rapid apoptotic tumor regression, with significant delay in re currence of Al tumors. Species-specific clusterin ASOs also increased the c ytotoxic effects of paclitaxel, reducing the 50% inhibitory concentration ( IC50) of PC-3 and Shionogi cells by 75% to 90%. Although clusterin ASOs had no effect on the growth of established Al Shionogi or PC-3 tumors, cluster in ASOs synergistically enhanced paclitaxel-induced tumor regression in bot h Shionogi and PC-3 models. Conclusions: Collectively, these data identify clusterin as an antiapoptosi s protein, upregulated in an adaptive cell-survival manner by androgen abla tion and chemotherapy, which confers resistance to various cell-death trigg ers. Inhibition of clusterin upregulation using clusterin ASOs can enhance cell death after treatment with androgen ablation and chemotherapy. (C) 200 1, Elsevier Science Inc.