In various prostate cancer models, androgen receptor (AR) expression and transcriptional activity are increased following continuous androgen ablation. It was proposed that inhibition of AR expression, achieved by administration of antisense oligonucleotides or antibodies, has a therapeutic benefit in these tumor models. In contrast, molecular mechanisms underlying development of resistance to nonsteroidal anti-androgens that are used as a monotherapy for prostate cancer remain largely unknown. To study these mechanisms, we have selected a LNCaP subline after 30 passages in the presence of the anti-androgen bicalutamide. Proliferation was determined by cell counting and AR levels were assessed by Western Blot. Reporter gene activity was measured in cells transiently transfected with the probasin luciferase reporter construct and treated with androgen. Proliferation of newly established LNCaP-Bic cells increased 4-fold and was not affected by androgen R1881 or anti-androgens. AR in the newly developed subline was expressed at similar levels as in LNCaP cells passaged in the absence of anti-androgen. Induction of AR activity by androgen in LNCaP-Bic cells was diminished by 30% compared to that in the LNCaP cell line. We assessed proliferative response and AR expression after treatment by vitamin E succinate (VES). VES caused a dose-dependent inhibition of growth of LNCaP cells. In contrast, proliferation of LNCaP cells was not down-regulated when they were treated with bicalutamide prior to VES. The inhibitory effect of VES was abolished in the subline selected in the presence of bicalutamide. Interestingly, AR expression was down-regulated by VES in both LNCaP sublines. These data suggest that a therapy approach to inhibit AR expression is not useful in cells which became bicalutamide-resistant. AR might be thus by-passed in prostate cancers that fail to respond to treatment with nonsteroidal anti-androgens.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]