AT-101 induces apoptosis in prostate cancer cell in vitro and delays the onset of androgen independence. Upregulation of Bcl-2 is one of the prominent mechanisms of androgen independent disease. We hypothesized that inhibition of Bcl-2 with AT-101 would delay the onset of androgen independent disease. Recently we reported the establishment of the VCaP prostate cancer cell line that expresses the wild type androgen receptor and is androgen sensitive. Further, we demonstrated that castration of mice harboring a VCaP xenograft induced the development of an androgen independent tumor accompanied by an upregulation of Bcl-2 expression. The data presented here applies the VCaP model of androgen independence to determine if the presence of AT-101 would delay the development of androgen independent disease. In vitro experiments demonstrated that AT-101 at 5 and 10 µM inhibited VCaP proliferation over a 72 hour period [Control: 2.76 ± 0.067; AT-1015µM: 0.45 ± 0.014; AT-10110µM: 0.38 ± 0.025; p < 0.001]. Further, AT-101 at 5 and 10 µM induced apoptosis over a similar 72 hour period and stimulated Caspase 3 and Caspase 7 activation. To determine the ability of AT-101 to induce apoptosis in VCaP androgen sensitive cells, VCaP cells were incubated in serum free + phenol red free DMEM in the presence or absence of dihydrotestosterone (100 nM) ± AT-101 (5 µM) for 72 hours [Control: 0.51 ± 0.15; AT-101: 1.61 ± 01; AT-101+DHT: 0.58 ± 0.21; p < 0.001]. Androgen depletion sensitized VCaP cells to AT-101 induced apoptosis while the addition of dihydrotestosterone (100 nM) protected AT-101 induced apoptosis. An increase in AT-101 induced apoptosis of VCaP androgen sensitive cells in an androgen depleted environment supports our hypothesis that AT-101 could delay the onset of androgen independent prostate cancer by inhibiting the upregulation of Bcl-2 in the subpopulation of cells that become androgen independent during castrate therapy.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA