Abstract Number: 798
Presentation Title: Androgen receptor, PI3K/mTOR and PSMA: Exploring and exploiting the interplay between therapeutic targets in prostate cancer
Presentation Time: Sunday, Apr 06, 2014, 1:00 PM - 5:00 PM
Location: Hall A-E, Poster Section 33
Poster Board Number: 12
Author Block: Jose D. Murga, Wells W. Magargal, II, Sameer M. Moorji, Vincent A. DiPippo, William C. Olson. Progenics Pharmaceuticals, Inc, Tarrytown, NY
Abstract Body: Introduction: Androgen receptor (AR), the PI3K/mTOR signaling pathway and prostate-specific membrane antigen (PSMA) represent significant potential targets for prostate cancer therapy. The present study examined the cross-regulation and co-targeting of these molecular pathways.
Methods: Cytotoxicity and the kinetics of antigen expression were evaluated in prostate cancer cell lines (LNCaP and C4-2) that vary according to androgen dependence. Expression of PSMA, prostate-specific antigen (PSA), and AR was evaluated in cells cultured in rapamycin and AR inhibitors. Cells were tested for susceptibility to PI3K/mTOR inhibitors used alone and in combination with PSMA ADC, a fully human PSMA monoclonal antibody conjugated to the microtubule disrupting agent monomethyl auristatin E (MMAE). Potential drug synergy or antagonism was evaluated using the Bliss independence method.
Results: In androgen-dependent LNCaP cells, rapamycin exerted antiproliferative effects that were accompanied by an increase in AR expression and signaling in the absence of any significant effect on PSMA expression. In androgen-independent C4-2 cells, rapamycin increased AR expression/signaling and PSMA expression in the absence of any significant anti-proliferative effect. AR inhibitors synergized with PSMA ADC in LNCaP and C4-2 cells, but PI3K/mTOR pathway inhibitors synergized with PSMA ADC in C4-2 cells only. More modest synergy was observed by combining non-targeted microtubule inhibitors with inhibitors of AR or mTOR. Compared with rapamycin, GDC0941 (PI3K inhibitor) and MK-2206 (Akt inhibitor), both upstream of mTOR, synergized less strongly with PSMA ADC in C4-2 cells.
Conclusions: In this study, AR and PI3K/mTOR pathways exhibited cross-regulation impacting PSMA expression. PSMA ADC synergized with AR and mTOR inhibitors via a multimodal mechanism involving increased PSMA expression and disruption of microtubule function. The findings support clinical exploration of regimens combining PSMA-targeted therapies with inhibitors of the AR and/or PI3K/mTOR signaling pathways.
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