Simultaneous targeting of the androgen receptor and PI3K/mTOR pathway in androgen-dependent and androgen-independent prostate cancer cells.

Abstract

e15049 Background: The progression of prostate cancer (PC) has been correlated to the gain of function of the androgen receptor (AR) and constitutive activation of Akt as a result of deregulation of the PTEN/PI3K/mTOR pathway. We postulate that simultaneous targeting of these pathways might be more effective than single inhibitors in decreasing AR activity and tumor growth in non-castrate and castration-resistant PC (CRPC). Methods: Androgen-dependent and -independent LNCaP cells (AD, AI) and Rv1 cells were treated with the dual PI3K/mTor inhibitor BEZ235 (Novartis), the PI3K inhibitor BKM120 (Novartis), rapamycin alone and each in combination with bicalutamide. Growth was measured by MTT assay, p-Akt, p-S6K and AR levels by Western, and AR transcriptional activity by PSA and CDC20 mRNA quantification by QT- PCR. Results: The IC50 for AD, AI and Rv1 after 72h treatment with BEZ235 were 2.16, 5.7 and 1.6 nM respectively; with BKM120 0.52, 0.48 and 0.8 μM respectively and with rapamycin 0.6, 1.8 and 1.6nM. The IC50 of BEZ235-bicalutamide were 1.04, 4.4 and 1.1nM; for BKM120-bicalutamide 0.33, 0.3 and 0.26 μM and for rapamycin-bicalutamide were 0.7, 0.25 and 85nM. Isobolograms confirmed the three combinations excepting rapamycin-bicalutamide in Rv1cells were synergistic in all cell lines and the IC50 for bicalutamide in AI and Rv1 cells reached the IC50 of AD cells (12.5 μM). At 24 hours BEZ235 inhibited Akt and S6K phosphorylation in all the cell lines more effectively than the BKM120 while rapamycin and bicalutamide increased p-Akt. However, while AR protein levels were only decreased after bicalutamide treatment of AD cells, the transcription of PSA and CDC20 were more significantly reduced by BEZ235 than BKM120. Conclusions: Combinations of bicalutamide with dual PI3K/mTOR inhibitors is synergistic and more effective in suppressing Akt activation than combinations with single PI3K or mTOR inhibitors. This suggests that blocking Akt activation by dual inhibitors and the ligand binding to AR might be more effective to reduce its gain of function, and may restore hormonal response in CRPC or circumvent the need for castration in recurrent PC. No significant financial relationships to disclose.