Combination of selective polo-like kinase 1 (PLK1) inhibitor PCM-075 with abiraterone in prostate cancer and non-androgen-driven cancer models.

Abstract

369 Background: The majority of metastatic castration-resistant prostate cancer (mCRPC) patients will become resistant to abiraterone. Drug combinations with abiraterone offer the possibility to extend patient benefit to anti-androgen therapy. PLK1, an essential mitotic kinase for onset of G2/M transition and cytokinesis, is over-expressed in prostate cancer, correlated positively with Gleason grade and PLK1 RNAi induces G2/M arrest and apoptosis in prostate cancer cells. PCM-075 (formerly NMS-1286937) is a potent, highly selective PLK1 inhibitor currently in clinical trials for the treatment of acute myeloid leukemia. Combination of PCM-075 with abiraterone was examined in mCRPC models and other cancer types for synergistic interaction. Methods: We used a variety of tumor cell lines (C4-2, LNCaP, BT-20, AU565, SK-OV-3), animal and computational modeling techniques to elucidate the mechanism and assess the potential clinical utility of synergistic tumor cell killing by PLK1 inhibitors (PLK1i), including PCM-075, with abiraterone. Results: Synergy was observed between abiraterone and PLK1i, including PCM-075, in models of CRPC (C4-2). In addition, PLK1i and abiraterone were synergistic in murine C4-2 xenografts. Unexpectedly, PLK1i sensitized a subset of non-prostate cancer cells to abiraterone, including AR-negative breast and ovarian cancer cells. In contrast to PLK1i, other mitotic arrest agents do not synergize with abiraterone. To elucidate the molecular basis this synergy, we screened a panel of cell lines and implemented a new computational method that links RNA expression patterns to drug combination synergy. This analysis implicated signaling through the retinoic acid (RA) nuclear receptors as a component of this synergy, which was validated experimentally. Increased basal expression of genes involved in RA metabolism in cancer cells is associated with increased synergy. Conclusions: Abiraterone has AR-independent effects that provide a mechanism and biomarkers predictive for synergistic killing when combined with the PLK1i PCM-075. This combination has potential to extend mCRPC patient benefit to abiraterone regardless of AR status.