Abstract 2567: Cabazitaxel chemotherapy targets mitotic kinesins resulting in multi-nucleation of prostate cancer cells: A novel mechanism of cross-resistance with antiandrogens in advanced CRPC

Abstract

Abstract Progression to castration-resistant prostate cancer (CRPC) is characterized by increased androgen receptor (AR) and activated AR signaling despite castrate levels of androgens. The FDA-approved next generation microtubule stabilizing taxane, Cabazitaxel (CBZ) and novel anti-androgen Enzalutamide (MDV) have demonstrated additional survival benefits for patients with advanced CRPC. The present study pursued the mechanism of therapeutic resistance to CBZ and antiandrogen treatment in models of CRPC. The effect CBZ and/or MDV was examined in human prostate cancer cells: androgen independent (DU145 and PC3), androgen responsive (LNCaP and VCaP) and CRPC (22Rv1 and PC3-ARv567, harboring AR variants). Cell viability assessment revealed that CRPC PC3-ARv567es and the androgen-sensitive VCaP cells exhibited resistance to CBZ; however the 22Rv1 cells responded to CBZ and MDV combination with a significant increase in growth (P<0.05). Confocal microscopy and Western blot analysis were used to establish the subcellular localization and protein expression in prostate cancer cells. Antiandrogen (MDV) treatment (24hrs;1uM) led to a cytoplasmic accumulation of AR, while treatment with CBZ (72hrs, 35 -100nM) decreased AR expression, but it did not inhibit its nuclear localization. Furthermore CBZ induced mono-astral spindle formation, centrosomal clustering and multi-nucleation, potentially via targeting the “pro-mitotic kinesins”, MCAK and HSET, regardless of androgen status. To determine the in vivo efficacy of CBZ and androgen axis targeting, we used a transgenic mouse model of prostate cancer (Dominant negative TGFβRII/TRAMP) that is driven to metastasis by epithelial-mesenchymal transition (EMT). Immunohistochemical profiling of prostate tumors from untreated control and CBZ treated mice demonstrated that combination of CBZ and castration-induced androgen depletion reduced kinesin and AR expression and reversed EMT, impairing prostate cancer progression. Furthermore, CBZ treatment restored normal glandular differentiation (by H&E), without significant effect on apoptosis in tumor epithelial cells. Cell proliferation was significantly decreased in response to castration-induced androgen depletion in combination with CBZ (2wks) (P<0.05). These findings support the ability of CBZ to target pro-mitotic kinesins, providing an insight into a new mechanism of action of this taxane that can be exploited for targeting CRPC patients with kinesin overexpression. Moreover, the in vivo evidence identified that CBZ chemotherapy has novel effects beyond suppressing tumor growth, by inducing prostate glandular differentiation. This study is of translational significance in introducing a novel mechanism to overcome cross-resistance to CBZ chemotherapy and anti-androgens in advanced CRPC. Citation Format: Sarah K. Martin, Hong Pu, Craig Horbinski, Zheng Cao, Natasha Kyprianou. Cabazitaxel chemotherapy targets mitotic kinesins resulting in multi-nucleation of prostate cancer cells: A novel mechanism of cross-resistance with antiandrogens in advanced CRPC. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2567. doi:10.1158/1538-7445.AM2015-2567