Abstract 2049: Preclinical profile of AMG900 in combination with HDACIs in prostate cancer

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Background: Histone deacetylase (HDAC) enzymes maintain the structural conformation of chromatin. Inhibition of HDACs induces G1 arrest and differentiation. Previous microarray analysis demonstrated downregulation of the aurora kinase-pathway in prostate cancer cell lines treated with HDAC-inhibitors (HDACIs) vorinostat and valproic acid (VPA). Hence we sought to combine these HDACIs with AMG900, a pan-Aurora kinase inhibitor, to assess potential additive or synergistic effects, hypothesizing that low-dose combinations will have a proapoptotic effect comparable to a higher dose of AMG900 as a single agent. Methods: We used MTS assays, clonogenic assays, beta-galactosidase staining and western blot analyses to investigate differences in proliferation and molecular markers with combinations of AMG900 and HDACIs compared to AMG900 alone. Results: In vitro treatment of a panel of prostate cancer cell lines with low-dose combinations of AMG900 with HDACIs revealed enhanced antiproliferative responses compared to single agent use. Short term MTS assays only demonstrated moderate synergism in DU-145 and LNCaP cells co-treated with VPA and synergism in PC3 cells co-treated with vorinostat, based on the Chou-Talalay-method (CalcuSyn). However, all cell lines demonstrated significant decreased long term survival when combining low-dose AMG900 (1nM) with HDACIs. In DU-145 and PC3 cells lines, the low-dose AMG900 (1nM) combinations demonstrated equivalent clonogenic survival to high dose AMG900 treatment (5nM), either alone or in combination with HDACIs. We noted morphologic changes in treated cell lines and explored senescence with beta-galactosidase staining. DU-145 and PC3 cells, when treated with a combination of AMG900 and HDACIs, demonstrated a significant increase in beta-galactosidase positive cells, suggesting cell senescence (10-20% in single agent vs 50% in low-dose combinations). We also explored the mechanisms associated with decreased clonogenic survival at low doses and found a significant increase in cleaved PARP in DU-145 cells with both combinations, and with Vorinostat in LNCaP cells, but not PC3 cells which have a baseline level of ongoing apoptosis. In addition, western blot analysis showed significant differences in ACH3, pH3 and Cyclin B1 in combination treatment compared to single agent use. Conclusions: A combination of low-dose AMG900 with HDACIs in prostate cancer cell lines demonstrates synergy and efficacy equivalent to high doses of AMG900 alone, confirming our hypothesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2049. doi:1538-7445.AM2012-2049