Abstract 3279: Enhanced in vivo inhibition of neuropeptide-mediated castration resistant prostate cancer progression by combination therapy with enzalutamide and saracatinib.

Abstract

Abstract Introduction: It has been shown that overexpression of the neuropeptides gastrin-releasing peptide (GRP) in LNCaP cells renders the cells castration-resistant through both androgen receptor (AR) activation and intracrine androgen biosynthesis. Aberrant activation of AR by GRP is mediated through Src kinase activation, which may be inhibited by the specific SFK inhibitor saracatinib. Inhibition of cognate AR activation requires anti-androgen. We hypothesize that treatment of this kind of CRPC demands the combination of saracatinib and new generation anti-androgen enzalutamide (MDV-3100). Materials and methods: LNCaP GRP-Pro cells grown in CS medium were treated with control, saracatinib (2 μM), enzalutamide (10 μM) or the combination. Cell proliferation over 7 days was monitored by MTT assays. Cell cycle distributions over 72 hours of treatment were analyzed by flow cytometry. Cells were collected to prepare nuclear and cytosolic lysates respectively and examined by Western Blotting analysis for AR, pSrc, pAkt, LC-3 and β-actin. Expression of full-length AR and variants were compared by RT-qPCR. Orthotopic injection of GRP-Pro cells into castrated SCID male mice was used as the animal model for drug treatment studies. Results: Enzalutamide or saracatinib alone only slightly inhibited CR cell growth but the combination brought it down to 27% of the control. Apoptosis was also enhanced with the combination. Enzalutamide only inhibited AR nuclear translocation in regular serum-kept GRP-Pro cells, while saracatinib inhibited the translocation in CS conditions. In the orthotopic model, neither treatments with saracatinib (25 mg/kg/daily) or enzalutamide (10 mg/kg/daily) alone showed any effect on tumor take, tumor weight or serum PSA levels. However, the combination treatment drastically reduced the tumor weights (0.66±0.13 g for controls vs. 0.24±0.07 g for the combo) and serum PSA levels (120.79±27.87 ng/ml vs. 19.19±7.45 ng/ml). Conclusions: For GRP mediated CRPC growth, neither saracatinib or enzalutamide alone is sufficient to inhibit AR translocation and tumor progression. Combination of the two significantly improved the treatment for the CRPC orthotopic tumor model. Citation Format: Joy C. Yang, Hao G. Ngyuen, Allen C. Gao, Christopher P. Evans. Enhanced in vivo inhibition of neuropeptide-mediated castration resistant prostate cancer progression by combination therapy with enzalutamide and saracatinib. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3279. doi:10.1158/1538-7445.AM2013-3279