Abstract 2712: A non-replicating adenovirus expressing Hey1 is cytotoxic to prostate cancer cells

Abstract

Androgen receptor (AR) signalling is active in most hormone-refractory prostate cancers (PCa) and suppression of its activity impedes cell proliferation. We demonstrate that Hey1, a co-repressor of AR, is a potential therapeutic transgene for treatment of PCa. A replication-defective adenovirus expressing Hey1 under control of the CMV promoter was generated (Ad5Hey1; E1 and E3 deleted) and found to be cytotoxic to human PCa cells, both AR-positive 22Rv1 and LNCaP and AR-negative DU145. The doses required to kill 50% of cells (EC50) were comparable to the cytotoxic E1A12S gene expressed from an identical vector (AdE1A12S). Ad5Hey1 repressed AR activity in a dose dependent manner in 22Rv1 cells both with and without mibolerone stimulation as determined by luciferase reporter assays. In 22Rv1 cells, the G2/M population increased in an Ad5Hey1 but not AdE1A12S dependent manner 48h after infection to 37.6±5.4% at 1000 particles per cell (ppc). An increase in cyclin B1 expression reflected the Ad5Hey1-dependent increase in G2/M phase. Expression of p53 increased with increasing doses of Ad5Hey1 whereas p21 levels increased at low doses but decreased at higher doses in 22Rv1 and LNCaP cells. At 1000ppc, a larger proportion of cells were in sub-G1 (38.5±7.5%) indicating that Ad5Hey1 induced apoptotic cell death. Apoptotic death was confirmed by caspase 3 activation in both Ad5Hey1 and AdE1A12S-infected cells by flow cytometry. Efficacy of Ad5Hey1 was also evaluated in vivo in combination with docetaxel, currently used in the clinic for treatment of PCa. In LNCaP xenograft in vivo models, Ad5Hey1 alone caused significant tumour growth inhibition with median time to tumour progression of 92d compared with 54d for animals with mock-treated tumours. Time to progression was further increased when Ad5Hey1 was combined with a sub-optimal dose of docetaxel with 75% of animals surviving at 110d compared with 40% of animals with Ad5Hey1 alone and none of the docetaxel treated animals surviving. Similar tumour growth inhibition was observed in models using DU145 xenografts; the combination of Ad5Hey1 with docetaxel significantly prolonged time to progression from 62d (single agents) to 96d when combined (5-8 animals/group). Furthermore, the antiandrogen bicalutamide, used as a therapy for hormone-dependent PCa, enhanced Ad5Hey1 cytotoxicity and decreased the EC50 of Ad5Hey1 alone by 14.5±10.5% and 33.5±2.5% for 5 and 10µM bicalutamide respectively in 22Rv1 cells. These data indicate that Hey1 can act as a cell death enhancer if over-expressed. Data is presented to suggest Hey1 can be expressed from a replication selective adenovirus to improve oncolytic anti-tumour efficacy in vitro and in PCa xenograft models. 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 2712. doi:1538-7445.AM2012-2712