Abstract 2713: Adenovirus E1A binding to p300 is essential for synergistic cell killing in combination with chemotherapeutic drugs in prostate cancer cells

Abstract

Abstract Commonly prostate cancer becomes insensitive to androgen ablation therapy, developing hormone-refractory metastatic PCa (HRPC). The available therapies for HRPC are palliative. Therefore, novel therapeutic strategies to target treatment resistant PCa are needed. Replication-selective oncolytic adenoviruses (ONYX-015, H-101, and CTL-102) represent a promising anticancer approach with proven efficacy in cancer cell lines, tumour xenografts in vivo and demonstrated safety in numerous clinical trials. It has been established that expression of the viral E1A gene in combination with chemodrugs is essential for the enhancement of cell killing. The E1A gene is the first viral gene to be expressed after infection and is an absolute requirement for viral gene expression and replication. Specific regions in the E1A proteins bind to numerous cellular factors to regulate the host cell function and the viral life cycle including p300, p400, pRb proteins and various transcription factors. We demonstrate that adenoviral mutants expressing only the small E1A12S protein potently sensitizes prostate cancer cell lines to the cytotoxic drugs mitoxantrone and docetaxel, the current standard of care for late stage prostate cancers. We generated AdE1A12S mutants with gene deletions in the regions binding p300 (AdE1A1104), p400 (AdE1A1102) and pRb (Ad1108) and potently expressed the E1A gene in the absence of viral replication. Preliminary findings suggest that binding to p300 (AdE1A12S, AdE1A1102, AdE1A1108) was essential for sensitization of the PCa cells to cytotoxic drugs. The decreases in EC50 values for mitoxantrone after infection with AdE1A1102 in PC3 and 22Rv1 cells were 40±5% and 37±3% respectively. In addition, all viruses binding p300, caused an accumulation of cells in the G2/M-phase in combination with mitoxantrone that increased from 68±2% to 80±5% with AdE1A1102 compared to mitoxantrone alone in PC3 cells. The G2/M accumulation was accompanied by higher levels of cyclin A and B in PC3 cells (AR-, p53-) but not in 22Rv1 cells (AR+, p53+). Under these conditions, using sub-optimal doses of mitoxantrone, p21 was induced an induction that could not be prevented by any E1A12S mutant. AdE1A1102 caused synergistic cell killing in combination with mitoxantrone in 10/20 conditions (CIα0.9) while the corresponding replicating mutant (dl1102) further increased the synergistic effects (CIα0.9) in 20/20 conditions. The AdE1A1104 and dl1104 in combination with mitoxantrone either caused antagonism or low levels of synergy in both cell lines. Data is presented to demonstrate that the enhanced cell killing with cytotoxic drugs and both replicating and non-replicating mutants is caused by increased apoptosis. Preliminary findings from miRNA-mRNA pathway analysis will be presented indicating activation of cell death programmes and inhibition of cell survival pathways. 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 2713. doi:1538-7445.AM2012-2713