Identification of adenovirus E1A gene regions involved in chemosensitisation of prostate cancer cells

Abstract

Replication-selective adenoviruses are promising anti-cancer therapies (virotherapy). Viruses can be engineered to selectively target cancer cells by deleting viral genes involved in cell cycle regulation. These deletions impair replication in normal cells, as the virus cannot overcome cellular checkpoints and pro-apoptotic pathways triggered by the infection. In cancer cells, however, these pathways are often deregulated hence viral propagation is not affected by these deletions. Despite the efforts to maximise potency and selectivity of adenoviruses as therapeutic agents, efficacy was poor when evaluated alone in clinical trials. Enhancement of efficacy was demonstrated in combination with chemotherapy and radiotherapy. A requirement for virus-mediated sensitisation to chemotherapy and enhancement of efficacy is the expression of the early viral gene E1A. However, the exact E1A regions required for increased cell death have not yet been identified. The E1A proteins bind to a variety of cellular factors, including the transcriptional and cell cycle regulators p300/CBP and pRb. This thesis describes the use of replication-selective and replication-defective adenoviruses expressing different mutation of the E1A gene in order to identify regions involved in chemosensitisation of prostate cancer cell lines to two cytotoxic drugs, mitoxantrone and docetaxel. Synergistic interactions were observed with all replication-selective adenoviruses and mitoxantrone in a cell dependent manner. The results obtained indicate that mutations in the p300/CBP binding site, but not pRb, impaired the sensitising activity of E1A to the cytotoxic drugs. Expression of E1A enhanced the arrest in the G2/M phase induced by mitoxantrone and increased the percentage of apoptotic cells in a process dependent on E1A binding to p300/CBP. Deletion of this binding site also attenuated the potency of replicating adenoviruses, indicating that binding to p300/CBP plays a central role in sensitisation to chemotherapy and control of viral cycle in prostate cancer cells.