14102 Background: The phenotypical characteristics and spread of ovarian cancer cells, suggest intraperitoneal gene therapy of this disease. Phase I trials have been conducted to investigate the potential clinical benefits of adenoviral E1A-based gene therapy. Further gene therapeutic approaches which aim to enhance the efficacy of E1A-induced apoptosis in a multimodal approach including conventional chemotherapy are planned. However, besides tumor-suppressive effects, E1A is also known to transform rodent cells in conjunction with other factors, e.g. an activated ras oncogene. In an effort to eliminate elements favouring malignant conversion, the potential therapeutic effect of the E1AdelCR2 deletion mutant on ovarian cancer cells was studied. Methods: To avoid any selection bias, a doxycyclin-regulated system was used to express E1A wildtype protein and the mutant E1AdelCR2 lacking the p105RB-binding motif. The effects of the E1A proteins on proliferation and induction of apoptosis in ovarian carcinoma cell lines was studied with a WST-1 assay and fluorcytometric analysis of FITC labelled AnnexinV. Results: As confirmed by Western blot analyses, expression of the mutant proteins was almost completely suppressed in the presence of doxycyclin. Substantial reduction in proliferation was achieved by expression of both wildtype E1A and E1AdelCR2. Expression of E1AdelCR2 was sufficient by itself to induce apoptosis in 8,7% of ovarian carcinoma cells as shown by an increase of the fraction of Annexin binding OVMZ-8 cells. A strong synergistic effect with an increase of the fraction of apoptotoc cells by 16.7% was found when the cells were treated with paclitaxel. Conclusion: Deletion of the CR2 sequence should increase the safety of therapeutic applications of E1A without affecting tumor suppression. A doxycyclin-regulated expression system was established allowing the elucidation of the mechanisms underlying the therapeutic effects of E1A in ovarian cancer cells in the future by means of expression profiling and quantification of activated components of signal transduction pathways. No significant financial relationships to disclose.
Cooperative effect of adenoviral p53 gene therapy and standard chemotherapy in ovarian cancer cells independent of the endogenous p53 status
