gms | German Medical Science

The phenotypical characteristics and spread of ovarian cancer, the most lethal gynaecologic malignancy, suggests intraperitoneal gene therapy of this disease. Phase I trials have been conducted to investigate the safety and clinical effects of adenoviral E1A in gene therapeutic approaches. However, besides tumor-suppressive effects, E1A is 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 E1A deletion mutants on ovarian cancer cells was studied. To avoid any selection bias, a doxycyclin-regulated system was used to express E1A mutants and study their effects on the proliferation of ovarian carcinoma cell lines. As confirmed by Western blot analyses, the expression of the mutant proteins was almost completely suppressed by addition of doxycyclin to the culture medium. A substantial reduction in proliferation was achieved by expression of the wildtype protein and the mutants E1AdelCR2 and E1AdelCR3Ex2 lacking the p105RB-binding motif. Therefore, deletion of the CR2 sequence should increase the safety of therapeutic application of E1A without affecting tumor suppression. The doxycyclin-regulated expression system was established to enable the elucidation of the mechanisms underlying the therapeutic effects of E1A in ovarian cancer cells, which are now analyzed by expression profiling and quantification of activated components of signal transduction pathways. In addition to their effect on proliferation, E1A variants promoted apoptosis of ovarian cancer cells induced by chemotherapeutic agents.