Herpes simplex virus thymidine kinase/ganciclovir-induced cell death is enhanced by co-expression of caspase-3 in ovarian carcinoma cells

There is a need to enhance the efficacy of genetic prodrug activation thera py using herpes simplex virus thymidine kinase (tk) and ganciclovir (GCV) f ollowing disappointing results in early clinical trials. tk/GCV has been sh own to lead to the activation of caspase-3, a potent executor of apoptosis. We demonstrate that co-expression of pro-caspase-3 with tk/GCV leads to en hanced cell death in ovarian carcinoma cells in vitro. Following transfecti on with recombinant adenoviral vectors encoding tk, GCV treatment leads to greater cell death in pro-caspase-3-expressing clones of SKOV3 and IGROV1 t han control cells, as well as more rapid activation of caspase-3 and more r apid cleavage of PARP. Flow cytometry suggests that there is a greater degr ee of S-phase block in the pro-caspase-3 -expressing clones than in control cells following treatment with tk/GCV. None of these effects is seen follo wing transfection with a control adenovirus that does not encode tk. The in creased cell death, early caspase-3 activation and PARP cleavage, and flow cytometric changes seen in pro-caspase-3-expressing cells can be partially inhibited by treatment with benzyloxycarbonyl-val-ala-asp fluoromethylketon e, a synthetic caspase inhibitor. Our data suggest that co-expression of pr o-caspase-3 may lead to a significant enhancement of the efficacy of tk/GCV therapy.