Eradication of Breast Cancer Xenografts by Hyperthermic Suicide Gene Therapy under the Control of the Heat Shock Protein Promoter

To investigate the usefulness of heat shock protein (HSP) promoter for breast cancer gene therapy, hyperthermia and HSV thymidine kinase (tk) suicide gene combination therapy was examined with mouse mammary cancer cell line FM3A. HSP promoter activity was markedly increased after heat shock (41-45°C), with maximum activation (about 400-fold) at 3 hr. An in vitro cytotoxic assay showed that HSP-tk-transduced FM3A cells became more sensitive (more than 50,000 times) to ganciclovir (GCV) with heat shock, but untreated cells showed no increased cytotoxic sensitivity to GCV compared with control FM3A cells. In addition to promoter-oriented selective cell killing, a "chemosensitization effect" as a bystander effect was demonstrated by hyperthermia and suicide gene combination therapy, using a non-heat-inducible promoter. Immunohistochemical analysis revealed that this synergistic killing effect was dependent on apoptotic cell death with upregulation of both Fas and FasL (Fas ligand) expression. We also examined...