2000 Volume 16 Issue 3 Pages 131-141
Hyperthermic therapy has been applied in many advanced malignancies, but tumor regression occurs only in thermo-sensitive cancers. To elucidate ways to overcome thermo-resistance and to improve the therapeutic efficiency of treating thermo-resistant cancers, we devised a novel application of cancer gene therapy in conjunction with hyperthermia. This strategy allows for selective cancer gene therapy under control of the heat-inducible HSP promoter. Heat-inducible activity of HSP promoter was examined in FM3A breast cancer cell line and MKN45 gastric cancer cell line using a luciferase assay reporter gene system. HSP promoter activity increased markedly following heat shock, and this increase depended on temperature and duration of treatment. Based on these results, we designed a suicide gene therapy using the Herpes simplex virus thymidine kinase gene ligated to the heat-inducible HSP promoter (HSP-tk). In in vitro cytotoxic assays HSP-tk transduced cells following heat treatment became 50, 000 times more sensitive than either non-transduced cells or HSP-tk transduced cells without heat treatment to ganciclovir (GCV). Immunohistochemical analysis revealed that Fas-mediated apoptosis was involved in the synergistic killing effect of combination therapy. Next, we examined the efficacy of HSP-tk gene therapy in vitro, cancer cell lines implants in subcutaneous or intraperitoneal models of balb/c nude mice were targeted using the HVJ-anionic-liposome method. Significant inhibition of tumor growth was observed in HSP-tk transduced tumors following hyperthermia as more than half of treated-mice showed complete tumor eradication. Prolonged survival was also observed in HSP-tk transducted mice with hyperthermia. In contrast, non-transduced mice treated with or without hyperthermia showed no prolongation of survival. Recently, another group reported an in vitro study that HSP promoter-mediated gene therapy is an effective treatment for prostate cancer studied. Taken together, these results demonstrate that the combined gene and hyperthermic therapy may be a feasible treatment that can target HSP-expressing carcinomas, even in advanced cases.
