One of the major goals of gene therapy is to regulate the expression of therapeutic genes in desired cells or tissues. For this purpose, heat-inducible vectors have been exploited for cancer gene therapy combined with hyperthermia, which can result in considerable improvement of therapeutic effects. In the present study, we constructed a novel heat-inducible gene expression system incorporating a transactivation system with a positive feedback loop of transcriptional amplification. The target gene expression mediated by the transactivator under the control of a heat shock protein 70B' promoter is enhanced by self-promoted transactivator gene expression. This expression system showed tight control of target gene expression together with high-level expression; enhanced expression of the reporter gene was observed in transfected cells upon heat treatment, while negligible gene expression was detected in non-heated cells. When a therapeutic gene was used as the target gene, a considerable cytotoxic effect was observed after heat treatment of cancer cells transfected with the plasmids. The heat-induced transgene expression system is a promising new approach for the development of both a safe and effective vector for hyperthermia-based cancer gene therapy.
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