Heat-directed suicide gene therapy for breast cancer

Adjuvant hyperthermia can improve treatment outcome for locally recurrent breast cancer (LRBC). Previously, we demonstrated that infection of human breast cancer cells with a recombinant adenovirus expressing β -galactosidase from the human hsp70b gene promoter (Ad.70b. β gal) results in 50- to 800-fold increases in reporter gene expression following heat treatment (30 minutes at 43°C). Here, we describe a heat-directed suicide gene therapy strategy based on an adenoviral vector (Ad.70b.CDTK) in which expression of the dual prodrug-activating E. coli cytosine deaminase/herpes simplex virus thymidine kinase (CDTK) fusion gene is under the control of the hsp70b promoter. Treatment of T47D and MCF-7 breast cancer cells with mild hyperthermia (43°C/30 minutes) and prodrugs (100 μ g/ml 5-fluorocytosine and 10 μ g/ml ganciclovir) following infection with Ad.70b.CDTK (10–100 PFU/cell) resulted in 30- to 60-fold decreases in clonogenic survival relative to control cultures treated with heat or prodrugs alone. Clonogenic survival declined even further (up to 240-fold) following heat treatment at 41.5°C for 120 minutes. A decreased clonogenic survival was accompanied by tumor cell apoptosis. These results demonstrate that this combined treatment strategy can be highly effective against heat- and radiation-resistant breast tumor cells and supports the continued development of heat-directed CDTK suicide gene therapy strategies for LRBC.