Gene transfer into human prostate adenocarcinoma cells with an adenoviral vector: Hyperthermia enhances a double suicide gene expression, cytotoxicity and radiotoxicity

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Abstract
We have previously developed a recombinant adenovirus containing a fusion gene of Escherichia coli cytosine deaminase (CD) and herpes simplex virus type 1 thymidine kinase (HSV-1 TK) controlled by a cytomegalovirus (CMV) enhancer-promoter. This replication-incompetent adenovirus effectively transduced the CD-TK gene into human prostate adenocarcinoma DU-145 or PC-3 cells. Interestingly, heat shock at 41°C for 4 hours elevated the level of CD-TK by approximately 5- to 20-fold at a multiplicity of infection (MOI) of 1. Heat-enhanced expression of CD-TK promoted cytotoxicity by 23-, 9-, or 47-fold in the presence of 50 μg/mL ganciclovir (GCV), 500 μg/mL 5-fluorocytosine (5-FC), or 50 μg/mL GCV+500 μg/mL 5-FC, respectively, at an MOI of 1. Moreover, there was an increase in radiosensitivity when adenovirus-infected cells were heated at 41°C for 4 hours followed by irradiation in the presence of the prodrugs. Virus+heat+1 μg/mL GCV treatment increased radiosensitivity by a dose-modifying factor (DMF) of 2.2, whereas virus+heat+10 μg/mL 5-FC exposure resulted in a DMF of 2.3. Radiosensitization was clearly enhanced as a result of combined prodrug exposure (DMF=4.4). Our results suggest that the efficiency in expression of suicide genes from an adenoviral vector used for cytotoxic anticancer therapy could be improved by combining heat treatment with radiation therapy.