In order to develop a safe and effective gene therapy for cancer, more powerful therapeutic genes must be selected and a gene transduction methodology needs to be devised that minimizes the total dose of vector required. We investigated the combination effect of 5-fluorouracil (5-FU), a first-choice drug for the treatment of colorectal cancer and adenovirus-mediated transfer of caspase-8 in DLD-1 colon cancer cells.
The degree of cell death was assessed by determining the percentage of cells which had died, and the degree of DNA fragmentation. The protein expression levels and degree of activation of caspase-8 were analyzed by Western blot analysis. The degree of transgene expression was assessed using adenoviral vectors expressing lacZ and GFP.
Combination treatment led to a significant induction of apoptosis, whereas treatment with either approach alone resulted in only minimal cytotoxicity. Caspase-8 was only activated in cells that received the combined treatment. Exposure to 5-FU increased the quantity of transgene expression per cell, 48 h post-infection. A potentiating effect of adenoviral treatment was also seen when 5-FU treatment was substituted by the overexpression of cyclin-dependent kinase inhibitors, p21WAF1/CIP1 and p27KIP1, suggesting that the cytostatic effect of 5-FU augmented apoptosis induced by caspase-8 gene transduction by inhibiting the dilution of gene products associated with cell division.
This combination strategy may be very useful in the treatment of 5-FU-resistant colorectal cancers and may also be more generally helpful in minimizing the dose of therapeutic vectors used in cancer gene therapy. Copyright © 2002 John Wiley & Sons, Ltd.