Enhancement of cyclophosphamide sensitivity in squamous cell carcinoma transfected with cytochrome P-450 2B1

Cyclophosphamide (CPA) has been shown to be quite effective and safe in the treatment of leukemia, but it had shown almost no efficacy in the treatment of solid tumors such as head and neck cancers. The purpose of this study was to determine whether head and neck squamous cell carcinomas can be made more sensitive to the cytotoxic effect of CPA by shifting the balance from the degradative to the activation pathway.

Human SCC-25 squamous carcinoma cells were transfected by adenoviral vector containing P-450 2B1 gene and were identified for P-450 2B1 expression by Northern blot analysis. In vitro cytotoxic assay after CPA exposure was performed using these cells. Human KB oral base squamous cell carcinoma cells were injected subcutaneously to the backs of nude mice. Then Ad.CMV-P-450 2B1 was injected intratumorally. At 48 hours after the injection of Ad.CMV-P-450 2B1, CPA was injected into the peritoneal cavity of the animals and the volume of the tumor was determined with the passage of time. All the animal procedures were performed under the guidance of the committee in our animal care facility.

The in vitro experiments found that transduction of the P-450 2B1 gene caused a nearly 30-fold increase in the sensitivity of the host cell line to CPA on the basis of the 50% inhibitory concentration. The in vivo experiments, which were conducted in nude mice, found that the combination of P-450 2B1 gene transduction and administration of CPA showed an inhibitory effect on tumor growth.

The P-450 2B1- cyclophosphamide system may be useful approach for gene therapy of squamous cell carcinomas of head and neck.