| Abstract: |
These studies were undertaken to determine the feasibility, safety, and efficacy of suicide gene therapy using adenoviral-mediated herpes simplex virus thymidine kinase (ADV/RSV-tk) and the prodrug ganciclovir (GCV) in an orthotopic murine bladder cancer model. We utilized a replication-defective adenoviral construct containing the β-galactosidase gene as a control and the herpes simplex virusthymidine kinase gene asthe therapeutic vector under the transcription control of the Rous sarcoma virus long terminal repeat promoter. Intravesically created, orthotopic bladder tumors were established in syngeneic C3H/He female mice. India ink injection and β-galactosidase studies were performed to determine if transurethral administration, direct tumor injection, or the combination was the most efficient route of virus administration. Optimal dosing of ADV/RSV-tk was determined by direct tumor injection with increasing viral doses and treatment with GCV. Treatment efficacy, long-term survival, and toxicity were determined in separate but similar controlled experiments. Growth curve studies demonstrated reliable tumor formation by 14 days. Direct transvesical tumor injection resulted in the best distribution and intratumor gene expression as measured by X-gal staining. Dose-ranging experiments demonstrated an optimal viral dose of 5 × 108 plaque-forming units and a greater than twofold reduction in tumor growth for the animals treated with ADV/RSV-tk compared to controls. Efficacy studies demonstrated a greater than threefold reduction in tumor growth. No clinical or gross pathologic toxicity was detected. Long-term survival results suggested a survival benefit for the treatment animals compared to controls. We conclude that ADV/RSV-tk in combination with GCV provides effective therapy for orthotopic murine bladder cancer by significantly inhibiting tumor growth with limited toxicity to the host. These data provide further support for testing this suicide gene therapy strategy in human Phase I trials. |
