Potentiation of antitumor activity of 1-phthalidyl 5-fluorouracil by acetazolamide.

The effect of acetazolamide (A.A.) on the antineoplastic activity of 1-phthalidyl 5-fluorouracil (PH-FU) against rat and mouse solid tumors was examined. A.A., an inhibitor of liver PH-FU hydrolase, had no antitumor activity but greatly enhanced the activity of PH-FU when coadministered. The potentiation was evaluated in terms of suppression of tumor growth and prolongation of the life-span of tumor-bearing animals. Studies also revealed that A.A. elevated the concentration of PH-FU in tumor tissues, where 5-fluorouracil is slowly liberated from PH-FU. The results are consistent with the hypothesis that A.A. prevents enzymic degradation of PH-FU in the liver and promotes its distribution into target organs.