INHIBITORY EFFECT OF 13-CIS-RETINOIC ACID ON URINARY-BLADDER CARCINOGENESIS INDUCED IN C57BL-6 MICE BY N-BUTYL-N-(4-HYDROXYBUTYL)-NITROSAMINE

Abstract

The effect of 13-cis-retinoic acid on the induction of urinary bladder carcinoma by N-butyl-N-(4-hydroxybutyl)nitrosamine (OH-BBN) was studied in male C57BL/6 mice. Animals received a total dose of either 90 or 140 mg of OH-BBN via gastric intubations of 7.5 or 10.0 mg of OH-BBN 2 times/wk for 6 or 7 wk, respectively. Seven days after the last OH-BBN intubation, animals were fed laboratory chow diet supplemented with either 200 mg of 13-cis-retinoic acid/kg or its placebo. Animals were killed at 6 mo. after the 1st carcinogen intubation. Highly invasive squamous and transitional cell carcinomas of the urothelium were found at autopsy. In the majority of these carcinomas, invasion of the bladder muscle wall by tumor cells had occurred. At the 2 dose levels of OH-BBN, feeding of 13-cis-retinoic acid reduced the incidence of both carcinomas and noninvasive papillomas, as well as the extent of neoplastic development in the urinary bladder. In mice receiving the lower dose of OH-BBN, the feeding of 13-cis-retinoic acid prevented the appearance of both squamous and transitional cell carcinomas with a reduction in incidence from 0-33% (P < 0.01). Apparently 13-cis-retinoic acid reduced not only the severity of highly invasive urinary bladder carcinomas but also the incidence of such cancers.