Retinoids prevent epithelial carcinogenesis induced by N-nitroso compounds.

Two new retinoic acid esters and retinamides synthesized in China, N-(4-ethoxycarbophenyl)retinamide (RI) and N-(4-carboxyphenyl)retinamide (RII), significantly inhibited carcinogenesis induced in the epithelium of the forestomach of mice by N-nitrososarcosine ethyl ester. RI also markedly inhibited carcinogenesis induced in the epithelium of the oesophagus and forestomach in rats by this ester. No sign of hypervitaminosis was noticed with doses as high as six times the therapeutic dose. RI also inhibited precancerous and cancerous lesions in the nasal cavity and nasopharynx and oesophagus of rats induced by dinitrosopiperazine. In a malignant oesophageal epithelial cell line from rats, RE25-3, established in our laboratory, RI and RII inhibited mitosis, proliferation rate, chromosomal aberrations and incorporation of 3H-thymidine into DNA. The ability to form colonies on agar plates was also inhibited by these two compounds.