Reserpine and carcinogenesis: inhibition of carcinoma formation in mice.

Long-term administration of reserpine, an alkaloid, significantly retarded the induction of squamous cell carcinomas by a chemical carcinogen, 3-methylcholanthrene (MCA) in Swiss male albino mice. The incidence and development of carcinomas in mice simultaneously treated with reserpine and MCA was notably lowered as compared to those occurring in mice treated with MCA alone at any time interval. DNA synthesis and the percentage of labeled cells with [3H]thymidine was also significantly decreased in the nuclei of tumor cells following reserpine and MCA administration as compared to the findings for cells treated with MCA alone (18.50 and 39.00%, respectively). Electron microscopic and cytologic observations of tumors revealed the predominance of large areas of cytolysis and disintegration with an increase of lysosomes, myelin figures, and a decrease of mitochondria and polyribosome populations in tumor cells treated with reserpine and MCA, as compared to those results after treatment with MCA only. These findings demonstrate that reserpine significantly inhibited the carcinoma induction by a chemical carcinogen (MCA) in mice, possibly by inducing an advanced cytolysis and decreasing DNA synthesis in mouse tumor cells.