Inhibition of methylcholanthrene-induced skin carcinogenesis in hairless mice by dimethyl sulfoxide.

Hairless mice were given 5 topical applications of 470 nmol 20-methylcholanthrene (MCA) at one week intervals. In one experimental group the MCA was dissolved in reagent grade acetone alone, in another group it was dissolved in a mixture consisting of 50% acetone and 50% dimethyl sulfoxide (DMSO). A control group received the mixed solvent alone. The animals were observed for development of papillomas and malignant tumors during 75 weeks. The group treated with MCA in acetone/DMSO had a higher mortality than the two other groups. The admixture of 50% DMSO to the solvent had a significant inhibitory effect on tumor and cancer rates and on cancer yield, whereas no effect could be observed on the tumor yield. Hence, 50% DMSO in the solvent has a moderate, but significant, inhibitor effect on MCA-induced skin carcinogenesis. Similar inhibitory effect of DMSO on the promotion phase in two stage-carcinogenesis protocols have been reported in the literature. The biochemical mechanisms behind this effect are unknown.