Effect of Nocardia rubra cell-wall skeleton treatment on tumor formation in two-stage chemical carcinogenesis of mouse skin

Summary In two-stage chemical carcinogenesis of mouse skin, Nocardia rubra cell-wall skeleton (N-CWS), a potent immunopotentiator, was injected SC at various times. The dorsal skin of C57BL/6 male mice (about 10 cm²) was painted with 20 g 7,12-dimethylbenz(a)anthracene (DMBA) in 0.1 ml acetone when the animals were 11 weeks old (initiation). Seven weeks later, they were painted with 2.5 g 12-0-tetradecanoyl-phorbol-13-acetate (TPA) in 0.1 ml acetone twice weekly for 30 weeks (promotion). The timing of N-CWS treatment was important. N-CWS treatment before initiation reduced the incidence of skin tumor and the mean number of skin tumors per mouse most effectively. It is speculated that the antitumor activity of N-CWS may be composed of at least two mechanisms, being achieved through the enhancement of immunological surveillance and through changes in the metabolism of chemical carcinogens.