The suppressive effect of S-methyl methanethiosulfonate (MMTS) on aflatoxin B-1 (AFB(1))- or methyl methanesulfonate (MMS)-induced was studied. MMTS significantly suppressed CA induced by both AFB(1) (an indirect-acting carcinogen) and MMS (a direct-acting carcinogen). Suppression was observed at all periods (6, 12, 18, 24 and 48 h) after AFB(1) or MMS treatment and in all doses of AFB(1) (5, 10 and 20 mg/kg) or MMS (50, 75 and 100 mg/kg) investigated. AFB(1)-induced CA was potently suppressed by MMTS given between 2 h before and 6 h after the AFB(1) injection. The suppression of AFB(1)-induced CA by MMTS paralleled the dose of MMTS when MMTS was given in a dose range of 1-20 mg/kg body weight. MMS-induced CA was potently suppressed by MMTS given between 2-h before and 2 h after the MMS injection. The suppressive effect of MMTS on MMS-induced CA paralleled the dose of MMTS when MMTS was given in a dose range of 1-15 mg/kg body weight. Diphenyl disulfide, which modifies -SH groups in proteins like MMTS, also significantly suppressed both AFB(1)- and MMS-induced CA. Although other mechanisms are not excluded, the suppression of carcinogen-induced CA by MMTS may result from the ability of MMTS to modify -SH groups in proteins. The juices of cabbage and onion, which contain considerable amounts of MMTS and S-methyl-L-cysteinesulfoxide (the precursor of MMTS), also significantly suppressed AFB(1)- or MMS-induced CA. These results suggest that MMTS is a possible chemopreventive agent against cancer. (C) 1997 Elsevier Science B.V.
