STRUCTURE MUTAGENICITY AND STRUCTURE CYTOTOXICITY STUDIES ON BROMINE-CONTAINING CYSTEINE S-CONJUGATES AND RELATED-COMPOUNDS

Glutathione and cysteine S-conjugates of several haloalkenes are nephr otoxic and cytotoxic. Chloroalkene-derived S-(1-chloroalkenyl)-L-cyste ine conjugates, but not fluoroalkene-derived S-(2,2-dihalo-1,1-difluor oethyl)-L-cysteine conjugates, are mutagenic in the Ames test, althoug h both types of S-conjugates are cytotoxic and nephrotoxic. Recent stu dies showed that bromine-containing S-(2,2-dihalo-1,1-difluoroethyl)-L -cysteine conjugates are mutagenic in the Ames test, thus challenging the generalization that S-(2,2-dihalo-1,1-difluoroethyl)-L-cysteine co njugates are not mutagenic. Hence a series of bromine-containing and b romine-lacking S-(2,2-dihalo-1,1-difluoroethyl)-L-cysteine conjugates was prepared, and their mutagenicity was assessed in the Ames test wit h Salmonella typhimurium TA2638 as the test strain. In addition, sever al indices of cytotoxicity, including cytotoxicity in LLC-PK1 cells, i nduction of Ca2+ release from pig kidney mitochondria, and DNA double- strand breaks in LLC-PK1 cells, were measured. The bromine-containing S-conjugates S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine (BCD-FC ), S-(2-bromo-1,1,2-trifluoroethyl)-L-cysteine (BTFC), and S-(2,2-dibr omo-1,1-difluoroethyl)-L-cysteine (DBDFC) were mutagenic in the Ames t est, whereas S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine (CTFC), S-(2 ,2-dichloro-1,1-difluoroethyl)-L-cysteine (DCDFC), and S-(1,1,2,2-tetr afluoroethyl)-L-cysteine (TFC), which lack bromine, were not. BCDFC, B TFC, CTFC, DBDFC, and TFC were cytotoxic in LLC-PK1 cells, and their c ytotoxicity was blocked by the cysteine conjugate beta-lyase inhibitor (aminooxy)acetic acid. DCDFC showed little cytotoxicity in LLC-PK1 ce lls. BCDFC, BTFC, CTFC, DBDFC, DCDFC, and TFC induced Ca2+ release fro m pig kidney mitochondria and DNA double-strand breaks in LLC-PK1 cell s. The data show a clear difference in the mutagenicity of bromine-con taining and bromine-lacking cysteine S-conjugates in the Ames test, bu t no remarkable differences among the S-conjugates in other indices of toxicity. Because mutagenicity is associated with the presence of bro mine, it is possible that its presence affords a route to novel metabo lites that react with both DNA and protein.