Structure-mutagenicity and structure-cytotoxicity studies on bromine-containing cysteine S-conjugates and related compounds.

Abstract

Glutathione and cysteine S-conjugates of several haloalkenes are nephrotoxic and cytotoxic. Chloroalkene-derived S-(1-chloroalkenyl)-L-cysteine conjugates, but not fluoroalkene-derived S-(2,2-dihalo-1,1-difluorethyl)-L-cysteine conjugates, are mutagenic in the Ames test, although both types of S-conjugates are cytotoxic and nephrotoxic. Recent studies 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 conjugates are not mutagenic. Hence a series of bromine-containing and bromine-lacking S-(2,2-dihalo-1,1-difluoroethyl)-L-cysteine conjugates was prepared, and their mutagenicity was assessed in the Ames test with Salmonella typhimurium TA2638 as the test strain. In addition, several indices of cytotoxicity, including cytotoxicity in LLC-PK1 cells, induction 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-dibromo-1,1-difluoroethyl)-L-cysteine (DBDFC) were mutagenic in the Ames test, whereas S-(2-chloro-1,1,2-trifluorethyl)-L-cysteine (CTFC), S-(2,2-dichloro-1,1-difluoroethyl)-L-cysteine (DCDFC), and S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (TFC), which lack bromine, were not. BCDFC, BTFC, CTFC, DBDFC, and TFC were cytotoxic in LLC-PK1 cells, and their cytotoxicity was blocked by the cysteine conjugate beta-lyase inhibitor (aminooxy)acetic acid.(ABSTRACT TRUNCATED AT 250 WORDS)