We previously found that 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCNU), a new chloroethylnitrosoureaanalogue presently in phase I clinical trials, is aselective cytotoxin that enters cells via the extraneuronaltransporter for monoamine transmitters (EMT). In thisstudy, we assessed whether EMT expression correlates withSarCNU cytotoxicity by determining EMT expression in 23human tumor cell lines with reverse-transcription PCR.Western blot analysis was used to measure protein levels ofthe DNA repair genes, O6-methylguanine-DNA methyltransferase(MGMT), and excision repair cross-complementing rodentrepair deficiency gene 2 (ERCC2). SarCNU cytotoxicitywas determined by the sulforhodamine B colorimetric anticancer-drug screening assay and correlated with gene expression.Almost all of the cell lines screened were positivefor EMT expression. However, seven cell lines (MGR-1,MGR-2, T98-G, SKI-1, SKNSH, 297, and GBM) expressedlow levels of EMT. Although there was no linear correlationbetween SarCNU cytotoxicity and EMT expression,SarCNU cytotoxicity significantly correlated with ERCC2protein levels, and MGMT-rich (Mer1) cell lines (MGMTprotein level >0.1) were more resistant to SarCNU thanMGMT-poor (Mer2) cell lines (MGMT protein level <0.1). Moreover, multiple regression analysis indicated that thebest correlation with SarCNU cytotoxicity was attainablewith EMT plus MGMT and ERCC2 expression. This studysuggests that in human tumor cell lines both EMT and DNArepair factors, specifically, MGMT and ERCC2, are importantdeterminants of SarCNU activity. Because EMT is expressedin a wide variety of human tumors, SarCNU shouldbe a more widely effective alternative chemotherapeuticagent.