Extraneuronal monoamine transporter expression and DNA repair vis-a-vis 2-chloroethyl-3-sarcosinamide-1-nitrosourea cytotoxicity in human tumor cell lines

We previously found that 2-chloroethyl-3-sarcosinamide-1-nitrosourea (SarCN U), a new chloroethylnitrosourea analogue presently in phase I clinical tri als, is a selective cytotoxin that enters cells via the extraneuronal trans porter for monoamine transmitters (EMT), In this study, we assessed whether EMT expression correlates with SarCNU cytotoxicity by determining EMT expr ession in 23 human tumor cell lines with reverse-transcription PCR, Western blot analysis was used to measure protein levels of the DNA repair genes, O-6-methylguanine-DNA methyltransferase (MGMT), and excision repair cross-c omplementing rodent repair deficiency gene 2 (ERCC2), SarCNU cytotoxicity w as determined by the sulforhodamine B colorimetric anticancer-drug screenin g assay and correlated with gene expression. Almost all of the cell lines s creened were positive for EMT expression. However, seven cell lines (MGR-1, MGR-2, T98-G, SKI-1, SKNSH, 297, and GBM) expressed low levels of EMT, Alt hough there was no linear correlation between SarCNU cytotoxicity and EMT e xpression, SarCNU cytotoxicity significantly correlated with ERCC2 protein levels, and MGMT-rich (Mer(+)) cell lines (MGMT protein level >0.1) were mo re resistant to SarCNU than MGMT-poor (Mer(-)) cell Lines (MGMT protein lev el <0.1). Moreover, multiple regression analysis indicated that the best co rrelation with SarCNU cytotoxicity was attainable dth EMT plus MGMT and ERC C2 expression. This study suggests that in human tumor cell. lines both EMT and DNA repair factors, specifically, MGMT and ERCC2, are important determ inants of SarCNU activity, Because EMT is expressed in a wide variety of hu man tumors, SarCNU should be a more widely effective alternative chemothera peutic agent.