Abstract 5498: Changes in expression of DNA repair genes in human leukemia cells treated with laromustine

Abstract

The anticancer prodrug laromustine induces cytotoxic DNA damage and has had clinical success against acute myelogenous leukemia and glioblastoma multiforme. The causative DNA damage is principally a G-C interstrand crosslink preceded by 2-chloroethylation of guanine O6 by a subspecies of laromustine generated in situ upon base-catalyzed activation. Another cogenerated electrophile, methylisocyanate, contributes synergistically with the DNA alkylating activity towards cytotoxicity. Given this synergism, DNA repair enzymes are considered likely targets of methylisocyanate, which can carbamoylate amines and sulfhydryls. The inhibition of O6-alkylguanine-DNA alkyltransferase (AGT) and DNA polymerase beta by laroumustine's carbamoylating activity, observed in vitro, may contribute to cytotoxicity. To further investigate the relationship between laromustine and DNA repair, drug-induced changes in the transcription of 88 DNA repair genes were measured in cultured human promyelocytic (HL-60) cells using quantitative real-time reverse transcriptase PCR. Cells were treated with laromustine or vehicle for six hours before harvesting mRNA for analysis. The expression of a subset of the tested genes emerged as significantly different in cells treated with laromustine as compared to control cells. Included among those genes with significantly increased expression were: NTHL1 (17 fold), PARP1 (8 fold), and AGT (5 fold). Included among those genes with significantly decreased expression were: PARP2 (-5 fold) and MSH6 (-74 fold). Increased expression of NTHL1, which encodes for an N-glycosylase that can remove damaged guanine bases, may reduce the effectiveness of laromustine's alkylation of guanine O6. A strong negative correlation between the level of AGT activity in patient samples and the efficacy of laromustine has already been established. Some of the gene products identified in this study, such as NTHL1, may emerge as possible cotherapeutic targets or markers for clinical screening. Citation Format: Kristen N. Robinson, Kathryn A. Coe, Justin E. Owumi, Kevin P. Rice. Changes in expression of DNA repair genes in human leukemia cells treated with laromustine. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5498. doi:10.1158/1538-7445.AM2014-5498