ORIGINAL ARTICLES: Translational researchTemozolomide chemoresistance heterogeneity in melanoma with different treatment regimens DNA damage accumulation contributionBoeckmann, Larsa; Nickel, Ann-Christinb; Kuschal, Christianea; Schaefer, Annikaa; Thoms, Kai-Martina; Schön, Michael P.a; Thomale, Jürgenb; Emmert, SteffenaAuthor Information aDepartment of Dermatology, Venereology, and Allergology, Georg August University Göttingen bInstitute of Cell Biology (Cancer Research), University of Duisburg-Essen, Germany Correspondence to Steffen Emmert, MD, Georg August University Göttingen, Department of Dermatology, Venereology, and Allergology, Von-Siebold-Str. 3, 37075 Göttingen Tel: +49 551 396410; fax: +49 551 398983; e-mail: [email protected] Received September 13, 2010 Accepted February 11, 2011 Melanoma Research: June 2011 - Volume 21 - Issue 3 - p 206-216 doi: 10.1097/CMR.0b013e328345af95 Buy Metrics Abstract The efficacy of temozolomide in melanoma treatment is low (response rate <20%) and may depend on the activity of O6-methylguanine DNA methyltransferase (MGMT) and mismatch repair. We identified melanoma cell lines with different sensitivities to single versus prolonged clinical dosing regimens of temozolomide treatment and assessed a variety of potential resistance mechanisms using this model. We measured mRNA expression and promoter methylation of MGMT and essential mismatch repair genes (MLH1, MSH2). Cell cycle distribution, apoptosis/necrosis induction, O6-methylguanine-adduct formation, and ABCB1 gene expression were assessed. We found that three cell lines, MelA, MelB, and MelC, were more sensitive to a single dose regimen than to a prolonged regimen, which would be expected to exhibit higher cytotoxicity. KAII and LIBR cell sensitivity was higher with regard to the prolonged treatment regimen, as expected. Only MelC expressed MGMT. Gene expression correlated well with promoter methylation. Temozolomide exposure did not alter mRNA expression. Different sensitivities to temozolomide were caused neither by delayed apoptosis induction due to early cell cycle arrest nor by O6-methylguanine-adduct formation or efflux transporter expression. MelC was the most resistant cell line with rapid elimination of O6-methylguanine adducts. This was in good agreement with its MGMT expression. The sensitive cell lines KAII and LIBR accumulated O6-methylguanine adducts after a second treatment cycle with temozolomide in contrast with the other three cell lines. We conclude that MGMT expression and DNA adduct accumulation are relevant factors in temozolomide chemosensitivity. Considering individualized temozolomide treatment regimens either by quantification of DNA adducts or by chemosensitivity testing seems worthwhile clinically. © 2011 Lippincott Williams & Wilkins, Inc.