• Shiv K Gupta, Sani H Kizilbash, Brett L Carlson, Ann C Mladek, Felix Boakye-Agyeman, Katrina K Bakken, Jenny L Pokorny, Mark A Schroeder, Paul A Decker, Ling Cen, Jeanette E Eckel-Passow, Gobinda Sarkar, Karla V Ballman, Joel M Reid, Robert B Jenkins, Roeland G Verhaak, Erik P Sulman, Gaspar J Kitange, and Jann N Sarkaria.
• Department of Radiation Oncology (SKG, BLC, ACM, KKB, JLP, MAS, LC, GJK, JNS), Division of Medical Oncology (SHK), Molecular Pharmacology and Experimental Therapeutics (FBA, JMR), Division of Biomedical Statistics and Informatics (PAD, JEEP, KVB), and Laboratory Medicine and Pathology (GS, RBJ), Mayo Clinic, Rochester MN; The University of Texas, MD Anderson Cancer Center, Houston, TX (RGV, EPS).
• J. Natl. Cancer Inst. 2016 May 1; 108 (5).

BackgroundSensitizing effects of poly-ADP-ribose polymerase inhibitors have been studied in several preclinical models, but a clear understanding of predictive biomarkers is lacking. In this study, in vivo efficacy of veliparib combined with temozolomide (TMZ) was evaluated in a large panel of glioblastoma multiforme (GBM) patient-derived xenografts (PDX) and potential biomarkers were analyzed.MethodsThe efficacy of TMZ alone vs TMZ/veliparib was compared in a panel of 28 GBM PDX lines grown as orthotopic xenografts (8-10 mice per group); all tests of statistical significance were two-sided. DNA damage was analyzed by γH2AX immunostaining and promoter methylation of DNA repair gene O6-methylguanine-DNA-methyltransferase (MGMT) by Clinical Laboratory Improvement Amendments-approved methylation-specific polymerase chain reaction.ResultsThe combination of TMZ/veliparib statistically significantly extended survival of GBM models (P < .05 by log-rank) compared with TMZ alone in five of 20 MGMT-hypermethylated lines (average extension in median survival = 87 days, range = 20-150 days), while the combination was ineffective in six MGMT-unmethylated lines. In the MGMT promoter-hypermethylated GBM12 line (median survival with TMZ+veliparib = 189 days, 95% confidence interval [CI] = 59 to 289 days, vs TMZ alone = 98 days, 95% CI = 49 to 210 days, P = .04), the profound TMZ-sensitizing effect of veliparib was lost when MGMT was overexpressed (median survival with TMZ+veliparib = 36 days, 95% CI = 28 to 38 days, vs TMZ alone = 35 days, 95% CI = 32 to 37 days, P = .87), and a similar association was observed in two nearly isogenic GBM28 sublines with an intact vs deleted MGMT locus. In comparing DNA damage signaling after dosing with veliparib/TMZ or TMZ alone, increased phosphorylation of damage-responsive proteins (KAP1, Chk1, Chk2, and H2AX) was observed only in MGMT promoter-hypermethylated lines.ConclusionVeliparib statistically significantly enhances (P < .001) the efficacy of TMZ in tumors with MGMT promoter hypermethylation. Based on these data, MGMT promoter hypermethylation is being used as an eligibility criterion for A071102 (NCT02152982), the phase II/III clinical trial evaluating TMZ/veliparib combination in patients with GBM.© The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

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