Delineation of MGMT Hypermethylation as a Biomarker for Veliparib-Mediated Temozolomide-Sensitizing Therapy of Glioblastoma.

Sensitizing 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. The 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. The 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. Veliparib 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.

Gupta SK ，Kizilbash SH ，Carlson BL ，Mladek AC ，Boakye-Agyeman F ，Bakken KK ，Pokorny JL ，Schroeder MA ，Decker PA ，Cen L ，Eckel-Passow JE ，Sarkar G ，Ballman KV ，Reid JM ，Jenkins RB ，Verhaak RG ，Sulman EP ，Kitange GJ ，Sarkaria JN ... -  《-》

Discordant in vitro and in vivo chemopotentiating effects of the PARP inhibitor veliparib in temozolomide-sensitive versus -resistant glioblastoma multiforme xenografts.

Effective sensitizing strategies potentially can extend the benefit of temozolomide (TMZ) therapy in patients with glioblastoma (GBM). We previously demonstrated that robust TMZ-sensitizing effects of the [poly (ADP-ribose) polymerase] (PARP) inhibitor veliparib (ABT-888) are restricted to TMZ-sensitive GBM xenografts. The focus of this study is to provide an understanding for the differential sensitization in paired TMZ-sensitive and -resistant GBM models. The impact of veliparib on TMZ-induced cytotoxicity and DNA damage was evaluated in vitro and in vivo in models of acquired TMZ resistance (GBM12TMZ-mgmt(High), GBM12TMZ-mgmt(Low), and U251TMZ), inherent TMZ resistance (T98G), and TMZ-sensitive (U251 and GBM12). In vivo drug efficacy, pharmacokinetics, and pharmacodynamics were analyzed using clinically relevant dosing regimens. Veliparib enhanced TMZ cytotoxicity and DNA-damage signaling in all GBM models in vitro with more pronounced effects in TMZ-resistant lines at 3 to 10 μmol/L veliparib. In vivo, combined TMZ/veliparib, compared with TMZ alone, significantly delayed tumor growth and enhanced DNA-damage signaling and γH2AX levels in the sensitive GBM12 xenograft line but not in the resistant GBM12TMZ lines. The pharmacokinetic profile of veliparib was similar for GBM12 and GBM12TMZ tumors with Cmax (∼1.5 μmol/L) in tissue significantly lower than concentrations associated with optimal in vitro sensitizing effects for resistant tumors. In contrast, robust suppression of PARP-1 expression by shRNA significantly increased TMZ sensitivity of U251TMZ in vitro and in vivo. In vitro cytotoxicity assays do not adequately model the therapeutic index of PARP inhibitors, as concentrations of veliparib and TMZ required to sensitize TMZ-resistant cancer cells in vivo cannot be achieved using a tolerable dosing regimen.

Gupta SK ，Mladek AC ，Carlson BL ，Boakye-Agyeman F ，Bakken KK ，Kizilbash SH ，Schroeder MA ，Reid J ，Sarkaria JN ... -  《-》

Efficacy of protracted temozolomide dosing is limited in MGMT unmethylated GBM xenograft models.

Cen L ，Carlson BL ，Pokorny JL ，Mladek AC ，Grogan PT ，Schroeder MA ，Decker PA ，Anderson SK ，Giannini C ，Wu W ，Ballman KV ，Kitange GJ ，Sarkaria JN ... -  《-》

Evaluation of MGMT promoter methylation status and correlation with temozolomide response in orthotopic glioblastoma xenograft model.

Kitange GJ ，Carlson BL ，Mladek AC ，Decker PA ，Schroeder MA ，Wu W ，Grogan PT ，Giannini C ，Ballman KV ，Buckner JC ，James CD ，Sarkaria JN ... -  《-》

Effect of lomeguatrib-temozolomide combination on MGMT promoter methylation and expression in primary glioblastoma tumor cells.

Taspinar M ，Ilgaz S ，Ozdemir M ，Ozkan T ，Oztuna D ，Canpinar H ，Rey JA ，Sunguroğlu A ，Castresana JS ，Ugur HC ... -  《-》