Discordant <i>In Vitro</i> and <i>In Vivo</i> Chemopotentiating Effects of the PARP Inhibitor Veliparib in Temozolomide-Sensitive versus -Resistant Glioblastoma Multiforme Xenografts

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.