Evaluation of PARP Inhibitor Sensitizing Strategies

The addition of temozolomide (TMZ) during and after radiation therapy improves survival for patients with newly diagnosed glioblastoma and is the current standard of care. However, the survival benefit of temozolomide therapy is limited by the development of TMZ resistance in the majority of patients.

Because of this, there's significant research interest in identifying molecular sensitizing strategies to improve the efficacy of temozolomide.

One promising strategy targeting the repair of TMZ-induced DNA damage is inhibition of poly-ADP-ribose polymerase (PARP).

PARP is indirectly involved in numerous repair pathways, and multiple preclinical studies have demonstrated significant enhancement of TMZ efficacy in various tumor models. Previously published studies suggest that PARP inhibitors disrupt base-excision repair (BER) of TMZ-induced DNA methylation lesions and suggest that essentially all tumors would be sensitized to TMZ by PARP inhibition through disruption of this repair process.

In contrast, in our preliminary studies using paired sensitive parental and derived TMZ-resistant xenograft lines, we demonstrated that the PARP inhibitor ABT-888 effectively sensitizes only tumors that are inherently sensitive to temozolomide.

Aside from potential effects on base-excision repair, PARP has critical functions in post-replication repair (PRR) of stalled replication forks, and from these observations, we hypothesize that PARP inhibitors will enhance the efficacy of TMZ in glioblastoma tumors that are inherently sensitive to TMZ and that disruption of PRR processing of persistent methylation damage is critical to this effect.

These observations have significant clinical implications for the development of PARP inhibitor strategies.

The focus of this application is to test these interconnected hypotheses using TMZ and two structurally distinct PARP inhibitors to optimize clinical development of PARP inhibitor strategies.