Phase Ib/II Study of Pamiparib Plus Radiation Therapy and/or Temozolomide in Adult Patients with Treatment-Naïve or Recurrent/Refractory Glioblastoma

Pamiparib, a small-molecule poly (ADP-ribose) polymerase (PARP) 1/2 inhibitor, demonstrates strong PARP-DNA complex trapping, antitumor activity, and blood-brain barrier penetration. This phase Ib/II dose-escalation study (NCT03150862) investigated pamiparib's tolerability/safety and efficacy when combined with radiotherapy and/or low-dose temozolomide (TMZ) in patients with treatment-naïve (Arms A and B) and recurrent/refractory (Arm C) glioblastoma. The recommended phase II dose for Arm A was pamiparib 60 mg twice daily (BID) for 6 weeks with 6-7 weeks radiotherapy; the recommended dose for Arm C was pamiparib 60 mg BID plus 60 mg TMZ (days 1-7; 28-day cycle). The Arm B escalation cohort completed enrollment; the expansion cohort was not opened. Grade ≥3 treatment-emergent adverse events (TEAEs)/serious TEAEs were observed in 55.0%/36.7% (Arm A), 44.4%/22.2% (Arm B), and 66.0%/38.3% (Arm C) of patients. Disease control and objective response rates were 67.9% and 11.3%, respectively, for treatment-naïve patients in the dose-escalation and -expansion studies, and 40.9% and 13.6%, respectively, for recurrent/refractory patients. Median overall survival for treatment-naïve <i>MGMT</i> unmethylated patients was 12.8 months and 7.3 months for recurrent/refractory <i>MGMT</i> methylated and unmethylated patients. Pamiparib with radiotherapy and/or low-dose TMZ was tolerable for treatment-naïve or recurrent/refractory glioblastoma. Treatment-emergent cytopenia was manageable and reversible with dose reductions/interruptions. Combination regimens demonstrated antitumor activity.