Escalation portion of phase II study to evaluate the safety, pharmacokinetics, and clinical activity of the PI3K/mTOR inhibitor paxalisib (GDC-0084) in glioblastoma (GBM) with unmethylated O6-methylguanine-methyltransferase (MGMT) promotor status.

Abstract

2550 Background: Paxalisib (previously GDC-0084) is a potent, oral, selective, brain-penetrant, small molecule inhibitor of class I phosphoinositide 3-kinase and mammalian target of rapamycin. The PI3K pathway is upregulated in ~85% of GBM cases and paxalisib has shown efficacy in preclinical models. A phase I study (NCT01547546) investigated paxalisib dosed once daily in 47 patients with recurrent high-grade gliomas and established a maximum tolerated dose (MTD) of 45mg once daily. The current phase Il study aims to explore the safety, tolerability, and clinical activity of paxalisib in newly diagnosed GBM and an unmethylated MGMT promotor following surgery and temozolomide chemoradiation per Stupp regimen. Methods: Part 1 of this study is an open-label, dose-escalation phase to assess the safety, tolerability and MTD. Dose-escalation started at 60mg and progressed in 15mg increments using a 3+3 design. Part 2 is an expansion cohort recruiting 20 patients randomized to administration in fed or fasted states at the MTD. Results: Part 1 is complete and reported here. Nine patients were recruited and an MTD of 60mg was determined. DLTs were hyperglycemia and oral mucositis. AEs were generally reversible and consistent with the PI3K inhibitor class with the most common events were rash, oral mucositis, and fatigue. PK at the MTD was broadly consistent with the data published for the phase 1 study. For eight response-evaluable patients in Part I the median progression-free survival (PFS) was 8.4 months, and 25% of patients remained progression free after 15 months of follow-up. Part 2 is ongoing. Conclusions: A higher MTD of 60mg was identified in newly diagnosed GBM with unmethylated MGMT promotor status than the 45mg MTD previously identified in recurrent high-grade glioma. An encouraging PFS signal is described in this poor-prognosis, unmethylated MGMT patient population. Clinical trial information: NCT03522298 .