Niraparib efficacy in patients with newly-diagnosed glioblastoma: Clinical readout of a phase 0/2 "trigger" trial.

2002 Background: Poly (ADP-ribose) polymerase (PARP) mediates DNA damage response; niraparib is an investigational PARP1/2-selective inhibitor. This Phase 0 study evaluates newly-diagnosed glioblastoma (GBM) tumor pharmacokinetics (PK) and pharmacodynamics (PD), graduating patients with O6-methylguanine methyltransferase (MGMT) unmethylated tumors into a therapeutic regimen of niraparib plus fractionated radiotherapy when PK threshold is met. Methods: Presumed newly-diagnosed GBM patients received 4 days of niraparib (300/200 mg QD) prior to planned resection 3-5 (cohort 1) or 8-10 hours (cohort2) following the last dose. Tumor tissue (Gadolinium enhancing and non-enhancing regions), cerebrospinal fluid (CSF), and plasma were collected. Total and unbound niraparib concentrations were measured using validated LC-MS/MS methods. PARP inhibition was assessed by quantification of PAR induction after ex vivo irradiation of surgical vs non-irradiated tissue. A PK ‘trigger’ determined eligibility for the Phase 2 component of the study and was defined as unbound niraparib > 5-fold biochemical IC50 (i.e., 19 nM) in non-enhancing tumor. Patients with MGMT unmethylated tumors in excess of the PK threshold were eligible for Phase 2 dosing of niraparib plus radiotherapy followed by a maintenance phase of niraparib monotherapy. Results: All Phase 0 patients (n=46) met the PK threshold. In non-enhancing tumor regions, the mean unbound concentration of niraparib was 335.1 nM (n=43) for cohort 1 and 331.9 nM (n=3) for cohort 2. PAR suppression after ex vivo radiation was observed in 73% of the patients (24/33). Nineteen of 27 (70.3%) patients with unmethylated tumors were enrolled into Phase 2. Five patients in Phase 2 experienced Grade 4 thrombocytopenia related to niraparib. All adverse events resolved without sequelae. At time of data cutoff, median progression-free survival was 11.7 months. Mature overall survival (OS) data will be reported for the first time. Conclusions: Niraparib achieves pharmacologically relevant concentrations in non-enhancing, newly-diagnosed GBM tissue in excess of any other studied PARP inhibitor. Accompanying PD effects were observed in patient tumor tissue. For the first time, we report on the clinical efficacy of the study. A global Phase 3, open-label, randomized 2-arm study comparing niraparib versus temozolomide in adult patients with newly diagnosed, MGMT unmethylated glioblastoma is being planned. Clinical trial information: NCT05076513 .