Abstract
Napabucasin is an orally-administered NQO1–bioactivatable investigational agent hypothesized to affect multiple oncogenic cellular pathways including STAT3. This open-label, multicenter, phase 1b/2 study assessed napabucasin plus temozolomide for recurrent/progressive GBM. Phase 1b objectives were safety/tolerability, recommended phase 2 dose (primary), preliminary antitumor activity, and pharmacokinetics/pharmacodynamics (secondary). Phase 2 objectives were preliminary antitumor activity via 6-month progression-free survival (PFS-6 [20% projected]) (primary); disease control rate; median PFS; objective response rate (ORR); and overall survival (OS) (secondary). Arm A enrolled repeat surgical resection candidates; arm B enrolled patients ineligible for further resection. Patients received napabucasin (oral, 480 mg twice-daily) plus temozolomide (150 mg/m2, days 1–5, 28-day cycles). Arm A closed after 4 patients enrolled to prioritize Arm B enrollment. Arm B data are reported. Arm B enrolled/treated 30 patients (median age=56.5 [range=19–83] years; median napabucasin duration=55.0 [range=1–743] days; previous temozolomide=22 [73.3%] patients); all stopped therapy (radiologic progressive disease [PD], n=20; clinically unacceptable toxicities, n=7; follow-up loss, n=2; clinical PD, n=1). Mean relative dose intensity was 67.2% for napabucasin and 90.9% for temozolomide; 14/30 (46.7%) and 25/30 (83.3%) patients received ≥ 90% intended napabucasin and temozolomide doses, respectively. All patients reported ≥ 1 treatment-emergent adverse event (TEAE, grade ≤4); grade 3 TEAEs (≥ 10% patients) were diarrhea (23.3%, 7/30) and abdominal pain (16.7%, 5/30). One patient reported a grade 4 TEAE (seizure, treatment unrelated). PFS-6 was 28.1% (80% CI=16.8%-40.5%). Median PFS was 1.9 months (95% CI=1.8–3.3), with PFS-12 and PFS-18 both 16.8% (80% CI=7.8%-28.8%). ORR was 10% (95% CI=2.1%-26.5%), with 3 partial responses, 6 stable disease, 14 PD, and 7 patients not evaluated. OS-12 was 28.3%. The napabucasin-plus-temozolomide safety profile was consistent with that anticipated for each agent. Napabucasin (480 mg twice-daily) was associated with grade 3 diarrhea and suboptimal compliance. Antitumor effects were observed per the primary endpoint in this patient population.