Phase 2 study of bizaxofusp, an IL-4R targeted toxin payload, in nonresectable recurrent GBM: Comparison of overall survival with contemporaneous eligibility-matched and propensity score balanced external control arm.

Abstract

2079 Background: Bizaxofusp (MDNA55) is designed to selectively deliver a potent toxin payload to tumor cells by targeting the IL-4 receptor (IL-4R) overexpressed by GBM, but not normal brain. Localized delivery of bizaxofusp minimizes risk of off-target toxicities and systemic exposure while eliciting effective tumor cell killing. Bizaxofusp was evaluated using convection-enhanced delivery in MDNA55-05 (NCT02858895), a single-arm, open-label, multi-center Ph2 study in nonresectable recurrent GBM (rGBM). Methods: The study population comprised of de novo IDH wild-type GBM patients with 1 st or 2 nd relapse that were non-resectable. Forty-four patients were administered a single treatment of bizaxofusp (range: 18-240 μg). The primary endpoint was OS; secondary endpoints were safety and tumor response. IL-4R expression in tumor biopsies was determined using a validated assay. OS was compared to an eligibility matched external control arm (emECA) of 81 contemporaneous rGBM subjects receiving standard of care. The emECA was further refined by propensity-score balancing (pbECA) to the bizaxofusp arm based on known prognostic factors, resulting in a weighted sample size of 40.8. OS was defined as time from relapse (to unify index date in both arms) or treatment start (for analysis of tumor response) to death/censor. Tumor response was assessed following RANO and mRANO criteria. Results: Bizaxofusp showed an acceptable safety profile at doses up to 240 μg. TRAEs were primarily neurological or aggravation of pre-existing neurological deficits associated with GBM and were manageable with standard measures. Results showed that IL-4R expression did not impact mOS except in patients receiving low doses of bizaxofusp. The bizaxofusp arm had significantly longer median OS (mOS) than contemporaneous emECA (12.4 vs 7.7 months; HR: 0.64, 95% CI 0.46-0.93; p = 0.02). Survival benefit was also evident when compared to the pbECA: (12.4 vs 7.2 months; HR: 0.72, 95% CI 0.46-1.1; p = 0.27). Patients with tumor control (SD or PR/CR, n=21) had significantly longer mOS than patients with tumor progression (n=23) (16.7 vs 8.5 months; HR = 0.5, 95% CI 0.27-0.9; p = 0.01). Among patients with tumor control who had pseudoprogression (PsP) per mRANO, mOS (22.8 months) was significantly longer than patients with tumor progression (HR: 0.49, 95% CI 0.25-0.98; p = 0.049). Conclusions: Bizaxofusp achieved significant OS benefit in patients with nonresectable rGBM compared to contemporaneous emECA. Patients who experienced tumor control, including those with PsP, showed significantly longer survival than patients with tumor progression. Phase 3 ready registrational trial will comprise a high dose bizaxofusp arm and a hybrid control arm with 1/3 randomized subjects and 2/3 pmECA. Clinical trial information: NCT02858895 .