Despite available therapies, patients with non-muscle-invasive bladder cancer (NMIBC) are impacted by recurrence and progression risk. Bel-sar (belzupacap sarotalocan) is a first-in-class virus-like drug conjugate composed of a tumor-targeting virus-like particle linked to a photoactivatable dye, inducing proimmunogenic tumor cell death and antitumor immune response. We report clinical and exploratory immune biomarker data from a phase 1 study in intermediate-risk and high-risk NMIBC.
Seventeen participants received focally injected bel-sar (100-200 µg) without (n = 5) or with (n = 12) light activation, followed by transurethral resection of bladder tumor (TURBT; 7-12 d later). Safety, feasibility, tolerability, and preliminary efficacy were assessed. Multiplex immunofluorescence was performed on paired tumor specimens from five responders receiving light-activated bel-sar.
Bel-sar was well tolerated, with only grade 1 adverse events, and no grade ≥2, serious, or dose-limiting toxicities. Among 10 efficacy-evaluable patients receiving light activation, four of five low-grade tumors achieved complete response. Responses were also observed in high-grade and untreated tumors, suggesting a urothelial field effect. Immune profiling demonstrated conversion of immune-cold or exhausted tumors into immunogenically primed tumors, with tertiary lymphoid structure formation, expansion of cytotoxic and memory CD4+ T cells, and marked natural killer cells and eosinophils recruitment. Limitations include the small sample size and short follow-up.
Bel-sar demonstrated focal administration feasibility, a favorable safety profile, and encouraging preliminary efficacy in NMIBC, with robust immune activation in treated and untreated tumors. These findings support bel-sar's continued development as a therapy combining local tumor eradication with durable immune surveillance.
European urology open science. 2026 Jun 13*** epublish ***
Jennifer Linehan, Piyush K Agarwal, Xianne Penny, Max Kates, Joseph Jacob, Seth P Lerner, Rhonda C Kines, John T Schiller, Elisabet de Los Pinos, Neal D Shore, Jill Hopkins, Joseph McQuaid, Sabine D Brookman-May
John Wayne Cancer Institute, Santa Monica, USA., University of Chicago, Chicago, USA., Aura Biosciences, Boston, USA., Johns Hopkins School of Medicine, Baltimore, USA., SUNY Upstate Medical University, Syracuse, USA., Baylor College of Medicine, Houston, USA., START Carolinas/Carolina Urologic Research Center, Myrtle Beach, USA.