Vir Biotechnology Announces First Patient Dosed in Phase 1 Dose-Expansion Cohorts Evaluating PSMA-Targeted PRO-XTEN Dual-Masked T-Cell Engager VIR-5500 In Patients With Metastatic Prostate Cancer
VIR
Published on 04/13/2026 at 03:06 pm EDT
Vir Biotechnology, Inc. announced that the first patient has been dosed in one of three expansion cohorts in the Phase 1 trial evaluating VIR-5500, a prostate-specific membrane antigen (PSMA)-targeted, PRO-XTEN dual-masked T-cell engager (TCE) for metastatic prostate cancer (NCT05997615). The Phase 1 trial is measuring the safety and efficacy of VIR-5500 monotherapy in late-line metastatic castration-resistant prostate cancer (mCRPC), and of VIR-5500 in combination with an androgen receptor pathway inhibitor (ARPI) in early-line mCRPC and metastatic hormone-sensitive prostate cancer (mHSPC). The monotherapy expansion cohort in late-line mCRPC is the first to begin enrollment based on the monotherapy dose-escalation data that showed VIR-5500 has a favorable safety profile and promising anti-tumor activity in mCRPC.
These safety and efficacy data were presented at the 2026 American Society of Clinical Oncology (ASCO) Genitourinary Cancers Symposium in February. Based on these data, the selected dose regimen to be evaluated in this monotherapy expansion cohort is Third Quarter 800/2000/3500 µg/kg step-up dosing. This expansion cohort will measure safety and efficacy, including Prostate-Specific Antigen (PSA) response rate and Objective Response Rate (ORR) in patients with mCRPC who are refractory following treatment with multiple prior lines of therapy including at least one second-generation ARPI and one taxane regimen in addition to standard-of-care radioligand-based therapy.
Dose-escalation of VIR-5500 in combination with enzalutamide continues in early-line mCRPC patients. The Company anticipates dosing of first patients in the combination dose-expansion cohorts in both early-line mCRPC and mHSPC over the coming months, followed by pivotal Phase 3 trials in 2027.