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News|Articles|October 9, 2026
FDA grants fast track designation to VIR-5500 for mCRPC
Author(s)Hannah Clarke
Fact checked by: Benjamin P. Saylor, Strategic Content Lead
VIR-5500 is a PSMA-targeted PRO-XTEN dual-masked T-cell engager entering phase 3 development for prostate cancer.
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The FDA has granted fast track designation to VIR-5500, an investigational prostate-specific membrane antigen (PSMA)-targeted PRO-XTEN dual-masked T-cell engager under development for late-line metastatic castration-resistant
Fast track designation is granted to investigational therapies that are intended to treat or prevent serious or life-threatening conditions and have the potential to address an unmet medical need. With this designation, the development process for VIR-5500 can benefit from more frequent engagement with the FDA and eligibility for accelerated approval and priority review.
VIR-5500 is being co-developed by Astellas Pharma and Vir Biotechnology.
“People living with advanced prostate cancer need new treatment options that can offer meaningful and durable benefit,” said Moitreyee Chatterjee-Kishore, executive vice president and head of oncology development, Astellas, in the news release.1 “This Fast Track designation reinforces the importance of advancing VIR-5500 with urgency, and we are committed to exploring its potential to make a meaningful difference for patients and their families.”
Data on VIR-5500
VIR-5500 is being evaluated in an open-label, nonrandomized phase 1 study (NCT05997615) designed to assess its safety, pharmacokinetics, and preliminary efficacy. The trial includes 6 dose-expansion cohorts.
The monotherapy cohorts are evaluating VIR-5500 in patients with mCRPC who are taxane-naïve, radioligand therapy-naïve, or previously exposed to radioligand therapy. Combination cohorts are assessing VIR-5500 with enzalutamide (Xtandi) in earlier-line mCRPC, with docetaxel in earlier-line mCRPC, and with darolutamide (Nubeqa) in metastatic hormone-sensitive prostate cancer.
Preliminary data from the phase 1 trial were presented at the 2026 ASCO Genitourinary Cancers Symposium in San Francisco, California.2 The study included patients with advanced mCRPC whose disease had progressed following multiple lines of therapy (median, 4 prior lines). A substantial portion of patients also presented with high tumor burden, with visceral metastases reported in nearly 50% of patients.
Overall, treatment was well tolerated, with no dose-limiting toxicities reported. Grade 3 or higher treatment-related adverse events occurred in 12% of patients and were considered manageable. Cytokine release syndrome (CRS) was observed in 50% of patients, but was predominantly grade 1 and did not require routine prophylactic steroids.
Efficacy data were reported from the highest-dose cohorts (3000 µg/kg or higher every 3 weeks; n = 22 of 58). Among prostate-specific antigen (PSA)-evaluable patients, PSA declines of at least 50% were observed in 82% (14 of 17) of patients, and PSA declines of at least 90% were reported in 53% (9 of 17) of patients. In RECIST-evaluable patients, the objective response rate was 45% (5 of 11), including confirmed responses in most responders (4 of 5).
According to Vir Biotechnology, phase 3 trials of VIR-5500 are expected to begin in 2027.
“Receiving Fast Track designation reflects the potential of VIR-5500 to address an area of serious unmet need in late-line mCRPC and the strong momentum we have achieved with Astellas as we prepare to enter pivotal phase 3 development in 2027,” said Marianne De Backer, president and CEO of Vir Biotechnology, in the news release.1 “We look forward to working with the FDA to rapidly advance the development of VIR-5500 for people living with mCRPC.”
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REFERENCES
1. Vir Biotechnology announces PSMA-targeted PRO-XTEN® dual-masked T-cell engager VIR-5500 received FDA Fast Track Designation for the treatment of prostate cancer. News release. Vir Biotechnology, Inc. October 8, 2026. Accessed October 9, 2026.
2.Vir Biotechnology reports positive updated phase 1 results for PSMA-targeting, PRO-XTEN dual-masked T-cell engager VIR-5500 in patients with metastatic prostate cancer. News release. Vir Biotechnology. February 23, 2026. Accessed October 9, 2026.
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