On October 8, 2026 Vir Biotechnology, Inc. (Nasdaq: VIR) reported that the U.S. Food and Drug Administration (FDA) granted Fast Track designation to VIR-5500, a PSMA-targeted PRO-XTEN dual-masked T-cell engager (TCE), for the treatment of late-line metastatic castration-resistant prostate cancer (mCRPC). VIR-5500 is being co-developed by Astellas Pharma Inc. and Vir Biotechnology through a global strategic collaboration.

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"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 Chief Executive Officer of Vir Biotechnology. "We look forward to working with the FDA to rapidly advance the development of VIR-5500 for people living with mCRPC."

"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. "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."

FDA Fast Track designation is intended to facilitate and expedite the development and review of drugs to treat serious conditions and fill an unmet need.

VIR-5500 is being evaluated in a Phase 1 study across six dose-expansion cohorts. The monotherapy dose-expansion cohorts include patients with taxane naïve mCRPC, radioligand therapy naïve mCRPC and radioligand therapy exposed mCRPC. The combination regimen dose-expansion cohorts include VIR-5500 in combination with enzalutamide in early-line mCRPC, VIR-5500 in combination with docetaxel in early-line mCRPC and VIR-5500 in combination with darolutamide in metastatic hormone sensitive prostate cancer (mHSPC). Phase 1 data reported earlier this year showed VIR-5500 was generally well tolerated and exhibited promising anti-tumor activity in patients with mCRPC. Phase 3 trials are anticipated to begin in 2027.

About VIR-5500

T-cell engagers (TCEs) are powerful anti-tumor agents that can direct the immune system, specifically T-cells, to destroy cancer cells. VIR-5500 is an investigational PRO-XTEN dual-masked TCE currently being evaluated in an open-label, non-randomized Phase 1 clinical trial (NCT05997615) designed to assess the safety, pharmacokinetics and preliminary efficacy in participants with metastatic castration-resistant prostate cancer (mCRPC).

VIR-5500 combines a bispecific PSMA and CD3 binding TCE with the PRO-XTEN masking technology. The PRO-XTEN masking technology is designed to keep the TCEs inactive (or masked) until they reach the tumor microenvironment, where tumor-specific proteases cleave off the mask and activate the TCEs, enabling killing of cancer cells by T-cells. By confining the activity to the tumor microenvironment, we aim to circumvent the traditionally high toxicity associated with unmasked TCEs and increase their efficacy and tolerability. Additionally, the mask is designed to help drug candidates stay in the bloodstream longer in their inactive form, allowing them to better reach the site of action and potentially allowing for less frequent dosing regimens.

About PRO-XTEN Dual-masked T-cell Engagers (TCEs)

T-cell engagers (TCEs) are powerful anti-tumor agents designed to direct the immune system, specifically T-cells, to destroy cancer cells. TCEs have become an important treatment option for blood cancers, but their usage in solid tumors has been limited due to toxicity. The universal PRO-XTEN masking technology is designed to extend the half-life of the molecule and to keep TCEs inactive (or masked) until they reach the tumor microenvironment, where tumor-specific proteases cleave off the mask and activate the TCEs, leading to killing of cancer cells by T-cells. By extending the half-life and confining activity to the tumor microenvironment, the PRO-XTEN technology could limit toxicity, widen the therapeutic index of TCEs, and potentially enable less frequent dosing regimens.

About Advanced Prostate Cancer

Prostate cancer remains a significant global health burden, representing the second leading cause of cancer-related mortality in men behind lung cancer.1 While diagnostic and therapeutic advances like androgen-directed therapy can improve outcomes in earlier settings, most patients ultimately relapse and develop metastatic hormone sensitive prostate cancer (mHSPC).2 mHSPC is characterized by its responsiveness to intensified hormonal interventions designed to reduce androgen levels or block their action. The majority of these patients eventually progress to metastatic castration-resistant prostate cancer (mCRPC).3 This stage is associated with poor clinical outcomes, including limited durability of existing therapies, with a 5-year survival rate of approximately 30%.4 There is a critical need for safer, more effective and precisely targeted therapies capable of improving long term disease control and quality of life across the prostate cancer continuum.

(Press release, Vir Biotechnology, OCT 8, 2026, View Source [SID1234673294])