Vir Biotechnology, Inc. has released encouraging safety and efficacy data from ongoing dose escalation trials for two of its dual-masked T-cell engagers (TCEs): Vir-5818 and Vir-5500. The preliminary results show promising clinical response signals in heavily pretreated patients with various solid tumors.
For Vir-5818, in patients receiving doses ≥400 µg/kg, tumor shrinkage was observed in 50% (10/20) of participants with various HER2-expressing cancers. Additionally, confirmed partial responses were seen in 33% (2/6) of participants with HER2-positive colorectal cancer (CRC).
On the other hand, Vir-5500 showed significant prostate-specific antigen (PSA) declines in 100% (12/12) of participants, with a confirmed PSA50 response in 58% (7/12) of metastatic castration-resistant prostate cancer (mCRPC) patients at the first step dose ≥120 µg/kg.
The safety profile for both Vir-5818 and Vir-5500 is promising, with the maximum tolerated dose (MTD) not yet reached for either TCE, and no dose-limiting cytokine release syndrome (CRS) observed. The initial clinical data also demonstrate the potential of the Pro-Xten™ masking technology to lead to minimal systemic unmasking and unlock an expanded therapeutic index.
Vir Biotechnology's Chief Executive Officer, Marianne De Backer, expressed optimism about the preliminary safety and efficacy data, stating that these candidates may enable efficacious and well-tolerated treatment regimens, potentially improving outcomes for people living with a range of solid tumors.
For Vir-5818, early efficacy data indicate that 50% of participants receiving doses ≥400 µg/kg experienced dose-dependent tumor shrinkage across multiple HER2-positive tumor types. In the case of Vir-5500, early efficacy data show encouraging signs of PSA responses, with PSA reductions observed in 100% of participants after an initial dose ≥120 µg/kg, and a PSA50 response confirmed in 58% of participants at the same dose.
Both Vir-5818 and Vir-5500 demonstrated a promising safety profile, with no dose-limiting toxicities observed up to 1000 µg/kg without prophylactic corticosteroids.
The safety and tolerability profile observed for Vir-5500 in ongoing dose escalation, together with the observed signs of early anti-tumor activity at low doses, may enable a wide therapeutic index.
Vir-5818, Vir-5500, and Vir-5525 are investigational, clinical candidates leveraging the Pro-Xten™ masking technology with three different TCEs targeting HER2, PSMA, and EGFR, respectively. These assets aim to increase efficacy and tolerability by directing the activity exclusively to the tumor microenvironment, potentially allowing less frequent dosing regimens for patients and clinicians. As a result of these announcements, the company's shares have moved 74.7% on the market, and are now trading at a price of $13.78. For the full picture, make sure to review Vir Biotechnology's 8-K report.
