CytomX Therapeutics announced that the first patient has been dosed with CX-801 in combination with KEYTRUDA (pembrolizumab), Merck’s anti-PD-1 therapy. This milestone occurred in the ongoing Phase 1 dose escalation study (NCT06462794) evaluating safety and initial clinical activity in patients with metastatic melanoma. The combination arm was initiated following the successful clearance of the first three CX-801 monotherapy dose escalation cohorts.
CX-801 is a dually masked interferon alpha-2b PROBODY cytokine, specifically designed to localize the immune-stimulating properties of Interferon alpha-2b to tumors while reducing systemic toxicities. This conditional activation aims to enable combination strategies with checkpoint inhibitors like KEYTRUDA, which has been limited by the poor tolerability of unmasked interferon alpha-2b.
The initiation of this combination therapy marks a significant step in advancing CX-801, a key asset in CytomX's pipeline, and leverages its clinical collaboration with Merck. Initial Phase 1a translational and biomarker data for CX-801 in advanced melanoma are expected in the second half of 2025.
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