CytomX Begins Dosing in Phase 1 Trial of CX-801 and KEYTRUDA for Metastatic Melanoma

SOUTH SAN FRANCISCO, CA, USA I May 19, 2025 I CytomX Therapeutics, Inc., a leader in developing specialized biologics, has begun a new phase in cancer treatment research. They have initiated dosing the first patient with CX-801 in combination with KEYTRUDA® (pembrolizumab), Merck's renowned anti-PD-1 therapy, as part of an ongoing Phase 1 clinical trial. This study aims to assess the safety and initial effectiveness of this combination in individuals with metastatic melanoma, a form of skin cancer that has spread to other parts of the body.

The drug CX-801 is a uniquely designed interferon (IFN) alpha-2b PROBODY® cytokine. CytomX has engineered this compound to exploit the immune-stimulating characteristics of Interferon alpha-2b while addressing its limitations. Historically, Interferon alpha-2b has shown cancer-fighting abilities across various cancers, including melanoma, but its broad use has been restricted due to severe systemic side effects. CX-801 aims to focus the therapeutic effects of IFN alpha-2b directly on tumors, thereby minimizing widespread toxicities and facilitating its use in combination therapies.

The latest step in CytomX's research entails a targeted Phase 1 dose escalation study of CX-801 specifically for metastatic melanoma. The study's combination arm, which pairs CX-801 with KEYTRUDA®, has progressed following the successful completion of the initial monotherapy dose escalation stages.

Dr. Wayne Chu, M.D., Chief Medical Officer of CytomX Therapeutics, expressed optimism about the potential of this new treatment approach. According to Dr. Chu, the combination therapy could significantly benefit patients who do not respond to PD-1 treatment, addressing a critical unmet need. He highlighted the proprietary technology of CytomX, which allows them to maintain drug potency while expanding the therapeutic index of interferon. This technology positions CX-801 as an ideal candidate for use alongside KEYTRUDA® in immuno-oncology treatments. Dr. Chu also anticipates releasing initial Phase 1a data related to translational and biomarker studies in advanced melanoma later in 2025.

CytomX Therapeutics is a biopharmaceutical company at the forefront of oncology, focusing on creating innovative conditionally activated biologics that concentrate their effects on the tumor environment. Their cutting-edge PROBODY® platform underpins their vision of developing safer and more effective cancer treatments. The company's pipeline is diverse, featuring candidates across various treatment strategies, including antibody-drug conjugates (ADCs), T-cell engagers, and immune modulators like cytokines.

Notably, CytomX's clinical-stage offerings include CX-2051 and CX-801. CX-2051 is a conditionally activated ADC targeting the epithelial cell adhesion molecule (EpCAM), equipped with a topoisomerase-1 inhibitor. This candidate is relevant to multiple epithelial cancers expressing EpCAM, such as colorectal cancer (CRC), and was developed in partnership with ImmunoGen. Meanwhile, CX-801 is recognized for its broad applicability in both traditionally immune-responsive and less responsive tumors.

CytomX has built strategic partnerships with several oncology industry leaders, including Amgen, Astellas, Bristol Myers Squibb, Regeneron, and Moderna. Through these collaborations, CytomX is advancing its mission to establish conditionally activated treatments as a new standard in cancer care.