Mucin 16 (MUC16) (MUC16)

Mucin 16 (MUC16), widely known as the ovarian cancer antigen CA-125, is a massive type I transmembrane glycoprotein primarily expressed on the surface of corneal, bronchial, and reproductive tract epithelia (UniProt: Q8WXI7). In malignancies, particularly epithelial ovarian cancer, MUC16 is overexpressed and plays a pivotal role in tumor progression, immune evasion, and metastasis through its interaction with mesothelin (Bast et al., 2011). The protein undergoes proteolytic cleavage at a juxtamembrane site, releasing a large N-terminal portion (CA-125) into the circulation, while a C-terminal fragment—comprising a portion of the extracellular domain, the transmembrane domain, and a cytoplasmic tail—remains anchored to the tumor cell surface (Chekmasova et al., 2010). This retained ectodomain is a highly attractive therapeutic target because, unlike the shed CA-125, it is not present in high concentrations in the blood, reducing the risk of antigen sink effects where circulating antigens neutralize the drug before it reaches the tumor (Crawford et al., 2019). Beyond its role as a physical barrier, MUC16 contributes to oncogenic signaling by modulating the Wnt/beta-catenin and JAK/STAT pathways, which enhances cell proliferation and survival. The interaction between the MUC16 ectodomain and mesothelin on peritoneal surfaces is a key driver of the peritoneal dissemination of ovarian cancer cells. Targeting the membrane-proximal region of MUC16 allows for the development of potent immunotherapies, such as bispecific antibodies like Ubamatamab and CAR-T cells, that can selectively eliminate cancer cells while overcoming the immunosuppressive tumor microenvironment. However, challenges remain, including the potential for off-target effects on normal mesothelial tissues and the management of cytokine release syndrome in T-cell engaging modalities.

Other names

CA-125Cancer antigen 125MUC-16Ovarian cancer-related tumor marker CA125FLJ14303

Drugs targeting the MUC16 retained ectodomain typically utilize bispecific antibody formats to engage T-cells (e.g., CD3 binding) or antibody-drug conjugates (ADCs) to deliver cytotoxic payloads directly to the tumor cell. By focusing on the membrane-proximal region, these agents avoid sequestration by the shed CA-125 antigen found in the circulation of cancer patients (Crawford et al., 2019).