Identification and Therapeutic Potential of AT1636: A Novel Antibody Targeting O-Mannosylated E-Cadherin Variant in Colon Cancer

The research focused on colorectal cancer (CRC) linked to Lynch syndrome, which is known for its high lymphocyte infiltration. A study was conducted to identify if antibodies with therapeutic potential could be extracted from patients with this condition. A patient who had overcome stage IV colon cancer and Lynch syndrome was selected for B-cell repertoire analysis, leading to the discovery of an antibody, AT1636, that targets an unrecognized O-mannosylated form of E-cadherin weighing 70kDa. E-cadherin's role in intercellular interactions is crucial for preventing cancer metastasis, and its dysregulation is a key feature of epithelial-mesenchymal transition (EMT).

The project was approved by the Medical Ethical Committee in Amsterdam, Netherlands. The BCL6 and Bcl-xL immortalization technique was utilized to explore the human antibody repertoire. Peripheral-blood memory B cells were collected from a patient with a pathogenic variant in the MSH6 gene, who had been diagnosed with stage IV CRC and liver metastasis, and had undergone treatment with avastin, capecitabine, and oxaliplatin. Nine years post-treatment, antibodies were screened for their binding to three distinct CRC cell lines and their lack of binding to fibroblasts through flow cytometry.

AT1636 was found to recognize the O-mannosylated E-cadherin variant (ECV), which, while present in all full-length E-cadherin expressing cells, shows tumor-specific binding based on the O-mannosylation pattern. The antibody's binding was determined to rely on the transmembrane O-mannosyltransferase targeting cadherins 3 (TMTC3), as demonstrated through shRNA knock-down. The coexistence of TMTC3 and E-cadherin in tumor cells was shown to be indicative of AT1636 binding. Moreover, the presence of ECV was linked to a strong de-adhesive, EMT-like phenotype.

Although AT1636 alone does not induce antibody-dependent cellular cytotoxicity (ADCC), a CD3-bispecific antibody format of AT1636 was found to effectively eliminate CRC cell lines. The study concludes that the AT1636 antibody, derived from a Lynch syndrome patient, binds to a previously unknown cancer-specific O-mannosylated form of E-cadherin, which could be implicated in tumor invasion and metastasis. The findings provide a basis for the development of AT1636-based therapeutics for CRC treatment.