Novel monoclonal antibody L2A5 specifically targeting sialyl-Tn and short glycans terminated by alpha-2–6 sialic acids

Incomplete O-glycosylation is a feature associated with malignancy resulting in the expression of truncated glycans such as the sialyl-Tn (STn) antigen. Despite all the progress in the development of potential anti-cancer antibodies, their application is frequently hindered by low specificities and cross-reactivity. In this study, a novel anti-STn monoclonal antibody named L2A5 was developed by hybridoma technology. Flow cytometry analysis showed that L2A5 specifically binds to sialylated structures on the cell surface of STn-expressing breast and bladder cancer cell lines. Moreover, immunoblotting assays demonstrated reactivity to tumour-associated O-glycosylated proteins, such as MUC1. Tumour recognition was further observed using immunohistochemistry assays, which demonstrated a high sensitivity and specificity of L2A5 mAb towards cancer tissue, using bladder and colorectal cancer tissues. L2A5 staining was exclusively tumoural, with a remarkable reactivity in invasive and metastasis sites, not detectable by other anti-STn mAbs. Additionally, it stained 20% of cases of triple-negative breast cancers, suggesting application in diseases with unmet clinical needs. Finally, the fine specificity was assessed using glycan microarrays, demonstrating a highly specific binding of L2A5 to core STn antigens and additional ability to bind 2–6-linked sialyl core-1 probes. In conclusion, this study describes a novel anti-STn antibody with a unique binding specificity that can be applied for cancer diagnostic and future development of new antibody-based therapeutic applications.

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This work was supported by the Bluepharma innovation award "Trifunctional antibodies and dendritic cell-based technologies: a combined approach to cancer immunotherapy" 2013 and the Scientific merit prize Santander - Totta - Lisbon New University - "Antibody engineering for breast cancer therapy" 2013. LRL is supported by the grant PD/BD/52476/2013 from the Portuguese Foundation for Science and Technology (FCT). The work is partially supported by FCT-MCTES through the grants IF/00033/2012 (ASP), SFRH/BPD/101827/2014 (LL) and SFRH/BPD/111048/2015 (JAF), the Wellcome Trust Biomedical Resource grant (WC) and the NSFC-Shandong Joint Fund (U1606403) (CL). The authors also acknowledge FCT funding for CI-IPOP research unit (PEst-OE/SAU/UI0776/201). co-financed by the European Regional Development Fund under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007728). FCT is co-financed by European Social Fund (ESF) under Human Potential Operation Programme (POPH) from National Strategic Reference Framework (NSRF). The funders did not play a role in the study design, data collection or decision to publish.