Abstract 3429: Improving druggability of a promising tumor target by the novel glycosylation-dependent mAb GT-008 for treatment of solid tumors

Aberrant O-glycosylation is a hallmark of cancer and can be used to improve druggability of targets for cancer immunotherapy. Tumors express cell surface proteins decorated with truncated O-glycans like Thomsen-Friedenreich (TF), Thomsen-nouveau (Tn) or sialylated Tn (sTn) antigens, which are virtually absent from normal tissues. Development of therapeutic mAbs against these hapten glycotopes is often hampered by weak affinities and low specificity, whereas peptide epitope targeting mAbs usually cannot distinguish between normal and tumor tissue. Both drawbacks can be circumvented by addressing combined protein/carbohydrate epitopes with mAbs that enable high affinity binding and high tumor specificity at the same time. We generated mAb GT-008 recognizing the glycoprotein CD24 with fundamental role in tumorigenesis and tumor progression, which is expressed on solid tumors, but also on healthy immune cells and tissues. GT-008 binds CD24 only in presence of a tumor-associated glycosylation thereby leading to reduced binding of the protein expressed on healthy cells.GT-008 was generated by immunization and single B cell cloning using different on- and off-target glycoforms for selection and screening. Binding and tumor selectivity were analyzed by ELISA, flow cytometry and immunohistochemistry on healthy and tumor tissues. Functionality was investigated by in vitro internalization and cytotoxicity assays with tumor and healthy cells. Compared to a conventional glycosylation-independent control antibody, GT-008 binds the protein target only in presence of TF O-glycosylation, but not the non-glycosylated protein, other glycoproteins carrying TF nor a synthetic TF O-glycoconjugate. GT-008 differentiates against the sialylated glycoform present on normal tissues. This leads to reduced binding to healthy human immune cells and tissues compared to the control mAb, whereas binding to cancer tissues from different indications (e.g. endometrium, breast, ovarian, prostate, a.o.) was retained. Additionally, its glycosylation dependent binding translates into tumor-selective internalization of GT-008 in vitro while sparing out CD24-positive immune cells. GT-008 has the potential to overcome limitations of conventional protein-targeting mAbs currently in clinical development by circumventing immune cell depletion and on-target/off-tumor toxicities associated with target expression on healthy cells. With its improved therapeutic window due to the strong differentiation between healthy and tumor tissue, GT-008 is exceptionally suitable for different therapeutic modalities, such as drug delivery (ADC, RIT) or cellular therapies (CARs). An in vitro and in vivo proof-of-concept study as therapeutic radioimmunoconjugate has been initiated. Citation Format: Johanna Gellert, Andreas Franz, Manon Weis, Evelyn Hartung, Stephanie Gurka, Antje Danielczyk, Lisa Weiß, Patrik Kehler. Improving druggability of a promising tumor target by the novel glycosylation-dependent mAb GT-008 for treatment of solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3429.