(462f) Antibody-Lectin Bispecifics for Targeting Glyco-Immune Checkpoints

Cancer immunotherapies, including checkpoint blockade antibodies, represent a breakthrough in cancer treatment with long-term remission observed in select patients. Unfortunately, many tumors remain unresponsive to existing immunotherapies, creating an urgent need to therapeutically target additional immune checkpoints that drive cancer progression. Glyco-immune checkpoints – in which cell-surface biopolymers decorated with sugars, or glycans, engage glycan-binding receptors on immune cells – have emerged as immune modulatory pathways that are misregulated in the context of cancer. In particular, recent evidence suggests that upregulation of the sialic acid monosaccharide on cancer cell surfaces allows tumors to resist treatment by engaging a family of inhibitory receptors called Siglecs on immune cells. However, the lack of glycan-binding reagents with high affinity and selectivity has historically prevented targeting of tumor-associated glycans for cancer immunotherapy.

To address this need, we have developed a new class of antibody-lectin bispecifics (AbLecs) targeting tumor-associated glycans for checkpoint blockade. In this approach, glycan-binding domains from immune receptors (e.g., Siglec receptors) are coupled to high-affinity binding domains from FDA-approved antibodies targeting common tumor-associated antigens (e.g., trastuzumab, rituximab, and cetuximab) via knobs-into-holes heterodimerization technology. Western blot and mass spectrometry results indicated correct heterodimeric assembly of four AbLec candidates, demonstrating the feasibility of the AbLec approach. We hypothesized that the high-affinity antibody arm will enable AbLecs to accumulate with high effective molarity on the cancer cell surface, permitting otherwise low affinity Siglec binding domains to bind and block cell surface sialic acids at therapeutically relevant concentrations. Indeed, we found that AbLecs bind human tumor cell lines at nanomolar concentrations and can block binding of Siglec receptor ectodomains in flow cytometry assays. Finally, we showed that AbLecs have the capacity to enhance killing of a variety of human tumor cell lines of leukemic, lymphatic, and epithelial origins by primary immune cells in vitro via antibody-dependent cellular phagocytosis (ADCP) and cytotoxicity (ADCC), compared to their FDA-approved parent antibodies. These studies provide proof-of-principle for AbLecs as a first-in-class, modular platform technology enabling blockade of glyco-immune checkpoints for cancer immunotherapy.