Chemical Programming of Macrophages via Direct Activating Receptor Labeling for Targeted Tumour Immunotherapy

Abstract

Antibody-recruiting molecules (ARMs) are therapeutic tools that simultaneously bind a hapten-specific serum antibody and a cancer cell surface protein, resulting in the activation and recruitment of an immune cell to the cancer surface. However, ARM efficacy is limited by the ability of ARMs to form a quaternary complex with the immune cell receptor, antibody, and cancer cell surface. The Rullo lab has previously developed and characterized a covalent ARM (cARM) that irreversibly links the ARM to the antibody and simplifies the quaternary binding equilibria. cARMs have shown a marked increase in both target immune recognition and therapeutic efficacy. However, cARM efficacy is still limited by the affinity of the antibody for the immune receptor. We aim to investigate how direct covalent engagement of the immune receptor and elimination the antibody-immune receptor binding equilibria impacts immune activation and therapeutic efficacy. This thesis focuses on the chemical programming of macrophages through direct covalent immune receptor engagement. We have developed and characterized covalent immune programmers (CIPs), which are molecules that contain a macrophage targeting domain and a tumour targeting domain. The macrophage targeting domain binds the activating receptor CD64 on the macrophage surface and contains a chemical warhead that covalently labels the receptor once bound. The tumour targeting domain can promote macrophage tumour engagement resulting in tumoricidal function. Flow cytometry experiments have shown that CIPS are able to bind Fc receptors specifically and effectively on the surface of macrophages. Further, CIPs were able to induce macrophage activation and induce target specific phagocytosis. These experiments have also shown that direct engagement of the receptor by the CIP is more effective than antibody-mediated engagement, suggesting that overall immune complex stability affects immune cell activation. Taken together, these concepts can be used to guide future immunotherapeutic design.