Conditional activation of NK cell function using chemically synthetic constrained bicyclic peptides directed against NKp46 and tumor-expressed antigens

Natural killer (NK) cells have the unique potential to recognize and kill tumor cells independently of MHC-I presentation of antigens, as well as to secrete cytokines that engage adaptive anti-tumor immunity and the function of cytolytic T cells. We have discovered and characterized chemically synthetic, constrained bicyclic peptides that bind with high affinity and specificity to NKp46, an activating receptor expressed selectively on NK cells in the tumor microenvironment. Chemical coupling to other bicyclic peptides specific for the tumor antigens EphA2 or MT-1 created NKp46 agonists whose function was completely conditional on binding to the tumor antigen. These chemical conjugates effectively convert the tumor antigen into a "kill me" signal for NK cells. Not only did these newly created tumor-immune cell agonists (TICAs) direct potent and efficient killing of human tumor cells by primary human NK cells in vitro, but they also caused secretion of the pro-inflammatory cytokines TNF and IFN{gamma}. Importantly, the TICAs directed production of FLT3 ligand, an essential mitogen for conventional dendritic cells which are central to the development of anti-tumor immunity in cancer. We illustrate the TICA-directed interaction of NK cells with tumor cells using confocal microscopy and we show that TICAs enable sustained function over multiple rounds of killing. These novel tools are well positioned to harness the potential of NK cells in the treatment of cancer.