LAUSR

Integrin associated protein (CD47) is an important target in immunotherapy, as it is expressed as a 'don't eat me' signal on many tumor cells. Interference with its counter molecule signal regulatory protein alpha (SIRPα), expressed on myeloid cells, can be achieved with blocking antibodies, but also by inhibiting the enzyme glutaminyl cyclase (QC) with small molecules. QC inhibition reduces N-terminal pyro-glutamate formation of CD47 at the SIRPα binding site. Here, we investigated the impact of QC inhibition on myeloid effector cell mediated tumor cell killing by epidermal growth factor receptor (EGFR) antibodies and the influence of antibody isotypes. SEN177 is a QC inhibitor and did not interfere with EGFR antibody mediated direct growth inhibition, complement-dependent cytotoxicity (CDC) or antibody-dependent cell-mediated cytotoxicity (ADCC) by mononuclear cells (MNC). However, binding of a human soluble SIRPα -Fc fusion protein to SEN177 treated cancer cells was significantly reduced in a dose-dependent manner, suggesting that pyro-glutamate formation of CD47 was affected. QC inhibition in tumor cells translated into enhanced antibody-dependent cellular phagocytosis (ADCP) by macrophages and enhanced ADCC by polymorphonuclear neutrophilic granulocytes (PMN). PMN-mediated ADCC was significantly more effective with EGFR antibodies of human IgG2 or IgA2 isotypes than with IgG1 antibodies, proposing that the selection of antibody isotypes may critically affect the efficacy of antibody therapy in the presence of QC inhibition. Importantly, QC inhibition also enhanced the therapeutic efficacy of EGFR antibodies in vivo. Together, these results suggest a novel approach to specifically enhance myeloid effector cell-mediated efficacy of EGFR antibodies by orally applicable small molecule QC inhibitors.