Tumour antigen targeted monoclonal antibodies incorporating a novel multimerisation domain significantly enhance antibody dependent cellular cytotoxicity against colon cancer

Tumour antigen targeted antibodies (mAbs) can induce natural killer (NK) cells to kill tumours through antibody dependent cellular cytotoxicity (ADCC) upon engagement of NK cell expressed FcγRIIIa. FcγRIIIa polymorphisms partially dictate the potency of the ADCC response. The high affinity FcγRIIIa-158-valine (V) polymorphism is associated with more potent ADCC response than the low affinity FcγRIIIa-158-phenylalanine (F) polymorphism. Because approximately 45% of patients are homozygous for the FcγRIIIa-158-F polymorphism (FF genotype), their ability to mount ADCC is impaired. We investigated whether a novel mAb capable of binding multiple antigen specific targets and engaging multiple low affinity FcγRIIIa receptors could further enhance ADCC against colon cancer in vitro. Specifically, we generated a novel anti-epidermal growth factor receptor (EGFR) antibody (termed a stradobody™) consisting of an unmodified Fab sequence and two Immunoglobulin G, subclass 1 (IgG1) Fc domains separated by an isoleucine zipper domain and the 12 amino-acid IgG2 hinge. The stradobody™ framework induced multimerisation and was associated with increased binding to the EGFR and FcγRIIIa. From a functional perspective, when compared to an unmodified anti-EGFR mAb with a sequence identical to cetuximab (a commercially available anti-EGFR mAb), stradobodies™ significantly enhanced ADCC. These effects were observed using both KRAS wild type HT29 and KRAS mutant SW480 colon cancer cells as targets, and by NK cells obtained from healthy donors and a cohort of patients with colon cancer. These data suggest that high avidity cross-linking of multiple tumour surface antigens and multiple NK cell associated FcγRIIIa molecules can enhance ADCC and partially overcome impaired ADCC by FF genotype individuals in vitro.