Characterization of HZ0412a, a novel potent humanized anti-IL-6 receptor antibody that blocks IL-6R binding to gp130

Dysregulated elevation of interleukin-6 (IL-6) signaling is implicated in the pathogenesis of multiple pathophysiological states, and the functional neutralization of the IL-6 pathway with monoclonal antibodies has been proven an effective therapeutic method in treating various diseases with abnormally enhanced IL-6 signaling, and its clinical indications are expanding. Here, we report that by using the conventional hybridoma technology and humanization mutation method, we develop a novel humanized anti-IL-6 receptor (IL-6R) antibody—namely, HZ0412a. In our study, we found that HZ0412a exhibits higher binding affinity to soluble recombinant human IL-6R than tocilizumab. Importantly, in contrast to tocilizumab—a humanized anti-IL-6R antibody approved by the US Food and Drug Administration for the treatment of rheumatoid arthritis, juvenile idiopathic arthritis, giant cell arteritis and Castleman’s disease—HZ0412a does not significantly affect the binding of IL-6 to IL-6R. Further analysis revealed that HZ0412a prevents IL-6R from binding to gp130 in vitro, while tocilizumab has a minimal effect under the same condition. Using various cell-based assays, we demonstrate that HZ0412a is noninferior to tocilizumab in inhibiting IL-6 signaling. Finally, we showed that HZ0412a is well tolerated in cynomolgus monkeys after a single subcutaneous injection at a dose of 1 or 5 mg/kg. Taken together, our results indicated that HZ0412a targets an epitope on human IL-6R that is different from that of tocilizumab, and the epitope region is essential for the interaction between IL-6R and gp130. This distinctive mode of action plus its high affinity to IL-6R led to the high potency of HZ0412a in suppressing in vitro IL-6 signaling.