Design and preclinical characterization of ALXN1210: A novel anti-C5 antibody with extended duration of action

Eculizumab, a monoclonal antibody (mAb) directed against complement protein C5, is considered to be the current standard of care for patients with paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome. This study describes the generation and preclinical attributes of ALXN1210, a new long-acting anti-C5 mAb, obtained through select modifications to eculizumab to both largely abolish target-mediated drug disposition (TMDD) and increase recycling efficiency via the neonatal Fc receptor (FcRn). To attenuate the effect of TMDD on plasma terminal half-life (t(1/2)), histidine substitutions were engineered into the complementarity-determining regions of eculizumab to enhance the dissociation rate of the mAb:C5 complex in the acidic early endosome relative to the slightly basic pH of blood. Antibody variants with optimal pH-dependent binding to C5 exhibited little to no TMDD in mice in the presence of human C5. To further enhance the efficiency of FcRn-mediated recycling of the antibody, two additional substitutions were introduced to increase affinity for human FcRn. These substitutions yielded an additional doubling of the t(½) of surrogate anti-mouse C5 antibodies with reduced TMDD in transgenic mice expressing the human FcRn. In conclusion, ALXN1210 is a promising new therapeutic candidate currently in clinical development for treatment of patients with PNH and atypical hemolytic uremic syndrome.