Design, Synthesis, and Biological Evaluation of a Novel Long-Acting Human Complement C3 Inhibitor Synthesized via the...

The complement system is essential for immune defense, but its dysregulation contributes to various complement-mediated disorders, including paroxysmal nocturnal hemoglobinuria (PNH). CP40 (a cyclic peptide also known as AMY101), effectively inhibits complement activation by preventing the initial binding of the C3 substrate to convertase. Despite its potency, CP40 has a very short plasma half-life when unbound to human C3, necessitating frequent dosing. We developed a novel PASylation-Lipidation Modular (PLM) platform. This platform incorporates a solubilizing PAS module and a half-life-extending lipid moiety into CP40 via a chemical linker. Systematic optimization of the spacer and lipid components in PLM-modified CP40 analogues identified 6C1 as a lead compound. Compared to CP40, 6C1 exhibited a 5-fold increase in antihemolytic potency in the classical complement pathway and a 6.3-fold improvement in solubility. In vivo studies demonstrated that PLM-CP40 analogues possess superior pharmacokinetic properties, with a 15.6-fold extension in half-life relative to unmodified CP40. Mechanistic studies revealed that the PLM platform extends half-life by interacting with albumin, which serves as a circulating depot for the compound. Surface plasmon resonance analysis and hemolysis assays postalbumin incubation demonstrated that PLM modifications maintain receptor affinity by strategically positioning the albumin-binding moiety away from the peptide region, preserving its biological activity. In a clinically relevant in vitro model of complement-mediated hemolysis in PNH, 6C1 effectively reduced erythrocyte lysis. The PLM platform thus offers a versatile strategy for enhancing peptide therapeutics by improving solubility, extending circulation time, and increasing efficacy, broadening their therapeutic potential.