Peptide Inhibitor of Complement C1 (PIC1) Rapidly Inhibits Complement Activation after Intravascular Injection in Rats

Abstract

The complement system has been increasingly recognized to play a pivotal role in a variety of inflammatory and autoimmune diseases. Consequently, therapeutic modulators of the classical, lectin and alternative pathways of the complement system are currently in pre-clinical and clinical development. Our laboratory has identified a peptide that specifically inhibits the classical and lectin pathways of complement and is referred to as Peptide Inhibitor of Complement C1 (PIC1). In this study, we determined that the lead PIC1 variant demonstrates a salt-dependent binding to C1q, the initiator molecule of the classical pathway. Additionally, this peptide bound to the lectin pathway initiator molecule MBL as well as the ficolins H, M and L, suggesting a common mechanism of PIC1 inhibitory activity occurs via binding to the collagen-like tails of these collectin molecules. We further analyzed the effect of arginine and glutamic acid residue substitution on the complement inhibitory activity of our lead derivative in a hemolytic assay and found that the original sequence demonstrated superior inhibitory activity. To improve upon the solubility of the lead derivative, a pegylated, water soluble variant was developed, structurally characterized and demonstrated to inhibit complement activation in mouse plasma, as well as rat, non-human primate and human serum in vitro. After intravenous injection in rats, the pegylated derivative inhibited complement activation in the blood by 90% after 30 seconds, demonstrating extremely rapid function. Additionally, no adverse toxicological effects were observed in limited testing. Together these results show that PIC1 rapidly inhibits classical complement activation in vitro and in vivo and is functional for a variety of animal species, suggesting its utility in animal models of classical complement-mediated diseases.

Discriminating complement‐mediated acute transfusion reaction for type O+ red blood cells transfused into a B+ recipient with the complement hemolysis using human erythrocytes (CHUHE) assay

“…To confirm that the hemolysis was occurring via antibodyinitiated complement activation, we tested whether PIC1, which inhibits classical pathway activation by preventing enzymatic activation of C1, 11,12 could inhibit the high degree of hemolysis resulting from Donor 1 plasma mixed with B1 RBCs. The addition of PIC1 dose dependently inhibited the hemolysis of Donor 1 plasma by up to 97% (p 5 0.013) (Fig.…”

Novel Evasion Mechanisms of the Classical Complement Pathway

“…In a very interesting finding, Sharp et al noted that while a 15 amino acid peptide derivative was able to block CP activation it was unable to displace C1r 2 C1s 2 from the C1 complex, unlike the in-tact HAstV-1 Coat Protein macromolecule (68). These observations strongly suggest that complete displacement of C1r 2 C1s 2 is not required to inhibit C1, but rather that HAstV-1 Coat Protein likely exerts its inhibitory effect by disrupting the orientation of C1q relative to C1r 2 C1s 2 within the C1 complex.…”

“…To this point, small peptide mimics of S. aureus SCIN-derived AP inhibitors have been reported (115), and a peptidic derivative of HAstV-1 Coat Protein (PIC1) has shown efficacy as complement inhibitor in in vivo (68, 116). The ability of SCIN-derived peptides and PIC1 to preserve the inhibitory activities present in full-length proteins is consistent with the idea that immune evasion molecules, which often appear to target relatively small functional “hot-spots” on their host targets, hold promise as templates for drug design.…”

Relationship Between Obesity and Immune System a Review Article

“…The demonstration of differential adipokine, cytokine and chemokine protein profile in control, lean and diet-induced obese mice may have implications for immune responsiveness and risk of disease [50]. Sharp JA et al, (2015) reported that, the complement system has been increasingly recognized to play a pivotal role in a variety of inflammatory and autoimmune diseases. Consequently, therapeutic modulators of the classical, lectin and alternative pathways of the complement system are currently in pre-clinical and clinical development [51].…”