The complement activation peptide C5a is a key immune modulator that is associated with numerous inflammatory diseases. C5a is a 74 amino acid residue peptide that binds to two 7-transmembrane receptors, termed C5aR1 and C5aR2. C5a is utilized to investigate C5aR1/2 receptor biology, and to screen for potential therapeutics. C5aR1 antagonists are being actively pursued as therapeutic modalities for multiple indications, however therapeutic applications for C5aR1 agonists have also been proposed. Laboratory sources of C5a currently stem from either low yield isolation of endogenous C5a from human serum, or production by recombinant expression. However, recombinant C5a from commercial sources have shown contaminants that interfere with common immune pathways.
In addition to the limitations of C5a production, the interrogation of C5aR1 specific activity remains limited due to a lack of receptor specificity of C5a. Although multiple peptide agonists for C5aR1 have been developed, none demonstrate selectivity, as they also activate C5aR2 and/or C3aR at functional concentrations.
To address these issues, we have developed a C5a toolkit which allows us to both address production limitations and the lack of receptor selectivity. We have developed a novel synthesis strategy to produce full length C5a without the need for ligation chemistry. We validated synthetic C5a by analysing its structure/activity compared to recombinant C5a, and also conjugated a lanthanide chelating cage to facilitate the interrogation C5aR1 binding.
We have also developed the first C5aR1 selective agonist compounds, with both bias receptor signaling (BM213) and unbiased receptor signaling (BM221). These compounds exhibit selectivity of >1000-fold for C5aR1 compared to C3aR/C5aR2. Importantly, both compounds exhibit similar functional profiles to C5a in C5aR1 mediated responses.