(54g) A Novel Small Molecule Inhibitor for Complement Alternative Pathway

Chiu, C., University of Pennsylvania
Kimura, Y., University of Pennsylvania
Napper, A. D., University of Pennsylvania
Song, W., University of Pennsylvania
Diamond, S. L., University of Pennsylvania

As the crucial innate immune system of human body to defend the exogenous pathogen, complement system includes classical, alternative and lectin pathways. These pathways would converge in to the final pathway when C3 convertase cleavage C3 into C3a and C3b, this may result in formation of membrane attack complex (MAC) which would cause the lysis of pathogen. Among these three pathways, recently studies and several animal models have demonstrated that alternative pathway plays an essential role in several disease pathogenesis like paroxysmal nocturnal hemoglobinuria (PNH), rheumatoid arthritis, ischemia reperfusion injury and age-related macular degeneration (AMD). Our laboratory developed the ELISA based assay which is able to determine the activity of the entire alternative pathway, we performed high throughput screen with this ELISA assay of the 62,139 compounds library from the National Institutes of Health Molecular Libraries Small Molecule Repository. Using orthogonal mixture strategy, we discovered 52 hits from the primary screening and 1 confirmed hit for the secondary screening. The single hit from IC50 confirmation, measured at 0.40 ± 0.07μM, was identified as a lead candidate of the complement alternative pathway inhibitor. This compound was also found to inhibit complement C1s enzyme, the initial component of the classical pathway. With the unstable nature of the compound, it self-degrades within water and assay buffer, thus making it a delicate compound for analysis. In addition to the confirmation by ELISA assay, we were able to verify its inhibition using biologic assays such as zymogen and rabbit hemolytic assay. Our aim is to identify the compound's target components in the complement alternative pathway in view to alter the associated disease pathogenesis.