Abstract
Complement is a key component of the innate immune system, recognizing pathogens and promoting their elimination. Complement component 3 (C3) is the central component of the system. Activation of C3 can be initiated by three distinct routes—the classical, the lectin and the alternative pathways—with the alternative pathway also acting as an amplification loop for the other two pathways. The protease factor D (FD) is essential for this amplification process, which, when dysregulated, predisposes individuals to diverse disorders including age-related macular degeneration and paroxysmal nocturnal hemoglobinuria (PNH). Here we describe the identification of potent and selective small-molecule inhibitors of FD. These inhibitors efficiently block alternative pathway (AP) activation and prevent both C3 deposition onto, and lysis of, PNH erythrocytes. Their oral administration inhibited lipopolysaccharide-induced AP activation in FD-humanized mice. These data demonstrate the feasibility of inhibiting the AP with small-molecule antagonists and support the development of FD inhibitors for the treatment of complement-mediated diseases.
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Acknowledgements
We thank T. Zoller for the preparation of the proline-based compound library, J. Wirsching, T. Doll and A. Isken for their assistance in generating the human FD knock-in mice, N. Buchanan for coordinating the maintenance of the mouse colony, F. Zink for assistance in preparing FD and KLK7 inhibitor complex crystals, S. Kapps for preparation of 15N-labeled human FD, C. Towler for small molecule crystallization experiments, C. Dentel and F. Tritsch for chemical syntheses, U. Argikar, A. Brown, S. Bailey and G. Marsh for pharmacokinetic and bioanalytical support, A. De Erkenez for performing human whole blood assays, and L. Ferrara for performing the AP hemolytic assay.
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N.O. and A.M.S. solved the structures by X-ray crystallography. S. Randl, U.H., A.V., E.L. and J.M. designed the FD structure-based inhibitors. S.D., C.D. and K.F. synthesized compounds. S. Rüdisser and P.E. performed NMR experiments for screening and binding affinity measurements. N.H. and P.E. conducted SPR experiments. F.C. generated the biochemical assay data. A.S. and J.W. performed the PNH surrogate assay and analyzed the data. A.M.R. performed the assays using erthrocytes from PNH patient and analyzed the data. S.B., B.K. and F.A.K. generated the human FD knock-in mice. B.G. and J.E. produced recombinant proteins. T.G. designed and interpreted pharmacokinetic studies. O.D. and S.-M.L. performed the in vivo studies in mice. S.F. and B.J. conceived experiments and supervised part of the work. J.M., J.E., A.S., R.H. and K.A. conceived experiments, supervised the work, and wrote the manuscript.
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All authors, with the exception of A.M.R., are former or current employees of Novartis and may hold Novartis stock. Experiments reported herein conducted by A.M.R. were funded by Novartis.
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Maibaum, J., Liao, SM., Vulpetti, A. et al. Small-molecule factor D inhibitors targeting the alternative complement pathway. Nat Chem Biol 12, 1105–1110 (2016). https://doi.org/10.1038/nchembio.2208
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DOI: https://doi.org/10.1038/nchembio.2208
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