Val-boroPro (Talabostat, PT-100), a nonselective inhibitor of post-proline cleaving serine proteases, stimulates mammalian immune systems through an unknown mechanism of action. Despite this lack of mechanistic understanding, Val-boroPro has attracted substantial interest as a potential anticancer agent, reaching phase 3 trials in humans. Here we show that Val-boroPro stimulates the immune system by triggering a proinflammatory form of cell death in monocytes and macrophages known as pyroptosis. We demonstrate that the inhibition of two serine proteases, DPP8 and DPP9, activates the pro-protein form of caspase-1 independent of the inflammasome adaptor ASC. Activated pro-caspase-1 does not efficiently process itself or IL-1β but does cleave and activate gasdermin D to induce pyroptosis. Mice lacking caspase-1 do not show immune stimulation after treatment with Val-boroPro. Our data identify what is to our knowledge the first small molecule that induces pyroptosis and reveals a new checkpoint that controls the activation of the innate immune system.
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We thank S. Fujisawa for microscopy assistance, E. De Stanchina and B. Qeriqi for assistance harvesting mBMDMs, C. Taabazuing for helpful comments and A. Kentsis and F. Brown (Molecular Pharmacology Program, Memorial Sloan Kettering Cancer Center) for the HL-60 cell line. This work was supported by the Josie Robertson Foundation (D.A.B.), the MSKCC Core Grant (P30 CA008748), the NCI (grant no. U54CA112962 to T.R.G.), HHMI (T.R.G.) and the NIH (CA174008-01A1 to W.W.B. and NIH NIGMS T32 GM115327-Tan to D.C.J.).
W.W.B. is a co-founder, advisor and board member of Arisaph Pharmaceuticals, a biotechnology company interested in developing boronic acid–based inhibitors of serine proteases as therapeutics.
Supplementary Results, Supplementary Tables 1 and 2 and Supplementary Figures 1–12. (PDF 14969 kb)
DMSO-treated RAW 264.7 cells. (MOV 17579 kb)
Etoposide-induced apoptosis in RAW 264.7 cells. (MOV 13930 kb)
Val-boroPro-induced pyroptosis in RAW 264.7 cells. (MOV 15726 kb)
1G244-induced pyroptosis in RAW 264.7 cells. (MOV 13860 kb)
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Okondo, M., Johnson, D., Sridharan, R. et al. DPP8 and DPP9 inhibition induces pro-caspase-1-dependent monocyte and macrophage pyroptosis. Nat Chem Biol 13, 46–53 (2017). https://doi.org/10.1038/nchembio.2229
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