Ac-FLTD-CMK is a selective gasdermin D (GSDMD) clevage inhibitor (IC50 = 46.7 nM, 329 nM, 1.49 μM, respectively, against GSDMD clevage by human caspase-1, -5, -4 in cell-free enzymatic assays) th at suppresses pyroptosis downstream of both canonical and noncanonical inflammasomes, as well as reduces IL-1β release following activation of the NLRP3 inflammasome in macrophages (10 μM 4h post 200 ng/mL LPS and 0.5h before ATP or nigericin). Ac-FLTD-CMK selectively blocks GSDMD clevage by inflammatory caspases without affecting apoptotic caspases (caspase-3 IC50 >100 μM) or apoptosis.