biostudies-literatureChatterjee BKUniversity of MichiganNIDDK NIH HHSNational Institute of Diabetes and Digestive and Kidney DiseasesNational Institute of General Medical SciencesNIGMS NIH HHSNIH HHSLife Sciences Institute880-895https://www.ebi.ac.uk/biostudies/studies/S-EPMC12007993biostudies-literatureUnknown20(4)The AMP transferase, FICD, is an emerging drug target fine-tuning stress signaling in the endoplasmic reticulum (ER). FICD is a bifunctional enzyme, catalyzing both AMP addition (AMPylation) and removal (deAMPylation) from the ER-resident chaperone BiP/GRP78. Despite increasing evidence linking excessive BiP/GRP78 AMPylation to human diseases, small molecules that inhibit pathogenic FICD variants are lacking. Using an <i>in vitro</i> high-throughput screen, we identify two small-molecule FICD inhibitors, C22 and C73. Both molecules significantly inhibit FICD-mediated BiP/GRP78 AMPylation in intact cells while only weakly inhibiting BiP/GRP78 deAMPylation. C22 and C73 also inhibit pathogenic FICD variants and improve proinsulin processing in β cells. Our study identifies and validates FICD ACS chemical biologySmall-Molecule FICD Inhibitors Suppress Endogenous and Pathologic FICD-Mediated Protein AMPylation.PMC12007993NIHDK48280S10 OD034346P30 DK020572R35 GM1305871R35GM142561R35GM130597R01 DK048280R35 GM142561Chakravorty ATruttmann MCBrooks CLLacy SMGiblin WArvan PRech JChatterjee BKAlam MfalseSmall-Molecule FICD Inhibitors Suppress Endogenous and Pathologic FICD-Mediated Protein AMPylation.The AMP transferase, FICD, is an emerging drug target fine-tuning stress signaling in the endoplasmic reticulum (ER). FICD is a bifunctional enzyme, catalyzing both AMP addition (AMPylation) and removal (deAMPylation) from the ER-resident chaperone BiP/GRP78. Despite increasing evidence linking excessive BiP/GRP78 AMPylation to human diseases, small molecules that inhibit pathogenic FICD variants are lacking. Using an <i>in vitro</i> high-throughput screen, we identify two small-molecule FICD inhibitors, C22 and C73. Both molecules significantly inhibit FICD-mediated BiP/GRP78 AMPylation in intact cells while only weakly inhibiting BiP/GRP78 deAMPylation. C22 and C73 also inhibit pathogenic FICD variants and improve proinsulin processing in β cells. Our study identifies and validates FICD 2025-01-01T00:00:00Z2025 Apr2026-06-01T05:54:03.033Z2025-07-03T03:04:34.217ZS-EPMC120079934003628910.1021/acschembio.4c00847