Small Molecule Inhibitors of Cyclophilin D To Protect Mitochondrial Function as a Potential Treatment for Acute Pancreatitis

Opening of the mitochondrial permeability transition pore (MPTP) causes mitochondrial dysfunction and necrosis in acute pancreatitis (AP), a condition without specific drug treatment. Cyclophilin D (CypD) is a mitochondrial matrix peptidyl-prolyl isomerase that regulates the MPTP and is a drug target for AP. We have synthesized urea-based small molecule inhibitors of cyclophilins and tested them against CypD using binding and isomerase activity assays. Thermodynamic profiles of the CypD/inhibitor interactions were determined by isothermal titration calorimetry. Seven new high-resolution crystal structures of CypD–inhibitor complexes were obtained to guide compound optimization. Compounds 4, 13, 14, and 19 were tested in freshly isolated murine pancreatic acinar cells (PACs) to determine inhibition of toxin-induced loss of mitochondrial membrane potential (ΔΨm) and necrotic cell death pathway activation. Compound 19 was found to have a Kd of 410 nM and a favorable thermodynamic profile, and it showed significant protection of ΔΨm and reduced necrosis of murine as well as human PACs. Compound 19 holds significant promise for future lead optimization.