MX1013, a dipeptide caspase inhibitor with potent in vivo antiapoptotic activity

Caspases play a critical role in apoptosis, and are considered to be key targets for the design of cytoprotective drugs. As part of our antiapoptotic drug‐discovery effort, we have synthesized and characterized Z‐VD‐fmk, MX1013, as a potent, irreversible dipeptide caspase inhibitor. MX1013 inhibits caspases 1, 3, 6, 7, 8, and 9, with IC 50 values ranging from 5 to 20 n M . MX1013 is selective for caspases, and is a poor inhibitor of noncaspase proteases, such as cathepsin B, calpain I, or Factor Xa (IC 50 values >10 μ M ). In several cell culture models of apoptosis, including caspase 3 processing, PARP cleavage, and DNA fragmentation, MX1013 is more active than tetrapeptide‐ and tripeptide‐based caspase inhibitors, and blocked apoptosis at concentrations as low as 0.5 μ M . MX1013 is more aqueous soluble than tripeptide‐based caspase inhibitors such as Z‐VAD‐fmk. At a dose of 1 mg kg −1 i.v., MX1013 prevented liver damage and the lethality caused by Fas death receptor activation in the anti‐Fas mouse‐liver apoptosis model, a widely used model of liver failure. At a dose of 20 mg kg −1 (i.v. bolus) followed by i.v. infusion for 6 or 12 h, MX1013 reduced cortical damage by approximately 50% in a model of brain ischemia/reperfusion injury. At a dose of 20 mg kg −1 (i.v. bolus) followed by i.v. infusion for 12 h, MX1013 reduced heart damage by approximately 50% in a model of acute myocardial infarction. Based on these studies, we conclude that MX1013, a dipeptide pan‐caspase inhibitor, has a good combination of in vitro and in vivo properties. It has the ability to protect cells from a variety of apoptotic insults, and is systemically active in three animal models of apoptosis, including brain ischemia. British Journal of Pharmacology (2003) 140 , 402–412. doi: 10.1038/sj.bjp.0705450