Characterization of the caspase inhibitor IDN-1965 in a model of apoptosis-associated liver injury

Previous studies have shown that caspase inhibitors are effective at protec ting against anti-Fas antibody (alpha -Fas)-mediated liver injury/lethality . The purpose of these experiments was to characterize more fully the effic acy of a broad-spectrum, irreversible caspase inhibitor, IDN-1965 (N-[(1,3- dimethylindole-2-carbonyl) valinyl]-3-amino-4-oxo-5-fluoropentanoic acid), in this model and the role of caspase inhibition in long-term protection. T he ED50 for IDN-1965 by i.p. administration, based on alanine aminotransfer ase activities, was 0.14 mg/kg. The caspase inhibitor was also efficacious when administered intravenously and orally (ED50 values of 0.04 and 1.2 mg/ kg, respectively). Histologically, marked reduction in Fas-induced apoptosi s with IDN-1965 (1 mg/kg, i.p.) was apparent at 6 h. Also, caspase 3-like a ctivities were decreased in a dose-dependent manner, but the inhibition of caspase activity was transient. Immunohistochemical studies demonstrated th at IDN-1965 greatly reduced the activation of caspase 3. In survival studie s, a single i.p. treatment of 1 mg/kg IDN-1965 or continuous i.p. infusion via osmotic pumps completely blocked lethality measured up to 7 days after alpha -Fas administration. IDN-1965 was also effective in inhibiting liver injury when administered as long as 3 h after or 1 h before alpha -Fas admi nistration. Lastly, Western blot analysis demonstrated that processing of c aspases 3, 6, and 8, as well as Bid (a protein responsible for the release of mitochondrial cytochrome C and amplification of the apoptotic cascade) w as inhibited by IDN-1965. In conclusion, the broad-spectrum caspase inhibit or IDN-1965 is markedly effective at inhibiting Fas-mediated apoptosis by m ultiple routes of administration. The therapeutic potential of caspase inhi bitors appears promising for the treatment of apoptosis-mediated liver inju ry based on potency and postinsult efficacy.