IN-VIVO INHIBITION OF CATHEPSIN-B BY PEPTIDYL (ACYLOXY)METHYL KETONES

Peptidyl (acyloxy)methyl ketones, previously established as potent irr eversible inhibitors of the cysteine proteinase cathepsin B in vitro, were investigated and optimized for their inhibitory activity in vivo. Incorporation of polar or charged functional groups in the inhibitor structure afforded effective cathepsin B inhibition, following dosing to rats. The most effective inhibitor, Z-Phe-Lys-CH2OCO-(2,4,6-Me(3))P h (8), was found to give ED(50) values of 18 mg/kg po (orally) and 5.0 mg/kg ip (intraperitoneally) at 4-5 h postdose, and 2.4 mg/kg sc (sub cutaneously) at 24 h postdose, for liver cathepsin B inhibition (measu red ex vivo). The subcutaneous route of administration of (acyloxy)met hyl ketone 8 also provided potent cathepsin B inhibition in certain pe ripheral tissues (e.g., ED(50) 1.0 mg/kg for skeletal muscle, 0.1 mg/k g for heart). These investigations demonstrate that peptidyl (acyloxy) methyl ketones such as 8 have promise as tools for the characterizatio n of in vivo biochemical processes and as therapeutic agents.