In vivo assay of specific kallikrein inhibitors

Kininogen sequence analogs containing amino acid residues around the Arg-Ser cleavage site of bovine kininogens were prepared with bulky aliphatic residues in the P3 position as specific inhibitors of tissue kallikrein. KKI-7 (containing a cyclohexylacetyl group) and KKI-8 (containing an adamantaneacetyl group) both inhibited human urinary kallikrein with KI = 4 microM. These inhibitors are 40 times more potent than the corresponding peptide containing the naturally occurring prolyl residue at P3 and one-seventh as susceptible to hydrolysis. KKI-7 and KKI-8 are poor inhibitors of human plasma kallikrein (KI = 244 and 358 microM, respectively) while their capacity to inhibit trypsin is 1/3 and 1/17, respectively, that of their inhibitory capacity for human urinary kallikrein. When KKI-7 was tested in a rat blood flow model, the infused peptide (50 micrograms/kg/min) depressed the response to injected rat submandibular kallikrein (200-500 ng) to 52% of the control response when it was injected less than 10 minutes after infusion was started and to 16% of the control response when it was injected between 10 and 30 minutes after infusion of the inhibitor, the response gradually returned toward normal. Similar results were obtained with porcine pancreatic kallikrein. Infusion of the inhibitor did not affect the response to bradykinin and infusion of the vehicle itself did not alter the response to either injected kallikrein or bradykinin. These analogs have greater specificity and stability than those previously developed and are appropriate for the in vivo inhibition of glandular kallikreins.