Design and synthesis of new orally active inhibitors of human neutrophil elastase.

To identify new orally active inhibitors, further modification of 1 (ONO-6818) was performed. Peptidic derivatives 4b, 4c and 4n showed more potent inhibitory activity than nonpeptidic derivatives 3a-c. As a result, a series of peptidic inhibitors, 4a-s and 5a-v, were discovered. Among these N-aryl derivatives 5a-g, 5i, 5m and 5o-v showed oral activity. Their oral activity showed good correlation with their metabolic stability. Compounds 5h and 5j-l, which were extremely metabolically unstable in hamster plasma, did not show oral activity. Oral activity was considered to be determined by a combination of at least two factors: oral absorption and metabolic stability.

Kinetic study of the hepatobiliary transport of a new prostaglandin receptor agonist.

The pharmacokinetics of the hepatobiliary transport of an anionic drug, 7,8-dihydro-5-[(E)-[[a-(3-pyridyl)-benzylidene]aminooxy]ethyl]-1- naphthyloxy]acetic acid (ONO-1301), a new prostaglandin (PG) I2 receptor agonist, was investigated in rats. During intravenous infusion of this compound, the drug concentrations in arterial blood, hepatic vein and liver and the biliary excretion rate were measured at steady state. At a low infusion rate, 30% of the ONO-1301 was extracted by the liver during a single pass, and the main clearance organ was demonstrated to be the liver. The total clearance, Cltot; hepatic extraction ratio, EH; and liver-to-plasma concentration ratio, Kp values, decreased as the infusion rate increased. Considering the infusion rate-dependent decrease in all three parameters, saturation of hepatic uptake was suggested to be the cause of the nonlinear pharmacokinetics. To confirm this hypothesis, the time profiles of the plasma and liver concentrations of ONO-1301 after intravenous administration of various doses (0.01-25 mg/kg) were analyzed in vivo. The early-phase hepatic uptake clearance at lower doses (0.01-1 mg/kg) was 28 ml/min/kg, which is close to the hepatic plasma flow rate. The uptake clearance also was decreased at the higher doses. The uptake mechanism was investigated with isolated rat hepatocytes. Both Na(+)-dependent and -independent uptake were observed and these were inhibited by hypothermia and ATP depletors, which suggests that the uptake is via carrier-mediated active transport. The initial uptake velocity exhibited concentration dependence, and the kinetic parameters were as follows: Km, 15.6 microM (Na(+)-dependent) and 3.8 microM (Na(+)-independent); Vmax, 5.9 nmol/min/mg (Na(+)-dependent) and 4.8 nmol/min/mg (Na(+)-independent). With these in vitro transport parameters, the plasma unbound fraction and the hepatic plasma flow rate, the hepatic uptake clearance was calculated from a mathematical model. The calculation also indicated that the uptake was so rapid that it was limited by the plasma flow rate. It is concluded that the carrier-mediated active transport systems demonstrated in vitro are responsible for the nonlinear pharmacokinetics of ONO-1301.

Effects of ONO-3708, an antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, on blood vessels.

The pharmacological properties of a novel thromboxane A2/prostaglandin endoperoxide receptor antagonist, ONO-3708, on blood vessels were examined in vitro and in vivo. ONO-3708, 10 microM, inhibited the rabbit aorta contractions induced by thromboxane A2, prostaglandin H2, 11,9-epoxymethano-prostaglandin H2 (U-46619) or prostaglandin F2 alpha without affecting the contractions induced by angiotensin II, serotonin or norepinephrine. ONO-3708, at a concentration of 1 to 100 nM, appeared to be a competitive inhibitor of the contractile responses of the canine basilar artery to 9,11-epithio-11,12-methano-thromboxane A2 (STA2), U-46619 and PGF2 alpha, and a non-competitive inhibitor of the contractile responses to 15-hydroperoxy-eicosatetraenoic acid (15-HPETE). In in vivo studies, ONO-3708 (10 and 100 micrograms/kg per min i.v.) ameliorated the decrease in diameter of the basilar artery induced by the i.v. infusion of STA2 (0.1 microgram/kg per min) in cats. Furthermore, infusion of ONO-3708 (10 and 30 micrograms/kg per min i.v.) prevented the cerebral vasospasm in an experimental subarachnoid hemorrhage model in dogs. These results indicate that ONO-3708 is a potent antagonist of the thromboxane A2/prostaglandin endoperoxide receptor in vitro and in vivo and may be of therapeutic use in preventing cerebral vasospasm.