Naphthamidine urokinase plasminogen activator inhibitors with improved pharmacokinetic properties.

A series of non-amide-linked 6-substituted-2-naphthamidine urokinase plasminogen activator (uPA) inhibitors are described. These compounds possess excellent binding activities and selectivities with significantly improved pharmacokinetic profiles versus previously described amide-linked inhibitors.

Both circulating and clot-bound plasminogen activator inhibitor-1 inhibit endogenous fibrinolysis in the rat.

The effects of both clot-bound and circulating plasminogen activator inhibitor-1 (PAI-1) on endogenous fibrinolysis were investigated in a rat model of pulmonary embolism. Iodine-125 fibrin(ogen)-labeled blood-clot homogenates were delivered through the left jugular vein to the lung microvasculature, and the subsequent extent of the clot lysis was monitored by measuring the release of 125I-fibrin degradation products (FDPs) into the blood. Clots that had incorporated activated PAI-1 ex vivo were subsequently protected from dissolution in vivo in a dose-responsive manner (half-maximal concentration [IC50] = 4.3 micrograms/ml). PAI-1-containing clots also resisted lysis, as measured by the release of the specific FDP D-dimer. Plasma levels of plasminogen activator (PA) and PAI activity were unaltered by administration of PAI-1-containing clots, and the clot-protective effects of clot-bound PAI-1 were reversed by exogenous tissue-type plasminogen activator administration. Clot lysis was also inhibited in a dose-responsive manner (IC50 = 58 micrograms/kg) by intravenous bolus delivery of activated PAI-1 to the circulation. The clot-protective effects of circulating PAI-1 were correlated with dose-dependent increases in plasma PAI-1 antigen and activity levels and decreases in plasma PA levels (IC50 = 37 micrograms/ml). There was no evidence of any accumulation of circulating PAI-1 in the lungs. Latent PAI-1, whether delivered with or delivered after the clot homogenates, did not affect the clot-lytic process. Activated and latent PAI-1 was cleared from the circulation in a monophasic manner, with a half-life of approximately 32 and 7 minutes, respectively. The results indicate that both clot-bound and circulating PAI-1 are potent inhibitors of fibrinolysis in vivo. Clot-bound PAI-1 may inhibit PAs in the immediate vicinity of the clots, whereas circulating PAI-1 may act systemically by controlling overall levels of PAs present in the blood.

Clearance of t-PA, PAI-1, and t-PA-PAI-1 complex in an isolated perfused rat liver system.

The role of physiologic inhibitors of tissue-type plasminogen activator (t-PA) in its clearance has not yet been defined. In this study, the clearance of t-PA, plasminogen activator inhibitor 1 (PAI-1), and t-PA-PAI-1 complex was determined in an isolated perfused rat liver system. The clearance of t-PA-PAI-1 complex was twice as fast as that of t-PA, whereas PAI-1 was cleared slowly. The half-lives for t-PA, determined by a two-compartmental pharmacokinetic model, were: alpha, 20.1 minutes, and beta, 120.0 minutes. The corresponding values for t-PA-PAI-1 complex were: alpha, 9.7 minutes, and beta, about 7 hours. The model microconstants were computed for t-PA and t-PA-PAI-1 complex and the marked difference between the "on" microconstants k12 for t-PA (0.026 +/- 0.001 min-1) and t-PA-PAI-1 complex (0.090 +/- 0.025 min-1) suggests that the effect on binding to liver cells is the most important factor in the faster clearance of t-PA-PAI-1 complex when compared with t-PA.

Studies of recombinant plasminogen activator inhibitor-1 in rabbits. Pharmacokinetics and evidence for reactivation of latent plasminogen activator inhibitor-1 in vivo.

The pharmacokinetics of human recombinant plasminogen activator inhibitor-1 (rPAI-1) was studied in rabbits. Latent rPAI-1 (0-2 units of tissue-type plasminogen activator neutralizing activity per microgram protein); reactivated rPAI-1 (approximately 150 units/micrograms); and chloramine T-oxidized, nonreactivatable rPAI-1 (approximately 0.7 units/microgram) were studied. The pharmacokinetic parameters for the disposition of rPAI-1 antigen after an intravenous bolus injection of 1.0 or 2.5 mg/kg rPAI-1 were very similar for all three forms: the initial volume of distribution was approximately 60 ml/kg, the initial half-life in plasma was 6 minutes, and the plasma clearance was approximately 4 ml/kg/min. The disposition of PAI activity after injection of reactivated rPAI-1 was similar to that of rPAI-1 antigen. Injection of latent rPAI-1 was associated with a nearly threefold increase in the specific activity of circulating PAI-1 from 2 units/micrograms to 5.0 +/- 1.1 units/micrograms (p less than 0.01) within 1 minute, followed by a cumulative 25-fold increase in specific activity over 1 hour (p = 0.01). In contrast, the specific activity of oxidized or reactivated preparations of rPAI-1 did not increase in the first several minutes after injection. These findings support the existence of a fast-acting but low-capacity mechanism for the reactivation of rPAI-1 in vivo.

Induction of plasminogen activator inhibitor by products released from platelets.

Activation of platelets and augmentation of plasma plasminogen activator inhibitor (PAI) type I activity accompany acute myocardial infarction. To determine whether the two may be related, platelet compounds including epidermal growth factor and transforming growth factor beta as well as platelet lysates were studied in rabbits in vivo. After intravenous infusion of epidermal growth factor (1 and 5 micrograms/kg), plasma PAI activity increased sevenfold and 20-fold, peaking at 2 hours. After infusions of transforming growth factor beta (0.2 and 0.5 microgram/kg), plasma PAI activity increased sevenfold and 12-fold but peaked more slowly (at 5 hours). After infusion of platelet lysates (lysates from 2.8 and 5.6 X 10(8) platelets/kg), the increase was 19-fold and 35-fold, with a peak at 4 hours. Platelet lysates induced a pronounced increase of plasma PAI type 1 messenger RNA (Northern blots) in aorta, liver, and myocardium. Anti-transforming growth factor beta neutralizing antibody markedly attenuated the plasma PAI increase. Concentrations in plasma of fibrinogen and alpha 2-antiplasmin were virtually unaffected under all conditions. Thus, platelet-associated growth factors and platelet lysates, shown previously to increase plasma PAI type 1 messenger RNA expression and protein production in cultured hepatocytes and vascular endothelial cells in vitro, augment plasma PAI in vivo as well. Accordingly, activation of platelets and release of platelet-associated growth factors appear to contribute to the increased plasma PAI seen after myocardial infarction.

The pharmacokinetics of plasminogen activator inhibitor-1 in the rabbit.

The pharmacokinetics of the activated and latent forms of plasminogen activator inhibitor-1 (PAI-1) isolated from HT1080 fibrosarcoma cells (HT1080 PAI-1) and a nonglycosylated form of human PAI-1 isolated from a yeast expression system (rPAI-1) were followed in the rabbit. As assessed by an immunologic assay specific for human PAI-1, guanidine HCI activated HT1080 PAI-1 and rPAI-1 entered the total plasma volume following intravenous bolus administration and exhibited a biphasic clearance pattern. The t1/2s of HT1080 PAI-1 for the initial and beta phases equalled 6.0 and 24.8 minutes, respectively. The t1/2s of rPAI-1 for the initial and beta phases equalled 8.8 and 34.0 minutes, respectively. Similar results were obtained by measuring PAI-1 activity in plasma and with trace amounts of 125I-rPAI-1, suggesting that the above pharmacokinetic behavior could also apply to endogenous PAI-1. The liver was the main site of rPAI-1 clearance. Unactivated, latent PAI-1 exhibited a very different pharmacokinetic profile. Over 80% of latent rPAI-1 cleared from the circulation within 10 minutes (t1/2 = 1.7 minutes). The difference in clearance behavior between activated and latent PAI-1 may be related to the ability of activated PAI-1, but not latent PAI-1, to rapidly form high-molecular-weight complexes with plasma binding factors which were observed in vitro and in vivo. Because PAI-1 could potentially tilt the fibrinolytic balance toward a prothrombotic state, its rapid clearance may represent an important control mechanism governing the circulating levels of this key component of the fibrinolytic pathway.