Structure-based design of potent, amidine-derived inhibitors of factor Xa: evaluation of selectivity, anticoagulant activity, and antithrombotic activity.

To enhance the potency of 1,2-dibenzamidobenzene-derived inhibitors of factor Xa (fXa), an amidine substituent was incorporated on one of the benzoyl side chains to interact with Asp189 in the S1 specificity pocket. Lead molecule 1 was docked into the active site of fXa to facilitate inhibitor design. Subsequently, iterative SAR studies and molecular modeling led to a 1000-fold increase in fXa affinity and a refined model of the new inhibitors in the fXa active site. Strong support for the computational model was achieved through the acquisition of an X-ray crystal structure using thrombin as a surrogate protein. The amidines in this series show high levels of selectivity for the inhibition of fXa relative to other trypsin-like serine proteases. Furthermore, the fXa affinity of compounds in this series (K(ass) = 50-500 x 10(6) L/mol) translates effectively into both anticoagulant activity in vitro and antithrombotic activity in vivo.

MDL 101,002, a free radical spin trap, is efficacious in permanent and transient focal ischemia models.

The present work describes the neuroprotective effects of the free radical spin trap, MDL 101,002, in models of permanent and transient focal ischemia. Permanent focal ischemia was carried out by occlusion of the distal segment of the middle cerebral artery (MCA) and CCA's in Spontaneously Hypertensive (SH) and Wistar rats. Transient focal ischemia was undertaken by occluding the origin of the MCA for 180 min by the intraluminar monofilament method in Wistar rats. With permanent distal MCA occlusion in SH rats, 100 mg/kg i.v. at 30 min post-ischemia resulted in a significant 40% reduction in infarct volume. Similarly, a 75 mg/kg bolus + 45 mg/kg-h dose of MDL 101,002 given i.v. at 5 min post-ischemia resulted in a 90% or 60% decrease in infarct volume in the mixed permanent/transient distal MCA model with Wistar rats using 120 or 180 min of CCA occlusion, respectively. When full reperfusion was established, after 180 min of occlusion in the proximal MCA model, a dose of 40 mg/kg + infusion and 75 mg/kg + infusion resulted in a significant 50% and 70% decrease in ischemic damage, respectively. MDL 101,002 is clearly an effective neuroprotective agent in all models examined. This work would suggest that this novel cyclic nitrone spin trap affords effective neuroprotection and is useful for the treatment of ischemic stroke.

Lipid-based delivery systems for improving the bioavailability and lymphatic transport of a poorly water-soluble LTB4 inhibitor.

Ontazolast is a potent inhibitor (IC50 = 1 nm) of calcium ionophore A23187-stimulated leukotriene B4 (LTB4) biosynthesis in human peripheral blood leukocytes. The compound is practically insoluble in water (0.14 microgram/mL) and previous studies in animals have demonstrated extensive presystemic drug clearance through hepatic first-pass metabolism. Bioavailability of a suspension formulation in rats was less than 1%, but increased to approximately 9% when administered as a 20% soybean oil-in-water emulsion. The emulsion formulation and three additional lipid-based formulations were administered by gavage to conscious, minimally restrained rats in a novel, double-cannulated model to determine the effects of formulation on systemic blood absorption and mesenteric lymph transport of ontazolast. The bioavailability of ontazolast was significantly and substantially enhanced by all of the lipid-based formulations. While these formulations also significantly increased the amount of ontazolast transported by the lymph, the total amounts transported were insufficient to account for the improvement in bioavailability, which may be due to the elimination or reduction of the barriers of poor aqueous solubility and slow dissolution to absorption of ontazolast from the gastrointestinal tract, or the effects of lipid on the gastrointestinal membrane permeability, transit time, or metabolism of ontazolast. Semisolid SEDDS formulations, composed of Peceol and Gelucire 44/14, produced bioavailability similar to the emulsion formulation. The total amount of ontazolast transported by the lymph varied directly with the amount of concurrent triglyceride transport and appeared to be favored by formulations that prolong gastric emptying time or promote rapid absorption of ontazolast from the gastrointestinal tract.