Oral antiplatelet efficacy and specificity of a novel nonpeptide platelet GPIIb/IIIa receptor antagonist, DMP 802

This study was undertaken to define the platelet glycoprotein alphaIIb beta3 integrin (GPII/IIIa) affinity, specificity, and oral antiplatelet efficacy of DMP 802, a small-molecule nonpeptide antiplatelet agent. Platelet GPIIb/IIIa integrin binding affinity and specificity for DMP 802 were determined by using binding and adhesion assays with cells from various species, including human. DMP 802 demonstrated a potent antiplatelet efficacy [median inhibitory concentration (IC50), 0.029 +/- 0.0042 microM] in inhibiting human platelet aggregation induced by 10 microM adenosine diphosphate (ADP), as assessed by light-transmittance aggregometry. DMP 802 inhibited 125I-fibrinogen binding to activated (ADP, epinephrine, and arachidonic acid at 100 microM each) gel purified human platelets with an IC50 of 0.012 +/- 0.003 microM. DMP 802 demonstrated tight association with unactivated human, baboon, or canine platelets (t(1/2) of dissociation, 32 +/- 2, 32 +/- 13, and 11 +/- 1 min, respectively). DMP 802 binds with high affinity to both unactivated and activated human platelets (Kd = 0.61 +/- 0.17, 0.57 +/- 0.21 nM, respectively). DMP 802 demonstrated species specificity in inhibiting platelet aggregation with IC50 values ranging from 0.025 to 0.092 microM (human, guinea pig, dog, swine, hamster) and 0.88-1.0 microM (rabbit and rat) in platelets obtained from these various species. DMP 802 demonstrated a high degree of specificity for platelet GPIIb/IIIa (alphaIIb/beta3) as compared with other integrins including alpha(v)beta3 (IC50, >10 microM), alpha(v)beta5 (IC50, >100 microM), alpha4beta1 (IC50, >100 microM), and alpha5beta1 (IC50, >10 microM). Oral antiplatelet efficacy of DMP 802 was examined after single oral (0.05-0.20 mg/kg) and after repeated oral dosing at 0.05 mg/kg daily for 5 days in mongrel dogs. Dose-dependent antiplatelet efficacy with an extended duration of antiplatelet efficacy was demonstrated based on ex vivo inhibition of platelet aggregation induced by 100 microM ADP. DMP 802 has an oral bioavailability of 14.9% in dogs. In conclusion, the alpha sulfonamide isoxazoline analog, DMP 802, is a novel oral antiplatelet agent with high affinity, relatively slow dissociation rate and specificity for human platelet GPIIb/IIIa receptors.

Intravenous and oral antiplatelet/antithrombotic efficacy and specificity of XR300, a novel nonpeptide platelet GPIIb/IIIa antagonist

Currently used antiplatelet drugs including aspirin, ticlopidine, and others are effective against certain but not all of the many endogenous platelet activators. Because of their limited efficacy, a significant number of serious thromboembolic complications still occur, highlighting the need for a more effective therapy. Thus our study was undertaken to define the antiplatelet efficacy, specificity, and the intravenous and oral antiplatelet/antithrombotic effects of a nonpeptide glycoprotein alphaIIb beta3 integrin (GPIIb/IIIa) antagonist XR300, an ethyl ester prodrug of XR299. XR300, on its conversion to the active form XR299, inhibited human platelet aggregation induced by 100 microM adenosine diphosphate (ADP) with a median inhibitory concentration (IC50) of 0.09 microM. Similarly, XR299 inhibited 125I-fibrinogen binding to human gel-purified platelets (IC50, 0.01 microM) regardless of the agonist used. In purified human GPIIb/IIIa, XR299 demonstrated a competitive high-affinity binding with an IC50 of 1.2 nM. XR299 demonstrated a high degree of specificity for platelet GPIIb/IIIa (alphaIIb beta3) as compared with other integrins including alpha(v)beta3, alpha(v)beta5, and alpha4beta1, where IC50 values were >10 microM. XR300 administered to mongrel dogs either intravenously (0.5-1.0 mg/kg, i.v.) or orally at 1.0-2.0 mg/kg, demonstrated maximal antiplatelet effects with rapid onset and extended duration. XR300 demonstrated maximal antithrombotic efficacy in preventing the incidence of occlusive thrombosis or cyclic flow reduction (CFR) in the carotid or femoral artery thrombosis models induced either electrolytically or by mechanical injury along with stenosis. In conclusion, XR300 is a novel intravenous and oral antiplatelet/antithrombotic agent with high affinity and specificity for platelet GPIIb/IIIa receptors.

Discovery of an orally active series of isoxazoline glycoprotein IIb/IIIa antagonists

Using isoxazoline XR299 (1a) as a starting point for the design of highly potent, long-duration GPIIb/IIIa antagonists, the effect of placing lipophilic substituents at positions alpha and beta to the carboxylate moiety was evaluated. Of the compounds studied, it was found that the n-butyl carbamate 24u exhibited superior potency and duration of ex vivo antiplatelet effects in dogs. Replacement of the benzamidin-4-yl moiety with alternative basic groups, elimination of the isoxazoline stereocenter, and reversal of the orientation of the isoxazoline ring resulted in lowered potency and/or duration of action.

Discovery of potent isoxazoline glycoprotein IIb/IIIa receptor antagonists

Using the isoxazoline as a common structural feature, three series of glycoprotein IIb/IIIa receptor antagonists were evaluated, culminating in the discovery of XR299 (30). In an in vitro assay of platelet inhibition, XR299 had an IC50 of 0.24 microM and was a potent antiplatelet agent when dosed intravenously in a canine model. It was shown through X-ray studies of the cinchonidine salt 49 that the receptor required the 5(R)-stereochemistry for high potency. The ethyl ester prodrug of XR299, XR300 (29), was orally active in the dog.

Novel nonpeptide antiplatelet glycoprotein IIb/IIIa receptor antagonist, DMP754: receptor binding affinity and specificity

OBJECTIVE

To define the antiplatelet efficacy and specificity of the glycoprotein IIb/IIIa complex (GPIIb/IIIa) antagonist prodrug DMP754 and its free acid form, XV459.

METHODS AND MATERIALS

DMP754 has an IC50 > 1 mumol/l, and, upon its conversion with esterases to its free acid form, demonstrated high potency (IC50 20-45 nmol/l) in inhibiting human platelet aggregation induced by 10 mumol/l adenosine diphosphate, 20 micrograms/ml collagen, 1 mmol/l epinephrine, 10 mumol/l platelet activating factor or 0.5 IU/ml thrombin. The in-vitro rate of hydrolysis of DMP754 or XV459 is much faster with human or canine liver esterases (t 1/2 = 2.4-23 min) than with plasma esterases (t 1/2 = 5.5-7.6 h). Platelet GpIIb/IIIa integrin binding affinity and specificity for XV459 were determined using cell binding/adhesion assays.

RESULTS

The range of IC50 values of XV459 in inhibiting platelet aggregation in platelet-rich plasma obtained from 12 subjects was 0.035-0.069 mumol/l with a mean IC50 of 0.050 +/- 0.003 mumol/l. Additionally, XV459 inhibited platelets obtained from mongrel dogs, baboons, sheep, guinea pigs, and mice with IC50 in the range 0.024-0.06 mumol/l, and IC50 in the range 0.16-5.8 mumol/l in pigs, rabbits, and rats. XV459 inhibited [125I]-fibrinogen binding to activated human platelets with an IC50 of 0.011 +/- 0.003 mumol/l. XV459 demonstrated a high degree of selectivity in specifically inhibiting fibrinogen binding to the platelet integrin, GPIIb/IIIa (IC50 = 0.00025 +/- 0.00005 mumol/l) compared with inhibiting other integrins (alpha v beta 3, IC50 > 10 mumol/l; or alpha v beta 5, alpha 5 beta 1, or alpha 4 beta 1, for which the IC50 exceeded 100 mumol/l).

CONCLUSION

DMP754 is a potent antiplatelet agent in inhibiting platelet aggregation, and has a high specificity and affinity for human platelet GPIIb/IIIa receptors.