ABSTRACT
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.
Subject(s)
Isoxazoles/pharmacology , Platelet Aggregation Inhibitors/pharmacology , Platelet Glycoprotein GPIIb-IIIa Complex/antagonists & inhibitors , Sulfonamides/pharmacology , Administration, Oral , Animals , Binding, Competitive , Blood Platelets/metabolism , Cell Adhesion/drug effects , Dogs , Enzyme-Linked Immunosorbent Assay , Female , Fibronectins/metabolism , Humans , Integrin alpha4beta1 , Integrins/metabolism , Male , Platelet Aggregation Inhibitors/administration & dosage , Platelet Aggregation Inhibitors/pharmacokinetics , Platelet Glycoprotein GPIIb-IIIa Complex/metabolism , Rats , Receptors, Lymphocyte Homing/metabolism , Receptors, Vitronectin/metabolism , Vitronectin/metabolismABSTRACT
Effects of losartan, L-159,282 and EXP597 on the in vivo binding of [125I-Sar1,Ile8]angiotensin II to kidney cortex and adrenal were examined in rats. Losartan, an AT1 receptor antagonist, completely blocked [125I-Sar1,Ile8]angiotensin II binding to the kidney cortex which contains only AT1 binding sites with an ID50 of 0.06 mg/kg. Losartan partially inhibited [125I-Sar1,Ile8]angiotensin II binding to the adrenal which contains equal amounts of AT1 and AT2 binding sites. Blockade by the AT1 receptor antagonist L-159,282 sufficiently increased the plasma levels of angiotensin II to block the AT2 receptor. EXP597 inhibited [125I-Sar1,Ile8]angiotensin II binding to the kidney cortex and adrenal almost totally with ID50s of 0.05 and 0.06 mg/kg, respectively. This result suggests that EXP597 exhibits almost equal binding affinity for AT1 and AT2 binding sites in vivo in rats.
Subject(s)
Angiotensin II/analogs & derivatives , Angiotensin Receptor Antagonists , Biphenyl Compounds/pharmacology , Imidazoles/pharmacology , Pyridines/pharmacology , Tetrazoles/pharmacology , Angiotensin II/antagonists & inhibitors , Angiotensin II/metabolism , Animals , Antihypertensive Agents/pharmacology , Losartan , Male , Rats , Rats, Sprague-Dawley , Sulfonamides/pharmacologyABSTRACT
A mathematical model has been developed to simulate the generation of thrombin by the tissue factor pathway. The model gives reasonable predictions of published experimental results without the adjustment of any parameter values. The model also accounts explicitly for the effects of serine protease inhibitors on thrombin generation. Simulations to define the optimum affinity profile of an inhibitor in this system indicate that for an inhibitor simultaneously potent against VIIa, IXa, and Xa, inhibition of thrombin generation decreases dramatically as the affinity for thrombin increases. Additional simulations show that the reason for this behavior is the sequestration of the inhibitor by small amounts of thrombin generated early in the reaction. This model is also useful for predicting the potency of compounds that inhibit thrombosis in rats. We believe that this is the first mathematical model of blood coagulation that considers the effects of exogenous inhibitors. Such a model, or extensions thereof, should be useful for evaluating targets for therapeutic intervention in the processes of blood coagulation.
