Disposition and exposure of the fibrinogen receptor antagonist XV459 on alphaIIBbeta3 binding sites in the guinea pig

Zasp regulates integrin activation

Integrins are heterodimeric adhesion receptors that link the extracellular matrix (ECM) to the cytoskeleton. Binding of the scaffold protein, talin, to the cytoplasmic tail of β-integrin causes a conformational change of the extracellular domains of the integrin heterodimer, thus allowing high-affinity binding of ECM ligands. This essential process is called integrin activation. Here we report that the Z-band alternatively spliced PDZ-motif-containing protein (Zasp) cooperates with talin to activate α5β1 integrins in mammalian tissue culture and αPS2βPS integrins in Drosophila. Zasp is a PDZ-LIM-domain-containing protein mutated in human cardiomyopathies previously thought to function primarily in assembly and maintenance of the muscle contractile machinery. Notably, Zasp is the first protein shown to co-activate α5β1 integrins with talin and appears to do so in a manner distinct from known αIIbβ3 integrin co-activators.

A double antibody radioimmunoassay for the determination of XV459, the active hydrolysis metabolite of roxifiban, in human plasma

A radioimmunoassay (RIA) was developed for the determination of XV459, the active hydrolysis metabolite of the oral prodrug roxifiban (DMP 754), in human plasma. XV459 is a potent antagonist of the glycoprotein IIb/IIIa receptor. The method utilizes a competitive double antibody format employing an 125I-labeled XV459 analogue tracer which competes with XV459 for antibody binding sites and a second antibody precipitation step to separate antibody bound analyte from free analyte. The method has a validated lower quantification limit of 0.35 ng/ml (0.81 nM) using 12.5 microl of plasma and with dilution can accommodate clinical plasma samples ranging up to 48.0 ng/ml (110.7 nM). Cross-validation to an existing quantitative liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method showed good correlation (r(2)=0.98). The RIA has been successfully used to assay over 10000 clinical samples with sensitivity and specificity comparable to the LC-MS/MS method, but with faster turn around time and at greatly reduced costs.

Integrated pharmacokinetic/pharmacodynamic model of XV459, a potent and specific GPIIb/IIIa inhibitor, in healthy male volunteers

Roxifiban is an oral prodrug of XV459, a potent and specific inhibitor of the glycoprotein (GP) IIb/IIIa receptor previously under investigation for the treatment of peripheral arterial disease and acute coronary care syndrome. The objective of the present analysis was to develop a pharmacokinetic/pharmacodynamic (PK/PD) model that would be used to guide dose selection in Phase 2. This was a randomized, sequential, rising multiple-dose study in 41 healthy male volunteers given doses of 0.5 to 1.25 mg daily for 7 to 10 days. Total XV459 was measured in plasma by a sensitive and specific LC/MS/MS method. The percent inhibition of platelet aggregation (%IPA) was evaluated in citrated plasma in response to 10 microM ADP using the initial slope of the response. The resulting PK data were fit to a two-compartment model with first-order absorption and saturable oral absorption. The pharmacodynamics was modeled using a direct sigmoidal Emax model. Modeling was performed using NONMEM V. Intersubject variability was moderate in both PK and PD (15.3%-18.5%), except for V2/F (64.8%). Residual variability was low at 11.8%. Platelet count influenced both CL/F and EC50. Age and weight did not explain any additional variability in either PK or PD. The model was shown to produce realistic data when used for simulation. Overall, the results suggest that XV459 concentrations in the range of 10 to 20 ng/ml will yield %IPA values in the range of 40% to 80% inhibition. Because of the pharmacodynamically mediated PK of XV459 (due to platelet binding), the EC50 and CL/F are negatively correlated, limiting the utility of plasma concentration monitoring.

Safety, tolerability, pharmacokinetics, and time course of pharmacologic response of the active metabolite of roxifiban, XV459, a glycoprotein IIb/IIIa antagonist, following oral administration in healthy volunteers

Roxifiban is an esterprodrug that is hydrolyzed, after oral administration, to the active glycoprotein (GP) IIb/IIIa antagonist, XV459. The objectives of the study were to investigate the safety, tolerability, pharmacokinetics, and the time course of the pharmacologic response of XV459 in escalating doses of roxifiban and to assess the effect of age, loading dose of roxifiban, and aspirin pretreatment on XV459 pharmacokinetics, pharmacologic response, and safety profile in a five-part double-blind, placebo-controlled study. Healthy male volunteers (ages 18-46 years) received 7 (0.75-1.5 mg; n = 20) and 10 (0.75-1.0 mg; n = 8) multiple, oral, qd doses of roxifiban or placebo (n = 5). Healthy older male and female volunteers (ages 47-75 years) received roxifiban qd doses (0.5-0.75 mg; n = 8) or placebo (n = 3) for 7 days. Healthy male subjects (ages 18-46 years; n = 16) received a 1.5 or 1.0 mg loading dose either with or without pretreatment of 325 mg aspirin once daily for 3 days followed by single daily doses of 1.0 mg roxifiban for 6 days. Measurable plasma concentrations of XV459 appeared rapidly and were sustained throughout the dosing interval of 24 hours. The pharmacokinetics of XV459 were nonlinear. Systemic exposure of XV459 plateaued at the 1-mg dose level; plasma concentrations approached steady state in 4 to 6 days for doses greater than 1.0 mg. The time course of pharmacologic response as measured by the inhibition of platelet aggregation in response to an ex vivo 10 microM adenosine 5'-diphosphate (ADP) agonist correlated closely to the plasma concentration of XV459. Potent inhibition of ADP-induced platelet aggregation (IPA) persisted over the entire dosing interval. A clear dose response was achieved with roxifiban doses of 0.5 and 1.0 mg. For doses greater than 1.0 mg, a dose-proportional increase in IPA was not observed. Both the pharmacokinetics and pharmacologic response of XV459 exhibited low intraindividual variability (coefficient of variation [CV] < 15%) and higher interindividual variability (CV < 30%). Pretreatment with aspirin and/or a loading dose of 1.5 mg roxifiban had no significant effect on the pharmacokinetics and pharmacologic response of XV459. A dose-related increase in template bleeding time was observed at 1.25- and 1.5-mg doses of roxifiban, as compared to placebo. However, these bleeding time increases in the 1.25- and 1.5-mg dose groups were not significantly different from those at the lower dose groups. Overall, once-daily oral administration of roxifiban was fairly well tolerated and provided sustained systemic drug exposure and pharmacologic response over the entire administration interval.

Pharmacokinetic/pharmacodynamic studies in drug product development

In the quest of ways for rationalizing and accelerating drug product development, integrated pharmacokinetic/pharmacodynamic (PK/PD) concepts provide a highly promising tool. PK/PD modeling concepts can be applied in all stages of preclinical and clinical drug development, and their benefits are multifold. At the preclinical stage, potential applications might comprise the evaluation of in vivo potency and intrinsic activity, the identification of bio-/surrogate markers, as well as dosage form and regimen selection and optimization. At the clinical stage, analytical PK/PD applications include characterization of the dose-concentration-effect/toxicity relationship, evaluation of food, age and gender effects, drug/drug and drug/disease interactions, tolerance development, and inter- and intraindividual variability in response. Predictive PK/PD applications can also involve extrapolation from preclinical data, simulation of drug responses, as well as clinical trial forecasting. Rigorous implementation of the PK/PD concepts in drug product development provides a rationale, scientifically based framework for efficient decision making regarding the selection of potential drug candidates, for maximum information gain from the performed experiments and studies, and for conducting fewer, more focused clinical trials with improved efficiency and cost effectiveness. Thus, PK/PD concepts are believed to play a pivotal role in streamlining the drug development process of the future.