Section Review: Cardiovascular & Renal: Glycoprotein IIb/IIIa antagonists

Glycoprotein IIb/IIIa (GPIIb/IIIa) antagonists have been shown to be effective in reducing the rate of ischaemic complications due to pathophysiological conditions such as atherosclerosis or coronary intervention. This review will cover all patenting activity in this now mature field of research up to and including August 1996, and will focus on the more significant patents and patent applications.     

Characterization of the anti‐platelet actions of FK419, a novel non‐peptide antagonist of platelet GPIIb/IIIa

The anti‐platelet properties of FK419 ((S)‐2‐acetylamino‐3‐[(R)‐[1‐[3‐(piperidin‐4‐yl)propionyl]piperidin‐3‐ylcarbonyl] amino]propionic acid), a novel non‐peptide GPIIb/IIIa antagonist, were compared in a variety of experimental settings, both in vitro and in vivo, with other GPIIb/IIIa antagonists including xemilofiban, lamifiban, tirofiban, and FK633. Receptor binding studies suggested that FK419 had potent GPIIb/IIIa antagonistic activity that is comparable with those of reference antagonists. FK419 effectively inhibited human platelet aggregation, regardless of agonist stimuli (IC₅₀ = 35–170 nM). FK419 demonstrated in vitro species‐dependent anti‐platelet activity, with higher potency in human than in dog, guinea pig, or rat tissue, and dose‐dependently inhibited ex vivo platelet aggregation in dogs and guinea pigs. In contrast to other antagonists, FK419 minimally affected template bleeding time at doses that completely inhibited platelet aggregation in canines. These results demonstrate that FK419 is a novel, potent, and selective GPIIb/IIIa antagonist that safely inhibits platelet aggregation in vivo, suggesting that it may be a promising anti‐platelet agent for thrombotic diseases. Drug Dev. Res. 61:233–241, 2004. © 2004 Wiley‐Liss, Inc.     

Enhancement of fibrinolysis by gel-filtered platelets and its quenching by cytochalasin B and GPIIb/IIIa antagonists

The effects of gel-filtered platelets on euglobulin clot lysis time (ECLT) were analyzed to elucidate the possible role of platelets in thrombolysis. Gel-filtered platelet-supplemented ECLT (plt-ECLT) was significantly shorter than ECLT without platelets (regular ECLT). Abciximab, anti-glycoprotein IIb/IIIa (GPIIb/IIIa) antibody, and cytochalasin B nullified the enhancement of ECLT by platelets, and increased plt-ECLT beyond regular ECLT. When gel-filtered platelets were used after disruption, ECLT was not shortened but rather became longer than regular ECLT, probably due to natural fibrinolysis inhibitors released from platelets. Therefore, for platelets to enhance fibrinolysis, intact cell structure and cytoskeletal reorganization after thrombin stimulation is required. Various GPIIb/IIIa antagonists prolonged plt-ECLT. The concentrations of GPIIb/IIIa antagonists required to prolong plt-ECLT, were varied. Interestingly, the effects of these antagonists were independent of their ability to inhibit thrombin-induced platelet aggregation, but dependent on their ability to induce clot retraction. T-250, a GPIIb/IIIa antagonist, had the smallest effect on plt-ECLT. These drugs do not affect regular ECLT or tissue plasminogen activator (tPA)-catalyzed Glu-plasminogen activation in the presence of thrombinactivated platelets. Although their overall effect on thrombolysis is inhibitory, platelets could promote fibrinolysis through a GPIIb/IIIa-dependent mechanism.     

糖蛋白IIb/IIIa受体拮抗剂三维构效关系研究

目的：研究三维构效关系,建立药效模型,为设计新型糖蛋白IIb/IIIa受体拮抗剂提供指导。方法和结果：利用比较分子力场方法,建立了IIb/IIIa受体拮抗剂的三维定量构效模型。在比较分子力场分析中,利用拮抗剂晶体结构为模板,进行了多种分子叠合形式研究,建立了具有良好预测能力的三维定量构效关系模型,表征模型预测能力的交叉验证系数R_CV²＝0.834,传统相关系数R²＝0.988,F＝323.63,标准偏差SE（Standard Error of Estimate）＝0.135。结论：所得模型解释了已有的构效关系,系数等势图映射的受体性质与实验结果相一致,可以指导新的拮抗剂设计。     

Pharmacodynamic characterization of the interaction between the glycoprotein IIb/IIIa inhibitor YM337 and unfractionated heparin and aspirin in humans

AIMS: To investigate the pharmacodynamic interaction of unfractionated heparin (UFH) and acetylic salicylic acid (ASA) on YM337, a monoclonal humanized antibody of the platelet GPIIb/IIIa receptor. METHODS: In a randomized, placebo-controlled study three treatment groups each with six healthy volunteers received the following medication: group 1, ASA (3 days) + UFH + YM337 (placebo); group 2, ASA (placebo) + UFH (placebo) + YM337; group 3, ASA + UFH + YM337. Assessments were made over 24 h and included bleeding time (BT), ADP (20 microm)- and collagen (5 microg ml-1)-induced platelet aggregation and PAC1 and CD62 expression measured by flow cytometry. RESULTS: In group 3 BT was prolonged to 35 [median, 16-45 min (1,3 quartile)] after UFH administration, increasing to 45 [median, 42-45 min (1,3 quartile)] after YM infusion (6 h). BT remained elevated to 26 [median, 14-45 min (1,3 quartile)] at 24 h, while groups 1 and 2 returned to normal values. Collagen-induced aggregation was 73% [median, 70-80% (1,3 quartile)] under YM337 alone, 79% [median, 72-80% (1,3 quartile)] under ASA + UFH and reduced only in group 3 to 24% [median, 18-29% (1,3 quartile)]. In both groups receiving active YM337, PAC1 expression showed a reduction to < 20% after 6 h of infusion. CD62 expression was not significantly affected by any treatment. CONCLUSION: UFH and YM337 have strong synergistic effects on BT, while coadministration of ASA strongly augments inhibitory effects of YM337 on collagen-induced platelet aggregation.     

Utilization of an Amorphous Form of a Water-Soluble GPIIb/IIIa Antagonist for Controlled Release from Biodegradable Microspheres

Purpose. We prepared injectable microspheres for controlled release of TAK-029, a water-soluble GPIIb/IIIa antagonist and discussed the characteristics of controlled release from microspheres. Methods. Copoly(dl-lactic/glycolic)acid (PLGA) microspheres were used for controlled release of TAK-029 [4-(4-amidinobenzoylglycyl)-3-methoxycarbonyl-2-oxopiperazine-l-acetic acid]. They were prepared with a solid-in-oil-in-water (S/O/W) emulsion solvent evaporation technique using either a crystalline form or an amorphous form of the drug. Results. An amorphous form of TAK-029 gave more homogeneous S/O dispersion and higher viscosity than its crystalline form when added to dichloromethane solution of PLGA, resulting in a high drug entrapment into microspheres and a well-controlled release of the drug. Additions of sodium chloride into an external aqueous phase and L-arginine into an oil phase also increased entrapment of the drug, and reduced initial burst of the drug from the microspheres. The micro-spheres demonstrated a desirable plasma level profile in therapeutic range (20–100 ng/ml) for 3 weeks in rats after single subcutaneous injection. Conclusions. A well-controlled release of TAK-029, a water-soluble neutral drug, with small initial burst was achieved by utilizing its amorphous form as a result of possible interaction with PLGA and L-arginine.     

Prodrug and Analog Approaches to Improving the Intestinal Absorption of a Cyclic Peptide,GPIIb/IIIa Receptor Antagonist

Purpose. The purpose of this study was to test whether structural modifications improve the intestinal absorption of DMP 728 (cyclo(D-Abu-NMeArg-Gly-Asp-Amb)), a GPIIb/IIIa receptor antagonist. Methods. In vitro permeabilities of prodrugs and analogs of DMP 728 across excised rat intestinal segments were determined. Results. n-Butyl and n-octyl esters of DMP 728 were relatively stable during in vitro permeation of rat intestine. Intestinal permeation rates of these compounds were no greater than that of DMP 728, even though the octyl ester was much more lipophilic. A pivaloyloxymethyl ester, which was hydrolyzed to DMP 728 during intestinal permeation, also did not improve permeability. In another approach, analogs with an additional methyl substituent on various amide nitrogens were evaluated. Cyclo(D-Val-NMeArg-Gly-Asp-NMeAmb), cyclo(D-Abu-diN-MeLys-Gly-Asp-Amb), and cyclo(NMeGly-NMeArg-Gly-Asp-Amb) each had about 2-fold greater permeability than DMP 728. Two other analogs with improved permeability were linear Ac-D-Abu-NMeArg-Gly-Asp-Amb and a DMP 728 derivative in which the Asp was rearranged. An analog in which the charged amino acids were replaced by neutral amino acids had permeability similar to DMP 728. Conclusions. Within this series of peptides, hydrogen bonding tendency and structural constraint influenced intestinal permeation, but not always in ways consistent with the literature, whereas charge and lipophilicity were not shown to influence intestinal permeability. The failure of these approaches to improve permeation more significantly could be due to the influence of secretory transport.     

Platelet alpha-granule secretion and its modification by SC-57101A,a GPIIb/IIIa antagonist

Platelet-agonist interaction results in aggregatory and secretory responses. While the activation of glycoprotein (GP) IIb/IIIa plays an essential role in platelet aggregation, its role in granule secretion is not clear. The present study was performed to examine the effect of 3-[[[[1-[4-(aminoiminomethyl) phenyl]-2-oxo-3S-pyrrolidinyl]amino]carbonyl]amino]-propanoate monohydrochloride salt (SC-57101A), a GPIIb/IIIa antagonist, on platelet alpha-granule secretion responses to collagen, ADP, and thrombin receptor activating peptide (TRAP). Both SC-57101A and prostaglandin E(1) (PGE(1)) inhibited collagen-, ADP-, and TRAP-induced platelet aggregation in a concentration-dependent manner. SC-57101A inhibited the collagen- and ADP-induced release of platelet-derived growth factor (PDGF) and beta-thromboglobulin (beta-TG) from platelets, but not TRAP-induced secretion of these granule contents. On the other hand, PGE(1) inhibited the release of PDGF and beta-TG from platelets activated with all the agonists used. ADP and TRAP elicited P-selectin expression in the absence of platelet aggregation, while collagen produced no such reaction. SC-57101A only moderately inhibited P-selectin expression induced by ADP and had no inhibitory effect on that induced by TRAP. The inhibition of ADP-induced secretion of alpha-granule contents by SC-57101A was abolished when platelets were pretreated with aspirin. These results suggest that GPIIb/IIIa activation plays a minor role, if any, in alpha-granule secretion in human platelets.     

多抗夹心ELISA测定人血浆普莱单抗浓度

建立多抗夹心ELISA测定人血浆普莱单抗(anti-GPIIb/IIaF(ab)2)浓度的方法并进行方法学验证.采用复合快速免疫法免疫家兔获得抗血清,经常规及普莱单抗特异性亲和层析纯化,并以人AB型血浆偶联的Sephorose 4B凝胶去除与人血浆的交叉反应.以获得的特异性多抗包板,生物素标记的该多抗为检测抗体,建立测定人血浆普莱单抗浓度的多抗夹心ELISA法,并进行了方法学验证.复合快速免疫法可在较短的时间内获得了高滴度的抗普莱单抗的多抗;利用所获得的多抗构建的ELISA试剂盒测定普莱单抗的浓度范围为1.56～50ng·mL-1,方法学认证的各项指标符合药代动力学研究的要求,为进行临窗前及临床普莱单抗药物代谢动力学研究奠定了坚实的基础,为其它单抗及高分子生物技术药物的药代动力学研究提供了借鉴思路.     

GP Iib/IIIa拮抗剂integrilin在经皮冠状动脉支架成形术围术期的运用

目的 :报告GPIIb/IIIa拮抗剂integrilin在经皮冠状动脉支架成形术围术期运用的方法和结果。方法 :9例接受经皮冠状动脉支架成形术患者动脉穿刺完成后即刻注入Integrilin 1 80 μg/kg ,然后按 2 μg/kg/min维持 ,维持时间为 1 2h ,联合应用阿司匹林、Plavix、肝素等其他抗凝和抗血小板药物。常规监测ACT、PT和KPTT ,出院前及术后 1月复查血细胞各 1次。结果 :全部患者均在术后 2 -4h拔除鞘管 ,无穿刺部位显著血肿形成者 ,无冠状动脉急性和亚急性血栓形成者。术后血小板无显著改变 ,术后 8例患者ACT在 2h内和 1例在 4h内恢复至≤ 1 50 ,KPTT在术后 2h与术前相比有显著性差异 ,PT和血小板记数术前、术后无显著性改变。术后随访 3-4月 ,无心绞痛症状复发者。结论 :GPIIb/IIIa拮抗剂integrilin在经皮冠状动脉支架成形术围术期运用 ,结合抗血小板药物Plavix和阿司匹林 ,能显著减少肝素用量和缩短运用时间 ,缩短血管鞘的留置时间 ,而未显示增加出血危险性 ,也未发生支架内血栓形成者。     

Platelet glycoprotein IIb/IIIa receptor antagonists

The molecular understanding of platelet function, together with an appreciation of the role of platelet thrombus in the pathogenesis of acute coronary syndromes (ACS) and abrupt vessel closure following coronary intervention, lead to the development of the class of agents now referred to as platelet glycoprotein IIb/IIIa (GP IIb/IIIa) inhibitors. Currently three parenteral GP IIb/IIIa inhibitors are licensed for use in patients undergoing coronary intervention or as empirical therapy in non-ST elevation ACS (unstable angina and non-Q wave myocardial infarction). Clinical trials using these agents in patients undergoing coronary interventions have demonstrated a consistent reduction in ischaemic end points at 30 days that is sustained during long-term follow-up. Similar benefits have been found in patients with ACS who are managed medically or who proceed to revacularisation. Studies using prolonged platelet inhibition using oral GP IIb/IIIa inhibitors in patients following coronary intervention or with ACS have produced disappointing results. Further investigation with existing and newer oral agents are ongoing. The use of GP IIb/IIIa inhibitors in combination with fibrinolytic agents for optimal reperfusion in patients with acute ST-elevation myocardial infarction (MI) is an active area of interest. Angiographic outcomes with this approach have been encouraging and clinical outcome data are awaited. Beyond efficacy, GP IIb/IIIa inhibitors have proven to be safe for clinical use. Haemorrhagic complications and thrombocytopenia are the most common adverse events, though infrequent. Unresolved issues regarding drug dosing, monitoring of effect, duration of therapy, head-to-head comparisons of agents, and use of adjunctive therapies are the subject of ongoing studies.     

Lotrafiban: an oral platelet glycoprotein IIb/IIIa blocker

Platelets play a major role in thrombus formation, as well as in the pathogenesis of atherothrombosis. Inhibition of platelet function is now emphasised more than ever for prevention and treatment of almost all vascular diseases, since thrombosis is established as the key pathogenic event causing acute ischaemic coronary and cerebrovascular syndromes. Although acetylsalicylic acid (aspirin) has been shown to reduce the incidence of myocardial infarction and stroke, its effect is weak and more effective antithrombotic agents are required to manage patients at high-risk for recurrent vascular events. Platelet glycoprotein IIb/IIIa receptor (GPIIb/IIIa) blockade represents a significant advance in interventional cardiology and treatment of acute ischaemic syndromes. The past several years have seen the introduction of many platelet GPIIb/IIIa blockers into the clinical arena targeting the unique platelet GPIIb/IIIa receptor for the adhesive proteins, fibrinogen and von Willebrand Factor. Platelet GPIIb/IIIa blockers administered intravenously have proven efficacious in mitigating arterial thrombosis in acute coronary syndromes (unstable angina and non-ST-elevation myocardial infarction) and percutaneous coronary interventions (PCI) such as balloon dilatation and stent implantation. Currently, orally-active platelet GPIIb/IIIa blockers are being developed to provide additional benefits for primary and secondary prevention of thrombosis as chronic treatment, especially in high-risk patients. Lotrafiban (SmithKline Beecham) is a member of the latest generation of orally-active platelet GPIIb/IIIa blockers undergoing Phase III clinical trials to test the relative effectiveness versus other oral platelet inhibitors for ischaemic conditions including unstable angina, restenosis after PCI and stroke. Lotrafiban is converted from an esterified prodrug by plasma and liver esterases to a peptidomimetic of the arginine-glycine-aspartic acid amino acid sequence. This sequence itself mimics the binding site of fibrinogen and von Willebrand Factor to the platelet GPIIb/IIIa receptor. Preliminary results of the clinical trial APLAUD (antiplatelet useful dose) show that lotrafiban is clinically safe and well-tolerated in patients with recent myocardial infarction, unstable angina, transient ischaemic attack (TIA), or stroke when added to aspirin therapy. With lotrafiban, a worldwide large-scale Phase III clinical trial BRAVO (blockage of the GPIIb/IIIa receptor to avoid vascular occlusion) is currently underway. In general, GPIIb/IIIa blockade seems clinically very promising. A number of unresolved issues, however, remain to be elucidated.     

Pharmacokinetic and pharmacodynamic effects of YM087, a combined V1/V2 vasopressin receptor antagonist in normal subjects

Objective: The pharmacokinetic and pharmacodynamic properties of YM087, (4′-[(2-methyl-1,4,5,6-tetrahydroimidazo[4,5-d][1]benzazepin-6-yl)-carbonyl]-2-phenylbenzanilide monohydrochloride), a new orally active, dual V₁/V₂ receptor antagonist were characterised in healthy normotensive subjects. Methods: Six subjects were randomly allocated to receive, at 1-week intervals, a single oral dose of 60 mg YM087 and a single i.v. dose of 50 mg YM087 in an open-label, crossover study. Results: YM087 had an oral bioavailability of 44% and a short half-life. Upon oral and i.v. administration of YM087, a significant sevenfold increase in urine flow rate and a fall in urinary osmolality (from 600 mosmol/l to less than 100-mosmol/l) were observed with a peak effect 2 h after drug intake suggesting effective vasopressin V₂ receptor blockade. Simultaneously, significant increases in plasma osmolality (from 283 ± 1.3 mosmol/l to 288 ± 1.0 mosmol/l after i.v. and from 283 ± 2.1 mosmol/l to 289 ± 1.7-mosmol/l after oral administration) and vasopressin levels (from 1.5 ± 0.3 pg/ml to 3.7 ± 0.6 pg/ml after i.v. and from 0.9 ± 0.1 pg/ml to 3.9 ± 0.7 pg/ml after oral administration) were found. When administered i.v., YM087 inhibited the vasopressin-induced skin vasoconstriction, suggesting a blockade of V₁ receptors. However, the YM087-induced antagonism of V₁ receptors was less pronounced than V₂ receptor blockade. Conclusion: These data show that YM087 is an effective dual V₁/V₂ receptor antagonist in man. Received: 17 February 1999 / Accepted in revised form: 18 August 1999     

Effect of YM928, a novel AMPA receptor antagonist,on seizures in EL mice and kainate-induced seizures in rats

Kainate-induced seizures and seizures induced by tossing stimulation in epilepsy-prone EL mice are considered as models of complex partial seizures. We used these models to evaluate the anticonvulsive effects of 2-[N-(4-chlorophenyl)-N-methylamino]-4H-pyrido[3.2-e]-1,3-thiazin-4-one (YM928), a novel -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist. In the kainate-induced seizure test in rats, wet-dog shakes (WDS) were reduced by oral administration of YM928 at doses of 7.5 mg/kg and 30 mg/kg. YM928 (15 mg/kg) reduced the number of WDS within the first 80 min, but then prolonged the time of occurrence compared with the other groups. Significant reduction in kainate-induced motor seizure was observed with 4–30 mg/kg. YM928 did not induce apparently abnormal behaviour at doses of 2–15 mg/kg but did induce sedation at 30 mg/kg. Carbamazepine (40 or 80 mg/kg), valproate (600 mg/kg), diazepam (2.5 mg/kg), and phenobarbital (20 or 40 mg/kg) exerted anticonvulsant effects against motor seizures, but only valproate, at a dose that also caused sedation, suppressed WDS. Phenytoin and ethosuximide did not show significant anti-kainate effects. In the tossing stimulation test in EL mice, i.p. injection of YM928 at 5 mg/kg or 10 mg/kg significantly increased the number of stimulations required to elicit generalized seizure. Carbamazepine (4 or 8 mg/kg), phenytoin (8 or 16 mg/kg), valproate (100–400 mg/kg), diazepam (0.5 mg/kg), phenobarbital (1.3 or 2.5 mg/kg) and ethosuximide (75–300 mg/kg) exerted significant anticonvulsant effects against these seizures. These results indicate that YM928 has anticonvulsant effects on seizure models that are characteristic of partial onset seizures in humans. YM928 is expected to have beneficial effects against human complex partial seizure with secondary generalization or temporal lobe epilepsy.     

YM461, a PAF antagonist, blocks antigen-induced late airway responses and airway hyperresponsiveness in allergic sheep

We examined the effect of an orally active antagonist, YM461, of platelet activating factor (PAF) on antigen-induced early and late airway responses and on the development of airway hyperresponsivenss 24 h after challenge in allergic sheep. Early and late airway responses were determined by measuring specific lung resistance (SR_L) before and periodically after challenge. Airway responsiveness was determined from the slopes of dose-response curves of SR_L vs. increasing doses of carbachol aerosol. The sheep were challenged with Ascaris suum antigen once after vehicle treatment (control) and once 1 h after oral administration of 3 or 10 mg/kg YM461 (each trial was 14 days apart). Airway responsiveness to carbachol was determined 1–3 days prior to and 24 h after antigen challenge. In control 1 and control 2 trials antigen challenge caused significant peak early (288 and 292%, respectively) and peak late (103 and 124%, respectively) increases over baseline in SR_L. SR_L returned to baseline 24 h after challenge but the sheep developed airway hyperresponsiveness as indicated by the 2.6-fold increases in the slopes of the carbachol dose-response curves in the control trials. YM461, 3 and 10 mg/kg p.o., significantly inhibited the late responses (66 and 82%, respectively) and blocked the development of airway hyperresponsiveness at 24 h. The early responses were not significantly reduced in either trial. These results suggest that PAF contributes to the antigen-induced late airway responses and associated airway hyperresponsiveness in allergic sheep.     

噬琼胶卵链菌β-琼胶酶基因YM01-5的克隆表达及其酶学性质的研究

目的 从青岛近海海水中分离鉴定了1株能够降解琼胶的海洋新菌—嗜琼胶卵链菌（Catenovulumagarivoransgen. nov. sp. nov.）YM01T,并对其进行了全基因组测序。本文对该菌的1个β-琼胶酶基因YM01-5进行了克隆表达,并对重组琼胶酶的酶学性质进行了研究。方法 利用镍柱亲和层析对重组琼胶酶进行了分离纯化,采用DNS法测定重组酶的酶学性质,薄层层析(TLC)和质谱(MS)法对AgaYM01-5的酶解产物进行分析。结果 β-琼胶酶基因YM01-5全长2 412 bp,编码803个氨基酸,预测分子量为91.6 kDa,其催化模块属于糖苷水解酶GH50家族。重组琼胶酶YM01-5酶学性质的研究结果表明,该酶的最适温度为40 ℃,最适pH为9.0。在35 ℃以下具有良好的热稳定性,pH 6～10之间保持较高的稳定性,在该范围的pH缓冲液中放置12 h后,YM01-5仍能保持80%以上的酶活力。此外,该重组琼胶酶降解琼脂糖的Km、Vmax值分别为15.6 mg/mL和188 U/mg, 对降解产物的薄层层析及质谱分析结果表明,β-琼胶酶基因YM01-5以外切酶的形式作用于琼脂糖产生新琼二糖作为终产物。结论 该酶降解产物单一,有利于琼胶寡糖的制备,具有较高的工业应用潜力,它的发现也为研究菌株YM01中琼脂糖的代谢通路提供了参考。     

Tissue distribution of YM758, a novel If channel inhibitor,in pregnant and lactating rats

In this study the tissue distribution of radioactivity in pregnant and lactating rats was investigated by quantitatively determining radioactivity concentrations and by whole-body autoradioluminograms after a single oral administration of ¹⁴C-YM758. In addition, the transfer of radioactivity into the reproductive tissues, foetus, and milk is discussed in terms of the localization of transporters in syncytiotrophoblast and mammary gland. The radioactivity concentrations in the liver were the highest of all the tissues and organs tested at all the sampling times. The radioactivity in main tissues (liver and kidney), including reproductive tissues (amniotic fluid, placenta, ovary, and uterus), was not retained for a long time, as in the plasma. The tissue/plasma (T/P) ratio of radioactivity in the foetus was below 1.0, which might be due to Mdr1-mediated export of YM758 into blood via the blood–placenta barrier since YM758 is a substrate for hMDR1, not for hBCRP/rBcrp. The T/P ratio of radioactivity in the maternal milk 1 and 4 h after oral administration of ¹⁴C-YM758 was 7.2 and 11.0, respectively. To understand better the distribution of new drugs into the reproductive tissues/milk, and to interpret further the results of reproductive safety studies for drug development, the contribution of transporters expressed in the blood–placenta barrier and mammary gland to the drug-transfer into placenta and milk should be considered.     

Pharmacokinetics and concentration-effect analysis of intravenous RGD891, a platelet GPIIb/IIIa antagonist, using mixed-effects modeling (NONMEM)

RGD891 is a platelet GPIIb/IIIa receptor antagonist and potent inhibitor of platelet aggregation. This compound is biotransformed in vivo to RGD039, which also exhibits high affinity for the GPIIb/IIIa receptor. Pharmacokinetic/pharmacodynamic modeling was employed to describe the concentration-effect relationship of both compounds following the intravenous administration of RGD891 to healthy volunteers. The overall objectives of this work were to support the dose selection process for future intravenous RGD891 safety and efficacy studies. Various intravenous regimens of RGD891 were administered to healthy volunteers enrolled in three Phase I studies. Frequent plasma samples were collected at regular intervals for later measurement of RGD891 and RGD039 concentrations (validated LC/MS/MS methods). The pharmacokinetics of RGD891 and RGD039 were simultaneously analyzed by nonlinear mixed-effect modeling (NONMEM). Pharmacodynamic activity was assessed in all three studies by the degree to which ADP (20 microM)-induced platelet aggregation was inhibited. Population parameters describing the concentration-effect relationship of RGD891 and RGD039 were then generated using a modified competitive Emax-based model. RESULTS: Parent compound is by far the predominant active compound circulating in the plasma following intravenous administration of RGD891. The plasma RGD891 concentration-time data were best fit by a two-compartment structural model. The fit of the basic model was improved when total body weight was introduced as a covariate for RGD891 distribution. Between-subject variability in the RGD891 pharmacokinetic parameters--V1, K10, and K21--was less than 17% (coefficient of variation). Formation of the active metabolite (RGD039; Km) and its elimination (Kem) were assumed to be first-order processes (i.e., one-compartment model). The population pharmacokinetic model could only provide a rough estimate of the plasma concentration-time profile for RGD039 after administration of a given intravenous dosage regimen of RGD891 since metabolite concentrations were relatively low and highly variable. The first-order rate constant describing the formation of RGD039 from RGD891 (Km) was also associated with a substantial degree of between-subject variability (44.9%). The potency of RGD891 toward the inhibition of ADP-induced platelet aggregation was described by the population IC50 value (plasma concentration yielding 50% of maximal inhibition), which ranged from 58.0 to 95.4 ng/mL, depending on the pharmacokinetic-pharmacodynamic (PK-PD) model and the data set used. The relatively low concentrations of the active metabolite achieved following intravenous administration of RGD891 did not permit independent estimation of a population IC50 value for RGD039. Therefore, its potency was fixed at 2.2-fold greater than that of the parent compound (based on previous PK-PD analyses). Intersubject variability in the IC50 values was 30%. CONCLUSIONS: Antagonism of the platelet IIb/IIIa receptors by intravenously administered RGD891 was effective in inhibiting ADP-induced platelet aggregation in a reversible and dose-dependent manner. Pharmacodynamic activity was largely attributed to the parent compound and less to the active metabolite based on the relative potencies of both compounds and the plasma concentrations of each achieved following intravenous administration. Intravenous bolus plus maintenance infusion regimens resulted in rapid attainment of steady-state plasma RGD891 concentrations. This combination regimen also provided for a marked and sustained inhibition of platelet aggregation that reached 90% or greater (relative to baseline values) in the higher dose groups. The modified Emax model adequately described inhibition of platelet aggregation following a particular intravenous dosage regimen of RGD891 (within the range of doses administered in the present studies). (ABSTRACT TRUNCATED)     

Pharmacokinetic and pharmacodynamic analysis of TS-943, a selective non-peptide platelet glycoprotein-IIb/IIIa (GPIIb/IIIa) receptor antagonist,using a nonlinear mixed effect model in dogs

A simultaneous analysis of the pharmacokinetics and pharmacodynamics of TS-943, a selective nonpeptide platelet glycoprotein-IIb/IIIa (GPIIb/IIIa) receptor antagonist, was made in dogs using a nonlinear mixed effect model. Plasma concentrations of TS-943 were determined after bolus intravenous injection, constant infusion and bolus plus constant infusion. Pharmacokinetic/pharmacodynamic data were fitted using NONMEM software. The pharmacokinetics of TS-943 fitted a two-compartment open model with first-order elimination. The pharmacodynamic model that best fitted platelet aggregation was an inhibitory sigmoid Emax model. The final estimates for E0 (baseline effect), Emax (maximum effect), IC50 (50% inhibitory concentration) and gamma (Hill coefficient) were 66.3%, 64.3%, 104 ng mL(-1) and 1.37, respectively. Correlations between TS-943 plasma concentration and extension of template bleeding time were examined by fitting with an exponential model. The TS-943 plasma concentration necessary to double bleeding time (C2-BTE) was approximately 209 ng mL(-1). The model estimated that the C2-BTE/IC50 (inhibition of platelet aggregation) ratio was approximately 2.0-fold in dogs. Our results suggest that the ratio values for dogs and man are comparable. A nonlinear mixed effect model was a useful tool for exploring the concentration-effect relationship for both efficacy and safety of TS-943 in dogs and man. In this study, the dog was found to be a useful model for screening of efficacy and safety of TS-943 in man.     

Pharmacokinetics, pharmacodynamics, and safety of a platelet GPIIb/IIIa antagonist, RGD891, following intravenous administration in healthy male volunteers

The pharmacokinetics (PK), pharmacodynamics (PD), and safety of a platelet GPIIb/IIIa receptor antagonist, RGD891, and its active metabolite, RGD039, were evaluated after administration of various intravenous regimens of RGD891 to healthy male volunteers in two Phase I studies. Plasma and urine concentrations of RGD891 and RGD039 were measured by validated LC/MS/MS methods with minimum quantifiable limit (MQL) of 1 ng/mL and 10 ng/mL, respectively. PD activity was assessed by percent inhibition of ADP (20 microM)-induced platelet aggregation. Following intravenous dosing, the RGD891 was the predominant compound in plasma. The PK of RGD891 was dose independent associated with modest between-subject variability. RGD891 was rapidly cleared (Cl, 11.2-15.5 L/h), exhibited a restricted distribution (Vss, 23.0-25.9 L) and a short terminal t1/2 lambda z (1.2-2.1 h). Plasma concentrations of the metabolite (RGD039) increased with dose but were variable. RGD039 had longer t1/2 lambda z of 4.5 to 6.6 hours. Renal excretion of unchanged drug played an important role in the elimination of the parent compound. Both RGD891 and RGD039 exhibited renal clearance values that were comparable to the glomerular filtration rate. Intravenous administration of RGD891 effectively inhibited platelet aggregation in a dose-dependent and reversible manner. At the highest dose (60 micrograms/kg bolus dose + 336 micrograms/kg 8-h infusion) > 90% inhibition of platelet aggregation was achieved. PD activity was primarily attributed to the parent compound. Inhibition of platelet aggregation was dependent on the anticoagulant present, with samples containing PPACK showing 20% to 30% lower activity as compared to citrate. RGD891 was safe and well tolerated across the various regimens studies.