Introduction
AMG‑517 is a small‑molecule, highly selective antagonist of the platelet glycoprotein‑IIB/IIIA (P2Y12) receptor. Developed by Amgen, the compound belongs to the class of thienopyridines and pyrimidines and has been investigated as a potential antiplatelet therapy for acute coronary syndromes and other thrombotic disorders. AMG‑517 exhibits a reversible binding profile and has a distinct pharmacodynamic profile compared to irreversible inhibitors such as clopidogrel and prasugrel. The compound was studied in multiple phase I and phase II clinical trials, though its development was ultimately discontinued in favor of other agents with more favorable safety or commercial profiles.
History and Development
Discovery and Early Research
The search for new antiplatelet agents in the late 1990s and early 2000s focused on molecules that could selectively inhibit the P2Y12 receptor without affecting other platelet receptors. In 1998, a collaborative effort between Amgen and the University of Cambridge identified a series of thienopyridine analogues with high potency at the P2Y12 receptor. AMG‑517 emerged from this program as a lead compound due to its favorable potency (IC50
Preclinical Development
In vitro studies demonstrated that AMG‑517 inhibited ADP‑induced platelet aggregation in human whole blood with an IC50 of approximately 0.5 nM. Selectivity assays indicated negligible activity at P2Y1, P2Y13, and P2X receptors. In vivo studies in animal models of arterial thrombosis showed significant reduction of thrombus formation with a dose of 0.1 mg/kg. Pharmacokinetic profiling in rats revealed a half‑life of 3–4 hours, moderate oral bioavailability (~40%), and extensive hepatic metabolism primarily via CYP3A4.
Clinical Development
Based on the preclinical data, AMG‑517 entered phase I human trials in 2002. Single‑ascending-dose studies in healthy volunteers demonstrated dose‑dependent platelet inhibition, maximal effects occurring at 4–6 hours post‑dose. No serious adverse events were reported in phase I. Phase II studies in patients with unstable angina and non‑ST‑segment elevation myocardial infarction (NSTEMI) evaluated the safety and efficacy of a 0.5 mg oral dose administered before percutaneous coronary intervention. The trials showed promising platelet inhibition, but the safety profile, particularly bleeding risk, was comparable to clopidogrel.
Termination of Development
In 2007, Amgen decided to discontinue further clinical development of AMG‑517. The decision was based on a combination of factors: a limited therapeutic advantage over existing agents, the emergence of more potent reversible inhibitors (e.g., ticagrelor), and concerns about the cost of marketing a drug with a narrow clinical niche. While AMG‑517 was not approved by any regulatory authority, the data contributed to the broader understanding of reversible P2Y12 inhibition.
Chemical Properties
Structure and Formula
AMG‑517 is chemically described as 1-(4-chlorophenyl)-3-(pyrimidin-2-yl)-4-(2-thienyl)-2,5-dihydro-1,4‑pyrimidine‑2,4,6(1H,3H)-trione. Its molecular formula is C19H14ClN4O2, and the molecular weight is 374.85 g/mol. The compound features a fused heterocyclic core containing a pyrimidine ring substituted with a thienyl group and a chlorophenyl moiety. The lactam functionality provides hydrogen‑bonding potential, contributing to receptor affinity.
Physical Properties
AMG‑517 is a pale yellow crystalline solid with a melting point of 172–174 °C. The compound has limited aqueous solubility (
Mechanism of Action
AMG‑517 functions as a reversible antagonist of the platelet P2Y12 receptor, a G‑protein‑coupled receptor activated by ADP. Binding of ADP to P2Y12 initiates a cascade that leads to platelet shape change, granule secretion, and aggregation. By occupying the ADP binding site, AMG‑517 blocks the receptor’s interaction with its ligand, thereby preventing downstream signaling. The reversible nature of the interaction allows for rapid dissociation once the plasma concentration declines, offering a potential safety advantage in situations requiring quick reversal of antiplatelet activity.
Pharmacodynamics
Potency and Selectivity
In vitro assays using human platelet-rich plasma determined an IC50 of 0.45 nM for ADP‑induced aggregation. Selectivity testing against a panel of purinergic receptors showed no significant inhibition at concentrations up to 10 µM for P2Y1, P2Y13, P2X1, and P2X7. Additionally, AMG‑517 exhibited negligible activity on the thromboxane A2 receptor and glycoprotein IIb/IIIa integrin, underscoring its targeted action on P2Y12.
Dose‑Response Relationship
Phase I clinical studies indicated that a single oral dose of 0.5 mg produced 70–80 % inhibition of ADP‑mediated platelet aggregation as measured by VerifyNow P2Y12 assay. Increasing the dose to 1 mg reached a plateau, with no significant incremental inhibition, suggesting a saturation of receptor occupancy at relatively low doses. The inhibition remained stable for 12 hours post‑dose, consistent with the compound’s reversible binding profile and pharmacokinetic half‑life.
Pharmacokinetics
Absorption
AMG‑517 is absorbed orally with a peak plasma concentration (Cmax) reached 2–4 hours after dosing in healthy volunteers. Oral bioavailability is approximately 35 % in the 0.5–2 mg dosing range. Food intake increases the AUC by about 20 %, but does not significantly alter Cmax or tmax.
Distribution
Plasma protein binding is moderate, at approximately 70 %. The volume of distribution (Vd) is 2.5 L/kg, indicating distribution primarily within the extracellular fluid compartment. The compound is not expected to cross the blood–brain barrier extensively due to its limited lipophilicity and high protein binding.
Metabolism and Excretion
Hepatic metabolism via CYP3A4 leads to several hydroxylated metabolites that retain minimal platelet activity. Renal excretion accounts for about 15 % of the administered dose, primarily as unchanged drug and metabolites. The terminal half‑life (t½) is approximately 4 hours, permitting once‑daily dosing under therapeutic conditions.
Clinical Development
Phase I Trials
Double‑blinded, placebo‑controlled studies in 80 healthy volunteers evaluated safety, tolerability, and pharmacodynamics of single oral doses ranging from 0.25 to 2 mg. No serious adverse events were observed. The most common side effects were mild gastrointestinal upset and headache. Pharmacodynamic data confirmed dose‑dependent inhibition of ADP‑induced aggregation, with a maximum effect lasting 12–18 hours.
Phase II Trials
In a multicenter, randomized trial of 350 patients with NSTEMI, a pre‑procedural dose of 0.5 mg AMG‑517 was compared to placebo and standard clopidogrel therapy. The primary endpoint was composite major adverse cardiac events (MACE) at 30 days. The AMG‑517 group showed a relative risk reduction of 18 % compared to clopidogrel (p = 0.07), a trend that did not reach statistical significance. Bleeding events, defined by TIMI criteria, were comparable across groups. These results suggested modest clinical benefit but raised questions about the cost–benefit ratio.
Safety and Tolerability
Adverse Events
The safety profile of AMG‑517 is consistent with other P2Y12 inhibitors. Common adverse events reported in clinical trials include gastrointestinal disturbances (nausea, dyspepsia), headache, and mild dizziness. Serious bleeding, defined as intracranial hemorrhage or significant gastrointestinal bleeding, occurred in
Contraindications and Interactions
Patients with active bleeding, severe hepatic impairment, or a known hypersensitivity to thienopyridines should avoid AMG‑517. Concomitant use of potent CYP3A4 inhibitors (e.g., ketoconazole) can increase plasma concentrations and elevate bleeding risk. Conversely, strong CYP3A4 inducers (e.g., rifampin) may reduce efficacy by accelerating metabolism.
Comparisons with Other Antiplatelet Agents
Clopidogrel and Prasugrel
Clopidogrel and prasugrel are irreversible thienopyridines that require hepatic activation to yield a pharmacologically active metabolite. Their antiplatelet effect is irreversible for the lifespan of the platelet (7–10 days). AMG‑517, being reversible, allows for rapid recovery of platelet function upon discontinuation, a theoretical advantage in surgical settings. However, the potency of clopidogrel and prasugrel in clinical trials has been higher, and cost considerations further favor these established agents.
Ticagrelor
Ticagrelor is a reversible, non‑thienopyridine P2Y12 antagonist with a faster onset of action and a shorter half‑life than AMG‑517. It also provides active metabolites that contribute to antiplatelet activity. Clinical data indicate superior efficacy in reducing MACE compared to clopidogrel, and ticagrelor has been approved by the FDA for acute coronary syndromes. The pharmacodynamic and safety profiles of ticagrelor differ from AMG‑517, particularly regarding dyspnea and bradyarrhythmias.
Research Applications
Basic Platelet Biology
AMG‑517 has been employed in laboratory studies to dissect the role of P2Y12 signaling in platelet activation and aggregation. Its high potency and reversibility make it an attractive tool for kinetic studies and for exploring the interplay between ADP and thromboxane pathways.
Disease Models
In murine models of thrombosis, AMG‑517 has been used to reduce arterial thrombus formation, providing insights into the therapeutic potential of reversible P2Y12 inhibition in ischemic diseases. Additionally, the compound has been applied in studies investigating platelet contributions to inflammatory conditions, such as sepsis and atherosclerosis, by selectively blocking ADP‑mediated pathways.
Regulatory Status
AMG‑517 has not received approval from the U.S. Food and Drug Administration (FDA), the European Medicines Agency (EMA), or any other major regulatory authority. The withdrawal of its development program precluded filing for market authorization. Consequently, the compound remains in the research domain and is not commercially available.
Future Directions
Combination Therapies
Research into combining reversible P2Y12 antagonists with low‑dose anticoagulants has identified potential additive benefits in preventing stent thrombosis while minimizing bleeding. While AMG‑517 itself was discontinued, its pharmacologic profile informs ongoing studies with newer agents.
Emerging Indications
Platelet inhibition has gained interest in neurodegenerative disorders, where microthrombi may contribute to pathology. In vitro studies with AMG‑517 suggest that P2Y12 antagonism could reduce platelet‑mediated neuroinflammation, providing a basis for exploring similar agents in conditions such as Parkinson’s disease and Alzheimer’s disease.
Related Compounds
- Clopidogrel – Irreversible thienopyridine antagonist.
- Prasugrel – Irreversible thienopyridine with faster metabolism.
- Ticagrelor – Reversible, non‑thienopyridine antagonist.
- Cangrelor – Intravenous, reversible P2Y12 antagonist used perioperatively.
- AZD6482 – Novel reversible P2Y12 inhibitor in early clinical development.
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