On July 20th, the FDA approved Ticagrelor (Tradename: Brilinta; Research Code: AZD-6140, NDA 022433), a purinergic receptor P2Y12 platelet antagonist indicated to reduce the rate of thrombotic cardiovascular events in patients with acute coronary syndrome (ACS).
Acute coronary syndrome is often the initial presentation of an individual manifesting coronary artery disease (CAD). ACS can present as unstable angina, non-ST elevation myocardial infarction, or ST elevation myocardial infarction. Typically, ACS begins with the rupture or erosion of a vulnerable plaque in a coronary artery, which results in the exposure of elements under the endothelial layer, such as collagen or von Willebrand factor, to circulating blood. These ligands trigger a series of responses, including platelet adhesion, activation, and aggregation.
Ticagrelor reduces the thrombotic risk in ACS by blocking the P2Y12 receptor on the platelet surface. This drug is the first reversible drug for the Purinergic receptor P2Y12, and prevents the binding of ADP by inducing a reversible conformational change. It is thus an allosteric antagonist. Inhibition of the signal transduction results in reduced exposure of fibrinogen-binding sites to the GP IIb/IIIa receptor and thereby impairment of platelet aggregation. Similarly to other approved drugs to treat ACS, such as Prasugrel (Tradename: Effient; ChEMBL ID: CHEMBL1201772) and contrary to clopidogrel (Tradename: Plavix; ChEMBL ID: CHEMBL1771) and ticlopidine (Tradename: Triclid (Discontinued); ChEMBL ID: CHEMBL833), ticagrelor is not a pro-drug, although its active metabolite (AR-C124910XX) has a comparable potency.
Purinergic receptor P2Y12 (Uniprot accession: Q9H244; ChEMBL ID: CHEMBL2001; OMIM: 609821) is a Rhodopsin-like receptor and therefore it is a member of the G-protein coupled receptor 1 family. The sequence of P2Y12 is:
>P2Y12 MQAVDNLTSAPGNTSLCTRDYKITQVLFPLLYTVLFFVGLITNGLAMRIFFQIRSKSNFI IFLKNTVISDLLMILTFPFKILSDAKLGTGPLRTFVCQVTSVIFYFTMYISISFLGLITI DRYQKTTRPFKTSNPKNLLGAKILSVVIWAFMFLLSLPNMILTNRQPRDKNVKKCSFLKS EFGLVWHEIVNYICQVIFWINFLIVIVCYTLITKELYRSYVRTRGVGKVPRKKVNVKVFI IIAVFFICFVPFHFARIPYTLSQTRDVFDCTAENTLFYVKESTLWLTSLNACLDPFIYFF LCKSFRNSLISMLKCPNSATSLSQDNRKKEQDGGDPNEETPM
There are no known 3D structures for this protein, but there are now several relevant homologous structures of other members of the family (see here for a current list of rhodopsin-like GPCR structures).
The -grel- or -grel USAN/INN stem covers primarily platelet P2Y12 receptor antagonists. Ticagrelor is the first reversible inhibitor of this class, and ticlopidine, clopidogrel and prasugrel all bind irreversibly to P2Y12. Other compounds in this class in late stage clinical development/registration include Portola Pharmaceuticals' elinogrel (Research code: PRT 060128), The Medicines Company's cangrelor (Research code: AR-C69931XX), and the Inspire Pharmaceuticals' regrelor (Research code: INS50589). Others at earlier stages of development include Arena Pharmaceuticals' temanogrel (Research code: APD791).
Ticagrelor (IUPAC: (1S,2S,3R,5S)-3-[7-[[(1R,2S)-2-(3,4-difluorophenyl)cyclopropyl]amino]-5-propylsulfanyltriazolo[4,5-d]pyrimidin-3-yl]-5-(2-hydroxyethoxy)cyclopentane-1,2-diol; SMILES: CCCSC1=NC2=C(C(=N1)N[C@@H]3C[C@H]3C4=CC(=C(C=C4)F)F)N=NN2[C@@H]5C[C@@H]([C@H]([C@H]5O)O)OCCO; PubChem:9871419; Chemspider:8047109, ChEMBLID: CHEMBL398435, Standard InChI Key:OEKWJQXRCDYSHL-FNOIDJSQSA-N) has a molecular weight of 522.6 Da, contains 4 hydrogen bond donors, 8 hydrogen bond acceptors, and has an ALogP of 2.37. Ticagrelor contains six defined stereocenters. Ticagrelor is a cyclopentyl-triazolo-pyrimidine and these agents are relatively resistant to enzymatic degradation by ectonucleotidases. Ticagrelor has clear structural resemblance to adenosine, the endogenous ligand for P2Y12, we have classified it as a natural product-derived small molecule drug.
Ticagrelor is available as an oral film-coated tablets of 90 mg, and the recommend daily dose is 180 mg (equivalent to 34.4 umol). It has an apparent volume of distribution of 88 L and its mean absolute bioavailability is 36% (range 30%-42%). Absorption of ticagrelor occurs with a median tmax of 1.5 h, and the formation of its active metabolite occurs with a median tmax of 2.5 hr. Both compounds are extensively bound to human plasma proteins (>99%). The mean plasma half-life (t1/2) is approximately 7 hours for ticagrelor and 9 hr for the active metabolite.
Ticagrelor is mainly metabolised by CYP3A4 and to a lesser extent by CYP3A5; therefore, other therapeutic agents that inhibit or induce these enzymes may alter their therapeutic effect or lead to adverse DDIs. In vitro metabolism studies demonstrate that ticagrelor and its active metabolite are inhibitors of the P-gp transporter. Ticagrelor has been studied in ACS in combination with aspirin. Maintenance doses of aspirin above 100 mg decreased the effectiveness of ticagrelor.
Ticagrelor has been issued with a black box warning because, like other antiplatelet agents, it can cause potentially fatal bleeding.