Aprepitant (MK-0869)

Aprepitant antagonizes the effects of substance P by binding to NK-1 receptors primarily in the CNS, but also in the periphery. Aprepitant, at concentrations of 0.1 nM displaces 50% of substance P from hNK1 receptors transfected in CHO or COS cells. In radioligand binding assays, Aprepitant is 3000-fold selective for the human cloned NK1 receptor versus the human cloned NK3 receptor and >50,000-fold selective over the human cloned NK2 receptor. In a range of assays at other human cloned G–protein coupled receptors, Aprepitant retains >50,000-fold selectivity for the human cloned NK1 receptor. Aprepitant is inactive in human monoamine oxidase A and B assays and at human serotonin 5–HT1A, 5–HT2A, 5–HT2c, 5–HT3, 5–HT5, 5–HT6, and 5–HT7 receptors (IC50>3 μM). In the PANLABS panel of radioligand binding screens using native animal tissues, Aprepitant inhibits [³H]substance P binding to native NK1 receptors in rat submaxillary gland; there are no significant interactions of Aprepitant with any other native animal G–protein coupled receptors or ion channels examined in the PANLABS screen. Aprepitant is inactive in monoamine uptake site (NE, 5–HT, DA) counterscreens using human and animal tissues (IC50> 3 μM) ^[1]

Aprepitant crosses the blood–brain barrier and occupied NK-1 receptors in the brain. Aprepitant has been shown to inhibit both acute and delayed emesis induced by cytotoxic chemotherapeutic such as cisplatin by blocking substance P. Aprepitant (3 mg/kg i.v. or p.o.) inhibits the emetic response to cisplatin (10 mg/kg i.v.). The anti-emetic protection afforded by Aprepitant (0.1 mg/kg i.v.) is enhanced by combined treatment with either dexamethasone (20 mg/kg i.v.) or the 5–HT3 receptor antagonist ondansetron (0.1 mg/kg i.v.). In a model of acute and delayed emesis, ferrets are dosed with cisplatin (5 mg/kg i.p.) and the retching and vomiting response recorded for 72 h. Pretreatment with Aprepitant (4–16 mg/kg p.o.) dose-dependently inhibits the emetic response to cisplatin. Once daily treatment with Aprepitant (2 and 4 mg/kg p.o.) completely prevents retching and vomiting in all ferrets tested. Further when daily dosing began at 24 h after cisplatin injection, when the acute phase of emesis had already become established, Aprepitant (4 mg/kg p.o. at 24 and 48 h after cisplatin) prevents retching and vomiting in three out of four ferrets. ^[1] Aprepitant also plays a key part in transmission of pain impulses from the peripheral receptors to the CNS and is involved in various behavioural, neurochemical and cardiovascular responses to stress. ^[2]