MK-3207 is a new, highly selective CGRP receptor antagonist that is approximately 40- to 65-fold more potent than telcagepant for the human CGRP receptor. The IC50 is 0.12 nM and The Ki value is 0.024 nM. It is highly selective versus human AM1, AM2, CTR, and AMY3. [1]
Calcitonin gene-related peptide (CGRP) is a 37 amino acid neuropeptide that is widely distributed in the central and peripheral nervous system. The CGRP receptor is composed of the calcitonin receptor-like receptor (CLR), a family B G protein-coupled receptor (GPCR), in association with receptor activity modifying protein 1 (RAMP1) and receptor component protein. A number of lines of evidence implicated CGRP in migraine pathophysiology, and this led to interest in the potential utility of CGRP receptor antagonists as novel therapeutics for migraine. [2]
MK-3207 displayed high affinity for the native human CGRP receptor in SK-N-MC cells and for the recombinant human receptor as measured by the ability to compete with 125I-hCGRP binding, with Ki values of 0.024 ± 0.001 nM and 0.022 ± 0.002 nM, respectively. MK-3207 displayed a similar affinity (Ki) for the rhesus monkey receptor (0.024 ± 0.001 nM) as for human, but it displayed 400-fold lower affinity for the canine and rat receptors, with values of 10 nM and 10 ± 1.2 nM , respectively. MK-3207 potently blocked human α-CGRP-stimulated cAMP responses in human CGRP receptor-expressing HEK293 cells, with an IC50 value of 0.12 ±0.02 nM . Addition of 50% human serum (IC50 =0.17 ± 0.02nM) had little effect on the apparent potency ofMK-3207. [3]
MK-3207 has EC50 and Emax values of approximately 0.8 ± 0.3 nM (mean ± S.E.) and 81 ± 5% (mean ± S.E.), respectively, for inhibition of CIDV in rhesus monkeys. The expected EC90 value in rhesus monkey is therefore approximately 7 nM (9-fold higher than the estimated EC50 value). After an oral dose of 10 mg/kg MK-3207, the CSF/plasma ratio is 2 to 3% . However, the CSF/ plasma ratio is approximately 30% of the unbound fraction (9.4%) in plasma, indicating that the central and peripheral compartments are not freely equilibrating.

References:
[1] David J Hewitt, Sheena K Aurora, David W Dodick et al. Randomized controlled trial of the CGRP receptor antagonist MK-3207 in the acute treatment of migraine. Cephalalgia 31(6) 712–722.
[2] Ian M. Bell, Steven N. Gallicchio, Michael R. Wood et al. Discovery of MK-3207: A Highly Potent, Orally Bioavailable CGRP Receptor Antagonist. ACS Med. Chem. Lett. 2010, 1, 24–29.
[3] Christopher A. Salvatore, Eric L. Moore, Amy Calamari, Jacquelynn J. Cook, et al. Pharmacological Properties of MK-3207, a Potent and Orally Active Calcitonin Gene-Related Peptide Receptor Antagonist. doi:10.1124/jpet.109.163816.