Cardiac action of the first G protein biased small molecule apelin agonist

Apelin peptide analogues displaying bias towards G protein signalling pathways have beneficial cardiovascular actions compared with the native peptide in humans in vivo. Our aim was to determine whether small molecule agonists could retain G protein bias. We have identified a biased small molecule, CMF-019, and characterised it in vitro and in vivo. In competition radioligand binding experiments in heart homogenates, CMF-019 bound to the human, rat and mouse apelin receptor with high affinity (pK(i) = 8.58 +/- 0.04, 8.49 +/- 0.04 and 8.71 +/- 0.06 respectively). In cell-based functional assays, whereas, CMF-019 showed similar potency for the G(alpha i) pathway to the endogenous agonist [Pyr(1)]apelin-13 (pD(2) = 10.00 +/- 0.13 vs 9.34 +/- 0.15), in beta-arrestin and internalisation assays it was less potent (pD(2) = 6.65 +/- 0.15 vs 8.65 +/- 0.10 and pD(2) = 6.16 +/- 0.21 vs 9.28 +/- 0.10 respectively). Analysis of these data demonstrated a bias of similar to 400 for the G(alpha i) over the beta-arrestin pathway and similar to 6000 over receptor internalisation. CMF-019 was tested for in vivo activity using intravenous injections into anaesthetised male Sprague-Dawley rats fitted with a pressure-volume catheter in the left ventricle. CMF-019 caused a significant increase in cardiac contractility of 606 +/- 112 mmHg/s (p < 0.001) at 500 nmol. CMF-019 is the first biased small molecule identified at the apelin receptor and increases cardiac contractility in vivo. We have demonstrated that G(alpha i) over beta-arrestin/internalisation bias can be retained in a non-peptide analogue and predict that such bias will have the therapeutic benefit following chronic use. CMF-019 is suitable as a tool compound and provides the basis for design of biased agonists with improved pharmacokinetics for treatment of cardiovascular conditions such as pulmonary arterial hypertension. (C) 2016 The Author(s). Published by Elsevier Inc.