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 (pKi = 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 Gαi pathway to the endogenous agonist [Pyr1]apelin-13 (pD2 = 10.00 ± 0.13 vs 9.34 ± 0.15), in β-arrestin and internalisation assays it was less potent (pD2 = 6.65 ± 0.15 vs 8.65 ± 0.10 and pD2 = 6.16 ± 0.21 vs 9.28 ± 0.10 respectively). Analysis of these data demonstrated a bias of ˜400 for the Gαi over the β-arrestin pathway and ˜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 Gαi over β-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.