Design and preclinical evaluation of a novel apelin-based PET radiotracer targeting APJ receptor for molecular imaging of angiogenesis

APJ has been extensively described in the pathophysiology of angiogenesis and cell proliferation. The prognostic value of APJ overexpression in many diseases is now established. This study aimed to design a PET radiotracer that specifically binds to APJ. Apelin-F13A-NODAGA (AP747) was synthesized and radiolabeled with gallium-68 ([⁶⁸Ga]Ga-AP747). Radiolabeling purity was excellent (> 95%) and stable up to 2 h. Affinity constant of [⁶⁷Ga]Ga-AP747 was measured on APJ-overexpressing colon adenocarcinoma cells and was in nanomolar range. Specificity of [⁶⁸Ga]Ga-AP747 for APJ was evaluated in vitro by autoradiography and in vivo by small animal PET/CT in both colon adenocarcinoma mouse model and Matrigel plug mouse model. Dynamic of [⁶⁸Ga]Ga-AP747 PET/CT biodistributions was realized on healthy mice and pigs for two hours, and quantification of signal in organs showed a suitable pharmacokinetic profile for PET imaging, largely excreted by urinary route. Matrigel mice and hindlimb ischemic mice were submitted to a 21-day longitudinal follow-up with [⁶⁸Ga]Ga-AP747 and [⁶⁸Ga]Ga-RGD₂ small animal PET/CT. [⁶⁸Ga]Ga-AP747 PET signal in Matrigel was significantly more intense than that of [⁶⁸Ga]Ga-RGD₂. Revascularization of the ischemic hind limb was followed by LASER Doppler. In the hindlimb, [⁶⁸Ga]Ga-AP747 PET signal was more than twice higher than that of [⁶⁸Ga]Ga-RGD₂ on day 7, and significantly superior over the 21-day follow-up. A significant, positive correlation was found between the [⁶⁸Ga]Ga-AP747 PET signal on day 7 and late hindlimb perfusion on day 21. We developed a new PET radiotracer that specifically binds to APJ, [⁶⁸Ga]Ga-AP747 that showed more efficient imaging properties than the most clinically advanced tracer of angiogenesis, [⁶⁸Ga]Ga-RGD₂.