A FIRST-IN-CLASS BRAIN-PENETRANT THERANOSTIC PROBE TARGETING THE APELIN RECEPTOR FOR GLIOBLASTOMA

Glioblastoma (GBM) is the most aggressive primary brain tumor and remains associated with a poor prognosis, with a 5-year survival rate of approximately 4%. We recently identified the apelin receptor (APJ), a class A G protein-coupled receptor, as a promising therapeutic target for GBM. Bioinformatic analyses of The Cancer Genome Atlas (TCGA) revealed significant overexpression of APJ and its endogenous ligand, apelin, in GBM relative to healthy brain tissue. Building on these findings, we developed a theranostic strategy based on a radiolabeled APJ ligand that enables positron emission tomography (PET)-based target validation and imaging, followed by radionuclide therapy using the same molecular scaffold. To this end, a ⁶⁴Cu-labeled-APJ ligand was rationally designed by conjugating an apelin-13 derivative to the blood-brain-barrier shuttle peptide Angiopep-2. The resulting radioligand exhibited nanomolar affinity for APJ. Functional characterization using BRET-based biosensors demonstrated full agonist activity for b-arrestin-2 recruitment at APJ, accompanied by robust receptor internalization and trafficking to early endosomes. In vivo stability and whole-body biodistribution studies in CD-1 mice revealed favorable pharmacokinetic properties, including moderate plasma protein binding (15–38%) and low accumulation in critical peripheral organs (e.g., heart, lung, and liver). Finally, using an orthotopic U87-MG GBM model with differential APJ expression, and monitoring tumor progression by magnetic resonance imaging (MRI) and secreted Gaussia luciferase, we demonstrated that APJ expression significantly contributes to tumor aggressiveness. Altogether, these findings support APJ-targeted theranostics as a novel and promising precision oncology strategy for glioblastoma.