High-Affinity Y1 Receptor Theranostics: First-in-Class Stabilized Nonapeptides for Breast Cancer Imaging and Therapy.

Theranostic agents integrate diagnostic and therapeutic capabilities into a single molecular platform, offering an advanced approach to personalized medicine. The neuropeptide Y1 receptor (Y1R) is a promising target for breast cancer theranostics given its overexpression across multiple disease stages. Building on the Y1R-selective antagonist [Lys2, Arg4]BVD-15, we report the systematic development of stabilized nonapeptide analogues through strategic modifications. Lead candidates were radiolabeled in >95% radiochemical purity and showed Y1R binding affinities up to 60-fold higher than the parent peptide, no detectable plasma degradation over 90 min, and half-lives of 42-55 min in liver and kidney homogenates. PET-CT imaging in HEK-Y1R and MCF-7 tumor models demonstrated selective tumor uptake, peaking at 19.2% ID/g in HEK-Y1R tumors, with biodistribution studies confirming specific tumor accumulation and progressive clearance over 48 h. Therapeutic evaluation of lead candidate [177Lu]Lu-31 in HEK-Y1R tumor-bearing mice showed dose-dependent tumor growth inhibition, supporting this peptide class as Y1R-targeted radionuclide therapeutics.