First-in-Class CD146-Targeting Peptide Probes for Noninvasive PET Imaging of Melanoma

The transmembrane glycoprotein CD146, overexpressed in solid tumors and tumor vasculature, is a compelling target reinforced by CD146-targeting antibody-drug conjugates (ADCs) in clinical trials. This development underscores the unmet need for noninvasive imaging tools to guide patient selection. Here, we report the first [68Ga]Ga-labeled peptide-based molecular imaging agents targeting CD146: [68Ga]Ga-DOTA-P1 and [68Ga]Ga-DOTA-P2. Both probes were reliably synthesized with radiochemical yield >90% within 15 min and radiochemical purity exceeding 95% (n = 5). [68Ga]Ga-DOTA-P1 and [68Ga]Ga-DOTA-P2 have good in vitro stability, and high affinity for CD146-positive cell, with Kd values of 152.3 nM and 205.1 nM, respectively. In vitro cellular assays demonstrated specific binding, and fluorescence imaging with the analog FITC-P1 visually confirmed robust CD146-mediated cellular uptake. In vivo PET/CT imaging demonstrated rapid tumor uptake and tissue excretion. A375 model showed a higher tumor-to-muscle ratio (5.33  ±  0.58) with [68Ga]Ga-DOTA-P1 at 30 min, whereas [68Ga]Ga-DOTA-P2 produced lower contrast (2.55  ±  0.58) due to its slower blood clearance; in addition, the imaging ability of [68Ga]Ga-DOTA-P1 was also verified in another CD146-positive model (SK-Mel-28). An immunohistochemical test was performed to assess CD146 distribution, showing low expression in normal tissues versus positive membrane-localized expression in A375 and SK-Mel-28 tumors. This work establishes [68Ga]Ga-DOTA-P1 as a rapid, high-contrast imaging tool for CD146-expressing malignancies, offering a practical strategy for noninvasive patient stratification in the era of targeted CD146 therapies.