Development and Preclinical Evaluation of a Novel ⁶⁸ Ga-Labeled Peptide Probe Targeting CD105 for Tumor Imaging

CD105 (endoglin) is a proliferation-associated transmembrane glycoprotein selectively expressed on activated endothelial cells in tumor neovasculature and serves as an attractive biomarker for imaging tumor angiogenesis. Here, we report the development of a novel CD105-targeted PET tracer, ⁶⁸Ga-DOTA-CDP, based on a high-affinity peptide (KD = 13.5 nM) identified from a combinatorial library. The radiotracer was obtained with high radiochemical purity (>97%), excellent stability in phosphate-buffered saline and fetal bovine serum, and favorable hydrophilicity. In vitro confocal imaging and flow cytometry demonstrated specific binding of CDP to CD105-positive HUVECs with minimal uptake in CD105-negative cells. Micro-PET imaging in multiple tumor-bearing mouse models, including 4T1, A549, H1975, MDA-MB-231, and JIMT-1 xenografts, enabled rapid tumor visualization at early time points following injection. Tracer uptake was significantly higher in CD105-high tumors compared with CD105-low tumors, with the highest accumulation observed in the triple-negative breast cancer model MDA-MB-231. Biodistribution studies revealed predominant renal clearance, low hepatic uptake, and favorable tumor-to-background ratios. Blocking experiments with excess unlabeled peptide markedly reduced tumor uptake, confirming receptor-mediated targeting. Immunohistochemical analysis further validated heterogeneous CD105 expression in tumor neovasculature and demonstrated a positive correlation between CD105 expression levels and PET-derived tumor uptake. Overall, ⁶⁸Ga-DOTA-CDP shows promise as a peptide-based PET tracer for noninvasive tumor angiogenesis imaging.