Ga-Labeled Cystine Knot Peptide Targeting Integrin αβ for Lung Cancer PET Imaging.

Integrin αβ has been considered as a promising biomarker for lung cancer, and its expression is often related to poor prognosis. An αβ-binding cystine knot peptide R1-MG was previously engineered and validated. Here, we developed a positron emission tomography (PET) probe of R1-MG for imaging αβ-positive lung cancer. Cystine knot peptide R1-MG was synthesized through solid-phase peptide synthesis chemistry and radiolabeled with Ga after being conjugated with 1,4,7,10-tetraazacyclododecane-,',″,‴-tetraacetic acid (DOTA). The stability of Ga-DOTA-R1-MG was analyzed in phosphate-buffered saline (PBS) (pH 7.4) and fetal bovine serum (FBS). The cell uptake assay of the probe was evaluated using αβ-positive (A549 and H1975) and αβ-negative (H1299) lung cancer cell lines. In addition, small animal PET imaging and biodistribution studies of Ga-DOTA-R1-MG were performed in αβ-positive and αβ-negative lung cancer models. Our study showed that Ga-DOTA-R1-MG exhibited excellent stability in PBS and FBS. Small animal PET imaging and biodistribution data revealed that Ga-DOTA-R1-MG displayed rapid and good tumor uptake in animal models with αβ-positive lung cancer, and the probe was rapidly cleared from the normal tissues, resulting in good tumor-to-normal tissue contrasts. Meanwhile, no obvious tumor uptake of Ga-DOTA-R1-MG was observed in animal models with αβ-negative lung cancer, demonstrating specific binding of the probe to integrin αβ. In conclusion, Ga-DOTA-R1-MG has great potential to be a promising PET tracer for imaging αβ-positive lung cancer.