68Ga-Labeled Cystine Knot Peptide Targeting Integrin αvβ6 for Lung Cancer PET Imaging

Integrin αvβ6 has been considered as a promising biomarker for lung cancer, and its expression is often related to poor prognosis. An αvβ6-binding cystine knot peptide R01-MG was previously engineered and validated. Here, we developed a positron emission tomography (PET) probe of R01-MG for imaging αvβ6-positive lung cancer. Cystine knot peptide R01-MG was synthesized through solid-phase peptide synthesis chemistry and radiolabeled with 68Ga after being conjugated with 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (DOTA). The stability of 68Ga-DOTA-R01-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 αvβ6-positive (A549 and H1975) and αvβ6-negative (H1299) lung cancer cell lines. In addition, small animal PET imaging and biodistribution studies of 68Ga-DOTA-R01-MG were performed in αvβ6-positive and αvβ6-negative lung cancer models. Our study showed that 68Ga-DOTA-R01-MG exhibited excellent stability in PBS and FBS. Small animal PET imaging and biodistribution data revealed that 68Ga-DOTA-R01-MG displayed rapid and good tumor uptake in animal models with αvβ6-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 68Ga-DOTA-R01-MG was observed in animal models with αvβ6-negative lung cancer, demonstrating specific binding of the probe to integrin αvβ6. In conclusion, 68Ga-DOTA-R01-MG has great potential to be a promising PET tracer for imaging αvβ6-positive lung cancer.