⁶⁸Ga-Labeled Cystine Knot Peptide Targeting Integrin α_vβ₆ for Lung Cancer PET Imaging

Integrin α_vβ₆ has been considered as a promising biomarker for lung cancer, and its expression is often related to poor prognosis. An α_vβ₆-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 α_vβ₆-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 α_vβ₆-positive (A549 and H1975) and α_vβ₆-negative (H1299) lung cancer cell lines. In addition, small animal PET imaging and biodistribution studies of ⁶⁸Ga-DOTA-R₀1-MG were performed in α_vβ₆-positive and α_vβ₆-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 α_vβ₆-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 α_vβ₆-negative lung cancer, demonstrating specific binding of the probe to integrin α_vβ₆. In conclusion, ⁶⁸Ga-DOTA-R₀1-MG has great potential to be a promising PET tracer for imaging α_vβ₆-positive lung cancer.