Radiosynthesis and biological evaluation of [68Ga]Ga-NOTA-STAT6 for PET imaging of brain metastasis

Abstract

Brain metastasis generally has a very poor prognosis. Positron emission tomography (PET) is a widely used, non-invasive medical imaging technique used to detect tumors. While 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is the most commonly used PET radiopharmaceutical, it is non-specific. [18F]FDG uptake reflects tissue energy utilization. Tumor biology is diverse, and personalized treatment requires target-specific radiopharmaceuticals for imaging-based patient-stratification. Signal transducer and activator of transcription 6 (STAT6) is a transcription regulator activated by cytokines interleukin-4 (IL-4) and interleukin-13 (IL-13), linked to inflammation and allergies, but is also overexpressed in some tumor types, where it has a role in tumor growth and metastasis. There is evidence that its inhibition can slow down tumor growth. STAT6 inhibitory peptide (STAT6-IP) is a peptide which contains an amino acid sequence derived from murine STAT6, and is designed to bind to and inhibit STAT6. The aim of this study was to synthesize and characterize [68Ga]Ga-NOTA-STAT6, evaluate its target binding in vitro using cryosectioned tumor sections, and study its potential as a radiopharmaceutical for PET imaging in vivo using a mouse model with brain metastasis. Radiosynthesis of [68Ga]Ga-NOTA-STAT6 proved to be straightforward and reproducible, and in vitro evaluation showed strong and heterogeneous tissue binding correlating with STAT6 expression, especially in the human breast cancer brain metastasis tissue samples. However, PET/CT images showed no specific uptake in the tumors in vivo, and overall biological evaluation of [68Ga]Ga-NOTA-STAT6 shows poor in vivo stability and rapid renal elimination.