A stapled chromogranin A-derived peptide homes in on tumors that express αvβ6 or αvβ8 integrins
In this study by Monieri et al., the MOLECUBES β-CUBE and X-CUBE were used as a non-invasive tool to longitudinally visualise and quantify the uptake of 5a-NOTA18F in mice in pancreatic cancer cells.
The αvβ6- and αvβ8-integrins are two cell-adhesion receptors that are upregulated in many tumors and involved in the activation of the latency-associated peptide (LAP)/TGFβ complex. These integrins represent potential targets for tumor imaging and therapy. This study investigates a potential new biomarker (called “5a”), which selectively recognizes the LAP/TGFβ complex-binding site of αvβ6 and αvβ8, in order to visualise and quantify the LAP/TGF β complex in pancreatic cancer cells.
Peptide 5a was labeled with IRDye 800CW (a near-infrared fluorescent dye) or with 18F-NOTA for PET imaging. The integrin-binding properties of free peptide and conjugates were then investigated using purified αvβ6/αvβ8 integrins and various αvβ6/αvβ8 single – or double-positive cancer cells. The tumor-homing, biodistribution and imaging properties of the conjugates were investigated in subcutaneous and orthotopic αvβ6-positive carcinomas of the pancreas and mice bearing subcutaneous αvβ8-positive prostate tumors.
In vitro studies showed that 5a can bind both integrins with high affinity and inhibit cell-mediated TGFβ activation. The 5a-IRDye and 5a-NOTA conjugates could bind purified αvβ6/αvβ8 integrins with no loss of affinity compared to free peptide and selectively recognized various αvβ6/αvβ8 single- or double-positive cancer cells. In vivo static and dynamic optical near-infrared and PET/CT imaging and biodistribution studies, performed in mice with subcutaneous and orthotopic αvβ6-positive carcinomas of the pancreas, showed high target-specific uptake of fluorescence- and radio-labeled peptide by tumors and low non-specific uptake in other organs and tissues, except for excretory organs. Significant target-specific uptake of fluorescence-labeled peptide was also observed in mice bearing αvβ8-positive prostate tumors.
The results demonstrate that 5a can home to αvβ6- and/or αvβ8-positive tumors. This indicates that 18F-NOTA-5a can be exploited as a ligand for delivering imaging or anticancer agents to αvβ6/αvβ8 single- or double-positive tumors. Furthermore, 5a can block the active site of αvβ6/αvβ8 and inhibit TGFβ activation, a potent immunosuppressive mechanism in tumors. The results suggest that 5a is a tumor-homing bi-selective inhibitor of αvβ6 and αvβ8 that could be exploited for targeting TGFβ activation.