ALOS4, a unique synthetic cyclic peptide without resemblance to known integrin ligand sequences, was discovered through repeated biopanning with pIII phage expressing a disulfide-constrained nonapeptide library. Binding assays using a FITC-labeled analogue demonstrated selective binding to immobilized αvβ3 and a lack of significant binding to other common proteins, such as bovine serum albumin and collagen. In B16F10 cell cultures, ALOS4 treatment at 72 h inhibited cell migration (30%) and adhesion (up to 67%). Immunofluorescent imaging an ALOS4-FITC analogue with B16F10 cells demonstrated rapid cell surface binding, and uptake and localization in the cytoplasm. Daily injections of ALOS4 (0.1, 0.3 or 0.5 mg/kg i.p.) to mice inoculated with B16F10 mouse melanoma cells in two different cancer models, metastatic and subcutaneous tumor, resulted in reduction of lung tumor count (metastatic) and tumor mass (subcutaneous) and increased survival of animals monitored to 45 and 60 days, respectively. Examination of cellular activity indicated that ALOS4 produces inhibition of cell migration and adhesion in a concentration-dependent manner. Collectively, these results suggest that ALOS4 is a structurally-unique selective αvβ3 integrin ligand with potential anti-metastatic activity.
Keywords: ALOS4; cancer; cyclic peptide; integrin; melanoma.