MSP68 as an effective radiation countermeasure - PROJECT DESCRIPTION: This R21 project aims to develop the pentapeptide MSP68 as a novel and effective medical countermeasure (MCM) to treat the deadly gastrointestinal acute radiation syndrome (GI- ARS) in individuals exposed to high doses of ionizing radiation. We have recently shown that the glycoprotein milk fat globule-epidermal growth factor-factor VIII (MFG-E8) mitigates GI-ARS and improves the survival of mice exposed to partial body irradiation (PBI). To develop a small-molecule mitigator of GI-ARS without many disadvantages of therapeutic glycoproteins, we screened a large number of oligopeptides derived from human MFG-E8 and identified the pentapeptide MSP68 (MFG-E8-derived short peptide 68) as the most potent MFG-E8’s small-molecule mimic. MSP68 has high affinity for β1-integrin (i.e., MFG-E8 receptor) and can block neutrophil adhesion to fibronectin, which is β1-integrin dependent. MSP68 also reduced gut bacterial translocation and improved the survival of injured mice, thus fully recapitulating MFG-E8 activities. Our preliminary results showed that post-treatment of PBI with MSP68 mitigated GI-ARS, with restored crypt depth, attenuated enterocyte mass loss, and reduced permeability barrier dysfunction. MSP68 also promoted the recovery of gut crypt Lgr5+ (leucine- rich repeat-containing G-protein coupled receptor 5) stem cells in PBI mice. In irradiated intestinal organoids generated from naïve mice, MSP68 significantly increased proliferation, Lgr5 mRNA, and the number of Lgr5+ stem cells. MSP68 also induced mRNA expression of clusterin (Clu) – the marker of the otherwise quiescent revival stem cells that replenish Lgr5+ stem cells after radiation injury. Clu+ revival stem cell activation is driven by p53, which can be activated by β1-integrin. We have found that the β1-integrin gene is highly expressed on Clu+ revival stem cells. Based on these solid preliminary results, we hypothesize that MSP68 can be developed as a novel and effective MCM for severe GI-ARS by restoring intestinal stem cells. In this project, we will develop the pentapeptide MSP68 as a MCM for GI-ARS by determining its mechanism of action, efficacy, and safety. Our ultimate goal is to obtain FDA approval to use MSP68 as an effective, safe, and easy to administer treatment for radiation victims with intestinal injury.
