MIIST305 mitigates gastrointestinal acute radiation syndrome injury and ameliorates radiation-induced gut microbiome dysbiosis

High-dose radiation exposure results in gastrointestinal (GI) acute radiation syndrome identified by the destruction of mucosal layer, intestinal growth barrier dysfunction, and aberrant inflammatory responses. Further, radiation causes gut microbiome dysbiosis characterized by diminished microbial diversity, mostly commensal bacteria, and the spread of bacterial pathogens that trigger the recruitment of immune cells and the production of pro-inflammatory factors that lead to further GI tissue damage. Currently, there are no U.S. Food and Drug Administration (FDA) approved countermeasures that can treat radiation-induced GI injuries. To meet this critical need, Synedgen Inc. has developed a glycopolymer radiomitigator (MIIST305) that is specifically targeted to the GI tract, which acts by intercalating into the mucus layer and the glycocalyx of intestinal epithelial cells that could potentially ameliorate the deleterious effects of radiation. Male C57BL/6J adult mice were exposed to 13 Gy partial body X-irradiation with 5% bone marrow shielding and MIIST305 was administered on days 1, 3, and 5 post-irradiation. Approximately 85% of the animals survived the irradiation exposure and were apparently healthy until the end of the 30-day study period. In contrast, no control, Vehicle-treated animals survived past day 10 at this radiation dose. We show that MIIST305 improved intestinal epithelial barrier function and suppressed systemic inflammatory responses mediated by radiation-induced pro-inflammatory cytokines. Taxonomic profiling and community structure of the fecal and colonic mucosa microbiota demonstrated that MIIST305 treatment increased microbial diversity and restored abundance of beneficial commensal bacteria, including <i>Lactobacillus</i> and <i>Bifidobacterium</i> genera while suppressing potentially pathogenic bacteria <i>Enterococcus</i> and <i>Staphylococcus</i> compared with Vehicle-treated animals. In summary, MIIST305 is a novel GI-targeted therapeutic that greatly enhances survival in mice exposed to lethal radiation and protects the GI tract from injury by restoring a balanced gut microbiota and reducing pro-inflammatory responses. Further development of this drug as an FDA-approved medical countermeasure is of critical importance.