CBLB613: A TLR 2/6 Agonist, Natural Lipopeptide of Mycoplasma arginini, as a Novel Radiation Countermeasure

To date, there are no safe and effective drugs available for protection against ionizing radiation damage. Therefore, a great need exists to identify and develop non-toxic agents that will be useful as radioprotectors or postirradiation therapies under a variety of operational scenarios. We have developed a new pharmacological agent, CBLB613 (a naturally occurring Mycoplasma-derived lipopeptide ligand for Toll-like receptor 2/6), as a novel radiation countermeasure. Using CD2F1 mice, we investigated CBLB613 for toxicity, immunogenicity, radioprotection, radiomitigation and pharmacokinetics. We also evaluated CBLB613 for its effects on cytokine induction and radiation-induced cytopenia in unirradiated and irradiated mice. The no-observable-adverse-effect level of CBLB613 was 1.79 mg/kg and 1 mg/kg for single and repeated doses, respectively. CBLB613 significantly protected mice against a lethal dose of ⁶⁰Co γ radiation. The dose reduction factor of CBLB613 as a radioprotector was 1.25. CBLB613 also mitigated the effects of ⁶⁰Co γ radiation on survival in mice. In both irradiated and unirradiated mice, the drug stimulated induction of interleukin-1β (IL-1β), IL-6, IL-10, IL-12, keratinocyte-derived chemokine, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor-1α. CBLB613 also reduced radiation-induced cytopenia and increased bone marrow cellularity in irradiated mice. Our immunogenicity study demonstrated that CBLB613 is not immunogenic in mice, indicating that it could be developed as a radioprotector and radiomitigator for humans against the potentially lethal effects of radiation exposure.