A first-in-human study of KMRC011, a potential treatment for acute radiation syndrome, to explore tolerability, pharmacokinetics, and pharmacodynamics.

KMRC011 is a novel Toll-like receptor 5 agonist under development as a treatment for acute radiation syndrome (ARS). The aim of this first-in-human study was to investigate the tolerability, pharmacokinetics, and pharmacodynamics of a single intramuscular dose of KMRC011 in healthy subjects. A randomized, single-blind, placebo-controlled, single dose-escalation study was conducted with the starting dose of 5 µg. Eight (4 only for 5 µg cohort) subjects per cohort were randomly assigned to KMRC011 or placebo in a 3:1 ratio. Dose-limiting toxicity (DLT) was assessed throughout the study. Serum concentrations of KMRC011, granulocyte colony-stimulating factor (G-CSF), and interleukin-6 (IL-6) were measured up to 48 h postdose. Based on safety review, the dose of KMRC011 escalated up to 20 µg, and consequently, a total of 4 dose levels (5, 10, 15, and 20 µg) were explored. The most common adverse event was injection site reaction, showing no dose-related trend. Three DLTs (2 cases of hepatic enzyme increased and 1 of pyrexia) were observed; 1 in the 15 µg cohort and 2 in the 20 µg cohort. A developed method could not detect any KMRC011 in serum. KMRC011 15 µg and 20 µg showed significant increases of G-CSF, IL-6, and absolute neutrophil counts, compared with the placebo. A single intramuscular administration of KMRC011 ranging from 5 to 15 µg was tolerated in healthy subjects. Doses of KMRC011 equal to or greater than 15 µg exerted TLR5 agonist-like activities by increasing serum G-CSF and IL-6. It suggests that KMRC011 has the potential for a treatment for ARS.

Radioprotective effect of newly synthesized toll-like receptor 5 agonist, KMRC011, in mice exposed to total-body irradiation.

Exposure to ionizing radiation leads to severe damages in radiosensitive organs and induces acute radiation syndrome, including effects on the hematopoietic system and gastrointestinal system. In this study, the radioprotective ability of KMRC011, a novel toll-like receptor 5 (TLR5) agonist, was investigated in C57BL6/N mice exposed to lethal total-body gamma-irradiation. In a 30-day survival study, KMRC011-treated mice had a significantly improved survival rate compared with control after 11 Gy total-body irradiation (TBI), and it was found that the radioprotective activity of KMRC011 depended on its dosage and repeated treatment. In a 5-day short-term study, we demonstrated that KMRC011 treatment stimulated cell proliferation and had an anti-apoptotic effect. Furthermore, KMRC011 increased the expressions of genes related to DNA repair, such as Rad21, Gadd45b, Sod2 and Irg1, in the small intestine of lethally irradiated mice. Interestingly, downregulation of NF-κB p65 in the mouse intestine by KMRC011 treatment was observed. This data indicated that KMRC011 exerted a radioprotective activity partially by regulating NF-κB signaling. Finally, peak expression levels of G-CSF, IL-6, IFN-γ, TNF-α and IP-10 induced by KMRC011 treatment were different depending on the route of administration and type of cytokine. These cytokines could be used as candidate biomarkers for the evaluation of KMRC011 clinical efficacy. Our data indicated that KMRC011 has radioprotective activity in lethally irradiated mice and may be developed as a therapeutic agent for radioprotection.

Repeated injection of KMRC011, a medical countermeasure for radiation, can cause adverse health effects in cynomolgus monkeys.

High-dose radiation-induced tissue damage is a major limiting factor in the medical application of nuclear technology. Herein, we tested 28-day repeated-dose toxicity of KMRC011, an agonist of toll-like receptor (TLR) 5, which is being developed as a medical countermeasure for radiation, using cynomolgus monkeys. KMRC011 (0.01, 0.02 or 0.04 mg/kg/day) was intramuscularly injected once daily for 4 weeks, and each two monkeys in both control and 0.04 mg/kg/day group were observed for an additional 2-week recovery period. There were no dose-related toxicological changes in mortality, clinical observations, body weight, food consumption, ophthalmological findings, electrocardiographs, coagulation, serum chemistry, organ weights, or urinalysis and urine chemistry. Although treatment-related changes, such as increased white blood cells, increased absolute and relative neutrophils, decreased relative lymphocytes and inflammatory lesions, were noted in the maximum dose group, these findings were not observed after the 2-week recovery period. Further, we considered that the kidneys and heart may be target organs of TLR5 agonists, as well as the spleen, and that autophagic signals can be triggered in tissue damage and the repair process. Importantly, accumulation of p62 protein, an indicator of autophagy, and a decrease of caveolin-1 protein, a regulator of TLR5 protein half-life, were found in both tissues from the highest dose group. Therefore, we conclude that the no-observed-adverse-effect level for KMRC011 may be greater than 0.04 mg/kg/day in male and female monkeys. Additionally, we propose that further studies are needed to identify the molecular signals, which are related to KMRC011-induced adverse effects.

TLR5 binding and activation by KMRC011, a flagellin-derived radiation countermeasure.

Entolimod (CBLB502) is a flagellin-derived radiation countermeasure currently under clinical trial. Entolimod exerts radioprotective activity by directly interacting with TLR5, an innate immune receptor, using the conserved domains of flagellin. Entolimod was designed to contain an artificially introduced N-terminal region that is not related to drug effects and might trigger unexpected toxic immunogenic reactions in humans. To refine the entolimod drug design, we engineered entolimod into KMRC011 by removing its ancillary region. The TLR5 binding and activating capacities of KMRC011 were assessed through biophysical and cellular analyses. KMRC011 forms an exceptionally stable complex with TLR5 at a 1:1 molar ratio with an equilibrium dissociation constant of ∼100 pM and potently activates TLR5. Moreover, alanine scanning mutagenesis identified the R90 and E114 residues of KMRC011 as a TLR5 activation hotspot. Further comparative analysis demonstrated that KMRC011 binds and activates TLR5 in a mode similar to that of entolimod. Thus, we propose that KMRC011 can be used in place of entolimod as a second-generation radiation countermeasure that shows none of the immunogenic side effects derived from the entolimod ancillary region.