Radiation Protection Of TLR2 / 6 Agonist CBLB601

Injury to the hematopoietic system and gastrointestine tract, and relatedcomplications such as bleeding, infection or even lethality are the directmanifestations of acute radiation syndrome (ARS), so there is an urgent need toexplore a safe, effective radioprotection or mitigation drug. Current studis indicatethat the activation of NF-κB by Toll-like receptor (TLR) agonists has an obviousprotection effect on radiation induced apoptosis and necrosis. The Toll-like receptorsrefer to a family of Pattern Recognition Receptors (PRRs) that act as a scout in theinnate and adaptive immune responses.By now,11TLRs hane been indetified inhuman beings.Due to the polymorphism as well as its importance in regulatingimmune reponses,more and more TLR-specific agonists have been approved fortherapeutic applications to infections,cancers,autoimmune diseases,allergic diseasesand radiation injury.Some homogenous complexes, including TLR1, TLR2andTLR6, could be activated by lipoprotein or lipopeptide derived from pathogenbacteria to induce innate immune responses. The activation of TLR2-NF-κB signalpathway could up-regulate the expression of NF-κB-dependentanti-apopsis,anti-oxidation and related cytokines so as to promote the recovery of theinjury to the hematopoietic system or gastrointestine tract.CBLB601(molecularpattern: R, R-pam2Cys-SKKKK), a synthetic lipopeptide of mycoplasm arginini,is aTLR2/6or TLR2/CD14specific agonist.CBLB601significantly protects thehematopoietic system from injury induced by radiation.The drug stimulatedinduction of granulocyte colony-stimulating factor (G-CSF),keratinocyte-derivedchemokine (KC) and IL-6.G-CSF and IL-6may play an important role in theradioprotection effect of CBLB601.Using C57/BL6mice, we investigated the effect of CBLB601on the lethality rate aswell as the peripheral blood cell counts after8.0Gy or6.5Gy60Co γ ray irradiationrespectively. We found that CBLB601dramatically enhanced the30-day survival of control).Significant difference in average survival time was observed betweenCBLB601group and irradiation control(P＜0.001). The number of leukocytes,erythrocytes, hemoglobins and platelets of the peripheral blood decreased rapidlyafter irradiation. In CBLB6010.15,0.5and0.75mg/kg group, leukocytopenia,erythropenia, decreased hemoglobin, thrombocytopenia and nuetropenia wereshortened and recovered in advance and the nadir was much higher than in PBSgroup(P＜0.01). Significant difference in lasting time of WBC counts less than3.0×109/L was observed in CBLB6010.15,0.5,0.75mg/kg, WR2721group andirradiation control(P＜0.05、 P＜0.001、 P＜0.01、 P＜0.001). Significantdifference in lasting time of NEUT counts less than1.0×109/L was also observed inCBLB6010.5,0.75mg/kg, WR2721group and irradiation control(P＜0.001、 P＜0.01、 P＜0.01). What’s more, the nadir of WBC, RBC and PLT in CBLB6010.5mg/kg group was even higher than in WR2721group(P＜0.05).Histopathological assay revealed that both CBLB601and WR2721obviouslyattenuated irradiation induced myeloid derived hematopoietic cytopenia, bleedingand edema in marrow cavity.In vivo studies indicated that CBLB601could activate NF-κB reporter gene in aTLR2/6dependent manner.The nuclear localization of NF-κB subunit p65andactivation of Erk MAPK and IL-6-STAT3pathway was also observed afterCBLb601stimulation in HUVEC cells. CBLB601dramatically promoted theclony-fomulating ability, inhibited apopsis of mouse bone marrow cells,andup-regulated the expression levels of serum G-CSF and IL-6. Pre-injection of IL-6monoclonal antibody obviousely attenuated the radioprotection activity of CBLB601,indicating that the role of IL-6was very important.This study revealed that CBLB601had a significant radioprotective activity andpotential of being developed as a noval radioprotection or mitigation agent.