PURPOSEDevelopment of mucositis is a frequent side effect of radiotherapy of patients with head-and-neck cancer. We have recently reported that bacterial flagellin, an agonist of Toll-like receptor 5 (TLR5), can protect rodents and primates from acute radiation syndrome caused by total body irradiation. Here we analyzed the radioprotective efficacy of TLR5 agonist under conditions of local, single dose or fractionated radiation treatment.METHODS AND MATERIALSMice received either single-dose (10, 15, 20, or 25 Gy) or fractioned irradiation (cumulative dose up to 30 Gy) of the head-and-neck area with or without subcutaneous injection of pharmacologically optimized flagellin, CBLB502, 30 min before irradiation.RESULTSCBLB502 significantly reduced the severity of dermatitis and mucositis, accelerated tissue recovery, and reduced the extent of radiation induced weight loss in mice after a single dose of 15 or 20 Gy but not 25 Gy of radiation. CBLB502 was also protective from cumulative doses of 25 and 30 Gy delivered in two (10 + 15 Gy) or three (3 × 10 Gy) fractions, respectively. While providing protection to normal epithelia, CBLB502 did not affect the radiosensitivity of syngeneic squamous carcinoma SCCVII grown orthotopically in mice. Use of CBLB502 also elicited a radiation independent growth inhibitory effect upon TLR5-expressing tumors demonstrated in the mouse xenograft model of human lung adenocarcinoma A549.CONCLUSIONCBLB502 combines properties of supportive care (radiotherapy adjuvant) and anticancer agent, both mediated via activation of TLR5 signaling in the normal tissues or the tumor, respectively.