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Molar mass35.0 kg/mol g·mol−1

Entolimod (CBLB502) is being developed by Cleveland Biolabs, Inc. for dual indications under the U.S. Food & Drug Administration’s (FDA) Animal Efficacy Rule as a pivotal-stage radiation countermeasure, and under the FDA’s traditional drug approval pathway as a cancer treatment.

Entolimod is a recombinant protein that acts as an agonist of toll-like receptor 5 (TLR5), an innate immunity receptor. Entolimod activation of TLR5 triggers NF-κB signaling, mobilizing an innate immune response that drives expression of numerous genes, including inhibitors of apoptosis, scavengers of reactive oxygen species, and a spectrum of protective or regenerative cytokines.

Radiation countermeasure[edit]

The FDA established the Animal Efficacy Rule in 2002 to permit the approval of certain drugs and biologics that are intended to reduce or prevent serious or life-threatening conditions based on evidence of safety from trial in healthy subjects and effectiveness from appropriate animal studies when human efficacy studies are not ethical or feasible.

Efficacy of entolimod as a radiation countermeasure has been assessed in animal models. These studies demonstrate that a single administration of entolimod given either before or after lethal total body irradiation leads to significant improvement in animal survival. Entolimod has been shown to reduce radiation damage to both hematopoietic (HP) and gastrointestinal (GI) tissues and improve tissue regeneration.

Two clinical studies that involved administration of a range of doses of entolimod in 150 healthy human subjects have been completed. Both studies demonstrated that administration of entolimod appears to be safe within a certain dose range. The most frequent adverse event associated with entolimod administration was a transient flu-like syndrome, which is consistent with the mechanism of action of the compound.

The FDA granted entolimod both Fast Track and Orphan Drug status for reducing the risk of death following a potentially lethal dose of total body irradiation during or after a radiation disaster.

Both the Department of Health and Human Services and the Department of Defense procure and maintain medical stockpiles to respond to bioterrorist and emerging infectious disease outbreaks. Under a declared state of emergency, countermeasures may be procured for the Strategic National Stockpile under an Emergency Use Authorization prior to their full FDA licensure approval.


Preclinical studies by ed have shown that entolimod has a suppressive effect on growth of TLR5 expressing tumors. Entolimod has also been shown to have an effect on several animal models of liver metastasis, regardless of TLR5 expression. Additionally, entolimod evidences a supportive care benefit in preclinical models when combined with radiation treatment and cytotoxic agents with adverse gastrointestinal (GI) effects. Tissue protective effects of TLR5 agonists are limited to normal tissues and do not involve protection of tumors from treatment.

A Phase I advanced solid tumor study is currently ongoing at Roswell Park Cancer Institute. The Principal Investigator for this trial is Alex Adjei, M.D., Ph.D., FACP, Chair of the Department of Medicine and Senior Vice President of Clinical Research at Roswell Park Cancer Institute.[1]

Additionally, entolimod may also be developed as an adjuvant to standard radiation and chemotherapy, which will allow using of more aggressive measures to attack malignant cells and increase the effectiveness of cancer treatment.


  1. ^ Clinical trial number NCT01527136 for "Entolimod in Treating Patients With Locally Advanced or Metastatic Solid Tumors That Cannot Be Removed By Surgery" at ClinicalTrials.gov

Further reading[edit]

  1. Burdelya, L. G.; Brackett, C. M.; Kojouharov, B.; Gitlin, I. I.; Leonova, K. I.; Gleiberman, A. S.; Aygun-Sunar, S.; Veith, J.; Johnson, C.; Haderski, G. J.; Stanhope-Baker, P.; Allamaneni, S.; Skitzki, J.; Zeng, M.; Martsen, E.; Medvedev, A.; Scheblyakov, D.; Artemicheva, N. M.; Logunov, D. Y.; Gintsburg, A. L.; Naroditsky, B. S.; Makarov, S. S.; Gudkov, A. V. (2013). "Central role of liver in anticancer and radioprotective activities of Toll-like receptor 5 agonist". Proceedings of the National Academy of Sciences. 110 (20): E1857–66. doi:10.1073/pnas.1222805110. PMC 3657788. PMID 23630282.
  2. Ding, X.; Bian, G.; Leigh, N. D.; Qiu, J.; McCarthy, P. L.; Liu, H.; Aygun-Sunar, S.; Burdelya, L. G.; Gudkov, A. V.; Cao, X. (2012). "A TLR5 Agonist Enhances CD8+ T Cell-Mediated Graft-versus-Tumor Effect without Exacerbating Graft-versus-Host Disease". The Journal of Immunology. 189 (10): 4719–27. doi:10.4049/jimmunol.1201206. PMID 23045613.
  3. Krivokrysenko, V. I.; Shakhov, A. N.; Singh, V. K.; Bone, F.; Kononov, Y.; Shyshynova, I.; Cheney, A.; Maitra, R. K.; Purmal, A.; Whitnall, M. H.; Gudkov, A. V.; Feinstein, E. (2012). "Identification of Granulocyte Colony-Stimulating Factor and Interleukin-6 as Candidate Biomarkers of CBLB502 Efficacy as a Medical Radiation Countermeasure". Journal of Pharmacology and Experimental Therapeutics. 343 (2): 497–508. doi:10.1124/jpet.112.196071. PMC 3477210. PMID 22837010.
  4. Yoon, S.-i.; Kurnasov, O.; Natarajan, V.; Hong, M.; Gudkov, A. V.; Osterman, A. L.; Wilson, I. A. (2012). "Structural Basis of TLR5-Flagellin Recognition and Signaling". Science. 335 (6070): 859–64. doi:10.1126/science.1215584. PMC 3406927. PMID 22344444.
  5. Mueller, K. L. (2012). "Flagellin Takes Its Toll". Science Signaling. 5 (212): ec62. doi:10.1126/scisignal.2002965.
  6. Burdelya, Lyudmila G.; Gleiberman, Anatoli S.; Toshkov, Ilia; Aygun-Sunar, Semra; Bapardekar, Meghana; Manderscheid-Kern, Patricia; Bellnier, David; Krivokrysenko, Vadim I.; Feinstein, Elena; Gudkov, Andrei V. (2012). "Toll-like Receptor 5 Agonist Protects Mice from Dermatitis and Oral Mucositis Caused by Local Radiation: Implications for Head-and-Neck Cancer Radiotherapy". International Journal of Radiation Oncology*Biology*Physics. 83 (1): 228–34. doi:10.1016/j.ijrobp.2011.05.055. PMC 3261342. PMID 22000579.
  7. Fukuzawa, N.; Petro, M.; Baldwin Wm, W. M.; Gudkov, A. V.; Fairchild, R. L. (2011). "A TLR5 Agonist Inhibits Acute Renal Ischemic Failure". The Journal of Immunology. 187 (7): 3831–9. doi:10.4049/jimmunol.1003238. PMC 3178726. PMID 21890657.
  8. Burdelya, L. G.; Krivokrysenko, V. I.; Tallant, T. C.; Strom, E.; Gleiberman, A. S.; Gupta, D.; Kurnasov, O. V.; Fort, F. L.; Osterman, A. L.; Didonato, J. A.; Feinstein, E.; Gudkov, A. V. (2008). "An Agonist of Toll-Like Receptor 5 Has Radioprotective Activity in Mouse and Primate Models". Science. 320 (5873): 226–30. doi:10.1126/science.1154986. PMC 4322935. PMID 18403709.
  9. Lu, J.; Sun, P. D. (2012). "The Structure of the TLR5-Flagellin Complex: A New Mode of Pathogen Detection, Conserved Receptor Dimerization for Signaling". Science Signaling. 5 (216): pe11. doi:10.1126/scisignal.2002963. PMC 3727914. PMID 22434932.
  10. Cai, Z.; Sanchez, A.; Shi, Z.; Zhang, T.; Liu, M.; Zhang, D. (2011). "Activation of Toll-like Receptor 5 on Breast Cancer Cells by Flagellin Suppresses Cell Proliferation and Tumor Growth". Cancer Research. 71 (7): 2466–75. doi:10.1158/0008-5472.CAN-10-1993. PMC 3074302. PMID 21427357.
  11. Bhattacharjee, Y. (2008). "MEDICINE: Drug Bestows Radiation Resistance on Mice and Monkeys". Science. 320 (5873): 163. doi:10.1126/science.320.5873.163. PMID 18403680.