Classes of Drugs that Mitigate Radiation Syndromes

We previously reported several vignettes on types and classes of drugs able to mitigate acute and, in at least one case, late radiation syndromes in mice. Most of these had emerged from high throughput screening (HTS) of bioactive and chemical drug libraries using ionizing radiation-induced lymphocytic apoptosis as a readout. Here we report the full analysis of the HTS screen of libraries with 85,000 small molecule chemicals that identified 220 "hits." Most of these hits could be allocated by maximal common substructure analysis to one of 11 clusters each containing at least three active compounds. Further screening validated 23 compounds as being most active; 15 of these were cherry-picked based on drug availability and tested for their ability to mitigate acute hematopoietic radiation syndrome (H-ARS) in mice. Of these, five bore a 4-nitrophenylsulfonamide motif while 4 had a quinoline scaffold. All but two of the 15 significantly (p < 0.05) mitigated H-ARS in mice. We had previously reported that the lead 4-(nitrophenylsulfonyl)-4-phenylpiperazine compound (NPSP512), was active in mitigating multiple acute and late radiation syndromes in mice of more than one sex and strain. Unfortunately, the formulation of this drug had to be changed for regulatory reasons and we report here on the synthesis and testing of active analogs of NPSP512 (QS1 and 52A1) that have increased solubility in water and in vivo bioavailability while retaining mitigator activity against H-ARS (p < 0.0001) and other radiation syndromes. The lead quinoline 057 was also active in multiple murine models of radiation damage. Taken together, HTS of a total of 150,000 bioactive or chemical substances, combined with maximal common substructure analysis has resulted in the discovery of diverse groups of compounds that can mitigate H-ARS and at least some of which can mitigate multiple radiation syndromes when given starting 24 h after exposure. We discuss what is known about how these agents might work, and the importance of formulation and bioavailability.

Radioprotectors.org: an open database of known and predicted radioprotectors

The search for radioprotectors is an ambitious goal with many practical applications. Particularly, the improvement of human radioresistance for space is an important task, which comes into view with the recent successes in the space industry. Currently, all radioprotective drugs can be divided into two large groups differing in their effectiveness depending on the type of exposure. The first of these is radioprotectors, highly effective for pulsed, and some types of relatively short exposure to irradiation. The second group consists of long-acting radioprotectors. These drugs are effective for prolonged and fractionated irradiation. They also protect against impulse exposure to ionizing radiation, but to a lesser extent than short-acting radioprotectors. Creating a database on radioprotectors is a necessity dictated by the modern development of science and technology. We have created an open database, Radioprotectors.org, containing an up-to-date list of substances with proven radioprotective properties. All radioprotectors are annotated with relevant chemical and biological information, including transcriptomic data, and can be filtered according to their properties. Additionally, the performed transcriptomics analysis has revealed specific transcriptomic profiles of radioprotectors, which should facilitate the search for potent radioprotectors.

Second-generation Probiotics Producing IL-22 Increase Survival of Mice After Total Body Irradiation

BACKGROUND/AIM

Intestinal damage induced by total body irradiation (TBI) reduces leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5)-expressing stem cells, goblet, and Paneth cells, breaching the epithelial lining, and facilitating bacterial translocation, sepsis, and death.

MATERIALS AND METHODS

Survival was measured after TBI in animals that received wild-type or recombinant bacteria producing interleukin-22 (IL-22). Changes in survival due to microbially delivered IL-22 were measured. Lactobacillus reuteri producing IL-22, or Escherichia coli-IL-22 were compared to determine which delivery system is better.

RESULTS

C57BL/6 mice receiving IL-22 probiotics at 24 h after 9.25 Gy TBI, demonstrated green fluorescent protein-positive bacteria in the intestine, doubled the number of Lgr5+ intestinal stem cells, and increased 30-day survival. Bacteria were localized to the jejunum, ileum, and colon.

CONCLUSION

Second-generation probiotics appear to be valuable for mitigation of TBI, and radiation protection during therapeutic total abdominal irradiation.

Radioprotective agents for radiation therapy: future trends

Only two radioprotective compounds, amifostine and palifermin, currently have the US FDA approval for use in radiation therapy. However, several agents have been reported that show therapeutic promise. Many of these agents are free radical scavengers/antioxidants. Superoxide dismutase and superoxide dismutase mimetics, nitroxides and dietary antioxidants are all being investigated. Recently, alternative strategies of drug development have been evolving, which focus on targeting the series of cellular insult recognition/repair responses initiated following radiation. These agents, which include cytokines/growth factors, angiotensin-converting enzyme inhibitors and apoptotic modulators, show promise of having significant impact on the mitigation of radiation injury. Herein, we review current literature on the development of radioprotectors with emphasis on compounds with proven or potential usefulness in radiation therapy.

Strategies for discovery of small molecule radiation protectors and radiation mitigators

Mitochondrial targeted radiation damage protectors (delivered prior to irradiation) and mitigators (delivered after irradiation, but before the appearance of symptoms associated with radiation syndrome) have been a recent focus in drug discovery for (1) normal tissue radiation protection during fractionated radiotherapy, and (2) radiation terrorism counter measures. Several categories of such molecules have been discovered: nitroxide-linked hybrid molecules, including GS-nitroxide, GS-nitric oxide synthase inhibitors, p53/mdm2/mdm4 inhibitors, and pharmaceutical agents including inhibitors of the phosphoinositide-3-kinase pathway and the anti-seizure medicine, carbamazepine. Evaluation of potential new radiation dose modifying molecules to protect normal tissue includes: clonogenic radiation survival curves, assays for apoptosis and DNA repair, and irradiation-induced depletion of antioxidant stores. Studies of organ specific radioprotection and in total body irradiation-induced hematopoietic syndrome in the mouse model for protection/mitigation facilitate rational means by which to move candidate small molecule drugs along the drug discovery pipeline into clinical development.

Screening of antimicrobial agents for in vitro radiation protection and mitigation capacity, including those used in supportive care regimens for bone marrow transplant recipients

Antibiotic and antifungal agents used in supportive care regimens for bone marrow transplantation recipients contribute to a significant dose-modifying effect of otherwise lethal total body irradiation. To determine whether drugs used in supportive care and other commonly used antibiotics such as tetracycline function as radiation protectors or damage mitigators in vitro, 13 drugs were tested for radiation protection and radiation damage mitigation of 32D cl 3 hematopoietic progenitor cells in clonagenic survival curves in vitro. Antibiotic/Antifungal agents including cilastatin, amikacin, ceftazidine, vancomycin, tetracycline, doxycycline, ciprofloxacin, metronidazole, methacycline, minocycline, meclocycline, oxytetracycline and rolitetracycline were added in 1, 10, or 100 micromolar concentrations to murine interleukin-3-dependent hematopoietic progenitor cell line 32D cl 3 cells either before or after irradiation of 0 to 8 Gy. Control irradiated 32D cl 3 cells showed radiosensitivity comparable to freshly explanted mouse marrow hematopoietic progenitor cells (D(0) 1.1+/-0.1 Gy, N 1.5+/-0.4). Positive control GS-nitroxide JP4-039 (known radiation mitigator) treated 32D cl 3 cells were radioresistant (D(0) 1.2+/-0.1, N 5.8+/-2.4 (p=0.009)). Of the 13 drugs tested, tetracycline was found to be a significant radiation mitigator (D(0) 0.9+/-0.1, N 13.9+/-0.4 (p=0.0027)). Thus, the radiation dose-modifying effect of some antibiotics, but not those currently used in the supportive care (antibiotic/antifungal regimens) for marrow transplant patients, may act as radiation damage mitigators for hematopoietic cells as well as decreasing the growth and inflammatory response to microbial pathogens.