Radioiodine-131 released from nuclear reactor accidents has dramatically increased the incidence of papillary thyroid cancer in exposed individuals. The deposition of ionizing radiation in cells results in double-strand DNA breaks (DSB) at fragile sites, and this early event can generate oncogenic rearrangements that eventually cause cancer. The aims of this study were to develop a method to show DNA DSBs induced by (131)I in thyroid cells; to test monovalent anions that are transported by the sodium/iodide symporter to determine whether they prevent (131)I-induced DSB; and to test other radioprotective agents for their effect on irradiated thyroid cells. Rat FRTL-5 thyroid cells were incubated with (131)I. DSBs were measured by nuclear immunofluorescence using antibodies to p53-binding protein 1 or γH2AX. Incubation with 1-10 μCi (131)I per milliliter for 90 min resulted in a dose-related increase of DSBs; the number of DSBs increased from a baseline of 4-15% before radiation to 65-90% after radiation. GH3 or CHO cells that do not transport iodide did not develop DSBs when incubated with (131)I. Incubation with 20-100 μm iodide or thiocyanate markedly attenuated DSBs. Perchlorate was about 6 times more potent than iodide or thiocyanate(.) The effects of the anions were much greater when each was added 30-120 min before the (131)I. Two natural organic compounds recently shown to provide radiation protection partially prevented DSBs caused by (131)I and had an additive effect with perchlorate. In conclusion, we developed a thyroid cell model to quantify the mitogenic effect of (131)I. (131)I causes DNA DSBs in FRTL-5 cells and had no effect on cells that do not transport iodide. Perchlorate, iodide, and thiocyanate protect against DSBs induced by (131)I.

The DEL assay in yeast detects DNA deletions that are inducible by many carcinogens. Here we use the colorimetric agent MTS to adapt the yeast DEL assay for microwell plate measurement of ionizing radiation-induced cell killing and DNA deletions. Using the microwell-based DEL assay, cell killing and genotoxic DNA deletions both increased with radiation dose between 0 and 2000 Gy. We used the microwell-based DEL assay to assess the effectiveness of varying concentrations of five different radioprotectors, N-acetyl-L-cysteine, L-ascorbic acid, DMSO, Tempol and Amifostine, and one radiosensitizer, 5-bromo-2-deoxyuridine. The microwell format of the DEL assay was able to successfully detect protection against and sensitization to both radiation-induced cytotoxicity and genotoxicity. Such radioprotection and sensitization detected by the micro-wellbased DEL assay was validated and compared with similar measurements made using the traditional agar-based assay format. The yeast DEL assay in microwell format is an effective tool for rapidly detecting chemical protectors and sensitizers to ionizing radiation and is automatable for chemical high-throughput screening purposes.

The possibility of a radiation disaster from a nuclear detonation or accident has existed for over 50 years and spawned much of the basic research in radiobiology in the 1950-60s. The recent Fukushima accident was yet another reminder that there remains a dire need to develop novel therapies against radiation-induced toxicities. Here we report on the development of two novel radiation countermeasure therapies: Yel001 and Yel002. These small, biologically active, drug-like molecules were uncovered in the DEL high throughput assay reducing radiation-induced cyto- and geno-toxicity in yeast. Radiation-modulating activity was further confirmed in yeast plate-based DEL Assay: addition of either Yel001 or Yel002 to irradiated cultures reduced cell death and genomic instability. Further, Yel compounds increases survival to 75% in vivo following an LD100/30 dose of ionizing radiation (IR) with the first therapeutic injection administered 24 hours post exposure followed by injections at 48,72,96, and 120 hours. Additionally, treatment with Yel001 and Yel002 compounds reduces radiation-induced leukemia from 90% to to 50% and 40% respectively. Of note, treatment with either Yel001 or Yel002 reduced spontaneous leukemia rate from 10% to 0%. Furthermore, Yel002 significantly prolonged the life of Atm deficient mice. Treatment with Yel002 following IR accelerates the recovery of the hematopoietic cells and protects stem cells after sub-lethal exposures. In addition, treatment with Yel002 reduces I131, EMS, MMS, UV, cigarette smoke extract as well as nitrogen mustard induced toxicity as well as genotoxicity showing a broad application spectrum. Proteomics shows that Yel002 induces DNA repair mediated by Atm signaling, homologous recombination, nonhomologous end joining, base excision repair, DNA damage binding proteins and chromosome segregation functions. Toxicity has not been observed in neither in vitro or in vivo administrations, even in a two generation teratogenicity assay. Overall, Yel compounds have much potential as stockpile therapies for radiation-induced lethality and cancer as well as spontaneous cancer: they are highly effective when administered up to 24hours post exposure, they reduce radiation-induced sequelae such as leukemia, and appear to have an acceptable toxicity profile. Citation Format: Robert H. Schiestl, Yelena Rivina, Michael Davoren. Novel radiation mitigators and cancer chemoprevention drugs. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4909. doi:10.1158/1538-7445.AM2014-4909

The possibility of a radiation disaster from a nuclear detonation or accident has existed for over 50 years and spawned much of the basic research in radiobiology in the 1950-60s. The recent Fukushima accident was yet another reminder that there remains a dire need to develop novel therapies against radiation-induced toxicities. Here we report on the development of two novel radiation countermeasure therapies: Yel001 and Yel002. These small, biologically active, drug-like molecules were uncovered in the DEL high throughput assay reducing radiation-induced cyto- and geno-toxicity in yeast. Radiation-modulating activity was further confirmed in yeast plate-based DEL Assay: addition of either Yel001 or Yel002 to irradiated cultures reduced cell death and genomic instability. Further, Yel compounds increases survival to 75% in vivo following an LD100/30 dose of ionizing radiation (IR) with the first therapeutic injection administered 24 hours post exposure followed by injections at 48,72,96, and 120 hours. Additionally, treatment with Yel001 and Yel002 compounds reduces radiation-induced leukemia from 90% to to 50% and 40% respectively. Of note, treatment with either Yel001 or Yel002 reduced spontaneous leukemia rate from 10% to 0%. Furthermore, Yel002 significantly prolonged the life of Atm deficient mice. Treatment with Yel002 following IR accelerates the recovery of the hematopoietic cells and protects stem cells after sub-lethal exposures. In addition, treatment with Yel002 reduces I131, EMS, MMS, UV, cigarette smoke extract as well as nitrogen mustard induced toxicity as well as genotoxicity showing a broad application spectrum. Proteomics shows that Yel002 induces DNA repair mediated by Atm signaling, homologous recombination, nonhomologous end joining, base excision repair, DNA damage binding proteins and chromosome segregation functions. Toxicity has not been observed in neither in vitro or in vivo administrations, even in a two generation teratogenicity assay. Overall, Yel compounds have much potential as stockpile therapies for radiation-induced lethality and cancer as well as spontaneous cancer: they are highly effective when administered up to 24hours post exposure, they reduce radiation-induced sequelae such as leukemia, and appear to have an acceptable toxicity profile. Citation Format: Robert H. Schiestl, Michael Davoren, Yelena Rivina. Novel radiation mitigators and anticancer drugs. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1793. doi:10.1158/1538-7445.AM2015-1793