Sep 24, 2013

Takahiro Kataoka (Okayama University)

Therapy involving radon gas volatilized from radon-enriched water is performed for various diseases at Misasa Medical Center, Okayama University Hospital. Many clinical studies have been reported, but no data are available explaining why radon inhalation results in positive effects. Therefore, we have been studying the mechanisms of the effects of radon using small animals. I have reported that radon inhalation activates anti-oxidative functions and inhibits oxidative damages [1]. However, to date there have been no quantitative reports on the anti-oxidative effects of radon so the optimal conditions for radon therapy remain undetermined. The purpose of this study was to compare the antioxidative effects of radon and antioxidant vitamins such as ascorbic acid (vitamin C) and α-tocopherol (vitamin E). Mice were subjected to intraperitoneal (i.p.) injection of carbon tetrachloride (CCl4) after inhaling approximately 1000 or 2000 Bq/m3 radon for 24 hours, or immediately after i.p. injection of ascorbic acid (100, 300, or 500 mg/kg bodyweight) or α-tocopherol (100, 300, or 500 mg/kg bodyweight). We estimated the inhibitory effects on CCl4-induced hepatopathy based on hepatic function-associated parameters, oxidative damage-associated parameters and histological changes. The results revealed that the therapeutic effects of radon inhalation were almost equivalent to treatment with ascorbic acid at a dose of 500 mg/kg or α-tocopherol at a dose of 300 mg/kg. The activities of superoxide dismutase, catalase, and glutathione peroxidase in the liver were significantly higher in mice exposed to radon than in mice treated with CCl4 alone. These findings suggest that radon inhalation has an anti-oxidative effect against CCl4-induced hepatopathy similar to the anti-oxidative effects of ascorbic acid or α-tocopherol due to the induction of anti-oxidative functions [2]. Next, we attempted to evaluate the quantitative effects of the activation of antioxidative activities in kidney induced by radon inhalation on CCl4-induced renal damage. In case of renal function, radon inhalation at a concentration of 2000 Bq/m3 has the inhibitory effects similar to α-tocopherol treatment at a dose of 300–500 mg/kg bodyweight. The activities of superoxide dismutase and catalase in kidneys were significantly higher in mice exposed to radon as compared to mice treated with CCl4 alone. These findings suggest that radon inhalation has an antioxidative effect against CCl4-induced renal damage similar to the antioxidative effects of α-tocopherol due to induction of antioxidative functions [3]. Quantitative evaluation of the activation of anti-oxidative functions after radon inhalation will provide a basis for future studies aimed at assessing new radon-based therapies. And then, the effects of low-dose irradiation are at the forefront of the public’s attention since the 2011 nuclear accident in Fukushima. However, it is difficult to explain the effects of low-dose irradiation in terms that the public can readily understand; therefore, these reports might provide a useful means to explain the effects of low-dose irradiation in relation to vitamins, which are common in our daily lives.

References:
[1]. Takahiro Kataoka. Award Article: Study of Antioxidative Effects and Anti-inflammatory Effects in Mice due to Low-dose X-irradiation or Radon Inhalation. Journal of Radiation Research. Journal of Radiation Research 54(4), 587-596, 2013 doi: 10.1093/jrr/rrs141
[2]. Takahiro Kataoka, Yuichi Nishiyama, Keiko Yamato, Junichi Teraoka, Yuji Morii, Akihiro Sakoda, Yuu Ishimori, Takehito Taguchi, Kiyonori Yamaoka. Comparative study on the inhibitory effects of antioxidant vitamins and radon on carbon tetrachloride-induced hepatopathy. Journal of Radiation Research 53(6), 830-839, 2012 doi: 10.1093/jrr/rrs057
[3]. Takahiro Kataoka, Keiko Yamato, Yuichi Nishiyama, Yuji Morii, Reo Etani, Yuji Takata, Katsumi Hanamoto, Atsuishi Kawabe, Akihiro Sakoda, Yuu Ishimori, Takehito Taguchi, Kiyonori Yamaoka. Comparative study on the inhibitory effects of α-tocopherol and radon on carbon tetrachloride-induced renal damage. Renal Failure 34(9)，1181-1187，2012 doi:10.3109/0886022X.2012.717496

Sep 11, 2013

Yuichiro Saito (Radiation Biology Center, Kyoto University)

Although RAD52 plays a critical role in the initiation of homologous recombination (HR) by facilitating the replacement of RPA with RAD51, the mechanism controlling RAD52 functions remains elusive. Here, we show that Bag101, a factor implicated in proteasome functioning, regulates RAD52 protein levels and subsequent HR. Firstly, LC-MS/MS analysis identified Bag101 which binds to Rad22, the fission yeast homologue of RAD52. Bag101 reduced HR frequency through its overexpression and conversely, HR frequencies were enhanced when it was deleted. Consistent with this observation, Rad22 protein levels were reduced in cells where bag101 was overexpressed even when Rad22 transcription was up-regulated, suggesting the operation of proteasome-mediated Rad22 degradation. Indeed, Rad22 protein levels were stabilized in proteasome mutants. Rad22 physically interacted with the BAG domain of Bag101, and a lack of this domain enhanced HR frequency. Similarly, radiation exposure triggered the dissociation of these proteins so that Rad22 was stabilized and able to enhance HR. These results suggest the contribution of Bag101-mediated protein degradation to maintenance of genome integrity in cells. Indeed, BAG family proteins have been reported to be overexpressed in several human tumors, such as leukemia, breast cancer, prostate cancer, and colon cancer [1, 2]. Our present results can explain a part of mechanistic links between HR and carcinogenesis, and help to develop new therapeutic agents.

References:
[1] Takayama, S. et al. Expression and Location of Hsp70/ Hsc-Binding Anti-Apoptotic Protein BAG-1 and Its Variants in Normal Tissues and Tumor Cell Lines. Cancer research 58, 3116–3131 (1998).
[2] Brimmell, M. et al. High level expression of differentially localized BAG-1 isoforms in some oestrogen receptor-positive human breast cancers. British journal of cancer 81, 1042–51 (1999).

Sep 06, 2013

Hironobu Yasui (Hokkaido University)

Glioblastoma is one of the intractable cancers and is highly resistant to ionizing radiation. This radioresistance is partly due to the presence of a hypoxic region which is widely found in advanced malignant gliomas. In the present study, we evaluated the effectiveness of the hypoxic cell sensitizer doranidazole (PR-350) using the C6 rat glioblastoma model, focusing on the status of blood brain barrier (BBB). Clonogenic assay using the rat C6 glioma cell line revealed that doranidazole significantly enhanced radiation-induced reproductive cell death in vitro under hypoxia, but not under normoxia. To investigate the status of the BBB in intracranial C6 gliom, we performed the Evans blue extravasation test. Autoradiography with [(14)C]-doranidazole was performed to examine the distribution of doranidazole in the glioma tumor. As a result, the BBB in C6-bearing brain was completely disrupted and [(14)C]-doranidazole specifically penetrated the tumor regions. Longitudinal analysis of tumor growth by T2-weighted MRI demonstrated that combined treatment with X-irradiation and doranidazole significantly inhibited the growth of C6 gliomas. Our results revealed that BBB disruption in glioma enables BBB-impermeable radiosensitizers to penetrate and distribute in the target region. This study is the first to propose that in malignant glioma the administration of hydrophilic hypoxic radiosensitizers could be a potent strategy for improving the clinical outcome of radiotherapy without side effects.

References:
[1] Yasui et al. The prospective application of a hypoxic radiosensitizer, doranidazole to rat intracranial glioblastoma with blood brain barrier disruption. BMC Cancer 13, 106 (2013)

Sep 01, 2013

Tatsuhiko Imaoka (National Institute of Radiological Sciences)

A variety of mechanisms have been inferred for combinatorial actions of multiple carcinogens, yet these mechanisms have not been well demonstrated in experimental carcinogenesis. We previously showed evidence of mechanistic interaction between high doses of Cs-137 gamma rays (2 Gy) and a chemical carcinogen, 1-methyl-1-nitrosourea (MNU, 40 mg/kg) [1]. In the present study [2], we extended this previous finding to lower doses and different chemical species found in the human environment. Female rats were gamma-irradiated (0.2, 0.5, 1.0 or 2 Gy) and/or exposed to MNU (20 or 40 mg/kg, single intraperitoneal injection) or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP; 40 mg/kg/day by gavage for 10 days) at 7 weeks of age and were observed until 50 weeks of age. 1) The risk of mammary cancer increased as a linear function of radiation dose (excess relative risk, 4.4 per Gy) in the absence of chemicals; mathematical analysis supported an additive increase when radiation was combined with a chemical carcinogen. 2) Hras mutations in carcinoma were characteristic of chemically-initated carcinogenesis; interestingly, these mutations were significantly overrepresented in carcinomas induced by the combination of radiation (0.2-1 Gy) and MNU, but not PhIP, supporting the previously identified interaction of radiation and MNU at the initiation level. 3) Analyses of gene expression profiles of carcinomas, either by previously identified classifier genes [3] or more comprehensive screening on microarrays followed by validation using test sample sets, failed to identify differences among carcinomas induced by single and combinatorial exposures to radiation (1 Gy) and chemicals. These results suggest a complex, multilevel interaction underlying the combinatorial action of radiation and chemical carcinogens in the present model.

References:
[1] Imaoka et al. Cooperative induction of rat mammary cancer by radiation and 1-methyl-1-nitrosourea via the oncogenic pathways involving c-Myc activation and H-ras mutation. International Journal of Cancer 115, 187-93 (2005)
[2] Imaoka et al. Molecular characterization of cancer reveals interactions between ionizing radiation and chemicals on rat mammary carcinogenesis. International Journal of Cancer (in press)
[3] Imaoka et al. Gene expression profiling distinguishes between spontaneous and radiation-induced rat mammary carcinomas. Journal of Radiation Research 49, 349-60 (2008)

Jun 09, 2014

Shigeyoshi Saito (Osaka University)

The in vivo detection of early cellular responses is important for predicting therapeutic efficacy for tumor radiotherapy. Mn2+ is used as a positive contrast agent in MRI (manganese-enhanced MRI; MEMRI) and is expected to behave as mimicry of Ca2+ in many biological systems. We conducted in vitro and in vivo MRI with Mn2+ administration to investigate whether MEMRI can be used to detect cell cycle alteration as an early tumor response after radiotherapy. Colon-26 cells or a subcutaneously grafted colon-26 tumor model were irradiated with 20 Gy of x-ray. One day after irradiation, a significant augmentation of G2/M-phase cells, indicating a cell-cycle arrest, was observed in the irradiated cells in comparison with the control cells, although both early and late apoptotic alterations were rarely observed. The MEMRI signal in radiation-exposed tumor cells was significantly lower than that in control cells in vitro. The MEMRI signal reduction was also observed in the in vivo tumor model, along with cell cycle alteration, detected by immunostaining (cyclin-D1 and Ki-67). Therefore, MEMRI after tumor radiotherapy was successfully used to detect cell cycle alteration as an early cellular response in vitro and in vivo. 

References:
Saito S, Hasegawa S, Sekita A, Bakalova R, Furukawa T, Murase K, Saga T, Aoki I. Manganese-Enhanced MRI Reveals Early-Phase Radiation-Induced Cell Alterations In Vivo. 
Cancer Res. 2013 Jun 1;73(11):3216-24. PMID:23695553