Sodium orthovanadate (vanadate), a potent mitigator of radiation-induced damage to the hematopoietic system in mice

Renal FGF23 signaling depends on redox protein Memo1 and promotes orthovanadate-sensitive protein phosphotyrosyl phosphatase activity

Memo1 deletion in mice causes premature aging and an unbalanced metabolism partially resembling Fgf23 and Klotho loss-of-function animals. We report a role for Memo's redox function in renal FGF23-Klotho signaling using mice with postnatally induced Memo deficiency in the whole body (cKO). Memo cKO mice showed impaired FGF23-driven renal ERK phosphorylation and transcriptional responses. FGF23 actions involved activation of oxidation-sensitive protein phosphotyrosyl phosphatases in the kidney. Redox proteomics revealed excessive thiols of Rho-GDP dissociation inhibitor 1 (Rho-GDI1) in Memo cKO, and we detected a functional interaction between Memo's redox function and oxidation at Rho-GDI1 Cys79. In isolated cellular systems, Rho-GDI1 did not directly affect FGF23-driven cell signaling, but we detected disturbed Rho-GDI1 dependent small Rho-GTPase protein abundance and activity in the kidney of Memo cKO mice. Collectively, this study reveals previously unknown layers in the regulation of renal FGF23 signaling and connects Memo with the network of small Rho-GTPases.

Feasibility of Reducing Animal Numbers in Radiation Countermeasure Experiments from Historic Levels when using Sample Size Calculations

Historically, animal numbers have most often been in the hundreds for experiments designed to estimate the dose reduction factor (DRF) of a radiation countermeasure treatment compared to a control treatment. Before 2010, researchers had to rely on previous experience, both from others and their own, to determine the number of animals needed for a DRF experiment. In 2010, a formal sample size formula was developed by Kodell et al. This theoretical work showed that sample sizes for realistic, yet hypothetical, DRF experiments could be less than a hundred animals and still have sufficient power to detect clinically meaningful DRF values. However, researchers have been slow to use the formula for their DRF experiments, whether from ignorance to its existence or hesitancy to depart from "tried and true" sample sizes. Here, we adapt the sample size formula to better fit usual DRF experiments, and, importantly, we provide real experimental evidence from two independent DRF experiments that sample sizes smaller than what have typically been used can still statistically detect clinically meaningful DRF values. In addition, we update a literature review of DRF experiments which can be used to inform future DRF experiments, provide answers to questions that researchers have asked when considering sample size calculations rather than solely relying on previous experience, whether their own or others', and, in the supplementary material, provide R code implementing the formula, along with several exercises to familiarize the user with the adapted formula.

SOV sensitizes gastric cancer cells to radiation by suppressing radiation-induced autophagy in vitro and in vivo

Vanadium is a transition metal that naturally occurs in the environment and has a variety of biological and physiological impacts on humans. Sodium orthovanadate (SOV), a well-known chemical compound of vanadium, has shown notable anti-cancer activity in various types of human malignancies. However, the effect of SOV on stomach cancer is yet undetermined. Furthermore, only a few studies have investigated the association of SOV and radiosensitivity with stomach cancer. Our study has investigated the ability of SOV to increase the sensitivity of gastric cancer cells to radiation. To detect autophagy triggered by ionizing radiation and the influence of SOV on cell radiosensitivity, the Cell Counting Kit-8 (CCK8) test, EDU staining experiment, colony formation assay, and immunofluorescence were performed. The possible synergistic effects of SOV and irradiation were examined in vivo using a xenograft mouse model of stomach cancer cells. Both in vitro and in vivo studies showed that SOV markedly reduced the growth of stomach cancer cells and improved their radiosensitivity. Our results showed that SOV increased gastric cancer cells' radiosensitivity, thereby blocking the radiation-induced autophagy-related protein, ATG10. Thus, SOV can be considered a potential agent for radiosensitizing gastric cancer.

A Study of Vanadate Group Substitution into Nanosized Hydroxyapatite Doped with Eu3+ Ions as a Potential Tissue Replacement Material

In this study, nanosized vanadate-substituted hydroxyapatites doped with 1 mol% and 2 mol% Eu3+ ions were obtained via the precipitation method. To evaluate the structure and morphology of the obtained compounds, the XRPD (X-ray powder diffraction) technique, Rietveld refinement, SEM-EDS (scanning electron microscopy-energy-dispersive spectrometry) and TEM (transmission electron microscopy) techniques as well as FTIR (Fourier transform infrared) spectroscopy were performed. Moreover, the chemical formula was confirmed using the ICP-OES (Inductively coupled plasma optical emission spectroscopy spectroscopy). The calculated average grain size for powders was in the range of 25 to 90 nm. The luminescence properties of vanadium-substituted hydroxyapatite were evaluated by recording emission spectra and excitation spectra as well as luminescence kinetics. The crucial step of this research was the evaluation of the biocompatibility of the synthesized nanomaterials. Therefore, the obtained compounds were tested toward sheep red blood cells and normal human dermal fibroblast to confirm the nontoxicity and biocompatibility of new nanosized Eu3+ ion-doped vanadate-hydroxyapatite. Moreover, the final step of the research allowed us to determine the time dependent ion release to the simulated body fluid environment. The study confirmed cytocompatibility of vanadium hydroxyapatite doped with Eu3+ ions.

Evaluation of sodium orthovanadate as a radioprotective agent under total-body irradiation and partial-body irradiation conditions in mice

PURPOSE

Our previous study indicated that sodium orthovanadate (vanadate), a strong inhibitor of p53, effectively suppressed the lethality from the hematopoietic (HP) and gastrointestinal (GI) syndromes after 12 Gy total-body irradiation (TBI) in mice. This conclusion, however, was inconsistent with the fact that p53 plays a radioprotective role in the intestinal epithelium. The death after TBI of around 12 Gy was attributed to a combined effect of HP and GI syndromes. To verify the effect from prophylactic administration of p53 inhibitor on protection of HP and GI syndromes, in this study, the radioprotective effects from vanadate were investigated in TBI and lower half-body irradiation (partial-body irradiation: PBI) mouse models.

METHODS

Female ICR mice were given a single injection of vanadate or vehicle, followed by a lethal dose of TBI or PBI. Radioprotective effects of vanadate against the irradiations were evaluated by analyzing survival rate, body weight, hematopoietic parameters, and histological changes in the bone marrow and intestinal epithelium.

RESULTS

TBI-induced HP syndrome was effectively suppressed by vanadate treatment. After TBI, the vanadate-treated mice retained better bone marrow cellularity and showed markedly higher survival rate compared to the vehicle-treated animals. In contrast, vanadate did not relieve loss of intestinal crypts and failed to rescue mice from GI death after PBI.

CONCLUSION

Vanadate is a p53 inhibitor that has been shown to be beneficial as a radiation protective agent against HP but was not effective in protecting against acute GI radiation injury.

Acute Toxicity Evaluation of Non-Innocent Oxidovanadium(V) Schiff Base Complex

The vanadium(V) complexes have been investigated as potential anticancer agents which makes it essential to evaluate their toxicity for safe use in the clinic. The large-scale synthesis and the acute oral toxicity in mice of the oxidovanadium(V) Schiff base catecholate complex, abbreviated as [VO(HSHED)dtb] containing a redox-active ligand with tridentate Schiff base (HSHED = N-(salicylideneaminato)-N’-(2-hydroxyethyl)-1,2-ethylenediamine) and dtb = 3,5-di-(t-butyl)catechol ligands were carried out. The body weight, food consumption, water intake as well biomarkers of liver and kidney toxicity of the [VO(HSHED)dtb] were compared to the precursors, sodium orthovanadate, and free ligand. The 10-fold scale-up synthesis of the oxidovanadium(V) complex resulting in the preparation of material in improved yield leading to 2–3 g (79%) material suitable for investigating the toxicity of vanadium complex. No evidence of toxicity was observed in animals when acutely exposed to a single dose of 300 mg/kg for 14 days. The toxicological results obtained with biochemical and hematological analyses did not show significant changes in kidney and liver parameters when compared with reference values. The low oral acute toxicity of the [VO(HSHED)dtb] is attributed to redox chemistry taking place under biological conditions combined with the hydrolytic stability of the oxidovanadium(V) complex. These results document the design of oxidovanadium(V) complexes that have low toxicity but still are antioxidant and anticancer agents.

Targets for protection and mitigation of radiation injury

Protection of normal tissues against toxic effects of ionizing radiation is a critical issue in clinical and environmental radiobiology. Investigations in recent decades have suggested potential targets that are involved in the protection against radiation-induced damages to normal tissues and can be proposed for mitigation of radiation injury. Emerging evidences have been shown to be in contrast to an old dogma in radiation biology; a major amount of reactive oxygen species (ROS) production and cell toxicity occur during some hours to years after exposure to ionizing radiation. This can be attributed to upregulation of inflammatory and fibrosis mediators, epigenetic changes and disruption of the normal metabolism of oxygen. In the current review, we explain the cellular and molecular changes following exposure of normal tissues to ionizing radiation. Furthermore, we review potential targets that can be proposed for protection and mitigation of radiation toxicity.

Long-term Consequences of Pelvic Irradiation: Toxicities, Challenges, and Therapeutic Opportunities with Pharmacologic Mitigators

A percentage of long-term cancer survivors who receive pelvic irradiation will develop treatment-related late effects, collectively termed pelvic radiation disease. Thus, there is a need to prevent or ameliorate treatment-related late effects in these patients. Modern radiotherapy methods can preferentially protect normal tissues from radiation toxicities to permit higher doses to targets. However, concerns about chronic small bowel toxicity, for example, still constrain the prescription dose. This provides strong rationale for considering adding pharmacologic mitigators. Implementation of modern targeted radiotherapy methods enables delivery of focused radiation to target volumes, while minimizing dose to normal tissues. In prostate cancer, these technical advances enabled safe radiation dose escalation and better local tumor control without increasing normal tissue complications. In other pelvic diseases, these new radiotherapy methods have not resulted in the low probability of normal tissue damage achieved with prostate radiotherapy. The persistence of toxicity provides rationale for pharmacologic mitigators. Several new agents could be readily tested in clinical trials because they are being or have been studied in human patients already. Although there are promising preclinical data supporting mitigators, no clinically proven options to treat or prevent pelvic radiation disease currently exist. This review highlights therapeutic options for prevention and/or treatment of pelvic radiation disease, using pharmacologic mitigators. Successful development of mitigators would reduce the number of survivors who suffer from these devastating consequences of pelvic radiotherapy. It is important to note that pharmacologic mitigators to ameliorate pelvic radiation disease may be applicable to other irradiated sites in which chronic toxicity impairs quality of life.

INVESTIGATION OF THE RADIOPROTECTIVE EFFECT OF ORTHOVANADATE IN MICE AFTER TOTAL BODY IRRADIATION

The increasing risk of acute large-scale exposure of ionising irradiation on the population underlines the necessity of developing effective radioprotective and mitigating agents. The aim of this work was to investigate the effect of sodium orthovanadate pre-treatment on mice exposed to high doses of gamma rays (from 5 to 13 Gy). The determination of median lethal dose within 30 days confirmed that orthovanadate applied to total-body-irradiated mice intra-peritoneally has a radioprotective but not a mitigating effect. With orthovanadate pre-treatment, the composition of cellularity in the bone marrow improved substantially and the main lymphocyte populations restored during the first month after irradiation. These findings contribute to 'gap-filling' in radioprotective effects and demonstrate the importance of haematological parameters in radiation-response prediction.

Development of p53-targeting drugs that increase radioresistance in normal tissues

Radiation damage to normal tissues is a serious concern in radiation therapy. Advances in radiotherapeutic technology have improved the dose distribution of the target volumes and risk organs, but damage to risk organs that are located within the irradiation field still limits the allowable prescription dose. To overcome this dose-limiting toxicity, and to further improve the efficacy of radiotherapy, the development of drugs that protect normal tissues but not cancer tissues from the effects of radiation are expected to be developed based on molecular target-based drugs. p53 is a well-known transcription factor that is closely associated with radiation-induced cell death. In radiation-injured tissues, p53 induces apoptosis in hematopoietic lineages, whereas it plays a radioprotective role in the gastrointestinal epithelium. These facts suggest that p53 inhibitor would be effective for radioprotection of the hematopoietic system, and that a drug that upregulates the radioprotective functions of p53 would enhance the radioresistance of gastrointestinal tissues. In this review, we summarize recent progress regarding the prevention of radiation injury by regulating p53 and provide new strategic insights into the development of radioprotectors in radiotherapy. J. Med. Invest. 66 : 219-223, August, 2019.

Mesenchymal stem cell-mediated Notch2 activation overcomes radiation-induced injury of the hematopoietic system

Radiation exposure severely damages the hematopoietic system. Although several radio-protectors have been proposed to prevent radiation-induced damage, most agents have limited efficacy. In the present study, we investigated whether mesenchymal stem cells (MSCs) could contribute to the expansion of hematopoietic cells and mitigate radiation-induced hematopoietic injury in vitro and in vivo. We found that co-culture with MSCs promoted hematopoietic progenitor/stem cell (HPSCs) maintenance by providing a bone marrow-like microenvironment. In addition, we showed that MSCs prevented radiation-induced damage to HPSCs, as evidenced by the lack of DNA damage and apoptosis. Intravenously injected MSCs rapidly migrated to the bone marrow (BM) and prevented loss of BM cellularity, which reduced lethality and ameliorated pancytopenia in the BM of whole body-irradiated mice. We demonstrated that MSC-derived Jagged1 attenuated radiation-induced cytotoxicity of HPSCs, and that this was mediated by Notch signaling and expression of downstream proteins Bcl2 and p63 in HPSCs. In addition, Notch2 depletion significantly reduced the MSC-mediated radio-protective effect in human- and mouse-derived HPSCs. Collectively, our data show that activation of Notch and its associated downstream signaling pathways prevent radiation-induced hematopoietic injury. Therefore, enhancing Jagged1-Notch2 signaling could provide therapeutic benefit by protecting the hematopoietic system against damage after radiation.

Role of drugs in the prevention and amelioration of radiation induced toxic effects

As the use of radiation technology for nuclear warfare or for the benefits of mankind (e.g. in radiotherapy or radio-diagnosis) is increasing tremendously, the risk of associated side effects is becoming a cause of concern. These effects, ranging from nausea/vomiting to death, may result from accidental or deliberate exposure and begin in seconds. Through this review paper, efforts have been done to critically review different compounds which have been investigated as radioprotectors and radiation mitigators. Radioprotectors are compounds which are administered just before or at the time of irradiation so as to minimize the radiation induced damage to normal tissues. And radiation mitigators are the compounds which can even minimize or ameliorate post irradiaion-toxicity provided they are administered before the onset of toxic symptoms. A variety of agents have been investigated for their preventive and ameliorative potential against radiation induced toxic effects. This review article has focused on various aspects of the promising representative agents belonging to different classes of radioprotectors and mitigators. Many compounds have shown promising results, but till date only amifostine and palifermin are clinically approved by FDA. To fill this void in pharmacological armamentarium, focus should be shifted towards novel approaches.

A Chemical Modulator of p53 Transactivation that Acts as a Radioprotective Agonist

Inhibiting p53-dependent apoptosis by inhibitors of p53 is an effective strategy for preventing radiation-induced damage in hematopoietic lineages, while p53 and p21 also play radioprotective roles in the gastrointestinal epithelium. We previously identified some zinc(II) chelators, including 8-quinolinol derivatives, that suppress apoptosis in attempts to discover compounds that target the zinc-binding site in p53. We found that 5-chloro-8-quinolinol (5CHQ) has a unique p53-modulating activity that shifts its transactivation from proapoptotic to protective responses, including enhancing p21 induction and suppressing PUMA induction. This p53-modulating activity also influenced p53 and p53-target gene expression in unirradiated cells without inducing DNA damage. The specificity of 5CHQ for p53 and p21 was demonstrated by silencing the expression of each protein. These effects seem to be attributable to the sequence-specific alteration of p53 DNA-binding, as evaluated by chromatin immunoprecipitation and electrophoretic mobility shift assays. In addition, 5-chloro-8-methoxyquinoline itself had no antiapoptotic activity, indicating that the hydroxyl group at the 8-position is required for its antiapoptotic activity. We applied this remarkable agonistic activity to protecting the hematopoietic and gastrointestinal system in mouse irradiation models. The dose reduction factors of 5CHQ in total-body and abdominally irradiated mice were about 1.2 and 1.3, respectively. 5CHQ effectively protected mouse epithelial stem cells from a lethal dose of abdominal irradiation. Furthermore, the specificity of 5CHQ for p53 in reducing the lethality induced by abdominal irradiation was revealed in Trp53-KO mice. These results indicate that the pharmacologic upregulation of radioprotective p53 target genes is an effective strategy for addressing the gastrointestinal syndrome. Mol Cancer Ther; 17(2); 432-42. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

Analysis of Hemogram of Radiation Workers in Tangshan, China

OBJECTIVES

This study aimed to investigate changes in peripheral blood cells of radiation workers and explore the impact of long-term ionizing radiation (IR) on human peripheral hemogram.

METHODS

With a cohort method, we selected 1,392 radiation workers (case group) and 1,430 non-health-ray-exposure history persons (control group) to detect and analyze their peripheral hemogram. FAITH3000 automatic biochemical analyzer was used for blood testing. Examination of peripheral hemogram includes the examination of white blood cells (WBCs), platelet (PLTs), red blood cells (RBCs), hemoglobin (Hb), lymphocytes (LYMs), and mononuclear cells (MOs). The data analysis was conducted with software SPSS19.0.

RESULTS

All the peripheral hemogram indicators (WBCs, RBCs, Hb, PLTs, LYMs, and MOs) in the case group, in accordance with the order of radiology diagnostic medical group, industrial inspection group, petroleum logging group, and radiotherapy medical group, showed a significant decreasing trend and were lower than those in the control group (all P < 0.05). Besides, with the increase of radiation seniority and accumulative radiation dose, all the peripheral hemogram indicators (WBCs, RBCs, Hb, PLTs, LYMs, and MOs) in the case group dramatically decreased and were lower than those in the control group (all P < 0.05). Seniority was in negative association with the expressions of WBCs, PLTs, RBCs, Hb, LYMs, and MOs and radiation dose with Hb, LYMs, and MOs (all P < 0.05).

CONCLUSION

Long-term IR has some effects on the health of radiation workers, thus protective measures should be further strengthened.

Radioprotective Agents: Strategies and Translational Advances

Radioprotectors are agents required to protect biological system exposed to radiation, either naturally or through radiation leakage, and they protect normal cells from radiation injury in cancer patients undergoing radiotherapy. It is imperative to study radioprotectors and their mechanism of action comprehensively, looking at their potential therapeutic applications. This review intimately chronicles the rich intellectual, pharmacological story of natural and synthetic radioprotectors. A continuous effort is going on by researchers to develop clinically promising radioprotective agents. In this article, for the first time we have discussed the impact of radioprotectors on different signaling pathways in cells, which will create a basis for scientific community working in this area to develop novel molecules with better therapeutic efficacy. The bright future of exceptionally noncytotoxic derivatives of bisbenzimidazoles is also described as radiomodulators. Amifostine, an effective radioprotectant, has been approved by the FDA for limited clinical use. However, due to its adverse side effects, it is not routinely used clinically. Recently, CBLB502 and several analog of a peptide are under clinical trial and showed high success against radiotherapy in cancer. This article reviews the different types of radioprotective agents with emphasis on the strategies for the development of novel radioprotectors for drug development. In addition, direction for future strategies relevant to the development of radioprotectors is also addressed.

Reactivity and Speciation of Anti-Diabetic Vanadium Complexes in Whole Blood and Its Components: The Important Role of Red Blood Cells

Reactions with blood components are crucial for controlling the antidiabetic, anticancer, and other biological activities of V(V) and V(IV) complexes. Despite extensive studies of V(V) and V(IV) reactions with the major blood proteins (albumin and transferrin), reactions with whole blood and red blood cells (RBC) have been studied rarely. A detailed speciation study of Na3[V(V)O4] (A), K4[V(IV)2O2(citr)2]·6H2O (B; citr = citrato(4-)); [V(IV)O(ma)2] (C; ma = maltolato(-)), and (NH4)[V(V)(O)2(dipic)] (D; dipic = pyridine-2,6-dicarboxylato(2-)) in whole rat blood, freshly isolated rat plasma, and commercial bovine serum using X-ray absorption near-edge structure (XANES) spectroscopy is reported. The latter two compounds are potential oral antidiabetic drugs, and the former two are likely to represent their typical decomposition products in gastrointestinal media. XANES spectral speciation was performed by principal component analysis and multiple linear regression techniques, and the distribution of V between RBC and plasma fractions was measured by electrothermal atomic absorption spectroscopy. Reactions of A, C, or D with whole blood (1.0 mM V, 1-6 h at 310 K) led to accumulation of ∼50% of total V in the RBC fraction (∼10% in the case of B), which indicated that RBC act as V carriers to peripheral organs. The spectra of V products in RBC were independent of the initial V complex, and were best fitted by a combination of V(IV)-carbohydrate (2-hydroxyacid moieties) and/or citrate (65-85%) and V(V)-protein (15-35%) models. The presence of RBC created a more reducing environment in the plasma fraction of whole blood compared with those in isolated plasma or serum, as shown by the differences in distribution of V(IV) and V(V) species in the reaction products of A-D in these media. At physiologically relevant V concentrations (<50 μM), this role of RBC may promote the formation of V(III)-transferrin as a major V carrier in the blood plasma. The results reported herein have broad implications for the roles of RBC in the transport and speciation of metal pro-drugs that have broad applications across medicine.

Vanadium(V) and -(IV) complexes of anionic polysaccharides: Controlled release pharmaceutical formulations and models of vanadium biotransformation products

Uncontrolled reactions in biological media are a main obstacle for clinical translation of V-based anti-diabetic or anti-cancer pro-drugs. We investigated the use of controlled-release pharmaceutical formulations to ameliorate this issue with a series of V(V) and (IV) complexes of anionic polysaccharides. Carboxymethyl cellulose, xanthan gum, or alginic acid formulations were prepared by the reactions of [VO4](3-) with one or two molar equivalents of biological reductants, L-ascorbic acid (AA) or L-cysteine (Cys), in the presence of excess polysaccharide at pH~7 or pH~4. XANES studies with the use of a previously developed library of model V(V), V(IV) and V(III) complexes showed that reactions in the presence of AA led mostly to the mixtures of five- and six-coordinate V(IV) species, while the reactions in the presence of Cys led predominantly to the mixtures of five- and six-coordinate V(V) species. The XANES spectra of some of these samples closely matched those reported previously for [VO4](3-) biotransformation products in isolated blood plasma, red blood cells, or cultured adipocytes, which supports the hypothesis that modified polysaccharides are major binders of V(V) and V(IV) in biological systems. Studies by EPR spectroscopy suggested predominant V(IV)-carboxylato binding in complexes with polysaccharides. One of the isolated products (a V(IV)-alginato complex) showed selective release of low-molecular-mass V species at pH~8, but not at pH~2, which makes it a promising lead for the development of V-containing formulations for oral administration that are stable in the stomach, but release the active ingredient in the intestines.

Evaluation of zinc (II) chelators for inhibiting p53-mediated apoptosis

In a previous study, we reported that sodium orthovanadate (vanadate) is the first known inhibitor that is capable of protecting mice from death from the radiation-induced gastrointestinal syndrome via its ability to block both transcription-dependent and transcription-independent p53 apoptotic pathways. In this paper, we report that vanadate has a unique activity for inducing the denaturation of p53 relative to other known radioprotective p53 inhibitors, pifithrin-α (PFTα) and pifithrin-µ (PFTµ). This potent radioprotective effect of vanadate prompted us to undertake a more extensive search for p53 inhibitors that can induce p53 denaturation. Based on the fact that p53 denaturation can be induced by the dissociation of a zinc ion, which is used as a structural factor of p53, we screened some zinc (II) chelators for the suppression of the DNA binding activity of p53 in vitro and the inhibition of radiation-induced p53-dependent apoptosis in MOLT-4 cells. The findings indicate that two of five zinc (II) chelators also suppressed apoptosis. Among the inhibitors tested, Bispicen (N,N'-Bis(2-pyridylmethyl)-1,2-ethanediamine) had the highest inhibition activity. A mechanistic study using cells bearing different p53 status or functions (i.e., p53-knockdown MOLT-4 transformant and its revertants, p53 mutant cells, p53-null cells), and p53-independent apoptotic stimuli revealed that the suppressive effect of Bispicen on apoptosis is specifically mediated through p53. Moreover, Bispicen, similar to vanadate, induces the denaturation of p53 as well as the blocking of both transcription-dependent and -independent apoptotic pathways. Our findings indicate that the use of zinc (II) chelators represent a new approach for protecting against radiation-induced p53-dependent apoptosis through the inhibition of p53-dependent apoptotic pathways.

AS-2, a novel inhibitor of p53-dependent apoptosis, prevents apoptotic mitochondrial dysfunction in a transcription-independent manner and protects mice from a lethal dose of ionizing radiation

In a previous study, we reported that some tetradentate zinc(II) chelators inhibit p53 through the denaturation of its zinc-requiring structure but a chelator, Bispicen, a potent inhibitor of in vitro apoptosis, failed to show any efficient radioprotective effect against irradiated mice because the toxicity of the chelator to mice. The unsuitability of using tetradentate chelators as radioprotectors prompted us to undertake a more extensive search for p53-inhibiting agents that are weaker zinc(II) chelators and therefore less toxic. Here, we show that an 8-hydroxyquinoline (8HQ) derivative, AS-2, suppresses p53-dependent apoptosis through a transcription-independent mechanism. A mechanistic study using cells with different p53 characteristics revealed that the suppressive effect of AS-2 on apoptosis is specifically mediated through p53. In addition, AS-2 was less effective in preventing p53-mediated transcription-dependent events than pifithrin-μ (PFTμ), an inhibitor of transcription-independent apoptosis by p53. Fluorescence visualization of the extranuclear distribution of AS-2 also supports that it is ineffective on the transcription-dependent pathway. Further investigations revealed that AS-2 suppressed mitochondrial apoptotic events, such as the mitochondrial release of intermembrane proteins and the loss of mitochondrial membrane potential, although AS-2 resulted in an increase in the mitochondrial translocation of p53 as opposed to the decrease of cytosolic p53, and did not affect the apoptotic interaction of p53 with Bcl-2. AS-2 also protected mice that had been exposed to a lethal dose of ionizing radiation. Our findings indicate that some types of bidentate 8HQ chelators could serve as radioprotectors with no substantial toxicity in vivo.

Practical advice on calculating confidence intervals for radioprotection effects and reducing animal numbers in radiation countermeasure experiments

The dose of a substance that causes death in P% of a population is called an LDP, where LD stands for lethal dose. In radiation research, a common LDP of interest is the radiation dose that kills 50% of the population by a specified time, i.e., lethal dose 50 or LD50. When comparing LD50 between two populations, relative potency is the parameter of interest. In radiation research, this is commonly known as the dose reduction factor (DRF). Unfortunately, statistical inference on dose reduction factor is seldom reported. We illustrate how to calculate confidence intervals for dose reduction factor, which may then be used for statistical inference. Further, most dose reduction factor experiments use hundreds, rather than tens of animals. Through better dosing strategies and the use of a recently available sample size formula, we also show how animal numbers may be reduced while maintaining high statistical power. The illustrations center on realistic examples comparing LD50 values between a radiation countermeasure group and a radiation-only control. We also provide easy-to-use spreadsheets for sample size calculations and confidence interval calculations, as well as SAS® and R code for the latter.