Agent for reducing radiation damage

Abstract

Provided is an agent for reducing radiation damage that can be relatively simply and inexpensively produced, and that has, as an active ingredient, a low-molecular compound having the action of reducing radiation damage.　The agent for reducing radiation damage comprises at least one compound selected from the group consisting of compounds represented by formula (Io) and physiologically-acceptable salts thereof. [In the formula, R is a halogen atom, a C1-7 alkyl group, or a C1-7 alkoxyl group, and n is an integer of 0-3; Z is a halogen atom, a C1-6 alkyl group, a C2-6 alkenyl group, a C2-6 alkynyl group, or an organic oxy group which is represented by OR8, m is an integer of 0-4, and R8 represents a C1-7 alkyl group, a C2-6 alkenyl group, or a C2-6 alkynyl group; when n is more than 1, each R may be the same or different, and when m is more than 1, each Z may be the same or different; R6 represents a hydrogen atom or a C1-6 alkyl group; R3 is a group selected from one from among OH, OR4, NHR4, and NR4R5, and R4 and R5 are the same or different, and represent an unsubstituted C1-4 alkyl group.]

Description

Radiation damage mitigation agent

[0001] This invention relates to a radiation damage mitigation agent.

[0002] Workers at nuclear power plants, clinical laboratory technicians handling radioactive reagents, and doctors and radiologic technologists engaged in X-ray examinations and radiation therapy for cancer are constantly exposed to small amounts of radiation during their work. Furthermore, in the event of a nuclear power plant accident, not only workers but also residents in surrounding areas may be exposed to radiation. Damage to various organs occurs depending on the amount of radiation exposure, and death can occur if the exposure exceeds a lethal dose.

[0003] Furthermore, recent statistics indicate that in Japan, one in two people will develop cancer in their lifetime, and one in three will die from it. Cancer treatment can be broadly divided into three categories: surgery, radiation therapy, and chemotherapy using anticancer drugs. Of these, radiation therapy is an effective treatment method that suppresses the proliferation of cancer cells by irradiating the cancerous area with radiation, but it is problematic because it not only damages the targeted cancerous tissue but also damages normal tissue present in the irradiated area.

[0004] Recently, intensity-modulated irradiation (IMRT) using a device called "Tomotherapy" has been used to mitigate radiation damage to normal tissue. This IMRT method utilizes computer technology to adjust the direction, position, size, range, and duration of radiation to match the complex shape of the cancerous lesion, thereby reducing the dose to normal tissue compared to conventional radiation therapy. However, in cancer patients with multiple lesions and large tumor volumes, even with IMRT, radiation damage to normal tissue cannot be avoided. Furthermore, radiation protection agents such as L-cysteine, glutathione, SOD (superoxide dismutase), GM-CSF (granulocyte-macrophage colony-stimulating factor), 5-aminolevulinic acid, romiplostim (thrombopoietin receptor agonist), nitroprusside, and lactoferrin have been reported (Patent Documents 1-3), but these have also not yet been shown to effectively mitigate radiation damage.

[0005] On the other hand, the present inventors have reported that 4-(2,4-difluorophenyl)-2-(1H-indole-3-yl)-4-oxobutanoic acid (i.e., MA5) has erythropoietin expression enhancing effects and therapeutic effects for mitochondrial diseases (Patent Document 4), organ fibrosis inhibitory effects (Patent Document 5), and hearing loss prevention or improvement effects (Patent Document 6). However, it was previously unknown that the compound in question has an effect of mitigating radiation damage.

[0006] International Publication No. 2014 / 017046 Pamphlet, Japanese Patent Publication No. 2011-207841, International Publication No. 2014 / 077358 Pamphlet, International Publication No. 2014 / 080640 Pamphlet, Japanese Patent Publication No. 2015-189670, Japanese Patent Publication No. 2019-116453

[0007] The object of the present invention is to provide a radiation damage mitigating agent that can be manufactured relatively easily and inexpensively, and which contains a low-molecular-weight compound as an active ingredient that has the effect of mitigating radiation damage.

[0008] The inventors of this invention have been diligently conducting research to solve the above-mentioned problems. In the process, they discovered that the compound described below has the effect of mitigating radiation damage, and thus completed the present invention.

[0009] In other words, the present invention is as follows: [1] A radiation damage mitigation agent comprising one or more compounds selected from the group consisting of compounds represented by the following formula (Io) and physiologically acceptable salts thereof. [In the formula, R is a halogen atom, a C1-C7 alkyl group, or a C1-C7 alkoxyl group, and n is an integer from 0 to 3; Z is a halogen atom, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, or OR ８ It is an organic oxy group represented by , where m is an integer from 0 to 4, and R ８ R represents an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms; when n and m are multiple, each R and each Z may be the same or different; R ６represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R ３ is OH, OR ４ , NHR ４ and NR ４ R ５ is a group selected from any one of them, and R ４ and R ５ are the same or different and are unsubstituted alkyl groups having 1 to 4 carbon atoms. ] [2] The radiation injury reducing agent according to [1] above, wherein the radiation is X-ray. [3] The radiation injury reducing agent according to claim 1, wherein the compound represented by formula (Io) is a compound represented by the following formula (I-1).

[0010] Further, as another embodiment of the present invention, one or more compounds selected from the group consisting of a compound represented by the following formula (Io) and its physiologically acceptable salts (also referred to as "the present compound" in this specification) are used. A method for reducing radiation injury or preventing radiation sickness (also referred to as "radiation injury"), which includes a step of administering to a subject (for example, a patient) who needs to reduce radiation injury, the present compound for use in reducing radiation injury, the present compound for use in preventing radiation sickness, the use of the present compound for manufacturing a radiation injury reducing agent, and the use of the present compound for manufacturing a radiation sickness preventing agent can be mentioned.

[0011]

[0012] The present compound has an effect of effectively reducing (suppressing) radiation injury. Therefore, the present compound is effective in preventing radiation sickness that may occur in radiation-exposed persons such as radiation therapy patients.

[0013] Figure 1A shows the results of analyzing the egg lethality after oviposition in larvae of wild-type N2 strain hermaphroditic nematodes (C. elegans) reared to adulthood in the presence (+MA5 in the figure) or absence (- in the figure) of compound #5, and then after X-ray irradiation (0 Gy) or (30 Gy or 60 Gy). Figure 1B shows the results of analyzing the developmental failure rate and post-developmental lethality rate of the next generation of nematodes that laid eggs and hatched after 60 Gy of X-ray irradiation in Figure 1A. The asterisk (*) in the figure indicates a statistically significant difference by chi-square test (p < 0.05). Figure 2A shows the results of analyzing the GFP-derived fluorescence signals and LAR-GECO-derived fluorescence signals in muscle cells of nematodes (ATU3301 strain) cultured in the presence (+MA5 in the figure) or absence (- in the figure) of compound #5, after X-ray irradiation (0 Gy) or without X-ray irradiation (60 Gy). Note that the spherical signals observed in each LAR-GECO image are nonspecific and overlap with the GFP-derived fluorescence signals (corresponding to the cell nucleus) in the upper panel. Figure 2B shows the results of analyzing the percentage of muscle cells with fragmented mitochondria based on the results of Figure 2A. "**" in the figure indicates a statistically significant difference (p < 0.01). This figure shows the results of analyzing the percentage of senescence-related β-galactosidase (SA-β-gal) positive cells after irradiating IMR-90 cell lines cultured in the presence (+MA5 in the figure) or absence (- in the figure) of compound #5 with 0 Gy, 4 Gy, or 8 Gy of X-rays. "**" and "***" in the figure indicate statistically significant differences (p < 0.01 and p < 0.001, respectively).

[0014] The radiation damage mitigating agent of the present invention is an agent containing the compound in question (hereinafter sometimes referred to as "the mitigating agent") that is specifically designated for the use of "mitigating radiation damage." The mitigating agent may be used as livestock feed, food and beverages, or pharmaceuticals (formulations) alone, or it may be mixed with additives and used in the form of a composition (livestock feed composition, food and beverage composition, or pharmaceutical composition). Examples of the above-mentioned food and beverages include health foods (functional foods, nutritional supplements, health supplements, fortified foods, nutritional adjustment foods, supplements, etc.) and health functional foods (foods for specified health uses, nutrient function foods, functional foods, etc.).

[0015] In this specification, "mitigating radiation damage" means that the level of damage to a living organism caused by radiation exposure is reduced or suppressed. Here, "damage to a living organism" includes, for example, cell death (e.g., apoptosis, necrosis, etc.), mitochondrial damage (e.g., mitochondrial fragmentation, calcium ion [Ca] in mitochondria). ２＋ Examples of adverse effects include increased concentration, genomic DNA damage in germ cells (e.g., sperm, eggs) (e.g., mutations), oxidation of biomolecules in cells (e.g., nucleic acids, proteins, lipids, etc.), and developmental disorders.

[0016] In this specification, "radiation" refers to radiation used in radiation therapy, and specifically includes electromagnetic waves such as X-rays and gamma rays; particle beams such as proton beams, fast neutron beams, and heavy ion beams (e.g., carbon, neon, argon); and X-rays can be preferably given as an example because their effectiveness has been demonstrated in the embodiment described later.

[0017] The compound in question has the effect of effectively reducing (suppressing) radiation damage. For this reason, the mitigating agent containing the compound in question as an active ingredient can be advantageously applied as a preventive agent for radiation sickness. In this specification, "radiation sickness" refers to any disease or condition caused by radiation damage, and may be acute or chronic radiation sickness. Examples of radiation sickness include diseases in various organs (central organs of the circulatory system [e.g., heart], respiratory organs [e.g., lungs], hematopoietic organs [e.g., bone marrow], cortical organs [e.g., skin], reproductive organs [e.g., testes]) caused by radiation damage (e.g., pneumonia, pericarditis, coronary artery disease, ischemic heart disease, conduction disorders, valvular heart disease, anemia, bleeding tendencies, alopecia, ulcers, azoospermia, amenorrhea, cataracts, leukemia, cancer, etc.) and cellular senescence caused by radiation damage.

[0018] The compounds included in this compound are not particularly limited, as long as they are one or more compounds selected from the group consisting of compounds represented by the following formula (Io) and physiologically acceptable salts thereof.

[0019]

[0020] In the above formula (Io), R is a halogen atom, a C1-C7 alkyl group, or a C1-C7 alkoxyl group. n is an integer from 0 to 3. Z is a halogen atom, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, or OR ８ This is an organic oxy group represented by . m is an integer from 0 to 4. R ８ R represents an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms. When n and m are multiple, each R and each Z may be the same or different. ６ R represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. ３ OH, OR ４ NHR ４ and NR ４ R ５ It is a base selected from one of the following. ４ and R ５These are the same or different unsubstituted alkyl groups having 1 to 4 carbon atoms.

[0021] (R) in the compound represented by the above formula (Io) ｎ When n is 0, it means unsubstituted; when n is an integer from 1 to 3, it means that 1 to 3 hydrogen atoms among the carbon atoms constituting the benzene ring are substituted, respectively, with a halogen atom, an alkyl group having 1 to 7 carbon atoms, or an alkoxyl group having 1 to 7 carbon atoms. When n is 2 or 3 (i.e., when the substituted benzene ring has 2 or 3 substituents), the substituents may be the same or different. (R) in the compound represented by the above formula (Io) ｎ Examples include 1 to 3 halogen atoms, 1 to 3 C1 to C7 alkyl groups, and 1 to 3 C1 to C7 alkoxyl groups.

[0022] (Z) in the compound represented by the above formula (Io) ｍ If m is 0, it means unsubstituted; if m is an integer from 1 to 4, then 1 to 4 hydrogen atoms among the hydrogen atoms bonded to the carbon atoms constituting the benzene ring are, respectively, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or OR ８ The organic oxy group represented by (R ８ (where represents an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms) means that it is substituted with an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms. When m is an integer from 2 to 4 (i.e., when the substituted benzene ring has 2 to 4 substituents), the substituents may be the same or different. (Z) in the compound represented by the above formula (Io) ｍ For example, one to three halogen atoms, one to three C1-C6 alkyl groups, one to three C2-C6 alkenyl groups, one to three C2-C6 alkynyl groups, one to three OR ８ Examples of organic oxy groups represented by [the formula shown] can be given.

[0023] The "alkyl group having 1 to 7 carbon atoms" in the above formula (Io) may be a linear or branched alkyl group. For example, a methyl group, an ethyl group, a propyl group, a 2-ethylbutyl group, a 2-methylpentyl group, a 3-methylpentyl group, etc. can be mentioned. Preferably, it is a methyl group, a 2-ethylbutyl group, a 2-methylpentyl group, or a 3-methylpentyl group.

[0024] The "alkoxyl group having 1 to 7 carbon atoms" in the above formula (Io) may be a linear or branched alkoxyl group. For example, a methoxy group, an ethoxy group, a propoxy group, etc. can be mentioned.

[0025] The "alkyl group having 1 to 6 carbon atoms" in the above formula (Io) means a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent. As the alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and a benzyl group are preferable.

[0026] The "alkenyl group having 2 to 6 carbon atoms" in the above formula (Io) means a linear or branched alkenyl group having 2 to 6 carbon atoms which may have a substituent. For example, an ethenyl group (vinyl group), a 1-propenyl group, a 2-propenyl group (allyl group), etc. can be mentioned.

[0027] The "alkynyl group having 2 to 6 carbon atoms" in the above formula (Io) means a linear or branched alkynyl group having 2 to 6 carbon atoms which may have a substituent. For example, an ethynyl group, a 1-propynyl group, a 1-butynyl group, a 1-pentynyl group, a 1-hexynyl group, etc. can be mentioned.

[0028] As the "halogen atom" in the above formula (Io), for example, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. can be mentioned.

[0029] Examples of the "unsubstituted C1-C4 alkyl group" in the above formula (Io) include methyl group, monochloromethyl group, ethyl group, 1-phenylethyl group, 2-phenylethyl group, 2-methoxyethyl group, 2,2,2-trichloroethyl group, propyl group, isopropyl group, hexafluoroisopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, R ４ and R ５ Examples include pyrrolidines, which are formed when nitrogen is combined with other elements.

[0030] When the compound in question has a chiral carbon atom and a chiral center related to axial chirality, such a compound contains all conceivable optical isomers, and these optical isomers can be used in any ratio. For example, a certain optically active compound can be used as an enantiomer, a racemic compound, or a mixture of enantiomers in any proportion, and when there are multiple chiral centers, it may be used as a mixture of diastereomers in any proportion.

[0031] Physiologically acceptable salts of the compound represented by the above formula (Io) include metal salts produced from aluminum, calcium, lithium, magnesium, potassium, sodium, and zinc, as well as organic salts produced from N,N'-dibenzylethylenediamine, chloroprocaine, choline, diethanolamine, ethylenediamine, N-methylglucamine, lysine, procaine, etc.

[0032] The synthesis method for this compound can be the method disclosed in Patent Document 4, International Publication No. 2019 / 235455, etc., but is not limited to these methods, and generally known synthesis methods can be used.

[0033] As for the compound represented by the above formula (Io), its effect has been demonstrated in the examples of this specification, therefore, the compound represented by the following formula (I-1) (i.e., in the above formula (Io), R is a fluorine atom, n is 2, m is 0, R ６ is a hydrogen atom, R ３ A compound in which the parentheses is OH (also referred to as "MA5" in this specification) is preferred.

[0034]

[0035] Examples of additives for this reducing agent include physiologically acceptable conventional carriers, binders, stabilizers, excipients, diluents, pH buffers, disintegrants, isotonic agents, coatings, solubilizers, lubricants, gliding agents, solubilizers, flavoring agents, sweeteners, solvents, gelling agents, nutrients, various oils, surfactants, preservatives, antioxidants, dispersants, chelating agents, thickeners, UV absorbers, emulsifying stabilizers, pH adjusters, pigments, fragrances, and other compounding components. Specific examples of such compounding components include water, physiological saline, animal fats and oils, vegetable oils, lactose, starch, gelatin, crystalline cellulose, gum, talc, magnesium stearate, hydroxypropylcellulose, polyalkylene glycol, polyvinyl alcohol, and glycerin.

[0036] The target recipients of this radiation-reducing agent can be any animal that requires reduction of radiation damage, such as subjects exposed to radiation (e.g., patients receiving radiation therapy) or subjects that have been exposed to radiation (e.g., patients who have received radiation therapy). Such patients can be any person suffering from some kind of disease, and cancer patients are preferred.

[0037] In this specification, animals include mammals (human or non-human mammals), birds, reptiles, amphibians, fish, invertebrates, etc. Other forms of animals include humans and livestock. Here, "livestock" means animals that are kept and bred by humans. Examples of such livestock include non-human mammals (e.g., rodents such as mice, rats, hamsters, and guinea pigs; lagomorphs such as rabbits; ungulates such as pigs, cattle, goats, horses, and sheep; carnivores such as dogs and cats), birds (e.g., chickens, quail, turkeys, pigeons, ducks, geese, etc.), fish (e.g., carp, goldfish, etc.), and invertebrates (e.g., silkworms, honeybees, etc.).

[0038] The method of ingesting (for example, administering) the mitigating agent in question is any method by which the compound contained in the mitigating agent is taken into the animal's body, and may be by oral ingestion (for example, oral administration in the form of powder, granules, tablets, capsules, syrups, etc.) or by parenteral ingestion (for example, parenteral administration in the form of topical preparations, transdermal preparations, transmucosal preparations, nasal preparations, enteral preparations, injections, suppositories, inhalants, patches, etc.).

[0039] The dosage of the mitigating agent and the compound contained in it should be determined appropriately according to the type, age, weight, sex, symptoms, and sensitivity to the drug of the animal to be administered the agent, for example, within the range of 1 μg to 200 mg / kg (body weight) / day. The mitigating agent is administered as a single dose or in multiple doses (for example, 2 to 4 times) per day, and the dosage may be adjusted according to the improvement of symptoms. When administering the mitigating agent to a subject exposed to radiation, the timing of administration may be before radiation exposure, simultaneously with radiation exposure, or both. When administering the mitigating agent to a subject exposed to radiation, it is preferable to administer it as soon as possible after radiation exposure (for example, within 1 day, within 12 hours, within 1 hour, etc.).

[0040] The radiation mitigation agent may contain components that have a radiation damage mitigation effect in addition to the compound in question. However, since the compound in question exhibits an excellent radiation damage mitigation effect on its own, it is preferable that the agent does not contain any components that have a radiation damage mitigation effect in addition to the compound in question (for example, compounds [e.g., antibiotics], proteins [e.g., antibodies], DNA, RNA).

[0041] The present invention will be described more specifically below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0042] 1. Radiation damage improvement effect of the compound in question on the next generation of nematodes hatched from irradiated nematodes. L4 stage larvae of wild-type N2 strain hermaphrodite nematodes were cultured for 24 hours on culture plates (E. coli OP-50 NGM agar medium) sprayed with DMSO (solvent) as a control ("compound #5-") and on the same culture plates sprayed with compound #5 to a final concentration of 10 μM ("compound #5+"). After the nematodes became adults, they were irradiated with 0 Gy, 30 Gy, or 60 Gy of X-rays using an X-ray irradiation device (M-100, Softex). The mortality rate of eggs laid within 8 hours after X-ray irradiation was analyzed (see Figure 1A). Furthermore, the developmental failure rate and post-developmental mortality rate of the next generation of nematodes that hatched after 60 Gy of X-ray irradiation were analyzed (see Figure 1B). Furthermore, eggs laid within eight hours of X-ray irradiation include those that were irradiated with X-rays when they were early embryos undergoing rapid cell division within the uterus of adult worms, and those that were irradiated with X-rays when they were developed oocytes just before fertilization (see reference "Nucleic Acids Res. 2000 Nov 1;28(21):4232-6.").

[0043] As a result, when nematodes were irradiated with 30 Gy or 60 Gy of X-rays, the mortality rate of the laid eggs increased in a dose-dependent manner compared to when they were not irradiated (0 Gy). However, when nematodes were reared in the presence of compound #5, no change in the egg mortality rate due to X-ray irradiation was observed (see Figure 1A). On the other hand, when the next generation of nematodes that were reared in the presence of compound #5 and irradiated with 60 Gy of X-rays were oviposed and hatched, the developmental failure rate and post-developmental mortality rate of the next generation of nematodes were analyzed. Compared to when nematodes were reared in the absence of compound #5, developmental failure of the next generation of nematodes was significantly suppressed, and the mortality rate was also significantly reduced (see Figure 1B).

[0044] These results indicate that the compound in question (compound #5) has the effect of reducing X-ray damage to the next generation of nematodes that are laid and hatched from nematodes irradiated with X-rays.

[0045] 2. Radiation damage improvement effect of the compound in question on irradiated nematodes: Nuclear-transferred GFP and mitochondrial-transferred GFP in the body wall muscle cells of nematodes, and mitochondrial Ca２＋ Adult genetically modified nematodes expressing the sensor LAR-GECO (red fluorescent substance) (ATU3301 strain [ccIs4251 [Pmyo-3::nucGFP-LacZ+Pmyo-3::mitochondrial GFP] aceIs1 [Pmyo-3::mitochondrial LAR-GECO+Pmyo2::RFP]]) (see reference "FASEB J. 2023 Apr;37(4):e22851.doi:") were cultured on DMSO (solvent) on culture plates (E. coli OP-50) respectively. The cells were cultured for 24 hours on NGM agar medium and on the culture plates in which compound #5 was scattered to a final concentration of 10 μM. After irradiation with 0 Gy or 60 Gy of X-rays using an X-ray irradiation device (M-100, Softex), mitochondrial fragmentation in the muscle cells of the parent nematode was analyzed using an FV10i confocal laser scanning microscope (Olympus) with the fluorescence signal derived from GFP as an indicator, and Ca in mitochondria was analyzed using the fluorescence signal derived from LAR-GECO as an indicator. ２＋ The concentration was analyzed (see Figure 2).

[0046] As a result, when nematodes cultured in the absence of compound #5 were not irradiated with X-rays (0 Gy), the GFP-derived fluorescence signal around the cell nucleus was elongated and connected. However, when irradiated with 60 Gy of X-rays, it became fragmented (see "-" in Figure 2A), and the proportion of muscle cells exhibiting such fragmentation increased significantly (see "-" in Figure 2B). Furthermore, with 60 Gy of X-ray irradiation, a LAR-GECO-derived fluorescence signal was observed overlapping with the GFP-derived fluorescence signal (see "-" in Figure 2A). On the other hand, when nematodes cultured in the presence of compound #5 were irradiated with 60 Gy of X-rays, such fragmentation was suppressed (see "+" in Figures 2A and B), and no LAR-GECO-derived fluorescence signal was detected (see "+" in Figure 2A).

[0047] These results indicate that the compound in question (compound #5) has the effect of suppressing mitochondrial fragmentation and mitochondrial damage in muscle cells caused by X-ray irradiation. Furthermore, since nematodes are used as a model organism for humans (see, for example, "Tokai University Institute for Advanced Life Sciences Bulletin, Vol. 1, March 2017" and "Nature. 2018. PMID: 30356218"), this compound (compound #5) is also useful in mitigating radiation damage in humans.

[0048] 3. Radiation damage improvement effect of the compound in question on irradiated human cell lines: 1 to 2 × 10 ４ Human fetal lung-derived normal fibroblast cell line (IMR-90 cell line) (obtained from ATCC) was seeded in a 96-well plate and cultured at 37°C in the presence of DMSO (solvent) or a culture medium containing 1 μM of compound #5 at 5% CO2. ２ The cells were cultured for 12 to 24 hours under these conditions. Subsequently, the IMR-90 cell line was irradiated with 0 Gy, 4 Gy, or 8 Gy of X-rays using an X-ray irradiation device (M-100, Softex), cultured for 10 days, and then stained with β-galactosidase using a Senescence Detection Kit (Biovision). Nine fields were randomly scanned from three wells, and the percentage of β-galactosidase-positive cells (i.e., SA-β-gal-positive cells) was measured. The culture medium used was E-MEM (Cell Growth Medium No. 104, KAC Co., Ltd.) containing 10% FBS (Fetal Bovine Serum) and 1% NEAA (Non-Essential Amino Acids).

[0049] As a result, when IMR-90 cell lines cultured in the absence of compound #5 were irradiated with X-rays, the proportion of SA-β-gal positive cells increased significantly compared to IMR-90 cell lines that were not irradiated with X-rays. In contrast, when IMR-90 cell lines were cultured in the presence of compound #5 and irradiated with X-rays, this increase in the proportion of SA-β-gal positive cells was significantly suppressed (see Figure 3).

[0050] These results indicate that while X-ray irradiation of the IMR-90 cell line increases the proportion of senescent cells, culturing the cell line in the presence of the compound in question (compound #5) can suppress the proportion of senescent cells.

[0051] This invention contributes to the prevention of radiation sickness caused by radiation therapy and the like.

Claims

1. A radioprotective agent comprising one or more compounds selected from the group consisting of a compound represented by the following formula (Io) and its physiologically acceptable salts. [In the formula, R is a halogen atom, an alkyl group having 1 to 7 carbon atoms, or an alkoxyl group having 1 to 7 carbon atoms, and n is any integer from 0 to 3; Z is a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, or an organic oxy group represented by OR ８ , m is any integer from 0 to 4, and R ８ represents an alkyl group having 1 to 7 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms; when n and m are plural, each R and each Z may be the same or different; R ６ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R ３ is a group selected from any one of OH, OR ４ , NHR ４ and NR ４ R ５ , and R ４ and R ５ are the same or different and are unsubstituted alkyl groups having 1 to 4 carbon atoms. ] 2. The radiation damage mitigating agent according to claim 1, wherein the radiation is X-rays.

3. The radiation damage mitigating agent according to claim 1, wherein the compound represented by formula (Io) is the compound represented by the following formula (I-1).

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