[Radioprotective properties of isothiourea derivatives with NO-inhibitory mechanism of action].

The study of the radioprotective activity of S-[2-alkyl (aryl) sulfonyl]-S-ethyl derivatives of (vinyl)-isothiourea in (he model of the survival of mice exposed to gamma-radiation at a dose of 10 Gy has shown that the incorporation of additional sulfur-containing groups does not increase the radioprotective properties of compounds. In contrast to aminoalkil thiols, the effectiveness of the radiation protection action of the isothiourea (ITU) derivatives studied clearly correlates with the NO-inhibitory activity. This fact allowed us to assume that the radioprotective effect of S-substituted ITU caused inhibition of the endogenous synthesis of NO, which promotes the development of circulatory hypoxia, and that a further search for the radioprotective agents in this class of chemicals should be considered as the search for effective inhibitors of NO-synthase (NOS). The theoretical analysis of the conformity of molecular structures to the composition and topology of the active center of NOS-inhibitors allowed us to prognosticate a number of new ITU derivatives with the potential NOS-inhibiting ability. As a result of further theoretical and experimental studies, four S,N-disubstituted ITU derivatives - active non-selective NOS-inhibitors, were first identified and synthesized. These compounds exhibited a pronounced and prolonged vasopressive effects at doses of 0.01-0.05 LD50/15 in the models of severe hemorrhagic and endotoxic shock, and provided 65-100% 30-day survival at doses of 0.2-0.3 LD50/15 in the mice irradiated by gamma-rays at a dose of 10 Gy (LD98/30).The findings suggest the pronounced radioprotective effect of NOS-inhibitors among the ITU-derivatives.

Radioprotective effect of sodium diethyldithiocarbamate (DDC) and S-2-aminoethyl-isothioronicadenosin-5-triphosphate (adeturon) in gamma-irradiated Escherichia coli cells.

The effect of sodium diethyldithiocarbamate (DDC) and S-2-aminoethyl-isothiouronicadenosin-5-triphosphate (adeturon) in the induction of Escherichia coli SOS response promoted by gamma-irradiation was studied by measuring the induction of sulA gene and the induction of lambda prophage. Furthermore, as a way of measure the exonuclease activity in gamma-irradiated cells in the presence or absence of both compounds, the DNA degradation was determined. Adeturon did not affected DNA degradation, but inhibited the induction of the SOS functions studied. On the contrary, DDC inhibited DNA degradation as well as the induction of the sulA gene, but enhanced lambda induction in E. coli lysogenic strains. These results indicate that both compounds diminish the DNA damage produced by gamma-irradiation and also suggest that the mechanisms of radioprotection must be different. Thus, radioprotection mediated by DDC should involve free hydroxyl radical scavenging and a minor activity of exonuclease. The enhancement of phage induction in E. coli cells that DDC produces could be attributed to its quelant effect and this would not be not probably directly related to radioprotection. Adeturon, as thiols, may serve also as scavenging agent of free hydroxyl radicals, diminishing indirectly the DNA damage level. In addition, adeturon must interact with DNA in the same form that other aminothiol compounds do it. This interaction, mediated by amino groups of adeturon, may serve to concentrate these compounds near of the DNA damage site, increasing the potential for the thiol portion of the molecule to donate hydrogen, decreasing the damage level on DNA molecule. However, adeturon do not modify the exonuclease activity. Some topic about the possible clinical application of both compounds are discussed.

Testing a combined radiation protection modality: chemical protector and local shielding.

The impact of combined radiation protection upon damage to critical organs-spleen, small intestine, and bone marrow was studied in adult rat males 3 days after whole-body exposure to 9.5 Gy gamma-ray dose. Adeturone, the chemical radioprotector used, was administered intraperitoneally at 1/17 of its LD50 dose. Local shielding of the abdomino-lumbal region was accomplished using a lead ring providing on average 28-30% attenuation of radiation exposure. This degree of physical abdomino-lumbal protection combined with adeturone (50 mg/kg) pretreatment resulted in mutual enhancement of the components' action, expansion of the chemical agent's therapeutic range, providing a combination with improved overall antiradiation properties.

Electrophoretic mobility of erythrocytes from adeturone-pretreated rats exposed to gamma or high-energy protons.

Change in electrophoretic mobility (EM) of erythrocytes was studied 6 hours after rats were exposed to a dose range (0.5-4 Gy) of high-energy protons (9 GeV/nucleon) or gamma rays (0.660 MeV), with or without adeturone pretreatment (300 mg/kg body weight). With either of the two radiation types used, EM of the cells was observed to undergo significant dose-related decline. As indicated by our findings, adeturone pretreatment failed to contribute to maintenance of normal erythrocyte surface charge in the case of proton irradiation, proving, nevertheless, effective against gamma-ray exposure at all dose levels used.

[Effect of adeturon on postradiation macromolecular synthesis in the peripheral blood leukocytes of gamma ray-irradiated rats]. / Vliianie adeturona na postradiatsionnyi sintez makromolekul v leikotsitakh perifericheskoi krovi obluchennykh gamma-luchami krys.

DNA, RNA and protein syntheses were studied in peripheral blood leucocytes of irradiated (1-7 Gy) rats. Adeturon was shown to produce a pronounced protective effect on DNA synthesis progressively inhibited by the doses applied. The protective effect of the agent was not manifest with the slightly increased synthesis of RNA. There was a trend toward normalization of the increased protein synthesis.

Adeturone protection of hemopoiesis in lethally irradiated mice and rats.

Experiments were carried out to investigate the possibility of providing chemical protection to blood forming organs and increasing animal survival rates in lethally irradiated H mice and Wistar rats. A 300 mg/kg dose of the radioprotective agent was injected intraperitoneally 15-30 min prior to irradiation with 8.0 Gy gamma rays. Recorded were 30-day survival rates and the state of hemopoiesis on days 3 and 10 postradiation as judged by spleen weight and total counts of spleno- and myelokaryocytes. At 8.0 Gy exposure was observed to cause severe spleen and bone-marrow hypoplasia on day 3 postradiation. Adeturone pretreatment provided slight protection to rat spleen and mouse bone marrow; by day 10, however, both animal species exhibited a vigorous proliferative response of nucleated cells in the bone marrow, which resulted in 75% survival rate among animals exposed to a lethal radiation dose.

[Radiation injuries to mice in relation to the modes of administration of adeturon]. / Radiatsionnoe porazhenie myshei v zavisimosti ot sposobov primeneniia adeturona.

In experiments with mice the influence of adeturon, a preparation obtained in Bulgaria, on the survival rate, leucocytes dynamics, cellularity of bone marrow and spleen, and on nucleic acids in the peripheral blood has been investigated. The comparative analysis of the results obtained indicates that the protective and therapeutic administration of adeturon is more effective than a single injection of the drug immediately after irradiation.

[Effect of the radioprotector adeturon on radiation injury in mice with Lewis carcinoma of the lung]. / Vliianie radioprotektora adeturona na radiatsionnoe porazhenie myshei s kartsinomoi legkikh L'iuisa.

A study was made of the radioprotective effect of Adeturon, a protective agent obtained in Bulgaria, on mice with Luis lung tumors exposed to fractionated radiation. The effect of the radioprotector on a radiation-induced injury to normal tissue was estimated by the number of leucocytes in the peripheral blood and its count, cellularity of bone marrow and spleen and the mass of the latter, and by the number of exogenous and endogenous CFUs. A pronounced radioprotective effect of Adeturon was implemented through maintaining or normalizing the indices under study impaired by tumor inoculation or irradiation.

Effect of Eleutherococcus extract on the radioprotective action of adeturone.

The effect of successive prophylactic administration of the adaptogen Eleutherococcus and the chemical radioprotector Adeturone on the radiation injury in rats is investigated. The experiments were carried out on sexually mature male Wistar rats weighing 170 +/- 10 g. For 14 days the animals drank water containing Eleutherococcus extract (Medexport), 5 g/kg body weight. On the 7th and 14th days the daily dose of the extract was administered totally using a probe. One hour prior to the last intake, the rats were irradiated with 3 Gr using a 137Cs source, 15 min earlier part of them were injected intraperitoneally with 300 mg/kg Adeturone. The effect of the independent and successive administration of the two agents on the postradiation damage and recovery was tested on the 1st, 3rd, 10th, 20th and 30th days after the irradiation by the change in the leucocyte count and in the quantity of nucleic acids in the leucocytic mass of the blood. The independent application of the adaptogen and radioprotector have a favourable effect only on the course of the recovery processes. Successive administration of the two agents results in mutual potentiation of the effects and guarantees a high degree of protection. This is probably due to an increase in the natural radiation resistance and to the rats' capacity for adaptation during the acute phase of the radiation stress.

Protection of monkeys against prolonged gamma-irradiation.

The radioprotective effect of the Bulgarian drug Adeturone was tested on prolonged irradiated monkeys. The animals were gamma-irradiated (137Cs) in a dose of 8.3 Gy (exposure rate 3.95 X 10(-3) mA.kg-1; (0.92 R.min-1]. Adeturone, given by i.v. injection at a dose of 100 mg.kg-1 body weight according to a pre- and postradiation scheme will afford protection to monkeys by ensuring 50% survival and mitigating the severity of some symptoms of radiation disease. A similar effect was obtained with ATP-administration by two i.m. injections of 37 mg.kg-1 body weight. The survival in control group was only 5% (LD95/45).

The effect of a normal tissue radioprotector Adeturone on the radiation sensitivity of Lewis lung carcinoma: an enhanced response.

The effect of the normal tissue radioprotector Adeturone (S-2-aminoethylisothiuronium adenosine-5'-triphosphate) on the response of primary and metastatic Lewis lung carcinoma to radiation was evaluated. It was found that this compound enhanced the antitumor effect of whole-body and local radiation. In experiments with whole-body radiation Adeturone eliminated the lethality due to radiation toxicity (for a daily treatment schedule--10 X 1 Gy/fraction) or reduced it from 50% to 25% (for an intermittent schedule--3 X 3.34 Gy/fraction). Following local radiation treatment combined with Adeturone, a higher TWI%, longer tumor doubling time and longer mean survival time were recorded than for either treatment alone. An enhanced activity against metastatic growth of Lewis lung carcinoma to the lungs was also found with combined therapy.

[Effect of isothiuronium alkylamidines and adeturon on the activity of lactate dehydrogenase and its isoenzymes in rat blood serum and organs]. / Vliianie izotiuronievykh alkilamidinov i adeturona na aktivnost' laktatdegidrogenazy i ee izofermentov v syvorotke krovi i organakh krys.

A study was made of the effect of four types of S-omega-carboxamidinoalkyl isothiourea, differing in the carbon chain length between amidine and isothiuronium groups, and adeturon on activity of lactate dehydrogenase (LDG) and its isoenzymes in blood serum and organs of rats. Adeturon and compounds with one and three methylene groups elicit a radioprotective effect whereas substances with an even number of methylene groups have no such an effect. The obtained data indicate that changes in activity of LDG and its isoenzymes depend upon the structure of the substance applied. This makes LDG an adequate model in comparative studying the specificity of biochemical effects induced by the radioprotective agents and substances similar in their structure but having no radioprotective efficiency.

[Antiradiation properties of adeturon and polyanion used separately and in combination]. / Izuchenie protivoluchevykh svoistv adeturona i polianiona v usloviiakh samostoiatel'nogo i sochetannogo primeneniia.

A study was made of the radioprotective effect of polyanion, a co-polymer of maleic and methacrylic acids, administered separately and in a combination with adeturon to irradiated (8 Gy, LD100/18) H male mice. Adeturon (300 mg/kg) was injected 15 min before, and polyanion (4 mg/kg) 24 h after gamma-irradiation. The effect of the preparations was assessed by the survival rate and hematologic indices (for instance, weight and cellularity of the spleen, bone marrow cellularity, and the number of leukocytes) at defined intervals within 30 days. Adeturon exerted a pronounced protective effect on the haemopoietic system of lethally exposed mice. The therapeutic effect of polyanion applied in a combination with adeturon was not enhanced and did not modify the effect of the latter.

Electrophoretic mobility of erythrocytes exposed to accelerated helium nuclei or to gamma-rays, as modified by adeturone.

The electrophoretic mobility of human erythrocytes exposed in whole blood or in cell suspensions to relatively low doses (0.7-2.5 Gy) of accelerated helium nuclei (4.6 GeV/nucleon) or of gamma-rays was found to diminish with increase in radiation dose, as measured at 3 h post-irradiation. Pre-treatment with a radioprotectant, adeturone (S-2-aminoethylisothiuronium adenosine-5'-triphosphate), allowed electrophoretic mobility to be maintained within normal limits, with more stable values in the case of alpha-irradiations. The experimental evidence is discussed in terms of the protectant's involvement in repair of radiation-induced conformational changes in surface membrane components.

[Increase in radiation effectiveness by adeturon in mice with Lewis carcinoma]. / Povyshenie éffektivnosti oblucheniia kartsinomy L'iuis myshei adeturonom.

There was an increase in the time of the implanted tumor doubling in size and in the life-span of animals treated with a combination of S-2-aminoethyl- isothiuronium ( adeturon ) and gamma-radiation as compared to those exposed to gamma-radiation alone.