[The grounds of interspices difference in radiation-genetic effects of low-level radiation].

Radiation-genetic effects are characterized by large quantitative difference. After the low dose radiation appearance of mutation is the largest in Drosophila, substantially lower in mice, especially if irradiation was protracted, and practically absent in humans. As the possible grounds of this difference the author consider the existence of non-specific repair mechanism, which has arouse during evolution for diminution of different detrimental impacts, including ionizing radiation. The efficacy of such mechanism of natural protection is determined by the efficacy of the repair mechanisms, which is elevated in compliance with specific life span, which is of necessity for its maintenance. The evolution has led to maximal development of this mechanism in human beings, and it is proved in particular in prevention of the hereditary effect of low-level radiation.

[Problems of radiobiology at the end of the 20th century]. / Problemy radiobiologii v kontse XX stoletiia.

The modern radiation biology is characterized by an increased interest in the effects of small doses. Some investigators consider the small doses of radiation as having the larger damaging efficacy than the higher doses, the majority of researchers hold the opinion of their decreased danger, while some scientist favor the hypothesis of hormesis the positive effect of the small doses of radiation exposure. The article describes new approaches to the development of the unified scientific strategy for resolving this problem.

[The autoregulation of intracellular oxygen tension and the modification of cellular radiosensitivity. The development of an adaptation hypothesis]. / Avtoreguliatsiia vnutrikletochnogo napriazheniia kisloroda i modifikatsiia radiochuvstvitel'nosti kletok. Razvitie adaptatsionnoi gipotezy.

A hypothesis is reported postulating that the range within which the intracellular oxygen content varies with changes in the external oxygenation conditions is responsible for the oxygen-dependent radiosensitivity modification that may be controlled by the diffusion resistance of a cytoplasmic membrane. The adaptation mechanism of intracellular Po2 autoregulation is involved when drastic changes in the oxygen content of the environment occur. As the oxygen content decreases this mechanism provides maximal values of the intracellular Po2 required for optimizing cell viability; the increased oxygen content prevents cells from oxygen intoxication.

[Polyradiomodification. Optimization of the combined use of hyperglycemia and local hyperthermia in tumor irradiation]. / Poliradiomodifikatsiia. Optimizatsiia sochetannogo primeneniia giperglikemii i lokal'noi gipertermii pri obluchenii opukholei.

Therapeutic potentialities of various types of polyradiomodification were compared in experiments on mice with solid Ehrlich carcinoma by using separate and combined use of short-term hyperglycemia (SH) and local hyperthermia (HT). In the combination of modifiers SH was always created 3 h after the beginning of glucose administration. Irradiation of tumors was performed in either of 5 moments: 4 h or immediately before SH, in-between SH and HT, 30 min. or 2.5 h after SH. Two control schemes, in which irradiation was combined with one of the modifiers only, corresponded to each polyradiomodification regimen. The combined use of SH and HT produced a more noticeable effect than their separate action. A maximum effect on a tumor was observed in the combined use of both modalities shortly after irradiation, and it was not accompanied by enhanced skin radiation injury in a tumor growth zone. Irradiation after or in-between SH and TH resulted in enhanced skin radiation reactions. Thus, the highest therapeutic effect was noted in those schemes of polyradiomodification in which SH and HT followed radiation treatment. SH and HT induced suppression of the blood supply in tumors played an important role in the optimization of the combined use of SH and HT with irradiation.

[Repeated irradiation of recurrent head and neck tumors using hyperthermia]. / Povtornoe obluchenie retsidivnykh opukholei golovy i shei s primeneniem gipertermii.

The authors presented an analysis of immediate and short-term results of therapy of 115 patients on thermoradio- and chemotherapy for recurrent head and neck tumors. Triple irradiation at single focal doses of 10 Gy at one-week intervals between fractions were employed taking into account radioresistance of recurrent tumors. After each session of irradiation the patients received polychemotherapy (cyclophosphamide, vinblastine, methotrexate) for 2 days. Local MWF-hyperthermia was provided before a session of irradiation and during drug administration. Complete or partial tumor regression was noted in 94% of the patients with the resultant improvement in their general status. The 3-year disease-free interval was noted in 41% of the patients. Radiation changes were restricted to atrophy of the skin and mucous membranes and stable disorders of salivation.

[Lethal effect of glucose load on tumor cells in hypoxia]. / Letal'noe deistvie gliukoznoi nagruzki na opukholevye kletki v usloviiakh gipoksii.

The in vitro treatment of the Ehrlich ascites tumour (EAT) cells with glucose for 15 and 60 min under hypoxic conditions leads to a decrease in their survival by a factor of 10(2) and 10(4). Glucose load is ineffective under normal oxygenation. The mass destruction of EAT cells under the influence of glucose takes place within the first 24 hours in the interphase. The lethal effect of different pH values on EAT cells is independent of the way by which the given pH value was reached (glucose load or phosphate buffer). The same values of pH lead to the same effect on EAT cells. The lethal effect markedly increased when the value of pH was lower than 5.6. It is concluded that the lethal effect of the glucose load is due to self acidification of EAT cells.

[Experimental evaluation of the role of blood flow inhibition in hyperglycemia-enhanced radiation damage to tumors]. / Eksperimental'naia otsenka roli ingibirovaniia krovotoka v usilenii giperglikemiei luchevogo porazheniia opukholei.

The authors provided experimental assessment of the role of the blood flow inhibition in enhancement of radiation injury to tumors using short-term hyperglycemia. Experiments on mice with Ehrlich solid carcinoma showed the dependence of a rise of the antitumor effect of preceding radiation induced by glucose and glucose combined with mexamine on a degree of the blood flow inhibition under the influence of these modifying agents. It was established that a considerable enhancement of radiation injury occurred but in such tumors where short-term hyperglycemia and mexamine decreased the blood flow level not less than 5-10 fold as estimated by 133Xe clearance. The results of the above experiments showed that noticeable inhibition of the blood flow in tumors was a necessary though, probably, not the only condition for a high efficacy of short-term hyperglycemia used as an adjuvant to radiotherapy.

[Combined use of metronidazole and short-term hyperglycemia during radiation therapy of tumors in rats]. / Kombinirovannoe primenenie metronidazola i kratkovremennoi giperglikemii pri luchevoi terapii opukholei krys.

A simultaneous combined treatment with metronidazole and short-term hyperglycaemia, in contrast to application of each of these agents alone, enhanced considerably the therapeutic effect of radiation (a single and fractionated exposure). This was indicated by the increased rate of tumor regression, the number of animals with transient remission, and the number of cured animals which exhibited no relapse throughout the entire 90-day period of observation.

[Polyradiomodification. Combined body protection in the total irradiation of mice during exogenous hypoxia]. / Poliradiomodifikatsiia. Kombinirovannaia zashchita organizma pri total'nom obluchenii myshei v usloviiakh ékzogennoi gipoksii.

A high efficacy of the combined use of nontoxic doses of two pharmaceuticals: cystamine (50 mg/kg) and mexamine (25 mg/kg) under the conditions of short-term exogenous hypoxia (7.5% O2) was found in (CBA X C57Bl)F1 mice. The dose modification factor using the survival rates was 2.56.

[The role of hypoxia in the effect of glucose load on irradiated tumor cells]. / Rol' gipoksii v deistvii gliukoznoi nagruzki na obluchennye opukholevye kletki.

In experiments on Ehrlich ascites tumor cells it was shown that hypoxia, which reduces the lethal effect of gamma-rays, can considerably enhance the injury of cells by glucose. Treatment of tumor cells with glucose in hypoxic conditions followed by exposure to ionizing radiation under both hypoxia and normal aeration causes a 6-7-fold increase in cell injury as compared to irradiation alone. Moreover, the glucose treatment in hypoxic conditions (without concomitant irradiation) may cause approximately 99% death of tumor cells. The data obtained permit to consider the glucose treatment as an effective means by breaking the tumor radioresistance conditioned by a pool of hypoxic cells.

[Enhancement of the antitumor effect of ionizing radiations in the combined use of metronidazole and induced hyperglycemia]. / Usilenie protivoopukholevogo deistviia ioniziruiushchikh izluchenii pri sochetannom primenenii metronidazola i giperglikemii.

The authors have shown that a more pronounced antitumor effect of radiation in the combined use of metronidazole and induced short-term hyperglycemia (STH) may result not only from the summation of the two effects: the sensitizing effect of metronidazole and decreased viability of irradiated cells caused by STH but also from the intensified cytotoxic effect of metronidazole on hypoxic tumor cells. It was also noted that when hypoxic cells subjected to the sensitizing effect of electron acceptor sensitizers are found in the normal and tumorous tissues (skin), STH use following irradiation in the presence of metronidazole enhances selectively the tumor radiation effect.