In modern methods of cancer therapy, combinations of influencing factors having various nature are widely used to achieve the highest therapeutic effect: ionizing radiation, chemotherapy drugs, hyperthermia, non-ionizing radiation, etc. The greatest cells damaging effect is achieved when the treatments are applied simultaneously. An increase in the interval between the treatments leads to final effect decrease. However, how the degree of the effect depends on the time gap has not been studied in detail. The paper presents the results of a study of this dependence with a different sequence of applied treatments. Combination of UV radiation and hyperthermia were examined. The choice of treatments is due to attention to the Vavilov-Cherenkov radiation, which arises when accompanies high-energy ionizing radiation used in oncotherapy and most of which is a continuous UV spectrum. And if we consider the Vavilov-Cherenkov radiation responsible for UV-like damages, which has its effect on the final result of the action of high-energy ionizing radiation, then it becomes clear that it is necessary to understand the behavior of UV light when it is used in combination with other damaging factors. Thus, the aim of the work is to study the effect of a sequence of applied treatments and the time gap between them on the magnitude of the final effect of the sequential action of UV light and hyperthermia on yeast cells. The dependence obtained in the work is of a multidirectional nature, changing from synergism to additivity, turning into antagonism with time gap rising. It is shown that the effect practically does not depend on the sequence of the treatments application, but significantly depends on the time gap between them. Such patterns were obtained for the first time. But it is indicates that when using in practice the combined action of ionizing radiation or UV light with hyperthermia, it should be remembered that the final effect can differ from expected.

Anna A. Oleshkevich, Specific features of change in enzymate activity in

Modification of the action of ionizing radiation by chemicals, used both to enhance its action and to weaken it’s known and is widely used in medical radiology. The article presents a comparative analysis of the modifying properties of three chemical radioprotectors (cysteamine, cysteine and cysteamine) when they are simultaneously act with to gama-rays, alpha-particles and ultraviolet radiation on yeast cells. The aim of the study was to compare the features of the manifestation of the properties of chemicals in relation to the protection of cells from UV-like damage when exposed to ionizing radiation or from damage caused by ultraviolet radiation. It was demonstrated that the cysteamine protects cells both from the damaging effects of gama-rays and from ultraviolet radiation, unlike cysteamine and cysteine, which protect cells exclusively from the effects of ionizing radiation. Moreover, cystamine does not change the effect of alpha-particles, which have a high ionization density of the substance, but practically do not cause excitation processes in biological objects. The obtained data indicate that cystamine realizes its protective properties against damage caused by ultraviolet radiation and UV-like damage resulting from the action of gama-rays due to the excitation of molecules or, more precisely, the ultraviolet component of Vavilov-Cherenkov luminescence accompanying the action of ionizing radiation.

Выявление общих закономерностей и математическое прогнозирование синергического взаимодействия гипертермии с ионизирующим излучением или солями тяжёлых металловТолкаева М.С., Белкина С.В., Воробей О.А., Жураковская Г.П., Петин В.Г

Previously developed mathematical model of simultaneous action of two inactivating agents has been adapted and tested to describe the results of sequential action. The possibility of applying the mathematical model to the interpretation and prognosis of the increase in radio-sensitivity of tumor cells as well as mammalian cells after sequential action of two high temperatures or hyperthermia and ionizing radiation is analyzed. The model predicts the value of the thermal enhancement ratio depending on the duration of thermal exposure, its greatest value, and the condition under which it is achieved.

In order to estimate the dependence of the synergistic enhancement ratio on the damage level induced by ionizing radiation and hyperthermia, data obtained by other authors for mammalian cells treated with sequential thermoradiation were used. The experimental results were described and interpreted by means of the mathematical model of synergism, according to which synergism is determined by additional lethal damage arising from the interaction of nonlethal sublesions induced by individual damaging agents.

The dependence of synergy enhancement ratio after the consecutive thermoradiation actions on dose rate and dose of ionizing radiation as well as on temperature and duration of its application was studied for yeast cells. The results published before were described and interpreted by means of the mathematical model of synergism in accordance with which the synergism is expected to result from the additional lethal damage arising from the interaction of sublesions induced by both agents.

The possibility of prediction of synergistic effects of ionizing radiation and different damaged factors on mammalian cells and plants has been performed. The model describes the data on combined action of these agents on the survival, cell transformation and the yield of mutation. It was shown that experimental results agreed with the predicted synergistic effectiveness. The model predicts the values of the synergistic enhancement ratio at any ratio of damages induced by the acting agents as well as the highest synergistic effect and the condition under which it is achieved.