The effect of electron-affinic radiosensitizers on ATP levels in V79 379A Chinese hamster cells

Design, synthesis, and biological activity of anti-angiogenic hypoxic cell radiosensitizer haloacetylcarbamoyl-2-nitroimidazoles

We designed, synthesized, and evaluated haloacetylcarbamoyl-2-nitroimidazoles, including chloro (KIN-1800, TX-1835, and TX-1836) and bromo derivatives (TX-1844, TX-1845, and TX-1846), as potential hypoxic cell radiosensitizers with antiangiogenic activities. To establish biological function owing to the haloacetylcarbamoyl group in the side-chain, we compared their in vitro radiosensitizing activities with those of their parent 2-nitroimidazoles without haloacetylcarbamoyl groups: misonidazole (MISO), TX-1831, and TX-1832, respectively. Both tert-butoxy substituted derivatives. TX-1835 and TX-1845, were more potent radiosensitizers than TX-1831. The p-tert-butylphenoxy-substituted derivatives, TX-1836 and TX-1846, and the methoxysubstituted derivatives, KIN-1800 and TX-1844, were stronger radiosensitizers than TX-1832 and MISO. We examined the anti-angiogenic activities of these 2-nitroimidazole derivatives containing haloacetylcarbamoyl group by the rat lung endothelial (RLE) cell proliferation assay and chick embryo chorioallantoic membrane (chick CAM) angiogenesis assay and showed that haloacetylcarbamoyl-2-nitroimidazoles were more potent angiogenic inhibitors than the corresponding desacetylcarbamoyl-2-nitroimidazoles. The in vivo chick CAM angiogenesis assay showed that the strong bromoacetylcarbamoyl-2-nitroimidazole radiosensitizers, such as TX-1845 and TX-1846, were the strongest angiogenic inhibitors among them. We concluded that the bromoacetylcarbamoyl-2-nitroimidazole radiosensitizers, such as TX-1845 and TX-1846, are promising as anti-angiogenic hypoxic cell radiosensitizers.

The evaluation of erythrocyte membrane response to combined treatment of radiation and nitroimidazoles

The effect of gamma-irradiation on human erythrocytes in the presence of nitroimidazoles in aerobic conditions was investigated. It was found that both 1-(2-nitroimidazole-1-y1)-3-methoxy-2-propanol (misonidazole, MISO) and 1-(2-methyl-4,5-dinitroimidazoyle)-3-chloro-2-hydroxypropane (4,5-NO2) inhibited membrane-bound ATPase activity without irradiation. Treatment with 4,5-NO2 enhanced the radiation-induced decrease in the activity, whereas irradiation after treatment of membranes with MISO had a variable, concentration-dependent effect. Irradiation of cells in the presence of MISO concentrations less than 34 micrograms/ml decreased reduced glutathione (GSH) levels and increased malondialdehyde (MDA) formation. With the same concentrations a marked oxidative effect of 4,5-NO2 was observed. Significant correlations between 4,5-NO2 concentrations, GSH levels and lipid peroxidation, and also between GSH and MDA levels, were observed. Increasing radiation doses decreased erythrocyte membrane sensitivity to the stabilizing effect of unsaturated fatty acids. This effect for oleic acid was elevated by 4,5-NO2 and suppressed by GSH and BHT. Therefore, it is concluded that in aerobic conditions the red blood cell membrane is a target to radiation and to hypoxic cell radiosensitizers.

Effect of arylidene-cyclopentenedione radiosensitizers on ATP synthesis in mitochondria: action as potent inhibitors of phosphate transport

The effects of the arylidene-cyclopentenedione radiosensitizers, KIH-200, 201 and 202 on ATP synthesis in mitochondria were examined. In spite of the close similarity of their chemical structure to that of the most potent known weakly acidic uncoupler, SF 6847, they did not show any uncoupling activity at concentrations of up to 50 microM. However, these three compounds were found to have very potent inhibitory effects on Pi-transport into mitochondria, all causing 50% inhibition (I50%) at about 7 microM. Thus they are much more potent than the commonly used Pi-transport inhibitors N-ethylmaleimide (I50% = about 40 microM), and mersalyl (I50% = about 30 microM). They may act as SH-reagents, and inhibit Pi-transport by modifying an SH-group(s) in the Pi-transporter.

Oral absorption of metronidazole in rabbits irradiated with cobalt-60 gamma radiation

The absorption of oral metronidazole in control rabbits and in rabbits irradiated with cobalt-60 gamma radiation was studied. It was observed that the bioavailability of metronidazole was significantly reduced in irradiated animals the reduction being dependent on the dose of radiation. The maximum decrease in absorption was seen 48 h post-irradiation.

Rapid-mixing studies of radiosensitivity with thiol-depleted mammalian cells

A moderate reduction in the non-protein thiol content of V79 379A Chinese hamster cells, obtained by pretreatment with buthionine sulphoximine (BSO), diethyl maleate (DEM) or N-ethyl maleimide (NEM), increase both the absolute radiosensitivity of the cells in hypoxia and the radiosensitizing effect of adding oxygen 7 ms after irradiation. Combined pretreatment of cells with BSO and NEM removes most of the non-protein thiol and some of the protein thiol; such treatment further increases the radiosensitivity of hypoxic cells but there is no further effect of adding oxygen 7 ms after irradiation. Addition of 2-mercaptoethanol to cells 7 ms after irradiation gives protection factors that increase with increasing severity of thiol depletion. Substantial radioprotection can still be observed when 2-mercaptoethanol is added 70 ms after irradiation of cells pretreated with BSO and NEM; there is no effect of adding 2-mercaptoethanol to such cells 50s after irradiation. These observations support the repair-fixation model of radiation damage and suggest that, in addition to the established role of non-protein thiol in chemical repair of radiation damage, other endogenous reducing agents such as protein thiol may be important in determining cellular radiosensitivity. A relatively long-lived thiol-modifiable component of radiation damage has been observed within hypoxic thiol-depleted cells.

A comparison of the intracellular uptake and radiosensitization efficiency in different media of uncharged 2-nitroimidazoles of varying lipophilicity

The effect of varying octanol: water partition coefficients, P, (range 0.026-260) on the uptake of uncharged 2-nitroimidazoles into Chinese hamster V79 379A cells has been studied. Average intracellular concentrations were measured by high performance liquid chromatography after centrifuging cells through oil or an aqueous medium. The ratio of intracellular concentration of radiosensitizer to extracellular concentration (Ci/Ce) for misonidazole (P = 0.43) was 0.85 for the oil method and 0.68 for the aqueous method. For values of P less than about 0.05 uptake was initially very slow and Ci was always less than Ce. When P greater than or equal to 0.1 uptake was rapid and then remained unchanged for times up to 3 h; for P greater than or equal to 10, Ci/Ce increased rapidly as P increased. Ro 31-1405 (P = 260) concentrated by a factor of 7 inside the cell. Although uptake was identical for cells suspended in full growth medium and PBS, radiosensitization was greater for cells in PBS: 1 mmol dm-3 misonidazole produced an enhancement ratio of 1.6 in full growth medium and 1.9 in PBS. This increase in radiosensitization could not be accounted for by protein binding. However, measurements on cellular non-protein sulphydryl (NPSH) demonstrated the levels to be reduced to about 60 per cent for cells in PBS. Similar reductions in NPSH levels have previously been shown not to increase the radiosensitivity of control cells but to increase greatly the effectiveness of nitroimidazole radiosensitizers.