RESUMEN
The extracellular pH (pHe) in many solid tumors is often lower than the pH of normal tissues. The K+/H+ ionophore nigericin is toxic to CHO cells when pHe is below but not above 6.5, and thus it has potential for selective killing of tumor cells in an acidic environment. This study examines the pH-dependent effects of nigericin on the response of CHO cells to radiation and heat treatment. Cells held for 4 h in Hank's balanced salt solution, after 9 Gy irradiation, exhibit potentially lethal damage recovery (PLDR) which is maximal at pHe 6.7-6.8. Addition of nigericin, postirradiation, not only inhibits PLDR when pHe is below 6.8, but interacts synergistically with radiation to reduce survival below that of cells plated immediately after irradiation when pHe is 6.4 or lower. Nigericin enhances heat killing of CHO cells perferentially under acidic conditions, and where neither heat nor drug treatment alone is significantly toxic. Survival of cells held for 30 min at 42.1 degrees C in the presence of 1.0 microgram/ml nigericin is 0.6, 0.08, 0.003, and 0.00003 at pHe 7.4, 6.8, 6.6, and 6.4, respectively, relative to survival of 1.0 in untreated cultures. The biochemical effects of nigericin at pHe 7.4 vs pHe 6.4 have been investigated. Nigericin inhibits respiration, stimulates glucose consumption, and causes dramatic changes in intracellular concentrations of Na+ and K+ at pHe 7.4 as well as 6.4. The drug reduces intracellular levels of ATP, GTP, and ADP but has more pronounced effects under acidic incubation conditions. Others have shown that nigericin equilibrates pHe and intracellular pH (pHi) only when pHe is 6.5 or lower. Our observations and those of others have led us to conclude that lowering of pHi by nigericin is either the direct or indirect cause of enhancement of radiation and heat killing of cells in an acidic environment.
Asunto(s)
Antibacterianos/farmacología , Supervivencia Celular/efectos de la radiación , Calor , Ionóforos/farmacología , Nigericina/farmacología , Animales , Línea Celular , Supervivencia Celular/efectos de los fármacos , Radioisótopos de Cobalto , Concentración de Iones de HidrógenoRESUMEN
The lethal and mutagenic effects of ionizing radiation delivered at high (53 Gy/h) and low (0.02 Gy/h) dose rates were measured in two closely related strains of mouse lymphoma L5178Y cells differing in radiation sensitivity (LY-R and LY-S). Strain LY-R was more resistant to the lethal effects of radiation than strain LY-S when exposed at either the high or low dose rate. The survival of strain LY-R was markedly enhanced by the reduction in dose rate. The dose-rate dependence of the survival of strain LY-S was less clear, because of the biphasic nature of its survival curve following low dose-rate radiation. However, if the initial slope of the low dose-rate survival curve is compared to the slope of the high dose-rate survival curve for strain LY-S, only a slight increase in survival at the low dose rate is apparent. Although more sensitive to the lethal effects of radiation, strain LY-S was less mutable at the hypoxanthine/guanine phosphoribosyl transferase locus by both low dose-rate and high dose-rate radiation than strain LY-R. Little dose-rate dependence was exhibited by either strain with regard to the mutagenic effects of radiation. Thus, for strain LY-R, which showed marked dose-rate dependence for survival but not for mutation, the ratio of mutational to lethal lesions was much greater following exposure to low dose-rate than to high dose-rate radiation.
Asunto(s)
Supervivencia Celular/efectos de la radiación , Leucemia L5178/patología , Leucemia Experimental/patología , Mutación , Tolerancia a Radiación , Animales , Línea Celular , Relación Dosis-Respuesta en la Radiación , Técnicas In Vitro , Ratones , Genética de Radiación , Factores de TiempoRESUMEN
A host-cell viral suicide enrichment procedure was used to isolate BHK strains sensitive to ionizing radiation. Of six strains surviving infection with irradiated herpes simplex virus (HSV), three were found to be more sensitive to ionizing radiation than the parental BHK cells. Thus the D0's of strains V1, V2, and V5 were 1.59, 1.41, and 1.49 Gy, respectively, while the D0 for the parental BHK strain was 1.79. Strains V1 and V2 were studied in more detail and found to exhibit hypersensitivity to ethyl methanesulfonate (EMS), methyl methanesulfonate, and N-methyl-N'-nitro-N-nitrosoguanidine, but not to uv radiation. Susceptibility to mutation in response to EMS was also compared in BHK and strains V1 and V2. The frequency of induction of ouabain-resistant cells was 140% of the parental strain in the case of strain V1 and 58% of the parental strain in the case of strain V2.
Asunto(s)
Alquilantes/farmacología , Línea Celular , Tolerancia a Medicamentos , Tolerancia a Radiación , Animales , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/efectos de la radiación , Cricetinae , Relación Dosis-Respuesta a Droga , Metanosulfonato de Etilo/farmacología , Riñón , Metilmetanosulfonato/farmacología , Metilnitronitrosoguanidina/farmacologíaRESUMEN
Survival, mutagenesis and transformation were measured in mouse embryo C3H 10T 1/2 cells following treatment with ethyl methanesulfonate (EMS). Ouabain-resistant cells and transformed cells were isolated, and reconstruction experiments were carried out to determine the optimum conditions for the measurement of mutation and transformation frequencies. Survival was measured by plating efficiency; mutagenesis was measured in terms of the induction of cells able to form colonies in the presence of ouabain; and transformation was measured by the induction of cells forming either morphologically altered colonies on a monolayer of contact-inhibited cells or of cells capable of forming colonies in semi-solid media. When confluent monolayers were incubated for 4 h after treatment with EMS, to allow excision repair before the resumption of DNA synthesis, survival as well as the frequencies of both mutation and transformation increased. When this repair (or holding) period was extended to 24 h, the frequencies of mutation and transformation both decreased as compared to the 4-h holding period. Thus, the holding periods affect the frequencies of EMS-induced mutagenesis and transformation similarly.