RSR13, an allosteric effector of haemoglobin, and carbogen radiosensitize FSAII and SCCVII tumours in C3H mice. (1/346)

Pre-clinical evaluation has demonstrated that 2-[4-(((3,5-dimethylanilino)carbonyl)methyl)phenoxy]-2-methylpropi onic acid (RSR13) acts as an allosteric effector of haemoglobin (Hb). RSR13 binding to Hb results in decreased haemoglobin-oxygen (Hb-O2) affinity, improved tumour oxygenation, and enhanced radiation-induced cell killing in several experimental tumour systems. In the present work, ex vivo clonogenic survival analyses are applied in two murine tumour systems to characterize the relationship between the magnitude of decrease in Hb-O2 affinity and radiosensitization, the influence of inspired pO2 upon this effect, and the efficacy of combining RSR13 and radiation during a course of repeated radiation exposures. For FSaII tumours in C3H mice breathing air, 100 mg kg(-1) RSR13 administered intraperitoneally produced an enhancement ratio (ER) of 1.3, but there was marked desensitization at a RSR13 dose of 300 mg kg(-1) (ER 0.6). The most likely reason for the increased radioresistance was insufficient oxygen loading of Hb in the pulmonary circulation due to reduced haemoglobin-oxygen affinity because carbogen breathing combined with 300 mg kg(-1) RSR13 reversed the effect and produced an ER of 1.8. In SCCVII tumours in C3H mice irradiated with eight fractions of 2.5 Gy over 4 days, the surviving fraction was reduced to 58-67% of control values when RSR13 was combined with radiation on days 1 and 2, days 3 and 4, or days 1-4. These results confirm that combining RSR13 and irradiation within a fractionated course of clinically relevant low-dose exposures provides significant radiosensitization. Additional preclinical experimentation is needed to define better the optimum dose-scheduling conditions for clinical applications.  (+info)

Genetic analysis of radiation-sensitive mutations in the slime mould Dictyostelium discoideum. (2/346)

The linkage of two mutations leading to increased sensitivity to ultraviolet light and 60Co gamma rays was determined in the slime mould Dictyostelium discoideum using a genetic analysis based on the parasexual cycle. Diploids were selected from a mixture of radiation-sensitive, temperature-resistant and radiation-resistant, temperature-sensitive haploids on the basis of simultaneous radiation and temperature resistance. Analysis of drug-resistant haploid segregants of the heterozygous diploids indicated that one of the radiation-sensitive mutations, radA20, was linked to linkage group I whereas the other, radB13, was linked to the recently defined linkage group VI.  (+info)

Change in centromeric and acentromeric micronucleus frequencies in human populations after chronic radiation exposure. (3/346)

Acute radiation exposure of humans was observed to induce various forms of cytogenetic damage, including increased frequencies of micronuclei and chromosomal aberrations. However, the cytogenetic effects of chronic low dose radiation exposure in vivo needs further characterization. Sixteen subjects with chronic low dose rates of gamma-radiation exposure from 60Co-contaminated steel in radioactive buildings were compared with seven non-exposed reference subjects for micronucleus frequencies after they relocated. By in situ hybridization using a digoxigenin-labeled anti-alpha all human centromere probe, the exposed subjects were shown to have a significant increase in cytochalasin B-modulated micronucleus (CBMN) frequencies, as well as a significant increase in centromere-positive (C+) CBMN, centromere-negative (C-) CBMN, total C+signals, single C+ MN signals and multiple C+ signals/1000 binucleated cells (BN). However, decreases in the ratios C+MN/C- MN and C+MN/total CBMN (%) were also noted in the exposed subjects. By mixed effects analysis, considering individuals from the same families, the C- MN and single C+ MN/1000 BN were both positively and moderately associated with previous cumulative exposure. When the time period of relocation post-exposure (relocation time or RT) was considered, total C+MN and multiple C+MN/1000 BN were negatively and significantly associated with RT. Moreover, the C+MN, C- MN, C+MN/C- MN ratio and single C+MN/1000 BN were all negatively and moderately associated with RT, but not with exposure dose. This suggested that acentromeric and single or multiple centromeric CBMN cytogenetic damage seems to disappear differentially in human subjects post chronic low dose radiation exposure.  (+info)

Granulocyte colony-stimulating factor and drugs elevating extracellular adenosine act additively to enhance the hemopoietic spleen colony formation in irradiated mice. (4/346)

The effects of combined administration of two drugs elevating extracellular adenosine, namely dipyridamole (DP) and adenosine monophosphate (AMP), and granulocyte colony-stimulating factor (G-CSF) on hemopoietic stem cells in vivo were investigated. The experiments were performed on mice using the endogenous spleen colony formation in gamma-irradiated animals as an endpoint. The results have shown that DP and AMP act additively with G-CSF to enhance spleen colony formation and thus the erythroid repopulation of the spleen. These findings indicate that the signaling pathways of G-CSF and drugs elevating extracellular adenosine can interact at the level of primitive hemopoietic stem cells. The enhancement of hemopoiesis-stimulating effects of G-CSF by DP and AMP, which are low-priced and clinically available drugs, could improve the cost-effectiveness of the therapy with G-CSF.  (+info)

Classification and behavior of canine mammary epithelial neoplasms based on life-span observations in beagles. (5/346)

As part of a study of the effects of low-level radiation, 1,343 Beagles, including 671 males and 672 females, were evaluated over their full lifetime for the occurrence of mammary neoplasia; there were 139 control males and 138 control females and 532 irradiated males and 534 irradiated females. All nodules found in surgical specimens or at necropsy were evaluated histologically. The overall incidence, metastasis and recurrence rates, and contribution to mortality of mammary neoplasms were determined. Based on this unique opportunity to correlate morphologic characteristics with ultimate biological behavior of all mammary tumors in a defined canine population, we propose a histogenetically based reclassification of epithelial mammary tumors. Of the 672 female dogs, 70.8% (476) had at least one mammary neoplasm; 60.7% (408) had more than one. Two male dogs had mammary neoplasms. Of 1,639 mammary carcinomas in the 672 females, 18.7% (307) were classified as ductular carcinomas (arising from the small interlobular or intralobular ductules), whereas 80.7% (1,322) were classified as adenocarcinomas of other histogenetic origin. Of 73 fatal carcinomas, ductular carcinomas accounted for 48 fatalities (65.8%), whereas other adenocarcinomas accounted for only 20 fatalities (27.4%). Radiation had no effect on this ratio. Ductular carcinomas also had a higher rate of metastasis than did adenocarcinomas. Existing classifications of mammary carcinomas do not recognize the characteristic morphologic features, the degree of malignancy, and the prognostic importance of these ductular carcinomas. Metastasis rates did not differ between simple and complex carcinomas or between those lesions and adenocarcinomas in mixed tumors. True carcinosarcomas metastasized more frequently (100%, or 5/5) than did adenocarcinomas in mixed tumors (34.4%, or 22/64), emphasizing the importance of not lumping these tumors under the classification of malignant mixed tumors.  (+info)

Radioprotective effects of sodium tungstate on hematopoietic injury by exposure to 60Co gamma-rays in Wistar rats. (6/346)

Radioprotective effects of sodium tungstate (ST) on 60Co gamma-ray induced decrease in hematocrit value and in survival rate in Wistar strain male rats were examined. A long-term administration of ST (less than 150 mg/kg body weight/day) for 60-300 days had no significant effects on body and organs weights and survival days. The LD50/60 in 20 weeks old rats was 220 mg/kg body weight/day. Daily administration of 38, 75 or 150 mg from 7 days before and after irradiation to 60 days significantly mitigated the decrease in hematocrit values, especially at 23 days after irradiation (P < 0.05). The highest mitigation rate of the decrease in hematocrit value was observed in rats administered at a dose of 38 mg ST/day. Simultaneously, a dose of 38 mg ST/day inhibited lethal effect of 60Co gamma-rays significantly. The dose-reduction factor for survival of 38 mg ST administered rats was 1.14.  (+info)

Base substitution spectra of nalidixylate resistant mutations induced by monochromatic soft X and 60Co gamma-rays in Bacillus subtilis spores. (7/346)

Bacillus subtilis spores were exposed to three types of photons, monochromatic soft X-rays with the energy corresponding to the absorption peak of phosphorus K-shell electron (2,153 eV) and with the slightly lower energy (2,147 eV), and 60Co gamma-rays. From the irradiated spores, 233 mutants exhibiting nalidixic acid resistance were isolated, and together with 94 spontaneous mutants, the sequence changes in the 5'-terminal region of the gyrA gene coding for DNA gyrase subunit A were determined. Among eighteen alleles of the gyrA mutations, eight were single-base substitutions, nine were tandem double-base substitutions, and one was a double substitution skipping a middle base pair. About 6% of the radiation-induced mutations were tandem double-base substitutions, whereas none was observed among the spontaneous ones. Among spontaneous mutations, A:T and G:C pairs were equally subjected to mutations, whereas the substitutions from G:C pairs and those to A:T pairs predominated among those induced with soft X-rays. The peak-energy X-rays were more effective in killing and causing mutations than the low-energy X-rays, however, there seemed no base-change events uniquely attributable to phosphorus K-shell absorption.  (+info)

Syrian hamster dermal cell immortalization is not enhanced by power line frequency electromagnetic field exposure. (8/346)

Several epidemiological studies have suggested associations between exposure to residential power line frequency electromagnetic fields and childhood leukaemia, and between occupational exposure and adult leukaemia. A variety of in vitro studies have provided limited supporting evidence for the role of such exposures in cancer induction in the form of acknowledged cellular end points, such as enhanced mutation rate and cell proliferation, though the former is seen only with extremely high flux density exposure or with co-exposure to ionizing radiation. However, in vitro experiments on a scale large enough to detect rare cancer-initiating events, such as primary cell immortalization following residential level exposures, have not thus far been reported. In this study, large cultures of primary Syrian hamster dermal cells were continuously exposed to power line frequency electromagnetic fields of 10 100 and 1000 microT for 60 h, with and without prior exposure to a threshold (1.5 Gy), or sub-threshold (0.5 Gy), immortalizing dose of ionizing radiation. Electromagnetic field exposure alone did not immortalize these cells at a detectable frequency (> or = 1 x 10(-7)); furthermore, such exposure did not enhance the frequency of ionizing radiation-induced immortalization.  (+info)