The influence of a protein synthesis inhibitor on sister-chromatid exchange in the plant Vicia faba

Amino acids excess increase SCEs in human lymphocytes

The effects of 21 amino acids on sister-chromatid exchanges (SCEs) in human lymphocytes were investigated. Addition of each of the 21 amino acids, originally in a composition of the culture medium RPMI 1640, at three different concentrations (10 micrograms/ml, 50 micrograms/ml and 100 micrograms/ml) caused a dose-independent increase in SCE frequency. The results indicated that amino acids, although indispensable for cells in vivo and in vitro, may be SCE-inducing agents.

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Dose-response function for Painter's SCE-model

The replication model for sister chromatid exchange (SCE), when introduced in 1980 by Painter, was claimed to be consistent with the one hit property of SCE. However, the argument offered in favour of the one hit property was based on a defective dose-response function, as shown in this paper, since dose as the independent parameter of any dose-response function was not included in the considerations. This missing part of the model's dose-response function is added and, by using Bessel functions, a formula for the complete dose-response function is presented. A re-examination of the newly derived function shows that, in the model, linearity holds only under certain restricted circumstances.

Isolation and characterization of Chinese hamster cell line resistant to monofunctional alkylating agents

A clonal derivative of a Chinese hamster Don D-6 cell line resistant to methyl methane sulfonate (MMS) has been isolated following mutagenesis by ethyl methane sulfonate (EMS). The clone, designated as MMSr-1, exhibited high resistance to killing by the monofunctional alkylating agents MMS and EMS. This characteristic had not been acquired by a transient adaptation to the alkylating agents but was found to be a stable heritable trait. MMSr-1 was more sensitive to high-molecular-weight chemicals, such as colchicine and puromycin, than Don D-6. Both MMSr-1 and its parental cells showed the same ability to take up radioactive MMS. The resistance of MMSr-1 appears not to be due to altered uptake of MMS. The resistance was accompanied by low chromosomal aberration and sister chromatid exchange (SCE) induction but not by mutability. Protein synthesis inhibitors such as cycloheximide and puromycin reduced the resistance to the same level as that in Don D-6. SCE induction by MMS in this clone was not antagonized by the protein synthesis inhibitors, whereas mutagenesis was reversed to the normal parental cell level by these inhibitors. Aphidicolin, a DNA-synthesis inhibitor, exhibited no such effects. These results suggest that MMSr-1 might have modified repair capacity, which can be normalized by treatment with the protein-synthesis inhibitors, for lethal DNA damage by monofunctional alkylating agents, and that SCE formation by the alkylating agents is closely correlated with chromosomal aberration and cell lethality.

Abrogation of etoposide-mediated cytotoxicity by cycloheximide

The antitumor agent etoposide interacts with DNA topoisomerase II to produce a unique form of DNA-enzyme intermediate referred to as a "cleavable complex". These drug-induced DNA strand breaks initiate poorly defined cell processes which result in lethality. To explore the mechanism of etoposide cytotoxicity, we studied the effect of protein synthesis inhibitor on Balb/C 3T3 fibroblasts and CCRF-CEM and L1210 leukemia cells by exposing these cell lines to cycloheximide for various periods of time prior to etoposide challenge. Cycloheximide alone during these periods of exposure was not cytotoxic; however, it conferred increasing cytoprotection from etoposide in a time-dependent fashion when it preceded etoposide. Although cycloheximide did cause a decrease in enzyme content and in etoposide-induced DNA cleavage of Balb/C 3T3 and the CCRF-CEM cell lines, cytoprotection by cycloheximide could not be accounted for completely by these phenomena since, in L1210 cells, cytoprotection was observed without significant change in DNA cleavage or enzyme content. Cycloheximide diminished DNA synthesis as well as protein synthesis. However, DNA synthesis resumed within 6 hr after removal of cycloheximide, in spite of the fact that cytoprotection persisted. Cycloheximide did not alter cell cycle distribution as measured by flow cytometry. Our data, therefore, clearly demonstrate that cycloheximide can diminish the cytotoxic potential of etoposide-mediated topoisomerase-DNA complexes. Elucidation of the mechanism by which cytoprotection occurs should shed light on the basis for the cytotoxic effect of topoisomerase II-active drugs.