Sequential and Reversible Inhibition of Synthesis of Ribonucleic Acid in the Nucleolus and Chromosomes: Effect of Benzamide and Substituted Benzimidazoles on Dipteran Salivary Glands

Mutagenic bioassay of certain pharmacological drugs. I. Thiabendazole (TBZ)

This report describes the chromosomal damage produced by 2-(4'-thiazolyl)benzimidazole or thiabendazole (TBZ) evaluated by "in vivo" and "in vitro" cytogenetic tests. The doses assayed in adult mice by the sister-chromatid exchange (SCE) and micronucleus tests were: 50, 100 and 200 mg/kg body weight; these are within the range of those used in human antihelminthic treatments. SCE frequency was increased only in the last dose (p less than 0.05). A significant increase of micronucleated cells was shown in the 3 doses assayed (p less than 0.001). A marked increase in abnormal anaphase-telophase cells was only detected with the two highest concentrations assayed (0.60-0.24 microgram/ml) p less than 0.01 and p less than 0.05 respectively. The observed genotoxic effects of this compound indicate that TBZ itself is a mutagenic agent.

Autoradiographic studies on RNA synthesis and transport in the salivary gland of Lygaeus sp. (Hemiptera-Lygaeidae)

Autoradiographic studies using 3H-uridine in the salivary gland of adult Lygaeus sp. were carried out. The gland cell nuclei, particularly the multiple nucleoli, are the sites of incorporation of the label exhibiting RNA synthesis. The labelled molecules (RNA) are transported to the cell cytoplasm and then into the gland lumen in which no turnover of the radioactivity is observed.

Specific activation of puff 93D of Drosophila melanogaster by benzamide and the effect of benzamide treatment on the heat shock induced puffing activity

A 10 or 20 min in vitro treatment of salivary glands of late 3rd instar larvae of Drosophila melanogaster with 1 mg/ml benzamide (BM) at 24 degrees C results in the specific induction of the 93D puff and at the same time all other chromosomal RNA synthesis is severely repressed. Incorporation of 3H-uridine in the nucleolus is not affected. In glands heat shocked (37 degrees C) for 20 min in presence of BM, all the temperature shock (TS) puffs are induced but they incorporate 3H-uridine to a lesser extent than in glands heat shocked in absence of BM. The 93D puff, which is highly induced by either of the treatments alone, is relatively less active in glands exposed to TS and BM simultaneously. When a 10 min BM treatment (at 24 degrees C) incorporation on all TS puffs is relatively less and significantly, in both cases, the 87C puff is much less active active (more so in TS followed by BM treated glands) than the 87A puff. Also, in both these treatments, the 93D puff does not show ant additive effect on the BM and TS treatments. These observations are discussed in the light of possible role of the 93D puff in modulating the heat shock response.

A comparative study of the effects of certain halogenated benzimidazole ribosides on RNA synthesis, cell proliferation, and interferon production

5-(or 6-)Bromo-4,5-(or 5,7-)dichloro-1-beta-D-ribofuranosylbenzimidazole, 5,6-dibromo-1-beta-D-ribofuranosylbenzimidazole, and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole show closely similar structure-activity relationships with respect to inhibition of cellular RNA synthesis, cellular proliferation, and influenza virus multiplication, and also with respect to enhancement of interferon production. The activities ofth ese compounds are ranked 20:2.5:1. The log dose-response curves constructed for inhibiton of FS-4 cell RNA synthesis show similar slopes and a leveling off at 60-70% inhibition of RNA synthesis at the highest concentrations of each compound tested. This evidence suggests that these three derivatives act through the same mechanism. It has been shown previously that the dichloro compound selectively inhibits nuclear heterogenous RNA and messenger RNA synthesis. The concentrations of the benzimidazole ribosides at which the rate of proliferation of human fibroblasts (FS-4) is reduced by 50% are as follows: monobromodichloro: 1.7 muM (0.68 mug/ml); dibromo: 12 muM (4.9 mug/ml); dichloro: 38 muM (12 mug/ml). All compounds reduce the exponential rate of cell proliferation in a dose-dependent manner. The inhibition of cell growth is reversible upon removal of the compounds from the medium. Protocols based on any one of the three halobenzimidazole ribosides give interferon yields from poly(I)-poly(C)-induced FS-4 cells which are comparable to the high yields obtained with the conventional cycloheximide-actinomycin D protocol. The enhancement of interferon yield depends on blocking of the synthesis of RNA which is involved in the shutoff of interferon production.

Action of dichlorobenzimidazole riboside on RNA synthesis in L-929 and HeLa cells

5,6-Dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) inhibits RNA synthesis in L-929 cells (mouse fibroblast line) and HeLa cells (human epitheloid carcinoma line) within 2 min of addition of the compound to the medium. By removing DRB from the medium, the inhibition is promptly and completely reversed after treatment of cells for as long as 1 h or even longer. The inhibitory effect of DRB on the overall rate of RNA synthesis is similar in L and HeLa cells and is markedly concentration-dependent in the low dose range (5-20 muM or 1.6-6.4 mug/ml), but not as higher concentrations of DRB. At a concentration of 12 muM, DRB has a highly selective inhibitory effect on the synthesis of nuclear heterogenous RNA in L cells. At higher concentrations, there is also inhibition of 45 S ribosomal precursor RNA synthesis, but at all concentrations the effect on heterogeneous RNA synthesis in L cells in considerably greater than that on preribosomal RNA synthesis. In HeLa cells, too, DRB has a selective effect on heterogeneous RNA synthesis, but quantitatively the selectivity of action is somewhat less pronounced. In both L and HeLa cells, the inhibition of synthesis of nuclear heterogeneous RNA is incomplete even at very high concentrations of DRB (150 muM). Thus, while DRB is a selective inhibitor of nuclear heterogeneous RNA synthesis, not all such RNA synthesis is sensitive to inhibition. It is proposed that messenger precursor RNA synthesis may largely be sensitive to inhibition by DRB. In short-term experiments, DRB has no effect on protein synthesis in L or HeLa cells. DRB has a slight to moderate inhibitory effect on uridine uptake into L cells and a moderate to marked effect on uptake of uridine into HeLa cells.

[RNA synthesis and translocation in root cells of Zea mays during early stages of germination]

RNA synthesis in root of germinating corn during the period extending from the 4th to the 8th hr after soaking is localized exclusively in the chromatin. This unusual situation allowed us to follow easily by section autoradiography the fate of the chromatin-synthesized RNA. The embryo was pulse-labeled with (3)H-uridine from the 6th to the 8th hr after soaking and chased with cold uridine (2 hr) and then left in water (40 hr). It was found that during the chase a large amount of the chromatin-synthesized RNA moves to the nucleolus, where it is accumulated, and that a small amount finally reaches the cytoplasm.

Labeling and other effects of actinomycin D on human chromosomes

(3)H-actinomycin D, a guanine-binding agent, labels fixed human chromosomes nonrandomly. Actinomycin D added in G2 inhibits secondary constrictions and breaks chromosomes. There is some tendency for label to be concentrated at the ends of chromosomes and near the centromere. Labeling with (3)H-thymidine in the late stage of DNA synthesis shows a different pattern and in general lacks the telomeric concentrations. The sites of actinomycin D-induced breaks do not show good correspondence with the sites of actinomycin D label.

Nucleolar 4s ribonucleic acid in dipteran salivary glands in the presence of inhibitor

1. Salivary glands of insect larvae accumulate newly made transfer RNA in the nucleolus when maintained in the presence of nucleoside antagonists that inhibit RNA synthesis preferentially at the chromosome. 2. The nucleus contains precursor transfer RNA, which, on the basis of the general evidence, may originate in the chromosome and then be methylated in the nucleolus. 3. The maturation of precursor ribosomal RNA is blocked in the nucleolus during inhibition. 4. The transport of nuclear RNA to cytoplasm is also blocked. 5. It is suggested that, if the transfer RNA accumulated in the nucleolus does indeed originate in the chromosome, the accumulation may result from the blockage of an obligatory transient association of the RNA with the nucleolus.