核酸代谢抑制剂对水稻光敏核不育性的影响

在稻穗分化的二次枝梗期后,观察比较了叶片喷施核酸代谢抑制剂5-FU对水稻光敏核不育性及幼穗发育的影响,结果表明：长日照下,5-FU在使农垦58S穗长缩短、颖花数减少的同时,却使其抽穗提前,可育性得到一定程度的恢复;5-FU处理还使农垦58的抽穗被完全阻止。在短日照下,5-FU处理则使农垦58S与农垦58在穗长与颖花数减少的同时,其抽穗反被延迟,可育性受到抑制而结实率显著降低,上述效应还可被随后施用的恢复剂乳清酸所弱化。因此可以认为光敏核不育现象与稻穗发育中核酸代谢的改变有关。     

氮素形态对烤烟光合特性影响的研究

1996～1997年连续二年进行了固定氮素用量,改变铵态、硝态氮肥的施用比例试验,对烤烟的一些光合生理特性进行了研究。试验结果表明,在烤烟生长前、中期,增施铵态氮施用比例,烤烟的叶绿素含量增加,但达100％铵态氮时,叶绿素含量反而下降,低于施用50％和75％铵态氮的处理;在烤烟生长后期．功能叶片叶绿素含量基本上与施用铵态氮比例高低—致,以100％铵态氮处理的叶绿素含量最高。另外增加铵态氮施用比例,烤烟功能叶片的希尔反应活性及光合磷酸化活性有所提高,但P/O比值基本不变。从叶绿素诱导荧光动力学特征参数及比值情况来看：增加铵态氮施用比例,Fm和Fv值升高;几种荧光参数的比值如Fd/Fs、Fv/Fo、Fv/Fm比值有所上升,但均以25％硝态氮+75％铵态氮的处理最高;并且其烤后烟叶的产量最高、品质最好。     

Inhibition of lettuce seed germination and seedling growth by antimetabolites of nucleic acids,and reversal by nucleic acid precursors and gibberellic acid

Summary Germination of White Paris lettuce seeds is inhibited by 2-thiouracil up to 24 hours. This inhibition is reversed by RNA precursors only. Seedling growth of lettuce is inhibited by 2-thiouracil and 5-fluorouracil; and white the effect of 2-thiouracil is counteracted by RNA precursors, inhibition due to 5-fluorouracil is not reversed significantly by any nucleic acid precursors. Possibly 2-thiouracil controls germination and seedling growth by interfering with RNA synthesis, while the effect of 5-fluorouracil is non-specific.In the presence of gibberellic acid, 5-fluorouracil and 2-thiouracil are relatively ineffective in causing inhibition of hypocotyl growth. Mechanism of gibberellic acid action remains obscure.     

Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta III. Effect of Certain Nucleic Acid and Protein Inhibitors on Photoinduction of Carotenoid Biosynthesis

Inhibitors of protein and nucleic acid synthesis such as puromycin,cycloheximide, 5-fluorodeoxyuridine and 5-fluorouracil havebeen used to study the dark reactions involved in photoregulationof carotenogenesis in Rhodotorula minuta. The results indicatedthat as already reported in other organisms, carotenogenic enzymesare synthesized first and, in turn, synthesize carotenoids inthe dark. Synthesis of the carotenogenic enzymes was absolutelydependent on oxygen and came to an end within 6 hr at 26?C underaerobic conditions. Photoregulation of this synthesis may occurat the translational level. 5-Fluorodeoxyuridine and 5-fluorouracilacted as chemical inducers of carotenogenesis in Rh. minutagrown in the dark. However, the site of the action of thesechemicals was assumed to be different from that of light, becausethe chemical and light effects on the induction of carotenogenesiswere additive. (Received September 16, 1981; Accepted March 3, 1982)     

Suppression of Thymidine Uptake of Human Lymphocytes by Co-trimoxazole

Co-trimoxazole (trimethoprim-sulphamethoxazole) causes a decrease in the uptake of labelled thymidine in lymphocytes cultured in the presence of phytohaemagglutinin. This phenomenon was observed in 60% of 25 subjects. In cultures affected by the drug the mean suppression was 84%. A small decrease in thymidine uptake was noted with trimethoprim and sulphamethoxazole separately, but the effect was much more pronounced with the combination of the two drugs. The mechanism responsible for this phenomenon is discussed. The action is probably not due to the ability of these drugs to interfere with folic acid metabolism and it is likely that there is no direct effect on DNA synthesis.The suppression of thymidine uptake by lymphocytes in vitro in the presence of co-trimoxazole may not have any obvious clinical significance. However, in view of a report of an immunosuppressive action of trimethoprim in mice, it is possible that the leucopenia observed in some patients treated with this drug may have been caused by a similar mechanism.These experiments show that lymphocytes in vitro are suppressed by co-trimoxazole in concentrations comparable to, or smaller than, those found in vivo under normal therapeutic conditions. They are therefore likely to be clinically relevant.     

Levels of viral glycoprotein provide a dose-dependent measure of tumor cell inhibition

A chemosensitivity assay utilizing small replicate Mm5mt/c1 C3H mammary tumor cell cultures was developed to determine whether changes in viral antigen expression and release into culture fluids could be utilized as an in vitro measure of chemotherapeutic drug effect. The 52,000 MW viral envelope glycoprotein (gp52) of the mouse mammary tumor virus (MMTV) was measured in culture fluids of control and drug-treated cultures while cell density was simultaneously determined by cell staining and OD 664 mu determination. While extracellular gp52 levels and cell density both progressively increased over 72 hours for control cultures, treatments with doxorubicin resulted in dose-dependent declines in both parameters at 24, 48, and 72 hours. Comparison of doxorubicin dosages for 50% reduction (ED50s) in both parameters (0.68uM and 1.1uM) revealed a similar coordinate reduction in both cell density and MMTVgp52. When gp52 levels were further examined as a general measure of effect for a broad spectrum of 6 drugs with differing mechanisms of action, coordinate declines in cell density and MMTVgp52 provided a time and dose-dependent dual measure of effect for each of the drugs tested. Coordinate declines resulted in the same following hierarchy of concentration-dependent drug potency: methotrexate greater than 5-fluorouracil greater than doxorubicin greater than N [phosphonacetyl- L aspartic acid] (PALA) greater than cis-platinum greater than cyclophosphamide. The dual measures of therapeutic effect afforded by this assay argue for its use as an in vitro measure of effect for optimizing drug treatments.     

Suppression of tumor promoter phorbolmyristate acetate-induced chromosome breakage by antioxidants and inhibitors of arachidonic acid metabolism

To gain insight into the mechanism of formation of chromosomal aberrations by the tumor promoter phorbolmyristate acetate (PMA) in human lymphocytes, we investigated the effect of antioxidants and inhibitors of arachidonic acid metabolism. Among the antioxidants bovine erythrocyte CuZn superoxide dismutase, glutathione peroxidase, mannitol (a scavenger of hydroxyl radicals), butylated hydroxytoluene and butylated hydroxyanisole were anticlastogenic while catalase and dimethylfuran (a scavenger of singlet oxygen) were inactive. These results show that the induction of aberrations by PMA occurs via indirect action, i.e. the intermediacy of superoxide and hydroxyl radicals. The following inhibitors of arachidonic acid metabolism were strongly anticlastogenic: the cyclo-oxygenase inhibitors indomethacin and flufenamic acid and the lipoxygenase inhibitor BN1015. Imidazole, nordihydroguaiaretic acid BN 1048 and 5,8,11,14-eicosatetraynoic acid were moderately active. The inhibitor of phospholipase A₂, fluocinolone acetonide, was also anticlastogenic.

We conclude that the oxidative metabolism of arachidonic acid is involved in the induction of chromosomal aberrations by PMA in human lymphocytes. However, because of the limited selectivity of these drugs, it is not yet possible to identify unambiguously the step(s) in the arachidonic acid cascade responsible for PMA clastogenicity.     

Application of high-performance liquid chromatography for recognition of covalent nucleic acid modification with anticancer drugs

Covalent modification of DNA by antineoplastic agents represents a potent biochemical lesion which can play a major role in drug mechanism of action. The ability to measure levels of DNA covalent modifications in target cells in vivo may, therefore, be seen as the ultimate form of therapeutic drug monitoring. Additionally, elucidation of the structure of critical DNA adducts and definition of their role in tumour cell cytotoxicity will provide more selective targets for rational drug design of new cancer chemotherapeutic agents. High-performance liquid chromatography has contributed significantly to all these areas. In vivo levels of nucleic acid covalent modifications are in the range of 1 in 10⁵–10⁸ nucleotides precluding the use of conventional high-performance liquid chromatographic detection methods. Several classes of natural product anticancer drugs have been shown to bond covalently to nucleic acids under optimal laboratory conditions. These have proved more accessible to high-performance liquid chromatographic analysis because of their lipophilicity and strong UV chromophores. However, the majority of experimental evidence to date suggests that with the exception of mitomycin C and morpholino-anthracyclines these compounds do not exert their primary mechanism of action through nucleic acid covalent modification. DNA adducts of alkylating and platinating agents are more difficult to detect by high-performance liquid chromatography and can be chemically unstable. These compounds interact with DNA on the basis of chemical kinetics. Thus, the principle sites of attachment tend to be with the most nucleophilic base (guanine) at its most reactive centre (N-7 position). Limited in vivo high-performance liquid chromatographic studies with all classes of anticancer drugs indicate a much more complex pattern of adductation than would have been anticipated from in vitro studies alone. Some of these differences are probably due to methodological artefacts but these studies stress the need for sensitive detection methods and reliable sample preparation (nucleic acid extraction and digestion techniques) when attempting to determine nucleic acid covalent modifications by anticancer drugs.     

谷氨酰胺营养生理研究进展

谷氨酰胺因其对人和动物中的重要生理作用而引起了广泛关注。谷氨酰氨是一种特殊的氨基酸,为快速繁殖细胞优先选择的呼吸燃料,如粘膜细胞和淋巴细胞;调节体内酸碱平衡;组织间氮的载体;核酸、核苷酸、氨基糖和蛋白质的重要前体。大量的证据表明谷氨酰胺是一种条件性必需氨基酸。在应激状况下,机体对谷氨酰胺的需要超过其合成能力,因此,可以通过肠外营养或饲料中添加谷氨酰胺以营养调控的方式加速动物体的康复。     

Effect of hypokinesia on nucleic acid and protein metabolism in the lymphoid organs of rats

Metabolism of nucleic acids and protein by lymphoid cells of the rat spleen and thymus was studied under conditions of 22-day hypokinesia. It was shown that in the course of hypokinesia the loss of cellular mass by the spleen and thymus was associated with varied biochemical changes in the remaining lymphoid cells. The thymocytes showed a significant activation of nucleic acid and protein biosynthesis. Meanwhile in spleen lymphocytes, DNA and RNA metabolism was inhibited with no appreciable changes in protein metabolism. Potential mechanisms of changes in metabolism of thymus and spleen lymphocytes under long-term hypokinesia are discussed.     

Cytotoxicity and genotoxicity of capecitabine in head and neck cancer and normal cells

The interaction between a chemical and a cell may strongly depend on whether this cell is normal or pathological. Side effects of anticancer drugs may sometimes overcome their benefit action, so it is important to investigate their effect in both the target and normal cells. Capecitabine (Xeloda, CAP), a prodrug of 5-fluorouracil, is mainly used in colon cancer, but little is known about its action in head and neck cancer. We compared the cyto- and genotoxicity of CAP in head and neck HTB-43 cells and normal human lymphocytes by comet assay and flow cytometry. CAP at concentration up to 50?μM significantly decreased the viability of the cancer cells, whereas it did not affect normal lymphocytes. The drug did not interact with isolated plasmid DNA, but it damaged DNA in both cancer and normal cells. However, the extent of the damage in the former was much higher than in the latter. CAP induced apoptosis in the cancer cells, but not in normal lymphocytes. Pre-treatment of the cells with the nitrone spin traps α-(4-pyridil-1-oxide)-N-tert-butylnitrone and N-tert-butyl-α-phenylnitrone decreased the extent of CAP induced DNA damage, suggesting that free radicals may be involved in the formation of DNA lesions induced by CAP. The drug evoked an increase in the G0/G1 cell population accompanied by a decrease in the S cell population. CAP may evoke a pronounced cyto- and genotoxic effects in head and neck cancer cells, whereas it may or may not induce such effects in normal cells to far lesser extent.     

Alteration of Carbon Metabolism by a Base Analog

The study of carbon metabolism by cultures of the yeast C. utilis exposed to 5-fluorouracil revealed that the growth rate and synthesis of macromolecules was altered. The amino acid composition of the metabolic pool of amino acids was vastly altered, but the protein composition was unchanged. It is suggested that the analog may exert a selective action on certain amino acids, and that this action may be related to a template-like mechanism.     

A new chemosensitivity test using a thermo-reversible gelation polymer for recurrent gynecologic cancer patients and a preliminary study of mechanisms of anticancer drug resistance

OBJECTIVES: TGP (thermo-reversible gelation polymer) is a high molecular compound that has so-gel transmitting temperature of 221C Since solid cancer tissue grows in this polymer three-dimensionally, and fibroblasts scarcely grow in it, TGP is suitable for chemosensitivity assays for solid tumors. In this study, a chemosensitivity test using TGP was applied to recurrent gynecologic cancer patients in order to evaluate its utility and efficacy. In some ovarian cancer cases, expression of anticancer drug resistance-related proteins was also analyzed. METHODS: Recurrent tumor tissues were surgically obtained with informed consent. After these tissues were minced and incubated for 4 days with CDDP, mitomycin C, 5-fluorouracil, paclitaxel, and CPT-11, the sensitivity against these drugs was estimated. Western blotting was performed in 8 recurrent ovarian cancer tissues in order to analyze the expression of Bcl-2, MRP2, BCRP, and GST-pi. RESULTS: The total evaluability rate of this assay was 90.6% (29/32). Sensitive drugs could be determined in 5 of 7 ascites samples (71.4%) and in 2 of 3 intra-tumoral fluid samples (66.7%). The overall clinical response rate of chemotherapy determined by these results was 50.0%. There were significant correlations between the IC50 of CDDP and Bcl-2, BCRP, GST-pi, and between that of 5-FU and MRP 2. CONCLUSIONS: Although this was a preliminary study, the chemosensitivity test using this new material appears to be useful for designing 'made-to order' salvage chemotherapy for pretreated recurrent gynecologic patients. In order to overcome multidrug resistance, the mechanisms of multidrug resistance should be further investigated.     

On the combined action of drugs on the lambda prophage induction in Escherichia coli K12 cells.

The capability of methotrexate, jododeoxyuridine and 5-fluorouracil to induce lambda prophage was compared when given alone or in combination. All these drugs were found to cause inducing conditions in Escherichia coli K12(lambda) cells. Combined action of jododeoxyuridine and methotrexate resulted in a pronounced increase in the number of free phages compared with that resulting the treatment either with methotrexate of jododeoxyuridine alone. Treatment with 5-fluorouracil caused inactivation of plaque forming ability in cells induced with methotrexate.     

Demethylating agent 5-aza-2-deoxycytidine enhances susceptibility of breast cancer cells to anticancer agents

DNA methylation plays an important role in regulation of gene expression and is increasingly being recognized as a determinant of chemosensitivity of human cancers. With the aim of improving the chemotherapeutic efficacy of breast carcinoma, the effect of DNA methyltransferase inhibitor, 5-Aza-2′-deoxycytidine (5-aza-CdR), on the chemosensitivity of anticancer drugs was investigated. The cytotoxicity of paclitaxel (PTX), adriamycin (ADR), and 5-fluorouracil (5-FU) was analyzed against human breast cancer cell lines, MDA MB 231 and MCF 7 cell lines using the MTT assay, and the synergy of 5-aza-CdR and these agents was determined by Drewinko’s fraction method. The effects of each single agent or the combined treatment on cell cycle arrest were analyzed by flow cytometric analysis. We also investigated the effect of each single agent or the combined treatment of anticancer drugs with 5-aza-CdR on the methylation status of the selected genes by methylation specific PCR. In MDA MB 231 cells, a synergistic antiproliferative effect was observed with a combination of 10 μM 5-aza-CdR and these three anticancer drugs, while in MCF 7 cells, a semiadditive effect was observed. Treatment with 5-aza-CdR and anticancer drug resulted in partial demethylation of a panel of genes including RARβ2, Slit2, GSTP1, and MGMT. Based on these findings, we propose that 5-aza-CdR enhances the chemosensitivity of anticancer drugs in breast cancer cells and may be a promising approach for increasing the chemotherapeutic potential of these anticancer agents for more effective management of breast carcinomas.     

氨基酸转运体在肿瘤代谢中的研究进展

代谢重编程是肿瘤的重要特征,是指肿瘤细胞为满足其快速增殖的生物合成与能量需求,对其糖代谢、脂代谢以及氨基酸代谢等代谢路径进行的重编程,以维持增长速度以及补偿能量代谢所造成的氧化还原压力。虽然不同的癌症代谢变化不同,但有些特征是所有癌症共有的,氨基酸代谢重编程是其中一个重要的特征。氨基酸进出细胞需要氨基酸转运体的协助,因而在肿瘤细胞中多种特定的氨基酸转运体均过表达。靶向氨基酸转运体通过影响肿瘤细胞的氨基酸代谢从而达到抗肿瘤的目的,是目前抗肿瘤药物的研究热点之一。主要介绍了几种在肿瘤代谢中发挥重要作用的氨基酸转运体以及靶向氨基酸转运体抗肿瘤治疗的研究进展及相关作用机制,旨在了解氨基酸转运体在抗肿瘤研究中的作用,以期促进靶向氨基酸转运体抗肿瘤药物的发展。     

F Nuclear Magnetic Resonance Analysis of 5-Fluorouracil Metabolism in Four Differently Pigmented Strains of Nectria haematococca

F nuclear magnetic resonance spectroscopy was used to study the metabolism of 5-fluorouracil in four strains of Nectria haematococca which displayed similar sensitivities to growth inhibition by this compound but differed in their pigmentation. The major metabolites, 5-fluorouridine and alpha-fluoro-beta-alanine, were excreted into the medium by all four strains. The classical ribofluoronucleotides (5-fluorouridine-5'-monophosphate, -diphosphate, and -triphosphate) and alpha-fluoro-beta-alanine were identified in the acid-soluble fraction of perchloric acid extracts of mycelia. Two hydrolysis products of 5-fluorouracil incorporated into RNA were found in the acid-insoluble pool. They were unambiguously assigned to 5-fluorouridine-2'-monophosphate and 3'-monophosphate with specific hydrolysis reactions on isolated RNA. The lack of fluorodeoxyribonucleotides and the fact that the four strains incorporated similar amounts of fluororibonucleotides into their RNAs strongly suggest an RNA-directed mechanism of cytotoxicity for 5-fluorouracil. The heavily pigmented wild type differed from the three low-pigmented strains in its low uptake of 5-fluorouracil and, consequently, in its reduced biosynthesis of 5-fluorouridine and alpha-fluoro-beta-alanine. At present, it is not clear whether this change in 5-fluorouracil metabolism is a side effect of pigment production or results from another event.     

Silencing of the MEG3 gene promoted anti-cancer activity and drug sensitivity in glioma

Aberrant expression of MEG3 has been shown in various cancers. The purpose of this study is to evaluate the effect of MEG3 on glioma cells and the use of potential chemotherapeutics in glioma by modulating MEG3 expression. Cell viability, migration and chemosensitivity were assayed. Cell death was evaluated in MEG3 overexpressing and MEG3 suppressed cells. MEG3 expression was compared in patient-derived glioma cells concerning IDH1 mutation and WHO grades. Silencing of MEG3 inhibited cell proliferation and reduced cell migration while overexpression of MEG3 promoted proliferation in glioma cells. MEG3 inhibition improved the chemosensitivity of glioma cells to 5-fluorouracil (5FU) but not to navitoclax. On the other hand, there is no significant effect of MEG3 expression on temozolamide (TMZ) treatment which is a standard chemotherapeutic agent in glioma. Suppression of the MEG3 gene in patient-derived oligodendroglioma cells also showed the same effect whereas glioblastoma cell proliferation and chemosensitivity were not affected by MEG3 inhibition. Further, as a possible cell death mechanism of action apoptosis was investigated. Although MEG3 is a widely known tumour suppressor gene and its loss is associated with several cancer types, here we reported that MEG3 inhibition can be used for improving the efficiency of known chemotherapeutic drug sensitivity. We propose that the level of MEG3 should be evaluated in the treatment of different glioma subtypes that are resistant to effective drugs to increase the potential effective drug applications.     

The Physical State of Viral Nucleic Acid and the Sensitivity of Viruses to Ultraviolet Light

Ultraviolet light action spectra in the range 2250 to 3020 A have been determined for the plaque-forming ability of the following bacteriophage and animal viruses: T-2, ϕx-174, R-17, fr, MS2, 7-S, fd, vesicular stomatitis, vaccinia, encephalomyocarditis, reovirus-3, and polyoma. Absolute quantum yields for the plaque-forming ability of MS2, fr, fd, ϕx-174, and T-2 were determined over the range 2250 to 3020 A. Relative quantum yields for plaque-forming ability indicated that viruses with single-stranded nucleic acid were on the average ten times more sensitive to UV than double-stranded viruses. In addition for ten of the twelve viruses a relation existed between the shape of their action spectra and the stranded state of their nucleic acid. The ratio of the inactivation cross-section at 2650 A to that at 2250 A for these viruses was 1.0 for single-stranded viruses and 2.0 for viruses with double-stranded nucleic acid. The above relations were dependent on the stranded state of the nucleic acid not the ribose or deoxyribose form of the sugar present.