The biological activity of platinum and methionine complexes: the antitumor action and inhibition of root growth by complexes of differing compositions and structures

The effect of 21 methionine-platinum(II) and (IV) complexes on growth and division of cells in maize seedling roots has been studied. The studied complexes did not possess properties inherent in typical cytostatic compounds, e.g. cis-dichlorodiammineplatinum (DDP). They inhibited root growth at higher concentrations as compared to DDP. In contrast to DDP, the studied complexes inhibited cell elongation to a similar or greater extent than cell division, did not prevent lateral root formation, and their inhibitory effect did not change with time. No correlation between the level of tumor growth inhibition and the pattern of root growth was observed.     

Pyrazolobenzodiazepines: Part I. Synthesis and SAR of a potent class of kinase inhibitors

A novel series of pyrazolobenzodiazepines 3 has been identified as potent inhibitors of cyclin-dependent kinase 2 (CDK2). Their synthesis and structure–activity relationships (SAR) are described. Representative compounds from this class reversibly inhibit CDK2 activity in vitro, and block cell cycle progression in human tumor cell lines. Further exploration has revealed that this class of compounds inhibits several kinases that play critical roles in cancer cell growth and division as well as tumor angiogenesis. Together, these properties suggest a compelling basis for their use as antitumor agents.     

Parallel solid synthesis of inhibitors of the essential cell division FtsZ enzyme as a new potential class of antibacterials

As a model system for designing new inhibitors of bacterial cell division, we studied the essential and highly conserved FtsZ GTPase from Pseudomonas aeruginosa. A collection of GTP analogues were prepared using the solid-phase parallel synthesis approach. The synthesized GTP analogues inhibited the GTPase activity of FtsZ with IC(50) values between 450microM and 2.6mM, and 5 compounds inhibited Staphylococcus aureus growth in a biological assay. The FtsZ spectrophotometric assay developed for screening of synthesized compounds is the first step in identification of antibacterials targeting the bacterial cell division essential proteins.     

Choline chloride effect on chloroplast ultrastructure and cell growth in Chlamydomonas reinhardtii

The influence of growth retardant choline chloride (0.02, 0.2 and 2 g/l) on cell size and division as well as chlorophyll accumulation and chloroplast ultrastructure of unicellular green algae Chlamydomonas was studied. It was shown that at any concentration used (0.02, 0.2, and 2 g/l) choline chloride decreased the rate of cell division. The content of chlorophyll and carotenoid per cell decreased and the sizes of cells increased at all concentrations of choline chloride. On the basis of electron microscopy data, the conclusion was made that an increase in the concentration of choline chloride intensified destruction processes in membranes of chloroplasts and other cell organelles.     

Structure-based virtual screening of novel tubulin inhibitors and their characterization as anti-mitotic agents

Microtubule cytoskeletons are involved in many essential functions throughout the life cycle of cells, including transport of materials into cells, cell movement, and proper progression of cell division. Small compounds that can bind at the colchicine site of tubulin have drawn great attention because these agents can suppress or inhibit microtubule dynamics and tubulin polymerization. To find novel tubulin polymerization inhibitors as anti-mitotic agents, we performed a virtual screening study of the colchicine binding site on tubulin. Novel tubulin inhibitors were identified and characterized by their inhibitory activities on tubulin polymerization in vitro. The structural basis for the interaction of novel inhibitors with tubulin was investigated by molecular modeling, and we have proposed binding models for these hit compounds with tubulin. The proposed docking models were very similar to the binding pattern of colchicine or podophyllotoxin with tubulin. These new hit compound derivatives exerted growth inhibitory effects on the HL60 cell lines tested and exhibited strong cell cycle arrest at G2/M phase. Furthermore, these compounds induced apoptosis after cell cycle arrest. In this study, we show that the validated derivatives of compound 11 could serve as potent lead compounds for designing novel anti-cancer agents that target microtubules.     

Growth and morphology of Asticcacaulis biprosthecum in defined media

The growth and morphology of cells of Asticcacaulis biprosthecum were studied in defined media to determine the effects of various compounds on the growth rate and on the expression of morphological events of the life cycle. The length of prosthecae could not be controlled by varying the concentration of inorganic phosphate as has been shown for other caulobacters. In defined media, growth was inhibited during conditions favoring rapid metabolism, apparently due to an absolute requirement for cells to complete all stages of the life cycle before cell division could occur. The morphology of cells grown under these conditions was aberrant, i.e., cells appeared elongated and branched and few prosthecae or swarmer cells were produced. Growth of a related bacterium, Asticcacaulis strain S-3, was not inhibited by conditions favoring rapid metabolism. During rapid growth, cell division in this organism occurs in the swarmer stage and prosthecae are not produced. Cell division in S-3 is not obligately coupled to completion of all stages in the complex life cycle, and morphogenesis can be controlled by cultural conditions.     

Growth patterns and alkaloid accumulation in hairy root and untransformed root cultures of Datura stramonium

The aim of this work was to study the possible relationship between alkaloid production and growth measured as: biomass increase and cellular division frequency, in Datura stramonium in vitro root cultures (hairy root and normal cultures). A comparison of growth values on a fresh and dry weight basis showed that there were differences between transformed and non-transformed lines. The differential growth between lines occurred due to a real biomass increase and not because of water accumulation. On the other hand, the rate of cell division showed a similar pattern for all lines studied. Therefore, the differences in growth are not due to different cell division rates, nor to the presence of larger meristems, but to the development and growth of lateral roots and the presence of active intercalary meristematic zones in each line. The maximum alkaloid production occurred when the cultures were not growing. This suggests an inverse relationship. Finally, the data support a specific model of growth at the level of cell division in root cultures which has not been described before in the literature. This revised version was published online in June 2006 with corrections to the Cover Date.     

Studies on the expression of a mutant with abnormal cell division in Chlamydomonas reinhardi

A mutant of Chlamydomonas reinhardi, in which cell and nuclear division are no longer synchronised, has been compared with wild type with the aim of clarifying the nature of the difference between the two strains. On entry into stationary phase, wild type cultures show a marked increase in protein, RNA and chlorophyll per cell, whereas mutant cultures do not show a comparable increase. The effect of chemicals which may interfere with particular aspects of the cell division process on the expression of the mutant have been studied. Vitamin B12 and the related compounds, benzimidazole, 5,6,dimethylbenzimidazole and cobaltous chloride increase the asynchrony between cell and nuclear division and consequently lead to the accumulation of large multinucleate cells. The mutant is less resistant than wild type to the inhibitory effects of caffeine.     

Cholesterogenesis and cell division in phytohemagglutinin-stimulated human lymphocytes: a comparative study with several inhibitors

It has been shown that when lymphocytes are stimulated by phytohemagglutinin the expected stimulation of DNA synthesis is preceded by stimulation of cholesterol synthesis. This confirms the existence of a relation between cell division and cholesterol synthesis. We studied the effect on cell division of six inhibitors of cholesterol biosynthesis, previously shown to interfere with different steps of the process: 7 beta-hydroxycholesterol, 25-hydroxycholesterol, lanost-7-en-3 beta, 32-diol, mevinolin, propiconazole, dodecylimidazole. Since experiments were performed in the presence of a high percentage of human serum, which provided cells with exogenous cholesterol via the LDL-receptor pathway, our investigation was focused on the role of newly synthesized cholesterol. The biosynthesis was evaluated by labeling cells with [14C]sodium acetate; to take into account variations of cell permeability to sodium acetate, the results were expressed as the percentage of total cellularly incorporated radioactivity transformed into cholesterol, after separation from all other labeled metabolites. These data were compared with the percentage of transformation into nonsaponifiable lipids, which varied in parallel with HMG-CoA reductase activity, as confirmed by direct enzymatic measurement. Cell division was assessed by simultaneous measurements of three parameters: thymidine incorporation into DNA, cell proliferation and cellular protein content. All the effectors strongly inhibited the conversion of labeled acetate into cholesterol, but cell division was not inhibited by two of them: propiconazole and 7 beta-hydroxycholesterol. These compounds only slightly inhibited the synthesis of nonsaponifiable lipids, which mainly consisted of methylsterols resulting from a blockage of lanosterol demethylation. Thus, it can be concluded that the nonsaponifiable metabolite essential for cell growth is not newly synthesized cholesterol. It was also found that inhibitors affected cell division only when they were added to the culture medium before the decline of cholesterol synthesis stimulation.     

The effect of the diterpene 5-epi-icetexone on the cell cycle of Trypanosoma cruzi

Numerous natural compounds have been used against Trypanosoma cruzi, the causative agent of Chagas' disease. Here, we studied the effect of the diterpene 5-epi-icetexone on growth and morphology of parasites synchronized with hydroxyurea, at different periods of time after removal of the nucleotide. We observed that the diterpene does not affect the growth of the parasites when added within 10 h after removal of hydroxyurea, but the compound was effective on growth when added to the cultures after 12 h. Thymidine incorporation was somewhat inhibited when the diterpene was added at 12 h after removal of hydroxyurea, possibly on the transition S/G2. Using transmission electron microscopy we observed that the diterpene induced a delay in the progression of cell division. We conclude that the compound, at cytostatic dose, affects the cell cycle of T. cruzi, possibly in the transition S/G2 phase and cell division. Further studies will focus to identify the molecular targets for the action of 5-epi-icetexone.     

The extracellular matrix guides the orientation of the cell division axis

The cell division axis determines the future positions of daughter cells and is therefore critical for cell fate. The positioning of the division axis has been mostly studied in systems such as embryos or yeasts, in which cell shape is well defined. In these cases, cell shape anisotropy and cell polarity affect spindle orientation. It remains unclear whether cell geometry or cortical cues are determinants for spindle orientation in mammalian cultured cells. The cell environment is composed of an extracellular matrix (ECM), which is connected to the intracellular actin cytoskeleton via transmembrane proteins. We used micro-contact printing to control the spatial distribution of the ECM on the substrate and demonstrated that it has a role in determining the orientation of the division axis of HeLa cells. On the basis of our analysis of the average distributions of actin-binding proteins in interphase and mitosis, we propose that the ECM controls the location of actin dynamics at the membrane, and thus the segregation of cortical components in interphase. This segregation is further maintained on the cortex of mitotic cells and used for spindle orientation.     

Spatial distribution of cell division rate can be deduced from that of p34(cdc2) kinase activity in maize leaves grown at contrasting temperatures and soil water conditions

We have investigated the spatial distributions of cell division rate, p34(cdc2) kinase activity, and amount of p34(cdc2a) in maize (Zea mays) leaves grown at contrasting temperatures and soil water conditions. An original method for calculating cell division rate in all leaf tissues is proposed. In all studied conditions, cell division rate was stable and maximum in the first 2 cm beyond the leaf insertion point, declined afterward, and reached zero at 7 cm from the insertion point. The spatial distribution of p34(cdc2) kinase activity, expressed on a per cell basis, followed the same pattern. In contrast, the amount of p34(cdc2a) was maximum in the first centimeter of the leaf, declined afterward, but remained at 20% of maximum in more distal zones with a near-zero cell division rate. A mild water deficit caused a reduction in cell division rate and p34(cdc2) kinase activity by approximately 45% in all leaf zones, but did not affect the amount of p34(cdc2a). Growth temperature affected to the same extent cell division rate and p34(cdc2) kinase activity, but only if p34(cdc2) kinase activity was assayed at growth temperature, and not if a standard temperature was used in all assays. A common linear relationship between cell division rate and p34(cdc2) kinase activity applied to all causes of changes in cell division rate, i.e. cell aging, water deficit, or changes in temperature. It is shown that temperature has two distinct and additive effects on p34(cdc2) kinase activity; first, an effect on the rate of the reaction, and second, an effect on the amount of p34(cdc2a).     

Structures of potent anticancer compounds bound to tubulin

Small molecules that bind to tubulin exert powerful effects on cell division and apoptosis (programmed cell death). Cell‐based high‐throughput screening combined with chemo/bioinformatic and biochemical analyses recently revealed a novel compound MI‐181 as a potent mitotic inhibitor with heightened activity towards melanomas. MI‐181 causes tubulin depolymerization, activates the spindle assembly checkpoint arresting cells in mitosis, and induces apoptotic cell death. C2 is an unrelated compound previously shown to have lethal effects on microtubules in tumorigenic cell lines. We report 2.60 Å and 3.75 Å resolution structures of MI‐181 and C2, respectively, bound to a ternary complex of αβ‐tubulin, the tubulin‐binding protein stathmin, and tubulin tyrosine ligase. In the first of these structures, our crystallographic results reveal a unique binding mode for MI‐181 extending unusually deep into the well‐studied colchicine‐binding site on β‐tubulin. In the second structure the C2 compound occupies the colchicine‐binding site on β‐tubulin with two chemical moieties recapitulating contacts made by colchicine, in combination with another system of atomic contacts. These insights reveal the source of the observed effects of MI‐181 and C2 on microtubules, mitosis, and cultured cancer cell lines. The structural details of the interaction between tubulin and the described compounds may guide the development of improved derivative compounds as therapeutic candidates or molecular probes to study cancer cell division.     

Untersuchungen über Beziehungen zwischen Zellteilung und Morphogenese bei Gewebekulturen von Daucus carota

Relationship between cell division and morphogenesis of tissue cultures of Daucus carota. I. Observations on rhizogenesis and formation of whole plants.—By using a chemically defined medium the conditions for formation of roots and embryos in callus of various tap root parts of domestic Daucus carota forms were investigated and compared. Whole carrot plants capable of generative reproduction were produced from callus as well as from cell and tissue suspensions. The influence of various phytohormones on differentiation and cell division activity of explants was studied. A close relationship between cell division activity and differential stains was established and explained as a result of the phytohormone action on the cell division rate.     

Potassium Uptake in Synchronous and Synchronized Cultures of Escherichia coli

Criteria are presented for distinguishing between synchronous and synchronized cultures (natural vs. forced synchrony) on the basis of characteristics of growth and division during a single generation. These criteria were applied in an examination of the uptake of potassium during the cell growth and division cycle in synchronous cultures and in a synchronized culture of Escherichia coli. In the synchronous cultures the uptake of ⁴²K doubled synchronously with cell number, corresponding to a constant rate of uptake per cell throughout the cell cycle. In the synchronized culture, uptake rates also remained constant during most of the cycle, but rates doubled abruptly well within the cycle. This constancy of ⁴²K uptake per cell supports an earlier interpretation for steady-state cultures that uptake is limited in each cell by a constant number of functional sites for binding, transport, or accumulation of compounds from the growth medium, and that the average number of such sites doubles late in each cell cycle. The abrupt doubling of the rate of uptake of potassium per cell in the synchronized culture appears because of partial uncoupling of cell division from activation or synthesis of these uptake sites.     

The effect of nitrogen starvation on the ultrastructure and pigment composition of chloroplasts in the acidothermophilic microalga Galdieria sulphuraria

We studied the effect of nitrogen starvation on growth indices, vitality, ultrastructure, and the photosynthetic apparatus of unique acidothermophilic microalga Galdieria sulphuraria (Galdieri) Merola. Long-term nitrogen starvation ceased G. sulphuraria growth and cell division. During the first days of starvation, phycobiliproteins degraded first, then the content of chlorophyll and carotenoids decreased to trace amounts, chloroplast reduced, cell wall became thinner, and storage compounds accumulated. However, the cells were alive. A comparison with the effects of nitrogen starvation on other photosynthesizing organisms showed that suppression of cell division, reduction of the photosynthetic apparatus to some minimum, and accumulation of storage compounds are a universal response to this stress.     

Studies on plant growth-regulating substances

A report of an alkoxypurine showing cytokinin activity is presented. This compound, 6-benzyloxypurine, has been tested in three tests and in two of these, a wheat leaf senescence and a young coleoptile test, the compound is as active as benzyladenine or kinetin. Although it is much less effective on molar basis than these compounds in a tobacco tissue culture test, it is as active at its optimum concentration. In addition to promoting cell division the presence of 6-benzyloxypurine leads to morphological differentiation within the tobacco stem tissue, and whole plants have been grown without altering the nutrient medium.     

Synchronous Division of an Endosymbiotic Methanogenic Bacterium In the Anaerobic Ciliate Plagiopyla Frontata Kahl

ABSTRACT The life cycle of a methanogenic bacterium, symbiotic within the marine, free-living anaerobic ciliate Plagiopyla frontata , was studied using light microscopy and transmission electron microscopy (TEM). the bacteria are disc-shaped. During the growth phase of the host, bacteria and hydrogenosomes (organelles which ferment pyruvate into acetate and hydrogen) are arranged in conglomerates resembling stacks of coins in which bacteria and hydrogenosomes alternate; hydrogenosomes always cap the ends of the stacks. During the growth phase, numbers of hydrogenosomes and bacteria remain constant (about 5,000 and 3,500 per cell, respectively). Hydrogenosomes increase in volume shortly after cell division. Methanogens increase in volume slowly during the growth phase of the ciliate and rapidly when the ciliate begins to divide. the hydrogenosomes divide mainly during the initial phases of cell division while the methanogens divide synchronously during the last phase of ciliate division. the timing of reproduction of the symbionts is controlled by the host-cell cycle. the ciliate is known to receive an energetic advantage from its symbionts. the suppression of continuous bacterial reproduction may trigger the secretion of excess bacterial production as soluble organic compounds, for use by the ciliate.     

Effects of copper and zinc on growth,morphology, and metabolism of Asterionella japonica (Cleve) 1

When exposed to elevated levels of copper or zinc, the diatom Asterionella japonica (Cleve) showed a reduced cell division rate and a marked increase in cell size. Metal-treated cells had greater cell volumes, dry weights, carbon, nitrogen, chlorophyll, and DNA contents, all in approximately the same proportion as control cells. Two protoplasts often appeared to be contained within one frustule. Metal-treated cells photosynthesized at near-normal rates on a per chlorophyll basis and above normal rates on a per cell basis. Excretion of photosynthetically fixed carbon was depressed by metal treatment; 10–22% of fixed carbon was excreted in control cells and typically less than 1% in treated cells. Thus, metal-treated cells showed an uncoupling of photosynthesis from cell division and continued to enlarge when fixed carbon could not be excreted or utilized in cell division.Uptake of sulphate and silicic acid proceeded at slower rates than other processes (e.g., nitrogen uptake or photosynthesis) in copper-treated cells. Free amino acids in copper-treated cells totalled ≈ 10% of control cell levels, with greatest proportional declines in methionine, cysteine, aspartic acid, valine, and isoleucine. Copper-treated cells resuspended in fresh medium shrank to normal size when exposed to methionine (which they accumulated), although cell division rates did not return to normal. These cells excreted 2–3 times as much fixed carbon as comparable EDTA-treated or untreated cells, neither of which decreased in size. Copper-treated cells appeared indistinguishable from silicon-limited cells (i.e., cells not dividing for lack of silicon) in a copper-free medium. Cells treated with the sulfhydryl binder PCMB divided at reduced rates and also swelled in a manner comparable to copper-treated cells. The results suggest that toxic metals may bind to sulfhydryl groups on cell membranes, impairing normal membrane function and reducing silicic acid uptake and amino-acid synthesis, thereby resulting in depressed cell division rates.