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Leslie Wilson

Publications and source records attributed to Leslie Wilson.

34 records · Page 2Linked to original sources
PubMed2004

Synergistic suppression of microtubule dynamics by discodermolide and paclitaxel in non-small cell lung carcinoma cells.

Discodermolide is a new microtubule-targeted antimitotic drug in Phase I clinical trials that, like paclitaxel, stabilizes microtubule dynamics and enhances microtubule polymer mass in vitro and in cells. Despite their apparently similar binding sites on microtubules, discodermolide acts synergistically with paclitaxel to inhibit proliferation of A549 human lung cancer cells (L. Martello et al., Clin. Cancer Res., 6: 1978-1987, 2000). To understand their synergy, we examined the effects of the two drugs singly and in combination in A549 cells and found that, surprisingly, their antiproliferative synergy is related to their ability to synergistically inhibit microtubule dynamic instability and mitosis. The combination of discodermolide and paclitaxel at their antiproliferative IC(50)s (7 nm for discodermolide and 2 nm for paclitaxel) altered all of the parameters of dynamic instability synergistically except the time-based rescue frequency. For example, together the drugs inhibited overall microtubule dynamicity by 71%, but each drug individually inhibited dynamicity by only 24%, giving a combination index (CI) of 0.23. Discodermolide and paclitaxel also synergistically blocked cell cycle progression at G(2)-M (41, 9.6, and 16% for both drugs together, for discodermolide alone, and for paclitaxel alone, respectively; CI = 0.59), and they synergistically enhanced apoptosis (CI = 0.85). Microtubules are unique receptors for drugs. The results suggest that ligands that bind to large numbers of binding sites on an individual microtubule can interact in a poorly understood manner to synergistically suppress microtubule dynamic instability and inhibit both mitosis and cell proliferation, with important consequences for combination clinical therapy with microtubule-targeted drugs.

Alkanes↗
PubMed2004

Antimitotic antifungal compound benomyl inhibits brain microtubule polymerization and dynamics and cancer cell proliferation at mitosis, by binding to a novel site in tubulin.

The antifungal agent benomyl [methyl-1-(butylcarbamoyl)-2-benzimidazolecarbamate] is used throughout the world against a wide range of agricultural fungal diseases. In this paper, we investigated the interaction of benomyl with mammalian brain tubulin and microtubules. Using the hydrophobic fluorescent probe 1-anilinonaphthalene-8-sulfonic acid, benomyl was found to bind to brain tubulin with a dissociation constant of 11.9 +/- 1.2 microM. Further, benomyl bound to at a novel site, distinct from the well-characterized colchicine and vinblastine binding sites. Benomyl altered the far-UV circular dichroism spectrum of tubulin and reduced the accessibility of its cysteine residues to modification by 5,5'-dithiobis-2-nitrobenzoic acid, indicating that benomyl binding to tubulin induces a conformational change in the tubulin. Benomyl inhibited the polymerization of brain tubulin into microtubules, with 50% inhibition occurring at a concentration of 70-75 microM. Furthermore, it strongly suppressed the dynamic instability behavior of individual brain microtubules in vitro as determined by video microscopy. It reduced the growing and shortening rates of the microtubules but did not alter the catastrophe or rescue frequencies. The unexpected potency of benomyl against mammalian microtubule polymerization and dynamics prompted us to investigate the effects of benomyl on HeLa cell proliferation and mitosis. Benomyl inhibited proliferation of the cells with an IC(50) of 5 microM, and it blocked mitotic spindle function by perturbing microtubule and chromosome organization. The greater than expected actions of benomyl on mammalian microtubules and mitosis together with its relatively low toxicity suggest that it might be useful as an adjuvant in cancer chemotherapy.

Animals↗
PubMed2004

Modulation of microtubule dynamics by tau in living cells: implications for development and neurodegeneration.

The neural microtubule-associated protein tau binds to and stabilizes microtubules. Because of alternative mRNA splicing, tau is expressed with either 3 or 4 C-terminal repeats. Two observations indicate that differences between these tau isoforms are functionally important. First, the pattern of tau isoform expression is tightly regulated during development. Second, mutation-induced changes in tau RNA splicing cause neuronal cell death and dementia simply by altering the isoform expression ratio. To investigate whether 3- and 4-repeat tau differentially regulate microtubule behavior in cells, we microinjected physiological levels of these two isoforms into EGFP-tubulin-expressing cultured MCF7 cells and measured the effects on the dynamic instability behavior of individual microtubules by time-lapse microscopy. Both isoforms suppressed microtubule dynamics, though to different extents. Specifically, 4-repeat tau reduced the rate and extent of both growing and shortening events. In contrast, 3-repeat tau stabilized most dynamic parameters about threefold less potently than 4-repeat tau and had only a minimal ability to suppress shortening events. These differences provide a mechanistic rationale for the developmental shift in tau isoform expression and are consistent with a loss-of-function model in which abnormal tau isoform expression results in the inability to properly regulate microtubule dynamics, leading to neuronal cell death and dementia.

Cell Line, Tumor↗
PubMed2004

Economic and psychologic costs for maternal caregivers of gastrostomy-dependent children.

OBJECTIVE: To examine the economic and psychologic costs of care provided by maternal caregivers to children with gastrostomy tube (GT) feedings. STUDY DESIGN: We conducted a 3-site study of primary maternal caregivers of 101 chronically ill children, with (n = 50) and without (n = 51) enteral nutrition support by GT to determine the time spent providing technical care, nontechnical care, and health care management and to assess depressive mood and quality of life. Associated costs were determined. RESULTS: Caregivers spent 339.7 +/- 34.1 (SEM) min/d to provide all care. Children with a GT required more than twice as much care time as children without a GT: 484.5 +/- 54.6 versus 197.8 +/- 30.6 min/d ( P < .0001). The mean annual total value of home care by the primary caregiver for a child with a GT was 37,232 dollars, compared with 15,004 dollars for the child without a GT. Caregivers of children with GT were no more depressed or less satisfied with their lives than caregivers of children without GT. CONCLUSIONS: Use of a GT for enteral nutrition support is associated with significant increased care time by the primary caregiver but not at additional psychologic cost compared with caring for chronically ill children.

Adult↗
PubMed2004

Resistance to microtubule-targeted cytotoxins in a K562 leukemia cell variant associated with altered tubulin expression and polymerization.

A vinblastine resistant cell line, KCVB2, was established by co-selecting the parental erythroleukemic cell line K562 with step-wise increased concentrations of vinblastine (Velban) in the presence of the cyclosporin D analogue PSC 833 (2 microM), a potent modulator of the multidrug resistance phenotype. KCVB2 cells are 8-fold resistant to the selecting agent, vinblastine, but also exhibit significant resistance to other vinca alkaloids, including 14-fold resistance to vinorelbine, as well as 6-fold cross-resistance to paclitaxel. Doubling time and morphology were similar to the parental K562 cells. Rt-PCR analysis revealed no alterations in the expression of the mdr1 and MRP genes. Intracellular vinblastine accumulation was unchanged. Disruption of the mitotic spindles and multiple mitotic asters occurred in both cell lines but required higher concentrations of vinblastine in KCVB2 cells than in K562 cells. Significant differences were observed in the tubulin content of KCVB2 cells: reduction of total tubulin content, increased polymerized fraction of total tubulin, and overexpression of class III beta-tubulin which is expressed at very low levels in the parental K562 cells. K562 cells transfected with murine class III beta-tubulin did not display the resistance pattern observed in KCVB2 cells. Revertants of KCVB2 manifested reversion to parental drug sensitivity, an increase in total tubulin level, and a decrease in polymerized tubulin. In conclusion, the KCVB2 cell line displays a novel mechanism of resistance to both depolymerizing and stabilizing microtubule-targeted cytotoxins which does not involve altered cellular drug accumulation, but corresponds to alterations in the total tubulin content and polymerization status, and may involve an effect on microtubule dynamics.

Antineoplastic Agents, Phytogenic↗
PubMed2003

Differential regulation of microtubule dynamics by three- and four-repeat tau: implications for the onset of neurodegenerative disease.

The microtubule (MT)-associated protein tau is important in neuronal development and in Alzheimer's and other neurodegenerative diseases. Genetic analyses have established a cause-and-effect relationship between tau dysfunction/misregulation and neuronal cell death and dementia in frontotemporal dementia and parkinsonism associated with chromosome 17; several mutations causing this dementia lead to increased ratios of four-repeat (4R) to three-repeat (3R) wild-type tau, and an attractive hypothesis is that the abnormally high ratio of 4R to 3R tau might lead to neuronal cell death by altering normal tau functions in adult neurons. Thus, we tested whether 3R and 4R tau might differentially modulate the dynamic instability of MTs in vitro using video microscopy. Although both isoforms promoted MT polymerization and decreased the tubulin critical subunit concentration to approximately similar extents, 4R tau stabilized MTs significantly more strongly that 3R tau. For example, 4R tau suppressed the shortening rate, whereas 3R tau had little or no detectable effect. Similarly, 3R tau had no effect on the length shortened during a shortening event, whereas 4R tau strongly reduced this parameter. Further, when MTs were diluted into buffer containing 4R tau, the MTs were stabilized and shortened slowly. In contrast, when diluted into 3R tau, the MTs were unstable and shortened rapidly. Thus, 4R tau stabilizes MTs differently and significantly more strongly than 3R tau. We suggest a "dosage effect" or haploinsufficiency model in which both tau alleles must be active and properly regulated to produce appropriate amounts of each tau isoform to maintain MT dynamics within a tolerable window of activity.

Alleles↗
PubMed2003

Suppression of centromere dynamics by Taxol in living osteosarcoma cells.

Taxol potently blocks mitosis at the transition from metaphase to anaphase, leading to apoptosis in many types of tumor cells. However, the precise mechanism of action of Taxol is not understood. Here we have tested the hypothesis that a primary mechanism of action of Taxol involves suppression of spindle microtubule dynamics. We have used centromere-binding protein B coupled to green fluorescent protein as a marker for the kinetochores and centromeres of chromosomes and analyzed the effects of low Taxol concentrations on the dynamics of centromeres during metaphase of mitosis in living human osteosarcoma (U2OS) cells by quantitative time-lapse confocal microscopy. In the absence of Taxol, the centromere pairs on attached sister chromatids alternately stretch apart and relax back together approximately 1.2 times/min due to tension on the kinetochores produced by the spindle microtubules (referred to here as centromere dynamics). We found that 50-100 nM Taxol significantly suppressed centromere dynamics. For example, Taxol reduced the mean separation distance between the sister centromeres from 0.73 to 0.65 microm, a distance equivalent to that observed in the complete absence of microtubules. The frequency of transitions between stretching and relaxing was also significantly diminished by Taxol (by 27%-35%). The suppressive effects of Taxol on centromere dynamics were associated with maximal accumulation of cells at mitosis (63%), a >90% block of the metaphase/anaphase transition, and complete inhibition of cell proliferation. The data strongly support the idea that the inhibition of centromere dynamics by Taxol prevents silencing of the mitotic spindle surveillance (checkpoint) mechanism. Because Taxol strongly suppresses microtubule dynamics, the data also indicate that centromere dynamics can be accounted for by microtubule dynamics and may not require significant energetic contributions from microtubule motors. The strict correlation between the degree of suppression of centromere dynamics by Taxol and the degree of mitotic block strongly indicates that the primary mechanism responsible for the mitotic block by Taxol in U2OS cells involves suppression of the polymerization dynamics of kinetochore microtubules.

Antineoplastic Agents, Phytogenic↗
PubMed2003

Dicoumarol: a unique microtubule stabilizing natural product that is synergistic with Taxol.

In studies on the antiproliferative actions of coumarin compounds, we discovered that dicoumarol (a coumarin anticoagulant; 3,3'-methylenebis[4-hydroxycoumarin]) inhibits the first cleavage of Strongylocentrotus purpuratus (sea urchin) embryos in a concentration-dependent manner with 50% inhibition occurring at a concentration of 10 microM. Because first cleavage in sea urchin embryos is highly selective for microtubule-targeted agents, we thought that the active compounds might inhibit cell division by interacting with tubulin or microtubules. We found that dicoumarol binds to bovine brain tubulin with a K(d) of 22 microM and that 0.1 microM dicoumarol strongly stabilizes the growing and shortening dynamics at the plus ends of the microtubules in vitro. Dicoumarol reduces the rate and extent of shortening, it increases the percentage of time the microtubules spend in an attenuated (paused) state, and it reduces the overall dynamicity of the microtubules. The antimitotic effects of the widely used cancer chemotherapeutic agent Taxol (paclitaxel) are also mediated by suppressing microtubule dynamics. We demonstrate that exposure to combinations of Taxol and dicoumarol results in a synergistic inhibition of cell division of sea urchin embryos. The results suggest that the antiproliferative mechanism of action of dicoumarol and possibly related pharmacophores may be mediated by tubulin binding and the stabilization of spindle microtubule dynamics. Because of its low toxicity and simple chemical structure, there is potential interest to explore combinations of antimitotic coumarins with other chemotherapeutic agents to improve efficacy and lower toxicity.

Animals↗
PubMed2003

Cost-effectiveness of intraoperative facial nerve monitoring in middle ear or mastoid surgery.

OBJECTIVES: Despite the utility of intraoperative facial nerve monitoring in reducing the risk of iatrogenic facial nerve injury during neurotologic surgery, its routine use during primary or revision surgery remains controversial. One of the major barriers to its acceptance is cost. This study evaluates the cost-effectiveness of intraoperative facial nerve monitoring during middle ear or mastoid surgery. RESEARCH DESIGN/METHODS: A simple decision analytic cost-effectiveness model and a societal approach were used to evaluate three cohorts of individuals who received (1) intraoperative facial nerve monitoring for both primary and revision middle ear or mastoid surgeries, or (2) facial nerve monitoring for revision surgeries only, or (3) no monitoring for any middle ear or mastoid surgeries. RESULTS: Our results strongly favored the use of intraoperative facial nerve monitoring in all patients undergoing middle ear or mastoid surgery, adding about $222.73 to $528.00 US dollars to the total cost. The strategy to monitor primary and revision surgeries had the greatest effectiveness and lowest cost, with an average quality-adjusted life-year (QALY) of 45.68 at an average cost of $238 US dollars. Facial nerve monitoring in revision patients only had similar QALYs (45.67) and higher costs ($292.1). Finally, the strategy not to monitor had the lowest QALY (45.65) and highest cost ($449.8). The analysis was robust across a wide range of changes in both costs and probabilities. CONCLUSIONS: Facial nerve monitoring is cost-effective, and its routine use should be adopted to reduce the risk of iatrogenic facial nerve injury during otologic surgery.

Cost-Benefit Analysis↗
PubMed2003

The effects of vinflunine, vinorelbine, and vinblastine on centromere dynamics.

Vinflunine is a novel fluorinated Vinca alkaloid currently in Phase II clinical trials, which in preclinical studies exhibited superior antitumor activity to that of two clinically useful Vinca alkaloids, vinorelbine and vinblastine. All three of the drugs block mitosis at the metaphase/anaphase transition, leading to apoptosis. The mechanism of the mitotic block is not known. On the basis of results with purified microtubules and in living interphase cells, we hypothesized that it involves suppression of spindle microtubule dynamics. Here we measured the effects of the three Vinca alkaloids on dynamics of centromeres and spindle kinetochore-microtubules by a novel approach involving quantitative time-lapse confocal microscopy in living mitotic human U2OS cells. Green fluorescent protein-labeled centromere-binding protein B was used to mark centromeres and kinetochore-microtubule plus ends. In controls, pairs of centromeres on sister chromatids alternated under tension between increasing and decreasing separation (stretching and relaxing). All three of the Vinca alkaloids suppressed centromere dynamics similarly at concentrations that block mitosis. At concentrations approximating the IC(50)s for mitotic accumulation (18.8 nM vinflunine, 7.3 nM vinorelbine, and 6.1 nM vinblastine), centromere dynamicity decreased by 44%, 25%, and 26%, respectively, and the time centromeres spent in a paused state increased by 63%, 52%, and 36%, respectively. Centromere relaxation rates, stretching durations, and transition frequencies all decreased. Thus all three of the drugs decreased the normal microtubule-dependent spindle tension at the centromeres/kinetochores, thereby preventing the signal for mitotic checkpoint passage. The strong correlation between suppression of kinetochore-microtubule dynamics and mitotic block indicates that the primary mechanism by which the Vinca alkaloids block mitosis is suppression of spindle microtubule dynamics.

Antineoplastic Agents, Phytogenic↗
PubMed2003

Suppression of microtubule dynamics by discodermolide by a novel mechanism is associated with mitotic arrest and inhibition of tumor cell proliferation.

Discodermolide is a new microtubule-targeted drug in Phase I clinical trials that inhibits tumor growth and induces G(2)-M cell cycle arrest. It is effective against paclitaxel-resistant cell lines and acts synergistically in combination with paclitaxel. Suppression of microtubule dynamics by microtubule-targeted drugs has been hypothesized to be responsible for their ability to inhibit mitotic progression and cell proliferation. To determine whether discodermolide blocks mitosis by an effect on microtubule dynamics, we analyzed the effects of discodermolide on microtubule dynamics in living A549 human lung cancer cells during interphase at concentrations that block mitosis and inhibit cell proliferation. We found that discodermolide (7-166 nM) significantly suppressed microtubule dynamic instability. At the IC(50) for proliferation (7 nM discodermolide, 72 h), overall dynamicity was reduced by 23%. The principal parameters of dynamic instability suppressed by discodermolide were the microtubule shortening rate and length shortened. In addition, discodermolide markedly increased the frequency of rescued catastrophes. At the discodermolide concentration that resulted in 50% of maximal mitotic block (83 nM, 20 h), most microtubules were completely non-dynamic, no anaphases occurred, and all spindles were abnormal. The dynamicity of the remaining dynamic microtubules was reduced by 62%. The results indicate that a principal mechanism of inhibition of cell proliferation and mitotic block by discodermolide is suppression of microtubule dynamics. Importantly, the results indicate significant additional stabilizing effects of discodermolide on microtubule dynamics as compared with those of paclitaxel that may in turn reflect differences in their binding sites and their effects on tubulin conformation.

Alkanes↗
PubMed2002

Intrinsically slow dynamic instability of HeLa cell microtubules in vitro.

The dynamic behavior of mammalian microtubules has been extensively studied, both in living cells and with microtubules assembled from purified brain tubulin. To understand the intrinsic dynamic behavior of mammalian nonneural microtubules, we purified tubulin from cultured HeLa cells. We find that HeLa cell microtubules exhibit remarkably slow dynamic instability, spending most of their time in an attenuated state. The tempered dynamics contrast sharply with the dynamics of microtubules prepared from purified bovine brain tubulin under similar conditions. In accord with their minimal dynamic instability, assembled HeLa cell microtubules displayed a slow treadmilling rate and a low guanosine-5'-triphosphate hydrolysis rate at steady state. We find that unlike brain tubulin, which consists of a heterogeneous mixture of beta-tubulin isotypes (beta(II), beta(III), and beta(IV) and a low level of beta(I)), HeLa cell tubulin consists of beta(I) tubulin ( approximately 80%) and a minor amount of beta(IV) tubulin ( approximately 20%). The slow dynamic behavior of HeLa cell microtubules in vitro differs strikingly from the dynamic behavior of microtubules in living cultured mammalian cells, supporting the idea that accessory factors create the robust dynamics that occur in cells.

Animals↗
PubMed2002

Minor alteration of microtubule dynamics causes loss of tension across kinetochore pairs and activates the spindle checkpoint.

We have previously identified the opium alkaloid noscapine as a microtubule interacting agent that binds stoichiometrically to tubulin and alters its conformation. Here we show that, unlike many other microtubule inhibitors, noscapine does not significantly promote or inhibit microtubule polymerization. Instead, it alters the steady-state dynamics of microtubule assembly, primarily by increasing the amount of time that the microtubules spend in an attenuated (pause) state. Further studies reveal that even at high concentrations, noscapine does not alter the tubulin polymer/monomer ratio in HeLa cells. Cells treated with noscapine arrest at mitosis with nearly normal bipolar spindles. Strikingly, although most of the chromosomes in these cells are aligned at the metaphase plate, the rest remain near the spindle poles, both of which exhibit loss of tension across kinetochore pairs. Furthermore, levels of the spindle checkpoint proteins Mad2, Bub1, and BubR1 decrease by 138-, 3.7-, and 3.9-fold, respectively, at the kinetochore region upon chromosome alignment. Our results thus suggest that an exquisite control of microtubule dynamics is required for kinetochore tension generation and chromosome alignment during mitosis. Our data also support the idea that Mad2 and Bub1/BubR1 respond to kinetochore-microtubule attachment and/or tension to different degrees.

Animals↗
PubMed2002

Determination of the size and chemical nature of the stabilizing "cap" at microtubule ends using modulators of polymerization dynamics.

The size and chemical nature of the stabilizing cap at microtubule (MT) ends has remained enigmatic, in large part because it has been difficult to detect and measure it directly. By pulsing steady-state suspensions of bovine brain microtubules (MTs) with trace quantities of [gamma(32)P]GTP and sedimenting the MTs through 50% sucrose cushions to reduce background contaminating (32)P to negligible levels, we were able to detect a small number of (32)P molecules that remain stably bound to the MTs (a mean of 25.5 molecules of (32)P per MT). Analysis of the chemical form of the stably bound (32)P by thin-layer chromatography revealed that it was all (32)P-orthophosphate ((32)P(i)). The (32)P(i) was determined to be located at the MT ends because colchicine and vinblastine, drugs that suppress tubulin incorporation into the MT by binding specifically at MT ends, reduced the quantity of the stably bound (32)P(i). Taxol, a drug that stabilizes MT dynamics by binding along the MT surface rather than at the ends, did not affect the stoichiometry of the bound (32)P(i). If the bound (32)P is equally distributed between the two ends, each end would contain 12-13 molecules of (32)P(i). Beryllium fluoride (BeF(3-)) and aluminum fluoride (AlF(4-)), inorganic phosphate analogues, suppressed the dynamic instability behavior of individual MTs and, thus, stabilized them. For example, BeF(3-) (70 microM) reduced the MT shortening rate by 2.5-fold and decreased the transition frequency from the growing or the attenuated state to rapid shortening by 2-fold. The data support the hypothesis that the stabilizing cap at MT ends consists of a single layer of tubulin GDP-P(i) subunits. The data also support the hypothesis that the mechanism giving rise to the destabilized GDP-tubulin core involves release of P(i) rather than hydrolysis of the GTP.

Aluminum Compounds↗
PubMed2002

Effects of novel taxanes SB-T-1213 and IDN5109 on tubulin polymerization and mitosis.

SB-T-1213 and IDN5109 are semisynthetic, orally available taxanes that are up to 400-fold more active than paclitaxel against drug-resistant cells. IDN5109 is in clinical trials. We investigated the primary target for SB-T-1213 and IDN5109 and whether the compounds interact with microtubules differently than paclitaxel. Unlike paclitaxel, at 1-10 microM both novel taxanes initiate microtubule polymerization in vitro with no lag. They enhance polymerization equally or more potently than paclitaxel. SB-T-1213 induces unusual microtubules with attached extra protofilaments or open sheets, and IDN5109 induces large protofilamentous sheets. Both inhibit HeLa cell proliferation, block mitosis at the metaphase/anaphase transition, bundle microtubules at high drug concentrations, and induce abnormal metaphase spindles and apoptosis. They target microtubules but alter their polymerization and structure differently than paclitaxel. These differences may play a role in their enhanced cytotoxicity and efficacy.

Antineoplastic Agents, Phytogenic↗