Natural products as new antimitotic compounds for anticancer drug development

Cell cycle control genes are frequently mutated in cancer cells, which usually display higher rates of proliferation than normal cells. Dysregulated mitosis leads to genomic instability, which contributes to tumor progression and aggressiveness. Many drugs that disrupt mitosis have been studied because they induce cell cycle arrest and tumor cell death. These antitumor compounds are referred to as antimitotics. Vinca alkaloids and taxanes are natural products that target microtubules and inhibit mitosis, and their derivatives are among the most commonly used drugs in cancer therapy worldwide. However, severe adverse effects such as neuropathies are frequently observed during treatment with microtubule-targeting agents. Many efforts have been directed at developing improved antimitotics with increased specificity and decreased likelihood of inducing side effects. These new drugs generally target specific components of mitotic regulation that are mainly or exclusively expressed during cell division, such as kinases, motor proteins and multiprotein complexes. Such small molecules are now in preclinical studies and clinical trials, and many are products or derivatives from natural sources. In this review, we focused on the most promising targets for the development of antimitotics and discussed the advantages and disadvantages of these targets. We also highlighted the novel natural antimitotic agents under investigation by our research group, including combretastatins, withanolides and pterocarpans, which show the potential to circumvent the main issues in antimitotic therapy.

Antimitotic and antimutagenic action of the Hymenaea stigonocarpa bark on dividing cells / Ação antimitótica e antimutagênica do ritidoma de Hymenaea stigonocarpa Mart ex Hayne na divisão celular

Abstract The objective of this study was to evaluate the action of Hymenaea stigonocarpa bark hydroalcoholic extract against a mutagenic compound using A. cepa meristematic root cells as a test system. The treatment groups were: Negative Control (NC) – distilled water; Positive Control (PC) – paracetamol at a concentration of 0.008 mg/mL, Jatoba Control (JC) – aqueous fraction jatobá-do-cerrado at 0.5 or 1.0 or 1.5 mg/mL, and Simultaneous Treatment (ST) - jatobá-do-cerrado aqueous fraction at a concentration of 0.5 or 1.0 or 1.5 mg/mL associated with paracetamol solution at a concentration of 0.008 mg/mL. All groups were analyzed at 24 and 48 h. Five onion bulbs (five replications) were used for each treatment group. The root tips were fixed in Carnoy and slides prepared by the crush technique. Cells were analyzed throughout the cell cycle, totaling 5,000 for each treatment group at each exposure time. Mitotic indices were subjected to statistical analysis using the chi-square test (p<0.05). From the results it was found that the ST group, at the three concentrations, significantly potentiated the antiproliferative effect of the test system cells when compared to PC, NC and TJ at the three concentrations. Furthermore, the three ST concentrations significantly reduced the number of cell aberrations when compared to the number of aberrant cells obtained for the PC, demonstrating antimutagenic action on the A. cepa test system cells.

Resumo O objetivo do presente trabalho foi avaliar a ação do extrato hidroalcólico do ritidoma de Hymenaea stigonocarpa frente a um composto mutagênico, utilizando como sistema teste as células meristemáticas de raízes de A. cepa. Os grupos tratamentos avaliados foram: Controle Negativo (CN) – água destilada; Controle Positivo (CP) – paracetamol na concentração de 0,008 mg/mL, Controle Jatobá (CJ) – fração aquosa de jatobá-do-cerrado na concentração de 0,5 ou 1,0 ou 1,5 mg/mL, e Tratamento Simultâneo (TS) – fração aquosa de jatobá-do-cerrado na concentração de 0,5 ou 1,0 ou 1,5 mg/mL associada a solução de paracetamol na concentração de 0,008 mg/mL. Todos os grupos foram analisados nos tempos de 24 e 48 h. Para cada grupo tratamento cinco bulbos de cebolas (cinco repetições) foram utilizados. As radículas foram fixadas em Carnoy e as lâminas preparadas pela técnica de esmagamento. Analisaram-se células em todo ciclo celular, totalizando 5.000 para cada grupo tratamento em cada tempo de exposição. Os índices mitóticos obtidos foram submetidos à análise estatística do Qui-quadrado (p<0,05). A partir dos resultados verificou-se que o grupo TS, nas três concentrações, potencializou o efeito antiproliferativo significativo as células do sistema teste quando comparado ao CP, CN e TJ nas três concentrações. Ainda, o TS nas três concentrações reduziu de forma significativa o número de aberrações celulares quando comparado com o número de células aberrantes obtidas para o CP, demonstrando ação antimutagênica as células do sistema teste A. cepa.

Search of new Antimitotics compounds from the Cuban flora / Búsqueda de nuevos compuestos con actividad antimitótica en la flora cubana

The main objective of anti-carcinogenic chemotherapy is to stop uncontrolled cellular proliferation. This has prompted us to begin a systematic survey of new effective inhibitors with ability to react with cytoskeletal components and arrest living, dividing cells. Even for traditional populations herbs-consuming, encouraging the use of species with chemopreventive actions could be helpful as part of life expectancy improvement strategies. Herbal products have significantly lower costs, exhibit little or no toxicity during long-term oral administration and are relatively available at large scale. Current work involved the screening of 85 extracts from Cuban medicinal plants, selected on the basis of traditional use, ethnobotanics and pharmacological information (antiparasitic, antitumour, abortive, etc.). Antitubulinic activity in the hydroalcoholics extracts was evaluated by using a modified version of the conventional turbidity assay of tubulin assembly/ disassembly. The activity limits of the news isolated antitubulin agents were thoroughly investigated. According to the presented results, the extracts displaying the highest antitubulinic activity were Tamarindus indica L., Lawsonia inermes L and Xanthium strumarium L.

Detener la proliferación celular es el principal propósito de la quimioterapia anticarcinogénica. Para ello se ha realizado una búsqueda a partir de fuentes naturales de nuevos inhibidores efectivos que reaccionen con los componentes del citoesqueleto y puedan detener la división celular. En poblaciones que tradicionalmente utilizan plantas medicinales se estimula el uso de aquellas especies con acción quimiopreventivas como parte de una estrategia que contribuya a la calidad de vida. Los productos herbarios tienen costos significativamente más bajos, exhiben poca o ninguna toxicidad durante la administración oral a largo plazo y están al alcance de todos. Nuestro trabajo consistió en realizar un tamizaje de 85 extractos de plantas medicinales cubanas seleccionadas en base al uso tradicional, en las encuestas etnobotánicas e información farmacológica (actividad antiparasitaria, antitumoral, abortiva, etc). La actividad antitubulínica fue evaluada mediante una versión modificada del ensayo turbimétrico del ensamblaje/desensamblaje de la tubulina. Se determinó la actividad límite de los nuevos agentes antitubulínicos siendo los extractos de Tamarindus indica L., Lawsonia inermes L and Xanthium strumarium L. los de mejor actividad antitubulínica según las condiciones ensayadas.

Does usnic acid affect microtubules in human cancer cells? / O ácido úsnico pode afetar microtúbulos em células cancerosas humanas?

Usnic acid, a lichen metabolite, is known to exert antimitotic and antiproliferative activities against normal and malignant human cells. Many chemotherapy agents exert their activities by blocking cell cycle progression, inducing cell death through apoptosis. Microtubules, protein structure involved in the segregation of chromosomes during mitosis, serve as chemotherapeutical targets due to their key role in cellular division as well as apoptosis. The aim of this work was to investigate whether usnic acid affects the formation and/or stabilisation of microtubules by visualising microtubules and determining mitotic indices after treatment. The breast cancer cell line MCF7 and the lung cancer cell line H1299 were treated with usnic acid 29 µM for 24 hours and two positive controls: vincristine (which prevents the formation of microtubules) or taxol (which stabilizes microtubules). Treatment of MCF7 and H1299 cells with usnic acid did not result in any morphological changes in microtubules or increase in the mitotic index. These results suggest that the antineoplastic activity of usnic acid is not related to alterations in the formation and/or stabilisation of microtubules.

O ácido úsnico, um metabólito de liquens, é conhecido por sua atividade antimitótica e antiproliferativa em células humanas normais e malignas. Muitos quimioterápicos exercem suas atividades bloqueando a progressão do ciclo celular e induzindo morte celular por apoptose. Os microtúbulos, estruturas protéicas envolvidas na segregação dos cromossomos durante a mitose, servem como alvo quimioterapêutico devido ao seu importante papel tanto na divisão celular quanto nos mecanismos de morte celular por apoptose. O objetivo deste trabalho foi investigar se o ácido úsnico afeta a formação e/ou estabilização dos microtúbulos, a partir da visualização de microtúbulos e determinação de índices mitóticos após o tratamento. Células de câncer de mama MCF7 e de câncer de pulmão H1299 foram tratadas por 24 horas com 29 µM de ácido úsnico e dois controles positivos: vincristina (que impede a formação de microtúbulos) e taxol (que estabiliza microtúbulos). O tratamento das células MCF7 e H1299 com o ácido úsnico não resultou em aumento do índice mitótico. Os resultados sugerem que a atividade antineoplásica do ácido úsnico não está relacionada a alterações na formação e/ou estabilização de microtúbulos.