Indicine N-oxide binds to tubulin at a distinct site and inhibits the assembly of microtubules: a mechanism for its cytotoxic activity

Study of Cytotoxicity of Spiro-Fused [3-Azabicyclo[3.1.0]hexane]oxindoles and Cyclopropa[a]pyrrolizidine-oxindoles Against Tumor Cell Lines

Background: A series of spiro-fused heterocyclic compounds containing cyclopropa[a]pyrrolizidine-2,3'-oxindole and 3-spiro[3-azabicyclo[3.1.0]-hexane]oxindole frameworks were synthesized and studied for their in vitro antiproliferative activity against human erythroleukemia (K562), cervical carcinoma (HeLa), acute T cell leukemia (Jurkat), melanoma (Sk-mel-2) and breast cancer (MCF-7) as well as mouse colon carcinoma (CT26) cell lines. Methods: Cell proliferation was evaluated in vitro by MTS assay. Confocal microscopy was used to study actin cytoskeleton structure and cell motility. Cell cycle analysis was evaluated by flow cytometry. Results: It was found that compounds 4, 8, 18 and 24 showed antiproliferative activity against the Jurkat, K-562, HeLa and Sk-mel-2 cell lines with IC50 ranging from 2 to 10 μM (72 h). Evaluation of the impact on cell cycle progression showed that the tested compounds achieved significant cell-cycle perturbation with a higher accumulation of cells in the SubG1 and G0/G1 phases of the cell cycle, in comparison to the negative control. I Incubation with tested compounds led to the disappearance of stress fibers (granular actin was distributed diffusely in the cytoplasm in up to 38% of treated HeLa cells) and changes in the number of filopodia-like deformations (reduced from 93% in control cells to 64% after treatment). The impact on the Sk-mel-2 cell actin cytoskeleton structure was even greater: granular actin was distributed diffusely in the cytoplasm in up to 90% of treated cells while the number of filopodia-like deformations was reduced by up to 23%. A scratch test performed on the human melanoma cell line showed that these cells did not fill the scratched strip and lose their ability to move under treatment. Conclusions: The obtained results support the antitumor effect of the tested spiro-compounds and encourage the extension of this study in order to improve their anticancer activity as well as reduce their toxicological risks.

A Review on Bioactive Compounds, Ethnomedicinal Importance and Pharmacological Activities of Talinum triangulare (Jacq.) Willd

Talinum triangulare (Jacq.) Willd. is a traditional leafy vegetable used by tribal communities for ethnomedicinal and ethnoculinary preparations. This article reviews the current knowledge of its multiple uses, including pharmacological activities and nutritional composition. The literature survey shows that it has been traditionally useful in the treatment of several diseases, such as anaemia, diabetes, measles, and ulcers and the preparation of various traditional foods. Analysis of the literature on its phytochemicals shows its richness in bioactive compounds. Further, research also shows that this plant has antidiabetic, antiobesity, antitumor, antiulcer, hepatoprotective, and neuroprotective activities besides anti-inflammatory and antioxidant properties. Nutrient analysis of the plant reveals the presence of Ca, Zn, Fe, vitamins C and E, dietary fibre and protein in considerable quantities. The results of the pharmacological studies on the antidiabetic, antiulcer and anti-anaemic activities provide support in favour of its ethnomedicinal uses. The presence of bioactive compounds and pharmacological activities show the usefulness of this plant as a functional food.

Pyrrolizidine Alkaloids-Pros and Cons for Pharmaceutical and Medical Applications

Heterocyclic organic compounds named pyrrolizidine alkaloids (PAs) belong to a group of alkaloids and are synthesized by either plants or microorganisms. Therefore, they are naturally occurring secondary metabolites. They are found in species applied in the pharmaceutical and food industries, thus a thorough knowledge of their pharmacological properties and toxicology to humans is of great importance for their further safe employment. This review is original because it synthesizes knowledge of plant and microbial PAs, which is unusual in the scientific literature. We have focused on the Boraginaceae family, which is unique due to the exceptional richness and diversity of its PAs in plant species. We have also presented the microbial sources of PAs, both from fungi and bacteria. The structure and metabolism of PAs have been discussed. Our main aim was to summarize the effects of PAs on humans, including both negative, toxic ones, mainly concerning hepatotoxicity and carcinogenicity, as well as potentially positive ones for pharmacological and medical applications. We have collected the results of studies on the anticancer activity of PAs from plant and microbial sources (mainly Streptomyces strains) and on the antimicrobial activity of PAs on different strains of microorganisms (bacteria and fungi). Finally, we have suggested potential applications and future perspectives.

Natural Products as Anticancer Agents: Current Status and Future Perspectives

Natural products have been an invaluable and useful source of anticancer agents over the years. Several compounds have been synthesized from natural products by modifying their structures or by using naturally occurring compounds as building blocks in the synthesis of these compounds for various purposes in different fields, such as biology, medicine, and engineering. Multiple modern and costly treatments have been applied to combat cancer and limit its lethality, but the results are not significantly refreshing. Natural products, which are a significant source of new therapeutic drugs, are currently being investigated as potential cytotoxic agents and have shown a positive trend in preclinical research and have prompted numerous innovative strategies in order to combat cancer and expedite the clinical research. Natural products are becoming increasingly important for drug discovery due to their high molecular diversity and novel biofunctionality. Furthermore, natural products can provide superior efficacy and safety due to their unique molecular properties. The objective of the current review is to provide an overview of the emergence of natural products for the treatment and prevention of cancer, such as chemosensitizers, immunotherapeutics, combinatorial therapies with other anticancer drugs, novel formulations of natural products, and the molecular mechanisms underlying their anticancer properties.

Cytotoxic mechanism of tioconazole involves cell cycle arrest at mitosis through inhibition of microtubule assembly

Tioconazole is one of the drugs used to treat topical mycotic infections. It exhibited severe toxicity during systemic administration; however, the molecular mechanism behind the cytotoxic effect was not well established. We employed HeLa cells as a model to investigate the molecular mechanism of its toxicity and discovered that tioconazole inhibited HeLa cell growth through mitotic block (37%). At the half-maximal inhibitory concentration (≈ 15 μM) tioconazole apparently depolymerized microtubules and caused defects in chromosomal congression at the metaphase plate. Tioconazole induced apoptosis and significantly hindered the migration of HeLa cells. Tioconazole bound to goat brain tubulin (K _d, 28.3 ± 0.5 μM) and inhibited the assembly of microtubules in the in vitro assays. We report for the first time that tioconazole binds near to the colchicine site, based on the evidence from in vitro tubulin competition experiment and computational analysis. The conformation of tubulin dimer was found to be "curved" upon binding with tioconazole in the MD simulation. Tioconazole in combination with vinblastine synergistically inhibited the growth of HeLa cells and augmented the percentage of mitotic block by synergistically inhibiting the assembly of microtubules. Our study indicates that the systemic adverse effects of tioconazole are partly due to its effects on microtubules and cell cycle arrest. Since tioconazole is well tolerated at the topical level, it could be developed as a topical anticancer agent in combination with other systemic anticancer drugs.

GRAPHICAL ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10616-021-00516-w.

Securinine induces mitotic block in cancer cells by binding to tubulin and inhibiting microtubule assembly: A possible mechanistic basis for its anticancer activity

AIM

Analysis of the anticancer and antimitotic activity of the plant derived alkaloid securinine along with its effect on the organization of cellular microtubules as well as its binding with purified goat brain tubulin in-vitro.

MATERIALS AND METHODS

The cytotoxicity of securinine on different cell lines was conducted using SRB assay. The effect of securinine on the cellular microtubules was analyzed using immunofluorescence microscopy. The binding of securinine on purified goat brain tubulin was evaluated using fluorescent spectroscopy.

KEY FINDINGS

Securinine effectively prevented the proliferation of cervical, breast and lung cancer cells with an IC₅₀ of 6, 10 and 11 μM respectively and induced minimal toxicity in HEK cell line. Securinine at concentrations higher than IC₅₀ induced significant depolymerization in interphase and mitotic microtubules and it suppressed the reassembly of cold depolymerized spindle microtubules in HeLa cells. In the wound healing assay, securinine effectively suppressed the migration of HeLa cells to close the wound. Securinine bound to tubulin with a Kd of 9.7 μM and inhibited the assembly of tubulin into microtubules. The treatment with securinine induced a mitochondrial dependent ROS response in HeLa cells which enhanced the cytotoxic effect of securinine. The result from gene expression studies indicates that securinine induced apoptosis in MCF-7 cells through p53 dependent pathway.

SIGNIFICANCE

Considering the strong anticancer and anti-metastatic property and low toxicity in non-malignant cell lines, we suggest that securinine can be used as a chemotherapeutic drug either alone or in combination with other known anticancer molecules.

Heliotropium indicum L.: From Farm to a Source of Bioactive Compounds with Therapeutic Activity

This study aimed to summarize the available data on the ethnomedicinal and phytopharmacological activities of Heliotropium indicum L. based on database reports. For this purpose, an up-to-date literature search was carried out in the Google Scholar, Scopus, Springer Link, Web of Science, ScienceDirect, ResearchGate, PubMed, Chem Spider, Elsevier, BioMed Central, and patent offices (e.g., USPTO, CIPO, NPI, Google patents, and Espacenet) for the published materials. The findings suggest that the plant contains many important phytochemicals, including pyrrolizidine alkaloids, indicine, echinitine, supinine, heleurine, heliotrine, lasiocarpine, acetyl indicine, indicinine, indicine N-oxide, cynoglossine, europine N-oxide, heleurine N-oxide, heliotridine N-oxide, heliotrine N-oxide, heliotrine, volatile oils, triterpenes, amines, and sterols. Scientific reports revealed that the herb showed antioxidant, analgesic, antimicrobial, anticancer, antituberculosis, antiplasmodial, anticataract, antifertility, wound healing, antiinflammatory, antinociceptive, antihyperglycemic, anthelmintic, diuretic, antitussive, antiglaucoma, antiallergic, and larvicidal activity. In conclusion, in vitro studies with animal models seem to show the potential beneficial effects of H. indicum against a wide variety of disorders and as a source of phytotherapeutic compounds. However, clinical studies are necessary to confirm the effects observed in animal models, determine the toxicity of the therapeutic dose and isolate the truly bioactive components.

Vanadocene dichloride induces apoptosis in HeLa cells through depolymerization of microtubules and inhibition of Eg5

Vanadocene dichloride (VDC), a vanadium containing metallocene dihalide exhibits promising anticancer activity. However, its mechanism of action remains elusive as several diverse targets and pathways have been proposed for its anticancer activity. In this study, we observed that VDC inhibited the proliferation of mammalian cancer cells and induced apoptotic cell death by altering the mitochondrial membrane potential and the expression of bcl2 and bax. Probing further into its anticancer mechanism, we found that VDC caused depolymerization of interphase microtubules and blocked the cells at mitosis with considerable proportion of cells exhibiting monopolar spindles. The reassembly of cold depolymerized microtubules was strongly inhibited in the presence of 10 μM VDC. VDC perturbed the microtubule-kinetochore interactions during mitosis as indicated by the absence of cold stable spindle microtubules in the cells treated with 20 μM VDC. Using goat brain tubulin, we found that VDC inhibited the steady-state polymer mass of microtubules and bound to tubulin at a novel site with a K_d of 9.71 ± 0.19 μM and perturbed the secondary structure of tubulin dimer. In addition, VDC was also found to bind to the mitotic kinesin Eg5 and inhibit its basal as well as microtubule stimulated ATPase activity. The results suggest that disruption of microtubule assembly dynamics and inhibition of the ATPase activity of Eg5 could be a plausible mechanism for the antiproliferative and antimitotic activity of VDC.Graphic abstract.

Current Knowledge and Perspectives of Pyrrolizidine Alkaloids in Pharmacological Applications: A Mini-Review

Pyrrolizidine alkaloids (PAs) are a widespread group of secondary metabolites in plants. PAs are notorious for their acute hepatotoxicity, genotoxicity and neurological damage to humans and animals. In recent decades, the application of PAs for beneficial biological activities to cure disease has drawn greater attention. Here, we review the current knowledge regarding the pharmacological properties of PAs and discuss PAs as promising prototypes for the development of new drugs.

Direct preparation of unprotected aminimides (R3N+-NH-) from natural aliphatic tertiary alkaloids (R3N) by [Mn(TDCPP)Cl]-catalysed N-amination reaction

A panel of natural aliphatic tertiary alkaloids (R3N) were directly converted to R3N+-NH- (without the need to prepare protected aminimides R3N+-NR'- followed by deprotection) by [Mn(TDCPP)Cl]-catalysed N-amination reaction, with O-(2,4-dinitrophenyl)hydroxylamine as the nitrogen source, in up to 98% yields under mild reaction conditions.

Alkaloids for cancer prevention and therapy: Current progress and future perspectives

Alkaloids are important chemical compounds that serve as a rich source for drug discovery. Numerous alkaloids screened from medicinal plants and herbs showed antiproliferative and anticancer effects on wide category of cancers both in vitro and in vivo. Vinblastine, vinorelbine, vincristine, and vindesine have already been successfully developed as anticancer drugs. The available and up-to-date information on the ethnopharmacological uses in traditional medicine, phytochemistry, pharmacology and clinical utility of alkaloids were collected using various resources (PubMed, ScienceDirect, Google Scholar and Springerlink). In this article, we provide a comprehensive and critical overview on naturally-occurring alkaloids with anticancer activities and highlight the molecular mechanisms of action of these secondary metabolites. Furthermore, this review also presents a summary of synthetic derivatives and pharmacological profiles useful to researchers for the therapeutic development of alkaloids. Based on the literature survey compiled in this review, alkaloids represent an important group of anticancer drugs of plant origin with enormous potential for future development of drugs for cancer therapy and management.

Zerumbone, a cyclic sesquiterpene, exerts antimitotic activity in HeLa cells through tubulin binding and exhibits synergistic activity with vinblastine and paclitaxel

Objectives

The aim of this study was to elucidate the antimitotic mechanism of zerumbone and to investigate its effect on the HeLa cells in combination with other mitotic blockers.

Materials and methods

HeLa cells and fluorescence microscopy were used to analyse the effect of zerumbone on cancer cell lines. Cellular internalization of zerumbone was investigated using FITC‐labelled zerumbone. The interaction of zerumbone with tubulin was characterized using fluorescence spectroscopy. The Chou and Talalay equation was used to calculate the combination index.

Results

Zerumbone selectively inhibited the proliferation of HeLa cells with an IC₅₀ of 14.2 ± 0.5 μmol/L through enhanced cellular uptake compared to the normal cell line L929. It induced a strong mitotic block with cells exhibiting bipolar spindles at the IC₅₀ and monopolar spindles at 30 μmol/L. Docking analysis indicated that tubulin is the principal target of zerumbone. In vitro studies indicated that it bound to goat brain tubulin with a Kd of 4 μmol/L and disrupted the assembly of tubulin into microtubules. Zerumbone and colchicine had partially overlapping binding site on tubulin. Zerumbone synergistically enhanced the anti‐proliferative activity of vinblastine and paclitaxel through augmented mitotic block.

Conclusion

Our data suggest that disruption of microtubule assembly dynamics is one of the mechanisms of the anti‐cancer activity of zerumbone and it can be used in combination therapy targeting cell division.

Apoptotic and Anti-Inflammatory Effects of Eupatorium japonicum Thunb. in Rheumatoid Arthritis Fibroblast-Like Synoviocytes

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease characterized by synovitis, hyperplasia, and the destruction of bone and cartilage. A variety of immunosuppressive biological agents have been developed because the pathogenesis of RA is related predominantly to the inflammatory response. However, rheumatoid arthritis fibroblast-like synovial cells (RAFLS), which are known to play an important role in RA progression, exhibit resistance to immunosuppressants through cancer-like properties. In this study, we identified a novel therapeutic compound for RA, which reduced inflammation and the abnormal proliferation of RAFLS in natural product library made from Korean native plants. Eupatorium japonicum Thunb. (EJT) extract, a component of the natural product library, most effectively reduced viability through the induction of ROS-mediated apoptosis in a dose-dependent manner. In addition, the increased ROS induced the expression of ATF4 and CHOP, key players in ER stress-mediated apoptosis. Interestingly, EJT extract treatment dose-dependently reduced the expression of IL-1β and the transcription of MMP-9, which were induced by TNF-α treatment, through the inhibition of NF-κB and p38 activation. Collectively, we found that EJT extract exerted apoptotic effects through increases in ROS production and CHOP expression and exerted anti-inflammatory effects through the suppression of NF-κB activation, IL-1β expression, and MMP-9 transcription.

Indirubin, a bis-indole alkaloid binds to tubulin and exhibits antimitotic activity against HeLa cells in synergism with vinblastine

Indirubin, a bis-indole alkaloid used in traditional Chinese medicine has shown remarkable anticancer activity against chronic myelocytic leukemia. The present work was aimed to decipher the underlying molecular mechanisms responsible for its anticancer attributes. Our findings suggest that indirubin inhibited the proliferation of HeLa cells with an IC₅₀ of 40 μM and induced a mitotic block. At concentrations higher than its IC₅₀, indirubin exerted a moderate depolymerizing effect on the interphase microtubular network and spindle microtubules in HeLa cells. Studies with goat brain tubulin indicated that indirubin bound to tubulin at a single site with a dissociation constant of 26 ± 3 μM and inhibited the in vitro polymerization of tubulin into microtubules in the presence of glutamate as well as microtubule-associated proteins. Molecular docking analysis and molecular dynamics simulation studies indicate that indirubin stably binds to tubulin at the interface of the α-β tubulin heterodimer. Further, indirubin stabilized the binding of colchicine on tubulin and promoted the cysteine residue modification by 5,5'-dithiobis-2-nitrobenzoic acid, indicating towards alteration of tubulin conformation upon binding. In addition, we found that indirubin synergistically enhanced the anti-mitotic and anti-proliferative activity of vinblastine, a known microtubule-targeted agent. Collectively our studies indicate that perturbation of microtubule polymerization dynamics could be one of the possible mechanisms behind the anti-cancer activities of indirubin.

Pyrrolizidine Alkaloids: Chemistry, Pharmacology, Toxicology and Food Safety

Pyrrolizidine alkaloids (PA) are widely distributed in plants throughout the world, frequently in species relevant for human consumption. Apart from the toxicity that these molecules can cause in humans and livestock, PA are also known for their wide range of pharmacological properties, which can be exploited in drug discovery programs. In this work we review the current body of knowledge regarding the chemistry, toxicology, pharmacology and food safety of PA.

In vitro evaluation of the cytotoxic and bactericidal mechanism of the commonly used pesticide triphenyltin hydroxide

Triphenyltin hydroxide (TPTH) is a widely used pesticide that is highly toxic to a variety of organisms including humans and a potential contender for the environmental pollutant. In the present study, the cytotoxic mechanism of TPTH on mammalian cells was analyzed using HeLa cells and the antibacterial activity was analyzed using B. subtilis and E. coli cells. TPTH inhibited the growth of HeLa cells with a half-maximal inhibitory concentration of 0.25 μM and induced mitotic arrest. Immunofluorescence microscopy analysis showed that TPTH caused strong depolymerization of interphase microtubules and spindle abnormality with the appearance of colchicine type mitosis and condensed chromosome. TPTH exhibited high affinity for tubulin with a dissociation constant of 2.3 μM and inhibited the in vitro microtubule assembly in the presence of glutamate as well as microtubule-associated proteins. Results from the molecular docking and in vitro experiments implied that TPTH may have an overlapping binding site with colchicine on tubulin with a distance of about 11 Å between them. TPTH also binds to DNA at the A-T rich region of the minor groove. The data presented in the study revealed that the toxicity of TPTH in mammalian cells is mediated through its interactions with DNA and its strong depolymerizing activity on tubulin. However, its antibacterial activity was not through FtsZ, the prokaryotic homolog of tubulin but perhaps through its interactions with DNA.

Pyrrolizidine alkaloids: occurrence, biology, and chemical synthesis

Covering: 2013 up to the end of 2015This review covers the isolation and structure of new pyrrolizidines; pyrrolizidine biosynthesis; biological activity, including the occurrence of pyrrolizidines as toxic components or contaminants in foods and beverages; and formal and total syntheses of naturally-occurring pyrrolizidine alkaloids and closely related non-natural analogues.

Interim relative potency factors for the toxicological risk assessment of pyrrolizidine alkaloids in food and herbal medicines

Pyrrolizidine alkaloids (PAs) are among the most potent natural toxins occurring in a broad spectrum of plant species from various families. Recently, findings of considerable contamination of teas/herbal infusions prepared from non-PA plants have been reported. These are obviously due to cross-contamination with minor amounts of PA plants and can affect both food and herbal medicines. Another source of human exposure is honey collected from PA plants. These findings illustrate the requirement for a comprehensive risk assessment of PAs, hampered by the enormous number of different PA congeners occurring in nature. Up to now, risk assessment is based on the carcinogenicity of certain PAs after chronic application to rats using the sum of detected PAs as dose metric. Because of the well-documented large structure-dependent differences between sub-groups of PA congeners with respect to their genotoxicity and (cyto)toxicity, however, this procedure is inadequate. Here we provide an overview of recent attempts to assess the risk of PA exposure and the available literature on the toxic effects and potencies of different congeners. Based on these considerations, we have derived interim Relative Potency (REP) factors for a number of abundant PAs suggesting a factor of 1.0 for cyclic di-esters and open-chain di-esters with 7S configuration, of 0.3 for mono-esters with 7S configuration, of 0.1 for open-chain di-esters with 7R configuration and of 0.01 for mono-esters with 7R configuration. For N-oxides we suggest to apply the REP factor of the corresponding PA. We are confident that the use of these values can provide a more scientific basis for PA risk assessment until a more detailed experimental analysis of the potencies of all relevant congeners can be carried out.

Synthesis, structure, photophysical, electrochemical properties and antibacterial activity of brominated BODIPYs

The unusual di-bromo product, 5b, confirmed by spectral analysis, showed the most potency with the lowest IC₅₀ and MIC values, with excellent activity comparable to the standard antibacterial drug, tetracycline.

Axial ligand modified high valent tin(iv) porphyrins: synthesis, structure, photophysical studies and photodynamic antimicrobial activities on Candida albicans

Photophysical studies, fluorescence imaging, single crystal X-ray structure analysis and DFT calculations revealed that compounds2and3show enhanced phototoxicity towardsCandida albicanscompared to compound1.