Recent histone deacetylase inhibitors in cancer therapy.

Cancer metastasis increases the complexity of the disease and escalates patient mortality. Traditional chemotherapy has been associated with low efficacy and marked side effects. Studies pivot toward histone deacetylase (HDAC) enzymes and inhibitors because they are critical for chromatin structure, gene regulation, and cellular activities that are linked to metastasis and cancer progression. HDAC inhibitors (HDACi) can alter gene expression patterns and can lead to cell-cycle arrest and apoptosis in neoplastic cells. Several HDACi drugs like vorinostat, romidepsin, panobinostat, and belinostat are approved by the Food and Drug Administration. China and Japan have approved the use of tucidinostat, a new subtype-selective HDACi that inhibits class 1 HDAC1, HDAC2, HDAC3, as well as class 2b HDAC10. These drugs have shown promising results in the treatment of multiple carcinoma including cervical cancer, T-cell lymphoma, brain cancer, and breast cancer. This review highlights the HDACi classes, the mechanism of action of these inhibitors, their preclinical and clinical efficacy, and the latest clinical trials and patents used in cancer therapeutics. Overall, this review focuses on patents and clinical trials data from 2019 onward to give a better viewpoint on current trends in HDACis as chemotherapy agents.

Sources and methods of manufacturing xanthan by fermentation of various carbon sources.

Xanthan gum, an anionic polysaccharide with an exceptionally high molecular weight, is produced by the bacterium Xanthomonas sp. It is a versatile compound that has been utilized in various industries for decades. Xanthan gum was the second exopolysaccharide to be commercially produced, following dextran. In 1969, the US Food and Drug Administration (FDA) approved xanthan gum for use in the food and pharmaceutical industries. The food industry values xanthan gum for its exceptional rheological properties, which make it a popular thickening agent in many products. Meanwhile, the cosmetics industry capitalizes on xanthan gum's ability to form stable emulsions. The industrial production process of xanthan gum involves fermenting Xanthomonas in a medium that contains glucose, sucrose, starch, etc. as a substrate and other necessary nutrients to facilitate growth. This is achieved through batch fermentation under optimal conditions. However, the increasing costs of glucose in recent years have made the production of xanthan economically unviable. Therefore, many researchers have investigated alternative, cost-effective substrates for xanthan production, using various modified and unmodified raw materials. The objective of this analysis is to investigate how utilizing different raw materials can improve the cost-efficient production of xanthan gum.

Toxicology of Nanoparticles in Drug Delivery.

Nanoparticles have revolutionized biomedicine especially in the field of drug delivery due to their intriguing properties such as systemic stability, level of solubility, and target site specificity. It can, however, be both beneficial and damaging depending on the properties in different environments, thus highlighting the importance of nanotoxicology studies before use in humans. Different types of nanoparticles have been used in drug delivery, and this review summarizes the recent toxicity studies of these nanoparticles. The toxicological evaluation of three widely used nanoparticles in drug delivery that are metal, lipid, and protein nanoparticles has been discussed in detail. Studies have recorded several toxic effects of various nanoparticles such as metal-based nanoparticles have been linked to increased oxidative stress and have the potential to infiltrate the cell nucleus and protein-based nanoparticles have been observed to have hepatotoxicity and nephrotoxicity as their adverse effects. Considering the increasing application of nanoparticles in drug delivery and the growing concerns of regulatory authorities regarding the toxicity of nanocarriers in living organisms, it requires urgent attention to identify the gap in toxicity studies. The review highlights the gap in toxicity studies and potential focus areas to overcome the existing challenges.

Inhibition of polo-like kinase 1 suppresses microtubule dynamics in MCF-7 cells.

Polo-like kinase 1 (Plk1) is a mitotic serine/threonine kinase implicated in spindle formation and cytokinesis in mammalian cells. Here, purified Plk1 was found to bind to reconstituted microtubules in vitro. Further, Plk1 was found to co-localize with interphase microtubules in MCF-7 cells and to co-immunoprecipitate with polymerized tubulin. The binding of Plk1 to interphase microtubules appeared to increase with an increase in the level of tubulin acetylation in MCF-7 cells. Interestingly, Plk1 inhibitor III, an inhibitor of Plk1 kinase activity, treatment increased the association of Plk1 with the interphase microtubules in MCF-7 cells. Therefore, the effect of inhibition of Plk1 kinase activity on the dynamic instability of microtubules was determined by time-lapse imaging in MCF-7 cells. Plk1 inhibitor III dampened the dynamic instability of microtubules. For example, Plk1 inhibitor III (3 µM) reduced the rate and extent of the growing phase by 28 and 48%, respectively, and inhibited the dynamicity of microtubules by 53% as compared to the microtubules in control MCF-7 cells. Plk1 inhibitor III treatment also increased the level of acetylated microtubules, indicating that it stabilizes microtubules. The findings indicated that Plk1 interacts with microtubules and Plk1 may have a role in the regulation of microtubule dynamics.

HDAC Inhibitors as Novel Anti-Cancer Therapeutics.

Malignant growth of cells is a condition characterized by unchecked cellular proliferation, genetic instability and epigenetic dysregulation. Up-regulated HDAC (Histone Deacetylase) enzyme activity is associated with a closed chromatin assembly and subsequent gene repression, forming a characteristic feature of malignantly transformed cells. Novel therapeutics are now targeting the zinc containing HDAC enzymes for treating various types of cancers. Recently, a spate of drugs acting via HDAC inhibition have been undergoing clinical trials and several patents present exciting molecules like PCI-24781 (Abexinostat), ITF- 2357 (Givinostat); MS-275 (Entinostat), MGCD 0103 (Mocetinostat), LBH-589 (Panobinostat), FK228 (Romidepsin), PXD-101 (Belinostat) and Valproic Acid to be used as alternatives or adjuvants to traditional chemotherapeutics. However, only three HDAC inhibitors have acquired FDA approval till date. Recently, PXD-101 obtained FDA approval for the treatment of Refractory or Relapsed Peripheral T cell lymphoma. The current article reviews patents that have introduced novel molecules that are HDAC isoform specific, superior to first generation HDAC inhibitors like SAHA (Suberoylanilide Hydroxamic Acid) and TSA (Trichostatin A) and can be modified structurally to reduce toxic side effects and increase specificity. These molecules can combine the best characteristics of an ideal HDAC inhibiting drug either as monotherapy or in combinatorial therapy for cancer treatment thus, indicating promise to be included in the next generation of target specific HDAC inhibiting drugs.

Transcription factor NF-κB associates with microtubules and stimulates apoptosis in response to suppression of microtubule dynamics in MCF-7 cells.

NF-κB, a master regulator of several signaling cascades, is known to be actively transported in the nucleus in response to various stimuli. Here, we found that NF-κB is associated with polymeric tubulin and co-localized with microtubules in MCF-7 cells. Using TN16, a known microtubule targeting agent, we found that microtubule dynamics plays a critical role in NF-κB-microtubule interaction. Treatment of cells with low concentrations of TN16 (25 and 50 nM) that suppressed microtubule dynamics without visibly affecting microtubule organization enhanced the association of NF-κB with microtubules and facilitated nuclear translocation of NF-κB. Colchicine and vinblastine also produced similar nuclear translocation of NF-κB. Further, nuclear import of NF-κB activated apoptotic pathway in the cells that were blocked in mitosis by TN16 treatment suggesting that NF-κB acts as a pro-apoptotic protein in response to the suppression of microtubule dynamics. Interestingly, in the presence of high concentrations of TN16 that extensively disrupted the microtubule network, though there was an increase in the apoptotic cell death, the interaction of NF-κB with microtubules and its nuclear import were significantly reduced. Under these conditions, we detected an increase in the level of phosphorylation and nuclear accumulation of ERK, a MAP kinase, suggesting that the induction of apoptosis was caused by ERK signaling. The results indicate that the interaction of NF-κB with microtubules, its nuclear accumulation and subsequent gene transcription are critically dependent on microtubule dynamics. The data suggest a correlation between the functional status of microtubules and different apoptotic mechanisms invoked in response to microtubule inhibitors.

Discrimination of ligands with different flexibilities resulting from the plasticity of the binding site in tubulin.

Tubulin, an α,ß heterodimer, has four distinct ligand binding sites (for paclitaxel, peloruside/laulimalide, vinca, and colchicine). The site where colchicine binds is a promising drug target for arresting cell division and has been observed to accommodate compounds that are structurally diverse but possess comparable affinity. This investigation, using two such structurally different ligands as probes (one being colchicine itself and another, TN16), aims to provide insight into the origin of this diverse acceptability to provide a better perspective for the design of novel therapeutic molecules. Thermodynamic measurements reveal interesting interplay between entropy and enthalpy. Although both these parameters are favourable for TN16 binding (ΔH < 0, ΔS > 0), but the magnitude of entropy has the determining role for colchicine binding as its enthalpic component is destabilizing (ΔH > 0, ΔS > 0). Molecular dynamics simulation provides atomistic insight into the mechanism, pointing to the inherent flexibility of the binding pocket that can drastically change its shape depending on the ligand that it accepts. Simulation shows that in the complexed states both the ligands have freedom to move within the binding pocket; colchicine can switch its interactions like a "flying trapeze", whereas TN16 rocks like a "swing cradle", both benefiting entropically, although in two different ways. Additionally, the experimental results with respect to the role of solvation entropy correlate well with the computed difference in the hydration: water molecules associated with the ligands are released upon complexation. The complementary role of van der Waals packing versus flexibility controls the entropy-enthalpy modulations. This analysis provides lessons for the design of new ligands that should balance between the "better fit" and "flexibility"', instead of focusing only on the receptor-ligand interactions.

Rational design, synthesis and biological evaluations of amino-noscapine: a high affinity tubulin-binding noscapinoid.

Noscapine and its derivatives are important microtubule-interfering agents shown to have potent anti-tumor activity. The binding free energies (ΔG (bind)) of noscapinoids computed using linear interaction energy (LIE) method with a surface generalized Born (SGB) continuum solvation model were in agreement with the experimental ΔG (bind) with average root mean square error of 0.082 kcal/mol. This LIE-SGB model guided us in designing a novel derivative of noscapine, amino-noscapine [(S)-3-((R)-9-amino-4-methoxy-6-methyl-5,6,7,8-tetrahydro [1, 3] dioxolo[4,5-g]isoquinolin-5-yl)-6,7-dimethoxy isobenzo-furan-1(3H)-one] that has higher tubulin binding activity (predicted ΔG (bind) = -6.438 kcal/mol and experimental ΔG (bind) = -6.628 kcal/mol) than noscapine, but does not significantly change the total extent of the tubulin subunit/polymer ratio. The modes of interaction of amino-noscapine with the binding pocket of tubulin involved three hydrogen bonds and are distinct compared to noscapine which involved only one hydrogen bond. Also the patterns of non-bonded interactions are albeit different between both the lignads. The 'blind docking' approach (docking of ligand with different binding sites of a protein and their evaluations) as well as the reasonable accuracy of calculating ΔG (bind) using LIE-SGB model constitutes the first evidence that this class of compounds binds to tubulin at a site overlapping with colchicine-binding site or close to it. Our results revealed that amino-noscapine has better anti-tumor activity than noscapine.

Microtubules as antifungal and antiparasitic drug targets.

INTRODUCTION: Diseases caused by fungi and parasites are major illnesses in humans as well as in animals. Microtubule-targeted drugs are highly effective for the treatment of fungal and parasitic infections; however, several human parasitic infections such as malaria, trypanosomiasis and leishmaniasis do not have effective remedial drugs. In addition, the emergence of drug-resistant fungi and parasites makes the discovery of new drugs imperative. AREAS COVERED: This article describes similarities and dissimilarities between parasitic, fungal and mammalian tubulins and focuses on microtubule-targeting agents and therapeutic approaches for the treatment of fungal and parasitic diseases. New microtubule-targeted antileishmanial, antimalarial and antifungal drugs, with structures, biological activities and related patents, are described. The potential of dsRNA against tubulin to inhibit proliferation of protozoan and helminthic parasites is also discussed. Patent documents up to 2010 have been searched on USPTO, Patentscope, and Espacenet resources. EXPERT OPINION: The article suggests that vaccination with tubulin may offer novel opportunities for the antiparasitic treatment. Native or recombinant tubulin used as antigen has been shown to elicit immune response and cure infection partially or fully in animals upon challenge by protozoan parasites and helminths, thus indicating the suitability of tubulin as a vaccine against parasitic diseases.

On the discovery of the nature of cholera toxin in India.

This brief account looks at the discovery of the nature of cholera toxin in India. During the late nineteenth and early twentieth centuries research on cholera was being carried out in Bombay and Calcutta. Robert Koch visited India in 1883 and isolated and purified vibrio cholera the following year.This paper considers the contribution of Dr Sambhu Nath De, known best as S. N. De, (1915-1985) to cholera toxin discovery and notes the 2009 Conference which honoured his memory.

HMBA depolymerizes microtubules, activates mitotic checkpoints and induces mitotic block in MCF-7 cells by binding at the colchicine site in tubulin.

10-[(3-Hydroxy-4-methoxybenzylidene)]-9(10H)-anthracenone (HMBA), a synthetic compound, has been reported to have a potent antitumor activity. In this study, we found that HMBA depolymerized microtubules in MCF-7 cells and produced aberrant spindles in the MCF-7 cells. It also reduced the distance between the centrosomes and activated the mitotic checkpoint proteins BubR1 and Mad2. Further, HMBA inhibited the progression of MCF-7 cells in mitosis and induced apoptotic cell death involving p53 pathway. In vitro, HMBA bound to purified brain tubulin with a dissociation constant of 4.1+/-0.9 microM. It inhibited microtubule assembly and increased the GTP hydrolysis rate of microtubule assembly. The compound did not alter the binding of 2'(or 3')-O-(trinitrophenyl) guanosine 5'-triphosphate (TNP-GTP), a fluorescent analogue of GTP, to tubulin suggesting that it did not inhibit the binding of GTP to tubulin. However, we obtained evidence indicating that HMBA perturbed the conformation of the GTP binding site in tubulin. In addition, an analysis of the modified Dixon plot suggested that HMBA competitively inhibited the binding of colchicine to tubulin. A computational analysis of the binding of HMBA to tubulin supported the finding that HMBA shared its binding site with colchicine in tubulin and indicated that the binding of HMBA to tubulin was primarily stabilized through hydrogen bonding.