Sulfonamide drugs binding to the colchicine site of tubulin: thermodynamic analysis of the drug-tubulin interactions by isothermal titration calorimetry

Novel Natural Product- and Privileged Scaffold-Based Tubulin Inhibitors Targeting the Colchicine Binding Site

Tubulin inhibitors are effective anticancer agents, however, there are many limitations to the use of available tubulin inhibitors in the clinic, such as multidrug resistance, severe side-effects, and generally poor bioavailability. Thus, there is a constant need to search for novel tubulin inhibitors that can overcome these limitations. Natural product and privileged structures targeting tubulin have promoted the discovery and optimization of tubulin inhibitors. This review will focus on novel tubulin inhibitors derived from natural products and privileged structures targeting the colchicine binding site on tubulin.

Copper(i)-catalyzed radical decarboxylative imidation of carboxylic acids with N-fluoroarylsulfonimides

An efficient copper-catalyzed radical decarboxylative imidation reaction is presented.

Iodine-catalyzed expeditious synthesis of sulfonamides from sulfonyl hydrazides and amines

A new synthesis of sulfonamides via an iodine-catalyzed sulfonylation of amines with arylsulfonyl hydrazides at room temperature is reported.

Iridium(iii)-catalyzed regioselective C7-sulfonamidation of indoles

Iridium(iii)-catalyzed direct C7-sulfonamidation of indoles with sulfonyl azides is described.

A general iodine-mediated synthesis of primary sulfonamides from thiols and aqueous ammonia

An efficient, practical and green methodology for the synthesis of primary sulfonamides has been developed. Various types of thiols can be applied as substrates and the desired sulfonamides can be obtained in good to excellent yields.

New pyrazolo[4,3-e][1,2,4]triazine sulfonamides as carbonic anhydrase inhibitors

New sulfonamide derivatives of pyrazolo[4,3-e][1,2,4]triazine were synthesized and investigated as antitumor agents through carbonic anhydrase (CA, EC 4.2.1.1) inhibition. The newly prepared compounds were tested for their anticancer activity against human breast cancer cell lines (MCF-7, MDA-MB-231) using a MTT assay and inhibition of [(3)H]thymidine incorporation into DNA. Preliminary biological studies with several CA isoforms, revealed that the new derivatives were ineffective as CA I and II inhibitors, but they showed activity against tumor-associated enzymes, such as CA IX. The most effective inhibitor against CA IX was compound 8e that exhibited an inhibition constant KI of 13.8nM, and derivatives 8c-8d with moderate activity (8c: KI=25.4nM; 8d: KI=24.5nM). Compounds 8g-8h exhibited acceptable activity (8g: KI=27.7nM; 8d: KI=26.6nM). The detailed synthesis, spectroscopic and biological data are also reported.

A novel rhodium-catalyzed domino-hydroformylation-reaction for the synthesis of sulphonamides

An efficient and highly selective domino hydroformylation-reductive sulphonamidation reaction has been developed for the synthesis of sulphonamides using a rhodium/phosphine catalyst.

Recent advances in C–S bond formation via C–H bond functionalization and decarboxylation

The development of mild and general methods for C–S bond formation has received significant attention because the C–S bond is indispensable in many important biological and pharmaceutical compounds.

Ionic Sal-SG Schiff bases as new synergetic chemotherapeutic candidates: synthesis, metalation with Pd(ii) and in vitro pharmacological evaluation

A series of novelN-(salicylidene)-sulfaguanidines (Sal-SG) bearing ionic liquid (IL) terminals (ILSSGH,4a–f) have been synthesized by Schiff base condensation of IL-functionalized salicylaldehydes (ILSal,3a–g) and sulfaguanidine (SG).

Ruthenium(ii) complexes containing a phosphine-functionalized thiosemicarbazone ligand: synthesis, structures and catalytic C–N bond formation reactions via N-alkylation

We report the coordination flexibility of phosphino-thiosemicarbazone in ruthenium(ii) complexes, together with their catalytic properties with regards to N-alkylation.

BPR0C305, an orally active microtubule-disrupting anticancer agent

BPR0C305 is a novel N-substituted indolyl glyoxylamide previously reported with in-vitro cytotoxic activity against a panel of human cancer cells including P-gp-expressing multiple drug-resistant cell sublines. The present study further examined the underlying molecular mechanism of anticancer action and evaluated the in-vivo antitumor activities of BPR0C305. BPR0C305 is a novel synthetic small indole derivative that demonstrates in-vitro activities against human cancer cell growth by inhibiting tubulin polymerization, disrupting cellular microtubule assembly, and causing cell cycle arrest at the G2/M phase. It is also orally active against leukemia and solid tumor growths in mouse models. Findings of these pharmacological and pharmacokinetic studies suggest that BPR0C305 is a promising lead compound for further preclinical developments.

Microtubule dynamics regulates Akt signaling via dynactin p150

Following activation at the plasma membrane, Akt is subsequently deactivated in the cytoplasm. Although activation and deactivation of Akt must sometimes be separated in order to elicit and control cellular responses, the exact details of the spatiotemporal organization of Akt signaling are incompletely understood. Here we show that microtubule dynamics specifically modulate the deactivation phase of Akt signaling. Localization of Akt to microtubules sustains its activity, while disruption of microtubules attenuates Akt signaling independent of its initial activation. Conversely, stabilization of microtubules elevates Akt signaling both in vitro and in muscle tissues in vivo. Localization of Akt to microtubules is mediated by the microtubule binding protein dynactin p150, which is shown to be a direct target of Akt. Finally, microtubule disruption-induced Akt deactivation contributes to delayed cell cycle progression and accelerated cell death. Taken together, we revealed that, after initiation, the overall intensity and duration of oncogenic Akt signaling are determined by microtubule dynamics, a mechanism that could be exploited for therapeutic purposes.

Efficient and versatile catalysis of N-alkylation of heterocyclic amines with alcohols and one-pot synthesis of 2-aryl substituted benzazoles with newly designed ruthenium(ii) complexes of PNS thiosemicarbazones

Efficient catalytic N-alkylation of amines using Ru(ii) catalysts with good yields and high selectivity.

Copper-mediated S–N formation via an oxygen-activated radical process: a new synthesis method for sulfonamides

A copper-mediated direct synthesis of sulfonamides via an oxygen-activated radical process has been developed.

Copper-catalyzed sulfonamides formation from sodium sulfinates and amines

A new and convenient method for the construction of sulfonamides via a copper-catalyzed oxidative coupling between sodium sulfinates and amines with 1 atm O2 or DMSO as the oxidant was described. This method provides efficient and robust synthesis of functional sulfonamides in good yields and excellent chemoselectivity. And detailed mechanistic studies showed that this transformation may go through a single electron transfer (SET) pathway.

Microtubule-associated proteins and tubulin interaction by isothermal titration calorimetry

Microtubules play an important role in a number of vital cell processes such as cell division, intracellular transport, and cell architecture. The highly dynamic structure of microtubules is tightly regulated by a number of stabilizing and destabilizing microtubule-associated proteins (MAPs), such as tau and stathmin. Because of their importance, tubulin-MAPs interactions have been extensively studied using various methods that provide researchers with complementary but sometimes contradictory thermodynamic data. Isothermal titration calorimetry (ITC) is the only direct thermodynamic method that enables a full thermodynamic characterization (stoichiometry, enthalpy, entropy of binding, and association constant) of the interaction after a single titration experiment. This method has been recently applied to study tubulin-MAPs interactions in order to bring new insights into molecular mechanisms of tubulin regulation. In this chapter, we review the technical specificity of this method and then focus on the use of ITC in the investigation of tubulin-MAPs binding. We describe technical issues which could arise during planning and carrying out the ITC experiments, in particular with fragile proteins such as tubulin. Using examples of stathmin and tau, we demonstrate how ITC can be used to gain major insights into tubulin-MAP interaction.

CIL-102 binds to tubulin at colchicine binding site and triggers apoptosis in MCF-7 cells by inducing monopolar and multinucleated cells

A plant dictamine analog, 1-[4-(furo[2,3-b]quinolin-4-ylamino)phenyl]ethanone (CIL-102) has been shown to exert potent anti-tumor activity. In this study, we examined the mode of interaction of CIL-102 with tubulin and unraveled the cellular mechanism responsible for its anti-tumor activity. CIL-102 bound to tubulin at a single site with a dissociation constant ~0.4 μM. Isothermal titration calorimetry revealed that CIL-102-tubulin interaction is highly enthalpy driven and that the binding affords a large negative heat capacity change (ΔC(p) = -790 cal mol(-1) K(-1)) with an enthalpy-entropy compensation. An analysis of the modified Dixon plot suggested that CIL-102 competitively inhibited the binding of podophyllotoxin, a colchicine-binding site agent, to tubulin. Computational modeling indicated that CIL-102 binds exclusively at the β-subunit of tubulin and that CIL-102 and colchicine partially share their binding sites on tubulin. It bound to tubulin reversibly and the binding was estimated to be ~1000 times faster than that of colchicine. CIL-102 potently inhibited the proliferation of MCF-7 cells, induced monopolar spindle formation and multi-nucleation. At half-maximal inhibitory concentration, the spindle microtubules were visibly depolymerized and disorganized. CIL-102 reduced the inter-polar distances of bipolar mitotic cells indicating that it impaired microtubule-kinetochore attachments. CIL-102-treatment induced apoptosis in MCF-7 cells in association with increased nuclear accumulation of p53 and p21 suggesting that apoptosis is triggered through a p53-p21 dependent pathway. The results indicated that CIL-102 exerted anti-proliferative activity by disrupting microtubule functions through tubulin binding and provided important insights into the differential mode of tubulin binding by CIL-102 and colchicine.

Discovery of small molecule inhibitors that interact with γ-tubulin

Recent studies have shown an overexpression of γ-tubulin in human glioblastomas and glioblastoma cell lines. As the 2-year survival rate for glioblastoma is very poor, potential benefit exists for discovering novel chemotherapeutic agents that can inhibit γ-tubulin, which is known to form a ring complex that acts as a microtubule nucleation center. We present experimental evidence that colchicine and combretastatin A-4 bind to γ-tubulin, which are to our knowledge the first drug-like compounds known to interact with γ-tubulin. Molecular dynamics simulations and docking studies were used to analyze the hypothesized γ-tubulin binding domain of these compounds. The suitability of the potential binding modes was evaluated and suggests the subsequent rational design of novel targeted inhibitors of γ-tubulin.

Room temperature synthesis and antibacterial activity of new sulfonamides containing n,n-diethyl-substituted amido moieties

Sulfonamide drugs which have brought about an antibiotic revolution in medicine are associated with a wide range of biological activities. We have synthesized a series of α-tolylsulfonamide, 1–11 and their substituted N,N-diethyl-2-(phenylmethylsulfonamido) alkanamide derivatives, 12–22 in improved and excellent yields in aqueous medium at room temperature through highly economical synthetic routes. The chemical structures of the synthesized compounds 1–22 were confirmed by analytical and spectral data such as IR, ¹H- and ¹³C-NMR, and mass spectra. The in vitro antibacterial activity of these compounds along with standard clinical reference, streptomycin, was investigated on two key targeted organisms. It was observed that 1-(benzylsulfonyl)pyrrolidine-2-carboxylic acid, 2 emerged as the most active compound against Staphylococcus aureus at MIC value of 1.8 μg/mL while 4-(3-(diethylamino)-3-oxo-2-(phenylmethylsulfonamido) propyl)phenyl phenylmethanesulfonate, 22 was the most active sulfonamide scaffold on Escherichia coli at MIC value of 12.5 μg/mL.

Identification of agents that induce apoptosis of multicellular tumour spheroids: enrichment for mitotic inhibitors with hydrophobic properties

Cell-based anticancer drug screening generally utilizes rapidly proliferating tumour cells grown as monolayer cultures. Hit compounds from such screens are not necessarily effective on hypoxic and slowly proliferating cells in 3-D tumour tissue. The aim of this study was to examine the potential usefulness of 3-D cultured tumour cells for anticancer drug screening. We used colon carcinoma multicellular spheroids containing hypoxic and quiescent cells in core areas for this purpose. Three libraries (∼11 000 compounds) were screened using antiproliferative activity and/or apoptosis as end-points. Screening of monolayer and spheroid cultures was found to identify different sets of hit compounds. Spheroid screening enriched for hydrophobic compounds: median XLogP values of 4.3 and 4.4 were observed for the hits in two independent screening campaigns. Mechanistic analysis revealed that the majority of spheroid screening hits were microtubuli inhibitors. One of these inhibitors was examined in detail and found to be effective against non-dividing cells in the hypoxic centres of spheroids. Spheroid screening represents a conceptually new strategy for anticancer drug discovery. Our findings have implications for drug library design and hit selection in projects aimed to develop drugs for the treatment of solid tumours.

Synthesis and cross-coupling of sulfonamidomethyltrifluoroborates

Sulfonamidomethyltrifluoroborates were successfully synthesized and cross-coupled with a wide range of aryl and heteroaryl chlorides, allowing the construction of a sulfonamidomethyl aryl linkage through a new disconnection, thus offering a new way to access such structurally interesting motifs.

MT119, a new planar-structured compound, targets the colchicine site of tubulin arresting mitosis and inhibiting tumor cell proliferation

Microtubule-targeted drugs are now indispensable for the therapy of various cancer types worldwide. In this article, we report MT119 [6-[2-(4-methoxyphenyl) -ethyl]-9-[(pyridine-3-ylmethyl)amino]pyrido[2',1':2,3]imida-zo[4,5-c]isoquinolin-5(6H)-one] as a new microtubule-targeted agent. MT119 inhibited tubulin polymerization significantly both in tumor cells and in cell-free systems, which was followed by the disruption of mitotic spindle assembly. Surface plasmon resonance-based analyses showed that MT119 bound to purified tubulin directly, with the K(D) value of 10.6 μM. The binding of MT119 in turn caused tubulin conformational changes as evidenced by the quenched tryptophan fluorescence, the reduction of the bis-ANS reactivity and the decreased DTNB-sulfhydryl reaction rate. Competitive binding assays further revealed that MT119 bound to tubulin at its colchicine site. Consequently, by inhibiting tubulin polymerization, MT119 arrested different tumor cells at mitotic phase, which contributed to its potent antitumor activity in vitro. MT119 was also similarly cytotoxic to vincristine-, adriamycin- or mitoxantrone-resistant cancer cells and to their corresponding parental cells. Together, these data indicate that MT119 represents a new class of colchicine-site-targeted inhibitors against tubulin polymerization, which might be a promising starting point for future cancer therapeutics.

Substituent diversity-directed synthesis of indole derivatives

This paper reports a versatile, good-yielding, solution-phase method that is a substituent diversity-directed synthesis of 1H-indoles (6-13, 17-20) and 1-hydroxyindoles (14, 15) starting from commercially available 1,5-difluoro-2,4-dinitrobenzene. The synthetic products possessed the maximum six diversity points.

Natural product Celastrol destabilizes tubulin heterodimer and facilitates mitotic cell death triggered by microtubule-targeting anti-cancer drugs

BACKGROUND

Microtubule drugs are effective anti-cancer agents, primarily due to their ability to induce mitotic arrest and subsequent cell death. However, some cancer cells are intrinsically resistant or acquire a resistance. Lack of apoptosis following mitotic arrest is thought to contribute to drug resistance that limits the efficacy of the microtubule-targeting anti-cancer drugs. Genetic or pharmacological agents that selectively facilitate the apoptosis of mitotic arrested cells present opportunities to strengthen the therapeutic efficacy.

METHODOLOGY AND PRINCIPAL FINDINGS

We report a natural product Celastrol targets tubulin and facilitates mitotic cell death caused by microtubule drugs. First, in a small molecule screening effort, we identify Celastrol as an inhibitor of neutrophil chemotaxis. Subsequent time-lapse imaging analyses reveal that inhibition of microtubule-mediated cellular processes, including cell migration and mitotic chromosome alignment, is the earliest events affected by Celastrol. Disorganization, not depolymerization, of mitotic spindles appears responsible for mitotic defects. Celastrol directly affects the biochemical properties of tubulin heterodimer in vitro and reduces its protein level in vivo. At the cellular level, Celastrol induces a synergistic apoptosis when combined with conventional microtubule-targeting drugs and manifests an efficacy toward Taxol-resistant cancer cells. Finally, by time-lapse imaging and tracking of microtubule drug-treated cells, we show that Celastrol preferentially induces apoptosis of mitotic arrested cells in a caspase-dependent manner. This selective effect is not due to inhibition of general cell survival pathways or mitotic kinases that have been shown to enhance microtubule drug-induced cell death.

CONCLUSIONS AND SIGNIFICANCE

We provide evidence for new cellular pathways that, when perturbed, selectively induce the apoptosis of mitotic arrested cancer cells, identifying a potential new strategy to enhance the therapeutic efficacy of conventional microtubule-targeting anti-cancer drugs.

Porphyrins affect the self-assembly of tubulin in solution

Self-assembly of tubulin heterodimers in solution has been studied in the past to predict the effects that ligands and/or conformational changes have on the formation of tubulin filaments. Self-assembly of tubulin in solution has produced formations similar to cellular microtubules (MTs). The present study reports on the effects that two porphyrins (protoporphyrin IX, PPIX and tetrakis(4-sulfonatophenyl)porphyrin, TPPS) produce on the self-assembly of tubulin alpha,beta-heterodimers in buffer solution. The study shows that, when incubated simultaneously with MT-stabilizing ligands (i.e., paclitaxel and guanosine triphosphate, GTP), porphyrins do not affect the ability of tubulin to form MT. However, if paclitaxel and GTP are added after tubulin has been allowed to self-assemble in the presence of either porphyrin, the ability to form MT-like structures is reduced or suppressed. We suggest that this effect is due to the formation of porphyrin-mediated aggregates that cannot be broken or elongated by the addition of GTP or paclitaxel.

Inhibitors of tubulin assembly identified through screening a compound library

Tubulin is the proposed target for drugs against cancer and helminths and is also a validated target in kinetoplastid parasites. With the aim of identifying new lead compounds against Leishmania sp., tubulin isolated from L. tarentolae was used to screen a 10 000 compound library. One compound, Chembridge No. 7992831 (5), displayed an IC(50) of 13 microm against Leishmania tubulin in an in vitro assembly assay and showed a greater than threefold selectivity over mammalian tubulin. Another compound, Chembridge No. 9067250 (8), exhibited good activity against mammalian tubulin (IC(50) = 5.0 microm). This compound was also toxic to several cancer cell lines with IC(50) values in the region of 1 microm. Subsequent testing of analogues of 8 contained within the library identified two compounds with greater potency against mammalian tubulin (IC(50) values of 1.1 and 2.8 microm). The more potent antitubulin agent also showed promising activity against cancer cell lines in vitro, with IC(50) values ranging from 0.18 to 0.73 microm.

Differential colchicine-binding across eukaryotic families: the role of highly conserved Pro268beta and Ala248beta residues in animal tubulin

Colchicine-tubulin interaction, responsible for the disruption of microtubule formation, has immense pharmacological importance but is poorly understood in terms of its biological significance. The interaction is characterized by a marked higher affinity of colchicine for animal tubulins compared to tubulins from plants, fungi and protists. From an analysis of tubulin sequences and colchicine-tubulin crystal structure, we propose that Pro268beta and Ala248beta (270beta and 250beta in the crystal structure 1SA0) in animal tubulin are crucial for the observed differential binding. We also suggest that mediated by the binding of endogenous molecules to the colchicine-binding site, microtubule assembly in eukaryotes may be modulated in a family specific manner.

Thermodynamic analysis of binding between drugs and glycosaminoglycans by isothermal titration calorimetry and fluorescence spectroscopy

The thermodynamics of the interaction of positively charged drug molecules with negatively charged glycosaminoglycans (GAGs) is investigated by isothermal titration calorimetry (ITC) and fluorescence spectroscopy. The drugs considered are propranolol hydrochloride, tacrine, and aminacrine, and the polymers used as model GAGs are dextran sulfate, chondroitin sulfate, and hyaluronic acid. The ITC results show that the interaction between drugs and GAGs is via direct binding and that GAGs bind to drugs at one set of sites. Large negative values of heat capacity change (DeltaC(p)) are observed upon binding of GAGs to drugs. Such negative DeltaC(p) is not expected for purely electrostatic interactions and suggests that hydrophobic and other interactions may be also involved in the binding process. These results are corroborated by fluorescence spectroscopy measurements, which show that specific drug/GAG complex formation is accompanied by a clear enhancement of the fluorescence intensity. The results highlight the importance of the formation of drug/GAG complexes as a primary step for the drug delivery process into cell membranes. It is concluded that the interactions are dependent on the nature of both GAG and drug and this is a fact to be taken into account when new drugs are designed.

S100A13-lipid interactions-role in the non-classical release of the acidic fibroblast growth factor

S100A13 is a 98-amino acid, calcium binding protein. It is known to participate in the non-classical secretion of signal peptide-less proteins, such as the acidic fibroblast growth factor. In this study, we investigate the lipid binding properties of S10013 using a number of biophysical techniques, including multidimensional NMR spectroscopy. Isothermal titration calorimetry and steady state fluorescence experiments show that apoS100A13 exhibits preferential binding to small unilamelar vesicles of l-phosphatidyl serine (pS). In comparison, Ca2+-bound S100A13 is observed to bind weakly to unilamelar vesicles (SUVs) of pS. Equilibrium thermal unfolding and limited trypsin digestion analysis reveal that apoS100A13 is significantly destabilized upon binding to SUVs of pS. Results of the far UV circular dichroism and ANS (8-anilino-1-napthalene sufonate) binding experiments indicate a subtle conformational change resulting in the increase in the solvent-accessible hydrophobic surface in the protein. Availability of the solvent-exposed hydrophobic surface(s) in apoS10013 facilitates its interaction with the lipid vesicles. Our data suggest that Ca2+ binding dictates the membrane binding affinity of S100A13. Based on the results of this study, a model describing the sequence of molecular events that possibly can occur during the non-classical secretion of FGF-1 is presented.