Exploring the effect of 2,3,4-trimethoxy-phenyl moiety as a component of indolephenstatins

Natural-Product-Inspired Discovery of Trimethoxyphenyl-1,2,4-triazolosulfonamides as Potent Tubulin Polymerization Inhibitors

An approach of natural product-inspired strategy and incorporation of an NP-privileged motif has been investigated for the discovery of new tubulin polymerization inhibitors. Two series, N-Arylsulfonyl-3-arylamino-5-amino-1,2,4-triazole derivatives, and their isomers were considered. The compounds were synthesized by construction of the N-aryl-1,2,4-triazole-3,5-diamine motif and sulfonylation. Although the chemo- and regioselectivity in sulfonylation were challenging due to multiple ring-tautomerizable-NH and exocyclic NH2 functionalities present in the molecular motifs, the developed synthetic method enabled the preparation of designed molecular skeletons with biologically important motifs. The approach also led to explore interesting molecular regio- and stereochemical aspects valuable for activity. The X-ray crystallography study indicated that the hydrogen bonding between the arylamine-NH and the arylsulfonyl-"O" unit and appropriate molecular-functionality topology allowed the cis-locking of two aryls, which is important for tubulin-binding and antiproliferative properties. All synthesized compounds majorly showed characteristic antiproliferative effects in breast cancer cells (MCF-7), and four compounds exhibited potent antiproliferative activity. One compound potently bound to tubulin at the colchicine site and inhibited tubulin polymerization in vitro. The compound significantly depolymerized microtubules in MCF-7 cells, arrested the cells at the G2/M phase, and induced cell death. This study represents the importance of the design strategy in medicinal chemistry and the molecular structural features relevant to anticancer anti-tubulin properties. The explored molecules have the potential for further development.

Identification and optimization of biphenyl derivatives as novel tubulin inhibitors targeting colchicine-binding site overcoming multidrug resistance

Microtubule targeting agents (MTAs) are among the most successful chemotherapeutic drugs, but their efficacy is often limited by the development of multidrug resistance (MDR). Therefore, the development of novel MTAs with the ability to overcome MDR is urgently needed. In this contribution, through modification of the unsymmetric biaryl compounds, we discovered a novel compound dxy-1-175 with potent anti-proliferative activity against cancer cells. Mechanistic study revealed that dxy-1-175 inhibited tubulin polymerization by interacting with the colchicine-binding site of tubulin, which caused cell cycle arrest at G₂/M phase. Based on the predicted binding model of dxy-1-175 with tubulin, a series of new 4-benzoylbiphenyl analogues were designed and synthesized. Among them, the hydrochloride compound 12e with improved solubility and good stability in human liver microsome, exhibited the most potent anti-proliferative activity with IC₅₀ value in the low nanomolar range, and markedly inhibited the growth of breast cancer 4T1 xenograft in vivo. Notably, 12e effectively overcame P-gp-mediated MDR and our preliminary data suggested that 12e may not be a substrate of P-glycoprotein (P-gp). Taken together, our study reveals a novel MTA 12e targeting the colchicine-binding site with potent anticancer activity and the ability to circumvent MDR.

Methylsulfanylpyridine based diheteroaryl isocombretastatin analogs as potent anti-proliferative agents

Isocombretastatins are the not isomerizable 1,1-diarylethene isomers of combretastatins. Both families of antimitotics are poorly soluble and new analogs with improved water solubility are needed. The ubiquitous 3,4,5-trimethoxyphenyl ring and most of its replacements contribute to the solubility problem. 39 new compounds belonging to two series of isocombretastatin analogs with 2-chloro-6-methylsulfanyl-4-pyridinyl or 2,6-bis(methylsulfanyl)-4-pyridinyl moieties replacing the 3,4,5-trimethoxyphenyl have been synthesized and their antimitotic activity and aqueous solubility have been studied. We show here that 2-chloro-6-methylsulfanylpyridines are more successful replacements than 2,6-bis(methylsulfanyl)pyridines, giving highly potent tubulin inhibitors and cytotoxic compounds with improved water solubilities. The optimal combination is with indole rings carrying polar substitutions at the three position. The resulting diheteroaryl isocombretastatin analogs showed potent cytotoxic activity against human cancer cell lines caused by tubulin inhibition, as shown by in vitro tubulin polymerization inhibitory assays, cell cycle analysis, and confocal microscopy studies. Cell cycle analysis also showed apoptotic responses following G₂/M arrest after treatment. Conformational analysis and docking studies were applied to propose binding modes of the compounds at the colchicine site of tubulin and were in good agreement with the observed SAR. 2-Chloro-6-methylsulfanylpyridines represent a new and successful trimethoxyphenyl ring substitution for the development of improved colchicine site ligands.

Identification of Essential 2D and 3D Chemical Features for Discovery of the Novel Tubulin Polymerization Inhibitors

Background:

Tubulin polymerization inhibitors interfere with microtubule assembly and their functions lead to mitotic arrest, therefore they are attractive target for design and development of novel anticancer compounds.

Objective:

The proposed novel and effective structures following the use of three-dimensionalquantitative structure activity relationship (3D-QSAR) pharmacophore based virtual screening clearly demonstrate the high efficiency of this method in modern drug discovery.

Method:

Combined computational approach was applied to extract the essential 2D and 3D features requirements for higher activity as well as identify new anti-tubulin agents.

Results:

The best quantitative pharmacophore model, Hypo1, exhibited good correlation of 0.943 (RMSD=1.019) and excellent predictive power in the training set compounds. Generated model AHHHR, was well mapped to colchicine site and three-dimensional spatial arrangement of their features were in good agreement with the vital interactions in the active site. Total prediction accuracy (0.92 for training set and 0.86 for test set), enrichment factor (4.2 for training set and 4.5 for test set) and the area under the ROC curve (0.86 for training set and 0.94 for the test set), the developed model using Extended Class FingerPrints of maximum diameter 4 (ECFP_4) was chosen as the best model.

Conclusion:

Developed computational platform provided a better understanding of requirement features for colchicine site inhibitors and we believe the results of this study might be useful for the rational design and optimization of new inhibitors.

Synthesis, Structure, Stability, and Inhibition of Tubulin Polymerization by RuII-p-Cymene Complexes of Trimethoxyaniline-Based Schiff Bases

Four trimethoxy- and dimethoxyphenylamine-based Schiff base (L1-L4)-bearing Ru^II-p-cymene complexes (1-4) of the chemical formula [Ru^II(η⁶-p-cymene)(L)(Cl)] were synthesized, isolated in pure form, and structurally characterized using single-crystal X-ray diffraction and other analytical techniques. The complexes showed excellent in vitro antiproliferative activity against various forms of cancer that are difficult to cure, viz., triple negative human metastatic breast carcinoma MDA-MB-231, human pancreatic carcinoma MIA PaCa-2, and hepatocellular carcinoma Hep G2. The ¹H nuclear magnetic resonance data in the presence of 10% dimethylformamide-d₇ or dimethyl sulfoxide-d₆ in phosphate buffer (pD 7.4, containing 4 mM NaCl) showed that the complexes immediately generate the aquated species that is stable for at least 24 h. Electrospray ionization mass spectrometry data showed that they do not bind with guanine nitrogen even in the presence of 5 molar equivalents of 9-EtG, during a period of 24 h. The best complex in the series, 1, exhibits an IC₅₀ of approximately 10-15 μM in the panel of tested cancer cell lines. The complexes do not enhance the production of reactive oxygen species in the cells. Docking studies with a tubulin crystal structure (Protein Data Bank entry 1SAO ) revealed that 1 and 3 as well as L1 and L3 have a high affinity for the interface of the α and β tubulin dimer in the colchicine binding site. The immunofluorescence studies showed that 1 and 3 strongly inhibited microtubule network formation in MDA-MB-231 cells after treatment with an IC₂₀ or IC₅₀ dose for 12 h. The cell cycle analysis upon treatment with 1 showed that the complexes inhibit the mitotic phase because the arrest was observed in the G2/M phase. In summary, 1 and 3 are Ru^II half-sandwich complexes that are capable of disrupting a microtubule network in a dose-dependent manner. They depolarize the mitochondria, arrest the cell cycle in the G2/M phase, and kill the cells by an apoptotic pathway.

Substitution at the indole 3 position yields highly potent indolecombretastatins against human tumor cells

Resistance to combretastatin A-4 is mediated by metabolic modification of the phenolic hydroxyl and ether groups of the 3-hydroxy-4-methoxyphenyl (B ring). Replacement of the B ring of combretastatin A-4 by a N-methyl-5-indolyl reduces tubulin polymerization inhibition (TPI) and cytotoxicity against human cancer cell lines but cyano, methoxycarbonyl, formyl, and hydroxyiminomethyl substitutions at the indole 3-position restores potent TPI and cytotoxicity against sensitive human cancer cell lines. These highly potent substituted derivatives displayed low nanomolar cytotoxicity against several human cancer cell lines due to tubulin inhibition, as shown by cell cycle analysis, confocal microscopy, and tubulin polymerization inhibitory activity studies, and promoted cell killing mediated by caspase-3 activation. Binding at the colchicine site was suggested by molecular modeling studies. Substituted combretastatins displayed higher potencies than the isomeric isocombretastatins and the highest potencies were achieved for the hydroxyiminomethyl (21) and cyano (23) groups, with TPI values in the submicromolar range and cytotoxicities in the nanomolar and subnanomolar range. Dose-response and time-course studies showed that drug concentrations as low as 1 nM (23) or 10 nM (21) led to a complete G₂/M cell cycle arrest after 15 h treatment followed by a high apoptosis-like cell response after 48-72 h treatment. The P-glycoprotein antagonist verapamil increased 21 and 23 cytotoxicity to IC₅₀ values of 10^-10 M, and highly potentiated the cytotoxic activity in 100-fold of the CHO derivative (17), in A-549 human non-small cell lung cancer cells. The cyano substituted indolecombretastatin 23 is by itself highly potent against rather resistant HT-29 and A-549 cell lines. A 3,4,5-trimethoxyphenyl ring always afforded more potent derivatives than a 2,3,4-trimethoxyphenyl ring.

Synthesis and biological evaluation of 2-aryl-benzimidazole derivatives of dehydroabietic acid as novel tubulin polymerization inhibitors

A series of novel 2-aryl-benzimidazole derivatives of dehydroabietic acid were synthesized and characterized by IR, 1H NMR, 13C NMR, MS and elemental analyses. All the target compounds were evaluated for their in vitro cytotoxic activity against SMMC-7721, MDA-MB-231, HeLa and CT-26 cancer cell lines and the normal hepatocyte cell line QSG-7701 through MTT assays. Among them, compound 6j displayed the most potent cytotoxic activity with IC50 values of 0.08 ± 0.01, 0.19 ± 0.04, 0.23 ± 0.05 and 0.42 ± 0.07 μM, respectively, and substantially reduced cytotoxicity against QSG-7701 cells (5.82 ± 0.38 μM). The treatment of SMMC-7721 cells with compound 6j led to considerable inhibition of cell migration ability. The influence of compound 6j on cell cycle distribution was assessed on SMMC-7721 cells, exhibiting a cell cycle arrest at the G2/M phase. Moreover, tubulin polymerization assays and immunofluorescence assays elucidated that compound 6j could significantly inhibit tubulin polymerization and disrupt the intracellular microtubule network. A molecular docking study provided insight into the binding mode of compound 6j in the colchicine site of tubulin. In addition, compound 6j was found to induce apoptosis of SMMC-7721 cells, an increase of intracellular ROS level and a loss of mitochondrial membrane potential in a dose-dependent manner. These findings provided new molecular scaffolds for the further development of novel antitumor agents targeting tubulin polymerization.

Studies on phenothiazines: New microtubule-interacting compounds with phenothiazine A-ring as potent antineoplastic agents

New phenothiazine derivatives 6-20 have been designed, synthesized and evaluated in vitro for their ability to inhibit tubulin polymerization and antiproliferative activity against 60 cancer cell lines, including several multi-drug resistant (MDR) tumor cell lines. The phenothiazine unit may successfully replace the classical 3,4,5-trimethoxyphenyle A ring of parent combretastatin A-4 or phenstatin, confirming previous studies. The most promising structural modulations have been realized on the B ring, the 2'-fluoro-4'-methoxy substitution in compound 6 and the 2'-trifluoromethyl-4'-methoxy substitution in compound 7 providing the best antitubulin and antitumor activity in the current study. Compounds 6-8 and 16 exhibited more important cell growth inhibition than parent phenstatin 2 on human colon Duke's type D, colorectal adenocarcinoma COLO 205 and on human kidney adenocarcinoma A498 cell lines. 10-Methylphenothiazine derivatives 19 and 20 did not show biological activity but exerted bright fluorescence and solvatochromism effects. These molecules deserve further chemical efforts in order to provide valuable tools for biophysical studies.

Microwave-assisted synthesis, molecular docking and antiproliferative activity of (3/5-aryl-1,2,4-oxadiazole-5/3-yl)(3,4,5-trimethoxyphenyl)methanone oxime derivatives

A microwave-assisted synthesis method of building a 1,2,4-oxadiazole skeleton was developed.

Studies on indolizines. Evaluation of their biological properties as microtubule-interacting agents and as melanoma targeting compounds

With the aim of investigating new analogues of phenstatin with an indolizin-3-yl unit, in particular as the B-ring, three new series of compounds (6-8, 9-34 and 54) were synthesized and tested for interactions with tubulin polymerization and evaluated for cytotoxicity on an NCI-60 human cancer cell lines panel. The replacement of the 3'-hydroxy-4'-methoxyphenyl B-ring of phenstatin with substituted indolizine unit results in the conservation of both antitubulin and cytotoxic effect. Indolizines 9 and 17 were the most effective in the present study and showed the highest antiproliferative effect on melanoma cell lines MDA-MB-435 (GI50 = 30 nM) and could serve as new lead compounds for the development of anti-cancer therapeutics.

Design, synthesis, and biological evaluation of stable colchicine binding site tubulin inhibitors as potential anticancer agents

To block the metabolically labile sites of novel tubulin inhibitors targeting the colchicine binding site based on SMART, ABI, and PAT templates, we have designed, synthesized, and biologically tested three focused sets of new derivatives with modifications at the carbonyl linker, the para-position in the C ring of SMART template, and modification of A ring of the PAT template. Structure-activity relationships of these compounds led to the identification of new benzimidazole and imidazo[4,5-c]pyridine-fused ring templates, represented by compounds 4 and 7, respectively, which showed enhanced antitumor activity and substantially improved the metabolic stability in liver microsomes compared to SMART. MOM group replaced TMP C ring and generated a potent analogue 15, which showed comparable potency to the parent SMART compound. Further modification of PAT template yielded another potent analogue 33 with 5-indolyl substituent at A ring.

Synthesis and cytotoxic activity of a new group of heterocyclic analogues of the combretastatins

A series of new analogs of combretastatin A-4 (CA-4, 1) with the A or B-ring replaced by a 3-oxo-2,3-dihydrofurocoumarin or a furocoumarin residue have been designed and synthesized by employing a cross-coupling approach. All the compounds were evaluated for their cytotoxic activity with respect to model cancer cell lines (CEM-13, MT-4, U-937) using conventional MTT assays. Structure-activity relationship analysis reveals that compounds 2, 3, 6–8 in which the (Z)-styryl substituent was connected to the 2-position of the 3-oxo-2,3-dihydrofurocoumarin core, demonstrated increased potency compared to 3-(Z)-styrylfurocoumarins 4, 5, 9–11. The methoxy-, hydroxyl- and formyl- substitution on the aromatic ring of the (Z)-styryl moiety seems to play an important role in this class of compounds. Compounds 2 and 3 showed the best potency against the CEM-13 cell lines, with CTD₅₀ values ranging from 4.9 to 5.1 μM. In comparison with CA-4, all synthesized compounds presented moderate cytotoxic activity to the T-cellular human leucosis cells MT-4 and lymphoblastoid leukemia cells CEM-13, but most of them were active in the human monocyte cell lines U-937.

Indole molecules as inhibitors of tubulin polymerization: potential new anticancer agents

Agents that interfere with tubulin function have a broad anti-tumor spectrum and they represent one of the most significant classes of anticancer agents. In the past few years, several small synthetic molecules that have an indole nucleus as a core structure have been identified as tubulin inhibitors. Among these, several aroylindoles, arylthioindoles, diarylindoles and indolylglyoxyamides have shown good inhibition towards the tubulin polymerization. This article reviews the synthesis, biological activities and SARs of these main classes of indoles. Brief mention has also been made about the fused indole analogs as tubulin inhibitors.

Original TDAE strategy using propargylic chloride: rapid access to 1,4-diarylbut-3-ynol derivatives

We report herein the first synthesis of propargylic alcohols using an organic reducing agent. Diarylbutynol derivatives are formed in moderate to good yields under mild conditions from the reaction of 1-(3-chloroprop-1-ynyl)-4-nitrobenzene with various aromatic aldehydes using tetrakis(dimethylamino)ethylene (TDAE) as reductant.

Domino approach to 2-aroyltrimethoxyindoles as novel heterocyclic combretastatin A4 analogues

Two series of 2-aroyltrimethoxyindoles were designed to investigate the effects of the replacement of the trimethoxyphenyl ring of phenstatin with a trimethoxyindole moiety. These compounds were efficiently prepared through a domino palladium-catalyzed sequence from 2-gem-dibromovinylanilines substituted by three methoxy groups and arylboronic acids under carbon monoxide atmosphere. These novel heterocyclic combretastatin A4 analogues were evaluated for their cell growth inhibitory properties and their ability to inhibit the tubulin polymerization.