Synthesis and biological evaluation of 2-amino-3-(3',4',5'-trimethoxybenzoyl)-6-substituted-4,5,6,7-tetrahydrothieno[2,3-c]pyridine derivatives as antimitotic agents and inhibitors of tubulin polymerization

Microtubules are among the most successful targets of compounds potentially useful for cancer therapy. A new series of inhibitors of tubulin polymerization based on the 2-amino-3-(3,4,5-trimethoxybenzoyl)-4,5,6,7-tetrahydrothieno[b]pyridine molecular skeleton was synthesized and evaluated for antiproliferative activity, inhibition of tubulin polymerization, and cell cycle effects. The most promising compound in this series was 2-amino-3-(3,4,5-trimethoxybenzoyl)-6-methoxycarbonyl-4,5,6,7-tetrahydrothieno[b]pyridine, which inhibits cancer cell growth with IC(50)-values ranging from 25 to 90 nM against a panel of four cancer cell lines, and interacts strongly with tubulin by binding to the colchicine site. In this series of N(6)-carbamate derivatives, any further increase in the length and in the size of the alkyl chain resulted in reduced activity.     

Design,synthesis and structure–activity relationship of 2-(3′,4′,5′-trimethoxybenzoyl)-benzo[b]furan derivatives as a novel class of inhibitors of tubulin polymerization

The biological importance of microtubules in mitosis and cell division makes them an interesting target for the development of anticancer agents. Small molecules such as benzo[b]furans are attractive as inhibitors of tubulin polymerization. Thus, a new class of inhibitors of tubulin polymerization based on the 2-(3′,4′,5′-trimethoxybenzoyl)-benzo[b]furan molecular skeleton, with electron-donating (Me, OMe or OH) or electron-withdrawing (F, Cl and Br) substituents on the benzene ring, was synthesized and evaluated for antiproliferative activity, inhibition of tubulin polymerization and cell cycle effects. Adding a methyl group at the C-3 position resulted in increased activity. The most promising compound in this series was 2-(3′,4′,5′-trimethoxybenzoyl)-3-methyl-6-ethoxy-benzo[b]furan, which inhibits cancer cell growth at nanomolar concentrations and interacts strongly with tubulin by binding to the colchicine site.     

Substituted 2-(3′,4′,5′-trimethoxybenzoyl)-benzo[b]thiophene derivatives as potent tubulin polymerization inhibitors

The central role of microtubules in cell division and mitosis makes them a particularly important target for anticancer agents. On our early publication, we found that a series of 2-(3′,4′,5′-trimethoxybenzoyl)-3-aminobenzo[b]thiophenes exhibited strong antiproliferative activity in the submicromolar range and significantly arrested cells in the G2–M phase of the cell cycle and induced apoptosis.In order to investigate the importance of the amino group at the 3-position of the benzo[b]thiophene skeleton, the corresponding 3-unsubstituted and methyl derivatives were prepared. A novel series of inhibitors of tubulin polymerization, based on the 2-(3,4,5-trimethoxybenzoyl)-benzo[b]thiophene molecular skeleton with a methoxy substituent at the C-4, C-5, C-6 or C-7 position on the benzene ring, was evaluated for antiproliferative activity against a panel of five cancer cell lines, for inhibition of tubulin polymerization and for cell cycle effects. Replacing the methyl group at the C-3 position resulted in increased activity compared with the corresponding 3-unsubstituted counterpart. The structure–activity relationship established that the best activities were obtained with the methoxy group placed at the C-4, C-6 or C-7 position. Most of these compounds exhibited good growth inhibition activity and arrest K562 cells in the G2–M phase via microtubule depolymerization.     

A new anti-tubulin agent containing the benzo[b]thiophene ring system.

A new type of inhibitor of tubulin polymerization was discovered based on the 3-aroyl-2-arylbenzo[b]thiophene molecular skeleton. The lead compound in this series, 2-(4'-methoxyphenyl)-3-(3',4',5'-trimethoxybenzoyl)-6-methoxybe nzo[b]thiophene 1, inhibited tubulin polymerization, caused an increase in the mitotic index of CA46 Burkitt lymphoma cells, and inhibited the growth of several human cancer cell lines.     

A novel tubulin inhibitor, 6h,suppresses tumor-associated angiogenesis and shows potent antitumor activity against non–small cell lung cancers

Tumor angiogenesis is closely associated with the metastasis and progression of non–small cell lung cancer (NSCLC), a highly vascularized solid tumor. However, novel therapeutics are lacking for the treatment of this cancer. Here, we developed a series of 2-aryl-4-(3,4,5-trimethoxy-benzoyl)-5-substituted-1,2,3-triazol analogs (6a–6x) as tubulin colchicine-binding site inhibitors, aiming to find a novel promising drug candidate for NSCLC treatment. We first identified 2-(2-fluorophenyl)-3-(3,4,5-trimethoxybenzoyl)-5-(3-hydroxyazetidin-1-yl)-2H-1,2,3-triazole (6h) as a hit compound, which inhibited angiogenesis induced by NSCLC cells both in vivo and in vitro. In addition, our data showed that 6h could tightly bind to the colchicine-binding site of tubulin and inhibit tubulin polymerization. We also found that 6h could effectively induce G2/M cell cycle arrest of A549 and H460 cells, inhibit cell proliferation, and induce apoptosis. Furthermore, we showed 6h had the potential to inhibit the migration and invasion of NSCLC cells, two basic characteristics of tumor metastasis. Finally, we found 6h could effectively inhibit tumor progression in A549 xenograft mouse models with minimal toxicity. Taken together, these findings provide strong evidence for the development of 6h as a promising microtubule colchicine-binding site inhibitor for NSCLC treatment.     

Anti-cancer activity of m-carborane-containing trimethoxyphenyl derivatives through tubulin polymerization inhibition

m-Carborane-containing compound 1a was identified as a cell growth inhibitor from a random screening of a boron compound library. As 1a is a mixture of diastereomers due to the presence of two chiral carbons, we designed achiral derivatives 2–4 and studied the structure-activity relationships of the methoxy groups on the benzene ring. 3,4,5-Trimethoxybenzyl derivative 2a and 3,4,5-trimethoxybenzoyl derivative 3a showed more potent anti-cancer activity against the human breast cancer cell line MDA-MB-453 than lead compound 1a. Compound 3a inhibited tubulin polymerization in a dose-dependent manner.     

1,5-Disubstituted 1,2,3-triazoles as cis-restricted analogues of combretastatin A-4: Synthesis, molecular modeling and evaluation as cytotoxic agents and inhibitors of tubulin

A series of cis-restricted 1,5-disubstituted 1,2,3-triazole analogues of combretastatin A-4 (1) have been prepared. The triazole 12f, 2-methoxy-5-(1-(3,4,5-trimethoxyphenyl)-1H-1,2,3-triazol-5-yl)aniline, displayed potent cytotoxic activity against several cancer cell lines with IC₅₀ values in the nanomolar range. The ability of triazoles to inhibit tubulin polymerization has been evaluated, and 12f inhibited tubulin polymerization with IC₅₀ = 4.8 μM. Molecular modeling experiments involving 12f and the colchicine binding site of ,β-tubulin showed that the triazole moiety interacts with β-tubulin via hydrogen bonding with several amino acids.     

Discovery of 1-benzoyl-3-cyanopyrrolo[1,2-a]quinolines as a new series of apoptosis inducers using a cell- and caspase-based high-throughput screening assay. Part 1: Structure-activity relationships of the 1- and 3-positions

1-Benzoyl-3-cyanopyrrolo[1,2-a]quinoline (2a) was identified as a novel apoptosis inducer through our caspase- and cell-based high-throughput screening assay. Compound 2a had good activity against several breast cancer cell lines but was much less active against several other cancer cell lines. SAR studies of 2a found that substitution at the 4-position of the 1-benzoyl group was important for activity. Replacing the 3-cyano group by an ester or ketone group led to inactive compounds. Interestingly, 4-substituted analogs such as 1-(4-(1H-imidazol-1-yl)benzoyl)-3-cyanopyrrolo[1,2-a]quinoline (2k) were found to be broadly and highly active in the caspase activation assay as well as in the cell growth inhibition assay with low nM EC(50) and GI(50) values in human breast cancer cells T47D, human colon cancer cells HCT116, and hepatocellular carcinoma cancer cells SNU398. Compound 2a was found not to inhibit tubulin polymerization up to 50 microM, while 2k was found to inhibit tubulin polymerization with an IC(50) value of 5 microM, indicating that certain substituents at the 4-position of the 1-benzoyl group can change the mechanism of action.     

Synthesis of 1-(3',4',5'-trimethoxy) phenyl naphtho[2,1b]furan as a novel anticancer agent

3',4',5'-Trimethoxy benzoyl-naphthalene 2-O-acetic acid (5) underwent base catalysed intramolecular condensation to yield exclusively 1-(3',4',5'-trimethoxy) phenyl naphtho[2,1-b]furan 8. The cyclised product 8 has been characterised by spectroscopy. The product 8 showed significant anticancer activity against human cancer cell lines COLO320DM (colon), CaCO2 (colon) and WRL68 (liver) at 0.7, 0.65 and 0.50 microg/ml concentrations, respectively, in the in vitro MTT assay.     

BF12, a Novel Benzofuran,Exhibits Antitumor Activity by Inhibiting Microtubules and the PI3K/Akt/mTOR Signaling Pathway in Human Cervical Cancer Cells

BF12 [(2E)‐3‐[6‐Methoxy‐2‐(3,4,5‐trimethoxybenzoyl)‐1‐benzofuran‐5‐yl]prop‐2‐enoic acid], a novel derivative of combretastatin A‐4 (CA‐4), was previously found to inhibit tumor cell lines, with a particularly strong inhibitory effect on cervical cancer cells. In this study, we investigated the microtubule polymerization effects and apoptosis signaling mechanism of BF12. BF12 showed a potent efficiency against cervical cancer cells, SiHa and HeLa, with IC₅₀ values of 1.10 and 1.06 μm , respectively. The cellular mechanism studies revealed that BF12 induced G2/M phase arrest and apoptosis in SiHa and HeLa cells, which were associated with alterations in the expression of the cell G2/M cycle checkpoint‐related proteins (cyclin B1 and cdc2) and alterations in the levels of apoptosis‐related proteins (P53, caspase‐3, Bcl‐2, and Bax) of these cells, respectively. Western blot analysis showed that BF12 inhibited the PI3 K/Akt/mTOR signaling pathway and induced apoptosis in human cervical cancer cells. BF12 was identified as a tubulin polymerization inhibitor, evidenced by the effective inhibition of tubulin polymerization and heavily disrupted microtubule networks in living SiHa and HeLa cells. By inhibiting the PI3 K/Akt/mTOR signaling pathway and inducing apoptosis in human cervical cancer cells, BF12 shows promise for use as a microtubule inhibitor.     

Novel [1,2,4]triazolo[1,5-a]pyrimidine derivatives as potent antitubulin agents: Design,multicomponent synthesis and antiproliferative activities

As restricted CA-4 analogues, a novel series of [1,2,4]triazolo[1,5-a]pyrimidines possessing 3,4,5-trimethoxylphenyl groups has been achieved successfully via an efficient one-pot three-component reaction of 3-(3,4,5-trimethoxyphenyl)-1H-1,2,4-triazol-5-amine, 1,3-dicarbonyl compounds and aldehydes. Initial biological evaluation demonstrated some of target compounds displayed potent antitumor activity in vitro against three cancer cell lines. Among them, the most highly active analogue 26 inhibited the growth of HeLa, and A549 cell lines with IC₅₀ values at 0.75, and 1.02 μM, respectively, indicating excellent selectivity over non-tumoural cell line HEK-293 (IC₅₀ = 29.94 μM) which suggested that the target compounds might possess a high safety index. Moreover, cell cycle analysis illustrated that the analogue 26 significantly induced HeLa cells arrest in G2/M phase, meanwhile the compound could dramatically affect cell morphology and microtubule networks. In addition, compound 28 exhibited potent anti-tubulin activity with IC₅₀ values of 9.90 μM, and molecular docking studies revealed the analogue occupied the colchicine-binding site of tubulin. These observations suggest that [1,2,4]triazolo[1,5-a]pyrimidines represent a new class of tubulin polymerization inhibitors and well worth further investigation aiming to generate potential anticancer agents.     

α-, β-, and γ-Tubulin Polymerization in Response to DNA Damage

Microtubules provide structural support for a cell and play key roles in cell motility, mitosis, and meiosis. They are also the targets of several anticancer agents, indicating their importance in maintaining cell viability. We have investigated the possibility that alterations in microtubule structure and tubulin polymerization may be part of the cellular response to DNA damage. In this report, we find that γ-radiation stimulates the production and polymerization of α-, β-, and γ- tubulin in hematopoeitic cell lines (Ramos, DP16), leading to visible changes in microtubule structures. We have found that this microtubule reorganization can be prevented by caffeine, a drug that concomitantly inhibits DNA damage-induced cell cycle arrest and apoptosis. Our results support the idea that microtubule polymerization is an important facet of the mammalian response to DNA damage.     

Synthesis of novel antimitotic agents based on 2-amino-3-aroyl-5-(hetero)arylethynyl thiophene derivatives

Microtubules are dynamic structures that play a crucial role in cellular division and are recognized as an important target for cancer therapy. In search of new compounds with strong antiproliferative activity and simple molecular structure, a new series of 2-amino-3-(3′,4′,5′-trimethoxybenzoyl)-5-(hetero)aryl ethynyl thiophene derivatives was prepared by the Sonogashira coupling reaction of the corresponding 5-bromothiophenes with several (hetero)aryl acetylenes. When these compounds were analyzed in vitro for their inhibition of cell proliferation, the 2- and 3-thiophenyl acetylene derivatives were the most powerful compounds, both of which exerted cytostatic effects at submicromolar concentrations. In contrast, the presence of a more flexible ethyl chain between the (hetero)aryl and the 5-position of the thiophene ring resulted in significant reduction in activity relative to the 5-(hetero)aryl acetylene substituted derivatives. The effects of a selected series of compounds on cell cycle progression correlated well with their strong antiproliferative activity and inhibition of tubulin polymerization. We found that the antiproliferative effects of the most active compounds were associated with increase of the proportion of cells in the G₂/M and sub-G₁ phases of the cell cycle.     

Synthesis, biological evaluation and molecular modeling of 1,2,3-triazole analogs of combretastatin A-1

The synthesis, cytotoxicity, inhibition of tubulin polymerization data and anti-angiogenetic effects of seven 1,5-disubstituted 1,2,3-triazole analogs and two 1,4-disubstituted 1,2,3-triazole analogs of combretastatin A-1 (1) are reported herein. The biological studies revealed that the 1,5-disubstituted 1,2,3-triazoles 3-methoxy-6-(1-(3,4,5-trimethoxyphenyl)-1H-1,2,3-triazol-5-yl)benzene-1,2-diol (6), 3-methoxy-6-(1-(3,4,5-trimethoxyphenyl)-1H-1,2,3-triazol-5-yl)benzene-1,2-diamine (8) and 5-(2,3-difluoro-4-methoxyphenyl)-1-(3,4,5-trimethoxyphenyl)-1H-1,2,3-triazole (9) were the three most active compounds regarding inhibition of both tubulin polymerization and angiogenesis. Molecular modeling studies revealed that combretastatins 1 and 2 and analogs 5-11 could be successfully docked into the colchicine binding site of α,β-tubulin.     

Synthesis,cytotoxic evaluation and molecular docking study of 2-alkylthio-4-(2,3,4-trimethoxyphenyl)-5-aryl-thiazoles as tubulin polymerization inhibitors

A series of cis-restricted 2-alkylthio-4-(2,3,4-trimethoxyphenyl)-5-aryl-thiazole analogues of combretastatin A-4 were synthesized and investigated for inhibition of cell proliferation against three cancer cell lines, HT-29, MCF-7, and AGS, and a normal mouse fibroblastic cell line, NIH-3T3, using an MTT assay. The biological study showed that 2-(methylthio) substituted compounds showed little cytotoxic activity against the four cell lines. In contrast, the presence of the 2-(benzylthio) group on the thiazole ring resulted in a significant improvement in cytotoxic activity relative to the 2-(methylthio) substituted derivatives. Furthermore, the inhibition of tubulin polymerization by some potent compounds was evaluated. All the compounds studied were moderate tubulin polymerization inhibitors. The flow cytometry analysis confirmed that the synthesized compounds led to cell cycle arrest at the G₂/M phase. Docking simulation was performed to insert these compounds into the crystal structure of tubulin at the colchicine binding site to determine a probable binding model.     

The effects of colchicine analogues on the reaction of tubulin with iodo[14C]acetamide and N,N'-ethylenebis(iodoacetamide)

We have previously found (Ludue?a, R. F., and Roach, M. C. (1981b) Biochemistry 20, 4444-4450) that colchicine and podophyllotoxin inhibit the alkylation of tubulin by iodo[14C]acetamide and the formation of an intrachain cross-link in the beta-tubulin subunit by N,N'-ethylenebis(iodoacetamide) (EBI). It was not clear whether these effects were due to conformational changes in tubulin induced by drugs or to direct steric blockage of the sulfhydryl groups involved. In an effort to characterize further these phenomena, we have examined the effects of single-ring and bicyclic analogues of colchicine on the reaction of tubulin with iodo[14C]acetamide and EBI. We have found that neither the A-ring analogues, 3,4,5-trimethoxybenzyl alcohol, 3,4,5-trimethoxybenzaldehyde, 2,3,4-trimethoxybenzaldehyde, and benzaldehyde, nor the C-ring analogues, tropolone and tropolone methyl ether, inhibited alkylation. In contrast, colchicine, podophyllotoxin, and nocodazole and the bicyclic analogues, 5-(2',3',4'-trimethoxyphenyl)-2-methoxytropone and combretastatin, inhibited tubulin alkylation. Since the presence of a bond joining the A and C rings seems to be the determining factor in the suppression of alkylation, it is likely that inhibition by colchicine of the reaction with iodo[14C] acetamide is due largely to a conformational change induced by colchicine. A different pattern was obtained when the effects on cross-link formation by EBI were examined. Here, all the A-ring analogues, the bicyclic analogues, and colchicine, podophyllotoxin, and nocodazole all inhibited formation of the cross-link, whereas the C-ring analogue tropolone methyl ether did not inhibit cross-link formation. Since compounds whose effect on alkylation is markedly different have the same effect on cross-link formation, it is possible that this effect is a steric one and that perhaps the A-ring of colchicine binds to tubulin very close to one of the sulfhydryls involved in the intrachain cross-link formed by EBI in beta-tubulin.     

Synthesis and biological evaluation of 3-functionalized 2-phenyl- and 2-alkylbenzo[b]furans as antiproliferative agents against human melanoma cell line

The key function of microtubules and mitotic spindle in cell division make them attractive targets in anticancer therapy. In the present study, functionalized in 3 position 2-phenyl- and 2-alkylbenzo[b]furans were synthesized and evaluated as antitumor agents. Among the synthesized derivatives 13a, 13b and 14 exhibited the most potent antiproliferative activity against human melanoma A375 cell line with IC₅₀ values of 2.85 µM, 0.86 µM, 0.09 µM, respectively. The most promising compound defined was 14 with three methoxy groups in the 3-aroyl substituent and 7-methoxy group in 2-phenylbenzo[b]furan skeleton. Tubulin polymerization assay, confocal microscopy imaging and flow cytometry analysis revealed that 2-phenyl-3-aroylbenzo[b]furans (13a, 13b and 14) inhibited tubulin polymerization leading to disruption of mitotic spindle formation, cell cycle arrest in G2/M phase and apoptosis.     

Design, synthesis, biochemical, and biological evaluation of nitrogen-containing trifluoro structural modifications of combretastatin A-4

A new trifluorinated amino-combretastatin analogue, (Z)-2-(4'-methoxy-3'-aminophenyl)-1-(3,4,5-trifluorophenyl)ethene, prepared by chemical synthesis, was found to be a potent inhibitor of tubulin assembly (IC(50)=2.9 microM), and cytotoxic against selected human cancer cell lines. This new lead compound is among the most active from a group of related structural modifications.     

Interaction of tubulin with bifunctional colchicine analogues: an equilibrium study

The interaction of tubulin with simple analogues of colchicine that contain both its tropolone and trimethoxyphenyl rings has been characterized, and the results were analyzed in terms of the simple bifunctional ligand model developed for the binding of colchicine [ Andreu , J. M., & Timasheff , S. N. (1982) Biochemistry 21, 534-543] on the basis of interactions of tubulin with single-ring analogues. The compound 2-methoxy-5-(2,3,4-trimethoxyphenyl)-2,4,6- cycloheptatrien -1-one has been found to bind reversibly to 0.86 +/- 0.06 site of purified calf brain tubulin with an equilibrium constant of (4.9 +/- 0.3) X 10(5) M-1 (25 degrees C), delta H degrees app = -1.6 +/- 0.7 kcal mol-1, and delta S degrees app = 20.5 +/- 2.5 eu. The binding appears specific for the colchicine site. The closely related compound 2-methoxy-5-[[3-(3,4,5-trimethoxyphenyl)-propionyl]amino] -2,4,6- cycloheptatrien -1-one interacts weakly with tubulin. Binding of the first analogue is accompanied by ligand fluorescence appearance, quenching of protein fluorescence, perturbation of the far-ultraviolet circular dichroism of tubulin, and induction of the tubulin GTPase activity, similarly to colchicine binding. Substoichiometric concentrations of the analogue inhibit microtubule assembly in vitro. Excess analogue concentration under microtubule-promoting conditions induces an abnormal cooperative polymerization of tubulin, similar to that of the tubulin-colchicine complex.     

Synthesis and antiproliferative evaluation of pyrazolo[1,5-a]-1,3,5-triazine myoseverin derivatives

Pyrazolo[1,5-a]-1,3,5-triazine myoseverin derivatives 1a–c were prepared from 4-(N-methyl-N-phenylamino)-2-methylsulfanylpyrazolo[1,5-a]-1,3,5-triazine 2. Their cytotoxic activity, inhibition of tubulin polymerization, and cell cycle effects were evaluated. Compounds 1a and 1c are potent tubulin inhibitors and displayed specific antiproliferative activity in colorectal cancer cell lines at micromolar concentrations.