A series of 3,6-diaryl-[1,2,4]triazolo[4,3-b]pyridazines were designed as a class of vinylogous CA-4 analogues. The easily isomerized (Z,E)-butadiene linker of vinylogous CA-4 was replaced by a rigid [1,2,4]triazolo[4,3-b]pyridazine scaffold. Twenty-one target compounds were synthesized and exhibited moderate to potent antiproliferative activity. The compound 4q with a 3-amino-4-methoxyphenyl moiety as the B-ring, comparable to CA-4 (IC50 = 0.009–0.012 μM), displayed the highly active antiproliferative activity against SGC-7901, A549, and HT-1080 cell lines with IC50 values of 0.014, 0.008, and 0.012 μM, respectively. Tubulin polymerization experiments indicated that 4q effectively inhibited tubulin polymerization, and immunostaining assay revealed that 4q significantly disrupted tubulin microtubule dynamics. Moreover, cell cycle studies revealed that compound 4q dramatically arrested cell cycle progression at G2/M phase in A549 cells. Molecular modeling studies showed that 4q could bind to the colchicine binding site on microtubules.Keywords: colchicine binding site; combretastatin A-4; molecular modeling; tubulin; [1,2,4]Triazolo[4,3-b]pyridazine;

•A series of antitubulin agents with a 5,5-fused-heterocycle scaffold were designed.•Compound 4f exhibited potent antiproliferative and antitubulin activities.•Compound 4f induced cell cycle arrest at G2/M phase.•The binding mode of 4f was determined by docking studies.A series of 3,6-diaryl-1H-pyrazolo[5,1-c][1,2,4]triazoles (I) and 3,6-diaryl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles (II) as antitubulin agents were designed, synthesized and bioevaluated. Compounds (II) 4a, 4d, 4f, 4j, 4l and 4n showed potent antiproliferative activity at sub-micromolar or nanomolar concentrations against SGC-7901, A549 and HT-1080 cell lines, indicating that the bioisosteric replacement of the carbonyl group and B-ring of SMART and ABI with a 5,5-fused-heterocycle scaffold successfully maintained potent antiproliferative activity. Compound 4f exhibited the most excellent antiproliferative activity against the three cancer cell lines (IC50 = 0.022–0.029 μM). Consistent with its potent antiproliferative activity, 4f also displayed excellent antitubulin activity (IC50 = 0.77 μM). Furthermore, compound 4f could dramatically affect cell morphology and microtubule networking, while cell cycle studies demonstrated that 4f significantly induced SGC-7901 cells arrest in G2/M phase. In addition, molecular docking studies supported the biological assay data and suggested that 4f may be a potential antitubulin agent.Download high-res image (398KB)Download full-size image

A series of 2-aryl-4-(3,4,5-trimethoxybenzoyl)-1,2,3-triazols were designed as analogs of substituted methoxybenzoyl-aryl-thiazole (SMART) under the consideration of geometric features. The target compounds were synthesized via concise and efficient processes including microwave-assisted cyclization, and were evaluated for their antiproliferative activity against three human cancer cell lines. Most compounds exhibited moderate antiproliferative activity with IC50 values in the micromolar to sub-micromolar range. Tubulin polymerization and immunofluorescence studies demonstrated that (Z)-9a was a potent microtubule-destabilizing agent and disrupted the polymerization dynamics. Moreover, (Z)-9a significantly induced accumulation of cells in the G2/M phase and caused microtubule destabilization. Molecular modeling studies showed that (Z)-9a probably binds to the colchicine site of tubulin.

•M-24 is newly synthesized analogue of nocodazole.•M-24 behaves as a tubulin inhibitor.•M-24 exhibits potent anticancer properties against HeLa and MCF-7 cells.•M-24 induces G2/M phase arrest and apoptosis in HeLa and MCF-7 cells.•The mechanisms of M-24 induced apoptosis in two cell lines are different.Methyl 5-[(1H-indol-3-yl)selanyl]-1H-benzoimidazol-2-ylcarbamate (M-24) is a newly synthesized analogue of nocodazole by our group and has been found to be active for some cancer cells. However, its sensitivity to different cell lines and the underlying anticancer mechanism are still unclear. In this study, we proved that M-24 had strong time- and dose-dependent anti-proliferative effects on human cervical cancer HeLa cells and human breast carcinoma MCF-7 cells. We demonstrated that the growth inhibitory effects of M-24 in both cell lines were associated with microtubule depolymerization. Furthermore, M-24 treatment resulted in cell cycle arrest at the G2/M phase in a dose-dependent manner with subsequent apoptosis induction. Western blotting analysis revealed that up-regulation of cyclin B1 and cdc2 was related with G2/M arrest in both cell lines. In addition, M-24-induced HeLa cell apoptosis was mainly associated with mitochondria-dependent intrinsic pathway. However, M-24-induced MCF-7 cell apoptosis was associated with both mitochondrial and death receptor pathway. In conclusion, M-24 caused apoptosis through disrupting microtubule assembly and inducing cell cycle arrest in HeLa and MCF-7 cells. Therefore, the novel compound M-24 is a promising microtubule-destabilizing agent that has great potential for the therapy of various malignancies especially human cervical and breast cancers.Download high-res image (288KB)Download full-size image

•BZML, as a novel CBSIs, has broad spectrum cytotoxic activity against various chemo-sensitive or -resistant cancer cells.•BZML is not a P-gp substrate and acts as an irreversible inhibitor of P-gp function in A549/Taxol cells.•BZML causes mitosis phase arrest by inhibiting tubulin polymerization in A549 and A549/Taxol cells.•BZML induces MC in A549/Taxol cells, which is different from apoptosis in A549 cells, to against apoptosis-resistance.Multidrug resistance (MDR) interferes with the efficiency of chemotherapy. Therefore, developing novel anti-cancer agents that can overcome MDR is necessary. Here, we screened a series of colchicine binding site inhibitors (CBSIs) and found that 5-(3, 4, 5-trimethoxybenzoyl)-4-methyl-2-(p-tolyl) imidazol (BZML) displayed potent cytotoxic activity against both A549 and A549/Taxol cells. We further explored the underlying mechanisms and found that BZML caused mitosis phase arrest by inhibiting tubulin polymerization in A549 and A549/Taxol cells. Importantly, BZML was a poor substrate for P-glycoprotein (P-gp) and inhibited P-gp function by decreasing P-gp expression at the protein and mRNA levels. Cell morphology changes and the expression of cycle- or apoptosis-related proteins indicated that BZML mainly drove A549/Taxol cells to die by mitotic catastrophe (MC), a p53-independent apoptotic-like cell death, whereas induced A549 cells to die by apoptosis. Taken together, our data suggest that BZML is a novel colchicine binding site inhibitor and overcomes MDR in A549/Taxol cells by inhibiting P-gp function and inducing MC. Our study also offers a new strategy to solve the problem of apoptosis-resistance.

•The combretastatin A-4/oltipraz hybrids were first introduced into CA-4 analogues.•A set of 4,5-diaryl-3H-1,2-dithiole-3-thiones and related compounds were synthesized.•4d and 5c showed potent antiproliferative activities at sub-micromolar IC50 values.•4d inhibited tubulin polymerization and caused cellular arrest in the G2/M phase.•4d was docked with a superimposed docked pose of CA-4.A new series of 4,5-diaryl-3H-1,2-dithiole-3-thiones and related compounds were designed and synthesised as combretastatin A-4/oltipraz hybrids. We evaluated the antiproliferative activities, inhibition of tubulin polymerization, and cell-cycle effects of these compounds. Several compounds in this series, such as 4d and 5c, displayed significant activity against SGC-7901, KB and HT-1080 cell lines, as determined using MTT assays. The most active compound, 4d, markedly inhibited tubulin polymerization, with an IC50 value of 4.44 μM being observed. In mechanistic studies, 4d caused cell arrest in G2/M phase, induced apoptotic cell death, and disrupted microtubule formation. Molecular docking studies revealed that 4d interacts and binds efficiently with the tubulin protein.

A series of new CA-4 analogues bearing maleic anhydride/N-substituted maleimide moiety were synthesized via a microwave-assisted process. They were evaluated for the anti-proliferative activities against three tumor cell lines (SGC-7901, HT-1080 and KB). Most compounds showed moderate potencies in micromolar range, with the most promising analogue 6f showing active at submicromolar concentration against HT-1080 cancer cells which was selected to investigate the antitumor mechanisms. In addition, molecular docking studies within the colchicine binding site of tubulin were also in good agreement with the tubulin polymerization inhibitory data and provided a basis for further structure-guided design of novel CA-4 analogues.

A series of (3/5-aryl-1,2,4-oxadiazole-5/3-yl)(3,4,5-trimethoxyphenyl)methanone oxime derivatives were synthesized via a rapid and facile microwave-assisted synthesis method of building a 1,2,4-oxadiazole skeleton using mandelic acid as the starting material. Twenty-four target compounds were evaluated for their in vitro antiproliferative activities against three human cancer cell lines (SGC-7901, A549 and HT-1080). Among them, 16b exhibited the highest potency against different tumour cell lines, especially the A549 cell line (IC50 = 87 nM). Structure–activity relationship (SAR) studies revealed that the aryl substituent at the C-5 position on the 1,2,4-oxadiazole ring is superior to that at the C-3 position. An oxime as a connector can obviously increase the potency, contrary to that in SMART derivatives. Moreover, 16b significantly induced a cell cycle arrest in the G2/M phase and caused microtubule destabilization. Molecular docking studies provided a theoretical binding mode of 16b at the colchicine site in the tubulin dimer. Our work laid the foundation for further structure-guided design of novel tubulin polymerization inhibitors.

A series of novel 2,3-diarylthiophene analogues of combretastatin A-4 (CA-4) were designed with a rigid thiophene moiety to retain the cis-olefin configuration of CA-4 and were subsequently synthesised. All of the target compounds were evaluated for their in vitro anti-proliferative activities. Among these compounds, 5f and 8d exhibited superior potency against different tumour cell lines with IC50 values at sub-micromolar levels. Moreover, compound 8d significantly inhibited tubulin polymerisation to microtubules and caused microtubule destabilisation. In addition, a molecular modelling study of compound 8d was performed to clarify its binding mode at the colchicine site in the tubulin dimer and to provide a basis for further structure-guided design of novel CA-4 analogues.

•A series of new non-purine XO inhibitors were designed and synthesized.•The selenium-containing heterocycle was first introduced into XO inhibitors.•Inhibitory activity of compound 9e was 3-fold more potent than that of febuxostat.•Steady-state kinetics data demonstrated that 9e was a mixed-type XO inhibitor.•Molecular docking studies gained an insight into binding mode of 9e with XO.A series of 2-phenyl-4-methyl-1,3-selenazole-5-carboxylic acid derivatives (8a–f, 9a–m) were synthesized and evaluated for inhibitory activity against xanthine oxidase in vitro. Structure–activity relationship analyses have also been presented. Most of the target compounds exhibited potency levels in the nanomolar range. Compound 9e emerged as the most potent xanthine oxidase inhibitor (IC50 = 5.5 nM) in comparison to febuxostat (IC50 = 18.6 nM). Steady-state kinetics measurements with the bovine milk enzyme indicated a mixed type inhibition with Ki and Ki′ values of 0.9 and 2.3 nM, respectively. A molecular modeling study on compounds 9e was performed to gain an insight into its binding mode with xanthine oxidase, and to provide the basis for further structure-guided design of new non-purine xanthine oxidase inhibitors related with 2-phenyl-4-methyl-1,3-selenazole-5-carboxylic acid scaffold.

•The selenium-containing heterocycle was first introduced into CA-4 analogues.•A series of novel 3,4-diaryl-1,2,5-selenadiazol derivatives were synthesized.•Several compounds were more potent than the standard CA-4.•3n was selected to investigate the antitumour mechanisms.•The binding mode of 3n was determined by docking studies.A set of novel selenium-containing heterocyclic analogues of combretastatin A-4 (CA-4) have been designed and synthesised using a rigid 1,2,5-selenadiazole as a linker to fix the cis-orientation of ring-A and ring-B. All of the target compounds were evaluated for their in vitro anti-proliferative activities. Among these compounds, compounds 3a, 3i, 3n and 3q exhibited superior potency against different tumour cell lines with IC50 values at the nanomolar level. Moreover, compound 3n significantly induced cell cycle arrest in the G2/M phase, inhibited tubulin polymerisation into microtubules and caused microtubule destabilisation. A molecular modelling study of compound 3n was performed to elucidate its binding mode at the colchicine site in the tubulin dimer and to provide a basis for the further structure-guided design of novel CA-4 analogues.

•A series of benzimidazole carbamates bearing indole moieties were synthesized.•The target compounds were evaluated on different human cancer cell lines.•The antiproliferative activity of 10a was equivalent to nocodazole.•10a and 7e were taken for cellular tubulin polymerization assay.•The binding mode of 10a was determined by docking studies.A series of novel benzimidazole carbamates bearing indole moieties with sulphur or selenium atoms connecting the aromatic rings were synthesised and evaluated for their antiproliferative activities against three human cancer cell lines (SGC-7901, A-549 and HT-1080) using an MTT assay. Compounds 10a, 10b, 7a, 7b and 7f showed significant activities against these cell lines. The most potent compound in this series, 10a, was selected to investigate its antitumour mechanism. In addition, molecular docking studies suggested that compound 10a interacts very closely with the nocodazole docking pose through hydrogen bonds at the colchicine binding site of tubulin.

The anti-mitotic agent, combretastatin A-4 (CA-4), is the lead compound of a new class of anti-cancer drugs that target tumor vasculature. 2-Methoxy-5-(2-(3, 4, 5-trimethoxyphenyl) thiophen-3-yl) aniline (DAT-230) is a structurally novel CA-4 analog with more stability. We investigated its anti-tumor activity and mechanisms in vitro and in vivo for the first time.Cytotoxicity was measured by MTT method. Apoptosis, mitochondria membrane potential (ΔΨm) and NO generation were measured by flow cytometry. Intracellular microtubule network was detected by immunofluorescence experiments. Protein expression was analyzed by Western blotting. In vivo, the anti-tumor activity was assessed using fibrosarcoma xenografts subcutaneously established in BALB/c nude mice. Vasculature perfusion was identified using fluorescent DNA-binding compound Hoechst 33342.DAT-230 exhibited potent anti-proliferative activity against various cancer cells. DAT-230-treatment in HT-1080 cells resulted in microtubule de-polymerization and G2/M phase arrest preceding apoptosis. Phosphor-cdc2 (thr14/tyr15) reduction, cyclin B1 accumulation and aberrant spindles denoted the cyclin B1-cdc2 complex active and M phase arrest in HT-1080 cells treated with DAT-230. Apoptosis induced by DAT-230 was related with the activation of caspase-9, caspase-3 and PARP cleavage, which were at the downstream of mitochondria. The decrease ratio of Bcl-2/Bax, elevation of NO and disruption of ΔΨm confirmed the causal relationship between DAT-230 and mitochondrial pathway. In vivo, DAT-230 delayed tumor growth, induced tumor perfusion decrease and extensive hemorrhagic-necrosis.DAT-230 is a promising microtubule inhibitor that has great potential for the treatment of fibrosarcoma in vitro and in vivo. Its potential to be a candidate of anti-cancer agent is worth being further investigated.

Two new series of biphenyls, analogs of aglycone of natural product fortuneanoside E, were prepared using Suzuki–Miyaura cross-coupling and selective magnesium iodide demethylation/debenzylation, and their mushroom tyrosinase inhibitory activity was evaluated. Most of the 4-hydroxy-3,5-dimethoxyphenyl biphenyl compounds (series II, 20–36) were in general more active than 3,4,5-trimethoxyphenyl biphenyl compounds (series I, 1–19). Structure–activity relationships study showed that monosaccharide substituents, such as glucose, were not necessary and the presence of 4-hydroxy-3,5-dimethoxyphenyl moiety was crucial for inhibitory activity. Among the compounds synthesised, compound 21 (IC50 = 0.02 mM) was found to be the most active one, which exhibited an activity that was 7 times higher than that of fortuneanoside E (IC50 = 0.14 mM) and 10 times higher than that of arbutin (IC50 = 0.21 mM), known as potent tyrosinase inhibitors. The inhibition kinetics analyzed by Lineweaver–Burk plots revealed that compound 21 was a competitive inhibitor (Ki = 0.015 mM).

An efficient selective demethylation and debenzylation method for aryl methyl/benzyl ethers using magnesium iodide under solvent-free conditions has been developed and applied to the synthesis of natural flavone and biphenyl glycosides. A variety of functional groups including glycoside were tolerated under the reaction conditions. Experimental results indicated that the removal of an O-benzyl group was easier than that of an O-methyl group, regardless of wherever they were meta or para to the carbonyl. Thus selective debenzylation can be achieved for substrates bearing both benzyloxy and methoxy groups.

A novel N-formylation and related reactions proceed from cyanides promoted by esters.

The first total synthesis of bulbophylol-B (1) has been achieved with the longest linear sequence of 12 steps and an overall yield of 17.9% via a new and practical approach to construct the dihydrodibenz[b,f]oxepin skeleton employing Wittig, selective reduction, and intramolecular Ullmann reactions as key steps.

An efficient selective demethylation and debenzylation method for aryl methyl/benzyl ethers using magnesium iodide under solvent-free conditions has been developed and applied to the synthesis of natural flavone and biphenyl glycosides. A variety of functional groups including glycoside were tolerated under the reaction conditions. Experimental results indicated that the removal of an O-benzyl group was easier than that of an O-methyl group, regardless of wherever they were meta or para to the carbonyl. Thus selective debenzylation can be achieved for substrates bearing both benzyloxy and methoxy groups.