Qi Guan

Synthesis and evaluation of benzimidazole carbamates bearing indole moieties for antiproliferative and antitubulin activities

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.

Synthesis and biological evaluation of novel 3,4-diaryl-1,2,5-selenadiazol analogues of combretastatin A-4

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.

3-(3-Hydroxy-4-methoxyphenyl)-4-(3,4,5-trimethoxyphenyl)-1,2,5-selenadiazole (G-1103), a novel combretastatin A-4 analog, induces G2/M arrest and apoptosis by disrupting tubulin polymerization in human cervical HeLa cells and fibrosarcoma HT-1080 cells.

Microtubule is a popular target for anticancer drugs. In this study, we describe the effect 3-(3-hydroxy-4-methoxyphenyl)-4-(3,4,5-trimethoxyphenyl)-1,2,5-selenadiazole (G-1103), a newly synthesized analog of combretastatin A-4 (CA-4), showing a strong time- and dose-dependent anti-proliferative effect on human cervical cancer HeLa cells and human fibrosarcoma HT-1080 cells. We demonstrated that the growth inhibitory effects of G-1103 in HeLa and HT-1080 cells were associated with microtubule depolymerization and proved that G-1103 acted as microtubule destabilizing agent. Furthermore, cell cycle analysis revealed that G-1103 treatment resulted in cell cycle arrest at the G2/M phase in a time-dependent manner with subsequent apoptosis induction. Western blot analysis revealed that down-regulation of cdc25c and up-regulation of cyclin B1 was related with G2/M arrest in HeLa and HT-1080 cells treatment with G-1103. In addition, G-1103 induced HeLa cell apoptosis by up-regulating cleaved caspase-3, Fas, cleaved caspase-8 expression, which indicated that G-1103 induced HeLa cell apoptosis was mainly associated with death receptor pathway. However, G-1103 induced HT-1080 cell apoptosis by up-regulating cleaved caspase-3, Fas, cleaved caspase-8, Bax and cleaved caspase-9 expression and down-regulating anti-apoptotic protein Bcl-2 expression, which indicated that G-1103 induced HT-1080 cell apoptosis was associated with both mitochondrial and death receptor pathway. Taken together, all the data demonstrated that G-1103 exhibited its antitumor activity through disrupting the microtubule assembly, causing cell cycle arrest and consequently inducing apoptosis in HeLa and HT-1080 cells. Therefore, the novel compound G-1103 is a promising microtubule inhibitor that has great potentials for therapeutic treatment of various malignancies.

Microwave-assisted synthesis and biological evaluation of 3,4-diaryl maleic anhydride/N-substituted maleimide derivatives as combretastatin A-4 analogues.

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.

BZML, a novel colchicine binding site inhibitor, overcomes multidrug resistance in A549/Taxol cells by inhibiting P-gp function and inducing mitotic catastrophe

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.

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 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.

Methyl 5-[(1H-indol-3-yl)selanyl]-1H-benzoimidazol-2-ylcarbamate (M-24), a novel tubulin inhibitor, causes G2/M arrest and cell apoptosis by disrupting tubulin polymerization in human cervical and breast cancer cells

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.

Design, synthesis and structure-activity relationship of 3,6-diaryl-7 H -[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines as novel tubulin inhibitors

A novel series of 3,6-diaryl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines were designed, synthesized and biologically evaluated as vinylogous CA-4 analogues, which involved a rigid [1,2,4]triazolo[3,4-b][1,3,4]thiadiazine scaffold to fix the configuration of (Z,E)-butadiene linker of A-ring and B-ring. Among these rigidly vinylogous CA-4 analogues, compounds 4d, 5b, 5i, 6c, 6e, 6g, 6i and 6k showed excellent antiproliferative activities against SGC-7901, A549 and HT-1080 cell lines with IC50 values at the nanomolar level. Compound 6i showed the most highly active antiproliferative activity against the three human cancer cell lines with an IC50 values of 0.011–0.015 µM, which are comparable to those of CA-4 (IC50 = 0.009–0.013 µM). Interestingly, SAR studies revealed that 3,4-methylenedioxyphenyl, 3,4-dimethoxyphenyl, 3-methoxyphenyl and 4-methoxyphenyl could replace the classic 3,4,5-trimethoxyphenyl in CA-4 structure and keep antiproliferative activity in this series of designed compounds. Tubulin polymerization experiments showed that 6i could effectively inhibit tubulin polymerization, which was corresponded with CA-4, and immunostaining experiments suggested that 6i significantly disrupted microtubule/tubulin dynamics. Furthermore, 6i potently induced cell cycle arrest at G2/M phase in SGC-7901 cells. Competitive binding assays and docking studies suggested that compound 6i binds to the tubulin perfectly at the colchicine binding site. Taken together, these results revealed that 6i may become a promising lead compound for new anticancer drugs discovery.

Synthesis and bioevaluation of N,4-diaryl-1,3-thiazole-2-amines as tubulin inhibitors with potent antiproliferative activity

A series of N,4-diaryl-1,3-thiazole-2-amines containing three aromatic rings with an amino linker were designed and synthesized as tubulin inhibitors and evaluated for their antiproliferative activity in three human cancer cell lines. Most of the target compounds displayed moderate antiproliferative activity, and N-(2,4-dimethoxyphenyl)-4-(4-methoxyphenyl)-1,3-thiazol-2-amine (10s) was determined to be the most potent compound. Tubulin polymerization and immunostaining experiments revealed that 10s potently inhibited tubulin polymerization and disrupted tubulin microtubule dynamics in a manner similar to CA-4. Moreover, 10s effectively induced SGC-7901 cell cycle arrest at the G2/M phase in both concentration- and time-dependent manners. The molecular docking results revealed that 10s could bind to the colchicine binding site of tubulin.

Direct cycle between co-product and reactant: an approach to improve the atom economy and its application in the synthesis and protection of primary amines

Two important goals of green chemistry are to maximize the efficiency of reactants and to minimize the production of waste. In this study, a novel approach to improve the atom economy of a chemical process was developed by incorporating a direct cycle between a co-product and a reactant of the same reaction. To demonstrate this concept, recoverable 3,4-diphenylmaleic anhydride (1) was designed and used for the atom-economical synthesis of aliphatic primary amines from aqueous ammonia. In each individual cycle, only ammonia and alkyl halide were consumed, and 1 was recovered in nearly a quantitative yield. In this approach for developing atom-economical protecting agents, 1 showed good performance as a recoverable protecting agent for primary amines. The broad substrate scope, good tolerance to various reaction conditions, and high reaction and recovery rates make 1 a valuable complement to conventional primary amine protecting agents.