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The advancement of cancer-fighting drugs has never been a simple linear process. Those drug design professionals begin to find inspiration from the nature after failing to find the ideal products by creative drug design and high-throughput screening. To obtain new molecules for inhibiting tubulin, podophyllotoxin was adopted as the leading compound and 1,3,4-oxadiazole was brought in to the C-4 site of podophyllotoxin in this research. A series of seventeen podophyllotoxin-derived esters have been achieved and then evaluated their antitumor activities against four different cancer cell lines: A549, MCF-7, HepG2, and HeLa. Among all the compounds, compound 7c showed the best antiproliferating properties with IC 50  = 2.54 ± 0.82 μm against MCF-7 cancer cell line. It was obvious that the content of ROS grew significantly in MCF-7 in a way depending on the dosage. The time- and dose-dependent cell cycle assays revealed that compound 7c could apparently block cell cycle in the phase of G2/M along with the upregulation of cyclin A2 and CDK2 protein. According to further studies, confocal microscopy experiment has certified that compound 7c could restrain cancer from growing by blocking the polymerization of microtubule. Meanwhile, compound 7c could be ideally integrated with the colchicine site of tubulin. In future, it would be feasible to selectively design tubulin inhibitors with the help of 3D-QSAR. This means that it is hopeful to develop compound 7c as a potential agent against cancer due to its biological characteristics., (© 2017 John Wiley & Sons A/S.)

In this study, we report the identification of a new shikonin-phenoxyacetic acid derivative, as an inhibitor of tubulin. A series of compounds were prepared; among them, compound 16 [(R)-1-(5,8-dihydroxy-1,4-dioxo-1,4-dihydronaphthalen-2-yl)-4-methylpent-3-enyl 2-(4- phenoxyphenyl) acetate] potently inhibited the function of microtubules, inducing cell growth inhibition, apoptosis of cancer cell lines in a concentration and time-dependent manner. Molecular docking involving 16 at the vinblastine binding site of tubulin indicated that a phenoxy moiety interacted with tubulin via hydrogen bonding with asparaginate (Asn) and tyrosine (Tyr). Analysis of microtubules with confocal microscopy demonstrated that 16 altered the microtubule architecture and exhibited a significant reduction in microtubule density. Cell cycle assay further proved that HepG2 cells were blocked in G2/M phase. Our study provides a new, promising compound for the development of tubulin inhibitors by proposing a new target for the anticancer activity of shikonin., (© 2014 John Wiley & Sons A/S.)

A series of shikonin derivatives (1-13) that were acylated selectively by various thiophene or indol carboxylic acids at the side chain of shikonin were synthesized, and their biological activities were also evaluated as potential tubulin inhibitors. Among them, compound 3 ((R)-1-(5,8-dihydroxy-1,4-dioxo-1,4-dihydronaphthalen-2-yl)-4-methylpent-3-enyl 3-(1H-indol-3-yl)propanoate) and compound 8 ((R)-1-(5,8-dihydroxy-1,4-dioxo-1,4-dihydronaphthalen-2-yl)-4-methylpent-3-enyl 2-(thiophen-3-yl)acetate) exhibited good antiproliferative activity of A875 (IC50  = 0.005 ± 0.001 μm, 0.009  ± 0.002 μm) and HeLa (IC50  = 11.84 ± 0.64 μm, 4.62  ± 0.31 μm) cancer cell lines in vitro, respectively. Shikonin (IC50  = 0.46 ± 0.002 μm, 4.80 ± 0.48 μm) and colchicine (IC50  = 0.75 ± 0.05 μm, 17.79 ± 0.76 μm) were used as references. Meanwhile, they also showed the most potent growth inhibitory activity against tubulin (IC50 of 3.96  ± 0.13 μm and 3.05 ± 0.30 μm, respectively), which were compared with shikonin (IC50  =  15.20 ± 0.25 μm) and colchicine (IC50  = 3.50 ± 0.35 μm). Furthermore, from the results of flow cytometer, we found compound 3 can really inhibit HeLa cell proliferation and has low cell toxicity. Based on the preliminary results, compound 3 with potent inhibitory activity in tumor growth may be a potential anticancer agent., (© 2013 John Wiley & Sons A/S.)

Inducing apoptosis is an important and promising therapeutic approach to overcome cancer. Here, we described a series of novel synthesized compounds, cinnamic acyl shikonin derivatives (1b-19b), which were synthesized starting from shikonin and cinnamic acids, which exhibit anticancer activity via inducing apoptosis in vitro. Our flow cytometry results showed that compound 8b((E)-1-(5,8-dihydroxy-1,4-dioxo-1,4-dihydronaphthalen-2-yl)-4-methylpent -3-enyl-3-(3-(trifluoromethyl) phenyl)acrylate) (IC(50) = 0.69, 0.65, 1.62 μM for human SW872-s, A875 and A549 cell lines, respectively) exhibited conspicuous anticancer activities and has low cell toxicity in vitro. Therefore, we considered that compound 8b is potentially to be a candidate of anticancer agent. The proliferation inhibitory effect of compound 8b was associated with its apoptosis-inducing effect by activating caspase-3, caspase-7, caspase-9, and PARP. When the level of cleaved caspase-3, cleaved caspase-7, cleaved caspase-9, and cleaved PARP are rise, apoptosis of cancer cells will be induced., (© 2012 John Wiley & Sons A/S.)