Polygamain, a new microtubule depolymerizing agent that occupies a unique pharmacophore in the colchicine site

Identification of novel microtubule inhibitors effective in fission yeast and human cells and their effects on breast cancer cell lines

Microtubules are critical for a variety of cellular processes such as chromosome segregation, intracellular transport and cell shape. Drugs against microtubules have been widely used in cancer chemotherapies, though the acquisition of drug resistance has been a significant issue for their use. To identify novel small molecules that inhibit microtubule organization, we conducted sequential phenotypic screening of fission yeast and human cells. From a library of diverse 10 371 chemicals, we identified 11 compounds that inhibit proper mitotic progression both in fission yeast and in HeLa cells. An in vitro assay revealed that five of these compounds are strong inhibitors of tubulin polymerization. These compounds directly bind tubulin and destabilize the structures of tubulin dimers. We showed that one of the compounds, L1, binds to the colchicine-binding site of microtubules and exhibits a preferential potency against a panel of human breast cancer cell lines compared with a control non-cancer cell line. In addition, L1 overcomes cellular drug resistance mediated by βIII tubulin overexpression and has a strong synergistic effect when combined with the Plk1 inhibitor BI2536. Thus, we have established an economically effective drug screening strategy to target mitosis and microtubules, and have identified a candidate compound for cancer chemotherapy.

Asymmetric Total Synthesis of Aglacins A, B, and E

An asymmetric photoenolization/Diels-Alder (PEDA) reaction between electron-rich 2-methylbenzaldehydes and unsaturated γ-lactones was developed to directly construct the basic tricyclic core of aryltetralin lactone lignans. This methodology enabled the first asymmetric total synthesis of aglacins A, B, and E and revision of the absolute configuration of these natural lignans. The strategy was also used to prepare the naturally occurring aryldihydronaphthalene-type lignans (-)-7,8-dihydroisojusticidin B and (+)-linoxepin in four and six steps, as well as 27 natural-product-like molecules containing a C8' quaternary center. We believe that the synthetic aglacins and small-molecule library provide new opportunities to carry out the SAR studies of the podophyllotoxin family of natural products.

Asymmetric Chemoenzymatic Synthesis of (-)-Podophyllotoxin and Related Aryltetralin Lignans

(-)-Podophyllotoxin is one of the most potent microtubule depolymerizing agents and has served as an important lead compound in antineoplastic drug discovery. Reported here is a short chemoenzymatic total synthesis of (-)-podophyllotoxin and related aryltetralin lignans. Vital to this approach is the use of an enzymatic oxidative C-C coupling reaction to construct the tetracyclic core of the natural product in a diastereoselective fashion. This strategy allows gram-scale access to (-)-deoxypodophyllotoxin and is readily adaptable to the preparation of related aryltetralin lignans.

Synthesis and Biological Evaluation of 4β-N-Acetylamino Substituted Podophyllotoxin Derivatives as Novel Anticancer Agents

A series of novel podophyllotoxin derivatives obtained by 4β-N-acetylamino substitution at C-4 position was designed, synthesized, and evaluated for in vitro cytotoxicity against four human cancer cell lines (EC-9706, HeLA, T-24 and H460) and a normal human epidermal cell line (HaCaT). The cytotoxicity test indicated that most of the derivatives displayed potent anticancer activities. In particular, compound 12h showed high activity with IC₅₀ values ranging from 1.2 to 22.8 μM, with much better cytotoxic activity than the control drug etoposide (IC₅₀: 8.4 to 78.2 μM). Compound 12j exhibited a promising cytotoxicity and selectivity profile against T24 and HaCaT cell lines with IC₅₀ values of 2.7 and 49.1 μM, respectively. Compound 12g displayed potent cytotoxicity against HeLA and T24 cells with low activity against HaCaT cells. According to the results of fluorescence-activated cell sorting (FACS) analysis, 12g induced cell cycle arrest in the G2/M phase accompanied by apoptosis in T24 and HeLA cells. Furthermore, the docking studies showed possible interactions between human DNA topoisomerase IIα and 12g. These results suggest that 12g merits further optimization and development as a new podophyllotoxin-derived lead compound.

Anti-tubulin agents of natural origin: Targeting taxol, vinca, and colchicine binding domains

Microtubules are a protein which is made of α- and β-heterodimer. It is one of the main components of the cell which play a vital role in cell division especially in G2/M-phase. It exists in equilibrium dynamic of polymerization and depolymerization of α- and β-heterodimer. It is one of the best targets for developing anti-cancer drugs. Various natural occurring molecules are well known for their anti-tubulin effect such as vinca, paclitaxel, combretastatin, colchicine etc. These microtubule-targeted drugs are acted through two processes (i) inhibiting depolymerization of tubulin (tubulin stabilizing agents) and (ii) inhibiting polymerization of tubulin (tubulin destabilizing agents). Now days, various binding domains have been explore through which these molecules are binding to tubulin but the three major binding domain of tubulin are taxol, vinca and colchicine binding domain. The present article mainly focus on the classification of various naturally occurring compounds on the basis of their inhibition processes (depolymerization and polymerization) and the site of interaction (targets taxol, vinca and colchicine binding domain) which has been hitherto reported. By placing all the naturally occurring taxol, vinca and colchicine binding site analogues at one place makes a better understanding of the tubulin interactions with known natural tubulin binders that would helps in the discovery of new and potent natural, semi-synthetic and synthetic analogues for treating cancer.

Antivascular and antitumor properties of the tubulin-binding chalcone TUB091

We investigated the microtubule-destabilizing, vascular-targeting, anti-tumor and anti-metastatic activities of a new series of chalcones, whose prototype compound is (E)-3-(3’’-amino-4’’-methoxyphenyl)-1-(5’-methoxy-3’,4’-methylendioxyphenyl)-2-methylprop-2-en-1-one (TUB091). X-ray crystallography showed that these chalcones bind to the colchicine site of tubulin and therefore prevent the curved-to-straight structural transition of tubulin, which is required for microtubule formation. Accordingly, TUB091 inhibited cancer and endothelial cell growth, induced G2/M phase arrest and apoptosis at 1-10 nM. In addition, TUB091 displayed vascular disrupting effects in vitro and in the chicken chorioallantoic membrane (CAM) assay at low nanomolar concentrations. A water-soluble L-Lys-L-Pro derivative of TUB091 (i.e. TUB099) showed potent antitumor activity in melanoma and breast cancer xenograft models by causing rapid intratumoral vascular shutdown and massive tumor necrosis. TUB099 also displayed anti-metastatic activity similar to that of combretastatin A4-phosphate. Our data indicate that this novel class of chalcones represents interesting lead molecules for the design of vascular disrupting agents (VDAs). Moreover, we provide evidence that our prodrug approach may be valuable for the development of anti-cancer drugs.

Arylidene indanone scaffold: medicinal chemistry and structure–activity relationship view

Arylidene indanone (AI) scaffolds are considered as the rigid cousins of chalcones, incorporating the α,β-unsaturated ketone system of chalcones forming a cyclic 5 membered ring.

Melampodium leucanthum, a source of cytotoxic sesquiterpenes with antimitotic activities

A new tricyclic sesquiterpene, named meleucanthin (1), was isolated from an extract of the leaves and branches of Melampodium leucanthum, along with four known germacranolide sesquiterpene lactones, leucanthin-A (2), leucanthin-B (3), melampodin-A acetate (4), and 3α-hydroxyenhydrin (5). The chemical structure of 1 was elucidated by analysis of 1D and 2D NMR and mass spectrometric data. All compounds exhibited antiproliferative and cytotoxic efficacy against PC-3 and DU 145 prostate cancer cells, as well as HeLa cervical cancer cells, with IC50 values ranging from 0.18 to 9 μM. These compounds were effective in clonogenic assays and displayed high cellular persistence. They were also found to be capable of circumventing P-glycoprotein-mediated drug resistance. Mechanism of action studies showed that 4 caused an accumulation of cells in the G2/M phase of the cell cycle, and 2-5 caused the formation of abnormal mitotic spindles. These results suggest the cytotoxic effects of these germacranolides involve inhibition of mitotic spindle function, and it is likely that other mechanisms additionally contribute to cell death. These studies also demonstrate the possibility of isolating new, biologically active compounds from indigenous Texas plants.

Design and synthesis of 6,7-methylenedioxy-4-substituted phenylquinolin-2(1H)-one derivatives as novel anticancer agents that induce apoptosis with cell cycle arrest at G2/M phase

Novel 6,7-methylenedioxy-4-substituted phenylquinolin-2(1H)-one derivatives 12a-n were designed and prepared through an intramolecular cyclization reaction and evaluated for in vitro anticancer activity. Among the synthesized compounds, 6,7-methylenedioxy-4-(2,4-dimethoxyphenyl)quinolin-2(1H)-one (12e) displayed potent cytotoxicity against several different tumor cell lines at a sub-micromolar level. Furthermore, results of fluorescence-activated cell sorting (FACS) analysis suggested that 12e induced cell cycle arrest in the G2/M phase accompanied by apoptosis in HL-60 and H460 cells. This action was confirmed by Hoechst staining and caspase-3 activation. Due to their easy synthesis and remarkable biological activities, 4-phenylquinolin-2(1H)-one analogs (4-PQs) are promising new anticancer leads based on the quinoline scaffold. Accordingly, compound 12e was identified as a new lead compound that merits further optimization and development as an anticancer candidate.

An overview of tubulin inhibitors that interact with the colchicine binding site

Tubulin dynamics is a promising target for new chemotherapeutic agents. The colchicine binding site is one of the most important pockets for potential tubulin polymerization destabilizers. Colchicine binding site inhibitors (CBSI) exert their biological effects by inhibiting tubulin assembly and suppressing microtubule formation. A large number of molecules interacting with the colchicine binding site have been designed and synthesized with significant structural diversity. CBSIs have been modified as to chemical structure as well as pharmacokinetic properties, and tested in order to find a highly potent, low toxicity agent for treatment of cancers. CBSIs are believed to act by a common mechanism via binding to the colchicine site on tubulin. The present review is a synopsis of compounds that have been reported in the past decade that have provided an increase in our understanding of the actions of CBSIs.

Amyrisins A-C, O-prenylated flavonoids from Amyris madrensis

Three new O-prenylated flavonoids, amyrisins A-C (1-3), were isolated from the leaves and twigs of Amyris madrensis, along with the known compound polygamain (4). The structures of 1-3 were elucidated on the basis of the analysis of spectroscopic data interpretation. Amyrisins B (2) and C (3) showed moderate cytotoxicity against PC-3 and DU 145 prostate cancer cells with IC(50) values of 17.5 and 23 μM, respectively, while amyrisin A (1) did not show any cytotoxicity at the highest concentration tested, 50 μM. Polygamain (4) exhibited potent antiproliferative and microtubule-depolymerizing activities.