Syntheses and antitumor activity of cis-restricted combretastatins: 5-membered heterocyclic analogues

2-Anilino-3-Aroylquinolines as Potent Tubulin Polymerization Inhibitors

Several 2-anilino-3-aroylquinolines were designed, synthesized, and screened for their cytotoxic activity against five human cancer cell lines: HeLa, DU-145, A549, MDA-MB-231, and MCF-7. Their IC50 values ranged from 0.77 to 23.6 μm. Among the series, compounds 7 f [(4-fluorophenyl)(2-((4-fluorophenyl)amino)quinolin-3-yl)methanone] and 7 g [(4-chlorophenyl)(2-((4-fluorophenyl)amino)quinolin-3-yl)methanone] showed remarkable antiproliferative activity against human lung cancer and prostate cancer cell lines. The IC50 values for inhibiting tubulin polymerization were 2.24 and 2.10 μm for compounds 7 f and 7 g, respectively, and were much lower than that of the reference compound E7010 [N-(2-(4-hydroxyphenylamino)pyridin-3-yl)-4-methoxybenzenesulfonamide]. Furthermore, flow cytometric analysis revealed that these compounds arrest the cell cycle at the G2 /M phase, leading to apoptosis. Apoptosis was also confirmed by mitochondrial membrane potential, Annexin V-FITC assay, and intracellular ROS generation. Immunohistochemistry, western blot, and tubulin polymerization assays showed that these compounds disrupt tubulin polymerization. Molecular docking studies revealed that these compounds bind efficiently to β-tubulin at the colchicine binding site.

Synthesis of (Z)-(arylamino)-pyrazolyl/isoxazolyl-2-propenones as tubulin targeting anticancer agents and apoptotic inducers

A new class of pyrazole and isoxazole conjugates were synthesized and evaluated for their cytotoxic activity against various human cancer cell lines. These compounds have shown significant cytotoxicity with lower IC50 values. FACS results revealed that A549 cells treated with these compounds arrested cells at the G2/M phase of the cell cycle apart from activating cyclin B1 protein levels. Particularly, compounds 9a and 9b demonstrated a remarkable inhibitory effect on tubulin polymerization and showed a pronounced inhibitory effect on tubulin polymerization with IC50 values of 1.28 μM and 0.28 μM respectively, whereas nocodazole, a positive control, has shown lower antitubulin activity with an IC50 value of 2.64 μM. Furthermore, these compounds induced apoptosis by loss of mitochondrial membrane potential, propidium iodide (PI) staining and the activation of caspase-3. Results of a fluorescence based competitive colchicine binding assay suggest that these conjugates bind successfully at the colchicine binding site of tubulin. These investigations reveal that such conjugates containing pyrazole with a trimethoxy phenyl ring and indole moieties have potential for the development of newer chemotherapeutic agents.

Lipophilic prodrug conjugates allow facile and rapid synthesis of high-loading capacity liposomes without the need for post-assembly purification

Dihydropyridopyrazoles are simplified synthetic analogues of podophyllotoxin that can effectively mimic its molecular scaffold and act as potent mitotic spindle poisons in dividing cancer cells. However, despite nanomolar potencies and ease of synthetic preparation, further clinical development of these promising anticancer agents is hampered due to their poor aqueous solubility. In this article, we developed a prodrug strategy that enables incorporation of dihydropyridopyrazoles into liposome bilayers to overcome the solubility issues. The active drug was covalently connected to either myristic or palmitic acid anchor via carboxylesterase hydrolyzable linkage. The resulting prodrugs were self-assembled into liposome bilayers from hydrated lipid films using ultrasound without the need for post-assembly purification. The average particle size of the prodrug-loaded liposomes was about 90 nm. The prodrug incorporation was verified by differential scanning calorimetry, spectrophotometry and gel filtration reaching maximum at 0.3 and 0.35 prodrug/lipid molar ratios for myristic and palmitic conjugates, respectively. However, the ratio of 0.2 was used in the particle size and biological activity experiments to maintain long-term stability of the prodrug-loaded liposomes against phase separation during storage. Antiproliferative activity was tested against HeLa and Jurkat cancer cell lines in vitro showing that the liposomal prodrug retained antitubulin activity of the parent drug and induced apoptosis-mediated cancer cell death. Overall, the established data provide a powerful platform for further clinical development of dihydropyridopyrazoles using liposomes as the drug delivery system.

Synthesis and anti-cancer screening of novel heterocyclic-(2H)-1,2,3-triazoles as potential anti-cancer agents

trans-Cyanocombretastatin A-4 (trans-CA-4) analogues have been structurally modified to afford their more stable CA-4-(2H)-1,2,3-triazole analogues. Fifteen novel, stable 4-heteroaryl-5-aryl-(2H)-1,2,3-triazole CA-4 analogues (8a-i, 9 and 11a-e) were evaluated for anti-cancer activity against a panel of 60 human cancer cell lines. These analogues displayed potent cytotoxic activity against both hematological and solid tumor cell lines with GI50 values in the low nanomolar range. The most potent compound, 8a, was a benzothiophen-2-yl analogue that incorporated a 3,4,5-trimethoxyphenyl moiety connected to the (2H)-1,2,3-triazole ring system. Compound 8a exhibited GI50 values of <10 nM against 80% of the cancer cell lines in the panel. Three triazole analogues, 8a, 8b and 8g, showed particularly potent growth inhibition against the triple negative Hs578T breast cancer cell line with GI50 values of 10.3 nM, 66.5 nM and 20.3 nM, respectively. Molecular docking studies suggest that these compounds bind to the same hydrophobic pocket at the interface of α- and β-tubulin that is occupied by colchicine and cis-CA-4, and are stabilized by Van der Waals' interactions with surrounding amino acid residues. Compound 8a was found to inhibit tubulin polymerization in vitro with an IC50 value of 1.7 µM. The potent cytotoxicity of these novel compounds and their inhibition of tubulin dynamics make these triazole analogues promising candidates for development as anti-cancer drugs.

IsoCombretaQuinazolines: Potent Cytotoxic Agents with Antitubulin Activity

A series of novel isocombretaquinazolines (isoCoQ) 4 were quickly prepared by coupling N-toluenesulfonylhydrazones with 4-chloroquinazolines under palladium catalysis. These compounds, which can be regarded as isocombretastatin A-4 (isoCA-4) analogues that lack the 3,4,5-trimethoxyphenyl ring, displayed nanomolar-level cytotoxicity against various human cancer cell lines and were observed to effectively inhibit tubulin polymerization. The isoCoQ compounds 2-methoxy-5-(1-(2-methylquinazolin-4-yl)vinyl)phenol (4 b), 4-[1-(3-fluoro-4-methoxyphenyl)vinyl]-2-methylquinazoline (4 c), and 2-methoxy-5-(1-(2-methylquinazolin-4-yl)vinyl)aniline (4 d), which respectively bear the greatest resemblance to isoCA-4, isoFCA-4, and isoNH2 CA-4, are able to arrest HCT116 cancer cells in the G2 /M cell-cycle phase at very low concentrations. Preliminary in vitro antivascular assay results show that 4 d is able to disrupt a network of capillary-like structures formed by human umbilical vein endothelial cells on Matrigel. All these results clearly demonstrate that replacement of the 3,4,5-trimethoxyphenyl ring of isoCA-4 with a quinazoline nucleus is a feasible approach toward new and highly promising derivatives with the potential for further development as antitubulin agents.

Synthesis and biological evaluation of 2,3-diarylthiophene analogues of combretastatin A-4

A series of novel 2,3-diarylthiophene analogues of combretastatin A-4 were synthesised and evaluated for their in vitro anti-proliferative activities.

Aryl-imidazothiadiazole analogues as microtubule disrupting agents

Disruption of tubulin polymerization and the docked pose of 5k in the colchicine binding site of tubulin.

Synthesis of 2-anilinopyridine–arylpropenone conjugates as tubulin inhibitors and apoptotic inducers

2-Anilinopyridine–arylpropenone conjugates as novel tubulin inhibitors and apoptotic inducers.

L-Proline catalyzed one-step synthesis of 4,5-diaryl-2H-1,2,3-triazoles from heteroaryl cyanostilbenes via [3+2] cycloaddition of azide

Use of a novel reagent has been established for the synthesis of a series of 4,5-diaryl-2H-1,2,3-triazoles (6a-i and 9a-e) from cyanostilbene analogs of benzo[b]thiophene, benzo[b]furan and indole, catalyzed by L-proline via Lewis base-catalyzed one-step [3+2]cycloaddition of azide. This method provides an efficient, simple and environmentally benign procedure that affords good yields and relatively short reaction times.

Prevention of cancer recurrence in tumor margins by stopping microcirculation in the tumor and tumor-host interface

Combretastatins interrupt blood flow of solid tumor vascular networks and lead to necrosis by blocking nutrients. However, tumors recover from tumor blood flow interruption-induced damage and develop viable rims. To investigate why cancer recurs and its prevention, we used a combretastatin derivative, Cderiv (=AC7700), and analyzed changes in tumor-host interface (T-HI) vessels, which were closest to cancer cells in the tumor margin after tumor vessel disruption, and the microenvironment surrounding them. Treatment with Cderiv (10 mg/kg) interrupted tumor blood flow in all regions of LY80 (a variant of Yoshida sarcoma) tumor, but not T-HI vessel blood flow. The same Cderiv dose given 72 h after 5 Gy irradiation stopped T-HI vessel blood flow and prevented cancer recurrence. Treatment in the reverse order, however, did not affect T-HI vessel blood flow. The greatest difference between the two treatments was the occurrence of gradual T-HI edema with the former. Severe T-HI edema compressed T-HI blood vessels, so that circulation stopped. Thus, the distance between a tumor margin and its nearest functioning host vessel became much larger, and the tumor marginal region became a microenvironment that lacked a nutritional supply. Cancer cells in tumor margins received nutrients through two circulation routes: tumor vessels and T-HI vessels. Our starvation methods, which involved treatment with Cderiv 72 h after 5 Gy irradiation, blocked both circulation routes and may have great potential as a clinical strategy to prevent cancer recurrence.

Synthesis, antimitotic and antivascular activity of 1-(3',4',5'-trimethoxybenzoyl)-3-arylamino-5-amino-1,2,4-triazoles

A new class of compounds that incorporated the structural motif of the 1-(3',4',5'-trimethoxtbenzoyl)-3-arylamino-5-amino-1,2,4-triazole molecular skeleton was synthesized and evaluated for their antiproliferative activity in vitro, interactions with tubulin, and cell cycle effects. The most active agent, 3c, was evaluated for antitumor activity in vivo. Structure-activity relationships were elucidated with various substituents on the phenyl ring of the anilino moiety at the C-3 position of the 1,2,4-triazole ring. The best results for inhibition of cancer cell growth were obtained with the p-Me, m,p-diMe, and p-Et phenyl derivatives 3c, 3e, and 3f, respectively, and overall, these compounds were more or less as active as CA-4. Their vascular disrupting activity was evaluated in HUVEC cells, with compound 3c showing activity comparable with that of CA-4. Compound 3c almost eliminated the growth of syngeneic hepatocellular carcinoma in Balb/c mice, suggesting that 3c could be a new antimitotic agent with clinical potential.

Synthesis, cytotoxicity, docking study, and tubulin polymerization inhibitory activity of novel 1-(3,4-dimethoxyphenyl)-5-(3,4,5-trimethoxyphenyl)-1H-1,2,4-triazole-3-carboxanilides

A series of novel 1-(3,4-methoxyphenyl)-5-(3,4,5-trimethoxyphenyl)-1H-1,2,4-triazole-3-carboxylic acid derivatives (4a-n) were synthesized and evaluated for their in vitro cytotoxic activity against the growth of four different human cell lines (hepatocarcinoma HepG2, breast adenocarcinoma MCF-7, colon carcinoma DLD-1, and leukemia HL-60). The anilides of m-anisidine 4e, o-anisidine 4f, and 3,5-difluoroaniline 4l demonstrated best results on MCF-7 cells and mean IC50 values of 7.79, 10.79, and 13.20 µM, respectively. The compounds produced a significant reduction in cellular microtubules at a concentration of 25 µg/mL, for microtubule loss. Molecular modeling studies involving compounds 4d, 4e, 4f, and 4l with the colchicine binding site of α,β-tubulin revealed hydrogen bonding and hydrophobic interactions with several amino acids in the colchicine binding site of β-tubulin.

Design, synthesis, and biological evaluation of novel pyridine-bridged analogues of combretastatin-A4 as anticancer agents

A series of novel pyridine-bridged analogues of combretastatin-A4 (CA-4) were designed and synthesized. As expected, the 4-atom linker configuration retained little cytotoxicities in the compounds 2e, 3e, 3g, and 4i. Activities of the analogues with 3-atom linker varied widely depending on the phenyl ring substitutions, and the 3-atom linker containing nitrogen represents the more favorable linker structure. Among them, three analogues (4h, 4s, and 4t) potently inhibited cell survival and growth, arrested cell cycle, and blocked angiogenesis and vasculature formation in vivo in ways comparable to CA-4. The superposition of 4h and 4s in the colchicine-binding pocket of tubulin shows the binding posture of CA-4, 4h, and 4s are similar, as confirmed by the competitive binding assay where the ability of the ligands to replace tubulin-bound colchicine was measured. The binding data are consistent with the observed biological activities in antiproliferation and suppression of angiogenesis but are not predictive of their antitubulin polymerization activities.

Rational approaches, design strategies, structure activity relationship and mechanistic insights for anticancer hybrids

A Hybrid drug which comprises the incorporation of two drug pharmacophores in one single molecule are basically designed to interact with multiple targets or to amplify its effect through action on another bio target as one single molecule or to counterbalance the known side effects associated with the other hybrid part(.) The present review article offers a detailed account of the design strategies employed for the synthesis of anticancer agents via molecular hybridization techniques. Over the years, the researchers have employed this technique to discover some promising chemical architectures displaying significant anticancer profiles. Molecular hybridization as a tool has been particularly utilized for targeting tubulin protein as exemplified through the number of research papers. The microtubule inhibitors such as taxol, colchicine, chalcones, combretasatin, phenstatins and vinca alkaloids have been utilized as one of the functionality of the hybrids and promising results have been obtained in most of the cases with some of the tubulin based hybrids exhibiting anticancer activity at nanomolar level. Linkage with steroids as biological carrier vector for anticancer drugs and the inclusion of pyrrolo [2,1-c] [1,4]benzodiazepines (PBDs), a family of DNA interactive antitumor antibiotics derived from Streptomyces species in hybrid structure based drug design has also emerged as a potential strategy. Various heteroaryl based hybrids in particular isatin and coumarins have also been designed and reported to posses' remarkable inhibitory potential. Apart from presenting the design strategies, the article also highlights the structure activity relationship along with mechanistic insights revealed during the biological evaluation of the hybrids.

Synthesis and evaluation of a series of quinolinyl trans-cyanostilbene analogs as anticancer agents

2-Quinolyl- and 3-quinolyl-cyanocombretastatin analogs exhibit potent growth inhibition against a panel of 60 human cancer cell lines.

Synthesis and antiproliferative activity of conformationally restricted 1,2,3-triazole analogues of combretastatins in the sea urchin embryo model and against human cancer cell lines

A series of 1,5-diaryl- and 4,5-diaryl-1,2,3-triazole derivatives of combretastatin A4 were synthesized and evaluated as antimitotic microtubule destabilizing agents using the sea urchin embryo model. Structure-activity relationship studies identified compounds substituted with 3,4,5-trimethoxyphenyl and 3,4-methylenedioxy-5-methoxyphenyl ring A and 4-methoxyphenyl ring B as potent antiproliferative agents with high cytotoxicity against a panel of human cancer cell lines including multi-drug resistant cells. 4,5-Diaryl-1,2,3-triazoles (C-C geometry) were found to be considerably more active than the respective 1,5-diaryl-1,2,3-triazoles (N-C geometry). Compound 10ad' induced G2/M cell cycle arrest and apoptosis in human T-leukemia Jurkat cells via caspase 2/3/9 activation and downregulation of the antiapoptotic protein XIAP. A mitotic catastrophe has been evaluated as another possible cell death mode.

Correlation of hydrogen-bonding propensity and anticancer profile of tetrazole-tethered combretastatin analogues

A series of 1,5-disubstituted tetrazole-tethered combretastatin analogues with extended hydrogen-bond donors at the ortho-positions of the aryl A and B rings were developed and evaluated for their antitubulin and antiproliferative activity. We wanted to test whether intramolecular hydrogen-bonding used as a conformational locking element in these analogues would improve their activity. The correlation of crystal structures with the antitubulin and antiproliferative profiles of the modified analogues suggested that hydrogen-bond-mediated conformational control of the A ring is deleterious to the bioactivity. In contrast, although there was no clear evidence that intramolecular hydrogen bonding to the B ring enhanced activity, we found that increased substitution on the B ring had a positive effect on antitubulin and antiproliferative activity. Among the various analogues synthesized, compounds 5d and 5e, having hydrogen-bonding donor groups at the ortho and meta-positions on the 4-methoxy phenyl B ring, are strong inhibitors of tubulin polymerization and antiproliferative agents having IC50 value in micromolar concentrations.

Tubulin-interactive stilbene derivatives as anticancer agents

Microtubules are dynamic polymers that occur in eukaryotic cells and play important roles in cell division, motility, transport and signaling. They form during the process of polymerization of α- and β-tubulin dimers. Tubulin is a significant and heavily researched molecular target for anticancer drugs. Combretastatins are natural cis-stilbenes that exhibit cytotoxic properties in cultured cancer cells in vitro. Combretastatin A-4 (3′-hydroxy-3,4,4′, 5-tetramethoxy-cis-stilbene; CA-4) is a potent cytotoxic cis-stilbene that binds to β-tubulin at the colchicine-binding site and inhibits tubulin polymerization. The prodrug CA-4 phosphate is currently in clinical trials as a chemotherapeutic agent for cancer treatment. Numerous series of stilbene analogs have been studied in search of potent cytotoxic agents with the requisite tubulin-interactive properties. Microtubule-interfering agents include numerous CA-4 and transresveratrol analogs and other synthetic stilbene derivatives. Importantly, these agents are active in both tumor cells and immature endothelial cells of tumor blood vessels, where they inhibit the process of angiogenesis. Recently, computer-aided virtual screening was used to select potent tubulin-interactive compounds. This review covers the role of stilbene derivatives as a class of antitumor agents that act by targeting microtubule assembly dynamics. Additionally, we present the results of molecular modeling of their binding to specific sites on the α- and β-tubulin heterodimer. This has enabled the elucidation of the mechanism of stilbene cytotoxicity and is useful in the design of novel agents with improved anti-mitotic activity. Tubulin-interactive agents are believed to have the potential to play a significant role in the fight against cancer.

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.

TR-644 a novel potent tubulin binding agent induces impairment of endothelial cells function and inhibits angiogenesis

TR-644 is a novel combretastatin A-4 (CA-4) analogue endowed with potent microtubule depolymerizing activity superior to that of the lead compound and it also has high affinity to colchicines binding site of tubulin. We tested TR-644 anti-angiogenic effects in human umbilical endothelial cells (HUVEC). It showed no significant effects on the growth of HUVEC cells at concentrations below 1,000 nM, but at much lower concentrations (10-100 nM) it induced inhibition of capillary tube formation, inhibition of endothelial cell migration and affected endothelial cell morphology as demonstrated by the disruption of the microtubule network. TR-644 also increased permeability of HUVEC cells in a time dependent manner. The molecular mechanism for the anti-vascular activity of TR-644 was investigated in detail. TR-644 caused G2/M arrest in endothelial cells and this effect correlated with downregulation of the expression of Cdc25C and Cdc2(Tyr15). Moreover TR-644 inhibited VEGF-induced phosphorylation of VE-cadherin but did not prevent the VEGF-induced phosphorylation of FAK. In chick chorioallantoic membrane in vivo assay, TR-644 (0.1-1.0 pmol/egg) efficiently counteracted the strong angiogenic response induced by FGF. Also CA-4, used as reference compound, caused an antagonistic effect, but in contrast, it induced per se, a remarkable angiogenic response probably due to an inflammatory reaction in the site of treatment. In a mice allogenic tumor model, immunohistochemical staining of tumors with anti-CD31 antibody showed that TR-644 significantly reduced the number of vessel, after 24 h from the administration of a single dose (30 mg/Kg).

Novel cis-restricted β-lactam combretastatin A-4 analogues display anti-vascular and anti-metastatic properties in vitro

Combretastatin A-4 (CA-4) is a naturally occurring microtubular-destabilising agent that possesses potent anti-tumour and anti-vascular properties both in vitro and in vivo. Clinical trials to date indicate that its water-soluble prodrug, combretastatin A-4 phosphate (CA-4P), is well tolerated at therapeutically useful doses. However, the stilbenoid structure of CA-4, consisting of two phenyl rings linked by an ethylene bridge, renders the compound readily susceptible to isomerisation from its biologically active cis-conformation to its more thermodynamically stable but inactive trans-isomer. To circumvent this problem, we synthesised a series of cis-restricted CA-4 analogues. Replacement of the ethylene bridge with a 1,4-diaryl-2-azetidinone (β-lactam) ring provided a rigid scaffold thus preventing cis-trans isomerisation. We previously documented that these tubulin-depolymerising β-lactam compounds potently induced cell cycle arrest and apoptosis in a variety of cancerous cell lines (including those displaying multidrug resistance) and ex vivo patient samples, whilst exerting only minimal toxicity to normal cells. The purpose of this study was to elucidate the effect of the β-lactam compounds on both tumour vascularisation and tumour cell migration, two critical elements that occur during the growth and metastatic progression of tumours. We established that two representative β-lactam compounds, CA-104 and CA-432, exerted both anti-endothelial effects [G2/M arrest and apoptosis of primary human umbilical vein endothelial cells (HUVECs)] and anti-angiogenic effects [inhibition of HUVEC migration and differentiation and reduced vascular endothelial growth factor (VEGF) release from MDA-MB-231 breast adenocarcinoma cells]. In addition, we established that lead analogue, CA-432, abrogated the migration of MDA-MB-231 cells indicating an anti-metastatic function for these compounds. In summary, our results to date collectively indicate that these cis-restricted β-lactam CA-4 analogues may prove to be useful alternatives to CA-4 in the treatment of cancer but with the added advantage of improved stability of the cis-isomer.

Starvation tactics for solid tumors: tumor blood flow interruption via a combretastatin derivative (Cderiv), and its microcirculation mechanism

Combretastatin can prevent the supply of nutrients to cancer cells by selectively interrupting tumor blood flow (TBF). Therefore, combretastatin may serve as a new anticancer drug that utilizes starvation tactics to attack solid tumors. Among combretastatin compounds, combretastatin A-4 and a combretastatin A-4 derivative (Cderiv) are now in phase III clinical trials. These two combretastatin compounds have similar chemical structures and provide marked TBF interruption. However, their mechanisms of action are reportedly quite different and remain controversial. Precise mechanisms of action of these agents must be elucidated so as to develop safe clinical treatments and wider clinical applications. By using various kinds of rodent tumors, we showed that Cderiv produced potent interruption of TBF in all primary tumors and metastatic foci, without exception, and had beneficial therapeutic effects including significantly improved survival. Cderiv caused host arterioles to constrict. However, a tumor vascular bed scarcely reacted to a direct topical application of Cderiv. In addition, the fact that Cderiv did not have cytotoxic drug-like accumulated toxicity usually caused by repeated administration means that inhibition of tubulin polymerization by Cderiv may not occur to a great degree in vivo. Therefore, at least for Cderiv, our studies demonstrated that TBF interruption was mainly caused indirectly, via enhancement of vascular resistance of host arterioles, rather than being caused by a direct effect of Cderiv on tumor vessels. In this review, I describe cancer therapy that utilizes such TBF interruption, which leads to Cderiv-induced necrosis, and discuss details of its microcirculation mechanism.

Design and synthesis of 3,5-disubstituted boron-containing 1,2,4-oxadiazoles as potential combretastatin A-4 (CA-4) analogs

We have designed and synthesized a small library of 3,5-disubstituted-1,2,4-oxadiazole containing combretastatin A-4 (CA-4) analogs. Our objective is to increase the efficacy of the CA-4 as an anti-tubulin and antimitotic agent by substituting the cis-alkene bond with one of its bioisosteres, the 1,2,4-oxadiazole ring. We also modified the substituents attached to both of the phenyl rings (ring A and B in Fig. 1) of CA-4 for the purpose of diversifying our analogs based on SAR. These compounds were synthesized via a coupling reaction between an amidoxime and a carboxylic acid in DMF solvent, with HOBt as a base, and utilizing EDCI as a coupling reagent. Using this protocol, we synthesized a small library of 10 compounds with moderate to good yields. A detailed biological study is currently undergoing in our laboratory to evaluate the activity of these compounds.

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.

(Z)-1-aryl-3-arylamino-2-propen-1-ones, highly active stimulators of tubulin polymerization: synthesis, structure-activity relationship (SAR), tubulin polymerization, and cell growth inhibition studies

Tubulin, the major structural component of microtubules, is a target for the development of anticancer agents. A series of (Z)-1-aryl-3-arylamino-2-propen-1-one (10) were synthesized and evaluated for antiproliferative activity in cell-based assay. The most active compound (Z)-1-(2-bromo-3,4,5-trimethoxyphenyl)-3-(3-hydroxy-4-methoxyphenylamino)prop-2-en-1-one (10ae) was tested in 20 tumor cell lines including multidrug resistant phenotype and was found to induce apoptosis in all these cell lines with similar GI(50) values. Flow cytometry studies showed that 10ae arrested the cells in G2/M phase of cell cycle. In addition to G2/M block, these compounds caused microtubule stabilization like paclitaxel and induced apoptosis via activation of the caspase family. The observations made in this investigation demonstrate that (Z)-1-Aryl-3-arylamino-2-propen-1-one (10) represents a new class of microtubule-stabilizing agents.

In vitro and in vivo biological evaluation of new 4,5-disubstituted 1,2,3-triazoles as cis-constrained analogs of combretastatin A4

To find new and better antivascular agents for cancer therapy, a series of combretastatin A4 (CA4) analogs were prepared from 1,3-diaryl-2-nitroprop-1-enes (6-12) obtained in a two-step synthesis from appropriate arylaldehydes and 2-aryl-1-nitroethanes (4 or 5). Treatment of these 1,3-diaryl-2-nitroprop-1-enes 6-12 by sodium azide in DMSO yielded the targeted compounds. The synthesized 1,2,3-triazoles disubstituted in 4- and 5-positions by one benzyl group and one aryl nucleus have also been tested for biological activities involved in antivascular action. It was found that several new compounds exhibited interesting biological activities in the nanomolar or low micromolar range, in terms of rounding up of endothelial cells, inhibition of tubulin polymerization, and cytotoxicity on B16 melanoma cancer cells. In silico docking studies of 11 and 19 within the active site of tubulin were also carried out in order to rationalize the inhibitory properties of these compounds and further understand their inhibition mechanism. In vivo evaluation of compounds 11 and 19 in mice bearing colon 26 carcinoma indicated modest anticancer activity.