Methylenedioxy-benzopyran analogs of podophyllotoxin, a new synthetic class of antimitotic agents that inhibit tubulin polymerization

A new class of compounds was synthesized and, based on structural analogy to podophyllotoxin, examined as potential microtubule inhibitors and evaluated for in vivo antineoplastic activity. These agents are derivatives of methylenedioxy-benzopyran bearing a phenyl substituent at position 8. The hydrogen atoms at positions 7 and 8 are in a trans configuration, in contrast to the cis configuration of analogous hydrogen atoms at positions 1 and 2 in podophyllotoxin. Compounds with a variety of substituents at positions 6 and 7 were examined, as well as compounds with varying methoxy substituent patterns on the phenyl ring attached at position 8. The most active compounds inhibited tubulin polymerization at concentrations approximately stoichiometric with tubulin, competitively inhibited the binding of colchicine to tubulin, and caused mitotic arrest at cytotoxic drug concentrations. No structure-activity correlations were obvious for the substituents at positions 6 and 7, but optimal activity was only observed when the phenyl substituent at position 8 was a trimethoxybenzene ring identical to the analogous ring in podophyllotoxin (i.e. methoxy groups at positions 3', 4' and 5'). Despite their structural and functional similarities to podophyllotoxin, however, the methylenedioxy-benzopyran derivatives subtly differ from the natural product in their interaction with tubulin, for they stimulated rather than inhibited tubulin-dependent GTP hydrolysis.     

Synthesis of B-ring homologated estradiol analogues that modulate tubulin polymerization and microtubule stability

2-Methoxyestradiol is a cytotoxic human metabolite of estradiol with the ability to bind to the colchicine site of tubulin and inhibit its polymerization, and its 2-ethoxy analogue is even more potent. On the basis of a hypothetical relationship between the structures of colchicine and 2-methoxyestradiol, a B-ring-expanded 2-ethoxyestradiol analogue was synthesized in which the B-ring of the steroid is replaced by the B-ring of colchicine. The synthesis relied on the B-ring expansion of available 6-keto estradiol derivatives as opposed to a total synthesis of the homologated steroid framework. The relative configurations of the acetamido substituents in both epimers of the final product were determined by NOESY NMR and confirmed by X-ray crystallography. The epimer having the 6alpha-acetamido substituent was more active as an inhibitor of tubulin polymerization, and it was also more cytotoxic than the 6beta-epimer. These results are consistent with the proposed structural resemblance of 2-methoxyestradiol and colchicine. Several of the synthetic intermediates proved to be potent inhibitors of tubulin polymerization. On the other hand, a 3,17beta-diacetylated, B-ring-expanded analogue of 2-ethoxyestradiol having a ketone at C-6 resembled paclitaxel (Taxol) in its ability to enhance tubulin polymerization and stabilize microtubules. The corresponding 3-acetate and the 17beta-acetate were both synthesized, and it was determined that the 17beta-acetate, but not the 3-acetate, conferred on the steroid derivative its paclitaxel-like activity.     

Development of hemiasterlin derivatives as potential anticancer agents that inhibit tubulin polymerization and synergize with a stilbene tubulin inhibitor

Hemiasterlins are cytotoxic tripeptides with antimicrotubule activity originally isolated from marine sponges. We have developed new hemiasterlin derivatives BF65 and BF78 that are highly potent to induce cancer cell death in the low nanomolar range. Examination of their mechanisms of cell cycle arrest and disruption of microtubules revealed an unusual characteristic in addition to anti-tubulin effect. Immunofluorescence staining revealed that A549 lung carcinoma cells treated with BF65 or BF78 exhibited both monopolar and multipolar mitotic spindles. Centrosomes were separated with short spindle microtubules in cells with multipolar spindles. In vitro tubulin polymerization assay confirmed that both BF65 and BF78 were highly potent to inhibit tubulin polymerization. These two compounds induced the formation of monoastral spindles suggesting that they might be inhibitors of mitotic kinesins such as KSP/Eg5. However, kinetic measurement of microtubule activated kinesin ATPase activity demonstrated that unlike the positive control monastrol, neither BF65 nor BF78 suppressed KSP/Eg5 activity. Hence the effect may be a variant form of tubulin inhibition. Similar to vinca alkaloids, BF compounds synergized with a colchicine site microtubule inhibitor stilbene 5c both in vitro and in vivo, which may provide a potential drug combination in the future clinical application.     

Synthesis and evaluation of stilbene and dihydrostilbene derivatives as potential anticancer agents that inhibit tubulin polymerization

An array of cis-, trans-, and dihydrostilbenes and some N-arylbenzylamines were synthesized and evaluated for their cytotoxicity in the five cancer cell cultures A-549 lung carcinoma, MCF-7 breast carcinoma, HT-29 colon adenocarcinoma, SKMEL-5 melanoma, and MLM melanoma. Several cis-stilbenes, structurally similar to combretastatins, were highly cytotoxic in all five cell lines and these were also found to be active as inhibitors of tubulin polymerization. The most active compounds also inhibited the binding of colchicine to tubulin. The most potent of the new compounds, both as a tubulin polymerization inhibitor and as a cytotoxic agent, was (Z)-1-(4-methoxyphenyl)-2-(3,4,5-trimethoxyphenyl)ethene (5a). This substance was almost as potent as combretastatin A-4 (1a), the most active of the combretastatins, as a tubulin polymerization inhibitor. Compound 5a was found to be approximately 140 times more cytotoxic against HT-29 colon adenocarcinoma cells and about 10 times more cytotoxic against MCF-7 breast carcinoma cells than combretastatin A-4. However, 5a was found to be about 20 times less cytotoxic against A-549 lung carcinoma cells, 30 times less cytotoxic against SKMEL-5 melanoma cells, and 7 times less cytotoxic against MLM melanoma cells than combretastatin A-4. The relative potencies 5a greater than 8a greater than 6a for the cis, dihydro, and trans compounds, respectively, as inhibitors of tubulin polymerization are in agreement with the relative potencies previously observed for combretastatin A-4 (1a), dihydrocombretastatin A-4 (1c), and trans-combretastatin A-4 (1b). The relative potencies 5a greater than 8a greater than 6a were also reflected in the results of the cytotoxicity assays. Structure-activity relationships of this group of compounds are also discussed.     

Novel indole-bearing combretastatin analogues as tubulin polymerization inhibitors

Background

The combretastatins are a class of natural stilbenoids. These molecules generally share three common structural features: a trimethoxy "A"-ring, a "B"-ring containing substituent often at C3′ and C4′, and an ethene bridge between the two rings, which provides necessary structural rigidity. Members of the combretastatin family possess varying ability to cause vascular disruption in tumors. Combretastatin binds to the colchicine binding site of β-subunit of tubulin. Despite having a similar name, combretastatin is unrelated to statins, a family of cholesterol-lowering drugs.

Results

New combretastatin 2-(1-acetyl-1H-indole-3-yl)-3-(phenyl) propenoic analogues (2a to 2y), bearing indole moiety at the place of ring A of combretastatin (CA4), were synthesized and evaluated for anticancer activity against various cancer cell lines such as THP-1 (leukemia), A-549 (lung), IGROV-1 (ovary), HEP-2 (liver), MCF-7 (breast), and DU-145 (prostate). Compound 2d showed anti-cancer activity against THP-1 and MCF-7 with IC₅₀ 0.80 and 0.37 μM, respectively, and 2y showed against MCF-7 with IC₅₀ 3.60 μM comparable to paclitaxel.

Conclusions

The target compounds bind to the colchicine binding site which is situated at α and β interface of tubulin and prevent polymerization as it was confirmed by immunofluorescence technique. The molecular docking further confirmed the binding of the potent compound 2d to the colchicine binding site at α and β interface of tubulin.     

Synthesis and biological evaluation of dihydrobenzofuran lignans and related compounds as potential antitumor agents that inhibit tubulin polymerization

A series of 19 related dihydrobenzofuran lignans and benzofurans was obtained by a biomimetic reaction sequence involving oxidative dimerization of p-coumaric, caffeic, or ferulic acid methyl esters, followed by derivatization reactions. All compounds were evaluated for potential anticancer activity in an in vitro human disease-oriented tumor cell line screening panel that consisted of 60 human tumor cell lines arranged in nine subpanels, representing diverse histologies. Leukemia and breast cancer cell lines were relatively more sensitive to these agents than were the other cell lines. Compounds 2c and 2d, but especially 2b (methyl (E)-3-?2-(3, 4-dihydroxyphenyl)-7-hydroxy-3-methoxycarbonyl-2, 3-dihydro-1-benzofuran-5-ylprop-2-enoate), the dimerization product of caffeic acid methyl ester, containing a 3',4'-dihydroxyphenyl moiety and a hydroxyl group in position 7 of the dihydrobenzofuran ring, showed promising activity. The average GI(50) value (the molar drug concentration required for 50% growth inhibition) of 2b was 0.3 microM. Against three breast cancer cell lines, 2b had a GI(50) value of <10 nM. Methylation, reduction of the double bond of the C(3)-side chain, reduction of the methoxycarbonyl functionalities to primary alcohols, or oxidation of the dihydrobenzofuran ring to a benzofuran system resulted in a decrease or loss of cytotoxic activity. Compound 2b inhibited mitosis at micromolar concentrations in cell culture through a relatively weak interaction at the colchicine binding site of tubulin. In vitro it inhibited tubulin polymerization by 50% at a concentration of 13 +/- 1 microM. The 2R, 3R-enantiomer of 2b was twice as active as the racemic mixture, while the 2S,3S-enantiomer had minimal activity as an inhibitor of tubulin polymerization. These dihydrobenzofuran lignans (2-phenyl-dihydrobenzofuran derivatives) constitute a new group of antimitotic and potential antitumor agents that inhibit tubulin polymerization.     

Design, synthesis, and biological evaluation of a series of lavendustin A analogues that inhibit EGFR and Syk tyrosine kinases, as well as tubulin polymerization.

A series of N-alkylamide analogues of the lavendustin A pharmacophore were synthesized and tested for inhibition of the epidermal growth factor receptor (EGFR) protein tyrosine kinase and the nonreceptor protein tyrosine kinase Syk. Although several compounds in the series were effective inhibitors of both kinases, it seemed questionable whether their inhibitory effects on these kinases were responsible for the cytotoxic properties observed in a variety of human cancer cell cultures. Accordingly, a COMPARE analysis of the cytotoxicity profile of the most cytotoxic member of the series was performed, and the results indicated that its cytotoxicity profile was similar to that of antitubulin agents. This mechanism of action was supported by demonstrating that most compounds in the series were moderately effective as inhibitors of tubulin polymerization. This suggests that the lavendustin A analogues reported here, as well as some of the previously reported lavendustin A analogues, may be acting as cytotoxic agents by a mechanism involving the inhibition of tubulin polymerization.     

Drugs that inhibit mycolic acid biosynthesis in Mycobacterium tuberculosis

Tuberculosis resurged in the late 1980s and now kills more than 2 million people a year. The reemergence of tuberculosis as a potential public health threat, the high susceptibility of human immunodeficiency virus-infected persons to the disease, and the proliferation of multi-drug-resistant (MDR) strains have created much scientific interest in developing new antimycobacterial agents to both treat Mycobacterium tuberculosis strains resistant to existing drugs, and shorten the duration of short-course treatment to improve patient compliance. Bacterial cell-wall biosynthesis is a proven target for new antibacterial drugs. Mycolic acids, which are key components of the mycobacterial cell wall, are alpha-alkyl, beta-hydroxy fatty acids, with a species-dependent saturated "short" arm of 20-26 carbon atoms and a "long" meromycolic acid arm of 50-60 carbon atoms. The latter arm is functionalized at regular intervals by cyclopropyl, alpha-methyl ketone, or alpha-methyl methylethers groups. The mycolic acid biosynthetic pathway has been proposed to involve five distinct stages: (i) synthesis of C20 to C26 straight-chain saturated fatty acids to provide the alpha-alkyl branch; (ii) synthesis of the meromycolic acid chain to provide the main carbon backbone, (iii) modification of this backbone to introduce other functional groups; (iv) the final Claisen-type condensation step followed by reduction; and (v) various mycolyltransferase processes to cellular lipids. The drugs shown to inhibit mycolic acid biosynthesis are isoniazid, ethionamide, isoxyl, thiolactomycin, and triclosan. In addition, pyrazinamide was shown to inhibit fatty acid synthase type I which, in turn, provides precursors for fatty acid elongation to long-chain mycolic acids by fatty acid synthase II. Here we review the biosynthesis of mycolic acids and the mechanism of action of antimicrobial agents that act upon this pathway. In addition, we describe molecular modeling studies on InhA, the bona-fide target for isoniazid, which should improve our understanding of the amino acid residues involved in the enzyme's mechanism of action and, accordingly, provide a rational approach to the design of new drugs.     

Synthesis and investigation of conformationally restricted analogues of lavendustin A as cytotoxic inhibitors of tubulin polymerization

A series of conformationally restricted analogues were synthesized in order to elucidate the possible effects of different amide conformations of lavendustin A derivatives on cytotoxicity in cancer cell cultures and on inhibition of tubulin polymerization. The conformationally restricted analogues were based on the oxazinedione and isoindolone ring systems. In addition, the amide bond was replaced by both cis and trans alkene moieties. Surprisingly, the results indicated very little effect of conformational restriction on biological activity. Because all of the compounds synthesized had similar cytotoxicities and potencies as tubulin polymerization inhibitors, the side chain present on the aniline ring system does not appear to be important in the biological effects of the lavendustins. The hydroquinone ring of lavendustin A may be a more important determinant of the biological activity than the structure surrounding the aniline ring.     

1-(N-alkylamino)-11-(N-ethylamino)-4,8-diazaundecanes: simple synthetic polyamine analogues that differentially alter tubulin polymerization

Polyamine analogues such as bis(ethyl)norspermine and N1-(cyclopropylmethyl)-N11-ethyl-4,8-diazaundecane (CPENSpm) act as potent modulators of cellular polyamine metabolism in vitro and possess impressive antitumor activity against a number of cell lines. Some of these polyamine analogues appear to produce their cell-type-specific cytotoxic activity through the superinduction of spermidine/spermine N1-acetyltransferase (SSAT). However, there are several analogues (e.g., N1-(cycloheptylmethyl)-N11-ethyl-4, 8-diazaundecane (CHENSpm)) which are effective cytotoxic agents but do not superinduce SSAT. We have previously demonstrated that CPENSpm and CHENSpm both initiate the cell death program, although by different mechanisms, and that CHENSpm (but not CPENSpm) induces a G2/M cell cycle arrest. We now report that one potential mechanism by which some polyamine analogues can retard growth and ultimately produce cytotoxicity is through interference with normal tubulin polymerization. In these studies, we compare the effects of the polyamine analogues CHENSpm, CPENSpm, and (S)-N1-(2-methyl-1-butyl)-N11-ethyl-4,8-diazaundecane (IPENSpm) on in vitro tubulin polymerization. These spermine analogues behave very differently from spermine and from each other in terms of tubulin polymerization rate, equilibrium levels, and time of polymerization initiation. These results demonstrate that structurally similar polyamine analogues with potent antitumor effects can produce significantly different cellular effects. The discovery of polyamine analogues that can alter tubulin polymerization provides a series of promising lead compounds that may have a similar spectrum of activity to more difficult to synthesize compounds typified by paclitaxel.     

Synthesis,anticancer activity,and inhibition of tubulin polymerization by conformationally restricted analogues of lavendustin A

Compounds in the lavendustin A series have been shown to inhibit both protein-tyrosine kinases (PTKs) and tubulin polymerization. Since certain lavendustin A derivatives can exist in conformations that resemble both the trans-stilbene structure of the PTK inhibitor piceatannol and the cis-stilbene structure of the tubulin polymerization inhibitor combretastatin A-4, the possibility exists that the ratio of the two types of activities of the lavendustins could be influenced through the synthesis of conformationally restricted analogues. Accordingly, the benzylaniline structure of a series of pharmacologically active lavendustin A fragments was replaced by either their cis- or their trans-stilbene relatives, and effects on both inhibition of tubulin polymerization and cytotoxicity in cancer cell cultures were monitored. Both dihydrostilbene and 1,2-diphenylalkyne congeners were also prepared and evaluated biologically. Surprisingly, conformational restriction of the bridge between the two aromatic rings of the lavendustins had no significant effect on biological activity. On the other hand, conversion of the three phenolic hydroxyl groups of the lavendustin A derivatives to their corresponding methyl ethers consistently abolished their ability to inhibit tubulin polymerization and usually decreased cytotoxicity in cancer cell cultures as well, indicating the importance of at least one of the phenolic hydroxyl groups. Further investigation suggested that the phenolic hydroxyl group in the salicylamide ring was required for activity, while the two phenol moieties in the hydroquinone ring could be methylated with retention of activity. Two of the lavendustin A derivatives displayed IC(50) values of 1.4 microM for inhibition of tubulin polymerization, which ranks them among the most potent of the known tubulin polymerization inhibitors.     

“一瓶法”合成鬼臼毒素类似物及其体外抗肿瘤活性

目的探讨天然产物鬼臼毒素类似物表鬼臼毒素（1）和4＇-脱甲基表鬼臼毒素（2）的简易合成方法，并测试其体外抗肿瘤活性。方法采用“一瓶法”合成目标产物，并通过MTT法和SRB法测定2个目标化合物的体外抗肿瘤活性。结果与结论通过对鬼臼毒素进行结构改造，得到合成其衍生物的常见化学反应的简易操作方法，化合物1和2的收率分别为86％和79％，其结构经。H-NMR和ESI—MS谱确证。活性测试结果表明，目标化合物对4种肿瘤细胞（HeLa细胞、SKOV3细胞、K562细胞、耐阿霉素I（562细胞）均具有较强的活性。     

Effect of diethylstilbestrol on the polymerization and alkylation of tubulin

Diethylstilbestrol is a drug used to treat prostate cancer. It is thought to bind to tubulin, the subunit protein of microtubules, at the colchicine‐binding site. We examined its interaction with tubulin in more detail. Diethylstilbestrol inhibits microtubule assembly, and seems to do so more effectively when tubulin polymerization is catalyzed by MAP2 rather than tau. Diethylstilbestrol also inhibits the intrachain cross‐linking of tubulin by N,N′‐ethylenebis‐(iodoacetamide) in a pattern similar to that shown by colchicine and the drugs which bind to tubulin at the colchicine‐binding site. Unlike most of this category of drugs, however, diethylstilbestrol accelerates, rather than inhibits, the decay of tubulin as measured by exposure of sulfhydryl groups and hydrophobic areas. It appears, therefore, that diethylstilbestrol interacts with tubulin in a manner similar to that of the analogs of the A‐ring of colchicine, whose effect on tubulin cross‐linking is similar to that of diethylstilbestrol and which also enhance tubulin decay. Drug Dev. Res. 48:104–112, 1999. © 1999 Wiley‐Liss, Inc.     

新型微管稳定剂吲哚美辛衍生物的合成与抗肿瘤活性研究

目的设计合成一系列吲哚美辛衍生物并测定其体外抗肿瘤和微管蛋白抑制活性。方法以5-甲氧基-2-甲基-3-吲哚乙酸为起始原料经两步酰化反应合成12个化合物,MTT法检测目标化合物对HT29、A549、Hep-2、MCF-7肿瘤细胞的抑制活性,同时采用浊度法评价其体外微管蛋白的抑制作用。结果 12种目标化合物均呈现了优于吲哚美辛的体外抗肿瘤作用和微管蛋白抑制活性,其中3位羧基侧链苯乙基取代的化合物12作用于人结肠癌细胞HT29的IC_(50)(2.2μmol)为吲哚美辛的400倍,并且可以干扰微管聚合,其作用于微管蛋白的IC_(50)为5.6μmol。结论改变吲哚美辛1位酰胺和3位羧酸侧链所得的系列衍生物是一类新型的以微管为靶点的抗肿瘤候选药物。     

Modification of tubulin cysteines by nitric oxide and nitroxyl donors alters tubulin polymerization activity

The modification of reduced cysteines of proteins by nitric oxide alters protein function, structure, and potentially, interactions with downstream signaling targets. We assessed the effect of the S-nitroso compounds S-nitrosoglutathione and S-nitroso-N-acetyl-penicillamine, the NO donor 2-(N,N-diethylamino)-diazenolate 2-oxide, and the nitroxyl donor Angeli's salt on the cysteines of the abundant cytoskeletal protein, tubulin. Total cysteine modification by each compound was quantitated and compared to peroxynitrite anion, an oxidant that we have studied previously. Angeli's salt was most effective at modifying the cysteines of tubulin and at inducing the formation of tubulin interchain disulfide bonds followed by peroxynitrite anion, S-nitrosoglutathione, S-nitroso-N-acetyl-penicillamine, and 2-(N,N-diethylamino)-diazenolate 2-oxide. S-nitrosation of tubulin by S-nitrosoglutathione and S-nitroso-N-acetyl-penicillamine was detected by the Saville assay. Our data show that tubulin interchain disulfide bond formation by these molecules correlated with inhibition of tubulin polymerization. Closer examination of the reaction of tubulin with S-nitrosoglutathione showed a concentration-dependent shift in the type of cysteine modification detected. More tubulin disulfides were detected at lower concentrations of S-nitrosoglutathione than at higher concentrations, suggesting that reduced glutathione, generated by the reaction of S-nitrosoglutathione with tubulin cysteines, reduced disulfides initially formed by S-nitrosoglutathione.     

Arylthioindoles, potent inhibitors of tubulin polymerization

Several arylthioindoles had excellent activity as inhibitors both of tubulin polymerization and of the growth of MCF-7 human breast carcinoma cells. Methyl 3-[(3,4,5-trimethoxyphenyl)thio]-5-methoxy-1H-indole-2-carboxylate (21), the most potent derivative, showed IC(50) = 2.0 microM, 1.6 times more active than colchicine and about as active as combretastatin A-4 (CSA4). Compound 21 inhibited the growth of the MCF-7 cells at IC(50) = 13 nM. Colchicine and CSA4 had 13 nM and 17 nM IC(50) values, respectively, with these cells.     

Structure-function studies with derivatives of 6-benzyl-1,3-benzodioxole, a new class of synthetic compounds which inhibit tubulin polymerization and mitosis

A new class of synthetic antineoplastic compounds, derivatives of 6-benzyl-1,3-benzodioxole, has significant antimitotic activity. These compounds inhibit microtubule assembly and are competitive inhibitors of the binding of colchicine to tubulin. Both their structure and their partial inhibition of tubulin-dependent GTP hydrolysis indicate that they are most comparable to podophyllotoxin of all known antimitotic drugs. Maximum activity required an intact dioxole ring, a methoxy or ethoxy substituent at position 5, and, on the benzyl moiety at position 6, a para-methoxy group. Additional methoxy groups on the benzyl substituent, to increase the apparent structural similarity to podophyllotoxin, resulted in major reduction of the antitubulin activity of these drugs.     

Teratogen metabolism: Activation of thalidomide and thalidomide analogues to products that inhibit the attachment of cells to concanavalin a coated plastic surfaces

Thalidomide metabolites inhibited the attachment of tumor cells to concanavalin A coated polyethylene surfaces. Thalidomide, itself, was non-inhibitory. Thalidomide activation to inhibitory products required hepatic microsomes, an NADPH-generating system, and molecular oxygen. Production of inhibitory metabolites was unaffected by either epoxide hydrolase or 1,2-epoxy-3,3,3-trichloropropane (TCPO), an inhibitor of epoxide hydrolase endogenous to hepatic S9 fraction. Therefore, the attachment inhibitor was probably not an arene oxide. Inhibition was not accompanied by cytotoxicity, as judged by trypan blue exclusion. Although uninduced hepatic microsomes from mice, rats and dogs had similar abilities to activate thalidomide, microsomes from Aroclor 1254 induced rats were relatively inactive in the system. Inhibitory metabolites were generated from the thalidomide analogues EM8. EM12, EM16. EM87, EM136, EM255, E350, phthalimide, phthalimido-phthalimide, indan, 1-indanone and 1,3-indandione. Glutarimide, glutamic acid and phthalic acid did not activate to inhibitory products.