Cancer preventive agents, Part 2: Synthesis and evaluation of 2-phenyl-4-quinolone and 9-oxo-9,10-dihydroacridine derivatives as novel antitumor promoters

2-Phenyl-4-quinolone and 9-oxo-9,10-dihydroacridine derivatives were synthesized and screened as potential antitumor promoters by examining the ability of the compounds to inhibit Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. Interestingly, compounds 14, 15, and 17 showed similar inhibitory effects (89-92%, 66-69%, and 24-29% at 1000, 500, and 100 mol ratio to TPA, respectively) against EBV-EA with potencies comparable to those of glycyrrhetic acid, a known natural antitumor-promoter.     

The amyloid peptide induces early genotoxic damage in human preneuron NT2

The antimutagenic activities of benzalacetone (4-phenyl-3-buten-2-one) and its structurally-related compounds were evaluated through their use as post-treatments for the UV-induced mutagenesis in Escherichia coli WP2s (uvrA) and the gamma-induced mutagenesis in Salmonella typhimurium TA2638, the latter of which is sensitive to oxidants. Structure-activity relationships were studied between IC(50) activity values, i.e. the dose (micromol/ml) at which the mutation frequency is reduced to 50% of the control, and electronic and hydrophobicity properties of the studied molecules. Benzalacetone and benzalacetone analogs, cinnamaldehyde and trans-1,1,1-trifluoro-4-phenyl-3-buten-2-one (TF), inhibited both forms of mutagenesis, but methyl cinnamate, cinnamic acid and cinnamamide did not. The IC(50) values of TF, for UV-induced mutagenesis and gamma-induced mutagenesis, were 0.028 and 0.045 micromol/ml, respectively, and one order of magnitude lower than those of cinnamaldehyde and benzalacetone. The three antimutagenic analogs listed in order of decreasing activity are: TF>cinnamaldehyde>benzalacetone. This order is proportional to the electron-withdrawing property of the terminal group attached to an alpha,beta-unsaturated carbonyl moiety in the side chain that is known to play an important role in the antimutagenicities of benzalacetone and related compounds. In UV-induced mutagenesis in E. coli WP2s, mono-substituted benzalacetones - the ring-substituents of which have electron-withdrawing properties - showed antimutagenic activity that correlated with their electronic property. In gamma-induced mutagenesis in S. typhimurium TA2638, the antimutagenic activities of mono-substituted benzalacetones were proportional to the substituent hydrophobicities (pi). The different effects on both the mutation-induced systems is suggested to be related to the relative permeability of the cell membranes and the different sensitivities to mutagens between E. coli WP2s and S. typhimurium TA2638. In addition, the antimutagenic activity against gamma-induced mutagenesis could be due to the ability of parent compounds or their derivatives to scavenge long-lived organic radicals; the radicals have been described to be generated as a result of the X-irradiation of cells by Koyama et al. [Mutat. Res. 421 (1998) 45].     

Triterpene acids from the leaves of Perilla frutescens and their anti-inflammatory and antitumor-promoting effects

Nine triterpene acids, viz., six of the ursane type, ursolic acid (1), corosolic acid (2), 3-epicorosolic acid (3), pomolic acid (4), tormentic acid (5) and hyptadienic acid (6), and three of the oleanane type, oleanolic acid (7), augustic acid (8) and 3-epimaslinic acid (9), among which 1 constituted the most predominant triterpene acid, were isolated and identified from ethanol extracts of the leaves of red perilla [Perilla frutescens (L.) Britton var. acuta Kudo] and green perilla [P. frutescens (L.) Britton var. acuta Kudo forma viridis Makino]. These eight compounds, 1, 2, 4-9, were evaluated for their inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation (1 microg/ear) in mice. All the compounds tested showed a marked anti-inflammatory effect, with a 50% inhibitory dose (ID50) of 0.09-0.3 mg per ear. In addition, an evaluation against the Epstein-Barr virus early antigen (EBV-EA) activation induced by TPA showed five compounds, 1-3, 5 and 9, with a potent inhibitory effect on EBV-EA induction (91-93% inhibition at 1x10(3) mol ratio/TPA). Furthermore, compound 5 exhibited strong antitumor-promoting activity in an in vivo two-stage carcinogenesis test of mouse tumor by using 7,12-dimethylbenz(a)anthracene (DMBA) as an initiator and TPA as a promoter.     

Cancer preventive agents 9. Betulinic acid derivatives as potent cancer chemopreventive agents

C-3 esterifications of betulinic acid (BA, 1) and its A-ring homolog, ceanothic acid (CA, 2), were carried out to provide sixteen terpenoids, 4–19, including nine new compounds (4–12). All synthesized compounds were evaluated in an in vitro antitumor-promoting assay using the Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. Among them, compounds 4–6, 11–14, 16, and 17 displayed remarkable inhibitory effects of EBV-EA activation. BA analog 6, which contains a prenyl-like group, showed the most potent inhibitory effect (100%, 76%, 37%, and 11% inhibition of EBA activation at 1000, 500, 100, and 10 mol ratio/TPA, respectively, with IC₅₀ value of 285 mol ratio/32 pmol TPA). Compound 6 merits further development as a cancer preventive agent.     

Anti-tumor promoting diterpenes from the stem bark of Thuja standishii (Cupressaceae).

Three new labdane-type diterpenoids, labda-8(17),13-dien-15,12R-olid-19-oic acid (1), 12S-hydroxylabda-8(17),13(16),14-trien-19-oic acid (2) and 13-ethoxylabda-8(17),11,14-trien-19-oic acid (3), along with known diterpenoids, trans-communic acid (4), totarol (5), 12-methoxyabieta-8,11,13-trien-11-ol (6), and 7 alpha,8 alpha-epoxy-6 alpha-hydroxyabieta-9(11),13-dien-12-one (7) were isolated from the stem bark of Thuja standishii. The structures of 1--3 were established by spectroscopic methods and chemical conversion. These compounds together with standishinal (8), 12-hydroxy-6,7-seco-abieta-8,11,13-trien-6,7-dial (9) and 6 alpha-hydroxysugiol (10) were tested for their inhibitory effects on Epstein--Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), as a test for potential cancer chemopreventive agents. Compound 10 showed strong inhibitory effect on EBV-EA induction (100% inhibition at 1000 mol ratio/TPA), and compounds 2 and 6 showed moderate inhibitory effects on EBV-EA induction. In addition, 15-oxolabda-8(17),11Z,13E-trien-19-oic acid (11) was found to exhibit the anti-tumor promoting activity in two-stage mouse skin carcinogenesis test using 7,12-dimethylbenz[a]anthracene and TPA.     

Multidrug-resistant cancer cell susceptibility to cytotoxic quassinoids, and cancer chemopreventive effects of quassinoids and canthin alkaloids

Twenty-three quassinoids (1-23), which were isolated previously from Simaroubaceous plants, were evaluated for cytotoxicity against three multidrug-resistant cancer cell lines, KB-VIN, KB-7d, and KB-CPT. Nine compounds (2-7 and 9-11) showed significant cytotoxicity in all three cell lines. Compounds 1, 12-14, 17, and 20 demonstrated significant activity against the KB-7d and KB-CPT cell lines, and compounds 18, 19, and 23 revealed notable activity only against KB-7d cells. Structure-activity relationships were drawn based on these data. In addition, six quassinoid derivatives (24-29) and four canthin alkaloids (30-33), which were isolated from Brucea antidysenterica, were examined for their inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate (TPA) induced Epstein-Barr virus early antigen (EBV-EA) activation as cancer chemopreventive agents. All of these compounds demonstrated significant inhibitory effects against EBV-EA activation.     

Anti-inflammatory and anti-tumor-promoting effects of triterpene acids and sterols from the fungus Ganoderma lucidum

A series of lanostane-type triterpene acids, including eleven lucidenic acids (3, 4, 9, 10, 13-19) and six ganoderic acids (20-22, 24, 26, 27), as well as six sterols (28-33), all isolated from the fruiting bodies of the fungus Ganoderma lucidum, were examined for their inhibitory effects on the induction of Epstein-Barr virus early antigen (EBV-EA) by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells, a known primary screening test for anti-tumor promoters. All of the compounds tested, except for ganolactone (27) and three sterols (29-31), showed potent inhibitory effects on EBV-EA induction, with IC(50) values of 235-370 mol ratio/32 pmol TPA. In addition, nine lucidenic acids (1, 2, 5-8, 11, 12, 18) and four ganoderic acids (20, 23-25) were found to inhibit TPA-induced inflammation (1 microg/ear) in mice, with ID(50) values of 0.07-0.39 mg per ear. Further, 20-hydroxylucidenic acid N (18) exhibited inhibitory effects on skin-tumor promotion in an in vivo two-stage mouse-skin carcinogenesis test based on 7,12-dimethylbenz[a]anthracene (DMBA) as initiator, and with TPA as promoter.     

Synthesis and anti-tumor-promoting activity of glycoglycerolipid analogues lacking the glycerol backbone

Glycoglycerolipid analogues lacking the glycerol backbone were prepared through a lipase catalyzed transesterification of beta-D-galactosylethylene glycol. The inhibitory effect of the resultant isomeric hexanoates at the primary alcoholic positions, beta-D-galactosylethylene glycol itself and nonyl beta-D-galactopyranoside, was tested on Epstein-Barr virus early antigen (EBV-EA) activation in Raji cells promoted by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), as a primary screening test for inhibitors of tumor promotion. All the compounds assayed were found to be less active than the reference 2-O-beta-D-galactopyranosylglycerol derivatives, of which they are simplified models, indicating that the anti-tumor-promoting activity is very closely related to the presence of a free hydroxymethylene group on the glycerol-like aglycone moiety.     

Cucurbitane triterpenoids from the leaves of Momordica charantia, and their cancer chemopreventive effects and cytotoxicities

Seventeen cucurbitane-type triterpenoids, 1-17, including six new compounds, (23E)-3β,25-dihydroxy-7β-methoxycucurbita-5,23-dien-19-al (1), (23S*)-3β-hydroxy-7β,23-dimethoxycucurbita-5,24-dien-19-al (6), (23R*)-23-O-methylmomordicine IV (7), (25ξ)-26-hydroxymomordicoside L (8), 25-oxo-27-normomordicoside L (9), and 25-O-methylkaravilagenin D (12), were isolated from a MeOH extract of the leaves of Japanese Momordica charantia. The structures of new compounds were elucidated on the basis of extensive spectroscopic analyses and comparison with literature. Compounds 1-17 were examined for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced with 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells, a known primary screening test for inhibitors of tumor promotion. Four compounds, 1, (23E)-3β,7β-dihydroxy-25-methoxycucurbita-5,23-dien-19-al (2), karavilagenin D (11), and 12, showed potent inhibitory effects on EBV-EA induction with IC(50) values in the range of 242-264 mol ratio/32 pmol TPA. In addition, compounds 1 and 11 exhibited inhibitory effects on skin-tumor promotion in an in vivo two-stage mouse skin carcinogenesis test based on 7,12-dimethylbenz[a]anthracene (DMBA) as initiator, and with TPA as a promoter. Furthermore, upon evaluation of the cytotoxic activities of compounds 1-17 against human cancer cell lines, compounds 2, 5-7, 9, and 14 showed potent activities against HL60 cell line, and compound 2 against SK-BR-3 cell line.     

Anti-tumor promoting effects of sesquiterpenes from Maytenus cuzcoina (Celastraceae)

Ten sesquiterpenoids (1-10), with a dihydro-beta-agarofuran skeleton, were isolated from Maytenus cuzcoina (Celastraceae). Their structures were elucidated on the basis of spectral analysis, including homo- and heteronuclear correlations NMR experiments (COSY, ROESY, HMQC and HMBC), and chemical correlations. The compounds have been tested for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), as a test for potential cancer chemopreventive agents. Compounds 1-3, 6 and 7 showed strong inhibitory effects on EBV-EA induction (100% inhibition at 1000 mol ratio/TPA). Their structure-activity relationship is discussed.     

N-Caffeoyl serotonin as selective COX-2 inhibitor

The inhibitory effects of the synthetic serotonin analogues (1-8) on COX (1 and 2) were evaluated. Two serotonin derivatives (4 and 8) showed inhibitory effect of COX (1 and 2). Especially, 4 exhibited excellent inhibitions on COX-2 with extremely high potency (IC(50)=42.5 μM). The inhibitory activities of cinnamic acid derivatives and serotonin were evaluated to clarify whether inhibitory activities of compound 4 and 8 are due to cinnamic acid moiety or serotonin moiety. Caffeic acid and N-caffeoyl serotonin (4) exhibited selective inhibition of COX-2 compared to aspirin. Comparison caffeic acid with 4 suggested that the linkage of caffeic acid and serotonin enhance COX-2 inhibition. Comparison of structures of caffeic acid and sinapic acid implied that catechol moiety of cinnamic acid derivatives is a major contributing factor for selective inhibition of COX-2. The selective COX-2 inhibitory activity of compound 4 is significant and could be employed as drugs against inflammatory and allergy.     

An antitumor promoter from Moringa oleifera Lam

In the course of studies on the isolation of bioactive compounds from Philippine plants, the seeds of Moringa oleifera Lam. were examined and from the ethanol extract were isolated the new O-ethyl-4-(alpha-L-rhamnosyloxy)benzyl carbamate (1) together with seven known compounds, 4(alpha-L-rhamnosyloxy)-benzyl isothiocyanate (2), niazimicin (3), niazirin (4), beta-sitosterol (5), glycerol-1-(9-octadecanoate) (6), 3-O-(6'-O-oleoyl-beta-D-glucopyranosyl)-beta-sitosterol (7), and beta-sitosterol-3-O-beta-D-glucopyranoside (8). Four of the isolates (2, 3, 7, and 8), which were obtained in relatively good yields, were tested for their potential antitumor promoting activity using an in vitro assay which tested their inhibitory effects on Epstein-Barr virus-early antigen (EBV-EA) activation in Raji cells induced by the tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA). All the tested compounds showed inhibitory activity against EBV-EA activation, with compounds 2, 3 and 8 having shown very significant activities. Based on the in vitro results, niazimicin (3) was further subjected to in vivo test and found to have potent antitumor promoting activity in the two-stage carcinogenesis in mouse skin using 7,12-dimethylbenz(a)anthracene (DMBA) as initiator and TPA as tumor promoter. From these results, niazimicin (3) is proposed to be a potent chemo-preventive agent in chemical carcinogenesis.     

Inhibitory effects of lapachol derivatives on epstein-barr virus activation

Sixteen derivatives (2-17) synthesized from the naphthoquinone lapachol (1), were tested for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), as a test for potential cancer chemopreventive agents. They exhibited a variety of inhibitory activities from very high to moderate, which allow us to suggest structure-activity relationships. Ten of these derivatives are reported for the first time, their structures being thoroughly determined by spectroscopic methods.     

Synthesis and inhibitory activity of new benzimidazole derivatives against Burkitt's lymphoma promotion

As a continuation to our previous work concerning antitumor benzimidazoles, we have synthesized series of new derivatives of 2-(1-benzyl-2-methyl-1H-benzimidazol-5-ylimino)-3-(substituted)-thiazolidin-4-one (6a-e), 3-(2-methyl-1H-benzimidazol-5-yl)-2-substituted-thiazolidin-4-one (9a-f) and we have studied their inhibitory activity against the Epstein-Barr virus-early antigen (EBV-EA) activation introduced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Compound 6d was found to be significantly active and compounds 5a and 6e were also active.     

Urease inhibitory activity of simple alpha,beta-unsaturated ketones

A variety of alpha,beta-unsaturated ketones were evaluated for their effect on the jack bean urease. Of 35 compounds tested, 2-cyclohepten-1-one (1), 2-cyclohexen-1-one (2), 2-cyclopenten-1-one (3), and 5,6-dihydro-2H-pyran-2-one (4) showed potent inhibitory activities against the enzyme. The most potent compound (1) (IC50=0.16 mM) showed similar inhibitory potency to hydroxyurea (IC50=0.095 mM). The inhibitory effects of 1, 2, 3, and 4 were significantly reduced by 2-mercaptoethanol or dithiothreitol. These data suggest that alpha,beta-unsaturated ketones inhibited the urease activity, possibly by a Michael-like addition of a protein SH group to the double bond of the alpha,beta-unsaturated carbonyl group.     

Cytotoxic activities and anti-tumor-promoting effects of microbial transformation products of prenylated chalcones from Angelica keiskei

Three prenylated chalcones, 4-hydroxyderricin (1), xanthoangelol (2), and xanthoangelol F (3), isolated from Angelica keiskei, were transformed by the fungus Aspergillus saitoi. These chalcones were converted to flavanones (i.e., 4, 8, and 12), and prenyl-chain-hydrated (i.e., 5, 7, 9-11, and 13) and ring-B-hydroxylated (i.e., 6) chalcones. The structures of three new metabolites, 7, 9, and 13, were established as 2″,3″-dihydro-4,3″-dihydroxyderricin, 6″,7″-dihydro-7″-hydroxyxanthoangelol, and 6″,7″-dihydro-7″-hydroxyxanthoangelol F, respectively. Upon evaluation of cytotoxic activities of compounds 1-13, the metabolite 7 exhibited potent cytotoxicity against HL60 cells, and this cell death was revealed to be mostly due to apoptosis. In addition, compounds 1-4, 7-10, 12, and 13 were examined for their inhibitory effects on the induction of Epstein-Barr virus early antigen (EBV-EA) by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. All compounds tested showed inhibitory effects against EBV-EA activation with potencies higher than that of β-carotene. Furthermore, the metabolite 13 exhibited inhibitory effect on skin tumor promotion in an in vivo two-stage mouse skin carcinogenesis test based on 7,12-dimethylbenz[a]anthracene (DMBA) as initiator, and with TPA as promoter.     

Anti-tumor promoting activity of bufadienolides from Kalanchoe pinnata and K. daigremontiana x tubiflora

Five bufadienolides (1-5) isolated from the leaves of Kalanchoe pinnata and K. daigremontiana x tubiflora (Crassulaceae) were examined for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation in Raji cells induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate. All bufadienolides showed inhibitory activity, and bryophyllin A (1) exhibited the most marked inhibition (IC50 = 0.4 microM) among the tested compounds. Bryophyllin C (2), a reduction analogue of 1, and bersaldegenin-3-acetate (3) lacking the orthoacetate moiety were less active. These results strongly suggest that bufadienolides are potential cancer chemopreventive agents.     

Antitumor promoting activities of 3-O-acyl-(-)epigallocatechins

As an exploratory investigation of antitumor promoting compounds, 3-O-acyl-(-)-epigallocatechins possessing a straight-, branched-, phenyl-inserted- or 1,4-phenylene-inserted-acyl chain of varying length from C4 to C18 were synthesized and evaluated their inhibitory effects against the activation of the Epstein-Barr virus early antigen (EBV-EA). It was indicated that the epigallocatechin derivatives having the straight- or branched-acyl chain of C8 to C11 carbon atoms achieve marked effects.     

Cancer preventive agents. Part 1: chemopreventive potential of cimigenol, cimigenol-3,15-dione, and related compounds

In continuation of our previous report, cimigenol (1) and 15 related compounds were screened as potential antitumor promoters by using the in vitro short-term 12-O-tetradecanoylphorbol-13-acetate (TPA)--induced Epstein-Barr virus early antigen (EBV-EA) activation assay. Cimigenol-3,15-dione (2) displayed the greatest potency (100% inhibition at 1000 mol ratio/TPA) and consequently was further examined for antitumor-promoting activity in a two-stage carcinogenesis assay of mouse skin tumors (DMBA/TPA). In this assay, compound 2 showed significant activity, reducing the number of papillomas per mouse to 48% of the control group at 20 weeks. In addition, compounds 1 and 2 were examined for antitumor-initiating activity in a two-stage carcinogenesis assay of mouse skin tumors induced by peroxynitrite as an initiator and TPA as a promoter. Results showed that these two triterpenoids were almost equipotent with epigallocatechin gallate (EGCG) and slightly more potent than tocinol (group V), the positive controls. Thus, compounds 1 and 2 exhibited not only strong antitumor-promoting activity but also significant antitumor-initiating effect on mouse skin. These data suggest that both compounds might be valuable chemopreventors.     

Synthesis, biological evaluation, and molecular docking studies of cinnamic acyl 1,3,4-thiadiazole amide derivatives as novel antitubulin agents

A series of cinnamic acyl 1,3,4-thiadiazole amide derivatives (6a-10e) have been designed and synthesized, and their biological activities were also evaluated as potential antiproliferation and tubulin polymerization inhibitors. Among all the compounds, 10e showed the most potent activity in vitro, which inhibited the growth of MCF-7 and A549 cell lines with IC(50) values of 0.28 and 0.52μg/mL, respectively. Compound 10e also exhibited significant tubulin polymerization inhibitory activity (IC(50)=1.16μg/mL). Docking simulation was performed to insert compound 10e into the crystal structure of tubulin at colchicine binding site to determine the probable binding model. Based on the preliminary results, compound 10e with potent inhibitory activity in tumor growth may be a potential anticancer agent.