Antimitotic and cytotoxic flavonols from Zieridium pseudobtusifolium and Acronychia porteri

Effects of substituent pattern on the intracellular target of antiproliferative benzo[b]thiophenyl chromone derivatives

A new biological scaffold was produced by replacing the 6π-electron phenyl ring-B of a natural flavone skeleton with a 10π-electron benzothiophene (BT). Since aromatic rings are important for ligand protein interactions, this expansion of the π-electron system of ring-B might change the bioactivity profile. One of the resulting novel natural product-inspired compounds, 2-(benzo[b]thiophen-3-yl)-5-hydroxy-7-isopropoxy-6-methoxyflavone (6), effectively arrested the cell cycle at the G2/M phase and displayed significant antiproliferative effects with IC₅₀ values of 0.05-0.08 μM against multiple human tumor cell lines, including a multidrug resistant line. A structure-activity relationship study revealed that a 10π-electron system with high aromaticity, juxtaposed 4-oxo and 5-hydroxy groups, and 7-alkoxy groups were important for potent antimitotic activity. Interestingly, two BT-flavonols (3-hydroxyflavone), 16 and 20, with 3-hydroxy and 5-alkoxy groups, induced distinct biological profiles affecting the cell cycle at the G1/S phase by inhibition of DNA replication through an interaction with topoisomerase I.

A pentamethoxylated flavone from Glycosmis ovoidea promotes apoptosis through the intrinsic pathway and inhibits migration of MCF-7 breast cancer cells

The rare flavone 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone (PMF) has been isolated from several plant species, and its cytotoxic activity has been reported against many types of cancer cells. In this study, PMF was purified from Glycomis ovoidea collected in Vietnam, and its antiproliferative effects and underlying mechanism of action were investigated against MCF-7 cells. PMF inhibited growth in MCF-7 > MCF-10A > MDA-MB-231 cells after 72 hr treatment, with IC50 values of 1.5, 1.9, and 8.6 μg/ml, respectively. Further experiments conducted with this compound in MCF-7 cells, showed the loss of mitochondrial membrane potential, reactive oxygen species overproduction, upregulation of BAX, cytochrome c, caspase-3 and PARP-1 and down-regulation of BCL-2 proteins as well as an increase in caspase-3/-7 activity, suggesting induction of the apoptotic intrinsic pathway. Furthermore, PMF increased cell cycle arrest in the G1 phase, which correlated with increments in the p53 and p21 levels. Additionally, MCF-7 cell migration was inhibited, which could be related to NF-κB p65 downregulation. Finally, PMF did not show toxicity in vivo in a zebrafish (Danio rerio) model. In conclusion, PMF induces cell death in MCF-7 cells through regulation of the BCL-2 protein family and may be proposed as a lead as a potential alternative for breast cancer therapy.

Acridone alkaloids and flavones from the leaves of Citrus reticulata

A new acridone alkaloid, reticarcidone A (1), decorated with an oxygenated isopentenyl group between C-1 and C-2, was isolated from the leaves of Citrus reticulata Blanco, together with nine known acridone alkaloids (2-10) and fifteen flavones compounds (11-25). The structure of those compounds were confirmed by analysis of comprehensive 1D and 2D NMR, and MS data. Reticarcidone A (1) was the first pyrano[2,3-a]acridone isolated from the genus Citrus. Some of these compounds showed moderated cytotoxicity against the five human tumor cell lines MCF-7, SMMC-7721, HL-60, A549 and SW480.

N-Benzylation of 6-aminoflavone by reductive amination and efficient access to some novel anticancer agents via topoisomerase II inhibition

Series of novel N-benzyl derivatives of 6-aminoflavone (9a-n) were synthesized and evaluated for anticancer and topoisomerase II enzyme inhibition activity. All the synthesized compounds were screened for in vitro anticancer activity against human breast cancer cell line (MCF-7) and human lung cancer cell line (A-549). Among the synthesized compounds, 9f and 9g were found to be the most potent anticancer agents against human breast cancer cell line (MCF-7) with IC₅₀ values of 9.35 µM and 9.58 µM, respectively. Compounds 9b, 9c and 9n exhibited promising anticancer activity against human lung cancer cell line (A-549) with 43.71%, 46.48% and 44.26% inhibition at the highest concentration of 10 µM, respectively. Compounds 9c, 9f and 9g have ability to inhibit the topoisomerase II enzyme. Compound 9f showed most potent topoisomerase II enzyme inhibition activity with IC₅₀ value of 12.11 µM. Further, these compounds have a high potential to be developed as a promising topoisomerase II inhibitors.

Towards modern anticancer agents that interact with tubulin

Tubulin is the primary target of an ever growing number of natural, semisynthetic and synthetic products as potential anticancer agents. The mechanisms of interaction of these molecules with tubulin are varied. These drug classes have shown to inhibit effectively several cancer types with IC₅₀ from midmicromolar to low nanomolar concentrations. However, some limiting obstacles still remain, such as the development of multidrug resistance and cytotoxicity. We have reviewed recent advances in different classes of tubulin binding agents, including colchicine site agents, Vinca alkaloids, tryprostatins, moroidin, hemiasterlin, diazonamide, taxanes, epothilones and laulimalide.

3'-Hydroxy-3,4'-dimethoxyflavone-induced cell death in human leukaemia cells is dependent on caspases and reactive oxygen species and attenuated by the inhibition of JNK/SAPK

Flavonoids are phenolic substances that appear to exert beneficial effects in several chronic diseases, including cancer. Structure-activity relationships of the cytotoxic activity of a series of flavonols and their 3-methyl ether derivatives established that 3'-hydroxy-3,4'-dimethoxyflavone (flavonoid 11) displayed strong cytotoxicity against human leukaemia cell lines (HL-60, U-937 and MOLT-3), and cells that over-express the anti-apoptotic proteins, Bcl-2 and Bcl-x_L, and against P-glycoprotein-overexpressing K-562/ADR cells. This compound induced G₂-M cell cycle arrest and it was a potent apoptotic inducer on HL-60, MOLT-3, U-937 and U-937/Bcl-2 cell lines. Cell death was (i) mediated by caspase activation, since it was prevented by the non-specific caspase inhibitor z-VAD-fmk and reduced by a selective caspase-9 inhibitor, (ii) associated with cytochrome c release, the dissipation of the inner mitochondrial membrane potential (ΔΨ_m) and the activation of the mitogen-activated protein kinase pathway and (iii) partially blocked by the inhibition of c-jun NH₂ terminal kinases/stress activated protein kinases (JNK/SAPK) signalling and by the free-radical scavenger N-acetyl-l-cysteine.

3'-Hydroxy-3,4'-dimethoxyflavone blocks tubulin polymerization and is a potent apoptotic inducer in human SK-MEL-1 melanoma cells

Flavonoids are naturally occurring polyphenolic compounds and are among the most promising anticancer agents. A series of flavonols and their 3-methyl ether derivatives were synthesized and assessed for cytotoxicity. It was found that 3'-hydroxy-3,4'-dimethoxyflavone (flavonoid 7a) displayed strong cytotoxicity against human SK-MEL-1 melanoma cells and blocked tubulin polymerization, but had no significant cytotoxic effects against quiescent or proliferating human peripheral blood mononuclear cells. Our analyses showed that flavonoid 7a induces G₂-M cell cycle arrest and apoptosis in melanoma cells which is associated with cytochrome c release and activation of both extrinsic and intrinsic apoptotic pathways of cell death.

Disease chemopreventive effects and molecular mechanisms of hydroxylated polymethoxyflavones

Recent increasing attention in research of polymethoxyflavones (PMFs) from Citrus genus because of their wide range of biological properties has been reported in various studies. Hydroxylated PMFs are unique flavones and recognized as the methoxy group of PMFs that is substituted for hydroxyl one. Hydroxylated PMFs are naturally existed in citrus peel and other plants as well as occurred as metabolites of their PMFs counterparts. Several in vitro and in vivo studies have documented the chemopreventive effects of hydroxylated PMFs including anti-cancer, anti-inflammation, anti-atherosclerosis, and neuroprotection. They function to regulate cell death, proliferation, differentiation, repair, and metabolism through acting on modulation of signaling cascade, gene transcription, and protein function and enzyme activity. The mechanisms of action of hydroxylated PMFs in disease chemoprevention depend on their structure, the number, and position of hydroxyl group. Although the efficacy of hydroxylated PMFs in chemoprevention and the oral bioavailability requires further investigation, they still provide great promise for improving human health. This review highlights the recent published data of hydroxylated PMFs with chemopreventive potential and the underlying mechanism involved.

Antivascular and anti-parasite activities of natural and hemisynthetic flavonoids from New Caledonian Gardenia species (Rubiaceae)

A series of 16 flavonoids were isolated and prepared from bud exudate of Gardenia urvillei and Gardenia oudiepe, endemic to New Caledonia. Most of them are rare polymethoxylated flavones. Some of these compounds showed noticeable activity against Leishmania (Leishmania) amazonensis, Plasmodium falciparum and Trypanosoma brucei gambiense, in addition to tubulin polymerization inhibition at low micromolar concentration. We also provide a full set of NMR data as some of the flavones were incompletely described.

Flavones: an important scaffold for medicinal chemistry

Flavones have antioxidant, anti-proliferative, anti-tumor, anti-microbial, estrogenic, acetyl cholinesterase, anti-inflammatory activities and are also used in cancer, cardiovascular disease, neurodegenerative disorders, etc. Also, flavonoids are found to have an effect on several mammalian enzymes like protein kinases that regulate multiple cell signaling pathways and alterations in multiple cellular signaling pathways are frequently found in many diseases. Flavones have been an indispensable anchor for the development of new therapeutic agents. The majority of metabolic diseases are speculated to originate from oxidative stress, and it is therefore significant that recent studies have shown the positive effect of flavones on diseases related to oxidative stress. Due to the wide range of biological activities of flavones, their structure-activity relationships have generated interest among medicinal chemists. The outstanding development of flavones derivatives in diverse diseases in very short span of time proves its magnitude for medicinal chemistry research. The present review gives detail about the structural requirement of flavone derivatives for various pharmacological activities. This information may provide an opportunity to scientists of medicinal chemistry discipline to design selective, optimize as well as poly-functional flavone derivatives for the treatment of multi-factorial diseases.

Phytochemistry and pharmacognosy of the genus Acronychia

The genus Acronychia (Rutaceae) comprise 44 species, most of which are represented by shrubs and small trees, distributed in a wide geographical area of South-Eastern Asia comprising China, India, Malaysia, Indonesia, Australia, and the islands of the western Pacific Ocean. Most of the species of the genus Acronychia have been used for centuries as natural remedies in the ethnomedical traditions of indigenous populations as anti-microbial, anti-fungal, anti-spasmodic, stomachic, anti-pyretic, and anti-haemorragic agent. Moreover fruits and aerial parts are used as food in salads and condiments, while the essential oil obtained from flowers and leaves has been employed in cosmetics production. Phytochemicals isolated from Acronychia spp. include acetophenones, quinoline and acridone alkaloids, flavonoids, cinnamic acids, lignans, coumarins, steroids, and triterpenes. The reported biological activities of the above mentioned natural compounds refer to anti-plasmodial, anti-cancer, anti-oxidant, anti-inflammatory, anti-fungal, and neuroprotective effects. The aim of this review is to examine in detail from a phytochemical and pharmacologically point of view what is reported in the current literature about the properties of phytopreparations or individual active principles obtained from plants belonging to the Acronychia genus.

Dihydroxypentamethoxyflavone down-regulates constitutive and inducible signal transducers and activators of transcription-3 through the induction of tyrosine phosphatase SHP-1

Because constitutive activation of signal transducers and activators of transcription-3 (STAT3) has been linked with cellular transformation, survival, proliferation, chemoresistance, and angiogenesis of various tumor cells, agents that can suppress STAT3 activation have potential as cancer therapeutics. In the present report, we identified a flavone from the leaves of a Thai plant, Gardenia obtusifolia, 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone (PMF), that has the ability to inhibit STAT3 activation. PMF inhibited both constitutive and interleukin-6-inducible STAT3 activation in multiple myeloma (MM) cells, as indicated by suppression of STAT3 phosphorylation, nuclear translocation, DNA binding, and STAT3-regulated gene expression. The inhibition of STAT3 by PMF was reversible. We found that the activation of various kinases including Janus-like kinase (JAK)-1, JAK-2, c-Src, extracellular signal-regulated kinases 1 and 2, AKT, and epidermal growth factor receptor, implicated in STAT3 activation, were inhibited by the flavone. It is noteworthy that pervanadate suppressed the ability of PMF to inhibit the phosphorylation of STAT3, suggesting that protein tyrosine phosphatase was involved. PMF induced the expression of SHP-1 and was linked to the dephosphorylation of STAT3, because its deletion by small interfering RNA abolished the PMF-induced constitutive and inducible STAT3 inhibition. STAT3 inhibition led to the suppression of proteins involved in proliferation (cyclin D1 and c-myc), survival (survivin, Mcl-1, Bcl-xL, Bcl-2, and cIAP-2), and angiogenesis (vascular endothelial growth factor). Finally, PMF inhibited proliferation and induced apoptosis of MM cells. PMF also significantly potentiated the apoptotic effects of Velcade and thalidomide in MM cells. Overall, these results suggest that PMF is a novel blocker of STAT3 activation and thus may have potential in suppression of tumor cell proliferation and reversal of chemoresistance in MM cells.

A novel pentamethoxyflavone down-regulates tumor cell survival and proliferative and angiogenic gene products through inhibition of IκB kinase activation and sensitizes tumor cells to apoptosis by cytokines and chemotherapeutic agents

Most anticancer drugs have their origin in traditional medicinal plants. We describe here a flavone, 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone (PMF), from the leaves of the Thai plant Gardenia obtusifolia, that has anti-inflammatory and anticancer potential. Because the nuclear factor-κB (NF-κB) pathway is linked to inflammation and tumorigenesis, we investigated the effect of PMF on this pathway. We found that PMF suppressed NF-κB activation induced by inflammatory agents, tumor promoters, and carcinogens. This suppression was not specific to the cell type. Although PMF did not directly modify the ability of NF-κB proteins to bind to DNA, it inhibited IκBα (inhibitory subunit of NF-κB) kinase, leading to suppression of phosphorylation and degradation of IκBα, and suppressed consequent p65 nuclear translocation, thus abrogating NF-κB-dependent reporter gene expression. Suppression of the NF-κB cell signaling pathway by the flavone led to the inhibition of expression of NF-κB-regulated gene products that mediate inflammation (cyclooxygenase-2), survival (XIAP, survivin, Bcl-xL, and cFLIP), proliferation (cyclin D1), invasion (matrix metalloproteinase-9), and angiogenesis (vascular endothelial growth factor). Suppression of antiapoptotic gene products by PMF correlated with the enhancement of apoptosis induced by tumor necrosis factor-α and the chemotherapeutic agents cisplatin, paclitaxel, and 5-flurouracil. Overall, our results indicate that PMF suppresses the activation of NF-κB and NF-κB-regulated gene expression, leading to the enhancement of apoptosis. This is the first report to demonstrate that this novel flavone has anti-inflammatory and anticancer effects by targeting the IKK complex.

Flavonoids in Cancer Prevention and Therapy: Chemistry, Pharmacology, Mechanisms of Action, and Perspectives for Cancer Drug Discovery

Among the numerous products available from plants, the flavonoid superfamily plays a central role by its large number of molecules (over 6000) and also by the role these products occupy in the normal physiology of plants. Flavonoids are secondary plant metabolites involved in several biological processes (e.g., germination, UV protection, insecticides) and are also involved in the attraction of pollinating agents via the vivid colors of the anthocyanin pigments found in flowers (e.g., blue, purple, yellow, orange, and red) [1–3]. Flavonoids are found in the normal human diet composed of green vegetables, onions, fruits (apples, grapes, strawberries, etc.), beverages (coffee, tea, beer, red wine) [4, 5], and isoflavonoids are mainly found in soya bean-derived products [6].

Semisynthesis of natural flavones inhibiting tubulin polymerization, from hesperidin

Semisynthesis of 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone (1), a natural flavone that binds with high affinity to tubulin, was performed from hesperidin, the very abundant Citrus flavanone, by a five-step sequence. The last step of the synthesis also gave rise to 5,3'-dihydroxy-3,6,7,4'-tetramethoxyflavone (= casticin or vitexicarpin) (10), 5,3'-dihydroxy-3,7,8,4'-tetramethoxyflavone (= gossypetin 3,7,8,4'-tetramethyl ether) (11), and, unexpectedly, 5,7,3'-trihydroxy-3,6,8,4'-tetramethoxyflavone (12) and 5,3'-dihydroxy-8-dimethylamino-3,6,7,4'-tetramethoxyflavone (= 8-dimethylaminocasticin) (13). Cytotoxicity and antitubulin activity of these five flavones, as well as 5,3'-dihydroxy-3,7,4'-trimethoxyflavone (= ayanin) (14) and intermediate 6,8-dibromo-ayanin (8), were evaluated. Comparison of the responses confirmed and clarified the influence of the A-ring substitution pattern on the biological activity.

Semisynthesis and antiproliferative evaluation of a series of 3'-aminoflavones

A series of 3'-aminoflavones 5,6,7,8-tetra- or 5,7-dioxygenated on the A-ring was synthesized from tangeretin or naringin, two natural Citrus flavonoids. These flavones were evaluated for antiproliferative activity, activation of apoptosis, and inhibition of tubulin assembly. The most antiproliferative flavones exhibit a common 5-hydroxy-6,7,8-trimethoxy substitution pattern on the A-ring.

Methylenedioxy- and methoxyflavones from Melicope coodeana syn. Euodia simplex

Three new natural products, 3,8-dimethoxy-5,7-dihydroxy-3',4'-methylenedioxyflavone, 3,6,8-trimethoxy-5,7-dihydroxy-3',4'-methylenedioxyflavone and 3,6,8,3',4'-pentamethoxy-5,7-dihydroxyflavone were isolated from Melicope coodeana syn. Euodia simplex (Rutaceae) along with 3,6,3'-trimethoxy-5,7,4'-trihydroxyflavone and 3,3'-dimethoxy-5,7,4'-trihydroxyflavone. The structural assignments are based on (1)H and (13)C NMR data, including discussion of the chemical shifts of C-2 in 3,5-dihydroxy- and 3-methoxy-5-hydroxyflavones. The presence of highly methoxylated and methylenedioxyflavones is characteristic of the genus Melicope, and the present findings support the recent transfer of Euodia simplex to Melicope.

Quinoline alkaloids from Acronychia laurifolia

Bioassay-directed fractionation of a root extract of Acronychia laurifolia (Rutaceae) using the KB-V1+ human tumor cell line led to the isolation of six quinoline alkaloids. One of these alkaloids is novel, namely, 2,3-methylenedioxy-4,7-dimethoxyquinoline and the other five were identified as the known compounds, evolitrine, gamma-fagarine, skimmianine, kokusaginine and maculosidine. Two known bis-tetrahydrofuran lignans, sesamolin and yangambin, were also identified. The structure of the new alkaloid was determined by spectroscopic methods. All of the isolates were evaluated against a panel of human cancer cell lines; four of the alkaloids showed weak cytotoxic activity.

Polyoxygenated flavones from the leaves of comptonella microcarpa

The leaves of Comptonella microcarpa have yielded one alkaloid, dictamnine, and four known polyoxygenated flavonoids, meliternatin, 3,5,8-trimethoxy-6,7-3',4'-dimethylenedioxyflavone, 7-(3-methylbut-2-enyloxy)-3,5,8-trimethoxy-3', 4'-methylenedioxyflavone (3), 7-hydroxy-3,5,8-trimethoxy-3', 4'methylenedioxyflavone. In addition, two new flavonoids were found whose structures were established on the basis of their spectral data as 7-hydroxy-3,5,6,8-tetramethoxy-3',4'-methylenedioxyflavone (1) and 7-(3-methylbut-2-enyloxy)-3,5,6,8-tetramethoxy-3', 4'-methylenedioxyflavone (2).

Tubulin as a target for anticancer drugs: agents which interact with the mitotic spindle

Tubulin is the biochemical target for several clinically used anticancer drugs, including paclitaxel and the vinca alkaloids vincristine and vinblastine. This review describes both the natural and synthetic agents which are known to interact with tubulin. Syntheses of the more complex agents are referenced and the potential clinical use of the compounds is discussed. This review describes the biochemistry of tubulin, microtubules, and the mitotic spindle. The agents are discussed in relation to the type of binding site on the protein with which they interact. These are the colchicine, vinca alkaloid, rhizoxin/maytansine, and tubulin sulfhydryl binding sites. Also included are the agents which either bind at other sites or unknown sites on tubulin. The literature is reviewed up to October 1997.

Structure-activity requirements for flavone cytotoxicity and binding to tubulin

A series of 79 flavones related to centaureidin (3,6,4'-trimethoxy-5, 7,3'-trihydroxyflavone, 1) was screened for cytotoxicity in the NCI in vitro 60-cell line human tumor screen. The resulting cytotoxicity profiles of these flavones were compared for degree of similarity to the profile of 1. Selected compounds were further evaluated with in vitro assays of tubulin polymerization and [3H]colchicine binding to tubulin. Maximum potencies for tubulin interaction and production of differential cytotoxicity profiles characteristic of 1 were observed only with compounds containing hydroxyl substituents at C-3' and C-5 and methoxyl groups at C-3 and C-4'.

Antitumor agents. 181. Synthesis and biological evaluation of 6,7,2',3',4'-substituted-1,2,3,4-tetrahydro-2-phenyl-4-quinolones as a new class of antimitotic antitumor agents

A novel series of 6,7,2',3',4'-substituted-1,2,3,4-tetrahydro-2-phenyl- 4-quinolones were synthesized and evaluated for interactions with tubulin and for cytotoxic activity against a panel of human tumor cell lines, including ileocecal carcinoma (HCT-8), breast cancer (MCF-7), lung carcinoma (A-549), epidermoid carcinoma of the nasopharynx (KB), renal cancer (CAKI-1), and melanoma cancer (SKMEL-2). Most compounds (18, 20, 22-27) showed potent cytotoxic and antitubulin effects. The most active compounds (23, 26, 27) demonstrated strong cytotoxic effects with ED50 values in the nanomolar or subnanomolar range in almost all tumor cell lines. Three active racemates (20, 22, 25) were separated into the enantiomers, and generally, the optically pure (-)-isomers (20a, 22a, 25a) exhibited greater biological activity than the racemates or (+)-isomers. Cytotoxicity and antitubulin activity were closely correlated, with the most active compounds (23, 26, 27) having effects comparable to those of colchicine, podophyllotoxin, and combretastatin A-4.

Inhibition of tubulin polymerization by 5,6-dihydroindolo[2,1-alpha]isoquinoline derivatives

6-Alkyl-12-formyl-5,6-dihydroindolo[2,1-alpha]isoquinolines have been shown to inhibit the growth of human mammary carcinoma cells by an unknown mode of action. One of the possible molecular targets is the tubulin system which is involved in cell division. A number of 5,6-dihydroindolo[2,1-alpha]isoquinolines with methoxy or hydroxy groups in positions 3, 9, and/or 10 and various functional groups such as formyl, acetyl, cyano, alkylimino, and alkylamino in position 12 were synthesized and evaluated for both inhibition of tubulin polymerization and cytostatic activity in MDA-MB 231 and MCF-7 human breast cancer cells. In the tubulin polymerization assay, only hydroxy derivatives were active, whereas both the hydroxy derivatives and some of the methoxy compounds inhibited cell growth. In order to establish a correlation between the inhibition of tubulin polymerization and cytostatic activity in the hydroxy series, two of the most active racemates were separated into the enantiomers. In both assays, the relative potencies of the hydroxy derivatives were in a similar order. Highest activity was found for the (+)-isomers of 6-propyl- (6b) and 6-butyl-12-formyl-5,6-hydro-3,9-dihydroxyindolo[2,1-alpha]isoquino line (6c) with IC50 values of 11 +/- 0.4 and 3.1 +/- 0.4 microM, respectively, for the polymerization of tubulin at 37 degrees C (colchicine: 2.1 +/- 0.1 microM). The active hydroxy derivatives displaced 40-70% of [3H]colchicine from its binding site in the tubulin at concentrations 10-fold higher than that of colchicine. The data suggest that hydroxy-substituted indolo[2,1-alpha]isoquinolines bind to the colchicine-binding site and inhibit the polymerization of tubulin. This action can be assumed to be responsible for the cytostatic activity of the hydroxy derivatives and might also contribute to the antitumor effect of the corresponding methyl ethers.

DNA topoisomerase I inhibitors: cytotoxic flavones from Lethedon tannaensis

From ethyl acetate and methanolic extracts of Lethedon tannaensis leaves, which were cytotoxic against murine leukemia (P-388) and human nasopharynx carcinoma (KB) cells, one new and six known 5-hydroxy-7-methoxyflavones variously substituted on the B ring were isolated and their structures determined by spectral analysis. Compounds active against KB cells were velutin (4) (IC50 4.8 microM), 7,3',5'-tri-O-methyltricetin (2) (IC50 22.2 microM), genkwanin (6) (IC50 30.6 microM), and the novel compound, 7,3',4'-tri-O-methyltricetin, named lethedocin (1) (IC50 47.6 microM). These flavones required the presence of hydroxyl groups at C-5 and C-4' and methoxyl groups at C-7 and C-3' for inhibition of calf thymus DNA topoisomerase I activity.

Antitumor agents. 166. Synthesis and biological evaluation of 5,6,7,8-substituted-2-phenylthiochromen-4-ones

As a continuation of our structure--activity relationship study of substituted 2-phenyl-4-quinolones and flavonoids as antitumor and antiviral agents, a series of 5,6,7,8-substituted-2-phenylthiochromen-4-ones has been synthesized by condensation of substituted thiophenols and ethyl benzoylacetates. Target compounds were evaluated for biological activity. Among them, compounds 7, 10, 12, and 13 displayed significant growth inhibitory action against a panel of tumor cell lines including human ileocecal carcinoma (HCT-8), murine leukemia (P-388), human melanoma (RPMI), and human central nervous system tumor (TE671) cells. Compounds 10, 12, and 19 displayed DNA topoisomerase I inhibitory activity in vitro and compound 11 was an in vitro, inhibitor of DNA topoisomerase II. Compound 11 was most active (ED50 value, 0.65 microM) against HIV in acutely infected H9 lymphocytes and had a therapeutic index of about 5.

Antitumor 2,3-dihydro-2-(aryl)-4(1H)-quinazolinone derivatives. Interactions with tubulin

A series of derivatives of 2,3-dihydro-2-(aryl)-4(1H)-quinazolinone (DHQZ) with known antitumor activity was re-evaluated in the National Cancer Institute cancer cell line screen. Analysis by the COMPARE algorithm suggested that their cytotoxicity derived from interactions with tubulin. Significant inhibition of tubulin assembly and of the binding of radiolabeled colchicine to tubulin was demonstrated with several of the compounds, particularly NSC 145669, 175635, and 175636. The DHQZ derivatives are structurally analogous to a number of antimitotic agents, flavonols and derivatives of 2-styrylquinazolin-4(3H)-one and of 2-phenyl-4-quinolone. Structure-activity analogies between these agents, the combretastatins, and the colchicinoids were analyzed and summarized.