A review on the dietary flavonoid kaempferol

Epidemiological studies have revealed that a diet rich in plant-derived foods has a protective effect on human health. Identifying bioactive dietary constituents is an active area of scientific investigation that may lead to new drug discovery. Kaempferol (3,5,7-trihydroxy-2-(4-hydroxyphenyl)-4H-1-benzopyran-4-one) is a flavonoid found in many edible plants (e.g. tea, broccoli, cabbage, kale, beans, endive, leek, tomato, strawberries and grapes) and in plants or botanical products commonly used in traditional medicine (e.g. Ginkgo biloba, Tilia spp, Equisetum spp, Moringa oleifera, Sophora japonica and propolis). Some epidemiological studies have found a positive association between the consumption of foods containing kaempferol and a reduced risk of developing several disorders such as cancer and cardiovascular diseases. Numerous preclinical studies have shown that kaempferol and some glycosides of kaempferol have a wide range of pharmacological activities, including antioxidant, anti-inflammatory, antimicrobial, anticancer, cardioprotective, neuroprotective, antidiabetic, anti-osteoporotic, estrogenic/antiestrogenic, anxiolytic, analgesic and antiallergic activities. In this article, the distribution of kaempferol in the plant kingdom and its pharmacological properties are reviewed. The pharmacokinetics (e.g. oral bioavailability, metabolism, plasma levels) and safety of kaempferol are also analyzed. This information may help understand the health benefits of kaempferol-containing plants and may contribute to develop this flavonoid as a possible agent for the prevention and treatment of some diseases.

A new view of carcinogenesis and an alternative approach to cancer therapy

During the last few decades, cancer research has focused on the idea that cancer is caused by genetic alterations and that this disease can be treated by reversing or targeting these alterations. The small variations in cancer mortality observed during the previous 30 years indicate, however, that the clinical applications of this approach have been very limited so far. The development of future gene-based therapies that may have a major impact on cancer mortality may be compromised by the high number and variability of genetic alterations recently found in human tumors. This article reviews evidence that tumor cells, in addition to acquiring a complex array of genetic changes, develop an alteration in the metabolism of oxygen. Although both changes play an essential role in carcinogenesis, the altered oxygen metabolism of cancer cells is not subject to the high genetic variability of tumors and may therefore be a more reliable target for cancer therapy. The utility of this novel approach for the development of therapies that selectively target tumor cells is discussed.

The dietary flavonoids myricetin and fisetin act as dual inhibitors of DNA topoisomerases I and II in cells

DNA topoisomerases (topos) are the target of several drugs commonly used in cancer chemotherapy; these drugs induce topo-DNA complexes with either topo I or topo II that eventually trigger cell death. The inhibition of these enzymes induces DNA alterations that may also lead to carcinogenic effects; indeed, an increased risk for developing leukemia has been observed in patients treated with some topo II inhibitors. Several flavonoids have been shown to interact with purified topo I and topo II, therefore suggesting that these compounds may possess both anticancer and carcinogenic activity. Because the activity of a drug on purified topoisomerases does not always represent the activity in the cell, the aim of this work is to evaluate the effects of several common dietary flavonoids on these enzymes in cells. Using the cell-based TARDIS assay, we have evaluated the effects of the flavonoids quercetin, apigenin, fisetin and myricetin on topo I and topo II in K562 human leukemia cells at several concentrations and exposure times. Quercetin and apigenin induced moderate levels of topo II-DNA complexes and did not induce topo I-DNA complexes in these cells. Fisetin induced neither topo I- nor topo II-DNA complexes, but behaved as a catalytic inhibitor of both enzymes. Myricetin induced high levels of topo-DNA complexes with both enzymes. In addition, murine embryo fibroblasts lacking topo IIbeta were resistant to myricetin-induced cell-growth inhibition, therefore suggesting that topo IIbeta is an important drug target for this flavonoid. These results support the idea that specific concentrations of some dietary flavonoids may produce topoisomerase-mediated carcinogenic and chemotherapeutic effects in vivo. The ability of myricetin to induce topo-DNA complexes with both topo I and topo II in leukemia cells may be therapeutically useful and deserves further study.

Role of oxygen in cancer: looking beyond hypoxia

Although cancer is considered to be a disease caused by DNA alterations, the high genetic variability of tumor cells makes it difficult to exploit these alterations for the treatment of cancer. The influence of non-genetic factors on cancer is increasingly being acknowledged and a growing line of research suggests that hypoxia (a decrease in normal oxygen levels) may play a fundamental role in the development of this disease. This line of research is supported by the fact that tumors often have hypoxic areas, that hypoxia activates the hypoxia-inducible factor 1 (HIF-1) and that HIF-1 activation plays a key role in cancer development. Evidence suggests, however, that the idea of hypoxia playing a central role in cancer development has some drawbacks. For instance, hypoxia has not been found in many tumors, HIF-1 activation has been observed in non-hypoxic tumor areas, and hypoxic tumor cells commonly have a reduced nutrient supply that restricts cell proliferation and tumor growth. This article reviews the literature that does not support the idea of hypoxia playing a central role in cancer development and discusses a broader view in which the role of oxygen in cancer is not limited to a reduction in its normal levels. According to this novel view, a deviation of the oxygen metabolism from the pathway that generates energy to the pathway that produces reactive oxygen species is crucial for cancer development. Interestingly, this switch in oxygen metabolism occurs under both hypoxic and normoxic conditions and may be exploited therapeutically.

Distribution and biological activities of the flavonoid luteolin

Epidemiological evidence suggests that flavonoids may play an important role in the decreased risk of chronic diseases associated with a diet rich in plant-derived foods. Flavonoids are also common constituents of plants used in traditional medicine to treat a wide range of diseases. The purpose of this article is to summarize the distribution and biological activities of one of the most common flavonoids: luteolin. This flavonoid and its glycosides are widely distributed in the plant kingdom; they are present in many plant families and have been identified in Bryophyta, Pteridophyta, Pinophyta and Magnoliophyta. Dietary sources of luteolin include, for instance, carrots, peppers, celery, olive oil, peppermint, thyme, rosemary and oregano. Preclinical studies have shown that this flavone possesses a variety of pharmacological activities, including antioxidant, anti-inflammatory, antimicrobial and anticancer activities. The ability of luteolin to inhibit angiogenesis, to induce apoptosis, to prevent carcinogenesis in animal models, to reduce tumor growth in vivo and to sensitize tumor cells to the cytotoxic effects of some anticancer drugs suggests that this flavonoid has cancer chemopreventive and chemotherapeutic potential. Modulation of ROS levels, inhibition of topoisomerases I and II, reduction of NF-kappaB and AP-1 activity, stabilization of p53, and inhibition of PI3K, STAT3, IGF1R and HER2 are possible mechanisms involved in the biological activities of luteolin.

Anticancer and carcinogenic properties of curcumin: considerations for its clinical development as a cancer chemopreventive and chemotherapeutic agent

A growing body of research suggests that curcumin, the major active constituent of the dietary spice turmeric, has potential for the prevention and therapy of cancer. Preclinical data have shown that curcumin can both inhibit the formation of tumors in animal models of carcinogenesis and act on a variety of molecular targets involved in cancer development. In vitro studies have demonstrated that curcumin is an efficient inducer of apoptosis and some degree of selectivity for cancer cells has been observed. Clinical trials have revealed that curcumin is well tolerated and may produce antitumor effects in people with precancerous lesions or who are at a high risk for developing cancer. This seems to indicate that curcumin is a pharmacologically safe agent that may be used in cancer chemoprevention and therapy. Both in vitro and in vivo studies have shown, however, that curcumin may produce toxic and carcinogenic effects under specific conditions. Curcumin may also alter the effectiveness of radiotherapy and chemotherapy. This review article analyzes the in vitro and in vivo cancer-related activities of curcumin and discusses that they are linked to its known antioxidant and pro-oxidant properties. Several considerations that may help develop curcumin as an anticancer agent are also discussed.

Curcumin as a DNA Topoisomerase II Poison

Curcumin, the major active component of the spice turmeric, is recognised as a safe compound with great potential for cancer chemoprevention and cancer therapy. It induces apoptosis, but its initiation mechanism remains poorly understood. Curcumin has been assessed on the human cancer cell lines, TK-10, MCF-7 and UACC-62, and their IC50 values were 12.16, 3.63, 4.28 microM respectively. The possibility of this compound being a topoisomerase II poison has also been studied and it was found that 50 microM of curcumin is active in a similar fashion to the antineoplastic agent etoposide. These results point to DNA damage induced by topoisomerase II poisoning as a possible mechanism by which curcumin initiates apoptosis, and increase the evidence suggesting its possible use in cancer therapy.

The warburg effect: why and how do cancer cells activate glycolysis in the presence of oxygen?

Cells can obtain energy through the oxygen-dependent pathway of oxidative phosphorylation (OXPHOS) and through the oxygen-independent pathway of glycolysis. Since OXPHOS is more efficient in generating ATP than glycolysis, it is recognized that the presence of oxygen results in the activation of OXPHOS and the inhibition of glycolysis (Pasteur effect). However, it has been known for many years that cancer cells and non-malignant proliferating cells can activate glycolysis in the presence of adequate oxygen levels (aerobic glycolysis or Warburg effect). Accumulating evidence suggests that the persistent activation of aerobic glycolysis in tumor cells plays a crucial role in cancer development; the inhibition of the increased glycolytic capacity of malignant cells may therefore represent a key anticancer strategy. Although some important knowledge has been gained in the last few years on this growing field of research, the basis of the Warburg effect still remains poorly understood. This communication analyzes why cancer cells switch from OXPHOS to glycolysis in the presence of adequate oxygen levels, and how these cells manage to avoid the inhibition of glycolysis induced by oxygen. Several strategies and drugs that may interfere with the glycolytic metabolism of cancer cells are also shown. This information may help develop anticancer approaches that may have clinical relevance.

Curcumin induces high levels of topoisomerase I- and II-DNA complexes in K562 leukemia cells

Recent data suggest that curcumin, a phytochemical with cancer chemopreventive potential, might be useful in the treatment of several solid and hematological malignancies. DNA topoisomerases (topos) are the target of several drugs commonly used in cancer chemotherapy. These drugs induce topo-DNA complexes with either topo I or topo II; then cellular processing converts these complexes into permanent DNA strand breaks that trigger cell death. Using the TARDIS in vivo assay, this study shows for the first time that curcumin induces topo I and topo II (alpha and beta)-DNA complexes in K562 leukemia cells. A comparative analysis revealed that the levels of these complexes were higher than those induced by several standard topo I and topo II inhibitors at equitoxic doses. Curcumin-induced topo I and topo II-DNA complexes were prevented by the antioxidant N-acetylcysteine; this suggests that, unlike the standard topo inhibitors, reactive oxygen species may mediate the formation of these complexes. Overall, this work shows that curcumin is capable of inducing topo-DNA complexes in cells with both topo I and topo II and increases the evidence suggesting that this dietary agent has potential to be tested in cancer chemotherapy.

Digitoxin as an anticancer agent with selectivity for cancer cells: possible mechanisms involved

Accumulating preclinical and clinical data suggest that the cardiac drug digitoxin might be used in cancer therapy. Recent reports have shown that digitoxin can inhibit the growth and induce apoptosis in cancer cells at concentrations commonly found in the plasma of cardiac patients treated with this drug. Several mechanisms have been associated with the anticancer activity of digitoxin, yet at present it is unknown why malignant cells are more susceptible to this cardiac glycoside than non-malignant cells. This report analyses the possible anticancer mechanisms of digitoxin and proposes that the inhibition of glycolysis may be a key mechanism by which this natural product selectively targets cancer cells. Finally, whether or not there is enough evidence to support the clinical evaluation of digitoxin in patients with cancer is discussed.

Dual role of hydrogen peroxide in cancer: Possible relevance to cancer chemoprevention and therapy

Accumulating evidence suggests that hydrogen peroxide (H(2)O(2)) plays an important role in cancer development. Experimental data have shown that cancer cells produce high amounts of H(2)O(2). An increase in the cellular levels of H(2)O(2) has been linked to several key alterations in cancer, including DNA alterations, cell proliferation, apoptosis resistance, metastasis, angiogenesis and hypoxia-inducible factor 1 (HIF-1) activation. It has also been observed that the malignant phenotype of cancer cells can be reversed just by decreasing the cellular levels of H(2)O(2). On the other hand, there is evidence that H(2)O(2) can induce apoptosis in cancer cells selectively and that the activity of several anticancer drugs commonly used in the clinic is mediated, at least in part, by H(2)O(2). The present report discusses that the high levels of H(2)O(2) commonly observed in cancer cells may be essential for cancer development; these high levels, however, seem almost incompatible with cell survival and may make cancer cells more susceptible to H(2)O(2)-induced cell death than normal cells. An understanding of this dual role of H(2)O(2) in cancer might be exploited for the development of cancer chemopreventive and therapeutic strategies.

Hypoxia-inducible factor 1 as a possible target for cancer chemoprevention

Despite the intense cancer research carried out in the last 30 years, cancer therapy has not managed to decrease cancer mortality. We need new strategies to control a disease that kills over six million people worldwide every year. It is accepted that cancer chemoprevention (the use of chemicals to prevent, stop, or reverse the process of carcinogenesis) is an essential approach to controlling cancer; yet, the clinical usefulness of this strategy is very limited. Successful implementation of cancer chemoprevention depends on a mechanistic understanding of the carcinogenesis process. Our knowledge about this process is still limited and may therefore be preventing cancer chemoprevention from becoming a widely used anticancer tool. This report discusses recent evidence that suggests that the activation of the hypoxia-inducible factor 1 (HIF-1) is a key event in carcinogenesis and may therefore represent a key target for cancer chemoprevention. Based on an understanding of the mechanisms responsible for HIF-1 activation, possible general strategies for targeting HIF-1 are proposed. Successful implementation of these strategies might turn the great promise of cancer chemoprevention into a fundamental tool for reducing the burden of this disease.

Why do tumors metastasize?

Approximately 90% of all cancer deaths can be attributed to the metastatic spread of primary tumors. An understanding of the process by which cells from a localized tumor invade adjacent tissues and migrate to distant organs is crucial for the development of anticancer strategies that can efficiently prevent this process. Although our knowledge of cancer has increased in recent years, the molecular mechanisms of tumor invasion and metastasis still remain elusive. This report discusses recent data that suggest that tumors metastasize because tumor cells have an alteration in oxygen metabolism (dysoxia). This alteration in oxygen metabolism would drive tumor invasion and metastasis via glycolysis-mediated extracellular acidification, excessive production of hydrogen peroxide (H(2)O(2)) and hypoxia-inducible factor 1 (HIF-1) activation. This new model might help develop cancer chemopreventive strategies for preventing tumor metastasis and thus reduce cancer mortality.

Digitoxin, at concentrations commonly found in the plasma of cardiac patients, antagonizes etoposide and idarubicin activity in K562 leukemia cells

Digitoxin is used in the treatment of cardiac congestion and some types of cardiac arrhythmias. The mechanism of action of this cardiac glycoside suggested that it might antagonize the anticancer activity of topoisomerase II poisons. The present report shows that digitoxin, at concentrations commonly found in the plasma of cardiac patients, significantly reduced etoposide and idarubicin-induced topoisomerase II cleavable complexes in K562 leukemia cells. This may lead to a reduction in the anticancer effect of these two topoisomerase II poisons when they are used in the clinic concurrently with digitoxin.

HIF-1: hypoxia-inducible factor or dysoxia-inducible factor?

Hypoxia-inducible factor 1 (HIF-1) activates the transcription of genes involved in diverse aspects of cellular and integrative physiology, including energy metabolism, cell growth, survival, invasion, migration or angiogenesis. The activity of this transcription factor is known to be increased by hypoxia, but also by a growing number of apparently unrelated factors that can activate it even in nonhypoxic conditions. Here I propose a model in which an alteration in oxygen metabolism is the key cellular event involved in HIF-1 activation under hypoxic and nonhypoxic conditions. This new perspective unifies previously unrelated observations and predicts cellular processes and therapeutic strategies that may modify HIF-1 activity. This may have relevance, for instance, to cancer, as HIF-1 overexpression is observed in many human cancers and has been associated with increased patient mortality.

Digitoxin inhibits the growth of cancer cell lines at concentrations commonly found in cardiac patients

The cardiac glycosides digitoxin (1) and digoxin (3) have been used in cardiac diseases for many years. During this time several reports have suggested the possible use of digitalis in medical oncology. Several analogues of digitoxin (1) were evaluated for growth inhibition activity in three human cancer cell lines; this study showed that digitoxin (1) was the most active compound and revealed some structural features that may play a role in the growth inhibition activity of these drugs. The IC50 values for 1 (3-33 nM) were within or below the concentration range seen in the plasma of patients with cardiac disease receiving this glycoside (20-33 nM). A renal adenocarcinoma cancer cell line (TK-10) was hypersensitive to this drug, and digitoxin toxicity on these cells was mediated by apoptosis. In vitro experiments showed that 1 at 30 nM induced levels of DNA-topoisomerase II cleavable complexes similar to etoposide, a topoisomerase II poison widely used in cancer chemotherapy. Using the individual cell assay TARDIS, cells exposed to 1 for 30 min showed low but statistically significant levels of DNA-topoisomerase II cleavable complexes; however these complexes disappeared after 24 h exposure.

A 4 year follow-up analysis of genotoxic damage in birds of the Donana area (south west Spain) in the wake of the 1998 mining waste spill

A total of 330 white storks (Ciconia ciconia) and 138 black kites (Milvus migrans) were blood sampled during four consecutive years in an area heavily contaminated as a consequence of a massive spillage of toxic acid mining waste rich in heavy metals that impacted on the Doñana National Park (south western Spain), in April 1998. The alkaline single cell gel electrophoresis (Comet) assay was performed as a genotoxicity test, in order to assess whether the high level of DNA damage first detected by us 1 year after the disaster was still present in birds in each of the successive 3 years. Our results clearly show that, when compared with control individuals from non-polluted areas, white storks and black kites born in the contaminated area for a period of up to 4 years after the toxic accident have suffered an increase of at least 2- to 10-fold in the level of their genetic damage through the study period. Taken as a whole, these observations seem to indicate that the toxic spill still appears to be affecting the wildlife 4 years after the mining disaster and that attempts at cleaning up the waste have proved ineffective based on DNA damage detection.

Cytotoxic effect of Plantago spp. on cancer cell lines

Methanolic extracts from seven Plantago species used in traditional medicine for the treatment of cancer, were evaluated for cytotoxic activity against three human cancer cell lines recommended by the National Cancer Institute (NCI, USA). The results showed that Plantago species exhibited cytotoxic activity, showing a certain degree of selectivity against the tested cells in culture. Since the flavonoids are able to strongly inhibit the proliferation of human cancer cell lines, we have identified luteolin-7-O-beta-glucoside as major flavonoid present in most of the Plantago species. Also, we have evaluated this compound and its aglycon, luteolin, for their cytotoxic and DNA topoisomerase I poisons activities. These results could justify the traditional use of the Plantago species and topoisomerase-mediated DNA damage might be a possible mechanism by which flavonoids of Plantago exert their cytotoxicity potential.

Synthesis and cytotoxic activity of different open indolocarbazole alkaloid analogues

An array of 4-(aryl or indolyl)pyrrolo[3,4-c]carbazole-1,3-diones (open analogues of indolocarbazole alkaloids), 10-(aryl or indolyl)pyrrolo[3,4-b]carbazole-1,3-diones, and different derivatives have been prepared using a Diels-Alder plus Fischer indolization approach and tested as cytotoxic agents. Some representative compounds display interesting cytotoxic profiles.

Anti-tumour activity of Digitalis purpurea L. subsp. heywoodii

Recent research has shown the anticancer effects of digitalis compounds suggesting their possible use in medical oncology. Four extracts obtained from the leaves of Digitalis purpurea subsp. heywoodii have been assessed for cytotoxic activity against three human cancer cell lines, using the SRB assay. All of them showed high cytotoxicity, producing IC50 values in the 0.78 - 15 microg/mL range with the methanolic extract being the most active, in non toxic concentrations. Steroid glycosides (gitoxigenin derivatives) were detected in this methanolic extract. Gitoxigenin and gitoxin were evaluated in the SRB assay using the three human cancer cell lines, showing IC50 values in the 0.13 - 2.8 microM range, with the renal adenocarcinoma cancer cell line (TK-10) being the most sensitive one. Morphological apoptosis evaluation of the methanolic extract and both compounds on the TK-10 cell line showed that their cytotoxicity was mediated by an apoptotic effect. Finally, possible mechanisms involved in apoptosis induction by digitalis compounds are discussed.

Flavonoids as anticancer agents: structure-activity relationship study

The protection against some forms of cancer provided by many common foods has been observed in multiple epidemiological studies. Non-nutritive dietary compounds, such as flavonoids, have been considered as the responsible agents for such observations and since then, much research activity has been done about their potential anticancer effect. As a result, these compounds have been shown to regulate proliferation and cell death pathways leading to cancer. Thus, flavonoids such as the synthetic flavone, flavopiridol; the soy isoflavonoid, genistein; the tea catechin epigallocatechin gallate; or the common dietary flavonol, quercetin, are emerging as prospective anticancer drug candidates and some of them have already entered in clinical trials. In view of the therapeutic potential of flavonoids, many researchers have tried to elucidate possible structure-activity relationships that might lead to new drug discovery. However, and possibly due to the information being very scattered, there is very little understanding about a possible relationship between the flavonoid structure and their anticancer activity. Besides their therapeutic potential, since lots of flavonoids are present in our diet, a greater understanding of their anticancer properties might also modify our dietary habits in order to attack cancer with an effective weapon, prevention. This paper seeks to show, in a brief but comprehensive way, the anticancer properties of flavonoids. Through an understanding of the cancer process and its treatment, flavonoids are studied as possible useful compounds in cancer prevention and cancer therapy. Furthermore, this review attempts to compile and discuss the literature studying structure-activity relationships, in order to show structural requirements implicated in the anticancer activity of flavonoids, which might help to rationalize their development as antitumor agents.

Flavonoids as DNA topoisomerase I poisons

The therapeutic anticancer potential of flavonoids shown by recent research needs a greater understanding of these compounds. They are antioxidants and antimutagenic agents that can inhibit tumor promotion and transformation and can modify the activity of a large number of mammalian enzyme systems, such as human DNA-topoisomerases. Poisons of topoisomerases generate toxic DNA damage by stabilization of the covalent DNA-topoisomerase cleavage complex and some of them have therapeutic efficacy in human cancer. The present investigation has assayed ten flavonoids, isolated in our laboratory, as topoisomerase I poisons obtaining myricetin and myricetin-3-galactoside as two new topoiosomerase I poisons. These two flavonoids, and the plant extract from which they were isolated, were assayed for cytotoxic activity against three human cancer cell lines using the SRB assay. Taking into account our previous research, structural requisites implicated in the topoisomerase poisoning are discussed.

DNA damage in birds after the mining waste spill in southwestern Spain: a Comet assay evaluation

In April 1998, an ecological disaster resulting from a massive toxic spill of mining acid waste rich in heavy metals posed a serious threat to the Doñana National Park in southwestern Spain. This especially important protected area is the nesting and breeding site for many endangered bird species; white storks (Ciconia ciconia) and black kites (Milvus migrans) are considered the more representative. The suitability of the Comet assay as a biomarker for genotoxic analysis in environmental biomonitoring has been recently validated in studies using different sentinel organisms such as fish, amphibians, rodents, or mollusks. Birds preying on a variety of invertebrate and vertebrate species in the marshlands are appropriate for evaluating the potential deleterious effects of the toxic spill on wildlife of the Dofiana area. Our study on wetland birds high on the aquatic trophic chain sampled within a few months after the toxic spill in the area around Doñana National Park has shown the accumulation of heavy metals. Fourteen months after the mine waste spill, blood samples from white storks and kites collected in the neighborhood of the park and from control birds at reference areas for comparison were examined by fluorescence image analysis after lymphocyte isolation, and by subsequent alkaline single-cell gel (SCG) electrophoresis, known as the Comet assay. Our results indicate that the exposed birds had a significantly increased level of genotoxic damage compared with control animals from noncontaminated locations.

A cytotoxic diarylheptanoid from Viscum cruciatum

A diarylheptanoid, 1,7-di-(3',4'-dihydroxyphenyl)-4-hepten-3-one, hirsutanone, has been isolated from the methanolic extract of the aerial parts of Viscum cruciatum (Viscaceae) and characterized by spectroscopic methods and chemical transformations. This compound showed cytotoxic activity against melanoma (UACC-62), renal (TK-10) and breast (MCF-7) cancer cell lines.

Cytotoxic compounds from Annonaceus species as DNA topoisomerase I poisons

BACKGROUND

In the search for cytotoxic natural products as DNA topoisomerase poisons, we have assessed six annonaceus compounds (the acetogenins annonacin and rolliniastatin-1, the styryl-lactones etharversin and altholactone and the alkaloids thaligrisine and cepharanone-B) for cytotoxic activity against three human cancer cell lines and then we evaluated these compounds as DNA topoisomerase poisons.

MATERIALS AND METHODS

The cytotoxicity parameters were determined following protocols established by the National Cancer Institute (NCI) using the SRB assay. In the topoisomerase assay, the supercoiled DNA produces open circle forms that are stabilised in the presence of DNA topoisomerase poisons and can be detected after a denaturation step by proteinase K-SDS.

RESULTS

The six compounds showed cytotoxic activity, with cepharanone B being the most cytotoxic one, even more than the antineoplastic agent etoposide on two cancer cell lines, although it is the only one that does not act as a DNA topoisomerase poison.

CONCLUSION

These results could justify the traditional use of the studied annonaceus species and topoisomerase-mediated DNA damage might be a possible mechanism by which five of these compounds exert their cytotoxicity.

Assessment of genotoxic damage by the comet assay in white storks (Ciconia ciconia) after the Doñana Ecological Disaster

Single cell gel electrophoresis, the so-called "Comet" assay, was performed as a genotoxicity test in white storks sampled in an area heavily contaminated after the ecological disaster in south western Spain. This disaster occurred as a consequence of a massive toxic spillage of acid waste rich in heavy metals that impacted on the Doñana National Park. The importance of this protected area as a breeding and wintering site for many endangered bird species makes this analysis of DNA damage of special interest. Our results clearly show that white storks born in the contaminated area 1 year after the toxic spill bear a high burden of genetic damage as compared with control individuals. The possible implications for future survival as well as reproductive rate are discussed.

Two new flavonol glycosides as DNA topoisomerase I poisons

Flavonoids are secondary plant metabolites whose anticancer properties are actually being studied from an epidemiological and pharmacological point of view. They are believed to be implicated in the lower risk of some forms of cancer observed in Asian countries, due to their capacity to control cell proliferation, to act on certain regulatory enzymes as protein kinases or topoisomerases. Based on these precedents, three flavonols isolated from a cytotoxic butanol extract from Retama sphaerocarpa Boissier have been assessed to study their topoisomerase I and II activity. Two new rhamnazin glycosides were found to have the ability to stabilize the cleavage complex human DNA topoisomerase I at concentrations in the 100-250 microM range, acting as topoisomersase I poisons.

Retamatrioside, a new flavonol triglycoside from Retama sphaerocarpa

A new flavonol triglycoside, retamatrioside (1), has been isolated from the aerial parts of Retama sphaerocarpa. The structure of 1 has been determined as rhamnazin 3-O-beta-D-glucopyranosyl-(1-->5)-[beta-D-apiofuranosyl(1-->2)]-al pha -L-arabinofuranoside, using spectroscopic methods.

Cytotoxic activity of flavonoids and extracts from Retama sphaerocarpa Boissier

Seven flavonoids isolated from chloroform, ethyl acetate and butanol extracts, obtained from the aerial parts of Retama sphaerocarpa, have been assessed for cytotoxic activity against three human cancer cell lines: TK-10 (renal adenocarcinoma), MCF-7 (breast adenocarcinoma) and UACC-62 (melanoma), using the SRB assay. All of them, extracts and flavonoids, were actives in, at least, one of the three cell lines at the recommended National Cancer Institute doses. They produce a dose-dependent inhibition of cell growth at concentrations in the 10(-6)-10(-4) M and 25-250 microg/ml range for the flavonoids and extracts respectively, being the flavonol rhamnazin the most cytotoxic.