Molecular modes of action of cytotoxic alkaloids: from DNA intercalation, spindle poisoning, topoisomerase inhibition to apoptosis and multiple drug resistance

Secondary metabolites in topical infectious diseases and nanomedicine applications

Topical infection affects nearly one-third of the world's population; it may result from poor sanitation, hygienic conditions and crowded living and working conditions that accelerate the spread of topical infectious diseases. The problems associated with the anti-infective agents are drug resistance and long-term therapy. Secondary metabolites are obtained from plants, microorganisms and animals, but they are metabolized inside the human body. The integration of nanotechnology into secondary metabolites is gaining attention due to their interaction at the subatomic and skin-tissue levels. Hydrogel, liposomes, lipidic nanoparticles, polymeric nanoparticles and metallic nanoparticles are the most suitable carriers for secondary metabolite delivery. Therefore, the present review article extensively discusses the topical applications of nanomedicines for the effective delivery of secondary metabolites.

The Potential of Anti-coronavirus Plant Secondary Metabolites in COVID-19 Drug Discovery as an Alternative to Repurposed Drugs: A Review

In early 2020, a global pandemic was announced due to the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), known to cause COVID-19. Despite worldwide efforts, there are only limited options regarding antiviral drug treatments for COVID-19. Although vaccines are now available, issues such as declining efficacy against different SARS-CoV-2 variants and the aging of vaccine-induced immunity highlight the importance of finding more antiviral drugs as a second line of defense against the disease. Drug repurposing has been used to rapidly find COVID-19 therapeutic options. Due to the lack of clinical evidence for the therapeutic benefits and certain serious side effects of repurposed antivirals, the search for an antiviral drug against SARS-CoV-2 with fewer side effects continues. In recent years, numerous studies have included antiviral chemicals from a variety of plant species. A better knowledge of the possible antiviral natural products and their mechanism against SARS-CoV-2 will help to develop stronger and more targeted direct-acting antiviral agents. The aim of the present study was to compile the current data on potential plant metabolites that can be investigated in COVID-19 drug discovery and development. This review represents a collection of plant secondary metabolites and their mode of action against SARS-CoV and SARS-CoV-2.

The Promise of Piperine in Cancer Chemoprevention

Cancer, characterized by the unregulated growth and dissemination of malignantly transformed cells, presents a significant global health challenge. The multistage process of cancer development involves intricate biochemical and genetic alterations within target cells. Cancer chemoprevention has emerged as a vital strategy to address this complex issue to mitigate cancer's impact on healthcare systems. This approach leverages pharmacologically active agents to block, suppress, prevent, or reverse invasive cancer development. Among these agents, piperine, an active alkaloid with a wide range of therapeutic properties, including antioxidant, anti-inflammatory, and immunomodulatory effects, has garnered attention for its potential in cancer prevention and treatment. This comprehensive review explores piperine's multifaceted role in inhibiting the molecular events and signaling pathways associated with various stages of cancer development, shedding light on its promising prospects as a versatile tool in cancer chemoprevention. Furthermore, the review will also delve into how piperine enhances the effectiveness of conventional treatments such as UV-phototherapy and TRAIL-based therapy, potentially synergizing with existing therapeutic modalities to provide more robust cancer management strategies. Finally, a crucial perspective of the long-term safety and potential side effects of piperine-based therapies and the need for clinical trials is also discussed.

Effect of Betanin, the Major Pigment of Red Beetroot (Beta vulgaris L.), on the Activity of Recombinant Human Cytochrome P450 Enzymes

Most of the currently available drugs are derived from natural sources, but they are used only after extensive chemical modifications to improve their safety and efficacy. Natural products are used in health supplements and cosmetic preparations and have been used as auxiliary drugs or alternative medicines. When used in combination with conventional drugs, these herbal products are known to alter their pharmacokinetics and pharmacodynamics, reducing their therapeutic effects. Moreover, herb-drug interactions (HDIs) may have serious side effects, which is one of the major concerns in health practice. It is postulated that HDIs affect the pathways regulating cytochrome P450 enzymes (CYPs). Betanin, the chief pigment of red beetroot (Beta vulgaris L.), has various types of pharmacological activity, such as anti-inflammatory, antioxidant, and anticancer effects. However, the potential risk of HDIs for betanin has not yet been studied. Thus, we aimed to predict more specific HDIs by evaluating the effects of betanin on CYPs (CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4), the major phase I metabolic enzymes, using fluorescence-/luminescence-based assays. Our results showed that betanin inhibited CYP3A4 activity in a dose-dependent manner (IC50 = 20.97 µΜ). Moreover, betanin acted as a competitive inhibitor of CYP3A4, as confirmed by evaluating Lineweaver-Burk plots (Ki value = 19.48 µΜ). However, no significant inhibitory effects were observed on other CYPs. Furthermore, betanin had no significant effect on CYP1A2, CYP2B6, or CYP2C9 induction in HepG2 cells. In conclusion, betanin acted as a competitive inhibitor of CYP3A4, and thus it should be used cautiously with other drugs that require metabolic enzymes as substrates. Additional in vivo studies and clinical trials are needed to further elucidate the HDIs of betanin.

Specific signature biomarkers highlight the potential mechanisms of circulating neutrophils in aneurysmal subarachnoid hemorrhage

Background: Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating hemorrhagic stroke with high disability and mortality. Neuroinflammation and the immunological response after aSAH are complex pathophysiological processes that have not yet been fully elucidated. Therefore, attention should be paid to exploring the inflammation-related genes involved in the systemic response to the rupture of intracranial aneurysms.

Methods: The datasets of gene transcriptomes were downloaded from the Gene Expression Omnibus database. We constructed a gene co-expression network to identify cluster genes associated with aSAH and screened out differentially expressed genes (DEGs). The common gene was subsequently applied to identify hub genes by protein-protein interaction analysis and screen signature genes by machine learning algorithms. CMap analysis was implemented to identify potential small-molecule compounds. Meanwhile, Cibersort and ssGSEA were used to evaluate the immune cell composition, and GSEA reveals signal biological pathways.

Results: We identified 602 DEGs from the GSE36791. The neutrophil-related module associated with aSAH was screened by weighted gene co-expression network analysis (WGCNA) and functional enrichment analysis. Several small molecular compounds were predicted based on neutrophil-related genes. MAPK14, ITGAM, TLR4, and FCGR1A have been identified as crucial genes involved in the peripheral immune activation related to neutrophils. Six significant genes (CST7, HSP90AB1, PADI4, PLBD1, RAB32, and SLAMF6) were identified as signature biomarkers by performing the LASSO analysis and SVM algorithms. The constructed machine learning model appears to be robust by receiver-operating characteristic curve analysis. The immune feature analysis demonstrated that neutrophils were upregulated post-aSAH and PADI4 was positively correlated with neutrophils. The NETs pathway was significantly upregulated in aSAH.

Conclusion: We identified core regulatory genes influencing the transcription profiles of circulating neutrophils after the rupture of intracranial aneurysms using bioinformatics analysis and machine learning algorithms. This study provides new insight into the mechanism of peripheral immune response and inflammation after aSAH.

Plant Secondary Metabolites as Defense Tools against Herbivores for Sustainable Crop Protection

Plants have evolved several adaptive strategies through physiological changes in response to herbivore attacks. Plant secondary metabolites (PSMs) are synthesized to provide defensive functions and regulate defense signaling pathways to safeguard plants against herbivores. Herbivore injury initiates complex reactions which ultimately lead to synthesis and accumulation of PSMs. The biosynthesis of these metabolites is regulated by the interplay of signaling molecules comprising phytohormones. Plant volatile metabolites are released upon herbivore attack and are capable of directly inducing or priming hormonal defense signaling pathways. Secondary metabolites enable plants to quickly detect herbivore attacks and respond in a timely way in a rapidly changing scenario of pest and environment. Several studies have suggested that the potential for adaptation and/or resistance by insect herbivores to secondary metabolites is limited. These metabolites cause direct toxicity to insect pests, stimulate antixenosis mechanisms in plants to insect herbivores, and, by recruiting herbivore natural enemies, indirectly protect the plants. Herbivores adapt to secondary metabolites by the up/down regulation of sensory genes, and sequestration or detoxification of toxic metabolites. PSMs modulate multi-trophic interactions involving host plants, herbivores, natural enemies and pollinators. Although the role of secondary metabolites in plant-pollinator interplay has been little explored, several reports suggest that both plants and pollinators are mutually benefited. Molecular insights into the regulatory proteins and genes involved in the biosynthesis of secondary metabolites will pave the way for the metabolic engineering of biosynthetic pathway intermediates for improving plant tolerance to herbivores. This review throws light on the role of PSMs in modulating multi-trophic interactions, contributing to the knowledge of plant-herbivore interactions to enable their management in an eco-friendly and sustainable manner.

Plant Secondary Metabolites as Defense Tools against Herbivores for Sustainable Crop Protection

Plants have evolved several adaptive strategies through physiological changes in response to herbivore attacks. Plant secondary metabolites (PSMs) are synthesized to provide defensive functions and regulate defense signaling pathways to safeguard plants against herbivores. Herbivore injury initiates complex reactions which ultimately lead to synthesis and accumulation of PSMs. The biosynthesis of these metabolites is regulated by the interplay of signaling molecules comprising phytohormones. Plant volatile metabolites are released upon herbivore attack and are capable of directly inducing or priming hormonal defense signaling pathways. Secondary metabolites enable plants to quickly detect herbivore attacks and respond in a timely way in a rapidly changing scenario of pest and environment. Several studies have suggested that the potential for adaptation and/or resistance by insect herbivores to secondary metabolites is limited. These metabolites cause direct toxicity to insect pests, stimulate antixenosis mechanisms in plants to insect herbivores, and, by recruiting herbivore natural enemies, indirectly protect the plants. Herbivores adapt to secondary metabolites by the up/down regulation of sensory genes, and sequestration or detoxification of toxic metabolites. PSMs modulate multi-trophic interactions involving host plants, herbivores, natural enemies and pollinators. Although the role of secondary metabolites in plant-pollinator interplay has been little explored, several reports suggest that both plants and pollinators are mutually benefited. Molecular insights into the regulatory proteins and genes involved in the biosynthesis of secondary metabolites will pave the way for the metabolic engineering of biosynthetic pathway intermediates for improving plant tolerance to herbivores. This review throws light on the role of PSMs in modulating multi-trophic interactions, contributing to the knowledge of plant-herbivore interactions to enable their management in an eco-friendly and sustainable manner.

Identification of dual binding mode of Orthodiffenes towards human topoisomerase-I and α-tubulin: exploring the potential role in anti-cancer activity via in silico study

The drugs prescribed for targeting the tumour growth comprise of chemotherapy regimen involving combinations to cell-cycle phase specific target receptors. The combination therapy with Topoisomerase-I (Topo-I) & anti-tubulin agents are in the clinical trial stages and have scope for identifying new chemical entities with dual binding and inhibiting potential. The checkpoint proteins present at the interface of cell-cycle phases are considered the link between these two that establish the connectivity across the two phases of cell-cycle. In the present study, this potential cross-link or dual targeting is explored via in silico analysis on the natural molecules, Orthodiffene (OD) A-F which are reported from the medicinal plant, Orthosiphon diffusus. These molecules have been reported to possess significant cytotoxicity against Jurkat and HL-60 cancer cells lines in vitro. A detailed in silico analysis on OD-series molecules to evaluate their plausible anticancer mechanism & potential, as well as their in situ ADMET profile study is reported here. The DFT analysis, molecular modelling and molecular dynamics (MD) collectively establishes Topoisomerase-I & α-Tubulin proteins to be the putative target responsible for the cytotoxic activities of OD-B. Orthodiffene series molecules found to be abiding by Lipinksi's rule of 5 for orally bioavailable drug molecule. The present data & study are useful for further exploration of developing new chemical entities based on the structures of OD-series molecules as dual-target inhibitors of Topo-I & tubulin proteins with better efficacies.

Targeting Drug Chemo-Resistance in Cancer Using Natural Products

Cancer is one of the leading causes of death globally. The development of drug resistance is the main contributor to cancer-related mortality. Cancer cells exploit multiple mechanisms to reduce the therapeutic effects of anticancer drugs, thereby causing chemotherapy failure. Natural products are accessible, inexpensive, and less toxic sources of chemotherapeutic agents. Additionally, they have multiple mechanisms of action to inhibit various targets involved in the development of drug resistance. In this review, we have summarized the basic research and clinical applications of natural products as possible inhibitors for drug resistance in cancer. The molecular targets and the mechanisms of action of each natural product are also explained. Diverse drug resistance biomarkers were sensitive to natural products. P-glycoprotein and breast cancer resistance protein can be targeted by a large number of natural products. On the other hand, protein kinase C and topoisomerases were less sensitive to most of the studied natural products. The studies discussed in this review will provide a solid ground for scientists to explore the possible use of natural products in combination anticancer therapies to overcome drug resistance by targeting multiple drug resistance mechanisms.

A Leaf Extract of Harrisonia abyssinica Ameliorates Neurobehavioral, Histological and Biochemical Changes in the Hippocampus of Rats with Aluminum Chloride-Induced Alzheimer's Disease

Aluminum (Al) is an omnipresent mineral element in the environment. The brain is a central target of Al toxicity, being highly susceptible to oxidative damage. Therefore, recognition of drugs or natural products that guard against Al-mediated neuronal cell death is a powerful strategy for prevention and treatment of neurodegenerative disorders. This work aimed to explore the potential of a leaf extract from Harrisonia abyssinica to modulate the neurobehavioral, biochemical and histopathological activities induced experimentally by Al in vivo. Rats subjected to Al treatment displayed a reduction in learning and memory performance in a passive avoidance test accompanied by a decrease in the hippocampal monoamine and glutamate levels in addition to suppression of Bcl2 expression. Moreover, malondialdehyde (MDA), inflammatory markers (TNF-α, IL-1β), apoptotic markers (caspase-3 and expression of Bax) and extracellular regulated kinase (ERK1/2) levels were elevated along with acetylcholinesterase (AChE) activity, histological changes and marked deposition of amyloid β plaques in the hippocampus region of the brain tissues being observed in Al-treated animals. Concomitant administration of the high dose of H. abyssinica (200 mg/kg b.w.) restored nearly normal levels of all parameters measured, rather than the low dose (100 mg/kg b.w.), an effect that was comparable to the reference drug (rivastigmine). Molecular docking revealed the appropriate potential of the extract components to block the active site of AChE and ERK2. In conclusion, H. abyssinica leaf extract conferred neuroprotection against Al-induced neurotoxic effects, most likely due to its high phenolic and flavonoid content.

Effects of plant alkaloids on mitochondrial bioenergetic parameters

Mitochondria are among the first responders to various stress factors that challenge cell and tissue homeostasis. Various plant alkaloids have been investigated for their capacity to modulate mitochondrial activities. In this study, we used isolated mitochondria from mouse brain and liver tissues to assess nicotine, anatabine and anabasine, three alkaloids found in tobacco plant, for potential modulatory activity on mitochondrial bioenergetics parameters. All alkaloids decreased basal oxygen consumption of mouse brain mitochondria in a dose-dependent manner without any effect on the ADP-stimulated respiration. None of the alkaloids, at 1 nM or 1.25 μM concentrations, influenced the maximal rate of swelling of brain mitochondria. In contrast to brain mitochondria, 1.25 μM anatabine, anabasine and nicotine increased maximal rate of swelling of liver mitochondria suggesting a toxic effect. Only at 1 mM concentration, anatabine slowed down the maximal rate of Ca²⁺-induced swelling and increased the time needed to reach the maximal rate of swelling. The observed mitochondrial bioenergetic effects are probably mediated through a pathway independent of nicotinic acetylcholine receptors, as quantitative proteomic analysis could not confirm their expression in pure mitochondrial fractions isolated from mouse brain tissue.

Multiple Molecular Mechanisms to Overcome Multidrug Resistance in Cancer by Natural Secondary Metabolites

Plant secondary metabolites (SMs) common natural occurrences and the significantly lower toxicities of many SM have led to the approaching development and use of these compounds as effective pharmaceutical agents; especially in cancer therapy. A combination of two or three of plant secondary metabolites together or of one SM with specific anticancer drugs, may synergistically decrease the doses needed, widen the chemotherapeutic window, mediate more effective cell growth inhibition, and avoid the side effects of high drug concentrations. In mixtures they can exert additive or even synergistic activities. Many SM can effectively increase the sensitivity of cancer cells to chemotherapy. In phytotherapy, secondary metabolites (SM) of medicinal plants can interact with single or multiple targets. The multi-molecular mechanisms of plant secondary metabolites to overcome multidrug resistance (MDR) are highlighted in this review. These mechanisms include interaction with membrane proteins such as P-glycoprotein (P-gp/MDR1); an ATP-binding cassette (ABC) transporter, nucleic acids (DNA, RNA), and induction of apoptosis. P-gp plays an important role in the development of MDR in cancer cells and is involved in potential chemotherapy failure. Therefore, the ingestion of dietary supplements, food or beverages containing secondary metabolites e.g., polyphenols or terpenoids may alter the bioavailability, therapeutic efficacy and safety of the drugs that are P-gp substrates.

Anti-TMV activity and mode of action of three alkaloids isolated from Chelidonium majus

BACKGROUND

Plant viral diseases are difficult to control and have caused serious damage to the agricultural industry. Recently, botanical biopesticides characterized by environment friendly, safe to non-target organism and not as susceptible to produce drug resistance, have exhibited great potential to be developed as antiviral agents. To screen the natural products with antiviral effect, three alkaloids possessed anti-tobacco mosaic virus (TMV) activity were isolated from Chelidonium majus and the modes of action were investigated.

RESULT

The anti-TMV effect of crude extracts at 10 mg mL^-1 was 51.73%. Bioassay-guided fractionation and isolation of the compounds with anti-TMV activity were performed on the methanol extract of C. majus yielding three bioactive alkaloids namely: chelerythrine (1), chelidonine (2), and sanguinarine (3). The results of bioassay showed that chelerythrine exhibited great inactivation, proliferation inhibition and protection effects against TMV at 0.5 mg mL^-1 with the efficiency of 72.67%, 77.52% and 59.34%, respectively. Chelidonine at 0.1 mg mL^-1 can provide 54.90% and 64.45% inhibitions on TMV through inducing resistance in two kinds of tobacco. Sanguinarine showed a weaker protection for resisting TMV in comparison to chelerythrine and chelidonine.

CONCLUSION

Chelerythrine and chelidonine displayed significant inhibitions on TMV with different modes of action. These results provided important evidence that the extracts in C. majus might be a potential source of new drugs in controlling virus disease agriculturally.

An Insight into the Mechanism of Holamine- and Funtumine-Induced Cell Death in Cancer Cells

Holamine and funtumine, steroidal alkaloids with strong and diverse pharmacological activities are commonly found in the Apocynaceae family of Holarrhena. The selective anti-proliferative and cell cycle arrest effects of holamine and funtumine on cancer cells have been previously reported. The present study evaluated the anti-proliferative mechanism of action of these two steroidal alkaloids on cancer cell lines (HT-29, MCF-7 and HeLa) by exploring the mitochondrial depolarization effects, reactive oxygen species (ROS) induction, apoptosis, F-actin perturbation, and inhibition of topoisomerase-I. The apoptosis-inducing effects of the compounds were studied by flow cytometry using the APOPercentage^TM dye and Caspase-3/7 Glo assay kit. The two compounds showed a significantly greater cytotoxicity in cancer cells compared to non-cancer (normal) fibroblasts. The observed antiproliferative effects of the two alkaloids presumably are facilitated through the stimulation of apoptosis. The apoptotic effect was elicited through the modulation of mitochondrial function, elevated ROS production, and caspase-3/7 activation. Both compounds also induced F-actin disorganization and inhibited topoisomerase-I activity. Although holamine and funtumine appear to have translational potential for the development of novel anticancer agents, further mechanistic and molecular studies are recommended to fully understand their anticancer effects.

Phytochemicals: Potential Lead Molecules for MDR Reversal

Multidrug resistance (MDR) is one of the main impediments in the treatment of cancers. MDR cancer cells are resistant to multiple anticancer drugs. One of the major mechanisms of MDR is the efflux of anticancer drugs by ABC transporters. Increased activity and overexpression of these transporters are important causes of drug efflux and, therefore, resistance to cancer chemotherapy. Overcoming MDR is a fundamental prerequisite for developing an efficient treatment of cancer. To date, various types of ABC transporter inhibitors have been employed but no effective anticancer drug is available at present, which can completely overcome MDR. Phytochemicals can reverse MDR in cancer cells via affecting the expression or activity of ABC transporters, and also through exerting synergistic interactions with anticancer drugs by addressing additional molecular targets. We have listed numerous phytochemicals which can affect the expression and activity of ABC transporters in MDR cancer cell lines. Phytochemicals in the groups of flavonoids, alkaloids, terpenes, carotenoids, stilbenoids, lignans, polyketides, and curcuminoids have been examined for MDR-reversing activity. The use of MDR-reversing phytochemicals with low toxicity to human in combination with effective anticancer agents may result in successful treatment of chemotherapy-resistant cancer. In this review, we summarize and discuss published evidence for natural products with MDR modulation abilities.

In vitro wound healing of tumor cells: inhibition of cell migration by selected cytotoxic alkaloids

Background

Cell migration is involved in several pathological processes such as tumor invasion, neoangiogenesis and metastasis. Microtubules are needed in directional migration.

Methods

To investigate the effects of microtubule-binding agents (paclitaxel, vinblastine, colchicine, podophyllotoxin), benzophenanthridine alkaloids (sanguinarine, chelerythrine, chelidonine) and other anti-tumor drugs (homoharringtonine, doxorubicin) on cell migration, we performed the in vitro wound healing assay. The interactions between selected alkaloids and microtubules were studied via U2OS cells expressing microtubule-GFP markers.

Results

The microtubule-binding natural products paclitaxel, vinblastine, colchicine and podophyllotoxin significantly altered microtubule dynamics in living cells and inhibited cell migration at concentrations below apparent cytotoxicity. The benzophenanthridine alkaloid sanguinarine, chelerythrine and chelidonine which affected microtubules in living cells, did not inhibit cell migration. Homoharringtonine (protein biosynthesis inhibitor) and doxorubicin significantly inhibited cell migration, however, they did not exert obvious effects on microtubules.

Conclusion

In this study, we demonstrated that microtubule-binding agents are effective anti-migrating agents; moreover, homoharringtonine and doxorubicin can be referred as anti-migrating agents, but direct microtubule dynamics are not involved in their mode of action. Our study provides evidence that some alkaloids and other microtubule-binding natural products may be interesting candidates for the development of novel agents against metastasis.

Electronic supplementary material

The online version of this article (10.1186/s40360-018-0284-4) contains supplementary material, which is available to authorized users.

Modulation of multidrug resistant in cancer cells by EGCG, tannic acid and curcumin

BACKGROUND

Cancer is one of the most common life-threatening diseases worldwide; many patients develop multidrug resistance after treatment with anticancer drugs. The main mechanism leading to multidrug resistance is the overexpression of ABC transporters in cancer cells. Chemosensitizers are needed to inhibit the activity of ABC transporters, resulting in higer intracellular concentration of anticancer drugs. Some secondary metabolites have been reported to be chemosensitizers by inhibiting ABC transporters. Epigallocatechin gallate (EGCG), tannic acid, and curcumin were employed in this study. Different assays were used to detect whether they have the ability to inhibit P-gp activity and overcome multidrug resistance in cancer cells overexpressing P-gp. Hypothesis/Purpose: CEM/ADR 5000 and Caco-2 cell lines, which overexpress P-gp, are multidrug resistant cell lines. We first detected whether the combination of polyphenols (EGCG, tannic acid, curcumin) and doxorubicin, an anticancer drug, is synergistic or not. To further understand the potential mechanism, EGCG, tannic acid, and curcumin were tested to check whether they have the ability to inhibit P-gp activity. When P-gp activity is inhibited, the intracellular concentration of doxorubicin is higher, resulting in enhanced cytotoxicity of doxorubicin.

STUDY DESIGN

The P-gp overexpressing human colon cancer cell line Caco-2 and human T-lymphoblastic leukemia cell line CEM/ADR 5000 were used in this study. Two-drug combinations (doxorubicin + polyphenol) and three-drug combinations (doxorubicin + polyphenol + digitonin) were tested to examine potential synergism. The potential mechanism leading to synergism would be the inhibition of P-gp activity. A Rhodamine 123 assay and Calcein-AM assay in Caco-2 and CEM/ADR 5000, respectively, were used to detect P-gp inhibition by EGCG, curcumin, and tannic acid.

METHODS

MTT assay was used to determine the cytotoxicity of doxorubicin, polyphenols and digitonin alone, and then their combinations. Furthermore, Rhodamine 123 and Calcein-AM were used to detect the effects of polyphenols on the activity of P-gp.

RESULTS

The results demonstrated that a combination of non-toxic concentrations of each polyphenol with doxorubicin synergistically sensitized Caco-2 and CEM/ADR 5000 cells. Furthermore, three-drug combinations (doxorubicin + polyphenol + digitonin) were much more effective. In addition, the activity of P-gp in Caco-2 and CEM/ADR 5000 cells was measured. Consistent with the combination results, tannic acid and curcumin decreased the activity of P-gp both in Caco-2 and CEM/ADR 5000. EGCG, which weakly affected the activity of P-gp in CEM/ADR 5000, only had an effect on P-gp under higher concentration in Caco-2 cells.

CONCLUSION

Our results show that EGCG, curcumin, and tannic acid, when combined with doxorubicin, can exert synergism, mediated by a reduced activity of P-gp. This study suggests that polyphenols, by modulating the activity of P-gp, may be used as chemosensitisers.

Cucurbitacins: elucidation of their interactions with the cytoskeleton

Cucurbitacins, a class of toxic tetracyclic triterpenoids in Cucurbitaceae, modulate many molecular targets. Here we investigated the interactions of cucurbitacin B, E and I with cytoskeletal proteins such as microtubule and actin filaments. The effects of cucurbitacin B, E and I on microtubules and actin filaments were studied in living cells (Hela and U2OS) and in vitro using GFP markers, immunofluorescence staining and in vitro tubulin polymerization assay. Cucurbitacin B, E and I apparently affected microtubule structures in living cells and cucurbitacin E inhibited tubulin polymerization in vitro with IC50 value of 566.91 ± 113.5 µM. Cucurbitacin E did not affect the nucleation but inhibited the growth phase and steady state during microtubule assembly in vitro. In addition, cucurbitacin B, E and I all altered mitotic spindles and induced the cell cycle arrest at G2/M phase. Moreover, they all showed potent effects on actin cytoskeleton by affecting actin filaments through the depolymerization and aggregation. The interactions of cucubitacin B, E and I with microtubules and actin filaments present new insights into their modes of action.

Inhibition of Cytochrome P450 (CYP3A4) Activity by Extracts from 57 Plants Used in Traditional Chinese Medicine (TCM)

Background:

Herbal medicine is widely used all over the world for treating various health disorders. It is employed either alone or in combination with synthetic drugs or plants to be more effective.

Objective:

The assessment of the effect of both water and methanol extracts of 57 widely used plants from Traditional Chinese Medicine (TCM) against the main phase I metabolizing enzyme CYP3A4 in vitro for the first time.

Materials and Methods:

The inhibition of cytochrome P450 activity was evaluated using a luminescence assay. The principal component analysis (PCA) was used to correlate the inhibitory activity with the main secondary metabolites present in the plant extracts. Molecular modeling studies on CYP3A4 (PDB ID 4NY4) were carried out with 38 major compounds present in the most active plant extracts to validate the observed inhibitory effect.

Results:

Aqueous extracts of Acacia catechu, Andrographis paniculata, Arctium lappa, Areca catechu, Bupleurum marginatum, Chrysanthemum indicum, Dysosma versipellis, and Spatholobus suberectus inhibited CYP3A4 is more than 85% (at a dose of 100 μg/mL). The corresponding methanol extracts of A. catechu, A. paniculata, A. catechu, Mahonia bealei, and Sanguisorba officinalis inhibited the enzyme by more than 50%. Molecular modeling studies revealed that two polyphenols, namely hesperidin and rutin, revealed the highest fitting scores in the active sites of the CYP3A4 with binding energies equal to -74.09 and -71.34 kcal/mol, respectively.

Conclusion:

These results provide evidence that many TCM plants can inhibit CYP3A4, which might cause a potential interference with the metabolism of other concomitantly administered herbs or drugs.

SUMMARY

In this study, the inhibitory activity of the aqueous and methanol extracts of 57 widely used plants from Traditional Chinese Medicine (TCM) against the main phase I metabolizing enzyme CYP3A4 was tested in vitro for the first time.

Aqueous extracts of Acacia catechu, Andrographis paniculata, Arctium lappa, Areca catechu, Bupleurum marginatum, Dysosma versipellis, and Spatholobus suberectus inhibited CYP3A4 by more than 85% (at a dose of 100 μg/mL).

The activity could be attributed to the presence of polyphenolics as revealed from the multivariate chemometric analysis and molecular modeling study.

These results provide evidence that many TCM plants can inhibit CYP3A4, which might cause a potential interference with the metabolism of other concomitantly administered herbs or drugs.

Abbreviation used: CHARMm: Chemistry at HARvard Macromolecular Mechanics, CYP: Cytochrome P450, DMSO: Dimethyl Sulfoxide, PCA: Principal Component Analysis, PDB: Protein Data Bank, TCM: Traditional Chinese Medicine

Cytoskeletal interference - A new mode of action for the anticancer drugs camptothecin and topotecan

The anticancer drugs camptothecin (CPT) and topotecan (TPT) are known DNA topoisomerase I inhibitors which cause DNA damage and lead to cell death. In this study we provide evidence that CPT and TPT also interfere with the elements of cytoskeleton - microtubules and actin filaments which could be partly responsible for their cytotoxic properties. CPT and TPT apparently affected microtubule structures in living cells (Hela and U2OS) and inhibited tubulin polymerization in vitro with IC50 values of 74.57±9.96µM and 121.55±58.68µM, respectively. TPT significantly affected the nucleation and growth phase during the microtubule assembly in vitro, whereas the mode of action of CPT was different in that it specifically affected the 'tread milling' of polymerized microtubules. Cell cycle effects of CPT and TPT varied with their concentrations. CPT and TPT induced G2/M arrest and promoted the population to 76.94±11.20% and 83.91±2.43% at a concentration of 9.4nM and 46.9nM, respectively. As the concentration increased, cells were blocked in S phase with a dose-dependent reduction in G2/M population. In addition, CPT and TPT exhibited a certain effect on actin filaments by reducing the mass of actin filaments. The interactions of CPT and TPT with microtubules and actin filaments present new insights into their modes of action.

The Interference of Selected Cytotoxic Alkaloids with the Cytoskeleton: An Insight into Their Modes of Action

Alkaloids, the largest group among the nitrogen-containing secondary metabolites of plants, usually interact with several molecular targets. In this study, we provide evidence that six cytotoxic alkaloids (sanguinarine, chelerythrine, chelidonine, noscapine, protopine, homoharringtonine), which are known to affect neuroreceptors, protein biosynthesis and nucleic acids, also interact with the cellular cytoskeleton, such as microtubules and actin filaments, as well. Sanguinarine, chelerythrine and chelidonine depolymerized the microtubule network in living cancer cells (Hela cells and human osteosarcoma U2OS cells) and inhibited tubulin polymerization in vitro with IC50 values of 48.41 ± 3.73, 206.39 ± 4.20 and 34.51 ± 9.47 μM, respectively. However, sanguinarine and chelerythrine did not arrest the cell cycle while 2.5 μM chelidonine arrested the cell cycle in the G₂/M phase with 88.27% ± 0.99% of the cells in this phase. Noscapine and protopine apparently affected microtubule structures in living cells without affecting tubulin polymerization in vitro, which led to cell cycle arrest in the G2/M phase, promoting this cell population to 73.42% ± 8.31% and 54.35% ± 11.26% at a concentration of 80 μM and 250.9 μM, respectively. Homoharringtonine did not show any effects on microtubules and cell cycle, while the known microtubule-stabilizing agent paclitaxel was found to inhibit tubulin polymerization in the presence of MAPs in vitro with an IC50 value of 38.19 ± 3.33 μM. Concerning actin filaments, sanguinarine, chelerythrine and chelidonine exhibited a certain effect on the cellular actin filament network by reducing the mass of actin filaments. The interactions of these cytotoxic alkaloids with microtubules and actin filaments present new insights into their molecular modes of action.

Assessment of the Cytotoxic and Apoptotic Eἀects of Chaetominine in a Human Leukemia Cell Line

Chaetominine is a quinazoline alkaloid originating from the endophytic fungus Aspergillus fumigatus CY018. In this study, we showed evidence that chaetominine has cytotoxic and apoptotic effects on human leukemia K562 cells and investigated the pathway involved in chaetominine-induced apoptosis in detail. Chaetominine inhibited K562 cell growth, with an IC50 value of 35 nM, but showed little inhibitory effect on the growth of human peripheral blood mononuclear cells. The high apoptosis rates, morphological apoptotic features, and DNA fragmentation caused by chaetominine indicated that the cytotoxicity was partially caused by its pro-apoptotic effect. Under chaetominine treatment, the Bax/Bcl-2 ratio was upregulated (from 0.3 to 8), which was followed by a decrease in mitochondrial membrane potential, release of cytochrome c from mitochondria into the cytosol, and stimulation of Apaf-1. Furthermore, activation of caspase-9 and caspase-3, which are the main executers of the apoptotic process, was observed. These results demonstrated that chaetominine induced cell apoptosis via the mitochondrial pathway. Chaetominine inhibited K562 cell growth and induced apoptotic cell death through the intrinsic pathway, which suggests that chaetominine might be a promising therapeutic for leukemia.

Two new cytotoxic furoquinoline alkaloids isolated from Aegle marmelos (Linn.) Correa

Two new cytotoxic furoquinoline alkaloids were isolated from the leaves of Aegle marmelos (Linn.) Correa; one from the total alkaloidal fraction (acid/base shake-out method) of the CHCl₃ extract and identified as 7,8-dihydroxy-4-hydrofuroquinoline and named trivially as Aegelbine-A. The other new alkaloid isolated from the pet. ether extract and identified as 4-hydro-7-hydroxy-8-prenyloxyfuroquinoline and named trivially as Aegelbine-B, together with a known alkaloid; aegeline and a known phenolic acid; ρ-hydroxybenzoic acid. The structures of all the isolated compounds were established based on 1D and 2D NMR spectroscopy and HR-ESI/MS. The cytotoxic activity of the isolated compounds was evaluated in vitro against HepG-2, PC3, A549 and MCF-7 cell lines. The obtained results revealed promising activity with structure-based relationship which is discussed briefly.

Cadaverine's Functional Role in Plant Development and Environmental Response

Cadaverine derives from lysine in a pathway that is distinct from that of the other well-characterized ornithine- or arginine-derived polyamines. Despite a multitude of studies in bacterial systems, cadaverine has garnered little attention in plant research. Nonetheless, many plants have been found to synthesize it. For instance, the Leguminosae have been shown to produce cadaverine and use it as a precursor in the biosynthesis of quinolizidine alkaloids, secondary metabolites that are involved in insect defense and also display therapeutic pharmacological properties. Cadaverine is also present in the environment; it can be produced by rhizosphere and phyllosphere microbes. Markedly, exogenous cadaverine application causes alterations in root-system architecture. Previous research suggests cadaverine has a role in stress response, with groups reporting an increase in content upon exposure to heat, drought, salt, and oxidative stress. However, data regarding the role of cadaverine in stress response remains conflicted, as some plant systems show enhanced tolerance to stresses in its presence, while others show increased sensitivity to the same stresses. In this review, we summarize recent findings on the role of cadaverine in plant growth, development, and stress response. We also address the possible roles rhizosphere and phyllosphere microbes may play in the delivery of exogenous cadaverine near plant organs, and discuss our current understanding of the molecular pathways that contribute to cadaverine homeostasis and response in plants.

Combinations of alkaloids affecting different molecular targets with the saponin digitonin can synergistically enhance trypanocidal activity against Trypanosoma brucei brucei

The flagellate Trypanosoma brucei causes sleeping sickness in humans and nagana in animals. Only a few drugs are registered to treat trypanosomiasis, but those drugs show severe side effects. Also, because some pathogen strains have become resistant, new strategies are urgently needed to combat this parasitic disease. An underexplored possibility is the application of combinations of several trypanocidal agents, which may potentiate their trypanocidal activity in a synergistic fashion. In this study, the potential synergism of mutual combinations of bioactive alkaloids and alkaloids with a membrane-active steroidal saponin, digitonin, was explored with regard to their effect on T. b. brucei. Alkaloids were selected that affect different molecular targets: berberine and chelerythrine (intercalation of DNA), piperine (induction of apoptosis), vinblastine (inhibition of microtubule assembly), emetine (intercalation of DNA, inhibition of protein biosynthesis), homoharringtonine (inhibition of protein biosynthesis), and digitonin (membrane permeabilization and uptake facilitation of polar compounds). Most combinations resulted in an enhanced trypanocidal effect. The addition of digitonin significantly stimulated the activity of almost all alkaloids against trypanosomes. The strongest effect was measured in a combination of digitonin with vinblastine. The highest dose reduction indexes (DRI) were measured in the two-drug combination of digitonin or piperine with vinblastine, where the dose of vinblastine could be reduced 9.07-fold or 7.05-fold, respectively. The synergistic effects of mutual combinations of alkaloids and of alkaloids with digitonin present a new avenue to treat trypanosomiasis but one which needs to be corroborated in future animal experiments.

Modes of Action of Herbal Medicines and Plant Secondary Metabolites

Plants produce a wide diversity of secondary metabolites (SM) which serve them as defense compounds against herbivores, and other plants and microbes, but also as signal compounds. In general, SM exhibit a wide array of biological and pharmacological properties. Because of this, some plants or products isolated from them have been and are still used to treat infections, health disorders or diseases. This review provides evidence that many SM have a broad spectrum of bioactivities. They often interact with the main targets in cells, such as proteins, biomembranes or nucleic acids. Whereas some SM appear to have been optimized on a few molecular targets, such as alkaloids on receptors of neurotransmitters, others (such as phenolics and terpenoids) are less specific and attack a multitude of proteins by building hydrogen, hydrophobic and ionic bonds, thus modulating their 3D structures and in consequence their bioactivities. The main modes of action are described for the major groups of common plant secondary metabolites. The multitarget activities of many SM can explain the medical application of complex extracts from medicinal plants for more health disorders which involve several targets. Herbal medicine is not a placebo medicine but a rational medicine, and for several of them clinical trials have shown efficacy.

Genomic profiling screens small molecules of metastatic prostate carcinoma

The aim of the present study was to investigate the pathogenesis of metastatic prostate carcinoma, to find the metabolic pathways changed in the disease and to screen out the potential therapeutic drugs. GSE38241 was downloaded from Gene Expression Omnibus; the Geoquery package was applied to preprocessed expression profiling, and the differentially-expressed genes (DEGs) were selected with limma (linear regression model packages). Next, WikiPathways cluster analysis was performed for DEGs on a Gene Set Analysis Toolkit V2 platform, and DEGs with hypergeometric algorithms were calculated through gene set enrichment analysis. A total of 1,126 DEGs were identified between the normal prostate and metastatic prostate carcinoma. In addition, KPNA4, SYT1, PLCB1, SPRED1, MBNL2, RNF165, MEF2C, MBNL1, ZFP36L1 and CELF2, were found to be likely to play significant roles in the process of metastatic prostate carcinoma. The small molecules STOCK1N-35874 and 5182598 could simulate the state of normal cells well, while the small molecules MS-275 and quinostatin could simulate the state of metastatic prostate carcinoma cells. In conclusions, the small molecules STOCK1N-35874 and 5182598 were identified to be good potential therapeutic drugs for the treatment of metastatic prostate carcinoma, while the two small molecules MS-275 and quinostatin could cause metastatic prostate carcinoma.

Synergistic antibacterial activity of the combination of the alkaloid sanguinarine with EDTA and the antibiotic streptomycin against multidrug resistant bacteria

Objectives

Drug combinations consisting of the DNA intercalating benzophenanthridine alkaloid sanguinarine, the chelator EDTA with the antibiotic streptomycin were tested against several Gram-positive and Gram-negative bacteria, including multi-resistant clinical isolates.

Methods

Microdilution, checkerboard and time kill curve methods were used to investigate the antibacterial activity of the individual drugs and the potential synergistic activity of combinations.

Key findings

Sanguinarine demonstrated a strong activity against Gram-positive and Gram-negative bacteria (minimum inhibitory concentrations, MIC = 0.5–128 μg/ml), while streptomycin was active against Gram-negative strains (MIC = 2–128 μg/ml). EDTA showed only bacteriostatic activity. Indifference to synergistic activity was seen in the two-drug combinations sanguinarine + EDTA and sanguinarine + streptomycin (fractional inhibitory concentration index = 0.1–1.5), while the three-drug combination of sanguinarine + EDTA + streptomycin showed synergistic activity against almost all the strains (except methicillin-resistant Staphylococcus aureus), as well as a strong reduction in the effective doses (dose reduction index = 2–16 times) of sanguinarine, EDTA and streptomycin. In time kill studies, a substantial synergistic interaction of the three-drug combination was detected against Escherichia coli and Klebsiella pneumoniae.

Conclusions

The combination of drugs, which interfere with different molecular targets, can be an important strategy to combat multidrug resistant bacteria.

The β-carboline alkaloid harmine inhibits telomerase activity of MCF-7 cells by down-regulating hTERT mRNA expression accompanied by an accelerated senescent phenotype

The end replication problem, which occurs in normal somatic cells inducing replicative senescence, is solved in most cancer cells by activating telomerase. The activity of telomerase is highly associated with carcinogenesis which makes the enzyme an attractive biomarker in cancer diagnosis and treatment. The indole alkaloid harmine has multiple pharmacological properties including DNA intercalation which can lead to frame shift mutations. In this study, harmine was applied to human breast cancer MCF-7 cells. Its activity towards telomerase was analyzed by utilizing the telomeric repeat amplification protocol (TRAP). Our data indicate that harmine exhibits a pronounced cytotoxicity and induces an anti-proliferation state in MCF-7 cells which is accompanied by a significant inhibition of telomerase activity and an induction of an accelerated senescence phenotype by over-expressing elements of the p53/p21 pathway.

The β-carboline alkaloid harmine inhibits telomerase activity of MCF-7 cells by down-regulating hTERT mRNA expression accompanied by an accelerated senescent phenotype

The end replication problem, which occurs in normal somatic cells inducing replicative senescence, is solved in most cancer cells by activating telomerase. The activity of telomerase is highly associated with carcinogenesis which makes the enzyme an attractive biomarker in cancer diagnosis and treatment. The indole alkaloid harmine has multiple pharmacological properties including DNA intercalation which can lead to frame shift mutations. In this study, harmine was applied to human breast cancer MCF-7 cells. Its activity towards telomerase was analyzed by utilizing the telomeric repeat amplification protocol (TRAP). Our data indicate that harmine exhibits a pronounced cytotoxicity and induces an anti-proliferation state in MCF-7 cells which is accompanied by a significant inhibition of telomerase activity and an induction of an accelerated senescence phenotype by over-expressing elements of the p53/p21 pathway.

Modulation of multidrug resistance in cancer cells by chelidonine and Chelidonium majus alkaloids

Cancer cells often develop multidrug resistance (MDR) which is a multidimensional problem involving several mechanisms and targets. This study demonstrates that chelidonine and an alkaloid extract from Chelidonium majus, which contains protoberberine and benzo[c]phenanthridine alkaloids, has the ability to overcome MDR of different cancer cell lines through interaction with ABC-transporters, CYP3A4 and GST, by induction of apoptosis, and cytotoxic effects. Chelidonine and the alkaloid extract inhibited P-gp/MDR1 activity in a concentration-dependent manner in Caco-2 and CEM/ADR5000 and reversed their doxorubicin resistance. In addition, chelidonine and the alkaloid extract inhibited the activity of the drug modifying enzymes CYP3A4 and GST in a dose-dependent manner. The alkaloids induced apoptosis in MDR cells which was accompanied by an activation of caspase-3, -8,-6/9, and phosphatidyl serine (PS) exposure. cDNA arrays were applied to identify differentially expressed genes after treatment with chelidonine and the alkaloid extract. The expression analysis identified a common set of regulated genes related to apoptosis, cell cycle, and drug metabolism. Treatment of Caco-2 cells with 50 μg/ml alkaloid extract and 50 μM chelidonine for up to 48 h resulted in a significant decrease in mRNA levels of P-gp/MDR1, MRP1, BCRP, CYP3A4, GST, and hPXR and in a significant increase in caspase-3 and caspase-8 mRNA. Thus, chelidonine is a promising model compound for overcoming MDR and for enhancing cytotoxicity of chemotherapeutics, especially against leukaemia cells. Its efficacy needs to be confirmed in animal models.

Digitonin synergistically enhances the cytotoxicity of plant secondary metabolites in cancer cells

In phytotherapy, extracts from medicinal plants are employed which contain mixtures of secondary metabolites. Their modes of action are complex because the secondary metabolites can react with single or multiple targets. The components in a mixture can exert additive or even synergistic activities. In this study, the cytotoxicity of some phytochemicals, including phenolics (EGCG and thymol), terpenoids (menthol, aromadendrene, β-sitosterol-O-glucoside, and β-carotene) and alkaloids (glaucine, harmine, and sanguinarine) were investigated alone or in combination with the cytotoxic monodesmosidic steroidal saponin digitonin in Caco-2, MCF-7, CEM/ADR5000, and CCRF-CEM cells. Digitonin was combined in non-toxic concentrations (5μM in each cell line; except in MCF-7 the concentration was 2μM), together with a selection of phenolics, terpenoids, and alkaloids to evaluate potential synergistic or additive effects. An enhanced cytotoxicity was observed in most combinations. Even multi-drug resistant (MDR) cells (such as CEM/ADR5000 cells), with a high expression of P-glycoprotein, were responsive to combinations. Sanguinarine was the most cytotoxic alkaloid against CEM/ADR5000, MCF-7, and CCRF-CEM cells alone and in combination with digitonin. As compared to sanguinarine alone, the combination was 44.53-, 15.38-, and 6.65-fold more toxic in each cell line, respectively. Most combinations synergistically increased the cytotoxicity, stressing the importance of synergy when using multi-target drugs and mixtures in phytotherapy.

Medicinal plants: a source of anti-parasitic secondary metabolites

This review summarizes human infections caused by endoparasites, including protozoa, nematodes, trematodes, and cestodes, which affect more than 30% of the human population, and medicinal plants of potential use in their treatment. Because vaccinations do not work in most instances and the parasites have sometimes become resistant to the available synthetic therapeutics, it is important to search for alternative sources of anti-parasitic drugs. Plants produce a high diversity of secondary metabolites with interesting biological activities, such as cytotoxic, anti-parasitic and anti-microbial properties. These drugs often interfere with central targets in parasites, such as DNA (intercalation, alkylation), membrane integrity, microtubules and neuronal signal transduction. Plant extracts and isolated secondary metabolites which can inhibit protozoan parasites, such as Plasmodium, Trypanosoma, Leishmania, Trichomonas and intestinal worms are discussed. The identified plants and compounds offer a chance to develop new drugs against parasitic diseases. Most of them need to be tested in more detail, especially in animal models and if successful, in clinical trials.

In-silico investigation of antitrypanosomal phytochemicals from Nigerian medicinal plants

BACKGROUND

Human African trypanosomiasis (HAT), a parasitic protozoal disease, is caused primarily by two subspecies of Trypanosoma brucei. HAT is a re-emerging disease and currently threatens millions of people in sub-Saharan Africa. Many affected people live in remote areas with limited access to health services and, therefore, rely on traditional herbal medicines for treatment.

METHODS

A molecular docking study has been carried out on phytochemical agents that have been previously isolated and characterized from Nigerian medicinal plants, either known to be used ethnopharmacologically to treat parasitic infections or known to have in-vitro antitrypanosomal activity. A total of 386 compounds from 19 species of medicinal plants were investigated using in-silico molecular docking with validated Trypanosoma brucei protein targets that were available from the Protein Data Bank (PDB): Adenosine kinase (TbAK), pteridine reductase 1 (TbPTR1), dihydrofolate reductase (TbDHFR), trypanothione reductase (TbTR), cathepsin B (TbCatB), heat shock protein 90 (TbHSP90), sterol 14α-demethylase (TbCYP51), nucleoside hydrolase (TbNH), triose phosphate isomerase (TbTIM), nucleoside 2-deoxyribosyltransferase (TbNDRT), UDP-galactose 4' epimerase (TbUDPGE), and ornithine decarboxylase (TbODC).

RESULTS

This study revealed that triterpenoid and steroid ligands were largely selective for sterol 14α-demethylase; anthraquinones, xanthones, and berberine alkaloids docked strongly to pteridine reductase 1 (TbPTR1); chromenes, pyrazole and pyridine alkaloids preferred docking to triose phosphate isomerase (TbTIM); and numerous indole alkaloids showed notable docking energies with UDP-galactose 4' epimerase (TbUDPGE). Polyphenolic compounds such as flavonoid gallates or flavonoid glycosides tended to be promiscuous docking agents, giving strong docking energies with most proteins.

CONCLUSIONS

This in-silico molecular docking study has identified potential biomolecular targets of phytochemical components of antitrypanosomal plants and has determined which phytochemical classes and structural manifolds likely target trypanosomal enzymes. The results could provide the framework for synthetic modification of bioactive phytochemicals, de novo synthesis of structural motifs, and lead to further phytochemical investigations.

Secondary Metabolites from Plants Inhibiting ABC Transporters and Reversing Resistance of Cancer Cells and Microbes to Cytotoxic and Antimicrobial Agents

Fungal, bacterial, and cancer cells can develop resistance against antifungal, antibacterial, or anticancer agents. Mechanisms of resistance are complex and often multifactorial. Mechanisms include: (1) Activation of ATP-binding cassette (ABC) transporters, such as P-gp, which pump out lipophilic compounds that have entered a cell, (2) Activation of cytochrome p450 oxidases which can oxidize lipophilic agents to make them more hydrophilic and accessible for conjugation reaction with glucuronic acid, sulfate, or amino acids, and (3) Activation of glutathione transferase, which can conjugate xenobiotics. This review summarizes the evidence that secondary metabolites (SM) of plants, such as alkaloids, phenolics, and terpenoids can interfere with ABC transporters in cancer cells, parasites, bacteria, and fungi. Among the active natural products several lipophilic terpenoids [monoterpenes, diterpenes, triterpenes (including saponins), steroids (including cardiac glycosides), and tetraterpenes] but also some alkaloids (isoquinoline, protoberberine, quinoline, indole, monoterpene indole, and steroidal alkaloids) function probably as competitive inhibitors of P-gp, multiple resistance-associated protein 1, and Breast cancer resistance protein in cancer cells, or efflux pumps in bacteria (NorA) and fungi. More polar phenolics (phenolic acids, flavonoids, catechins, chalcones, xanthones, stilbenes, anthocyanins, tannins, anthraquinones, and naphthoquinones) directly inhibit proteins forming several hydrogen and ionic bonds and thus disturbing the 3D structure of the transporters. The natural products may be interesting in medicine or agriculture as they can enhance the activity of active chemotherapeutics or pesticides or even reverse multidrug resistance, at least partially, of adapted and resistant cells. If these SM are applied in combination with a cytotoxic or antimicrobial agent, they may reverse resistance in a synergistic fashion.

Genus Bupleurum: a review of its phytochemistry, pharmacology and modes of action

Objectives Radix Bupleuri represents one of the most successful and widely used herbal drugs in Asia for treatment of many diseases over the past 2000 years. Thorough studies have been carried out on many species of this genus and have generated immense data about the chemical composition and corresponding biological activity of extracts and isolated secondary metabolites. In this work, we review the chemistry and pharmacology of the genus Bupleurum and explore the relationships between the pharmacological effects and the chemical composition of these drugs.

Key findings  Early studies on the genus Bupleurum had focused only on the traditional uses of the plants in the treatment of inflammatory disorders and infectious diseases. After chemical profiling, several groups of secondary metabolites were characterized with relevant biological activity: triterpene saponins (saikosaponins), lignans, essential oils and polysaccharides. As a result, present interest is now focused on the bioactivity of the isolated triterpene saponins acting as immunomodulatory, anti‐inflammatory and antiviral agents, as well as on the observed ant‐iulcer activity of the polysaccharides and anti‐proliferative activity of different lignans. Many saikosaponins exhibited very potent anti‐inflammatory, hepatoprotective and immunomodulatory activities both in vivo and in vitro.

Conclusions  Further investigations and screenings are required to explore other Bupleurum species, to evaluate the clinical safety and possible interactions with other drugs or herbs. Standardization of Bupleuri extracts is crucial for them being integrated into conventional medicine due to large chemical and biological variations between different species and varieties.

Quinoline alkaloids as intercalative topoisomerase inhibitors

Quinoline alkaloids are abundant in the Rutaceae, and many have exhibited cytotoxic activity. Because structurally related antitumor alkaloids such as camptothecin and fagaronine are known to function as intercalative topoisomerase poisons, it is hypothesized that cytotoxic Stauranthus alkaloids may also serve as intercalative topoisomerase inhibitors. To test this hypothesis theoretically, ten Stauranthus quinoline alkaloids were examined for potential intercalation into DNA using a molecular docking approach. Four of the alkaloids (stauranthine, skimmianine, 3',6'-dihydroxy-3',6'-dihydrostauranthine, and trans-3',4'-dihydroxy-3',4'-dihydrostauranthine) were able to intercalatively dock consistently into DNA. In order to probe the intermolecular interactions that may be responsible for intercalation of these quinoline alkaloids, density functional calculations have been carried out using both the B3LYP and M06 functionals. M06 calculations indicated favorable pi-pi interactions between either skimmianine or stauranthine and the guanine-cytosine base pair. Furthermore, the lowest-energy face-to-face orientation of stauranthine with guanine is consistent with favorable dipole-dipole orientations, favorable electrostatic interactions, and favorable frontier molecular orbital interactions. Likewise, the lowest-energy face-to-face orientation of stauranthine with the guanine-cytosine base pair reveals favorable electrostatic interactions as well as frontier molecular orbital interactions. Thus, not only can quinoline alkaloids dock intercalatively into DNA, but the docked orientations are also electronically favorable.

Alkaloids induce programmed cell death in bloodstream forms of trypanosomes (Trypanosoma b. brucei)

The potential induction of a programmed cell death (PCD) in Trypanosoma b. brucei by 55 alkaloids of the quinoline, quinolizidine, isoquinoline, indole, terpene, tropane, steroid, and piperidine type was studied by measuring DNA fragmentation and changes in mitochondrial membrane potential. For comparison, the induction of apoptosis by the same alkaloids in human leukemia cells (Jurkat APO-S) was tested. Several alkaloids of the isoquinoline, quinoline, indole and steroidal type (berberine, chelerythrine, emetine, sanguinarine, quinine, ajmalicine, ergotamine, harmine, vinblastine, vincristine, colchicine, chaconine, demissidine and veratridine) induced programmed cell death, whereas quinolizidine, tropane, terpene and piperidine alkaloids were mostly inactive. Effective PCD induction (EC(50) below 10 microM) was caused in T. brucei by chelerythrine, emetine, sanguinarine, and chaconine. The active alkaloids can be characterized by their general property to inhibit protein biosynthesis, to intercalate DNA, to disturb membrane fluidity or to inhibit microtubule formation.