Flavonoid-related modulators of multidrug resistance: synthesis, pharmacological activity, and structure-activity relationships

Can We Improve Diosmetin Activity? The State-of-the-Art and Promising Research Directions

Diosmetin is a natural substance widely distributed in nature, with documented multidirectional biological effects. The wide spectrum of biological activity of diosmetin gives hope that derivatives of this flavonoid may also be used as drugs or dietary supplements used in many diseases. Modification of the structure may, on the one hand, lead to an increase in biological potency, new biological activity, or an increase in solubility and thus bioavailability. This is an important direction of research because the use of pure diosmetin is limited due to its low bioavailability. This work is an attempt to collect information on the possibility of modifying the structure of diosmetin and its impact on biological activity.

Strategic developments in the drug delivery of natural product dihydromyricetin: applications, prospects, and challenges

Dihydromyricetin (DHM) is an important natural flavonoid that has attracted much attention because of its various functions such as protecting the cardiovascular system and liver, treating cancer and neurodegenerative diseases, and anti-inflammation effect, etc. Despite its great development potential in pharmacy, DHM has some problems in pharmaceutical applications such as low solubility, permeability, and stability. To settle these issues, extensive research has been carried out on its physicochemical properties and dosage forms to produce all kinds of DHM preparations in the past ten years. In addition, the combined use of DHM with other drugs is a promising strategy to expand the application of DHM. However, although invention patents for DHM preparations have been issued in several countries, the current transformation of DHM research results into market products is insufficient. To date, there is still a lack of deep research into the pharmacokinetics, pharmacodynamics, toxicology, and action mechanism of DHM preparations. Besides, preparations for combined therapy of DHM with other drugs are scarcely reported, which necessitates the development of dosage forms for this application. Apart from medicine, the development of DHM in the food industry is also of great potential. Due to its multiple effects and excellent safety, DHM preparations can be developed for functional drinks and foods. Through this review, we hope to draw more attention to the development potential of DHM and the above challenges and provide valuable references for the research and development of other natural products with a similar structure-activity relationship to this drug.

Mechanism of Interactions of dsDNA Binding with Apigenin and Its Sulfamate Derivatives Using Multispectroscopic, Voltammetric, and Molecular Docking Studies

DNA binding investigations are critical for designing better pharmaceutical compounds since the binding of a compound to dsDNA in the minor groove is critical in drug discovery. Although only one in vitro study on the DNA binding mode of apigenin (APG) has been conducted, there have been no electrochemical and theoretical studies reported. We hereby report the mechanism of binding interaction of APG and a new class of sulfonamide-modified flavonoids, apigenin disulfonamide (ADSAM) and apigenin trisulfonamide (ATSAM), with deoxyribonucleic acid (DNA). This study was conducted using multispectroscopic instrumentation techniques, which include UV-vis absorption, thermal denaturation, fluorescence, and Fourier transform infrared (FTIR) spectroscopy, and electrochemical and viscosity measurement methods. Also, molecular docking studies were conducted at room temperature under physiological conditions (pH 7.4). The molecular docking studies showed that, in all cases, the lowest energy docking poses bind to the minor groove of DNA and the apigenin-DNA complex was stabilized by several hydrogen bonds. Also, π-sulfur interactions played a role in the stabilization of the ADSAM-DNA and ATSAM-DNA complexes. The binding affinities of the lowest energy docking pose (schematic diagram of table of content (TOC)) of APG-DNA, ADSAM-DNA, and ATSAM-DNA complexes were found to be -8.2, -8.5, and -8.4 kcal mol-1, respectively. The electrochemical binding constants K b were determined to be (1.05 × 105) ± 0.04, (0.47 × 105) ± 0.02, and (8.13 × 105) ± 0.03 for APG, ADSAM, and ATSAM, respectively (all of the tests were run in triplicate and expressed as the mean and standard deviation (SD)). The K b constants calculated for APG, ADSAM, and ATSAM are in harmony for all techniques. As a result of the incorporation of dimethylsulfamate groups into the APG structure, in the ADSAM-dsDNA and ATSAM-dsDNA complexes, in addition to hydrogen bonds, π-sulfur interactions have also contributed to the stabilization of the ligand-DNA complexes. This work provides new insights that could lead to the development of prospective drugs and vaccines.

Dihydromyricetin reverses MRP2-induced multidrug resistance by preventing NF-κB-Nrf2 signaling in colorectal cancer cell

BACKGROUD

Dihydromyricetin (DMY), a natural flavonoid compound from the leaves of the Chinese medicinal herb Vitis heyneana, has been shown to have the potential to combat chemoresistance by inhibiting Nrf2/MRP2 signaling in colorectal cancer (CRC) cells. However, the precise underlying molecular mechanism and its therapeutic target are not well understood.

PURPOSE

Our study aims to investigate the effects of DMY on multidrug resistance (MDR), and elucidate the underlying mechanisms.

STUDY DESIGN

In vitro, HCT116/OXA and HCT8/VCR cells were employed as our MDR models. The cells were treated with DMY (50 µM) or MK-571 (50 µM) plus oxaliplatin (OXA) (10 µM) or vincristine (VCR) (10 µM) for 48 h. In vivo, we used BALB/c mice as a CRC xenograft mouse model. BALB/c mice were given DMY (100 mg/kg), OXA (5 mg/kg) and DMY (100 mg/kg) combined with OXA (5 mg/kg) via intraperitoneal route every 2 days per week for 4 weeks.

METHODS

We used MTT and colony forming assays to detect DMY's ability to reverse MDR. Flow cytometric analysis was used to detect apoptosis. Immunocytochemistry was used to detect the localization of Nrf2 and NF-κB/p65. Western blot, qRT-PCR and reporter gene assays were employed to measure the protein and gene transcriptional levels (MRP2, Nrf2, NF-κB/p65). Moreover, chromatin immunoprecipitation (ChIP) assay was used to investigate the endogenous promoter occupancy of NF-κB/p65. Finally, immunohistochemistry and TUNEL staining were used to detect protein expression and apoptosis in vivo.

RESULTS

DMY restored chemosensitivity (OXA and VCR) by inhibiting both MRP2 expression and its promoter activity in HCT116/OXA and HCT8/VCR cell lines. Furthermore, DMY could inhibit NF-κB/p65 expression, reducing NF-κB/p65 translocation to the nucleus to silence Nrf2 signaling, which is necessary for MRP2 expression. Overexpressing NF-κB/p65 expression reduced the reversal effect of DMY. In addition, NF-κB/p65 regulated Nrf2 expression by directly binding to its specific promoter region and activating its transcription. Finally, we proved that the combination of OXA and DMY has a synergistic tumor suppression effect in vivo.

CONCLUSION

Our study provided a novel mechanism of DMY boosted chemosensitivity in human CRC. The downstream signals of DMY, NF-κB or Nrf2 could also be potential targets for the treatment of CRC.

P. Cardoso D, U. Ferreira MJ. Overcoming Multidrug Resistance: Flavonoid and Terpenoid Nitrogen-Containing Derivatives as ABC Transporter Modulators

Multidrug resistance (MDR) in cancer is one of the main limitations for chemotherapy success. Numerous mechanisms are behind the MDR phenomenon wherein the overexpression of the ATP-binding cassette (ABC) transporter proteins P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance protein 1 (MRP1) is highlighted as a prime factor. Natural product-derived compounds are being addressed as promising ABC transporter modulators to tackle MDR. Flavonoids and terpenoids have been extensively explored in this field as mono or dual modulators of these efflux pumps. Nitrogen-bearing moieties on these scaffolds were proved to influence the modulation of ABC transporters efflux function. This review highlights the potential of semisynthetic nitrogen-containing flavonoid and terpenoid derivatives as candidates for the design of effective MDR reversers. A brief introduction concerning the major role of efflux pumps in multidrug resistance, the potential of natural product-derived compounds in MDR reversal, namely natural flavonoid and terpenoids, and the effect of the introduction of nitrogen-containing groups are provided. The main modifications that have been performed during last few years to generate flavonoid and terpenoid derivatives, bearing nitrogen moieties, such as aliphatic, aromatic and heterocycle amine, amide, and related functional groups, as well as their P-gp, MRP1 and BCRP inhibitory activities are reviewed and discussed.

Flavonoids as P-gp Inhibitors: A Systematic Review of SARs

P-glycoprotein, also known as ABCB1 in the ABC transporter family, confers the simultaneous resistance of metastatic cancer cells towards various anticancer drugs with different targets and diverse chemical structures. The exploration of safe and specific inhibitors of this pump has always been the pursuit of scientists for the past four decades. Naturally occurring flavonoids as benzopyrone derivatives were recognized as a class of nontoxic inhibitors of P-gp. The recent advent of synthetic flavonoid dimer FD18, as a potent P-gp modulator in reversing multidrug resistance both in vitro and in vivo, specifically targeted the pseudodimeric structure of the drug transporter and represented a new generation of inhibitors with high transporter binding affinity and low toxicity. This review concerned the recent updates on the structure-activity relationships of flavonoids as P-gp inhibitors, the molecular mechanisms of their action and their ability to overcome P-gp-mediated MDR in preclinical studies. It had crucial implications on the discovery of new drug candidates that modulated the efflux of ABC transporters and also provided some clues for the future development in this promising area.

Analogues of the Lignan Pinoresinol as Novel Lead Compounds for P-glycoprotein (P-gp) Inhibitors

To find novel P-gp-inhibitors, a library of pregnane X receptor (PXR) ligands and the ZINC DrugsNow library were superimposed on the P-gp inhibitor (+)-pinoresinol (1) used as a query for a three-dimensional similarity search. After determining the TanimotoCombo index of similarity with 1, eight compounds from the PXR library and two ZINC compounds were selected for biological evaluation. The P-gp inhibition study showed that compounds 7, 8, and 9 successfully increased intracellular doxorubicin (DOX) accumulation in the P-gp overexpressed Lucena 1 cells from 25, 12.5, and 6.25 μM, respectively. Among a series of analogues of 9, compounds 26-30 were shown to be active, with 26 and 27 causing a significant increase in DOX accumulation from 1.56 μM and rendering Lucena 1 sensitive to DOX from 1.56 and 0.78 μM, respectively. Molecular modeling studies showed that both compounds bind to the P-gp at transmembrane helices (TMH) 4, 5, and 6, with 27 also showing contacts with TMH 3.

Hesperetin-5,7,3'-O-triacetate suppresses airway hyperresponsiveness in ovalbumin-sensitized and challenged mice without reversing xylazine/ketamine-induced anesthesia in normal mice

Background

We recently reported that hesperetin-5,7,3’-O-triacetate (HTA) dually inhibited phosphodiesterase (PDE)3/4 with a therapeutic ratio of 20.8. The application and development of PDE4 inhibitors for treating asthma or COPD are limited by their side effects, such as nausea, vomiting and gastric hypersecretion. PDE4 inhibitors were reported to reverse xylazine/ketamine-induced anesthesia in rats and triggered vomiting in ferrets. Thus the reversing effect of HTA on xylazine/ketamine-induced anesthesia in mice was studied to assess emetic effect of HTA. The aim of this study was to prove the therapeutic effect of HTA without vomiting effect at an effective dose for treating COPD.

Methods

Ten female BALB/c mice in each group were sensitized by ovalbumin (OVA) on days 0 and 14. On day 21, these mice were emphasized the sensitization by Freund’s complete adjuvant. Mice were challenged by 1% OVA nebulization on days 28, 29, and 30. Airway hyperresponsiveness (AHR) was assessed on day 32 in each group, using the FlexiVent system to determine airway resistance (R_L) and lung dynamic compliance (C_dyn) in anesthetized ovalbumin (OVA)-sensitized and challenged mice. Each group was orally administered HTA (10 ~ 100 μmol/kg), roflumilast (1 and 5 mg/kg) or vehicles (controls) 2 h before and 6 and 24 h after OVA provocation. For comparison, sham-treated mice were challenged with saline instead of 1% OVA. The ability to reverse xylazine/ketamine-induced anesthesia by HTA or roflumilast for 3 h was determined in normal mice. We used roflumilast, a selective PDE4 inhibitor and bronchodilator for severe COPD approved by the US Food and Drug Administration, as a reference drug.

Results

In the results, HTA (100 μmol/kg, p.o.) or roflumilast (5 mg/kg, p.o.) significantly suppressed all R_L values of MCh at 0.78 ~ 25 mg/mL and enhanced C_dyn values of MCh at 3.125 ~ 25 mg/mL compared to OVA-sensitized and -challenged control mice. Orally administered 1, 3 or 10 mg/kg roflumilast, but not 30 or 100 μmol/kg HTA, significantly reversed xylazine/ketamine-induced anesthesia.

Conclusions

In contrast to roflumilast, HTA may ameliorate COPD but induce few side effects of nausea, vomiting and gastric hypersecretion at an effective dose for treating COPD, because HTA did not reverse xylazine/ketamine-induced anesthesia in mice.

Design, Synthesis, and Cytotoxic Evaluation of Certain 7-Chloro-4-(piperazin-1-yl)quinoline Derivatives as VEGFR-II Inhibitors

Signaling pathway inhibition of VEGFR-II is visualized as valuable tool in cancer management. In the current study, the synthesis of novel 1-4-(7-chloroquinolin-4-yl)piperazin-1-yl)-2-(N-substituted-amino)-ethanone derivatives (4a-t) was achieved through the amination of 2-chloro-1-(4-(7-chloroquinolin-4-yl)piperazin-1-yl)ethanone (3) with different secondary amines. The structures of the target compounds were confirmed by IR, ¹ H-NMR, ¹³ C-NMR, HRMS, and microanalysis. Compounds 4a-t were subjected to in vitro anticancer screening against human breast cancer (MCF-7) and prostate cancer (PC3) cell lines. The highest cytotoxicty against both cell lines was displayed by 2-(4-(4-bromobenzyl)piperazin-1-yl)-1-(4-(7-chloroquinolin-4-yl)piperazin-1-yl)ethanone (4q), with IC₅₀ values of 6.502 and 11.751 μM against MCF-7 and PC3 cells, respectively, compared with the standard drug doxorubicin (MCF-7: 6.774 μM, PC3: 7.7316 μM). Due to its notable activity toward MCF-7 cells, 4q was further evaluated as VEGFR-II inhibitor, showing an IC₅₀ of 1.38 μM compared to sorafenib (0.33 μM). The docking study proved that 4q has a binding mode akin to that of VEGFR-II inhibitors.

The Control of Auxin Transport in Parasitic and Symbiotic Root-Microbe Interactions

Most field-grown plants are surrounded by microbes, especially from the soil. Some of these, including bacteria, fungi and nematodes, specifically manipulate the growth and development of their plant hosts, primarily for the formation of structures housing the microbes in roots. These developmental processes require the correct localization of the phytohormone auxin, which is involved in the control of cell division, cell enlargement, organ development and defense, and is thus a likely target for microbes that infect and invade plants. Some microbes have the ability to directly synthesize auxin. Others produce specific signals that indirectly alter the accumulation of auxin in the plant by altering auxin transport. This review highlights root-microbe interactions in which auxin transport is known to be targeted by symbionts and parasites to manipulate the development of their host root system. We include case studies for parasitic root-nematode interactions, mycorrhizal symbioses as well as nitrogen fixing symbioses in actinorhizal and legume hosts. The mechanisms to achieve auxin transport control that have been studied in model organisms include the induction of plant flavonoids that indirectly alter auxin transport and the direct targeting of auxin transporters by nematode effectors. In most cases, detailed mechanisms of auxin transport control remain unknown.

Pd(OAc)2/SPPh3 accelerated activation of gem-dichloroalkenes for the construction of 3-arylchromones

The Pd-catalyzed regioselective intramolecular nucleophilic substitution of gem-dichloroalkene derivatives with salicylaldehydes leading to the synthesis of 3-arylchromones has been developed.

Methyl 3-hydroxyimino-11-oxoolean-12-en-28-oate (HIMOXOL), a synthetic oleanolic acid derivative, induces both apoptosis and autophagy in MDA-MB-231 breast cancer cells

HIMOXOL (methyl 3-hydroxyimino-11-oxoolean-12-en-28-oate) is a synthetic derivative of oleanolic acid (OA). HIMOXOL revealed the highest cytotoxic effect among tested synthetic OA analogs. In this study we focused on elucidating the cytotoxic mechanism of HIMOXOL in MDA-MB-231 breast cancer cells. HIMOXOL reduced MDA-MB-231 cell viability with an IC50 value of 21.08±0.24μM. In contrast to OA, the tested compound induced cell death by activating apoptosis and the autophagy pathways. More specifically, we found that HIMOXOL was able to activate the extrinsic apoptotic pathway, which was proven by observation of caspase-8, caspase-3 and PARP-1 protein activation in Western blot analysis. An increase in the ratio of Bax/Bcl-2 protein levels was also detected. Moreover, HIMOXOL triggered microtubule-associated protein LC3-II expression and upregulated beclin 1. This observed compound activity was modulated by mitogen-activated protein kinases and NFκB/p53 signaling pathways. Together, these data suggest that HIMOXOL, a synthetic oleanolic acid derivative which activates dual cell death machineries, could be a potential and novel chemotherapeutic agent.

Inhibitory effects of hesperetin derivatives on guinea pig phosphodiesterases and their ratios between high- and low-affinity rolipram binding

The phosphodiesterase (PDE)4 molecule exists as two distinct conformers, PDE4H and PDE4L , which have high and low affinities, respectively, for the selective PDE4 inhibitor, rolipram. The inhibition of PDE4H and PDE4L is associated with adverse responses, such as nausea, vomiting, and gastric hypersecretion, and with anti-inflammatory and bronchodilator effects, respectively. We determined the therapeutic (PDE4H/PDE4L) ratios of hesperetin-7-O-methylether, hesperetin-5,7,3'-O-trimethylether (HTME), hesperetin-7-O-acetate, hesperetin-7,3'-O-diacetate, hesperetin-5,7,3'-O-triacetate (HTA), hesperetin-5,7,3'-O-tripropionate, hesperetin-5,7,3'-O-tributyrate, hesperetin-5,7,3'-O-triisobutyrate, and hesperetin-5,7,3'-O-tripivatate, and compared these ratios to those of hesperetin, hesperetin-7,3'-O-dimethylether, hesperidin, and hesperidin-3'-O-methylether to identify derivatives with therapeutic ratios and to characterize the structure-activity relationships among these compounds. The activities of PDE isozymes 1 through 5 were measured using a two-step procedure using [(3)H]adenosine 3',5'-cyclic monophosphate or [(3)H]guanosine 3',5'-cyclic monophosphate as substrates. The inhibitory concentration (IC50) for 50% of PDE4 inhibition and effective concentration (EC50) for replacing 50% of [(3)H]rolipram binding on high-affinity rolipram-binding sites was taken as the PDE4L and PDE4H value, respectively. The HTME and the HTA dually inhibited PDE3 and PDE4, and displayed PDE4H/PDE4L ratios of 18.3 and 20.8, respectively, suggesting that they may be candidate drugs for treating asthma and chronic obstructive pulmonary disease (COPD) because the combined inhibition of PDE3 and PDE4 has synergistically anti-inflammatory and bronchodilator effects in COPD patients.

Differential inhibition of human colon cancer cells by structurally similar flavonoids of citrus

A number of studies in the recent years have evaluated the anti-proliferative activity of flavonoids. Although certain studies investigated the structure-activity based on the phenotypic assays, no study has correlated the flavonoids structure with the ability to alter gene/protein expression. Present study was focused to understand the structure-function relationship of citrus flavonoids in terms of their ability to alter the gene expression in the colon adenocarcinoma cells. Eight structurally related flavonoids found in citrus were evaluated for their ability to inhibit colon cancer (SW480) cells, as well as change the expression of apoptosis related genes/proteins. Apigenin and quercetagetin demonstrated most significant inhibition of cell proliferation with 63.6% and 45.7% inhibition of cell growth at 200μM after 48h of incubation, respectively. The cell death was also confirmed by images of fluorescently tagged cells. Furthermore, up-regulation of Bax/Bcl2 protein ratio as well as activation of Caspase3 at 200μM at 48h confirmed the induction of apoptosis by apigenin and quercetagetin. In addition, results suggest that the change in Bax/Bcl2 ratio by apigenin and quercetagetin seems to be due to their ability to alter the expression of bax and bcl2 transcription. Results of the currents study suggest that among the citrus flavonoids, double bond between C2 and C3 and hydroxyl group at C3, C6 are highly decisive for the proliferation inhibition and apoptosis induction ability. Taken together, these results demonstrate that among the major flavonoids of citrus, apigenin and quercetagetin have potent anti-cancer activity through inducing apoptosis in SW480 human colon cancer cells.

Seven things we think we know about auxin transport

Polar transport of the phytohormone auxin and the establishment of localized auxin maxima regulate embryonic development, stem cell maintenance, root and shoot architecture, and tropic growth responses. The past decade has been marked by dramatic progress in efforts to elucidate the complex mechanisms by which auxin transport regulates plant growth. As the understanding of auxin transport regulation has been increasingly elaborated, it has become clear that this process is involved in almost all plant growth and environmental responses in some way. However, we still lack information about some basic aspects of this fundamental regulatory mechanism. In this review, we present what we know (or what we think we know) and what we do not know about seven auxin-regulated processes. We discuss the role of auxin transport in gravitropism in primary and lateral roots, phototropism, shoot branching, leaf expansion, and venation. We also discuss the auxin reflux/fountain model at the root tip, flavonoid modulation of auxin transport processes, and outstanding aspects of post-translational regulation of auxin transporters. This discussion is not meant to be exhaustive, but highlights areas in which generally held assumptions require more substantive validation.

Wogonin potentiates the antitumor action of etoposide and ameliorates its adverse effects

Wogonin, a flavone in the roots of Scutellaria baicalensis, reduced etoposide-induced apoptotic cell death in normal cells, such as bone marrow cells and thymocytes. On the other hand, wogonin potentiated the proapoptotic or cytotoxic action of etoposide in tumor cells, such as Jurkat, HL-60, A549, and NCI-H226. These contradictory actions of wogonin on apoptosis are distinguished by normal or cancer cell types. Wogonin had no effect on apoptosis induced by other anticancer agents in the tumor cells. Thus, the potentiation effect of wogonin was observed only in etoposide-induced apoptosis in tumor cells. In a functional assay for P-glycoprotein (P-gp), wogonin suppressed excretion of calcein, a substrate for P-gp, in these tumor cells. Moreover, wogonin decreased the excretion of radiolabeled etoposide and accordingly increased intracellular content of this agent in the cells. P-gp inhibitors showed a similar potentiation effect on etoposide-induced apoptosis in these tumor cells. Thus, wogonin is likely to potentiate the anticancer action of etoposide due to P-gp inhibition and accumulation of this agent. These findings suggest that wogonin may be a useful chemotherapeutic adjuvant to potentiate the pharmacological action of etoposide and ameliorate its adverse effects.

Semisynthesis of natural flavones inhibiting tubulin polymerization, from hesperidin

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

CJY, an isoflavone, reverses P-glycoprotein-mediated multidrug-resistance in doxorubicin-resistant human myelogenous leukaemia (K562/DOX) cells

In an effort to develop safe and effective multidrug-resistance (MDR) reversing agents, the effect of CJY, an isoflavone, on the P-glycoprotein (P-gp) function and P-gp-mediated MDR was evaluated in doxorubicin-resistant human myelogenous leukaemia (K562/DOX) cells. The results showed that CJY caused a marked increase in accumulation and a notable decrease in efflux of rhodamine 123 (Rh123). The inhibitory effect of the agent on P-gp function persisted for at least 120 min after removal of 2.5 μM CJY from the incubation medium. The doxorubicin-induced cytotoxicity, apoptosis and cell cycle perturbations were significantly potentiated by CJY. The intracellular accumulation of doxorubicin was also enhanced. The compound exhibited potent effects in-vitro on the reversal of P-gp-mediated MDR, suggesting that it could become a candidate as an effective MDR reversing agent in cancer chemotherapy.

Plant polyphenols and multidrug resistance: Effects of dietary flavonoids on drug transporters in Caco-2 and MDCKII-MDR1 cell transport models

The hypothesis tested was that specific flavonoids such as epicatechin gallate, epigallocatechin gallate, genistein, genistin, naringenin, naringin, quercetin and xanthohumol will modulate cellular uptake and permeability (P(e)) of multidrug-resistant substrates, cyclosporin A (CSA) and digoxin, across Caco-2 and MDCKII-MDR1 cell transport models. (3)H-CSA/(3)H-digoxin transport and uptake experiments were performed with and without co-exposure of the flavonoids. Aglycone flavonoids reduced the P(e) of CSA to a greater extent than glycosylated flavonoids with 30 microM xanthohumol producing the greatest effect (7.2 x 10(-6) to 6.6 x 10(-7) and 17.9 x 10(-6) to 4.02 x 10(-6) cm s(-1) in Caco-2 and MDCKII-MDR1 cells, respectively); while no measurable effects were seen with digoxin. Xanthohumol significantly demonstrated (1) saturable efflux, (2) increased uptake of (3)H-digoxin and (3) decreased uptake of (3)H-CSA in the Caco-2 cells. The transport data suggests that xanthohumol effects transport of CSA in a manner that is distinct from the digoxin efflux pathway and suggests that intestinal transport of these MDR1 substrates is more complex than previously reported.

Cancer phytotherapeutics: role for flavonoids at the cellular level

Dietary foods and fruits possess an array of flavonoids with unique chemical structure and diverse bioactivities relevant to cancer. Numerous epidemiological studies have validated the inverse relation between the consumption of flavonoids and the risk of cancer. Flavonoids possess cancer blocking and suppressing effects. Flavonoids modulate various CYPs involved in carcinogen activation and scavenging reactive species formed from carcinogens by CYP-mediated reactions. They induce biosynthesis of several CYPs. They are involved in the regulation of enzymes of phase-II responsible for xenobiotic biotransformation and colon microflora. Since cytochromes P450, P-gp and phase-II enzymes are involved in the metabolism of drugs and in the processes of chemical carcinogenesis, interactions of flavonoids with these systems hold great promise for their therapeutic potential. The role of flavonoids also includes the inhibition of activation of pro-carcinogens, inhibition of proliferation of cancer cells, selective death of cancer cells by apoptosis, inhibition of metastasis and angiogenesis, activation of immune response against cancer cells, modulation of the inflammatory cascade and the modulation of drug resistance. This has greatly extended the goal of cancer therapy from eradicating the affected cells to control of the cancer phenotype. Phytotherapy is being used in combination with other therapies as phytonutrients have been shown to work by nutrient synergy.

Inhibitory effects of quercetin derivatives on phosphodiesterase isozymes and high-affinity [(3) H]-rolipram binding in guinea pig tissues

Rolipram has high (PDE4(H)) and low (PDE4(L)) affinities for phosphodiesterase (PDE)-4, respectively. In general, it is believed that inhibitions by PDE4(H) and PDE4(L) are respectively associated with an adverse response and with anti-inflammatory and bronchodilating effects. This has provided a rational basis for designing new compounds with high PDE4(H)/PDE4(L) ratios. In the present study, we attempted to determine the PDE4(H)/PDE4(L) ratios of quercetin (1), qercetin-3-O-methylether (3-MQ, 2), quercetin-3,7,4'-O-trimethylether (ayanin, 3), quercetin-3,7,3',4'-O- tetramethylether (QTME, 4), quercetin-3,5,7,3',4'-O-petamethylether (QPME, 5), quercetin-3,5,7,3',4'-O-pentaacetate (QPA, 6), and quercetin-3-O-methyl-5,7,3',4'-O-tetraacetate (QMTA, 7). The activities of PDE1 approximately 5, which were partially separated from homogenates of guinea pig lungs and hearts, were measured by a two-step procedure using adenosine 3',5'-cyclic monophosphate (cAMP) with [(3) H]-cAMP or guanosine 3',5'-cyclic monophosphate (cGMP) with [(3) H]-cGMP as substrates. The IC(50) values of all of these compounds except quercetin (1), 3-MQ (2), and QMTA (7) on PDE1 approximately 5 inhibition were determined. The anti-inflammatory effects of PDE4 inhibitors were reported to be associated with inhibition of PDE4 catalytic activity. Therefore, these IC(50) values for PDE4 inhibition were taken as the PDE4(L) values. The effective concentration (EC(50)), at which one half of the [(3) H]-rolipram bound to high-affinity rolipram binding sites (HARBSs) of brain cell membranes was replaced, was defined as the PDE4(H) value. In the present results, the PDE4(H)/PDE4(L) ratios of quercetin (1), ayanin (3), and QPME (5) were >30, >19, and 11, respectively (Table 1), which are higher than or equal to that of AWD12-281, the selective PDE4 inhibitor with the greatest potential currently undergoing clinical trials for treating asthma and chronic obstructive pulmonary disease.

Functionalized chalcones as selective inhibitors of P-glycoprotein and breast cancer resistance protein

A library of chalcones with basic functionalities were screened for inhibition of P-glycoprotein (Pgp, ABCB1) by the calcein-AM accumulation assay on MDCKII/MDR1 cells. Three members that had ring A substituted with 5-(1-ethylpiperidin-4-yl) and 2,4-dimethoxy groups were found to increase calcein-AM accumulation to a greater extent than verapamil, a Pgp inhibitor. These compounds were subsequently shown to enhance the uptake of doxorubicin by MCF-7 cells that over-expressed Pgp. However, when tested for inhibition of the breast cancer resistance protein (BCRP, ABCG2) by the mitoxantrone uptake assay, the same compounds fared poorly. In comparison, a non-basic chalcone (5-14, 3-(4-chlorophenyl)-1-(2,4-dimethoxyphenyl)prop-2-en-1-one) increased mitoxantrone uptake by BCRP over-expressing MCF-7 cells (MCF-7/MX) by more than 300% at 5 microM. Thus, introducing a basic group on the chalcone template enhanced Pgp inhibition at the expense of BCRP inhibition. The basic chalcones were also better Pgp inhibitors than their non-basic counterparts which may in turn be better BCRP inhibitors. Structure activity analysis showed that lipophilicity of the chalcones was not the overriding factor for Pgp inhibitory activity. Rather, good activity was associated with appropriately placed electron donor atoms, of which the meta-disubstituted dimethoxy motif on either ring A or B was of particular relevance. In spite of differing structural requirements for inhibition of Pgp and BCRP, chalcone 3-100 [3-(2,4-dimethoxyphenyl)-1-(4-(piperazin-1-yl)phenyl)prop-2-en-1-one] inhibited both Pgp and BCRP to a reasonable extent and may be a useful starting point for the design of dual inhibitors.

Separating the roles of acropetal and basipetal auxin transport on gravitropism with mutations in two Arabidopsis multidrug resistance-like ABC transporter genes

Two Arabidopsis thaliana ABC transporter genes linked to auxin transport by various previous results were studied in a reverse-genetic fashion. Mutations in Multidrug Resistance-Like1 (MDR1) reduced acropetal auxin transport in roots by 80% without affecting basipetal transport. Conversely, mutations in MDR4 blocked 50% of basipetal transport without affecting acropetal transport. Developmental and auxin distribution phenotypes associated with these altered auxin flows were studied with a high-resolution morphometric system and confocal microscopy, respectively. Vertically grown mdr1 roots produced positive and negative curvatures threefold greater than the wild type, possibly due to abnormal auxin distribution observed in the elongation zone. However, upon 90 degrees reorientation, mdr1 gravitropism was inseparable from the wild type. Thus, acropetal auxin transport maintains straight growth but contributes surprisingly little to gravitropism. Conversely, vertically maintained mdr4 roots grew as straight as the wild type, but their gravitropism was enhanced. Upon reorientation, curvature in this mutant developed faster, was distributed more basally, and produced a greater total angle than the wild type. An amplified auxin asymmetry may explain the mdr4 hypertropism. Double mutant analysis indicated that the two auxin transport streams are more independent than interdependent. The hypothesis that flavanols regulate MDR-dependent auxin transport was supported by the epistatic relationship of mdr4 to the tt4 phenylpropanoid pathway mutation.

Effects of Various Methoxyflavones on Vincristine Uptake and Multidrug Resistance to Vincristine in P-gp-Overexpressing K562/ADM Cells

PURPOSE

Some methoxyflavones (MFs) are known to inhibit the function of P-glycoprotein. The aim of this study is to characterize the reversal of multidrug resistance (MDR) by MFs.

METHODS

The effects of 19 MFs, including 3,5,6,7,8,3',4'-heptamethoxyflavone, nobiletin, and tangeretin, and flavone on the uptake of [3H]vincristine into an adriamycin-resistant variant of human chronic myelogenous leukemia (K562/ADM) cells were investigated. Potentiation of vincristine-induced growth inhibition by these MFs was also tested in K562/ADM cells by means of WST-1 [2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium] assay.

RESULTS

All MFs (20 microM) tested increased the uptake of [3H]vincristine. 3,5,6,7,8,3',4'-heptamethoxyflavone, nobiletin, tangeretin, quercetagetin and quercetin pentamethylether showed especially potent effects. The increase in the uptake of [3H]vincristine was proportional to the number of methoxyl moieties. While substitution with a methoxyl moiety at the C3 position was the most influential, methoxyl substitution at both the C3' and C5' positions resulted in a decrease in the potentiation of uptake. Furthermore, there was a significant correlation between the potencies for increasing [3H]vincristine uptake and for growth inhibition assessed by WST-1 assay.

CONCLUSIONS

MFs increased the uptake of [3H]vincristine into MDR cells and exhibited MDR-reversing effects. Their potencies were influenced by the number and positions of the methoxyl moieties.

Synthesis and antimalarial evaluation of a series of piperazinyl flavones

A series of 27 flavonoid derivatives containing a piperazinyl chain have been synthesized and tested for their antiplasmodial activity. Diverse substitution patterns on piperazinyl and flavone moieties were examined and found to affect the activity differently. The most active compounds, which have a 2,3,4-trimethoxybenzylpiperazinyl chain attached to the flavone at the 7-phenol group, showed in vitro activity against chloroquine-sensitive (Thai) and -resistant (FcB1,K1) Plasmodium falciparum strains in the micromolar to submicromolar range. One of them was active when given orally in a Plasmodium yoelii nigeriensis infected mouse model.

Structure-activity studies on the protection of Trimetazidine derivatives modified with nitroxides and their precursors from myocardial ischemia-reperfusion injury

Trimetazidine, the known anti-anginal and anti-ischemic drug, was modified by pyrroline and tetrahydropyridine nitroxides and their hydroxylamine and sterically hindered secondary amine precursors. The synthesized new compounds proved to be better superoxide scavenger molecules compared to the parent Trimetazidine in an in vitro experiment. This reactive oxygen species (ROS) scavenging activity was further supported by ischemia/reperfusion (I/R) studies on Langendorff-perfused rat hearts pretreated with Trimetazidine and with the modified Trimetazidine derivatives before ischemia. Two of the investigated compounds, containing 2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrole and 4-phenyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrole substituents on the piperazine ring, provided significant protection from the cardiac dysfunction caused by I/R. The protective effect could be attributed to the combined anti-ischemic and antioxidant effects.

New derivatives of silybin and 2,3-dehydrosilybin and their cytotoxic and P-glycoprotein modulatory activity

Large series of O-alkyl derivatives (methyl and benzyl) of silybin and 2,3-dehydrosilybin was prepared. Selective alkylation of the silybin molecule was systematically investigated. For the first time we present here, for example, preparation of 19-nor-2,3-dehydrosilybin. All prepared silybin/2,3-dehydrosilybin derivatives were tested for cytotoxicity on a panel of drugs sensitive against multidrug resistant cell lines and the ability to inhibit P-glycoprotein mediated efflux activity. We have identified effective and relatively non-cytotoxic inhibitors of P-gp derived from 2,3-dehydrosilybin. Some of them were more effective inhibitors at concentrations lower than a standard P-gp efflux inhibitor cyclosporin A. Another group of 2,3-dehydrosilybin derivatives also had better inhibitory effects on P-gp efflux but a cytotoxicity comparable with that of parent 2,3-dehydrosilybin. Structural requirements for improving inhibitory activity and reducing toxicity of 2,3-dehydrosilybin were established. Effect of E-ring substitution as well as an influence of the substituent size at the C-7-OH position of A-ring on P-gp-inhibitory activity was evaluated for the first time in this study.

Cellular efflux of auxin catalyzed by the Arabidopsis MDR/PGP transporter AtPGP1

Directional transport of the phytohormone auxin is required for the establishment and maintenance of plant polarity, but the underlying molecular mechanisms have not been fully elucidated. Plant homologs of human multiple drug resistance/P-glycoproteins (MDR/PGPs) have been implicated in auxin transport, as defects in MDR1 (AtPGP19) and AtPGP1 result in reductions of growth and auxin transport in Arabidopsis (atpgp1, atpgp19), maize (brachytic2) and sorghum (dwarf3). Here we examine the localization, activity, substrate specificity and inhibitor sensitivity of AtPGP1. AtPGP1 exhibits non-polar plasma membrane localization at the shoot and root apices, as well as polar localization above the root apex. Protoplasts from Arabidopsis pgp1 leaf mesophyll cells exhibit reduced efflux of natural and synthetic auxins with reduced sensitivity to auxin efflux inhibitors. Expression of AtPGP1 in yeast and in the standard mammalian expression system used to analyze human MDR-type proteins results in enhanced efflux of indole-3-acetic acid (IAA) and the synthetic auxin 1-naphthalene acetic acid (1-NAA), but not the inactive auxin 2-NAA. AtPGP1-mediated efflux is sensitive to auxin efflux and ABC transporter inhibitors. As is seen in planta, AtPGP1 also appears to mediate some efflux of IAA oxidative breakdown products associated with apical sites of high auxin accumulation. However, unlike what is seen in planta, some additional transport of the benzoic acid is observed in yeast and mammalian cells expressing AtPGP1, suggesting that other factors present in plant tissues confer enhanced auxin specificity to PGP-mediated transport.