Dietary regulation of P-gp function and expression

Synthesis and evaluation of WK-X-34 derivatives as P-glycoprotein (P-gp/ABCB1) inhibitors for reversing multidrug resistance

The emergence of multidrug resistance (MDR) in malignant tumors is one of the leading threats encountered currently by many chemotherapeutic agents. A proposed strategy to overcome MDR is to disable the efflux function of P-glycoprotein (P-gp/ABCB1), a critical member of the ABC transporter family that significantly increases the efflux of various anticancer drugs from tumor cells. In this study, structural modification of a third-generation P-gp inhibitor WK-X-34 based on bioisosteric and fragment-growing strategies led to the discovery of the adamantane derivative PID-9, which exhibited the best MDR reversal activity (IC50 = 0.1338 μM, RF = 78.6) in this series, exceeding those of the reported P-gp inhibitors verapamil and WK-X-34. In addition, compared with WK-X-34, PID-9 showed decreased toxicity to cells. Furthermore, the mechanism studies revealed that the reversal activity of adamantane derivatives PID-5, PID-7, and PID-9 stemmed from the inhibition of P-gp efflux. These results indicated that compound PID-9 is the most effective P-gp inhibitor among them with low toxicity and high MDR reversal activity, which provided a fundamental structural reference for further discovery of novel, effective, and non-toxic P-gp inhibitors.

Cardiac PET Imaging of ATP Binding Cassette (ABC) Transporters: Opportunities and Challenges

Adenosine triphosphate binding cassette (ABC) transporters are a broad family of membrane protein complexes that use energy to transport molecules across cells and/or intracellular organelle lipid membranes. Many drugs used to treat cardiac diseases have an affinity for these transporters. Among others, P-glycoprotein (P-gp) plays an essential role in regulating drug concentrations that reach cardiac tissue and therefore contribute to cardiotoxicity. As a molecular imaging modality, positron emission tomography (PET) has emerged as a viable technique to investigate the function of P-gp in organs and tissues. Using PET imaging to evaluate cardiac P-gp function provides new insights for drug development and improves the precise use of medications. Nevertheless, information in this field is limited. In this review, we aim to examine the current applications of ABC transporter PET imaging and its tracers in the heart, with a specific emphasis on P-gp. Furthermore, the opportunities and challenges in this novel field will be discussed.

Essential role of P-glycoprotein in the mechanism of action of oliceridine

Mu opioid receptor (MOR) agonists comprise the most effective analgesics, but their therapeutic utility is limited by adverse effects. One approach for limiting such effects has been to develop "biased" MOR agonists that show preference for activating G protein over β-Arrestin signaling. However, the notion of biased agonism has been challenged by recent studies. Oliceridine (Olinvyk®, TRV-130, OLC) is a selective MOR agonist approved by the FDA in 2020 for pain management in controlled clinical settings. Oliceridine purportedly demonstrates diminished adverse effects compared to morphine or other MOR agonists, a profile attributed to its biased agonism. However, recent studies suggest that oliceridine does not display biased agonism but instead weak intrinsic efficacy for G protein and β-Arrestin activation. Nevertheless, these insights have been derived from in vitro studies. To better understand oliceridine's in vivo efficacy profile, we performed a comprehensive assessment of its in vitro and in vivo pharmacology using both cultured cells and rodents. In vitro, oliceridine displayed high MOR affinity and weak intrinsic efficacy. In vivo, oliceridine showed impaired brain penetrance and rapid clearance, effects we attributed to its interaction with the P-glycoprotein (P-gp) efflux transporter. Moreover, we found that P-gp was essential for oliceridine's in vivo efficacy and adverse effect profiles. Taken together with prior studies, our results suggest that oliceridine's in vivo efficacy and adverse effect profiles are not attributed solely to its weak intrinsic efficacy or biased agonism but, to a large extent, its interaction with P-gp as well.

Fluorescence-based methods for studying activity and drug-drug interactions of hepatic solute carrier and ATP binding cassette proteins involved in ADME-Tox

In humans, approximately 70% of drugs are eliminated through the liver. This process is governed by the concerted action of membrane transporters and metabolic enzymes. Transporters mediating hepatocellular uptake of drugs belong to the SLC (Solute carrier) superfamily of transporters. Drug efflux either toward the portal vein or into the bile is mainly mediated by active transporters of the ABC (ATP Binding Cassette) family. Alteration in the function and/or expression of liver transporters due to mutations, disease conditions, or co-administration of drugs or food components can result in altered pharmacokinetics. On the other hand, drugs or food components interacting with liver transporters may also interfere with liver function (e.g., bile acid homeostasis) and may even cause liver toxicity. Accordingly, certain transporters of the liver should be investigated already at an early stage of drug development. Most frequently radioactive probes are applied in these drug-transporter interaction tests. However, fluorescent probes are cost-effective and sensitive alternatives to radioligands, and are gaining wider application in drug-transporter interaction tests. In our review, we summarize our current understanding about hepatocyte ABC and SLC transporters affected by drug interactions. We provide an update of the available fluorescent and fluorogenic/activable probes applicable in in vitro or in vivo testing of these ABC and SLC transporters, including near-infrared transporter probes especially suitable for in vivo imaging. Furthermore, our review gives a comprehensive overview of the available fluorescence-based methods, not directly relying on the transport of the probe, suitable for the investigation of hepatic ABC or SLC-type drug transporters.

The Effects of Jabara Juice on the Intestinal Permeation of Fexofenadine

Jabara juice and its component narirutin inhibit the activity of organic anion-transporting polypeptides (OATPs) 1A2 and OATP2B1, which are considered to play significant roles in the intestinal absorption of fexofenadine. In this study, we investigated the effects of jabara juice on the intestinal absorption of fexofenadine in mice and the inhibitory effects of jabara juice and narirutin on the permeation of fexofenadine using Caco-2 cell monolayers and LLC-GA5-COL300 cell monolayers. In the in vivo study, the area under the plasma concentration-time curve (AUC) of fexofenadine in mice was increased 1.8-fold by jabara juice. In the permeation study, 5% jabara juice significantly decreased the efflux ratio (ER) of fexofenadine for Caco-2 monolayers. Furthermore, the ERs of fexofenadine and digoxin, which is a typical substrate of P-glycoprotein (P-gp), for LLC-GA5-COL300 cell monolayers were decreased in a concentration-dependent manner by jabara juice extract, suggesting that jabara juice may increase the intestinal absorption of fexofenadine by inhibiting P-gp, rather than by narirutin inhibiting OATPs. The present study showed that jabara juice increases the intestinal absorption of fexofenadine both in vivo and in vitro. The intestinal absorption of fexofenadine may be altered by the co-administration of jabara juice in the clinical setting.

The Challenge and Importance of Integrating Drug-Nutrient-Genome Interactions in Personalized Cardiovascular Healthcare

Despite the rich armamentarium of available drugs against different forms of cardiovascular disease (CVD), major challenges persist in their safe and effective use. These include high rates of adverse drug reactions, increased heterogeneity in patient responses, suboptimal drug efficacy, and in some cases limited compliance. Dietary elements (including food, beverages, and supplements) can modulate drug absorption, distribution, metabolism, excretion, and action, with significant implications for drug efficacy and safety. Genetic variation can further modulate the response to diet, to a drug, and to the interaction of the two. These interactions represent a largely unexplored territory that holds considerable promise in the field of personalized medicine in CVD. Herein, we highlight examples of clinically relevant drug–nutrient–genome interactions, map the challenges faced to date, and discuss their future perspectives in personalized cardiovascular healthcare in light of the rapid technological advances.

Interaction of Phytocompounds of Echinacea purpurea with ABCB1 and ABCG2 Efflux Transporters

Preparations of Echinacea purpurea (E. purpurea) are widely used for the management of upper respiratory infections, influenza, and common cold, often in combination with other conventional drugs. However, the potential of phytochemical constituents of E. purpurea to cause herb-drug interactions via ABCB1 and ABCG2 efflux transporters remains elusive. The purpose of this study was to investigate the impact of E. purpurea-derived caffeic acid derivatives (cichoric acid and echinacoside) and tetraenes on the mRNA and protein expression levels as well as on transport activity of ABCB1 and ABCG2 in intestinal (Caco-2) and liver (HepG2) cell line models. The safety of these compounds was investigated by estimating EC₂₀ values of cell viability assays in both cell lines. Regulation of ABCB1 and ABCG2 protein in these cell lines were analyzed after 24 h exposure to the compounds at 1, 10, and 50 μg/mL. Bidirectional transport of 0.5 μg/mL Hoechst 33342 and 5 μM rhodamine across Caco-2 monolayer and profiling for intracellular concentrations of the fluorophores in both cell lines were conducted to ascertain inhibition effects of the compounds. Cichoric acid showed no cytotoxic effect, while the EC₂₀ values of tetraenes and echinacoside were 45.0 ± 3.0 and 52.0 ± 4.0 μg/mL in Caco-2 cells and 28.0 ± 4.3 and 62.0 ± 9.9 μg/mL in HepG2 cells, respectively. In general, the compounds showed heterogeneous induction of ABCB1 with the strongest 3.6 ± 1.2-fold increase observed for 10 μg/mL tetraenes in Caco-2 cells (p < 0.001). However, the compounds did not induce ABCG2. None of the phytocompounds inhibited significantly net flux of the fluorophores across Caco-2 monolayers. Overall, tetraenes moderately induced ABCB1 but not ABCG2 in Caco-2 and HepG2 cells while no compound significantly inhibited activity of these transporters at clinically relevant concentration to cause herb-drug interactions.

Piperine: Old Spice and New Nutraceutical?

BACKGROUND

Many of the activities associated with pepper fruits have been attributed to piperine, the most active compound present in these spices.

OBJECTIVE

This paper aims to provide an overview of the known properties of piperine, i.e. piperine's chemistry, its physiological activity, documented interactions as a bioenhancer and reported data concerning its toxicity, antioxidant properties and anticancer activity.

DISCUSSION

It is known that piperine possesses several properties. In its interaction with other drugs, it can act as a bioavailability enhancer; this effect is also manifested in combination with other nutraceuticals, e.g. with curcumin, i.e. piperine can modify curcumin's antioxidant, anti-inflammatory, antimicrobial and anticancer effects. Piperine displays significant immunomodulating, antioxidant, chemopreventive and anticancer activity; these effects have been shown to be dose-dependent and tissue-specific. However, the main limitation associated with piperine seems to be its low bioavailability, a disadvantage that innovative formulations are overcoming.

CONCLUSION

It is predicted that an increasing number of studies will focus on piperine, especially those directed towards unraveling its properties at molecular level. The current knowledge about the action of piperine will form a foundation for ways to improve piperine's bioavailability e.g. exploitation of different carrier systems. The therapeutical applications of this compound will be clarified, and piperine will be recognized as an important nutraceutical.

The Application of Nanotechnology in the Codelivery of Active Constituents of Plants and Chemotherapeutics for Overcoming Physiological Barriers during Antitumor Treatment

Antitumor therapy using a combination of drugs has shown increased clinical efficacy. Active constituents derived from plants can offer several advantages, such as high efficiacy, low toxicity, extensive effects, and multiple targets. At present, the combination of plants' active constituents and chemotherapeutic drugs has attracted increased attention. Nanodrug delivery systems (NDDSs) have been widely used in tumor-targeted therapy because of their efficacy of delivering antitumor drugs. The in vivo process of tumor-targeted NDDSs has several steps. They include blood circulation, tumor accumulation and penetration, target cell internalization and uptake, and drug release and drug response. In each step, NDDSs encounter multiple barriers that prevent their effective delivery to target sites. Studies have been performed to find alternative strategies to overcome these barriers. We reviewed the recent progress of codelivery of active constituents of plants and chemotherapeutics using NDDSs. Progress into transversing the physiological barriers for more effective in vivo antitumor delivery will be discussed in this review.

Using Caffeine and Free Amino Acids To Enhance the Transepithelial Transport of Catechins in Caco-2 Cells

Catechins are well-known to possess health-promoting functions. The interaction of the catechins with other components in tea could alter their absorption and efflux. This study investigated whether the absorption of catechins is affected by caffeine and amino acids using the Caco-2 monolayer cell model. We found that (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), and (-)-epicatechin (EC) were all actively effluxed. Co-transportation of EGCG, ECG, or EC with caffeine, theanine, serine, or glycine increased their apparent permeability coefficient [ P_app(AP-BL)] value by 3.42-5.40- fold, 1.19-5.75-fold, and 1.55-8.01-fold, respectively. Meanwhile, their efflux ratio values were significantly decreased. Moreover, the expression of multi-drug resistance protein 2 (MRP2) after 3 h of incubation with either 50 μM EGCG or 50 μM EC was elevated by 1.58- and 2.98-fold, respectively, while 50 μM ECG had no significantly effects. In addition, the expression of P-glycoprotein (P-gp) after treatment with either 50 μM EGCG, 50 μM ECG, or 50 μM EC was enhanced by 1.53-, 1.63-, and 1.80-fold, respectively. The addition of either caffeine or any one of the three amino acids decreased the expression of both MRP2 and P-gp induced by EGCG, and the expression of P-gp induced by ECG or EC also decreased. In contrast, only glycine decreased the expression of MRP2 induced by EC. Taken together, our data indicated that caffeine and theanine, glycine, or serine in tea might increase the absorption of catechins by the selectively suppressed expression of the efflux transporters induced by catechins.

An update on polyphenol disposition via coupled metabolic pathways

INTRODUCTION

Polyphenols, which are widely distributed in plants and the human diets, are known to have numerous biological activities. However, the low bioavailability of polyphenols is mediated by coupled metabolic pathways. Areas covered: The key role of the interplay between drug metabolic enzymes (DMEs) and efflux transporters (ETs), nuclear receptors (NRs), and intestinal microflora in the disposition of polyphenols is summarized. Expert opinion: ETs are shown to act as a 'revolving door', facilitating and/or controlling cellular polyphenol glucuronide/sulfate excretion. Elucidating the mechanisms underlying the glucuronidation/sulfation-transport interplay and structure-activity relationships (SAR) of glucuronide/sulfate efflux by an ET is important. Some new physiologically based pharmacokinetic (PBPK) models could be developed to predict the interplay between glucuronides/sulfates and ETs. Additionally, the combined actions of uridine-5'-diphosphate glucuronosyltransferases, ETs, and intestinal microflora/enterocyte-derived β-glucuronidase enable triple recycling (local, enteric, and enterohepatic recycling), thereby increasing the residence time of polyphenols and their glucuronides in the local intestine and liver. Further studies are necessary to explore these recycling mechanisms and interactions between polyphenols and the intestinal microbiota. Since NRs govern the inducible expression of target genes that encode DMEs and ETs. Determination of the regulation mechanism mediated by NRs using transgenic and knockout animals is still needed.

Application of alkaloids in reversing multidrug resistance in human cancers

Multidrug resistance (MDR) in human cancer is one of greatest challenges in cancer therapy. Natural products, especially the alkaloids, exert reversed effects on MDR with low toxicity, by interacting with various targets. In this review article, we summarize the recent progress made in the research of the main alkaloids, including classification, function, mechanism, research status, and application in reversing MDR.

The effects of dietary and herbal phytochemicals on drug transporters

Membrane transporter proteins (the ABC transporters and SLC transporters) play pivotal roles in drug absorption and disposition, and thus determine their efficacy and safety. Accumulating evidence suggests that the expression and activity of these transporters may be modulated by various phytochemicals (PCs) found in diets rich in plants and herbs. PC absorption and disposition are also subject to the function of membrane transporter and drug metabolizing enzymes. PC-drug interactions may involve multiple major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity. This review summarizes the reported in vitro and in vivo interactions between common dietary PCs and the major drug transporters. The oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs and PCs are considered, along with their possible interactions with the ABC and SLC transporters which influence these processes.

Mechanisms of drug resistance in colon cancer and its therapeutic strategies

Drug resistance develops in nearly all patients with colon cancer, leading to a decrease in the therapeutic efficacies of anticancer agents. This review provides an up-to-date summary on over-expression of ATP-binding cassette (ABC) transporters and evasion of apoptosis, two representatives of transport-based and non-transport-based mechanisms of drug resistance, as well as their therapeutic strategies. Different ABC transporters were found to be up-regulated in colon cancer, which can facilitate the efflux of anticancer drugs out of cancer cells and decrease their therapeutic effects. Inhibition of ABC transporters by suppressing their protein expressions or co-administration of modulators has been proven as an effective approach to sensitize drug-resistant cancer cells to anticancer drugs in vitro. On the other hand, evasion of apoptosis observed in drug-resistant cancers also results in drug resistance to anticancer agents, especially to apoptosis inducers. Restoration of apoptotic signals by BH3 mimetics or epidermal growth factor receptor inhibitors and inhibition of cancer cell growth by alternative cell death pathways, such as autophagy, are effective means to treat such resistant cancer types. Given that the drug resistance mechanisms are different among colon cancer patients and may change even in a single patient at different stages, personalized and specific combination therapy is proposed to be more effective and safer for the reversal of drug resistance in clinics.

Mechanisms of drug resistance in colon cancer and its therapeutic strategies

Drug resistance develops in nearly all patients with colon cancer, leading to a decrease in the therapeutic efficacies of anticancer agents. This review provides an up-to-date summary on over-expression of ATP-binding cassette (ABC) transporters and evasion of apoptosis, two representatives of transport-based and non-transport-based mechanisms of drug resistance, as well as their therapeutic strategies. Different ABC transporters were found to be up-regulated in colon cancer, which can facilitate the efflux of anticancer drugs out of cancer cells and decrease their therapeutic effects. Inhibition of ABC transporters by suppressing their protein expressions or co-administration of modulators has been proven as an effective approach to sensitize drug-resistant cancer cells to anticancer drugs in vitro. On the other hand, evasion of apoptosis observed in drug-resistant cancers also results in drug resistance to anticancer agents, especially to apoptosis inducers. Restoration of apoptotic signals by BH3 mimetics or epidermal growth factor receptor inhibitors and inhibition of cancer cell growth by alternative cell death pathways, such as autophagy, are effective means to treat such resistant cancer types. Given that the drug resistance mechanisms are different among colon cancer patients and may change even in a single patient at different stages, personalized and specific combination therapy is proposed to be more effective and safer for the reversal of drug resistance in clinics.

Enhancing Activity of Anticancer Drugs in Multidrug Resistant Tumors by Modulating P-Glycoprotein through Dietary Nutraceuticals

Multidrug resistance is a principal mechanism by which tumors become resistant to structurally and functionally unrelated anticancer drugs. Resistance to chemotherapy has been correlated with overexpression of p-glycoprotein (p-gp), a member of the ATP-binding cassette (ABC) superfamily of membrane transporters. P-gp mediates resistance to a broad-spectrum of anticancer drugs including doxorubicin, taxol, and vinca alkaloids by actively expelling the drugs from cells. Use of specific inhibitors/blocker of p-gp in combination with clinically important anticancer drugs has emerged as a new paradigm for overcoming multidrug resistance. The aim of this paper is to review p-gp regulation by dietary nutraceuticals and to correlate this dietary nutraceutical induced-modulation of p-gp with activity of anticancer drugs.

The phytoestrogen genistein enhances multidrug resistance in breast cancer cell lines by translational regulation of ABC transporters

Breast cancer is the most frequent malignancy in women. Multidrug resistance due to overexpression of ABC drug transporters is a common cause of chemotherapy failure and disease recurrence. Genistein (GNT) is a phytoestrogen present in soybeans and hormone supplements. We investigated the effect of GNT on the expression and function of ABC transporters in MCF-7 and MDA-MB-231 breast cancer cell lines. Results demonstrated an induction at the protein level of ABCC1 and ABCG2 and of ABCC1 in MCF-7 and MDA-MB-231, respectively. MCF-7 cells showed a concomitant increase in doxorubicin and mitoxantrone efflux and resistance, dependent on ABCG2 activity. ABCC1 induction by GNT in MDA-MB-231 cells modified neither drug efflux nor chemoresistance due to simultaneous acute inhibition of the transporter activity by GNT. All inductions took place at the translational level, as no increment in mRNA was observed and protein increase was prevented by cycloheximide. miR-181a, already demonstrated to inhibit ABCG2 translation, was down-regulated by GNT, explaining translational induction. Effects were independent of classical estrogen receptors. Results suggest potential nutrient-drug interactions that could threaten chemotherapy efficacy, especially in ABCG2-expressing tumors treated with substrates of this transporter.

Association of ABCB1 polymorphisms with prognostic outcomes of anthracycline and cytarabine in Chinese patients with acute myeloid leukemia

PURPOSE

To investigate the influence of ABCB1 polymorphisms on prognostic outcomes in Chinese patients with de novo intermediate-risk acute myeloid leukemia (AML) and to examine the gene expression level in relation to the genetic variation.

METHODS

In total, 263 Chinese intermediate-risk AML patients treated with anthracycline and cytarabine were enrolled. G2677T, C1236T, and C3435T of the ABCB1 gene were analyzed by the allele-specific matrix-assisted laser desorption. Expression of ABCB1 messenger RNA (mRNA) was tested in 101 patients of known genotype and haplotype for ABCB1 polymorphisms. Basic clinical characteristics of these patients were collected from medical records.

RESULTS

Survival analysis showed that patients with AML (TTT haplotype) had a longer overall survival (OS) (p < 0.001, 29.2 months, 95 % confidence interval [CI], 26.9-31.5 months) and relapse-free survival (RFS) (p = 0.005, 21.8 months, 95 % CI, 19.5-24.0 months) compared with those without TTT haplotype (21.9 months, 95 % CI, 19.6-24.2 months; 16.5 months, 95 % CI, 14.6-18.5 months). After adjusting for age; gender; leukocyte count; hemoglobin level; platelet levels; French, American, and British classification; lactate dehydrogenase levels; Eastern Cooperative Oncology Group performance status; nucleophosmin gene; and fms-related tyrosine kinase 3 gene, the multivariate survival analysis showed that the TTT haplotype appeared to be a predicting factor for OS (p = 0.001, hazard ratio = 1.854, 95 % CI, 1.301-2.641) and RFS (p = 0.009, hazard ratio = 1.755, 95 % CI, 1.153-2.671). Moreover, a significant association between the TTT haplotype and relapse in AML patients was observed in this study (p = 0.002, odds ratio = 0.410, 95 % CI, 0.235-0.715). Gene expression level was significantly lower in patients with the TTT haplotype than in the patients with the other haplotypes (p = 0.004).

CONCLUSIONS

The findings suggested the TTT haplotype was possibly related to the OS, RFS, and relapse in Chinese patients with AML.

ABCB11 and ABCB1 gene polymorphisms impact on telaprevir pharmacokinetic at one month of therapy

In 2011 direct-acting antivirals, including telaprevir, have been developed to achieve a better antiviral effect. It was reported that telaprevir is a substrate of P-glycoprotein (ABCB1) and cytochrome P450 3A4. The aim of this retrospective study was the evaluation of the influence of some single nucleotide polymorphisms (SNPs) of genes (ABCB1, SLC28A2/3, SLC29A1) involved in TLV and RBV transport and their correlation with plasma TLV drug exposure at 1 month of therapy. We also investigated the association of a SNP in ABCB11 gene, whose role in TLV transport was not yet shown. Twenty-nine HCV-1 patients treated with telaprevir, ribavirin and pegylated-interferon-α were retrospectively analyzed; allelic discrimination was performed by real-time PCR. Telaprevir Ctrough levels were influenced by Metavir score (P=0.023), ABCB1 2677 G>T (P=0.006), ABCB1 1236 C>T (P=0.015) and ABCB11 1131 T>C (P=0.033) SNPs. Regarding ABCB1 3435 C>T, a not statistically significant trend in telaprevir plasma concentration was observed. Metavir score (P=0.002, OR -336; 95% CI -535;-138), ABCB1 2677 (P=0.020, OR 497; 95% CI 86; 910), ABCB11 1131 (P=0.002, OR 641; 95% CI 259;1023) and CNT2 -146 (P=0.006, OR -426; 95% CI -721;-132) were able to predict telaprevir plasma levels in the regression analysis. Other SNPs showed no association. This study reveals BSEP implication in telaprevir transport and confirms the involvement and influence of P-glycoprotein on telaprevir plasma levels. To date, no similar data concerning pharmacogenetics and pharmacokinetics were published, but further studies in different and bigger cohorts are needed.

Reversal of P-glycoprotein (P-gp) mediated multidrug resistance in colon cancer cells by cryptotanshinone and dihydrotanshinone of Salvia miltiorrhiza

OBJECTIVE

Multidrug resistance (MDR) of cancer cells to a broad spectrum of anticancer drugs is an obstacle to successful chemotherapy. Overexpression of P-glycoprotein (P-gp), an ATP-binding cassette (ABC) membrane transporter, can mediate the efflux of cytotoxic drugs out of cancer cells, leading to MDR and chemotherapy failure. Thus, development of safe and effective P-gp inhibitors plays an important role in circumvention of MDR. This study investigated the reversal of P-gp mediated multidrug resistance in colon cancer cells by five tanshinones including tanshinone I, tanshinone IIA, cryptotanshinone, dihydrotanshinone and miltirone isolated from Salvia miltiorrhiza (Danshen), known to be safe in traditional Chinese medicine.

METHODS

The inhibitory effects of tanshinones on P-gp function were compared using digoxin bi-directional transport assay in Caco-2 cells. The potentiation of cytotoxicity of anticancer drugs by effective tanshinones were evaluated by MTT assay. Doxorubicin efflux assay by flow cytometry, P-gp protein expression by western blot analysis, immunofluorescence for P-gp by confocal microscopy, quantitative real-time PCR and P-gp ATPase activity assay were used to study the possible underlying mechanisms of action of effective tanshinones.

RESULTS

Bi-directional transport assay showed that only cryptotanshinone and dihydrotanshinone decreased digoxin efflux ratio in a concentration-dependent manner, indicating their inhibitory effects on P-gp function; whereas, tanshinone I, tanshinone IIA and miltirone had no inhibitory effects. Moreover, both cryptotanshinone and dihydrotanshinone could potentiate the cytotoxicity of doxorubicin and irinotecan in P-gp overexpressing SW620 Ad300 colon cancer cells. Results from mechanistic studies revealed that these two tanshinones increased intracellular accumulation of the P-gp substrate anticancer drugs, presumably by down-regulating P-gp mRNA and protein levels, and inhibiting P-gp ATPase activity.

CONCLUSIONS

Taken together, these findings suggest that cryptotanshinone and dihydrotanshinone could be further developed for sensitizing resistant cancer cells and used as an adjuvant therapy together with anticancer drugs to improve their therapeutic efficacies for colon cancer.

Andrographis paniculata Extract and Andrographolide Modulate the Hepatic Drug Metabolism System and Plasma Tolbutamide Concentrations in Rats

Andrographolide is the most abundant terpenoid of A. paniculata which is used in the treatment of diabetes. In this study, we investigated the effects of A. paniculata extract (APE) and andrographolide on the expression of drug-metabolizing enzymes in rat liver and determined whether modulation of these enzymes changed the pharmacokinetics of tolbutamide. Rats were intragastrically dosed with 2 g/kg/day APE or 50 mg/kg/day andrographolide for 5 days before a dose of 20 mg/kg tolbutamide was given. APE and andrographolide reduced the AUC_0–12 h of tolbutamide by 37% and 18%, respectively, compared with that in controls. The protein and mRNA levels and enzyme activities of CYP2C6/11, CYP1A1/2, and CYP3A1/2 were increased by APE and andrographolide. To evaluate whether APE or andrographolide affected the hypoglycemic action of tolbutamide, high-fat diet-induced obese mice were used and treated in the same manner as the rats. APE and andrographolide increased CYP2C6/11 expression and decreased plasma tolbutamide levels. In a glucose tolerance test, however, the hypoglycemic effect of tolbutamide was not changed by APE or andrographolide. These results suggest that APE and andrographolide accelerate the metabolism rate of tolbutamide through increased expression and activity of drug-metabolizing enzymes. APE and andrographolide, however, do not impair the hypoglycemic effect of tolbutamide.

Interactions between herbs and conventional drugs: overview of the clinical data

This article provides an overview of the clinical evidence of interactions between herbal and conventional medicines. Herbs involved in drug interactions--or that have been evaluated in pharmacokinetic trials--are discussed in this review. While many of the interactions reported are of limited clinical significance and many herbal products (e.g. black cohosh, saw palmetto, echinacea, hawthorn and valerian) seem to expose patients to minor risk under conventional pharmacotherapy, a few herbs, notably St. John's wort, may provoke adverse events sufficiently serious to endanger the patients' health. Healthcare professionals should remain vigilant for potential interactions between herbal medicines and prescribed drugs, especially when drugs with a narrow therapeutic index are used.

Interactions of dietary phytochemicals with ABC transporters: possible implications for drug disposition and multidrug resistance in cancer

Common foods, such as fruits and vegetables, contain a large variety of secondary metabolites known as phytochemicals, many of which have been associated with health benefits. However, there is a limited knowledge of the processes by which these, mainly charged, phytochemicals (and/or their metabolites) are absorbed into the body, reach their biological target, and how they are eliminated. Recent studies have indicated that some of these phytochemicals are substrates and modulators of specific members of the superfamily of ABC transporting proteins. In this review, we present the reported interactions between the different classes of phytochemicals and ABC transporters and the mechanism by which they modulate the activity of these transporters. We also discuss the implications that such interactions may have on the pharmacokinetics of xenobiotics and the possible role of phytochemicals in the reversal of multidrug resistance in cancer chemotherapy.

Induction of expression and functional activity of P-glycoprotein efflux transporter by bioactive plant natural products

The effect of bioactive plant natural products on the expression and functional activity of P-glycoprotein (P-gp) is poorly understood. Interactions of bioactive plant-based food and dietary supplements with P-gp can cause significant alteration of pharmacokinetic properties of P-gp substrate drugs when used in combination. This can augment toxicity and/or interfere with the drug's therapeutic outcomes. This study investigated the effects of diverse commonly used plant natural products on the expression and activity of P-gp in human adenocarcinoma cells (LS-180). These natural products included the tobacco cembranoid (1S,2E,4R,6R,7E,11E)-2,7,11-cembratriene-4,6-diol (cembratriene), the palm oil-derived γ-tocotrienol, the extra-virgin olive oil-derived secoiridoid oleocanthal, and the triterpene acid asiatic acid derived from Melaleuca ericifolia and abundant in several other common plant dietary supplements. Treatment with 25μM of cembratriene, oleocanthal, γ-tocotrienol, or asiatic acid showed 2.3-3.0-fold increase in P-gp expression as demonstrated by Western blotting. These results were consistent with those obtained by quantitative analysis of fluorescent micrographs for P-gp. Accumulation studies demonstrated 31-38% decrease in rhodamine 123 intracellular levels when LS-180 cells were treated with the investigated compounds as a result of P-gp induction. Bioactive natural products can up-regulate the P-gp expression and functionality, which may induce herb/food-drug interactions when concomitantly used with P-gp substrate drugs.

In vitro modulation of ABCB1/P-glycoprotein expression by polyphenols from Mangifera indica

Many plant compounds are able to modulate the activity and/or the expression of the major multidrug transporter ABCB1/P-glycoprotein (P-gp). In this study, mango (Mangifera indica L.) stem bark extract (MSBE), its main polyphenol mangiferin and the mangiferin aglycone derivative norathyriol, as well as catechin, gallic acid and quercetin, were investigated for their potential ability to influence ABCB1 gene and P-gp expression in HK-2 cells, a proximal tubule line constitutively expressing this transporter. Western blot analysis demonstrated a concentration-dependent decrease in P-gp in cells cultured in the presence of MSBE for 72 h. Gallic acid and quercetin also decreased the levels of P-gp at all studied concentrations, whereas catechin was almost ineffective. However, in cells exposed to mangiferin (10-200 microM), the P-gp amount showed a concentration- and time-dependent increase, being 2-fold higher than the controls after 72 h. Norathyriol (5 microM) induced P-gp, but the effect decreased at higher concentrations. The changes in the P-gp protein amount were correlated with relative changes in the ABCB1 mRNA content and with the efflux activity of the transporter. The transcriptional inhibitor 1-d-ribofuranosylbenzimidazole (DRB) contrasted the increased expression of ABCB1 by mangiferin, suggesting that the increase could be due to transcriptional up-regulation of ABCB1 mRNA. Mangiferin-treated cells overexpressing the transporter were protected against the cytotoxicity of the known P-gp substrate cyclosporine A. However, the opposite effect was not observed in cells pretreated with MSBE. These results demonstrate that MSBE and mango polyphenols, already shown in our previous studies to influence P-gp activity, may also interact with ABCB1/P-gp at the expression level. In particular, we show for the first time that the main mango polyphenol mangiferin up-regulates this multidrug transporter. The molecular mechanisms and the consequences of these effects, including the possibility of interactions with conventional drugs or other herbal constituents, remain to be elucidated.