Reversal of in vitro cellular MRP1 and MRP2 mediated vincristine resistance by the flavonoid myricetin

Recent advances in BCRP-induced breast cancer resistance treatment with marine-based natural products

Breast cancer is the prominent cause of cancer-related death in women globally in terms of incidence and mortality. Despite, recent advances in the management of breast cancer, there are still a lot of cases of resistance to medicines, which is currently one of the biggest problems faced by researchers across the globe. Out of several mechanisms, breast cancer resistance protein (BCRP) arbitrated drug resistance is a major concern. Hormonal, cytotoxic and immunotherapeutic drugs are used in the systemic therapy of breast cancer. It is vital to choose drugs based on the clinical and molecular attributes of the tumor to provide better treatment with greater efficacy and minimal harm. Given the aforementioned necessity, the use of marine flora in treating breast cancer cannot be neglected. The scientists also stressed the value of marine-derived goods in avoiding breast cancer resistance. Future research into the identification of anticancer drugs will heavily draw upon the marine environment's ample supply of marine-derived natural products (MNPs), which have a wide range of biological functions. Cell cycle arrest, induction of apoptosis and anti-angiogenic, anti-proliferative and anti-metastasis actions are all part of their processes. The overview of breast cancer, the mechanisms underlying its resistance, recent clinical trials based on marine-derived products in breast cancer and the use of marine products in the treatment of breast cancer are highlighted in this paper. Moreover, the authors also emphasised the importance of marine-derived products in preventing breast cancer resistance.

Protective Effects of Myricetin on Benzo[a]pyrene-Induced 8-Hydroxy-2'-Deoxyguanosine and BPDE-DNA Adduct

Benzo[a]pyrene (B[a]P), a group 1 carcinogen, induces mutagenic DNA adducts. Myricetin is present in many natural foods with diverse biological activities, such as anti-oxidative and anti-cancer activities. The aim of this study was to investigate the protective effects of myricetin against B[a]P-induced toxicity. Treatment of B[a]P induced cytotoxicity on HepG2 cells, whereas co-treatment of myricetin with B[a]P reduced the formation of the B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE)-DNA adduct, which recovered cell viability. Furthermore, we found a protective effect of myricetin against B[a]P-induced genotoxicity in rats, via myricetin-induced inhibition of 8-hydroxy-2′-deoxyguanosine (8-OHdG) and BPDE-DNA adduct formation in the liver, kidney, colon, and stomach tissue. This inhibition was more prominent in the liver than in other tissues. Correspondingly, myricetin regulated the phase I and II enzymes that inhibit B[a]P metabolism and B[a]P metabolites conjugated with DNA by reducing and inducing CYP1A1 and glutathione S-transferase (GST) expression, respectively. Taken together, this showed that myricetin attenuated B[a]P-induced genotoxicity via regulation of phase I and II enzymes. Our results suggest that myricetin is anti-genotoxic, and prevents oxidative DNA damage and BPDE-DNA adduct formation via regulation of phase I and II enzymes.

Defying Multidrug Resistance! Modulation of Related Transporters by Flavonoids and Flavonolignans

Multidrug resistance (MDR) is a major challenge for the 21th century in both cancer chemotherapy and antibiotic treatment of bacterial infections. Efflux pumps and transport proteins play an important role in MDR. Compounds displaying inhibitory activity toward these proteins are prospective for adjuvant treatment of such conditions. Natural low-cost and nontoxic flavonoids, thanks to their vast structural diversity, offer a great pool of lead structures with broad possibility of chemical derivatizations. Various flavonoids were found to reverse both antineoplastic and bacterial multidrug resistance by inhibiting Adenosine triphosphate Binding Cassette (ABC)-transporters (human P-glycoprotein, multidrug resistance-associated protein MRP-1, breast cancer resistance protein, and bacterial ABC transporters), as well as other bacterial drug efflux pumps: major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), small multidrug resistance (SMR) and resistance-nodulation-cell-division (RND) transporters, and glucose transporters. Flavonoids and particularly flavonolignans are therefore highly prospective compounds for defying multidrug resistance.

Transport-Mediated Oxaliplatin Resistance Associated with Endogenous Overexpression of MRP2 in Caco-2 and PANC-1 Cells

Our recent publications showed that multidrug resistance protein 2 (MRP2, encoded by the ABCC2 gene) conferred oxaliplatin resistance in human liver cancer HepG2 cells. However, the contribution of MRP2 to oxaliplatin resistance remains unclear in colorectal and pancreatic cancer lines. We investigated the effects of silencing MRP2 by siRNA on oxaliplatin accumulation and sensitivity in human colorectal cancer Caco-2 cells and pancreatic cancer PANC-1 cells. We characterized the effects of oxaliplatin on MRP2 ATPase activities using membrane vesicles. Over-expression of MRP2 (endogenously in Caco-2 and PANC-1 cells) was associated with decreased oxaliplatin accumulation and cytotoxicity, but those deficits were reversed by inhibition of MRP2 with myricetin or siRNA knockdown. Silencing MRP2 by siRNA increased oxaliplatin-induced apoptotic rate in Caco-2 and PANC-1 cells. Oxaliplatin stimulated MRP2 ATPase activity with a concentration needed to reach 50% of the maximal stimulation (EC₅₀) value of 8.3 ± 0.7 µM and Hill slope 2.7. In conclusion, oxaliplatin is a substrate of MRP2 with possibly two binding sites, and silencing MRP2 increased oxaliplatin accumulation and cytotoxicity in two widely available gastrointestinal tumour lines (PANC-1 and Caco-2).

Identification of MRP2 as a targetable factor limiting oxaliplatin accumulation and response in gastrointestinal cancer

Oxaliplatin is important for the clinical treatment of colorectal cancer and other gastrointestinal malignancies, but tumour resistance is limiting. Several oxaliplatin transporters were previously identified but their relative contributions to determining oxaliplatin tumour responses and gastrointestinal tumour cell sensitivity to oxaliplatin remains unclear. We studied clinical associations between tumour expression of oxaliplatin transporter candidate genes and patient response to oxaliplatin, then experimentally verified associations found with MRP2 in models of human gastrointestinal cancer. Among 18 oxaliplatin transporter candidate genes, MRP2 was the only one to be differentially expressed in the tumours of colorectal cancer patients who did or did not respond to FOLFOX chemotherapy. Over-expression of MRP2 (endogenously in HepG2 and PANC-1 cells, or induced by stable transfection of HEK293 cells) decreased oxaliplatin accumulation and cytotoxicity but those deficits were reversed by inhibition of MRP2 with myricetin or siRNA knockdown. Mice bearing subcutaneous HepG2 tumour xenografts were sensitised to oxaliplatin antitumour activity by concurrent myricetin treatment with little or no increase in toxicity. In conclusion, MRP2 limits oxaliplatin accumulation and response in human gastrointestinal cancer. Screening tumour MRP2 expression levels, to select patients for treatment with oxaliplatin-based chemotherapy alone or in combination with a MRP2 inhibitor, could improve treatment outcomes.

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.

Delineating the Role of βIV-Tubulins in Pancreatic Cancer: βIVb-Tubulin Inhibition Sensitizes Pancreatic Cancer Cells to Vinca Alkaloids

Pancreatic cancer (PC) is a lethal disease which is characterized by chemoresistance. Components of the cell cytoskeleton are therapeutic targets in cancer. βIV-tubulin is one such component that has two isotypes-βIVa and βIVb. βIVa and βIVb isotypes only differ in two amino acids at their C-terminus. Studies have implicated βIVa-tubulin or βIVb-tubulin expression with chemoresistance in prostate, breast, ovarian and lung cancer. However, no studies have examined the role of βIV-tubulin in PC or attempted to identify isotype specific roles in regulating cancer cell growth and chemosensitivity. We aimed to determine the role of βIVa- or βIVb-tubulin on PC growth and chemosensitivity. PC cells (MiaPaCa-2, HPAF-II, AsPC1) were treated with siRNA (control, βIVa-tubulin or βIVb-tubulin). The ability of PC cells to form colonies in the presence or absence of chemotherapy was measured by clonogenic assays. Inhibition of βIVa-tubulin in PC cells had no effect chemosensitivity. In contrast, inhibition of βIVb-tubulin in PC cells sensitized to vinca alkaloids (Vincristine, Vinorelbine and Vinblastine), which was accompanied by increased apoptosis and enhanced cell cycle arrest. We show for the first time that βIVb-tubulin, but not βIVa-tubulin, plays a role in regulating vinca alkaloid chemosensitivity in PC cells. The results from this study suggest βIVb-tubulin may be a novel therapeutic target and predictor of vinca alkaloid sensitivity for PC and warrants further investigation.

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.

Myricetin: A Dietary Molecule with Diverse Biological Activities

Myricetin is a common plant-derived flavonoid and is well recognised for its nutraceuticals value. It is one of the key ingredients of various foods and beverages. The compound exhibits a wide range of activities that include strong anti-oxidant, anticancer, antidiabetic and anti-inflammatory activities. It displays several activities that are related to the central nervous system and numerous studies have suggested that the compound may be beneficial to protect against diseases such as Parkinson's and Alzheimer's. The use of myricetin as a preserving agent to extend the shelf life of foods containing oils and fats is attributed to the compound's ability to protect lipids against oxidation. A detailed search of existing literature revealed that there is currently no comprehensive review available on this important molecule. Hence, the present work includes the history, synthesis, pharmaceutical applications and toxicity studies of myricetin. This report also highlights structure-activity relationships and mechanisms of action for various biological activities.

Genetic and biochemical study of dual hereditary jaundice: Dubin-Johnson and Gilbert's syndromes. Haplotyping and founder effect of deletion in ABCC2

Dual hereditary jaundice, a combination of Dubin-Johnson and Gilbert's syndromes, is a rare clinical entity resulting from the compound defects of bilirubin conjugation and transport. We aimed to study the hereditary jaundice in 56 members from seven seemingly unrelated Roma families, to find the causal genetic defect and to estimate its origin in Roma population. On the basis of biochemical results of total and conjugated serum bilirubin and clinical observations, ABCC2 gene, TATA box and phenobarbital enhancer (PBREM) of UGT1A1 gene were analyzed by sequencing, RFLP and fragment analysis. We found a novel variant c.1013_1014delTG in the eighth exon of ABCC2 gene in 17 individuals in homozygous state. Dual defect NG_011798.1:c.[1013_1014delTG]; NG_002601.2:g.[175492_175493insTA] in homozygous state was found in four subjects. Biochemical analyses of porphyrins and coproporphyrin isomers in urine performed by HPLC showed inverted ratio of excreted coproporphyrin, with the predominance of coproporphyrin I (up to 100%), typical for patients with Dubin-Johnson syndrome. Pursuant cultural and social specifics of the population led us to suspect a founder effect; therefore, we performed a haplotype study using genotyping data from Affymetrix Genome-Wide Human SNP Array 6.0. As a result, we detected a common 86 kbp haplotype encompassing promoter and part of the ABCC2 coding region among all families, and estimated the age of the ancestral variant to 178-185 years. In this study, we found a novel deletion in ABCC2 gene, described genetic and biochemical features of dual hereditary jaundice and confirmed the existence of founder effect and common haplotype among seven Roma families.

Multidrug Resistance-Associated Protein 2 (MRP2) Mediated Transport of Oxaliplatin-Derived Platinum in Membrane Vesicles

The platinum-based anticancer drug oxaliplatin is important clinically in cancer treatment. However, the role of multidrug resistance-associated protein 2 (MRP2) in controlling oxaliplatin membrane transport, in vivo handling, toxicity and therapeutic responses is unclear. In the current study, preparations of MRP2-expressing and control membrane vesicles, containing inside-out orientated vesicles, were used to directly characterise the membrane transport of oxaliplatin-derived platinum measured by inductively coupled plasma mass spectrometry. Oxaliplatin inhibited the ATP-dependent accumulation of the model MRP2 fluorescent probe, 5(6)-carboxy-2,'7'-dichlorofluorescein, in MRP2-expressing membrane vesicles. MRP2-expressing membrane vesicles accumulated up to 19-fold more platinum during their incubation with oxaliplatin and ATP as compared to control membrane vesicles and in the absence of ATP. The rate of ATP-dependent MRP2-mediated active transport of oxaliplatin-derived platinum increased non-linearly with increasing oxaliplatin exposure concentration, approaching a plateau value (Vmax) of 2680 pmol Pt/mg protein/10 minutes (95%CI, 2010 to 3360 pmol Pt/mg protein/10 minutes), with the half-maximal platinum accumulation rate (Km) at an oxaliplatin exposure concentration of 301 μM (95% CI, 163 to 438 μM), in accordance with Michaelis-Menten kinetics (r² = 0.954). MRP2 inhibitors (myricetin and MK571) reduced the ATP-dependent accumulation of oxaliplatin-derived platinum in MRP2-expressing membrane vesicles in a concentration-dependent manner. To identify whether oxaliplatin, or perhaps a degradation product, was the likely substrate for this active transport, HPLC studies were undertaken showing that oxaliplatin degraded slowly in membrane vesicle incubation buffer containing chloride ions and glutathione, with approximately 95% remaining intact after a 10 minute incubation time and a degradation half-life of 2.24 hours (95%CI, 2.08 to 2.43 hours). In conclusion, MRP2 mediates the ATP-dependent active membrane transport of oxaliplatin-derived platinum. Intact oxaliplatin and its anionic monochloro oxalate ring-opened intermediate appear likely candidates as substrates for MRP2-mediated transport.

Modulators of the human ABCC2: hope from natural sources?

Human ABCC2 is an ATP-binding cassette transporter involved in the export of endobiotics and xenobiotics. It is involved in cisplatin resistance in cancer cells, particularly in ovarian cancer. The few known ABCC2 modulators are poorly efficient, so it is necessary to explore new ways to select and optimize efficient compounds ABCC2. Natural products offer an original scaffold for such a strategy and brings hope for this aim. This review covers basic knowledge about ABCC2, from distribution and topology aspects to physiological and pathological functions. It summarizes the effect of natural products as ABCC2 modulators. Certain plant metabolites act on different ABCC2 regulation levels and therefore are promising candidates to block the multidrug resistance mediated by ABCC2 in cancer cells.

3β-Acetyl tormentic acid reverts MRP1/ABCC1 mediated cancer resistance through modulation of intracellular levels of GSH and inhibition of GST activity

ABC transporter overexpression is an important mechanism of multidrug resistance (MDR) and one of the main obstacles to successful cancer treatment. As these proteins actively remove chemotherapeutics from the tumor cells, the pharmacological inhibition of their activity is a possible strategy to revert drug resistance. Moreover, the ability of MDR inhibitors to sensitize resistant cells to conventional drugs is important for their clinical use. Evidence has shown that the multidrug resistance protein 1 (MRP1/ABCC1) is a negative prognostic marker in patients with lung, gastric, or breast cancers or neuroblastoma. Previous data have shown that 3β-acetyl tormentic acid (3ATA) inhibits the transport activity of the protein MRP1/ABCC1. In this study, we evaluated the ability of 3ATA to sensitize an MDR cell line (GLC4/ADR), which overexpresses MRP1, and investigated the anti-MRP1 mechanisms activated by 3ATA. The results showed that 3ATA is able to reverse the resistance of the MDR cell line to doxorubicin and vincristine, two drugs that are commonly used in cancer chemotherapy. Regarding the sensitizing mechanism induced by 3ATA, this work shows that the triterpene does not modulate the expression of MRP1/ABCC1 but is able to reduce total intracellular glutathione (GSH) levels and decrease the activity of glutathione-s-transferase (GST), the enzyme responsible for the glutathione conjugation of xenobiotics. Together, these results show that 3ATA sensitizes the MDR cell line overexpressing MRP1/ABCC1 to antineoplastic drugs and that this effect is mediated by the modulation of intracellular levels of GSH and GST activity.

Urinary coproporphyrin I/(I + III) ratio as a surrogate for MRP2 or other transporter activities involved in methotrexate clearance

AIMS

The urinary coproporphyrin I/(I + III) ratio may be a surrogate for MRP2 activity. We conducted a prospective study in patients receiving methotrexate (MTX) to examine the relationship between this ratio and the pharmacokinetics of a MRP2 substrate.

METHODS

Three urine samples were collected from 81 patients for UCP I/(I + III) ratio determination: one before (P1), one at the end of MTX infusion (P2), and one on the day of hospital discharge (P3). Three polymorphisms of ABCC2 were analysed and their relationships with basal UCP I/(I + III) ratio values assessed. All associated drugs were recorded and a drug interaction score (DIS) was assigned. Population pharmacokinetic analysis was conducted to assess whether MTX clearance (MTXCL) was associated with the basal UCP I/(I + III) ratio, its variation during MTX infusion, the DIS or other common covariates.

RESULTS

The basal UCP I/(I + III) ratio was not associated with ABCC2 polymorphisms and did not differ according to the DIS. Significant changes in the ratio were observed over time, with an increase between P1 and P2 and a decrease at P3 (P < 0.001). No association was found between basal UCP I/(I + III) ratio and MTXCL. The final model indicates that MTXCL was dependent on the change in the ratio between P1 and P3, DIS and creatinine clearance.

CONCLUSION

The basal UCP I/(I + III) ratio is not predictive of MTXCL. However, it is sensitive to the presence of MTX, so it is plausible that it reflects a function modified in response to the drug.

Deconstructing breast cancer cell biology and the mechanisms of multidrug resistance

Cancer complexity constantly challenges the way that clinicians manage breast cancer therapy. Tumor heterogeneity and intratumoral stroma characteristics allow cells with different phenotypes and deregulated apoptotic, proliferative and migration abilities to co-exist contributing to a disappointing therapeutic response. While new approaches are being associated with conventional chemotherapy, such as hormonal therapy or target monoclonal antibodies, recurrence and metastasization are still observed. Membrane transporters are the cell's first line of contact with anticancer drugs having a major role in multidrug resistance events. This structural-based activity enables the cell to be drug-resistant by decreasing drug intracellular concentration through an efflux-transport mechanism, mainly associated with overexpression of ATP-binding cassette (ABC) proteins. This review focuses on some of the important structural and biological properties of the malignant cell and tumor microenvironment, addressing the role of the membrane ABC transporters in therapeutic outcomes, and highlighting related molecular pathways that may represent meaningful target therapies.

Interaction of immunosuppressive drugs with human organic anion transporter (OAT) 1 and OAT3, and multidrug resistance-associated protein (MRP) 2 and MRP4

Renal proximal tubule transporters can play a key role in excretion, pharmacokinetic interactions, and toxicity of immunosuppressant drugs. Basolateral organic anion transporters (OATs) and apical multidrug resistance-associated proteins (MRPs) contribute to the active tubular uptake and urinary efflux of these drugs, respectively. We studied the interaction of 12 immunosuppressants with OAT1- and OAT3-mediated [(3)H]-methotrexate (MTX) uptake in cells, and adenosine triphosphate-dependent [(3)H]-MTX transport in membrane vesicles isolated from human embryonic kidney 293 cells overexpressing human MRP2 and MRP4. Our results show that at a clinically relevant concentration of 10 μM, mycophenolic acid inhibited both OAT1- and OAT3-mediated [(3)H]-MTX uptake. Cytarabine, vinblastine, vincristine, hydrocortisone, and mitoxantrone inhibited only OAT1, whereas tacrolimus, azathioprine, dexamethasone, cyclosporine, and 6-mercaptopurine had no effect on both transporters. Cyclophosphamide stimulated OAT1, but did not affect OAT3. With regard to the apical efflux transporters, mycophenolic acid, cyclophosphamide, hydrocortisone, and tacrolimus inhibited MRP2 and MRP4, whereas mitoxantrone and dexamethasone stimulated [(3)H]-MTX transport by both transporters. Cyclosporine, vincristine, and vinblastine inhibited MRP2 only, whereas 6-mercaptopurine inhibited MRP4 transport activity only. Cytarabine and azathioprine had no effect on either transporter. In conclusion, we charted comprehensively the differences in inhibitory action of various immunosuppressive agents against the 4 key renal anion transporters, and we provide evidence that immunosuppressant drugs can modulate OAT1-, OAT3-, MRP2-, and MRP4-mediated transport of MTX to different extents. The data provide a better understanding of renal mechanisms underlying drug-drug interactions and nephrotoxicity concerning combination regimens with these compounds in the clinic.

SIRT1-mediated FoxO1 deacetylation is essential for multidrug resistance-associated protein 2 expression in tamoxifen-resistant breast cancer cells

Our previous studies have shown that multidrug resistance protein 2 (MRP2) is overexpressed in tamoxifen-resistant MCF-7 breast cancer cells (TAMR-MCF-7 cells) and forkhead box-containing protein, O subfamily1 (FoxO1), functions as a key regulator of multidrug resistance 1 (MDR1) gene transcription. This study aimed to investigate the role of FoxO1 in regulating MRP2 gene expression in TAMR-MCF-7 cells. The proximal promoter region of the human MRP2 gene contains four putative FoxO binding sites, and MRP2 gene transcription was stimulated by FoxO1 overexpression in MCF-7 cells. Subcellular fractionation and immunoblot analyses revealed that basal MRP2 expression and nuclear levels of FoxO1 were enhanced in TAMR-MCF-7 cells compared to MCF-7 cells and the enhanced MRP2 gene transcription was suppressed by FoxO1 siRNA. Because nuclear localization of FoxO1 is regulated by SIRT1 deacetylase, we were further interested in whether SIRT1 is involved in MRP2 expression. Overexpression of SIRT1 with FoxO1 potentiated the gene transcriptional activity of MRP2, and the basal activity and expression of SIRT1 was increased in TAMR-MCF-7 cells. In addition, SIRT1 inhibition reduced both the nuclear FoxO1 levels and MRP2 expression and enhanced cytotoxic effects of paclitaxel and doxorubicin in TAMR-MCF-7 cells. These results suggest that FoxO1 activation via SIRT1-mediated deacetylation is closely related with up-regulation of MRP2 in TAMR-MCF-7 cells.

Effect of quercetin on the transport of N-acetyl 5-aminosalicylic acid

OBJECTIVES

The aim of this study was to investigate the transporter-mediated transport of N-acetyl 5-aminosalicylic acid (Ac-5-ASA) and the effect of quercetin on Ac-5-ASA transport.

METHODS

Caco-2 cell monolayers grown in Transwells were used to study the transport of Ac-5-ASA in the absence or presence of quercetin, and apical-to-basolateral and basolateral-to-apical apparent permeability (PappAB and PappBA values, respectively) was determined. The effect of transporter inhibitors, such as MK571, quinidine and mitoxantrone, on the transport of Ac-5-ASA was investigated.

KEY FINDINGS

In the absence of transporter mediators, the transport of Ac-5-ASA was much higher in the basolateral-to-apical direction than in the opposite direction. The PappBA/PappAB ratio of Ac-5-ASA was 4.89. Quercetin inhibited the apical efflux of Ac-5-ASA and decreased the PappBA/PappAB ratio to 1.05. Of the transporter inhibitors, MK571 decreased the PappBA/PappAB ratio to 1.07; however, neither quinidine nor mitoxantrone had an effect on Ac-5-ASA transport.

CONCLUSIONS

Ac-5-ASA was excreted by multidrug resistance-associated protein 2 from Caco-2 cells, and its transport was inhibited by quercetin. Our findings suggest that dose levels of sulfasalazine or 5-aminosalicylic acid can be decreased by coadministration of quercetin, leading to improved pharmaceutical care for inflammatory bowel diseases.

The effects of flavonoids on the ABC transporters: consequences for the pharmacokinetics of substrate drugs

INTRODUCTION

The flavonoids are a large group of dietary plant compounds with suggested health benefits. There is accumulating evidence that many of these flavonoids can interact with the major drug transporters (and metabolizing enzymes) in the body, leading to alterations in the pharmacokinetics of substrate drugs, and thus their efficacy and toxicity.

AREAS COVERED

This review summarizes and updates the reported in vitro and in vivo interactions between common dietary flavonoids and the major drug-effluxing ABC transporters; these include P-glycoprotein, breast cancer resistance protein and multidrug resistance proteins 1 and 2. In contrast to previous reviews, the ADME of flavonoids are considered, along with their glycosides and Phase II conjugates. The authors also consider their possible interactions with the ABC transporters in the oral absorption, distribution into pharmacological sanctuaries and excretion of substrate drugs. Electronic databases, including PubMed, Scopus and Google Scholar were searched to identify appropriate in vitro and in vivo ABC transporter-flavonoid interactions, particularly within the last 10 years.

EXPERT OPINION

Caution is advised when taking flavonoid-containing supplements or herbal remedies concurrently with drugs. Further clinical studies are warranted to explore the impact of flavonoids and their metabolites on the pharmacokinetics, efficacy and toxicity of drugs.

Microarray and pathway analysis highlight Nrf2/ARE-mediated expression profiling by polyphenolic myricetin

SCOPE

Myricetin is a dietary flavonol and widely distributed in many edible plants. It has been reported to have many bioactivities and considered as a promising chemopreventive compound. The present study aimed to investigate the influences of myricetin on gene expressions in genome-wide and underlying mechanisms.

METHODS AND RESULTS

Among total 44K gene probes, myricetin treatment upregulated the signals of 143 gene probes (0.33% of total probes) and downregulated signals of 476 gene probes (1.08% of total probes) by greater than or equal to twofold in HepG2 cells. The network pathway analysis revealed that nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated antioxidant response element (ARE) activation is involved in myricetin-induced genes expressions. Molecular data revealed that myricetin activated Nrf2-ARE pathway by inhibiting Nrf2 ubiquitination and protein turnover, stimulating Nrf2 expression and kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated protein 1 modification. All of these events finally increased nuclear Nrf2 accumulation and ARE-binding activity to enhance ARE-mediated genes expressions. Additionally, treatment with Nrf2 small interfering RNA attenuated the myricetin-induced ARE activity and gene expression.

CONCLUSION

An Nrf2-mediated ARE activation is involved in myricetin-induced expression profiling in hepatic cells.

Discovering natural product modulators to overcome multidrug resistance in cancer chemotherapy

Multidrug resistance caused by the overexpression of ABC drug transporters is a major obstacle in clinical cancer chemotherapy. For several years, it appeared that direct inhibition of ABC transporters would be the cheapest and most efficient way to combat this problem. Unfortunately, progress in finding a potent, selective inhibitor to modulate ABC transporters and restore drug sensitivity in multidrug-resistant cancer cells has been slow and challenging. Candidate drugs should ideally be selective, potent and relatively non-toxic. Many researchers in recent years have turned their attention to utilizing natural products as the building blocks for the development of the next generation of inhibitors, especially after the disappointing results obtained from inhibitors of the first three generations at the clinical trial stage. The first step is to discover natural substances (distinct from the first three generation inhibitors) that are potent, selective and relatively non-toxic in order to be used clinically. Here, we present a brief overview of the prospect of using natural products to modulate the function of ABC drug transporters clinically and their impact on human physiology and pharmacology.

Luteolin induces apoptosis in multidrug resistant cancer cells without affecting the drug transporter function: involvement of cell line-specific apoptotic mechanisms

Bioflavonoids are of considerable interest to human health as these serve as antioxidant and anticancer agents. Although epidemiological and experimental studies suggest that luteolin, a natural bioflavonoid, exhibits chemopreventive properties, its effectiveness as an antiproliferative agent against multidrug resistant (MDR) cancers is unclear. Thus, we assessed the antiproliferative effects of luteolin and associated molecular mechanisms using two MDR cancer cell lines that express high levels of P-glycoprotein and ABCG2. In this article, we demonstrate that luteolin induces apoptosis in P-glycoprotein- and ABCG2-expressing MDR cancer cells without affecting the transport functions of these drug transporters. Analysis of various proliferative signaling pathways indicated that luteolin-induced apoptosis involves reactive oxygen species generation, DNA damage, activation of ATR → Chk2 → p53 signaling pathway, inhibition of NF-kB signaling pathway, activation of p38 pathway and depletion of antiapoptotic proteins. Importantly, use of luteolin in these analyses also identified specific molecular characteristics of NCI-ADR/RES and MCF-7/Mito(R) cells that highlight their different tissue origins. These results suggest that luteolin possesses therapeutic potential to control the proliferation of MDR cancers without affecting the physiological function of drug transporters in the body tissues.

Reversing agents for ATP-binding cassette drug transporters

The multidrug resistance (MDR) phenotype exhibited by cancer cells is believed to be the major barriers to successful chemotherapy in cancer patients. The major form of MDR phenotype is contributed by a group of ATP-binding cassette (ABC) drug transporters which include P-glycoprotein, multidrug resistance-associated protein 1, and breast cancer resistance protein. There has been intense search for compounds which can act to reverse MDR phenotype in cultured cells, in animal models, and ultimately in patients. The ongoing search for MDR modulators, compounds that act directly on the ABC transporter proteins to block their activity, has led to three generations of drugs. Some of the third-generation MDR modulators have demonstrated encouraging results compared to earlier generation MDR modulators in clinical trials. These modulators are less toxic and they do not affect the pharmacokinetics of anti-cancer drugs. Significant numbers of natural products have also been identified for their effectiveness in reversing MDR in a manner similar to the MDR modulators. Other MDR reversing strategies that have been studied quite extensively are also reviewed and discussed in this chapter. These include strategies aimed at destroying mRNAs for ABC drug transporters, approaches in inhibiting transcription of ABC transporter genes, and blocking of ABC transporter activity using antibodies. This review summarizes the development of reversing agents for ABC drug transporters up to the end of 2008, and provides an optimistic view of what we have achieved and where we could go from here.

Montelukast is a potent and durable inhibitor of multidrug resistance protein 2-mediated efflux of taxol and saquinavir

The ATP binding cassette (ABC)-transporters are energy dependent efflux pumps which regulate the pharmacokinetics of both anti-cancer chemotherapeutic agents, e.g. taxol, and of human immunodeficiency virus-1 (HIV-1) protease inhibitors (HPIs), e.g. saquinavir. Increased expression of several ABC-transporters, especially P-glycoprotein (P-gp) and multidrug resistance protein 2 (MRP2), are observed in multidrug resistant (MDR) tumor cells and on HIV-1 infected lymphocytes. In addition, due to their apical expression on vascular endothelial barriers, both P-gp and MRP2 are of crucial importance towards dictating drug access into sequestered tissues. However, although a number of P-gp inhibitors are currently in clinical trials, possible inhibitors of MRP2 are not being thoroughly investigated. The experimental leukotriene receptor antagonist (LTRA), MK-571 is known to be a potent inhibitor of MRP transporters. Using the MRP2 over-expressing Madin-Darby canine kidney cell line, MDCKII-MRP2, we evaluated whether the clinically approved LTRAs, e.g. montelukast (Singulair) and zafirlukast (Accolate), can similarly suppress MRP2-mediated efflux. We compared the efficacy of increasing concentrations (20-100 microM) of MK-571, montelukast, and zafirlukast, in suppressing the efflux of calcein-AM, a fluorescent MRP substrate, and the radiolabeled [(3)H-] drugs, taxol and saquinavir. Montelukast was the most potent inhibitor (p<0.01) of MRP2-mediated efflux of all three substrates. Montelukast also increased (p<0.01) the duration of intracellular retention of both taxol and saquinavir. More than 50% of the drugs were retained in cells even after 90 min post removal of montelukast from the medium. Our findings implicate that montelukast, a relatively safe anti-asthmatic agent, may be used as an adjunct therapy to suppress the efflux of taxol and saquinavir from MRP2 overexpressing cells.

Inhibitory effect of flavonoids on the efflux of N-acetyl 5-aminosalicylic acid intracellularly formed in Caco-2 cells

N-acetyl 5-aminosalicylic acid (5-AcASA) that was intracellularly formed from 5-aminosalicylic acid (5-ASA) at 200 microM was discharged 5.3, 7.1, and 8.1-fold higher into the apical site than into the basolateral site during 1, 2, and 4-hour incubations, respectively, in Caco-2 cells grown in Transwells. The addition of flavonols (100 microM) such as fisetin and quercetin with 5-ASA remarkably decreased the apically directed efflux of 5-AcASA. When 5-ASA (200 microM) was added to Caco-2 cells grown in tissue culture dishes, the formation of 5-AcASA decreased, and, in addition, the formed 5-AcASA was found to be accumulated within the cells in the presence of such flavonols. Thus, the decrease in 5-AcASA efflux by such flavonols was attributed not only to the inhibition of N-acetyl-conjugation of 5-ASA but to the predominant cellular accumulation of 5-AcASA. Various flavonoids also had both of the effects with potencies that depend on their specific structures. The essential structure of flavonoids was an absence of a hydroxyl substitution at the C5 position on the A-ring of flavone structure for the inhibitory effect on the N-acetyl-conjugation of 5-ASA, and a presence of hydroxyl substitutions at the C3' or C4' position on the B-ring of flavone structure for the promoting effect on the cellular accumulation of 5-AcASA. Both the decrease in 5-AcASA apical efflux and the increase in 5-AcASA cellular accumulation were also caused by MK571 and indomethacin, inhibitors of MRPs, but not by quinidine, cyclosporin A, P-glycoprotein inhibitors, and mitoxantrone, a BCRP substrate. These results suggest that certain flavonoids suppress the apical efflux of 5-AcASA possibly by inhibiting MRPs pumps located on apical membranes in Caco-2 cells.

Topological polar surface area defines substrate transport by multidrug resistance associated protein 1 (MRP1/ABCC1)

Multidrug resistance-associated protein 1 (MRP1/ABCC1) is a very promiscuous transporter. Herein we used topological polar surface area (TPSA), a descriptor defined as the sum of surfaces of polar atoms in a molecule, to analyze drug transport by MRP1. We suggested that compounds with high TPSA are transported while those with low TPSA are not. The conjugation to GSH increases TPSA values favoring transport. A strong correlation between TPSA and transport properties (K(m)) was also found.

Perturbation of the lipid phase of a membrane is not involved in the modulation of MRP1 transport activity by flavonoids

The expression of transmembrane transporter multidrug resistance-associated protein 1 (MRP1) confers the multidrug-resistant phenotype (MDR) on cancer cells. Since the activity of the other MDR transporter, P-glycoprotein, is sensitive to membrane perturbation, we aimed to check whether the changes in lipid bilayer properties induced by flavones (apigenin, acacetin) and flavonols (morin, myricetin) were related to their MRP1 inhibitory activity. All the flavonoids inhibited the efflux of MRP1 fluorescent substrate from human erythrocytes and breast cancer cells. Morin was also found to stimulate the ATPase activity of erythrocyte ghosts. All flavonoids intercalated into phosphatidylcholine bilayers as judged by differential scanning calorimetry and fluorescence spectroscopy with the use of two carbocyanine dyes. The model of an intramembrane localization for flavones and flavonols was proposed. No clear relationship was found between the membrane-perturbing activity of flavonoids and their potency to inhibit MRP1. We concluded that mechanisms other than perturbation of the lipid phase of membranes were responsible for inhibition of MRP1 by the flavonoids.

Development of inhibitors of ATP-binding cassette drug transporters: present status and challenges

BACKGROUND

Multi-drug resistance (MDR) of cancer cells is an obstacle to effective chemotherapy of cancer. The ATP-binding cassette (ABC) transporters, including P-glycoprotein (ABCB1), MRP1 (ABCC1) and ABCG2, play an important role in the development of this resistance. An attractive approach to overcoming MDR is the inhibition of the pumping action of these transporters. Several inhibitors/modulators of ABC transporters have been developed, but cytotoxic effects and adverse pharmacokinetics have prohibited their use. The ongoing search for such inhibitors/modulators that can be applied in the clinic has led to three generations of compounds. The most recent inhibitors are more potent and less toxic than first-generation compounds, yet some are still prone to adverse effects, poor solubility and unfavorable changes in the pharmacokinetics of the anticancer drugs.

OBJECTIVE

This review provides an update of the published work on the development of potent modulators to overcome MDR in cancer cells, their present status in clinical studies and suggestions for further improvement to obtain better inhibitors.

METHODS

This review summarizes recent advances in the development of less toxic modulators, including small molecules and natural products. In addition, a brief overview of other novel approaches that can be used to inhibit ABC drug transporters mediating MDR has also been provided.

CONCLUSION

The multifactorial nature of MDR indicates that it may be important to develop modulators that can simultaneously inhibit both the function of the drug transporters and key signaling pathways, which are responsible for development of this phenomenon.

Drug transport in corneal epithelium and blood-retina barrier: emerging role of transporters in ocular pharmacokinetics

Corneal epithelium and blood-retina barrier (i.e. retinal capillaries and retinal pigment epithelium (RPE)) are the key membranes that regulate the access of xenobiotics into the ocular tissues. Corneal epithelium limits drug absorption from the lacrimal fluid into the anterior chamber after eyedrop administration, whereas blood-retina barrier restricts the entry of drugs from systemic circulation to the posterior eye segment. Like in general pharmacokinetics, the role of transporters has been considered to be quite limited as compared to the passive diffusion of drugs across the membranes. As the functional role of transporters is being revealed it has become evident that the transporters are widely important in pharmacokinetics. This review updates the current knowledge about the transporters in the corneal epithelium and blood-retina barrier and demonstrates that the information is far from complete. We also show that quite many ocular drugs are known to interact with transporters, but the studies about the expression and function of those transporters in the eye are still sparse. Therefore, the transporters probably have greater role in ocular pharmacokinetics than we currently realise.

Flavonoid-mediated inhibition of intestinal ABC transporters may affect the oral bioavailability of drugs, food-borne toxic compounds and bioactive ingredients

The transcellular transport of ingested food ingredients across the intestinal epithelial barrier is an important factor determining bioavailability upon oral intake. This transcellular transport of many chemicals, food ingredients, drugs or toxic compounds over the intestinal epithelium can be highly dependent on the activity of membrane bound ATP binding cassette (ABC) transport proteins, able to export the compounds from the intestinal cells. The present review describes the ABC transporters involved in the efflux of bioactive compounds from the intestinal cells, either to the basolateral blood side, facilitating absorption, or back into the intestinal lumen, reducing bioavailability. The role of the ABC transporters in intestinal transcellular uptake also implies a role for inhibitors of these transporters in modulation of the bioavailability upon oral uptake. The present paper focuses on the role of flavonoids as important modulators or substrates of intestinal ABC transport proteins. Several examples of such an effect of flavonoids are presented. It can be concluded that flavonoid-mediated inhibition of ABC transporters may affect the bioavailability of drugs, bioactive food ingredients and/or food-borne toxic compounds upon oral uptake. All together it appears that the flavonoid-mediated interactions at the level of the intestinal ABC transport proteins may be an important mechanism for unexpected food-drug, food-toxin or food-food interactions. The overview also indicates that future studies should focus on i) in vivo validation of the flavonoid-mediated effects on bioavailability of drugs, toxins and beneficial bioactive food ingredients detected in in vitro models, and on ii) the role of flavonoid phase II metabolism in modulating the activity of the flavonoids to act as ABC transporter inhibitors and/or substrates.