Role of the breast cancer resistance protein (ABCG2) in drug transport

Breast Cancer Resistance Protein Abundance, but Not mRNA Expression, Correlates With Estrone-3-Sulfate Transport in Caco-2

Transporter mRNA and protein expression data are used to extrapolate in vitro transporter kinetics to in vivo drug disposition predictions. Breast cancer resistance protein (BCRP) possesses broad substrate specificity; therefore, understanding BCRP expression-activity relationships are necessary for the translation to in vivo. Bidirectional transport of estrone-3-sulfate (E-3-S), a BCRP probe, was evaluated with respect to relative BCRP mRNA expression and absolute protein abundance in 10- and 29-day cultured Caco-2 cells. BCRP mRNA expression was quantified by real-time PCR against a housekeeper gene, Cyclophilin A. The BCRP protein abundance in total membrane fractions was quantified by targeted proteomics, and [(3)H]-E-3-S bidirectional transport was determined in the presence or absence of Ko143, a potent BCRP inhibitor. BCRP mRNA expression was 1.5-fold higher in 29- versus 10-day cultured cells (n = 3), whereas a 2.4-fold lower (p < 0.001) BCRP protein abundance was observed in 29- versus 10-day cultured cells (1.28 ± 0.33 and 3.06 ± 0.22 fmol/μg protein, n = 6, respectively). This correlated to a 2.45-fold lower (p < 0.01) efflux ratio for E-3-S in 29- versus 10-day cultured cells (8.97 ± 2.51 and 3.32 ± 0.66, n = 6, respectively). Caco-2 cell BCRP protein abundance, but not mRNA levels, correlates with BCRP activity, suggesting that extrapolation strategies incorporating BCRP protein abundance-activity relationships may be more successful.

Association between the concentration of imatinib in bone marrow mononuclear cells, mutation status of ABCB1 and therapeutic response in patients with chronic myelogenous leukemia

Low concentrations of imatinib (IM) in bone marrow cells have been linked with poor prognosis in patients with chronic myeloid leukemia (CML), which may be caused by the emergence of ATP-binding cassette transporter B1 (ABCB1) mutations. The aim of present study was to investigate how clinical outcomes vary among patients with different single nucleotide polymorphisms (SNPs) of ABCB1. A total of 48 adult patients with CML and higher than median ABCB1 mRNA levels were selected for testing of ABCB1 SNPs. In 28 of the 48 patients, the IM concentration and expression levels of human organic cation transporter 1 (hOCT1) and ABCB1 in bone marrow mononuclear cells (BMMCs) were also tested. Correlations between treatment outcomes and IM concentration or the SNP status of ABCB1 were analyzed. Patients were classified by therapeutic response as major molecular response (MMR) (n=11), complete cytogenetic response (CCyR) (n=19) and non-CCyR (n=18) groups. It was found that the concentration of IM in BMMCs of the CCyR group was significant higher than that of the resistant groups (P=0.013). In addition, the IM concentration was positively correlated with the expression of hOCT1 mRNA (R=0.456, P=0.033), but negatively correlated with the expression of ABCB1 mRNA (R=-0.491, P=0.015). Furthermore, the mRNA expression level of ABCB1 was not associated with therapeutic response, but SNPs of the ABCB1 gene were associated with the response to IM. In conclusion, the concentration of IM in BMMCs may be regulated by the ABCB1 gene, and SNPs of the ABCB1 gene predict the therapeutic response to IM in patients with CML.

Tea nanoparticle, a safe and biocompatible nanocarrier, greatly potentiates the anticancer activity of doxorubicin

An infusion-dialysis based procedure has been developed as an approach to isolate organic nanoparticles from green tea. Tea nanoparticle (TNP) can effectively load doxorubicin (DOX) via electrostatic and hydrophobic interactions. We established an ABCB1 overexpressing tumor xenograft mouse model to investigate whether TNP can effectively deliver DOX into tumors and bypass the efflux function of the ABCB1 transporter, thereby increasing the intratumoral accumulation of DOX and potentiating the anticancer activity of DOX. MTT assays suggested that DOX-TNP showed higher cytotoxicity toward CCD-18Co, SW620 and SW620/Ad300 cells than DOX. Animal study revealed that DOX-TNP resulted in greater inhibitory effects on the growth of SW620 and SW620/Ad300 tumors than DOX. In pharmacokinetics study, DOX-TNP greatly increased the SW620 and SW620/Ad300 intratumoral concentrations of DOX. But DOX-TNP had no effect on the plasma concentrations of DOX. Furthermore, TNP is a safe nanocarrier with excellent biocompatibility and minimal toxicity. Ex vivo IHC analysis of SW620 and SW620/Ad300 tumor sections revealed evidence of prominent antitumor activity of DOX-TNP. In conclusion, our findings suggested that natural nanomaterials could be useful in combating multidrug resistance (MDR) in cancer cells and potentiating the anticancer activity of chemotherapeutic agents in cancer treatment.

ABCG2/BCRP interaction with the sea grass Thalassia testudinum

BACKGROUND

The aqueous ethanolic extract from leaves of the marine plant Thalassia testudinum has shown antioxidant, cytoprotective, and neuroprotective properties. The chemical composition of this extract, rich in polyphenols, could interfere with active transport of drugs out of the cell and circumvent the phenomenon of multidrug resistance (MDR). The extract can act as an MDR modulator through its interaction with efflux transporters. The ABCG2/BCRP has been shown to confer MDR acting in tumor cells.

METHODS

To evaluate the interaction of ABCG2/BCRP with the extract, studies in cells overexpressing human BCRP transporter and its murine ortholog Bcrp1 were performed.

RESULTS AND CONCLUSIONS

T. testudinum extract could be included as MDR modulator, as interaction with ABCG2/BCRP has been shown through flow cytometry and MTT assays. The cells overexpressing ABCG2/BCRP in the presence of the extract (25-150 μg/mL) decreased the survival rates of the anti-tumoral mitoxantrone. Our results support its inclusion as a possible MDR modulator against tumor cells that overexpress ABCG2/BCRP.

ABCG2 in peptic ulcer: gene expression and mutation analysis

The aim of this study was to evaluate the participation of polymorphism at position C421A and mRNA expression of the ABCG2 gene in the development of peptic ulcers, which is a very common and severe disease. ABCG2, encoded by the ABCG2 gene, has been found inter alia in the gastrointestinal tract, where it plays a protective role eliminating xenobiotics from cells into the extracellular environment. The materials for the study were biopsies of gastric mucosa taken during a routine endoscopy. For genotyping by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) at position C421A, DNA was isolated from 201 samples, while for the mRNA expression level by real-time PCR, RNA was isolated from 60 patients. The control group of healthy individuals consisted of 97 blood donors. The dominant genotype in the group of peptic ulcer patients and healthy individuals was homozygous CC. No statistically significant differences between healthy individuals and the whole group of peptic ulcer patients and, likewise, between the subgroups of peptic ulcer patients (infected and uninfected with Helicobacter pylori) were found. ABCG2 expression relative to GAPDH expression was found in 38 of the 60 gastric mucosa samples. The expression level of the gene varies greatly among cases. The statistically significant differences between the intensity (p = 0.0375) of H. pylori infection and ABCG2 gene expression have been shown. It was observed that the more intense the infection, the higher the level of ABCG2 expression.

Allocrite Sensing and Binding by the Breast Cancer Resistance Protein (ABCG2) and P-Glycoprotein (ABCB1)

The ATP binding cassette (ABC) transporters ABCG2 and ABCB1 perform ATP hydrolysis-dependent efflux of structurally highly diverse compounds, collectively called allocrites. Whereas much is known about allocrite-ABCB1 interactions, the chemical nature and strength of ABCG2-allocrite interactions have not yet been assessed. We quantified and characterized interactions of allocrite with ABCG2 and ABCB1 using a set of 39 diverse compounds. We also investigated potential allocrite binding sites based on available transporter structures and structural models. We demonstrate that ABCG2 binds its allocrites from the lipid membrane, despite their hydrophilicity. Hence, binding of allocrite to both transporters is a two-step process, starting with a lipid-water partitioning step, driven mainly by hydrophobic interactions, followed by a transporter binding step in the lipid membrane. We show that binding of allocrite to both transporters increases with the number of hydrogen bond acceptors in allocrites. Scrutinizing the transporter translocation pathways revealed ample hydrogen bond donors for allocrite binding. Importantly, the hydrogen bond donor strength is, on average, higher in ABCG2 than in ABCB1, which explains the higher measured affinity of allocrite for ABCG2. π-π stacking and π-cation interactions play additional roles in binding of allocrite to ABCG2 and ABCB1. With this analysis, we demonstrate that these membrane-mediated weak electrostatic interactions between transporters and allocrites allow for transporter promiscuity toward allocrites. The different sensitivities of the transporters to allocrites' charge and amphiphilicity provide transporter specificity. In addition, we show that the different hydrogen bond donor strengths in the two transporters allow for affinity tuning.

Comparative Aspects of Molecular Mechanisms of Drug Resistance through ABC Transporters and Other Related Molecules in Canine Lymphoma

The most important causes of treatment failure in canine lymphoma include intrinsic or acquired drug resistance. Thus, elucidation of molecular mechanisms of drug resistance is essential for the establishment of better treatment alternatives for lymphoma patients. The overexpression of drug transporters is one of the most intensively studied mechanisms of drug resistance in many tumors. In canine lymphoma, it has also been shown that the overexpression of drug efflux pumps such as P-glycoprotein is associated with drug-resistant phenotypes. Canine lymphoma has many pathological similarities to human non-Hodgkin’s lymphoma, and they also share similar molecular mechanisms of drug resistance. We have previously demonstrated the association of the overexpression of drug transporters with drug resistance and indicated some molecular mechanisms of the regulation of these transporters’ expressions in canine and human lymphoid tumor cells. However, it has also been indicated that other known or novel drug resistance factors should be explored to overcome drug resistance in lymphoma. In this review, we summarize the recent findings on the molecular mechanisms of drug resistance and possible strategies to develop better treatment modalities for canine lymphoma from the comparative aspects with human lymphoid tumors.

Design of inhibitors of BCRP/ABCG2

BCRP/ABCG2, a second member of ABC transporter subclass G, has been shown to be overexpressed in several solid tumors, acute myelogenous leukemia and chronic myeloid leukemia. A variety of chemically unrelated anticancer drugs have been found to be transported by ABCG2 leading to their lower intracellular accumulation and hence causing chemoresistance. Until now several efforts have been taken to identify potent and selective inhibitors of ABCG2. Recent studies carried out to deign BCRP inhibitors have been able to point out the effect of the substitution pattern in compound scaffolds on the potency, selectivity and cytotoxicity of ABCG2 inhibitors.

Influence of multidrug resistance and drug transport proteins on chemotherapy drug metabolism

INTRODUCTION

Chemotherapy involving the use of anticancer drugs remains an important strategy in the overall management of patients with metastatic cancer. Acquisition of multidrug resistance remains a major impediment to successful chemotherapy. Drug transporters in cell membranes and intracellular drug metabolizing enzymes contribute to the resistance phenotype and determine the pharmacokinetics of anticancer drugs in the body.

AREAS COVERED

ATP-binding cassette (ABC) transporters mediate the transport of endogenous metabolites and xenobiotics including cytotoxic drugs out of cells. Solute carrier (SLC) transporters mediate the influx of cytotoxic drugs into cells. This review focuses on the substrate interaction of these transporters, on their biology and what role they play together with drug metabolizing enzymes in eliminating therapeutic drugs from cells.

EXPERT OPINION

The majority of anticancer drugs are substrates for the ABC transporter and SLC transporter families. Together, these proteins have the ability to control the influx and the efflux of structurally unrelated chemotherapeutic drugs, thereby modulating the intracellular drug concentration. These interactions have important clinical implications for chemotherapy because ultimately they determine therapeutic efficacy, disease progression/relapse and the success or failure of patient treatment.

Blood brain barrier: a challenge for effectual therapy of brain tumors

Brain tumors are one of the most formidable diseases of mankind. They have only a fair to poor prognosis and high relapse rate. One of the major causes of extreme difficulty in brain tumor treatment is the presence of blood brain barrier (BBB). BBB comprises different molecular components and transport systems, which in turn create efflux machinery or hindrance for the entry of several drugs in brain. Thus, along with the conventional techniques, successful modification of drug delivery and novel therapeutic strategies are needed to overcome this obstacle for treatment of brain tumors. In this review, we have elucidated some critical insights into the composition and function of BBB and along with it we have discussed the effective methods for delivery of drugs to the brain and therapeutic strategies overcoming the barrier.

The modulation of ABC transporter-mediated multidrug resistance in cancer: a review of the past decade

ATP-binding cassette (ABC) transporters represent one of the largest and oldest families of membrane proteins in all extant phyla from prokaryotes to humans, which couple the energy derived from ATP hydrolysis essentially to translocate, among various substrates, toxic compounds across the membrane. The fundamental functions of these multiple transporter proteins include: (1) conserved mechanisms related to nutrition and pathogenesis in bacteria, (2) spore formation in fungi, and (3) signal transduction, protein secretion and antigen presentation in eukaryotes. Moreover, one of the major causes of multidrug resistance (MDR) and chemotherapeutic failure in cancer therapy is believed to be the ABC transporter-mediated active efflux of a multitude of structurally and mechanistically distinct cytotoxic compounds across membranes. It has been postulated that ABC transporter inhibitors known as chemosensitizers may be used in combination with standard chemotherapeutic agents to enhance their therapeutic efficacy. The current paper reviews the advance in the past decade in this important domain of cancer chemoresistance and summarizes the development of new compounds and the re-evaluation of compounds originally designed for other targets as transport inhibitors of ATP-dependent drug efflux pumps.

Modification of topoisomerases in mammospheres derived from breast cancer cell line: clinical implications for combined treatments with tyrosine kinase inhibitors

BACKGROUND

Accumulating evidences suggest that tumors are driven by a small population of cells, termed "cancer stem cells" (CSCs), which may be resistant to current therapeutic approaches. In breast carcinoma, the CSCs have been identified as a CD44+/CD24- cell population. These rare cells are able to grow as non-adherent sphere-like structures, termed "mammospheres", which enables their isolation and expansion in culture. To design efficient strategies for the complete eradication of CSCs, it is important to identify enzymes and proteins that are known as anti-cancer targets, and differ in their properties from those present in the none CSCs. Here we investigated the activity and expression of type I and type II DNA topoisomerases (topo I and topo II) in CSCs and their response to anti-topoisomerase inhibitors.

METHODS

MCF7 breast cancer cells, PC3 prostate cancer cells and 4 T1-Luc-Oct3/4pG mouse mammary carcinoma cells were grown on low-attachment dishes in specific medium and allowed to form spheres. Enrichment of CSC population was verified by immunostaining, flow cytometry or fluorescent microscopy imaging. Nuclear protein extracts were prepared and topoisomerases activity and protein levels were determined. Cell viability was examined by the MTT and Neutral Red assays.

RESULTS

Unlike the adherent MCF7 cell line, topo I activity is decreased and topo II activity is increased in the CSCs. However, the relative levels of the enzyme proteins were similar in both mammospheres and adherent cells. Topo I activity in mammospheres is regulated, at least in part, by PARP-1, as observed by the recovery of topo I activity after treatment with PARP-1 inhibitor 3-Aminobenzamide. Mammosphere-derived cells show reduced sensitivity to topo I inhibitor, camptothecin, and increased sensitivity to topo II inhibitor etoposide. Intact mammospheres show increased resistance to both drugs. A combined treatment of intact mammospheres with either CPT and gefitinib, or etoposide and erlotinib, increased the anti-cancer effect of both drugs.

CONCLUSIONS

The data of this study suggest that the understanding of biological behavior of essential enzymes such as topoisomerases, in CSCs' progression and early stages of tumor development, is important for developing new strategies for cancer treatment as well as new therapies for advanced disease.

Transporters at CNS barrier sites: obstacles or opportunities for drug delivery?

The blood-brain barrier (BBB) and blood-cerebrospinal fluid (BCSF) barriers are critical determinants of CNS homeostasis. Additionally, the BBB and BCSF barriers are formidable obstacles to effective CNS drug delivery. These brain barrier sites express putative influx and efflux transporters that precisely control permeation of circulating solutes including drugs. The study of transporters has enabled a shift away from "brute force" approaches to delivering drugs by physically circumventing brain barriers towards chemical approaches that can target specific compounds of the BBB and/or BCSF barrier. However, our understanding of transporters at the BBB and BCSF barriers has primarily focused on understanding efflux transporters that efficiently prevent drugs from attaining therapeutic concentrations in the CNS. Recently, through the characterization of multiple endogenously expressed uptake transporters, this paradigm has shifted to the study of brain transporter targets that can facilitate drug delivery (i.e., influx transporters). Additionally, signaling pathways and trafficking mechanisms have been identified for several endogenous BBB/BCSF transporters, thereby offering even more opportunities to understand how transporters can be exploited for optimization of CNS drug delivery. This review presents an overview of the BBB and BCSF barrier as well as the many families of transporters functionally expressed at these barrier sites. Furthermore, we present an overview of various strategies that have been designed and utilized to deliver therapeutic agents to the brain with a particular emphasis on those approaches that directly target endogenous BBB/BCSF barrier transporters.

Investigation of the functional single-nucleotide polymorphisms in the BCRP transporter and susceptibility to colorectal cancer

Breast cancer resistance protein (BCRP) protects tissues by actively transporting xenobiotics and their metabolites out of the cells. BCRP is expressed in the apical membrane of normal intestinal and colonic epithelium. The BCRP substrates include a number of structurally unrelated compounds, such as drugs, pesticides, carcinogens and endogenous compounds. Although the functional and common BCRP alleles, 34G>A and 421C>A, are shown to vary by ethnicity, their potential mechanism has not been adequately described with regards to affecting the susceptibility to colorectal cancer. The present study aimed to evaluate the effects of the BCRP variants on the susceptibility to colorectal cancer and to predict the individual responses to xenobiotics transferred by BCRP. BCRP 421C>A was significantly associated with the colorectal cancer risk (odds ratio, 16.12; P=0.005). These findings are the first results of BCRP allele distributions in the Turkish population and provide an understanding of the correlation between therapeutic approaches and etiology of colorectal cancer.

Influence of single-nucleotide polymorphisms on deferasirox C trough levels and effectiveness

Deferasirox (DFX) is the only once-daily oral chelator for iron overload and its pharmacokinetic has been related with response to therapy. Our aim was to evaluate DFX plasma concentrations according to single-nucleotide polymorphisms in genes involved in its metabolism (UGT1A1, UGT1A3, CYP1A1, CYP1A2 and CYP2D6) and elimination (MRP2 and BCRP1). Further aim was to define a plasma concentration cutoff value predicting an adequate response to therapy. Plasma concentrations were determined at the end of dosing interval (C trough) using an high-performance liquid chromatography-ultraviolet method. Allelic discrimination was performed by real-time PCR. C trough levels were influenced by UGT1A1C>T rs887829, CYP1A1C>A rs2606345, CYP1A2A>C rs762551, CYP1A2C>T rs2470890 and MRP2G>A rs2273697 polymorphisms. A DFX plasma efficacy cutoff value of 20,000 ng ml(-1) was identified; CYP1A1C>A rs2606345 AA and CYP1A2C>T rs2470890 TT genotypes may predict this value, suggesting a negative predictive role in therapy efficacy. Our data suggest the feasibility of a pharmacogenetic-based DFX dose personalization.

Repositioning of Tyrosine Kinase Inhibitors as Antagonists of ATP-Binding Cassette Transporters in Anticancer Drug Resistance

The phenomenon of multidrug resistance (MDR) has attenuated the efficacy of anticancer drugs and the possibility of successful cancer chemotherapy. ATP-binding cassette (ABC) transporters play an essential role in mediating MDR in cancer cells by increasing efflux of drugs from cancer cells, hence reducing the intracellular accumulation of chemotherapeutic drugs. Interestingly, small-molecule tyrosine kinase inhibitors (TKIs), such as AST1306, lapatinib, linsitinib, masitinib, motesanib, nilotinib, telatinib and WHI-P154, have been found to have the capability to overcome anticancer drug resistance by inhibiting ABC transporters in recent years. This review will focus on some of the latest and clinical developments with ABC transporters, TKIs and anticancer drug resistance.

Role of the breast cancer resistance protein (BCRP/ABCG2) in drug transport--an update

The human breast cancer resistance protein (BCRP, gene symbol ABCG2) is an ATP-binding cassette (ABC) efflux transporter. It was so named because it was initially cloned from a multidrug-resistant breast cancer cell line where it was found to confer resistance to chemotherapeutic agents such as mitoxantrone and topotecan. Since its discovery in 1998, the substrates of BCRP have been rapidly expanding to include not only therapeutic agents but also physiological substances such as estrone-3-sulfate, 17β-estradiol 17-(β-D-glucuronide) and uric acid. Likewise, at least hundreds of BCRP inhibitors have been identified. Among normal human tissues, BCRP is highly expressed on the apical membranes of the placental syncytiotrophoblasts, the intestinal epithelium, the liver hepatocytes, the endothelial cells of brain microvessels, and the renal proximal tubular cells, contributing to the absorption, distribution, and elimination of drugs and endogenous compounds as well as tissue protection against xenobiotic exposure. As a result, BCRP has now been recognized by the FDA to be one of the key drug transporters involved in clinically relevant drug disposition. We published a highly-accessed review article on BCRP in 2005, and much progress has been made since then. In this review, we provide an update of current knowledge on basic biochemistry and pharmacological functions of BCRP as well as its relevance to drug resistance and drug disposition.

Tyrosine kinase inhibitors as reversal agents for ABC transporter mediated drug resistance

Tyrosine kinases (TKs) play an important role in pathways that regulate cancer cell proliferation, apoptosis, angiogenesis and metastasis. Aberrant activity of TKs has been implicated in several types of cancers. In recent years, tyrosine kinase inhibitors (TKIs) have been developed to interfere with the activity of deregulated kinases. These TKIs are remarkably effective in the treatment of various human cancers including head and neck, gastric, prostate and breast cancer and several types of leukemia. However, these TKIs are transported out of the cell by ATP-binding cassette (ABC) transporters, resulting in development of a characteristic drug resistance phenotype in cancer patients. Interestingly, some of these TKIs also inhibit the ABC transporter mediated multi drug resistance (MDR) thereby; enhancing the efficacy of conventional chemotherapeutic drugs. This review discusses the clinically relevant TKIs and their interaction with ABC drug transporters in modulating MDR.

ABC transporters in multi-drug resistance and ADME-Tox of small molecule tyrosine kinase inhibitors

The past decade has seen tremendous efforts in the research and development of new chemotherapeutic drugs using target-based approaches. These efforts have led to the discovery of small molecule tyrosine kinase inhibitors (TKIs). Following the initial approval of imatinib by the US FDA in 2001, more than 15 TKIs targeting different tyrosine kinases have been approved, and numerous others are in various phases of clinical evaluation. Unlike conventional chemotherapy that can cause non-discriminating damage to both normal and cancerous cells, TKIs attack cancer-specific targets and therefore have a more favorable safety profile. However, although TKIs have had outstanding success in cancer therapy, there has been increasing evidence of resistance to TKIs. The enhanced efflux of TKIs by ATP-binding cassette (ABC) transporters over-expressed in cancer cells has been found to be one such important resistance mechanism. Another major drawback of TKI therapies that has been increasingly recognized is the extensive inter-individual pharmacokinetic variability, in which ABC transporters seem to play a major role as well. This review covers recent findings on the interactions of small molecule TKIs with ABC transporters. The effects of ABC transporters on anticancer efficacy and the absorption, distribution, metabolism, excretion, and toxicity (ADME-Tox) of the small molecule TKIs are summarized in detail. Since TKIs have been found to not only serve as substrates of ABC transporters, but also as modulators of these proteins via inhibition or induction, their influence upon ABC transporters and potential role on TKI-drug interactions are discussed as well.

ABC transporters in fish species: a review

ATP-binding cassette (ABC) proteins were first recognized for their role in multidrug resistance (MDR) in chemotherapeutic treatments, which is a major impediment for the successful treatment of many forms of malignant tumors in humans. These proteins, highly conserved throughout vertebrate species, were later related to cellular detoxification and accounted as responsible for protecting aquatic organisms from xenobiotic insults in the so-called multixenobiotic resistance mechanism (MXR). In recent years, research on these proteins in aquatic species has highlighted their importance in the detoxification mechanisms in fish thus it is necessary to continue these studies. Several transporters have been pointed out as relevant in the ecotoxicological context associated to the transport of xenobiotics, such as P-glycoproteins (Pgps), multidrug-resistance-associated proteins (MRPs 1-5) and breast cancer resistance associated protein (BCRP). In mammals, several nuclear receptors have been identified as mediators of phase I and II metabolizing enzymes and ABC transporters. In aquatic species, knowledge on co-regulation of the detoxification mechanism is scarce and needs to be addressed. The interaction of emergent contaminants that can act as chemosensitizers, with ABC transporters in aquatic organisms can compromise detoxification processes and have population effects and should be studied in more detail. This review intends to summarize the recent advances in research on MXR mechanisms in fish species, focusing in (1) regulation and functioning of ABC proteins; (2) cooperation with phase I and II biotransformation enzymes; and (3) ecotoxicological relevance and information on emergent pollutants with ability to modulate ABC transporters expression and activity. Several lines of evidence are clearly suggesting the important role of these transporters in detoxification mechanisms and must be further investigated in fish to underlay the mechanism to consider their use as biomarkers in environmental monitoring.

Hepatocellular exposure of troglitazone metabolites in rat sandwich-cultured hepatocytes lacking Bcrp and Mrp2: interplay between formation and excretion

Inhibition of bile acid transport by troglitazone (TGZ) and its major metabolite, TGZ sulfate (TS), may lead to hepatocellular accumulation of toxic bile acids; TS accumulation and hepatotoxicity may be associated with impaired TS biliary excretion. This study evaluated the impact of impaired transport of breast cancer resistance protein (Bcrp) and multidrug resistance-associated protein 2 (Mrp2) on the hepatobiliary disposition of generated metabolites, TS and TGZ glucuronide (TG). Sandwich-cultured hepatocytes (SCH) from Mrp2-deficient (TR(-)) rats in combination with Bcrp knockdown using RNA interference were employed. The biliary excretion index (BEI) of generated TS was not significantly altered by impaired Bcrp (20.9 to 21.1%) and/or Mrp2 function (24.4% and 17.5% in WT and TR(-) rat SCH, respectively). Thus, loss-of-function of Mrp2 and/or Bcrp do not appear to be risk factors for increased hepatocellular TS accumulation in rats, potentially because of a compensatory transporter(s) that excretes TS into bile. Further investigations revealed that the compensatory TS biliary transporter was not the bile salt export pump (Bsep) or P-glycoprotein (P-gp). Interestingly, TGZ sulfation was significantly decreased in TR(-) compared with WT rat SCH (total recovery: 2.8 versus 5.0% of TGZ dose), resulting in decreased hepatocellular TS accumulation, even though sulfotransferase activity in TR(-) rat hepatocyte S9 fraction was similar. Hepatocellular TG accumulation was significantly increased in TR(-) compared with WT rat SCH due to increased glucuronidation and negligible TG biliary excretion. These data emphasize that the interplay between metabolite formation and excretion determines hepatocellular exposure to generated metabolites such as TS and TG.

Motesanib (AMG706), a potent multikinase inhibitor, antagonizes multidrug resistance by inhibiting the efflux activity of the ABCB1

Cancer cells often become resistant to chemotherapy through a phenomenon known as multidrug resistance (MDR). Several factors are responsible for the development of MDR, preeminent among them being the accelerated drug efflux mediated by overexpression of ATP binding cassette (ABC) transporters. Some small molecule tyrosine kinase inhibitors (TKIs) were recently reported to modulate the activity of ABC transporters. Therefore, the purpose of this study was to determine if motesanib, a multikinase inhibitor, could reverse ABCB1-mediated MDR. The results showed that motesanib significantly sensitized both ABCB1-transfected and drug-selected cell lines overexpressing this transporter to its substrate anticancer drugs. Motesanib significantly increased the accumulation of [(3)H]-paclitaxel in ABCB1 overexpressing cells by blocking the efflux function of ABCB1 transporter. In contrast, no significant change in the expression levels and localization pattern of ABCB1 was observed when ABCB1 overexpressing cells were exposed to 3μM motesanib for 72h. Moreover, motesanib stimulated the ATPase activity of ABCB1 in a concentration-dependent manner, indicating a direct interaction with the transporter. Consistent with these findings, the docking studies indicated favorable binding of motesanib within the transmembrane region of homology modeled human ABCB1. Here, we report for the first time, motesanib, at clinically achievable plasma concentrations, antagonizes MDR by inhibiting the efflux activity of the ABCB1 transporter. These findings may be useful for cancer combination therapy with TKIs in the clinic.

Co-administration of rivaroxaban with drugs that share its elimination pathways: pharmacokinetic effects in healthy subjects

AIMS

The anticoagulant rivaroxaban is an oral, direct Factor Xa inhibitor for the management of thromboembolic disorders. Metabolism and excretion involve cytochrome P450 3A4 (CYP3A4) and 2J2 (CYP2J2), CYP-independent mechanisms, and P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) (ABCG2).

METHODS

The pharmacokinetic effects of substrates or inhibitors of CYP3A4, P-gp and Bcrp (ABCG2) on rivaroxaban were studied in healthy volunteers.

RESULTS

Rivaroxaban did not interact with midazolam (CYP3A4 probe substrate). Exposure to rivaroxaban when co-administered with midazolam was slightly decreased by 11% (95% confidence interval [CI] -28%, 7%) compared with rivaroxaban alone. The following drugs moderately affected rivaroxaban exposure, but not to a clinically relevant extent: erythromycin (moderate CYP3A4/P-gp inhibitor; 34% increase [95% CI 23%, 46%]), clarithromycin (strong CYP3A4/moderate P-gp inhibitor; 54% increase [95% CI 44%, 64%]) and fluconazole (moderate CYP3A4, possible Bcrp [ABCG2] inhibitor; 42% increase [95% CI 29%, 56%]). A significant increase in rivaroxaban exposure was demonstrated with the strong CYP3A4, P-gp/Bcrp (ABCG2) inhibitors (and potential CYP2J2 inhibitors) ketoconazole (158% increase [95% CI 136%, 182%] for a 400 mg once daily dose) and ritonavir (153% increase [95% CI 134%, 174%]).

CONCLUSIONS

Results suggest that rivaroxaban may be co-administered with CYP3A4 and/or P-gp substrates/moderate inhibitors, but not with strong combined CYP3A4, P-gp and Bcrp (ABCG2) inhibitors (mainly comprising azole-antimycotics, apart from fluconazole, and HIV protease inhibitors), which are multi-pathway inhibitors of rivaroxaban clearance and elimination.

Linsitinib (OSI-906) antagonizes ATP-binding cassette subfamily G member 2 and subfamily C member 10-mediated drug resistance

In this study we investigated the effect of linsitinib on the reversal of multidrug resistance (MDR) mediated by the overexpression of the ATP-binding cassette (ABC) subfamily members ABCB1, ABCG2, ABCC1 and ABCC10. Our results indicate for the first time that linsitinib significantly potentiate the effect of anti-neoplastic drugs mitoxantrone (MX) and SN-38 in ABCG2-overexpressing cells; paclitaxel, docetaxel and vinblastine in ABCC10-overexpressing cells. Linsitinib moderately enhanced the cytotoxicity of vincristine in cell lines overexpressing ABCB1, whereas it did not alter the cytotoxicity of substrates of ABCC1. Furthermore, linsitinib significantly increased the intracellular accumulation and decreased the efflux of [(3)H]-MX in ABCG2-overexpressing cells and [(3)H]-paclitaxel in ABCC10-overexpressing cells. However, linsitinib, at a concentration that reversed MDR, did not significantly alter the expression levels of either the ABCG2 or ABCC10 transporter proteins. Furthermore, linsitinib did not significantly alter the intracellular localization of ABCG2 or ABCC10. Moreover, linsitinib stimulated the ATPase activity of ABCG2 in a concentration-dependent manner. Overall, our study suggests that linsitinib attenuates ABCG2- and ABCC10-mediated MDR by directly inhibiting their function as opposed to altering ABCG2 or ABCC10 protein expression.

Masitinib antagonizes ATP-binding cassette subfamily G member 2-mediated multidrug resistance

In this in vitro study, we determined whether masitinib could reverse multidrug resistance (MDR) in cells overexpressing the ATP binding cassette subfamily G member 2 (ABCG2) transporter. Masitinib (1.25 and 2.5 μM) significantly decreases the resistance to mitoxantrone (MX), SN38 and doxorubicin in HEK293 and H460 cells overexpressing the ABCG2 transporter. In addition, masitinib (2.5 μM) significantly increased the intracellular accumulation of [³H]-MX, a substrate for ABCG2, by inhibiting the function of ABCG2 and significantly decreased the efflux of [³H]-MX. However, masitinib (2.5 μM) did not significantly alter the expression of the ABCG2 protein. In addition, a docking model suggested that masitinib binds within the transmembrane region of a homology-modeled human ABCG2 transporter. Overall, our in vitro findings suggest that masitinib reverses MDR to various anti-neoplastic drugs in HEK293 and H460 cells overexpressing ABCG2 by inhibiting their transport activity as opposed to altering their levels of expression.

In silico prediction of inhibition of promiscuous breast cancer resistance protein (BCRP/ABCG2)

BACKGROUND

Breast cancer resistant protein has an essential role in active transport of endogenous substances and xenobiotics across extracellular and intracellular membranes along with P-glycoprotein. It also plays a major role in multiple drug resistance and permeation of blood-brain barrier. Therefore, it is of great importance to derive theoretical models to predict the inhibition of both transporters in the process of drug discovery and development. Hitherto, very limited BCRP inhibition predictive models have been proposed as compared with its P-gp counterpart.

METHODOLOGY/PRINCIPAL FINDINGS

An in silico BCRP inhibition model was developed in this study using the pharmacophore ensemble/support vector machine scheme to take into account the promiscuous nature of BCRP. The predictions by the PhE/SVM model were found to be in good agreement with the observed values for those molecules in the training set (n= 22, r2 =0.82, qCV2=0.73, RMSE= 0.40, s = 0.24), test set (n =97, q2=0.75-0.89, RMSE= 0.31, s= 0.21), and outlier set (n= 16, q2 =0.72-0.91, RMSE= 0.29, s=0.17). When subjected to a variety of statistical validations, the developed PhE/SVM model consistently met the most stringent criteria. A mock test by HIV protease inhibitors also asserted its predictivity.

CONCLUSIONS/SIGNIFICANCE

It was found that this accurate, fast, and robust PhE/SVM model can be employed to predict the BCRP inhibition of structurally diverse molecules that otherwise cannot be carried out by any other methods in a high-throughput fashion to design therapeutic agents with insignificant drug toxicity and unfavorable drug-drug interactions mediated by BCRP to enhance clinical efficacy and/or circumvent drug resistance.

ABCG2 gene amplification and expression in esophageal cancer cells with acquired adriamycin resistance

Resistance to chemotherapeutic agents is the main reason for treatment failure in patients with cancer. The primary mechanism of multidrug resistance (MDR) is the overexpression of drug efflux transporters, including ATP‑binding cassette transporter G2 (ABCG2). To the best of our knowledge, the MDR mechanisms of esophageal cancer have not been described. An adriamycin (ADM)-resistant subline, Eca109/ADM, was generated from the Eca109 esophageal cancer cell line by a stepwise selection in ADM from 0.002 to 0.02 ng/µl. The resulting subline, designated Eca109/ADM, revealed a 3.29-fold resistance against ADM compared with the Eca109 cell line. The ABCG2 gene expression in the Eca109/ADM cells was increased compared with that of the Eca109 cells. The cellular properties of the Eca109/ADM cells were detected by reverse transcription polymerase chain reaction (RT-PCR), flow cytometry and western blotting. The ABCG2 expression levels were detected by RT-PCR and flow cytometry, and the drug efflux effect was detected by flow cytometry. The present study detected the correlation between ABCG2 and the multidrug resistance of esophageal cancer. ABCG2 gene expression and the drug efflux effect of the Eca109/ADM cells were increased compared with those of the Eca109 cells. Collectively, the results of this study indicated that the overexpression of ABCG2 in the Eca109/ADM cells resulted in drug efflux, which may be responsible for the development of esophageal cancer MDR.

Phase 0 and phase III transport in various organs: combined concept of phases in xenobiotic transport and metabolism

The historical phasing concept of drug metabolism and elimination was introduced to comprise the two phases of metabolism: phase I metabolism for oxidations, reductions and hydrolyses, and phase II metabolism for synthesis. With this concept, biological membrane barriers obstructing the accessibility of metabolism sites in the cells for drugs were not considered. The concept of two phases was extended to a concept of four phases when drug transporters were detected that guided drugs and drug metabolites in and out of the cells. In particular, water soluble or charged drugs are virtually not able to overcome the phospholipid membrane barrier. Drug transporters belong to two main clusters of transporter families: the solute carrier (SLC) families and the ATP binding cassette (ABC) carriers. The ABC transporters comprise seven families with about 20 carriers involved in drug transport. All of them operate as pumps at the expense of ATP splitting. Embedded in the former phase concept, the term "phase III" was introduced by Ishikawa in 1992 for drug export by ABC efflux pumps. SLC comprise 52 families, from which many carriers are drug uptake transporters. Later on, this uptake process was referred to as the "phase 0 transport" of drugs. Transporters for xenobiotics in man and animal are most expressed in liver, but they are also present in extra-hepatic tissues such as in the kidney, the adrenal gland and lung. This review deals with the function of drug carriers in various organs and their impact on drug metabolism and elimination.

An experimental approach to evaluate the impact of impaired transport function on hepatobiliary drug disposition using Mrp2-deficient TR- rat sandwich-cultured hepatocytes in combination with Bcrp knockdown

Breast cancer resistance protein (BCRP) and multidrug resistance-associated protein 2 (MRP2) are members of the ATP binding cassette (ABC) transporter family located in the canalicular membrane of hepatocytes that mediate biliary excretion of many drugs and endogenous compounds. BCRP and MRP2 have overlapping substrate profiles. Predicting drug disposition in the setting of altered transport function has important clinical significance. This investigation was designed to establish an in vitro model system to evaluate the impact of impaired Mrp2 and Bcrp function on hepatobiliary drug disposition. To achieve Bcrp knockdown by RNA interference (RNAi), sandwich-cultured hepatocytes (SCH) from Mrp2-deficient (TR(-)) and wild-type (WT) rats were infected with adenoviral vectors to express shRNA targeting Bcrp (Ad-siBcrp) at multiplicity of infection (MOI) of 1-10. MOI of 5 was identified as optimal. At MOI of 5, viral infection as well as WT or TR(-) status was statistically significant predictors of the rosuvastatin (RSV) biliary excretion index (BEI), consistent with the known role of Bcrp and Mrp2 in the biliary excretion of RSV in vivo in rats. Relative to WT rat SCH, marginal mean BEI (%) of RSV in TR(-) rat SCH decreased by 28.6 (95% CI: 5.8-51.3). Ad-siBcrp decreased marginal mean BEI (%) of RSV by 13.3 (7.5-9.1) relative to SCH infected with adenoviral vectors expressing a nontargeting shRNA (Ad-siNT). The BEI of RSV was almost ablated in TR(-) rat SCH with Bcrp knockdown (5.9 ± 3.0%) compared to Ad-siNT-infected WT rat SCH (45.4 ± 6.6%). These results demonstrated the feasibility of Bcrp knockdown in TR(-) rat SCH as an in vitro system to assess the impact of impaired Bcrp and Mrp2 function. At MOI of 5, viral infection had minimal effects on RSV total accumulation, but significantly decreased marginal mean taurocholate total accumulation (pmol/mg of protein) and BEI (%) by 9.9 (7.0-12.8) and 7.5 (3.7-11.3), respectively, relative to noninfected SCH. These findings may be due to off-target effects on hepatic bile acid transporters, even though no changes in protein expression levels of the hepatic bile acid transporters were observed. This study established a strategy for optimization of the knockdown system, and demonstrated the potential use of RNAi in SCH as an in vitro tool to predict altered hepatobiliary drug disposition when canalicular transporters are impaired.

Celecoxib Up Regulates the Expression of Drug Efflux Transporter ABCG2 in Breast Cancer Cell Lines

Elevated expression of the drug efflux transporter ABCG2 seems to correlate with multidrug resistance of cancer cells. Specific COX-2 inhibitor celecoxib has been shown to enhance the sensitivity of cancer cells to anticancer drugs. To clarify whether ABCG2 inhibition is involved in the sensitizing effect of celecoxib, we investigated whether the expression of ABCG2 in breast cancer cell lines, could be modulated by celecoxib. The expression of the multidrug resistant gene (ABCG2) at mRNA and protein level was detected by real-time quantitative reverse transcription-polymerase chain reaction and flow cytometry analysis, respectively. Among three human breast cancer cell lines ABCG2 and COX-2 were highly expressed in MCF7-MX and MDA-MB-231 cells, respectively. The COX-2 inhibitor celecoxib up-regulated the expression of ABCG2 mRNA in MCF-7 and MCF7-MX cells, which was accompanied by increased ABCG2 protein expression. While celecoxib was able to block the 12-O-tetradecanoylphorbol-13-acetate (TPA)-mediated increase in COX-2 expression in MDA-MB-231 cells, it increased the expression of ABCG2 up to 4.27 times to the control level at mRNA level and with less intensity at protein level. Our findings provide evidence that celecoxib up-regulates ABCG2 expression in human breast cancer cells and proposed that ABCG2 is not involved in chemosensitizing effects of celecoxib.

Protein profiling of ovarian cancers by immunohistochemistry to identify potential target pathways

Background

To determine the protein expression profile (PEP) of primary and recurrent ovarian cancer patients in order to predict therapeutic targets for chemotherapy.

Methods

Tissue samples were submitted for PEP in two formats, including formalin-fixed paraffin-embedded tissue for immunohistochemistry (IHC) and fresh frozen tissue for oligonucleotide microarray (MA) gene expression assays. Specimens were analyzed for 18 protein markers and 88 MA genes. A series of Generalized Linear Models (GLM) was used to predict the proportion of positive results by histology for each biomarker.

Results

Four hundred and twenty-eight specimens were analyzed for IHC and 67 specimens for MA analysis. The majority of specimens, 82%, were serous histology and 35.3% of specimens were poorly differentiated. Sixty percent of specimens were advanced stage, 62% were from a primary diagnosis, and 53% were obtained from a metastatic site. BCRP, ER, MGMT, and RRM1 proteins were overexpressed in 85%, 47%, 93%, and 47% of serous carcinomas, respectively. The MGMT and RRM1 biomarkers were significantly overexpressed in serous (p < .001) and endometrioid (p = .01) histologies when compared to clear cell histology. MGMT was significantly elevated in 93% of serous and endometrioid samples, compared to 62% of samples with clear cell histology. Those proteins most often underexpressed included Her2/neu, SPARC, and c-kit, seen in less than 1%, 4%, and 5% of specimens, respectively.

Conclusions

PEP is a reliable and effective way of analyzing ovarian cancer specimens. PEP target identification does not appear to vary significantly with site evaluated, ovarian or other abdominal pelvic tissue, or primary versus recurrent disease. Variability in the expression of drug targets, including BCRP, ER, MGMT, and RRM1 could impact decision making pertaining to which therapeutic strategies carry the best chances for controlling disease.

Electronic supplementary material

The online version of this article (doi:10.1186/2053-6844-1-4) contains supplementary material, which is available to authorized users.

C-4 gem-dimethylated oleanes of Gymnema sylvestre and their pharmacological activities

Gymnema sylvestre R. Br., one of the most important medicinal plants of the Asclepiadaceae family, is a herb distributed throughout the World, predominantly in tropical countries. The plant, widely used for the treatment of diabetes and as a diuretic in Indian proprietary medicines, possesses beneficial digestive, anti-inflammatory, hypoglycemic and anti-helmentic effects. Furthermore, it is believed to be useful in the treatment of dyspepsia, constipation, jaundice, hemorrhoids, cardiopathy, asthma, bronchitis and leucoderma. A literature survey revealed that some other notable pharmacological activities of the plant such as anti-obesity, hypolipidemic, antimicrobial, free radical scavenging and anti-inflammatory properties have been proven too. This paper aims to summarize the chemical and pharmacological reports on a large group of C-4 gem-dimethylated pentacyclic triterpenoids from Gymnema sylvestre.

Investigation of quinazolines as inhibitors of breast cancer resistance protein (ABCG2)

Chemotherapy is one of the major forms of cancer treatment. Unfortunately, tumors are prone to multidrug resistance leading to failure of treatment. Breast cancer resistance protein (BCRP), the second member of ABC transporter subfamily G, has been found to play a major role in drug efflux and hence multidrug resistance. Until now, very few potent and selective BCRP inhibitors like Ko143 have been identified. In the search for more potent and selective BCRP inhibitors, we synthesized and investigated a series of differently substituted quinazoline compounds. Several variations at positions 2, 4, 6 and 7 of the quinazoline scaffold were carried out to develop a structure-activity-relationship analysis for these compounds. It was found that compounds bearing a phenyl substituent at position 2 of the 4-anilinoquinazoline scaffold were most potent. On the aniline ring at position 4 of the quinazoline moiety substituents like NO2, CN, CF3 led to very high BCRP inhibition potencies. The most potent compounds were further investigated for their intrinsic cytotoxicity and their ability to reverse the multidrug resistance. Compound 20, an anilinoquinazoline bearing a phenyl ring at position 2 and meta-nitro substitution on the 4-anilino ring, was found to have the highest therapeutic ratio. The most active compounds from each variation were also investigated for their effect on BCRP expression. It was found that compound 20 has no significant effect on BCRP expression, while compound 31 decreased the surface BCRP expression. The only difference in the two compounds was the presence of a 3,4-dimethoxyphenyl ring in compound 31 instead of phenyl substitution at position 2 of the quinazoline moiety. From the study of all target compounds, compound 20 was the most prominent compound having inhibitory potency even higher than Ko143, the most potent BCRP inhibitor known. Compound 20 was also found to be selective towards BCRP with a very high therapeutic ratio.

Reversal of multidrug resistance by the anti-malaria drug artesunate in the esophageal cancer Eca109/ABCG2 cell line

The overexpression of ATP-binding cassette (ABC) transporters confers multidrug resistance (MDR) to tumor cells. ABCG2 is a member of the ABC superfamily. The present study aimed to investigate the correlation between ABCG2 expression and the MDR of esophageal cancer and to estimate the therapeutic benefit of downregulating ABCG2 expression and reversing chemoresistance in esophageal cells using artesunate (Art). The Eca109/ABCG2 cell line was established by transfecting the ABCG2 gene into Eca109 cells. The Eca109/ABCG2 esophageal cancer cells with ABCG2 gene overexpression were resistant to adriamycin (ADM), daunorubicin (DNR) and mitoxantrone (MIT), which indicated that ABCG2 may be associated with drug resistance in esophageal cancer. Art is a noteworthy antimalarial agent, particularly in severe and drug-resistant cancer cases, as Art is able to reverse drug resistance. In the present study, Art also exerted profound anticancer activity. The mechanism for the reversal of multidrug resistance by Art in esophageal carcinoma was analyzed using cellular experiments, but still remains largely unknown.

Protoporphyrin IX accumulation disrupts mitochondrial dynamics and function in ABCG2-deficient hepatocytes

Targeted inhibition of multidrug ABCG2 transporter is believed to improve cancer therapeutics. However, the consequences of ABCG2 inhibition have not been systematically evaluated since ABCG2 is expressed in several organs including the liver. Here, we demonstrate that ABCG2-deficient hepatocytes have increased amounts of fragmental mitochondria accompanied by disruption of mitochondrial dynamics and functions. This disruption was due to ABCG2 knockout elevating intracellular protoporphyrin IX, which led to upregulation of DRP-1-mediated mitochondrial fission. The finding that ABCG2 deficiency can generate dysfunctional mitochondria in hepatocytes raises concerns regarding the systematic use of ABCG2 inhibitor in cancer patients.

The interaction between human breast cancer resistance protein (BCRP) and five bisbenzylisoquinoline alkaloids

BCRP is one of the key factors to drug absorption, distribution and elimination. Bisbenzylisoquinoline alkaloids are a large family of natural phytochemicals with great potential for clinical use. In this study, the interaction between BCRP and five bisbenzylisoquinoline alkaloids (neferine, isoliensinine, liensinine, dauricine and tetrandrine) were evaluated using LLC-PK1/BCRP cell model. The intracellular accumulation and bi-directional transport studies were conducted, and then molecular docking analysis was carried out employing a homology model of BCRP. Our study revealed that the permeability of these five alkaloids was not high, the Papp values were all less than 6.5 × 10(-6)cm/s. Liensinine and dauricine were substrates of BCRP: at lower concentration (10 μM), the net efflux ratios were 2.87 and 1.64 respectively. And their cellular accumulation was lower in LLC-PK1/BCRP cells than in LLC-PK1 cells. On the other hand, tetrandrine, isoliensinine and neferine were not substrates of BCRP. On the basis of docking studies, a direct hydrogen bond was formed between liensinine and arginine 482 which is a hot spot of BCRP for substrate specificity; and dauricine had hydrophobic interaction with BCRP. In conclusion, our study indicated that BCRP could mediate the excretion of liensinine and dauricine, thus influence their pharmacological activity and disposition.

Pharmacogenetic study of deferasirox, an iron chelating agent

Transfusion-associated iron overload induces systemic toxicity. Deferasirox, a convenient long acting oral agent, has recently been introduced in clinical practice with a promising efficacy. But there are some patients who experience drug-related toxicities and cannot tolerate it. To investigate effect of genetic variations on the toxicities and find optimal target population, we analyzed the genetic polymorphisms of UDP-glucuronosyltransferase 1A (UGT1A) subfamily, multi-drug resistance-associated protein 2 (MRP2) and breast cancer resistance protein (BCRP). A total of 20 functional genetic polymorphisms were analyzed in 98 patients who received deferasirox to reduce transfusion-induced iron overload. We retrospectively reviewed the medical records to find out the drug-related toxicities. Fifteen (15.3%) patients developed hepatotoxicity. Patients without wild-type allele carrying two MRP2 haplotypes containing −1774 del and/or −24T were at increased risk of developing hepatotoxicity compared to patients with the wild-type allele on multivariate analysis (OR = 7.17, 95% CI = 1.79–28.67, P = 0.005). Creatinine elevation was observed in 9 patients (9.2%). Body weight ≥40 kg and homozygosity for UGT1A1*6 were risk factors of creatinine elevation (OR = 8.48, 95% CI = 1.7–43.57, P = 0.010 and OR = 14.17, 95% CI = 1.34–150.35, P = 0.028). Our results indicate that functional genetic variants of enzymes to metabolize and transport deferasirox are associated with drug-related toxicities. Further studies are warranted to confirm the results as the pharmacogenetic biomarkers of deferasirox.

CD147 mediates chemoresistance in breast cancer via ABCG2 by affecting its cellular localization and dimerization

CD147 and ABCG2 both have been reported to mediate Multidrug resistance (MDR) in breast cancer. Recent study demonstrates that CD147 could form a complex with ABCG2 on the cell membrane in primary effusion lymphoma. However, whether these two molecules regulate each other in breast cancer and result in MDR is not clear. We established four MCF-7 cell lines transfected with CD147 and/or ABCG2 and found that CD147 could increase the expression and dimerization of ABCG2, affect its cellular localization and regulate its drug transporter function. The findings derived from cells were confirmed subsequently in clinic samples of chemotherapy-sensitive/resistant breast cancer.

Identification of novel breast cancer resistance protein (BCRP) inhibitors by virtual screening

Breast cancer resistance protein (BCRP; ABCG2) is an efflux transporter that plays an important role in multidrug resistance to antineoplastic drugs. The identification of drugs as BCRP inhibitors could aid in designing better therapeutic strategies for cancer treatment and will be critical for identifying potential drug-drug interactions. In the present study, we applied ligand-based virtual screening combined with experimental testing for the identification of novel drugs that can possibly interact with BCRP. Bayesian and pharmacophore models generated with known BCRP inhibitors were validated with an external test set. The resulting models were applied to predict new potential drug candidates from a database with more than 2000 FDA-approved drugs. Thirty-three drugs were tested in vitro for their inhibitory effects on BCRP-mediated transport of [(3)H]-mitoxantrone in MCF-7/AdrVp cells. Nineteen drugs were identified with significant inhibitory effect on BCRP transport function. The combined strategy of computational and experimental approaches in this paper has suggested potential drug candidates and thus represents an effective tool for rational identification of modulators of other proteins.

Progress in research of markers for cancer stem cells in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignant tumors in China, with high morbidity or mortality. In recent years, there has been a growing amount of evidence supporting the existence of a rare proportion of tumor cells termed cancer stem cells (CSCs) in diverse solid malignancies including ESCC. CSCs are closely related to the poor biological behaviors and drug resistance of ESCC. Markers for CSCs play an important role in the separation of CSCs, and the research on CSC markers can help clarify the mechanisms behind tumor development and guide tumor treatment.