Hepatic drug transporters and nuclear receptors:Regulation by therapeutic agents

The canalicular membrane represents the excretory pole of hepatocytes.Bile is an important route of elimination of potentially toxic endo-and xenobiotics(including drugs and toxins),mediated by the major canalicular transporters:multidrug resistance protein 1(MDR1, ABCB1),also known as P-glycoprotein,multidrug resistance-associated protein 2(MRP2,ABCC2),and the breast cancer resistance protein(BCRP,ABCG2).Their activities depend on regulation of expression and proper localization at the canalicular membrane,as regulated by transcriptional and post-transcriptional events,respectively.At transcriptional level,specific nuclear receptors(NR)s modulated by ligands,co-activators and co-repressors,mediate the physiological requirements of these transporters.This complex system is also responsible for alterations occurring in specific liver pathologies.We briefly describe the major ClassⅡNRs, pregnane X receptor(PXR)and constitutive androstane receptor(CAR),and their role in regulating expression of multidrug resistance proteins.Several therapeutic agents regulate the expression of relevant drug transporters through activation/inactivation of these NRs.We provide some representative examples of the action of therapeutic agents modulating liver drug transporters, which in addition,involve CAR or PXR as mediators.

Oligomerization of drug transporters:Forms,functions,and mechanisms

Drug transporters are essential players in the transmembrane transport of a wide variety of clinical drugs.The broad substrate spectra and versatile distribution pattern of these membrane proteins infer their pharmacological and clinical significance.With our accumulating knowledge on the three-dimensional structure of drug transporters,their oligomerization status has become a topic of intense study due to the possible functional roles carried out by such kind of post-translational modification(PTM).In-depth studies of oligomeric complexes formed among drug transporters as well as their interactions with other regulatory proteins can help us better understand the regulatory mechanisms of these membrane proteins,provide clues for the development of novel drugs,and improve the therapeutic efficacy.In this review,we describe different oligomerization forms as well as their structural basis of major drug transporters in the ATP-binding cassette and solute carrier superfamilies,summarize our current knowledge on the influence of oligomerization for protein expression level and transport function of these membrane proteins,and discuss the regulatory mechanisms of oligomerization.Finally,we highlight the challenges associated with the current oligomerization studies and propose some thoughts on the pharmaceutical application of this important drug transporter PTM.

Ultra-conservative noncoding RNA uc.243 confers chemo-resistance by facilitating the efflux of the chemotherapeutic drug in ovarian cancer

Background:Despite improvements in objective response rates to cisplatin-based combination chemotherapy,the majority of advanced ovarian cancer remains suboptimal,resulting in poor survival.it has been found that non-coding RNAs(ncRNAs)not only participate in the transmission of signals between various cells but also participate in tumor immunity and anti-tumor immune responses,thereby regulating tumor occurrence and development.However,the function and detailed mechanism of ultraconserved RNA(ucRNA)in ovarian cancer chemoresistance is still unclear.Methods:Western blotting assay,Quantitative real-time PCR analysis(qPCR),and Kaplan-Meier Plotter analysis were performed to analyze the expression and prognosis of uc.243 in ovarian carcinoma.Cytotoxicity assay and Annexin V assay were performed to analyze the function of uc.243 in cisplatin resistance in ovarian cancer cells.RNA pull-down and qPCR experiments were performed to explore the molecular mechanism of uc.243 enhancing cisplatin resistance in ovarian cancer cells.Results:Herein,we found that uc.243 was remarkably upregulated and correlated with patient survival in chemoresistance ovarian cancer patients compared with chemo-sensitive ovarian cancer.Functional experiment displayed that uc.243 induced cisplatin resistance on ovarian cancer cells by facilitating the efflux of cisplatin(CDDP);but inhibiting the expression of uc.243 significantly reverses this function.Mechanistically,uc.243 can inhibit the binding of RNA binding protein DGCR8 microprocessor complex subunit to pri-miR-155,thereby inhibiting the cleavage of pri-miR-155 and decrease in mature miR-155,subsequently upregulates the expression of ATP binding cassette subfamily B member(ABCB1,ABCC2).Conclusion:Our research findings indicate that uc.243 can induce chemotherapy resistance in ovarian cancer,suggesting that it may become a new prognostic biomarker for malignant ovarian cancer.

Advances in Research of Mechanism of Herb-Drug Interactions

With the concurrent consumption of herbal medicines and conventional drugs,herb-drug interactions(HDIs)have become the most important clinical consequence of this practice.A general overview and the significance of pharmacokinetic and pharmacodynamic HDIs are provided,detailing basic mechanism,especially the metabolic enzymes and drug transporters,such as CYP450 and P-gp.

Multifactorial nature of hepatocellular carcinoma drug resistance: Could plant polyphenols be helpful?

Primary hepatocellular carcinoma （HCC） is a quite frequent tumor which results in high mortality and most often exhibits a poor response to present drug therapies. Clearly, a thorough understanding of the biological bases of this malignancy might suggest new strategies for its treatment. Here we examine the evidences that both ＂pharmacological＂ mechanisms （e.g. drug transporter or detoxification enzyme over-expression） and alterations in other critical factors, including the IAPs （Inhibitory of Apoptosis Proteins）, involved in enhancement of cell survival and proliferation may determine the therapeutic resistance of HCC; we also underline the possible role in the process of the activation of transcription factors, like NF-κB, capable of contemporaneously up-regulating the mechanisms discussed. On this basis, we finally comment on the possible use of natural multi-targeted antitumoral agents like plant polyphenols to achieve sensitization to treatments in HCC.

The exciting potential of nanotherapy in brain-tumor targeted drug delivery approaches

Delivering therapeutics to the central nervous system（CNS） and brain-tumor has been a major challenge. The current standard treatment approaches for the brain-tumor comprise of surgical resection followed by immunotherapy, radiotherapy, and chemotherapy. However, the current treatments are limited in providing significant benefits to the patients and despite recent technological advancements; brain-tumor is still challenging to treat. Brain-tumor therapy is limited by the lack of effective and targeted strategies to deliver chemotherapeutic agents across the blood-brain barrier（BBB）. The BBB is the main obstacle that must be overcome to allow compounds to reach their targets in the brain. Recent advances have boosted the nanotherapeutic approaches in providing an attractive strategy in improving the drug delivery across the BBB and into the CNS. Compared to conventional formulations, nanoformulations offer significant ad vantages in CNS drug delivery approaches. Considering the above facts, in this review, the physiological/anatomical features of the brain-tumor and the BBB are briefly discussed. The drug transport mechanisms at the BBB are outlined. The approaches to deliver chemotherapeutic drugs across the CNS into the brain-tumor using nanocarriers are summarized. In addition, the challenges that need to be addressed in nanotherapeutic approaches for their enhanced clinical application in brain-tumor therapy are discussed.

Pharmacogenomics of Drug Metabolizing Enzymes and Transporters:Relevance to Precision Medicine

The interindividual genetic variations in drug metabolizing enzymes and transporters influence the efficacy and toxicity of numerous drugs. As a fundamental element in precision med- icine, pharmacogenomics, the study of responses of individuals to medication based on their genomic information, enables the evaluation of some specific genetic variants responsible for an individual＇s particular drug response. In this article, we review the contributions of genetic polymorphisms to major individual variations in drug pharmacotherapy, focusing specifically on the pbarmacogenomics of phase-I drug metabolizing enzymes and transporters. Substantial frequency differences in key variants of drug metabolizing enzymes and transporters, as well as their possible functional consequences, have also been discussed across geographic regions. The current effort illustrates the common presence of variability in drug responses among individuals and across all geographic regions. This information will aid health-care professionals in prescribing the most appropriate treatment aimed at achieving the best possible beneficial outcomes while avoiding unwanted effects for a particular patient.

Novel biomarkers GEP/ABCB5 regulate response to adjuvant transarterial chemoembolization after curative hepatectomy for hepatocellular carcinoma

Background: Transarterial chemoembolization(TACE) is the most commonly used adjuvant therapy for hepatocellular carcinoma(HCC) after curative resection. Responses to TACE are variable due to tumor and patient heterogeneity. We had previously demonstrated that expression of Granulin-epithelin precursor(GEP) and ATP-dependent binding cassette(ABC)B5 in liver cancer stem cells was associated with chemoresistance. The present study aimed to evaluate the association between GEP/ABCB5 expression and response to adjuvant TACE after curative resection for HCC. Methods: Patients received adjuvant TACE after curative resection for HCC and patients received curative resection alone were identified from a prospectively collected database. Clinical samples were retrieved for biomarker analysis. Patients were categorized into 3 risk groups according to their GEP/ABCB5 status for survival analysis: low(GEP-/ABCB5-), intermediate(either GEP +/ABCB5-or GEP-/ABCB5 +) and high(GEP +/ABCB5 +). Early recurrence(recurrence within 2 years after resection) and disease-free survival were analyzed. Results: Clinical samples from 44 patients who had followed-up for more than 2 years were retrieved for further biomarker analysis. Among them, 18 received adjuvant TACE and 26 received surgery alone. Patients with adjuvant TACE in the intermediate risk group was associated with significantly better overall survival and 2-year disease-free survival than those who had surgery alone( P = 0.036 and P = 0.011, respectively). Adjuvant TACE did not offer any significant differences in the early recurrence rate, 2-year disease-free survival and overall survival for patients in low and high risk groups. Conclusions: Adjuvant TACE can only provide survival benefits for patients in the intermediate risk group(either GEP +/ABCB5-or GEP-/ABCB5 +). A larger clinical study is warranted to confirm its role in patient selection for adjuvant TACE.

Nicotinic receptors modulate antitumor therapy response in triple negative breast cancer cells

BACKGROUND Triple negative breast cancer is more aggressive than other breast cancer subtypes and constitutes a public health problem worldwide since it has high morbidity and mortality due to the lack of defined therapeutic targets.Resistance to chemotherapy complicates the course of patients’treatment.Several authors have highlighted the participation of nicotinic acetylcholine receptors(nAChR)in the modulation of conventional chemotherapy treatment in cancers of the airways.However,in breast cancer,less is known about the effect of nAChR activation by nicotine on chemotherapy treatment in smoking patients.AIM To investigate the effect of nicotine on paclitaxel treatment and the signaling pathways involved in human breast MDA-MB-231 tumor cells.METHODS Cells were treated with paclitaxel alone or in combination with nicotine,administered for one or three 48-h cycles.The effect of the addition of nicotine(at a concentration similar to that found in passive smokers’blood)on the treatment with paclitaxel(at a therapeutic concentration)was determined using the 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.The signaling mediators involved in this effect were determined using selective inhibitors.We also investigated nAChR expression,and ATP“binding cassette”G2 drug transporter(ABCG2)expression and its modulation by the different treatments with Western blot.The effect of the treatments on apoptosis induction was determined by flow cytometry using annexin-V and 7AAD markers.RESULTS Our results confirmed that treatment with paclitaxel reduced MDA-MB-231 cell viability in a concentration-dependent manner and that the presence of nicotine reversed the cytotoxic effect induced by paclitaxel by involving the expression of functionalα7 andα9 nAChRs in these cells.The action of nicotine on paclitaxel treatment was linked to modulation of the protein kinase C,mitogen-activated protein kinase,extracellular signal-regulated kinase,and NF-κB signaling pathways,and to an up-regulation of ABCG2 protein expression.We also detected that nicotine significantly reduced the increase in cell apoptosis induced by paclitaxel treatment.Moreover,the presence of nicotine reduced the efficacy of paclitaxel treatment administered in three cycles to MDA-MB-231 tumor cells.CONCLUSION Our findings point to nAChRs as responsible for the decrease in the chemotherapeutic effect of paclitaxel in triple negative tumors.Thus,nAChRs should be considered as targets in smoking patients.

Construction and characterization of a humanized SLCO1B1 rat model with its application in evaluating the uptake of different statins

Organic anion-transporting polypeptides IB1(OATPIB1)plays a crucial role in the transport of statins.However,there are too few animal models related to OATPIB1,especially humanized animal models.In this study,the human SLCOIB1 cDNA was inserted into the second exon of the rat Slcolb2 gene using CRISPR/Cas9 technology.Pharmacokinetic characteristics of statins were conducted in wild-type(WT),humanized OATPIB1(hOATPIB1),and OATPIB2 knockout(OATPIB2 KO)rats,respec-tively.The results showed that human OATPIB1 was successfully expressed in rat liver and exhibited transport function.Furthermore,the pharmacokinetic results revealed that OATPIB1 exhibited varying uptake levels of pivastatin,rosuvastatin,and fluvastatin,leading to different levels of exposure within the body.These results were consistent with those obtained from in vitro experiments using overexpressed cell lines.In conclusion,we established a novel humanized SLCOIBI transgenic rat model to assess the role of human OATPIB1 in the uptake of different statins.The different uptake mediated by OATPIB1 may be an important reason for the different efficacy of statins.The hOATPIB1 rat is a promising model for improving the prediction of human drug transport.

MicroRNAs and cancer drug resistance: over two thousand characters in search of a role

MicroRNAs(miRNAs),a group of small regulatory noncoding RNAs,transformed our thinking on gene regulation.More than two thousand human miRNAs have been identified thus far.These bind imperfectly to the 3’-untranslated region of target mRNA and have been involved in several pathological conditions including cancer.In fact,major hallmarks of cancer,such as the cell cycle,cell proliferation,survival and invasion are modulated by miRNAs.Cancer drug resistance(CDR)has also been described as being modulated by miRNAs.CDR remains a burden for cancer therapy and patients’outcome,often resulting in more aggressive tumours that tend to metastasize to distant organs.In this review we discuss the role of miRNAs influencing drug metabolism and drug influx/efflux,two important mechanisms of CDR.

3D organoids derived from the small intestine:An emerging tool for drug transport research

Small intestine in vitro models play a crucial role in drug transport research.Although conventional 2 D cell culture models,such as Caco-2 monolayer,possess many advantages,they should be interpreted with caution because they have relatively poor physiologically reproducible phenotypes and functions.With the development of 3 D culture technology,pluripotent stem cells(PSCs)and adult somatic stem cells(ASCs)show remarkable self-organization characteristics,which leads to the development of intestinal organoids.Based on previous studies,this paper reviews the application of intestinal 3 D organoids in drug transport mediated by P-glycoprotein(P-gp),breast cancer resistance protein(BCRP)and multidrug resistance protein 2(MRP2).The advantages and limitations of this model are also discussed.Although there are still many challenges,intestinal 3 D organoid model has the potential to be an excellent tool for drug transport research.

Berberine reverses multidrug resistance in Candida albicans by hijacking the drug efflux pump Mdr1p

Clinical use of antimicrobials faces great challenges from the emergence of multidrug-resistant pathogens. The overexpression of drug efflux pumps is one of the major contributors to multidrug resistance(MDR). Reversing the function of drug efflux pumps is a promising approach to overcome MDR. In the life-threatening fungal pathogen Candida albicans, the major facilitator superfamily(MFS) transporter Mdr1p can excrete many structurally unrelated antifungals, leading to MDR. Here we report a counterintuitive case of reversing MDR in C. albicans by using a natural product berberine to hijack the overexpressed Mdr1p for its own importation. Moreover, we illustrate that the imported berberine accumulates in mitochondria and compromises the mitochondrial function by impairing mitochondrial membrane potential and mitochondrial Complex I. This results in the selective elimination of Mdr1 p overexpressed C. albicans cells. Furthermore, we show that berberine treatment can prolong the mean survival time of mice with blood-borne dissemination of Mdr1p overexpressed multidrug-resistant candidiasis. This study provides a potential direction of novel anti-MDR drug discovery by screening for multidrug efflux pump converters.

Development of Human in vitro Brain-blood Barrier Model from Induced Pluripotent Stem Cell-derived Endothelial Cells to Predict the in vivo Permeability of Drugs

An in vitro blood-brain barrier(BBB) model is critical for enabling rapid screening of the BBB permeability of the drugs targeting on the central nervous system.Though many models have been developed, their reproducibility and renewability remain a challenge. Furthermore, drug transport data from many of the models do not correlate well with the data for in vivo BBB drug transport.Induced-pluripotent stem cell(i PSC) technology provides reproducible cell resources for in vitro BBB modeling.Here, we generated a human in vitro BBB model by differentiating the human i PSC(hi PSC) line GM25256 into brain endothelial-type cells. The model displayed BBB characteristics including tight junction proteins(ZO-1,claudin-5, and occludin) and endothelial markers(von Willebrand factor and Ulex), as well as high transendothelial electrical resistance(TEER)(1560 X.cm2±230 X.cm2) and c-GTPase activity. Co-culture with primary rat astrocytes significantly increased the TEER of the model(2970 X.cm2 to 4185 X.cm2). RNAseq analysis confirmed the expression of key BBB-related genes in the hi PSC-derived endothelial cells in comparison with primary human brain microvascular endothelial cells,including P-glycoprotein(Pgp) and breast cancer resistant protein(BCRP). Drug transport assays for nine CNS compounds showed that the permeability of non-Pgp/BCRP and Pgp/BCRP substrates across the model was strongly correlated with rodent in situ brain perfusion data for these compounds(R2= 0.982 and R2= 0.9973,respectively), demonstrating the functionality of the drug transporters in the model. Thus, this model may be used to rapidly screen CNS compounds, to predict the in vivo BBB permeability of these compounds and to study the biology of the BBB.

An update on placental drug transport and its relevance to fetal drug exposure

Pregnant women are often complicated with diseases that require treatment with medication.Most drugs administered to pregnant women are off-label without the necessary dose,efficacy,and safety information.Knowledge concerning drug transfer across the placental barrier is essential for understanding fetal drug exposure and hence drug safety and efficacy to the fetus.Transporters expressed in the placenta,including adenosine triphosphate(ATP)-binding cassette efflux transporters and solute carrier uptake transporters,play important roles in determining drug transfer across the placental barrier,leading to fetal exposure to the drugs.In this review,we provide an update on placental drug transport,including in vitro cell/tissue,ex vivo human placenta perfusion,and in vivo animal studies that can be used to determine the expression and function of drug transporters in the placenta as well as placental drug transfer and fetal drug exposure.We also describe how the knowledge of placental drug transfer through passive diffusion or active transport can be combined with physiologically based pharmacokinetic modeling and simulation to predict systemic fetal drug exposure.Finally,we highlight knowledge gaps in studying placental drug transport and predicting fetal drug exposure and discuss future research directions to fill these gaps.

Taxane resistance in castration-resistant prostate cancer: mechanisms and therapeutic strategies

Despite its good initial response and significant survival benefit in patients with castrationresistant prostate cancer(CRPC), taxane therapy inevitably encounters drug resistance in all patients.Deep understandings of taxane resistant mechanisms can significantly facilitate the development of new therapeutic strategies to overcome taxane resistance and improve CRPC patient survival. Multiple pathways of resistance have been identified as potentially crucial areas of intervention. First, taxane resistant tumor cells typically have mutated microtubule binding sites, varying tubulin isotype expression,and upregulation of efflux transporters. These mechanisms contribute to reducing binding affinity and availability of taxanes. Second, taxane resistant tumors have increased stem cell like characteristics,indicating higher potential for further mutation in response to therapy. Third, the androgen receptor pathway is instrumental in the proliferation of CRPC and multiple hypotheses leading to this pathway reactivation have been reported. The connection of this pathway to the AKT pathway has received significant attention due to the upregulation of phosphorylated AKT in CRPC. This review highlights recent advances in elucidating taxane resistant mechanisms and summarizes potential therapeutic strategies for improved treatment of CRPC.

Altered cisplatin pharmacokinetics during nonalcoholic steatohepatitis contributes to reduced nephrotoxicity

Disease-mediated alterations to drug disposition constitute a significant source of adverse drug reactions.Cisplatin(CDDP)elicits nephrotoxicity due to exposure in proximal tubule cells during renal secretion.Alterations to renal drug transporter expression have been discovered during nonalcoholic steatohepatitis(NASH),however,associated changes to substrate toxicity is unknown.To test this,a methionine-and choline-deficient diet-induced rat model was used to evaluate NASH-associated changes to CDDP pharmacokinetics,transporter expression,and toxicity.NASH rats administered CDDP(6 mg/kg,i.p.)displayed 20%less nephrotoxicity than healthy rats.Likewise,CDDP renal clearance decreased in NASH rats from 7.39 to 3.83 mL/min,renal secretion decreased from 6.23 to 2.80 mL/min,and renal CDDP accumulation decreased by 15%,relative to healthy rats.Renal copper transporter-1 expression decreased,and organic cation transporter-2 and ATPase copper transporting protein-7 b increased slightly,reducing CDDP secretion.Hepatic CDDP accumulation increased 250%in NASH rats relative to healthy rats.Hepatic organic cation transporter-1 induction and multidrug and toxin extrusion protein-1 and multidrug resistance-associated protein-4 reduction may contribute to hepatic CDDP sequestration in NASH rats,although no drug-related toxicity was observed.These data provide a link between NASH-induced hepatic and renal transporter expression changes and CDDP renal clearance,which may alter nephrotoxicity.

Germline variants in cancer therapy

Cancer pharmacogenetics implies a complex combination of germline variants from the patient and somatic mutations in tumor cells.Somatic mutations meanwhile have become drugable targets or biomarkers,whereas germline mutations potentially predict adverse drug effects or drug response.Here,we evaluate hereditary variants in biotransforming enzymes and drug transporters,such as thiopurine S-methyltransferase,UDP-glucuronosyltransferase(UGT1A1),dihydropyrimidine dehydrogenase(DPD),as well as ABC transporters(ABCB1,ABCG2 and ABCC subfamily)with respect to cytostatics and targeted therapies.Furthermore,gene expression regulation with regards to epigenetics and posttranscriptional modification are discussed.