High-affinity interaction of tyrosine kinase inhibitors with the ABCG2 multidrug transporter

Pretreatment of cancer cells with inhibitors of PKCδ, EGFR, and JNK increased intracellular hypericin content and enhanced the effectiveness of photodynamic therapy

Photodynamic therapy (PDT) is an effective, minimally invasive treatment for certain cancers that uses photosensitizers (PSs) to selectively destroy tumor cells upon light activation. However, the breast cancer resistance protein (BCRP) plays a critical role in limiting PDT efficacy through active efflux of various PSs from the cancer cells. Hypericin (HY), a potent and promising natural PS, is also a preferential BCRP substrate, and its cytotoxic effect in PDT is reduced in BCRP-overexpressing cells. Thus, the main aim of our study was to investigate the potential of the modulators of signaling molecules possibly involved in BCRP regulation to sensitize cancer cells (A549, HT-29, RPMI-8226, and RPMI-8226/MR20) to hypericin-mediated PDT (HY-PDT). We assessed the effects of inhibitors of epidermal growth factor receptor (EGFR) (Tyr - tyrphostin AG 1478) and c-Jun N-terminal kinase (JNK) (SP - SP600125, Lico - licochalcone A), as well as protein kinase C (PKC) activator (TPA) and inhibitor (Rot - rottlerin). Our results showed that all modulators enhanced HY-PDT efficacy, but the extent of sensitization, as well as the specific effects, varied depending on the cell line. Pretreatment with Tyr, SP, and Lico significantly improved HY-PDT in RPMI-8226 and RPMI-8226/MR20 cells, while Rot pretreatment had the strongest effect in A549 and HT-29 cells. More importantly, the sensitizing effects of the inhibitors were linked to increased intracellular HY accumulation, indicating reduced BCRP efflux activity. While the exact mechanisms behind these effects require further investigation, our findings suggest that targeting BCRP and associated signaling pathways could enhance PDT outcomes in cancer treatment.

Membrane drug transporters in cancer: From chemoresistance mechanism to therapeutic strategies

Chemoresistance is a multifactorial phenomenon and the primary cause to the ineffectiveness of oncotherapy and cancer recurrence. Membrane drug transporters are crucial for drug delivery and disposition in cancer cells. Changes in the expression and functionality of these transporters lead to decreased intracellular accumulation and reduced toxicity of antineoplastic drugs. As the mechanism has been better understood and genetic engineering technology progressed quickly in recent years, some novel targeting strategies have come to light. This article summarizes the regulatory mechanisms of membrane drug transporters and provides an extensive review of current approaches to address transporters-mediated chemoresistance. These strategies include the use of chemical inhibitors to block efflux transporters, the development of copper chelators to enhance platinum drug uptake, the delivery of genetic drugs to alter transporter expression, the regulation of transcription and post-translational modifications. Additionally, we provide information of the clinical trial performance of the related targeting strategies, along with the ongoing challenges. Even though some clinical trials failed due to unexpected side effects and limited therapeutic efficacy, the advent of targeting membrane drug transporters still presents a hopeful path for overcoming chemoresistance.

A novel acquired resistance mechanism to 5-aminolevulinic acid-mediated photodynamic therapy with ABCG2 inhibition

We report the occurrence of acquired tumor cell resistance to 5-aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) in combination with ABCG2 inhibition. ALA-PDT in combination with either an ABCG2 tool inhibitor Ko143 or a repurposed clinically-relevant ABCG2 inhibitor lapatinib was highly effective in eradicating the H4 human glioma cells, resulting in minimal cell survival after treatment. However, after seven rounds of repeated treatments with light dose escalation, the resultant tumor cells became resistant to the combination therapy. The resistant sublines and the parental cell line showed similar ABCG2 activities and protein levels, indicating that it was not ABCG2 that caused the resistance. They also exhibited similar responses to PpIX-PDT and mTOR inhibitor AZD2014, suggesting that alterations in PDT sensitivity and mTOR pathway had little contribution to the development of resistance phenotype. By determining the intracellular and extracellular PpIX levels, the activities and protein levels of heme biosynthesis enzymes, we found that porphobilinogen deaminase (PBGD) activity and protein level were significantly reduced in the resistant sublines, causing resistance to PDT by substantially reducing PpIX biosynthesis. A novel acquired resistance mechanism to ALA-PDT with ABCG2 inhibition has been uncovered.

The association of ABC proteins with multidrug resistance in cancer

Multidrug resistance (MDR) poses one of the primary challenges for cancer treatment, especially in cases of metastatic disease. Various mechanisms contribute to MDR, including the overexpression of ATP-binding cassette (ABC) proteins. In this context, we reviewed the literature to establish a correlation between the overexpression of ABC proteins and MDR in cancer, considering both in vitro and clinical studies. Initially, we presented an overview of the seven subfamilies of ABC proteins, along with the subcellular localization of each protein. Subsequently, we identified a panel of 20 ABC proteins (ABCA1-3, ABCA7, ABCB1-2, ABCB4-6, ABCC1-5, ABCC10-11, ABCE1, ABCF2, ABCG1, and ABCG2) associated with MDR. We also emphasize the significance of drug sequestration by certain ABC proteins into intracellular compartments. Among the anticancer drugs linked to MDR, 29 were definitively identified as substrates for at least one of the three most crucial ABC transporters: ABCB1, ABCC1, and ABCG2. We further discussed that the most commonly used drugs in standard regimens for mainly breast cancer, lung cancer, and acute lymphoblastic leukemia could be subject to MDR mediated by ABC transporters. Collectively, these insights will aid in conducting new studies aimed at a deeper understanding of the clinical MDR mediated by ABC proteins and in designing more effective pharmacological treatments to enhance the objective response rate in cancer patients.

A Structural Bioinformatics-Guided Study of Adenosine Triphosphate-Binding Cassette (ABC) Transporters and Their Substrates

Adenosine triphosphate-binding cassette (ABC) transporters form a ubiquitous superfamily of integral membrane proteins involved in the translocation of substrates across membranes. Human ABC transporters are closely linked to the pathogenesis of diseases such as cancer, metabolic diseases, and Alzheimer's disease. In this study, four ABC transporters were chosen based on (I) their importance in humans and (II) their score in a structural bioinformatics screen aimed at the prediction of crystallisation propensity. The top-scoring ABC transporters' orthologs (Mus musculus-mouse ABCB5, Ailuropoda melanoleuca-giant panda ABCB6, Myotis lucifugus-little brown bat ABCG1 and Mus musculus ABCG4) were then expressed in Saccharomyces cerevisiae with a combined green fluorescent protein and polyhistidine tag, enabling visualisation and purification. After partial purification and in the presence of the detergent (n-dodecyl-β-D-maltoside), the kinetic parameters of the ATP hydrolysis reactions of the orthologs were determined, as well as the extent of stimulation of their activity when presented with putative substrates. We discuss the efficiency of such bioinformatics approaches and make suggestions for their improvement and wider application in membrane protein-structure determination.

Acquired resistance to tyrosine kinase targeted therapy: mechanism and tackling strategies

Over the past two decades, tyrosine kinase inhibitors (TKIs) have rapidly emerged as pivotal targeted agents, offering promising therapeutic prospects for patients. However, as the cornerstone of targeted therapies, an increasing number of TKIs have been found to develop acquired resistance during treatment, making the challenge of overcoming this resistance a primary focus of current research. This review comprehensively examines the evolution of TKIs from multiple perspectives, with particular emphasis on the mechanisms underlying acquired resistance, innovative drug design strategies, inherent challenges, and future directions.

Mobocertinib antagonizes multidrug resistance in ABCB1- and ABCG2-overexpressing cancer cells: In vitro and in vivo studies

Overexpression of ATP-binding cassette (ABC) transporters, particularly ABCB1 and ABCG2, strongly correlates with multidrug resistance (MDR), rendering cancer chemotherapy ineffective. Exploration and identification of novel inhibitors targeting ABCB1 and ABCG2 are necessary to overcome the related MDR. Mobocertinib is an approved EGFR/HER2 inhibitor for non-small cell lung cancer (NSCLC) with EGFR exon 20 insertion mutations. This study demonstrates that mobocertinib can potentially reverse ABCB1- and ABCG2-mediated MDR. Our findings indicate a strong interaction between mobocertinib and these two proteins, supported by its high binding affinity with ABCB1 and ABCG2 models. Through inhibiting the drug efflux function of ABCB1 and ABCG2, mobocertinib facilitates substrate drugs accumulation, thereby re-sensitizing substrate drugs in drug-resistant cancer cells. Additionally, mobocertinib inhibited the ATPase activity of ABCB1 and ABCG2 without changing the expression levels or subcellular localization. In the tumor-bearing mouse model, mobocertinib boosted the antitumor effect of paclitaxel and topotecan, resulting in tumor regression. In summary, our study uncovers a novel potential for repurposing mobocertinib as a dual inhibitor of ABCB1 and ABCG2, and suggests the combination of mobocertinib with substrate drugs as a strategy to counteract MDR.

Tyrosine kinase inhibitors in cancers: Treatment optimization - Part II

Real-life populations are more heterogeneous than those included in prospective clinical studies. In cancer patients, comorbidities and co-medications favor the appearance of severe adverse effects which can significantly impact quality of life and treatment effectiveness. Most of tyrosine kinase inhibitors (TKI) have been developed with flat oral dosing exposing patients to the risk of poor adherence due to side effects. Additionally, genetic or physiological factors, differences in diet, and drug-drug interactions can lead to inter-individual variability affecting treatment outcomes and increasing the risk of adverse events. Knowledge of the different factors of variability allows individualized patient management. This review examines the effects of adherence, food intake, and pharmaceutical form on the pharmacokinetics of oral TKI, as well as evaluating pharmacokinetics considerations improving TKI management. Concentration-effectiveness and concentration-toxicity data are presented for the selected TKI, and a simple therapeutic drug monitoring schema is outlined to help individualize dosing of oral TKI.

Genetic Variants in the ABCB1 and ABCG2 Gene Drug Transporters Involved in Gefitinib-Associated Adverse Reaction: A Systematic Review and Meta-Analysis

This systematic review and meta-analysis aimed to verify the association between the genetic variants of adenosine triphosphate (ATP)-binding cassette subfamily B member 1 (ABCB1) and ATP-binding cassette subfamily G member 2 (ABCG2) genes and the presence and severity of gefitinib-associated adverse reactions. We systematically searched PubMed, Virtual Health Library/Bireme, Scopus, Embase, and Web of Science databases for relevant studies published up to February 2024. In total, five studies were included in the review. Additionally, eight genetic variants related to ABCB1 (rs1045642, rs1128503, rs2032582, and rs1025836) and ABCG2 (rs2231142, rs2231137, rs2622604, and 15622C>T) genes were analyzed. Meta-analysis showed a significant association between the ABCB1 gene rs1045642 TT genotype and presence of diarrhea (OR = 5.41, 95% CI: 1.38-21.14, I2 = 0%), the ABCB1 gene rs1128503 TT genotype and CT + TT group and the presence of skin rash (OR = 4.37, 95% CI: 1.51-12.61, I2 = 0% and OR = 6.99, 95%CI: 1.61-30.30, I2= 0%, respectively), and the ABCG2 gene rs2231142 CC genotype and presence of diarrhea (OR = 3.87, 95% CI: 1.53-9.84, I2 = 39%). No ABCB1 or ABCG2 genes were positively associated with the severity of adverse reactions associated with gefitinib. In conclusion, this study showed that ABCB1 and ABCG2 variants are likely to exhibit clinical implications in predicting the presence of adverse reactions to gefitinib.

Imperatorin Restores Chemosensitivity of Multidrug-Resistant Cancer Cells by Antagonizing ABCG2-Mediated Drug Transport

The high expression of the ATP-binding cassette (ABC) drug transporter ABCG2 in cancer cells contributes to the emergence of multidrug resistance (MDR) in individuals afflicted with either solid tumors or blood cancers. MDR poses a major impediment in the realm of clinical cancer chemotherapy. Recently, substantial endeavors have been dedicated to identifying bioactive compounds isolated from nature capable of counteracting ABCG2-mediated MDR in cancer cells. Imperatorin, a natural coumarin derivative renowned for its diverse pharmacological properties, has not previously been explored for its impact on cancer drug resistance. This study investigates the chemosensitizing potential of imperatorin in ABCG2-overexpressing cancer cells. Experimental results reveal that at sub-toxic concentrations, imperatorin significantly antagonizes the activity of ABCG2 and reverses ABCG2-mediated MDR in a concentration-dependent manner. Furthermore, biochemical data and in silico analysis of imperatorin docking to the inward-open conformation of human ABCG2 indicate that imperatorin directly interacts with multiple residues situated within the transmembrane substrate-binding pocket of ABCG2. Taken together, these results furnish substantiation that imperatorin holds promise for further evaluation as a potent inhibitor of ABCG2, warranting exploration in combination drug therapy to enhance the effectiveness of therapeutic agents for patients afflicted with tumors that exhibit high levels of ABCG2.

Perspectives on drug repurposing to overcome cancer multidrug resistance mediated by ABCB1 and ABCG2

The overexpression of the human ATP-binding cassette (ABC) transporters in cancer cells is a common mechanism involved in developing multidrug resistance (MDR). Unfortunately, there are currently no approved drugs specifically designed to treat multidrug-resistant cancers, making MDR a significant obstacle to successful chemotherapy. Despite over two decades of research, developing transporter-specific inhibitors for clinical use has proven to be a challenging endeavor. As an alternative approach, drug repurposing has gained traction as a more practical method to discover clinically effective modulators of drug transporters. This involves exploring new indications for already-approved drugs, bypassing the lengthy process of developing novel synthetic inhibitors. In this context, we will discuss the mechanisms of ABC drug transporters ABCB1 and ABCG2, their roles in cancer MDR, and the inhibitors that have been evaluated for their potential to reverse MDR mediated by these drug transporters. Our focus will be on providing an up-to-date report on approved drugs tested for their inhibitory activities against these drug efflux pumps. Lastly, we will explore the challenges and prospects of repurposing already approved medications for clinical use to overcome chemoresistance in patients with high tumor expression of ABCB1 and/or ABCG2.

Early in vitro evidence indicates that deacetylated sialic acids modulate multi-drug resistance in colon and lung cancers via breast cancer resistance protein

Cancers utilize sugar residues to engage in multidrug resistance. The underlying mechanism of action involving glycans, specifically the glycan sialic acid (Sia) and its various functional group alterations, has not been explored. ATP-binding cassette (ABC) transporter proteins, key proteins utilized by cancers to engage in multidrug resistant (MDR) pathways, contain Sias in their extracellular domains. The core structure of Sia can contain a variety of functional groups, including O-acetylation on the C6 tail. Modulating the expression of acetylated-Sias on Breast Cancer Resistance Protein (BCRP), a significant ABC transporter implicated in MDR, in lung and colon cancer cells directly impacted the ability of cancer cells to either retain or efflux chemotherapeutics. Via CRISPR-Cas-9 gene editing, acetylation was modulated by the removal of CAS1 Domain-containing protein (CASD1) and Sialate O-Acetyl esterase (SIAE) genes. Using western blot, immunofluorescence, gene expression, and drug sensitivity analysis, we confirmed that deacetylated Sias regulated a MDR pathway in colon and lung cancer in early in vitro models. When deacetylated Sias were expressed on BCRP, colon and lung cancer cells were able to export high levels of BCRP to the cell's surface, resulting in an increased BCRP efflux activity, reduced sensitivity to the anticancer drug Mitoxantrone, and high proliferation relative to control cells. These observations correlated with increased levels of cell survival proteins, BcL-2 and PARP1. Further studies also implicated the lysosomal pathway for the observed variation in BCRP levels among the cell variants. RNASeq data analysis of clinical samples revealed higher CASD1 expression as a favorable marker of survival in lung adenocarcinoma. Collectively, our findings indicate that deacetylated Sia is utilized by colon and lung cancers to engage in MDR via overexpression and efflux action of BCRP.

5-Aminolevulinic Acid as a Theranostic Agent for Tumor Fluorescence Imaging and Photodynamic Therapy

5-Aminolevulinic acid (ALA) is a naturally occurring amino acid synthesized in all nucleated mammalian cells. As a porphyrin precursor, ALA is metabolized in the heme biosynthetic pathway to produce protoporphyrin IX (PpIX), a fluorophore and photosensitizing agent. ALA administered exogenously bypasses the rate-limit step in the pathway, resulting in PpIX accumulation in tumor tissues. Such tumor-selective PpIX disposition following ALA administration has been exploited for tumor fluorescence diagnosis and photodynamic therapy (PDT) with much success. Five ALA-based drugs have now received worldwide approval and are being used for managing very common human (pre)cancerous diseases such as actinic keratosis and basal cell carcinoma or guiding the surgery of bladder cancer and high-grade gliomas, making it the most successful drug discovery and development endeavor in PDT and photodiagnosis. The potential of ALA-induced PpIX as a fluorescent theranostic agent is, however, yet to be fully fulfilled. In this review, we would like to describe the heme biosynthesis pathway in which PpIX is produced from ALA and its derivatives, summarize current clinical applications of ALA-based drugs, and discuss strategies for enhancing ALA-induced PpIX fluorescence and PDT response. Our goal is two-fold: to highlight the successes of ALA-based drugs in clinical practice, and to stimulate the multidisciplinary collaboration that has brought the current success and will continue to usher in more landmark advances.

ATP-binding cassette efflux transporters and MDR in cancer

Of the many known multidrug resistance (MDR) mechanisms, ATP-binding cassette (ABC) transporters expelling drug molecules out of cells is a major factor limiting the efficacy of present-day anticancer drugs. In this review, we highlights updated information on the structure, function, and regulatory mechanisms of major MDR-related ABC transporters, such as P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1), and breast cancer resistance protein (BCRP), and the effect of modulators on their functions. We also provide focused information on different modulators of ABC transporters that could be utilized against the emerging MDR crisis in cancer treatment. Finally, we discuss the importance of ABC transporters as therapeutic targets in light of future strategic planning for translating ABC transporter inhibitors into clinical practice.

Hydroxygenkwanin Improves the Efficacy of Cytotoxic Drugs in ABCG2-Overexpressing Multidrug-Resistant Cancer Cells

Hydroxygenkwanin, a flavonoid isolated from the leaves of the Daphne genkwa plant, is known to have pharmacological properties; however, its modulatory effect on multidrug resistance, which is (MDR) mediated by ATP-binding cassette (ABC) drug transporters, has not been investigated. In this study, we examine the interaction between hydroxygenkwanin, ABCB1, and ABCG2, which are two of the most well-characterized ABC transporters known to contribute to clinical MDR in cancer patients. Hydroxygenkwanin is not an efflux substrate of either ABCB1 or ABCG2. We discovered that, in a concentration-dependent manner, hydroxygenkwanin significantly reverses ABCG2-mediated resistance to multiple cytotoxic anticancer drugs in ABCG2-overexpressing multidrug-resistant cancer cells. Although it inhibited the drug transport function of ABCG2, it had no significant effect on the protein expression of this transporter in cancer cells. Experimental data showing that hydroxygenkwanin stimulates the ATPase activity of ABCG2, and in silico docking analysis of hydroxygenkwanin binding to the inward-open conformation of human ABCG2, further indicate that hydroxygenkwanin sensitizes ABCG2-overexpressing cancer cells by binding to the substrate-binding pocket of ABCG2 and attenuating the transport function of ABCG2. This study demonstrates the potential use of hydroxygenkwanin as an effective inhibitor of ABCG2 in drug combination therapy trials for patients with tumors expressing higher levels of ABCG2.

A curated binary pattern multitarget dataset of focused ATP-binding cassette transporter inhibitors

Multitarget datasets that correlate bioactivity landscapes of small-molecules toward different related or unrelated pharmacological targets are crucial for novel drug design and discovery. ATP-binding cassette (ABC) transporters are critical membrane-bound transport proteins that impact drug and metabolite distribution in human disease as well as disease diagnosis and therapy. Molecular-structural patterns are of the highest importance for the drug discovery process as demonstrated by the novel drug discovery tool ‘computer-aided pattern analysis’ (‘C@PA’). Here, we report a multitarget dataset of 1,167 ABC transporter inhibitors analyzed for 604 molecular substructures in a statistical binary pattern distribution scheme. This binary pattern multitarget dataset (ABC_BPMDS) can be utilized for various areas. These areas include the intended design of (i) polypharmacological agents, (ii) highly potent and selective ABC transporter-targeting agents, but also (iii) agents that avoid clearance by the focused ABC transporters [e.g., at the blood-brain barrier (BBB)]. The information provided will not only facilitate novel drug prediction and discovery of ABC transporter-targeting agents, but also drug design in general in terms of pharmacokinetics and pharmacodynamics.

Measurement(s)	Influx • Efflux • Tracer • Transport velocity
Technology Type(s)	Fluorometry • Radioactivity • Plate reader • Flow cytometer • Tracer distribution
Factor Type(s)	half-maximal inhibition concentration
Sample Characteristic - Organism	Homo sapiens
Sample Characteristic - Environment	cell culture
Sample Characteristic - Location	Kingdom of Norway • Germany • Australia • Latvia

Targeting the SREBP-1/Hsa-Mir-497/SCAP/FASN Oncometabolic Axis Inhibits the Cancer Stem-like and Chemoresistant Phenotype of Non-Small Cell Lung Carcinoma Cells

Background: Lung cancer remains a leading cause of cancer-related death, with an annual global mortality rate of 18.4%. Despite advances in diagnostic and therapeutic technologies, non–small cell lung carcinoma (NSCLC) continues to be characterized by a poor prognosis. This may be associated with the enrichment of cancer stem cells (CSCs) and the development of chemoresistance—a double-edged challenge that continues to impede the improvement of long-term outcomes. Metabolic reprogramming is a new hallmark of cancer. Sterol regulatory element-binding proteins (SREBPs) play crucial regulatory roles in the synthesis and uptake of cholesterol, fatty acids, and phospholipids. Recent evidence has demonstrated that SREBP-1 is upregulated in several cancer types. However, its role in lung cancer remains unclear. Objective: This study investigated the role of SREBP-1 in NSCLC biology, progression, and therapeutic response and explored the therapeutic exploitability of SREBP-1 and SREBP-1-dependent oncometabolic signaling and miRNA epigenetic regulation. Methods: We analyzed SREBP-1 levels and biological functions in clinical samples and the human NSCLC cell lines H441 and A549 through shRNA-based knock down of SREBP function, cisplatin-resistant clone generation, immunohistochemical staining of clinical samples, and cell viability, sphere-formation, Western blot, and quantitative PCR assays. We conducted in-silico analysis of miRNA expression in NSCLC samples by using the Gene Expression Omnibus (GSE102286) database. Results: We demonstrated that SREBP-1 and SCAP are highly expressed in NSCLC and are positively correlated with the aggressive phenotypes of NSCLC cells. In addition, downregulation of the expression of tumor-suppressing hsa-miR-497-5p, which predictively targets SREBP-1, was observed. We also demonstrated that SREBP-1/SCAP/FASN lipogenic signaling plays a key role in CSCs-like and chemoresistant NSCLC phenotypes, especially because the fatostatin or shRNA targeting of SREBP-1 significantly suppressed the viability, cisplatin resistance, and cancer stemness of NSCLC cells and because treatment induced the expression of hsa-miR-497. Conclusion: Targeting the SREBP-1/hsa-miR-497 signaling axis is a potentially effective anticancer therapeutic strategy for NSCLC.

Rationally Screened and Designed ABCG2-Binding Aptamers for Targeting Cancer Stem Cells and Reversing Multidrug Resistance

The ATP-binding cassette, subfamily G, isoform 2 protein (ABCG2), as an important member of ABC transporters, plays a key role in multidrug resistance (MDR) in cancer and has been widely considered as a marker of cancer stem cells (CSC). Reagents capable of simultaneously targeting ABCG2 and reversing MDR have great clinical application values, but their development is highly challenging. Herein, ABCG2 glycosylated extracellular region-binding aptamers were efficiently screened by a cladded molecularly imprinted polymer (cMIP)-based in vitro screening method and further rationally engineered into cyclic bivalent aptamers. Experiments showed that both the monovalent and cyclic bivalent aptamers could specifically bind ABCG2 and thereby specially target CSC of human colorectal carcinomas (CoCSC), while the latter could effectively reverse MDR in drug-resistant liver cancer cells (HepG2/ADR). Different from currently predominant small molecule inhibitors, the reversal of MDR relied on a different mechanism; the cyclic bivalent aptamers bound the two monomers of ABCG2 dimers simultaneously and thereby blocked the ABCG2-mediated drug-pumping channel, resulting in increased intracellular accumulation of substrate drugs. This study opened a new access to the development of affinity reagents for targeting CSC and reversing MDR, holding great prospects in cancer diagnosis and treatment.

The multi-targeted tyrosine kinase inhibitor SKLB610 resensitizes ABCG2-overexpressing multidrug-resistant cancer cells to chemotherapeutic drugs

The overexpression of ATP-binding cassette (ABC) transporter ABCB1 (P-glycoprotein) or ABCG2 (BCRP/MXR/ABCP) in cancer cells is frequently associated with the development of multidrug resistance (MDR) in cancer patients, which remains a major obstacle to effective cancer treatment. By utilizing energy derived from ATP hydrolysis, both transporters have been shown to reduce the chemosensitivity of cancer cells by actively effluxing cytotoxic anticancer drugs out of cancer cells. Knowing that there are presently no approved drugs or other therapeutics for the treatment of multidrug-resistant cancers, in recent years, studies have investigated the repurposing of tyrosine kinase inhibitors (TKIs) to act as agents against MDR mediated by ABCB1 and/or ABCG2. SKLB610 is a multi-targeted TKI with potent activity against vascular endothelial growth factor receptor 2 (VEGFR2), platelet-derived growth factor receptor (PDGFR), and fibroblast growth factor receptor 2 (FGFR2). In this study, we investigate the interaction of SKLB610 with ABCB1 and ABCG2. We discovered that neither ABCB1 nor ABCG2 confers resistance to SKLB610, but SKLB610 selectively sensitizes ABCG2-overexpressing multidrug-resistant cancer cells to cytotoxic anticancer agents in a concentration-dependent manner. Our data indicate that SKLB610 reverses ABCG2-mediated MDR by attenuating the drug-efflux function of ABCG2 without affecting its total cell expression. These findings are further supported by results of SKLB610-stimulated ABCG2 ATPase activity and in silico docking of SKLB610 in the drug-binding pocket of ABCG2. In summary, we reveal the potential of SKLB610 to overcome resistance to cytotoxic anticancer drugs, which offers an additional treatment option for patients with multidrug-resistant cancers and warrants further investigation.

Sophoraflavanone G Resensitizes ABCG2-Overexpressing Multidrug-Resistant Non-Small-Cell Lung Cancer Cells to Chemotherapeutic Drugs

Elevated expression of the ATP-binding cassette (ABC) drug transporter ABCG2 in cancer cells contributes to the development of the multidrug resistance phenotype in patients with advanced non-small-cell lung cancer (NSCLC). Due to the lack of U.S. Food and Drug Administration (FDA)-approved synthetic inhibitors of ABCG2, significant efforts have been invested in discovering bioactive compounds of plant origin that are capable of reversing ABCG2-mediated multidrug resistance in cancer cells. Sophoraflavanone G (SFG), a phytoncide isolated from the plant species Sophora flavescens, is known to possess a wide spectrum of pharmacological activities, including antibacterial, anti-inflammatory, antimalarial, and antiproliferative effects. In the present study, the chemosensitizing effect of SFG in ABCG2-overexpressing NSCLC cells was investigated. Experimental results demonstrate that at subtoxic concentrations SFG significantly reversed ABCG2-mediated multidrug resistance in a concentration-dependent manner. Additional biochemical data and in silico docking analysis of SFG to the inward-open conformation of human ABCG2 indicate that SFG inhibited the drug transport function of ABCG2 by interacting with residues within the transmembrane substrate-binding pocket of ABCG2. Collectively, these findings provide evidence that SFG has the potential to be further tested as an effective inhibitor of ABCG2 to improve the efficacy of therapeutic drugs in patients with advanced NSCLC.

Scaffold fragmentation and substructure hopping reveal potential, robustness, and limits of computer-aided pattern analysis (C@PA)

Computer-aided pattern analysis (C@PA) was recently presented as a powerful tool to predict multitarget ABC transporter inhibitors. The backbone of this computational methodology was the statistical analysis of frequently occurring molecular features amongst a fixed set of reported small-molecules that had been evaluated toward ABCB1, ABCC1, and ABCG2. As a result, negative and positive patterns were elucidated, and secondary positive substructures could be suggested that complemented the multitarget fingerprints. Elevating C@PA to a non-statistical and exploratory level, the concluded secondary positive patterns were extended with potential positive substructures to improve C@PA's prediction capabilities and to explore its robustness. A small-set compound library of known ABCC1 inhibitors with a known hit rate for triple ABCB1, ABCC1, and ABCG2 inhibition was taken to virtually screen for the extended positive patterns. In total, 846 potential broad-spectrum ABCB1, ABCC1, and ABCG2 inhibitors resulted, from which 10 have been purchased and biologically evaluated. Our approach revealed 4 novel multitarget ABCB1, ABCC1, and ABCG2 inhibitors with a biological hit rate of 40%, but with a slightly lower inhibitory power than derived from the original C@PA. This is the very first report about discovering novel broad-spectrum inhibitors against the most prominent ABC transporters by improving C@PA.

Epidermal growth factor receptor inhibitor-induced diarrhea: clinical incidence, toxicological mechanism, and management

The epidermal growth factor receptor (EGFR) family is a class of receptor tyrosine kinase playing a central role in carcinogenesis and cancer progression. The members of this family, particularly EGFR and human epidermal growth factor receptor 2 (HER2), are the most extensively studied drug targets for malignancy. Today, numerous tyrosine kinase inhibitors targeting EGFR family have been developed to combat non-small-cell lung cancer and breast cancer. However, severe gastrointestinal (GI) toxicity leading to dose reduction and treatment discontinuation hampers the therapeutic outcome of EGFR inhibitors. Diarrhea is one of the most frequent GI side effects, especially when it comes to second-generation EGFR inhibitors. Enterocytes apoptosis and increased inflammation accompany with many oral EGFR inhibitors. Loperamide and budesonide are the first-line treatment to manage such adverse effects. However, current prophylaxis and management are all empirical interventions to relieve the symptom. They do not specifically target the toxicological mechanism of EGFR inhibitors. Hereby, those anti-diarrhea agents do not work well when used in cancer patients experiencing EGFR inhibitor-induced diarrhea. On the other hand, the toxicological mechanism of EGFR inhibitor-induced diarrhea is poorly understood. Thus, determining the mechanism behind such diarrhea is urgently in need for developing genuinely effective anti-diarrhea agents. This review aims to call attention to EGFR inhibitor-induced diarrhea, a highly occurring and devastating cancer drug toxicity.

Clinically-Relevant ABC Transporter for Anti-Cancer Drug Resistance

Multiple drug resistance (MDR), referring to the resistance of cancer cells to a broad spectrum of structurally and mechanistically unrelated drugs across membranes, severely impairs the response to chemotherapy and leads to chemotherapy failure. Overexpression of ATP binding cassette (ABC) transporters is a major contributing factor resulting in MDR, which can recognize and mediate the efflux of diverse drugs from cancer cells, thereby decreasing intracellular drug concentration. Therefore, modulators of ABC transporter could be used in combination with standard chemotherapeutic anticancer drugs to augment the therapeutic efficacy. This review summarizes the recent advances of important cancer-related ABC transporters, focusing on their physiological functions, structures, and the development of new compounds as ABC transporter inhibitors.

C@PA: Computer-Aided Pattern Analysis to Predict Multitarget ABC Transporter Inhibitors

Based on literature reports of the last two decades, a computer-aided pattern analysis (C@PA) was implemented for the discovery of novel multitarget ABCB1 (P-gp), ABCC1 (MRP1), and ABCG2 (BCRP) inhibitors. C@PA included basic scaffold identification, substructure search and statistical distribution, as well as novel scaffold extraction to screen a large virtual compound library. Over 45,000 putative and novel broad-spectrum ABC transporter inhibitors were identified, from which 23 were purchased for biological evaluation. Our investigations revealed five novel lead molecules as triple ABCB1, ABCC1, and ABCG2 inhibitors. C@PA is the very first successful computational approach for the discovery of promiscuous ABC transporter inhibitors.

Medically Important Alterations in Transport Function and Trafficking of ABCG2

Several polymorphisms and mutations in the human ABCG2 multidrug transporter result in reduced plasma membrane expression and/or diminished transport function. Since ABCG2 plays a pivotal role in uric acid clearance, its malfunction may lead to hyperuricemia and gout. On the other hand, ABCG2 residing in various barrier tissues is involved in the innate defense mechanisms of the body; thus, genetic alterations in ABCG2 may modify the absorption, distribution, excretion of potentially toxic endo- and exogenous substances. In turn, this can lead either to altered therapy responses or to drug-related toxic reactions. This paper reviews the various types of mutations and polymorphisms in ABCG2, as well as the ways how altered cellular processing, trafficking, and transport activity of the protein can contribute to phenotypic manifestations. In addition, the various methods used for the identification of the impairments in ABCG2 variants and the different approaches to correct these defects are overviewed.

Rational drug design of 6-substituted 4-anilino-2-phenylpyrimidines for exploration of novel ABCG2 binding site

In the search for novel, highly potent, and nontoxic adjuvant chemotherapeutics to resolve the major issue of ABC transporter-mediated multidrug resistance (MDR), pyrimidines were discovered as a promising compound class of modern ABCG2 inhibitors. As ABCG2-mediated MDR is a major obstacle in leukemia, pancreatic carcinoma, and breast cancer chemotherapy, adjuvant chemotherapeutics are highly desired for future clinical oncology. Very recently, docking studies of one of the most potent reversers of ABCG2-mediated MDR were reported and revealed a putative second binding pocket of ABCG2. Based on this (sub)pocket, a series of 16 differently 6-substituted 4-anilino-2-phenylpyrimidines was designed and synthesized to explore the potential increase in inhibitory activity of these ABCG2 inhibitors. The compounds were assessed for their influence on the ABCG2-mediated pheophorbide A transport, as well as the ABCB1- and ABCC1-mediated transport of calcein AM. They were additionally evaluated in MDR reversal assays to determine their half-maximal reversal concentration (EC₅₀). The 6-substitution did not only show increased toxicity against ABCG2-overexpressing cells in combination with SN-38 but also a negative influence on cell viability in general. Nevertheless, several candidates had EC₅₀ values in the low double-digit nanomolar concentration range, qualifying them as some of the most potent reversers of ABCG2-mediated MDR. In addition, five novel multitarget ABCB1, ABCC1, and ABCG2 inhibitors were discovered, four of them exerting their inhibitory power against the three stated transporters at least in the single-digit micromolar concentration range.

Impact of histamine type-2 receptor antagonists on the anticancer efficacy of gefitinib in patients with non-small cell lung cancer

PURPOSE

Gefitinib is one of the standard treatments for non-small cell lung cancer (NSCLC) with epidermal growth factor receptor mutations. It has been reported that acid suppressants (AS) decrease the anti-tumor effect of gefitinib by reducing its solubility. AS is sometimes necessary in cancer patients; however, previous reports have not shown the most compatible AS with gefitinib administration in cancer patients. This study was conducted to determine if histamine type 2 receptor antagonists (H2RAs) can affect the anti-tumor efficacy of gefitinib.

METHODS

Eighty-seven patients with NSCLC who were administered gefitinib were retrospectively investigated. Patients who were co-administered H2RA were compared with non-AS control patients. H2RA was administered once a day at about 3-5 or 8-12 h after gefitinib intake. The primary endpoint of this study was progression-free survival (PFS), and secondary endpoints were overall survival (OS), overall response rate (ORR), and adverse effects.

RESULTS

Median PFS in H2RA group and control group was 8.0 months and 9.0 months, respectively, with no significant difference (p = 0.82). The incidence of liver dysfunction was significantly less in patients administered H2RA, whereas there were no differences between the two groups with regard to skin toxicity and diarrhea. Multivariate analysis suggested that H2RA co-administration is not a risk factor for worse PFS and OS (hazard ratio of 0.95, 0.86; 95% confidence interval of 0.60-1.48, 0.52-1.43; p = 0.82 and 0.60, respectively).

CONCLUSION

This study demonstrated that concomitant administration of H2RA with gefitinib does not affect the efficacy of gefitinib.

Superior Pyrimidine Derivatives as Selective ABCG2 Inhibitors and Broad-Spectrum ABCB1, ABCC1, and ABCG2 Antagonists

In the search for highly effective modulators addressing ABCG2-mediated MDR, 23 pyrimidines were synthesized and biologically assessed. Seven derivatives with (a) nitrogen- and/or halogen-containing residue(s) had extraordinary potencies against ABCG2 (IC₅₀ < 150 nM). The compounds competitively inhibited ABCG2-mediated Hoechst 33342 transport but were not substrates of ABCG2. The most potent MDR reverser, compound 19, concentration-dependently increased SN-38-mediated cancer cell death at 11 nM (EC₅₀), time-dependently doubled SN-38 toxicity in a period of 7 days at 10 nM, and half-maximally accelerated cell death combined with SN-38 at 17 nM. No induction of ABCG2 was observed. Furthermore, 11 pyrimidines were revealed as triple ABCB1/ABCC1/ABCG2 inhibitors. Five possessed IC₅₀ values below 10 μM against each transporter, classifying them as some of the 50 most potent multitarget ABC transporter inhibitors. The most promising representative, compound 37, reversed ABCB1-, ABCC1-, and ABCG2-mediated MDR, making it one of the three most potent ABC transporter inhibitors and reversers of ABC transporters-mediated MDR.

circSETD3 Contributes to Acquired Resistance to Gefitinib in Non-Small-Cell Lung Cancer by Targeting the miR-520h/ABCG2 Pathway

Gefitinib is a first-line treatment for patients with non-small-cell lung cancer (NSCLC), but acquired resistance is a major obstacle to its therapeutic efficacy, and the underlying mechanisms are not fully elucidated. Recent studies have indicated that circular RNAs play a crucial role in chemoresistance, but their expression and function in NSCLC cells with acquired resistance to gefitinib are largely unknown. In this study, we determined that circSETD3 was significantly upregulated in gefitinib-resistant NSCLC cell lines and the plasma of gefitinib-resistant NSCLC patients. circSETD3 markedly decreased the gefitinib sensitivity of NSCLC cells both in vitro and in nude mice xenografts. It could directly bind to miR-520h and lead to the upregulation of ATP-binding cassette subfamily G member 2 (ABCG2), an efflux transporter of gefitinib, resulting in a reduced intracellular gefitinib concentration. Moreover, we reported that the downregulation of serine/arginine splicing factor 1 (SRSF1) contributed to, at least in part, the increased expression of circSETD3 in NSCLC cells with acquired resistance to gefitinib. Taken together, our findings indicated that circSETD3 may serve as a prognostic biomarker and a potential therapeutic target for acquired resistance to gefitinib in NSCLC.

Targeting Pharmacokinetic Drug Resistance in Acute Myeloid Leukemia Cells with CDK4/6 Inhibitors

Pharmacotherapy of acute myeloid leukemia (AML) remains challenging, and the disease has one of the lowest curability rates among hematological malignancies. The therapy outcomes are often compromised by the existence of a resistant AML phenotype associated with overexpression of ABCB1 and ABCG2 transporters. Because AML induction therapy frequently consists of anthracycline-like drugs, their efficiency may also be diminished by drug biotransformation via carbonyl reducing enzymes (CRE). In this study, we investigated the modulatory potential of the CDK4/6 inhibitors abemaciclib, palbociclib, and ribociclib on AML resistance using peripheral blood mononuclear cells (PBMC) isolated from patients with de novo diagnosed AML. We first confirmed inhibitory effect of the tested drugs on ABCB1 and ABCG2 in ABC transporter-expressing resistant HL-60 cells while also showing the ability to sensitize the cells to cytotoxic drugs even as no effect on AML-relevant CRE isoforms was observed. All tested CDK4/6 inhibitors elevated mitoxantrone accumulations in CD34⁺ PBMC and enhanced accumulation of mitoxantrone was found with abemaciclib and ribociclib in PBMC of FLT3-ITD^- patients. Importantly, the accumulation rate in the presence of CDK4/6 inhibitors positively correlated with ABCB1 expression in CD34⁺ patients and led to enhanced apoptosis of PBMC in contrast to CD34⁻ samples. In summary, combination therapy involving CDK4/6 inhibitors could favorably target multidrug resistance, especially when personalized based on CD34⁻ and ABCB1-related markers.

M3814, a DNA-PK Inhibitor, Modulates ABCG2-Mediated Multidrug Resistance in Lung Cancer Cells

M3814, also known as nedisertib, is a potent and selective DNA-dependent protein kinase (DNA-PK) inhibitor under phase 2 clinical trials. ABCG2 is a member of the ATP-binding cassette (ABC) transporter family that is closely related to multidrug resistance (MDR) in cancer treatment. In this study, we demonstrated that M3814 can modulate the function of ABCG2 and overcome ABCG2-mediated MDR. Mechanistic studies showed that M3814 can attenuate the efflux activity of ABCG2 transporter, leading to increased ABCG2 substrate drugs accumulation. Furthermore, M3814 can stimulate the ABCG2 ATPase activity in a concentration-dependent manner without affecting the ABCG2 protein expression or cell surface localization of ABCG2. Moreover, the molecular docking analysis indicated a high affinity between M3814 and ABCG2 transporter at the drug-binding cavity. Taken together, our work reveals M3814 as an ABCG2 modulator and provides a potential combination of co-administering M3814 with ABCG2 substrate-drugs to overcome MDR.

ABC Transporter-Mediated Multidrug-Resistant Cancer

ATP-binding cassette (ABC) transporters are involved in active pumping of many diverse substrates through the cellular membrane. The transport mediated by these proteins modulates the pharmacokinetics of many drugs and xenobiotics. These transporters are involved in the pathogenesis of several human diseases. The overexpression of certain transporters by cancer cells has been identified as a key factor in the development of resistance to chemotherapeutic agents. In this chapter, the localization of ABC transporters in the human body, their physiological roles, and their roles in the development of multidrug resistance (MDR) are reviewed. Specifically, P-glycoprotein (P-GP), multidrug resistance-associated proteins (MRPs), and breast cancer resistance protein (BCRP/ABCG2) are described in more detail. The potential of ABC transporters as therapeutic targets to overcome MDR and strategies for this purpose are discussed as well as various explanations for the lack of efficacy of ABC drug transporter inhibitors to increase the efficiency of chemotherapy.

Metabolome Analysis Reveals Dermal Histamine Accumulation in Murine Dermatitis Provoked by Genetic Deletion of P-Glycoprotein and Breast Cancer Resistance Protein

PURPOSE

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are xenobiotic transporters which pump out variety types of compounds, but information on their interaction with endogenous substrates in the skin is limited. The purpose of the present study was to clarify possible association of these transporters in dermal accumulation of inflammatory mediators.

METHODS

Dermatitis model was constructed by repeated topical application of oxazolone in wild-type, and P-gp and BCRP gene triple knockout (Mdr1a/1b/Bcrp^-/-) mice to observe difference in phenotype. Target metabolome analysis of 583 metabolites was performed using skin and plasma.

RESULTS

Dermatitis and scratching behavior in dermatitis model of Mdr1a/1b/Bcrp^-/- mice were more severe than wild-type mice, suggesting protective roles of these transporters. This hypothesis was supported by the metabolome analysis which revealed that concentration of histamine and other dermatitis-associated metabolites like urate and serotonin in the dermatitis skin, but not normal skin, of Mdr1a/1b/Bcrp^-/- mice was higher than that of wild-type mice. Gene expression of P-gp and BCRP was reduced in oxazolone-treated skin and the skin of patients with atopic dermatitis or psoriasis.

CONCLUSIONS

These results suggest possible association of these efflux transporters with dermal inflammatory mediators, and such association could be observed in the dermatitis skin.

Identification of anticancer OATP2B1 substrates by an in vitro triple-fluorescence-based cytotoxicity screen

Membrane transporters play an important role in the absorption, distribution, metabolism and excretion of drugs. The cellular accumulation of many drugs is the result of the net function of efflux and influx transporters. Efflux transporters such as P-glycoprotein/ABCB1 have been shown to confer multidrug resistance in cancer. Although expression of uptake transporters has been confirmed in cancer cells, their role in chemotherapy response has not been systematically investigated. In the present study we have adapted a fluorescence-based cytotoxic assay to characterize the influence of key drug-transporters on the toxicity of approved anticancer drugs. Co-cultures of fluorescently labeled parental and transporter-expressing cells (expressing ABCB1, ABCG2 or OATP2B1) were screened against 101 FDA-approved anticancer drugs, using a novel, automated, triple fluorescence-based cytotoxicity assay. By measuring the survival of parental and transporter-expressing cells in co-cultures, we identify those FDA-approved anticancer drugs, whose toxicity is influenced by ABCB1, ABCG2 or OATP2B1. In addition to confirming known substrates of ABCB1 and ABCG2, the fluorescence-based cytotoxicity assays identified anticancer agents whose toxicity was increased in OATP2B1 expressing cells. Interaction of these compounds with OATP2B1 was verified in dedicated transport assays using cell-impermeant fluorescent substrates. Understanding drug-transporter interactions is needed to increase the efficacy of chemotherapeutic agents. Our results highlight the potential of the fluorescence-based HT screening system for identifying transporter substrates, opening the way for the design of therapeutic approaches based on the inhibition or even the exploitation of transporters in cancer cells.

Ciprofloxacin Enhances the Chemosensitivity of Cancer Cells to ABCB1 Substrates

ABCB1 is one of the major drug efflux transporters that is known to cause multidrug resistance (MDR) in cancer patients receiving chemotherapy for the treatment of solid tumors and hematological malignancies. Inhibition of ABCB1 efflux function is important for maintaining the intracellular concentration of chemotherapeutic drugs. Here, we evaluated ciprofloxacin for its ability to reverse MDR caused by the overexpression of ABCB1. Cytotoxicity of ciprofloxacin was determined by the MTT assay. The chemosensitizing effects of ciprofloxacin were determined in combination with ABCB1 substrates. The intracellular accumulation and efflux of ABCB1 substrates was measured by a scintillation counter, and protein expression was determined by the Western blotting. Vanadate-sensitive ATPase assay was performed to determine the effect of ciprofloxacin on the ATPase activity of ABCB1, and docking analysis was done to determine the interaction of ciprofloxacin with ABCB1. Ciprofloxacin significantly potentiated the cytotoxic effects of ABCB1 substrates in ABCB1-overexpressing cells. Furthermore, ciprofloxacin increased the intracellular accumulation and decreased the efflux of [³H]-paclitaxel without altering the expression of ABCB1. Ciprofloxacin stimulated the ATPase activity of ABCB1 in a concentration-dependent manner. Our findings showed that ciprofloxacin potently inhibits the ABCB1 efflux function and it has potential to be developed as a combination anticancer therapy.

Breast cancer resistance protein is the enemy of hypericin accumulation and toxicity of hypericin-mediated photodynamic therapy

Breast cancer resistance protein (BCRP) belongs to the family of ATP-binding cassette (ABC) transporters, overexpression of which can confer a multidrug-resistant phenotype in cancer cells and tumors. BCRP mediates efflux of numerous xenobiotics, including various chemotherapeutic agents and photosensitizers. Hypericin (HY) is a naturally-occurring photosensitizer synthesized by plants of the genus Hypericum. Our recently published results indicate that accumulation of HY in cancer cells of different tissue origin can be affected mostly by BCRP. Considering all known facts, the main goal of this study was to verify whether not only HY accumulation but also toxicity of HY-mediated photodynamic therapy (PDT) can be affected by the presence of some ABC transporters. To specifically prove our hypothesis, we used an experimental model of human leukemia cell lines differing in the expression level of the main drug efflux transporters P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1) and BCRP. The lowest HY accumulation, and consequently the highest resistance to HY-PDT, was found in cells overexpressing BCRP. Moreover, pretreatment with BCRP inhibitor Ko143 significantly increased HY accumulation and sensitized cells to HY-PDT. Therefore, our findings represent direct evidence that BCRP is the nemesis of HY accumulation and toxicity of HY-PDT. Thus, we should emphasize that individualized screening for BCRP expression and activity may represent a useful tool for prediction of HY-mediated photodynamic diagnosis (PDD) or PDT effectiveness.

ABCC10 Plays a Significant Role in the Transport of Gefitinib and Contributes to Acquired Resistance to Gefitinib in NSCLC

Gefitinib, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (EGFR-TKI), is used clinically as first-line therapy in patients with advanced non-small cell lung cancer (NSCLC) with EGFR activating mutations, but the inevitable development of acquired resistance limits its efficacy. In up to 30–40% of NSCLC cases, the mechanism underlying acquired resistance remains unknown. ATP-binding cassette (ABC) transporters are a family of membrane proteins that can significantly influence the bioavailability of numerous drugs, and have confirmed to play an essential role in multidrug resistance (MDR) in cancer chemotherapy. However, their role in acquired resistance to gefitnib in NSCLC has not been well studied. Here, through RNA sequencing (RNA-Seq) technology we assessed the differentially expressed ABC transporters in gefitinib-sensitive (PC9 and H292) and gefitinib-resistant (PC9/GR and H292/GR) NSCLC cells, with ABCC10 identified as a transporter of interest. Both ABCC10 mRNA and protein were significantly increased in acquired gefitinib-resistant NSCLC cells, independent of EGFR mutation status. In vitro transport assay showed that ABCC10 could actively efflux gefitinib, with an efflux ratio (ER) of 7.8. Further results from in vitro cell line models and in vivo xenograft models showed that overexpression of ABCC10 led to a reduction in gefitinib sensitivity through decreasing the intracellular gefitinib accumulation. Our data suggest that ABCC10 has an important role in acquired resistance to gefitinib in NSCLC, which can serve as a novel predictive marker and a potential therapeutic target in gefitinib treatment.

Effects of Various Pharmaceutical Excipients on the Intestinal Transport and Absorption of Sulfasalazine, a Typical Substrate of Breast Cancer Resistance Protein Transporter

Breast cancer resistance protein (BCRP) transporter is an efflux transporter that utilizes energy from adenosine triphosphate hydrolysis to push its substrates, regardless of the concentration gradient. Its presence on the apical membrane of the intestinal mucosa is a major obstacle for the intestinal absorption of its substrates. In this study, we examined the effects of various pharmaceutical excipients on the intestinal transport and absorption of sulfasalazine, a BCRP substrate. Four excipients, including 0.05% and 0.075% BL-9EX, 0.01% and 0.05% Brij 97, 0.075% Labrasol, and 0.05% and 0.1% Tween 20 decreased the secretory transport of sulfasalazine in an in vitro diffusion chamber. Further investigation in an in situ closed loop experiment in rats showed that 0.05% and 0.1% BL-9EX and 0.1% Brij 97 effectively enhanced the intestinal absorption of sulfasalazine while maintaining minimal toxicity to the intestinal mucosa. However, 0.1% Brij 97 also increased the intestinal absorption of 5(6)-carboxyfluorescein, a paracellular marker compound. These findings suggest that BL-9EX might effectively inhibit the BCRP-mediated efflux of sulfasalazine in vivo, indicating that BL-9EX could improve the intestinal absorption of sulfasalazine and other BCRP substrates.

Modelling ponatinib resistance in tyrosine kinase inhibitor-naïve and dasatinib resistant BCR-ABL1+ cell lines

TKI resistance remains a major impediment to successful treatment of CML. In this study, we investigated the emerging modes of ponatinib resistance in TKI-naïve and dasatinib resistant BCR-ABL1+ cell lines. To investigate potential resistance mechanisms, ponatinib resistance was generated in BCR-ABL1+ cell-lines by long-term exposure to increasing concentrations of ponatinib. Two cell lines with prior dasatinib resistance demonstrated BCR-ABL1 kinase domain (KD) mutation(s) upon exposure to ponatinib. In one of these cell lines the T315I mutation had emerged during dasatinib exposure. When further cultured with ponatinib, the T315I mutation level and BCR-ABL1 mRNA expression level were increased. In the other cell line, compound mutations G250E/E255K developed with ponatinib exposure. In contrast, the ponatinib resistant cell lines that had no prior exposure to other TKIs (TKI-naïve) did not develop BCR-ABL1 KD mutations. Rather, both of these cell lines demonstrated Bcr-Abl-independent resistance via Axl overexpression. Axl, a receptor tyrosine kinase, has previously been associated with imatinib and nilotinib resistance. Ponatinib sensitivity was restored following Axl inhibition or shRNA-mediated-knockdown of Axl, suggesting that Axl was the primary driver of resistance and a potential target for therapy in this setting.

2,4,6-Substituted Quinazolines with Extraordinary Inhibitory Potency toward ABCG2

Several members of the ABC transporter superfamily play a decisive role in the development of multidrug resistance (MDR) in cancer. One of these MDR associated efflux transporters is ABCG2. One way to overcome this MDR is the coadministration of potent inhibitors of ABCG2. In this study, we identified novel inhibitors containing a 2,4,6-substituted quinazoline scaffold. Introduction of a 6-nitro function led to extraordinarily potent compounds that were highly selective for ABCG2 and also able to reverse the MDR toward the chemotherapeutic drugs SN-38 and mitoxantrone. The binding of substrate Hoechst 33342 and the two potent inhibitors 31 and 41 which differ in their mechanism of inhibition was rationalized using the recently published cryo-EM structures of ABCG2. For a better understanding of the interaction between the inhibitors and ABCG2, additional investigations regarding the ATPase activity, the interaction with Hoechst 33342, and with the conformational sensitive 5D3 antibody were carried out.

Metabolic Reprogramming During Multidrug Resistance in Leukemias

Cancer outcome has improved since introduction of target therapy. However, treatment success is still impaired by the same drug resistance mechanism of classical chemotherapy, known as multidrug resistance (MDR) phenotype. This phenotype promotes resistance to drugs with different structures and mechanism of action. Recent reports have shown that resistance acquisition is coupled to metabolic reprogramming. High-gene expression, increase of active transport, and conservation of redox status are one of the few examples that increase energy and substrate demands. It is not clear if the role of this metabolic shift in the MDR phenotype is related to its maintenance or to its induction. Apart from the nature of this relation, the metabolism may represent a new target to avoid or to block the mechanism that has been impairing treatment success. In this mini-review, we discuss the relation between metabolism and MDR resistance focusing on the multiple non-metabolic functions that enzymes of the glycolytic pathway are known to display, with emphasis with the diverse activities of glyceraldehyde-3-phosphate dehydrogenase.

Hypericin affects cancer side populations via competitive inhibition of BCRP

OBJECTIVE

Cancer stem-like cells (CSLCs) are considered a root of tumorigenicity and resistance. However, their identification remains challenging. The use of the side population (SP) assay as a credible marker of CSLCs remains controversial. The SP assay relies on the elevated activity of ABC transporters that, in turn, can be modulated by hypericin (HYP), a photosensitizer and bioactive compound of St. John's Wort (Hypericum perforatum), a popular over-the-counter antidepressant. Here we aimed to comprehensively characterize the SP phenotype of cancer cells and to determine the impact of HYP on these cells.

METHODS

Flow cytometry and sorting-based assays were employed, including CD24-, CD44-, CD133-, and ALDH-positivity, clonogenicity, 3D-forming ability, ABC transporter expression and activity, and intracellular accumulation of HYP/Hoechst 33342. The tumorigenic ability of SP, nonSP, and HYP-treated cells was verified by xenotransplantation into immunodeficient mice.

RESULTS

The SP phenotype was associated with elevated expression of several investigated transporters and more intensive growth in non-adherent conditions but not with higher clonogenicity, tumorigenicity or ALDH-positivity. Despite stimulated BCRP level and MRP1 activity, HYP reversibly decreased the SP proportion, presumably via competitive inhibition of BCRP. HYP-selected SP cells acquired additional traits of resistance and extensively eliminated HYP.

CONCLUSIONS

Our results suggest that SP is not an unequivocal CSLC-marker. However, SP could play an important role in modulating HYP-treatment and serve as a negative predictive tool for HYP-based therapies. Moreover, the use of supplements containing HYP by cancer patients should be carefully considered, due to its proposed effect on drug efflux and complex impact on tumor cells, which have not yet been sufficiently characterized.

Tyrosine kinase inhibitors enhanced the efficacy of conventional chemotherapeutic agent in multidrug resistant cancer cells

Multidrug resistance (MDR) triggered by ATP binding cassette (ABC) transporter such as ABCB1, ABCC1, ABCG2 limited successful cancer chemotherapy. Unfortunately, no commercial available MDR modulator approved by FDA was used in clinic. Tyrosine kinase inhibitors (TKIs) have been administrated to fight against cancer for decades. Almost TKI was used alone in clinic. However, drug combinations acting synergistically to kill cancer cells have become increasingly important in cancer chemotherapy as an approach for the recurrent resistant disease. Here, we summarize the effect of TKIs on enhancing the efficacy of conventional chemotherapeutic drug in ABC transporter-mediated MDR cancer cells, which encourage to further discuss and study in clinic.

Voruciclib, a Potent CDK4/6 Inhibitor, Antagonizes ABCB1 and ABCG2-Mediated Multi-Drug Resistance in Cancer Cells

Background/Aims: The overexpression of ATP-Binding Cassette (ABC) transporters has known to be one of the major obstacles impeding the success of chemotherapy in drug resistant cancers. In this study, we evaluated voruciclib, a CDK 4/6 inhibitor, for its chemo-sensitizing activity in ABCB1- and ABCG2- overexpressing cells. Methods: Cytotoxicity and reversal effect of voruciclib was determined by MTT assay. The intracellular accumulation and efflux of ABCB1 and ABCG2 substrates were measured by scintillation counter. The effects on expression and intracellular localization of ABCB1 and ABCG2 proteins were determined by Western blotting and immunofluorescence, respectively. Vanadate-sensitive ATPase assay was done to determine the effect of voruciclib on the ATPase activity of ABCB1 and ABCG2. Flow cytometric analysis was done to determine the effect of voruciclib on apoptosis of ABCB1 and ABCG2-overexpressing cells and docking analysis was done to determine the interaction of voruciclib with ABCB1 and ACBG2 protein. Results: Voruciclib significantly potentiated the effect of paclitaxel and doxorubicin in ABCB1-overexpressing cells, as well as mitoxantrone and SN-38 in ABCG2-overexpressing cells. Voruciclib moderately sensitized ABCC10- overexpressing cells to paclitaxel, whereas it did not alter the cytotoxicity of substrates of ABCC1. Furthermore, voruciclib increased the intracellular accumulation and decreased the efflux of substrate anti-cancer drugs from ABCB1- or ABCG2-overexpressing cells. However, voruciclib did not alter the expression or the sub-cellular localization of ABCB1 or ABCG2. Voruciclib stimulated the ATPase activity of both ABCB1 and ABCG2 in a concentration-dependent manner. Lastly, voruciclib exhibited a drug-induced apoptotic effect in ABCB1- or ABCG2- overexpressing cells. Conclusion: Voruciclib is currently a phase I clinical trial drug. Our findings strongly support its potential use in combination with conventional anti-cancer drugs for cancer chemotherapy.

Genetic and ethnic modulation of cardiovascular toxicity of vascular endothelial growth factor inhibitors

Vascular endothelial growth factor (VEGF) inhibitors, including monoclonal antibodies and tyrosine kinase inhibitors (TKIs), are important as anticancer treatments through curbing tumour angiogenesis and growth. VEGF inhibitors have significant cardiovascular effects. By blocking VEGF receptors, ligands, or signal pathways, VEGF inhibitors disturb the balance between vasodilation and vasoconstriction, undermine endothelial cell integrity, and activate cardiomyocyte apoptosis. VEGF inhibitors increase risks of hypertension, heart failure, thromboembolism and arrhythmia. Genetic and geographic studies showed that genetic polymorphisms likely play significant predictive or prognostic roles in cardiovascular toxicity associated with VEGF inhibitors. This review updates current understandings of VEGF inhibitors on cardiovascular toxicity, explores potential mechanisms, and clarifies whether genetic or ethnic factors contribute to their adverse effects. Key Messages VEGF inhibitors disturb the balance between vasodilation and vasoconstriction, undermine endothelial cell integrity and activate cardiomyocyte apoptosis. VEGF inhibitors increase risks of hypertension, heart failure, thromboembolism and arrhythmia. Genetic and geographic studies showed that genetic polymorphisms likely play significant predictive or prognostic roles in cardiovascular toxicity associated with VEGF inhibitors.

Effective Drug Delivery in Diffuse Intrinsic Pontine Glioma: A Theoretical Model to Identify Potential Candidates

Despite decades of clinical trials for diffuse intrinsic pontine glioma (DIPG), patient survival does not exceed 10% at two years post-diagnosis. Lack of benefit from systemic chemotherapy may be attributed to an intact bloodbrain barrier (BBB). We aim to develop a theoretical model including relevant physicochemical properties in order to review whether applied chemotherapeutics are suitable for passive diffusion through an intact BBB or whether local administration via convection-enhanced delivery (CED) may increase their therapeutic potential. Physicochemical properties (lipophilicity, molecular weight, and charge in physiological environment) of anticancer drugs historically and currently administered to DIPG patients, that affect passive diffusion over the BBB, were included in the model. Subsequently, the likelihood of BBB passage of these drugs was ascertained, as well as their potential for intratumoral administration via CED. As only non-molecularly charged, lipophilic, and relatively small sized drugs are likely to passively diffuse through the BBB, out of 51 drugs modeled, only 8 (15%)-carmustine, lomustine, erlotinib, vismodegib, lenalomide, thalidomide, vorinostat, and mebendazole-are theoretically qualified for systemic administration in DIPG. Local administration via CED might create more therapeutic options, excluding only positively charged drugs and drugs that are either prodrugs and/or only available as oral formulation. A wide variety of drugs have been administered systemically to DIPG patients. Our model shows that only few are likely to penetrate the BBB via passive diffusion, which may partly explain the lack of efficacy. Drug distribution via CED is less dependent on physicochemical properties and may increase the therapeutic options for DIPG.