Role of breast cancer resistance protein (BCRP/ABCG2) in cancer drug resistance

Cadmium transport by mammalian ATP-binding cassette transporters

Cellular responses to toxic metals depend on metal accessibility to intracellular targets, reaching interaction sites, and the intracellular metal concentration, which is mainly determined by uptake pathways, binding/sequestration and efflux pathways. ATP-binding cassette (ABC) transporters are ubiquitous in the human body-usually in epithelia-and are responsible for the transfer of indispensable physiological substrates (e.g. lipids and heme), protection against potentially toxic substances, maintenance of fluid composition, and excretion of metabolic waste products. Derailed regulation and gene variants of ABC transporters culminate in a wide array of pathophysiological disease states, such as oncogenic multidrug resistance or cystic fibrosis. Cadmium (Cd) has no known physiological role in mammalians and poses a health risk due to its release into the environment as a result of industrial activities, and eventually passes into the food chain. Epithelial cells, especially within the liver, lungs, gastrointestinal tract and kidneys, are particularly susceptible to the multifaceted effects of Cd because of the plethora of uptake pathways available. Pertinent to their broad substrate spectra, ABC transporters represent a major cellular efflux pathway for Cd and Cd complexes. In this review, we summarize current knowledge concerning transport of Cd and its complexes (mainly Cd bound to glutathione) by the ABC transporters ABCB1 (P-glycoprotein, MDR1), ABCB6, ABCC1 (multidrug resistance related protein 1, MRP1), ABCC7 (cystic fibrosis transmembrane regulator, CFTR), and ABCG2 (breast cancer related protein, BCRP). Potential detoxification strategies underlying ABC transporter-mediated efflux of Cd and Cd complexes are discussed.

ABCG2 and SLC1A5 functionally interact to rewire metabolism and confer a survival advantage to cancer cells under oxidative stress

ABCG2, a member of the ABC transporter superfamily, is overexpressed in many human tumors and has long been studied for its ability to export a variety of chemotherapeutic agents, thereby conferring a multidrug resistance (MDR) phenotype. However, several studies have shown that ABCG2 can also confer an MDR-independent survival advantage to tumor cells exposed to stress. While investigating the mechanism by which ABCG2 enhances survival in stressful milieus, we have identified a physical and functional interaction between ABCG2 and SLC1A5, a member of the solute transporter superfamily and the primary transporter of glutamine in cancer cells. This interaction was accompanied by increased glutamine uptake, increased glutaminolysis, and rewired cellular metabolism, as evidenced by an increase in key metabolic enzymes and alteration of glutamine-dependent metabolic pathways. Specifically, we observed an increase in glutamine metabolites shuttled to the TCA cycle, and an increase in the synthesis of glutathione, accompanied by a decrease in basal levels of reactive oxygen species and a marked increase in cell survival in the face of oxidative stress. Notably, the knockdown of SLC1A5 or depletion of exogenous glutamine diminished ABCG2-enhanced autophagy flux, further implicating this solute transporter in ABCG2-mediated cell survival. This is, to our knowledge, the first report of a functionally significant physical interaction between members of the two major transporter superfamilies. Moreover, these observations may underlie the protective role of ABCG2 in cancer cells under duress and suggest a novel role for ABCG2 in the regulation of metabolism in normal and diseased states.

Novel naphthoquinone-1H-1,2,3-triazole hybrids: Design, synthesis and evaluation as inductors of ROS-mediated apoptosis in the MCF-7 cells

The search for novel anticancer drugs is essential to expand treatment options, overcome drug resistance, reduce toxicity, promote innovation, and tackle the economic impact. The importance of these studies lies in their contribution to advancing cancer research and enhancing patient outcomes in the battle against cancer. Here, we developed new asymmetric hybrids containing two different naphthoquinones linked by a 1,2,3-1H-triazole nucleus, which are potential new drugs for cancer treatment. The antitumor activity of the novel compounds was tested using the breast cancer cell lines MCF-7 and MDA-MB-231, using the non-cancer cell line MCF10A as control. Our results showed that two out of twenty-two substances tested presented potential antitumor activity against the breast cancer cell lines. These potential drugs, named here 12g and 12h were effective in reducing cell viability and promoting cell death of the tumor cell lines, exhibiting minimal effects on the control cell line. The mechanism of action of the novel drugs was assessed revealing that both drugs increased reactive oxygen species production with consequent activation of the AMPK pathway. Therefore, we concluded that 12g and 12h are novel AMPK activators presenting selective antitumor effects.

Phytochemical constituents, in-vitro anticancer activity and computational studies of Cymbopogon schoenanthus

The cytotoxic effects of Cymbopogon schoenanthus L. aerial part ethanol extract were examined against some cancer cell lines, and HUVEC normal cell lines using MTT assay. The ethanolic extract was prepared by ultrasonic-assisted extraction and analyzed by GC-MS and HPLC. The extract was found to be rich in terpene compounds. The extract proved to be highly selective and effective against breast and prostate cancer cell lines (MDA-MB-435, MCF-7, and DU 145) with IC50 as low as 0.7913 ± 0.14, 12.841 ± 0.21, and 30.51 ± 0.18 µg/ml, respectively. In silico modeling was performed to investigate the binding orientation and affinity of the major identified compounds against Polo-like kinase (PLK1 protein) a cancer molecular target using molecular docking and molecular dynamic whereas eudesm-5-en-11-ol, piperitone, and 2,3-dihydrobenzofuran displayed better binding affinity and stability against PLK1 compared to the reference drug. These findings encourage further in vivo studies to assess the anti-cancer effects of C. schoenanthus extract and its components.

Drug resistance mechanisms in cancers: Execution of pro-survival strategies

One of the quintessential challenges in cancer treatment is drug resistance. Several mechanisms of drug resistance have been described to date, and new modes of drug resistance continue to be discovered. The phenomenon of cancer drug resistance is now widespread, with approximately 90% of cancer-related deaths associated with drug resistance. Despite significant advances in the drug discovery process, the emergence of innate and acquired mechanisms of drug resistance has impeded the progress in cancer therapy. Therefore, understanding the mechanisms of drug resistance and the various pathways involved is integral to treatment modalities. In the present review, I discuss the different mechanisms of drug resistance in cancer cells, including DNA damage repair, epithelial to mesenchymal transition, inhibition of cell death, alteration of drug targets, inactivation of drugs, deregulation of cellular energetics, immune evasion, tumor-promoting inflammation, genome instability, and other contributing epigenetic factors. Furthermore, I highlight available treatment options and conclude with future directions.

Understanding Cancer's Defense against Topoisomerase-Active Drugs: A Comprehensive Review

In recent years, the emergence of cancer drug resistance has been one of the crucial tumor hallmarks that are supported by the level of genetic heterogeneity and complexities at cellular levels. Oxidative stress, immune evasion, metabolic reprogramming, overexpression of ABC transporters, and stemness are among the several key contributing molecular and cellular response mechanisms. Topo-active drugs, e.g., doxorubicin and topotecan, are clinically active and are utilized extensively against a wide variety of human tumors and often result in the development of resistance and failure to therapy. Thus, there is an urgent need for an incremental and comprehensive understanding of mechanisms of cancer drug resistance specifically in the context of topo-active drugs. This review delves into the intricate mechanistic aspects of these intracellular and extracellular topo-active drug resistance mechanisms and explores the use of potential combinatorial approaches by utilizing various topo-active drugs and inhibitors of pathways involved in drug resistance. We believe that this review will help guide basic scientists, pre-clinicians, clinicians, and policymakers toward holistic and interdisciplinary strategies that transcend resistance, renewing optimism in the ongoing battle against cancer.

Blood-brain barrier transporters: An overview of function, dysfunction in Alzheimer's disease and strategies for treatment

The blood-brain-barrier (BBB) has a major function in maintaining brain homeostasis by regulating the entry of molecules from the blood to the brain. Key players in BBB function are BBB transporters which are highly expressed in brain endothelial cells (BECs) and critical in mediating the exchange of nutrients and waste products. BBB transporters can also influence drug delivery into the brain by inhibiting or facilitating the entry of brain targeting therapeutics for the treatment of brain disorders, such as Alzheimer's disease (AD). Recent studies have shown that AD is associated with a disrupted BBB and transporter dysfunction, although their roles in the development in AD are not fully understand. Modulation of BBB transporter activity may pose a novel approach to enhance the delivery of drugs to the brain for enhanced treatment of AD. In this review, we will give an overview of key functions of BBB transporters and known changes in AD. In addition, we will discuss current strategies for transporter modulation for enhanced drug delivery into the brain.

Enhanced reversal of ABCG2-mediated drug resistance by replacing a phenyl ring in baicalein with a meta-carborane

Success of chemotherapy is often hampered by multidrug resistance. One mechanism for drug resistance is the elimination of anticancer drugs through drug transporters, such as breast cancer resistance protein (BCRP; also known as ABCG2), and causes a poor 5-year survival rate of human patients. Co-treatment of chemotherapeutics and natural compounds, such as baicalein, is used to prevent chemotherapeutic resistance but is limited by rapid metabolism. Boron-based clusters as meta-carborane are very promising phenyl mimetics to increase target affinity; we therefore investigated the replacement of a phenyl ring in baicalein by a meta-carborane to improve its affinity towards the human ABCG2 efflux transporter. Baicalein strongly inhibited the ABCG2-mediated efflux and caused a fivefold increase in mitoxantrone cytotoxicity. Whereas the baicalein derivative 5,6,7-trimethoxyflavone inhibited ABCG2 efflux activity in a concentration of 5 μm without reversing mitoxantrone resistance, its carborane analogue 5,6,7-trimethoxyborcalein significantly enhanced the inhibitory effects in nanomolar ranges (0.1 μm) and caused a stronger increase in mitoxantrone toxicity reaching similar values as Ko143, a potent ABCG2 inhibitor. Overall, in silico docking and in vitro studies demonstrated that the modification of baicalein with meta-carborane and three methoxy substituents leads to an enhanced reversal of ABCG2-mediated drug resistance. Thus, this seems to be a promising basis for the development of efficient ABCG2 inhibitors.

ATP-Binding Cassette Subfamily G Member 2 in Acute Myeloid Leukemia: A New Molecular Target?

Despite the progress in the knowledge of disease pathogenesis and the identification of many molecular markers as potential targets of new therapies, the cure of acute myeloid leukemia remains challenging. Disease recurrence after an initial response and the development of resistance to old and new therapies account for the poor survival rate and still make allogeneic stem cell transplantation the only curative option. Multidrug resistance (MDR) is a multifactorial phenomenon resulting from host-related characteristics and leukemia factors. Among these, the overexpression of membrane drug transporter proteins belonging to the ABC (ATP-Binding Cassette)-protein superfamily, which diverts drugs from their cellular targets, plays an important role. Moreover, a better understanding of leukemia biology has highlighted that, at least in cancer, ABC protein's role goes beyond simple drug transport and affects many other cell functions. In this paper, we summarized the current knowledge of ABCG2 (formerly Breast Cancer Resistance Protein, BCRP) in acute myeloid leukemia and discuss the potential ways to overcome its efflux function and to revert its ability to confer stemness to leukemia cells, favoring the persistence of leukemia progenitors in the bone marrow niche and justifying relapse also after therapy intensification with allogeneic stem cell transplantation.

The mechanisms of multidrug resistance of breast cancer and research progress on related reversal agents

Chemotherapy is the mainstay in the treatment of breast cancer. However, many drugs that are commonly used in clinical practice have a high incidence of side effects and multidrug resistance (MDR), which is mainly caused by overexpression of drug transporters and related enzymes in breast cancer cells. In recent years, researchers have been working hard to find newer and safer drugs to overcome MDR in breast cancer. In this review, we provide the molecule mechanism of MDR in breast cancer, categorize potential lead compounds that inhibit single or multiple drug transporter proteins, as well as related enzymes. Additionally, we have summarized the structure-activity relationship (SAR) based on potential breast cancer MDR modulators with lower side effects. The development of novel approaches to suppress MDR is also addressed. These lead compounds hold great promise for exploring effective chemotherapy agents to overcome MDR, providing opportunities for curing breast cancer in the future.

Metabolism-guided development of Ko143 analogs as ABCG2 inhibitors

ATP-binding cassette subfamily G member 2 (ABCG2), an efflux transporter, is involved in multiple pathological processes. Ko143 is a potent ABCG2 inhibitor; however, it is quickly metabolized through carboxylesterase 1-mediated hydrolysis of its t-butyl ester moiety. The current work aimed to develop more metabolically stable ABCG2 inhibitors. Novel Ko143 analogs were designed and synthesized by replacing the unstable t-butyl ester moiety in Ko143 with an amide group. The synthesized Ko143 analogs were evaluated for their ABCG2 inhibitory activity, binding mode with ABCG2, cytotoxicity, and metabolic stability. We found that the amide modification of Ko143 led to metabolically stable ABCG2 inhibitors. Among these Ko143 analogs, K2 and K34 are promising candidates with favorable oral pharmacokinetic profiles in mice. In summary, we synthesized novel Ko143 analogs with improved metabolic stability, which can potentially be used as lead compounds for the future development of ABCG2 inhibitors.

Black Phosphorus as a Targeting PPAR-γ Agonist to Reverse Chemoresistance in Patient-derived Organoids, Mice, and Pancreatic Tumor Cells

Black phosphorus (BP) exhibits significant potential for clinical applications. However, further research is necessary to uncover the unknown biological functions of BP and broaden its applications across various fields. This study investigates the potential of BP as a targeting PPAR-γ agonist to overcome chemoresistance in the treatment of pancreatic adenocarcinoma (PAAD) using 2D and 3D cell lines, patient-derived organoids (PDOs), and mouse models. RNA-sequencing analysis shows that BP treatment enriches differentially expressed genes in the PPAR pathway, and molecular modeling predicts the potential docking site between BP and PPAR-γ. Transcriptional activity assays are further to verify the activation of PPAR-γ. BP-activated PPAR-γ inhibits cancer stem cell (CSC) properties and expression of biomarkers such as CD44 and c-Myc, which are involved in chemoresistance. Notably, CD44 overexpression in tumor cells renders them susceptible to BP while insensitive to gemcitabine. This indicates that BP preferentially targets stem-like cells, which exhibit heightened resistance to chemotherapeutic drugs. A combination treatment strategy involving BP and gemcitabine is developed, demonstrating enhanced treatment efficacy of PAAD in both in vitro and in vivo models. Thus, BP serves as a PPAR-γ agonist capable of reversing chemoresistance, establishing it as a potent anti-tumor approach for the treatment of PAAD.

Divergent features of ERβ isoforms in triple negative breast cancer: progress and implications for further research

Estrogen receptor β (ERβ) was discovered more than 20 years ago. However, the extent and role of ERβ expression in breast cancer remain controversial, especially in the context of triple-negative breast cancer (TNBC). ERβ exists as multiple isoforms, and a series of studies has revealed an inconsistent role of ERβ isoforms in TNBC. Our recent results demonstrated contrasting functions of ERβ1 and ERβ2/β5 in TNBC. Additional research should be conducted to explore the functions of individual ERβ isoforms and develop targeted drugs according to the relevant mechanisms. Consequently, a systematic review of ERβ isoforms is necessary. In this review, we overview the structure of ERβ isoforms and detail what is known about the function of ERβ isoforms in normal mammary tissue and breast cancer. Moreover, this review highlights the divergent features of ERβ isoforms in TNBC. This review also provides insights into the implications of targeting ERβ isoforms for clinical treatment. In conclusion, this review provides a framework delineating the roles and mechanisms of different ERβ isoforms in TNBC and sheds light on future directions for basic and clinical research.

Expression, Function and Trafficking of the Human ABCG2 Multidrug Transporter Containing Mutations in an Unstructured Cytoplasmic Loop

The human ABCG2 multidrug transporter plays a crucial role in the absorption and excretion of xeno- and endobiotics, contributes to cancer drug resistance and the development of gout. In this work, we have analyzed the effects of selected variants, residing in a structurally unresolved cytoplasmic region (a.a. 354-367) of ABCG2 on the function and trafficking of this protein. A cluster of four lysines (K357-360) and the phosphorylation of a threonine (T362) residue in this region have been previously suggested to significantly affect the cellular fate of ABCG2. Here, we report that the naturally occurring K360del variant in human cells increased ABCG2 plasma membrane expression and accelerated cellular trafficking. The variable alanine replacements of the neighboring lysines had no significant effect on transport function, and the apical localization of ABCG2 in polarized cells has not been altered by any of these mutations. Moreover, in contrast to previous reports, we found that the phosphorylation-incompetent T362A, or the phosphorylation-mimicking T362E variants in this loop had no measurable effects on the function or expression of ABCG2. Molecular dynamics simulations indicated an increased mobility of the mutant variants with no major effects on the core structure of the protein. These results may help to decipher the potential role of this unstructured region within this transporter.

Nucleoside-based anticancer drugs: Mechanism of action and drug resistance

Nucleoside-based drugs, recognized as purine or pyrimidine analogs, have been potent therapeutic agents since their introduction in 1950, deployed widely in the treatment of diverse diseases such as cancers, myelodysplastic syndromes, multiple sclerosis, and viral infections. These antimetabolites establish complex interactions with cellular molecular constituents, primarily via activation of phosphorylation cascades leading to consequential interactions with nucleic acids. However, the therapeutic efficacy of these agents is frequently compromised by the development of drug resistance, a continually emerging challenge in their clinical application. This comprehensive review explores the mechanisms of resistance to nucleoside-based drugs, encompassing a wide spectrum of phenomena from alterations in membrane transporters and activating kinases to changes in drug elimination strategies and DNA damage repair mechanisms. The critical analysis in this review underlines complex interactions of drug and cell and also guides towards novel therapeutic strategies to counteract resistance. The development of targeted therapies, novel nucleoside analogs, and synergistic drug combinations are promising approaches to restore tumor sensitivity and improve patient outcomes.

Monoacylglycerol Lipase Inhibitor JJKK048 Ameliorates ABCG2 Transporter-Mediated Regorafenib Resistance Induced by Hypoxia in Triple Negative Breast Cancer Cells

Triple negative breast cancer (TNBC) is among the most aggressive and deadly cancer subtypes. Intra-tumoral hypoxia is associated with aggressiveness and drug resistance in TNBC. One of the underlying mechanisms of hypoxia-induced drug resistance is the elevated expression of efflux transporters such as breast cancer resistant protein (ABCG2). In the present study, we investigated the possibility of ameliorating ABCG2-mediated drug resistance in hypoxic TNBC cells by monoacylglycerol lipase (MAGL) inhibition and the consequent downregulation of ABCG2 expression. The effect of MAGL inhibition on ABCG2 expression, function, and efficacy of regorafenib, an ABCG2 substrate was investigated in cobalt dichloride (CoCl2) induced pseudohypoxic TNBC (MDA-MB-231) cells, using quantitative targeted absolute proteomics, qRT-PCR, anti-cancer drug accumulation in the cells, cell invasiveness and resazurin-based cell viability assays. Our results showed that hypoxia-induced ABCG2 expression led to low regorafenib intracellular concentrations, reduced the anti-invasiveness efficacy, and elevated half maximal inhibitory concentration (IC50) of regorafenib in vitro MDA-MB-231 cells. MAGL inhibitor, JJKK048, reduced ABCG2 expression, increased regorafenib cell accumulation, which led to higher regorafenib efficacy. In conclusion, hypoxia-induced regorafenib resistance due to ABCG2 over-expression in TNBC cells can be ameliorated by MAGL inhibition.

Refinement of safety and efficacy of anti-cancer chemotherapeutics by tailoring their site-specific intracellular bioavailability through transporter modulation

Low intracellular bioavailability, off-site toxicities, and multi drug resistance (MDR) are the major constraints involved in cancer chemotherapy. Many anticancer molecules fail to become a good lead in drug discovery because of their poor site-specific bioavailability. Concentration of a molecule at target sites is largely varied because of the wavering expression of transporters. Recent anticancer drug discovery strategies are paying high attention to enhance target site bioavailability by modulating drug transporters. The level of genetic expression of transporters is an important determinant to understand their ability to facilitate drug transport across the cellular membrane. Solid carrier (SLC) transporters are the major influx transporters involved in the transportation of most anti-cancer drugs. In contrast, ATP-binding cassette (ABC) superfamily is the most studied class of efflux transporters concerning cancer and is significantly involved in efflux of chemotherapeutics resulting in MDR. Balancing SLC and ABC transporters is essential to avoid therapeutic failure and minimize MDR in chemotherapy. Unfortunately, comprehensive literature on the possible approaches of tailoring site-specific bioavailability of anticancer drugs through transporter modulation is not available till date. This review critically discussed the role of different specific transporter proteins in deciding the intracellular bioavailability of anticancer molecules. Different strategies for reversal of MDR in chemotherapy by incorporation of chemosensitizers have been proposed in this review. Targeted strategies for administration of the chemotherapeutics to the intracellular site of action through clinically relevant transporters employing newer nanotechnology-based formulation platforms have been explained. The discussion embedded in this review is timely considering the current need of addressing the ambiguity observed in pharmacokinetic and clinical outcomes of the chemotherapeutics in anti-cancer treatment regimens.

Recent advances in access to overcome cancer drug resistance by nanocarrier drug delivery system

Cancer is currently one of the most intractable diseases causing human death. Although the prognosis of tumor patients has been improved to a certain extent through various modern treatment methods, multidrug resistance (MDR) of tumor cells is still a major problem leading to clinical treatment failure. Chemotherapy resistance refers to the resistance of tumor cells and/or tissues to a drug, usually inherent or developed during treatment. Therefore, an urgent need to research the ideal drug delivery system to overcome the shortcoming of traditional chemotherapy. The rapid development of nanotechnology has brought us new enlightenments to solve this problem. The novel nanocarrier provides a considerably effective treatment to overcome the limitations of chemotherapy or other drugs resulting from systemic side effects such as resistance, high toxicity, lack of targeting, and off-target. Herein, we introduce several tumor MDR mechanisms and discuss novel nanoparticle technology applied to surmount cancer drug resistance. Nanomaterials contain liposomes, polymer conjugates, micelles, dendrimers, carbon-based, metal nanoparticles, and nucleotides which can be used to deliver chemotherapeutic drugs, photosensitizers, and small interfering RNA (siRNA). This review aims to elucidate the advantages of nanomedicine in overcoming cancer drug resistance and discuss the latest developments.

The Alternating Access Mechanism in Mammalian Multidrug Resistance Transporters and Their Bacterial Homologs

Multidrug resistance (MDR) proteins belonging to the ATP-Binding Cassette (ABC) transporter group play a crucial role in the export of cytotoxic drugs across cell membranes. These proteins are particularly fascinating due to their ability to confer drug resistance, which subsequently leads to the failure of therapeutic interventions and hinders successful treatments. One key mechanism by which multidrug resistance (MDR) proteins carry out their transport function is through alternating access. This mechanism involves intricate conformational changes that enable the binding and transport of substrates across cellular membranes. In this extensive review, we provide an overview of ABC transporters, including their classifications and structural similarities. We focus specifically on well-known mammalian multidrug resistance proteins such as MRP1 and Pgp (MDR1), as well as bacterial counterparts such as Sav1866 and lipid flippase MsbA. By exploring the structural and functional features of these MDR proteins, we shed light on the roles of their nucleotide-binding domains (NBDs) and transmembrane domains (TMDs) in the transport process. Notably, while the structures of NBDs in prokaryotic ABC proteins, such as Sav1866, MsbA, and mammalian Pgp, are identical, MRP1 exhibits distinct characteristics in its NBDs. Our review also emphasizes the importance of two ATP molecules for the formation of an interface between the two binding sites of NBD domains across all these transporters. ATP hydrolysis occurs following substrate transport and is vital for recycling the transporters in subsequent cycles of substrate transportation. Specifically, among the studied transporters, only NBD2 in MRP1 possesses the ability to hydrolyze ATP, while both NBDs of Pgp, Sav1866, and MsbA are capable of carrying out this reaction. Furthermore, we highlight recent advancements in the study of MDR proteins and the alternating access mechanism. We discuss the experimental and computational approaches utilized to investigate the structure and dynamics of MDR proteins, providing valuable insights into their conformational changes and substrate transport. This review not only contributes to an enhanced understanding of multidrug resistance proteins but also holds immense potential for guiding future research and facilitating the development of effective strategies to overcome multidrug resistance, thus improving therapeutic interventions.

Aptamers against cancer drug resistance: Small fighters switching tactics in the face of defeat

Discovering novel cancer therapies has attracted extreme interest in the last decade. In this regard, multidrug resistance (MDR) to chemotherapies is the primary challenge in cancer treatment. Cancerous cells are growingly become resistant to existing chemotherapeutics by employing diverse mechanisms, highlighting the significance of discovering approaches to overcome MDR. One promising strategy is utilizing aptamers as unique tools to target elements or signalings incorporated in resistance mechanisms or develop active targeted drug delivery systems or chimeras enabling the precise delivery of novel agents to inhibit the conventionally undruggable resistance elements. Further, due to their advantages over their proteinaceous counterparts, particularly antibodies, including improved targeting action, enhanced thermal stability, easier production, and superior tumor penetration, aptamers are emerging and have frequently been considered for developing cancer therapeutics. Here, we highlighted significant chemoresistance pathways and thoroughly discussed using aptamers as prospective tools to surmount cancer MDR.

ABCG2 in Acute Myeloid Leukemia: Old and New Perspectives

Despite recent advances, prognosis of acute myeloid leukemia (AML) remains unsatisfactory due to poor response to therapy or relapse. Among causes of resistance, over-expression of multidrug resistance (MDR) proteins represents a pivotal mechanism. ABCG2 is an efflux transporter responsible for inducing MDR in leukemic cells; through its ability to extrude many antineoplastic drugs, it leads to AML resistance and/or relapse, even if conflicting data have been reported to date. Moreover, ABCG2 may be co-expressed with other MDR-related proteins and is finely regulated by epigenetic mechanisms. Here, we review the main issues regarding ABCG2 activity and regulation in the AML clinical scenario, focusing on its expression and the role of polymorphisms, as well as on the potential ways to inhibit its function to counteract drug resistance to, eventually, improve outcomes in AML patients.

Understanding common key indicators of successful and unsuccessful cancer drug trials using a contrast mining framework on ClinicalTrials.gov

Clinical trials are essential to the process of new drug development. As clinical trials involve significant investments of time and money, it is crucial for trial designers to carefully investigate trial settings prior to designing a trial. Utilizing trial documents from ClinicalTrials.gov, we aim to understand the common characteristics of successful and unsuccessful cancer drug trials to provide insights about what to learn and what to avoid. In this research, we first computationally classified cancer drug trials into successful and unsuccessful cases and then utilized natural language processing to extract eligibility criteria information from the trial documents. To provide explainable and potentially modifiable recommendations for new trial design, contrast mining was applied to discoverhighly contrasted patterns with a significant difference in prevalence between successful (completion with advancement to the next phase) and unsuccessful (suspended, withdrawn, or terminated) groups. Our method identified contrast patterns consisting of combinations of drug categories, eligibility criteria, study organization, and study design for nine major cancers. In addition to a literature review for the qualitative validation of mined contrast patterns, we found that contrast-pattern-based classifiers using the top 200 contrast patterns as feature representations can achieve approximately 80% F₁ score for eight out of ten cancer types in our experiments. In summary, aligning with the modernization efforts of ClinicalTrials.gov, our study demonstrates that understanding the contrast characteristics of successful and unsuccessful cancer trials may provide insights into the decision-making process for trial investigators and therefore facilitate improved cancer drug trial design.

Nucleolin aptamer conjugated MSNPs-PLR-PEG multifunctional nanoconstructs for targeted co-delivery of anticancer drug and siRNA to counter drug resistance in TNBC

The emergence of drug resistance in cancer cells is among the major challenges for treating cancer. In the last few years, the co-delivery of drug and siRNA has shown promising results against drug-resistant cancers. In the present study, we developed mesoporous silica-based multifunctional nanocarrier for co-delivery against drug-resistant triple-negative breast cancer (TNBC) cells. We synthesized the nanocarrier by modifying mesoporous silica nanoparticles with poly-L-arginine, polyethylene glycol and AS1411 aptamer to impart siRNA binding ability, biocompatibility, and cancer cell specificity, respectively. We optimized the loading of doxorubicin (DOX) within the developed nanocarrier to avoid interference with siRNA binding. We ascertained the target specificity by performing a receptor blockade assay during cellular uptake studies. The cytotoxic efficacy of DOX and siRNA co-delivered using the developed nanocarrier was assessed using DOX-resistant MDA-MB-231 TNBC cells. The nanocarrier exhibited >10-fold and 40-fold reduction in the IC₅₀ values of DOX due to co-delivery with BCl-xL and BCL-2 siRNA, respectively. The results were further validated using a 3-D in vitro cell culture system. This study demonstrates that the targeted co-delivery of drug and siRNA has a strong potential to overcome drug resistance in TNBC cells.

In Vivo Reversal of P-Glycoprotein-Mediated Drug Resistance in a Breast Cancer Xenograft and in Leukemia Models Using a Novel, Potent, and Nontoxic Epicatechin EC31

The modulation of P-glycoprotein (P-gp, ABCB1) can reverse multidrug resistance (MDR) and potentiate the efficacy of anticancer drugs. Tea polyphenols, such as epigallocatechin gallate (EGCG), have low P-gp-modulating activity, with an EC₅₀ over 10 μM. In this study, we optimized a series of tea polyphenol derivatives and demonstrated that epicatechin EC31 was a potent and nontoxic P-gp inhibitor. Its EC₅₀ for reversing paclitaxel, doxorubicin, and vincristine resistance in three P-gp-overexpressing cell lines ranged from 37 to 249 nM. Mechanistic studies revealed that EC31 restored intracellular drug accumulation by inhibiting P-gp-mediated drug efflux. It did not downregulate the plasma membrane P-gp level nor inhibit P-gp ATPase. It was not a transport substrate of P-gp. A pharmacokinetic study revealed that the intraperitoneal administration of 30 mg/kg of EC31 could achieve a plasma concentration above its in vitro EC₅₀ (94 nM) for more than 18 h. It did not affect the pharmacokinetic profile of coadministered paclitaxel. In the xenograft model of the P-gp-overexpressing LCC6MDR cell line, EC31 reversed P-gp-mediated paclitaxel resistance and inhibited tumor growth by 27.4 to 36.1% (p < 0.001). Moreover, it also increased the intratumor paclitaxel level in the LCC6MDR xenograft by 6 fold (p < 0.001). In both murine leukemia P388ADR and human leukemia K562/P-gp mice models, the cotreatment of EC31 and doxorubicin significantly prolonged the survival of the mice (p < 0.001 and p < 0.01) as compared to the doxorubicin alone group, respectively. Our results suggested that EC31 was a promising candidate for further investigation on combination therapy for treating P-gp-overexpressing cancers.

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.

Enhancement of the antitumor effect of 5-fluorouracil with modulation in drug transporters expression using PI3K inhibitors in colorectal cancer cells

AIMS

5-Fluorouracil (5-FU) represents the cornerstone for colorectal cancer therapy. However, resistance to its action is a major hindrance. This study aimed to investigate the effectiveness of suppressing the activity of PI3K/Akt/mTOR signaling pathway on the chemosensitivity of colorectal cancer cells to 5-FU, as well as to delineate the possible underlying cellular mechanisms and the expected modulation in the expression of specific ABC drug transporters.

MAIN METHODS

HCT116 and Caco-2 cells were incubated with 5-FU, LY294002, or PI-103 individually or in combination. Cell viability was monitored using MTT assay. The expression of a panel of drug transporters was evaluated by RT-PCR. Immunofluorescence staining was applied to evaluate the expression pattern of phospho-AKT, phospho-mTOR, and ABGG2. HPLC evaluated the enhancement in the 5-FU cellular uptake. Cell apoptosis was detected by flow cytometry, and cell morphological changes following treatment were inspected under a fluorescence microscope. Additionally, the migration ability of cells following our suggested treatment combination was examined by wound healing assay.

KEY FINDINGS

The results reveal a notable enhancement in the cytotoxicity of a low dose of 5-FU when combined with a PI3K inhibitor (LY294002 or PI-103). This enhancement was influenced by the significant reduction in the expression of p-AKT and p-mTOR and was also mediated by a significant suppression in the expression of ABCG2 and ABCC5. Consequently, we detected an increase in the cellular uptake and concentration of 5-FU in cells treated with this combination rather than a single 5-FU treatment. Our Suggested combination treatment also induced cell apoptosis and reduced the migration ability of cells.

SIGNIFICANCE

Our data provide evidence that survival signaling pathways represent distinctive targets for the enhancement of chemotherapeutic sensitivity. The antitumor efficacy of 5-FU is enhanced when combined with a PI3K inhibitor, and this effect was mediated by alterations in the expression of specific drug transporters.

The More the Better-Investigation of Polymethoxylated N-Carboranyl Quinazolines as Novel Hybrid Breast Cancer Resistance Protein Inhibitors

The ineffectiveness and failing of chemotherapeutic treatments are often associated with multidrug resistance (MDR). MDR is primarily linked to the overexpression of ATP-binding cassette (ABC) transporter proteins in cancer cells. ABCG2 (ATP-binding cassette subfamily G member 2, also known as the breast cancer resistance protein (BCRP)) mediates MDR by an increased drug efflux from the cancer cells. Therefore, the inhibition of ABCG2 activity during chemotherapy ought to improve the efficacy of the administered anti-cancer agents by reversing MDR or by enhancing the agents' pharmacokinetic properties. Significant efforts have been made to develop novel, powerful, selective, and non-toxic inhibitors of BCRP. However, thus far the clinical relevance of BCRP-selective MDR-reversal has been unsuccessful, due to either adverse drug reactions or significant toxicities in vivo. We here report a facile access towards carboranyl quinazoline-based inhibitors of ABCG2. We determined the influence of different methoxy-substitution patterns on the 2-phenylquinazoline scaffold in combination with the beneficial properties of an incorporated inorganic carborane moiety. A series of eight compounds was synthesized and their inhibitory effect on the ABCG2-mediated Hoechst transport was evaluated. Molecular docking studies were performed to better understand the structure-protein interactions of the novel inhibitors, exhibiting putative binding modes within the inner binding site. Further, the most potent, non-toxic compounds were investigated for their potential to reverse ABCG2-mediated mitoxantrone (MXN) resistance. Of these five evaluated compounds, N-(closo-1,7-dicarbadodecaboran(12)-9-yl)-6,7-dimethoxy-2-(3,4,5-trimethoxyphenyl)-quinazolin-4-amine (DMQCd) exhibited the strongest inhibitory effect towards ABCG2 in the lower nanomolar ranges. Additionally, DMQCd was able to reverse BCRP-mediated MDR, making it a promising candidate for further research on hybrid inorganic-organic compounds.

The Role of ABC Transporters in Skin Cells Exposed to UV Radiation

ABC transporters are expressed in skin cells to protect them against harmful xenobiotics. Moreover, these transmembrane proteins have a number of additional functions that ensure skin homeostasis. This review summarizes the current knowledge about the role of specific ABC proteins in the skin, including multi-drug resistance transporters (MDR1/3), the transporter associated with antigen processing 1/2 (TAP1/2), the cystic fibrosis transmembrane conductance regulator (CFTR), sulfonylurea receptors (SUR1/2), and the breast cancer resistance protein (BCRP). Additionally, the effect of UV radiation on ABC transporters is shown. The exposure of skin cells to UV radiation often leads to increased activity of ABC transporters-as has been observed in the case of MDRs, TAPs, CFTR, and BCRP. A different effect of oxidative stress has been observed in the case of mitochondrial SURs. However, the limited data in the literature-as indicated in this article-highlights the limited number of experimental studies dealing with the role of ABC transporters in the physiology and pathophysiology of skin cells and the skin as a whole. At the same time, the importance of such knowledge in relation to the possibility of daily exposure to UV radiation and xenobiotics, used for both skin care and the treatment of its diseases, is emphasized.

Mechanisms of Drug Resistance in Ovarian Cancer and Associated Gene Targets

In the United States, over 100,000 women are diagnosed with a gynecologic malignancy every year, with ovarian cancer being the most lethal. One of the hallmark characteristics of ovarian cancer is the development of resistance to chemotherapeutics. While the exact mechanisms of chemoresistance are poorly understood, it is known that changes at the cellular and molecular level make chemoresistance challenging to treat. Improved therapeutic options are needed to target these changes at the molecular level. Using a precision medicine approach, such as gene therapy, genes can be specifically exploited to resensitize tumors to therapeutics. This review highlights traditional and novel gene targets that can be used to develop new and improved targeted therapies, from drug efflux proteins to ovarian cancer stem cells. The review also addresses the clinical relevance and landscape of the discussed gene targets.

Are active efflux transporters contributing to infant drug exposure via breastmilk? A longitudinal study

Although most drugs are considered safe and compatible with breastfeeding, cases of toxic drug exposure have been reported. Active efflux transporters have been implicated as a mechanism in the transfer of drugs from mother to baby via breastmilk. Using breastmilk as a source of human mammary epithelial cells, this novel longitudinal study investigated the expression of four active transporters, namely, MDR1, MRP1, MRP2 and BCRP in the lactating human breast. BCRP gene was found to be strongly overexpressed with levels peaking at 5 months postpartum, potentially indicating a time where a breastfed infant may be at risk of inadvertent exposure to BCRP substrates. Serum albumin, a major component of human breastmilk was increasingly downregulated as lactation progresses. Xanthine oxidase/dehydrogenase, an enzyme in breastmilk attributed to a reduced risk of gastroenteritis caused by Escherichia coli and Salmonella enteritides, was downregulated. Lysozyme and fatty acid synthase are progressively upregulated. This study also shows that breastmilk-derived epithelial cells, when propagated in culture, exhibit characteristics significantly different to those derived directly from breastmilk. This serves to warn that in vitro studies are not a true representation of in vivo processes in the lactating breast; hence, application of in vitro data should be conducted with caution.

Tamoxifen resistance-related ceRNA network for breast cancer

Background: Tamoxifen (TMX) is one of the most widely used drugs to treat breast cancer (BC). However, acquired drug resistance is still a major obstacle to its application, rendering it crucial to explore the mechanisms of TMX resistance in BC. This aims of this study were to identify the mechanisms of TMX resistance and construct ceRNA regulatory networks in breast cancer. Methods: GEO2R was used to screen for differentially expressed mRNAs (DEmRNAs) leading to drug resistance in BC cells. MiRTarbase and miRNet were used to predict miRNAs and lncRNAs upstream, and the competing endogenous RNA (ceRNA) regulatory network of BC cell resistance was constructed by starBase. We used the Kaplan-Meier plotter and Gene Expression Profiling Interactive Analysis (GEPIA) to analyze the expression and prognostic differences of genes in the ceRNA network with core axis, and qRT-PCR was used to further verify the above conclusions. Results: We found that 21 DEmRNAs were upregulated and 43 DEmRNA downregulated in drug-resistant BC cells. DEmRNAs were noticeably enriched in pathways relevant to cancer. We then constructed a protein-protein interaction (PPI) network based on the STRING database and defined 10 top-ranked hub genes among the upregulated and downregulated DEmRNAs. The 20 DEmRNAs were predicted to obtain 113 upstream miRNAs and 501 lncRNAs. Among them, 7 mRNAs, 22 lncRNAs, and 11 miRNAs were used to structure the ceRNA regulatory network of drug resistance in BC cells. 4 mRNAs, 4 lncRNAs, and 3 miRNAs were detected by GEPIA and the Kaplan-Meier plotter to be significantly associated with BC expression and prognosis. The differential expression of the genes in BC cells was confirmed by qRT-PCR. Conclusion: The ceRNA regulatory network of TMX-resistant BC was successfully constructed and confirmed. This will provide an important resource for finding therapeutic targets for TMX resistance, where the discovery of candidate conventional mechanisms can aid clinical decision-making. In addition, this resource will help discover the mechanisms behind this type of resistance.

Permeation enhancers loaded bilosomes for improved intestinal absorption and cytotoxic activity of doxorubicin

The clinical utility of doxorubicin is compromised due to dose related toxic side effects and limited oral bioavailability with no oral formulation being marketed. Enhancement of intestinal absorption and magnification of cytotoxicity can overcome these limitations. Accordingly, the objective was to probe penetration enhancers, bilosomes and their combinations for enhanced intestinal absorption and improved cytotoxicity of doxorubicin. Piperine and dipyridamole were tested as enhancers alone or encapsulated in bilosomes comprising Span60, cholesterol and bile salts. Bilosomes were nanosized spherical vesicles with negative zeta potential and were able to entrap doxorubicin with efficiency ranging from 45.3 % to 53 %. Intestinal absorption studies utilized in-situ rabbit intestinal perfusion which revealed site dependent doxorubicin absorption correlating with regional distribution of efflux transporters. Co-perfusion with the enhancer increased intestinal absorption with further augmentation after bilosomal encapsulation. The latter increased the % fraction absorbed by 4.5-6 and 1.8-2.5-fold from jejuno-ileum and colon, respectively, depending on bilosomes composition. Additionally, doxorubicin cytotoxicity against breast cancer cells (MCF-7) was significantly improved after bilosomal encapsulation and the recorded doxorubicin IC₅₀ value was reduced from 13.3 μM to 0.1 μM for the best formulation. The study introduced bilosomes encapsulating absorption enhancers as promising carriers for enhanced cytotoxicity and oral absorption of doxorubicin.

How Far beyond Diabetes Can the Benefits of Glucagon-like Peptide-1 Receptor Agonists Go? A Review of the Evidence on Their Effects on Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is characterized by poor survival rate and quality of life, while available treatments remain generally limited. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) originally emerged as drugs for the management of diabetes, but have also been shown to alleviate cardiorenal risk. Furthermore, they have demonstrated a wide range of extraglycemic effects that led to their evaluation as potential therapies for a variety of diseases beyond diabetes, such as obesity, neurogenerative disorders and nonalcoholic fatty liver disease. Given the presence of the GLP-1 receptor in hepatocytes, animal data suggest that GLP-1 RAs could regulate molecular pathways that are deeply involved in the genesis and progression of HCC, including inflammatory responses, tumor cell proliferation and oxidative stress, through direct and indirect effects on liver cells. However, future studies must assess several aspects of the benefit-to-risk ratio of the use of GLP-1 RAs in patients with HCC, including co-administration with approved systemic therapies, the incidence of gastrointestinal side effects in a high-risk population, and weight loss management in individuals with poor nutritional status and high rates of cancer cachexia. In this narrative review, we discuss the potential role of GLP-1 analogs in the treatment of HCC, focusing on the molecular mechanisms that could justify a possible benefit, but also referring to the potential clinical implications and areas for future research.

Relationship between CYP2C8, UGT1A1, and ABCG2 gene polymorphisms and the exposure, efficacy, and toxicity of eltrombopag in the treatment of refractory aplastic anemia

PURPOSE

Eltrombopag (ELT) is an effective drug for relapsed/refractory aplastic anemia (AA). Our previous study showed that ELT concentration was correlated with the effects of ELT. However, the factors affecting ELT concentration in patients with relapsed/refractory AA were not clarified. Therefore, we aimed to evaluate correlations between drug disposition-related gene polymorphisms and the concentration, efficacy, and toxicity of ELT.

METHODS

Forty-five patients who underwent ELT administration from January 2018 to January 2019 at Peking Union Medical Colleague Hospital (PUMCH) were included. The corresponding clinical information was also collected. ELT plasma concentrations were detected by high-performance liquid chromatography-mass spectrometry (HPLC/MS). CYP2C8, (UGT)1A1, and ABCG21 were genotyped by polymerase chain reaction (PCR). The influence of gene polymorphisms on the plasma concentration, efficacy, and toxicity of ELT was analyzed.

RESULTS

The mean dose required to obtain the optimal effects was significantly lower in the UGT1A1*6 variant carriers than in the UGT1A1*6 WT carriers. There was a significant correlation between the (UGT)1A1*6 polymorphism and higher ELT plasma concentrations (> 11.2 μg/mL). By logistic regression analysis, the efficacy of ELT was related to plasma concentration and a combined genotype of (UGT)1A1*6 and ABCG2. There were no significant associations between genotypes and adverse drug reactions (ADRs) or ELT concentrations and ADRs.

CONCLUSION

UGT1A1*6 is a predictor of the ELT plasma concentration and may help to determine the initial therapeutic dose in relapsed/refractory AA patients. Both drug exposure and patient genotype should be considered for better responses to ELT.

PFKFB3 regulates cancer stemness through the hippo pathway in small cell lung carcinoma

PFKFB3 (6-phosphofructo-2-kinase) is the rate-limiting enzyme of glycolysis and is overexpressed in several human cancers that are associated with poor prognosis. High PFKFB3 expression in cancer stem cells promotes glycolysis and survival in the tumor microenvironment. Inhibition of PFKFB3 by the glycolytic inhibitor PFK158 and by shRNA stable knockdown in small cell lung carcinoma (SCLC) cell lines inhibited glycolysis, proliferation, spheroid formation, and the expression of cancer stem cell markers CD133, Aldh1, CD44, Sox2, and ABCG2. These factors are also associated with chemotherapy resistance. We found that PFK158 treatment and PFKFB3 knockdown enhanced the ABCG2-interacting drugs doxorubicin, etoposide, and 5-fluorouracil in reducing cell viability under conditions of enriched cancer stem cells (CSC). Additionally, PFKFB3 inhibition attenuated the invasion/migration of SCLC cells by downregulating YAP/TAZ signaling while increasing pLATS1 via activation of pMST1 and NF2 and by reducing the mesenchymal protein expression. PFKFB3 knockdown and PFK158 treatment in a H1048 SCLC cancer stem cell-enriched mouse xenograft model showed significant reduction in tumor growth and weight with reduced expression of cancer stem cell markers, ABCG2, and YAP/TAZ. Our findings identify that PFKFB3 is a novel target to regulate cancer stem cells and its associated therapeutic resistance markers YAP/TAZ and ABCG2 in SCLC models.

Breast Cancer Stem Cells: Signaling Pathways, Cellular Interactions, and Therapeutic Implications

Breast cancer stem cells (BCSCs) constitute a small population of cells within breast cancer and are characterized by their ability to self-renew, differentiate, and recapitulate the heterogeneity of the tumor. Clinically, BCSCs have been correlated with cancer progression, metastasis, relapse, and drug resistance. The tumorigenic roles of BCSCs have been extensively reviewed and will not be the major focus of the current review. Here, we aim to highlight how the crucial intrinsic signaling pathways regulate the fate of BCSCs, including the Wnt, Notch, Hedgehog, and NF-κB signaling pathways, as well as how different cell populations crosstalk with BCSCs within the TME, including adipocytes, endothelial cells, fibroblasts, and immune cells. Based on the molecular and cellular activities of BCSCs, we will also summarize the targeting strategies for BCSCs and related clinical trials. This review will highlight that BCSC development in breast cancer is impacted by both BCSC endogenous signaling and external factors in the TME, which provides an insight into how to establish a comprehensively therapeutic strategy to target BCSCs for breast cancer treatments.

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.

DNA Copy Number Aberrations and Expression of ABC Transporter Genes in Breast Tumour: Correlation with the Effect of Neoadjuvant Chemotherapy and Prognosis of the Disease

One of the important reasons for the ineffectiveness of chemotherapy in breast cancer (BC) is considered to be the formation of a multidrug resistance phenotype in tumour cells, which is caused by the expression of energy-dependent ABC transporters. The aim of this work was to assess chromosomal aberrations and the level of transcripts of all 49 known ABC transporter genes in breast tumours. Materials and Methods. The study included 129 patients with breast cancer. A microarray study of all tumour samples was carried out on microchips. Results. This study established that the presence of a deletion in genes ABCB1, ABCB4, ABCB8, ABCC7, ABCC11, ABCC12, ABCF2, and ABCG4 is associated with an objective response to treatment (p ≤ 0.05). A decrease in the expression of genes was associated with a good response to chemotherapy, whereas an increase in expression caused the progression and stabilization of the tumour. Analysis of metastatic-free survival rates showed that the presence of ABCB1/4 and ABCC1/6 deletions was associated with 100% survival (log-rank test p = 0.01 and p = 0.03). Conclusions. The study showed that the aberrant state of ABC transporter genes, as well as a decrease in the expression of these genes, is a predictor of the effectiveness of therapeutic treatment and a potential prognostic marker of metastatic survival.

Characterization of SN38-resistant T47D breast cancer cell sublines overexpressing BCRP, MRP1, MRP2, MRP3, and MRP4

Background

Although several novel resistant breast cancer cell lines have been established, only a few resistant breast cancer cell lines overexpress breast cancer resistance proteins (BCRP). The aim of this study was to establish new resistant breast cancer cell lines overexpressing BCRP using SN38 (7-ethyl-10-hydroxycamptothecin), an active metabolite of irinotecan and was to discover genes and mechanisms associated with multidrug resistance.

Methods

SN38-resistant T47D breast cancer cell sublines were selected from the wild-type T47D cells by gradually increasing SN38 concentration. The sensitivity of the cells to anti-cancer drugs was assessed by 3-(4,5-methylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Expression profiles of the resistance-related transporters were examined using RT-qPCR, and western blot analysis. Intracellular fluorescent dye accumulation in the resistant cells was determined using flow cytometry.

Results

The SN38-resistant T47D breast cancer cell sublines T47D/SN120 and T47D/SN150 were established after long-term exposure (more than 16 months) of wild-type T47D cells to 120 nM and 150 nM SN38, respectively. T47D/SN120 and T47D/SN150 cells were more resistant to SN38 (14.5 and 59.1 times, respectively), irinotecan (1.5 and 3.7 times, respectively), and topotecan (4.9 and 12 times, respectively), than the wild-type parental cells. Both T47D/SN120 and T47D/SN150 sublines were cross-resistant to various anti-cancer drugs. These resistant sublines overexpressed mRNAs of MRP1, MRP2, MRP3, MRP4, and BCRP. The DNA methylase inhibitor 5-aza-2′-deoxycytidine and the histone deacetylase inhibitor trichostatin A increased the expression levels of BCRP, MRP1, MRP2, MRP3, and MRP4 transcripts in T47D/WT cells. Fluorescent dye accumulation was found to be lower in T47D/SN120 and T47D/SN150 cells, compared to that in T47D/WT cells. However, treatment with known chemosensitizers increased the intracellular fluorescent dye accumulation and sensitivity of anti-tumor agents.

Conclusion

T47D/SN120 and T47D/SN150 cells overexpressed MRP1, MRP2, MRP3, MRP4, and BCRP, which might be due to the suppression of epigenetic gene silencing via DNA hypermethylation and histone deacetylation. Although these resistant cells present a higher resistance to various anti-cancer drugs than their parental wild-type cells, multidrug resistance was overcome by treatment with chemosensitizers. These SN38 resistant T47D breast cancer cell sublines expressing resistance proteins can be useful for the development of new chemosensitizers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09446-y.

O6-Methylguanine-DNA Methyltransferase and ATP-Binding Cassette Membrane Transporter G2 Promotor Methylation: Can Predict the Response to Chemotherapy in Advanced Breast Cancer?

Background

ATP-binding cassette membrane transporter G2 (ABCG2) gene is one of transporter family and well characterized for their association with chemoresistance. Promoter methylation is a mechanism for regulation of gene expression. O6-Methyl guanine DNA methyl transferase (MGMT) gene plays a fundamental role in DNA repair. MGMT has the ability to remove alkyl adducts from DNA at the O6 position of guanine. Alkylating agents exert their function through adding these alkyls adducts to DNA leading to cell death unless it is repaired by MGMT. MGMT promoter was found to be methylated in several malignancies. The aim of the present work is to study the relation of MGMT and ABCG2 promoter methylation status in advanced breast cancer patients to response to cyclophosphamide-doxorubicin (AC) based therapeutic regime.

Methods

This retrospective study included Forty-two female patients with advanced breast cancer assessed before receiving chemotherapy and after the completion of regimens. They were grouped into responders and non-responders according to RECIST criteria. Methylation analysis of MGMT and ABCG2 genes were performed on breast cancer tissues.

Results

MGMT promoter was methylated in 40.5% of the cases. ABCG2 promoter was methylated in 14.3% of cases. There was no statistically significant association between MGMT and ABCG2 promoter methylation status and clinicopathological parameters. There was statistically significant association between methylation status of both promoters and response to AC when followed by Taxane.

Conclusion

Methylation of MGMT and ABCG2 promoters combined could be a potential predictive factor for response to cyclophosphamide-doxorubicin based therapeutic regime.

S-20, a steroidal saponin from the berries of black nightshade, exerts anti-multidrug resistance activity in K562/ADR cells through autophagic cell death and ERK activation

Multidrug resistance (MDR) is a major cause of chemotherapy failure. Adriamycin (ADR) has been widely used to treat cancer, however, as a substrate of the adenosine triphosphate binding cassette (ABC) transporter, it is easy to develop drug resistance during the treatment. Here, we demonstrated that steroidal saponin S-20 isolated from the berries of black nightshade has comparable cytotoxicity in ADR-sensitive and resistant K562 cell lines. Autophagy is generally considered to be a protective mechanism to mediate MDR during treatment. However, we found that S-20-induced cell death in K562/ADR is associated with autophagy. We further explored the underlying mechanisms and found that S-20 induces caspase-dependent apoptosis in ADR-sensitive and resistant K562 cell lines. Most importantly, S-20-induced autophagy activates the ERK pathway and then inhibits the expression of drug resistance protein, which is the main reason to overcome K562/ADR resistance, rather than apoptosis. Taken together, our findings emphasize that S-20 exerts anti-multidrug resistance activity in K562/ADR cells through autophagic cell death and ERK activation, which may be considered as an effective strategy.

Novel microtubule inhibitor SQ overcomes multidrug resistance in MCF-7/ADR cells by inhibiting BCRP function and mediating apoptosis

The occurrence of multidrug resistance (MDR) is one of the impediments in the clinical treatment of breast cancer, and MDR breast cancer has abnormally high breast cancer resistance protein (BCRP/ABCG2) expression. However, there are currently no clinical drugs that inhibit this target. Our previous study found that 2-Methoxy-5((3,4,5-trimethosyphenyl)seleninyl) phenol (SQ0814061/SQ), a small molecule drug with low toxicity to normal tissues, could target microtubules, inhibit the proliferation of breast cancer, and reduce its migration and invasion abilities. However, the effect and the underlying mechanism of SQ on MDR breast cancers are still unknown. Therefore, in this study, we investigated the effect of SQ on adriamycin-resistant MCF-7 (MCF-7/ADR) cells and explored the underlying mechanism. The MTT assay showed that SQ had potent cytotoxicity to MCF-7/ADR cells. In particular, the results of western blot and flow cytometry proved that SQ could effectively inhibit the expression of BCRP in MCF-7/ADR cells to decrease its drug delivery activity. In addition, SQ could block the cell cycle at G2/M phase in parental and MCF-7/ADR cells, thereby mediating cell apoptosis, which was related with the inhibition of PI3K-Akt-MDM2 pathway. Taken together, our findings indicate that SQ overcomes multidrug resistance in MCF-7/ADR cells by inhibiting BCRP function and mediating apoptosis through PI3K-Akt-MDM2 pathway inhibition.

Systemic Mobilization of Breast Cancer Resistance Protein in Response to Oncogenic Stress

Simple Summary

The drug efflux mediated by xenobiotic transporters is one of the best recognized mechanisms of multidrug resistance in cancer that leads to the failure of therapeutic approaches. The aim of our research was to examine the influence of a growing tumor on the activity of xenobiotic transport in the host. Our study reveals a strong correlation between the development of melanoma tumor in mice and the level of breast cancer resistance protein, one of the major xenobiotic transporters, and its transcript in the normal tissues of the hosts distant from the tumor site. The systemic effects of the tumor are confirmed by a drastically enhanced xenobiotic transport, which is correlated with changes in the level of cytokines in blood. Such an unexpected type of tumor–host interaction, which leads to the systemic upregulation of breast cancer resistance protein, and very likely of other xenobiotic transporters too, has broad implications for cancer therapies, including chemotherapy and photodynamic therapy. Our findings shed new light on the biology of cancer and the complexity of cancer–host interactions that should be taken into account in the design of new generations of anti-cancer drugs and personalized medicine.

Abstract

The breast cancer resistance protein (BCRP or ABCG2) involved in cancer multidrug resistance (MDR), transports many hydrophobic compounds, including a number of anti-cancer drugs. Our comprehensive study using a mouse model reveals that a subcutaneously growing tumor strongly affects the expression of BCRP in the host’s normal organs on both the transcriptional and translational level. Additionally, the efflux of BCRP substrates is markedly enhanced. The levels of BCRP and its transcript in normal tissues distant from the tumor site correlate with tumor growth and the levels of cytokines in the peripheral blood. Thus, oncogenic stress causes transient systemic upregulation of BCRP in the host’s normal tissues and organs, which is possibly mediated via cytokines. Because BCRP upregulation takes place in many organs as early as the initial stages of tumor development, it reveals a most basic mechanism that may be responsible for the induction of primary MDR. We hypothesize that such effects are not tumor-specific responses, but rather constitute a more universal defense strategy. The xenobiotic transporters are systemically mobilized due to various stresses, seemingly in a pre-emptive manner so that the body can be quickly and efficiently detoxified. Our findings shed new light on the biology of cancer and on the complexity of cancer–host interactions and are highly relevant to cancer therapies as well as to the design of new generations of therapeutics and personalized medicine.

Quinoxaline Derivatives as a Promising Scaffold for Breast Cancer Treatment

According to Global Cancer Statistics 2021, female breast cancer has exceeded lung cancer as the most frequently diagnosed cancer. As a result of this widespread breast cancer, it was necessary...

Identification of Pathway-Based Biomarkers with Crosstalk Analysis for Overall Survival Risk Prediction in Breast Cancer

Recently, many studies have investigated the role of gene-signature on the prognostic assessment of breast cancer (BC), however, the tumor heterogeneity and sequencing noise have limited the clinical usage of these models. Pathway-based approaches are more stable to the perturbation of certain gene expression. In this study, we constructed a prognostic classifier based on survival-related pathway crosstalk analysis. We estimated pathway’s deregulation scores (PDSs) for samples collected from public databases to select survival-related pathways. After pathway crosstalk analysis, we conducted K-means clustering analysis to cluster the patients into G1 and G2 subgroups. The survival outcome of the G2 subgroup was significantly worse than the G1 subgroup. Internal and external dataset exhibits high consistency with the training dataset. Significant differences were found between G2 and G1 subgroups on pathway activity, gene mutation, immune cell infiltration levels, and in particular immune cells/pathway’s activities were significantly negatively associated with BC patient’s outcomes. In conclusion, we established a novel classifier reflecting the overall survival risk of BC and successfully validated its clinical usage on multiple BC datasets, which could offer clinicians inspiration in formulating the clinical treatment plan.

Multidrug efflux transporter ABCG2: expression and regulation

The adenosine triphosphate (ATP)-binding cassette efflux transporter G2 (ABCG2) was originally discovered in a multidrug-resistant breast cancer cell line. Studies in the past have expanded the understanding of its role in physiology, disease pathology and drug resistance. With a widely distributed expression across different cell types, ABCG2 plays a central role in ATP-dependent efflux of a vast range of endogenous and exogenous molecules, thereby maintaining cellular homeostasis and providing tissue protection against xenobiotic insults. However, ABCG2 expression is subjected to alterations under various pathophysiological conditions such as inflammation, infection, tissue injury, disease pathology and in response to xenobiotics and endobiotics. These changes may interfere with the bioavailability of therapeutic substrate drugs conferring drug resistance and in certain cases worsen the pathophysiological state aggravating its severity. Considering the crucial role of ABCG2 in normal physiology, therapeutic interventions directly targeting the transporter function may produce serious side effects. Therefore, modulation of transporter regulation instead of inhibiting the transporter itself will allow subtle changes in ABCG2 activity. This requires a thorough comprehension of diverse factors and complex signaling pathways (Kinases, Wnt/β-catenin, Sonic hedgehog) operating at multiple regulatory levels dictating ABCG2 expression and activity. This review features a background on the physiological role of transporter, factors that modulate ABCG2 levels and highlights various signaling pathways, molecular mechanisms and genetic polymorphisms in ABCG2 regulation. This understanding will aid in identifying potential molecular targets for therapeutic interventions to overcome ABCG2-mediated multidrug resistance (MDR) and to manage ABCG2-related pathophysiology.