Small and Innovative Molecules as New Strategy to Revert MDR

4-{3-[(Pyridin-4-ylmethyl)amino]-[1,2,4]triazolo[4,3-b][1,2,4]triazin-6-yl}phenol: An improved anticancer agent in hepatocellular carcinoma and a selective MDR1/MRP modulator

Hepatocellular carcinoma is the most common type of primary liver cancer. However, multidrug resistance (MDR) is a major obstacle to the effective chemotherapy of cancer cells. This report documents the rational design, synthesis, and biological evaluation of a novel series of triazolotriazines substituted with CH2NH-linked pyridine for use as dual c-Met/MDR inhibitors. Compound 12g with IC50 of 3.06 μM on HepG2 cells showed more potency than crizotinib (IC50 = 5.15 μM) in the MTT assay. In addition, 12g inhibited c-Met kinase at a low micromolar level (IC50 = 0.052 μM). 12g significantly inhibited P-gp and MRP1/2 efflux pumps in both cancerous HepG2 and BxPC3 cells starting from the lower concentrations of 3 and 0.3 µM, respectively. 12g did not inhibit MDR1 and MRP1/2 in noncancerous H69 cholangiocytes up to the concentration of 30 and 60 µM, respectively. Current results highlighted that cancerous cells were more susceptible to the effect of 12g than normal cells, in which the inhibition occurred only at the highest concentrations, suggesting a further interest in 12g as a selective anticancer agent. Overall, 12g, as a dual c-Met and P-gp/MRP inhibitor, is a promising lead compound for developing a new generation of anticancer agents.

pH-Responsive Polypropylene Sulfide Magnetic Nanocarrier-Mediated Chemo-Hyperthermia Kills Breast Cancer Stem Cells by Long-Term Reversal of Multidrug Resistance and Chemotherapy Resensitization

Cancer stem cells (CSCs) present a formidable challenge in cancer treatment due to their inherent resistance to chemotherapy, primarily driven by the overexpression of ABC transporters and multidrug resistance (MDR). Despite extensive research on pharmacological small-molecule inhibitors, effectively managing MDR and improving chemotherapeutic outcomes remain elusive. On the other hand, magnetic hyperthermia (MHT) holds great promise as a cancer therapeutic, but there is limited research on its potential to reverse MDR in breast CSCs and effectively eliminate CSCs through combined chemo-hyperthermia. To address these gaps, we developed tumor microenvironment-sensitive, drug-loaded poly(propylene sulfide) (PPS)-coated magnetic nanoparticles (PPS-MnFe). These nanoparticles were employed to investigate hyperthermia sensitivity and MDR reversion in breast CSCs, comparing their performance to that of small-molecule inhibitors. Additionally, we explored the efficacy of combined chemo-hyperthermia in killing CSCs. CSC-enriched breast cancer cells were subjected to low-dose MHT at 42 °C for 30 min and then treated with the chemical MDR inhibitor salinomycin (SAL). The effectiveness of each treatment in inhibiting MDR was assessed by measuring the efflux of the MDR substrate, rhodamine 123 (R123) dye. Notably, MHT induced a prolonged reversal of MDR activity compared with SAL treatment alone. After successfully inhibiting MDR, the breast CSCs were exposed to chemotherapy using paclitaxel to trigger synergistic cell death. The combination of MHT and chemotherapy demonstrated remarkable reductions in stemness properties, MDR reversal, and the effective eradication of breast CSCs in this innovative dual-modality approach.

The effects and mechanisms of aloe-emodin on reversing adriamycin-induced resistance of MCF-7/ADR cells

Multidrug resistance (MDR) is one of the major obstacles for clinical effective chemotherapy. In this study, the effects and possible mechanisms of aloe-emodin (AE) were investigated on reversing the adriamycin (ADR)-induced resistance of MCF-7/ADR cells. AE could significantly reverse the ADR resistance in MCF-7/ADR cells. The combination of AE (20 μM) and ADR had no effect on the P-glycoprotein (P-gp) level, but notably promoted the accumulation of ADR in drug-resistant cells. The efflux function of P-gp required ATP, but AE reduced the intracellular ATP level. AE played a reversal role might through inhibiting the efflux function of P-gp. The research result of energy metabolism pathways indicated that combination of AE and ADR could inhibit glycolysis, tricarboxylic acid (TCA) cycle, glutamine metabolism, and related amino acid synthesis pathways. Moreover, we found AE not only reversed ADR-induced resistant but also induced autophagy as a defense mechanism. In addition, the combination of AE and ADR arrested G2/M cell cycle and induced apoptosis through DNA damage, ROS generation, caspase-3 activation. Our study indicated that AE could be a potential reversal agent to resensitize ADR resistant in tumor chemotherapy and inhibiting autophagy might be an effective strategy to further enhance the reversal activity of AE.

Recent development in the discovery of PARP inhibitors as anticancer agents: a patent update (2016-2020)

INTRODUCTION

Discovery of small molecules that impede the activity of single-strand DNA repair enzyme, PARP1, has led to four marketed drugs for the treatment of advanced-stage cancers. Hence, there is a renewed enthusiasm in the PARP inhibitor discovery arena. To reduce nonspecific interactions or potential toxicities, and to understand the role of other minimally explored PARP enzymes, exciting new findings have emerged toward the development of selective inhibitors and targeted chemical biology probes. Importantly, the conventional PARP inhibitor design has evolved in a way that could potentially lead to multienzyme-targeting - a polypharmacological approach against aggressive cancers.

AREAS COVERED

This review comprises recent progress made in the development of PARP inhibitors, primarily focused on human cancers. Discovery of novel PARP inhibitors with pan, selective, and multi-target inhibition using in vitro and in vivo cancer models is summarized and critically evaluated. Emphasis is given to patents published during 2016-2020, excluding TNKS 1/2 inhibitors.

EXPERT OPINION

The outstanding success demonstrated by the FDA approved PARP inhibitors has fueled further clinical evaluations for expansion of their clinical utilities. The current clinical investigations include new candidates as well as marketed PARP-targeted drugs, both as single agents and in combination with other chemotherapeutics. Recent advances have also unveiled critical roles of other PARPs in oncogenic signal transduction, in addition to those of the well-documented PARP1/2 and TNKS1/2 enzymes. Further studies on lesser-known PARP members are urgently needed for functional annotations and for understanding their roles in cancer progression and other human diseases.

The Novel Benzamide Derivative, VKNG-2, Restores the Efficacy of Chemotherapeutic Drugs in Colon Cancer Cell Lines by Inhibiting the ABCG2 Transporter

The overexpression of ATP-binding cassette transporter, ABCG2, plays an important role in mediating multidrug resistance (MDR) in certain types of cancer cells. ABCG2-mediated MDR can significantly attenuate or abrogate the efficacy of anticancer drugs by increasing their efflux from cancer cells. In this study, we determined the efficacy of the novel benzamide derivative, VKNG-2, to overcome MDR due to the overexpression of the ABCG2 transporter in the colon cancer cell line, S1-M1-80. In vitro, 5 μM of VKNG-2 reversed the resistance of S1-M1-80 cell line to mitoxantrone (70-fold increase in efficacy) or SN-38 (112-fold increase in efficacy). In contrast, in vitro, 5 μM of VKNG-2 did not significantly alter either the expression of ABCG2, AKT, and PI3K p110β protein or the subcellular localization of the ABCG2 protein compared to colon cancer cells incubated with the vehicle. Molecular docking data indicated that VKNG-2 had a high docking score (-10.2 kcal/mol) for the ABCG2 transporter substrate-drug binding site whereas it had a low affinity on ABCB1 and ABCC1 transporters. Finally, VKNG-2 produced a significant concentration-dependent increase in ATPase activity (EC50 = 2.3 µM). In conclusion, our study suggests that in vitro, VKNG-2 reverses the resistance of S1-M1-80, a cancer cell line resistant to mitoxantrone and SN-38, by inhibiting the efflux function of the ABCG2 transporter.

Co-Delivery of Berberine Chloride and Tariquidar in Nanoliposomes Enhanced Intracellular Berberine Chloride in a Doxorubicin-Resistant K562 Cell Line Due to P-gp Overexpression

The MDR phenomenon has become a major obstacle in the treatment of cancers, and among the strategies to reverse it, the inhibition of P-gp function and expression is essential to increase for effective anticancer drugs. In the present paper, the co-delivery of berberine chloride and tariquidar loaded nanoliposomes was investigated with the aim of enhancing solubility and improving desired effects for the antineoplastic drug and the P-gp inhibitor. Developed nanoliposomes were loaded with the electron-dense enzyme horseradish peroxidase, and analyzed by TEM to investigate their ability to enter in both K562 and K562/DOXO cell lines. Receptor-mediated endocytosis was evidenced for both cell lines. Nanoliposomes were loaded with tariquidar, berberine chloride, or both, maintaining chemical and physical characteristics—i.e., size, homogeneity, and encapsulation efficiency—and high suitability for parenteral administration. Tariquidar was able to reverse the MDR in the K562/DOXO cell line. Tariquidar- and berberine chloride-loaded nanoliposomes showed a significant increase of berberine chloride accumulation in tumor cells, which could be correlated with resensitization of the resistant cells to the antitumor agent. These results suggest that the co-delivery of the P-gp inhibitor, tariquidar, and the cytotoxicity inducer, berberine chloride, looks like a promising approach to overcome the MDR.

BSA-Stabilized Mesoporous Organosilica Nanoparticles Reversed Chemotherapy Resistance of Anaplastic Thyroid Cancer by Increasing Drug Uptake and Reducing Cellular Efflux

Anaplastic thyroid cancer (ATC) is a highly aggressive and the most lethal type of thyroid cancer. The standard-of-care for unresectable ATC is radiotherapy and chemotherapy, usually based on doxorubicin (Dox). However, most patients develop resistance shortly after treatment. To overcome the drug resistance, we synthesized the mesoporous organosilica nanoparticles (MONPs) loaded with Dox and stabilized the nanocomposites by bovine serum albumin (BSA). The surface area and pore volume of MONPs were 612.653 m²/g and 0.589 cm³/g. The loading capacity of Dox-MONPs reached 47.02%. Compared to Dox-MONPs and free Dox, BSA-Dox-MONPs had more durable tumor-killing power on both drug-sensitive cell line HTh74 and drug-resistant cell line HTh74R. The cellular uptake of BSA-Dox-MONPs was 28.14 and 65.53% higher than that of Dox-MONP in HTh74 and HTh74R. Furthermore, the BSA coating decreased the efflux rate of nanocomposites in HTh74 (from 38.95 to 33.05%) and HTh74R (from 43.03 to 32.07%). In summary, BSA-Dox-MONPs reversed the chemotherapy resistance of ATC cells via increased drug uptake and inhibited drug efflux, offering a promising platform for the treatment of chemo-resistant ATC.

An allomaltol derivative triggers distinct death pathways in luminal a and triple-negative breast cancer subtypes

Breast cancer is the most common cancer in women that shows a predisposition to metastasize to the distant organs. Kojic acid is a natural fungal metabolite exhibiting various biological activities. Compounds derived from kojic acid have been extensively studied and proved to demonstrate anti-neoplastic features on different cancer types. In the present study, allomaltol-structural analog of kojic acid and its seven derivatives including four novel compounds, have been synthesized, characterized and their possible impact on breast cancer cell viability was investigated. It was discovered that compound 5, bearing 3,4-dichlorobenzyl piperazine moiety, could decrease the viability of both MCF-7 and MDA-MB-231 cell lines distinctively. To ascertain the death mechanism, cells were subjected to different tests following the application of IC₅₀ concentration of compound 5. Data obtained from lactate dehydrogenase activity and gene expression assays pointed out that necrosis had taken place predominantly in MDA-MB-231. On the other hand, in MCF-7 cells, the p53 apoptotic pathway was activated by overexpression of the pro-apoptotic TP53 and Bax genes and suppression of the anti-apoptotic Mdm-2 and Bcl-2 genes. Furthermore, Bax/Blc-2 ratio was escalated by 3.5 fold in the study group compared to the control. Compound 5 did not provoke drug resistance in MCF-7 cells since the Mdr-1 gene expression, drug efflux, and H₂O₂ content remained unaltered. As for MDA-MB-231 cells, only a 1.4 fold increase in the Mdr-1 gene expression was detected. These results indicate the advantage of the allomaltol derivative over the chemotherapeutic agents conventionally used for breast cancer treatment that can be highly toxic and mostly lead to drug resistance. Thus, this specific allomaltol derivative offers an alternative therapeutic approach for breast cancer which needs further investigation.

Aberrant DNA Methylation of ABC Transporters in Cancer

ATP-binding cassette (ABC) transporters play a crucial role in multidrug resistance (MDR) of cancers. They function as efflux pumps, resulting in limited effectiveness or even failure of therapy. Increasing evidence suggests that ABC transporters are also involved in tumor initiation, progression, and metastasis. Tumors frequently show multiple genetic and epigenetic abnormalities, including changes in histone modification and DNA methylation. Alterations in the DNA methylation status of ABC transporters have been reported for a variety of cancer types. In this review, we outline the current knowledge of DNA methylation of ABC transporters in cancer. We give a brief introduction to structure, function, and gene regulation of ABC transporters that have already been investigated for their DNA methylation status in cancer. After giving an overview of the applied methodologies and the CpGs analyzed, we summarize and discuss the findings on aberrant DNA methylation of ABC transporters by cancer types. We conclude our review with the discussion of the potential to target aberrant DNA methylation of ABC transporters for cancer therapy.

MICA enhances sensitivity to cisplatin in patients with extensive small cell lung cancer via downregulation of ABCG2

Immunotherapy utilizing natural killer cell-activated receptor natural-killer group-2 member D ligands (NKG2DLs) has had preclinical success in the treatment of small cell lung cancer. The present study aimed to investigate the association between NKG2Ls and chemoresistance. The mRNA expression of six NKG2DLs associated with progression-free survival time (PFS) and first-line chemotherapy were assessed in the present study. Major histocompatibility complex class I polypeptide-related sequence A (MICA)-overexpressing NCI-H446 cell line was constructed, and the mRNA expression levels of 11 genes associated with chemotherapy sensitivity were determined. The results demonstrated that MICA was positively and significantly associated with PFS. Furthermore, MICA expression was 1.6 times higher in patients with prolonged PFS compared with the rapid chemoresistance group. ATP binding cassette subfamily G member 2 (ABCG2) mRNA expression was associated with chemotherapy resistance and significantly downregulated in the cell line overexpressing MICA. Moreover, following addition of nicardipine (an ABCG2 inhibitor), chemotherapeutic sensitivity increased in the MICA-overexpressing cell line. Taken together, the results of the present study suggested that MICA may enhance the chemosensitivity of patients with extensive small cell lung cancer by downregulating ABCG2.

Overcoming Doxorubicin Resistance with Lipid-Polymer Hybrid Nanoparticles Photoreleasing Nitric Oxide

We report on tailored lipid-polymer hybrid nanoparticles (NPs) delivering nitric oxide (NO) under the control of visible light as a tool for overcoming doxorubicin (DOX) resistance. The NPs consist of a polymeric core and a coating. They are appropriately designed to entrap DOX in the poly(lactide-co-glycolide) core and a NO photodonor (NOPD) in the phospholipid shell to avoid their mutual interaction both in the ground and excited states. The characteristic red fluorescence of DOX, useful for its tracking in cells, is well preserved upon incorporation within the NPs, even in the copresence of NOPD. The NP scaffold enhances the NO photoreleasing efficiency of the entrapped NOPD when compared with that of the free compound, and the copresence of DOX does not significantly affect such enhanced photochemical performance. Besides, the delivery of DOX and NOPD from NPs is also not mutually influenced. Experiments carried out in M14 DOX-resistant melanoma cells demonstrate that NO release from the multicargo NPs can be finely regulated by excitation with visible light, at a concentration level below the cytotoxic doses but sufficient enough to inhibit the efflux transporters mostly responsible for DOX cellular extrusion. This results in increased cellular retention of DOX with consequent enhancement of its antitumor activity. This approach, in principle, is not dependent on the type of chemotherapeutic used and may pave the way for new treatment modalities based on the photoregulated release of NO to overcome the multidrug resistance phenomenon and improve cancer chemotherapies.

Synthesis of novel dual target inhibitors of PARP and HSP90 and their antitumor activities

Poly (ADP-ribose) polymerase (PARP) inhibitors have achieved great success in clinical application, especially for the prolonged survival of cisplatin-sensitive ovarian cancer patients. However, there are still many patients who do not respond to PARP inhibitors. Novel PARP inhibitors with higher activity are urgently needed. Herein we report a series of compounds by molecular hybridization PARP-1 inhibitor Olaparib (Ola) with HSP90 inhibitor C0817 (one curcumin derivative). All synthesized compounds were evaluated for their antiproliferative activity in vitro, and some were further assessed for their inhibitory activities of the PARP enzyme and HSP90 affinity. Our results indicated that compound 4 could bind to HSP90 and cause static quenching, indicating that compound 4 was able to bind to HSP90, moreover, downstream molecular breast cancer 1 (BRAC-1) was reduced. In conclusion, dual target inhibitors of PARP and HSP90 exhibited stronger selective cytotoxicities against cancer.

Curcumin-Loaded Solid Lipid Nanoparticles Bypass P-Glycoprotein Mediated Doxorubicin Resistance in Triple Negative Breast Cancer Cells

Multidrug resistance (MDR) is a critical hindrance to the success of cancer chemotherapy. The main thing responsible for MDR phenotypes are plasma-membranes associated with adenosine triphosphate (ATP) Binding Cassette (ABC) drug efflux transporters, such as the P-glycoprotein (Pgp) transporter that has the broadest spectrum of substrates. Curcumin (CURC) is a Pgp inhibitor, but it is poorly soluble and bioavailable. To overcome these limitations, we validated the efficacy and safety of CURC, loaded in biocompatible solid lipid nanoparticles (SLNs), with or without chitosan coating, with the goal of increasing the stability, homogeneous water dispersibility, and cellular uptake. Both CURC-loaded SLNs were 5–10-fold more effective than free CURC in increasing the intracellular retention and toxicity of doxorubicin in Pgp-expressing triple negative breast cancer (TNBC). The effect was due to the decrease of intracellular reactive oxygen species, consequent inhibition of the Akt/IKKα-β/NF-kB axis, and reduced transcriptional activation of the Pgp promoter by p65/p50 NF-kB. CURC-loaded SLNs also effectively rescued the sensitivity to doxorubicin against drug-resistant TNBC tumors, without signs of systemic toxicity. These results suggest that the combination therapy, based on CURC-loaded SLNs and doxorubicin, is an effective and safe approach to overcome the Pgp-mediated chemoresistance in TNBC.

3',4'-Dihydro-2'H-spiro[indoline-3,1'-isoquinolin]-2-ones as potential anti-cancer agents: synthesis and preliminary screening

Both tetrahydroisoquinolines (THIQs) and oxindoles (OXs) display a broad range of biological activities including anti-cancer activity, and are therefore recognized as two privileged scaffolds in drug discovery. In the present study, 24 3',4'-dihydro-2'H-spiro[indoline-3,1'-isoquinolin]-2-ones, designed as molecular hybrids of THIQ and OX, were synthesized and screened in vitro against 59 cell lines in the NCI-60 screen. Twenty compounds displayed weak to moderate inhibition of cell proliferation; among them, three compounds displayed at least 50% inhibition of cell proliferation. The compounds appeared to target primarily renal cell cancer lines; however, leukaemia, melanoma, non-small cell lung cancer, prostate, ovarian and even breast cancer cell lines were also affected. Therefore, this class of spirooxindoles may provide useful leads in the search for new anti-cancer agents.

Development of an Aryloxazole Derivative as a Brain-Permeable Anti-Glioblastoma Agent

Glioblastoma drug development has been difficult due to the extremely low blood brain barrier (BBB) penetration of conventional anti-cancer agents. P-glycoprotein, an efflux membrane transporter, is responsible for the poor brain uptake of small and hydrophobic drug substances. To develop brain-penetrable anti-tumor agents, we designed colchicine derivatives containing an aryloxazole moiety, which is known to inhibit P-glycoprotein. Among those tested, an aryloxazole derivative named KIST-G1 showed the strongest anti-glioblastoma cell proliferation activity (IC₅₀ = 3.2 ± 0.8 nM). Compared to colchicine, KIST-G1 showed dramatically increased BBB-permeable properties presenting 51.7 ± 0.5 (10^-6 cm/s) parallel artificial membrane permeability assay (PAMPA) permeability and 45.0 ± 6.0% of P-gp inhibition. Aid by the BBB-permeable properties, KIST-G1 (5 mg/kg) suppressed glioblastoma cell growth and migration almost completely in the brain of glioblastoma xenograft models by showing 98.2 ± 0.1% reduced tumor area compared with phosphate buffered saline (PBS)-injected control. In comparison, temozolomide, which is the most widely used drug for glioblastoma, showed only moderate effects. Our results demonstrate the effectiveness of an aryloxazole moiety in targeting brain tumors and suggest KIST-G1 as a potent anti-glioblastoma agent.

Chk1 Inhibitor MK-8776 Restores the Sensitivity of Chemotherapeutics in P-glycoprotein Overexpressing Cancer Cells

P-glycoprotein (P-gp), which is encoded by the ATP-binding cassette (ABC) transporter subfamily B member 1 (ABCB1) gene, is one of the most pivotal ABC transporters that transport its substrates across the cell membrane. Its overexpression is one of the confirmed causes of multidrug resistance (MDR), which results in the failure of cancer treatment. Here, we report that checkpoint kinase (Chk) 1 inhibitor MK-8776, a drug candidate in clinical trial, can restore the sensitivity of chemotherapeutics that are substrates of P-gp in KB-C2, SW620/Ad300 cells and human embryonic kidney (HEK)293/ABCB1 cells that overexpress P-gp. MK-8776 remarkably enhanced the cellular [³H]-paclitaxel accumulation and suppressed the efflux function of P-gp without reducing its expression and affecting its cellular localization in cancer cells. Furthermore, MK-8776 (0–40 μM) stimulated the activity of ATPase in P-gp, which was 4.1-fold greater than the control. In addition, MK-8776 formed a cation–π bond and π–π interaction with key residues of the substrate-binding site in P-gp, as indicated by computer-aided molecular docking study. Our study indicated that MK-8776 may significantly enhance the sensitivity of chemotherapeutics that are substrates of P-gp, providing important information for its application in the reversal of MDR.

Systematic Review on Cytotoxic and Anticancer Potential of N-Substituted Isatins as Novel Class of Compounds Useful in Multidrug-Resistant Cancer Therapy: In Silico and In Vitro Analysis

As the emergence of resistance to clinical cancer treatments poses a significant problem in cancer management, there is a constant need to explore novel anticancer agents which have the ability to overcome multidrug resistance (MDR) mechanisms. The search for the development of novel isatin-based antitumor agents accelerated after the approval by the Food and Drug Administration (FDA) of sunitinib malate, a C-3 isatin derivative, as a multitargeted receptor tyrosine kinase inhibitor. However, it is interesting to note that, over the last decade, various N-substituted analogs of isatin with intact carbonyl functionalities have been found to show more promising anticancer potential than its C-3 derivatives. Microtubule-targeting agents are a class of anticancer drugs which affect mitosis by targeting microtubules and suppressing their dynamic behavior. This review presents a systematic compilation of the in vitro cytotoxic and anticancer properties of various N-substituted isatins and illustrates their mechanism of action to overcome MDR by acting as microtubule-destabilizing agents. Predictions of the biological activities and cytotoxic effects of potential N-substituted isatins against various cancer cell lines have also been performed using the PASS computer-aided drug discovery program. Findings from such in vitro and in silico studies will act as a guide for the development of structure-activity relationship and will facilitate the design and exploration of more potent analogs of isatin with high potency and lower side effects for treatment of drug-resistant cancer. Mechanism of action of N-substituted isatin as microtubule-destabilizing agent on tumor cells. N-Substituted isatins bind to colchicine binding site on β-tubulin, which inhibits microtubule polymerization and thereby destabilizes microtubule dynamics, resulting in mitotic arrest leading to tumor cell growth suppression.

Glesatinib, a c-MET/SMO Dual Inhibitor, Antagonizes P-glycoprotein Mediated Multidrug Resistance in Cancer Cells

Multidrug resistance (MDR) is one of the leading causes of treatment failure in cancer chemotherapy. One major mechanism of MDR is the overexpressing of ABC transporters, whose inhibitors hold promising potential in antagonizing MDR. Glesatinib is a dual inhibitor of c-Met and SMO that is under phase II clinical trial for non-small cell lung cancer. In this work, we report the reversal effects of glesatinib to P-glycoprotein (P-gp) mediated MDR. Glesatinib can sensitize paclitaxel, doxorubicin, colchicine resistance to P-gp overexpressing KB-C2, SW620/Ad300, and P-gp transfected Hek293/ABCB1 cells, while has no effect to their corresponding parental cells and negative control drug cisplatin. Glesatinib suppressed the efflux function of P-gp to [³H]-paclitaxel and it didn't impact both the expression and cellular localization of P-gp based on Western blot and immunofluorescent analysis. Furthermore, glesatinib can stimulate ATPase in a dose-dependent manner. The docking study indicated that glesatinib interacted with human P-gp through several hydrogen bonds. Taken together, c-Met/SMO inhibitor glesatinib can antagonize P-gp mediated MDR by inhibiting its cell membrane transporting functions, suggesting new application in clinical trials.

Effect of Y6, an epigallocatechin gallate derivative, on reversing doxorubicin drug resistance in human hepatocellular carcinoma cells

Cancer cells can acquire resistance to a wide variety of diverse and unrelated drugs, this phenomenon is termed multidrug resistance (MDR). Multidrug resistance has been an obstacle to the success of cancer chemotherapy. The present study investigated the reversal effect of Y₆, a new compound obtained by chemically modifying the structure of epigallocatechin-3-gallate (EGCG) extracted from green tea. Y₆ was proven to be effective in inhibiting cell proliferation and reversing drug resistance in doxorubicin (DOX) resistant human hepatocellular carcinoma cells (BEL-7404/DOX). BEL-7404/DOX cells were treated with either doxorubicin combination regimen (doxorubicin plus Y₆ or epigallocatechin-3-gallate or verapamil separately) or doxorubicin alone. The results showed that cell proliferation was inhibited and late cell apoptosis increased in the combination treatment group, especially in the group treated with doxorubicin plus Y₆. Further analysis revealed that the expressions of hypoxia-inducible factor-1α and multidrug resistance 1/P-glycoprotein decreased at both messenger RNA and protein levels by treatments with combined drugs compared to doxorubicin alone. Our results indicated that Y₆, as a drug resistance reversal agent, increased the sensitivity of drug resistant cells to doxorubicin. The mechanisms of actions of Y₆ in reversal effect were associated with the decreased expression of hypoxia-inducible factor-1α and multidrug resistance 1/P-glycoprotein.

Pro-inflammatory and anti-inflammatory compounds exert similar effects on P-glycoprotein in blood–brain barrier endothelial cells

Objectives

The effects of anti-inflammatory glucocorticoids dexamethasone (DX) and hydrocortisone (HC), pro-inflammatory cytokine interleukin-1β (IL-1β) and dietary long-chain polyunsaturated fatty acids (PUFAs) on expression and activity of the ATP-binding cassette transporter P-glycoprotein (P-GP) were studied in porcine brain endothelial cells (PBECs).

Methods

Primary PBECs were treated for 24 h with glucocorticoids, IL-1β and long-chain PUFAs. P-GP activity was determined by measuring intracellular calcein accumulation and P-GP expression by Western blotting. The effect of PUFAs on membrane fluidity was assessed by fluorescence recovery after photobleaching (FRAP).

Key findings

Dexamethasone, HC and IL-1β significantly increased P-GP expression and activity. The effect of IL-1β was attenuated by the IL-1 receptor antagonist (IL-1RA). This is the first report of the combined actions of IL-1β and IL-1RA on P-GP expression and the first evidence of glucocorticoid-mediated P-GP up-regulation in PBECs. Arachidonic acid (AA), docosahexaenoic acid (DHA) and eicosapentenoic acid (EPA) significantly decreased P-GP activity without affecting expression or membrane fluidity. AA, DHA and EPA counteracted IL-1β-mediated increases in P-GP activity, while AA and EPA, but not DHA, counteracted glucocorticoid-mediated increase in P-GP activity.

Conclusions

While glucocorticoids and IL-1β possess opposing actions in inflammation, they demonstrate functional consistency by increasing P-GP expression and activity in PBECs.

Broad blocking of MDR efflux pumps by acetylshikonin and acetoxyisovalerylshikonin to generate hypersensitive phenotype of malignant carcinoma cells

Cytotoxic activities of acetylshikonin and acetoxyisovalerylshikonin alone and in combination with chemotherapeutic agents against parental and drug resistant cell lines were determined using the MTT assay. Effects of Shikonin derivatives on BCRP, MDR1 and MRP transcript and protein levels were relatively measured. Finally, accumulation and efflux kinetics were conducted. The results revealed cell- and concentration-dependency of the cell cytotoxicity. Acetylshikonin and acetoxyisovalerylshikonin transiently made the mRNA ocean turbulent, but FACS analyses using fluorescent-labeled antibodies showed no significant change in the MDR-protein levels. Functional kinetics revealed significant block of MDR1, BCRP and MRP transporter in the presence of shikonin derivatives. Maximum accumulation fold changes was quantified to be 4.4 and consequently, acetoxyisovalerylshikonin pretreated EPG85.257RDB cells was chemosensitized to daunorubicin tension 3.1-fold. Although, the MDR blockage was reported to follow time- and cell-dependent patterns, MDR1, BCRP and MRP2 responses to the shikonins are concentration-independent. These data suggest uncompetitive transporter blockage behavior of these agents. The results indicated that shikonin derivatives stimulate uptake and reduce efflux of chemotherapeutic agents in the malignant cancer cells, suggesting that chemotherapy in combination with shikonin compounds may be beneficial to cancer cells that overexpress multidrug resistance transporters.

Understanding of human ATP binding cassette superfamily and novel multidrug resistance modulators to overcome MDR

Indeed, multi-drug resistance (MDR) is a significant obstacle to effective chemotherapy. The overexpression of ATP-binding cassette (ABC) membrane transporters is a principal cause of enhanced cytotoxic drug efflux and treatment failure in various types of cancers. At cellular level, the pumps of ABC family regulate the transportation of numerous substances including drugs in and out of the cells. In past, the overexpression of ABC pumps suggested a well-known mechanism of drug resistance in cancers as well as infectious diseases. In oncology, the search for new compounds for the inhibition of these hyperactive ABC pumps either genetically or functionally, growing interest to reverse multi-drug resistance and increase chemotherapeutic effects. Several ABC pump inhibitor/modulators has been explored to address the cancer associated MDR. However, the clinical results are still disappointing and conventional chemotherapies are constantly failed in successful eradication of MDR tumors. In this context, the structural and functional understanding of different ATP pumps is most important. In this concise review, we elaborated basic crystal structure of ABC transporter proteins as well as its critical elements such as different domains, motifs as well as some important amino acids which are responsible for ATP binding and drug efflux as well as demonstrated an ATP-switch model employed by various ABC membrane transporters. Furthermore, we briefly summarized different newly identified MDR inhibitors/modulators, deployed alone or in combination with cytotoxic agents to deal with MDR in different types of cancers.

Exploring Jolkinol D Derivatives To Overcome Multidrug Resistance in Cancer

Macrocyclic monoacyl lathyrane derivatives bearing a benzoyl moiety were previously found to be strong ABCB1 modulators. To explore the effects of different substituents of the aromatic moiety, 14 new compounds (1.1-1.7, 1.10, and 2.1-2.4) were prepared from jolkinol D (1), obtained from Euphorbia piscatoria, and from jolkinodiol (2), its hydrolysis derivative. Compounds 1.8 and 1.9, having aliphatic moieties, were also obtained. The reversal of ABCB1-mediated MDR was evaluated through functional and chemosensitivity assays on the human ABCB1-gene-transfected L5178Y mouse T-lymphoma cell line. Structure-activity relationships showed that addition of electron-donating groups to the aromatic moiety improved the activity. The effects on the ATPase activity of the strongest modulator (1.3) and the inactive jolkinol D (1) were also investigated and compared. Moreover, in the chemosensitivity assay, most of the compounds interacted synergistically with doxorubicin. Compounds 1.1-1.10 and 2.1-2.4 were further assessed for their collateral sensitivity effect against the human cancer cells: EPG85-257 (gastric) and EPP85-181 (pancreatic), and the matching drug-selected cells EPG85-257RDB, EPG85-257RNOV, EPP85-181RDB, and EPP85-181RNOV. The most promising ones (1.8 and 1.10) along with compound 3, previously selected, were investigated as apoptosis inducers. The compounds were able to induce apoptosis through caspase-3 activation, with significant differences being observed between the parental and resistant cells.

N-Heterocyclic choline analogues based on 1,2,3,4-tetrahydro(iso)quinoline scaffold with anticancer and anti-infective dual action

BACKGROUND

Pharmacological effects of biologically active "small molecules" can be improved by their targeted modification, which affects drug delivery and interaction with tumor cells and microorganisms. We aimed to evaluate anticancer and antimicrobial activity of lipid-like choline derivatives modified via simultaneous introduction of tetrahydro(iso)quinoline based pharmacophore system at nitrogen atom and long chain alkyl substituent at oxygen atom.

METHODS

Target compounds were synthesized under phase-transfer catalysis conditions followed by quaternization, and evaluated for cytotoxicity and NO-generation ability on HT-1080 and MG-22A tumor cell lines and NIH 3T3 normal mouse fibroblasts, and screened for antimicrobial activity against gram-positive (Staphylococcus aureus and Bacillus cereus) and gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis) and fungi (Candida albicans and Aspergillus niger). Inhibitory action of active compounds towards E. coli DNA gyrase was investigated.

RESULTS

Target compounds exhibit high selective cytotoxicity (LC₅₀ < 1 μg/mL) and NO-induction ability, and reveal strong antimicrobial activity with MIC and MBC/MFC values of 0.5-32 μg/mL, predominantly vs. gram-positive bacteria and fungi. Tested substances displayed inhibitory effect towards E. coli DNA gyrase, though less than ciprofloxacin. Tetrahydroisoquinoline derivatives and compounds possessing substituents with chain length of 10 and 11 carbon atoms have highest indices of activities.

CONCLUSIONS

Lipid-like N-heterocyclic choline analogues based on 1,2,3,4-tetrahydro(iso)quinoline scaffold, possessing very high cytotoxicity with attendant strong antimicrobial activity are the leads for developing effective dual action therapeutics.

Light-Regulated NO Release as a Novel Strategy To Overcome Doxorubicin Multidrug Resistance

Nitric oxide (NO) release from a suitable NO photodonor (NOP) can be fine-tuned by visible light stimuli at doses that are not toxic to cells but that inhibit several efflux pumps; these are mainly responsible for the multidrug resistance of the anticancer agent doxorubicin (DOX). The strategy may thus increase DOX toxicity against resistant cancer cells. Moreover, a novel molecular hybrid covalently joining DOX and NOP showed similar increased toxicity toward resistant cancer cells and, in addition, lower cardiotoxicity than DOX. This opens new and underexplored approaches to overcoming the main therapeutic drawbacks of this chemotherapeutic based on light-controlled release of NO.

Coumarin derivatives as potential antitumor agents: Growth inhibition, apoptosis induction and multidrug resistance reverting activity

A small library of coumarins, carrying butynyl-amino chains, was synthesized continuing our studies in the field of MDR reverting ageEnts and in order to obtain multipotent agents to combat malignancies. In particular, the reported anticancer and chemopreventive natural product 7-isopentenyloxycoumarin was linked to different terminal amines, selected on the basis of our previously reported results. The anticancer behaviour and the MDR reverting ability of the new compounds were evaluated on human colon cancer cells, particularly prone to develop the MDR phenotype. Some of the new derivatives showed promising effects, directly acting as cytotoxic compounds and/or counteracting MDR phenomenon. Compound 1e emerged as the most interesting of this series, showing a multipotent biological profile and suggesting that conjugation of an appropriate coumarin core with a properly selected butynyl-amino chain allows to obtain novel hybrid molecules endowed with improved in vitro antitumor activity.

A-803467, a tetrodotoxin-resistant sodium channel blocker, modulates ABCG2-mediated MDR in vitro and in vivo

ATP-binding cassette subfamily G member 2 (ABCG2) is a member of the ABC transporter superfamily proteins, which has been implicated in the development of multidrug resistance (MDR) in cancer, apart from its physiological role to remove toxic substances out of the cells. The diverse range of substrates of ABCG2 includes many antineoplastic agents such as topotecan, doxorubicin and mitoxantrone. ABCG2 expression has been reported to be significantly increased in some solid tumors and hematologic malignancies, correlated to poor clinical outcomes. In addition, ABCG2 expression is a distinguishing feature of cancer stem cells, whereby this membrane transporter facilitates resistance to the chemotherapeutic drugs. To enhance the chemosensitivity of cancer cells, attention has been focused on MDR modulators. In this study, we investigated the effect of a tetrodotoxin-resistant sodium channel blocker, A-803467 on ABCG2-overexpressing drug selected and transfected cell lines. We found that at non-toxic concentrations, A-803467 could significantly increase the cellular sensitivity to ABCG2 substrates in drug-resistant cells overexpressing either wild-type or mutant ABCG2. Mechanistic studies demonstrated that A-803467 (7.5 μM) significantly increased the intracellular accumulation of [³H]-mitoxantrone by inhibiting the transport activity of ABCG2, without altering its expression levels. In addition, A-803467 stimulated the ATPase activity in membranes overexpressed with ABCG2. In a murine model system, combination treatment of A-803467 (35 mg/kg) and topotecan (3 mg/kg) significantly inhibited the tumor growth in mice xenografted with ABCG2-overexpressing cancer cells. Our findings indicate that a combination of A-803467 and ABCG2 substrates may potentially be a novel therapeutic treatment in ABCG2-positive drug resistant cancers.

Jatrophane diterpenes and cancer multidrug resistance - ABCB1 efflux modulation and selective cell death induction

BACKGROUND

Modulation of P-glycoprotein (ABCB1) and evaluation of the collateral sensitivity effect are among the most promising approaches to overcome multidrug resistance (MDR) in cancer. In a previous study, two rare 12,17-cyclojatrophanes (1-2) and other novel jatrophanes (3-4), isolated from Euphorbia welwitschii, were screened for collateral sensitivity effect. Herein, the isolation of another jatrophane (5) is presented, being the broader goal of this work to investigate the role of euphowelwitschines A (1) and B (2), welwitschene (3), epoxywelwitschene (4) and esulatin M (5) as ABCB1 modulators and/or collateral sensitivity agents.

METHODS

Compounds 1-5 were evaluated for ABCB1 modulation ability through combination of transport and chemosensitivity assays, using a mouse T-lymphoma MDR1-transfected cell model. Moreover, the nature of interaction of compound 4 with ABCB1 was studied, using an ATPase assay. The MDR-selective antiproliferative activity of compound 5 was evaluated against gastric (EPG85-257) and pancreatic (EPP85-181) human cancer cells and their drug-selected counterparts (EPG85-257RDB, EPG85-257RNOV, EPP85-181RDB, EPP85-181RNOV). The drug induced cell death was investigated for compounds 4 and 5, using the annexin V/PI staining and the active caspase-3 assay.

RESULTS

The jatrophanes 1-5 were able to modulate the efflux activity of ABCB1, and at 2µM, 3-5 maintained the strong modulator profile. Structure activity results indicated that high conformational flexibility of the twelve-membered ring of compounds 3-5 favored ABCB1 modulation, in contrast to the tetracyclic scaffold of compounds 1 and 2. The effects of epoxywelwitschene (4) on the ATPase activity of ABCB1 showed it to interact with the transporter and to be able to reduce the transport of a second subtrate. Drug combination experiments also corroborated the anti-MDR potential of these diterpenes due to their synergistic interaction with doxorubicin (combination index <0.7). Esulatin M (5) showed a strong MDR-selective antiproliferative activity against EPG85-257RDB and EPP85-181RDB cells, with IC50 of 1.8 and 4.8 µM, respectively. Compounds 4 and 5 induced apoptosis via caspase-3 activation. A significant discrimination was observed between the resistant cell lines and parental cells.

CONCLUSIONS

This study strengthens the role of jatrophane diterpenes as lead candidates for the development of MDR reversal agents, higlighting the action of compounds 4 and 5.

Synthesis, Antiproliferative, and Multidrug Resistance Reversal Activities of Heterocyclic α,β-Unsaturated Carbonyl Compounds

A series of heterocyclic α,β-unsaturated carbonyl compounds (1a-1d, 2a-2d, 3a-3d, 4a-3d, and 5a-5d) with 1,5-diaryl-3-oxo-1,4-pentadienyl pharmacophore were synthesized for the development of anticancer and multidrug resistance reverting agents. The antiproliferative activities were tested against nine human cancer cell lines. Approximately 73% of the IC50 values were below 5 μm, while 35% of these figures were submicromolar, and compounds 3a-3d with 4-trifluoro methyl in the arylidene benzene rings were the most potent, since their IC50 values are between 0.06 and 3.09 μm against all cancer cell lines employed. Meanwhile, their multidrug resistance reversal properties and cellular uptake were further examined. The data displayed that all of these compounds could reverse multidrug resistance, particularly, compounds 3a and 4a demonstrated both potent multidrug resistance reverting properties and strong antiproliferative activities, which can be taken as leading molecules for further research of dual effect agents in tumor chemotherapy.

Korean red ginseng extract enhances paclitaxel distribution to mammary tumors and its oral bioavailability by P-glycoprotein inhibition

1. Drug efflux by P-glycoprotein (P-gp) is a common resistance mechanism of breast cancer cells to paclitaxel, the primary chemotherapy in breast cancer. As a means of overcoming the drug resistance-mediated failure of paclitaxel chemotherapy, the potential of Korean red ginseng extract (KRG) as an adjuvant chemotherapy has been reported only in in vitro. Therefore, we assessed whether KRG alters P-gp mediated paclitaxel efflux, and therefore paclitaxel efficacy in in vitro and vivo models. 2. KRG inhibited P-gp protein expression and transcellular efflux of paclitaxel in MDCK-mdr1 cells, but KRG was not a substrate of P-gp ATPase. In female rats with mammary tumor, the combination of paclitaxel with KRG showed the greater reduction of tumor volumes, lower P-gp protein expression and higher paclitaxel distribution in tumors, and greater oral bioavailability of paclitaxel than paclitaxel alone. 3. From these results, KRG increased systemic circulation of oral paclitaxel and its distribution to tumors via P-gp inhibition in rats and under the current study conditions.

The effect of ABCB1 polymorphisms on the outcome of breast cancer treatment

The ABCB1 gene encodes a permeability glycoprotein, which is one of the most extensively studied human adenosine-triphosphate (ATP)-dependent efflux transporters. Permeability glycoprotein is expressed in the apical membranes of tissues such as intestine, liver, blood–brain barrier, kidney, placenta, and testis and contributes to intracellular drug disposition. It is also highly expressed in tumor cells conferring drug resistance, which is one of the major problems in the efficacy of cancer chemotherapy treatment. ABCB1 is highly polymorphic, and three well-known single-nucleotide polymorphisms such as 1236C>T, 2677G>T/A, and 3435C>T have been found to be associated with altered messenger RNA levels, protein folding, and drug pharmacokinetics. Many association studies and meta-analyses have demonstrated the clinical impact of ABCB1 polymorphisms in breast cancer treatment outcomes with respect to therapeutic response, chemotoxicity, and overall survival. Therefore, the aim of this review was to evaluate the effects of ABCB1 polymorphisms on the outcome of breast cancer treatment which, in future, would be important for tailoring individualized anticancer therapy.

Mutual regulation and targeting of multidrug resistance and cancer stem phenotype

Targeting stemness mechanisms leads to the suppression of ABC transporter activity and elimination of CSCs.

The sialyl-glycolipid stage-specific embryonic antigen 4 marks a subpopulation of chemotherapy-resistant breast cancer cells with mesenchymal features

Introduction

Chemotherapy resistance resulting in incomplete pathologic response is associated with high risk of metastasis and early relapse in breast cancer. The aim of this study was to identify and evaluate biomarkers of treatment-resistant tumor cells.

Methods

We performed a cell surface marker screen in triple-negative breast cancer patient-derived xenograft models treated with standard care genotoxic chemotherapy. Global expression profiling was used to further characterize the identified treatment-resistant subpopulations.

Results

High expression of sialyl-glycolipid stage-specific embryonic antigen 4 (SSEA4) was found in residual tumor cells surviving chemotherapy and in samples from metastatic patients who relapsed after neoadjuvant chemotherapy. Gene and microRNA (miRNA) expression profiling linked SSEA4 positivity with a mesenchymal phenotype and a deregulation of drug resistance pathways. Functional assays demonstrated a direct link between epithelial–mesenchymal transition (EMT) and SSEA4 expression. Interestingly, SSEA4 expression, EMT, and drug resistance seemed to be regulated posttranscriptionally. Finally, high expression of CMP-N-acetylneuraminate-β-galactosamide-α-2,3-sialyltransferase 2 (ST3GAL2), the rate-limiting enzyme of SSEA4 synthesis, was found to be associated with poor clinical outcome in breast and ovarian cancer patients treated with chemotherapy.

Conclusions

In this study, we identified SSEA4 as highly expressed in a subpopulation of tumor cells resistant to multiple commonly used chemotherapy drugs, as well as ST3GAL2, the rate-limiting enzyme of SSEA4 synthesis, as a predictive marker of poor outcome for breast and ovarian cancer patients undergoing chemotherapy. Both biomarkers and additionally identified regulatory miRNAs may be used to further understand chemoresistance, to stratify patient groups in order to avoid ineffective and painful therapies, and to develop alternative treatment regimens for breast cancer patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0652-6) contains supplementary material, which is available to authorized users.

Common stemness regulators of embryonic and cancer stem cells

Pluripotency of embryonic stem cells (ESCs) and induced pluripotent stem cells is regulated by a well characterized gene transcription circuitry. The circuitry is assembled by ESC specific transcription factors, signal transducing molecules and epigenetic regulators. Growing understanding of stem-like cells, albeit of more complex phenotypes, present in tumors (cancer stem cells), provides a common conceptual and research framework for basic and applied stem cell biology. In this review, we highlight current results on biomarkers, gene signatures, signaling pathways and epigenetic regulators that are common in embryonic and cancer stem cells. We discuss their role in determining the cell phenotype and finally, their potential use to design next generation biological and pharmaceutical approaches for regenerative medicine and cancer therapies.

Pharmacokinetic and pharmacodynamic study of tariquidar (XR9576), a P-glycoprotein inhibitor, in combination with doxorubicin, vinorelbine, or docetaxel in children and adolescents with refractory solid tumors

PURPOSE

P-glycoprotein (Pgp), an ATP-dependent transport protein, confers multidrug resistance in cancer cells. Tariquidar binds and inhibits Pgp. To assess the toxicity, pharmacokinetics (PK), and pharmacodynamics of tariquidar, we conducted a phase I trial of tariquidar in combination with doxorubicin, docetaxel, or vinorelbine in children and adolescents with recurrent or refractory solid tumors.

METHODS

Patients less than 19 years of age with refractory or recurrent solid tumors were eligible. Tariquidar (1, 1.5, or 2 mg/kg) was administered alone and in combination with doxorubicin, docetaxel, or vinorelbine. PK of tariquidar and cytotoxic drugs was performed. Pgp function was assessed by a rhodamine efflux assay and (99m)Tc-sestamibi scintigraphy. Tumor Pgp expression was assessed by immunohistochemistry. Response was assessed using Response Evaluation Criteria in Solid Tumors.

RESULTS

Twenty-nine subjects were enrolled. No tariquidar-related dose-limiting toxicity (DLT) was observed. DLT related to cytotoxic drugs occurred in 12 % of subjects receiving tariquidar 2 mg/kg. When administered in combination with tariquidar, the clearance of docetaxel and vinorelbine was reduced compared to prior studies. Inhibition of rhodamine efflux was dose dependent. After tariquidar administration, (99m)Tc-sestamibi accumulation in tumor increased by 22 %. Objective responses (1 complete, 2 partial) were observed. There was no association between tumor Pgp expression and response.

CONCLUSION

A tolerable and biologically active dose of tariquidar was established in children and adolescents. This trial demonstrates that modulators of resistance can be evaluated in combination with chemotherapy, and pharmacokinetic and pharmacodynamic endpoints can be useful in determination of recommended dose in children and adolescents.

Differential expression and functionality of ATP-binding cassette transporters in the human hair follicle

BACKGROUND

ATP-binding cassette (ABC) transporters are involved in the active transport of an extremely diverse range of substrates across biological membranes. These transporters are commonly implicated in the development of multidrug resistance and are also involved in numerous physiological and homeostatic processes, including lipid transport, cell migration and differentiation.

OBJECTIVES

To close the knowledge gap in the expression of ABC transporters in the human hair follicle (HF).

METHODS

Quantitative polymerase chain reaction (qPCR) of ABC genes and immunofluorescence microscopy analysis of cryosections of human HFs.

RESULTS

By qPCR analysis, numerous members of the ABC transporter superfamily, such as ABCB1, ABCG2 and ABCA12, were found to be transcribed in full-length human scalp HFs. Immunofluorescence microscopy demonstrated that the intrafollicular protein expression of different xenobiotic ABC transporters (ABCB1, ABCC1, ABCC4, ABCG2) varies greatly, with ABCG2 expression restricted primarily to the epithelial stem cell region of the outer root sheath (bulge), whereas expression of ABCB1, ABCC1 and ABCC4 was more widespread. Lipid transporters ABCA1, ABCA12 and ABCA4 were almost uniformly expressed throughout the HF epithelium. Functional ABCB1/G2 activity was demonstrated by exclusion of the substrate dye, Hoechst 33342. In the bulge, this was reversed by ABCB1 and ABCG2 inhibition.

CONCLUSIONS

These data encourage further investigation of ABC transporters as potentially important regulators of HF epithelial biology. Clinically, pharmacological modulation of the activity of selected intrafollicular ABC transporters may permit novel therapeutic interventions, such as protecting HF stem cells from chemotherapy-induced damage, counteracting cholesterol-associated hypertrichosis, and manipulating the intrafollicular prostaglandin balance in androgenetic alopecia.