Tyrosine Kinase Inhibitors Influence ABCG2 Expression in EGFR-Positive MDCK BCRP Cells via the PI3K/Akt Signaling Pathway

Acryloylphenylcarboxamides: A New Class of Breast Cancer Resistance Protein (ABCG2) Modulators

Chalcones are easily synthesized natural precursors of secondary plant metabolites, and their derivatives show various biological activities including inhibition of ABC transporters. Especially, their role as inhibitors of ABCG2, the most recently discovered ABC transporter involved in multidrug resistance, inspired the synthesis of new structurally diverse derivatives. Therefore, we combined the typical chalcone moiety with several acid chlorides by using an amide linker at position 2', 3', or 4' on ring A of the chalcone. The resulting 35 compounds covered a wide spectrum of substitution patterns, which allowed development of structure-activity relationships and to find the optimal structural features for further investigations. Synthesized acryloylphenylcarboxamides were investigated for their inhibitory activity against ABCG2 and their behavior toward ABCB1 and ABCC1. Furthermore, for the most promising compounds, their intrinsic cytotoxicity and their ability to reverse ABCG2-mediated multidrug resistance were determined.

Synthesis and Investigation of Tetrahydro-β-carboline Derivatives as Inhibitors of the Breast Cancer Resistance Protein (ABCG2)

The breast cancer resistance protein (ABCG2) transports chemotherapeutic drugs out of cells, which makes it a major player in mediating multidrug resistance (MDR) of cancer cells. To overcome this mechanism, inhibitors of ABCG2 can be used. Only a few potent and selective ABCG2 inhibitors have been discovered, i.e., fumitremorgin C (FTC), Ko143, and the alkaloid harmine, which contain a tetrahydro-β-carboline or β-carboline backbone, respectively. However, toxicity and or instability prevent their use in vivo. Therefore, there is a need for further potent inhibitors. We synthesized and pharmacologically investigated 37 tetrahydro-β-carboline derivatives. The inhibitory activity of two compounds (51, 52) is comparable to that of Ko143, and they are selective for ABCG2 over ABCB1. Furthermore, they are able to reverse the ABCG2-mediated resistance toward SN-38 and inhibit the ATPase activity. The cytotoxicity data show that their inhibitory effect is substantially higher than their toxicity.

Synthesis and Biological Evaluation of 4-Anilino-quinazolines and -quinolines as Inhibitors of Breast Cancer Resistance Protein (ABCG2)

Chemotherapeutic treatment of cancer often fails due to overexpression of the ATP-binding cassette (ABC) transport proteins, like ABCG2, triggering active efflux of various structurally unrelated drugs. This so-called multidrug resistance (MDR) may be reversed by selective, potent, and nontoxic inhibitors of ABCG2. As only a few potent inhibitors are known, new compounds based on a 4-substituted-2-phenylquinazoline scaffold were investigated. Substitution with hydroxy, cyano, nitro, acetamido, and fluoro led to high inhibitory activities toward ABCG2. The ability to reverse MDR of the most active compounds was confirmed in a MTT efficacy assay. Moreover, a negligibly low intrinsic cytotoxicity was found resulting in a high therapeutic ratio. Investigations of the inhibitory activity toward ABCB1 and ABCC1 yielded a high selectivity toward ABCG2 for the quinazoline compounds. Quinoline-based analogues showed lower inhibitory activity and selectivity. The study yielded a variety of promising compounds, some with superior properties compared to those of the standard inhibitor Ko143.

The combination of quinazoline and chalcone moieties leads to novel potent heterodimeric modulators of breast cancer resistance protein (BCRP/ABCG2)

During the last decade it has been found that chalcones and quinazolines are promising inhibitors of ABCG2. The combination of these two scaffolds offers a new class of heterocyclic compounds with potentially high inhibitory activity against ABCG2. For this purpose we investigated 22 different heterodimeric derivatives. In this series only methoxy groups were used as substituents as these had been proven superior for inhibitory activity of chalcones. All compounds were tested for their inhibitory activity, specificity and cytotoxicity. The most potent ABCG2 inhibitor in this series showed an IC50 value of 0.19 μM. It possesses low cytotoxicity (GI50 = 93 μM), the ability to reverse MDR and is nearly selective toward ABCG2. Most compounds containing dimethoxy groups showed slight activity against ABCB1 too. Among these three compounds (17, 19 and 24) showed even higher activity toward ABCB1 than ABCG2. All inhibitors were further screened for their effect on basal ATPase activity. Although the basal ATPase activity was partially stimulated, the compounds were not transported by ABCG2. Thus, quinazoline-chalcones are a new class of effective ABCG2 inhibitors.

Pyrrolopyrimidine Derivatives as Novel Inhibitors of Multidrug Resistance-Associated Protein 1 (MRP1, ABCC1)

Five series of pyrrolo[3,2-d]pyrimidines were synthesized and evaluated with respect to potency and selectivity toward multidrug resistance-associated protein 1 (MRP1, ABCC1). This transport protein is a major target to overcome multidrug resistance in cancer patients. We investigated differently substituted pyrrolopyrimidines using the doxorubicin selected and MRP1 overexpressing small cell lung cancer cell line H69 AR in a calcein AM and daunorubicin cell accumulation assay. New compounds with high potency and selectivity were identified. Piperazine residues at position 4 bearing large phenylalkyl side chains proved to be beneficial for MRP1 inhibition. Its replacement by an amino group led to decreased activity. Aliphatic and aliphatic-aromatic variations at position 5 and 6 revealed compounds with IC50 values in high nanomolar range. All investigated compounds had low affinity toward P-glycoprotein (P-gp, ABCB1). Pyrrolopyrimidines with small substituents showed moderate inhibition against breast cancer resistance protein (BCRP, ABCG2).

Cytotoxicity of the Sesquiterpene Lactones Neoambrosin and Damsin from Ambrosia maritima Against Multidrug-Resistant Cancer Cells

Multidrug resistance is a prevailing phenomenon leading to chemotherapy treatment failure in cancer patients. In the current study two known cytotoxic pseudoguaianolide sesquiterpene lactones; neoambrosin (1) and damsin (2) that circumvent MDR were identified. The two cytotoxic compounds were isolated using column chromatography, characterized using 1D and 2D NMR, MS, and compared with literature values. The isolated compounds were investigated for their cytotoxic potential using resazurin assays and thereafter confirmed with immunoblotting and in silico studies. MDR cells overexpressing ABC transporters (P-glycoprotein, BCRP, ABCB5) did not confer cross-resistance toward (1) and (2), indicating that these compounds are not appropriate substrates for any of the three ABC transporters analyzed. Resistance mechanisms investigated also included; the loss of the functions of the TP53 and the mutated EGFR. The HCT116 p53^-/- cells were sensitive to 1 but resistant to 2. It was interesting to note that resistant cells transfected with oncogenic ΔEGFR exhibited hypersensitivity CS toward (1) and (2) (degrees of resistances were 0.18 and 0.15 for (1) and (2), respectively). Immunoblotting and in silico analyses revealed that 1 and 2 silenced c-Src kinase activity. It was hypothesized that inhibition of c-Src kinase activity may explain CS in EGFR-transfected cells. In conclusion, the significant cytotoxicity of 1 and 2 against different drug-resistant tumor cell lines indicate that they may be promising candidates to treat refractory tumors.

Pharmacology of novel small-molecule tubulin inhibitors in glioblastoma cells with enhanced EGFR signalling

We recently reported that CMPD1, originally developed as an inhibitor of MK2 activation, primarily inhibits tubulin polymerisation and induces apoptosis in glioblastoma cells. In the present study we provide detailed pharmacological investigation of CMPD1 analogues with improved molecular properties. We determined their anti-cancer efficacy in glioblastoma cells with enhanced EGFR signalling, as deregulated EGFR often leads to chemoresistance. Eight analogues of CMPD1 with varying lipophilicity and basicity were synthesised and tested for efficacy in the cell viability assay using established glioblastoma cell lines and patient-derived primary glioblastoma cells. The mechanism of action for the most potent analogue 15 was determined using MK2 activation and tubulin polymerisation assays, together with the immunofluorescence analysis of the mitotic spindle formation. Apoptosis was analysed by Annexin V staining, immunoblotting analysis of bcl-2 proteins and PARP cleavage. The apoptotic activity of CMPD1 and analogue 15 was comparable across glioblastoma cell lines regardless of the EGFR status. Primary glioblastoma cells of the classical subtype that are characterized by enhanced EGFR activity were most sensitive to the treatment with CMPD1 and 15. In summary, we present mechanism of action for a novel small molecule tubulin inhibitor, compound 15 that inhibits tubulin polymerisation and mitotic spindle formation, induces degradation of anti-apoptotic bcl-2 proteins and leads to apoptosis of glioblastoma cells. We also demonstrate that the enhanced EGFR activity does not decrease the efficacy of tubulin inhibitors developed in this study.

Paclitaxel induces apoptosis and reduces proliferation by targeting epidermal growth factor receptor signaling pathway in oral cavity squamous cell carcinoma

Oral cavity cancer is common worldwide. Furthermore, the epidermal growth factor receptor (EGFR) signaling pathway is considered to be constitutively activated in oral cancers. Paclitaxel is widely accepted as an antitumor drug as it effectively inhibits the cell cycle. This study predominantly explores the possible molecule mechanism of paclitaxel on oral cancer treatment. Cell viability was first detected using an MTT assay. Cell apoptosis was examined by Hoechst staining and flow cytometry using an annexin-V and propidium iodide kit. Specific EGFR signaling pathways were further explored through western blot analysis. Abnormal protein expression levels were determined via immunofluoresence. Additionally, the protein levels of matrix metalloproteinase (MMP)-2 and 9 were determined using ELISA. Paclitaxel significantly inhibited oral cancer cell viability in a time- and dose-dependent manner. Paclitaxel also enhanced oral cancer cell apoptosis via increased Bim and Bid protein expression. Furthermore, paclitaxel was observed to inhibit oral cancer cell proliferation through increased MMP-2 and MMP-9 protein levels. Paclitaxel inhibited the growth of the oral cancer cell line, tea8113 malignant proliferation and enhanced tea8113 cell apoptosis through inhibiting the EGFR signaling pathway.

Design of inhibitors of BCRP/ABCG2

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

Paclitaxel resistance in MCF-7/PTX cells is reversed by paeonol through suppression of the SET/phosphatidylinositol 3-kinase/Akt pathway

Breast cancer is one of the most prevalent types of malignant tumor. Paclitaxel is widely used in the treatment of breast cancer; however, the major problem contributing to the failure of chemotherapy in breast cancer is the development of drug resistance. Therefore, it is necessary to identify novel therapeutic targets and reversal agents for breast cancer. In the present study, the protein expression levels of SET, protein phosphatase 2A (PP2A) and phosphatidylinositol 3-kinase (PI3K)/Akt pathway were determined in MCF-7/PTX human breast carcinoma paclitaxel-resistant cells using western blot analysis. Small interference RNAs (siRNAs) were used to knock down the gene expression of SET in MCF-7/PTX cells and the cell viability was assessed following treatment with paclitaxel, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assays and flow cytometry. In addition, western blot analysis was used to determined PI3K/Akt pathway activity following SET knockdown. Furthermore, the reversal effects of paeonol on paclitaxel, and its underlying mechanisms of action, were investigated using western blot analysis and reverse transcription-quantitative polymerase chain reaction. The results demonstrated that increased levels of SET and PI3K/Akt pathway proteins were present in the MCF-7/PTX cells, compared with normal MCF-7 cells. Knockdown of SET significantly sensitized MCF-7/PTX cells to paclitaxel and induced cell apoptosis. In addition, the expression levels of the adenosine triphosphate binding cassette (ABC) transporter proteins were significantly reduced in the MCF-7/PTX cells compared with the normal MCF-7 cells. SET-induced paclitaxel resistance was found to be associated with the activation of the PI3K/Akt pathway. Paeonol significantly reduced the mRNA and protein expression levels of SET in the MCF-7/PTX cells. Furthermore, paeonol significantly sensitized the MCF-7/PTX to paclitaxel via regulation of ABC transporters, B cell lymphoma-2 (Bcl-2) and Bcl-2-associated X protein. In addition, paeonol inhibited SET-mediated paclitaxel resistance by attenuating PI3K/Akt pathway activity in the MCF-7/PTX cells. In conclusion, the results of the present study demonstrated that SET was associated with paclitaxel resistance in MCF-7/PTX cells, and that paeonol reversed paclitaxel resistance in MCF-7/PTX cells by downregulating the activity of the SET/PP2A/Akt pathway.

Icotinib antagonizes ABCG2-mediated multidrug resistance, but not the pemetrexed resistance mediated by thymidylate synthase and ABCG2

ABCG2 is a potential biomarker causing multidrug resistance (MDR) in Non-Small Cell Lung Cancer (NSCLC). We conducted this study to investigate whether Icotinib, a small-molecule inhibitor of EGFR tyrosine kinase, could interact with ABCG2 transporter in NSCLC. Our results showed that Icotinib reversed ABCG2-mediated MDR by antagonizing the drug efflux function of ABCG2. Icotinib stimulated the ATPase activity in a concentration-dependent manner and inhibited the photolabeling of ABCG2 with [125I]-Iodoarylazidoprazosin, demonstrating that it interacts at the drug-binding pocket. Homology modeling predicted the binding conformation of Icotinib at Asn629 centroid-based grid of ABCG2. However, Icotinib at reversal concentration did not affect the expression levels of AKT and ABCG2. Furthermore, a combination of Icotinib and topotecan exhibited significant synergistic anticancer activity against NCI-H460/MX20 tumor xenografts. However, the inhibition of transport activity of ABCG2 was insufficient to overcome pemetrexed resistance in NCI-H460/MX20 cells, which was due to the co-upregulated thymidylate synthase (TS) and ABCG2 expression. This is the first report to show that the up-regulation of TS in ABCG2-overexpressing cell line NCI-H460/MX20 may play a role of resistance to pemetrexate. Our findings suggested different possible strategies of overcoming the resistance of topotecan and pemetrexed in the NSCLC patients.

LRIG1, human EGFR inhibitor, reverses multidrug resistance through modulation of ABCB1 and ABCG2

In our previous study, we have found that leucine-rich repeats and immunoglobulin-like domains 1(LRIG1) can improve the chemosensitivity in U251 cells whereas the role of LRIG1 in multidrug resistance (MDR) remains unknown. Here, we reported that LRIG1 can reverse MDR by inhibiting epidermal growth factor (EGF) receptor (EGFR) and secondary inhibiting ATP-binding cassette, sub-family B member 1(ABCB1) and ATP-binding cassette, sub-family G (WHITE), member 2 (ABCG2). Our data showed that the expression of LRIG1 was significantly higher in O6-methylguanine DNA methyltransferase (MGMT) Promoter Methylation positive glioblastoma tissues compared to MGMT Promoter Methylation negative glioblastoma tissues. In addition, we found that LRIG1 expression was significantly decreased in MDR cells U251/TMZ compared to U251cells. Our results demonstrated that over-expression of LRIG1 can reverse the MDR. The expression of ABCB1 and ABCG2 were markedly suppressed when LRIG1 was over-expressed, supporting the negative relationship between LRIG1 level and ABCB1 and ABCG2 level in human specimen. Furthermore, we found that LRIG1 downregulated ABCB1 and ABCG2 through suppressing EGFR expression. In case of EGFR knockdown, the effect of LRIG1 on regulating MDR, ABCB1 and ABCG2 was partially compromised. Our results, for the first time, showed that LRIG1 can reverse MDR in glioblastoma, by negatively regulating EGFR and secondary suppressing the levels of ABCB1 and ABCG2.

ARRY-334543 reverses multidrug resistance by antagonizing the activity of ATP-binding cassette subfamily G member 2

ARRY-334543 is a small molecule inhibitor of ErbB1 and ErbB2 tyrosine kinases. We conducted this study to determine whether ARRY-334543 can enhance the efficacy of conventional anticancer drugs through interaction with ABC transporters. Lung cancer cell line NCI-H460 and its ABCG2-overexpressing NCI-H460/MX20, as well as the ABCG2-, ABCB1-, and ABCC10-overexpressing transfected cell lines were used for the reversal study. Our results demonstrated that ARRY-334543 (1.0 μM) significantly reversed ABCG2-mediated multidrug resistance (MDR) by directly inhibiting the drug efflux function of ABCG2, resulting in the elevated intracellular accumulation of chemotherapeutic drugs in the ABCG2-overexpressing cell lines. In addition, in isolated membranes, ARRY-334543 stimulated ATPase activity and inhibited photolabeling of ABCG2 with [(125)I]-iodoarylazidoprazosin in a concentration-dependent manner indicating that this drug directly interacts at the drug-binding pocket of this transporter. ARRY-334543 (1.0 μM) only slightly reversed ABCB1- and partially reversed ABCC10-mediated MDR suggesting that it exhibits high affinity toward ABCG2. Moreover, homology modeling predicted the binding conformation of ARRY-334543 at Arg482 centroid-based grid of ABCG2. However, ARRY-334543 at reversal concentrations did not affect the expression level of ABCG2, AKT and ERK1/2 and regulate the re-localization of ABCG2. We conclude that ARRY-334543 significantly reverses drug resistance mediated by ABCG2.

Heterocyclic cyclohexanone monocarbonyl analogs of curcumin can inhibit the activity of ATP-binding cassette transporters in cancer multidrug resistance

Curcumin (CUR) is a phytochemical that inhibits the xenobiotic ABC efflux transporters implicated in cancer multidrug resistance (MDR), such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins 1 and 5 (MRP1 and MRP5). The use of CUR in the clinic however, is complicated by its instability and poor pharmacokinetic profile. Monocarbonyl analogs of CUR (MACs) are compounds without CUR's unstable β-diketone moiety and were reported to have improved stability and in vivo disposition. Whether the MACs can be used as MDR reversal agents is less clear, as the absence of a β-diketone may negatively impact transporter inhibition. In this study, we investigated 23 heterocyclic cyclohexanone MACs for inhibitory effects against P-gp, BCRP, MRP1 and MRP5. Using flow cytometry and resistance reversal assays, we found that many of these compounds inhibited the transport activity of the ABC transporters investigated, often with much greater potency than CUR. Overall the analogs were most effective at inhibiting BCRP and we identified three compounds, A12 (2,6-bis((E)-2,5-dimethoxy-benzylidene)cyclohexanone), A13 (2,6-bis((E)-4-hydroxyl-3-methoxybenzylidene)-cyclohexanone) and B11 (3,5-bis((E)-2-fluoro-4,5-dimethoxybenzylidene)-1-methylpiperidin-4-one), as the most promising BCRP inhibitors. These compounds inhibited BCRP activity in a non-cell line, non-substrate-specific manner. Their inhibition occurred by direct transporter interaction rather than modulating protein or cell surface expression. From these results, we concluded that MACs, such as the heterocyclic cyclohexanone analogs in this study, also have potential as MDR reversal agents and may be superior alternatives to the unstable parent compound, CUR.

Interactions of ABCG2 (BCRP) with epidermal growth factor receptor kinase inhibitors developed for molecular imaging

The objective of this study was to investigate in vitro the interactions between novel epidermal growth factor receptor kinase inhibitors (EGFRIs) developed for positron emission tomography (PET) imaging and the major efflux transporter breast cancer resistance protein (BCRP/ABCG2). Seven compounds were evaluated, using the ATPase activity assays and Madin-Darbey canine kidney (MDCK) cells overexpressing BCRP. Five of the tested compounds activated BCRP ATPase to various extent. Overexpression of BCRP conferred resistance to ML04, ML06, methoxy-Br-ML03, and PEG6-ML05 (IC₅₀ values for inhibition of control cell proliferation 2.1 ± 0.6, 2.2 ± 0.7, 1.8 ± 1.2, and 2.8 ± 3.1 μM, respectively, compared to >50 μM in MDCK-BCRP cells). At submicromolar concentrations, none of the EGFRIs significantly inhibited BCRP. Immunoblotting studies indicated that BCRP expression is evident in cell lines utilized for in vivo tumor grafting in small animal PET imaging studies. Thus, the intensity of EGFRIs radioactivity signals previously observed in tumor xenografts reflects an interplay between transporter-mediated distribution of the probe into tumor cells and target binding. Concomitant use of efflux transporter inhibitors may help distinguish between the contribution of efflux transport and EGFR binding to the tissue signal.

Abcc10 status affects mammary tumour growth, metastasis, and docetaxel treatment response

Background:

Resistance to chemotherapeutic agents is a major obstacle to cancer treatment. A group of ABC efflux pumps, the Multidrug Resistance Proteins, is a source of resistance. Herein, we investigated the role of ABCC10 in mammary tumours, given the important role we have defined for ABCC10 in transporting taxanes, and the recognition that some ABCC proteins have roles in tumour growth.

Methods:

ABCC10 expression was correlated to human breast cancer subtype using breast tissue microarrays. Real-time quantitative PCR and western blot analysis were used to examine ABCC10 expression in human breast cancer lines. Abcc10^−/− mice were crossed to MMTV-PyVmT mice to produce Abcc10^−/−vs Abcc10^+/+ mammary tumours and derivative cell lines. We used allograft and cellular assays to perform baseline and drug sensitization analysis of tumours and cell lines.

Results:

Clinical sample analyses indicated that ABCC10 was more highly expressed in Her2+ and ER+ than in Her2−, ER−, and triple-negative breast cancer. Unexpectedly, PyVmT; Abcc10^−/− tumours grew more rapidly than PyVmT; Abcc10^+/+ tumours and were associated with significantly reduced apoptosis and metastasis. PyVmT; Abcc10^−/− lines were less migratory than PyVmT; Abcc10^+/+ lines. Finally, we showed increased survival of docetaxel-treated MMTV-PyVmT; Abcc10^−/− mice compared with wild-type mice.

Conclusions:

These data identify roles for Abcc10 in breast cancer pathogenesis and in vivo docetaxel resistance.

The role of the dysfunctional akt-related pathway in cancer: establishment and maintenance of a malignant cell phenotype, resistance to therapy, and future strategies for drug development

Akt serine/threonine kinases, or PKB, are key players in the regulation of a wide variety of cellular activities, such as growth, proliferation, protection from apoptotic injuries, control of DNA damage responses and genome stability, metabolism, migration, and angiogenesis. The Akt-related pathway responds to the stimulation mediated by growth factors, cytokines, hormones, and several nutrients. Akt is present in three isoforms: Akt1, Akt2, and Akt3, which may be alternatively named PKB α , PKB β , and PKB γ , respectively. The Akt isoforms are encoded on three diverse chromosomes and their biological functions are predominantly distinct. Deregulations in the Akt-related pathway were observed in many human maladies, including cancer, cardiopathies, neurological diseases, and type-2 diabetes. This review discusses the significance of the abnormal activities of the Akt axis in promoting and sustaining malignancies, along with the development of tumor cell populations that exhibit enhanced resistance to chemo- and/or radiotherapy. This occurrence may be responsible for the relapse of the disease, which is unfortunately very often related to fatal consequences in patients.

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

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

A high-content assay strategy for the identification and profiling of ABCG2 modulators in live cells

ABCG2 is a member of the ATP-binding cassette (ABC) family of transporters, the overexpression of which has been implicated in resistance to various chemotherapeutic agents. Though a number of cell-based assays to screen for inhibitors have been reported, they do not provide a content-rich platform to discriminate toxic and autofluorescent compounds. To fill this gap, we developed a live high-content cell-based assay to identify inhibitors of ABCG2-mediated transport and, at the same time, assess their cytotoxic effect and potential optical interference. We used a pair of isogenic U87MG human glioblastoma cell lines, with one stably overexpressing the ABCG2 transporter. JC-1 (J-aggregate-forming lipophilic cation 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazol carbocyanine iodide) was selected as the optimal reporter substrate for ABCG2 activity, and the resulting assay was characterized by a Z' value of 0.50 and a signal-to-noise (S/N) ratio of 14 in a pilot screen of ∼ 7,000 diverse chemicals. The screen led to the identification of 64 unique nontoxic positives, yielding an initial hit rate of 1%, with 58 of them being confirmed activity. In addition, treatment with two selected confirmed positives suppressed the side population of U87MG-ABCG2 cells that was able to efflux the Hoechst dye as measured by flow cytometry, confirming that they constitute potent new ABCG2 transporter inhibitors. Our results demonstrate that our live cell and content-rich platform enables the rapid identification and profiling of ABCG2 modulators, and this new strategy opens the door to the discovery of compounds targeting the expression and/or trafficking of ABC transporters as an alternative to functional inhibitors that failed in the clinic.

Synthesis and biological evaluation of flavones and benzoflavones as inhibitors of BCRP/ABCG2

Multidrug resistance (MDR) often leads to a failure of cancer chemotherapy. Breast Cancer Resistance Protein (BCRP/ABCG2), a member of the superfamily of ATP binding cassette proteins has been found to confer MDR in cancer cells by transporting molecules with amphiphilic character out of the cells using energy from ATP hydrolysis. Inhibiting BCRP can be a solution to overcome MDR. We synthesized a series of flavones, 7,8-benzoflavones and 5,6-benzoflavones with varying substituents at positions 3, 3' and 4' of the (benzo)flavone structure. All synthesized compounds were tested for BCRP inhibition in Hoechst 33342 and pheophorbide A accumulation assays using MDCK cells expressing BCRP. All the compounds were further screened for their P-glycoprotein (P-gp) and Multidrug resistance-associated protein 1 (MRP1) inhibitory activity by calcein AM accumulation assay to check the selectivity towards BCRP. In addition most active compounds were investigated for their cytotoxicity. It was observed that in most cases 7,8-benzoflavones are more potent in comparison to the 5,6-benzoflavones. In general it was found that presence of a 3-OCH3 substituent leads to increase in activity in comparison to presence of OH or no substitution at position 3. Also, it was found that presence of 3',4'-OCH3 on phenyl ring lead to increase in activity as compared to other substituents. Compound 24, a 7,8-benzoflavone derivative was found to be most potent being 50 times selective for BCRP and showing very low cytotoxicity at higher concentrations.

Reversal of MRP7 (ABCC10)-mediated multidrug resistance by tariquidar

Multidrug resistance protein 7 (MRP7, ABCC10) is a recently discovered member of the ATP-binding cassette (ABC) family which are capable of conferring resistance to a variety of anticancer drugs, including taxanes and nucleoside analogs, in vivo. MRP7 is highly expressed in non-small cell lung cancer cells, and Mrp7-KO mice are highly sensitive to paclitaxel, making MRP7 an attractive chemotherapeutic target of non-small cell lung cancer. However, only a few inhibitors of MRP7 are currently identified, with none of them having progressed to clinical trials. We used MRP7-expressing cells to investigate whether tariquidar, a third generation inhibitor of P-glycoprotein, could inhibit MRP7-mediated multidrug resistance (MDR). We found that tariquidar, at 0.1 and 0.3 µM, significantly potentiated the sensitivity of MRP7-transfected HEK293 cells to MRP7 substrates and increased the intracellular accumulation of paclitaxel. We further demonstrated that tariquidar directly impaired paclitaxel efflux and could downregulate MRP7 protein expression in a concentration- and time-dependent manner after prolonged treatment. Our findings suggest that tariquidar, at pharmacologically achievable concentrations, reverses MRP7-mediated MDR through inhibition of MRP7 protein expression and function, and thus represents a promising therapeutic agent in the clinical treatment of chemoresistant cancer patients.