Gene Summary

Gene:ABCG2; ATP binding cassette subfamily G member 2 (Junior blood group)
Aliases: MRX, MXR, ABCP, BCRP, BMDP, MXR1, ABC15, BCRP1, CD338, GOUT1, MXR-1, CDw338, UAQTL1, EST157481
Summary:The membrane-associated protein encoded by this gene is included in the superfamily of ATP-binding cassette (ABC) transporters. ABC proteins transport various molecules across extra- and intra-cellular membranes. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, White). This protein is a member of the White subfamily. Alternatively referred to as a breast cancer resistance protein, this protein functions as a xenobiotic transporter which may play a major role in multi-drug resistance. It likely serves as a cellular defense mechanism in response to mitoxantrone and anthracycline exposure. Significant expression of this protein has been observed in the placenta, which may suggest a potential role for this molecule in placenta tissue. Multiple transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Apr 2012]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:ATP-binding cassette sub-family G member 2
Source:NCBIAccessed: 16 March, 2017


What does this gene/protein do?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 16 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 16 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (7)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: ABCG2 (cancer-related)

Onishi H, Suyama K, Yamasaki A, et al.
CD24 Modulates Chemosensitivity of MCF-7 Breast Cancer Cells.
Anticancer Res. 2017; 37(2):561-565 [PubMed] Related Publications
The role of cluster of differentiation (CD) 24 in breast cancer remains unclear; previously, we showed that CD24 suppresses malignant phenotypes by inactivating Hedgehog signaling through signal transducer and activator of transcription (STAT) 1 inhibition. In this study, we examined how CD24 affects chemosensitivity in breast cancer cells. The CD44(+)CD24(+) breast cancer cell line MCF-7 was transfected with CD24 with/without STAT1 siRNA, and chemosensitivity to 5-fluorouracil (5-FU) and cis-diamminedichloroplatinum (CDDP) was measured. CD24 inhibition reduced chemosensitivity to 5-FU, while STAT1 inhibition did not affect chemosensitivity to 5-FU in CD24 siRNA-transfected cells. Conversely, CD24 inhibition did not affect chemosensitivity to CDDP, while STAT1 inhibition reduced chemosensitivity to CDDP in CD24 siRNA-transfected cells. STAT1 inhibition, but not CD24 inhibition, reduced expression of the ATP-binding cassette (ABC) transporter genes, ABCB1 and ABCG2. In conclusion, CD24 inhibition may modulate chemosensitivity according to drug type, but ABC transporter expression appears not to contribute to this mechanism. This study contributes to determining the role of CD24 in breast cancer.

Pak PJ, Kang BH, Park SH, et al.
Antitumor effects of herbal mixture extract in the pancreatic adenocarcinoma cell line PANC1.
Oncol Rep. 2016; 36(5):2875-2883 [PubMed] Related Publications
A recent study showned that complementary medicine is gradually gaining wide acceptance. In the present study, the herbal mixture extract (H3) composed of 3 oriental herbal plants was investigated for anticancer activity in vitro and in vivo. H3 inhibited PANC1 cell growth by promoting G0/G1 arrest (11% increase) and apoptotic cell death (9% increase). H3 also suppressed stem cell-like side population cells (4% decrease) and migration activity (24% decrease). In contrast, gemcitabine decreased side population cells and migration activity by 3 and 11%, respectively. These effects of H3 and gemcitabine were further studied by examining the expression of apoptosis-associated genes (CXCR4, JAK2 and XIAP) and stem cell-associated genes (ABCG2, POU5F1 and SOX2). We also found that H3 suppressed tumor growth by 46% in a PANC1‑xenograft model, while gemcitabine caused a 36% decrease. The antitumor effects of H3 were confirmed by western blot analysis for COX-2 and cytochrome c expression. Furthermore, necrotic cell death and erythrocyte-containing cavities were detected in tumor tissue by hematoxylin and eosin (H&E) staining. Notably, the combinatorial therapy (H3 and gemcitabine) increased tumor growth compared to that in the control. In conclusion, the present study shows that H3 has promise as a therapeutic agent against pancreatic cancer and its cancer stem cells.

Kobayashi M, Funayama R, Ohnuma S, et al.
Wnt-β-catenin signaling regulates ABCC3 (MRP3) transporter expression in colorectal cancer.
Cancer Sci. 2016; 107(12):1776-1784 [PubMed] Free Access to Full Article Related Publications
We determined the gene expression profiles for 48 ATP binding cassette (ABC) transporters in matched colon cancer and normal colon tissues in order to provide insight into the mechanisms underlying expression of transporters related to colon carcinogenesis. The expression of ABCB1, ABCC1, ABCC2, ABCC3, and ABCG2 was altered in association with colon carcinogenesis. Among these transporters, the expression of ABCC3 was repressed by Wnt signaling pathway in colon cancer cell lines. Knockdown of the pathway components transcription factor 7-like 2 (TCF7L2) or β-catenin thus increased ABCC3 expression, whereas activation of Wnt signaling with inhibitors of glycogen synthase kinase-3β (GSK-3β) reduced it. ChIP and luciferase reporter assays also showed that TCF7L2 binds to the ABCC3 locus and regulates its expression. Finally, overexpression of ABCC3 in colon cancer cells conferred resistance to anticancer drug-induced cytotoxicity. Our data thus suggest that Wnt signaling represses ABCC3 expression during colon carcinogenesis, and that subsequent upregulation of ABCC3 expression during drug treatment might contribute to acquired drug resistance.

Slemc L, Kunej T
Transcription factor HIF1A: downstream targets, associated pathways, polymorphic hypoxia response element (HRE) sites, and initiative for standardization of reporting in scientific literature.
Tumour Biol. 2016; 37(11):14851-14861 [PubMed] Related Publications
Hypoxia-inducible factor-1α (HIF-1α) has crucial role in adapting cells to hypoxia through expression regulation of many genes. Identification of HIF-1α target genes (HIF-1α-TGs) is important for understanding the adapting mechanism. The aim of the present study was to collect known HIF-1α-TGs and identify their associated pathways. Targets and associated genomics data were retrieved using PubMed, WoS ( ), HGNC ( ), NCBI ( ), Ensemblv.84 ( ), DAVID Bioinformatics Resources ( /), and Disease Ontology database ( ). From 51 papers, we collected 98 HIF-1α TGs found to be associated with 20 pathways, including metabolism of carbohydrates and pathways in cancer. Reanalysis of genomic coordinates of published HREs (hypoxia response elements) revealed six polymorphisms within HRE sites (HRE-SNPs): ABCG2, ACE, CA9, and CP. Due to large heterogeneity of results presentation in scientific literature, we also propose a first step towards reporting standardization of HIF-1α-target interactions consisting of ten relevant data types. Suggested minimal checklist for reporting will enable faster development of a complete catalog of HIF-1α-TGs, data sharing, bioinformatics analyses, and setting novel more targeted hypotheses. The proposed format for data standardization is not yet complete but presents a baseline for further optimization of the protocol with additional details, for example, regarding the experimental validation.

Ma Y, Wang B, Guo Y, et al.
Inhibition of miR-196a affects esophageal cancer cell growth in vitro.
Biomed Pharmacother. 2016; 84:22-27 [PubMed] Related Publications
Esophageal cancer (EC) is one of the most common causes of cancer-related mortality worldwide. Several oncogenes such as miR-196a have been implicated in the carcinogenesis and progression of EC. The purpose of this study was to determine the effects of anti-miR-196a on the growth and survival of human EC cells in vitro. We found that miR-196a was highly expressed in both TE1 and EC109 cells and that miR-196a knockdown inhibited cell proliferation and migration. Furthermore, miR-196a knockdown sensitized EC cells to radiation treatment and chemotherapy. Inhibition of miR-196a also altered cell cycle progression and induced G2/M arrest, which was related to changes in the levels of cyclin B1. ABCG2, which was highly expressed in untransfected EC cells, was inhibited by miR-196a knockdown. Thus, our results confirm the fact that miR-196a is highly involved in the biological behavior of EC progression in vitro. We conclude that miR-196a is a useful biological marker and potential therapeutic target for the clinical treatment of human EC.

Cai J, Peng T, Wang J, et al.
Isolation, Culture and Identification of Choriocarcinoma Stem-Like Cells from the Human Choriocarcinoma Cell-Line JEG-3.
Cell Physiol Biochem. 2016; 39(4):1421-32 [PubMed] Related Publications
BACKGROUND/AIMS: Cancer stem cells (CSCs) exhibit enhanced proliferative capacity and resistance to chemotherapy; however, choriocarcinoma CSCs have not yet been reported. In this study the human choriocarcinoma cell line JEG-3 was cultured in serum free media, and the characteristics of suspension and parental adherent JEG-3 cells were compared.
METHODS: Cell proliferation, colony-formation, soft agar clonogenicity, and transwell invasion assays were performed in vitro, and tumor xenografts in BALB/c nude mice were used to evaluate stem cell properties.
RESULTS: In serum-supplemented medium (SSM), JEG-3 cells were 4.51 ± 1.71% CD44+, 7.67 ± 2.67% CD133+, and 13.85 ± 2.95% ABCG2+. In serum-free medium (SFM), the expression of these markers increased to 53.08 ± 3.15%, 47.40 ± 2.67%, and 78.70 ± 7.16%, respectively. Moreover, suspension JEG-3 cells exhibited enhanced colony-formation capability as well as invasive and proliferative ability in vitro, alongside enhanced tumorigenic properties in vivo. Suspension JEG-3 cells also exhibited resistance to the chemotherapeutic drugs methotrexate, fluorouracil and etoposide. When seeded in serum supplemented medium, suspension JEG-3 cells readopted an adherent phenotype and continued to differentiate with no significant difference in the morphology between suspension and parent cells.
CONCLUSION: In this study, choriocarcinoma stem-like cells (CSLCs) were isolated from the human choriocarcinoma JEG-3 cell line by SFM culture and characterized.

Arrigoni E, Galimberti S, Petrini M, et al.
ATP-binding cassette transmembrane transporters and their epigenetic control in cancer: an overview.
Expert Opin Drug Metab Toxicol. 2016; 12(12):1419-1432 [PubMed] Related Publications
INTRODUCTION: Members of the ATP-binding cassette (ABC) transmembrane transporters control the passage of several substrates across cell membranes, including drugs. This means that ABC transporters may exert a significant influence on the kinetics and dynamics of pharmacological agents, being responsible for the occurrence of multidrug-resistant (MDR) phenotype. Pharmacogenetic analyses have shed light on gene expression and polymorphisms as possible markers predictive of transporter activity. However, a non-negligible part of the variability in drug pharmacokinetics and pharmacodynamics still remains. Further research has demonstrated that different epigenetic mechanisms exert a coordinated control over ABC genes, and on the corresponding MDR phenotype. Areas covered: DNA methylation and histone modifications (namely acetylation, methylation, phosphorylation, etc.) significantly impact gene expression, as well as noncoding RNA molecules that are involved in the post-transcriptional control of the ABC transporters ABCB1, ABCC1 and ABCG2. We describe the epigenetic mechanisms of gene expression control for ABC transporters and their relevant association with the MDR phenotype in human cancer. Expert opinion: The clinical meaning of those observations is discussed in the review, highlighting the importance of the epigenetic control of the ABC transporters for the clinical therapeutic outcomes that despite their effects and applications, requires further investigation.

Vishnoi K, Mahata S, Tyagi A, et al.
Human papillomavirus oncoproteins differentially modulate epithelial-mesenchymal transition in 5-FU-resistant cervical cancer cells.
Tumour Biol. 2016; 37(10):13137-13154 [PubMed] Related Publications
Etiological role of viral proteins E6 and E7 of high-risk HPV in cervical carcinogenesis is well established. However, their contribution in chemoresistance and epithelial-mesenchymal transition (EMT) that leads to advanced metastatic lesions and chemoresistance is poorly defined. In the present study, contribution of viral oncoproteins in acquisition of EMT character during onset of chemoresistance was assessed. A chemoresistant cell line (SiHaCR) was developed from an established HPV16-positive cervical cancer cell line, SiHa, by escalating selection pressure of 5-fluorouracil (5-FU). Expression of Survivin, ABCG2, Snail, Slug, Twist, and Vimentin was examined in SiHa and SiHaCR cells by reverse transcriptase-PCR (RT-PCR) and immunoblotting assays. Mesenchymal phenotype in SiHaCR cells was confirmed by assessment of migration and invasion potentials. SiHaCR cells displayed elevated level of functional and molecular markers associated with chemoresistance (Survivin, ABCG2) and EMT (Snail, Slug, Twist, Vimentin) and reduced E-cadherin. SiHaCR also showed increased levels of HPV16 E6 and E7 transcripts. Specific silencing of HPV16 E6, but not E7 using corresponding siRNA, demonstrated a differential involvement of HPV oncogenes in manifestation of EMT. HPV16 E6 silencing resulted in reduction of Slug and Twist expression. However, the expression of Snail and Vimentin was only marginally affected. In contrast, there was an increase in the expression of E-cadherin. A reduced migration and invasion capabilities were observed only in E6-silenced SiHaCR cells, which further confirmed functional contribution of HPV16 E6 in manifestation of EMT. Taken together, our study demonstrated an active involvement of HPV16 E6 in regulation of EMT, which promotes chemoresistance in cervical cancer.

Lin S, Zhou S, Jiang S, et al.
NEK2 regulates stem-like properties and predicts poor prognosis in hepatocellular carcinoma.
Oncol Rep. 2016; 36(2):853-62 [PubMed] Related Publications
NEK2 has been estimated to play an important role in cancer progression. However, its relevance in hepatocellular carcinoma (HCC) has not yet been explored. Immunohistochemistry revealed NEK2 expression was upregulated in HCC. NEK2-positive hepatocellular carcinoma patients were associated with poor prognosis after surgery compared with NEK2-negative patients based on Kaplan-Meier curves. Deletion of NEK2 reduced self-renewal properties and chemotherapeutic resistance, and decreased the stemness associated genes in cell lines. NEK2 was associated with unfavorable outcomes in HCC patients, and was revealed to regulate self-renewal property by means of Wnt/β-catenin signaling, and chemotherapeutic resistance by preferential regulation of the expression of ABCG2 and ALDH1A1 in HCC cells.

Liu Y, Lu R, Gu J, et al.
Aldehyde dehydrogenase 1A1 up-regulates stem cell markers in benzo[a]pyrene-induced malignant transformation of BEAS-2B cells.
Environ Toxicol Pharmacol. 2016; 45:241-50 [PubMed] Related Publications
Recently, Aldehyde dehydrogenase 1A1 (ALDH1A1) has been proposed to be a common marker of cancer stem cells and can be induced by benzo[a]pyrene (B[a]P) exposure. However, the underlying mechanism of how ALDH1A1 contributes to B[a]P-induced carcinogenesis in human bronchial epithelial cells remains unclear. Here, we found that B[a]P up-regulated expression levels of stem cell markers (ABCG2, SOX2, c-Myc and Klf4), epithelial-mesenchymal transition (EMT) associated genes (SNAIL1, ZEB1, TWIST and β-CATENIN) and cancer-related long non-coding RNAs (lncRNAs; HOTAIR and MALAT-1) in malignant B[a]P-transformed human bronchial epithelial cells (BEAS-2B-T cells), and these up-regulations were dependent on increased expression of ALDH1A1. The inhibition of endogenous ALDH1A1 expression down-regulated expression levels of stem cell markers and reversed the malignant phenotype as well as reduced the chemoresistance of BEAS-2B-T cells. In contrast, the overexpression of ALDH1A1 in BEAS-2B cells increased the expression of stem cell markers, facilitated cell transformation, promoted migratory ability and enhanced the drug resistance of BEAS-2B cells. Overall, our data indicates that ALDH1A1 promotes a stemness phenotype and plays a critical role in the BEAS-2B cell malignant transformation induced by B[a]P.

Zambo I, Hermanova M, Zapletalova D, et al.
Expression of nestin, CD133 and ABCG2 in relation to the clinical outcome in pediatric sarcomas.
Cancer Biomark. 2016; 17(1):107-16 [PubMed] Related Publications
BACKGROUND: Nestin, CD133 and ABCG2 are recently discussed as putative markers, co-expression of which might determine a cancer stem cell (CSC) phenotype in sarcomas.
OBJECTIVE: Our study is focused on immunohistochemical analysis of nestin, CD133 and ABCG2 expression in rhabdomyosarcoma, Ewing sarcoma and osteosarcoma. Furthermore, we also analyzed the possible correlation of nestin, CD133 and ABCG2 expression levels with the patient outcome to identify potential prognostic values of these three putative CSC markers in the same cohorts.
METHODS: Using immunohistochemistry, expression of nestin, CD133 and ABCG2 was analyzed in 24 rhabdomyosarcoma, 22 Ewing sarcoma and 10 osteosarcoma tissue samples and expression levels of these markers were correlated with clinical outcome.
RESULTS: High nestin levels indicate poor prognosis in patients with Ewing sarcoma (P = 0.001), and high CD133 expression is associated with shorter survival in rhabdomyosarcoma patients (P = 0.002). In contrast, no significant relationship was found between ABCG2 expression and the clinical outcome.
CONCLUSIONS: Our analysis represents the first complex study of these three putative CSCs markers together in three different types of pediatric sarcomas and showed their possible prognostic values in these tumors.

Šemeláková M, Jendželovský R, Fedoročko P
Drug membrane transporters and CYP3A4 are affected by hypericin, hyperforin or aristoforin in colon adenocarcinoma cells.
Biomed Pharmacother. 2016; 81:38-47 [PubMed] Related Publications
Our previous results have shown that the combination of hypericin-mediated photodynamic therapy (HY-PDT) at sub-optimal dose with hyperforin (HP) (compounds of Hypericum sp.), or its stable derivative aristoforin (AR) stimulates generation of reactive oxygen species (ROS) leading to antitumour activity. This enhanced oxidative stress evoked the need for an explanation for HY accumulation in colon cancer cells pretreated with HP or AR. Generally, the therapeutic efficacy of chemotherapeutics is limited by drug resistance related to the overexpression of drug efflux transporters in tumour cells. Therefore, the impact of non-activated hypericin (HY), HY-PDT, HP and AR on cell membrane transporter systems (Multidrug resistance-associated protein 1-MRP1/ABCC1, Multidrug resistance-associated protein 2-MRP2/ABCC2, Breast cancer resistance protein - BCRP/ABCG2, P-glycoprotein-P-gp/ABCC1) and cytochrome P450 3A4 (CYP3A4) was evaluated. The different effects of the three compounds on their expression, protein level and activity was determined under specific PDT light (T0+, T6+) or dark conditions (T0- T6-). We found that HP or AR treatment affected the protein levels of MRP2 and P-gp, whereas HP decreased MRP2 and P-gp expression mostly in the T0+ and T6+ conditions, while AR decreased MRP2 in T0- and T6+. Moreover, HY-PDT treatment induced the expression of MRP1. Our data demonstrate that HP or AR treatment in light or dark PDT conditions had an inhibitory effect on the activity of individual membrane transport proteins and significantly decreased CYP3A4 activity in HT-29 cells. We found that HP or AR significantly affected intracellular accumulation of HY in HT-29 colon adenocarcinoma cells. These results suggest that HY, HP and AR might affect the efficiency of anti-cancer drugs, through interaction with membrane transporters and CYP3A4.

Jia M, Wei Z, Liu P, Zhao X
Silencing of ABCG2 by MicroRNA-3163 Inhibits Multidrug Resistance in Retinoblastoma Cancer Stem Cells.
J Korean Med Sci. 2016; 31(6):836-42 [PubMed] Free Access to Full Article Related Publications
To investigate the function and regulation mechanism of ATP-binding cassette, subfamily G, member 2 (ABCG2) in retinoblastoma cancer stem cells (RCSCs), a long-term culture of RCSCs from WERI-Rb1 cell line was successfully established based on the high expression level of ABCG2 on the surface of RCSCs. To further explore the molecular mechanism of ABCG2 on RCSCs, a microRNA that specifically targets ABCG2 was predicted. Subsequently, miR-3163 was selected and confirmed as the ABCG2-regulating microRNA. Overexpression of miR-3163 led to a significant decrease in ABCG2 expression. Additionally, ABCG2 loss-of-function induced anti-proliferation and apoptosis-promoting functions in RCSCs, and multidrug resistance to cisplatin, carboplatin, vincristine, doxorubicin, and etoposide was greatly improved in these cells. Our data suggest that miR-3163 has a significant impact on ABCG2 expression and can influence proliferation, apoptosis, and drug resistance in RCSCs. This work may provide new therapeutic targets for retinoblastoma.

Sribenja S, Natthasirikul N, Vaeteewoottacharn K, et al.
 Thymosin β10 as a predictive biomarker of response to 5-fluorouracil chemotherapy in cholangiocarcinoma.
Ann Hepatol. 2016 Jul-Aug; 15(4):577-85 [PubMed] Related Publications
UNLABELLED:  Introduction and aim. 5-Fluorouracil (5-FU) is the most commonly used chemotherapeutic drug in the treatment of cholangiocarcinoma (CCA). Since development of drug resistance to 5-FU in CCA patients is the primary cause of treatment failure, a better understanding of the mechanism of drug resistance of this cancer is essential to improve the efficacy of 5-FU in CCA therapy.
MATERIAL AND METHODS: A 5-FU resistant CCA cell line (M214-5FUR) for a comparative chemo-resistance study was established. Real time RT-PCR was used to determine gene expression levels. Cell cytotoxicity was measured by the MTT assay. Protein expression levels were detected by the immunofluorescene method.
RESULTS: It was found that 5-FU resistance was associated with the overexpression of T?10 in CCA cell lines. 5-FU treatment at various concentrations induced the expressions of T?10 and ABC transporters (ABCB1, ABCG2 ABCA3) in two CCA cell lines, KKU-M055 and KKU-M214. M214-5FUR, a 5-FU-resistant cell line, exhibited a 5-FU resistant phenotype with a 16-fold extremely high expression of T?10 and ABC transporters, as compared to the parental cells, KKU-M214. siRNA targeted to T?10 significantly reduced expression of ABC transporters tested in the M214-5FUR cells (P < 0.05).
CONCLUSIONS: The present novel findingsof T?10 connected with drug resistance as shown in this study provides a new insight for the therapeutic value of T?10 as a predictive biomarker of 5-FU chemoresistance. Inhibiting T?10 may be a valuable adjunct for suppression of ABC transporters and sensitizing chemotherapy treatment, especially 5-FU in CCA patients.

Yonemura Y, Canbay E, Ishibashi H, et al.
5-Aminolevulinic Acid Fluorescence in Detection of Peritoneal Metastases.
Asian Pac J Cancer Prev. 2016; 17(4):2271-5 [PubMed] Related Publications
BACKGROUND: The value of 5-aminolevulinic acid (ALA) in fluorescence detection of peritoneal metastases and the underlying mechanisms were evaluated in patients with peritoneal surface malignancies.
MATERIALS AND METHODS: Oral 5-ALA was administered at a concentration of 20 mg ⁄kg body weight with 50 ml of water 2 hours prior to surgery (n=115). The diagnostic value of 5-ALA based fluorescence production was evaluated following white light inspection during prior to cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. Then, peptide transporter PEPT1 (ALA influx transporter) and ATP-binding cassette transporter ABCG2 (porphyrin efflux transporter) gene expression was determined with quantitative real time (qRT)-PCR and pathological diagnoses confirmed for all tissue samples.
RESULTS: The 5-ALA based photodynamic detection rate was 17% for appendiceal mucinous neoplasms, 54% for colorectal cancers, 33% for gastric cancers, 67% for diffuse malign peritoneal mesotheliomas, and 89% for epithelial ovarian cancer of peritoneal metastases. 5-ALA was detected in all cases of peritoneal metastases originating from cholangiocarcinomas whereas it was not able to detect any in granulosa cell and gastrointestinal stromal tumor cases. Furthermore, PEPT1 was overexpressed whereas ABCG2 expression was downregulated in tumors detected with fluorescence.
CONCLUSIONS: 5-ALA provided 100% specificity and high sensitivity to detect peritoneal metastases in subgroups of patients with peritoneal surface mailgnancies. ALA influx transporter PEPT1 and porphyrin efflux transporter ABCG2 genes are important in tumor specific 5-ALA induced fluorescence in vivo. Further studies should clarify diagnostic utility of 5-ALA in peritoneal surface malignancies.

Wang WJ, Sui H, Qi C, et al.
Ursolic acid inhibits proliferation and reverses drug resistance of ovarian cancer stem cells by downregulating ABCG2 through suppressing the expression of hypoxia-inducible factor-1α in vitro.
Oncol Rep. 2016; 36(1):428-40 [PubMed] Related Publications
Hypoxia in tumors is closely related to drug resistance. It has not been verified whether hypoxia-inducible factor-1α (HIF-1α) or ABCG2 is related to hypoxia-induced resistance. Ursolic acid (UA), when used in combination with cisplatin can significantly increase the sensitivity of ovarian cancer stem cells (CSCs) to cisplatin, but the exact mechanism is unknown. The cell growth inhibitory rate of cisplatin under different conditions was evaluated using Cell Counting Kit-8 (CCK-8) in adherence and sphere cells (SKOV3, A2780, and HEY). The expression of HIF-1α and ABCG2 was tested using quantitative PCR, western blotting, and immuno-fluorescence under different culture conditions and treated with UA. Knockdown of HIF-1α by shRNA and LY294002 was used to inhibit the activity of PI3K/Akt pathway. Ovarian CSCs express stemness-related genes and drug resistance significantly higher than normal adherent cells. Under hypoxic conditions, the ovarian CSCs grew faster and were more drug resistant than under normoxia. UA could inhibit proliferation and reverse the drug resistance of ovarian CSC by suppressing ABCG2 and HIF-1α under different culture conditions. HIF-1α inhibitor YC-1 combined with UA suppressed the stemness genes and ABCG2 under hypoxic condition. The PI3K/Akt signaling pathway activation plays an important functional role in UA-induced downregulation of HIF-1α and reduction of ABCG2. UA inhibits the proliferation and reversal of drug resistance in ovarian CSCs by suppressing the expression of downregulation of HIF-1α and ABCG2.

Wu H, Zhang J, Shi H
Expression of cancer stem markers could be influenced by silencing of p16 gene in HeLa cervical carcinoma cells.
Eur J Gynaecol Oncol. 2016; 37(2):221-5 [PubMed] Related Publications
Effect of the tumor suppression gene p16 on the biological characteristics of HeLa cervical carcinoma cells was explored. The expression of p16 protein was increased in HeLa tumor sphere cells, and no significant difference in tumor spheres from the first to the fourth passages. Compared with those of parental HeLa cells, the proportion of CD44+/CD24- and ABCG2+ cells increased significantly in tumor spheres. However after the cells were silenced by the p16-sh289 vector, expression of P16 protein and the cell number of CD44+/CD24- and ABCG2+ decreased. Moreover, HeLa cells with p16 gene silencing showed decreased abilities of sphere formation and matrigel invasion. More HeLa cells with p16 gene silence were needed for tumor formation in nude mice. Tumor size and weight in mouse model established with p16 gene silenced HeLa cells were less than those with HeLa parental cell model. The present results indicate that silencing of the p16 gene inhibits expression of cancer stem cell markers and tumorigenic ability of HeLa cells.

Seo EJ, Saeed M, Law BY, et al.
Pharmacogenomics of Scopoletin in Tumor Cells.
Molecules. 2016; 21(4):496 [PubMed] Related Publications
Drug resistance and the severe side effects of chemotherapy necessitate the development of novel anticancer drugs. Natural products are a valuable source for drug development. Scopoletin is a coumarin compound, which can be found in several Artemisia species and other plant genera. Microarray-based RNA expression profiling of the NCI cell line panel showed that cellular response of scopoletin did not correlate to the expression of ATP-binding cassette (ABC) transporters as classical drug resistance mechanisms (ABCB1, ABCB5, ABCC1, ABCG2). This was also true for the expression of the oncogene EGFR and the mutational status of the tumor suppressor gene, TP53. However, mutations in the RAS oncogenes and the slow proliferative activity in terms of cell doubling times significantly correlated with scopoletin resistance. COMPARE and hierarchical cluster analyses of transcriptome-wide mRNA expression resulted in a set of 40 genes, which all harbored binding motifs in their promoter sequences for the transcription factor, NF-κB, which is known to be associated with drug resistance. RAS mutations, slow proliferative activity, and NF-κB may hamper its effectiveness. By in silico molecular docking studies, we found that scopoletin bound to NF-κB and its regulator IκB. Scopoletin activated NF-κB in a SEAP-driven NF-κB reporter cell line, indicating that NF-κB might be a resistance factor for scopoletin. In conclusion, scopoletin might serve as lead compound for drug development because of its favorable activity against tumor cells with ABC-transporter expression, although NF-κB activation may be considered as resistance factor for this compound. Further investigations are warranted to explore the full therapeutic potential of this natural product.

Saeed ME, Meyer M, Hussein A, Efferth T
Cytotoxicity of South-African medicinal plants towards sensitive and multidrug-resistant cancer cells.
J Ethnopharmacol. 2016; 186:209-23 [PubMed] Related Publications
ETHNOPHARMACOLOGICAL RELEVANCE: Traditional medicine plays a major role for primary health care worldwide. Cancer belongs to the leading disease burden in industrialized and developing countries. Successful cancer therapy is hampered by the development of resistance towards established anticancer drugs.
AIM: In the present study, we investigated the cytotoxicity of 29 extracts from 26 medicinal plants of South-Africa against leukemia cell lines, most of which are used traditionally to treat cancer and related symptoms.
MATERIAL AND METHODS: We have investigated the plant extracts for their cytotoxic activity towards drug-sensitive parental CCRF-CEM leukemia cells and their multidrug-resistant P-glycoprotein-overexpressing subline, CEM/ADR5000 by means of the resazurin assay. A panel of 60 NCI tumor cell lines have been investigated for correlations between selected phytochemicals from medicinal plants and the expression of resistance-conferring genes (ABC-transporters, oncogenes, tumor suppressor genes).
RESULTS: Seven extracts inhibited both cell lines (Acokanthera oppositifolia, Hypoestes aristata, Laurus nobilis, Leonotis leonurus, Plectranthus barbatus, Plectranthus ciliates, Salvia apiana). CEM/ADR5000 cells exhibited a low degree of cross-resistance (3.35-fold) towards the L. leonurus extract, while no cross-resistance was observed to other plant extracts, although CEM/ADR5000 cells were highly resistant to clinically established drugs. The log10IC50 values for two out of 14 selected phytochemicals from these plants (acovenoside A and ouabain) of 60 tumor cell lines were correlated to the expression of ABC-transporters (ABCB1, ABCB5, ABCC1, ABCG2), oncogenes (EGFR, RAS) and tumor suppressors (TP53). Sensitivity or resistance of the cell lines were not statistically associated with the expression of these genes, indicating that multidrug-resistant, refractory tumors expressing these genes may still respond to acovenoside A and ouabain.
CONCLUSION: The bioactivity of South African medicinal plants may represent a basis for the development of strategies to treat multidrug-resistant tumors either by phytotherapeutic approaches with whole plant preparations or by classical drug development with isolated compounds such as acovenoside A or ouabain.

Rigalli JP, Tocchetti GN, Arana MR, et al.
The phytoestrogen genistein enhances multidrug resistance in breast cancer cell lines by translational regulation of ABC transporters.
Cancer Lett. 2016; 376(1):165-72 [PubMed] Related Publications
Breast cancer is the most frequent malignancy in women. Multidrug resistance due to overexpression of ABC drug transporters is a common cause of chemotherapy failure and disease recurrence. Genistein (GNT) is a phytoestrogen present in soybeans and hormone supplements. We investigated the effect of GNT on the expression and function of ABC transporters in MCF-7 and MDA-MB-231 breast cancer cell lines. Results demonstrated an induction at the protein level of ABCC1 and ABCG2 and of ABCC1 in MCF-7 and MDA-MB-231, respectively. MCF-7 cells showed a concomitant increase in doxorubicin and mitoxantrone efflux and resistance, dependent on ABCG2 activity. ABCC1 induction by GNT in MDA-MB-231 cells modified neither drug efflux nor chemoresistance due to simultaneous acute inhibition of the transporter activity by GNT. All inductions took place at the translational level, as no increment in mRNA was observed and protein increase was prevented by cycloheximide. miR-181a, already demonstrated to inhibit ABCG2 translation, was down-regulated by GNT, explaining translational induction. Effects were independent of classical estrogen receptors. Results suggest potential nutrient-drug interactions that could threaten chemotherapy efficacy, especially in ABCG2-expressing tumors treated with substrates of this transporter.

Huang JS, Yao CJ, Chuang SE, et al.
Honokiol inhibits sphere formation and xenograft growth of oral cancer side population cells accompanied with JAK/STAT signaling pathway suppression and apoptosis induction.
BMC Cancer. 2016; 16:245 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Eliminating cancer stem cells (CSCs) has been suggested for prevention of tumor recurrence and metastasis. Honokiol, an active compound of Magnolia officinalis, had been proposed to be a potential candidate drug for cancer treatment. We explored its effects on the elimination of oral CSCs both in vitro and in vivo.
METHODS: By using the Hoechst side population (SP) technique, CSCs-like SP cells were isolated from human oral squamous cell carcinoma (OSCC) cell lines, SAS and OECM-1. Effects of honokiol on the apoptosis and signaling pathways of SP-derived spheres were examined by Annexin V/Propidium iodide staining and Western blotting, respectively. The in vivo effectiveness was examined by xenograft mouse model and immunohistochemical tissue staining.
RESULTS: The SP cells possessed higher stemness marker expression (ABCG2, Ep-CAM, Oct-4 and Nestin), clonogenicity, sphere formation capacity as well as tumorigenicity when compared to the parental cells. Treatment of these SP-derived spheres with honokiol resulted in apoptosis induction via Bax/Bcl-2 and caspase-3-dependent pathway. This apoptosis induction was associated with marked suppression of JAK2/STAT3, Akt and Erk signaling pathways in honokiol-treated SAS spheres. Consistent with its effect on JAK2/STAT3 suppression, honokiol also markedly inhibited IL-6-mediated migration of SAS cells. Accordingly, honokiol dose-dependently inhibited the growth of SAS SP xenograft and markedly reduced the immunohistochemical staining of PCNA and endothelial marker CD31 in the xenograft tumor.
CONCLUSIONS: Honokiol suppressed the sphere formation and xenograft growth of oral CSC-like cells in association with apoptosis induction and inhibition of survival/proliferation signaling pathways as well as angiogenesis. These results suggest its potential as an integrative medicine for combating oral cancer through targeting on CSCs.

Karthikeyan C, Malla R, Ashby CR, et al.
Pyrimido[1″,2″:1,5]pyrazolo[3,4-b]quinolines: Novel compounds that reverse ABCG2-mediated resistance in cancer cells.
Cancer Lett. 2016; 376(1):118-26 [PubMed] Related Publications
Overexpression of ATP-binding cassette transporter (ABC) subfamily G2 in cancer cells is known to elicit a MDR phenotype, ultimately resulting in cancer chemotherapy failure. Here, we report, for the first time, the effect of eight novel pyrimido[1″,2″:1,5]pyrazolo[3,4-b]quinoline (IND) derivatives that inhibit ABCG2 transporter restoring cancer cell chemosensitivity. IND -4, -5, -6, -7, and -8, at 10 µM, and nilotinib at 5 µM, significantly potentiated (8-10 fold) the cytotoxicity of the ABCG2 substrates mitoxantrone (MX) and doxorubicin in HEK293 cells overexpressing ABCG2 transporter, MX (~14 fold) in MX-resistant NCI-H460/MX-20 small cell lung cancer, and of topotecan (~7 fold) in S1-M1-80 colon cancer cells which all stably expressing ABCG2. In contrast, cytotoxicity of cisplatin, which is not an ABCG2 substrate, was not altered. IND-5,-6,-7, and -8 significantly increased the accumulation of rhodamine-123 in multidrug resistant NCI-H460/MX-20 cells overexpressing ABCG2. Both IND-7 and -8, the most potent ABCG2 inhibitors, had the highest affinities for the binding sites of ABCG2 in modeling studies. In conclusion, the beneficial actions of new class of agents warrant further development as potential MDR reversal agents for clinical anticancer agents that suffer from ABCG2-mediated MDR insensitivity.

Campos-Arroyo D, Maldonado V, Bahena I, et al.
Probenecid Sensitizes Neuroblastoma Cancer Stem Cells to Cisplatin.
Cancer Invest. 2016; 34(3):155-66 [PubMed] Related Publications
We used both in vitro cultures of neuroblastoma cell lines and nude-mice xenotransplants to explore the effects of co-administration of cisplatin and probenecid. Probenecid sensitized neuroblastoma cells, including tumor cells with stem features, to the effects of cisplatin, both in vitro and in vivo. This effect was mediated by an increase in the apoptotic cell death and a concomitant decrease in cell proliferation. This effect is accompanied by modulation of the mRNA and protein of the drug efflux transporters MDR1, MRP2, and BCRP. The co-administration of probenecid with cisplatin should be explored as a possible therapeutic strategy.

Harwood MD, Neuhoff S, Rostami-Hodjegan A, Warhurst G
Breast Cancer Resistance Protein Abundance, but Not mRNA Expression, Correlates With Estrone-3-Sulfate Transport in Caco-2.
J Pharm Sci. 2016; 105(4):1370-5 [PubMed] Related Publications
Transporter mRNA and protein expression data are used to extrapolate in vitro transporter kinetics to in vivo drug disposition predictions. Breast cancer resistance protein (BCRP) possesses broad substrate specificity; therefore, understanding BCRP expression-activity relationships are necessary for the translation to in vivo. Bidirectional transport of estrone-3-sulfate (E-3-S), a BCRP probe, was evaluated with respect to relative BCRP mRNA expression and absolute protein abundance in 10- and 29-day cultured Caco-2 cells. BCRP mRNA expression was quantified by real-time PCR against a housekeeper gene, Cyclophilin A. The BCRP protein abundance in total membrane fractions was quantified by targeted proteomics, and [(3)H]-E-3-S bidirectional transport was determined in the presence or absence of Ko143, a potent BCRP inhibitor. BCRP mRNA expression was 1.5-fold higher in 29- versus 10-day cultured cells (n = 3), whereas a 2.4-fold lower (p < 0.001) BCRP protein abundance was observed in 29- versus 10-day cultured cells (1.28 ± 0.33 and 3.06 ± 0.22 fmol/μg protein, n = 6, respectively). This correlated to a 2.45-fold lower (p < 0.01) efflux ratio for E-3-S in 29- versus 10-day cultured cells (8.97 ± 2.51 and 3.32 ± 0.66, n = 6, respectively). Caco-2 cell BCRP protein abundance, but not mRNA levels, correlates with BCRP activity, suggesting that extrapolation strategies incorporating BCRP protein abundance-activity relationships may be more successful.

Bai XY, Zhang XC, Yang SQ, et al.
Blockade of Hedgehog Signaling Synergistically Increases Sensitivity to Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors in Non-Small-Cell Lung Cancer Cell Lines.
PLoS One. 2016; 11(3):e0149370 [PubMed] Free Access to Full Article Related Publications
Aberrant activation of the hedgehog (Hh) signaling pathway has been implicated in the epithelial-to-mesenchymal transition (EMT) and cancer stem-like cell (CSC) maintenance; both processes can result in tumor progression and treatment resistance in several types of human cancer. Hh cooperates with the epidermal growth factor receptor (EGFR) signaling pathway in embryogenesis. We found that the Hh signaling pathway was silenced in EGFR-TKI-sensitive non-small-cell lung cancer (NSCLC) cells, while it was inappropriately activated in EGFR-TKI-resistant NSCLC cells, accompanied by EMT induction and ABCG2 overexpression. Upregulation of Hh signaling through extrinsic SHH exposure downregulated E-cadherin expression and elevated Snail and ABCG2 expression, resulting in gefitinib tolerance (P < 0.001) in EGFR-TKI-sensitive cells. Blockade of the Hh signaling pathway using the SMO antagonist SANT-1 restored E-cadherin expression and downregulate Snail and ABCG2 in EGFR-TKI-resistant cells. A combination of SANT-1 and gefitinib markedly inhibited tumorigenesis and proliferation in EGFR-TKI-resistant cells (P < 0.001). These findings indicate that hyperactivity of Hh signaling resulted in EGFR-TKI resistance, by EMT introduction and ABCG2 upregulation, and blockade of Hh signaling synergistically increased sensitivity to EGFR-TKIs in primary and secondary resistant NSCLC cells. E-cadherin expression may be a potential biomarker of the suitability of the combined application of an Hh inhibitor and EGFR-TKIs in EGFR-TKI-resistant NSCLCs.

Low SK, Fukunaga K, Takahashi A, et al.
Association Study of a Functional Variant on ABCG2 Gene with Sunitinib-Induced Severe Adverse Drug Reaction.
PLoS One. 2016; 11(2):e0148177 [PubMed] Free Access to Full Article Related Publications
Sunitinib is a tyrosine kinase inhibitor and used as the first-line treatment for advanced renal cell carcinoma (RCC). Nevertheless, inter-individual variability of drug's toxicity was often observed among patients who received sunitinib treatment. This study is to investigate the association of a functional germline variant on ABCG2 that affects the pharmacokinetics of sunitinib with sunitinib-induced toxicity of RCC patients in the Japanese population. A total of 219 RCC patients were recruited to this pharmacogenetic study. ABCG2 421C>A (Q141K) was genotyped by using PCR-Invader assay. The associations of both clinical and genetic variables were evaluated with logistic regression analysis and subsequently receiver operating characteristic (ROC) curve was plotted. About 43% (92/216) of RCC patients that received sunitinib treatment developed severe grade 3 or grade 4 thrombocytopenia according to the National Cancer Institute-Common Terminology Criteria for Adverse Events version 3.0, the most common sunitinib-induced adverse reaction in this study. In the univariate analysis, both age (P = 7.77x10(-3), odds ratio (OR) = 1.04, 95%CI = 1.01-1.07) and ABCG2 421C>A (P = 1.87x10(-2), OR = 1.71, 95%CI = 1.09-2.68) showed association with sunitinib-induced severe thrombocytopenia. Multivariate analysis indicated that the variant ABCG2 421C>A is suggestively associated with severe thrombocytopenia (P = 8.41x10(-3), OR = 1.86, 95% CI = 1.17-2.94) after adjustment of age as a confounding factor. The area under curve (AUC) of the risk prediction model that utilized age and ABCG2 421C>A was 0.648 with sensitivity of 0.859 and specificity of 0.415. Severe thrombocytopenia is the most common adverse reaction of sunitinib treatment in Japanese RCC patients. ABCG2 421C>A could explain part of the inter-individual variability of sunitinib-induced severe thrombocytopenia.

Hirose T, Fujita K, Kusumoto S, et al.
Association of pharmacokinetics and pharmacogenomics with safety and efficacy of gefitinib in patients with EGFR mutation positive advanced non-small cell lung cancer.
Lung Cancer. 2016; 93:69-76 [PubMed] Related Publications
OBJECTIVES: Gefitinib is a potent epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor and is a key drug for patients with EGFR mutation-positive advanced non-small cell lung cancer (NSCLC). The pharmacokinetics of orally administered gefitinib varies greatly among patients. We prospectively evaluated the association of pharmacokinetics and pharmacogenomics with the safety and efficacy of gefitinib in patients with EGFR mutation-positive advanced NSCLC.
PATIENTS AND METHODS: Pharmacokinetics was evaluated with samples of peripheral blood obtained on day 1 before treatment and 1, 3, 5, 8, and 24h after gefitinib (250 mg per day) was administered and on days 8 and 15 as the trough values. The plasma concentration of gefitinib was analyzed with high-performance liquid chromatography. The genotypes of ABCG2, ABCB1, CYP3A4, CYP3A5, and CYP2D6 genes were analyzed with direct sequencing.
RESULTS: The subjects were 35 patients (21 women; median age, 72 years; range, 53 to 90 years) with stage IV adenocarcinoma harboring EGFR mutations. The median peak plasma concentration (Cmax) was 377 (range, 168-781)ng/mL. The median area under the curve (AUC) of the plasma concentration of gefitinib from 0 to 24h was 4893 (range, 698-13991) ng/mL h. The common adverse events were skin toxicity (68% of patients), diarrhea (46%), and liver injury (63%). One patient died of drug-induced interstitial lung disease (ILD). The overall response rate was 82.9% (95% confidence interval, 66.4%-93.4%). The median progression-free survival time was 10 months, and the median survival time was 25 months. The pharmacokinetics and pharmacogenomics were not associated with significantly different toxicities, response rates, or survival times with gefitinib. However, the AUC and Cmax were highest and the trough value on day 8 was the second highest in one patient who died of drug-induced ILD.
CONCLUSION: Elevated gefitinib exposure might be associated with drug-induced ILD.

Ye P, Xing H, Lou F, et al.
Histone deacetylase 2 regulates doxorubicin (Dox) sensitivity of colorectal cancer cells by targeting ABCB1 transcription.
Cancer Chemother Pharmacol. 2016; 77(3):613-21 [PubMed] Related Publications
PURPOSE: Histone deacetylases (HDACs) have been shown to regulate cell cycle, differentiation, and apoptosis of colorectal cancer (CRC) cells, while their roles in drug sensitivity remain unclear. The objectives of the present study were to investigate the effects of HDAC2 on drug resistance of CRC cells.
METHODS: We measured the expression of class I HDACs (HDAC1, 2, 3, 8) in CRC and human normal colonic epithelial cells. Additionally, we inhibited HDAC2 via siRNA or overexpressed it via pcDNA/HDAC2 transfection to evaluate its roles in doxorubicin (Dox) sensitivity.
RESULTS: Our present study showed HDAC2 was significantly increased in CRC cell lines as compared to human normal colonic epithelial cells. Silencing of HDAC2 can obviously enhance the sensitivity of HCT-116 and SW480 cells to dDox. Further, knockdown of HDAC2 can significantly (p < 0.05) downregulate the expression of ABCB1, while not ABCG2, ABCC1, ABCA1, or ABCC2. Inhibition of HDAC2 decreased ABCB1 promoter activities and the phosphorylation of c-fos and c-Jun, which can directly interact with the ABCB1 promoter and then promote its transcription. Overexpression of HDAC2 by pcDNA/HDAC2 transfection significantly increased the sensitivity of CRC cells to Dox and upregulated the levels of P-gp, p-c-fos, and p-c-Jun.
CONCLUSIONS: Our data revealed that HDAC2 can regulate Dox sensitivity of CRC cells by targeting ABCB1 transcription. It suggested that HDAC2 might be an important target for CRC therapy. Further, the combination of HDAC2-specific inhibitor and anticancer drugs including Dox might be an efficiency approach to elevate the treatment outcome of CRC.

Elsnerova K, Mohelnikova-Duchonova B, Cerovska E, et al.
Gene expression of membrane transporters: Importance for prognosis and progression of ovarian carcinoma.
Oncol Rep. 2016; 35(4):2159-70 [PubMed] Related Publications
Membrane transporters (such as ABCs, SLCs and ATPases) act in carcinogenesis and chemoresistance development, but their relevance for prognosis of epithelial ovarian cancer (EOC) remains poorly understood. We evaluated the gene expression profile of 39 ABC and 12 SLC transporters and three ATPases in EOC tissues and addressed their putative role in prognosis and clinical course of EOC patients. Relative gene expression in a set of primary EOC (n=57) and in control ovarian tissues (n=14) was estimated and compared with clinical data and survival of patients. Obtained data were validated in an independent set of patients (n=60). Six ABCs and SLC22A18 gene were significantly overexpressed in carcinomas when compared with controls, while expression of 12 ABCs, five SLCs, ATP7A and ATP11B was decreased. Expression of ABCA12, ABCC3, ABCC6, ABCD3, ABCG1 and SLC22A5 was higher in high grade serous carcinoma compared with other subtypes. ABCA2 gene expression significantly associated with EOC grade in both sets of patients. Notably, expression level of ABCA9, ABCA10, ABCC9 and SLC16A14 significantly associated with progression-free survival (PFS) of the disease in either pilot or validation sets. ABCG2 level associated with PFS in the pooled set of patients. In conclusion, ABCA2, ABCA9, ABCA10, ABCC9, ABCG2 and SLC16A14 present novel putative markers of EOC progression and together with the revealed relationship between ABCA12, ABCC3, ABCC6, ABCD3, ABCG1 and SLC22A5 expression, and high grade serous type of EOC should be further examined by larger follow-up study.

Jandu H, Aluzaite K, Fogh L, et al.
Molecular characterization of irinotecan (SN-38) resistant human breast cancer cell lines.
BMC Cancer. 2016; 16:34 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Studies in taxane and/or anthracycline refractory metastatic breast cancer (mBC) patients have shown approximately 30% response rates to irinotecan. Hence, a significant number of patients will experience irinotecan-induced side effects without obtaining any benefit. The aim of this study was to lay the groundwork for development of predictive biomarkers for irinotecan treatment in BC.
METHODS: We established BC cell lines with acquired or de novo resistance to SN-38, by exposing the human BC cell lines MCF-7 and MDA-MB-231 to either stepwise increasing concentrations over 6 months or an initial high dose of SN-38 (the active metabolite of irinotecan), respectively. The resistant cell lines were analyzed for cross-resistance to other anti-cancer drugs, global gene expression, growth rates, TOP1 and TOP2A gene copy numbers and protein expression, and inhibition of the breast cancer resistance protein (ABCG2/BCRP) drug efflux pump.
RESULTS: We found that the resistant cell lines showed 7-100 fold increased resistance to SN-38 but remained sensitive to docetaxel and the non-camptothecin Top1 inhibitor LMP400. The resistant cell lines were characterized by Top1 down-regulation, changed isoelectric points of Top1 and reduced growth rates. The gene and protein expression of ABCG2/BCRP was up-regulated in the resistant sub-lines and functional assays revealed BCRP as a key mediator of SN-38 resistance.
CONCLUSIONS: Based on our preclinical results, we suggest analyzing the predictive value of the BCRP in breast cancer patients scheduled for irinotecan treatment. Moreover, LMP400 should be tested in a clinical setting in breast cancer patients with resistance to irinotecan.

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