Resistant Sublines Research Articles

Abstract 474: Alterations of micro-RNAs are associated with melanoma resistance to BRAF inhibitors: Role of miR-126

Abstract Altered expression of miRNAs has been demonstrated in tumor tissue and plasma/serum of cancer patients. miRNAs have been shown to have both diagnostic and prognostic significance and to potentially constitute novel targets and therapeutic agents for cancer treatment. Experimental evidences also support an involvement of miRNAs in tumor cell response to therapy. In this study, we explored the role of miRNAs in melanoma resistance to BRAF inhibitors (BRAFi). The melanoma cell line A375 and its dabrafenib-resistant subline A375R, which displays increased invasiveness and VEGF secretion, were analyzed for miRNA expression using Affymetrix GeneChip® miRNA 3.1 microarrays. Differential expression of selected miRNAs was confirmed in the two cell lines using qRT-PCR. miR-126, previously shown to act as a tumor suppressor gene in melanoma, was chosen for additional studies that were performed also in a second pair of matched melanoma cell lines, sensitive or resistant to dabrafenib (i.e SK-Mel28 and SK-Mel28R). The resistant sublines were transfected with 50 nM Pre-miR hsa-miR-126 miRNA Precursor (pre-miRNA-126) or Pre-miR miRNA Precursor Negative Control#1 (Ambion®) and analyzed for proliferation 6 days later using the MTT assay. Seventy-two hours after transfection, the cells were also assayed for invasion of the extracellular matrix and VEGF-A secretion using Boyden Chamber and ELISA assays, respectively. In 33 melanoma patients treated with BRAFi, alone or in combination with MEKi, plasma samples were collected before the beginning of therapy (T0), and two months later (T2) and subjected to miRNA expression profiling by small RNA-seq. A375R cells displayed 13 up-regulated miRNAs and 32 down-regulated miRNAs with respect to A375 cells (SAM analysis; fold change ≥ 2). Down-regulation of miR-126 was confirmed by qRT-PCR analysis in both A375R and SK-Mel28R cells. Restoration of miR-126 expression in A375R and SK-Mel28R cells by pre-miRNA-126 transfection impaired proliferation, invasion and secretion of VEGF-A, a validated target of miR-126. Fifthy and 28 circulating miRNAs were differentially expressed at T0 and at T2, respectively, between patients who responded to therapy (n=28) and patients who did not (n=5). Our results demonstrate that down-regulation of miR-126 expression is associated with acquired resistance to dabrafenib in melanoma cells and suggest that restoration of this miRNA in dabrafenib-resistant melanomas might restrain tumor growth and metastasis. They also show that in melanoma patients with primary resistance to BRAFi, a set of circulating miRNAs is differentially expressed with respect to patients responding to therapy, suggesting a potential role of circulating miRNAs as biomarkers for early prediction of drug response. Supported by the Italian Ministry of Health, grant 5PerMille-2010 and AIRC, IGP 17585 Citation Format: Simona Caporali, Lauretta Levati, Ester Alvino, Adriana Amaro, Pedro Miguel Lacal, Laura Bonmassar, Cristian Bassi, Laura Lupini, Gian Carlo Antonini Cappellini, Ulrich Pfeffer, Massimo Negrini, Nadia Felli, Alessandra Carè, Giandomenico Russo, Stefania D'Atri. Alterations of micro-RNAs are associated with melanoma resistance to BRAF inhibitors: Role of miR-126 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 474.

Abstract 5846: Drug resistance in chronic myeloid leukemia: Impact of methylation on gene expression in imatinib and nilotinib resistance

Abstract Background: Chronic myeloid leukemia (CML) is one of the most extensively studied hematopoietic disorders. Caused by reciprocal translocation t(9;22) and formation of the Philadelphia chromosome, it leads to constitutive expression of the BCR-ABL kinase and malignant transformation. Targeted therapy using tyrosine kinase inhibitors (TKI), such as imatinib or nilotinib, led to tremendous success in treatment. However, resistances are an uprising problem in patient cure. Besides BCR-ABL-dependent mechanisms (i.e. BCR-ABL amplification, mutations), cellular alterations of gene expression and its regulation are involved. Therefore, we performed an in vitro-study in K-562 CML cells to investigate changes of gene expression and epigenetics, as well as occurrence of mutations during the course of imatinib or nilotinib resistance. Methods: We analyzed mRNA expression, DNA-methylation and mutation status of treatment-naïve and TKI-resistant sublines (0.5 µM, 2 µM imatinib; 100 nM nilotinib) of the in vitro-cell line model (K-562). mRNA expression was analyzed using Affymetrix Human Gene 2.0 ST arrays and DNA-methylation by Infinium MethylationEPIC BeadChips (Illumina); exome sequencing was performed at GATC, Konstanz, Germany. Target verification was performed using qRT-PCR, pyrosequencing or Sanger sequencing. Effects on TKI-susceptibility were analyzed using transfection experiments with analyses of cell viability (WST-1 assay) and apoptosis (Caspase Glo 9 assay). Results: Cell resistant to low imatinib doses exhibited differentially expression of 485 mRNAs compared to treatment-naïve cells, whereas at high dose-resistance 166 mRNAs differed. 151 genes showed expression changes independent from the imatinib dose. In addition, we found 45 genes with expression changes during the course of imatinib resistance, i.e. the drug efflux transporter ABCG2, which was significantly upregulated at low and downregulated at high imatinib doses. A total of 254 genes was associated with nilotinib resistance, while 71 genes were differentially expressed in all resistant sublines. Regarding methylation and occurrence of mutations in imatinib resistance, we observed distinct variations pointing to genetic changes, especially at high-dose resistance, i.e. in the promoter region of microRNA-212, a proven regulator of ABCG2. In nilotinib resistance, we found 125 genes differentially methylated during development of resistance. Conclusions: Our data indicate that development of resistance to tyrosine kinase inhibitors is based on complex expression profile changes that can in part be explained by epigenetic alteration e.g. in drug efflux transporters. Besides, the mechanisms underlying resistances to imatinib or nilotinib seem to be dissimilar. After verification in clinical studies, these in vitro findings could be relevant in attempts to overcome TKI-resistances. Citation Format: Meike Kaehler, Inga Nagel, Henrike Bruckmueller, Ruwen Boehm, Ole Ammerpohl, Ingolf Cascorbi. Drug resistance in chronic myeloid leukemia: Impact of methylation on gene expression in imatinib and nilotinib resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5846.

PO-471 Exosomes and transferring of hormonal resistance of breast cancer cells

IntroductionThe main goal of the present work was the study of the molecular mechanism of acquired hormonal resistance of tumour cells, in particular - the study of the intercellular interactions and exosomes and their role in the progression of the resistance.Material and methodsHormone responsive MCF-7 and hormone resistant MCF-7/T breast cancer cells were cultured in standard DMEM medium supplemented with 10% fetal calf serum. The transcriptional activities of NF-kB and AP-1 were determined by reporter luciferase assays. Then exosomes from cell supernatant were isolated by differential ultracentrifugation using standard protocol.Results and discussionsHere, using the estrogen-dependent MCF-7 breast cancer cells and estrogen-independent MCF-7/T cells we have demonstrated the ability of the resistant cells-derived exosomes to initiate the estrogen-independent growth of the parent MCF-7 cells. The subsequent analysis of the key signalling proteins revealed the ability of the exosomes of the resistant cells to inhibit the oestrogen signalling as well as to stimulate the Akt protein kinase and transcription factors AP-1 and NF-kB in the recipient cells. Importantly, the cell treatment with PI3K/Akt inhibitor wortmannin prevented the exosome-induced resistance giving the additional evidence for central role of this pathway in the mediating of exosomal resistance.The data validation was performed on the resistant subline MCF-7/M which was selected under long-term cultivation of the parent MCF-7 cells with biguanide metformin and demonstrated the cross-resistance to metformin and tamoxifen. We have shown that the exosomes of the resistant MCF-7/M cells lead to the partial resistance of the parent cells to both drugs. Moreover, the acquired resistance was characterised with the analogues signalling rearrangement: inhibition of the oestrogen signalling and activation of the Akt, AP-1 and NF-kB proteins - similar to the described above hormonal resistance. Advanced analysis of the exosomal microRNA revealed 27 microRNA differentially expressed in the exosomes of the resistant cells and associated with the progression of hormonal resistance.ConclusionTotally, we demonstrated the new mechanism of horizontal transferring of hormonal resistance by exosomes, identified the possible intercellular targets of exosomes and revealed the main features of the exosomal transcriptome. This study was supported by Russian Science Foundation, grant 14-15-00362 M.K.

A New Photosensitized Oxidation-Responsive Nanoplatform for Controlled Drug Release and Photodynamic Cancer Therapy.

Abnormal biochemical alteration such as unbalanced reactive oxygen species (ROS) levels has been considered as a potential disease-specific trigger to deliver therapeutics to target sites. However, in view of their minute variations in concentration, short lifetimes, and limited ranges of action, in situ generation of ROS with specific manipulations should be more effective for ROS-responsive drug delivery. Here we present a new delivery nanoplatform for photodynamic therapy (PDT) with on-demand drug release regulated by light irradiation. Rose bengal (RB) molecules, which exhibit a high yield of ROS generation, were encapsulated in a mixture of chitosan (CTS), poly(vinyl alcohol) (PVA), and branched polyethylenimine ( bPEI) with hydrophobic iron oxide nanoparticles through an oil-in-water emulsion method. The as-prepared magnetic nanoclusters (MNCs) with a tripolymer coating displayed high water dispersibility, efficient cellular uptake, and the cationic groups of CTS and bPEI were effective for RB loading through electrostatic interaction. The encapsulation efficiency of RB in MNCs could be further improved by increasing the amount of short bPEI chains. During the photodynamic process, controlled release of the host molecules (i.e., RB) or guest molecules (i.e., paclitaxel) from the bPEI-based nanoplatform was achieved simultaneously through a photooxidation action sensitized by RB. This approach promises specific payload release and highly effective PDT or PDT combined therapy in various cancer cell lines including breast (MCF-7 and multidrug resistant MCF-7 subline), SKOV-3 ovarian, and Tramp-C1 prostate. In in vivo xenograft studies, the nanoengineered light-switchable carrier also greatly augments its PDT efficacy against multidrug resistant MCF-7/MDR tumor as compared with free drugs. All the above findings suggest that the substantial effects of enhanced drug distribution for efficient cancer therapy was achieved with this smart nanocarrier capable of on demand drug release and delivery, thus exerting its therapeutic activity to a greater extent.

The inhibitory effect of kokusaginine on the growth of human breast cancer cells and MDR-resistant cells is mediated by the inhibition of tubulin assembly

The emergence of multidrug resistance (MDR) is a significant challenge in breast carcinoma chemotherapy. Kokusaginine isolated from Dictamnus dasycarpus Turcz. has been reported to show cytotoxicity in several human cancer cell lines including breast cancer cells MCF-7. In this study, kokusaginine showed the potent inhibitory effect on MCF-7 multidrug resistant subline MCF-7/ADR and MDA-MB-231 multidrug resistant subline MDA-MB-231/ADR. Kokusaginine markedly induced apoptosis in a concentration-dependent manner in MCF-7/ADR cells. Furthermore, kokusaginine reduced P-gp mRNA and protein levels, and suppressed P-gp function especially in MCF-7/ADR cells. In addition, kokusaginine showed to inhibit tubulin assembly and the binding of colchicine to tubulin by binding directly to tubulin and affects tubulin formation in vitro. Taken together, these results support the potential therapeutic value of kokusaginine as an anti-MDR agent in chemotherapy for breast carcinoma.

Contribution of microRNA-200b-3p to radiation therapy resistance in 22RV1 prostate cancer cells.

89 Background: Radiation therapy (RT) is a standard treatment option for men with localized prostate cancer. Despite having well-established treatment regimens, such men still fail RT at a rate of up to 30-50%. RT resistant phenotype is a key component leading to treatment failure. MicroRNAs (miRNAs) can influence the response to RT, and the abundance or lack of certain miRNAs can induce a RT resistant phenotype through alteration of survival pathways. We show that altered expression of miR-200b-3p plays an important role in contributing to RT resistance. Methods: RT resistant subline from the parental 22RV1 prostate cancer cell line was generated by exposure to fractionated RT – 22RV1-RT. The global expression level of miRNAs and mRNA was determined, using the Affymetrix GeneChip®: miRNA 4.0 and Human Gene 2.0 ST Arrays. Parental and 22RV1-RT cells were transfected with miR-200b-3p mimics or negative control. The influence of miR-200b-3p on cellular proliferation, morphology, migration, clonogenic survival and response to RT was determined by standard assays. Results: MiR-200b-3p was the only miRNA that was statistically differentially expressed between the two cell lines. There were 39 differentially expressed genes. Of the 65 genes predicted to be regulated by miR-200b-3p as identified from miRTarBase, only Fibronectin 1 (FN1) was in common. FN1 was up-regulated in 22RV1- RT cells. MiR-200b-3p mimics; in comparison to negative control mimics, suppressed cell proliferation in both cell lines. Both cell lines with negative control mimics have fibroblastic-type morphology and display a stretched shape following RT. While, cells transfected with miR-200b-3p mimics demonstrated a round morphology and formed clusters following RT. Over-expression of miR-200b-3p mimics inhibited cell migration synergically with RT and demonstrated a lower degree of clonogenic survival following RT in 22RV1-RT cells compared to negative control mimics. Surprisingly, miR-200b-3p mimics reversed the observed RT resistance and the sensitivity to RT was to the same degree as the parental 22RV1 cells. Conclusions: Together, these data suggest that miR-200b-3p independently contributes to RT resistance in 22RV1 prostate cancer cells.

Differential Characterization of Temozolomide-Resistant Human Glioma Cells.

Glioblastoma multiforme (GBM) is the most common type of primary and malignant tumor occurring in the adult central nervous system. Temozolomide (TMZ) has been considered to be one of the most effective chemotherapeutic agents to prolong the survival of patients with glioblastoma. Many glioma cells develop drug-resistance against TMZ that is mediated by increasing O-6-methylguanine-DNA methyltransferase (MGMT) levels. The expression of connexin 43 was increased in the resistant U251 subline compared with the parental U251 cells. The expression of epithelial–mesenchymal transition (EMT)-associated regulators, including vimentin, N-cadherin, and β-catenin, was reduced in the resistant U251 subline. In addition, the resistant U251 subline exhibited decreased cell migratory activity and monocyte adhesion ability compared to the parental U251 cells. Furthermore, the resistant U251 subline also expressed lower levels of vascular cell adhesion molecule (VCAM)-1 after treatment with recombinant tumor necrosis factor (TNF)-α. These findings suggest differential characteristics in the drug-resistant GBM from the parental glioma cells.

Cytotoxic Activity of Extracts from Plants of Central Argentina on Sensitive and Multidrug-Resistant Leukemia Cells: Isolation of an Active Principle from Gaillardia megapotamica.

Plants are a significant reservoir of cytotoxic agents, including compounds with the ability to interfere with multidrug-resistant (MDR) cells. With the aim of finding promising candidates for chemotherapy, 91 native and naturalized plants collected from the central region of Argentina were screened for their cytotoxic effect toward sensitive and MDR P-glycoprotein (P-gp) overexpressing human leukemia cells by means of MTT assays. The ethanol extracts obtained from Aldama tucumanensis, Ambrosia elatior, Baccharis artemisioides, Baccharis coridifolia, Dimerostemma aspilioides, Gaillardia megapotamica, and Vernonanthura nudiflora presented outstanding antiproliferative activity at 50 μg/mL, with inhibitory values from 93 to 100%, when tested on the acute lymphoblastic leukemia (ALL) cell line CCRF-CEM and the resistant derivative CEM-ADR5000, while 70–90% inhibition was observed against the chronic myelogenous leukemia (CML) cell K562 and its corresponding resistant subline, Lucena 1. Subsequent investigation showed these extracts to possess marked cytotoxicity with IC50 values ranging from 0.37 to 29.44 μg/mL, with most of them being below 7 μg/mL and with ALL cells, including the drug-resistant phenotype, being the most affected. G. megapotamica extract found to be one of the most effective and bioguided fractionation yielded helenalin (1). The sesquiterpene lactone displayed IC50 values of 0.63, 0.19, 0.74, and 0.16 μg/mL against K562, CCRF-CEM, Lucena 1, and CEM/ADR5000, respectively. These results support the potential of these extracts as a source of compounds for treating sensitive and multidrug-resistant leukemia cells and support compound 1 as a lead for developing effective anticancer agents.

2 - A carrot a day keeps recurrence away! The use of vitamin A and its metabolic products in the circumvention of cisplatin resistance via Aldehyde Dehydrogenase 1 (ALDH1)

Despite advances in personalised medicine, cisplatin remains the mainstay in NSCLC management, however the develop-ment of pan-resistance to platinum agents has become a major clinical challenge. Novel drug design, preclinical and clinical trials working toward the approval of new drugs is a lengthy and costly process and in the interim research has turned its focus to overcoming resistance and repurposing drugs. Cancer stem cells (CSCs) have been hypothesised to be the initiating cells of resistance and recurrence. ALDH1-positive cells have been identified as a CSC subpopulation within cisplatin resistant (CisR) NSCLC sublines. ALDH1 converts retinal to retinoic acid during the metabolism of retinol (vitamin A), retinoic acid induces cell differentiation. All-trans retinoic acid (ATRA) is a well-established chemotherapeutic agent in the treatment of acute promyelocytic leukaemia; it induces the terminal differentiation of immature cells. We hypothesise that retinol and ATRA will deplete the ALDH1-positive CSC population thereby increasing or restoring cisplatin sensitivity.

Investigation of epithelial-mesenchymal transition induced by cisplatin on human laryngeal resistant cancer cells

Objective:To investigate the mechanism between epithelial-mesenchymal transition (EMT) and cisplatin induced resistant cell subline and the malignant biological characteristics, to explore EMT in human hep-2 laryngeal resistant cells. Method:Using cisplatin-resistant cells (hep-2/CDDP) and non-resistant cells (hep-2) established in our previous study; the invasion and migration biological behaviors were detected by transwell and scratch assay; the expressions of E-cadherin, Zo-1, Snail, Slug, Twist1, Vimentinon in the mRNA level were detected by RT-qPCR and the protein level by Western blot. Result:Transwell and scratch assay show the invasion and migration behaviors were increased in hep-2/CDDP cells (P<0.05), the epithelial marker E-cadherin and Zo-1 were downregulated in hep-2/CDDP cells (all P<0.05), transcription factor Snail, Slug were upregulated in mRNA and protein level (all P<0.01) while Twist1 had no significant changed in protein level (P>0.05), the expression of mesenchymal marker Vimentin was also increased in mRNA and protein levels in cisplatin resistant cells (P<0.01). It was confirmed that the hep-2/CDDP cells possessed EMT phenotypes. Conclusion:The cisplatin resistant laryngeal cancer cells perform higherinvasion and migration biological behaviors,and the mechanisms of increased ability of invasion and migration induced by cisplatin was associated to eEMT, study on signal path related to EMT may overcome cisplatin resistance and reduce invasion and migration behaviors.

Adaptive phenotype drives resistance to androgen deprivation therapy in prostate cancer

BackgroundProstate cancer (PCa), the second most common cancer affecting men worldwide, shows a broad spectrum of biological and clinical behaviour representing the epiphenomenon of an extreme heterogeneity. Androgen deprivation therapy is the mainstay of treatment for advanced forms but after few years the majority of patients progress to castration-resistant prostate cancer (CRPC), a lethal form that poses considerable therapeutic challenges.MethodsWestern blotting, immunocytochemistry, invasion and reporter assays, and in vivo studies were performed to characterize androgen resistant sublines phenotype in comparison to the parental cell line LNCaP. RNA microarray, mass spectrometry, integrative transcriptomic and proteomic differential analysis coupled with GeneOntology and multivariate analyses were applied to identify deregulated genes and proteins involved in CRPC evolution.ResultsTreating the androgen-responsive LNCaP cell line for over a year with 10 μM bicalutamide both in the presence and absence of 0.1 nM 5-α-dihydrotestosterone (DHT) we obtained two cell sublines, designated PDB and MDB respectively, presenting several analogies with CRPC. Molecular and functional analyses of PDB and MDB, compared to the parental cell line, showed that both resistant cell lines were PSA low/negative with comparable levels of nuclear androgen receptor devoid of activity due to altered phosphorylation; cell growth and survival were dependent on AKT and p38MAPK activation and PARP-1 overexpression; their malignant phenotype increased both in vitro and in vivo. Performing bioinformatic analyses we highlighted biological processes related to environmental and stress adaptation supporting cell survival and growth. We identified 15 proteins that could direct androgen-resistance acquisition. Eleven out of these 15 proteins were closely related to biological processes involved in PCa progression.ConclusionsOur models suggest that environmental factors and epigenetic modulation can activate processes of phenotypic adaptation driving drug-resistance. The identified key proteins of these adaptive phenotypes could be eligible targets for innovative therapies as well as molecules of prognostic and predictive value.

Schisandrin A reverses doxorubicin-resistant human breast cancer cell line by the inhibition of P65 and Stat3 phosphorylation.

Multidrug resistance (MDR) in breast cancer therapy occurs frequently. Thus, anti-MDR agents from natural products or synthetic compounds were tested extensively. We have also explored the reverse effect and mechanism of Schisandrin A (Sch A), a natural product, on MCF-7 breast cancer doxorubicin (DOX)-resistant subline MCF-7/DOX. MTT assay was performed to measure the viability of MCF-7 cells to assess the reverse effect of Sch A. Western blot analysis was used to study the protein levels. Laser scanning confocal microscopy was performed to detect the intercellular DOX and Rhodamine 123 accumulation. The qRT-PCR was used to analysis the target gene expression. Dual-luciferase reporter assay was performed to test the transcriptional activity of P-glycoprotein (P-gp). Sch A, at the concentration of 20µM, showed selective reverse effect (better than the positive control, verapamil at 5µM) on MCF-7/DOX cell line but not on BEL-7402/DOX, Hep G2/DOX, and K-562/DOX cells. In addition, Sch A enhanced DOX-induced cleavage of Caspase-9 and PARP levels by increasing intracellular DOX accumulation and inhibiting P-gp function. Furthermore, Sch A selectively suppressed P-gp at gene and protein levels in MCF-7/DOX cells which express high level of MDR1 but not MRP1, MRP3, or BCRP. Besides, Sch A showed inhibitory effect on P-gp transcriptional activity. Sch A significantly reduced p-IκB-α (Ser32) and p-Stat3 (Tyr705) levels which mediate P-gp expression. In addition, Stat3 knockdown enhanced the reverse effect of siP65. The combined effect of siStat3 and siP65 was better than Sch A single treatment in MCF-7/DOX cells. Sch A specifically reverses P-gp-mediated DOX resistance in MCF-7/DOX cells by blocking P-gp, NF-κB, and Stat3 signaling. Inhibition of P65 and Stat3 shows potent anti-MDR effect on MCF-7/DOX cells.

Association between Twist and multidrug resistance gene-associated proteins in Taxol®-resistant MCF-7 cells and a 293 cell model of Twist overexpression.

Multidrug resistance (MDR) severely limits the effectiveness of chemotherapy. Previous studies have identified Twist as a key factor of acquired MDR in breast, gastric and prostate cancer. However, the underlying mechanisms of action of Twist in MDR remain unclear. In the present study, the expression levels of MDR-associated proteins, including lung resistance-related protein (LRP), topoisomerase IIα (TOPO IIα), MDR-associated protein (MRP) and P-glycoprotein (P-gp), and the expression of Twist in cancerous tissues and pericancerous tissues of human breast cancer, were examined. In order to simulate Taxol® resistance in cells, a Taxol®-resistant human mammary adenocarcinoma cell subline (MCF-7/Taxol®) was established by repeatedly exposing MCF-7 cells to high concentrations of Taxol® (up to 15 µg/ml). Twist was also overexpressed in 293 cells by transfecting this cell line with pcDNA5/FRT/TO vector containing full-length hTwist cDNA to explore the dynamic association between Twist and MDR gene-associated proteins. It was identified that the expression levels of Twist, TOPO IIα, MRP and P-gp were upregulated and LRP was downregulated in human breast cancer tissues, which was consistent with the expression of these proteins in the Taxol®-resistant MCF-7 cell model. Notably, the overexpression of Twist in 293 cells increased the resistance to Taxol®, Trichostatin A and 5-fluorouracil, and also upregulated the expression of MRP and P-gp. Taken together, these data demonstrated that Twist may promote drug resistance in cells and cancer tissues through regulating the expression of MDR gene-associated proteins, which may assist in understanding the mechanisms of action of Twist in drug resistance.

Selection and characterization of a human ovarian cancer cell line resistant to auranofin.

The anti-arthritic drug auranofin exerts also potent antitumour activity in in vitro and in vivo models, whose mechanisms are not yet well defined. From an auranofin-sensitive human ovarian cancer cell line A2780, a highly resistant (>20-fold) subline (A2780/AF-R) was developed and characterized. Marked reduction of gold accumulation occurred in auranofin-resistant A2780 cells. Also, moderately higher thioredoxin reductase activity in A2780/AF-R cells was observed while no changes in intracellular glutathione content occurred. Resistance to auranofin was associated with a low level of cross-resistance to some investigational gold compounds as well as to oxaliplatin and other anticancer drugs with different mode of action (i.e. melphalan, vinblastine, doxorubicin, etoposide, and paclitaxel). Reduced gold accumulation was associated to substantial gene expression changes in various influx (e.g. SLC22A1, SLC47A1, SLCO1B1) and efflux (e.g. ABCB1, ABCC2, ABCC3) transporters. The expression levels of selected proteins (i.e. SLC22A1, SLC47A1, P-gp) were also changed accordingly. These data provide evidence that multiple drug transporters may act as mediators of transport of auranofin and other gold compounds in cancer cells. Further investigation into the molecular mechanisms mediating transport of auranofin and new gold complexes in view of their potential clinical application in the treatment of cancer is warranted.

Endocrine Therapy of Estrogen Receptor-Positive Breast Cancer Cells: Early Differential Effects on Stem Cell Markers.

Endocrine therapy of breast cancer, which either deprives cancer tissue of estrogen or prevents estrogen pathway signaling, is the most common treatment after surgery and radiotherapy. We have previously shown for the estrogen-responsive MCF-7 cell line that exposure to tamoxifen, or deprivation of estrogen, leads initially to inhibition of cell proliferation, followed after several months by the emergence of resistant sub-lines that are phenotypically different from the parental line. We examined the early responses of MCF-7 cells following either exposure to 4-hydroxytamoxifen or deprivation of estrogen for periods of 2 days-4 weeks. Endocrine-sensitive or -resistant breast cancer cell lines were used to examine the expression of the stem cell gene SOX2, and the Wnt effector genes AXIN2 and DKK1 using quantitative PCR analysis. Breast cancer cell lines were used to assess the anti-proliferative effects (as determined by IC50 values) of Wnt pathway inhibitors LGK974 and IWP-2. Hormone therapy led to time-dependent increases of up to 10-fold in SOX2 expression, up to threefold in expression of the Wnt target genes AXIN2 and DKK1, and variable changes in NANOG and OCT4 expression. The cells also showed increased mammosphere formation and increased CD24 surface protein expression. Some but not all hormone-resistant MCF-7 sub-lines, emerging after long-term hormonal stress, showed up to 50-fold increases in SOX2 expression and smaller increases in AXIN2 and DKK1 expression. However, the increase in Wnt target gene expression was not accompanied by an increase in sensitivity to Wnt pathway inhibitors LGK974 and IWP-2. A general trend of lower IC50 values was observed in 3-dimensional spheroid culture conditions (which allowed enrichment of cells with cancer stem cell phenotype) relative to monolayer cultures. The endocrine-resistant cell lines showed no significant increase in sensitivity to Wnt inhibitors. Hormone treatment of cultured MCF-7 cells leads within 2 days to increased expression of components of the SOX2 and Wnt pathways and to increased potential for mammosphere formation. We suggest that these responses are indicative of early adaptation to endocrine stress with features of stem cell character and that this facilitates the survival of emerging hormone-resistant cell populations.

Establishing Dual Resistance to EGFR-TKI and MET-TKI in Lung Adenocarcinoma Cells In Vitro with a 2-step Dose-escalation Procedure.

Drug resistance is a major challenge in cancer therapy. The generation of resistant sublines in vitro is necessary for discovering novel mechanisms to overcome this challenge. Here, a 2-step dose-escalation method for establishing dual-resistance to an epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI), gefitinib, and a MET-TKI, PHA665752, is described. This method is based on simple stepwise dose-escalation of inhibitors for inducing acquired resistance in cell lines. The alternate method for generating resistant sublines involves exposing the cells to high concentrations of the inhibitor in one step. The stepwise dose-escalation method has a higher possibility of successfully inducing acquired resistance than this method. Activating EGFR mutations are biomarkers of a response to treatment with EGFR-TKI, which is an applied first-line treatment for non-small cell lung cancers (NSCLC) that harbor these mutations. However, despite reports of effective responses, the use of EGFR-TKI is limited because tumors inevitably acquire resistance. The major mechanisms behind EGFR-TKI resistance include a secondary mutation at the gatekeeper site, T790M in exon 20 of EGFR, and a bypass signal of MET. Thus, a potential solution for this issue would be a combination of EGFR-TKI and MET-TKI. This combined treatment has been shown to be effective in an in vitro study model. Acquired gefitinib-resistance was established through MET-amplification by stepwise dose-escalation of gefitinib for 12 months, and a cell line named PC-9MET1000 was generated in a previous study. To further investigate the mechanisms of acquired MET-TKI and EGFR-TKI resistance, a MET-TKI, PHA665752, was administered to these cells with stepwise dose-escalation in the presence of gefitinib for 12 months. This protocol has also been successfully applied for a number of combination therapies to establish acquired resistance to other inhibitor molecules.

The activation of SRC family kinases and focal adhesion kinase with the loss of the amplified, mutated EGFR gene contributes to the resistance to afatinib, erlotinib and osimertinib in human lung cancer cells.

Second- and third-generation inhibitors of epidermal growth factor receptor (EGFR) tyrosine kinase activity (EGFR-TKIs) are improving the treatment of patients with non-small cell lung cancer. Here we established two sublines (BR1-8 and BR2-3) resistant to a second-generation inhibitor, afatinib, from the human lung cancer cell line HCC827 that harbors a mutation that activates the tyrosine kinase activity of EGFR. These afatinib-resistant sublines were resistant to first-generation EGFR-TKIs, gefitinib and erlotinib, and a third-generation EGFR-TKI, osimertinib. These resistant sublines showed markedly reduced levels of multiple EGFR family proteins, including the activated mutant EGFR, and complete loss of EGFR amplification as compared with their parental HCC827 cells harboring amplification of EGFR gene. Treatment with the multikinase inhibitor dasatinib or transfection with a SRC small interfering RNA inhibited cell survival and AKT phosphorylation in drug-resistant sublines to a greater extent compared with HCC827 cells. Further, the migration of drug-resistant cells was greater compared with that of HCC827 cells and was inhibited by dasatinib or an FAK inhibitor. These findings indicate that compensatory activation of SRC family kinases (SFKs) and FAK supports the survival and migration of afatinib-resistant cells when the expression of multiple EGFR family proteins was mostly abrogated. Combinations of potent drugs that target SFKs and FAK may overcome the resistance of lung cancer cells to second-generation TKIs.

Abstract 3156: Multiple acquired resistance mechanisms against third generation EGFR-TKI osimeritinib in non-smal cell lung cancer cells

Abstract Background Osimertinib (AZD9291; Tagrisso) is a third generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) known to be effective against the EGFR-T790M variant, which is accounts for half of the acquired resistance mechanisms to the first generation EGFR-TKIs. However, resistance to osimertinib is likely to progress and the study of potential osimertinib-resistance mechanisms in advanced is necessary. In this study, we investigated the molecular and cellular profiles of the acquired resistance cells to osimertinib in EGFR-mutant non-small cell lung cancers. Materials and Methods Five EGFR-mutant cell lines were exposed to osimertinib by stepwise escalation or high-concentration exposure methods, and resistant sublines to osimertinib were established. The molecular profiles and cellular phenotypes of these resistant sublines were characterized. Results EGFR-C797S mutation which was reported to be a major mechanism of resistance to osimertinib in clinical samples was not detected in established resistance cells by using direct sequencing. Several osimertinib-resistance cell lines displayed MET amplification, and some of these cells were sensitive to the combination of osimertinib plus MET inhibitor crizotinib. However, one cell line that displayed MET amplification was not sensitive to this combination therapy. On the other hand, several osimertinib-resistance cell lines displayed epithelial-to-mesenchymal transition (EMT) features. The HCC827-derived subline established by the high-concentration exposure method exhibited not only EMT features but also cancer stem cell (CSC)-like properties, including aldehyde dehydrogenase isoform 1 (ALDH1A1) and ATP binding cassette subfamily B member 1 (ABCB1) overexpression. Conclusion We established osimertinib-resistant cells and found that MET amplification, EMT, and CSC -like features were observed. These findings may provide clues to overcome acquired resistance to EGFR-TKIs. In some cell lines, however, the mechanisms of acquired resistance to osimertinib were not revealed yet. Citation Format: Kei Namba, Kazuhiko Shien, Takahiro Yoshioka, Hidejiro Torigoe, Hiroki Sato, Hiromasa Yamamoto, Junichi Soh, Kazunori Tsukuda, Shinichi Toyooka. Multiple acquired resistance mechanisms against third generation EGFR-TKI osimeritinib in non-smal cell lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3156. doi:10.1158/1538-7445.AM2017-3156

Abstract 3075: Analysis of microRNA profiles involved in the resistance to trifluridine

Abstract Background: Trifluridine (FTD) is a key component of the novel oral antitumor drug trifluridine/tipiracil, which was approved for the treatment of patients with metastatic colorectal cancer refractory to standard chemotherapies. A comprehensive analysis of miRNA profiles was performed in cell lines resistant to FTD established by ourselves, in order to explore the underlying mechanisms of resistance to the drug. Method: We established subline resistance to FTD through continuous administration and increasing dose of the drug for 5 months using the colorectal cancer cell line DLD-1. Total RNA was extracted at intervals whilst establishing FTD resistant sublines, and miRNA expression was analyzed by microarray. The expression of miRNA that was significantly downregulated in the FTD resistant subline was knocked down to test its involvement in resistance to FTD. Cell viability was evaluated by crystal violet cytotoxicity test. Results: The established FTD-resistant sublines showed more than 22-fold higher resistance to FTD and no cross-resistance to 5-FU. miRNA and mRNA clustered in the genome locus located in chromosome 9, 9p22.32 were downregulated in the FTD-resistant cell line, one of which was the miRNA let-7d-5p, which is one of the let-7 family and is known to target oncogenes and several key components of the cell cycle and cell proliferation. Anti-let-7d-5p treated DLD-1 was less sensitive to FTD than compared to control. The IC50 values of FTD were 16.8 µM and 7.6 µM for the anti-let-7d-5p treated cells and control respectively. On the other hand, overexpression of let-7d-5p in DLD-1 using let-7d-5p mimic increased the sensitivity to FTD compared to control. The IC50 values of FTD were 3.7 µM and 13.9 µM in the let-7d-5p overexpression cells and control respectively. 5FU sensitivity was only altered slightly in anti- let-7d-5p treated or let-7d-5p mimic treated cells. These data suggest that let-7d-5p is more relevant to sensitivity for FTD than that of 5FU. Conclusion: Let-7d-5p expression level influenced FTD sensitivity more effectively than 5FU. It suggests that the let-7d-5p is a potential predictive marker for trifluridine/tipiracil treatment in the clinical setting. Citation Format: Kenta Tsunekuni, Jun Koseki, Masamitsu Konno, Ayumu Asai, Norihiro Nishida, Hugh Colvin, Koichi Kawamoto, Yuichiro Doki, Masaki Mori, Hideshi Ishii. Analysis of microRNA profiles involved in the resistance to trifluridine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3075. doi:10.1158/1538-7445.AM2017-3075

Abstract 707: Personalization of dexamethasone in acute lymphoblastic leukemia

Abstract Synthetic glucocorticoids, such as dexamethasone (Dex), are pivotal in the treatment of childhood acute lymphoblastic leukemia (ALL) but are associated with significant variability, both in terms of toxicity and efficacy. We aimed to investigate three key variables to better understand how Dex personalization may be achieved: pharmacokinetics (PK), intracellular Dex accumulation, and cellular response, following Dex binding to the glucocorticoid receptor (GR) in ALL cells. For Dex PK studies, blood samples were collected post oral administration on one of the first three days of induction chemotherapy in 99 patients on the UKALL 2011 trial receiving either 6mg/m2 for28 days (standard arm) or 10mg/m2 for 14 days (short arm). Plasma Dex levels were analysed using a validated LC/MS method, and a non-compartmental pharmacokinetic analysis. To assess intracellular Dex levels, cell lines, primagraft (n=9) and primary patient samples (n=6) were studied. The plasma Dex LC/MS method was optimized to quantify Dex in ALL cell lysates. Dex accumulation was also assessed using flow cytometric analysis of Dex conjugated to FITC. Cellular Dex sensitivity was assessed using Alamar Blue assays. There was a wide Dex PK variability, with AUC0-12h, and Cmax significantly higher on the short compared to the standard arm; 564 (202-1606) versus 408 (142-1009), median (range), p=0.0003 and 0.0006, respectively. However there was substantial overlap between the two arms, with a number of patients on the standard arm exhibiting higher exposures than those on short therapy. Dex GI50 values ranged from 37 - &amp;gt; 1000 nM and 2 - &amp;gt; 1000 nM in cell lines and patient samples respectively. Western blotting indicated wildtype GR in all samples, with R3D11 and REH cell lines serving as hemizygous deleted and GR negative controls. Dex accumulation in cell lines was 2.1 and 1.8 (range 1.2 - 2.1) pmol/106 cells in PreB697 and Dex resistant sub-lines, respectively. While patient samples exhibited greater variability, Dex accumulation was not significantly different between sensitive and resistant cells; mean of 1.0 versus 1.4 (range 0.1-2.3, 0.4-4.4 pmol/ 106 cells, p=0.17). Flow cytometry Dex FITC accumulation confirmed these data, with a mean fluorescence intensity of 4.2 versus 4.1 (range 1.5-5.9, 2.0 - 9.1, respectively; p=0.97). These data suggest that while PK and cellular response are hugely variable, variations in drug accumulation do not appear to play a key role in Dex response in ALL cells. Importantly, 62% of patient cell samples had Dex GI50 values greater than plasma concentrations observed in any patient, on both arms on the UKALL 2011 trial. A combined approach incorporating PK assessments and cellular response in ALL cells should be further investigated, to allow a comprehensive understanding of Dex pharmacology with a view to optimizing its clinical utility. Citation Format: Rosanna K. Jackson, Ali Alhammer, Zach Dixon, Gareth J. Veal, Julie AE Irving. Personalization of dexamethasone in acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 707. doi:10.1158/1538-7445.AM2017-707