Imatinib-resistant Cell Lines Research Articles

The Relationship between MicroRNA Expression Profiling in Imatinib-Resistant Cell Line K562/G and Potential Mechanism through FOXO3/Bcl-6 Signaling Pathway

To investigate the drug resistant related FOXO3/Bcl-6 signaling pathway in K562/G cell line and its related microRNA(miRNA) mechanisms. The drug resistance potency of imatinib on K562/G was detected by MTT assay. The expression of FOXO3 and Bcl-6 proteins in K562 and K562/G cells was detected by Western blot. Real-time PCR (RT-PCR) was used to detect the expression of FOXO3 and Bcl-6 mRNA. The miRNA expression profiling in K562 and K562/G cells was analyzed by microarray technique, and the miRNA targeted to FOXO/Bcl-6 signaling pathway was identified. The expression of FOXO3 and Bcl-6 protein was significantly increased in K562/G cells as compared with that in K562 cells (P<0.01), the expression level of Bcl-6 mRNA showed no increase in K562/G cells. However, FOXO3 mRNA was up-regulated in K562/G cells (P<0.05). MiRNA microarray results showed that 109 miRNAs were expressed differentially in K562 and K562/G cells. The expression of 81 miRNAs were up-regulated while 28 miRNAs were down-regulated. Through reverse prediction by bioinformatics, miR-6718-5p, miR-5195-5p, miR-4711-3p, miR-4763-5p, miR-4664-5p and miR-3176 were related to FOXO/Bcl-6 signaling pathway. The FOXO3/Bcl-6 signaling pathway contributes to imatinib resistance in K562/G cell line, and the miRNA expression profiles showed significant differences between K562/G and K562 cells.

Research on the Mechanism of SIRT1/AMPK Inducing Resistance to Imatinib in K562 Cells By Inhibiting Srebp to Promote Lipid Metabolism

Background Leukemia stem cells (LSC) have the characteristics of independent of BCR-ABL kinase activity and metabolic reprogramming to support self-renewal. They are the root cause of the occurrence of chronic myeloid leukemia (CML), mediating TKI resistance and leading to clonal evolution. LSC self-renewal depends on the activity of SIRT1, the enhanced of SIRT1 induces LSC mitochondrial metabolic reprogramming. Studies have shown that SIRT1 and abnormally activated lipid metabolism are important reasons for inducing CML resistance to imatinib.Objective Study the mechanism of SIRT1 regulating lipid metabolism and intervention strategies under imatinib therapy.Method Liquid chromatography coupled with mass spectrometry (LC-MS) were used to analysis the lipid metabolism in imatinib-resistant CML cell line K562-R under low-glucose conditions. RT-qPCR and Western blot were used to detect the key enzymes related to lipid metabolism, and the SIRT1 inhibitor TV-6 was given to study the regulation mechanism of SIRT1 on lipid metabolism.Result Firstly, we found that the glycolysis/gluconeogenesis pathway and fatty acid metabolism were abnormal in K562-R cells by metabolomics, compared with normal culture conditions, the expression of SIRT1 and AMPK were significantly increased, the expression of fatty acid synthesis-related genes (SREBP, FASN, ACC, SCD1) was significantly reduced, and the fatty acid β oxidation rate-limiting enzyme CPT-1 is significantly increased inK562-R cells under low-glucose conditions. Therefore, in the low-glucose environment, the expression of the above genes was reversed after the application of the SIRT1 inhibitor TV-6.Conclusion K562-R imatinib-resistant cells can down-regulate the expression of SREBP through up-regulated SIRT1/AMPK pathway under low-glucose conditions, thereby inhibiting the expression of transcription factors involved in lipogenesis, reducing fatty acid synthesis, and providing the imatinib-resistant cells with the energy which required for proliferation.Keyword Chronic myeloid leukemia; Metabolomics; Lipid metabolism; SIRT1/AMPK DisclosuresNo relevant conflicts of interest to declare.

Altered apoptotic protein expressions characterize the survival of Bcr-Abl-independent drug-resistant chronic myeloid leukemia cell line

Apoptosis is a programmed cellular process that occurs in pathological and physiological pathways and it is one of the most studied topics in cell biology. To understand the underlying mechanism of apoptosis plays an important role in the molecular pathogenesis of many diseases including cancers. Chronic myeloid leukemia (CML) is a clonal myeloproliferative malignancy arising from the neoplastic transformation of the hematopoietic stem cell. Here, we used a Bcr-Abl-independent, imatinib-resistant K562 subpopulation (K562-IR) generated and characterized earlier in our laboratory. We showed that the proteins Bcl-2, Bim, RIP, p-MAPK(Erk1/Erk2) and NF-кB which play critical roles in cell death pathways are downregulated, Lamin A/C protein expression is upregulated in K562-IR derivative cells compared to K562 ancestral cells. Our data provide new information on the expression of apoptotic molecules in a Bcr-Abl-independent imatinib-resistant CML cell line.

H2O2 mediated FLIP and XIAP down-regulation involves increased ITCH expression and ERK-Akt crosstalk in imatinib resistant Chronic Myeloid Leukemia cell line K562

Regulation of anti-apoptotic protein FLICE-like inhibitory protein (FLIP) and X-linked inhibitor of apoptosis protein (XIAP) remains a crucial step in the cell fate determination and thus targeting these anti-apoptotic proteins could be a viable strategy for the treatment of cancer. However the regulation of FLIP and XIAP is not very well established till date. Here we have shown that ROS decreased XIAP and FLIP by activation of ubiquitin-proteasomal pathway in imatinib resistant K562 cells. Activation of the components of MAPK pathway, ERK and JNK, played a crucial role in XIAP and FLIP degradation because ectopic expression or knock down of ERK and JNK changed the pattern of ROS mediated down-regulation of these two proteins. We have also found that JNK and ERK differentially regulates FLIP and XIAP, respectively. Moreover, our data suggests that activated ERK decreased Akt phosphorylation and thus its binding to and stabilization of XIAP. On the other hand, JNK activation increased E3 ubiquitin ligase ITCH expression and its binding to FLIP which leads to its degradation. Thus, we have, for the first time elucidated that ROS mediated ERK-Akt crosstalk regulates XIAP. We have also shown for the first time that ROS regulates ITCH expression which controls FLIP degradation.

The BCRP inhibitor febuxostat enhances the effect of nilotinib by regulation of intracellular concentration.

Nilotinib is a substrate of the breast cancer resistance protein (BCRP), which is a drug efflux transporter encoded by ABCG2 and regulates the pharmacokinetics of its substrates. We investigated the interaction between nilotinib and BCRP in chronic myeloid leukemia (CML) cells. An imatinib-resistant K562 cell line (K562/IM-R) treated with nilotinib was analyzed for BCRP expression, proliferation, apoptosis, and intracellular nilotinib concentration. K562/IM-R cells cultured with tyrosine kinase inhibitors (TKIs) showed an increased cell count and retained viability, whereas the growth of parental K562 cells was severely inhibited, suggesting that BCRP is involved in developing resistance to TKIs. Nilotinib-treated K562/IM-R cells showed a reduction in apoptosis; however, febuxostat pretreatment resulted in increased apoptosis. The intracellular concentration of nilotinib in K562/IM-R cells was significantly reduced compared to that in parental K562 cells, and febuxostat-pretreated K562/IM-R cells showed an increased intracellular nilotinib level compared to cells without pretreatment. The reduction in nilotinib levels caused by BCRP in CML cells might play a crucial role in resistance to TKIs. Moreover, febuxostat, as a BCRP inhibitor, could enhance nilotinib sensitivity, and combination therapy with nilotinib and febuxostat may represent a promising strategy for treatment of CML.

The role of novel fusion genes in human GIST cell lines derived from imatinib-resistant GIST patients: A therapeutic potential of fusion gene

Gastrointestinal stromal tumor (GIST) is the most common sarcoma in the gastrointestinal (GI) tract. Approximately 85% of the GIST is associated with a c-KIT mutation. A few GISTs show mutations in the gene encoding platelet-derived growth factor receptor alpha (PDGFR α or PDGFRA) without c-KIT gene mutation. GIST without c-KIT or PDGFRA mutations, which called wild type GIST, is about 5–10% of the total GIST. Fusion genes were also reported as one of the factors associated with carcinogenesis and drug resistance. With five cell lines derived from imatinib-resistant patients, novel fusion genes were identified from RNA sequencing and both physiological role and therapeutic potential were elucidated. Next-generation sequencing (NGS) analysis and lentiviral transduction were used to effect of fusion gene on GISTs. All the GIST cell lines carried c-KIT-positivity. Three different fusion gene analysis methods were used to find candidate fusion genes, including EIF3K-ACTN4, SYNCRIP-SNX14 and EXOC2-AK7. A novel interchromosomal fusion gene of the candidates, especially EXOC2-AK7, was confirmed in both tissue and cell line. The transduction of fusion gene increased the proliferation compared with the control group. Additionally, the fusion gene increased wound coverage capability. The fusion gene-transduced cell lines were more sensitive than the control group in the treatment of imatinib. In conclusion, five different imatinib-resistant GIST cell lines including the EXOC2-AK7 fusion gene derived from GIST-R5 represent important research tools for the investigation of cancer cell mechanisms underlying drug resistance and genetic variation. Furthermore, our study may facilitate pre-clinical studies of new therapeutic strategies.

Correction of Bcl-x splicing improves responses to imatinib in chronic myeloid leukaemia cells and mouse models.

Imatinib mesylate (IM) resistance has become a major clinical problem for chronic myeloid leukaemia (CML). It is known that Bcl-x splicing is deregulated and is involved in multiple malignant cancer initiation and chemotherapy resistance, including CML. The aim of the present study was to correct the abnormal splicing of Bcl-x in CML and investigate the subsequent malignant phenotype changes, especially response to IM. The aberrant Bcl-x splicing in CML cells was effectively restored using vivo-Morpholino Antisense Oligomer (vMO). CCK-8 cell viability assay and flow cytometry showed that restoring of Bcl-x splicing increases IM-induced growth inhibition and apoptosis of K562 cells. Moreover, a more significant similar phenomenon was observed in imatinib-resistant CML cell lines K562/G01. Finally, establishment of CML xenograft model had also proved that correcting Bcl-x splicing in vivo can also enhance the anti-tumor effect of IM. Our findings suggest that vMO co-operating with IM can effectively increase the sensitivity of CML cells to IM both in vitro and in vivo, and Bcl-x splicing could become good candidates for chemotherapy-sensitized target in IM-resistant CML.

Cross-talk between Bcr-abl and the Thioredoxin System in Chronic Myeloid Leukaemia: Implications for CML Treatment.

Chronic myeloid leukaemia (CML) is currently treated with inhibitors of the CML specific oncoprotein, bcr-abl. While this strategy is initially successful, drug resistance can become a problem. Therefore, new targets need to be identified to ensure the disease can be appropriately managed. The thioredoxin (Trx) system, comprised of Trx, thioredoxin reductase (TrxR), and NADPH, is an antioxidant system previously identified as a target for therapies aimed at overcoming drug resistance in other cancers. We assessed the effectiveness of TrxR inhibitors on drug resistant CML cells and examined links between TrxR and the bcr-abl cell-signalling pathway. Two TrxR inhibitors, auranofin and [Au(d2pype)2]Cl, increased intracellular ROS levels and elicited apoptosis in both sensitive and imatinib resistant CML cells. Inhibition of TrxR activity by these pharmacological inhibitors, or by specific siRNA, also resulted in decreased bcr-abl mRNA and protein levels, and lower bcr-abl downstream signalling activity, potentially enhancing the effectiveness of TrxR inhibitors as CML therapies. In addition, imatinib resistant CML cell lines showed upregulated expression of the Trx system. Furthermore, analysis of datasets showed that CML patients who did not respond to imatinib had higher Trx mRNA levels than patients who responded to treatment. Our study demonstrates a link between the Trx system and the bcr-abl protein and highlights the therapeutic potential of targeting the Trx system to improve CML patients’ outcomes.

Lyn regulates creatine uptake in an imatinib-resistant CML cell line

BackgroundImatinib mesylate (imatinib) is the first-line treatment for newly diagnosed chronic myeloid leukemia (CML) due to its remarkable hematologic and cytogenetic responses. We previously demonstrated that the imatinib-resistant CML cells (Myl-R) contained elevated Lyn activity and intracellular creatine pools compared to imatinib-sensitive Myl cells. MethodsStable isotope metabolic labeling, media creatine depletion, and Na+/K+-ATPase inhibitor experiments were performed to investigate the origin of creatine pools in Myl-R cells. Inhibition and shRNA knockdown were performed to investigate the specific role of Lyn in regulating the Na+/K+-ATPase and creatine uptake. ResultsInhibition of the Na+/K+-ATPase pump (ouabain, digitoxin), depletion of extracellular creatine or inhibition of Lyn kinase (ponatinib, dasatinib), demonstrated that enhanced creatine accumulation in Myl-R cells was dependent on uptake from the growth media. Creatine uptake was independent of the Na+/creatine symporter (SLC6A8) expression or de novo synthesis. Western blot analyses showed that phosphorylation of the Na+/K+-ATPase on Tyr 10 (Y10), a known regulatory phosphorylation site, correlated with Lyn activity. Overexpression of Lyn in HEK293 cells increased Y10 phosphorylation (pY10) of the Na+/K+-ATPase, whereas Lyn inhibition or shRNA knockdown reduced Na+/K+-ATPase pY10 and decreased creatine accumulation in Myl-R cells. Consistent with enhanced uptake in Myl-R cells, cyclocreatine (Ccr), a cytotoxic creatine analog, caused significant loss of viability in Myl-R compared to Myl cells. ConclusionsThese data suggest that Lyn can affect creatine uptake through Lyn-dependent phosphorylation and regulation of the Na+/K+-ATPase pump activity. General significanceThese studies identify kinase regulation of the Na+/K+-ATPase as pivotal in regulating creatine uptake and energy metabolism in cells.

Coordinated targeting of CK2 and KIT in gastrointestinal stromal tumours

BackgroundMost gastrointestinal stromal tumours (GIST) are driven by activating oncogenic mutations of KIT/PDGFRA, which provide a compelling therapeutic target. Our previous studies showed that CDC37, regulated by casein kinase 2 (CK2), is a crucial HSP90 cofactor for KIT oncogenic function and a promising and more selective therapeutic target in GIST.MethodsBiologic mechanisms of CK2-mediated CDC37 regulation were assessed in GISTs by immunoblotting, immunoprecipitations, knockdown and inactivation assays. The effects of a combination of KIT and CK2 inhibition were assessed by immunoblotting, cell viability, colony growth, cell cycle analysis, apoptosis, migration and invasiveness.ResultsCK2 overexpression was demonstrated by immunoblotting in GIST cell lines and patient biopsies. Treatment with a specific CK2 inhibitor, CX4945, leads to CDC37 dephosphorylation and inhibits KIT signalling in imatinib-sensitive and in imatinib-resistant GIST cell lines. Immunoprecipitation demonstrated that CK2 inhibition blocks KIT:HSP90:CDC37 interaction in GIST cells. Coordinated inhibition of CK2 and KIT by CX4945 (or CK2 shRNA) and imatinib, respectively, leads to increased apoptosis, anti-proliferative effects and cell cycle arrest and decreased p-AKT and p-S6 expression, migration and invasiveness in all GIST cell lines compared with either intervention alone, indicating additive effects of inhibiting these two important regulators of GIST biology.ConclusionOur findings suggest that combinatorial inhibition of CK2 and KIT warrants evaluation as a novel therapeutic strategy in GIST, especially in imatinib-resistant GIST.

Preclinical Activity of the MPS1 Inhibitor S81694 in Acute Lymphoblastic Leukemia (ALL)

Introduction: The dual-specificity protein kinase, monopolar spindle 1 (Mps1) is one the main kinases of the spindle assembly checkpoint (SAC) critical for accurate segregation of sister chromatids during mitosis. A hallmark of cancer cells is chromosomal instability caused by deregulated cell cycle checkpoints and SAC dysfunction. Mps1 is known to be overexpressed in several solid tumors including triple negative breast cancer. Thus, Mps1 seems to be a promising target and small molecules targeting Mps1 entered clinical trials in solid tumors. ALL originates from malignant transformation of B-and T-lineage lymphoid precursors with a variety of genetic aberrations including chromosome translocations, mutations, and aneuploidies in genes responsible for cell cycle regulation and lymphoid cell development. While outcome is excellent for pediatric patients and younger adults, relapsed and refractory disease still remain a clinical challenge for elder patients. Here, we demonstrate for the first time preclinical efficacy of the small molecule Mps1 inhibitor (Mps1i) S81694 in T- and B- ALL cells including BCR-ABL1+-driven B-ALL. Materials and Methods: Expression of Mps1 was determined by RT-qPCR and WB in JURKAT, RS4-11 and BCR-ABL1+ cells (BV-173 and TOM-1). A small molecule Mps1i (S81694) was tested alone (0 to 1000nM) or in combination with imatinib, dasatinib, nilotinib and ponatinib in BCR-ABL1+ ALL cell lines. Cell viability and IC50 was assessed by MTS assays after exposure to Mps1i for 72h. In combination experiments, compounds were added simultaneously and relative cell numbers were determined at 72h with MTS assays and combination index (CI) values were calculated according to the Bliss model. Induction of apoptosis was evaluated by annexin-V exposure and PI incorporation at 72h with increasing doses of Mps1i. Cell-cycle distribution was determined by cytofluorometric analysis detecting nuclear propidium iodide (PI) intercalation at 48h. Phosphorylation of Mps1 was detected in synchronized (by nocodazole and MG-132) cells by immunofluorescence using an anti phospho-Mps1 antibody detecting Thr33/Ser37 residues. Time-lapse microscopy was used in cell lines in presence or absence of S81694 to determine mitosis duration. Bone marrow (BM) nucleated patient cells were obtained after informed consent and incubated in methylcellulose with cytokines with or without Mps1i for 2 weeks to determine colony growth. Results: Expression of Mps1 could be detected by RT-qPCR and at the protein level by WB in all cell lines (Figure 1A and B ). IC50 after Mps1i exposure alone was 126nM in JURKAT cells, 51nM in RS4-11 cells, 75nM in BV-173 cells and 83nM in TOM-1. Significant apoptosis as detected by phosphatidylserine exposure and PI incorporation in all cell lines with BCR-ABL1+ cell lines BV-173 and TOM-1 cells being the most sensitive (80% and 60% apoptotic cells respectively)(Figure 1C). Upon Mps1i exposure we observed targeted inhibition of Mps1 phosphorylation at Thr33/Ser37 residues indicating the specific on target effect of S81694 by inhibiting Mps1 autophosphorylation (Figure 1D and E). Cell cycle profile was generally lost after treatment with S81694 in all cell lines indicating aberrant 2n/4n distribution due to SAC abrogation (Figure 1F). Furthermore, we demonstrated that S81694 exposure accelerated significantly mitosis in BV-173 cell line from 36 minutes to 19 minutes indicating effective inhibition of SAC function (Figure 1G). Interestingly, S81694 induced significant apoptosis (70%) in the imatinib resistant BV173 cell line bearing the E255K-BCR-ABL1-mutation. Combination of S81694 with TKI imatinib, dasatinib and nilotinib (but not ponatinib) was strongly synergistic in BCR-ABL1+ cells (Figure 1H). Finally, we observed inhibition of colony formation in a patient with BCR-ABL1+ B-ALL after exposure to 100nM and 250nM S81694 (reduction of 85% and 100% respectively)(Figure 1I). Conclusion: Mps1i S81694 yields significant preclinical activity in T-and B-cell ALL including BCR-ABL1+ models. Interestingly S81694 was efficacious in a TKI resistant cell line. Disclosures Kaci: Institut de Recherches Internationales Servier (IRIS): Employment. Garrido:Institut de Recherches Internationales Servier (IRIS): Employment. Burbridge:Institut de Recherches Internationales Servier (IRIS): Employment. Dombret:AGIOS: Honoraria; CELGENE: Consultancy, Honoraria; Institut de Recherches Internationales Servier (IRIS): Research Funding. Braun:Institut de Recherches Internationales Servier (IRIS): Research Funding.

Preclinical development of HQP1351, a multikinase inhibitor targeting a broad spectrum of mutant KIT kinases, for the treatment of imatinib-resistant gastrointestinal stromal tumors

BackgroundImatinib shows limited efficacy in patients with gastrointestinal stromal tumors (GISTs) carrying secondary KIT mutations. HQP1351, an orally bioavailable multikinase BCR-ABL inhibitor, is currently in clinical trials for the treatment of T315I mutant chronic myelogenous leukemia (CML), but the potential application in imatinib-resistant GISTs carrying secondary KIT mutations has not been explored.MethodsThe binding activities of HQP1351 with native or mutant KIT were first analyzed. Imatinib-sensitive GIST T1 and imatinib-resistant GIST 430 cells were employed to test the in vitro antiproliferative activity. Colony formation assay, cell migration assay and cell invasion assay were performed to evaluate the clonogenic, migration and invasion ability respectively. Flow cytometry and western blot analysis were used to detect cell apoptosis, cell cycle and signaling pathway. In vivo antitumor activity was evaluated in mouse xenograft models derived from GIST cell lines.ResultsHQP1351 potently inhibited both wild-type and mutant KIT kinases. In both imatinib-resistant and sensitive GIST cell lines, HQP1351 exhibited more potent or equivalent antiproliferative activity compared with ponatinib, a third generation BCR-ABL and KIT inhibitor. HQP1351 led to more profound inhibition of cell colony formation, cell migration and invasion, cell cycle arrest and cell apoptosis than ponatinib. Furthermore, HQP1351 also inhibited p-KIT, p-AKT, p-ERK1/2, and p-STAT3 to a higher extent than ponatinib. Finally, in xenograft tumor models derived from imatinib-resistant GIST cancer cell lines, HQP1351 exhibited antitumor activity superior to ponatinib.ConclusionsCollectively, our in vitro and in vivo results suggest that the therapeutic application of HQP1351 in imatinib-resistant GIST patients deserves further investigation in clinical trials.

PS930 SENSITIZATION OF PH+ ALL RESISTANT TO IMATINIB BY TARGETING SPHINGOLIPID METABOLISM

Background:Acute lymphoblastic leukemia (ALL) is formed by accumulation of lymphoblasts in bone marrow and peripheral blood. The most common subtype of ALL is philadelphia positive ALL (Ph+ ALL) which is characterized by having BCR/ABL protein. For the treatment of Ph+ALL tyrosine kinase inhibitors (TKI) such as imatinib are used. However, 60–75% of the patients can still develop resistance against the TKIs and die within 5 years. Bioactive sphingolipids are a group of lipid family having ceramide as the central molecule, that play roles in many cellular mechanisms including proliferation, apoptosis, inflammation, metastasis. Ceramide is known to induce apoptosis which makes this sphingolipid a useful tool in cancer treatment. Sphingolipids can be generated through different pathways including de novo synthesis, recycling and salvage pathways. Previous studies showed that bioactive sphingolipids and genes in the pathway have been involved in response to TKI treatment in Ph+ALL.Aims:Here, we studied the roles of bioactive sphingolipids on the growth inhibitory effects of imatinib and exploit sphingolipid metabolism by majorly inhibiting glucosylceramide synthase (GCS) to further sensitize cells to imatinib and/or overcome resistance to imatinib in Ph+ ALL.Methods:Imatinib resistant cell line SD‐1R is generated by clonal selection from parental SD‐1 cell line by exposing the cells to gradually increased concentration of imatinib. Intracellular lipid levels were measured by HPLC/MS/MS. Cell viability is detected by MTT and trypan blue exclusion assay. Gene and protein expression levels were detected by real time PCR and western blotting, respectively.Results:We detected that intracellular levels of sphingolipids: ceramide, sphingosine and sphingomyelin is increased in response to imatinib in parental SD‐1 cells but not in newly generated SD‐1R cells. The data showed that these changes are not detectable in SD‐1 cells when imatinib is applied in presence of myriocin which is a palmitoyltransferase inhibitor that blocks the first step of de novo synthesis pathway in sphingolipids suggesting that imatinib induced changes in sphingolipids are due to induction of de novo synthesis pathway and a defect in this pathway is contributing the regulation of imatinib resistance in SD‐1R cells. Interestingly, another sphingolipid hexosylceramide which is a product of further metabolization of ceramide by the enzyme GCS, levels were elevated in both SD‐1 and SD‐1R cells. Knowing that, an FDA approved drug eliglustat, which is a GCS inhibitor used in Gaucher's disease is used to block the conversion of ceramide to hexosylceramide to accumulate apoptotic ceramide levels to sensitize cells to imatinib. Indeed, at the lipid levels, this combination resulted in a greater increase in ceramide and sphingosine levels. The reflection of these changes on cell growth was also detected and in parental SD‐1 cells, eliglustat application with imatinib is sensitized the cells to imatinib induced growth inhibition by 50% whereas eliglustat and imatinib cotreatment was able to overcome imatinib resistance in SD‐1R cells and inhibiting cell growth by 60–70% at 48 h.Summary/Conclusion:Taken together for the first time in the literature, we showed that pharmacological inhibition of GCS by eliglustat and imatinib cotreatment has synergistic cytostatic effects on imatinib resistant Ph+ ALL cells. Additionally, inducing the accumulation of ceramide (and/or sphingosine) by this cotreatment might be used as an approach to sensitize intrinsically / acquired resistant Ph+ ALL.

Molecular prediction of chronic myeloid leukemia risk and resistance to imatinib.

e18543 Background: Chronic myeloid leukemia (CML) is characterized by the Bcr-Abl genetic translocation which leads to constitutive tyrosine kinase signaling. Treatment with tyrosine kinase inhibitors as imatinib eliminates CML cells, but resistance often occurs. No specific molecular risk factors or imatinib-resistance predictors have been validated so far, thus the aim of this study was to determine genetic factors that would allow for a better management of this disease. Methods: An age and gender matched case-control study of 57 CML patients and 63 healthy controls was performed. In vitro experiments were performed on K562 cells and an imatinib-resistant K562R cell line. CML patients were treated with imatinib and stratified into responders (complete molecular response after three months, CMR) and non-responders. RNA was isolated from blood leukocytes or cells and used for cDNA synthesis. Gene expression levels were evaluated by real-time PCR and the results analyzed using the delta-delta-Ct method. Differences in expression levels and their prognostic/predictive potentials were evaluated by t-test, linear regression analysis and receiver operating characteristics curve, with statistical significance set at p &lt; 0.05. Results: In CML patients, the Bcl2 and IGF-1R mRNA expression level were higher than in controls (1.03 ± 0.06 vs. 0.92 ± 0.18, p &lt; 0.0001; 1.14 ± 0.15 vs. 1.03 ± 0.15, p = 0.0001, respectively). Prior to treatment, the Bcl2 mRNA levels were lower for the K562 than for the resistant K562R cell line (1.13±0.04 vs. 1.62±0.01, p &lt; 0.0001), and the same was observed for IGF-1R (1.22±0.01 vs. 1.29±0.01, p = 0.001). Patients who achieved a CMR after imatinib treatment had significantly lower pre-treatment levels of Bcl-2 and IGF-1R (0.99 ± 0.05 vs. 1.04 ± 0.06, p = 0.005; 1.12 ± 0.02 vs. 1.15 ± 0.04, p = 0.0123, respectively) compared to patients who did not achieve a CMR, which confirmed the in vitro observed data. Conclusions: High levels of Bcl-2 and IGF-1R mRNA were detected in CML patients, and the analysis of their expression might be used as a low-cost CML screening tool. Successful imatinib treatment was correlated with significantly lower pre-treatment Bcl-2 and IGF-1R levels in vitro and in vivo, which might also be used as a low-cost molecular predictor of a favorable clinical response .

Potentiation of imatinib by cilostazol in sensitive and resistant gastrointestinal stromal tumor cell lines involves YAP inhibition.

Despite the introduction of tyrosine kinase inhibitors, gastrointestinal stromal tumors (GIST) resistance remains a major clinical challenge. We previously identified phosphodiesterase 3A (PDE3A) as a potential therapeutic target expressed in most GIST. The PDE3 inhibitor cilostazol reduced cell viability and synergized with the tyrosine kinase inhibitor imatinib (Gleevec™) in the imatinib-sensitive GIST882 cell line. Here, we found that cilostazol potentiated imatinib also in the imatinib-resistant GIST48 cell line. Cilostazol induced nuclear exclusion, hence inactivation, of the transcriptional co-activator YAP, in a cAMP-independent manner. Verteporfin, a YAP/TEAD interaction inhibitor, reduced by 90% the viability of both GIST882 and GIST48 cells. Our results highlight the potential use of compounds targeting PDE3A or YAP in combined multitherapy to tackle GIST resistance.

Andrographolide and its potent derivative exhibit anticancer effects against imatinib-resistant chronic myeloid leukemia cells by downregulating the Bcr-Abl oncoprotein

Chronic myelogenous leukemia (CML) is clinically treated with imatinib, which inhibits the kinase activity of the Bcr-Abl oncoprotein. However, imatinib resistance remains a common clinical issue. Andrographolide, the major compound of the medicinal plant Andrographis paniculata, was reported to exhibit anticancer activity. In this study, we explored the therapeutic potential of andrographolide and its derivative, NCTU-322, against both imatinib-sensitive and imatinib-resistant human CML cell lines. Both andrographolide and NCTU-322 downregulated the Bcr-Abl oncoprotein in imatinib-resistant CML cells through an Hsp90-dependent mechanism similar to that observed in imatinib-sensitive CML cells. In addition, NCTU-322 had stronger effects than andrographolide on downregulation of Bcr-Abl oncoprotein, induction of Hsp90 cleavage and cytotoxicity of CML cells. Notably, andrographolide and NCTU-322 could induce differentiation, mitotic arrest and apoptosis of both imatinib-sensitive and imatinib-resistant CML cells. Finally, the anticancer activity of NCTU-322 against imatinib-resistant CML cells was demonstrated in vivo. In summary, our data demonstrated that andrographolide and NCTU-322 inhibit Bcr-abl function via a mechanism different from that of imatinib, and they induced multiple anticancer effects in both imatinib-sensitive and resistant CML cells. Our findings demonstrate that andrographolide and NCTU-322 are potential therapeutic agents again CML.

Intracellular concentration and transporters in imatinib resistance of gastrointestinal stromal tumor

Background: We aimed to investigate the role of intracellular imatinib concentration in drug resistance and the expression of candidate drug transporters in gastrointestinal stromal tumor (GIST) cell lines.Method: The imatinib concentrations were measured by the liquid chromatography-tandem mass spectrometry (LC-MS/MS). The expression of candida te drug transporters was detected by qRT-PCR.Results: The tissue imatinib concentrations in imatinib resistant patients were significantly lower than that of sensitive patients (p < .05). Compared with parental cell lines, the intracellular imatinib concentration was notably lower in imatinib resistant GIST cell lines. For candidate transporters, MRP1 and BCRP were overexpressed in resistant GIST cell lines.Conclusion: The intracellular imatinib concentration may play a crucial role in imatinib resistance and the intracellular differences of imatinib concentration may be induced by the upregulation of efflux transporters. Our study highlights the importance of intracellular imatinib concentration and the potential of using imatinib transporters as therapeutic targets for patients with GIST.

Lncrna RP1-68D18.2 Promotes K562 Cell Line Resistance to Imatinib through CD44 and Its Downstream Signal Molecules

As the first-generation tyrosine kinase inhibitor specifically targeting the BCR-ABL oncoprotein, imatinib has been successfully used in the therapy for chronic myelogenous leukemia (CML) with a significant response and good compliance. However, imatinib resistance becomes the main reason for failure of the treatment of CML. In addition to the common BCR-ABL dependence of imatinib resistance, e.g. BCR-ABL kinase domain mutations and BCR-ABL gene amplification, BCR-ABL independence also plays important roles, which involves alteration of dynamics of drug import and efflux, persistent or compensatory activation of signaling pathways etc. Recently, several studies have reported the correlation of lncRNA with resistance of chemotherapeutic drugs in many cancers. Here, we report, for the first time, discernible overexpression of lncRNARP1-68D18.2 and CD44 mRNA in the imatinib resistant chronic myelogenous leukemia cell line K562R, using lncRNA and mRNA microarray, and further verify it using qPCR. Knockdown of RP1-68D18.2 in K562R cell lines increased their sensitivity to imatinib, and simultaneously caused a decrease in CD44 and c-Myc protein levels. Correspondingly, overexpression of RP1-68D18.2 in K562, a sensitive cell line, led to a slightly decrease in imatinib sensitivity and partially reverse downregulation of c-Myc, p-ERK and p-MEK caused by imatinib treatment. Analysis of correlations revealed positive correlation between RP1-68D18.2 and CD44 mRNA expression in the primary CML blasts and hematological malignant cell lines. We conclude that overexpression of RP1-68D18.2 could promote imatinib resistance in the K562R cell line through the regulation of CD44 and its downstream signal molecules. DisclosuresNo relevant conflicts of interest to declare.

(-)-Epigallocatechin-3-gallate induces cell apoptosis in chronic myeloid leukaemia by regulating Bcr/Abl-mediated p38-MAPK/JNK and JAK2/STAT3/AKT signalling pathways.

Epigallocatechin-3-gallate (EGCG), a major polyphenolic constituent of green tea, possesses remarkable chemopreventive and therapeutic potential against various types of cancer, including leukaemia. However, the molecular mechanism involved in chronic myeloid leukaemia (CML), especially imatinib-resistant CML cells, is not completely understood. In the present study, we investigated the effect of EGCG on the growth of Bcr/Abl+ CML cell lines, including imatinib-resistant cell lines and primary CML cells. The results revealed that EGCG could inhibit cell growth and induce apoptosis in CML cells. The mechanisms involved inhibition of the Bcr/Abl oncoprotein and regulation of its downstream p38-MAPK/JNK and JAK2/STAT3/AKT pathways. In conclusion, we documented the anti-CML effects of EGCG in imatinib-sensitive and imatinib-resistant Bcr/Abl+ cells, especially T315I-mutated cells.

Abstract 366: Association of MLL2/KMT2D and MLL3/KMT2C with chronic myeloid leukemia

Abstract Chronic myeloid leukemia (CML) is a clonal myeloproliferative neoplasm linked to the Philadelphia chromosome presence that generates the BCR-ABL1 fusion oncogene. Tyrosine kinase inhibitors (TKI) such as imatinib mesylate (IM) dramatically improved the treatment efficiency and survival of CML patients by targeting BCR-ABL tyrosine kinase. Although patients in the chronic phase respond well to treatment, patients in the accelerated phase or blast crisis usually show therapy resistance and CML relapse. It is crucial, therefore, to identify biomarkers to predict CML genetic evolution and resistance to TKI therapy, considering not only the effects of genetic aberrations but also the role of epigenetic alterations during the disease. Although dysregulations in epigenetic modulators such as histone methyltrasnferases have already been described for some hematologic malignancies, to date very limited data is available for CML, especially when considering the MLL2/KMT2D and MLL3/KMT2C genes of histone methyltrasnferases. Here we investigated the expression profile of both genes in CML patients in different stages of the disease, in patients showing different responses to therapy with IM and in non-neoplastic control samples. Imatinib sensitive and resistant CML cell lines were also used to investigate whether treatment with other tyrosine kinase inhibitors interfered in their expression. Both genes were either upregulated or with basal expression level during the chronic phase compared to controls. Interestingly, MLL3/KMT2C and specially MLL2/KMT2D levels decreased during disease progression correlating with distinct clinical stages. Furthermore, MLL2/KMT2D was decreased in patients resistant to IM treatment. Our results established a new association between MLL2/KMT2D and MLL3/KMT2C genes with CML and suggest that MLL2/KMT2D is associated with disease evolution and may be a potential marker to predict the development of therapy resistance. Citation Format: Doralina do Amaral Rabello Ramos, Vivian D'Afonseca da Silva Ferreira, Maria Gabriela Berzoti-Coelho, Sandra Mara Burin, Cíntia Leticia Magro, Maira da Costa Cacemiro, Belinda Pinto Simões, Felipe Saldanha-Araujo, Fabíola Attié Castro, Fábio Pittella-Silva. Association of MLL2/KMT2D and MLL3/KMT2C with chronic myeloid leukemia [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 366.