K562R Cells Research Articles

Distinct EphB4-mediated mechanisms of apoptotic and resistance to dasatinib in human chronic myeloid leukemia and K562 cell lines

ObjectiveTo determine the role and mechanism of EphB4 in dasatinib (DAS) resistance in advanced chronic myeloid leukemia (CML), we explored the EphB4-mediated apoptotic and matrix microenvironment pathway in human CML and K562 cell lines. MethodHeparinized bone marrow samples were obtained from enrolled five patients (identified as A to E and visits identified by number) at initial diagnosis (A1–E1) and in the DAS-resistance advanced phase (A2–E2). Meanwhile, highly DAS-resistant cells, named K562-R cells, were obtained from K562-W cells with increasing concentrations of DAS. Stable under-expressing EphB4 cells (K562-R-EphB4-sh) were obtained from K562-R cells by RNA interference. K562-W, K562-R and K562-R-EphB4-sh cells (108) were respectively injected subcutaneously on the dorsal surface of BALB/C female nude mice to establish the xenografts models. ResultThe mRNA/protein of EphB4 was overexpressed in the DAS-resistant A2–E2 in comparison with the A1–E1 human cell lines. Further, compared with K562-R cells, the expressions of EphB4 and p-Rac1/Cdc42 protein/mRNA were significantly downregulated in K562-R-EphB4-sh cells (P<0.01). K562–R cells showed the highest DAS resistance (IC50 10.54±0.67μg/ml), but K562-R-EphB4-sh cells became sensitive to DAS (IC50 1.02±0.1μg/ml, P<0.01). The expression of EphB4/p-RhoA/MCL-1 protein was gradually increased in the stimulating of EphrinB2-Fc, which partly made K562-R-EphB4-sh cells restore sensitivity to DAS (4.18±0.30μg/ml). Meanwhile, the K562-R-EphB4-sh xenografts group had relatively good efficacy compared to K562-R xenografts nude mice receiving the same dose of DAS. The analysis of xenografts tissue also suggested parallel results with the overexpression of EphB4/RhoA/ROCK1/PTEN/MCL-1 in K562-R xenografts, which decreased in the A2-R-EphB4-sh xenografts (P<0.01). ConclusionsThe present study found that a new DAS resistance pathway of EphB4 overexpression was triggered by EphrinB2-Fc, which induced the resistance to DAS by activating RhoA/ROCK1/PTEN/MCL-1 signaling.

Anti-Leukemia Effect and Mechanism of Oridonin on Imatinib-Sensitive and Imatinib-Resistant K562 Cells

To explore the molecular mechanism of resistance to imatinib in K562 cells(K562-R) and the anti-proliferative effect of oridonin (OR), as well as its mechanism in imatinib-sensitive and imatinib-resistant K562 cells (K562-S and K562-R cells). The expression of p-Lyn in K562-S and K562-R cells were detected by Western blot. The anti-proliferative effect of OR in K562-S and K562-R cells was assayed by MTT, the morphological changes were examined with microscope, the cell apoptosis was detected by flow cytometry, the expressions of BCL-2 and Akt/mTOR signaling pathway were detected by Western blot. The over-expression of p-Lyn was detcected in K562-R cells, OR inhibited the proliferation of K562-S and K562-R cells and the value of IC50 was 4.23±1.30, 4.97±2.23 µmol/L, respectively. The apoptotic rate was obviously enhanced after OR treatment for 24 h, compared with control group. OR down-regulated the expression of p-Lyn, mTOR signaling pathway and BCL-2 protein. Over-expression of p-Lyn may be involved in the mechanism of resistance to imatinib. OR can inhibit the proliferation of K562-S and K562-R cells through down-regulating p-Lyn, inhibiting mTOR signaling pathway and down-regulating expression of BCL-2 protein.

Erratum to: A novel tubulin polymerization inhibitor, MPT0B206, downregulates Bcr-Abl expression and induces apoptosis in imatinib-sensitive and imatinib-resistant CML cells.

Imatinib, a Bcr-Abl-specific inhibitor, is effective for treating chronic myeloid leukemia (CML), but drug resistance has emerged for this disease. In this study, we synthesized a novel tubulin polymerization inhibitor, MPT0B206 (N-[1-(4-methoxy-benzenesulfonyl)-2,3-dihydro-1H-indol-7-yl]-formamide), and demonstrated its apoptotic effect and mechanism in imatinib-sensitive K562 and imatinib-resistant K562R CML cells. Western blotting and immunofluorescence microscopy showed that MPT0B206 induced microtubule depolymerization in K562 and K562R cells. MPT0B206 inhibited the growth of these cells in a concentration- and time-dependent manner. It did not affect the viability of normal human umbilical vein endothelial cells. MPT0B206 induced G2/M cell cycle arrest and the appearance of the mitotic marker MPM-2 in K562 and K562R cells, which is associated with the upregulation of cyclin B1 and the dephosphorylation of Cdc2. Treatment of K562 and K562R cells with MPT0B206 induced apoptosis and reduced the protein levels of procaspase-9 and procaspase-3 and increased caspase-3 activity and PARP cleavage. MPT0B206 also reduced the levels of the antiapoptotic proteins Mcl-1 and Bcl-2 and increased the level of the apoptotic protein Bax. Additional experiments showed that MPT0B206 markedly downregulated Bcr-Abl mRNA expression and total and phosphorylated Bcr-Abl protein levels and inhibited the phosphorylation of its downstream proteins STAT5, MAPK, and AKT, and the protein level of c-Myc in K562 and K562R cells. Furthermore, MPT0B206 triggered viability reduction and apoptosis in CML cells carrying T315I-mutated Bcr-Abl. Together, these results suggest that MPT0B206 is a promising alternative for treating imatinib-resistant CML.

Time-series analysis in imatinib-resistant chronic myeloid leukemia K562-cells under different drug treatments.

SummaryChronic myeloid leukemia (CML) is characterized by the accumulation of active BCR-ABL protein. Imatinib is the first-line treatment of CML; however, many patients are resistant to this drug. In this study, we aimed to compare the differences in expression patterns and functions of time-series genes in imatinib-resistant CML cells under different drug treatments. GSE24946 was downloaded from the GEO database, which included 17 samples of K562-r cells with (n=12) or without drug administration (n=5). Three drug treatment groups were considered for this study: arsenic trioxide (ATO), AMN107, and ATO+AMN107. Each group had one sample at each time point (3, 12, 24, and 48 h). Time-series genes with a ratio of standard deviation/average (coefficient of variation) >0.15 were screened, and their expression patterns were revealed based on Short Time-series Expression Miner (STEM). Then, the functional enrichment analysis of time-series genes in each group was performed using DAVID, and the genes enriched in the top ten functional categories were extracted to detect their expression patterns. Different time-series genes were identified in the three groups, and most of them were enriched in the ribosome and oxidative phosphorylation pathways. Time-series genes in the three treatment groups had different expression patterns and functions. Time-series genes in the ATO group (e.g. CCNA2 and DAB2) were significantly associated with cell adhesion, those in the AMN107 group were related to cellular carbohydrate metabolic process, while those in the ATO+AMN107 group (e.g. AP2M1) were significantly related to cell proliferation and antigen processing. In imatinib-resistant CML cells, ATO could influence genes related to cell adhesion, AMN107 might affect genes involved in cellular carbohydrate metabolism, and the combination therapy might regulate genes involved in cell proliferation.

Cholesterol esterification inhibition and imatinib treatment synergistically inhibit growth of BCR-ABL mutation-independent resistant chronic myelogenous leukemia.

Since the advent of tyrosine kinase inhibitors (TKIs) such as imatinib, nilotinib, and dasatinib, chronic myelogenous leukemia (CML) prognosis has improved greatly. However, ~30–40% of patients develop resistance to imatinib therapy. Although most resistance is caused by mutations in the BCR-ABL kinase domain, 50–85% of these patients develop resistance in the absence of new mutations. In these cases, targeting other pathways may be needed to regain clinical response. Using label-free Raman spectromicroscopy, we evaluated a number of leukemia cell lines and discovered an aberrant accumulation of cholesteryl ester (CE) in CML, which was found to be a result of BCR-ABL kinase activity. CE accumulation in CML was found to be a cancer-specific phenomenon as untransformed cells did not accumulate CE. Blocking cholesterol esterification with avasimibe, a potent inhibitor of acyl-CoA cholesterol acyltransferase 1 (ACAT-1), significantly suppressed CML cell proliferation in Ba/F3 cells with the BCR-ABLT315I mutation and in K562 cells rendered imatinib resistant without mutations in the BCR-ABL kinase domain (K562R cells). Furthermore, the combination of avasimibe and imatinib caused a profound synergistic inhibition of cell proliferation in K562R cells, but not in Ba/F3T315I. This synergistic effect was confirmed in a K562R xenograft mouse model. Analysis of primary cells from a BCR-ABL mutation-independent imatinib resistant patient by mass cytometry suggested that the synergy may be due to downregulation of the MAPK pathway by avasimibe, which sensitized the CML cells to imatinib treatment. Collectively, these data demonstrate a novel strategy for overcoming BCR-ABL mutation-independent TKI resistance in CML.

Selection of P-Glycoprotein Inhibitor and Formulation of Combinational Nanoformulation Containing Selected Agent Curcumin and DOX for Reversal of Resistance in K562 Cells.

To select P-glycoprotein (P-gp) inhibitor from natural source for reversal of DOX resistance in K562 cells and to develop selected one in to nanoformulation in combination with DOX. DOX resistant K562 (K562R) cells were developed and reversal of resistance by P-gp inhibitor was validated by co-treatment with verapamil. The p-gp inhibitors were evaluated for their potential to inhibit P-gp (calcein assay) and to reverse drug resistance (XTT cell viability assay). The selected agent, curcumin was formulated in to liposome along with DOX and characterized for size, zeta potential, encapsulation efficiency and release rate. Uptake, P-gp inhibition and reversal of acquired drug resistance in K562R cells were performed. P-gp inhibitors such as biochanin-A and curcumin were marked suitable for combination with DOX. However, only curcumin could increase the sensitivity of DOX at all dosing levels, therefore used for further studies. Liposomes loaded with curcumin were formulated and characterized where a prolonged release was observed. The uptake of liposomal curcumin was comparable to nanodispersed curcumin but had lower cytotoxicity. DOX and curcumin coloaded liposomes successfully reversed DOX resistance in K562 cells. The coloaded liposomes increased the safety of curcumin with improved efficacy thus can be employed for reversal of acquired DOX resistance.

Downregulation of miR-224 and let-7i contribute to cell survival and chemoresistance in chronic myeloid leukemia cells by regulating ST3GAL IV expression

Acquired resistance to imatinib is frequently associated with poor clinical outcome of chronic myeloid leukemia (CML) patient. To date, evidence indicates that protein glycosylation and its upstream regulators might be implicated in tumorigenesis and chemoresistance occurrence. In current study we initially explored N-glycan profiles on the surface of CML cell lines and bone marrow mononuclear cells (BMMC) of CML patients by using mass spectrometry (MS) analysis. An elevated sialylation was detected in K562R cells (CML cells with imatinib resistance phenotype) compare to K562 cells. By quantitative real time-PCR (qRT-PCR) and western blotting analysis we observed that imatinib resistant K562R cells exhibited marked high levels of CMP-N-acetylneuraminate-beta-galactosamide-alpha-2,3-sialyltransferase (ST3Gal IV) as compared to imatinib sensitive K562 cells. Further studies revealed that manipulated expression of ST3GAL IV led to the significant alterations of cell cycle distribution, apoptotic signal, cell proliferation and the effectiveness of imatinib treatment. Using microRNA array, miRNA database searching and luciferase reporter assay, we identified that miR-224 and let-7i directly regulate the expression of ST3GAL IV gene. Moreover, engineered expression of miR-224 and let-7i in K562 and K562R cells could significantly affect ST6Gal IV-induced proliferation rate and drug-resistance. Thus we propose that miR-224 and let-7i regulate the proliferation and chemosensitivity of CML cells probably via targeting ST3GAL IV.

Secretion of IL-1β from imatinib-resistant chronic myeloid leukemia cells contributes to BCR–ABL mutation-independent imatinib resistance

Abstract Some cases of chronic myelogenous leukemia are resistant to tyrosine kinase inhibitors (TKIs) independently of mutation in BCR–ABL, but the detailed mechanism underlying this resistance has not yet been elucidated. In this study, we generated a TKI-resistant CML cell line, K562R, that lacks a mutation in BCR–ABL. Interleukin-1β(IL-1β) was upregulated in imatinib-resistant K562R than in the parental cell line K562S, and higher levels of IL-1β contributed to the imatinib resistance of K562R and to cell survival. In addition, IL-1β secreted by K562R cells could stimulate a bone marrow stromal cell line to produce chemokines, such as CXCL11, that lead to the migration of the CML cells into the stroma. Thus, elevated IL-1β production from TKI-resistant K562R cells may contribute to TKI resistance by increasing cell viability and promoting cell migration.

Original Vinca Derivatives: From P-Glycoprotein Substrates to P-Glycoprotein Inhibitors.

The first example of vinca derivatives 16-18 able to modulate P-glycoprotein (Pgp) efflux activity is reported. They were elaborated in two steps from vinorelbine 3 (VLN) by a modification of the velbenamine moiety. These compounds were able to decrease efficiently Pgp mediated influx and efflux of rhodamine-123 (Rho) and to restore the cytotoxicity of vinorelbine 3 (VLN) and doxorubicin (Dox) on K562R (dox-resistant) cell lines.

The role of long noncoding RNA HOTAIR in the acquired multidrug resistance to imatinib in chronic myeloid leukemia cells

ABSTRACTObjectives: Imatinib, a breakpoint cluster region-Abelson murine leukemia tyrosine kinase inhibitor, has revolutionized the treatment of chronic myelogenous leukemia (CML). However, the development of multidrug resistance (MDR) limits the clinical application of imatinib. In this study, we aimed to investigate the mechanisms of long noncoding RNA (lncRNA) HOTAIR in CML resistance to imatinib.Methods: Thirty-four CML patients were divided into multidrug resistance protein 1 (MRP1)-low and MRP1-high groups according to the median expression. Real-time PCR (qPCR) was used to detect the expression of lncRNA HOTAIR in CML patients, and MTT assay and flow cytometry assay were employed to detect the biological function of silencing lncRNA HOTAIR on the cell survival rate and apoptotic rate. An imatinib-resistant human CML cell line K562 (K562-R) was established, and western blot was used to detect the impact of lncRNA HOTAIR on the activation of PI3K/Akt signaling pathway.Results: Our results showed that lncRNA HOTAIR was greatly upregulated in the MRP1-high patients as well as in the K562-imatinib-resistant cells compared with control. Knockdown of HOTAIR expression downregulated the MRP1 expression levels in the K562-imatinib cells and resulted in higher sensitivity to the imatinib treatment. In addition, the activation of PI3K/Akt was greatly attenuated when HOTAIR was knocked down in K562-imatinib cells.Discussions: These data suggest that the knockdown of HOTAIR may play a crucial role in improving acquired resistance to imatinib in CML K562-R cells via PI3K/Akt pathway.Conclusions: LncRNA HOTAIR modulates CML cell MDR in a PI3K/Akt-dependent way.

A novel tubulin polymerization inhibitor, MPT0B206, downregulates Bcr-Abl expression and induces apoptosis in imatinib-sensitive and imatinib-resistant CML cells.

Imatinib, a Bcr-Abl-specific inhibitor, is effective for treating chronic myeloid leukemia (CML), but drug resistance has emerged for this disease. In this study, we synthesized a novel tubulin polymerization inhibitor, MPT0B206 (N-[1-(4-methoxy-benzenesulfonyl)-2,3-dihydro-1H-indol-7-yl]-formamide), and demonstrated its apoptotic effect and mechanism in imatinib-sensitive K562 and imatinib-resistant K562R CML cells. Western blotting and immunofluorescence microscopy showed that MPT0B206 induced microtubule depolymerization in K562 and K562R cells. MPT0B206 inhibited the growth of these cells in a concentration- and time-dependent manner. It did not affect the viability of normal human umbilical vein endothelial cells. MPT0B206 induced G2/M cell cycle arrest and the appearance of the mitotic marker MPM-2 in K562 and K562R cells, which is associated with the upregulation of cyclin B1 and the dephosphorylation of Cdc2. Treatment of K562 and K562R cells with MPT0B206 induced apoptosis and reduced the protein levels of procaspase-9 and procaspase-3 and increased caspase-3 activity and PARP cleavage. MPT0B206 also reduced the levels of the antiapoptotic proteins Mcl-1 and Bcl-2 and increased the level of the apoptotic protein Bax. Additional experiments showed that MPT0B206 markedly downregulated Bcr-Abl mRNA expression and total and phosphorylated Bcr-Abl protein levels and inhibited the phosphorylation of its downstream proteins STAT5, MAPK, and AKT, and the protein level of c-Myc in K562 and K562R cells. Furthermore, MPT0B206 triggered viability reduction and apoptosis in CML cells carrying T315I-mutated Bcr-Abl. Together, these results suggest that MPT0B206 is a promising alternative for treating imatinib-resistant CML.

EphB4-VAV1 signaling pathway is associated with imatinib resistance in chronic myeloid leukemia cells

Imatinib (IM) resistant Chronic Myeloid Leukemia (CML) is an important issue to be addressed while treating CML patients. The present study analyzes the role of EphB4-VAV1 signaling in IM-resistant CML. EphB4 and VAV1 were overexpressed in IM-resistant CML patients and K562-R cell line (K562-R). Then, we established stable under-expressing EphB4 cell line K562-R-EphB4-sh. VAV1 was down-regulated in K562-R-EphB4-sh cells. K562-R-EphB4-sh cells gained re-sensitivity to IM and K562-R cells showed mild IM resistance. However, EphB4 was no changed when the VAV1 was down-regulated. EphB4 and VAV1 were overexpressed in IM-resistant CML, VAV1might be the downstream moleculars of EphB4. These results suggest a potential role of EphB4-VAV1 signaling as therapeutic target of IM-resistant CML.

Secretion of IL-1β from imatinib-resistant chronic myeloid leukemia cells contributes to BCR-ABL mutation-independent imatinib resistance.

Some cases of chronic myelogenous leukemia are resistant to tyrosine kinase inhibitors (TKIs) independently of mutation in BCR-ABL, but the detailed mechanism underlying this resistance has not yet been elucidated. In this study, we generated a TKI-resistant CML cell line, K562R, that lacks a mutation in BCR-ABL. Interleukin-1β (IL-1β) was more highly expressed in K562R than in the parental cell line K562S, and higher levels of IL-1β contributed to the imatinib resistance of K562R. In addition, IL-1β secreted from K562R cells affected stromal cell production of CXCL11, which in turn promoted migration of K562R cells into the stroma. Thus, elevated IL-1β production from TKI-resistant K562R cells may contribute to TKI resistance by increasing cell viability and promoting cell migration.

Heme oxygenase-1 contributes to imatinib resistance by promoting autophagy in chronic myeloid leukemia through disrupting the mTOR signaling pathway.

Heme oxygenase-1 (HO-1) has been verified to play an important role in imatinib (IM)-resistant chronic myeloid leukemia (CML) cells, but the mechanism remains unclear. In drug resistant CML cells, HO-1 expression abnormally increased and that of autophagy-related protein LC-3I/II also increased, so we herein postulated HO-1 was associated with autophagy. HO-1 expressions in IM-sensitive/resistant K562/K562R cells were regulated through lentiviral mediation. K562 cells transfected with HO-1 resisted IM and underwent obvious autophagy. After HO-1 expression was silenced in K562R cells, autophagy was inhibited and the sensitivity to IM was increased. The findings were related with the inhibitory effects of high HO-1 expression on the mTOR signaling pathway that negatively regulated autophagy. High HO-1 expression promoted autophagy by inhibiting mTOR. Similar to the cell line results, mononuclear cells of IM-resistant CML patients became significantly sensitive to IM when HO-1 expression was inhibited. In summary, HO-1, which is involved in the development of chemoresistance in leukemia cells by regulating autophagy, may be a novel target for improving leukemia therapy.

EphB4/ephrinB2 Contributes to Imatinib Resistance in Chronic Myeloid Leukemia Involved in Cytoskeletal Proteins.

Introduction: The mechanism of EphB4/ephrinB2 in the resistance of chronic myelogenous leukemia to imatinib keeps unknown.Methods: The imatinib resistant chronic myelogenous leukemia cell line-K562-R, was established. EphB4 receptor expression was detected in patients and resistant cells. Cell migration and drug sensitivity were tested in the EphB4 knockdown cells and mouse models.Results: The EphB4 receptor was over-expressed in blast crisis patients compared to chronic phase patients. The level of EphB4 receptor expression was associated with a complete cytogenetic response within 12 months. Enhanced expression of the EphB4 receptor was detected in the K562-R cells. EphB4 knockdown inhibited cell migration ability and restored sensitivity to imatinib in vitro and in vivo. Restored sensitivity to imatinib was observed in K562-R cells, along with increased levels of phospho-EphB4 and decreased phosphorylation levels of RhoA, Rac1, and Cdc42.Conclusion: Our study illustrates that aberrant activation of EphB4/ephrinB2 may mediate chronic myeloid leukemia resistance involved in cytoskeletal proteins.

Anti-Proliferative Effects of Dendrophthoe pentandra Methanol Extract on BCR/ABL-Positive and Imatinib-Resistant Leukemia Cell Lines

Background:Imatinib mesylate, a tyrosine kinase inhibitor specifically targeting the BCR/ABL fusion protein, induces hematological remission in patients with chronic myeloid leukemia (CML). However, the majority of CML patients treated with imatinib develop resistance with prolonged therapy. Dendrophthoe pentandra (L.) Miq. is a Malaysian mistletoe species that has been used as a traditional treatment for several ailments such as smallpox, ulcers, and cancers.Methods:We developed a resistant cell line (designated as K562R) by long-term co-culture of a BCR/ABL positive CML cell line, K562, with imatinib mesylate. We then investigated the anti-proliferative effects of D. pentandra methanol extract on parental K562 and resistant K562R cells. Trypan blue exclusion assays were performed to determine the IC50 concentration; apoptosis and cell cycle analysis were conducted by flow cytometry.Results:D. pentandra extract had greater anti-proliferative effects towards K562R (IC50= 192 μg/mL) compared to K562 (500 μg/mL) cells. Upon treatment with D. pentandra extract at the IC50 concentration: K562 but not K562R demonstrated increase in apoptosis and cell cycle arrest in the G2/M phase.Conclusion:D. pentandra methanol extract exerts potent anti-proliferative effect on BCR/ABL positive K562 cells.

EphB4/EphrinB2 Contributes to Imatinib Resistance in Chronic Myeloid Leukemia Involved in Cytoskeletal Proteins

Background and Objective: Through the introduction ofthe tyrosine kinase inhibitor(TKI) significantly improves the prognosis, drug resistance is still a major obstacle to cure chronic myelogenous leukaemia (CML).Many documents have suggested aberrant activation of EphB4/ephrin B2 participate in imatinib-resistant CML patients but the role and mechanism have largely remained elusive. Our previous study found that Homoharringtonine overcome imatinib resistance by blocking the EphB4/RhoA pathway in K562. Then, we established IM resistance CML cell line (K562-R) and EphB4 knock down IM resistance CML cell line (K562-R-EphB4-sh). Furthermore, we performed the experiment to address the hypothesis that aberrant over expressed of EphB4 might play an important role in of Imatinib-resistant chronic myeloid leukemia cells.Methods and Results: EphB4 receptor was over expressed in CML -Blast Crisis (BC) patients and resistant cell lines by western blot (P <0.05) and mRNA(P <0.01).We evaluated the imatinib response in 22 CML-CP patients (400mg/d or 600mg/d).EphB4 mRNA levels in cancer cells correlated with the corresponding BCR-ABL transcript level of at 3 months in each case (y=24.461x-2.3491 R2 =0.8756, P<0.0001).These patients were then equally divided into two groups according to relative EphB4 mRNA median level (0.979217).The level of EphB4 receptor expression was significantly associated with 12-month CCyR(The 12-month CCyR rate in low EphB4 group was 72.7% VS36.3% in high EphB4 groups (P<0.01)).Cell invasive ability decreased in K562-R-EphB4-sh cells (K562-R13.56±2.70;K562-R-EphB4-sh 5.78±2.54 n=3) meanwhile cells restored sensitivity(IC50μM: K562-R 2.7621±0.0154; K562-R-EphB4-sh0.6908±0.0623; K562 0.1179±0.0379) to IM in vitro and in vivo (tumor volume after IM treatment (mm3):K562-R 2301.25±555.76; K562-R-EphB4-sh1630.16±412.01; K562 806.15±202.31);The apoptosis rate of K562-R-EphB4-sh (25.27±1.27)had been showed much higher than that ofK562-R (7.23±1.97). In addition, the proportion of cells in G0/G1 phase was significantly decreased in K562-R-EphB4-sh cells (13.58%)than K562-R( 29.30%), but higher than K562( 6.37%).When co-cultured cells with ephrinB2 ligand, restored sensitivity to IM was observed in K562-R cells( IC50μM : ephrinB2-Fc1.071±0.039; IgG-Fc2.697±0.145; Blank control 2.663±0.102), apoptosis rate (ephrin B2-Fc(42.72 ± 0.95) %;was higher than IgG Fc group (28.77 ± 1.64) % or the control group (28.93 ± 1.49) % (P <0.001) with group treated with IM (2.7 µg/ml, 24 hours), along with significantly increased level of phospho-EphB4 (450nm absorbance:ephrinB2-Fc0.920±0.031;IgG-Fc0.379±0.008; blank control0.381±0.005) and decreased phosphorylation level of cytoskeletal proteins RhoA, Rac1, Cdc42(P <0.05).Conclusion: Our study illustrated that aberrant activation EphB4/ EphrinB2 may mediate chronic myeloid leukemia resistance involved in cytoskeletal proteins. DisclosuresNo relevant conflicts of interest to declare.

Abstract 3848: Subtype-specific DNA damage dependent and independent functions of damage repair proteins confer chemo-resistance to leukemia

Abstract Resistance to chemotherapy is a major challenge in the field of leukemia. Since, cancer cells can acquire resistance to DNA damage based therapy by modulating DNA Damage Repair (DDR) pathways, an in-depth understanding of DDR is important for novel drug discoveries. Hence, to understand relation between DDR and resistance we used doxorubicin resistant sub-line (K562-R) of K562 and Mitoxantrone resistant sub-line (HL60/MX) of HL60 as a model system. We show that lethal doses of Mitoxantrone to HL60 and HL60/MX do not induce DNA DSBs (double strand breaks) and accordingly there is no activation of Chk2, although there is equal uptake of drug in both, sensitive and resistant cell types. Since Mitoxantrone produce DSBs by targeting TOP2B, we checked the expression of TOPB2 and found significant decrease in the levels of topoisomerase 2 B (TOP2B). Moreover, negative regulator of TOPB2, mir 21-5P is upregulation in untreated HL60/MX explaining the absence of DSBs in HL-60/MX with Mitoxantrone treatment. Surprisingly, although there are no DSBs induced, we find high levels of DNA-PKcs, MRE11 and Rad50 in HL-60/MX. Furthermore, inhibition of DNA-PKcs re-sensitizes HL-60/MX cells to Mitoxantrone, suggesting a DNA damage independent role for DNA-PK in HL-60/MX cells. Recently DNA-PKcs is shown to play key role in fat metabolism. Indeed we find significant differences in the metabolism of HL60 and HL-60/MX where HL-60 cells use glucose but HL-60/MX cells show reduced glucose and glutamine metabolism and an over expression of fatty acid synthase. However link between DNA-PKcs over expression and differential metabolism in these cells still need to be explored. Interestingly, in contrast to HL60 model, Doxorubicin does induce equal DSBs in K562 and K562-R cells. However K562-R cells hyperactivate ATM and Chk2 to repair their DNA and survive. Importantly, we show that K562 start to show elevated activation of ATM and Chk-2 as early as two rounds of drug treatment. Accordingly, ATM inhibition leads to induction of apoptosis in resistant K562 cells. In conclusion, we show that K562 and HL60 cells use the DNA double strand break repair proteins in DNA damage dependent and independent pathways to acquire resistance to DSB inducing chemo therapeutics. Our data also highlight the importance of considering subtype specific therapeutics in leukemia. Note: This abstract was not presented at the meeting. Citation Format: Sameer Salunkhe, Ekjot Kaur, Ashwin Ramaswamy, Ketaki Patkar, Shilpee Dutt. Subtype-specific DNA damage dependent and independent functions of damage repair proteins confer chemo-resistance to leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3848. doi:10.1158/1538-7445.AM2015-3848

Synthesis and biological evaluation of novel aromatic-heterocyclic biphenyls as potent anti-leukemia agents

As a continuation to our previous research, twenty-eight aromatic-heterocyclic biphenyls were designed and synthesized as novel Bcr–Abl inhibitors. The title compounds were investigated for their antiproliferative activities against wild K562 cells and Imatinib-resistant K562 cells (K562R). The results indicated that most of them exhibited potent Bcr–Abl inhibition and moderate antiproliferative potency against K562 cells. Furthermore, three compounds 3, 7 and 21 displayed moderate antiproliferative activities against K562R cells. Molecular docking indicated that 3 bound more tightly with Bcr–AblT315I compared to Bcr–AblWT. The higher affinity was consistent with its relatively promising K562R cell growth inhibition. These aromatic-heterocyclic biphenyls could be considered as novel lead compound for optimized as Bcr–AblT315I inhibitors. They provide a good starting point for the further development of novel anti-leukemia agents capable of dealing with clinical acquired resistance against Imatinib.

Wogonoside induces growth inhibition and cell cycle arrest via promoting the expression and binding activity of GATA-1 in chronic myelogenous leukemia cells.

GATA-1, a zinc finger transcription factor, has been demonstrated to play a key role in the progression of leukemia. In this study, we investigate the effects of wogonoside, a naturally bioactive flavonoid derived from Scutellaria baicalensis Georgi, on cell growth and cell cycle in chronic myeloid leukemia (CML) cells, and uncover its underlying mechanisms. The experimental design comprised CML cell lines K562, imatinib-resistant K562 (K562r) cells, and primary CML cells, treated in vitro or in vivo, respectively, with wogonoside; growth and cell cycle were then evaluated. We found that wogonoside could induce growth inhibition and G0/G1 cell cycle arrest in both normal and K562r cells. Wogonoside promotes the expression of GATA-1 and facilitates the binding to methyl ethyl ketone (MEK) and p21 promoter, thus inhibiting MEK/extracellular signal-regulated kinase signaling and cell cycle checkpoint proteins, including CDK2, CDK4, cyclin A, and cyclin D1, and increasing p21 expression. Furthermore, in vivo studies showed that administration of wogonoside decreased CML cells and prolonged survival in NOD/SCID mice with CML cell xenografts. In conclusion, these results clearly revealed the inhibitory effect of wogonoside on the growth in CML cells and suggested that wogonoside may act as a promising drug for the treatment of imatinib-resistant CML.