Mycophenolic Acid overcomes imatinib and nilotinib resistance of chronic myeloid leukemia cells by apoptosis or a senescent-like cell cycle arrest.

International audienceWe used K562 cells sensitive or generated resistant to imatinib or nilotinib to investigate their response to mycophenolic acid (MPA). MPA induced DNA damage leading to cell death with a minor contribution of apoptosis, as revealed by annexin V labeling (up to 25%). In contrast, cell cycle arrest and positive staining for senescence-associated β-galactosidase activity were detected for a large cell population (80%). MPA-induced cell death was potentialized by the inhibition of autophagy and this is associated to the upregulation of apoptosis. In contrast, senescence was neither decreased nor abrogated in autophagy deficient K562 cells. Primary CD34 cells from CML patients sensitive or resistant to imatinib or nilotinib respond to MPA although apoptosis is mainly detected. These results show that MPA is an interesting tool to overcome resistance in vitro and in vivo mainly in the evolved phase of the disease

Pioglitazone together with imatinib in chronic myeloid leukemia: A proof of concept study

BACKGROUND We recently reported that peroxisome proliferator‐activated receptor γ agonists target chronic myeloid leukemia (CML) quiescent stem cells in vitro by decreasing transcription of STAT5. Here in the ACTIM phase 2 clinical trial, we asked whether pioglitazone add‐on therapy to imatinib would impact CML residual disease, as assessed by BCR‐ABL1 transcript quantification. METHODS CML patients were eligible if treated with imatinib for at least 2 years at a stable daily dose, having yielded major molecular response (MMR) but not having achieved molecular response 4.5 (MR4.5) defined by BCR‐ABL1/ABL1 IS RNA levels ≤ 0.0032%. After inclusion, patients started pioglitazone at a dosage of 30 to 45 mg/day in addition to imatinib. The primary objective was to evaluate the cumulative incidence of patients having progressed from MMR to MR4.5 over 12 months. RESULTS Twenty‐four patients were included (age range, 24‐79 years). No pharmacological interaction was observed between the drugs. The main adverse events were weight gain in 12 patients and a mean decrease of 0.4 g/dL in hemoglobin concentration. The cumulative incidence of MR4.5 was 56% (95% confidence interval, 37%‐76%) by 12 months, despite a wide range of therapy duration (1.9‐15.5 months), and 88% of 17 evaluable patients who were still on imatinib reached MR4.5 by 48 months. The cumulative incidence of MMR to MR4.5 spontaneous conversions over 12 months was estimated to be 23% with imatinib alone in a parallel cohort of patients. CONCLUSION Pioglitazone in combination with imatinib was well tolerated and yielded a favorable 56% rate. These results provide a proof of concept needing confirmation within a randomized clinical trial (EudraCT 2009‐011675‐79). Cancer 2017;123:1791–1799. © 2016 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes

The Expression of Myeloproliferative Neoplasm-Associated Calreticulin Variants Depends on the Functionality of ER-Associated Degradation

BACKGROUND: Mutations in CALR observed in myeloproliferative neoplasms (MPN) were recently shown to be pathogenic via their interaction with MPL and the subsequent activation of the Janus Kinase - Signal Transducer and Activator of Transcription (JAK-STAT) pathway. However, little is known on the impact of those variant CALR proteins on endoplasmic reticulum (ER) homeostasis. METHODS: The impact of the expression of Wild Type (WT) or mutant CALR on ER homeostasis was assessed by quantifying the expression level of Unfolded Protein Response (UPR) target genes, splicing of X-box Binding Protein 1 (XBP1), and the expression level of endogenous lectins. Pharmacological and molecular (siRNA) screens were used to identify mechanisms involved in CALR mutant proteins degradation. Coimmunoprecipitations were performed to define more precisely actors involved in CALR proteins disposal. RESULTS: We showed that the expression of CALR mutants alters neither ER homeostasis nor the sensitivity of hematopoietic cells towards ER stress-induced apoptosis. In contrast, the expression of CALR variants is generally low because of a combination of secretion and protein degradation mechanisms mostly mediated through the ER-Associated Degradation (ERAD)-proteasome pathway. Moreover, we identified a specific ERAD network involved in the degradation of CALR variants. CONCLUSIONS: We propose that this ERAD network could be considered as a potential therapeutic target for selectively inhibiting CALR mutant-dependent proliferation associated with MPN, and therefore attenuate the associated pathogenic outcomes

The Necrotic Signal Induced by Mycophenolic Acid Overcomes Apoptosis-Resistance in Tumor Cells

The amount of inosine monophosphate dehydrogenase (IMPDH), a pivotal enzyme for the biosynthesis of the guanosine tri-phosphate (GTP), is frequently increased in tumor cells. The anti-viral agent ribavirin and the immunosuppressant mycophenolic acid (MPA) are potent inhibitors of IMPDH. We recently showed that IMPDH inhibition led to a necrotic signal requiring the activation of Cdc42.Herein, we strengthened the essential role played by this small GTPase in the necrotic signal by silencing Cdc42 and by the ectopic expression of a constitutive active mutant of Cdc42. Since resistance to apoptosis is an essential step for the tumorigenesis process, we next examined the effect of the MPA–mediated necrotic signal on different tumor cells demonstrating various mechanisms of resistance to apoptosis (Bcl2-, HSP70-, Lyn-, BCR-ABL–overexpressing cells). All tested cells remained sensitive to MPA–mediated necrotic signal. Furthermore, inhibition of IMPDH activity in Chronic Lymphocytic Leukemia cells was significantly more efficient at eliminating malignant cells than apoptotic inducers.These findings indicate that necrosis and apoptosis are split signals that share few if any common hub of signaling. In addition, the necrotic signaling pathway induced by depletion of the cellular amount of GTP/GDP would be of great interest to eliminate apoptotic-resistant tumor cells

Effect of ABCG2, OCT1, and ABCB1(MDR1) Gene Expression on Treatment-Free Remission in a EURO-SKI Subtrial

Introduction Tyrosine kinase inhibitors (TKIs) can safely be discontinued in chronic myeloid leukemia (CML) patients with sustained deep molecular response. ABCG2 (breast cancer resistance protein), OCT1 (organic cation transporter 1), and ABCB1 (multidrug resistance protein 1) gene products are known to play a crucial role in acquired pharmacogenetic TKI resistance. Their influence on treatment-free remission (TFR) has not yet been investigated. Materials and Methods RNA was isolated on the last day of TKI intake from peripheral blood leukocytes of 132 chronic phase CML patients who discontinued TKI treatment within the European Stop Tyrosine Kinase Inhibitor Study trial. Plasmid standards were designed including subgenic inserts of OCT1, ABCG2, and ABCB1 together with GUSB as reference gene. For expression analyses, quantitative real-time polymerase chain reaction was used. Multiple Cox regression analysis was performed. In addition, gene expression cutoffs for patient risk stratification were investigated. Results The TFR rate of 132 patients, 12 months after TKI discontinuation, was 54% (95% confidence interval [CI], 46%-62%). ABCG2 expression (‰) was retained as the only significant variable (P = .02; hazard ratio, 1.04; 95% CI, 1.01-1.07) in multiple Cox regression analysis. Only for the ABCG2 efflux transporter, a significant cutoff was found (P = .04). Patients with an ABCG2/GUSB transcript level >4.5‰ (n = 93) showed a 12-month TFR rate of 47% (95% CI, 37%-57%), whereas patients with low ABCG2 expression (≤4.5‰; n = 39) had a 12-month TFR rate of 72% (95% CI, 55%-82%). Conclusion In this study, we investigated the effect of pharmacogenetics in the context of a CML treatment discontinuation trial. The transcript levels of the efflux transporter ABCG2 predicted TFR after TKI discontinuation

Widespread white matter microstructural abnormalities in bipolar disorder: evidence from mega- and meta-analyses across 3033 individuals

Fronto-limbic white matter (WM) abnormalities are assumed to lie at the heart of the pathophysiology of bipolar disorder (BD); however, diffusion tensor imaging (DTI) studies have reported heterogeneous results and it is not clear how the clinical heterogeneity is related to the observed differences. This study aimed to identify WM abnormalities that differentiate patients with BD from healthy controls (HC) in the largest DTI dataset of patients with BD to date, collected via the ENIGMA network. We gathered individual tensor-derived regional metrics from 26 cohorts leading to a sample size of N = 3033 (1482 BD and 1551 HC). Mean fractional anisotropy (FA) from 43 regions of interest (ROI) and average whole-brain FA were entered into univariate mega- and meta-analyses to differentiate patients with BD from HC. Mega-analysis revealed significantly lower FA in patients with BD compared with HC in 29 regions, with the highest effect sizes observed within the corpus callosum (R2 = 0.041, Pcorr < 0.001) and cingulum (right: R2 = 0.041, left: R2 = 0.040, Pcorr < 0.001). Lithium medication, later onset and short disease duration were related to higher FA along multiple ROIs. Results of the meta-analysis showed similar effects. We demonstrated widespread WM abnormalities in BD and highlighted that altered WM connectivity within the corpus callosum and the cingulum are strongly associated with BD. These brain abnormalities could represent a biomarker for use in the diagnosis of BD. Interactive three-dimensional visualization of the results is available at www.enigma-viewer.org

La résistance à l'imatinib dans la leucémie myéloïde chronique (étude des mécanismes moléculaires)

La leucémie myéloide chronique (LMC) eest caractérisée par l'expression d'une oncoprotéine de fusion Bcr-Abl qui résulte de la translocation chromosomique réciproque t(9,22)(q11;q34) qui génère le chromosome Philadelphie (Ph). Bcr-Abl est la cible de l'inhibiteur imatinib (Gleevec®). Chez 20 % des patients traités par l'imatinib, une absence de réponse est observée dès le début du traitement ou après une réponse initiale. Malgré l'efficacité de l'imatinib dans la LMC, la résistance à cet inhibiteur est désormais le principal challenge pour la prise en charge des patients. La lignée cellulaire K562 est une lignée érythroleucémique issue d'une patiente atteinte de LMC en crise blastique. Cette lignée BCR-ABL est sensible à l'imatinib (K562-s). La lignée résistante (K562-r) générée à partir de la lignée sensible par pression de sélection en présence d'imatinib ne présente aucun des mécanismes de résistance à l'imatinib connus à ce jour. Nous avons mis en évidence un nouveau mécanisme de résistance à l'imatinib impliquant la protéine chaperonne Hsp70. La surexpression de cette protéine est corrélée à une augmentation de son ARNm. Cet ARNm qui possède une région de stabilisation en 3' (ARE) a une demi-vie plus longue dans la lignée K562-r et ceci met en jeu la séquence ARE à laquelle pourraient se lier des facteurs en trans permettant sa stabilisation. Un double polymorphisme est observé dans les régions HRE et 5'UTR du promoteur du gène HSPA 1A. Un système rapporteur a permis de montrer que ce double polymorphisme induit une traduction plus élevée qui pourrait être la conséquence d'une structure secondaire particulière de l'ARNm permettant une meilleure fixation des complexes de traduction.Imatinib is the treatment in front-line for chronic myeloid leukemia (CML), a myeloproliferative syndrome characterised by the recombinant tyrosine kinase Bcr-Abl. Imatinib inhibits Bcr-Abl kinase activity leading to apoptosis of leukemic cells sparing normal hematopoiesis. Several mechanisms of resistance to imatinib have been identified both in vitro and in vivo Bcr-Abl mutations, an over-expression of the Bcr-Abl mutations, an over-expression of the Bcr-Abl kinase itself or other tyrosine kinase bypass. To identify unknown mechanism, we used an imatinib resistant cell line (K562-R) generated from the eythroblastic cell line K562 (K562-S) for which none of described mechanisms of resistance have been detected. Results from a proteomic study detected solely 6 over expressed spots and 8 under expressed spots in K562-R. Among the proteins identified an heat shock protein Hsp70 which have an increased expression level in K562-R. The role of Hsp70 in imatinib resistance has been characterized and was correlated to an increase of its mRNA. An ARE sequence which is present in the 3'UTR of the mRNA is involved in the stabilisation of the mRNA. A double single nucleotide polymorphism (SNP) was detected in the promoter of HSPA1A in the HRE and 5'untranslated regions of the HSPA1A gene. The distribution of these SNP was heterozygous in K562-S while K562-R shares an intringing distribution. Lucefirase promoterless vector was used to make constructs containing the four different haplotypes and shown an increased translation with the haplotype CG. Study is in progress to investigate the transfactors involved in the mRNA stabilisation and translational increase.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF