title: Determination of genes and microRNAs involved in the resistance to fludarabine in vivo in chronic lymphocytic leukemia.
abstract: BACKGROUND
  Chronic lymphocytic leukemia (CLL) cells are often affected by genomic aberrations targeting key regulatory genes. Although fludarabine is the standard first line therapy to treat CLL, only few data are available about the resistance of B cells to this purine nucleoside analog in vivo. Here we sought to increase our understanding of fludarabine action and describe the mechanisms leading to resistance in vivo. We performed an analysis of genomic aberrations, gene expression profiles, and microRNAs expression in CLL blood B lymphocytes isolated during the course of patients' treatment with fludarabine.
  
  
  RESULTS
  In sensitive patients, the differentially expressed genes we identified were mainly involved in p53 signaling, DNA damage response, cell cycle and cell death. In resistant patients, uncommon genomic abnormalities were observed and the resistance toward fludarabine could be characterized based on the expression profiles of genes implicated in lymphocyte proliferation, DNA repair, and cell growth and survival. Of particular interest in some patients was the amplification of MYC (8q) observed both at the gene and transcript levels, together with alterations of myc-transcriptional targets, including genes and miRNAs involved in the regulation of cell cycle and proliferation. Differential expression of the sulfatase SULF2 and of miR-29a, -181a, and -221 was also observed between resistant and sensitive patients before treatment. These observations were further confirmed on a validation cohort of CLL patients treated with fludarabine in vitro.
  
  
  CONCLUSIONS
  In the present study we identified genes and miRNAs that may predict clinical resistance of CLL to fludarabine, and describe an interesting oncogenic mechanism in CLL patients resistant to fludarabine by which the complete MYC-specific regulatory network was altered (DNA and RNA levels, and transcriptional targets). These results should prove useful for understanding and overcoming refractoriness to fludarabine and also for predicting the clinical outcome of CLL patients before or early during their treatment.
authors.affiliation: Laboratory of Experimental Hemato-Oncology, CRP-Santé, Luxembourg, Luxembourg. etienne.moussay@crp-sante.lu
authors.forename: Etienne
authors.initials: E
authors.lastname: Moussay
authors.forename: Valérie
authors.initials: V
authors.lastname: Palissot
authors.forename: Laurent
authors.initials: L
authors.lastname: Vallar
authors.forename: Hélène A
authors.initials: HA
authors.lastname: Poirel
authors.forename: Thomas
authors.initials: T
authors.lastname: Wenner
authors.forename: Victoria
authors.initials: V
authors.lastname: El Khoury
authors.forename: Nasséra
authors.initials: N
authors.lastname: Aouali
authors.forename: Kris
authors.initials: K
authors.lastname: Van Moer
authors.forename: Bernadette
authors.initials: B
authors.lastname: Leners
authors.forename: François
authors.initials: F
authors.lastname: Bernardin
authors.forename: Arnaud
authors.initials: A
authors.lastname: Muller
authors.forename: Pascale
authors.initials: P
authors.lastname: Cornillet-Lefebvre
authors.forename: Alain
authors.initials: A
authors.lastname: Delmer
authors.forename: Caroline
authors.initials: C
authors.lastname: Duhem
authors.forename: Fernand
authors.initials: F
authors.lastname: Ries
authors.forename: Eric
authors.initials: E
authors.lastname: van Dyck
authors.forename: Guy
authors.initials: G
authors.lastname: Berchem
mesh_terms: D000368:Aged; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D055028:Comparative Genomic Hybridization; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D020869:Gene Expression Profiling; D016259:Genes, myc / Q000235:genetics; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy / Q000235:genetics*; D008297:Male; D035683:MicroRNAs / Q000235:genetics*; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D014740:Vidarabine / Q000031:analogs & derivatives* / Q000627:therapeutic use
chemical_list: D000970:Antineoplastic Agents; D035683:MicroRNAs; D016159:Tumor Suppressor Protein p53; D014740:Vidarabine; C024352:fludarabine