Determination of genes and microRNAs involved in the resistance to fludarabine in vivo in chronic lymphocytic leukemia

Abstract

BackgroundChronic 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.ResultsIn 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.ConclusionIn 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.

In VitroSensitivity of CLL Cells to Fludarabine May Be Modulated by the Stimulation of Toll-like Receptors

“…We previously showed that the miR-221/222 cluster is upregulated in CLL cells by CpG treatment and modulates the expression of p27KIP1 protein (42). Of note, miR-221 and miR-222 were recently shown to play a key role in chemoresistance of solid tumors (43) and to be upregulated in vivo in patients with CLLs refractory to fludarabine treatment (44). Our previous data (42) suggest that the observed TLR-mediated drug resistance in CLL may also be influenced by upregulation of miR221/222 cluster.…”

Differential microRNA Profiles and Their Functional Implications in Different Immunogenetic Subsets of Chronic Lymphocytic Leukemia

“…In particular, certain miRNAs are deregulated in CLL compared with normal B cells (23)(24)(25)(26), whereas distinct microRNA signatures are associated with prognostic factors and disease progression (24)(25)(26)(27)(28)(29), response to treatment (30,31) and various other disease characteristics (26,32,33).…”

Role of miRNAs in the Response to Anticancer Therapy

“…In a similar study involving 50 chronic lymphocytic leukemia patients, fludarabine resistance was associated with decreased miR-29a and increased miR-181a expression [28].…”