Comparison of Differential Gene Expression Profiles of Relapsed Patients with Acute Promyelocytic Leukemia Treated with Arsenic Trioxide with the Profile of An Arsenic Trioxide Resistant NB4 Cell Line.

Abstract 3460

Poster Board III-348

Arsenic trioxide (ATO) has proven efficacy in the management of patients with acute promyelocytic leukemia (APL). Approximately 20% of patients treated with an ATO based regimen relapse. The long term remission rate with ATO in relapsed patients is significantly inferior to that seen in newly diagnosed cases. The biological mechanisms of resistance to ATO in these patients have not been evaluated. We undertook a gene expression profile study to address the potential mechanisms of resistance in patients with relapsed APL. The study included 8 patients at diagnosis and 8 patients at relapse from whom total RNA was extracted from bone marrow mononuclear cells with > 90% promyelocytes (enriched with lineage depletion cocktail as required). This was then subjected to a one color 44K Agilent cDNA array. Data was normalized, filtered and analyzed using Gene Spring software (Ver.10). Using unpaired t-Test, 1744 genes were identified to be differentially expressed (>2 fold) between samples at diagnosis and at relapse. Out of the 865 up regulated genes, the collagen family genes COL5A1 and COL2A1, haematopoietic lineage specific genes CD34 and TdT, C-Lectin family COLEC1 and TRIM15 were found to be 10 fold higher in relapse. About 880 genes were down regulated in relapse which included ABCA1, LEP, TUSC1 and XIST. We generated an ATO resistant NB4 cell line by chronic and gradual exposure to ATO over a period of 1 year. Gene expression profile of naïve and resistant NB4 cell lines arrayed in replicates were obtained. Comparison of relapsed patients and the ATO resistant NB4 cell line data revealed 51 genes were up regulated and 41 were down regulated commonly and in the same direction between these 2 groups in comparison to newly diagnosed patients and naïve NB4 cell line. By gene ontology (GO) analysis of these 92 common genes using Biointerpreter software the following biological processes were identified, namely; differentiation (47 genes), cell adhesion (14 genes), cell proliferation (17 genes), transcription factors and gene regulation (33 genes), apoptosis (11 genes), ECM remodeling (10 genes) and cell migration (5 genes). Of interest in the up-regulated gene list were anti-apoptotic gene BAG4, cell adhesion genes COL2A1 and JAM3 and differentiation gene COLEC11. The prominent down regulated genes included the ABC transporter family gene ABCA1, TNF receptor super family gene TNFRSF14 and the aldehyde dehydrogenase family gene ALDH8A1. These data provide the first evidence of the possible mechanisms of resistance to ATO in APL but needs further evaluation and validation.