Imatinib Mesilate Modifies Genes Involved in Hematopoiesis in Non Clonal Bone Marrow Cells from CML Patients in Complete Cytogenetic Response.

Imatinib mesilate (IM) is the standard treatment for newly diagnosed patients with chronic phase (CP) CML. Bcr-Abl signaling has a wide range of biological activities, mainly mediated through activation of Ras/mitogen-activated protein kinase (MAPK) pathways, with broad effects on changes in cell adhesion (through Rho), proliferation (MAPK pathway) and apoptosis (through Akt). IM’s efficacy results from a blockade of these effects. Extensive work on the gene-expression profiling of CML cell lines under IM therapy has been published in order to predict disease transformation or IM resistance. Nevertheless, information on the effects of IM on the residual non clonal bone marrow (BM) hematopoietic compartment is scarce, and this is an important issue, since most responding patients will require long term treatment with IM. Therefore, in the present work we have assessed the gene expression profile (GEP) of whole BM hematopoietic cells from 20 patients with CP-CML in CCR after 6 to 12 months on IM therapy and compared it with that of 6 normal BM donors. Total RNA (100-500 ng) was amplified and labeled using the “GeneChip Two-Cycle cDNA Synthesis Kit” and hybridized to “Human Genome U133A” microarray (Affymetrix). Processing of genechip data was carried out using the Robust Multi-chip Average (RMA) and the Affymetrix Microarray Suite v.5 (MAS5) gene expression algorithms. The Significance Analysis of Microarrays (SAM) algorithm identified gene expression changes in a total of 490 genes (125 up and 365 down-regulated) when samples from CCR CML patients were compared to normal BM samples. Differential genes were grouped in 4 different areas, based on their function: proliferation, apoptosis, ubiquitination and adhesion. In CCR CML samples, there was a lower expression of genes involved in cell proliferation (e.g. C6ORF108, CENPE, CENP5, ESPL1 or GAS6) and cell cycle progression (e.g. PLCB1, ZW10, CUL4A or FOSB). There was an upregulation of genes involved in the induction of apoptosis (e.g. CDC2L2, FOXO3A, ING2, ING3, RYBP or TNFRSF1B) and in the ubiquitination of proteins (e.g. ARIH1, FBXW7, RKHD2, RNF7, SUMO1, UBA2 or UBE2W). Regarding cell-to-cell adhesion, several genes involved in this processes were downregulated (e.g. ITGBL1, CTNNA1, PCDHGA1, TROAP, FLOT2, IGSF4B, SELP, SIGLEC6, ADAM22 and STAB1). In addition, in all CML samples the erythropoietin receptor (Epo-R) gene was downregulated. This is of interest since many patients on IM therapy display a slightly low Hb level, regardless of circulating Epo levels. In summary, IM induces a decrease in proliferation and increase in apoptosis and ubiquitination in residual non clonal BM cells from CCR CML patients. In addition, IM diminishes cell-to-cell adhesion and downregulates the expression of the Epo receptor in the hematopoietic compartment of these patients.