Imatinib Mesylate Affects the Expression of Lipid Metabolism Genes in K562, a Chronic Myeloid Leukemia Cell Line

Background: Imatinib mesylate (IM) is a tyrosine kinase inhibitor designed to inhibit the BCR-ABL fusion protein, the hallmark of chronic myeloid leukemia (CML). Interestingly, IM treatment possesses a rapid lipid-lowering effect on patients with hyperlipidemia, particularly those receiving 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCoAR) inhibitors. While it is known that IM may competitively inhibit statin metabolism, the lipid-lowering effect of IM is not fully understood. Therefore, we have studied the effects of IM on a family of genes critically involved in lipid metabolism, including low density lipoprotein receptor (LDL-R), HMGCoAR, cholesteryl ester transfer protein (CETP), apolipoprotein B (apoB) and apolipoprotein B editing complex (apobec1), in K562, a CML cell line model.

Methods:

Cell cultures and treatments: K562 cells were grown in DMEM supplemented with 10% FCS. Cells were treated with IM or DMSO (1mM) and were harvested after 24–96 hours. Untreated cells served as a control as did the DMSO-treated cells.

RNA extraction and cDNA synthesis: RNA was extracted using Trizol reagent method and reverse transcribed using random primers and M-MLV.

Real-time PCR assays: Real-time PCR assays were conducted using assays on demand for the different genes (Applied Biosystems, Foster City, CA, USA) and performed on Applied Biosystems 7900HT Prism® real-time PCR instrument with a 100ng equivalent of cDNA, in a total volume of 20 ml 1X Taqman master mix (Applied Biosystems). Results were quantified using the delta-delta cycle threshold method, normalized to actin beta and expressed as “fold-change from control”.

Statistics: Results were analyzed using unpaired students’ t-test.

Results: LDL-R, HMGcoAR, CETP, apobec1 and apoB genes expression were evaluated in untreated K562 cells (control) and following treatment with DMSO (negative control) or IM for 24 to 96 hours. IM treatment of K562 cells significantly affected the expression of lipid-related genes. Namely, a time-dependent increase in LDL-R (3–6 fold), HMGcoAR (2–5 fold) and CETP (4–50 fold) expressions were documented following IM treatment. No increase in expression of these genes was observed in untreated and DMSO treated controls. Basal apobec1 and apoB expression detected in untreated K562 cells was abolished following IM but not DMSO treatment.

Discussion: Putative mechanisms for the decrease in serum cholesterol and triglycerides observed in some patients treated with IM include reduced intestinal absorption and inhibition of platelet derived growth factor receptor (PDGFR), resulting in decreased lipoprotein lipase (LPL) synthesis. Our novel observation proposes another explanation, namely a direct effect of IM on central lipid-related genes.

Conclusions: The direct effect of IM on lipid-related genes, together with the fact that in cell culture IM inhibits proliferation and induces apoptosis, suggest a possible role of lipids in apoptosis/cell cycle pathways. This possibility is currently the subject of further investigation.