Inactivation of P16 (INK4a) Gene by Promoter Hypermethylation is Associated with Disease Progression in Chronic Myelogenous Leukaemia

Abstract

Background: Chronic Myelogenous Leukemia (CML) has a typical progressive course with transition from a chronic phase to a terminal blast crisis phase. The mechanisms that lead to disease progression remain to be elucidated. Promoter hypermethylation is one of the putative mechanisms underlying the inactivation of negative cell-cycle regulators in haematological malignancies. Therefore, aim of our study was to examine whether the methylation status of P16 (INK4a) gene is a useful biomarker in the development and progression of CML.Material and Methods: The methylation status of p16INK4A gene was evaluated by Methylation Specific Polymerase Chain Reaction (MSP) in 200 CML patients among which, 81 were in CP-CML, 54 in AP-CML and 65 in BC-CML.Results: The p16INK4A gene was hypermethylated in 84 of 200 (42%) of CML patients (P<0.0001). Among the three stages p16 (INK4A) promoter gene was methylated in 26% (CP-CML), 43% (AP-CML and 68% (BCCML) patient (P<0.0001). Methylation was more frequent in blastic and accelerated phase patients than in chronic phase. A significant correlation was found between p16INK4A methylation and loss of Imatinib response. Similarly higher frequency of p16INK4A methylation was reported in CML patients with haematological (P<0.02) and molecular resistances (P<0.04). Significantly higher (p<0.0001) frequency of p16INK4A promoter methylation was reported in patients with thrombocytopenia. However no correlation was found between p16INK4a hypermethylation and other clinic-pathological parameters like age, gender, BCR-ABL transcripts etc.Conclusion: Our results suggest that p16INK4a is a primary target for inactivation by promoter methylation in the disease progression of CML patients and that its detection is useful in the follow up of patients with a high risk of developing CML and resistance to Imatinib therapy.