CO-RELATION OF P-GLYCOPROTEIN AND PLASMA IMATINIB IN IMATINIB RESPONDERS AND NON-RESPONDERS PATIENTS WITH CHRONIC MYELOID LEUKAEMIA

Objective: To measure and compare P-glycoprotein (P-gp) expressions in imatinib responders and non-responders with chronic myeloid leukemia-chronic phase (CML-CP) and correlate with plasma imatinib levels. Methods: Patients were classified into two groups based on their haematological and cytogenetic responses to imatinib: responders and non-responders. Liquid chromatography-mass spectrometry was used to measure plasma imatinib levels, while flow cytometry was used to evaluate leucocyte P-gp expression. Results: The median plasma imatinib trough levels in non-responders were 496 (217-3150) ng/ml compared to 2245 (454-4270) ng/ml in the responders, which was statistically significant (p=0.0003). The proportion of patients expressing P-gp in granulocytes was higher in the non-responder group than in the responder group (75% vs. 62.5%). The ratio of mean fluorescence intensity (RFI) revealed that non-responders had higher median P-gp expression than did respondents MFI (1.16(1.06-1.50) and 1.12(1.01-1.38), respectively; p = 0. 2307). In both groups, there was a negative correlation between P-gp expression and plasma imatinib trough levels (-0.4384 vs.-0.2848). Conclusion: Imatinib median plasma trough levels in non-responders were considerably lower. This was highly supported by P-gp expression in granulocytes, which is inversely related to imatinib plasma trough levels; however, the difference was not statistically significant, which could be attributed to the small number of patients. This could be the cause of imatinib resistance in non-responder CML-CP patients, and P-gp levels should be evaluated to optimize treatment in patients who do not achieve hematologic or cytogenetic response