Measurement of imatinib uptake by flow cytometry

One of the essential parameters of targeted therapy efficiency in cancer treatment is the amount of drug reaching the therapeutic target area. Imatinib (IM) was the first specifically targeted drug to be developed and has revolutionized the treatment of patients with chronic myeloid leukemia (CML). To evaluate cellular uptake of IM, we developed a method based on the chemical structure of the molecule and using the natural UV fluorescence that we quantified by flow cytometry. In two CML cell lines, we obtained a satisfactory relationship between intracellular IM (ICIM) levels and media concentrations, and we found a strong correlation between ICIM at 1 h and IM efficacy at 24 h, demonstrating that ICIM at 1 h might be a relevant predictive parameter of cell sensitivity. Our method was more sensitive than the standard physicochemical method. We applied our method to primary cells and found cell morphology-dependent IM accumulation. Moreover, in CML cells from patients at diagnosis, IM accumulation was heterogeneous. In all cases, ICIM at the single-cell level was much higher than in culture media arguing in favor of a predominantly active uptake process. We developed a simple method directly applicable to primary cells that has shown two major advantages: only a small number of cells are required, and cell subsets can be identified according to morphological criteria and/or the presence of particular antigenic sites. This method provides a new tool to assess CML cell sensitivity to IM, and ICIM levels in native CML cells could be used to monitor therapeutic response.