Pomolic Acid-Induced Apoptosis in Cells from Chronic Myeloid Leukemic Patients Is Not Affected by the MDR Phenotype and Status of Disease.

Pomolic acid (PA), isolated from Chrysobalanus icaco, is a pentaciclic triterpene highly effective in inhibiting the growth and promotes cell death in the human chronic myeloid leukemia (CML) K562 cell line. In addition, PA is also very effective in blocking the proliferation of K562-Lucena-1, a vincristine-resistant derivative of K562 that displays multidrug resistance (MDR) phenotype. Due to antiproliferative and antiapoptotic effect of PA on positive and negative MDR leukemic cells, and considering that some patients with CML exhibit resistance to imatinib, the aim of this work was to investigate if PA could have an effective role in induce apoptosis in cells from CML patients. Fourteen peripheral blood samples from CML patients in various stages (three in blastic phase and eleven in chronic phase being one juvenile patient) including previously clinically imatinib resistant patients were studied. Informed consent was obtained according to institutional guidelines. Cells from patients were plated in 96 well tissue culture plates for 24h and then treated with two different concentrations of PA: 12.5 μg/ml and 25 μg/ml. Drug-induced apoptosis was evaluated by annexin V/propidium iodide assessed by fluorescence-activated cell-sorting (FACS). Functional MDR phenotype was performed by measuring the fluorescent dye rhodamine-123 efflux in the presence or absence of the MDR blocker cyclosporin A. These experiments were analysed by FACS. Functional activity of MDR was observed in 9 out of 14 samples and it was independent of CML stage. Using 12.5 μg/ml and 25μg/ml concentrations, the apoptotic effect of PA ranged from 10.5 to 53.1 (median: 31.5) and 14.7 to 65.9 (median: 42.2), respectively. These results were also independent of CML stage being even effective in blastic phase and in juvenile CML, which have a clinically aggressive course. Our data demonstrate that PA is a potent anti-leukemic agent not only for MDR positive CML patients but also especially for the blastic phase in the setting of imatinib resistance.