OBJECTIVELeukemia is the most common malignancy in children. Combined chemotherapy is currently the primary treatment modality. During the past decade, very high cure rates of childhood acute lymphoblastic leukemia (ALL) have been reported both at home and abroad. However, the cure rates of children with acute myeloid leukemia (AML) remain low due to the multiple-drug resistance (MDR). P-glycoprotein (P-gp) is one of the most important mechanisms of MDR for leukemia cells. However, the function of the protein, the clinical application of its reversal agents and the efficacy of the combination of the reversal agents remain to be elucidated. The present study aimed to evaluate the P-gp pump function on leukemia cell membrane and the effects of the combined administration of the reversal agents cyclosporin A (CSA) and verapamil (VER) through the observation of Calcein-AM (C-AM) metabolism in the cell line K562 and its multi-drug resistant subline K562/VCR.

METHODSThe mean fluorescence intensity (MFI) of C-AM inside the cytoplasm was analyzed with flow cytometry (FCM). The events of K562 and K562/VCR cells treated and untreated with CSA, VER and CSA + VER were acquired at time points 0, 30, 60, 90 and 120 minutes, respectively, and the data obtained were analyzed with CellQuest software.

RESULTSThe C-AM in the K562 and K562/VCR varied more apparently in the fist 24 hours. In addition, the MFI of the C-AM in K562 was significantly higher than that in K562/VCR cells indicating that the P-gp pump molecules were functioning. The MFIs of the CSA, VER and CSA + VER groups co-cultured with K562/VCR cells were 4014 +/- 219, 3879 +/- 116 and 4158 +/- 302, respectively after 120 min of incubation, significantly higher as compared to that of control group (3251 +/- 107, P < 0.05). On the other hand, significant inhibition of the efflux from the K562/VCR cell line was also noticed after the same time period of incubation with the MFIs of 2237 +/- 155, 1932 +/- 233 and 2231 +/- 147, respectively in the three groups, which was significantly higher than that of control group (1622 +/- 191, P < 0.05). CSA, VER and CSA + VER could increase the uptake and inhibit the efflux of C-AM by K562/VCR cells, while no evident influence on those functions inside the parental cell line K562 cells was noticed.

CONCLUSIONSCSA, VER and CSA + VER could increase the uptake and reduce the efflux of C-AM by K562/VCR cells while no significant difference between the CSA + VER and CSA or VER was noticed. P-gp pump function and the effects of its reversal agents on leukemic cells can be rapidly and easily evaluated by using the C-AM and FCM.