Enhanced cytotoxic effect of Ara-C by low intensity ultrasound to HL-60 cells

A clonogenic assay was tested in order to determine the effects of low intensity ultrasound on HL-60 cells in the presence of cytosine arabinoside (Ara-C). HL-60 cells were exposed to ultrasound at an intensity of 0.3 W/cm2 (48 kHz). Cells were then cultured for 8 days and the number of colonies was statistically analyzed (ANOVA). Ultrasound exposure alone for 120 s resulted in no significant decrease of colonies compared to non-treated cells (P0=0.1426). Significant differences (P0<0.005) were obtained between ultrasound treated and untreated cells in the presence of various concentrations of Ara-C (2×10−9, 1×10−8, 2×10−8, 5×10−8, 1×10−7 M). Morphological evaluation of ultrasound irradiated cells with scanning electron microscopy showed minor disruption of cell surface and disappearance of microvilli. These observations suggests that low intensity ultrasound altered the cell membrane thus resulting in change in Ara-C uptake into HL-60 cells.