Effect of Verapamil on Cellular Uptake of Tc-99m MIBI and Tetrofosmin on Several Cancer Cells

Kim, Dae Hyun; Yoo, Jung Ah; Bae, Jin Ho; Jeong, Shin Young; Suh, Myung Rang; Ahn, Byeong Cheol; Lee, Kyu Bo; Lee, Jaetae

Abstract

PURPOSE
Cellular uptake of 99mTc-sestamibi (MIBI) and 99mTc-tetrofosmin (TF) is low in cancer cells expressing multidrug resistance (MDR) by p-glycoprotein (Pgp) or multidrug related protein (MRP). Verapamil is known to increase cellular uptake of MIBI in MDR cancer cells, but is recently reported to have different effects on tracer uptake in certain cancer cells. This study was prepared to evaluate effects of verapamil on cellular uptake of MIBI and TF in several cancer cells. MATERIALS AND METHODS: Cellular uptakes of Tc-99m MIBI and TF were measured in erythroleukemia K562 cell, breast cancer MCF7 cell, and human ovarian cancer SK-OV-3 cells, and data were compared with those of doxorubicin-resistant K562 (Ad) cells. RT-PCR and Western blot analysis were used for the detection of mdr1 mRNA and Pgp expression, and to observe changes in isotypes of PKC enzyme. Effects of verapamil on MIBI and TF uptake were evaluated at different concentrations upto 200 micro M at 1x10 (6) cells/ml at 37degrees C. Radioactivity in supernatant and pellet was measured with gamma counter to calculate cellular uptake ratio. Toxicity of verapamil was measured with MTT assay. RESULTS: Cellular uptakes of MIBI and TF were increased by time in four cancer cells studied. Co-incubation with verapamil resulted in an increase in uptake of MIBI and TF in K562 (Adr) cell at a concentration of 100 micro M and the maximal increase at 50 micro M was 10-times to baseline. In contrast, uptakes of MIBI and TF in K562, MCF7, SK-OV3 cells were decreased with verapamil treatment at a concentration over 1 micro M. With a concentration of 200 micro M verapamil, MIBI and TF uptakes in K562 cells were decreased to 1.5 % and 2.7% of those without verapamil, respectively. Cellular uptakes of MIBI and TF in MCF7 and SK-OV-3 cells were not changed with 10 micro M, but were also decreased with verapamil higher than 10 micro M, resulting 40% and 5% of baseline at 50 micro M. MTT assay of four cells revealed that K562, MCF7, SK-OV3 were not damaged with verapamil at 200 micro M. CONCLUSION: Although verapamil increases uptake of MIBI and TF in MDR cancer cells, cellular uptakes were further decreased with verapamil in certain cancer cells, which is not related to cytotoxicity of drug. These results suggest that cellular uptakes of both tracers might differ among different cells, and interpretation of changes in tracer uptake with verapamil in vitro should be different when different cell lines are used.