COMPARISON OF UPTAKE OF TC-99M-MIBI, TC-99M-TETROFOSMIN AND TC-99M-Q12 INTO HUMAN BREAST-CANCER CELL-LINES

Technetium-99m hexakis-2-methoxyisobutylisonitrile (MIBI), Tc-99m-tetr ofosmin and Tc-99m-Q12 were all introduced for myocardial imaging but found additional applications as they are taken up by different rumour s, enabling imaging of these lesions in patients. The aim of this stud y was to compare the uptake characteristics of these compounds in vitr o in the human adenocarcinoma breast cell lines MCF-7 and ZR-75. It wa s shown that Tc-99m-MIBI had the highest cellular uptake (15.9%+/-0.5% dose/mg protein after 60 min in MCF-7, and 14.2%+/-0.4% dose/mg prote in in ZR-75), followed by Tc-99m-tetrofosmin (6.8%+/-0.6% dose/mg prot ein in MCF-7, and 8.2%+/-0.2% dose/mg protein in ZR-75) and Tc-99m-Q12 (3.2%+/-0.1% dose/mg protein in MCF-7, and 3.5%+/-0.3% dose/mg protei n in ZR-75 cells). For ail three compounds tenfold differences in spec ific activity did not influence total cell-associated radioactivity. U ptake of Tc-99m-MIBI and Tc-99m-tetrofosmin was obviously lower at 4 d egrees C than at 37 degrees C, whereas Tc-99m-Q12 uptake showed only s light temperature dependence. When uptake was compared in cells grown to different cell densities (1 mg/ml cellular protein versus 0.3 mg/ml ), no differences in uptake were detected when uptake was corrected fo r the amount of cellular protein present in the dishes. Furthermore, f or all compounds it was shown that cellular radioactivity decreased ra pidly after washing. Apart from the differences in cellular uptake of the three compounds after 60 min, no differences in residual cellular radioactivity after washing were found between the different compounds when expressed as a percentage of their 60-min uptake, suggesting tha t the efflux process of the radiolabelled compounds was similar. The d ifferences in cell-associated activity after 60 min were thus presumab ly caused by differences in uptake. It was concluded that of the Tc-la belled compounds tested, Tc-99m-MIBI had the highest cellular retentio n in both human breast tumour cell lines. However, for imaging in vivo not only radioactivity in the target organ is important, but also the ratio of radioactivity in the target Versus that in the background. T herefore, further studies in vivo need to be performed to investigate which compound is the optimal imaging agent.