Effects of induction of multi-drug resistance on accumulation of 99mTc-sestamibi in vitro.

The aim of our study was to evaluate the speed of induction of drug-resistance and its effects on intracellular MIBI accumulation in established human cell lines in-vitro. Four out of 5 cell lines were sensitive to vincristine, 1 cell line was vincristine-resistant. All vincristine sensitive cell lines became vincristine-resistant following drug exposure. Resistance in low-drug concentrations occurred as early as 24 hours after exposure and progressed to a roughly 1000-times enhanced resistance within 7 days. Induction of drug-resistance was associated with significantly decreased MIBI accumulation in 2 cell lines but was uneffected in 1 cell line, that was primarily drug sensitive as well as in one cell line that was primarily drug-resistant. Our data indicate, that induction of MDR is an extremely rapid process and the development of drug resistance is not always associated with enhanced MIBI extrusion.