Efflux Pumps Modulation in Colorectal Adenocarcinoma Cell Lines: The Role of Nuclear Medicine

Abstract

Introduction: Multidrug resistance (MDR) is one of the major problems of chemotherapy. Overexpression of efflux pumps, such as P-glycoprotein (Pgp), multiple resistance-related protein 1 (MRP-1) and lung resistance protein (LRP) can lead to MDR. Verapamil and L-buthionine-sulfoximine (BSO) are two modulators of these proteins. This study aims to compare <sup>99m</sup>Tc-Sestamibi transport kinetics in human colorectal adenocarcinoma cell lines, in the presence and absence of the MDR modulators verapamil and BSO. Material and Methods: MDR proteins expression was evaluated in sensitive (WiDr) and resistant (LS1034) human colorectal adenocarcinoma cell lines. Intracellular and plasma membrane Pgp and MRP1, and LRP expression was analyzed by flow-cytometry and western blot. Cellular transport kinetics was assessed using <sup>99m</sup>Tc-Sestamibi. MDR modulation was evaluated though retention studies in resistant cells after incubation with the modulators. Results: Pgp expression was significantly higher (p≤0.001) in resistant cells. These results were confirmed by western blot analysis. <sup>99m</sup>Tc-Sestamibi uptake and retention percentage were significantly higher (p<0.001 and p<0.01, respectively) in the sensitive cells for all time-points considered. In resistant cells there were no significant differences when we consider the curves as a whole, considering cells incubated versus non-incubated with MDR modulators. However, for the first minutes after incubation with <sup>99m</sup>Tc-Sestamibi, there were differences among the MDR modulators used (p<0.05). Conclusions: In vitro kinetic studies using <sup>99m</sup>Tc-Sestamibi could indicate MDR phenotype in colorectal adenocarcinoma cells. As the modulators used showed a reversion of the retention profile only for the first minutes, their administration should occur immediately before the administration of cytotoxic drugs

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