TC-99m MIBI SPECT imaging in patients with lung carcinoma: is it a functional probe of multidrug resistance genes?

Objective: Multidrug-resistance (MDR) phenotype concerns altered membrane transport that results in lower cell concentrations of cytotoxic drug in many cancer types, including lung cancer, and is related to the overexpression of a variety of proteins that act as adenosine triphosphate-dependent extrusion pumps. Tc-99m Sestamibi (MIBI) is a transport substrate for P-glycoprotein (Pgp) pump. In this study, we assessed the uptake and clearance of technetium-99m-2-hexakis 2-methoxyisobutylisonitrile (Tc-99m MIBI) from the tumor and its correlation with messenger RNA (mRNA) levels of Pgp, MDR-associated protein (MRP1), and lung resistance protein (LRP) in lung carcinoma.

Methods: This study was carried out on 19 patients (mean age, 60.1 +/- 2.07 years) with advanced-stage lung carcinoma. The tumor samples obtained by bronchoscopy were assessed to estimate the levels of Pgp, MRP1, and LRP expression on mRNA level by quantitative real-time reverse-transcription polymerase chain reaction. Tc-99m MIBI chest imaging was performed 15 and 180 minutes after injection of 740 MBq Tc-99m MIBI. The early (T/Be) and delayed (T/Bd) Tc-99m MIBI uptakes and washout rate (WR) of Tc-99m MIBI from the tumor were measured.

Results: No correlation was found between the T/Be Tc-99m MIBI uptake of tumors (T/Be) and the levels of Pgp mRNA, MRP1 mRNA, and LRP mRNA by reverse-transcription polymerase chain reaction. There was a correlation between the mean T/Bd Tc-99m MIBI uptake and Pgp expression of the tumors (P = 0.001, Spearman rho = - 0.702). There was a correlation between the WR of Tc-99m MIBI from the tumor and Pgp expression of the tumor (P = 0.000, Spearman rho = 0.875). Washout rate of Tc-99m MIBI was not related to the levels of MRP1 mRNA (P = 0.93, Spearman rho = 0.02) or LRP mRNA (P = 0.47, Spearman rho = 0.177).

Conclusions: Increased WR of Tc-99m MIBI is related in Pgp over expression of the tumor. Tc-99m MIBI single photon emission computed tomography imaging may be a functional probe of overexpression of Pgp in patients with lung carcinoma. However, Tc-99m MIBI single photon emission computed tomography imaging cannot be used to identify the MDR involved in the MRP1 or LRP in these patients.