ABSTRACT
UNLABELLED: It was reported recently that 99mTc-hexakis-2-methoxyisobutyl isonitrile (MIBI) uptake is drastically reduced in cancer cells that express the multidrug resistance (MDR) product, Pgp 170 kDa (Pgp), suggesting that 99mTc-MIBI is a transport substrate for this transmembrane glycoprotein. In our study, we explored if another pump, a multidrug resistance-associated protein (MRP), could affect 99mTc-MIBI uptake. In addition, we studied the involvement of intracellular glutathione (GSH) as a modulator of 99mTc-MIBI uptake by both Pgp and MRP proteins. METHODS: MDR1 and MRP gene expression in seven human tumor cell lines was determined on a transcriptional level by reverse transcriptase polymerase chain reaction and on a protein level using immunocytochemistry. Technetium-99m-MIBI uptake was quantified by measuring radioactivity retained in the cells incubated at 37 degrees C in the presence or absence of buthionine sulfoximine (BSO), which depletes cellular GSH. The cellular GSH content was determined with Ellman's reagent. RESULTS: Cell lines were classified according to their phenotypic characteristics: 1/MRP-/Pgp-: breast cancer cells (MCF7), lung carcinoma cells (H69S) and mouth epidermoid tumor cells (KB 3.1), 2/MRP-/Pgp+: MCF7 mdr+, KBA.1; and 3/MRP+/Pgp-: small-cell lung carcinoma (H69 AR and A 549). Technetium-99m-MIBI uptake was significantly lower in cells expressing MRP as well as Pgp compared to MRP/Pgp cells. Depletion of GSH by BSO resulted in an increase of 99mTc-MIBI uptake in multidrug resistant cells overexpressing MRP but not expressing Pgp. CONCLUSION: Technetium-99m-MIBI is extruded by both Pgp and MRP efflux pumps. However, MRP action is indirect and involves intracellular GSH for a presumed interaction with the 99mTc-MIBI before its effLux. Technetium-99m-MIBI seems to be a good candidate for a noninvasive marker to diagnose MDR1 related to Pgp and MRP expression in tumors of different origin.
Subject(s)
ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism , ATP-Binding Cassette Transporters/metabolism , Genes, MDR , Glutathione/metabolism , Radiopharmaceuticals/pharmacokinetics , Technetium Tc 99m Sestamibi/pharmacokinetics , ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics , ATP-Binding Cassette Transporters/genetics , Drug Resistance, Multiple , Humans , Immunohistochemistry , In Vitro Techniques , Multidrug Resistance-Associated Proteins , Polymerase Chain Reaction , Tumor Cells, Cultured/metabolismSubject(s)
ATP Binding Cassette Transporter, Subfamily B, Member 1 , Antineoplastic Agents/therapeutic use , Drug Resistance, Multiple/genetics , Neoplasms/diagnostic imaging , Neoplasms/drug therapy , Technetium Tc 99m Sestamibi , ATP Binding Cassette Transporter, Subfamily B, Member 1/analysis , ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics , Gene Expression , Humans , RNA, Messenger/analysis , Radionuclide ImagingABSTRACT
The new potential tracer of bone imaging, AHBDP-Sn(II)-TcO.3H(2)O was synthesized by reducing the TcO(4) (-) to TcO(2) (+) in the presence of AHBDP and Sn(ll)'s reducing agent. We found that tin rapidly forms a stable complex with AHBDP, giving AHBDP-Sn(II).3H(2)O. In the excess of AHBDP-Sn(ll).3H(2)O, the AHBDP-Sn(II).3H(2)O coordinates with TcO(2) (+) to give AHBDP-Sn(II)-TcO.3H(2)O which could polymerise or oligomerise to give hydrophobic species. The overall process appears as a first-order reaction (K= 0.67 +/- 0.005s(-1)). In rats, the fixation of AHBDP-Sn(II)-(99m)TcO. 3H(2)O on bone is homogeneous and the scintigraphic images have the same quality as those of 1-hydroxymethane-1,1-diphosphonate-Technetium (HMDP-(99m)Tc). The activity in non-target organs was neglible.
