Involvement of glutathione in loss of technetium-99m-MIBI accumulation related to membrane MDR protein expression in tumor cells.
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.


CONCLUSIONS
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.
Laboratory of Radiopharmacology, Upres 2360 IOCMH, Bobigny, France.
J L
JL
Moretti
M
M
Duran Cordobes
A
A
Starzec
V
V
de Beco
J
J
Vergote
F
F
Benazzouz
B
B
Boissier
H
H
Cohen
N
N
Safi
S
S
Piperno-Neumann
J C
JC
Kouyoumdjian
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D018432:Drug Resistance, Multiple; D019450:Genes, MDR; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D016133:Polymerase Chain Reaction; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D017256:Technetium Tc 99m Sestamibi / Q000493:pharmacokinetics*; D014407:Tumor Cells, Cultured / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D005978:Glutathione; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi