Expression of recombinant human multidrug resistance P-glycoprotein in insect cells confers decreased accumulation of technetium-99m-sestamibi.
The multidrug-resistant P-glycoprotein is a M(r) 170,000 plasma membrane protein encoded by the mammalian multidrug resistance gene (MDR) which appears to function as an efflux transporter of a variety of potent chemotherapeutic agents.


METHODS
To directly demonstrate that 99mTc-sestamibi is recognized by the human P-glycoprotein, we overexpressed recombinant human MDR1 P-glycoprotein in host Sf9 insect cells using a baculoviral vector and correlated expression of the gene product with 99mTc-sestamibi accumulation.


RESULTS
In parental Sf9 cells and in wild-type baculoviral infected (control) cells, 99mTc-sestamibi accumulation asymptotically approached a plateau of 650 fmoles (mg protein)-1 (nMo)-1 and 337 fmoles (mg protein)-1 (nMo)-1, respectively. In MDR1 baculoviral infected cells, P-glycoprotein expression was maximal at 72 hr postinfection, while 99mTc-sestamibi accumulation was reduced to 12 fmole (mg protein)-1 (nMo)-1. Verapamil (500 microM), the classical MDR modulator, produced an approximately 300% enhancement of 99mTc-sestamibi accumulation in Sf9 cells expressing MDR1 P-glycoprotein, but only a 50% enhancement in parental Sf9 cells, consistent with verapamil-induced inhibition of P-glycoprotein-mediated 99mTc-sestamibi efflux.


CONCLUSIONS
These data demonstrate that the recombinant protein is transiently expressed in a functional state capable of drug transport in Sf9 cell membranes and that 99mTc-sestamibi is a transport substrate recognized by the human MDR1 P-glycoprotein. Technetium-99m-sestamibi may prove useful for functionally characterizing P-glycoprotein expression in human tumors in vivo.
Rao
V V
VV
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
Chiu
M L
ML
Kronauge
J F
JF
Piwnica-Worms
D
D
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics*; D002478:Cells, Cultured; D004351:Drug Resistance / Q000235:genetics*; D015870:Gene Expression; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics*; D009036:Moths / Q000166:cytology; D017256:Technetium Tc 99m Sestamibi / Q000493:pharmacokinetics*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D017256:Technetium Tc 99m Sestamibi