title: Expression of recombinant human multidrug resistance P-glycoprotein in insect cells confers decreased accumulation of technetium-99m-sestamibi.
abstract: 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.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: V V
authors.initials: VV
authors.lastname: Rao
authors.forename: M L
authors.initials: ML
authors.lastname: Chiu
authors.forename: J F
authors.initials: JF
authors.lastname: Kronauge
authors.forename: D
authors.initials: D
authors.lastname: Piwnica-Worms
mesh_terms: 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*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D017256:Technetium Tc 99m Sestamibi