title: Detection of in vivo P-glycoprotein inhibition by PSC 833 using Tc-99m sestamibi.
abstract: Tc-99m sestamibi is a substrate of P-glycoprotein (Pgp) that has been proposed for use as a functional imaging agent for the multidrug resistance-1 phenotype. In vitro, retention of sestamibi by cells that overexpress Pgp can be modified by the presence of Pgp antagonists. In a Phase I trial of the Pgp reversal agent PSC 833, we show that the effects of this reversal agent can also be demonstrated in patients. Nine patients with metastatic renal carcinoma were studied three times: at baseline, approximately 1 day after vinblastine infusion, and while on PSC 833. One patient with metastatic adrenocortical cancer was also studied. Time activity curves and areas under the curve (AUCs) were obtained for tumor, liver, lung, and myocardium, and organ:heart AUC ratios were generated. With PSC 833, tumor visualization was enhanced, and statistically significant increases were found in AUC ratios for tumor and liver compared to baseline. For the liver, significant differences were also found between the vinblastine versus PSC 833 scans but not between the baseline versus vinblastine scans. This study demonstrates that sestamibi retention by tumor and liver is altered in the presence of the reversal agent PSC 833, presumably reflecting inhibition of Pgp. Thus, sestamibi may be useful in vivo as a means of monitoring the effects of this and other reversal agents on various tumors and normal tissues that express Pgp.
authors.affiliation: Department of Nuclear Medicine, Warren G. Magnuson Clinical Center, Division of Clinical Sciences, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Chen
authors.forename: B
authors.initials: B
authors.lastname: Meadows
authors.forename: J
authors.initials: J
authors.lastname: Regis
authors.forename: G
authors.initials: G
authors.lastname: Kalafsky
authors.forename: T
authors.initials: T
authors.lastname: Fojo
authors.forename: J A
authors.initials: JA
authors.lastname: Carrasquillo
authors.forename: S E
authors.initials: SE
authors.lastname: Bates
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000328:Adult; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000009:adverse effects* / Q000493:pharmacokinetics; D002292:Carcinoma, Renal Cell / Q000000981:diagnostic imaging* / Q000188:drug therapy* / Q000473:pathology; D003524:Cyclosporins / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi; D014018:Tissue Distribution; D014747:Vinblastine / Q000008:administration & dosage
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D003524:Cyclosporins; D019275:Radiopharmaceuticals; D014747:Vinblastine; D017256:Technetium Tc 99m Sestamibi; C070272:valspodar