title: 99mTc-MIBI imaging as a predictor of therapy response in osteosarcoma compared with multidrug resistance-associated protein and P-glycoprotein expression.
abstract: In vitro studies have demonstrated that (99m)Tc-methoxyisobutylisonitrile ((99m)Tc-MIBI) is a transport substrate of multidrug resistance (MDR)-related proteins. The aim of this clinical study was to evaluate whether (99m)Tc-MIBI scintigraphy was a functional imaging tool for in vivo detection of multidrug resistance-associated protein (MRP) expression in osteosarcoma and to investigate the role of MRP and (99m)Tc-MIBI imaging to predict the clinical outcome. We also examined whether the scintigraphic parameters would help to distinguish the functional capacity of P-glycoprotein (Pgp) and MRP.
  
  
  METHODS
  Twenty-four patients with a diagnosis of osteosarcoma were studied before neoadjuvant chemotherapy. Tumor-to-background ratios of both early (10 min) and delayed (1 h) images and the percentage washout rate (WR%) of (99m)Tc-MIBI were calculated. Immunohistochemical analysis of MRP and Pgp was performed on biopsy specimens, and the response to preoperative chemotherapy was assessed by histopathologic examination.
  
  
  RESULTS
  Fifteen of 24 osteosarcoma samples in our series (62.5%) showed significant expression of MRP. The level of MRP expression was significantly correlated with the WR% of (99m)Tc-MIBI (r = 0.58, P = 0.003), and the WR% of (99m)Tc-MIBI was significantly faster in patients with high MRP expression than in those with a low MRP score (P = 0.007). The clearance rate of (99m)Tc-MIBI was significantly slower in tumor samples with negative or low expression of both Pgp and MRP (16% +/- 6.2%) when compared with osteosarcomas with high expression of both proteins (31.7% +/- 8.7%) (P = 0.001). There was not a significant difference between the WR% of (99m)Tc-MIBI in tumors with coexpression of both proteins and in tumors with high expression of either Pgp or MRP. Both the rate of MRP expression and the WR% of (99m)Tc-MIBI were significantly correlated with response rate.
  
  
  CONCLUSIONS
  Our results suggest that the WR% of (99m)Tc-MIBI is correlated with MRP expression. Both the WR% of (99m)Tc-MIBI and MRP expression are correlated with therapy response. (99m)Tc-MIBI can be used as a general probe for functional imaging of both Pgp and MRP; however, it is not capable of differentiating the functional status of either MDR-related glycoprotein.
authors.affiliation: Department of Nuclear Medicine, Ege University Medical Faculty, Izmir, Turkey. zburak@egenet.com.tr
authors.forename: Zeynep
authors.initials: Z
authors.lastname: Burak
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Moretti
authors.forename: Ozden
authors.initials: O
authors.lastname: Ersoy
authors.forename: Ulus
authors.initials: U
authors.lastname: Sanli
authors.forename: Mehmet
authors.initials: M
authors.lastname: Kantar
authors.forename: Feyzi
authors.initials: F
authors.lastname: Tamgac
authors.forename: Gülçin
authors.initials: G
authors.lastname: Basdemir
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D014408:Biomarkers, Tumor / Q000032:analysis / Q000378:metabolism; D001859:Bone Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D002648:Child; D005260:Female; D005266:Femoral Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D012516:Osteosarcoma / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000378:metabolism*; D011237:Predictive Value of Tests; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D013223:Statistics as Topic; D017256:Technetium Tc 99m Sestamibi / Q000493:pharmacokinetics; D016896:Treatment Outcome
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D014408:Biomarkers, Tumor; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi