99mTc-MIBI Imaging as a Predictor of Therapy Response in Osteosarcoma Compared with Multidrug Resistance–Associated Protein and P-Glycoprotein Expression

In vitro studies have demonstrated that 99mTc-methoxyisobutyli-sonitrile (99mTc-MIBI) is a transport substrate of multidrug resis-tance (MDR)–related proteins. The aim of this clinical study was to evaluate whether 99mTc-MIBI scintigraphy was a functional imaging tool for in vivo detection of multidrug resistance–asso-ciated protein (MRP) expression in osteosarcoma and to inves-tigate the role of MRP and 99mTc-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 neoad-juvant chemotherapy. Tumor-to-background ratios of both early (10 min) and delayed (1 h) images and the percentage washout rate (WR%) of 99mTc-MIBI were calculated. Immunohistochem-ical analysis of MRP and Pgp was performed on biopsy speci