Abstract
1106
Objectives Imaging the functional transport activity of breast cancer resistance protein (BCRP, ABCG2) would assist in the stratification of chemotherapeutic choices. Galmydar, a fluorescent and moderately hydrophobic Ga(III) monocationic complex, was evaluated as a substrate capable of monitoring BCRP functional transport activity. To assess the sensitivity and specificity of Galmydar, cellular accumulation was determined in BCRP-transfected cells. To assess the potential for molecular imaging of BCRP-mediated functional transport activity at the blood brain barrier (BBB) in vivo, 68Ga-Galmydar microPET/CT imaging was performed in knockout mouse models.
Methods Live-cell fluorescence microscopy and 67Ga-radiotracer uptake assays were performed in HEK293 cells, stably transfected with BCRP (HEK293/BCRP) or control plasmid (HEK293/WT), at 37°C under standard growth conditions after incubation for 30 and 90 min, respectively. Cellular accumulation, localization and quantitative uptake, was measured in the absence or presence of 5 µM Ko143, a potent BCRP antagonist. 68Ga-Galmydar live-animal microPET/CT brain imaging was performed in ABCG2‑/- (BCRP knockout, KO), mdr1a/1b‑/- (Pgp double knockout, dKO) in the absence and presence of 10 mg/kg Ko143, and mdr1a/1b‑/-ABCG2‑/- (Pgp-BCRP triple knockout, tKO) mouse models, 15 and 60 min post-intravenous injection.
Results Cellular accumulation profiles of Galymdar are inversely proportional to BCRP expression in HEK293 cells, observed via live-cell fluorescence microscopy and 67Ga-radiotracer uptake assays. BCRP antagonist Ko143 induces accumulation in HEK293/BCRP cells, indicating target sensitivity and specificity. Finally, microPET imaging shows higher initial penetration and retention of 68Ga-Galmydar in brains of KO, dKO, and tKO mice compared to age-matched WT counterparts.
Conclusions Fluorescence microscopy, 67Ga-radiotracer cellular uptake, and 68Ga-microPET live-animal imaging data establish Galmydar as a probe capable of imaging BCRP-mediated functional transport in vivo.
Research Support Financial assistance to this work was provided by grants from the National Institutes of Health in part by RO1 HL111163 (VS), R33 AG033328 (VS), American Health Assistance Foundation (A2007-383: VS), and P50AG05681 (PI: Morris, Pilot: VS).