68Ga-Galuminox: A Potential PET Tracer for Imaging ROS-Mediated Activity (2020)

3116 Objectives: Reactive oxygen species (ROS) are by-products of numerous enzymatic reactions in various cell compartments, including the cytoplasm, cell membrane, endoplasmic reticulum (ER), and mitochondria thus regulating normal cell processes, such as metabolic function and signaling. Oxidative stress represents an imbalance between production of ROS and their elimination or mitigation by antioxidants. Therefore, the overproduction of ROS is involved in the pathogenesis of several diseases, such as arteriosclerosis, heart failure, cancer, neurocognitive and neurodegenerative disorders, and diabetes mellitus. To assess contribution of oxidative stress prevalent in pathophysiology of disease states, herein, we perform characterization of Galuminox, a new molecular imaging probe, and biochemical validation through Doxorubicin (DOX)-induced ROS in rat cardiomyoblasts using live-cell imaging and pharmacokinetics in DOX-treated Bl6 mice, deploying its 68Ga-Galuminox counterpart. Galuminox could offer a noninvasive tool for detection of DOX-induced ROS in cellulo and in vivo.
 Methods: Galuminox was obtained via reaction of either GaCl3 or 68GaCl3 and the precursor ligand, and purified on C-18 column using radio-HPLC employing an eluent, gradient mixture of ethanol and saline. The appropriate fraction was collected, concentrated, re-suspended in ethanol, and diluted with saline for performing in cellulo and vivo experiments. To evaluate the cellular accumulation studies, H9c2 cells were plated and incubated with DOX or vehicle for 24h at 37°C under a continuous flux of 5% CO2, and treated with Galuminox (20 µM; 60min). Images were acquired using a Nikon A1R scanning confocal microscope with a 20x objective utilizing 405 nm laser line using NIS-Elements software. The cellular uptake of Galuminox was quantified and analyzed using the Image J software package (NIH). Pharmacokinetics studies were performed in mice either pretreated for 5 days with DOX (20 mg/kg) or vehicle (saline). All mice were sacrificed by cervical dislocation, organs excised, counted for γ activity, and normalized to injected dose.
 Results: Following tail-vein injections, the quantitative pharmacokinetic data demonstrate a higher uptake of 68Ga-Galuminox in DOX-treated C57BL6 mice (Heart: 1.4 fold; Muscle: 3-fold; and Fat: 5 fold) compared to their untreated controls thus suggesting ability to monitor drug induced ROS in heart, muscle and fat. In rats, Galuminox shows higher accumulation in DOX-treated rat cardiomyoblasts compared with vehicle treated controls (H9c2 cells). Similar to MitoSox, a well-validated dye for monitoring ROS, Galuminox also identified DOX-induced or starvation-induced ROS activity in H9c2 cells as detected by single-cell fluorescent imaging. Following uptake into H9c2 cells, Galuminox localizes to lysosomes in punctae pattern suggestive of mitophagic removal of ROS-injured mitochondria.
 Conclusions: Our data collectively indicate 68Ga-Galuminox as a novel ROS probe. Further biochemical validation is needed to identify contributing ROS species and dynamic range.
Funding: NIH P41EB025815; R01 HL111163.