[18F]KS1, a novel ascorbate-based ligand images ROS in tumor models of rodents and nonhuman primates

Abstract

Over production of reactive oxygen species (ROS) caused by altered redox regulation of signaling pathways is common in many types of cancers. While PET imaging is recognized as the standard tool for cancer imaging, there are no clinically-approved PET radiotracers for ROS-imaging in cancer diagnosis and treatment. An ascorbate-based radio ligand promises to meet this urgent need. Our laboratory recently synthesized [¹⁸F] KS1, a fluoroethoxy furanose ring-containing ascorbate derivative, to track ROS in prostate tumor-bearing mice. Here we report cell uptake assays of [¹⁸F]KS1 with different ROS-regulating agents, PET imaging in head and neck squamous cell carcinoma (HNSCC) mice, and doxorubicin-induced rats; PET imaging in healthy and irradiated hepatic tumor-bearing rhesus to demonstrate its translational potential. Our preliminary evaluations demonstrated that KS1 do not generate ROS in tumor cells at tracer-level concentrations and tumor-killing properties at pharmacologic doses. [¹⁸F]KS1 uptake was low in HNSCC pretreated with ROS blockers, and high with ROS inducers. Tumors in high ROS-expressing SCC-61 took up significantly more [¹⁸F]KS1 than rSCC-61 (low-ROS expressing HNSCC); high uptake in doxorubicin-treated rats compared to saline-treated controls. Rodent biodistribution and PET imaging of [¹⁸F]KS1 in healthy rhesus monkeys demonstrated its favorable safety, pharmacokinetic properties with excellent washout profile, within 3.0 h of radiotracer administration. High uptake of [¹⁸F]KS1 in liver tumor tissues of the irradiated hepatic tumor-bearing monkey showed target selectivity. Our strong data in vitro, in vivo, and ex vivo here supports the high translational utility of [¹⁸F]KS1 to image ROS.

Keywords: Ascorbate; Biodistribution, Radioligands; Cancer; Positron emission tomography imaging; Reactive oxygen species.