Development and characterization of [99mTc]Tc-lornoxicam as a potential COX-assisted radiopharmaceutical for inflammation imaging

Abstract

Inflammation is a protective biological response; however, prolonged or dysregulated inflammation is associated with different pathological disorders. Conventional imaging techniques primarily visualize structural changes, while molecular radiotracers strongly support the understanding of the functional and biochemical characterization of inflammatory processes. The development of targeted radiopharmaceuticals for inflammation imaging remains a significant challenge in nuclear medicine. Oxicam-class non-steroidal anti-inflammatory drugs, particularly those associated with cyclooxygenase (COX) inhibition, provide a rational platform to develop inflammation-targeted radiopharmaceuticals. Therefore, the objective of this study is the synthesis and biological evaluation of [99mTc]Tc-lornoxicam as a SPECT inflammation imaging radiopharmaceutical. The radiosynthesis of [99mTc]Tc-lornoxicam was performed to optimize the reaction conditions, such as pH, lornoxicam concentration, SnCl2·2H2O concentration, and reaction time, using 2 mCi of radioactivity at ambient reaction temperature. Radiochemical quality was evaluated using instant thin-layer chromatography quality control (ITLC-QC) analysis and high-performance liquid chromatography (HPLC), and the in vitro stability, serum protein binding, and octanol/water partition coefficient (log P) of radiotracers were also determined. In vivo biodistribution was evaluated in turpentine-induced sterile inflammation and E. coli-induced infection rat models. Furthermore, scintigraphic imaging of radiotracer localization was carried out using single-photon emission computed tomography (SPECT) in New Zealand white rabbits. Under optimized reaction conditions, 94% radiochemical yield (RCY) was recorded. The stability study showed 90% and 92% intact radiocomplexes at 2 h in serum and saline, respectively, which further degraded to 82% and 86% at 4 h, respectively. A protein binding of 64% and a log P value of 1.23 ± 0.03 were recorded. Biodistribution study revealed sustained uptake in inflammatory tissue, demonstrating T/NT ratios of 2.45, 2.33, 2.13, and 2.28 at 5 min, 30 min, 2 h, and 4 h post-injection (p.i), respectively. SPECT imaging showed greater uptake of [99mTc]Tc-lornoxicam in sterile inflammation compared to E. coli infection, while free 99mTc showed nonspecific distribution. [99mTc]Tc-lornoxicam demonstrated a high labeling yield, satisfactory stability, moderate lipophilicity, and preferential inflammation-associated localization. These findings support the potential of the radiotracer as a COX-targeted radiopharmaceutical for inflammation imaging, although further molecular investigations are warranted to establish its COX-specific targeting mechanism.