First ex vivo study demonstrating that 99mTc-NTP 15-5 radiotracer binds to human articular cartilage

Preclinical data pointed to (99m)Tc-NTP 15-5 as a good candidate for single photon emission computed tomography (SPECT) imaging of cartilaginous disease. We set out to investigate and quantify (99m)Tc-NTP 15-5 ex vivo uptake by human articular cartilage relative to bone (99m)Tc-hydroxymethylene diphosphonate (HMDP) radiotracer.Three osteoarthritic human tibial plateaux and four tibiofemoral joints were incubated with (99m)Tc-NTP 15-5 and (99m)Tc-HMDP for 2 h. Affinity of tracers for cartilage was determined by visual analysis of SPECT/CT acquisitions and measurement of cartilage to cortical bone uptake ratios.Cartilage to cortical bone uptake ratios were 3.90 ± 2.35 and 0.76 ± 0.24, respectively, for (99m)Tc-NTP 15-5 and (99m)Tc-HMDP radiotracers. Visual analysis of fused SPECT/CT slices showed selective, intense (99m)Tc-NTP 15-5 accumulation in articular cartilage, whereas (99m)Tc-HMDP binding was low. Interestingly, a cartilage defect visualized on CT was clearly associated with focal decreased uptake of (99m)Tc-NTP 15-5.The tracer (99m)Tc-NTP 15-5 is of major interest for human cartilage molecular imaging and could find clinical applications in osteoarthritis staging and monitoring.