Successful imaging of osteoarthritis with 99mTc radiolabeled chondroitin sulfate (CS) in dogs

251 Objectives In previous ex-vivo studies we proved a specific uptake of 99mTcCS in human articular cartilage. As a next step for the clinical use we investigated its in-vivo uptake in dogs. Methods Radiolabeling of CS, as Condrosulf (IBSA, Lugano, Switzerland) was performed using 25 mg of CS and 20-40 MBq/kg of 99mTc by tin method. In-vivo uptake of 99mTcCS was evaluated in dogs (n=6, castrated male, 5 years, 15-23 kg). 5 healthy dogs served as controls and 1 with clinical and radiological signs of osteoarthritis in the carpal, elbow, and tarsal joint was examined. The tracer i.v. injected into the external cephalic vein. The uptake was monitored up to 24h using a planar gamma camera (Diacam, MiE GmbH, Germany) with low energy high resolution collimator and dedicated software (Scintron, MiE GmbH, Germany), by regional planar or whole body ventral and dorsal acquisition under sedation or anaesthesia. Results In control dogs we did not detect any specific uptake of 99mTcCS in the cartilage. In contrast, in dog suffering from osteoarthritis a significant, specific, persistent uptake between 4-6h in tarsal, carpal and cubital joints was documented. The whole body biodistribution after 4-6h in the healthy dogs showed tracer accumulation in both kidneys, spleen, liver, and stomach (2.2-2.9%, 0-3%, 17.7-27.3%, and 3.2-6.0%, respectively). Median target (joint) to background (mid antebrachium) ratio in the osteoarthritis joints after 4,6 and 24h was 2.6, 3.1, 2.9 and 1.4, 1.5, and 1.6, respectively in controls. Target to background ratio using soft tissue as a background was 1.3, 1.8, and 1.9 in osteoarthritis joints after 4, 6, and 24h and 1.0, 0.8 and 1.0,respectively in controls. None of the dogs experienced any side effects. Conclusions These preliminary results suggest that 99mTcCS might become a promising diagnostic tool for imaging osteoarthritis. More extensive and detailed examinations in dogs are required, however, before extending this methodology for application in humans.