Radiolabeled Chondroitin Sulfate (99mTcCS): Uptake and Binding Studies in Human Articular Chondrocytes and Cartilage in Osteoarthritis

Background: Chondroitin sulfate (CS), as Condrosulf (IBSA, Lugano, Switzerland) is used for treatment in patient with osteoarthritis (OA). A suitable and specific radiotracer for imaging of OA is not established yet. For this reason we radiolabeled CS and evaluated its action in OA. The aim of this study was to compare chondrocyte binding of 99mTcCS with cartilage uptake in tissues from patients with OA of different stage and severity. Methods: Radiolabeling of CS was performed using 99mTc (150- 180 MBq)/stannous chloride method. Uptake of 99mTcCS (185kBq) was studied in human cartilage tissue samples from patients undergoing knee arthroplasty (n=4, 63-82a). Human articular chondrocytes were isolated from these tissue samples for uptake (37 °C) and binding studies (4 °C) using cell suspension (one million cells/tube) as well as monolayer cultures (15,000 cells/well). Results: Labelling efficiency ranged 82.3-93.3%, specific activity of 99mTcCS was 4.5-4.9 mCi/?Mol. We observed prolonged uptake of the tracer in tissue pieces up to 48 h amounting to a maximum of 49.2±2.2% of the total dose in heavily (grade III) versus 29.7±3.1% in mildly degenerated area (grade II). By autoradiography the uptake was also increasing with time in both areas of degeneration reaching saturation between 24-48 h. The maximum uptake was much higher in grade III tissues as compared to grade II tissues and amounted to 55.3±3.2% vs. 30.1±1.5%. The tracer uptake of chondrocytes in suspension culture after 24 h amounted to 16.9±1.3% from heavy degenerate and 10.8±2.1% from mild degenerate cartilage samples. Binding studies performed in monolayer cultures showed that both specific and non-specific binding from heavy and mild degenerate cartilage chondrocytes at 75 nmol/well reached the maximum binding after 2 h at this CS concentration. 62.4 % vs. 48.8% were bound by these cell populations originated from grade III and II OA cartilage. Conclusions: These findings demonstrate high specificity (chondrotropism) of 99mTcCS for OA cartilage and significant interaction with chondrocytes and extracellular matrix depending on OA stage, supporting the clinical application of 99mTcCS as a promising diagnostic tool in OA imaging and monitoring of therapy.