Development of imaging agents for the visualisation of cartilage in vivo

s / Osteoarthritis and Cartilage 23 (2015) A82eA416 A205 327 DEVELOPMENT OF IMAGING AGENTS FOR THE VISUALISATION OF CARTILAGE IN VIVO N.H. Lim y, H. Hu z, M. Nazare x, O. Plettenburg x, H. Nagase y, C. Schultz z. yUniv. of Oxford, Oxford, United Kingdom; z EMBL, Heidelberg, Germany; x Sanofi Aventis, Frankfurt, Germany Purpose: OA disease progression in both humans and animal models is poorly defined by current X-Ray and MRI imaging methods. The main tissue of interest, cartilage, does not absorb X-rays and has non-optimal signal: noise with MRI, necessitating different MRI techniques. We aim to develop a cartilage-specific imaging agent to improve our ability to image OA disease progression in vivo. Methods: We synthesised a family of imaging agents based on a DOTA (1,4,7,10-tetraazacyclododecane-1.4.7.10-tetraactic acid) backbone. DOTA offers the advantage of allowing multivalent decoration with a collagen II binding peptide for cartilage specificity, as well as being able to coordinate gadolinium ions for future MRI imaging. The Cy5.5 fluorophore was also incorporated to enable in vivo optical imaging and later visualisation of distribution by confocal fluorescence microscopy of cryosecions of the joint post-mortem. Results: Using in vivo optical imaging, we characterised the retention of the DOTA-collagen II binding peptide compounds and their scrambled controls following intra-articular injection. DOTA with one collagen II binding peptide (1TP) was retained in the joint with a half life of 210 hours, compared to 12 hours for its scrambled control (1SP). This half life was increased to over 1000 hours with 3 collagen binding peptides (3TP). Confocal fluorescence microscopy of cryosections of the joint showed that 1TP and 3TP was present in the cartilage, but was excluded from the pericellular matrix of the chondrocytes. Conclusions:We have demonstrated that the DOTA-collagen II binding peptide imaging agents bind specifically to cartilage in vivo and that the strength of this binding can be changed with valency. Further work is being carried out to utilise these cartilage imaging agents in different imagingmodalities to obtain information about the status of cartilage in