Targeting human synovium using homing peptides identified by in vivo phage display
Rheumatoid arthritis (RA) is a chronic inflammatory condition affecting diarthrodial synovial joints. Non-random patterns of inflammatory cell recruitment suggest the presence of synovial-specific vascular determinants which enable recruitment of specific inflammatory cell subsets. Using a model whereby human synovial and skin tissue is transplanted into SCID mice, we have previously used in vivo peptide phage display to identify novel peptide sequences which confer synovial homing specificity to human synovium. This synovial localisation was blocked by co-administration of free peptide thus confirming its specificity. In this project the in vivo homing properties of the peptide were further explored. The synovial localization of the synovial-specific phage was shown to be specifically increased after intragraft injection of TNFα. Sequence homology was shown between the expressed CKSTHDRLC (3.1) peptide and an extracellular domain of the leucocyte integrin mac-1. The homing properties of the free peptide were investigated by conjugation to the radioisotopes 111In and 99mTc. No significant differences were found in vivo between homing of the 3.1 monomeric peptide to transplanted human skin and synovium. The influence of valency and size of the molecules were investigated through the development of novel techniques: polymerization of the peptide was achieved by conjugation to radiolabelled streptavidin and fluorescent microspheres. In vivo experiments found no significant difference between localization of polymerised 3.1 or scrambled control peptide to either transplanted skin or synovium with either construct. Despite the negative results reported here, the techniques described have potential for the investigation of other targeted short-peptide sequences. Finally, the model was further developed as a tool for the pre-clinical imaging of human synovium in vivo using an 111In- conjugated anti-E-selectin antibody. It was shown that this could be used to resolve specific from non-specific uptake and hence represents, potentially, a powerful new tool for the development of human tissue-specific targeting strategies.
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