Synthesis and evaluation of cyclosporine A-loaded polysialic acid–polycaprolactone micelles for rheumatoid arthritis

Polysialic acid (PSA) has been identified as a natural, hydrophilic polymer that can be used to extend circulation time and improve therapeutic efficacy when used as the basis of drug carrier systems. Here, to further investigate the potential of PSA to alter the pharmacokinetic and pharmacodynamic profiles of associated therapeutics, PSA-based micelles were formed via self-assembly of PSA grafted with polycaprolactone (PCL) at a critical micelle concentration of 84.7 ± 13.2 μg/ml. Cyclosporine A (CyA), a therapeutic used in the treatment of rheumatoid arthritis, was loaded into the PSA–PCL micelles with a loading capacity and loading efficiency of 0.09 ± 0.02 mg CyA/mg PSA–PCL and 29.3 ± 6.4%, respectively. CyA loading resulted in a size increase from 73.8 ± 12.4 nm to 107.5 ± 9.3 nm at 25 °C and from 138.4 ± 40.7 nm to 195.3 ± 52.1 nm at 37 °C, favorable size ranges for drug delivery to inflamed tissue characterized by leaky vasculature, as occurs during rheumatoid arthritis pathogenesis. As an indicator of the stealth nature the micelles are expected to exhibit in vivo, the fixed aqueous layer thickness of the PSA–PCL micelles was determined to be 0.63 ± 0.02 nm, comparable to that obtained for traditionally utilized poly(ethylene glycol) coated liposomes. The PSA–PCL micelles had a negligible effect on the viability of the SW982 synovial fibroblast cell line. Fluorescent microscopy was utilized to demonstrate uptake by the synovial fibroblasts through a non-receptor mediated form of endocytosis and partitioning of CyA into the membrane.

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