TARGETING OF CATIONIC LIPOSOMES TO THE SYNOVIAL ENDOTHELIUM OF RHEUMATOID JOINTS – A NEW PROMISING DRUG DELIVERY SYSTEM

Abstract

Background: The healthy endothelium consists of quiescent endothelial cells that, under appropriate stimulation, can undergo profound changes leading to an activated phenotype. Activated endothelial cells of the synovial vasculature play a major role in the inflammatory process occurring in rheumatoid arthritis (RA) and enhanced angiogenesis contributes to the development and maintenance of RA. Thus, the endothelium can be used as an gateway for drug delivery and therapy. Cationic liposomes have been shown to target angiogenic endothelial cells in chronic inflammation in mice, also shown in tumors. They may also serve as potent vehicles for drug delivery to the synovial vasculature of rheumatoid joints.

Methods: To test whether cationic liposomes can serve as vehicles for drug delivery in RA we investigated the targeting of fluorescently labelled cationic liposomes (LipoRed) to the activated synovial vasculature of knees from arthritic mice. In a second step we used cationic liposomes carrying the compound MDG-12 (Endo-MDG-12) to study the effects of a targeted delivery of this drug to the inflamed joints in Antigen induced Arthritis (AIA). Targeting of LipoRed to the synovial vasculature was analysed by intravital microscopy (IVM) in mice with AIA. Synovial tissue was investigated at day 8 after AIA induction. Time resolved binding of liposomes was quantified at functional vessels of the microvasculature. Mice with AIA were intravenously treated with EndoMDG-12 in a therapeutic setting. Knee joints were subjected to clinical scoring and histopathology analysis.

Results: In a time dependent manner, intravenously applied LipoRed enriched more then three fold in the synovial vasculature of AIA mice when compared with healthy mice. In AIA animals maximum binding measured as relative fluorescence (Fmax=142 RFU) was already achieved 5 min after LiopoRed application (tmax) and dropped to the half maximum after 100 min (tmax/2)compared with healthy mice with a Fmax=48 RFU, tmax=15 min and tmax/2=60 min. Treatment of AiA animals with EndoMDG-12 showed a clear attenuation of the course of the disease. Analysis of the clinical score and thickness of knee joints showed a significant decrease of both parameters compared with the control group.

Conclusion: Based on our in vivo data, cationic liposomes seem to be very well suited to deliver compounds to rheumatoid joints for diagnosis and/or therapy. Furthermore, our results from animal experiments suggest that cationic liposomes like EndoMDG-12 could be a promising treatment option for RA.