Camptothecin (CPT), a potent topoisomerase I inhibitor, was originally discovered as an anticancer agent to induce programmed cell death of cancer cells. Recent evidence suggests that, similar to cancer, alterations in apoptosis and over-proliferation of key effector cells in the arthritic joint result in rheumatoid arthritis (RA) pathogenesis. Initial in vitro studies have suggested that camptothecin inhibits synoviocyte proliferation, matrix metalloproteinases expression in chrondrocytes and angiogenesis. This study is one of the first to test, in vivo, RA as a new indication for CPT.
To circumvent insolubility, instability and toxicity of CPT, we used biocompatible, biodegradable and targeted sterically stabilized micelles (SSM) as nanocarriers for CPT (CPT-SSM). We also surface-modified CPT-SSM with vasoactive intestinal peptide (VIP) for active targeting. We then determined whether this nanomedicine abrogated collagen-induced arthritis (CIA) in mice.
Based on our findings, this is the first study to report that CPT was found to be efficacious against CIA at concentrations significantly lower than usual anti-cancer dose. Furthermore, a single subcutaneous injection of CPT-SSM-VIP (0.1 mg/kg) administered to CIA mice mitigated joint inflammation for at least 32 days thereafter without systemic toxicity. CPT alone needed at least 10-fold higher dose to achieve the same effect, albeit with some vacuolization in liver histology.
We propose that CPT-SSM-VIP is a promising targeted nanomedicine and should be further developed as a safe, long-acting, disease-modifying pharmaceutical product for RA.