Abstract:
Multiple sclerosis (MS) is a multi-faceted disease, and is believed to be caused by an autoimmune response to myelin antigens in the central nervous system. Experimental autoimmune encephalomyelitis (EAE), an animal model for MS. manifests itself in various forms that parallel many aspects of MS, including the appearance of symptoms, initiation events, and pathophysiology. The hallmark of any immune response is the antigen-specific proliferation of immune cells, and during the initiation events of EAE, proliferating CD4+ T cells are the primary mediators of disease. This thesis explores if targeting these proliferating cells with the anti-mitotic compounds paclitaxel and peloruside A can delay or prevent the unset of EAE, thus providing a novel therapeutic avenue for MS research.
The anti-cancer compound, paclitaxel, is an anti-mitotic drug that prevents microtubule depolymerisation. Although paclitaxel has been used in the clinical setting to treat cancer for over a decade, it has been determined that paclitaxel stimulates murine toll-like receptor 4 (TLR4) complex, which is the major LPS receptor. A novel microtubule-stabilising compound, peloruside, is currently subject to intensive investigations due to its functional similarity to paclitaxel. The results from this project found that peloruside and paclitaxel inhibited the proliferation of mitogen-stimulated splenocytes with IC50 values of 83 nM and 30 nM, respectively, but did not affect the viability of non-proliferating cells In contrast to paclitaxel, peloruside did not cause the TLR4-mediated production of the inflammatory mediators. TNF-ε, IL-12, and nitric oxide, when cultured with IFN-ε stimulated murine macrophages. Interestingly, when LPS was included with either paclitaxel or peloruside A, both drugs decreased the production of TNF-e and nitric oxide from macrophages, suggesting that microtubule-stabilising compounds may have anti-inflammatory effects.
To identify any immunomodifying effects of paclitaxel in vivo, paclitaxel was administered to mice that were immunised with the myelin protein MOG in complete Freund's adjuvant (CFA) to induce EAE. When Taxol was administered to mice for 5 consecutive days immediately following CFA/MOG immunisation, the onset of EAE was delayed by approximately I week. Moreover, the administration of peloruside following the same treatment regime also resulted in a similar delay of disease onset. Taxol treatments, however, lead to significant mortality in immunised, but not unimmunised mice. Interestingly, although Taxol is an anti-mitotic drug, the proliferation of antigen-specific T cells was not inhibited in vivo by the Taxol treatment. The findings revealed in this thesis present an opportunity to pursue a new avenue of research for the therapeutic treatment of MS sufferers, and possibly other inflammatory autoimmune disorders.
