Multiple sclerosis: Mitoxantrone promotes differential effects on immunocompetent cells in vitro

Mitoxantrone is an anti-neoplastic anthracenedione derivative that, based on its immunosuppressive properties, is approved for the treatment of severe forms of relapsing-remitting or secondary progressive multiple sclerosis (MS). Whether the beneficial clinical effects of mitoxantrone in MS are due to a broad immunosuppression, or whether there is a specific mechanism of action remains unknown. Peripheral blood mononuclear cells (PBMCs) from untreated or interferon-beta-treated patients with MS or from healthy donors were stimulated in the presence or absence of mitoxantrone. Irrespective of the source of the cells and the cellular phenotype, mitoxantrone inhibited proliferation of activated PBMCs, B lymphocytes, or antigen-specific T-cell lines (TCLs) stimulated on antigen-presenting cells (APCs) in a dose-dependent manner. For functional analysis, TCLs or APCs were incubated separately with mitoxantrone. Pre-incubation of APC more effectively impaired TCL proliferation than pre-incubation of TCLs. Production of cytokines, expression of activation markers, matrix metalloproteinases, and chemokine receptors were not influenced substantially by mitoxantrone. In contrast, in dendritic cells (DCs), mitoxantrone interfered with the antigen-presenting capabilities. For evaluation of apoptotic cell death of target cells, annexin-V-conjugates and a DNA fragmentation assay were applied. Mitoxantrone induced apoptosis of PBMCs, monocytes and DCs at low concentrations, whereas higher doses caused cell lysis. Our observations suggest that the beneficial effects of mitoxantrone in MS result (i) from its immunosuppressive action based on nonspecific cytotoxic effects on lymphocytes, (ii) by inducing programmed cell death of professional APCs, such as DCs.