In vitro activity: Mitoxantrone induces DNA fragmentation and the proteolytic cleavage of poly(ADP-ribose) polymerase (PARP), a marker of the activation of caspases, in all the patients studied, demonstrating that the cytotoxic effect of mitoxantrone is due to induction of apoptosis. Mitoxantrone activates NFkappaB and stimulates IkappaBalpha degradation in the promyelocytic leukemia cell line HL60 but not in the variant cells, HL60/MX2 cells, which lack the beta isoform of topoisomerase II and express a truncated alpha isoform that results in an altered subcellular distribution. Mitoxantrone inhibits proliferation of activated PBMCs, B lymphocytes, or antigen-specific T-cell lines (TCLs) stimulated on antigen-presenting cells (APCs) in a dose-dependent manner. Mitoxantrone induces apoptosis of PBMCs, monocytes and DCs at low concentrations, whereas higher doses causes cell lysis.

Kinase Assay: Mitoxantrone inhibits PKC in a competitive manner with respect to histone H1, and its Ki value is 6.3 μM and in a non-competitive manner with respect to phosphatidylserine and ATP. Treatment of B-CLL cells for 48 h with mitoxantrone (0.5 μg/mL) induces a decrease in cell viability. Mitoxantrone induces DNA fragmentation and the proteolytic cleavage of poly(ADP-ribose) polymerase (PARP), demonstrating that the cytotoxic effect of mitoxantrone is due to induction of apoptosis. Mitoxantrone shows cytotoxicity to human breast carcinoma cell lines MDA-MB-231 and MCF-7 with IC50 values of 18 and 196 nM, respectively.

Cell Assay: The human breast carcinoma cell lines MDA-MB-231 and MCF-7 are seeded in standard 96-well plates. One day after seeding, the culture medium is changed and replaced by medium containing different concentration of Mitoxantrone (10-5 to 5 μM) with or without DHA (30 μM) during 7 days. Viability of cells are measured as a whole by the tetrazolium salt assay.