Mitoxantrone diacetate is a potent topoisomerase II inhibitor. Mitoxantrone diacetate also inhibits protein kinase C ( PKC ) activity with an IC 50 of 8.5 μM. Mitoxantrone diacetate induces apoptosis of B-CLL (B-chronic lymphocytic leukaemia) cells. Mitoxantrone diacetate shows antitumor activity. Mitoxantrone diacetate also has anti- orthopoxvirus activity with EC 50 s of 0.25 μM and and 0.8 μM for cowpox and monkeypox, respectively.