Doxorubicin (DOX) is a drug widely used in cancer chemotherapy. Although it has been proven that DOX kills tumor cells, the triggered modes of cell death are not fully understood. There is some evidence that, depending on the dose of DOX, the treated cells undergo senescence, mitotic catastrophe, apoptosis or necrosis. The aim of this study was to assess the type of CHO AA8 cell death induced with different DOX doses. In this context, we also assessed organization and distribution of F-actin, which integrity was suggested to be indispensable for apoptosis. Following treatment with 0.5 and 1 microM DOX, the giant multinucleated cells with extended network of fine microfilaments appeared. Notably, in the nuclei of the enlarged cells microscopy and cytometric analysis showed the presence of F-actin. DOX (2.5 microM) caused the appearance of the giant cells and with apoptotic features and signs of autophagy vacuolization. Flow cytometric studies indicated a dose-dependent increase in the number of TUNEL-positive cells and cells stained with both Annexin V and PI. Cell cycle analysis revealed the increase in the hyperploid DNA content. Our results suggest that treatment of CHO AA8 cells with different DOX doses caused mitotic catastrophe that was followed by apoptosis with signs of autophagy. The increase in F-actin content in the nuclei of the dying cells was evident. We hypothesize that in CHO AA8 cells F-actin may be involved in chromatin reorganization undergoing cell death.