ABSTRACT
Cell death of human breast cancer cell line MCF-7/pDsRed2-Mito, caused by independent- or multi-administration of three anticancer drugs, cyclophosphamide [CPA], doxorubicin [DXR], and 5-fluorouracil [5-FU], was studied using fluorescence and electron microscopy. In our previous study using cell viability assays, microscopic inspection of heterochromatin condensation, a DNA fragmentation assay, and flow cytometric analyses, the death of MCF-7 cells was classified into two groups. The cell death induced by CPA or 5-FU was classified as apoptotic, while the cell death induced by DXR treatment or a mixture of all three anticancer drugs was classified as non-apoptotic. Here, we examined the morphology of the whole cell and its organelles, including the mitochondria, using electron microscopy. Mitochondria are of particular interest because they are the key organelle for the molecular apoptotic-death cascade. To monitor mitochondrial morphology, we used our previously constructed MCF-7/pDsRed2-Mito line, generated by introducing the pDsRed2-Mito vector into MCF-7 cells. The mitochondria in these cells emit red fluorescence. We found that the administration of DXR alone or of all three anticancer drugs together resulted in the clumping of the red-fluorescent materials on both sides of the round dying cells, interrupted by the nucleus. Detailed electron microscopic observation revealed that the novel morphology of the dying MCF-7 cells might be owing, not to destruction of the mitochondrial membrane, but to the tight structure of the nuclear membrane. Other anticancer drugs showed different, characteristic features in electron microscopic images, which suggested that death induced by anti-cancer drugs in the human breast cancer cell line, MCF-7, may result from any of a number of diverse processes.