[Study of cell death in squamous cell carcinoma cell line KM-1 treated by cisplatin]

The mode of cell death (apoptosis or necrosis) in oral squamous cell carcinoma cell line (KM-1) exposed to Cisplatin was studied by various techniques including flow cytometry. All of the cells were killed by 48 hours' treatment with 100 microM CDDP. The proportion of the apoptotic cells was, approximately, only 95%, while the rest was necrosis. These results were demonstrated by observation of cellular morphology, agarose gel electrophoresis of DNA, flow cytometric analysis of propidium iodide (cell membrane integrity)/rhodamine 123 (mitochondrial activity), and flow cytometric measurement of sub-G1 peak population in DNA histogram. Although all the necrotic cells (91%) lost cell membrane integrity without DNA fragmentation, 46.9% cells revealed positive staining by TdT assay which identifies 3'-OH ends of DNA strands. These data suggest the possibility that the cytocidal mechanism of CDDP might involve single-strand breakage of DNA, but not double-strand breakage as occurred in apoptosis.