Cytotoxic effect of neocarzinostatin on human lymphoid cells

Effect of a protein antitumor antibiotic, neocarzinostatin (NCS) was examined on Epstein-Barr virus (EBV)-carrying human lymphoid cell lines and normal human lymphocytes. A marked cytotoxic effect of NCS on umbilical cord lymphocytes freshly transformed by EBV was observed, whereas the cells before transformation were affected only very little by NCS. Majority of long-term cultured cell lines were affected only slightly, while shorter-term cultured lines were more susceptible to the effect of NCS. An uptake of FITC-labeled NCS into cells was examined by fluorescence microscopy. The incorporation by the freshly transformed cells was higher than that by the longer-term cultured cell lines. Normal lymphyocytes or heat-killed cells, however, incorporated FITC-NCS very little. On the basis of the known mode of action of NCS on DNA and the present observation, the cytotoxicity of NCS appeared to be exerted within the cells.