benzophenones, xanthones, anthraquinones, phenylbutanone glucoside, stilbene glucoside, isoflavones, isoflavanones and stilbenes (TS=0.3-31.7), coumarin derivatives (TS=1.0- >11.0), procyanidines and flavonoids (TS=1.0->7.4), hydrolysable tannins (TS=1.0-8.2), triterpene aglycones and glycosides (TS=0.65->2.8), cycloartane glycosides and chromones

Three antitumor antibiotics, mitomycin C, bleomycin sulfate and peplomycin sulfate, were compared for their tumor-specific cytotoxicity, using human oral squamous cell lines (HSC-2, HSC-3, HSC-4, Ca9-22 and NA), human promyelocytic leukemic cell line HL-60 and human normal oral cell types (gingival fibroblast HGF, pulp cell HPC and periodontal ligament fibroblast HPLF). Among these three compounds, mitomycin C showed the highest tumor-specificity, due to its higher cytotoxic activity against human oral tumor cell lines than bleomycin and peplomycin. However, there was considerable variation of drug sensitivity among the six tumor cell lines. Mitomycin C induced internucleosomal DNA fragmentation and caspase-3, -8 and -9 activation in HL-60 cells only after 24 h. On the other hand, mitomycin C induced no clear-cut DNA fragmentation in HCS-2 cells, although it activated caspase-3, -8 and -9 to a slightly higher extent. Western blot analysis demonstrated that mitomycin C did not induce any apparent change in the intracellular concentration of anti-apoptotic protein (Bcl-2) and pro-apoptotic proteins (Bax, Bad). Electron microscopy of mitomycin C-treated HL60 cells showed intact mitochondria (as regards to integrity and size) and cell surface microvilli, without production of an apoptotic body or autophagosome, at an early stage after treatment. The present study suggests the incomplete induction of apoptosis or the induction of another type of cell death by mitomycin C treatment. The ideal anticancer agents are those having higher cytotoxicity against tumor cell lines than against normal cells, regardless of the types of cell death. There has been no systematic study of the screening of a variety of natural and synthetic compounds for their tumor-specific cytotoxicity. A total of 500 compounds have been randomly screened for their tumor-specific cytotoxic activity, using several human normal and tumor cell lines as targets (1). Among them, doxorubicin, an anthracylin antibiotic, displayed the highest level of tumor specific cytotoxicity (evaluated by the tumorspecificity index (TS)=255) (2), followed by cyclic ·,‚unsaturated ketones (TS>229) (3) and nocobactines (TS=44-80) (4). On the other hand, flavones, flavonols (3hydroxyflavones) and isoprenoid-substituted flavonoids, benzophenones, xanthones, anthraquinones, phenylbutanone glucoside, stilbene glucoside, isoflavones, isoflavanones and stilbenes (TS=0.3-31.7), coumarin derivatives (TS=1.0>11.0), procyanidines and flavonoids (TS=1.0->7.4), hydrolysable tannins (TS=1.0-8.2), triterpene aglycones and glycosides (TS=0.65->2.8), cycloartane glycosides and chromones (TS=0.7-1.4), furostaol glycosides (TS=0.4>17.0), ·,‚-unsaturated ketones (TS=0.6-1.9), hydroxyketones (TS=1.0->17.6), ‚-diketones (TS=0.3-6.3), styrylchromones (TS=1.4-27.3), dihydroisoxazole and isoxazole derivatives (TS=0.9-1.6) showed much lower tumor-specificity (1). These findings urged us to investigate other classes of antitumor antibiotics for their antitumor potency against oral carcinoma. Mitomycin C, bleomycin and peplomycin (Figure 1) are three frequently used antitumor antibiotics for the treatment of breast, lung, stomach, intestinal, testicular, cholioepithelial, seminal and oral carcinoma (5-7). In this study, the tumor-specific cytotoxic activity of these three compounds was compared, using three human normal oral cell types (gingival fibrobast HGF, pulp cell HPC and periodontal ligament fibroblast HPLF), human oral 3373 Correspondence to: Hiroshi Sakagami, Division of Pharmacology, Department of Diagnostic and Therapeutic Sciences, Meikai University School of Dentistry, Sakado, Saitama 350-0283, Japan. Tel: (+81) 49-279-2758, 2759, Fax: (+81) 49-285-5171, e-mail: [email protected]