A total of twenty benzo[b]cyclohept[e] [1,4]
oxazines and their S-analogs, and
2-aminotropone derivatives were investigated for their cytotoxicity against three human normal cells and four tumor cell lines. These compounds showed moderate
tumor-specific cytotoxicity. The cytotoxicity was enhanced by bromination at the
tropone ring and replacement by formylbenzene. The cytotoxicity of 2-(2-hydroxyanilino)
tropone was enhanced by introduction of
bromine or isopropyl group to the
tropone ring. The presence of a
hydroxyl group at ortho or para-position should be necessary for the appearance of cytotoxicity and
tumor-specificity. The highly active derivatives,
7-bromo-2-(4-hydroxyanilino)tropone [16] and
4-isopropyl-2-(2-hydroxyanilino)tropone [20], induced internucleosomal DNA fragmentation and
caspase-3, -8 and -9 activation in human promyelocytic
leukemia HL-60 cells, but only at concentrations twice or four times higher than CC(50) values. These compounds induced no discernible DNA fragmentation, and activated
caspases much more weakly in human
oral squamous cell carcinoma HSC-2 cells. Both [16] and [20] failed to induce the production of acidic organelles, a marker of autophagy, in contrast to the nutritional
starvation. These data demonstrated that 2-aminotropones showed relatively higher
tumor-specificity than benzo[b]cyclohept[e] [1,4]oxazine, and that 2-aminotropones induced little or no apoptotic cell death in
oral squamous cell carcinoma, in contrast to HL-60 cells.