Fused oxazepine-naphthoquinones as novel cytotoxic agents with diverse modes of action in yeast

The naphthoquinone moiety is commonly found in numerous natural cytotoxic compounds with diverse and pleiotropic modes of action (MOAs). The moiety can exist as a standalone pharmacophore or combined with other pharmacophores to enrich their MOAs. Here, we report that the synthetic fusion of naphthoquinones and oxazepines provides potent cytotoxic compounds with diverse MOAs. Fused oxazepine-naphthoquinones were identified through a cytotoxic screen in <i>Saccharomyces cerevisiae</i>. The two most active compounds, CM-568 and CM-728, contained the same 3-pyridyl appendage in the oxazepine ring and were further evaluated along with close chemical derivatives. Both were highly cytotoxic, killing yeast cells in the low micromolar range; however, the role of reactive oxygen species in their MOA was significantly different. Investigations with yeast strains specifically designed to assess cell cycle, chromatin compaction, and nucleolar activity suggest that at lethal concentrations, cells die shortly after drug exposure through programmed death. Conversely, at sublethal concentrations, cell cycle progression is severely impaired. Interestingly, CM-568 labels cells with highly refractive non-fluorescent parallel rods. We conclude that the oxazepine moiety confers novel cytotoxic MOAs to naphthoquinones, which may be potentially useful in pharmacology.