Novel ethanocycloheptono [3,4,5-kl]benzo[a]xanthene induces apoptosis in BEL-7402 cells.

A novel polycyclic bridged-ring xanthene 2 was synthesized by nucleophilic substitution followed by Michael addition reaction between parent dibenzoxanthene 1 and acetylacetone. The structure of compound 2 was also confirmed by single-crystal X-ray diffraction. We studied the binding activity of this compound with bovine serum albumin (BSA) by fluorescent and UV-visible spectra. The results showed that compound had strong binding ability with BSA. Cell viability in five tumor cell lines was studied by MTT assay. The cytotoxic effect of bridged-ring xanthene 2 against BEL-7402 cells was examined by morphological analyses and biochemical assays. Significant nuclear damages of BEL-7402 cells were observed after cells were treated with compound in a comet assay. The compound also caused DNA damage and S phase arrest in BEL-7402 cells. The efficient induction of apoptosis by the compound was confirmed by flow cytometry. Additionally, the characteristic nuclear and morphological changes during apoptotic cell death were investigated by fluorescent microscopy. The compound 2 enhanced the reactive oxygen species (ROS) and decreased the mitochondrial membrane potential. Western blot assay indicated that the compound can active caspase-3, caspase-7, down-regulate the level of Bcl-2, Bcl-x, and up-regulate the level of pro-apoptosis protein Bax. The compound 2 induces apoptosis of BEL-7402 cells through a ROS-mediated mitochondrial dysfunction pathway.