Antitumor Effects of 8-Deoxylactucin in RB355 Human Retinoblastoma Cells Are Mediated via Apoptosis Induction, Reactive Oxygen Species Production, and Cell Cycle Arrest.

BACKGROUND Retinoblastoma is a rare malignancy arising from the immature cells of the retina, generally in children up to the age of 3 years. Here, we assessed the anticancer effects of a natural sesquiterpene lactone - 8-deoxylactucin - on the growth of the retinoblastoma RB355 and normal RPE cells. MATERIAL AND METHODS Cell viability was assessed by 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and apoptosis was assessed by DAPI staining and annexin V/propidium iodide (PI) assay. Reactive oxygen species (ROS) levels were determined by fluorescence microscopy. Flow cytometry was used to determine the cell cycle distribution. Protein expression was determined by Western blot analysis. RESULTS The results showed that 8-deoxylactucin exerted selective and potent anticancer effects on the RB355 cells and exhibited an IC50 of 25 µM. Nonetheless, the cytotoxic effects of 8-deoxylactucin on the normal RPF cells were comparatively lower, as evident from the IC₅₀ of 65 µM. 8-Deoxylactucin increased the production of ROS and triggering apoptosis of RB355 cells. The induction of 8-deoxylactucin-induced apoptosis was also accompanied with increased cleavage of caspase 3, upregulation of Bax, and downregulation of Bcl-2. The 8-deoxylactucin-induced cell cycle arrest of RB355 cells was also associated with inhibition of cyclin A and B1 expression, as well as the inhibition of Cdc2 phosphorylation. CONCLUSIONS 8-Deoxylactucin inhibits the growth of RB355 cells by apoptosis, cell cycle arrest, and increased production of ROS.