Eucalrobusone C suppresses cell proliferation and induces ROS-dependent mitochondrial apoptosis via the p38 MAPK pathway in hepatocellular carcinoma cells.

Background: Eucalyptus extracts have anti-cancer activity against various cancer cells. Formyl-phloroglucinol meroterpenoids (FPMs), which are typical secondary metabolites of the genera Eucalyptus, have many important pharmacological activities.

Purpose: Eucalrobusone C (EC), a new bioactive phytochemical, was first isolated from the leaves of Eucalyptus robusta in our laboratory. EC is a FPM, and our previous research revealed that EC showed strongest cytotoxicity in three cancer models than other compounds isolated from the leaves of E. robusta. This study investigated its anti-tumor effects on human hepatocellular carcinoma (HCC) and its underlying mechanisms.

Methods: Cell viability was measured by MTT assay. Cell cycle, apoptosis and mitochondrial transmembrane potential were determined by flow cytometry. Immunofluorescence was determined by a laser scanning confocal microscope. Protein levels were analyzed by Western blotting.

Results: Our results showed that EC exerted strong anti-proliferative activity against HCC cells in a concentration- and time-dependent manner. EC markedly induced apoptosis through the caspase-dependent mitochondrial pathway, and the cell cycle was arrested at S phase. SB203580, a p38 MAPK inhibitor, effectively decreased cell death caused by EC. Moreover, the ROS scavenger N-acetyl cysteine (NAC) significantly attenuated apoptosis induced by EC and reversed EC-induced p38 MAPK activation.

Conclusion: Our findings indicate that EC induces mitochondrial-dependent apoptosis in HCC cells through ROS generation and p38 MAPK activation, making EC a promising candidate for further development as an anticancer agent for HCC cells.