Sclareol Inhibits Hypoxia-Inducible Factor-1α Accumulation and Induces Apoptosis in Hypoxic Cancer Cells

Purpose: The hypoxia in solid tumors is associated with the resistance to chemo/radiotherapy.Hypoxia-inducible factor-1 (HIF-1) plays a key role in cell remodeling to hypoxia. Therefore, theinhibition of HIF-1 accumulation is considered a hopeful strategy for the treatment of cancer.Here, we aimed to evaluate the geno- and cytotoxicity properties of sclareol, a natural bicyclicditerpene alcohol, on A549 cells in CoCl2-induced hypoxia.Methods: The cytotoxicity and apoptosis-inducing properties of sclareol on the A549 cell wereevaluated using MTT assay and Annexin V/PI staining, respectively in hypoxia. DAPI staining,DNA ladder, and comet assay were used to evaluate the genotoxicity. Further, the qPCRtechnique was employed to assess the expression of HIF-1α, HIF-1β, and downstream targetgenes (GluT1, and Eno1). Finally, the level of HIF-1α protein was evaluated through Westernblotting in sclareol-treated cells in hypoxia.Results: The inhibitory concentration (IC50) of sclareol against A549 cells was 8 μg/mL at 48hours in hypoxia. The genotoxicity of sclareol was confirmed in the cells treated with sclareolin hypoxia. Sclareol induced ~46% apoptosis and also necrosis in the hypoxic condition. TheqPCR analyses showed an enhanced suppression of HIF-1α, HIF-1β, GluT1, and Eno1 due tothe sclareol treatment in the hypoxia. Moreover, protein quantification analysis showed dosedependentlydegradation of HIF-1α in hypoxia upon treatment with sclareol.Conclusion: The results obtained here indicate that sclareol possesses dose-dependentcytotoxicity effects against A549 cells in hypoxia through inhibition of HIF-1α proteinaccumulation, increasing cell sensitivity to intracellular oxygen levels, and disruption of celladaptation to hypoxia.