Autophagy Inhibition Promotes Gambogic Acid-induced Suppression of Growth and Apoptosis in Glioblastoma Cells

Objective: To investigate the effects of gambogic acid (GA) on the growth of human malignant glioma cells.
Methods: U251MG and U87MG human glioma cell lines were treated with GA and growth and proliferationwere investigated by MTT and colony formation assays. Cell apoptosis was analyzed by annexin V FITC/PI flowcytometry, mitochondrial membrane potential assays and DAPI nuclear staining. Monodansylcadaverine (MDC)staining and GFP-LC3 localisation were used to detect autophagy. Western blotting was used to investigate themolecular changes that occurred in the course of GA treatment.
Results: GA treatment significantly suppressedcell proliferation and colony formation, induced apoptosis in U251 and U87MG glioblastoma cells in a timeanddose-dependent manner. GA treatment also lead to the accumulation of monodansylcadaverine (MDC)in autophagic vacuoles, upregulated expressions of Atg5, Beclin 1 and LC3-II, and the increase of punctatefluorescent signals in glioblastoma cells pre-transfected with GFP-tagged LC3 plasmid. After the combinationtreatment of autophagy inhitors and GA, GA mediated growth inhibition and apoptotic cell death was furtherpotentiated.
Conclusion: Our results suggested that autophagic responses play roles as a self-protective mechanismin GA-treated glioblastoma cells, and autophagy inhibition could be a novel adjunctive strategy for enhancingchemotherapeutic effect of GA as an anti-malignant glioma agent.