Innate or acquired drug resistance and consequent tumor relapse in lung cancer patients have been linked to activities of cancer stem cells (CSCs). Therefore, targeting CSCs is suggested as an effective approach for non-small cell lung cancer (NSCLC) therapy. In this study, we demonstrated that garcinol, a polyisoprenylated benzophenone isolated from fruiting bodies of Garcinia indica, and possessing anti-inflammatory, antioxidant, acetyltransferase inhibitory, and anticancer activities, modulates activities of lung CSCs (LCSCs) and their associated aggressiveness. Herein, we demonstrated the inhibitory effect of garcinol on the LCSC phenotype of human NSCLC cells using analytical drug cytotoxicity or cell viability, flow cytometric, and functional assay approaches. Garcinol significantly diminished the ability of the H441 and A549 NSCLC cell lines to form spheres. In parallel assays, garcinol inhibited differentiated lung cancer cell and LCSC viability in dose-dependent manners. Consistent with these observations, flow cytometric data showed that garcinol reduced the putative LCSC pool, evidenced by the dose-dependent decreasing proportion of side-population (SP) cells and associated ALDH activity in garcinol-treated H441 cells, compared to the control group. Additionally, functional assays showed that garcinol markedly diminished the ability of H441 and A549 cells to form colonies. Mechanistically, garcinol impaired phosphorylation of LRP6, a co-receptor of Wnt and STAT3. In the same assay, garcinol down-regulated β-catenin, Dvl2, Axin2, and cyclin D1 expressions in NSCLC-generated spheres, suggesting its ability to regulate the Wnt/β-catenin signaling pathway. The results were further verified in vivo using H441 LCSC mouse xenograft model where administration of garcinol significantly inhibited tumor growth. Taken together, we demonstrated herein that garcinol modulates the LCSC phenotype via regulation of Wnt/β-catenin signaling and inactivation of STAT3, thus showing that garcinol may be a putative novel anti-LCSC therapeutic agent.
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