Effect of pongol methyl ether on cancer stem cell phenotypes in human non-small cell lung cancer cells

Abstract

Cancer stem cells (CSCs) are an important therapeutic target. The therapeutic agents targeting CSCs should lead to improved clinical outcomes. This study demonstrated the CSC suppressing activity of pongol methyl ether (PME), a pure compound from Millettia erythrocalyx Gagnep. CSC-suppressing effects were evaluated by colony formation assay, anchorage independent growth assay, spheroid formation assay and detection of CSC markers. The related CSC cell signals were evaluated by Western blot, immunofluorescence and molecular docking analysis. Proteins affected by PME treatment were subjected to bioinformatic analysis. Protein–protein interaction (PPI) networks were constructed by the Search Tool for Interactions of Chemicals (STITCH). The Kyoto Encyclopedia of Genes and Genomes (KEGG) mapper were used to confirm the underlying pathways. The non-toxic concentrations of PME (5–25 µM) significantly suppressed the ability of lung cancer cells to form colonies, grow in an anchorage-independent manner and generate tumor spheroids. PME at 25 µM significantly decreased the CSC markers (CD133 and ALDH1A1) and pluripotent transcription factors (Oct4 and Nanog). Akt, the key upstream signal of CSC control, was significantly decreased by the PME treatment. The molecular docking indicated that PME was bound to Akt-1 with a binding affinity of -9.2 kcal/mol greater than the Akt-1 inhibitor (reference compound; CQW). The STITCH network identified a total of 15 proteins interacted in PPI networks, and Akt-1 was identified as a central protein. The KEGG mapper indicated that the selected CSC markers were mostly involved in the ‘signalling pathways regulating pluripotency of stem cells’ pathway map and Akt, Oct4 and Nanog were the regulatory proteins in the dominant pathway. In addition, PME (10–25 µM) can suppress spheroid formation and reduce CSC-specific marker expression in patient-derived primary lung cancer cells. This study revealed a novel pharmacological effect and the underlying physiological mechanism of PME that can attenuate CSC phenotypes in human lung cancer cells and may be developed for lung cancer therapy.