Youngbin Kim

Background/Objectives: Honokiol (HK), a bioactive phenolic compound, exhibits significant anti-cancer properties. This study aimed to investigate the anti-cancer effects of HK in colorectal cancer (CRC) cells by focusing on its direct interaction with heat shock protein 27 (Hsp27) as a molecular target, and to elucidate the underlying mechanisms involved. Methods: HK was isolated via silica/ODS chromatography. Anchorage-independent growth of CRC cells was quantified using a soft agar assay with increasing HK concentrations. Apoptosis and cell cycle were analyzed by flow cytometry, and cell viability by MTS assay. Hsp27 binding to HK was validated by pull-down assay with HK-conjugated Sepharose 4B beads. Hsp27 knockdown was performed using lentiviral shRNA in CRC cells. Molecular docking of HK-Hsp27 interaction employed Schrödinger Suite 2016. Protein expressions, including chaperone and apoptotic proteins, were evaluated by Western blotting. Results: HK dose-dependently suppressed anchorage-independent growth of CRC cells and induced G₀/G₁ arrest. It triggered apoptosis through cytochrome c release, PARP cleavage, and Bcl-2 downregulation. HK directly bound to the α-crystallin domain of Hsp27 at Asn102 and His103 residues, confirmed by computational molecular docking and site-directed mutagenesis. Hsp27 knockdown in CRC cells dramatically reduced anchorage-independent growth. HK markedly decreased Hsp27 protein levels while having less effect on other heat shock proteins in CRC cells. Conclusions: HK exerts anti-cancer effects in CRC cells, associated with Hsp27 inhibition, resulting in suppressed cell growth and increased apoptosis. This interaction between HK and Hsp27 may support a mechanistic foundation supporting the potential utility of HK as a natural therapeutic agent for CRC.