Mammea siamensis Flower Extract-Induced Cell Death Apoptosis in HCT116 Colon Cancer Cells via Vacuolar-Type H⁺-ATPase Inhibition Associated with GSK-3β/β-Catenin, PI3K/Akt/NF-κB, and MAPK Signaling Pathway

Abstract

Background and Objective: Mammea siamensis (MS) is a Thai herb used in traditional medicine. Previous studies have reported the antiproliferative effects of its constituents in various cancer cell lines. However, the effects of MS extract on cytotoxicity and molecular mechanisms of apoptosis induction in HCT116 colon cancer cells have not been fully explored. Methods and Results: The cytotoxic effect of MS extract on HCT116 cells was assessed using the MTT assay. MS extract increased cytotoxicity in a concentration-dependent manner. It also induced nuclear morphological changes and disrupted the mitochondrial membrane potential (ΔΨm), as assessed by Hoechst 33342 and JC-1 staining, respectively. These findings indicated that MS extract induced apoptosis, which was further confirmed by flow cytometry showing an increase in the sub-G1 phase. To investigate the expression of signaling proteins, Western blot analysis was conducted. The results showed that MS extract activated caspase activity (caspase-8, -9, and -7) and inhibited PARP activity. Additionally, MS extract upregulated pro-apoptotic proteins (tBid, Bak, and cytochrome c) while downregulating anti-apoptotic proteins (Bcl-2 and Bcl-xL). Mechanistic studies revealed that MS extract activated MAPK pathways while inactivating the PI3K/Akt/NF-κB and GSK-3β/β-catenin pathways. Notably, MS extract also inhibited V-ATPases, as evaluated by acridine orange staining and Western blot analysis. Conclusions: Our findings suggest that MS extract induces apoptosis via the activation of both intrinsic and extrinsic pathways associated with the key signaling pathways. Therefore, MS extract shows potential as a therapeutic agent for colon cancer.