β-Sitosterol Enhances the Anticancer Efficacy of Oxaliplatin in COLO-205 Cells via Apoptosis and Suppression of VEGF-A, NF-κB-p65, and β-Catenin

Colon cancer (CC) is a common malignancy characterized by poor prognostic outcomes and considerable mortality. Oxaliplatin (OXP) is commonly used in the treatment of CC; however, its efficacy may be limited by side effects and the development of resistance. β-sitosterol (β-Sit), a phytosterol derived from plants, has been documented to be effective in the treatment of tumors. This study aimed to investigate the potential of β-Sit to enhance the antitumor efficacy of OXP in COLO-205 cells, focusing on apoptosis induction and suppression of the vascular endothelial growth factor A (VEGF-A)/survival pathway. Molecular docking studies were performed to assess the binding affinity of β-Sit with the target proteins B-cell lymphoma 2 (Bcl-2), phosphoinositide 3-kinase (PI3K), and VEGF receptor-2 (VEGFR-2). COLO-205 cells were treated with OXP, β-Sit, or a combination of OXP + β-Sit for 48 h. The combination treatment substantially lowered the IC₅₀ achieved with 3.24 µM of OXP and 36.01 µM of β-Sit, compared to 25.64 µM for OXP alone and 275.9 µM for β-Sit alone, demonstrating a pronounced synergistic impact. The combined therapy altered the cell cycle distribution by decreasing the number of cells in the G0/G, S, and G2/M phases, coupled with an increase in the Sub-G1 population. Furthermore, apoptosis was augmented by a shift in cell death from necrosis to late apoptosis, as indicated by an increased <i>BAX/BCL2</i> ratio relative to each treatment alone. Moreover, the inhibitory effect on angiogenesis was enhanced via the reduction of VEGF-A, and β-catenin and nuclear factor κB (NF-κB-p65) were suppressed, thereby preventing the growth and survival of resistant cancer cells. Additionally, molecular docking supported high binding affinities of β-Sit to Bcl-2, PI3K, and VEGFR-2. This study highlights the potential of β-Sit to enhance the anti-cancer efficacy of OXP in CC.