Synergistic Inhibition of Colon Cancer Cell Proliferation via p53, Bax, and Bcl-2 Modulation by Curcumin and Plumbagin Combination

Cancer is a major contributor to global morbidity and mortality. Among the different forms of cancer, colorectal cancer (CRC) is the third most frequently diagnosed cancer in men and the second most common cancer type in women globally. We aimed to explore the possible synergistic anticancer potential of curcumin (Cur) and plumbagin (PL) in the human colon cancer cell line (HCT-116). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)/cytotoxicity assay revealed IC₅₀ values of 7.7 and 7.5 μM for Cur and PL, respectively, as a separate entity. However, the combined treatment of Cur + PL significantly enhanced the cancer cell growth inhibitory potential compared with solitary treatments with an IC₅₀ value of 6.8 μM. The combined treatment also led to the induction of apoptosis by 41%, cell cycle arrest at the G2/M phase, while Bax and p53 genes were found to be upregulated and the Bcl-2 gene was downregulated compared to the untreated/solvent control. Furthermore, combined treatment elevated reactive oxygen species (ROS) production by 59% and resulted a decline in the mitochondrial membrane potential (MMP) compared to the control. Catalase and superoxide dismutase (SOD) activities were significantly reduced, leading to enhanced lipid peroxidation (LPO) and compromised membrane integrity, which were also confirmed by 4′,6-diamidino-2-phenylindole (DAPI) + propoidium iodide (PI) staining were also noted. Our in vitro data were further supported by molecular docking, which showed a higher binding energy of the proteins (Bax, Bcl-2, and p53) with Cur + PL. Overall, our findings highlight the potent synergistic effects of the Cur and PL combination, which can be exploited as a combination therapy for CRC.