Delphinidin, an anthocyanidin in pigmented fruits and vegetables, induces apoptosis and cell cycle arrest via suppression of NF-\#312;B pathway in human colon cancer HCT116 cells

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Colon cancer is the third most common cancer in men and women and accounts for 10% of all cancers related deaths in the United States. Because of unsatisfactory treatment options for colon cancer, there is a need to develop novel treatment approaches for this malignancy. One such strategy is through chemoprevention by the use of non-toxic dietary substances and botanical products. Delphinidin is the most abundant and major anthocyanidin present in pigmented fruits (pomegranate, berries and dark grapes) and vegetables (egg plant, tomato, carrot, purple sweet potatoes, red cabbage and red onion) and possesses strong anti-oxidant and anti-inflammatory properties. In the present study, we investigated the effect of delphinidin on the growth and proliferation of human colon cancer HCT116 cells. As assessed by MTT assay, treatment of cells with delphinidin (30-240 µM; 48 hrs) caused dose-dependent growth inhibitory effects. TUNEL (terminal deoxynucleotide transferase dUTP nick-end labeling) assay indicated that delphinidin treatment (120, 180 and 240 μM; 48 hrs) dose-dependently induced apoptosis by 18%, 35% and 38% respectively. In dephinidin treated cells suppression in the protein expression of poly (ADP-ribose) polymerase (116 kDa) and procaspase-3 was observed. Furthermore, cell cycle analysis using flow cytometry showed that delphinidin treatment (120, 180 and 240μM; 48 hrs) resulted in a G2/M arrest by 34% 39% and 30% respectively. NF-κB provides a mechanistic link between inflammation and cancer, and is a major factor controlling the ability of both pre-neoplastic and malignant cells to resist apoptosis-based tumor surveillance mechanisms. We therefore, explored NF-κB signaling pathway. The immunoblot analysis demonstrated that the treatment of HCT116 cells with delphinidin resulted in the inhibition of (i) IKKα, (ii) NF-κB/p65 and (iii) degradation and phosphorylation of IκBα. Immunoblot analysis also indicated that delphinidin treatment of cells resulted in inhibition of translocation of NF-κB/p65. These data were further confirmed by performing electrophoretic mobility shift assay and enzyme-linked immunosorbent assay. We found that treatment of cells with delphinidin inhibited NF-κB DNA-binding activity. Our results suggest that delphinidin treatment of HCT116 cells suppresses NF-κB pathway, resulting in G2/M phase arrest and apoptosis. We suggest that delphinidin could be a potent inhibitor of NF-κB signaling in human HCT116 cells and suggests its potential use as a cancer therapeutic agent against colon cancer.