Nobiletin Induces Apoptosis and Potentiates the Effects of the Anticancer Drug 5-Fluorouracil in p53-Mutated SNU-16 Human Gastric Cancer Cells

Nobiletin is a typical polymethoxyl flavone from citrus fruits that has anticancer properties, but the molecular mechanism of its inhibitory effects on the growth of p53-mutated SNU-16 human gastric cancer cells has not been explored. In this study, nobiletin was found to be effective at inhibiting the proliferation of SNU-16 cells than other flavonoids. Nobiletin induced the death of SNU-16 cells through apoptosis, as evidenced by the increased cell population in the sub-G1 phase, the appearance of fragmented nuclei, an increase in the Bax/Bcl-2 ratio, the proteolytic activation of caspase-9, an increase in caspase-3 activity, and the degradation of poly(ADP-ribose) polymerase (PARP) protein. We found that the combination of nobiletin plus the anticancer drug 5-fluorouracil (5-FU) reduced the viability of SNU-16 cells in a concentration-dependent manner and exhibited a synergistic anticancer effect (combination index = 0.38) when 5-FU was used at relatively low concentrations. The expression of p53 protein increased after treatment with 5-FU, but not nobiletin, whereas the expression of p21 WAF1/CIP1 protein increased after treatment with nobiletin, but not 5-FU. The cellular responses to nobiletin and 5-FU occurred through different pathways. The results of this study suggest the potential application of nobiletin to the enhancement of 5-FU efficiency in p53 mutant tumors.