GRN A synergized with cisplatin to inhibit cancer cell proliferation. Cytotoxicity of GRN A, cisplatin, and the combination of the two drugs. HepG2 (a) and BEL7402 (b) cancer cells were plated on 96 plates. After an incubation for 48 h, cells were treated with certain concentrations of GRN A, cisplatin, and the combination of the two drugs. The inhibitory rate of the cell growth was analyzed by an MTS assay, as described in the materials and methods section. (c, d) Combination index (CI) Plot. A CI of GRN A and cisplatin was analyzed using the Chou-Talalay approach. CI values were plotted as a function of the fractional affection (Fa) from 0.39 to 0.85 in HepG2 and BEL7402 cells. CI > 1.3, antagonism; CI 1.1–1.3, moderate antagonism; CI 0.9–1.1, additive effect; CI 0.8–0.9, slight synergism; CI 0.6–0.8, moderate synergism; CI 0.4–0.6, synergism; CI < 0.4, strong synergism. (t-test, n ≥ 3 *** p < 0.001)