Figure 3.

A-F. Isobolograms showing additive interactions between CDDP, SAHA and VPA with respect to their anti-proliferative effects on three cancer cell lines (A549, NCI-H1563 and NCI-H2170) measured in vitro by the MTT assay. The median inhibitory concentrations (IC50) for CDDP, SAHA and VPA are plotted graphically on the X- and Y-axes, respectively. The solid lines on the X and Y axes represent the S.E.M. for the IC₅₀ values for the studied drugs administered alone. The lower and upper isoboles of additivity represent the curves connecting the IC₅₀ values for CDDP and SAHA or VPA administered alone. The dotted line starting from the point (0, 0) corresponds to the fixed-ratio of 1:1 for the combination of CDDP with SAHA or VPA. The diagonal dashed line connects the IC₅₀ for CDDP and SAHA or VPA on the X- and Y-axes. The points A’ and A” (A, C, D, F) depict the theoretically calculated IC_{50 add} values for both, lower and upper isoboles of additivity. The point A (B, E) depicts the theoretically calculated IC_{50 add} value. The point M represents the experimentally-derived IC_{50 mix} value for total dose of the mixture expressed as proportions of CDDP and SAHA or VPA that produced a 50% anti-proliferative effect (50% isobole) in three cancer cell lines (A549, NCI-H1563 and NCI-H2170) measured in vitro by the MTT assay. On the graph, the S.E.M. values are presented as horizontal and vertical error bars for every IC₅₀ value. The experimentally-derived IC₅₀ mix value is placed close to the points: A” (A, D), A (B, E) and within the area bounded by two lines of additivity (C, F), indicating additive interaction between CDDP and SAHA or VPA in three cancer cell lines (A549, NCI-H1563 and NCI-H2170) measured in vitro by the MTT assay.