Table 2.

Type I isobolographic analysis of interactions (for non-parallel log-probit dose–response relationship curves (DRRCs) between CDDP and SAHA or VPA at the fixed-ratio combination of 1:1 in MDA-MB-231 with increased (Notch1^highMDA-MB-231) or decreased (Notch1^lowMDA-MB-231) activity of Notch1 measured in vitro by the MTT assay. Results are presented as median inhibitory concentrations (IC₅₀ values in μg/mL ± S.E.M.) for two-drug mixtures, determined either experimentally (IC₅₀ mix) or theoretically calculated (IC₅₀ add) from the equations of additivity (Tallarida 2006, 2007), blocking proliferation in 50% of tested cells in cancer cell lines (MDA-MB-231 with increased or decreased activity of Notch1) measured in vitro by the MTT assay. n mix—total number of items used at those concentrations whose expected anti-proliferative effects ranged between 16% and 84% (i.e., 4 and 6 probits) for the experimental mixture; n add—total number of items calculated for the additive mixture of the drugs examined; L IC₅₀ add value calculated from the equation for the lower line of additivity; U IC₅₀ add value calculated from the equation for the upper line of additivity. Statistical evaluation of data was performed with an unpaired Student’s t-test.

Cell Line	Notch1 Activity	Combination	IC50 mix (μg/mL)	nmix	L IC50 add (μg/mL)	nadd	U IC50 Add (μg/mL)	nadd
Notch1highMDA-MB-231	Increased	CDDP+SAHA	0.382 ± 0.137	24	0.392 ± 0.253	50	0.902 ± 0.244	50
Notch1highMDA-MB-231	Increased	CDDP+VPA	286.9 ± 193.2	30	303.5 ± 255.7	56	336.0 ± 272.0	56
Notch1lowMDA-MB-231	Decreased	CDDP+SAHA	0.903 ± 0.407	30	0.391 ± 0.279	50	0.629 ± 0.310	50
Notch1lowMDA-MB-231	Decreased	CDDP+VPA	381.5 ± 192.9	30	289.7 ± 214.5	56	392.8 ± 246.0	56