Type I isobolographic analysis of interactions (for non-parallel DRRCs) between CDDP and SAHA or VPA at the fixed-ratio combination of 1:1 in three cancer cell lines (MCF7, T47D and MDA-MB-231) 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 three cancer cell lines (MCF7, T47D and MDA-MB-231) measured in vitro by the MTT assay. nmix—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; nadd—total number of items calculated for the additive mixture of the drugs examined (nadd = n_CDDP + n_SAHA− 4) or (nadd = n_CDDP + n_VPA− 4);#–IC50 add value calculated from the equation for the lower line of additivity;&–IC50 add value calculated from the equation for the upper line of additivity.Statistical evaluation of data was performed with unpaired Student’s t-test according to Tallarida (2000). There was no statistical difference between the IC50 mix and IC50 add values with unpaired Student’s t-test and thus, the analyzed interactions were additive in two cancer cell lines (MCF7 and T47D) as measured by the MTT assay in vitro. Similarly, no significant difference was observed between the IC50 mix and IC50 add values for the combination of CDDP with SAHA in the MDA-MB-231 cell line. In contrast, the IC50 mix value for the combination of CDDP with VPA was significantly higher than its corresponding IC50 add values (P*P50 mix value.Type I isobolographic analysis of interactions (for non-parallel DRRCs) between CDDP and SAHA or VPA at the fixed-ratio combination of 1:1 in three cancer cell lines (MCF7, T47D and MDA-MB-231) measured in vitro by the MTT assay.