Evaluation of the Synergistic Effect of the Combination of Doxorubicin and Vorinostat on Breast Tumor Cells Using the Loewe Model

Abstract

The combination of two or more medications is increasingly more common in the development of new treatment guidelines for common diseases. Thus, the use of combinations of histone deacetylase inhibitors with chemotherapeutic agents is a current trend in solid tumor treatment. The aim of this study was to investigate an effective vorinostat (SAHA) to doxorubicin (DOX) ratio for the treatment of different subtypes of breast cancer. The survival of HCC-1954, SKBR-3, MCF-7, MCF-7/ADR, MDA-MB-231 cell lines was assessed under incubation conditions with 64 variants of SAHA and DOX combinations using the MTT assay. This made it possible to determine the effect of interactions of SAHA/DOX combinations (antagonistic, additive, synergistic), as well as calculate the SAHA/DOX synergy index using the Loewe additivity model. The effect of SAHA/DOX ratios with the highest synergistic index for each tumor cell line was confirmed using the Chou-Talalay method. It was shown that the SAHA/DOX combination exhibited the greatest synergism in relation to HCC-1954, MCF-7/ADR and SKBR-3 cell lines belonging to the HER2-positive subtype. The average value of SAHA/DOX ratio with the highest synergy against breast cancer cells was 30:1 (SAHA to DOX, respectively). The ability of SAHA/DOX combination to effectively trigger apoptosis was confirmed in the most sensitive to SAHA/DOX therapy HCC-1954 cells. Thus, the Loewe model made it possible to identify the drug combination with the highest synergistic anticancer effect, which was confirmed using Chou-Talalay method. The data obtained demonstrates great potential of SAHA/DOX combination (30:1) for the treatment of HER2-positive breast cancer.