The ATP assay, but not the MTT assay, detects further cytotoxicity of the combination of anthracycline-based therapy with histone deacetylase inhibitor (valproic acid) in breast cancer cells

Abstract

Purpose: It has been investigated that whether or not the combination of valproic acid (a histone deacetylase inhibitor) with anthracycline-based chemotherapy (FEC: 5-fluorouracil+epirubicine+ cyclophosphamide) would change the cytotoxic effects of FEC in breast cancer cells.

Methods: The effect of valproic acid and its combination with FEC has been tested on MDA-MB-231 and MCF-7 human breast cancer cell lines. Anti-growth effects of treatments were determined by the MTT and ATP assays, while the detection of apoptosis was performed by the caspase-cleaved cytokeratin 18 assay.

Results: Valproic acid treatment had anti-growth effect on the cell lines used at clinically achievable dose (0.6 mM). According to the MTT assay, the combination of valproic acid with different doses (50-200% Test Drug Concentration) of FEC did not result in any significant change over FEC-only treatment in both cell lines. However, according to the ATP assay, there has been found that the combination of 100% Test Drug Concentration FEC with valproic acid yielded more efficacy compared to FEC-alone. FEC induced the apoptosis in MCF-7 cells but the addition of valproic acid to FEC did not enhance apoptosis.

Conclusion: According to the ATP assay, the use of valproic acid at the clinically achievable dose (0.6 mM) with different doses of FEC further increased the cytotoxic effect of FEC. However, this effect was not observed in the MTT assay. A caution should therefore be taken on the evaluation of the cytotoxic effect of valproic acid in cell lines.