The present study investigated the mechanism underlying the antitumor activity of the histone deacetylases inhibitor valproic acid (VPA), alone and in combination with doxorubicin, a synthetic chenodeoxycholic acid derivative (HS-1200), or the proteasome inhibitor lactacystin on cultured anaplastic thyroid carcinoma KAT-18 cells. Cell viability was evaluated by trypan-blue exclusion. Western blotting determined caspase and histone deacetylase activities and expression of poly(ADP)-ribose polymerase. Induction of apoptosis was identified by Hoechst staining, DNA electrophoresis, DNA hypoploidy and cell cycle phase analysis, and measurement of mitochondrial membrane potential. Subcellular translocation of apoptosis inducing factor and caspase-activated DNase after treatment was determined by confocal microscopy following immunofluorescent staining. VPA treatment increased apoptotic death of KAT-18 cells. VPA treatment was also associated with degradation of procaspase-3, procaspase-7, and poly(ADP)-ribose polymerase; induction of histone hyperacetylation; condensation of peripheral chromatin; decreased mitochondrial membrane potential and DNA content; and decreased translocation of apoptosis inducing factor and caspase-activated DNase. VPA in combination with doxorubicin, HS-1200, or lactacystin, applied at the highest concentrations that did not induce KAT-18 cell death, efficiently induced apoptosis in KAT-18 cells. The results suggest VPA combination therapy may represent an alternative therapeutic strategy for anaplastic thyroid carcinoma.

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