Valproic acid (VPA), an inhibitor of histone deacetylases, inhibits the growth of leukemia cells and induces their differentiation in vitro. In the present study, VPA in combination with two differentiating agents, 13-cis retinoic acid and 1,25-dihydroxyvitamin D3, was given to 19 previously untreated patients with MDS or CMML. Eight patients had to discontinue treatment before week 16 due to toxicity. According to international working group criteria, three patients (16%) responded to treatment. No correlation between VPA serum level, histone acetylation or clinical response was observed.
