The anti-epileptic drug valproic acid (VPA) acts as an inhibitor of histone deacetylases. In combination with retinoic acid (RA), VPA triggers myeloid differentiation of primary acute myeloid leukemia (AML) blasts in vitro. In vivo, VPA posses an antineoplastic activity as indicated by pre-clinical studies in murine models of leukemia, renal and lung metastatic tumors. Therefore, we have designed a phase II clinical study in which VPA was combined with RA (VPA-RA) in the AML treatment. Eigth chemotherapy-resistant or high risk AML patients not eligible for additional intensive therapy (median age 61.5 yrs), were treated at the Hematology Units of the Universities “La Sapienza” and “Tor Vergata” Rome-Italy. VPA (Depakin[Sanofi-Wintrop]) was administrated from day 1 to day 28, at the initial dosage of 10 mg/kg/die p.o. with dose escalation until optimal VPA plasma levels (80–110ug/ml). RA (Vesanoid [Roche]) at the dosage of 45 mg/m2 p.o./d, divided in two administrations, was added once the optimal VPA plasma levels were reached or at day 14 and continued until day 28. Four patients had a history of MDS, three patients had a FAB M0, M1 and M2 de novo AMLs, while the remaining case was a myeloid blast crisis (FAB M0) of a Ph+ve CML. Cytogenetic characterization in the other patients revealed normal karyotype in one case, a pseudodiploid [der(12)] in one, hyperdiploid (+8) in one, complex K with a 7q- alteration in one, while in the three remaining cases the karyotype was not evaluable. Pre-treatment leukemic infiltration ranged from 22% to 95%. VPA plasma level >60mg/ml was reached between 8 to 28 days (median 14.5 days). In three patients, VPA-RA treatment induced hyperleukocytosis (>50x 109/l) at day 16, 21 and 24, respectively, that was treated with chemotherapy (HU in two cases and low dose Ara-C in 1 case). Hematological improvement (≥50% decrease in packed red blood cell or platelet transfusion requirement) was observed in one case, a stable disease in five cases and disease progression in two cases. Peripheral blood and/or bone marrow samples were collected at day 0,3,7,14,21,28 for morphologic, immunophenotypic, cytogenetic and molecular studies. All patients showed features of myeloid-monocytic and/or erythroid differentiation of the leukemic clone, as revealed by morphologic, cytochemical, immunophenotypic analyses and by Q-RT-PCR of myeloid gene expression (GATA 1, MPO, CSF2Rb, etc.). Of note that high degree of myeloid differentiation correlated with early achievement of therapeutic VPA plasma levels and histone hyper-acetylation, as measured by immunocytochemistry and immunoblotting using antiacetylated histone H3 and H4 antibodies. Finally, differentiation of the leukemic clone was proven by FISH analysis showing the presence of the +8 and 7q- in maturing elements in patients whose leukemia blasts carried these cytogenetic lesions. The VPA-RA combination is a well tolerated treatment that induces phenotypic changes of the leukemic clone through chromatine remodelling. Further studies are needed to optimise this regimen with the aim of improving clinical response in leukemia patients.

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