Phase I Pharmacokinetic and Pharmacodynamic Evaluation of Combined Valproic Acid/Doxombicin Treatment in Dogs with Spontaneous Cancer

摘要

Purpose: Histone deacetylase inhibitors (HDACi) are targeted anticancer agents with a well-documented ability to act synergistically with cytotoxic agents. We recently showed that the HDACi valproic acid sensitizes osteosarcoma cells to doxombidn in vitro and in vivo. As there are no published reports on the clinical utility of HDACi in dogs with spontaneous cancers, we sought to determine a safe and biologically effective dose of valproic acid administered prior to a standard dose of doxorubidn.Methods: Twenty-one dogs were enrolled into eight cohorts in an accelerated dose-escalation trial consisting of pretreatment with oral valproic acid followed by doxorubicin on a three-week cycle. Blood and tumor tissue were collected for determination of serum valproic acid concentration and evaluation of pharmacodynamic effects by immunofluorescence cytochemistry and immunohistochemistry. Serum and complete blood counts were obtained for determination of changes in doxorubicin pharmacokinetics or hematologic effects.Results: All doses of valproic acid were well tolerated. Serum valproic acid concentrations increased linearly with dose. Doxorubicin pharmacokinetics were comparable with those in dogs receiving doxorubicin alone. A positive correlation was detected between valproic acid dose and histone hyperacetyla-tion in peripheral blood mononudear cells. No potentiation of doxorubicin-induced myelosuppression was observed. Histone hyperacetylation was documented in tumor and peripheral blood mononudear cells. Responses induded 2 of 21 complete, 3 of 21 partial, 5 of 21 stable disease, and 11 of 21 progressive disease.Conclusions: Valproic acid can be administered to dogs at doses up to 240 mg/kg/day prior to a standard dose of doxorubicin. In addition, we have developed the pharmacokinetic/pharmacodynamic tools necessary for future studies of novel HDACi in the dinical setting of canine cancer.