9569 Background: Vorinostat, an orally administered histone deacetylase inhibitor, has potent antitumor activity against human cell lines in vitro (IC50 0.5 to 5 μM) and in xenograft models. A phase I trial of vorinostat was conducted in children with recurrent or refractory solid tumors to determine the maximum tolerated dose (MTD), dose limiting toxicity (DLT), pharmacokinetics (PK) of vorinostat, and to assess accumulation of histone acetylation in peripheral blood mononuclear cells (PBMCs). Methods: Vorinostat was administered once daily at dose levels of 180, 230, and 300 mg/m2/d. Courses were 28 days in duration, without interruption. PK analysis was performed during the 1st course. Vorinostat's ability to induce acetyl-histone (H3) accumulation in vivo was studied by western blot analysis. Results: 30 patients, 17 males, median age 15 years (range 4–21), were enrolled; 24 patients were fully evaluable for toxicity. At 180 mg/m2/d, 1/6 pts developed DLT (deep vein thrombosis) and at 230 mg/m2/d 1/6 pts developed DLT (hypokalemia). At 300 mg/m2/d, DLTs consisted of reversible hypokalemia (n=1), neutropenia (n=1) and thrombocytopenia (n=2), defining the MTD as 230 mg/m2/d. Other non-dose limiting grade 3 or 4 toxicities included elevated ALT/AST, hyperbilirubinemia, leucopenia, and lymphopenia. Western blot analysis of PBMC protein isolates found clear evidence of dose- dependent accumulation of acetylated H3 histones. 1 patient with a spindle cell sarcoma received 8 courses and 1 patient with a low-grade astrocytoma had an unconfirmed minor response. Conclusions: Vorinostat is well tolerated in children with recurrent or refractory solid tumors and inhibits histone deacetylase activity in PBMC. The recommended phase II dose for children with solid tumors is 230 mg/m2/d. No significant financial relationships to disclose.

No abstract