Phenylbutyrate to Treat Children With Progressive or Recurrent Brain Tumors

This study will examine the safety and effectiveness of treating brain tumors in children with a continuous infusion of phenylbutyrate. A breakdown product of this drug, phenylacetate, is normally found in low concentrations in the blood. At much higher concentrations, phenylbutyrate and phenylacetate are active against cancer in animals. Patients between 2 and 21 years old with a brain tumor that has progressed or recurred after radiation or chemotherapy, including bone marrow transplant, may be eligible for this study. Candidates will be screened with a medical history and physical examination, blood tests, magnetic resonance imaging (MRI) or computerized tomography (CT) of the head and, if needed, a spinal fluid test and bone marrow test. Study participants will have a continuous infusion of phenylbutyrate for two 28-day cycles-every day, 24 hours a day, 7 days a week. The medicine will be infused through a thin tube (catheter) placed in a large vein in the upper chest, delivered through a portable infusion pump. Patients will be hospitalized for at least 3 days when the treatment begins. If there are no side effects at that time, the infusions can continue on an outpatient basis. The patient or care giver will receive the medicine in 4-day supplies and will be taught how to change the bag and tubing daily for drug administration, as well as how to use the infusion pump. Patients will be monitored with weekly blood tests to look for side effects and measure blood levels of phenylbutyrate. They will have a physical examination at least once a week. At the end of the second 28-day cycle, patients will have a CT or MRI scan to evaluate the tumor's response to treatment. Patients whose tumor has grown will stop treatment and come off the study. Those whose tumor has remained stable or shrunk may continue phenylbutyrate as long as the treatment is beneficial and there are no serious side effects. CT or MRI scans will be done after every 2 cycles (or sooner if needed) to evaluate the treatment. Patients with certain tumor types (medulloblastoma, PNET, ependymoma, malignant germ cell tumor and pineoblastoma) or who have symptoms that indicate there might be tumor along the spinal cord may have a spinal tap. For this procedure, the patient lies on the side and a needle is inserted between two vertebrae (bones of the spine) in the lower back, into the cerebrospinal fluid space. A sample of fluid is drawn for testing for cancer cells. If the tumor has spread through the spinal fluid, a spinal tap will be done every other cycle (every 2 months) to monitor the effects of therapy.

Phenylbutyrate is an aromatic fatty acid that is converted to phenylacetate in vivo by mitochondrial Beta-oxidation to phenylacetate. Preclinical studies have shown that continuous exposure to phenylacetate or phenylbutyrate can induce tumor cytostasis and differentiation in a wide variety of cell lines including malignant gliomas and neuroblastomas. However, phenylbutyrate has been shown to be a more potent differentiating agent than phenylacetate in a variety of tumor cell lines. In addition, phenylbutyrate appears to have molecular activities that are distinct from phenylacetate and may induce apoptosis. Phase I trials in adults and children have established the feasibility of administering phenylbutyrate on a prolonged schedule. A phase II trial of phenylbutyrate administered as a continuous intravenous infusion will be performed in children with recurrent or progressive brain tumors.