Abstract
BACKGROUND: Glioblastoma is the most aggressive adult primary malignant brain tumor. It is associated with poor prognosis (median survival of 12-15 months) despite treatment. Combination chemotherapy with carmustine (BCNU) or temozolomide (TMZ) with the MGMT inhibitor O6-benzylguanine (O6BG) has been used but it has been associated with dose limiting hematopoietic toxicity. OBJECTIVE: To assess safety and efficacy of a retroviral vector encoding the O6BG-resistant MGMTP140K gene for transduction and autologous transplantation of hematopoietic stem cells (HSCs) in MGMT unmethylated, newly diagnosed GBM patients in an attempt to chemoprotect bone marrow during combination O6BG/TMZ therapy. METHODS: Seven patients have been enrolled in the first cohort of the study. Following tumor resection, patients underwent standard radiation therapy without TMZ followed by G-CSF mobilization, aphaeresis and conditioning with 600 mg/m2 BCNU prior to infusion of gene-modified cells. Post transplant, patients were treated with 28-day cycles of single dose TMZ (472mg/m2) with 48-hour intravenous O6BG (120mg/m2 bolus, followed by 30mg/m2/24h). RESULTS: The BCNU dose was nonmyeloablative. Gene marking in pre-infusion colony forming units (CFUs) was robust in most patients. Similarly, following engraftment, gene marking in white blood cells and sorted granulocytes assessed by real-time PCR was high. Patients have received up to nine cycles of O6BG/TMZ with evidence for selection of gene-modified cells and tolerable hematologic toxicity. This is significantly more cycles compared to recurrent patients receiving O6BG/TMZ in the absence of gene modified, chemoprotected cells (Quinn et al., 2005) (p < 0.05). No extra-hematopoietic toxicity has been observed thus far and all seven patients exhibited improved survival over historical controls. The longest surviving patient is 56+ months from the diagnosis without evidence of disease progression. CONCLUSIONS: These data demonstrate feasibility of achieving significant engraftment of MGMTP140K- modified cells with a well-tolerated dose of BCNU. Combination of TMZ and O6BG is well tolerated in this setting and patients with newly diagnosed GBM exhibiting unmethylated MGMT promoter achieve prolonged survivals.