STI571 (Gleevec) improves tumor growth delay and survival in irradiated mouse models of glioblastoma

Purpose: Glioblastoma multiforme (GBM) is a devastating brain neoplasm that is essentially incurable. Although radiation therapy prolongs survival, GBMs progress within areas of irradiation. Recent studies in invertebrates have shown that ST1571 (Gleevec; Novartis, East Hanover, NJ) enhances the cytotoxicity of ionizing radiation. In the present study, the effectiveness of ST1571 in combination with radiation was studied in mouse models of GBM. Methods and Materials: Murine GL261 and human D54 GBM cell lines formed tumors in brains and hind limbs of C57BL6 and nude mice, respectively. GL261 and D54 cells were treated with 5 mu mol/L of ST1571 for I h and/or irradiated with 3 Gy. Protein was analyzed by Western immunoblots probed with antibodies to caspase 3, cleaved caspase 3, phospho-Akt, Akt, and platelet-derived growth factor receptor (PDGFR) alpha and beta. Tumor volumes were assessed in mice bearing GL261 or D54 tumors treated with 21 Gy administered in seven fractionated doses. Histologic sections from ST1571-treated mice were stained with phospbo-Akt and phospho-PDGFR beta antibodies. Kaplan-Meier survival curves were used to study the response of mice bearing intracranial implants of GL261. Results: ST1571 penetrated the blood-brain barrier, which resulted in a reduction in phospho-PDGFR in GBM. ST1571-induced apoptosis in GBM was significantly enhanced by irradiation. ST1571 combined with irradiation induced caspase 3 cleavage in GBM cells. Glioblastoma multiforme response to therapy correlated with an increase in tumor growth delay and survival when ST1571 was administered in conjunction with daily irradiation. Conclusion: These findings suggest that ST1571 has the potential to augment radiotherapy and thereby improve median survival. (c) 2006 Elsevier Inc.