Abstract
Background: The development of resistance to temozolomide (TMZ), a standard chemotherapeutic, limits the effective treatment of glioblastoma (GBM). Focal adhesion kinase (FAK) and proline rich tyrosine kinase 2 (Pyk2) regulate proliferation and invasion of GBM cells. We found that TMZ activates FAK and Pyk2 signaling in GBM. We hypothesized that pharmacological inhibitors of Pyk2/FAK together with TMZ can enhance the inhibitory effect of TMZ on tumor growth and dispersal and improve the treatment outcome. Methods: Primary human GBM cell cultures and a C57Bl/6-GL261 mouse glioma implantation model were used. Pyk2 (Tyr579/580) and FAK (Tyr925) phosphorylation was analyzed by western blotting. Viability, cell cycle, migration, invasion and invadopodia formation were investigated in vitro. Animal survival, tumor size and invasion, TUNEL apoptotic cell death and the Ki67 proliferation index were evaluated in vivo upon treatment with TMZ (50 mg/kg, once/day, orally) and the Pyk2/FAK inhibitor PF-562271 (once/daily, 50 mg/kg, orally) vs. TMZ monotherapy. Results: In vitro studies revealed significantly reduced viability, cell cycle progression, invasion and invadopodia with TMZ (100 µM) + PF-562271 (16 nM) compared with TMZ alone. In vivo studies demonstrated that combinatorial treatment led to prominent reductions in tumor size and invasive margins, extensive signs of apoptosis and a reduced proliferation index, together with a 15% increase in the survival rate in animals, compared with TMZ monotherapy. Conclusion: TMZ + PF-562271 eliminates TMZ-related Pyk2/FAK activation in GBM and improves the treatment efficacy.