Cooperation Between C-Met And Focal Adhesion Kinase Pathways In Medulloblastoma And Implications For Therapy

Abstract Our laboratory previously demonstrated the involvement of the tyrosine kinase receptor c-Met and its ligand hepatocyte growth factor (HGF) in medulloblastoma malignancy. The nonreceptor tyrosine kinases FAK and Pyk2, are key players in the progression of different cancers and are critical signaling effectors linking integrin and growth factor signaling. However, their role in medulloblastoma malignancy remains unexplored. In this study, using a protein array approach, we found that c-Met phosphorylates FAK and Pyk2. We therefore studied the interactions between c-Met and FAK/Pyk2 and their implications for medulloblastoma therapy. D425, DAOY and ONS-76 medullobalstoma cell lines were treated with HGF for various times and the activation of FAK and Pyk2 was assessed by immunoblotting. HGF induced a strong phosphorylation of FAK at Tyr397, Tyr576/577 and Tyr925, which are important for the maximal adhesion-induced activation of FAK and signaling to downstream effectors. HGF induced phosphorylation of FAK at Ser910, which is involved in modulating binding/stability of downstream signaling proteins. Similarly, medulloblastoma cell treatment with HGF resulted in a strong and fast phosphorylation of Pyk2 at Tyr402, reported to promote invasion and migration. To determine if FAK and/or Pyk2 mediate c-Met-dependent malignant functions in medulloblastoma, FAK and Pyk2 expressions were inhibited with siRNA and the effects of this inhibition on various malignancy parameters in medulloblastoma cells were studied. siRNA-mediated inhibition of FAK or Pyk2 led to a significant inhibition of basal and HGF-induced medulloblastoma cell invasion, cell migration and cell proliferation in all cell lines. The above data therefore showed that c-Met activates FAK and Pyk2 and that FAK and Pyk2 mediate the malignant effects of FAK in medulloblastoma. Based on these findings, we hypothesized that combined c-Met and FAK inhibitions would have additive effects on the inhibition of medulloblastoma malignancy. To test this hypothesis, we assessed the effects on medulloblastoma malignancy parameters of single or combined treatments of cells with the clinically applicable c-Met inhibitor PF-2341066 (crizotinib) and the FAK inhibitor PF-573228. We found a significant additive inhibitory effect of both inhibitors on medulloblastoma cell migration and cell invasion (p<0.05). Therefore, combining c-Met inhibitors with FAK inhibitors constitutes a new potential strategy for medulloblastoma therapy. Additionally, treatment of medullobastoma tumors generated in SCID mice flanks, with PF-2341066 significantly reduced tumor growth. Altogether, our study describes for the first time a role for FAK/Pyk2 in medulloblastoma malignancy, uncovers new interactions between c-Met and FAK/Pyk2, and proposes combining anti-c-Met and anti-FAK inhibitors as a new strategy for medulloblastoma therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1252. doi:1538-7445.AM2012-1252