Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase which is over-expressed in various human epithelial tumor types and in some cases this has been linked to poor clinical outcome. FAK is found at focal adhesions which are sites of integrin clustering at the cell-extracellular matrix interface, where it provides both signaling and scaffolding functions. It is involved in a number of processes which can impact on the malignant phenotype including cell migration, invasion and survival, the importance of which are not fully understood. In support however, of a direct role for FAK in tumorigenesis we have shown, using targeted deletion of fak in mouse skin, the absolute requirement for FAK in malignant tumor formation (McLean et al., Gene Dev 18:2998-3003, 2004). Careful analysis of the relative requirements of the scaffolding and kinase functions of FAK requires re-constitution of the corresponding FAK mutants into a null background. To address this we have made use of the skin carcinogenesis model and generated squamous cell carcinoma (SCC) cell lines in which fak was then genetically deleted in culture (SCC-ED1-/-). Wild type FAK (WT) and a kinase inactive FAK (K454R; KD) were then expressed in the SCC-ED1-/- cells. Genetic deletion of fak in fibroblasts leads to a defect in cell migration and initial characterization of the SCC-ED1 cells showed that the ability of SCC-ED1-/- cells to close a wound was significantly impaired. This was associated with an inability of the cells lacking FAK to polarize towards the edge of the wound. Deletion of fak did not alter the ability of SCC-ED1 cells to proliferate on plastic however, FAK was required for their growth in soft agar. Reconstitution of FAK-WT but not FAK-KD into the SCC-ED1-/- cells restored their ability to grow in soft agar. PF-562,271 is a novel small molecule inhibitor of the kinase activity of FAK and treatment of the SCC-ED1 cells with PF-562,271 inhibited their growth in soft agar at concentrations which inhibited FAK kinase activity, while having no effect on growth on plastic. In both cases there was no evidence of apoptosis in the cultures and at the end of the experiment the cells could be recovered from the agar and re-cultured on plastic. Thus the requirement of FAK for growth in soft agar is dependent on the kinase activity. When injected into the flanks of immune-compromised mice the SCC-ED1 cells rapidly formed tumors. In contrast, there was a significant delay in the onset of tumor growth in SCC-ED1-/- cells. This was restored by expression of FAK-WT but not FAK-KD. Understanding the importance of the FAK kinase domain in tumorigenesis is critical as PF-562,271 is now in clinical development for the treatment of solid tumors.
Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1765.
100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO