From the Division of Medical Oncology and Hematology, Princess Margaret Hospital, University of Toronto, Toronto, ON, Canada
Authors disclosures of potential conflicts of interest are found at the end of this article.
Address reprint requests to Lillian L. Siu, MD, FRCPC, Associate Professor, University of Toronto, Princess Margaret Hospital, 610 University Ave, Suite 5-718, Toronto, Ontario M5G 2M9, Canada; e-mail: lillian.siu{at}uhn.on.ca
Overview: Focal adhesion kinase (FAK) is a ubiquitously expressed nonreceptor protein tyrosine kinase that localizes to protein complexes called focal adhesions (FAs), the cytoskeletal platform interacting with proteins of the extracellular matrix. It integrates signals from several sources, particularly the integrins and receptor tyrosine kinases that also colocalize to FAs. Maximal activation of FAK requires adoption of an optimal conformation followed by the sequential phosphorylation of key tyrosine residues by auto- and/or transphosphorylation. Binding of Src to FAK is a pivotal part of this process, resulting in reciprocal activation of both kinases. Activated FAK can then modulate a variety of downstream signaling pathways. The major effects of FAK activation are increased cell migration, invasion, survival, proliferation, and angiogenesis. Given these characteristics and a very consistent association between increased FAK expression/signaling and increased tumorigenicity, FAK appears to be a pivotal pathway in cancer. Several agents currently in clinical development potently inhibit FAK. However, because most of these also inhibit other targets, it is difficult to quantify the contribution FAK inhibition makes to their therapeutic effects. A newer generation of inhibitors specific for the FAK family is entering early-phase clinical trials. To date, adenosine triphosphate-mimetic, competitive inhibitors of FAK and proline-rich tyrosine kinase 2, such as PF-00562271, have been well tolerated and have demonstrated cytostatic activity. Ongoing trials will determine the optimal use of this class of agents, either singly in minimal-burden states or in combination with other agents.