Abstract: Malignant tumour growth is affected by a variety of normal surrounding cellular compartments. Angiogenesis supplies oxygen and nutrients to tumour cells and interstitial tissues (fibroblasts, macrophage/monocytes and osteoclasts) influence invasion and metastatic spread of tumour cells. These biological reactions of normal cells as well as tumour cell behaviors are regulated by protein phosphorylation and subsequent intermolecular interactions. Protein tyrosine kinase is one of the best players in this scenario. Thus, targeting protein tyrosine kinases is an attractive strategy for the treatment of advanced cancer patients.
Fes was originally identified as a cellular counterpart of an oncogene product, v-Fps, and represents a unique structural property with large N-terminal region containing two coiled-coil domains, followed by an SH2 domain and a catalytic domain. Coiled-coil domains are involved in intermolecular oligomerization, and association between the SH2 domain and the catalytic domain is involved in kinase activation. Until recently, most studies on Fes have been performed with myeloid hematopoietic cells, one of the major sites of its expression in normal tissues. Targeting disruption of c-fes gene showed minimal effect. When activated mutant Fes was expressed in the skin, increase in vascularity and hemangioma formation were observed, indicative of its role in angiogenesis. Fes forms oligomers in cells, which is responsible for the regulation of kinase activity, and expression of kinase-dead Fes exerts dominant negative effect on endogenous Fes. Endothelial cells express Fes and no specific synthetic inhibitor for Fes is currently available. We expressed kinase-dead Fes in endothelial cells and examined its role in proangiogenic factor-treated cells. WE found that its expression inhibited FGF-2- and angiopoietin 2 (Ang 2)-directed chemotaxis, and sonic hedgehog- and stromal-derived factor (SDF)-1alpha-promoted morphological differentiation. In VEGF-A-treated cells, Fes was activated and was involved in PI3-kinase activation. However, Fes inactivation was compensated by other signaling molecules (VEGF receptor-2, Src and IRS-I) for the PI3-kinase activation in VEGF-A-treated endothelial cells and no dominant negative effect was observed. It is now widely accepted that VEGF-A blockade rapidly cause the resistance to this therapy. One of the mechanisms of this resistance is the alteration of the dependence of tumour angiogenesis from VEGF-A to other proangiogenic factors, such as FGF-2, Ang 2 and SDF-1alpha. Thus, it seems likely that the inhibition of Fes activity may be a second line antiangiogenic therapy for VEGF-A-independent tumours.
The role of Fes in solid tumour cell growth was not well examined because of its limited expression in normal epithelail cells. Recently, inactivating mutation of Fes was found in colorectal cancer cells and two groups have shown that kinase-dead Fes was favorable for breast tumourigenesis in mutant mice and colon cancer cell growth in vitro. This tumour-suppressive function of Fes may be cell-type dependent, because downregulation of Fes by siRNA inhibited the proliferation of human renal carcinoma cells and expression of kinase-dead Fes showed no effect on tumor growth in nude mice. Further studies on other tumour cell types are warranted whether inhibition of Fes activity as an antiangiogenic therapy may accelerate tumour growth in vivo.
It is also urgent to find synthetic small molecular weight kinase inhibitors for Fes to examine the role of Fes in normal and pathological conditions. During the screening of previously published synthetic kinase inhibitors, we found that gefitinib, an EGF receptor tyrosine kinase inhibitor inhibits FGF-2- and VEGF-A-induced Fes activity in endothelial cells, and chemotaxis toward FGF-2-, but not VEGF-A. The effect was indirect because gefitinib failed to inhibit purified Fes activity in in vitro kinase assay. It is elusive what is the direct activator of Fes that is sensitive to gefitinib-treatment. Nevertheless, the results suppose the idea that gefitinib may be used as a second line antiangiogenic agent.

Brief Biography of the Speaker:
Shigeru Kanda is a Head of the Department of Experimental and Clinical Laboratory Medicine and the Palliative Care Team, National Hospital Organization Nagasaki Hospital, Nagasaki, Japan. He started his career as an urological surgeon and obtained his Ph.D. with the studies on the growth regulation of renal tubular cells. He worked as a visiting scientist at Ludwig Institute for Cancer Research, Uppsala, Sweden, where he began to study the signal transduction pathways leading to angiogenesis. He authored or co-authored over 85 scientific papers published in peer-reviewed journals. He wrote a chapter entitled Studies of the endothelial cell-specific signal transduction pathways. New paradigm for the development of potent anti-angiogenic therapies. In: Trends in Angiogenesis Research edited by R. V. Zubar, Nova Science Publisher, Inc, pp. 43-69, 2005. and he is members of American Association for Cancer Research and American Society of Biochemistry and Molecular Biology. He is also an Editorial Board of "Oncology Letters".