Novel inhibitor for fibroblast growth factor receptor tyrosine kinase Naparat Kammasud, a Chantana Boonyarat, b Satoshi Tsunoda, c Hiroaki Sakurai, c Ikuo Saiki, c David S. Grierson d and Opa Vajragupta a, * a Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Mahidol University, 447 Sri-Ayudhya Road, Bangkok 10400, Thailand b Faculty of Pharmaceutical Sciences, Khon Kaen University, Khon Kaen 40002, Thailand c Division of Pathogenic Biochemistry, Department of Bioscience, Institute of Natural Medicine, University of Toyama, Japan d UMR 176 CNRS, Institut Curie, Section Recherche, Centre Universitaire, Bat.110-112, 91405 Orsay cedex, France Received 16 March 2007; revised 8 June 2007; accepted 18 June 2007 Available online 26 June 2007 Abstract—NP603, the 6-dimethoxy phenyl indolin-2-one, was designed as FGF receptor 1 inhibitor by computational study. NP603 was synthesized and found to be more active against endothelial proliferation of HUVEC after the rhFGF-2 stimulation than SU6668 with minimum effective dose of 0.4 lM but with similar potency as SU16g. NP603 inhibited the tyrosine phosphor- ylation in FGF receptor and the activation of extracellular signal-regulated kinase and c-Jun-N-terminal-kinase after the rhFGF- 2 stimulation. The increase in activity of NP603 supports the role of Lys514 movement in ligand–receptor binding in modeling study as the movement accommodates the hydrophobic interaction at the receptor pocket leading to the enhancement of binding capacity. Ó 2007 Elsevier Ltd. All rights reserved. Receptor tyrosine kinases (RTKs) have been shown to be important mediators of signal transduction in cells. 1–5 These transmembrane molecules characteristi- cally consist of an extracellular ligand-binding domain connected through a segment in the plasma membrane to an intracellular tyrosine kinase domain. Binding of the ligand to the receptor results in receptor dimeriza- tion and stimulation of the receptor-associated tyro- sine kinase activity, which leads to phosphorylation of tyrosine residues on both the receptor and other intracellular molecules. These changes in tyrosine phosphorylation initiate a signaling cascade leading to a variety of cellular responses, one of which is angi- ogenesis. 6,7 Growth factors, including the vascular endothelial growth factors (VEGF), the fibroblast growth factors (FGF), and the platelet-derived growth factors (PDGF) and their associated receptor tyrosine kinases, are major regulators of angiogenesis. RTKs are important therapeutic targets for cancer drug discovery and development. Amongst the many inhibitors undergoing development, 3-substituted indo- lin-2-ones were found to exhibit high potency and selectivity against PDGF and VEGF (Flk-1) RTKs. SU5402 and SU5416 have been shown to be specific inhibitors of the kinase activity of the fibroblast growth factor receptor (FGFR) and vascular endothe- lial growth factor receptor (VEGFR), respectively, whereas SU6668 showed inhibitory activity against FGFR, VEGFR, and PDGFR. 8,9 The pyrido[2,3- d]pyrimidine PD173074, a potential drug candidate, was similarly found to be highly selective for the FGFR1. This molecule is a nanomolar inhibitor of FGFR1 and is also a submicromolar inhibitor of VEGFR2. Structure–activity relationship (SAR) data for compounds in the pyrido[2,3-d]pyrimidine series indicate that binding affinity and selectivity for FGFR1 is attained through modification of the phenyl group attached to the 6-position of the pyrido[2,3- d]pyrimidine scaffold. In general, derivatization at the 3- and 5-positions of the phenyl ring increases selectiv- ity for FGFR1, especially when the attached group is larger than a methyl. The SAR data are in good agreement with the surface observed in the structure for PD173074 bound in the FGFR1 kinase domain (PDB accession code 2FGI). 10 0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2007.06.058 Keywords: FGFR1; FGFR1 inhibitor; SU6668; Phenyl indolin-2-one; Docking; Binding mode; Antiproliferation; Antiangiogenesis. * Corresponding author. Tel.: +66 2 6448677; fax: +66 2 6448695; e-mail: pyovj@mahidol.ac.th Bioorganic & Medicinal Chemistry Letters 17 (2007) 4812–4818