Abstract A139: Discovery and biological profiling of potent fibroblast growth factor receptor (FGFR) kinase inhibitors derived from in silico design with in vivo antitumor activity against FGFR2‐dependent human tumors

Dysregulation of members of the FGFR tyrosine kinase family has been increasingly implicated in a number of human cancers, including gastric, breast, endometrial, and bladder carcinomas. A proprietary structure‐based design paradigm was employed to identify inhibitors which favor a mode of binding that is distinct from the commonly described ATP competitive inhibitors. A molecular template was identified (ARQ 523) which, upon further modification, provided molecules that were shown to inhibit FGFR kinases in the low micromolar range, to bind to FGFR2 in an enantiomeric‐specific fashion, to bind to unphosphorylated FGFR2 with a K D of 5 µM; and, after pre‐incubation with inactive FGFR2, to prevent a fluorescent analogue of ATP from binding to the enzyme. We have designated this novel type of kinase inhibitor as “ATP‐exclusionary” or “Type IV” to differentiate these inhibitors from extant molecules. Following a lead optimization campaign, biochemical potencies of 1 nM or less against FGFR kinases with corresponding increases in binding affinities to FGFR2 in biophysical assays were documented in several compounds in two distinct series. These compounds showed sub‐micromolar activity in both FGFR2‐dependent pharmacodynamic and cytotoxicity assays, and demonstrated a moderately high degree of selectivity across the human kinome. A representative compound showed marked FGFR2 pharmacodynamic suppression and corresponding growth inhibition in KATO III and SNU‐16 human gastric carcinoma cells. In addition, growth of SNU‐16 tumor xenografts in athymic mice was markedly suppressed (58% regression as compared to vehicle‐treated controls) after daily intraperitoneal administration for 9 days. A paired Ba/F3 xenograft model was also employed, using both Ba/F3 cells transfected with either FGFR2 or the unrelated insulin receptor. Significant tumor growth inhibition (77% inhibition as compared to vehicle‐treated controls) was observed in treated mice bearing FGFR2‐transfected Ba/F3 tumors but not in the insulin receptor transfectants. In summary, we have achieved proof‐of‐principle of a structure‐based kinase inhibitor design paradigm for the identification of a series of FGFR kinase inhibitors that exhibits a preference for the inactive form of the kinase and excludes ATP upon binding. One advanced lead molecule demonstrated the ability to exert profound anti‐tumor effects against cancer cell lines in which FGFR2 is the dominant oncogenic driver. The opportunity now exists to significantly expand the number of new chemotypes available for drug discovery against disease‐relevant kinases in oncology and in other therapeutic areas, since it is predicted that approximately half of the human kinome is amenable to this novel mode of inhibition. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A139.