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The Tie family of receptor tyrosine kinases plays a crucial role in the development and function of endothelial tissues. Genetic studies have revealed specific roles for the Tie receptors (Tie1 & Tie2) and their ligands (angiopoietins) in promoting the survival, maturation and functional integrity of the vasculature. Inhibition of Tie2 is expected to disrupt angiogenesis and tumor growth via inhibition of vascular modeling.

In an effort to develop inhibitors of Tie2, we designed the (4-amino-7H-pyrrolo[2,3-d]pyrimidin-5-yl)(phenyl)methanone template as a new scaffold for Tie2 inhibition. Our initial efforts focused on the elucidation of the structure-activity relationships of the pyrrolopyrimidine series with the goal of enhancing potency and selectivity. This led us to the 5-keto-pyrrolopyrimidine series with either a sulfonamide or urea linker. Sulfonamides are less potent, but selective Tie2 inhibitors, whereas ureas are very potent but non-selective versus Trk.

Both series show moderate to high microsomal clearance, possibly due to the metabolically labile N7 tail (e.g. cyclopentyl) and/or the lipophilic nature of these series. Other key issues included low VDss, low apparent microsomal Km (i.e. saturation of metabolism), and/or HERG channel activity. To resolve these PK issues, our chemistry efforts concentrated on extensive analoging at the N7 position and substitution of the phenyl core. We demonstrated that replacement of the N7 tail with a small, less lipophilic group (e.g. iPr) results in significant improvement in the metabolic stability of these series. Furthermore, substitution on the phenyl core with small substituents (e.g. alkyl, halo, ether) or replacement with a heterocycle (e.g. pyridine) was found to enhance Tie2 potency and improve in vitro and in vivo pharmacokinetic properties.

These efforts led to the discovery of CE-355774, CE-245,677 and PF-371,989, each dual Tie2/Trk inhibitors. These compounds demonstrate excellent in vitro activity, and CE-245,677 & PF-371,989 were selected for further preclinical evaluation due to their superior ADME properties. In particular, CE-245,677 is a potent reversible inhibitor of Tie2 and TrkA/B kinases with a cellular IC50 of 4.7 and 1 nM, resp., displays >100x selectivity against a number of other angiogenic receptor tyrosine kinases (e.g. KDR, PDGFR, FGFR) and gene family panels, and demonstrates good oral absorption in in vivo rat PK studies (F=80%).

In summary, detailed SAR studies were executed on the (4-amino-7H-pyrrolo[2,3-d]pyrimidin-5-yl)(phenyl)methanone template, producing potent inhibitors of Tie2 with IC50s ranging from 5-100 nM, identifying CE-245,677 and PF-371,989 for further preclinical study. Design, synthesis, inhibitor activity, selectivity profile, ADME properties as well as complete inhibitor chemical structures of analogs leading to the identification to CE-245,677 will be presented.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA