This paper describes the implementation of a biochemical and biophysical screening strategy to identify and optimize small molecule Akt1 inhibitors that act through a mechanism distinct from that observed for kinase domain ATP-competitive inhibitors. With the aid of an unphosphorylated Akt1 cocrystal structure of 12j solved at 2.25 Å, it was possible to confirm that as a consequence of binding these novel inhibitors, the ATP binding cleft contained a number of hydrophobic residues that occlude ATP binding as expected. These Akt inhibitors potently inhibit intracellular Akt activation and its downstream target (PRAS40) in vitro. In vivo pharmacodynamic and pharmacokinetic studies with two examples, 12e and 12j, showed the series to be similarly effective at inhibiting the activation of Akt and an additional downstream effector (p70S6) following oral dosing in mice.

Activation of DNA damage checkpoint pathways, including Chk2, serves as an anticancer barrier in precancerous lesions. In an effort to identify small-molecule activators of Chk2, the authors developed a quantitative cell-based assay using a highcontent analysis (HCA) platform. Induction of phosphorylated Chk2 was evaluated using several different parameters, including fold induction, Kolmogorov-Smirnov score, and percentage of positively stained cells. These measurements were highly correlated and provided an accurate method for compound ranking/binning, structure-activity relationship studies, and lead identification. Screening for Chk2 activators was undertaken with a target-focused library and a diversified library from ArQule chemical space. Several compounds exhibited submicromolar EC 50 values for phosphorylated Chk2 induction. These compounds were further analyzed for Chk2-dependent cytotoxicity, as assessed through a high-content cell death assay in combination with siRNA silencing of Chk2 expression. Several compounds were identified and showed specific inhibition or lethality in a target-dependent manner. Therefore, identification of DNA damage checkpoint pathway activators by HCA is an attractive approach for discovering the next generation of targeted cancer therapeutics. (Journal of Biomolecular Screening 2008:538-543)

Herein we describe the implementation of a biochemical and biophysical screening strategy to discover small molecules that inhibit Akt through a mechanism distinct from ATP-competitive inhibitors. A series of novel derivatives of the core scaffold 3H-imidazo[4,5-b]pyridine were identified and optimized. These Akt inhibitors demonstrated potent inhibition of intracellular Akt and downstream targets including PRAS40 activation in vitro. Pharmacodynamic and pharmacokinetic studies in vivo demonstrated the effectiveness of the series at inhibiting the activation of Akt and an additional downstream effector (p70S6) following oral dosing in mice. Co-crystallization studies with un-phosphorylated Akt1 revealed that as a consequence of binding these novel, potent and selective, ATP-independent inhibitors the ATP binding cleft is occupied by non-polar residues which are associated as tight clusters. The cleft is closed with a ‘hydrophobic lock’ which may function to sterically exclude the binding of both ATP and ATP-competitive inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-1. doi:1538-7445.AM2012-LB-1