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.

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ABSTRACT:3,4-Dihydro-2,2-dimethyl-2H-naphthol[1,2-b]pyran-5,6-dione (ARQ 501; ␤-lapachone) showed promising anticancer activity in phase I clinical trials as monotherapy and in combination with cytotoxic drugs. ARQ 501 is currently in multiple phase II clinical trials. In vitro incubation in fresh whole blood at 37°C revealed that ARQ 501 is stable in plasma but disappears rapidly in whole blood. Our data showed that extensive metabolism in red blood cells (RBCs) was mainly responsible for the rapid disappearance of ARQ 501 in whole blood. By comparison, covalent binding of ARQ 501 and/or its metabolites to whole blood components was a minor contributor to the disappearance of this compound. Sequestration of intact ARQ 501 in RBCs was not observed. Cross-species metabolite profiles from incubating [ 14 C]ARQ 501 in freshly drawn blood were characterized using a liquid chromatography-mass spectrometry-accurate radioactivity counter. The results show that ARQ 501 was metabolized more rapidly in mouse and rat blood than in dog, monkey, and human blood, with qualitatively similar metabolite profiles. Six metabolites were identified in human blood using ultra-high performance liquid chromatography/time-of-flight mass spectrometry, and the postulated structure of five metabolites was confirmed using synthetic standards. We conclude that the primary metabolic pathway of ARQ 501 in human blood involved oxidation of the two adjacent carbonyl groups to produce dicarboxylic and monocarboxylic metabolites, elimination of a carbonyl group to form a ring-contracted metabolite, and lactonization to produce two metabolites with a pyrone ring to form a ring-contracted metabolite. Metabolism by RBCs may play a role in clearance of ARQ 501 from the blood compartment in cancer patients.

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