Abstract 1368: Fragment-based design, synthesis and biological evaluation of a series of novel PDK1 inhibitors

Abstract

Abstract The PDK1 is a monomeric serine/threonine kinase and a promising oncology target of significant current interest for drug development due to its central role in the PI3K/AKT/mTOR pathway. It phosphorylates highly conserved Ser or Thr residues in the activation loop of several AGC super family kinases including PKC, SGK, PKB/Akt, p70S6K, and PDK-1 itself. Approximately, 40-50% of all tumors involve mutations in the PTEN protein, which results in elevated levels of PIP3 and enhanced activation of PKB/AKT, p70S6K, and SGK. It has been proposed that inhibitors of PDK-1 could provide a valuable therapeutic approach to targeting cancer, particularly those with PTEN deficiencies. Using a fragment-based design strategy, we screened a collection of 1100 low molecular weight (< 250 MW) fragments against the PDK1 kinase and identified 9 fragments with moderate inhibitory activity against PDK1 (IC50 values from 45-82 μM). Of these fragments, those based off of a 5-Br,4-I-1H-indazol-3-amine scaffold seemed the most promising based on initial activity and in keeping with the “rule of 3” for fragment-based drug design. Subsequent molecular docking studies using a crystal structure of PDK1 allowed for the structural rationalization of how these fragments bound in the ATP-binding pocket (hydrogen bonding to S160/A162 hinge residues) and provided insight for further optimization. Concurrently, we carried out scaffold-hopping searches at 2-site points for hydrophobic and solvent pocket fragments. With the addition of one fused heterocyclic ring, the potency increased to 8.8 and 10.9 μM. Our systematic fragment based workflow led to the preparation of target molecules in 4 steps beginning with the condensation, cyclization, and reduction and finally installing the hydrophobic binding site fragments under normal amide coupling. Subsequent SAR and follow-up screening led to the discovery of HCI-1680, a potent PDK1 inhibitor with an IC50 of 97 nM. Additional productive interactions sites with PDK1 were introduced to further improve both biochemical and cellular activities in panel of cancer cells. In cell-based assays HCI-1680 demonstrated enhanced activity in PTEN-deficient cell lines compared to PTEN-wild type lines. HCI-1680 and additional compounds from this series were also shown to inhibit the activation of AKT and other downstream signaling molecules. Kinase selectivity profiling, additional cell-based assays, and animal studies are ongoing. The details of these studies will be presented. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1368. doi:10.1158/1538-7445.AM2011-1368