The unfolded protein response (UPR) is a signal transduction pathway that coordinates cellular adaptation to microenvironmental stresses that include hypoxia, nutrient deprivation, and change in redox status. These stress stimuli are common in many tumors and thus targeting components of the UPR signaling is an attractive therapeutic approach. We have identified a first-in-class, small molecule inhibitor of the eukaryotic initiation factor 2-alpha kinase 3 (EIF2AK3) or PERK, one of the three mediators of UPR signaling. GSK2656157 is an ATP-competitive inhibitor of PERK enzyme activity with an IC 50 of 0.9 nmol/L. It is highly selective for PERK with IC 50 values >100 nmol/L against a panel of 300 kinases. GSK2656157 inhibits PERK activity in cells with an IC 50 in the range of 10-30 nmol/L as shown by inhibition of stress-induced PERK autophosphorylation, eIF2a substrate phosphorylation, together with corresponding decreases in ATF4 and CAAT/enhancer binding protein homologous protein (CHOP) in multiple cell lines. Oral administration of GSK2656157 to mice shows a dose-and time-dependent pharmacodynamic response in pancreas as measured by PERK autophosphorylation. Twice daily dosing of GSK2656157 results in dose-dependent inhibition of multiple human tumor xenografts growth in mice. Altered amino acid metabolism, decreased blood vessel density, and vascular perfusion are potential mechanisms for the observed antitumor effect. However, despite its antitumor activity, given the on-target pharmacologic effects of PERK inhibition on pancreatic function, development of any PERK inhibitor in human subjects would need to be cautiously pursued in cancer patients.

Akt kinases 1, 2, and 3 are important regulators of cell survival and have been shown to be constitutively active in a variety of human tumors. GSK690693 is a novel ATP-competitive, low-nanomolar pan-Akt kinase inhibitor. It is selective for the Akt isoforms versus the majority of kinases in other families; however, it does inhibit additional members of the AGC kinase family. It causes dose-dependent reductions in the phosphorylation state of multiple proteins downstream of Akt, including GSK3B, PRAS40, and Forkhead. GSK690693 inhibited proliferation and induced apoptosis in a subset of tumor cells with potency consistent with intracellular inhibition of Akt kinase activity. In immune-compromised mice implanted with human BT474 breast carcinoma xenografts, a single i.p. administration of GSK690693 inhibited GSK3B phosphorylation in a dose-and time-dependent manner. After a single dose of GSK690693, >3 Mmol/L drug concentration in BT474 tumor xenografts correlated with a sustained decrease in GSK3B phosphorylation. Consistent with the role of Akt in insulin signaling, treatment with GSK690693 resulted in acute and transient increases in blood glucose level. Daily administration of GSK690693 produced significant antitumor activity in mice bearing established human SKOV-3 ovarian, LNCaP prostate, and BT474 and HCC-1954 breast carcinoma xenografts. Immunohistochemical analysis of tumor xenografts after repeat dosing with GSK690693 showed reductions in phosphorylated Akt substrates in vivo. These results support further evaluation of GSK690693 as an anticancer agent.

Overexpression of AKT has an antiapoptotic effect in many cell types, and expression of dominant negative AKT blocks the ability of a variety of growth factors to promote survival. Therefore, inhibitors of AKT kinase activity might be useful as monotherapy for the treatment of tumors with activated AKT. Herein, we describe our lead optimization studies culminating in the discovery of compound 3g (GSK690693). Compound 3g is a novel ATP competitive, pan-AKT kinase inhibitor with IC 50 values of 2, 13, and 9 nM against AKT1, 2, and 3, respectively. An X-ray cocrystal structure was solved with 3g and the kinase domain of AKT2, confirming that 3g bound in the ATP binding pocket. Compound 3g potently inhibits intracellular AKT activity as measured by the inhibition of the phosphorylation levels of GSK3beta. Intraperitoneal administration of 3g in immunocompromised mice results in the inhibition of GSK3beta phosphorylation and tumor growth in human breast carcinoma (BT474) xenografts.

b-Ketoacyl-ACP synthase III (FabH), an essential enzyme for bacterial viability, catalyzes the initiation of fatty acid elongation by condensing malonyl-ACP with acetyl-CoA. We have determined the crystal structure of FabH from Staphylococcus aureus, a Gram-positive human pathogen, to 2 Å resolution. Although the overall structure of S. aureus FabH is similar to that of Escherichia coli FabH, the primer binding pocket in S. aureus FabH is significantly larger than that present in E. coli FabH. The structural differences, which agree with kinetic parameters, provide explanation for the observed varying substrate specificity for E. coli and S. aureus FabH. The rank order of activity of S. aureus FabH with various acyl-CoA primers was as follows: isobutyryl-> hexanoyl-> butyryl-> isovaleryl-> > acetyl-CoA. The availability of crystal structure may aid in designing potent, selective inhibitors of S. aureus FabH.Keywords: Staphylococcus aureus; FabH; X-ray crystallography; kinetics; substrate specificity Bacterial b-ketoacyl-ACP synthase (KAS) enzymes are important in the elongation steps of fatty acid biosynthesis Khandekar et al. 2003). KAS I (FabB) and KAS II (FabF) are involved in the condensation of malonyl-ACP with a growing acyl-ACP chain to form b-ketoacyl-ACP, which is a substrate for b-ketoacyl-ACP reductase (FabG). KAS III (FabH) catalyzes the initiation of fatty acid biosynthesis by condensing malonyl-ACP with acetyl-CoA. FabH from Gram-negative Escherichia coli has been studied extensively. It is encoded by the fabH gene, and is a homodimer with a monomeric molecular weight of 35 kDa (Han et al. 1998;Khandekar et al. 2003). It has been cloned, expressed, and purified by several groups, and has been extensively characterized both mechanistically and structurally (Qiu et al. 1999a;Davies et al. 2000;Khandekar et al. 2000). The E. coli FabH crystal structure has been solved in the presence and the absence of the substrate, acetyl-CoA (Qiu et al. 1999a(Qiu et al. , 2001Davies et al. 2000). In the crystal structure, the close approximation of Cys112 to CoA suggests it may play an important role in catalysis. Modeling based on a bound CoA molecule has identified His244 and Asn274 as additional residues that might be involved in catalysis.Staphylococcus aureus (S. aureus) is a Gram-positive human pathogen that causes diseases in humans, including skin infections, scalded-skin syndrome, and toxic