A highly selective, cell-permeable furin inhibitor BOS-318 rescues key features of cystic fibrosis airway disease

In cystic fibrosis (CF), excessive furin activity plays a critical role in the activation of the epithelial sodium channel (ENaC), dysregulation of which contributes to airway dehydration, ineffective mucociliary clearance (MCC), and mucus obstruction. Here, we report a highly selective, cell-permeable furin inhibitor, BOS-318, that derives selectivity by eliciting the formation of a new, unexpected binding pocket independent of the active site catalytic triad. Using human ex vivo models, BOS-318 showed significant suppression of ENaC, which led to enhanced airway hydration and an ∼30-fold increase in MCC rate. Furin inhibition also protected ENaC from subsequent activation by neutrophil elastase, a soluble protease dominant in CF airways. Additional therapeutic benefits include protection against epithelial cell death induced by Pseudomonas aeruginosa exotoxin A. Our findings demonstrate the utility of selective furin inhibition as a mutation-agnostic approach that can correct features of CF airway pathophysiology in a manner expected to deliver therapeutic value.

Pharmacological targeting of the unfolded protein response for disease intervention

Accumulation of unfolded proteins at the endoplasmic reticulum (ER) is a salient attribute of many human diseases including obesity, liver disorders, cancer, diabetes and neurodegeneration. To restore ER proteostasis, cells activate the unfolded protein response (UPR), a signaling pathway that imposes adaptive programs or triggers apoptosis of damaged cells. The UPR is critical to sustain the normal function of specialized secretory cells (i.e., pancreatic β cells and B lymphocytes) and to control the production of lipids and cholesterol in the liver. In the context of disease, adaptive UPR responses have been linked to the growth of solid tumors, whereas chronic ER stress contributes to cell dysfunction in brain diseases, metabolic syndromes, among other conditions. Here we discuss recent developments in the design and optimization of novel compounds to manipulate UPR signaling and their efficacy in various disease models.

Oral treatment targeting the unfolded protein response prevents neurodegeneration and clinical disease in prion-infected mice

During prion disease, an increase in misfolded prion protein (PrP) generated by prion replication leads to sustained overactivation of the branch of the unfolded protein response (UPR) that controls the initiation of protein synthesis. This results in persistent repression of translation, resulting in the loss of critical proteins that leads to synaptic failure and neuronal death. We have previously reported that localized genetic manipulation of this pathway rescues shutdown of translation and prevents neurodegeneration in a mouse model of prion disease, suggesting that pharmacological inhibition of this pathway might be of therapeutic benefit. We show that oral treatment with a specific inhibitor of the kinase PERK (protein kinase RNA-like endoplasmic reticulum kinase), a key mediator of this UPR pathway, prevented UPR-mediated translational repression and abrogated development of clinical prion disease in mice, with neuroprotection observed throughout the mouse brain. This was the case for animals treated both at the preclinical stage and also later in disease when behavioral signs had emerged. Critically, the compound acts downstream and independently of the primary pathogenic process of prion replication and is effective despite continuing accumulation of misfolded PrP. These data suggest that PERK, and other members of this pathway, may be new therapeutic targets for developing drugs against prion disease or other neurodegenerative diseases where the UPR has been implicated.

Discovery of GSK2656157: An Optimized PERK Inhibitor Selected for Preclinical Development

We recently reported the discovery of GSK2606414 (1), a selective first in class inhibitor of protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), which inhibited PERK activation in cells and demonstrated tumor growth inhibition in a human tumor xenograft in mice. In continuation of our drug discovery program, we applied a strategy to decrease inhibitor lipophilicity as a means to improve physical properties and pharmacokinetics. This report describes our medicinal chemistry optimization culminating in the discovery of the PERK inhibitor GSK2656157 (6), which was selected for advancement to preclinical development.

Characterization of a novel PERK kinase inhibitor with antitumor and antiangiogenic activity

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, eIF2α 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.

Discovery of 7-methyl-5-(1-{[3-(trifluoromethyl)phenyl]acetyl}-2,3-dihydro-1H-indol-5-yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine (GSK2606414), a potent and selective first-in-class inhibitor of protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK)

Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is activated in response to a variety of endoplasmic reticulum stresses implicated in numerous disease states. Evidence that PERK is implicated in tumorigenesis and cancer cell survival stimulated our search for small molecule inhibitors. Through screening and lead optimization using the human PERK crystal structure, we discovered compound 38 (GSK2606414), an orally available, potent, and selective PERK inhibitor. Compound 38 inhibits PERK activation in cells and inhibits the growth of a human tumor xenograft in mice.

Acylprolinamides: a new class of peptide deformylase inhibitors with in vivo antibacterial activity

A new class of PDF inhibitor with potent, broad spectrum antibacterial activity is described. Optimization of blood stability and potency provided compounds with improved pharmacokinetics that were suitable for in vivo experiments. Compound 5c, which has robust antibacterial activity, demonstrated efficacy in two respiratory tract infection models.

Novel amino-piperidines as potent antibacterials targeting bacterial type IIA topoisomerases

We have identified a series of amino-piperidine antibacterials with a good broad spectrum potency. We report the investigation of various subunits in this series and advanced studies on compound 8. Compound 8 possesses good pharmacokinetics, broad spectrum antibacterial activity and demonstrates oral efficacy in a rat lung infection model.

Structure-based design of potent and selective 3-phosphoinositide-dependent kinase-1 (PDK1) inhibitors

Phosphoinositide-dependent protein kinase-1(PDK1) is a master regulator of the AGC family of kinases and an integral component of the PI3K/AKT/mTOR pathway. As this pathway is among the most commonly deregulated across all cancers, a selective inhibitor of PDK1 might have utility as an anticancer agent. Herein we describe our lead optimization of compound 1 toward highly potent and selective PDK1 inhibitors via a structure-based design strategy. The most potent and selective inhibitors demonstrated submicromolar activity as measured by inhibition of phosphorylation of PDK1 substrates as well as antiproliferative activity against a subset of AML cell lines. In addition, reduction of phosphorylation of PDK1 substrates was demonstrated in vivo in mice bearing OCl-AML2 xenografts. These observations demonstrate the utility of these molecules as tools to further delineate the biology of PDK1 and the potential pharmacological uses of a PDK1 inhibitor.

Aminoindazole PDK1 Inhibitors: A Case Study in Fragment-Based Drug Discovery

Fragment screening of phosphoinositide-dependent kinase-1 (PDK1) in a biochemical kinase assay afforded hits that were characterized and prioritized based on ligand efficiency and binding interactions with PDK1 as determined by NMR. Subsequent crystallography and follow-up screening led to the discovery of aminoindazole 19, a potent leadlike PDK1 inhibitor with high ligand efficiency. Well-defined structure-activity relationships and protein crystallography provide a basis for further elaboration and optimization of 19 as a PDK1 inhibitor.

Abstract LB-42: PDK1 knockdown selectively inhibits growth of cancer cells harboring activating mutations involved in MAPK signaling

Phosphoinositide-dependent protein kinase-1 (PDK1) is a master regulator of the AGC family of kinases and an integral component of the PI3K/AKT/mTOR pathway which is the most commonly deregulated signaling pathway across all cancers. Increased PDK1 activity confers chemoresistance in tumor cell lines, and reduced PDK1 expression prevents the onset of tumorigenesis in mouse models. To demonstrate that PDK1 is a promising target for cancer therapy, we used a siRNA-based approach to determine the effects of PDK1 knockdown in cancer cells and primary early-passage normal cells. Loss of PDK1 protein caused a significant reduction in phosphorylation of two PDK1 substrates, AKT (T308) and RSK1 (S221). Interestingly, knockdown of PDK1 protein had preferential growth inhibitory effects in cancer cells containing activating mutations of KRAS or BRAF, compared to cells with wild-type KRAS or BRAF. In KRAS/BRAF-mutant cells, apoptosis was evidenced by PARP-1 cleavage and an increase in the number of sub-G1 DNA content. Overexpression of mouse PDK1 rescued these cells from apoptosis, confirming the specificity of the siRNA-mediated effects. Consistent with these observations, stable expression of mutant KRAS (G12V) in NL-20 immortalized normal lung epithelial cells sensitized these cells to apoptosis upon knockdown of the PDK1 protein. Importantly, overexpression of a kinase-dead mouse PDK1 mutant did not rescue cells from apoptosis, suggesting that the kinase activity is required for these PDK1 functions. Based on these results, we sought to identify inhibitors of the kinase activity of PDK1 for development as anticancer agents. GSK2334470 was identified as a potent inhibitor of PDK1 kinase (IC50 0.5 nmol/l) that demonstrated a high level of specificity to PDK1 in an in vitro kinase panel. In cell-based mechanistic assays, GSK2334470 effectively inhibited phosphorylation of the PDK1-dependent phosphorylation sites [AKT T308 (IC50: 100 nmol/L) and RSK S221 (IC50: 291 nmol/L)], but not the PDK1-independent phosphorylation site on AKT, S473 (IC50: >30 umol/L). Antiproliferative effects were seen in several cell lines using low micromolar concentrations of inhibitor; however, no correlation between growth inhibition and KRAS/BRAF mutations was observed. Further optimization may be necessary for improved potency and KRAS/BRAF selectivity. Currently, efforts are underway to better understand the disconnect between siRNA data and compound data in several experimental cancer models, particularly in those where KRAS or BRAF mutations predominate.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-42.

Abstract LB-116: GSK2334470: A potent and highly selective inhibitor of PDK1

Phosphoinositide-dependent protein kinase-1 (PDK1) is a master regulator of the AGC family of kinases and an integral component of the PI3K/AKT/mTOR pathway which is the most commonly deregulated signaling pathway across all cancers. In vivo studies have shown that AKT, p70S6K, RSK and protein kinase C are key mediators of PDK1 function, regulating diverse cellular processes. Activation of these substrates by PDK1 leads to an increase in glucose uptake, protein synthesis, and inhibition of pro-apoptotic proteins. Conversely, knockdown of PDK1 protein levels in tumor cells leads to decreased tumor cell proliferation and increased apoptosis. Furthermore, a hypomorphic mutation of PDK1 suppresses tumorigenesis in PTEN+/- mice. Taken together, these observations suggest that an inhibitor of PDK1 could be beneficial in treating cancer. Therefore, we initiated a medicinal chemistry program to discover PDK1 inhibitors as potential anticancer agents.

We have identified an aminoindazole PDK1 inhibitor, GSK2334470, derived from a fragment screening hit which we optimized using structure-based design and PDK1 protein crystallography. Potency and kinase selectivity were attributed to key interactions within the ATP binding site between the inhibitor and the back pocket and glycine-rich loop of PDK1. GSK2334470 is a potent inhibitor of PDK1 kinase (IC50 = 0.5 nM) with a high level of specificity for PDK1 based on test results from in an in vitro kinase selectivity panel of more than 280 kinases. In PC-3 cells, GSK2334470 effectively inhibited phosphorylation of AKTT308 (IC50 = 113 nM) and RSKS221 (IC50 = 293 nM) but not AKTS473 (IC50 > 30,000 nM). These results are consistent with the high specificity of GSK2334470 for PDK1 inhibition. In a panel of approximately 300 cell lines, GSK2334470 demonstrated modest antiproliferative activity overall, with low micromolar activity seen in several breast cancer cell lines and in a variety of hematological cancer cells. Interestingly, GSK2334470 displayed sub-micromolar antiproliferative activity against AML cell lines that are clinically classified as M4 and M5 FAB-subtypes. Therefore, we evaluated the pharmacodynamics of GSK2334470 in mice implanted with OCI-AML2 xenografts. GSK2334470 dosed i.p. at 100 mg/kg resulted in 58 and 29% inhibition of AKTT308 phosphorylation at 3 and 6 h, respectively and 57 and 71% inhibition of RSKS221 phosphorylation at 3 and 6 h, respectively. There was no observed change on AKTS473 phosphorylation. Our results demonstrate that GSK23334470 is a potent, highly selective PDK1 inhibitor which can decrease PDK1 signaling in a tumor xenograft model.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-116.