5-Stabilized phosphatidylinositol 3,4,5-trisphosphate analogues bind Grp1 PH, inhibit phosphoinositide phosphatases, and block neutrophil migration

SHIP1 therapeutic target enablement: Identification and evaluation of inhibitors for the treatment of late-onset Alzheimer's disease

INTRODUCTION

The risk of developing Alzheimer's disease is associated with genes involved in microglial function. Inositol polyphosphate-5-phosphatase (INPP5D), which encodes Src homology 2 (SH2) domain-containing inositol polyphosphate 5-phosphatase 1 (SHIP1), is a risk gene expressed in microglia. Because SHIP1 binds receptor immunoreceptor tyrosine-based inhibitory motifs (ITIMs), competes with kinases, and converts PI(3,4,5)P3 to PI(3,4)P2, it is a negative regulator of microglia function. Validated inhibitors are needed to evaluate SHIP1 as a potential therapeutic target.

METHODS

We identified inhibitors and screened the enzymatic domain of SHIP1. A protein construct containing two domains was used to evaluate enzyme inhibitor potency and selectivity versus SHIP2. Inhibitors were tested against a construct containing all ordered domains of the human and mouse proteins. A cellular thermal shift assay (CETSA) provided evidence of target engagement in cells. Phospho-AKT levels provided further evidence of on-target pharmacology. A high-content imaging assay was used to study the pharmacology of SHIP1 inhibition while monitoring cell health. Physicochemical and absorption, distribution, metabolism, and excretion (ADME) properties were evaluated to select a compound suitable for in vivo studies.

RESULTS

SHIP1 inhibitors displayed a remarkable array of activities and cellular pharmacology. Inhibitory potency was dependent on the protein construct used to assess enzymatic activity. Some inhibitors failed to engage the target in cells. Inhibitors that were active in the CETSA consistently destabilized the protein and reduced pAKT levels. Many SHIP1 inhibitors were cytotoxic either at high concentration due to cell stress or they potently induced cell death depending on the compound and cell type. One compound activated microglia, inducing phagocytosis at concentrations that did not result in significant cell death. A pharmacokinetic study demonstrated brain exposures in mice upon oral administration.

DISCUSSION

3-((2,4-Dichlorobenzyl)oxy)-5-(1-(piperidin-4-yl)-1H-pyrazol-4-yl) pyridine activated primary mouse microglia and demonstrated exposures in mouse brain upon oral dosing. Although this compound is our recommended chemical probe for investigating the pharmacology of SHIP1 inhibition at this time, further optimization is required for clinical studies.

Highlights

Cellular thermal shift assay (CETSA) and signaling (pAKT) assays were developed to provide evidence of src homology 2 (SH2) domain-contaning inositol phosphatase 1 (SHIP1) target engagement and on-target activity in cellular assays.A phenotypic high-content imaging assay with simultaneous measures of phagocytosis, cell number, and nuclear intensity was developed to explore cellular pharmacology and monitor cell health.SHIP1 inhibitors demonstrate a wide range of activity and cellular pharmacology, and many reported inhibitors are cytotoxic.The chemical probe 3-((2,4-dichlorobenzyl)oxy)-5-(1-(piperidin-4-yl)-1H-pyrazol-4-yl) pyridine is recommended to explore SHIP1 pharmacology.

Suppressive Role of Bam32/DAPP1 in Chemokine-Induced Neutrophil Recruitment

Bam32 (B cell adaptor molecule of 32 kDa) functions in the immune responses of various leukocytes. However, the role of neutrophil Bam32 in inflammation is entirely unknown. Here, we determined the role of Bam32 in chemokine CXCL2-induced neutrophil chemotaxis in three mouse models of neutrophil recruitment. By using intravital microscopy in the mouse cremaster muscle, we found that transmigrated neutrophil number, neutrophil chemotaxis velocity, and total neutrophil chemotaxis distance were increased in Bam32^−/− mice when compared with wild-type (WT) mice. In CXCL2-induced mouse peritonitis, the total emigrated neutrophils were increased in Bam32^−/− mice at 2 but not 4 h. The CXCL2-induced chemotaxis distance and migration velocity of isolated Bam32^−/− neutrophils in vitro were increased. We examined the activation of small GTPases Rac1, Rac2, and Rap1; the levels of phospho-Akt2 and total Akt2; and their crosstalk with Bam32 in neutrophils. The deficiency of Bam32 suppressed Rap1 activation without changing the activation of Rac1 and Rac2. The pharmacological inhibition of Rap1 by geranylgeranyltransferase I inhibitor (GGTI298) increased WT neutrophil chemotaxis. In addition, the deficiency of Bam32, as well as the inhibition of Rap1 activation, increased the levels of CXCL2-induced Akt1/2 phosphorylation at Thr308/309 in neutrophils. The inhibition of Akt by SH-5 attenuated CXCL2-induced adhesion and emigration in Bam32^−/− mice. Together, our results reveal that Bam32 has a suppressive role in chemokine-induced neutrophil chemotaxis by regulating Rap1 activation and that this role of Bam32 in chemokine-induced neutrophil recruitment relies on the activation of PI3K effector Akt.

Discovery and development of small molecule SHIP phosphatase modulators

Inositol phospholipids play an important role in the transfer of signaling information across the cell membrane in eukaryotes. These signals are often governed by the phosphorylation patterns on the inositols, which are mediated by a number of inositol kinases and phosphatases. The src homology 2 (SH2) containing inositol 5-phosphatase (SHIP) plays a central role in these processes, influencing signals delivered through the PI3K/Akt/mTOR pathway. SHIP modulation by small molecules has been implicated as a treatment in a number of human disease states, including cancer, inflammatory diseases, diabetes, atherosclerosis, and Alzheimer's disease. In addition, alteration of SHIP phosphatase activity may provide a means to facilitate bone marrow transplantation and increase blood cell production. This review discusses the cellular signaling pathways and protein-protein interactions that provide the molecular basis for targeting the SHIP enzyme in these disease states. In addition, a comprehensive survey of small molecule modulators of SHIP1 and SHIP2 is provided, with a focus on the structure, potency, selectivity, and solubility properties of these compounds.

The PH domain of phosphoinositide-dependent kinase-1 exhibits a novel, phospho-regulated monomer-dimer equilibrium with important implications for kinase domain activation: single-molecule and ensemble studies

Phosphoinositide-dependent kinase-1 (PDK1) is an essential master kinase recruited to the plasma membrane by the binding of its C-terminal PH domain to the signaling lipid phosphatidylinositol-3,4,5-trisphosphate (PIP3). Membrane binding leads to PDK1 phospho-activation, but despite the central role of PDK1 in signaling and cancer biology, this activation mechanism remains poorly understood. PDK1 has been shown to exist as a dimer in cells, and one crystal structure of its isolated PH domain exhibits a putative dimer interface. It has been proposed that phosphorylation of PH domain residue T513 (or the phospho-mimetic T513E mutation) may regulate a novel PH domain dimer-monomer equilibrium, thereby converting an inactive PDK1 dimer to an active monomer. However, the oligomeric states of the PH domain on the membrane have not yet been determined, nor whether a negative charge at position 513 is sufficient to regulate its oligomeric state. This study investigates the binding of purified wild-type (WT) and T513E PDK1 PH domains to lipid bilayers containing the PIP3 target lipid, using both single-molecule and ensemble measurements. Single-molecule analysis of the brightness of the fluorescent PH domain shows that the PIP3-bound WT PH domain on membranes is predominantly dimeric while the PIP3-bound T513E PH domain is monomeric, demonstrating that negative charge at the T513 position is sufficient to dissociate the PH domain dimer and is thus likely to play a central role in PDK1 monomerization and activation. Single-molecule analysis of two-dimensional (2D) diffusion of PH domain-PIP3 complexes reveals that the dimeric WT PH domain diffuses at the same rate as a single lipid molecule, indicating that only one of its two PIP3 binding sites is occupied and there is little penetration of the protein into the bilayer as observed for other PH domains. The 2D diffusion of T513E PH domain is slower, suggesting the negative charge disrupts local structure in a way that allows deeper insertion of the protein into the viscous bilayer, thereby increasing the diffusional friction. Ensemble measurements of PH domain affinity for PIP3 on plasma membrane-like bilayers reveal that the dimeric WT PH domain possesses a one order of magnitude higher target membrane affinity than the previously characterized monomeric PH domains, consistent with a dimerization-triggered, allosterically enhanced affinity for one PIP3 molecule (a much larger affinity enhancement would be expected for dimerization-triggered binding to two PIP3 molecules). The monomeric T513E PDK1 PH domain, like other monomeric PH domains, exhibits a PIP3 affinity and bound state lifetime that are each 1 order of magnitude lower than those of the dimeric WT PH domain, which is predicted to facilitate release of activated, monomeric PDK1 to the cytoplasm. Overall, the study yields the first molecular picture of PH domain regulation via electrostatic control of dimer-monomer conversion.

Molecular analysis of protein-phosphoinositide interactions

Diverse biological processes including cell growth and survival require transient association of proteins with cellular membranes. A large number of these proteins are drawn to a bilayer through binding of their modular domains to phosphoinositide (PI) lipids. Seven PI isoforms are found to concentrate in distinct pools of intracellular membranes, and this lipid compartmentalization provides an efficient way for recruiting PI-binding proteins to specific cellular organelles. The atomic-resolution structures and membrane docking mechanisms of a dozen PI effectors have been elucidated in the last decade, offering insight into the molecular basis for regulation of the PI-dependent signaling pathways. In this chapter, I summarize the mechanistic aspects of deciphering the 'PI code' by the most common PI-recognizing domains and discuss similarities and differences in the membrane anchoring mechanisms.

Elevated miR-155 promotes inflammation in cystic fibrosis by driving hyperexpression of interleukin-8

Cystic Fibrosis (CF) is characterized by a massive proinflammatory phenotype in the lung arising from profound expression of inflammatory genes, including interleukin-8 (IL-8). We have previously reported that IL-8 mRNA is stabilized in CF lung epithelial cells, resulting in concomitant hyperexpression of IL-8 protein. However, the mechanistic link between mutations in CFTR and acquisition of the proinflammatory phenotype in the CF airway has remained elusive. We hypothesized that specific microRNAs (miRNAs) might mediate this linkage. To identify the potential link, we screened an miRNA library for differential expression in ΔF508-CFTR and wild type CFTR lung epithelial cell lines. Of 22 differentially and significantly expressed miRNAs, we found that expression of miR-155 was more than 5-fold elevated in CF IB3-1 lung epithelial cells in culture, compared with control IB3-1/S9 cells. Clinically, miR-155 was also highly expressed in CF lung epithelial cells and circulating CF neutrophils biopsied from CF patients. We report here that high levels of miR-155 specifically reduced levels of SHIP1, thereby promoting PI3K/Akt activation. However, overexpressing SHIP1 or inhibition of PI3K in CF cells suppressed IL-8 expression. Finally, we found that phospho-Akt levels were elevated in CF lung epithelial cells and were specifically lowered by either antagomir-155 or elevated expression of SHIP1. We therefore suggest that elevated miR-155 contributes to the proinflammatory expression of IL-8 in CF lung epithelial cells by lowering SHIP1 expression and thereby activating the PI3K/Akt signaling pathway. These data suggest that miR-155 may play an important role in the activation of IL-8-dependent inflammation in CF.

Synthesis of 4-C-alkyl inositol 1,4,5-trisphosphates and 1,3,4,5-tetrakisphosphates

The preparation of 2,3,6-O-tribenzyl- and 2,6-O-dibenzyl-myo-inositols with beta-primary, secondary, and tertiary 4-C-alkyl or aryl groups is reported. Five of these novel polyols are elaborated to 4-C-alkyl Ins(1,4,5)P(3) and Ins(1,3,4,5)P(4) analogues. Regio- and stereoselective introduction of 4-C-alkyl or aryl substituents proceeded via a 4-exo-methylene oxide. Subsequent regioselective reduction of an orthobenzoate provided a divergent method to access both InsP(3) and InsP(4) precursors. Previously unreported phosphorylation of the tertiary hydroxyl and global deprotection afforded novel analogues that retain their full complement of polar and charged binding features.