Because phosphoinositide 3-kinase (PI3K) plays a central role in cellular activation, proliferation, and survival, pharmacologic inhibitors targeting components of the PI3K pathway are actively being developed as therapeutics for the treatment of inflammatory disorders and cancer. These targeted drugs inhibit the activity of either PI3K itself or downstream protein kinases. However, a previously unexplored, alternate strategy is to activate the negative regulatory phosphatases in this pathway. The SH2-containing inositol-5-phosphatase SHIP1 is a normal physiologic counterregulator of PI3K in immune/hematopoietic cells that hydrolyzes the PI3K product phosphatidylinositiol-3,4,5-trisphosphate (PIP 3 ). We now describe the identification and characterization of potent and specific small-molecule activators of SHIP1. These compounds represent the first small-molecule activators of a phosphatase, and are able to activate recombinant SHIP1 enzyme in vitro and stimulate SHIP1 activity in intact macrophage and mast cells. Mechanism of activation studies with these compounds suggest that they bind a previously undescribed, allosteric activation domain within SHIP1. Furthermore, in vivo administration of these compounds was protective in mouse models of endotoxemia and acute cutaneous anaphylaxis, suggesting that SHIP1 agonists could be used therapeutically to inhibit the PI3K pathway. IntroductionIn response to extracellular signals, phosphoinositide 3-kinase (PI3K) becomes activated and phosphorylates phosphatidylinositol-4,5-bisphosphate (PI-4,5-P 2 ) within the plasma membrane to generate phosphatidylinositol-3,4,5-bisphosphate (PIP 3 ). PIP 3 then initiates a cascade of downstream signaling pathways by interacting with pleckstrin homology (PH) domain-containing proteins, such as protein kinase B (PKB, also known as Akt), that regulate cellular activation, proliferation and/or survival, depending on the cell type and stimulus. 1 Cellular levels of PIP 3 are normally tightly regulated by both PI3K and the 5Ј inositol phosphatases SHIP1 (SH2 domain-containing inositol phosphatase) and SHIP2, as well as the 3Ј inositol phosphatase PTEN, which dephosphorylates PIP 3 . 2,3 Of these, SHIP1 is unique in that its expression is restricted primarily to immune and hematopoietic cells. 2,4 SHIP's role in immune cell homeostasis is shown both by the myeloproliferative syndrome observed in SHIP1 Ϫ/Ϫ mice, as well as the hypersensitivity of SHIP1 Ϫ/Ϫ mice and cells to immune stimulation. 5,6 SHIP1 mediates signaling from the inhibitory Fc␥RIIB receptor, 7 and is important in terminating signal transduction from activating immune/hematopoietic cell receptor systems. 8 Diminished SHIP1 activity or expression has been observed in human inflammatory diseases 9 and hematopoietic malignancies. [10][11][12][13] Because dysregulated activation of the PI3K pathway contributes to inflammatory/immune disorders and cancer, intense efforts have been invested into the development of inhibitors of PI3K itself, as well as downstream protein kinas...

Background: mTORC1 is dysregulated in human disease, and there is an interest in the development of mTORC1 inhibitors. Niclosamide inhibits mTORC1 signaling, but its mode of action remains unclear. Results: Niclosamide extrudes protons from lysosomes, thus lowering cytoplasmic pH and inhibiting mTORC1 signaling. Conclusion: Cytoplasmic acidification inhibits mTORC1 signaling. Significance: Our findings may aid the design of niclosamide-based anticancer therapeutic agents.

Tuberculosis, caused by Mycobacterium tuberculosis infection, is a major cause of morbidity and mortality in the world today. M. tuberculosis hijacks the phagosome-lysosome trafficking pathway to escape clearance from infected macrophages. There is increasing evidence that manipulation of autophagy, a regulated catabolic trafficking pathway, can enhance killing of M. tuberculosis. Therefore, pharmacological agents that induce autophagy could be important in combating tuberculosis. We report that the antiprotozoal drug nitazoxanide and its active metabolite tizoxanide strongly stimulate autophagy and inhibit signaling by mTORC1, a major negative regulator of autophagy. Analysis of 16 nitazoxanide analogues reveals similar strict structural requirements for activity in autophagosome induction, EGFP-LC3 processing and mTORC1 inhibition. Nitazoxanide can inhibit M. tuberculosis proliferation in vitro. Here we show that it inhibits M. tuberculosis proliferation more potently in infected human THP-1 cells and peripheral monocytes. We identify the human quinone oxidoreductase NQO1 as a nitazoxanide target and propose, based on experiments with cells expressing NQO1 or not, that NQO1 inhibition is partly responsible for mTORC1 inhibition and enhanced autophagy. The dual action of nitazoxanide on both the bacterium and the host cell response to infection may lead to improved tuberculosis treatment.

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Two biomimetic approaches have been used to synthesize analogs of the SHIP1‐activating sponge meroterpenoid pelorol (1). One approach started from the chiral pool plant natural product sclareolide, which has the same absolute configuration as pelorol. The second approach utilized an enantioselective polyene cyclization to efficiently access both absolute configurations of the pelorol meroterpenoid skeleton and to prepare A‐ring functionalized compounds. Selected analogs have been evaluated for water solubility and biological activity. It was found that the undesirable catechol and ester functionalities in 1 could be removed to give MN100 (3), without a decrease in SHIP1‐activating ability. A further refinement led to the resorcinol analog 18, which is the most effective SHIP1‐activating pelorol analog made to date. The HCl salt of ent‐28, a C‐3 amino analog of 18, is about 500,000‐fold more soluble in water than MN100 (3). (±)‐28·HCl activates SHIP1 in vitro, inhibits Akt phosphorylation in stimulated MOLT‐4 (SHIP+) cells, and is active in a dose‐dependent manner in a mouse model of inflammation when administered by oral gavage (ED50 ≈ 0.1 mg/kg). Pelorol analogs ent‐28 or (±)‐28 are promising chemical tools for further preclinical in vivo evaluation of the potential of SHIP1 activators as therapeutics for treating hematopoietic diseases involving aberrant activation of PI3K cell signaling.