Browsing by Subject "Orlistat"

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    Lysosomal Acid Lipase Is Required for Donor T Cells to Induce Graft-versus-Host Disease
    (Cell Press, 2020-10-27) Nguyen, Hung D.; Ticer, Taylor; Bastian, David; Kuril, Sandeepkumar; Li, Hong; Du, Hong; Yan, Cong; Yu, Xue-Zhong; Pathology and Laboratory Medicine, School of Medicine
    Graft-versus-host disease (GVHD) limits the success of allogeneic hematopoietic cell transplantation (allo-HCT). Lysosomal acid lipase (LAL) mediates the intrinsic lipolysis of cells to generate free fatty acids (FFAs), which play an essential role in the development, proliferation, and function of T cells. Here, we find that LAL is essential for donor T cells to induce GVHD in murine models of allo-HCT. Specifically, LAL is required for donor T cell survival, differentiation, and alloreactivity in GVHD target organs, but not in lymphoid organs. LAL induces the differentiation of donor T cells toward GVHD pathogenic Th1/Tc1 and Th17 while suppressing regulatory T cell generation. LAL-/- T cells succumb to oxidative stress and become anergic in target organs. Pharmacologically targeting LAL effectively prevents GVHD development while preserving the GVL activity. Thus, the present study reveals the role of LAL in T cell alloresponse and pathogenicity and validates LAL as a target for controlling GVHD and tumor relapse after allo-HCT.
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    MECHANISM OF ORLISTAT HYDROLYSIS BY FATTY ACID SYNTHASE THIOESTERASE
    (Office of the Vice Chancellor for Research, 2012-04-13) Liu, Jing-Yuan; Zhang, Jian-Ting
    Fatty acid synthase (FASN) is the sole protein capable of de novo synthesis of free fatty acids. The fatty acid synthesis cycle begins with the condensa-tion of acetyl-CoA and malonyl-CoA, and continues with the elongation of the fatty acid chain, which is tethered to an acyl carrier protein domain (ACP), via a repeating cycle. At the end of elongation, the thioesterase (TE) domain of FASN cleaves the bond between the fatty acid and ACP, releasing the fatty acid. FASN has been found to be over-expressed in a wide variety of human cancers, and this over-expression is correlated to a higher meta-static potential and poorer prognosis in cancer patients. Orlistat, an FDA ap-proved drug for obesity treatment, is a compound found to reversibly inhibit FASN TE by covalently binding to the active site serine within the TE domain. In crystal structure studies, a hydrolyzed form of orlistat can also be ob-served in the active site of TE, demonstrating that orlistat is not a stable in-hibitor of FASN. In this study, we examined the mechanism of orlistat hy-drolysis within the TE domain of FASN using molecular dynamics simula-tions. We found that the hexanoyl tail of orlistat is capable of shifting while covalently bound to the active site serine, and that this shift is accompanied by the destabilization of a hydrogen bond that exists between a hydroxyl moiety of orlistat and the active site histidine, allowing a catalytic water molecule to enter the active site with the proper orientation for catalysis of the covalent bond between orlistat and serine. These findings suggest that the hexanoyl tail of orlistat plays an important role in its hydrolysis and may guide the future design of new inhibitors that target the TE domain of FASN with greater endurance for potential use in the treatment of cancer.
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    Molecular mechanism of orlistat hydrolysis by the thioesterase of human fatty acid synthase for targeted drug discovery
    (2014) Miller, Valerie Fako; Zhang, Jian-Ting; Jerde, Travis J.; Liu, Jing-Yuan; Pflug, Beth R.; Pollok, Karen E.; Safa, Ahmad R.
    Fatty acid synthase (FASN) is over-expressed in many cancers, and novel inhibitors that target FASN may find use in the treatment of cancers. It has been shown that orlistat, an FDA approved drug for weight loss, inhibits the thioesterase (TE) of FASN, but can be hydrolyzed by TE. To understand the mechanisms of TE action and for designing better FASN inhibitors, I examined the mechanism of orlistat hydrolysis by TE using molecular dynamics simulations. I found that the hexyl tail of orlistat undergoes a conformational transition, destabilizing a hydrogen bond that forms between orlistat and the active site histidine. A water molecule can then hydrogen bond with histidine and become activated to hydrolyze orlistat. These findings suggest that rational design of inhibitors that block hexyl tail transition may lead to a more potent TE inhibitor. To search for novel inhibitors of TE, I performed virtual DOCK screening of FDA approved drugs followed by a fluorogenic assay using recombinant TE protein and found that proton pump inhibitors (PPIs) can competitively inhibit TE. PPIs, which are used for the treatment of gastroesophageal reflux and peptic ulcers, work to decrease gastric acid production by binding irreversibly with gastric hydrogen potassium ATPase in the stomach. Recently, PPIs have been reported to reduce drug resistance in cancer cells when used in combination with chemotherapeutics, although the mechanism of resistance reduction is unknown. Further investigation showed that PPIs are able to decrease FASN activity and cancer cell proliferation in a dose-dependent manner. These findings provide new evidence that FDA approved PPIs may synergistically suppress cancer cells by inhibiting TE of FASN and suggests that the use of PPIs in combinational therapies for the treatment of many types of cancer, including pancreatic cancer, warrants further investigation.