Identification of Purple Acid Phosphatase Inhibitors by Fragment-Based Screening: Promising New Leads for Osteoporosis Therapeutics

Authors

  • Daniel Feder,

    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia
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  • Waleed M. Hussein,

    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia
    2. Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy, Helwan University, Ein Helwan, Helwan, Egypt
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  • Daniel J. Clayton,

    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia
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  • Meng-Wei Kan,

    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia
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  • Gerhard Schenk,

    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia
    2. Department of Chemistry, National University of Ireland – Maynooth, Maynooth, Co. Kildare, Ireland
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  • Ross P. McGeary,

    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia
    2. School of Pharmacy, The University of Queensland, Brisbane, Qld 4072, Australia
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  • Luke W. Guddat

    Corresponding author
    1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia
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Corresponding author: Luke W. Guddat, luke.guddat@uq.edu.au

Abstract

Purple acid phosphatases are metalloenzymes found in animals, plants and fungi. They possess a binuclear metal centre to catalyse the hydrolysis of phosphate esters and anhydrides under acidic conditions. In humans, elevated purple acid phosphatases levels in sera are correlated with the progression of osteoporosis and metabolic bone malignancies, making this enzyme a target for the development of new chemotherapeutics to treat bone-related illnesses. To date, little progress has been achieved towards the design of specific and potent inhibitors of this enzyme that have drug-like properties. Here, we have undertaken a fragment-based screening approach using a 500-compound library identifying three inhibitors of purple acid phosphatases with Ki values in the 30–60 μm range. Ligand efficiency values are 0.39–0.44 kcal/mol per heavy atom. X-ray crystal structures of these compounds in complex with a plant purple acid phosphatases (2.3–2.7 Å resolution) have been determined and show that all bind in the active site within contact of the binuclear centre. For one of these compounds, the phenyl ring is positioned within 3.5 Å of the binuclear centre. Docking simulations indicate that the three compounds fit into the active site of human purple acid phosphatases. These studies open the way to the design of more potent and selective inhibitors of purple acid phosphatases that can be tested as anti-osteoporotic drug leads.

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