Structure-activity studies of PTPRD phosphatase inhibitors identify a 7-cyclopentymethoxy illudalic acid analog candidate for development

The mechanism of covalent inhibition of LAR phosphatase by illudalic acid

Leukocyte antigen-related (LAR) phosphatase is a receptor-type protein tyrosine phosphatase involved in cellular signaling and associated with human disease including cancer and metabolic disorders. Selective inhibition of LAR phosphatase activity by well characterized and well validated small molecules would provide key insights into the roles of LAR phosphatase in health and disease, but identifying selective inhibitors of LAR phosphatase activity has been challenging. Recently, we described potent and selective inhibition of LAR phosphatase activity by the fungal natural product illudalic acid. Here we provide a detailed biochemical characterization of the adduct formed between LAR phosphatase and illudalic acid. A mass spectrometric analysis indicates that two cysteine residues are covalently labeled by illudalic acid and a related analog. Mutational analysis supports the hypothesis that inhibition of LAR phosphatase activity is due primarily to the adduct with the catalytic cysteine residue. A computational study suggests potential interactions between the illudalic acid moiety and the enzyme active site. Taken together, these data offer novel insights into the mechanism of inhibition of LAR phosphatase activity by illudalic acid.

Selecting the appropriate hurdles and endpoints for pentilludin, a novel antiaddiction pharmacotherapeutic targeting the receptor type protein tyrosine phosphatase D

Substance use disorders provide challenges for development of effective medications. Use of abused substances is likely initiated, sustained and "quit" by complex brain and pharmacological mechanisms that have both genetic and environmental determinants. Medical utilities of prescribed stimulants and opioids provide complex challenges for prevention: how can we minimize their contribution to substance use disorders while retaining medical benefits for pain, restless leg syndrome, attention deficit hyperactivity disorder, narcolepsy and other indications. Data required to support assessments of reduced abuse liability and resulting regulatory scheduling differs from information required to support licensing of novel prophylactic or therapeutic anti-addiction medications, adding further complexity and challenges. I describe some of these challenges in the context of our current efforts to develop pentilludin as a novel anti-addiction therapeutic for a target that is strongly supported by human and mouse genetic and pharmacologic studies, the receptor type protein tyrosine phosphatase D (PTPRD).

Substrate-selective positive allosteric modulation of PTPRD’s phosphatase by flavonols

The receptor type protein tyrosine phosphatase D (PTPRD) is expressed by neurons and implicated in interesting phenotypes that include reward from addictive substances, restless leg syndrome and neurofibrillary tangle densities in Alzheimer's disease (AD-NFTs). However, the brain phosphotyrosine phosphoprotein (PTPP) substrates for PTPRD's phosphatase have not been clearly defined. Although we have identified small molecule inhibitors of PTPRD's phosphatase that are candidates for reducing reward from addictive substances, no positive allosteric modulators of this phosphatase that might be candidates for reducing AD-NFTs have been reported. We now report identification of candidate brain substrates for PTPRD based on their increased phosphorylation in knockout vs wildtype animals, coexpression with PTPRD in neuronal subtypes and brisk dephosphorylation by recombinant human PTPRD phosphatase. We also report discovery that quercetin and other flavonols, though not closely-related flavones, enhance rates of PTPRD's dephosphorylation of a group of these candidate substrate PTPPs but not others. This substrate-selective positive allosteric modulation provides a novel pharmacological action. Flavonol-mediated increases in PTPRD's dephosphorylation of the GSK3 β and α kinases that hyperphosphorylate tau, the major component of AD-NFTs, could help to explain recent data concerning genetic and dietary impacts on Alzheimer's disease.