ABSTRACT
Autotaxin (ATX), or ecto-nucleotide pyrophosphatase/phosphodiesterase 2 (ENPP2), is a secreted lysophospholipase D that hydrolyses lysophosphatidylcholine into the lipid mediator lysophosphatidic acid (LPA), a mitogen and chemoattractant for many cell types. ATX has been implicated in tumour progression and inflammation, and might serve as a biomarker. Here we describe the development of a fluorescent activity-based probe that covalently binds to the active site of ATX. The probe consists of a lysophospholipid-based backbone linked to a trapping moiety that becomes reactive after phosphate ester hydrolysis, and a Cy5 fluorescent dye to allow visualisation of active ATX. The probe reacts specifically with the three known isoforms of ATX, it competes with small-molecule inhibitors for binding to ATX and allows ATX activity in plasma to be determined. Our activity-based reporter will be useful for monitoring ATX activity in biological fluids and for inhibitor screening.
Subject(s)
Enzyme Inhibitors/chemistry , Fluorescent Dyes/chemistry , Multienzyme Complexes/metabolism , Phosphodiesterase I/metabolism , Pyrophosphatases/metabolism , Catalytic Domain , Enzyme Inhibitors/chemical synthesis , Fluorescent Dyes/chemical synthesis , Humans , Multienzyme Complexes/antagonists & inhibitors , Multienzyme Complexes/genetics , Phosphodiesterase I/antagonists & inhibitors , Phosphodiesterase I/genetics , Phosphoric Diester Hydrolases , Protein Binding , Protein Isoforms/antagonists & inhibitors , Protein Isoforms/genetics , Protein Isoforms/metabolism , Pyrophosphatases/antagonists & inhibitors , Pyrophosphatases/genetics , Recombinant Proteins/antagonists & inhibitors , Recombinant Proteins/genetics , Recombinant Proteins/metabolismABSTRACT
Autotaxin (ATX) is an extracellular enzyme that hydrolyzes lysophosphatidylcholine (LPC) to produce the lipid mediator lysophosphatidic acid (LPA). The ATX-LPA signaling axis has been implicated in diverse physiological and pathological processes, including vascular development, inflammation, fibrotic disease, and tumor progression. Therefore, targeting ATX with small molecule inhibitors is an attractive therapeutic strategy. We recently reported that 2,4-thiazolidinediones inhibit ATX activity in the micromolar range. Interestingly, inhibitory potency was dramatically increased by introduction of a boronic acid moiety, designed to target the active site threonine in ATX. Here we report on the discovery and further optimization of boronic acid based ATX inhibitors. The most potent of these compounds inhibits ATX-mediated LPC hydrolysis in the nanomolar range (IC(50) = 6 nM). The finding that ATX can be targeted by boronic acids may aid the development of ATX inhibitors for therapeutic use.
Subject(s)
Boronic Acids/chemical synthesis , Boronic Acids/pharmacology , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/pharmacology , Multienzyme Complexes/antagonists & inhibitors , Phosphodiesterase I/antagonists & inhibitors , Pyrophosphatases/antagonists & inhibitors , Boronic Acids/chemistry , Boronic Acids/metabolism , Cell Line , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/metabolism , Humans , Inhibitory Concentration 50 , Lysophosphatidylcholines/metabolism , Magnetic Resonance Spectroscopy , Mass Spectrometry , Multienzyme Complexes/metabolism , Phosphodiesterase I/metabolism , Phosphoric Diester Hydrolases , Pyrophosphatases/metabolism , Signal Transduction , Structure-Activity Relationship , Thiazolidinediones/chemical synthesis , Thiazolidinediones/chemistry , Thiazolidinediones/metabolism , Thiazolidinediones/pharmacologyABSTRACT
Autotaxin (ATX) is a secreted nucleotide pyrophosphatase/phosphodiesterase that functions as a lysophospholipase D to produce the lipid mediator lysophosphatidic acid (LPA), a mitogen, chemoattractant, and survival factor for many cell types. The ATX-LPA signaling axis has been implicated in angiogenesis, chronic inflammation, fibrotic diseases and tumor progression, making this system an attractive target for therapy. However, potent and selective nonlipid inhibitors of ATX are currently not available. By screening a chemical library, we have identified thiazolidinediones that selectively inhibit ATX-mediated LPA production both in vitro and in vivo. Inhibitor potency was approximately 100-fold increased (IC(50) approximately 30 nM) after the incorporation of a boronic acid moiety, designed to target the active-site threonine (T210) in ATX. Intravenous injection of this inhibitor into mice resulted in a surprisingly rapid decrease in plasma LPA levels, indicating that turnover of LPA in the circulation is much more dynamic than previously appreciated. Thus, boronic acid-based small molecules hold promise as candidate drugs to target ATX.
Subject(s)
Boronic Acids/metabolism , Lysophospholipids/metabolism , Animals , Cell Line, Tumor , Cell Movement , Drug Design , Drug Evaluation, Preclinical/methods , Glycoproteins/chemistry , Humans , Inhibitory Concentration 50 , Lipids/chemistry , Male , Mice , Multienzyme Complexes/metabolism , Phosphodiesterase I/metabolism , Phosphoric Diester Hydrolases/chemistry , Pyrophosphatases/metabolism , Signal Transduction , Thiazolidinediones/chemistryABSTRACT
The purpose of the present study was to evaluate the performance of various parametric reference tissue models for quantification of [11C]PIB studies. Several models with and without fixing the reference tissue efflux rate constant (k'(2)) were investigated using both simulations and clinical data. The following parametric methods were evaluated: receptor parametric mapping (basis function implementation of the simplified reference tissue model with and without fixed k'(2)), reference Logan, and several multi-linear reference tissue methods (again with and without fixed k'(2)). In addition, standardised uptake value ratios with cerebellum (SUV(r)) were evaluated. Simulations were used to assess the effects of variation in flow (R(1)), fractional blood volume (V(b)) and binding potential (BP(ND)) itself on precision and accuracy of parametric BP(ND). For clinical studies, most parametric methods showed comparable performance, with poorest results for SUV(r). Best performance was obtained for receptor parametric mapping (RPM2) and one of the multi-linear reference tissue models (MRTM2), both with fixed k'(2): BP(ND) outcome was less affected by noise and the images showed better contrast than other tested methods. RPM2 and MRTM2 also provided best accuracy and precision in the simulation studies and are therefore the methods of choice for parametric analysis of clinical [11C]PIB studies.
Subject(s)
Alzheimer Disease/diagnostic imaging , Alzheimer Disease/metabolism , Benzothiazoles/pharmacokinetics , Brain/diagnostic imaging , Brain/metabolism , Models, Biological , Aged , Aniline Compounds , Computer Simulation , Female , Humans , Image Interpretation, Computer-Assisted/methods , Male , Middle Aged , Positron-Emission Tomography/methods , Radiopharmaceuticals/pharmacokinetics , Reproducibility of Results , Sensitivity and Specificity , ThiazolesABSTRACT
With proteasome inhibitors in use in the clinic for the treatment of multiple myeloma and with clinical trials in progress investigating the treatment of a variety of hematologic and solid malignancies, accurate methods that allow profiling of proteasome inhibitor specificity and efficacy in patients are in demand. Here, we describe the development, full biochemical validation, and comparison of fluorescent proteasome activity reporters that can be used to profile proteasome activities in living cells with high sensitivity. Seven of the synthesized probes tested label proteasomes in lysates, although the fluorescent dye used affects their specificity. Two differentially labeled probes tested are suitable for studying proteasome activity in living cells by gel-based assays, by confocal laser scanning microscopy, and by flow cytometry. We established methods using these fluorescent reporters to profile proteasome activity in different mouse tissues, carefully avoiding postlysis artifacts, and we show that proteasome subunit activity is regulated in an organ-specific manner. The techniques described here could be used to study in vivo pharmacological properties of proteasome inhibitors.
Subject(s)
Fluorescent Dyes , Proteasome Endopeptidase Complex/metabolism , Animals , Cell Line, Tumor , Cell Survival , Fluorescent Dyes/chemistry , Humans , Mice , Molecular Structure , Protein Subunits/metabolismABSTRACT
The objective of this investigation was to determine the functional role of adenosine receptor subtypes in the regulation of blood-brain barrier (BBB) permeability. The presence of the equilibrative es and ei nucleoside transporters at the BBB was also determined. Studies were conducted in an experimental in vitro BBB model comprising bovine brain capillary endothelial cells (BCECs) and rat astrocytes (RAs). The presence of the receptors and transporters was investigated by a combination of RT-PCR and radioligand binding assays. Changes in paracellular permeability were investigated on basis of changes in trans-endothelial-electrical-resistance (TEER) and transport of paracellular markers. In BCECs the presence of A(2A) and A(3) receptors and the es nucleoside transporter was demonstrated. The A(1) receptor was absent, while the presence of the A(2B) receptor and the ei nucleoside transporter remained uncertain. In RAs the presence of all four receptor subtypes and the es and ei nucleoside transporters was demonstrated. Upon application of selective agonists no significant changes in TEER or the transport of the paracellular markers were observed. The functional role of adenosine receptor subtypes in regulating the paracellular permeability of the BBB is probably small. It is unlikely therefore that the BBB transport of synthetic adenosine analogues is modified by permeability changes. The es nucleoside transporter might play a role in the BBB transport of synthetic adenosine analogues.
Subject(s)
Adenosine/metabolism , Blood-Brain Barrier/physiology , Receptors, Purinergic P1/metabolism , Adenosine/analogs & derivatives , Animals , Astrocytes/metabolism , Biological Transport/physiology , Brain/blood supply , Capillaries/cytology , Cattle , Cell Membrane Permeability , Cells, Cultured , Coculture Techniques , Drug Design , Endothelium, Vascular/metabolism , Humans , Models, Biological , Nucleoside Transport Proteins/metabolism , Radioligand Assay , Rats , Reverse Transcriptase Polymerase Chain Reaction , Species SpecificityABSTRACT
Novel 2,8-disubstituted adenosine derivatives were synthesized in good overall yields starting from 2-iodoadenosine. Binding affinities were determined for rat adenosine A(1) and A(2A) receptors and human A(3) receptors. Some compounds displayed good adenosine A(2A) receptor affinities, with most of the 2-(1-hexynyl)- and 2-[(E)-1-hexenyl]-substituted derivatives having K(i) values in the nanomolar range. Although the introduction of an 8-alkylamino substituents decreased the affinity for the adenosine A(2A) receptor somewhat, the selectivity for this receptor compared to A(3) was improved significantly. The 8-methylamino (12) and 8-propylamino (14) derivatives of 2-(1-hexynyl)adenosine (3), showed reasonable A(2A) receptor affinities with K(i) values of 115 and 82nM, respectively, and were 49- and 26-fold selective for the adenosine A(2A) receptor compared to the A(3) receptor. The compounds were also evaluated for their ability to stimulate the cAMP production in CHO cells expressing the human adenosine A(2A) receptor. 2-(1-Hexynyl)adenosine (3) and 2-[(E)-1-hexenyl]adenosine (4) both showed submaximal levels of produced cAMP, compared to the reference full agonist CGS 21680, and thus behaved as partial agonists. Most 8-alkylamino-substituted derivatives of 3, displayed similar cAMP production as 3, and behaved as partial agonists as well. Introduction of alkylamino groups at the 8-position of 4, showed a slight reduction of the efficacy compared to 4, and these compounds were partial agonists also.
Subject(s)
Adenosine A2 Receptor Agonists , Adenosine/analogs & derivatives , Adenosine/chemical synthesis , Adenosine/pharmacology , Adenosine A1 Receptor Agonists , Animals , Brain/metabolism , CHO Cells/drug effects , Cricetinae , Cyclic AMP/analysis , Cyclic AMP/biosynthesis , Humans , Methylamines/chemistry , Methylamines/pharmacology , Models, Chemical , Propylamines/chemistry , Propylamines/pharmacology , Radioligand Assay , Rats , Structure-Activity RelationshipABSTRACT
Novel 2,5'-disubstituted adenosine derivatives were synthesized in good overall yields starting from commercially available guanosine. Binding affinities were determined for rat adenosine A(1) and A(2A) receptors and human A(3) receptors. E(max) values were determined for the stimulation or inhibition of cAMP production in CHO cells expressing human adenosine A(2A) (EC(50) values as well) or A(3) receptors, respectively. The compounds displayed affinities in the nanomolar range for both the adenosine A(2A) and A(3) receptor, without substantial preference for either receptor. The derivatives with a 2-(1-hexynyl) group had the highest affinities for both receptors; compound 4 (2-(1-hexynyl)adenosine) had the highest affinity for the adenosine A(2A) receptor with a K(i) value of 6 nM (A(3)/A(2A) selectivity ratio of approximately 3), whereas compound 37 (2-(1-hexynyl)-5'-S-methyl-5'-thioadenosine) had the highest affinity for the adenosine A(3) receptor with a K(i) value of 15 nM (A(2A)/A(3) selectivity ratio of 4). In general, compounds with a relatively small 5'-S-alkyl-5'-thio substituent (methyl-5'-thio) displayed the highest affinities for both the adenosine A(2A) and A(3) receptor; the larger ones (n- or i-propyl-5'-thio) increased the selectivity for the adenosine A(3) receptor. The novel compounds were also evaluated in cAMP assays for their (partial) agonistic behavior. Overall, the disubstituted derivatives behaved as partial agonists for both the adenosine A(2A) and A(3) receptor. The compounds showed somewhat higher intrinsic activities on the adenosine A(2A) receptor than on the A(3) receptor. Compounds 37, 40 and 45, 48, with either a 5'-S-methyl-5'-thio or a 5'-S-i-propyl-5'-thio substituent had the lowest intrinsic activities on the adenosine A(2A) receptor. For the A(3) receptor, compounds 34, 35, 38, 39, and 46, 47, with a 5'-S-ethyl-5'-thio or a 5'-S-n-propyl-5'-thio substituent had the lowest intrinsic activities.