A Fluorescence Polarization Activity-Based Protein Profiling Assay in the Discovery of Potent, Selective Inhibitors for Human Nonlysosomal Glucosylceramidase

Human nonlysosomal glucosylceramidase (GBA2) is one of several enzymes that controls levels of glycolipids and whose activity is linked to several human disease states. There is a major need to design or discover selective GBA2 inhibitors both as chemical tools and as potential therapeutic agents. Here, we describe the development of a fluorescence polarization activity-based protein profiling (FluoPol-ABPP) assay for the rapid identification, from a 350+ library of iminosugars, of GBA2 inhibitors. A focused library is generated based on leads from the FluoPol-ABPP screen and assessed on GBA2 selectivity offset against the other glucosylceramide metabolizing enzymes, glucosylceramide synthase (GCS), lysosomal glucosylceramidase (GBA), and the cytosolic retaining β-glucosidase, GBA3. Our work, yielding potent and selective GBA2 inhibitors, also provides a roadmap for the development of high-throughput assays for identifying retaining glycosidase inhibitors by FluoPol-ABPP on cell extracts containing recombinant, overexpressed glycosidase as the easily accessible enzyme source

Design, Synthesis and Structural Analysis of Glucocerebrosidase Imaging Agents

Gaucher disease (GD) is a lysosomal storage disorder caused by inherited deficiencies in β-glucocerebrosidase (GBA). Current treatments require rapid disease diagnosis and a means of monitoring therapeutic efficacy, both of which may be supported by the use of GBA-targeting activity-based probes (ABPs). Here, we report the synthesis and structural analysis of a range of cyclophellitol epoxide and aziridine inhibitors and ABPs for GBA. We demonstrate their covalent mechanism-based mode of action and uncover binding of the new N- functionalised aziridines to the ligand binding cleft. These inhibitors became scaffolds for the development of ABPs; the O6-fluorescent tags of which bind in an allosteric site at the dimer interface. Considering GBA’s preference for O6- and N -functionalised reagents, we synthesised a bi-functional aziridine ABP which we hoped would offer a more powerful imaging agent. Whilst this ABP binds to two unique active site clefts of GBA, no further benefit in potency was achieved over our first generation ABPs. Nevertheless, such ABPs should serve useful in the study of GBA in relation to GD and inform the design of future probes

Synthesis of 6-Hydroxysphingosine and alpha-Hydroxy Ceramide Using a Cross-Metathesis Strategy

In this paper, a new synthetic route toward 6-hydroxysphingosine and alpha-hydroxy ceramide is described. The synthesis employs a cross-metathesis to unite a sphingosine head allylic alcohol with a long-chain fatty acid alkene that also bears an allylic alcohol group. To allow for a productive CM coupling, the sphingosine head allylic alcohol was protected with a cyclic carbonate moiety and a reactive CM catalyst system, consisting of Grubbs II catalyst and CuI, was employe

Bis-pyridylethenyl benzene as novel backbone for amyloid-β binding compounds

Detection of cerebral β-amyloid (Aβ) by targeted contrast agents is of great interest for in vivo diagnosis of Alzheimer's disease (AD). Partly because of their planar structure several bis-styrylbenzenes have been previously reported as potential Aβ imaging agents. However, these compounds are relatively hydrophobic, which likely limits their in vivo potential. Based on their structures, we hypothesized that less hydrophobic bis-pyridylethenylbenzenes may also label amyloid. We synthesized several bis-pyridylethenylbenzenes and tested whether these compounds indeed display improved solubility and lower LogP values, and studied their fluorescent properties and Aβ binding characteristics. Bis-pyridylethenylbenzenes showed a clear affinity for Aβ plaques on both human and murine AD brain sections. Competitive binding experiments suggested a different binding site than Chrysamine G, a well-known stain for amyloid. With a LogP value between 3 and 5, most bis-pyridylethenylbenzenes were able to enter the brain and label murine amyloid in vivo with the bis(4-pyridylethenyl)benzenes showing the most favorable characteristics. In conclusion, the presented results suggest that bis-pyridylethenylbenzene may serve as a novel backbone for amyloid imaging agents

Identification and development of biphenyl substituted iminosugars as improved dual glucosylceramide synthase/neutral glucosylceramidase inhibitors

This work details the evaluation of a number of N-alkylated deoxynojirimycin derivatives on their merits as dual glucosylceramide synthase/neutral glucosylceramidase inhibitors. Building on our previous work, we synthesized a series of D-gluco and L-ido-configured iminosugars N-modified with a variety of hydrophobic functional groups. We found that iminosugars featuring N-pentyloxymethylaryl substituents are considerably more potent inhibitors of glucosylceramide synthase than their aliphatic counterparts. In a next optimization round, we explored a series of biphenyl-substituted iminosugars of both configurations (D-gluco and L-ido) with the aim to introduce structural features known to confer metabolic stability to drug-like molecules. From these series, two sets of molecules emerge as lead series for further profiling. Biphenyl-substituted L-ido-configured deoxynojirimycin derivatives are selective for glucosylceramidase and the nonlysosomal glucosylceramidase, and we consider these as leads for the treatment of neuropathological lysosomal storage disorders. Their D-gluco-counterparts are also potent inhibitors of intestinal glycosidases, and because of this characteristic, we regard these as the prime candidates for type 2 diabetes therapeutic

Synthesis of 6‑Hydroxysphingosine and α‑Hydroxy Ceramide Using a Cross-Metathesis Strategy

In this paper, a new synthetic route toward 6-hydroxysphingosine and α-hydroxy ceramide is described. The synthesis employs a cross-metathesis to unite a sphingosine head allylic alcohol with a long-chain fatty acid alkene that also bears an allylic alcohol group. To allow for a productive CM coupling, the sphingosine head allylic alcohol was protected with a cyclic carbonate moiety and a reactive CM catalyst system, consisting of Grubbs II catalyst and CuI, was employed

In vitro and in vivo comparative and competitive activity-based protein profiling of GH29 alpha-L-fucosidases

GH29 alpha-L-fucosidases catalyze the hydrolysis of alpha-L-fucosidic linkages. Deficiency in human lysosomal alpha-L-fucosidase (FUCA1) leads to the recessively inherited disorder, fucosidosis. Herein we describe the development of fucopyranose-configured cyclophellitol aziridines as activity-based probes (ABPs) for selective in vitro and in vivo labeling of GH29 alpha-L-fucosidases from bacteria, mice and man. Crystallographic analysis on bacterial alpha-L-fucosidase confirms that the ABPs act by covalent modification of the active site nucleophile. Competitive activity-based protein profiling identified L-fuconojirimycin as the single GH29 alpha-L-fucosidase inhibitor from eight configurational isomer

Identification and Development of Biphenyl Substituted Iminosugars as Improved Dual Glucosylceramide Synthase/Neutral Glucosylceramidase Inhibitors

This work details the evaluation of a number of N-alkylated deoxynojirimycin derivatives on their merits as dual glucosylceramide synthase/neutral glucosylceramidase inhibitors. Building on our previous work, we synthesized a series of d-<i>gluco</i> and l-<i>ido</i>-configured iminosugars N-modified with a variety of hydrophobic functional groups. We found that iminosugars featuring <i>N</i>-pentyloxy­methylaryl substituents are considerably more potent inhibitors of glucosylceramide synthase than their aliphatic counterparts. In a next optimization round, we explored a series of biphenyl-substituted iminosugars of both configurations (d-<i>gluco</i> and l-<i>ido</i>) with the aim to introduce structural features known to confer metabolic stability to drug-like molecules. From these series, two sets of molecules emerge as lead series for further profiling. Biphenyl-substituted l-<i>ido</i>-configured deoxynojirimycin derivatives are selective for glucosylceramidase and the nonlysosomal glucosylceramidase, and we consider these as leads for the treatment of neuropathological lysosomal storage disorders. Their d-<i>gluco</i>-counterparts are also potent inhibitors of intestinal glycosidases, and because of this characteristic, we regard these as the prime candidates for type 2 diabetes therapeutics