PDA-Based Glyconanomicelles for Hepatocellular Carcinoma Cells Active Targeting Via Mannose and Asialoglycoprotein Receptors.

Hepatocellular carcinoma (HCC) is the sixth most common neoplasia and the fourth most common cause of cancer-related mortality worldwide. Sorafenib is the first-line molecular therapy for patients in an advanced stage of HCC. However, the recommended clinical dose of Sorafenib is associated with several complications, which derive from its lack of cell specificity and its very low water solubility. To circumvent these drawbacks, in the present study we developed two sugar-coated polydiacetylene-based nanomicelles-Sorafenib carriers targeting mannose and asialoglycoprotein receptors (MR and ASGPR, respectively). The strategies allowed the inducement of apoptosis and reduction of cell proliferation at a nanomolar, instead of micromolar, range in liver cancer cells. The study showed that, contrary to literature data, Sorafenib included into the pMicMan (Man = mannose) vector (targeting MR) is more efficient than pMicGal (Gal = galactose) (targeting ASGPR). Indeed, pMicMan increased the endosomal incorporation with an increased intracellular Sorafenib concentration that induced apoptosis and reduced cell proliferation at a low concentration range (10-20 nM).

Unexpected loss of stereoselectivity in glycosylation reactions during the synthesis of chondroitin sulfate oligosaccharides.

Here, we present an exploratory study on the fluorous-assisted synthesis of chondroitin sulfate (CS) oligosaccharides. Following this approach, a CS tetrasaccharide was prepared. However, in contrast to our previous results, a significant loss of ß-selectivity was observed in [2 + 2] glycosylations involving N-trifluoroacetyl-protected D-galactosamine donors and D-glucuronic acid (GlcA) acceptors. These results, together with those obtained from experiments employing model monosaccharide building blocks, highlight the impact of the glycosyl acceptor structure on the stereoselectivity of glycosylation reactions. Our study provides useful data about the substitution pattern of GlcA units for the efficient synthesis of CS oligomers.

Probing the Inhibitor versus Chaperone Properties of sp²-Iminosugars towards Human ß-Glucocerebrosidase: A Picomolar Chaperone for Gaucher Disease.

A series of sp²-iminosugar glycomimetics differing in the reducing or nonreducing character, the configurational pattern (d-gluco or l-ido), the architecture of the glycone skeleton, and the nature of the nonglycone substituent has been synthesized and assayed for their inhibition properties towards commercial glycosidases. On the basis of their affinity and selectivity towards GH1 ß-glucosidases, reducing and nonreducing bicyclic derivatives having a hydroxylation profile of structural complementarity with d-glucose and incorporating an N'-octyl-isourea or -isothiourea segment were selected for further evaluation of their inhibitory/chaperoning potential against human glucocerebrosidase (GCase). The 1-deoxynojirimycin (DNJ)-related nonreducing conjugates behaved as stronger GCase inhibitors than the reducing counterparts and exhibited potent chaperoning capabilities in Gaucher fibroblasts hosting the neuronopathic G188S/G183W mutation, the isothiourea derivative being indeed one of the most efficient chaperone candidates reported up to date (70% activity enhancement at 20 pM). At their optimal concentration, the four selected compounds promoted mutant GCase activity enhancements over 3-fold; yet, the inhibitor/chaperoning balance became unfavorable at much lower concentration for nonreducing as compared to reducing derivatives.

Inhibitor versus chaperone behaviour of d-fagomine, DAB and LAB sp(2)-iminosugar conjugates against glycosidases: A structure-activity relationship study in Gaucher fibroblasts.

A library of sp(2)-iminosugar conjugates derived from the piperidine iminosugar d-fagomine and the enantiomeric pyrrolidine iminosugars DAB and LAB has been generated in only two steps involving direct coupling of the fully unprotected polyhydroxylated heterocycles with isothiocyanates, to give monocyclic thiourea adducts, and further intramolecular nucleophilic displacement of the δ-located primary hydroxyl group by the thiocarbonyl sulphur atom, affording bicyclic isothioureas. These transformations led to a dramatic shift in the inhibitory selectivity from α- to ß-glucosidases, with inhibition potencies that depended strongly on the nature of the aglycone-type moiety in the conjugates. Some of the new derivatives behaved as potent inhibitors of human ß-glucocerebrosidase (GCase), the lysosomal enzyme whose dysfunction is responsible for Gaucher disease. Moreover, GCase inhibition was 10-fold weaker at pH 5 as compared to pH 7, which is generally considered as a good property for pharmacological chaperones. Surprisingly, most of the compounds strongly inhibited GCase in wild type fibroblasts at rather low concentrations, showing an unfavourable chaperone/inhibitor balance on disease-associated GCase mutants in cellulo. A structure-activity relationship analysis points to the need for keeping a contiguous triol system in the glycone moiety of the conjugates to elicit a chaperone effect. In any case, the results reported here represent a proof of concept of the utmost importance of implementing diversity-oriented strategies for the identification and optimization of potent and specific glycosidase inhibitors and chaperones.

pH-Responsive Pharmacological Chaperones for Rescuing Mutant Glycosidases.

A general approach is reported for the design of small-molecule competitive inhibitors of lysosomal glycosidases programmed to 1) promote correct folding of mutant enzymes at the endoplasmic reticulum, 2) facilitate trafficking, and 3) undergo dissociation and self-inactivation at the lysosome. The strategy is based on the incorporation of an orthoester segment into iminosugar conjugates to switch the nature of the aglycone moiety from hydrophobic to hydrophilic in the pH 7 to pH 5 window, which has a dramatic effect on the enzyme binding affinity. As a proof of concept, new highly pH-responsive glycomimetics targeting human glucocerebrosidase or α-galactosidase with strong potential as pharmacological chaperones for Gaucher or Fabry disease, respectively, were developed.

Stereoselective synthesis of 2-acetamido-1,2-dideoxynojirimycin (DNJNAc) and ureido-DNJNAc derivatives as new hexosaminidase inhibitors.

2-Acetamido-1,2-dideoxyiminosugars are selective and potent inhibitors of hexosaminidases and therefore show high therapeutic potential for the treatment of various diseases, including several lysosomal storage disorders. A stereoselective synthesis of 2-acetamido-1,2-dideoxynojirimycin (DNJNAc), the iminosugar analog of N-acetylglucosamine, with a high overall yield is here described. This novel procedure further allowed accessing ureido-DNJNAc conjugates through derivatization of the endocyclic amine on a key pivotal intermediate. Remarkably, some of the ureido-DNJNAc representatives behaved as potent and selective inhibitors of ß-hexosaminidases, including the human enzyme, being the first examples of neutral sp(2)-iminosugar-type inhibitors reported for these enzymes. Moreover, the amphiphilic character of the new ureido-DNJNAc is expected to confer better drug-like properties.

Fluorinated hydroxypiperidines as selective ß-glucosidase inhibitors.

A new series of fluoroallylamines derived from hydroxypiperidines was prepared and evaluated against various glycosidases. The short synthesis of target molecules involved the modified Julia reaction between aldehydes and functionalized fluoroaminosulfones. Biological studies revealed good and selective ß-glucosidase inhibition in the micromolar range for two compounds, while the non-fluorinated analogue of the most active compound was selective towards α-glucosidase.

Molecular basis of 1-deoxygalactonojirimycin arylthiourea binding to human α-galactosidase a: pharmacological chaperoning efficacy on Fabry disease mutants.

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by mutations in the GLA gene often leading to missense α-galactosidase A (α-Gal A) variants that undergo premature endoplasmic reticulum-associated degradation due to folding defects. We have synthesized and characterized a new family of neutral amphiphilic pharmacological chaperones, namely 1-deoxygalactonojirimycin-arylthioureas (DGJ-ArTs), capable of stabilizing α-Gal A and restoring trafficking. Binding to the enzyme is reinforced by a strong hydrogen bond involving the aryl-N'H thiourea proton and the catalytic aspartic acid acid D231 of α-Gal A, as confirmed by a 2.55 Å resolution cocrystal structure. Selected candidates enhanced α-Gal A activity and ameliorate globotriaosylceramide (Gb3) accumulation and autophagy impairments in FD cell cultures. Moreover, they acted synergistically with the proteostasis regulator 4-phenylbutyric acid, appearing to be promising leads as pharmacological chaperones for FD.

Structural basis of pharmacological chaperoning for human ß-galactosidase.

GM1 gangliosidosis and Morquio B disease are autosomal recessive diseases caused by the defect in the lysosomal ß-galactosidase (ß-Gal), frequently related to misfolding and subsequent endoplasmic reticulum-associated degradation. Pharmacological chaperone (PC) therapy is a newly developed molecular therapeutic approach by using small molecule ligands of the mutant enzyme that are able to promote the correct folding and prevent endoplasmic reticulum-associated degradation and promote trafficking to the lysosome. In this report, we describe the enzymological properties of purified recombinant human ß-Gal(WT) and two representative mutations in GM1 gangliosidosis Japanese patients, ß-Gal(R201C) and ß-Gal(I51T). We have also evaluated the PC effect of two competitive inhibitors of ß-Gal. Moreover, we provide a detailed atomic view of the recognition mechanism of these compounds in comparison with two structurally related analogues. All compounds bind to the active site of ß-Gal with the sugar-mimicking moiety making hydrogen bonds to active site residues. Moreover, the binding affinity, the enzyme selectivity, and the PC potential are strongly affected by the mono- or bicyclic structure of the core as well as the orientation, nature, and length of the exocyclic substituent. These results provide understanding on the mechanism of action of ß-Gal selective chaperoning by newly developed PC compounds.

Iminosugar-based glycopolypeptides: glycosidase inhibition with bioinspired glycoprotein analogue micellar self-assemblies.

Biomimetic nanoparticles prepared by self-assembly of iminosugar-based glycopolypeptides evidenced remarkable multivalency properties when inhibiting α-mannosidase activity. This approach paves the way to obtain biologically active drug delivery systems having glycosidase inhibition potency.

Synthesis of substituted exo-glucals via a modified Julia olefination and identification as selective ß-glucosidase inhibitors.

A series of fluorine and non-fluorine-substituted C-glucosylidenes (exo-glucals) has been synthesized via a modified Julia olefination. The deprotected exo-glucals were prepared in five steps from commercially available d-gluconolactone. The evaluation of this original family of compounds against a panel of glycosidases showed a highly specific in vitro activity towards mammalian ß-glucosidase depending on the double bond substituents.

The multivalent effect in glycosidase inhibition: probing the influence of valency, peripheral ligand structure, and topology with cyclodextrin-based iminosugar click clusters.

In view of recent reports of a strong multivalent effect in glycosidase inhibition, a library of ß-CD-based multivalent iminosugars has been efficiently synthesized by way of Cu(I) -catalyzed azide-alkyne cycloaddition (CuAAC). In combination with the first application of isothermal titration calorimetry (ITC) experiments to the study of multivalent iminosugar-enzyme interactions, the inhibition properties of these click clusters were evaluated on a panel of glycosidases. The structural parameters that were varied include valency, peripheral ligand structure, and topology. The inhibition results obtained with the iminosugar clusters further highlight the importance of multivalency in the inhibition of α-mannosidase. Generally, the evaluated multivalent iminosugars displayed comparable thermodynamic signatures of binding towards α-mannosidase (Jack bean): that is, large negative enthalpies of complexation coupled with small entropies of either sign. In addition, the enthalpy-entropy compensation observed in all tested cases may be attributed to a common mechanism of dissociation for the enzyme-multivalent iminosugar interactions. The measured binding stoichiometries indicated that each iminosugar cluster interacts with no more than one protein molecule.

Stereoselective synthesis of 2-acetamido-1,2-dideoxyallonojirimycin (DAJNAc), a new potent hexosaminidase inhibitor.

A practical synthesis of the previously unreported N-acetyl-D-allosamine glycomimetic DAJNAc is described. The reaction sequence involves Pd-catalyzed allylic substitution by phthalimide in an azaheterobicyclic scaffold as the key step. The new iminosugar resulted in being a stronger ß-N-acetylglucosaminidase (human placenta) competitive inhibitor than the D-gluco (DNJNAc) and D-galacto (DGJNAc) stereoisomers.

A bicyclic 1-deoxygalactonojirimycin derivative as a novel pharmacological chaperone for GM1 gangliosidosis.

Lysosomal ß-galactosidase (ß-Gal) deficiency causes a group of disorders that include neuronopathic GM1 gangliosidosis and non-neuronopathic Morquio B disease. We have previously proposed the use of small molecule ligands of ß-Gal as pharmacological chaperones (PCs) for the treatment of GM1 gangliosidosis brain pathology. Although it is still under development, PC therapy has yielded promising preclinical results in several lysosomal diseases. In this study, we evaluated the effect of bicyclic 1-deoxygalactonojirimycin (DGJ) derivative of the sp(2)-iminosugar type, namely 5N,6S-(N'-butyliminomethylidene)-6-thio-1- deoxygalactonojirimycin (6S-NBI-DGJ), as a novel PC for human mutant ß-Gal. In vitro, 6S-NBI-DGJ had the ability to inhibit the activity of human ß-Gal in a competitive manner and was able to protect this enzyme from heat-induced degradation. Computational analysis supported that the rigid glycone bicyclic core of 6S-NBI-DGJ binds to the active site of the enzyme, with the aglycone N'-butyl substituent, in a precise E-orientation, located at a hydrophobic region nearby. Chaperone potential profiling indicated significant increases of enzyme activity in 24 of 88 ß-Gal mutants, including four common mutations. Finally, oral administration of 6S-NBI-DGJ ameliorated the brain pathology of GM1 gangliosidosis model mice. These results suggest that 6S-NBI-DGJ is a novel PC that may be effective on a broad range of ß-Gal mutants.

The multivalent effect in glycosidase inhibition: probing the influence of architectural parameters with cyclodextrin-based iminosugar click clusters.

In contrast to most lectins, glycosidases may appear to be unpromising targets for multivalent binding because they display only a single active site. To explore the potential of multivalency on glycosidase inhibition, unprecedented cyclodextrin-based iminosugar conjugates have been designed and prepared. The synthesis was performed by way of Cu(I) -catalyzed azide-alkyne cycloaddition reaction under microwave activation between propargylated multivalent ß-cyclodextrins and an azide-armed N-alkyl 1-deoxynojirimycin derivative. Evaluation with a panel of glycosidases of this new class of glycomimetic clusters revealed the strongest affinity enhancement observed to date for a multivalent glycosidase inhibitor, with binding enhancement up to four orders of magnitude over the corresponding monovalent ligand for α-mannosidase. These results demonstrate that the multivalency concept extends beyond carbohydrate-lectin recognition processes to glycomimetic-enzyme inhibition.