Aminocyclitols as Pharmacological Chaperones for Glucocerebrosidase, a Defective Enzyme in Gaucher Disease

Stereodivergent synthesis of right- and left-handed iminoxylitol heterodimers and monomers. Study of their impact on β-glucocerebrosidase activity

A library of dimers and heterodimers of both enantiomers of 2-O-alkylated iminoxylitol derivatives has been synthesised and evaluated on β-glucocerebrosidase (GCase), the enzyme responsible for Gaucher disease (GD). Although the objective was to target simultaneously the active site and a secondary binding site of the glucosidase, the (-)-2-iminoxylitol moiety seemed detrimental for imiglucerase inhibition and no significant enhancement was obtained in G202R, N370S and L444P fibroblasts. However, all compounds having at least one (+)-2-O-alkyl iminoxylitol are GCase inhibitors in the nano molar range and are significant GCase activity enhancers in G202R fibroblats, as confirmed by a decrease of glucosylceramide levels and by co-localization studies.

Synthesis and evaluation of hydroxymethylaminocyclitols as glycosidase inhibitors

Four series of C7N aminocyclitol analogues of glucose were synthesized by stereocontrolled epoxide opening of hydroxyl protected forms of the cyclohexane epoxides cyclophellitol and 1,6-epi-cyclophellitol. The resulting hydroxymethyl substituted aminocyclitols were tested as glycosidase inhibitors. Cyclitols having an amino group in an α configuration at a position equivalent to the anomeric in the sugar were found to be low micromolar inhibitors of the α-glucosidase from baker's yeast with Ki's near to 2 μM. On the other hand, N-octyl aminocyclitols having the nitrogen substituents in an α or β configuration were found to be good inhibitors of recombinant β-glucocerebrosidase with Ki values between 8.3 and 17 μM, and also inhibited lysosomal β-glucosidase activity in live cells at low-micromolar concentrations. A computational docking study suggests a differential binding among the different series of β-glucocerebrosidase inhibitors. In agreement with the experimental results, the binding poses obtained indicate that the presence of an alkyl lipid substituent in the inhibitor mimicking one of the lipid chains in the substrate is critical for potency. In contrast, the matching of hydroxymethyl substituents in the aminocyclitols and the parent glucosylceramide does not seem to be strictly necessary for potent inhibition, indicating the risk of simplifying structural analogies in sugar mimetic design.

Glucocerebrosidase enhancers for selected Gaucher disease genotypes by modification of α-1-C-substituted imino-D-xylitols (DIXs) by click chemistry

A series of hybrid analogues was designed by combination of the iminoxylitol scaffold of parent 1C9-DIX with triazolylalkyl side chains. The resulting compounds were considered potential pharmacological chaperones in Gaucher disease. The DIX analogues reported here were synthesized by CuAAC click chemistry from scaffold 1 (α-1-C-propargyl-1,5-dideoxy-1,5-imino-D-xylitol) and screened as imiglucerase inhibitors. A set of selected compounds were tested as β-glucocerebrosidase (GBA1) enhancers in fibroblasts from Gaucher patients bearing different genotypes. A number of these DIX compounds were revealed as potent GBA1 enhancers in genotypes containing the G202R mutation, particularly compound DIX-28 (α-1-C-[(1-(3-trimethylsilyl)propyl)-1H-1,2,3-triazol-4-yl)methyl]-1,5-dideoxy-1,5-imino-D-xylitol), bearing the 3-trimethylsilylpropyl group as a new surrogate of a long alkyl chain, with approximately threefold activity enhancement at 10 nM. Despite their structural similarities with isofagomine and with our previously reported aminocyclitols, the present DIX compounds behaved as non-competitive inhibitors, with the exception of the mixed-type inhibitor DIX-28.

Glucocerebrosidase inhibitors for the treatment of Gaucher disease

Gaucher disease is a progressive lysosomal storage disorder caused by a deficiency in the activity of β-glucocerebrosidase and is characterized by the accumulation of the glycosphingolipid glucosylceramide in the lysosomes of macrophages that leads to dysfunction in multiple organ system. An emerging strategy for the treatment of Gaucher disease is pharmacological chaperone therapy, based on the use of β-glucocerebrosidase inhibitors that are capable of enhancing residual hydrolytic activity at subinhibitory concentrations. In this article, the most common lysosomal storage disorder, Gaucher disease, is introduced and the current therapeutic strategies based on the use of enzyme inhibitors to ameliorate this disease are discussed, with a focus on the efforts being made toward finding and optimizing novel molecules as pharmacological chaperones for Gaucher disease that offer the promise to remedy this malady.

Thiophosphate and thiophosphonate analogues of glucose-1-phosphate: synthesis and enzymatic activity with a thymidylyltransferase

Synthetic methods were investigated for the preparation of O and S-glucosyl thiophosphates and glucosyl 1C-thiophosphonate. Four protected glucosyl thiophosphate compounds were synthesized and characterized as precursors to glucose 1-thiophosphate. The effect of various reaction conditions and the nature of the carbohydrate and thiophosphate protecting groups and how they impact both the yields and α/β diastereoselectivity of the glucosyl thiophosphate products were explored. A novel isomerization from an O-linked to S-linked glucosyl thiophosphate was observed. α-D-Glucose-1C-thiophosphonate was synthesized and evaluated as a substrate for the thymidylyltransferase, Cps2L. Tandem mass spectrometric analysis determined the position of sulfur in the sugar nucleotide product.

Raising the roof: the preferential pharmacological stimulation of Th1 and th2 responses mediated by NKT cells

Natural killer T (NKT) cells serve as a bridge between the innate and adaptive immune systems, and manipulating their effector functions can have therapeutic significances in the treatment of autoimmunity, transplant biology, infectious disease, and cancer. NKT cells are a subset of T cells that express cell-surface markers characteristic of both natural killer cells and T cells. These unique immunologic cells have been demonstrated to serve as a link between the innate and adaptive immune systems through their potent cytokine production following the recognition of a range of lipid antigens, mediated through presentation of the major histocompatibility complex (MHC) class I like CD1d molecule, in addition to the NKT cell's cytotoxic capabilities upon activation. Although a number of glycolipid antigens have been shown to complex with CD1d molecules, most notably the marine sponge derived glycolipid alpha-galactosylceramide (α-GalCer), there has been debate as to the identity of the endogenous activating lipid presented to the T-cell receptor (TCR) via the CD1d molecule on antigen-presenting cells (APCs). This review aims to survey the use of pharmacological agents and subsequent structure-activity relationships (SAR) that have given insight into the binding interaction of glycolipids with both the CD1d molecules as well as the TCR and the subsequent immunologic response of NKT cells. These studies not only elucidate basic binding interactions but also pave the way for future pharmacological modulation of NKT cell responses.

Discovery, structure-activity relationship, and biological evaluation of noninhibitory small molecule chaperones of glucocerebrosidase

A major challenge in the field of Gaucher disease has been the development of new therapeutic strategies including molecular chaperones. All previously described chaperones of glucocerebrosidase are enzyme inhibitors, which complicates their clinical development because their chaperone activity must be balanced against the functional inhibition of the enzyme. Using a novel high throughput screening methodology, we identified a chemical series that does not inhibit the enzyme but can still facilitate its translocation to the lysosome as measured by immunostaining of glucocerebrosidase in patient fibroblasts. These compounds provide the basis for the development of a novel approach toward small molecule treatment for patients with Gaucher disease.

Potent aminocyclitol glucocerebrosidase inhibitors are subnanomolar pharmacological chaperones for treating gaucher disease

Amino-myo-inositol derivatives have been found to be potent inhibitors of glucocerebrosidase (GCase), the β-glucosidase enzyme deficient in Gaucher disease (GD). When tested using lymphoblasts derived from patients with GD homozygous for N370S or L444P mutations, the compounds enhanced GCase activity at very low concentrations. The most potent inhibitor, (1R,2S,3R,4S,5S,6R)-5-(nonylamino)-6-(nonyloxy)cyclohexane-1,2,3,4-tetraol had a K(i) of 1 nM using isolated enzyme and an IC(50) of 4.3 nM when assayed in human fibroblast cell culture. This aminocyclitol produced maximum increases of GCase activities of 90% in N370S lymphoblasts at 1 nM and 40% in L444P at 0.01 nM following a three-day incubation. In addition to inhibitory potency, this compound has the permeability, subcellular distribution, and cell metabolism characteristics that are important for use as a pharmacological chaperone. It is a remarkable finding that picomolar concentrations of aminocyclitols are sufficient to enhance activity in the L444P variant, which produces a severe neuronopathic form of GD without clinical treatment.

Non-iminosugar glucocerebrosidase small molecule chaperones

Small molecule chaperones are a promising therapeutic approach for the Lysosomal Storage Disorders (LSDs). Here, we report the discovery of a new series of non-iminosugar glucocerebrosidase inhibitors with chaperone capacity, and describe their structure activity relationship (SAR), selectivity, cell activity phamacokinetics.

The myo-1,2-Diaminocyclitol Scaffold Defines Potent Glucocerebrosidase Activators and Promising Pharmacological Chaperones for Gaucher Disease

A series of cyclitol derivatives with myo-configuration are β-glucocerebrosidase (GCase) inhibitors and show excellent characteristics for the development of pharmacological chaperones for enzyme deficiency in Gaucher disease (GD). The most potent inhibitor, (1S,2R,3R,4S,5R,6S)-5,6-bis(nonylamino)cyclohexane-1,2,3,4-tetraol, displayed a K i value of 26 nM in isolated enzyme and also inhibited GCase in wild-type (wt) human fibroblasts at nanomolar concentrations. This diaminocyclitol produced maximum increases of GCase activities of 60% in N370S lymphoblasts at 100 nM and 30% in L444P at 1 nM following a 3-day incubation, showing the permeability, subcellular distribution, and cell metabolism characteristics for use as pharmacological chaperone.

Computational prediction of structure-activity relationships for the binding of aminocyclitols to β-glucocerebrosidase

Glucocerebrosidase (GCase, acid β-Glucosidase) hydrolyzes the sphingolipid glucosylceramide into glucose and ceramide. Mutations in this enzyme lead to a lipid metabolism disorder known as Gaucher disease. The design of competitive inhibitors of GCase is a promising field of research for the design of pharmacological chaperones as new therapeutic agents. Using a series of recently reported molecules with experimental binding affinities for GCase in the nanomolar to micromolar range, we here report an extensive theoretical analysis of their binding mode. On the basis of molecular docking, molecular dynamics, and binding free energy calculations using the linear interaction energy method (LIE), we provide details on the molecular interactions supporting ligand binding in the different families of compounds. The applicability of other computational approaches, such as the COMBINE methodology, is also investigated. The results show the robustness of the standard parametrization of the LIE method, which reproduces the experimental affinities with a mean unsigned error of 0.7 kcal/mol. Several structure-activity relationships are established using the computational models here provided, including the identification of hot spot residues in the binding site. The models derived are envisaged as important tools in ligand-design programs for GCase inhibitors.

Evaluation of quinazoline analogues as glucocerebrosidase inhibitors with chaperone activity

Gaucher disease is a lysosomal storage disorder (LSD) caused by deficiency in the enzyme glucocerebrosidase (GC). Small molecule chaperones of protein folding and translocation have been proposed as a promising therapeutic approach to this LSD. Most small molecule chaperones described in the literature contain an iminosugar scaffold. Here we present the discovery and evaluation of a new series of GC inhibitors with a quinazoline core. We demonstrate that this series can improve the translocation of GC to the lysosome in patient-derived cells. To optimize this chemical series, systematic synthetic modifications were performed and the SAR was evaluated and compared using three different readouts of compound activity: enzymatic inhibition, enzyme thermostabilization, and lysosomal translocation of GC.

Second-generation iminoxylitol-based pharmacological chaperones for the treatment of Gaucher disease

A series of O-alkyl iminoxylitol derivatives was synthesized and evaluated as β-glucocerebrosidase (GCase) inhibitors. This structure-activity study shows a dramatic influence of the position of the alkyl chain (α-C1, O2, O3, or O4) on human GCase inhibition. Remarkably, 1,2-shift of the alkyl chain from C1 to O2 was found to maintain high inhibitory potency toward GCase as well as chaperone activity at sub-inhibitory concentration (10 nM). Removal of the stereogenic center at the pseudo-anomeric position led to shorter and more practical synthetic sequences. 2-O-Alkyl iminoxylitol derivatives constitute a new promising class of leads for the treatment of Gaucher disease by means of pharmacological chaperone therapy.

Pharmacological small molecules for the treatment of lysosomal storage disorders

IMPORTANCE OF THE FIELD

Inherited lysosomal storage diseases often cause severe disability and have a devastating effect on quality of life. Enzyme replacement therapy (ERT) forms a cornerstone in the treatment of lysosomal enzyme deficiencies. Although for some lysosomal disorders ERT is lifesaving, important intrinsic restrictions of the approach are limited access of infused enzyme to less accessible body compartments such as the CNS, the burden of frequent intravenous administration, the emergence of antibodies and the high associated costs. Pharmacological small molecules may overcome these limitations.

AREAS COVERED IN THIS REVIEW

Several novel therapeutic approaches using small molecules are emerging: substrate reduction therapy, pharmacological chaperone therapy, premature nonsense mutation suppressors and proteostasis regulators.

WHAT THE READER WILL GAIN

Based on an extensive literature search up until June 2010, we here review the various therapeutic approaches with small compounds, including those currently in clinical use and those that have entered clinical trials. Compounds that are still in the preclinical phase are also briefly discussed.

TAKE HOME MESSAGE

pharmacological small molecules are a new class of agents that show great promise for the treatment of lysosomal storage disorders.

Promising results of the chaperone effect caused by imino sugars and aminocyclitol derivatives on mutant glucocerebrosidases causing Gaucher disease

Gaucher disease is an autosomal recessive disorder. It is characterized by the accumulation of glucosylceramide in lysosomes of mononuclear phagocyte system, attributable to acid beta-glucosidase deficiency. The main consequences of this disease are hepatosplenomegaly, skeletal lesions and, sometimes, neurological manifestations. At sub-inhibitory concentrations, several competitive inhibitors act as chemical chaperones by inducing protein stabilization and increasing enzymatic activity. Here we tested two iminosugars (NB-DNJ and NN-DNJ) and four aminocyclitols with distinct degrees of lipophilicity as pharmacological chaperones for glucocerebrosidase (GBA). We report an increase in the activity of GBA using NN-DNJ, NB-DNJ and aminocyclitol 1 in stably transfected cell lines, and an increment with NN-DNJ and aminocyclitol 4 in patient fibroblasts. These results on specific mutations validate the use of chemical chaperones as a therapeutic approach for Gaucher disease. However, the development and analysis of new compounds is required in order to find more effective therapeutic agents that are active on a broader range of mutations.

Three classes of glucocerebrosidase inhibitors identified by quantitative high-throughput screening are chaperone leads for Gaucher disease

Gaucher disease is an autosomal recessive lysosomal storage disorder caused by mutations in the glucocerebrosidase gene. Missense mutations result in reduced enzyme activity that may be due to misfolding, raising the possibility of small-molecule chaperone correction of the defect. Screening large compound libraries by quantitative high-throughput screening (qHTS) provides comprehensive information on the potency, efficacy, and structure-activity relationships (SAR) of active compounds directly from the primary screen, facilitating identification of leads for medicinal chemistry optimization. We used qHTS to rapidly identify three structural series of potent, selective, nonsugar glucocerebrosidase inhibitors. The three structural classes had excellent potencies and efficacies and, importantly, high selectivity against closely related hydrolases. Preliminary SAR data were used to select compounds with high activity in both enzyme and cell-based assays. Compounds from two of these structural series increased N370S mutant glucocerebrosidase activity by 40-90% in patient cell lines and enhanced lysosomal colocalization, indicating chaperone activity. These small molecules have potential as leads for chaperone therapy for Gaucher disease, and this paradigm promises to accelerate the development of leads for other rare genetic disorders.