A contradictory treatment for lysosomal storage disorders: inhibitors enhance mutant enzyme activity

Glycosidase inhibition by ring-modified castanospermine analogues: tackling enzyme selectivity by inhibitor tailoring

Synthesis of a panel of iso(thio)urea-type ring-modified castanospermine analogues bearing a freely mutarotating pseudoanomeric hydroxyl group results in tight-binding beta-glucosidase inhibitors with unusual binding signatures; the presence of an N-octyl substituent imparts a remarkable anomeric selectivity, promoting strong binding of the appropriate beta-anomer by the beta-glucosidase.

Molecular interaction of imino sugars with human alpha-galactosidase: Insight into the mechanism of complex formation and pharmacological chaperone action in Fabry disease

Enzyme enhancement therapy (EET) for Fabry disease involving imino sugars has been developed and attracted interest. It is thought that imino sugars act as pharmacological chaperones for wild-type and mutant alpha-galactosidases (GLAs) in cells, but the mechanisms underlying the molecular interactions between the imino sugars and the enzyme have not been clarified yet. We examined various kinds of imino sugars and found that galactostatin bisulfite (GBS) inhibited GLA in vitro and increased the enzyme activity in cultured Fabry fibroblasts as in the case of 1-deoxygalactonojirimycin (DGJ). Then, we analyzed the molecular interactions between the imino sugars and recombinant human GLA by means of isothermal titration calorimetry and surface plasmon resonance biosensor assays, and first determined the thermodynamic and binding-kinetics parameters of imino sugar and GLA complex formation. The results revealed that DGJ bound to the enzyme more strongly than GBS, the binding of DGJ to the enzyme protein being enthalpy-driven. In the case of GBS, the reaction was mainly enthalpy-driven, but there was a possibility that entropy-driven factors were involved in the binding. Structural analysis in silico revealed that both the chemicals fit into the active-site pocket and undergo hydrogen bonding with residues comprising the active-site pocket including the catalytic ones. The side chain of GBS was oriented towards the entrance of the active-site pocket, and thus it could be in contact with residues comprising the wall of the active-site pocket. Thermodynamic, kinetic and structural studies should provide us with a lot of information for improving EET for Fabry disease.

Isofagomine induced stabilization of glucocerebrosidase

Structurally destabilizing mutations in acid beta-glucosidase (GCase) can result in Gaucher disease (GD). The iminosugar isofagomine (IFG), a competitive inhibitor and a potential pharmacological chaperone of GCase, is currently undergoing clinical evaluation for the treatment of GD. An X-ray crystallographic study of the GCase-IFG complex revealed a hydrogen bonding network between IFG and certain active site residues. It was suggested that this network may translate into greater global stability. Here it is demonstrated that IFG does increase the global stability of wild-type GCase, shifting its melting curve by approximately 15 degrees C and that it enhances mutant GCase activity in pre-treated N370S/N370S and F213I/L444P patient fibroblasts. Additionally, amide hydrogen/deuterium exchange mass spectroscopy (H/D-Ex) was employed to identify regions within GCase that undergo stabilization upon IFG-binding. H/D-Ex data indicate that the binding of IFG not only restricts the local protein dynamics of the active site, but also propagates this effect into surrounding regions.

Identification of pharmacological chaperones for Gaucher disease and characterization of their effects on beta-glucocerebrosidase by hydrogen/deuterium exchange mass spectrometry

Point mutations in beta-glucocerebrosidase (GCase) can result in a deficiency of both GCase activity and protein in lysosomes thereby causing Gaucher Disease (GD). Enzyme inhibitors such as isofagomine, acting as pharmacological chaperones (PCs), increase these levels by binding and stabilizing the native form of the enzyme in the endoplasmic reticulum (ER), and allow increased lysosomal transport of the enzyme. A high-throughput screen of the 50,000-compound Maybridge library identified two, non-carbohydrate-based inhibitory molecules, a 2,4-diamino-5-substituted quinazoline (IC(50) 5 microM) and a 5-substituted pyridinyl-2-furamide (IC(50) 8 microM). They raised the levels of functional GCase 1.5-2.5-fold in N370S or F213I GD fibroblasts. Immunofluorescence confirmed that treated GD fibroblasts had decreased levels of GCase in their ER and increased levels in lysosomes. Changes in protein dynamics, monitored by hydrogen/deuterium-exchange mass spectrometry, identified a domain III active-site loop (residues 243-249) as being significantly stabilized upon binding of isofagomine or either of these two new compounds; this suggests a common mechanism for PC enhancement of intracellular transport.

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.

Preclinical efficacy and safety of 1-deoxygalactonojirimycin in mice for Fabry disease

Fabry disease is an inborn error of glycosphingolipid metabolism caused by deficiency of alpha-galactosidase A (alpha-Gal A) activity. It has been shown that protein misfolding is primarily responsible for the enzyme deficiency in a large proportion of mutations identified in Fabry patients with residual enzyme activity, and 1-deoxygalactonojirimycin (DGJ) can effectively increase the residual enzyme activity in cultured patient's cells. Herein, we demonstrate the preclinical efficacy and safety of DGJ in transgenic mice that express human mutant alpha-Gal A activity. alpha-Gal A activity in heart, kidney, spleen, and liver was increased dose- and time-dependently. The mutant alpha-Gal A was increased in cardiomyocytes and distal convoluted tubules of the transgenic mice in a null background after 2 weeks of DGJ treatment. Globotriaosylceramide storage was remarkably reduced in kidney of mice after a 4-week treatment at a dosage of approximately 3 mg/kg body weight/day. The half-life of DGJ was less than 1 day in all major issues and that of the enzyme synthesized during the DGJ treatment period was approximately 4 days. No abnormality of blood chemistry and pathological tissue damage was found in mice treated with DGJ at approximately 30 mg/kg body weight/day for 9 weeks. Furthermore, no change was observed in appearance, growth, fertility, and life span in mice during a 2-year period of continuous administration of DGJ at the effective dosage. These preclinical results indicate that DGJ is effective in restoring mutant enzyme activity in tissues and reversing substrate storage in kidney and is well tolerated in mice.

Phenotype, diagnosis, and treatment of Gaucher's disease

Gaucher's disease continues to be a model for applications of molecular medicine to clinical delineation, diagnosis, and treatment. Analyses of several thousand affected individuals have broadened the range of the pan-ethnic disease variants, provided initial genotype and phenotype correlations, and established the effectiveness of enzyme therapy. Large numbers of affected individuals worldwide have provided insight into the effect of disease variation related to ethnic origin, prognosis, and outcome. The ability to safely and effectively use enzyme therapy to inhibit or reverse visceral-disease progression and involvement has provided impetus for design of new enzyme therapies, and creation of substrate depletion and pharmacological chaperone strategies. Such innovations could provide interventions that are effective for neuronopathic variants and, potentially, could be more cost effective than other treatments. These developments are novel, clinically important, advancements for patients with other lysosomal storage diseases and genetic diseases.

In vivo and in vitro examination of stability of primary hyperoxaluria-associated human alanine:glyoxylate aminotransferase

Primary hyperoxaluria type I is a severe kidney stone disease caused by mutations in the protein alanine:glyoxylate aminotransferase (AGT). Many patients have mutations in AGT that are not deleterious alone but act synergistically with a common minor allele polymorphic variant to impair protein folding, dimerization, or localization. Although studies suggest that the minor allele variant itself is destabilized, no direct stability studies have been carried out. In this report, we analyze AGT function and stability using three approaches. First, we describe a yeast complementation growth assay for AGT, in which we show that human AGT can substitute for function of yeast Agx1 and that mutations associated with disease in humans show reduced growth in yeast. The reduced growth of minor allele mutants reflects reduced protein levels, indicating that these proteins are less stable than wild-type AGT in yeast. We further examine stability of AGT alleles in vitro using two direct methods, a mass spectrometry-based technique (stability of unpurified proteins from rates of H/D exchange) and differential scanning fluorimetry. We also examine the effect of known ligands pyridoxal 5'-phosphate and aminooxyacetic acid on stability. Our work establishes that the minor allele is destabilized and that pyridoxal 5'-phosphate and aminooxyacetic acid binding significantly stabilizes both alleles. To our knowledge, this is the first work that directly measures relative stabilities of AGT variants and ligand complexes. Because previous studies suggest that stabilizing compounds (i.e. pharmacological chaperones) may be effective for treatment of primary hyperoxaluria, we propose that the methods described here can be used in high throughput screens for compounds that stabilize AGT mutants.

Prediction of response of mutated alpha-galactosidase A to a pharmacological chaperone

OBJECTIVE

To examine the relationship between types and locations of mutations of the enzyme alpha-galactosidase (Gal) A in Fabry disease and the response to the pharmacological chaperone 1-deoxygalactonojirimycin (DGJ).

METHODS

T cells grown from normal individuals or from patients with Fabry disease were tested for response to treatment with DGJ by increased activity of alpha-Gal A.

RESULTS

Cells from normal controls responded with a 28% increase in alpha-Gal A activity, whereas response in Fabry individuals was mutation dependent ranging from no increase to fully normal activity. Nine truncation mutations (all nonresponsive) and 31 missense mutations were tested. Three groups of missense mutations were categorized: responders with activity more than 25% of normal, nonresponders, with less than 7% and an intermediate response group. In normal cells and in responders an increase in the mature lysosomal form of alpha-Gal A was observed after DGJ treatment. Nonresponders showed little or no protein with or without DGJ. The intermediate response group showed an increase in band intensity but incomplete processing of the enzyme to the mature form.

CONCLUSION

Mapping the missense mutations to the structure of alpha-Gal A identified several factors that may influence response. Mutations in regions that are not in alpha-helix or beta-sheets, neither involved in disulfide bonds nor with an identified functional or structural role were more likely to respond. Predictability is, however, not precise and testing of each mutation for response to pharmacological chaperone therapy is necessary for Fabry disease and related lysosomal storage disorders.

Glycosphingolipid disorders of the brain

Glycosphingolipids, comprising a ceramide lipid backbone linked to one/more saccharides, are particularly abundant on the outer leaflet of the eukaryotic plasma membrane and play a role in a wide variety of essential cellular processes. Biosynthesis and subsequently degradation of these lipids is tightly regulated via the involvement of numerous enzymes, and failure of an enzyme to participate in the metabolism results in storage of the enzyme's substrate, giving rise to a lysosomal storage disease. The characteristics, severity and onset of the disease are dependent on the enzyme deficient and the residual activity. Most lysosomal storage disorders found thus far are caused by a defect in the catabolic activity of a hydrolase, causing progressive accumulation of its substrate, predominantly in the lysosome. Storage of gangliosides, sialic acid containing glycosphingolipids, mostly found in the central nervous system, is a hallmark of neuronopathic forms of the disease, that include GM1 and GM2 gangliosidoses, Gaucher type II and III and Niemann-Pick C. Models for these diseases have provided valuable insight into the disease pathology and potential treatment methods.Treatment of these rare but severe disorders proves challenging due to restricted access of therapeutics through the blood-brain barrier. However, recent advances in enzyme replacement, bone marrow transplantation, gene transfer, substrate reduction and chaperon-mediated therapy provide great potential in treating these devastating disorders.

Chemical tools to investigate sphingolipid metabolism and functions

Sphingolipids comprise an important group of biomolecules, some of which have been shown to play important roles in the regulation of many cell functions. From a structural standpoint, they all share a long 2-amino-1,3-diol chain, which can be either saturated (sphinganine), hydroxylated at C4 (phytosphingosine), or unsaturated at C4 (sphingosine) as in most mammalian cells. N-acylation of sphingosine leads to ceramide, a key intermediate in sphingolipid metabolism that can be enzymatically modified at the C1-OH position to other biologically important sphingolipids, such as sphingomyelin or glycosphingolipids. In addition, both ceramide and sphingosine can be phosphorylated at C1-OH to give ceramide-1-phosphate and sphingosine-1-phosphate, respectively. To better understand the biological and biophysical roles of sphingolipids, many efforts have been made to design synthetic analogues as chemical tools able to unravel their structure-activity relationships, and to alter their cellular levels. This last approach has been thoroughly studied by the development of specific inhibitors of some key enzymes that play an important role in biosynthesis or metabolism of these intriguing lipids. With the above premises in mind, the aim of this review is to collect, in a systematic way, the recent efforts described in the literature leading to the development of new chemical entities specifically designed to achieve the above goals.

In vitro inhibition of glycogen-degrading enzymes and glycosidases by six-membered sugar mimics and their evaluation in cell cultures

We investigated in vitro inhibition of mammalian carbohydrate-degrading enzymes by six-membered sugar mimics and their evaluation in cell cultures. 1-Deoxynojirimycin (DNJ) showed no significant inhibition toward glycogen phosphorylase (GP) but was a potent inhibitor of another glycogen-degrading enzyme, amylo-1,6-glucosidase (1,6-GL), with an IC(50) value of 0.16 microM. In primary rat hepatocytes, the inhibition of glycogen breakdown by DNJ reached plateau at 100 microM with 25% inhibition and then remained unchanged. The potent GP inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol (D-AB1) inhibited hepatic glucose production with an IC(50) value of about 9 microM and the inhibition by D-AB1 was further enhanced in the presence of DNJ. DNJ and alpha-homonojirimycin (HNJ) are very potent inhibitors of rat intestinal maltase, with IC(50) values of 0.13 and 0.08 microM, respectively, and also showed a similar strong inhibition toward maltase in Caco-2 cell model system, with IC(50) value of 0.05 and 0.10 microM, respectively. D-Isofagomine (D-IFG) and L-IFG are competitive and noncompetitive inhibitors of human lysosomal beta-glucosidase (beta-GL), respectively, with K(i) values of 8.4 nM and 6.9 microM. D-IFG increased intracellular beta-GL activity by twofold at 10 microM in Gaucher N370S cell line as an 'active-site-specific' chaperone, and surprisingly a noncompetitive inhibitor L-IFG also increased intracellular beta-GL activity by 1.6-fold at 500 microM.

A counterintuitive approach to treat enzyme deficiencies: use of enzyme inhibitors for restoring mutant enzyme activity

Pharmacological chaperone therapy is an emerging counterintuitive approach to treat protein deficiencies resulting from mutations causing misfolded protein conformations. Active-site-specific chaperones (ASSCs) are enzyme active-site directed small molecule pharmacological chaperones that act as a folding template to assist protein folding of mutant proteins in the endoplasmic reticulum (ER). As a result, excessive degradation of mutant proteins in the ER-associated degradation (ERAD) machinery can be prevented, thus restoring enzyme activity. Lysosomal storage disorders (LSDs) are suitable candidates for ASSC treatment, as the levels of enzyme activity needed to prevent substrate storage are relatively low. In addition, ASSCs are orally active small molecules and have potential to gain access to most cell types to treat neuronopathic LSDs. Competitive enzyme inhibitors are effective ASSCs when they are used at sub-inhibitory concentrations. This whole new paradigm provides excellent opportunity for identifying specific drugs to treat a broad range of inherited disorders. This review describes protein misfolding as a pathophysiological cause in LSDs and provides an overview of recent advances in the development of pharmacological chaperone therapy for the diseases. In addition, a generalized guidance for the design and screening of ASSCs is also presented.

Lending a helping hand, screening chemical libraries for compounds that enhance beta-hexosaminidase A activity in GM2 gangliosidosis cells

Enzyme enhancement therapy is an emerging therapeutic approach that has the potential to treat many genetic diseases. Candidate diseases are those associated with a mutant protein that has difficulty folding and/or assembling into active oligomers in the endoplasmic reticulum. Many lysosomal storage diseases are candidates for enzyme enhancement therapy and have the additional advantage of requiring only 5-10% of normal enzyme levels to reduce and/or prevent substrate accumulation. Our long experience in working with the beta-hexosaminidase (EC 3.2.1.52) isozymes system and its associated deficiencies (Tay-Sachs and Sandhoff disease) lead us to search for possible enzyme enhancement therapy-agents that could treat the chronic forms of these diseases which express 2-5% residual activity. Pharmacological chaperones are enzyme enhancement therapy-agents that are competitive inhibitors of the target enzyme. Each of the known beta-hexosaminidase inhibitors (low microm IC50) increased mutant enzyme levels to >or= 10% in chronic Tay-Sachs fibroblasts and also attenuated the thermo-denaturation of beta-hexosaminidase. To expand the repertoire of pharmacological chaperones to more 'drug-like' compounds, we screened the Maybridge library of 50,000 compounds using a real-time assay for noncarbohydrate-based beta-hexosaminidase inhibitors and identified several that functioned as pharmacological chaperones in patient cells. Two of these inhibitors had derivatives that had been tested in humans for other purposes. These observations lead us to screen the NINDS library of 1040 Food and Drug Administration approved compounds for pharmacological chaperones. Pyrimethamine, an antimalarial drug with well documented pharmacokinetics, was confirmed as a beta-hexosaminidase pharmacological chaperone and compared favorably with our best carbohydrate-based pharmacological chaperone in patient cells with various mutant genotypes.

Active-site-specific chaperone therapy for Fabry disease. Yin and Yang of enzyme inhibitors

Protein misfolding is recognized as an important pathophysiological cause of protein deficiency in many genetic disorders. Inherited mutations can disrupt native protein folding, thereby producing proteins with misfolded conformations. These misfolded proteins are consequently retained and degraded by endoplasmic reticulum-associated degradation, although they would otherwise be catalytically fully or partially active. Active-site directed competitive inhibitors are often effective active-site-specific chaperones when they are used at subinhibitory concentrations. Active-site-specific chaperones act as a folding template in the endoplasmic reticulum to facilitate folding of mutant proteins, thereby accelerating their smooth escape from the endoplasmic reticulum-associated degradation to maintain a higher level of residual enzyme activity. In Fabry disease, degradation of mutant lysosomal alpha-galactosidase A caused by a large set of missense mutations was demonstrated to occur within the endoplasmic reticulum-associated degradation as a result of the misfolding of mutant proteins. 1-Deoxygalactonojirimycin is one of the most potent inhibitors of alpha-galactosidase A. It has also been shown to be the most effective active-site-specific chaperone at increasing residual enzyme activity in cultured fibroblasts and lymphoblasts established from Fabry patients with a variety of missense mutations. Oral administration of 1-deoxygalactonojirimycin to transgenic mice expressing human R301Q alpha-galactosidase A yielded higher alpha-galactosidase A activity in major tissues. These results indicate that 1-deoxygalactonojirimycin could be of therapeutic benefit to Fabry patients with a variety of missense mutations, and that the active-site-specific chaperone approach using functional small molecules may be broadly applicable to other lysosomal storage disorders and other protein deficiencies.

The pathogenesis and treatment of acid sphingomyelinase-deficient Niemann-Pick disease

Patients with types A and B Niemann-Pick disease (NPD) have an inherited deficiency of acid sphingomyelinase (ASM) activity. The clinical spectrum of this disorder ranges from the infantile, neurological form that results in death by 3 years of age (type A NPD) to the non-neurological form (type B NPD) that is compatible with survival into adulthood. Intermediate cases also have been reported, and the disease is best thought of as a single entity with a spectrum of phenotypes. ASM deficiency is panethnic, but appears to be more frequent in individuals of Middle Eastern and North African descent. Current estimates of the disease incidence range from approximately 0.5 to 1 per 100,000 births. However, these approximations likely under estimate the true frequency of the disorder since they are based solely on cases referred to biochemical testing laboratories for enzymatic confirmation. The gene encoding ASM (SMPD1) has been studied extensively; it resides within an imprinted region on chromosome 11, and is preferentially expressed from the maternal chromosome. Over 100 SMPD1 mutations causing ASM-deficient NPD have been described, and some useful genotype-phenotype correlations have been made. Based on these findings, DNA-based carrier screening has been implemented in the Ashkenazi Jewish community. ASM 'knockout' mouse models also have been constructed and used to investigate disease pathogenesis and treatment. Based on these studies in the mouse model, an enzyme replacement therapy clinical trial has recently begun in adult patients with non-neurological ASM-deficient NPD.

Mutant alpha-galactosidase A enzymes identified in Fabry disease patients with residual enzyme activity: biochemical characterization and restoration of normal intracellular processing by 1-deoxygalactonojirimycin

Fabry disease is a lysosomal storage disorder caused by the deficiency of alpha-Gal A (alpha-galactosidase A) activity. In order to understand the molecular mechanism underlying alpha-Gal A deficiency in Fabry disease patients with residual enzyme activity, enzymes with different missense mutations were purified from transfected COS-7 cells and the biochemical properties were characterized. The mutant enzymes detected in variant patients (A20P, E66Q, M72V, I91T, R112H, F113L, N215S, Q279E, M296I, M296V and R301Q), and those found mostly in mild classic patients (A97V, A156V, L166V and R356W) appeared to have normal K(m) and V(max) values. The degradation of all mutants (except E59K) was partially inhibited by treatment with kifunensine, a selective inhibitor of ER (endoplasmic reticulum) alpha-mannosidase I. Metabolic labelling and subcellular fractionation studies in COS-7 cells expressing the L166V and R301Q alpha-Gal A mutants indicated that the mutant protein was retained in the ER and degraded without processing. Addition of DGJ (1-deoxygalactonojirimycin) to the culture medium of COS-7 cells transfected with a large set of missense mutant alpha-Gal A cDNAs effectively increased both enzyme activity and protein yield. DGJ was capable of normalizing intracellular processing of mutant alpha-Gal A found in both classic (L166V) and variant (R301Q) Fabry disease patients. In addition, the residual enzyme activity in fibroblasts or lymphoblasts from both classic and variant hemizygous Fabry disease patients carrying a variety of missense mutations could be substantially increased by cultivation of the cells with DGJ. These results indicate that a large proportion of mutant enzymes in patients with residual enzyme activity are kinetically active. Excessive degradation in the ER could be responsible for the deficiency of enzyme activity in vivo, and the DGJ approach may be broadly applicable to Fabry disease patients with missense mutations.

Crystal Structures of Complexes of N-Butyl- and N-Nonyl-Deoxynojirimycin Bound to Acid β-Glucosidase

Gaucher disease is caused by mutations in the gene encoding acid beta-glucosidase (GlcCerase), resulting in glucosylceramide (GlcCer) accumulation. The only currently available orally administered treatment for Gaucher disease is N-butyl-deoxynojirimycin (Zavesca, NB-DNJ), which partially inhibits GlcCer synthesis, thus reducing levels of GlcCer accumulation. NB-DNJ also acts as a chemical chaperone for GlcCerase, although at a different concentration than that required to completely inhibit GlcCer synthesis. We now report the crystal structures, at 2A resolution, of complexes of NB-DNJ and N-nonyl-deoxynojirimycin (NN-DNJ) with recombinant human GlcCerase, expressed in cultured plant cells. Both inhibitors bind at the active site of GlcCerase, with the imino sugar moiety making hydrogen bonds to side chains of active site residues. The alkyl chains of NB-DNJ and NN-DNJ are oriented toward the entrance of the active site where they undergo hydrophobic interactions. Based on these structures, we make a number of predictions concerning (i) involvement of loops adjacent to the active site in the catalytic process, (ii) the nature of nucleophilic attack by Glu-340, and (iii) the role of a conserved water molecule located in a solvent cavity adjacent to the active site. Together, these results have significance for understanding the mechanism of action of GlcCerase and the mode of GlcCerase chaperoning by imino sugars.

Synthesis of 4-O-glycosylated 1-deoxynojirimycin derivatives as disaccharide mimics-based inhibitors of human β-glucocerebrosidase

Examples of a new type of inhibitor of human beta-glucocerebrosidase based on imino-disaccharides as glycosylceramide mimetics have been synthesized by way of the glycosylation of 1-deoxynojirimycin derivatives with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide.

N4-phenyl modifications of N2-(2-hydroxyl)ethyl-6-(pyrrolidin-1-yl)-1,3,5-triazine-2,4-diamines enhance glucocerebrosidase inhibition by small molecules with potential as chemical chaperones for Gaucher disease

A series of 1,3,5-triazine-2,4,6-triamines were prepared and analyzed as inhibitors of glucocerebrosidase. Synthesis, structure activity relationships and the selectivity of chosen analogues against related sugar hydrolases enzymes are described.

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.

Screening for pharmacological chaperones in Fabry disease

As a prerequisite for clinical trials of pharmacological chaperone therapy (PCT) for Fabry disease, we developed a rapid screening assay for enhancement of endogenous alpha-galactosidase A (alpha-Gal A) in patient-derived cells. We used a T-cell based system to screen 11 mutations causing Fabry disease for enhanceability using 1-deoxygalactonojirimycin (DGJ). When patient-derived T-cells were grown in the presence of DGJ, alpha-Gal A activity increased to more than 50% of normal in several mutations but was unaffected in others. In addition to the mutation R301Q, reported previously, A97V, R112H, R112C, A143T, and L300P were enhanceable, but R356W, G132R, A143P, R220X, and 30delG were not. The level of alpha-Gal A activity achieved provides a basis for the therapeutic trial of DGJ in patients with similarly enhanceable enzyme. This assay method has general utility in other disorders in assessing the degree of enhancement of activity of mutated proteins by PCT.

Inhibiting HIV-1 integrase by shifting its oligomerization equilibrium

Proteins are involved in various equilibria that play a major role in their activity or regulation. The design of molecules that shift such equilibria is of great therapeutic potential. This fact was demonstrated in the cases of allosteric inhibitors, which shift the equilibrium between active and inactive (R and T) states, and chemical chaperones, which shift folding equilibrium of proteins. Here, we expand these concepts and propose the shifting of oligomerization equilibrium of proteins as a general methodology for drug design. We present a strategy for inhibiting proteins by "shiftides": ligands that specifically bind to an inactive oligomeric state of a disease-related protein and modulate its activity by shifting the oligomerization equilibrium of the protein toward it. We demonstrate the feasibility of our approach for the inhibition of the HIV-1 integrase (IN) protein by using peptides derived from its cellular-binding protein, LEDGF/p75, which specifically inhibit IN activity by a noncompetitive mechanism. The peptides inhibit the DNA-binding of IN by shifting the IN oligomerization equilibrium from the active dimer toward the inactive tetramer, which is unable to catalyze the first integration step of 3' end processing. The LEDGF/p75-derived peptides inhibit the enzymatic activity of IN in vitro and consequently block HIV-1 replication in cells because of the lack of integration. These peptides are promising anti-HIV lead compounds that modulate oligomerization of IN via a previously uncharacterized mechanism, which bears advantages over the conventional interface dimerization inhibitors.

Novel therapeutic targets for the treatment of Fabry disease

Fabry disease is an X-linked lysosomal storage disorder resulting from deficient activity of alpha-galactosidase A. The traditional concept that is used to explain the complications of the disease involves progressive accumulation of globotriaosylceramide in endothelial and smooth muscle cells, resulting in vascular damage. Clinically, progressive renal insufficiency, cardiac involvement and brain pathology evolves. Two pharmaceutical companies have developed enzyme replacement therapy in Fabry disease. Although the first clinical trials showed great promise, it is clear that long-term effects are not as robust as was anticipated. Stabilisation of renal function and decreases in cardiac hypertrophy has been observed, but some patients may experience progressive complications. As there are recent indications that serum components contribute to the pathophysiology of Fabry disease, fundamental studies are needed to unravel the precise role and identity of these factors. Combination of these basic studies with clinical follow up may ultimately reveal when the 'point of no return' is reached. Advanced renal insufficiency seems to be a clinical indicator of lack of response, but other signs and symptoms are probably related to adverse outcome. It is anticipated that in the future controlled studies in early symptomatic or presymptomatic patients will be required. In addition, alternative strategies such as substrate reduction or chaperone therapy, either alone or in combination with enzyme replacement therapy, should be explored. Because Fabry disease is rare, collaborative efforts should be undertaken and openness of data should be strived for.

High-throughput screening for human lysosomal beta-N-Acetyl hexosaminidase inhibitors acting as pharmacological chaperones

The adult forms of Tay-Sachs and Sandhoff diseases result when the activity of beta-hexosaminidase A (Hex) falls below approximately 10% of normal due to decreased transport of the destabilized mutant enzyme to the lysosome. Carbohydrate-based competitive inhibitors of Hex act as pharmacological chaperones (PC) in patient cells, facilitating exit of the enzyme from the endoplasmic reticulum, thereby increasing the mutant Hex protein and activity levels in the lysosome 3- to 6-fold. To identify drug-like PC candidates, we developed a fluorescence-based real-time enzyme assay and screened the Maybridge library of 50,000 compounds for inhibitors of purified Hex. Three structurally distinct micromolar competitive inhibitors, a bisnaphthalimide, nitro-indan-1-one, and pyrrolo[3,4-d]pyridazin-1-one were identified that specifically increased lysosomal Hex protein and activity levels in patient fibroblasts. These results validate screening for inhibitory compounds as an approach to identifying PCs.

[Iminosugars: current and future therapeutic applications]

The replacement of the oxygen-containing ring (pyranose, furanose) of monosaccharides by a nitrogen-containing ring (pyrrolidine, piperidine) leads to a particularly interesting class of glycomimetics: iminosugars. The first synthesis of such a sugar analog by Prof. H. Paulsen in 1966 (5-amino-5-deoxy-D-glucose) was followed by the discovery in Japan, a few months later, of the same compound from bacterial extracts by S. Inouye. The compound was named nojirimycin. Whereas this compound was shown in 1966 to exhibit modest antibiotic activities, the properties of iminosugars as powerful glycosidase inhibitors were discovered only many years later (1976) by chemists at Bayer. Since then, these compounds have been extensively studied and other biological properties have been discovered: inhibition of glycosyltransferases, of glycogen phosphorylase, of purine nucleoside phosphorylases, etc. The first therapeutic agent of this family is Miglitol, a drug that is used to modulate sugar absorption in the case of non-insulin-dependent diabetes; a second iminosugar has been recently put on the market, N-butyl-1-deoxynojirimycin, under the trade name Zavesca, for the treatment of lysosomal diseases (Gaucher disease in particular). Other therapeutic applications are under investigations, for example for the treatment of certain forms of cancer, of Fabry disease and viral infections (hepatitis B).

Pharmacological Enhancement of Mutated α-Glucosidase Activity in Fibroblasts from Patients with Pompe Disease

We investigated the use of pharmacological chaperones for the therapy of Pompe disease, a metabolic myopathy due to mutations of the gene encoding the lysosomal hydrolase alpha-glucosidase (GAA) and characterized by generalized glycogen storage in cardiac and skeletal muscle. We studied the effects of two imino sugars, deoxynojirimycin (DNJ) and N-butyldeoxynojirimycin (NB-DNJ), on residual GAA activity in fibroblasts from eight patients with different forms of Pompe disease (two classic infantile, two non-classic infantile onset, four late-onset forms), and with different mutations of the GAA gene. We demonstrated a significant increase of GAA activity (1.3-7.5-fold) after imino sugar treatment in fibroblasts from patients carrying the mutations L552P (three patients) and G549R (one patient). GAA enhancement was confirmed in HEK293T cells where the same mutations were overexpressed. No increase of GAA activity was observed for the other mutations. Western blot analysis showed that imino sugars increase the amount of mature GAA molecular forms. Immunofluorescence studies in HEK293T cells overexpressing the L552P mutation showed an improved trafficking of the mutant enzyme to lysosomes after imino sugar treatment. These results provide a rationale for an alternative treatment, other than enzyme replacement, to Pompe disease.

Pharmacotherapeutic strategies using small molecules for the treatment of glycolipid lysosomal storage disorders

The glycolipid lysosomal storage diseases are a collection of rare, inherited disorders of metabolism associated with heterogeneous pathologies and reduced life expectancy. Reduction of the substrate that accumulates due to catabolic enzyme deficiency can be mediated by an increasing number of therapeutic approaches, including enzyme replacement, pharmacological intervention to reduce substrate synthesis or enhance residual enzyme activity, and cell or gene therapy. The success of one agent, the imino sugar miglustat, has provided the impetus for using similar molecules for enzyme enhancement, or chaperone-mediated therapy for exiting medical conditions and for conditions where no disease-specific therapy is available. The advantages of using small molecules as therapy for the family of lysosomal storage disorders are discussed with reference to existing enzyme replacement therapies.

Therapy for Gaucher disease: don't stop thinking about tomorrow

While enzyme replacement therapy for Gaucher disease has been widely used and appears to be an efficacious and safe treatment, this success should not be a reason for complacency. Other treatment strategies currently under consideration for patients with Gaucher disease include gene therapy, substrate reduction therapy and chaperone therapy. Furthermore, improvements in enzyme therapy could also have a significant clinical impact. Individuals with Gaucher disease and other lysosomal disorders will greatly benefit from continual refinement and optimization of the current therapy, as well as from the development of new treatment modalities that offer improvements in efficacy, cost, safety and availability.

Chemical chaperones improve transport and enhance stability of mutant alpha-glucosidases in glycogen storage disease type II

Glycogen storage disease type II (GSDII; Pompe disease or acid maltase deficiency) is an autosomal recessive disorder caused by lysosomal acid alpha-glucosidase (AalphaGlu) deficiency and manifests predominantly as skeletal muscle weakness. Defects in post-translational modification and transport of mutant AalphaGlu species are frequently encountered and may potentially be corrected with chaperone-mediated therapy. In the present study, we have tested this hypothesis by using deoxynojirimycin and derivatives as chemical chaperones to correct the AalphaGlu deficiency in cultured fibroblasts from patients with GSDII. Four mutant phenotypes were chosen: Y455F/Y455F, P545L/P545L, 525del/R600C and D645E/R854X. In case of Y455F/Y455F and P545L/P545L, N-(n-butyl)deoxynojirimycin (NB-DNJ) restored the transport, maturation and activity of AalphaGlu in a dose dependent manner, while it had no effect on the reference enzyme beta-hexosaminidase. NB-DNJ promoted export from the endoplasmic reticulum (ER) to the lysosomes and stabilized the activity of mutant AalphaGlu species, Y455F and P545L, inside the lysosomes. In long-term culture, the AalphaGlu activity in the fibroblasts from the patients with mutant phenotypes, Y455F/Y455F and P545L/P545L, increased up to 14.0- and 7.9-fold, respectively, in the presence of 10mumol/L NB-DNJ. However, the effect of NB-DNJ on Y455F/Y455F subsided quickly after removal of the compound. We conclude that NB-DNJ acts in low concentration as chemical chaperone for certain mutant forms of AalphaGlu that are trapped in the ER, poorly transported or labile in the lysosomal environment. Chemical chaperone therapy could create new perspectives for therapeutic intervention in GSDII.

Structure of acid beta-glucosidase with pharmacological chaperone provides insight into Gaucher disease

Gaucher disease results from mutations in the lysosomal enzyme acid beta-glucosidase (GCase). Although enzyme replacement therapy has improved the health of some affected individuals, such as those with the prevalent N370S mutation, oral treatment with pharmacological chaperones may be therapeutic in a wider range of tissue compartments by restoring sufficient activity of endogenous mutant GCase. Here we demonstrate that isofagomine (IFG, 1) binds to the GCase active site, and both increases GCase activity in cell lysates and restores lysosomal trafficking in cells containing N370S mutant GCase. We also compare the crystal structures of IFG-bound GCase at low pH with those of glycerol-bound GCase at low pH and apo-GCase at neutral pH. Our data indicate that IFG induces active GCase, which is secured by interactions with Asn370. The design of small molecules that stabilize substrate-bound conformations of mutant proteins may be a general therapeutic strategy for diseases caused by protein misfolding and mistrafficking.

Sphingolipid metabolism diseases

Human diseases caused by alterations in the metabolism of sphingolipids or glycosphingolipids are mainly disorders of the degradation of these compounds. The sphingolipidoses are a group of monogenic inherited diseases caused by defects in the system of lysosomal sphingolipid degradation, with subsequent accumulation of non-degradable storage material in one or more organs. Most sphingolipidoses are associated with high mortality. Both, the ratio of substrate influx into the lysosomes and the reduced degradative capacity can be addressed by therapeutic approaches. In addition to symptomatic treatments, the current strategies for restoration of the reduced substrate degradation within the lysosome are enzyme replacement therapy (ERT), cell-mediated therapy (CMT) including bone marrow transplantation (BMT) and cell-mediated "cross correction", gene therapy, and enzyme-enhancement therapy with chemical chaperones. The reduction of substrate influx into the lysosomes can be achieved by substrate reduction therapy. Patients suffering from the attenuated form (type 1) of Gaucher disease and from Fabry disease have been successfully treated with ERT.

Hydrophilic iminosugar active-site-specific chaperones increase residual glucocerebrosidase activity in fibroblasts from Gaucher patients

Gaucher disease is an autosomal recessive lysosomal storage disorder caused by the deficient activity of glucocerebrosidase. Accumulation of glucosylceramide, primarily in the lysosomes of cells of the reticuloendothelial system, leads to hepatosplenomegaly, anemia and skeletal lesions in type I disease, and neurologic manifestations in types II and III disease. We report herein the identification of hydrophilic active-site-specific chaperones that are capable of increasing glucocerebrosidase activity in the cultured fibroblasts of Gaucher patients. Screening of a variety of natural and synthetic alkaloid compounds showed isofagomine, N-dodecyl deoxynojirimycin, calystegines A3, B1, B2 and C1, and 1,5-dideoxy-1,5-iminoxylitol to be potent inhibitors of glucocerebrosidase. Among them, isofagomine was the most potent inhibitor of glucocerebrosidase in vitro, and the most effective active-site-specific chaperone capable of increasing residual glucocerebrosidase activity in fibroblasts established from Gaucher patients with the most prevalent Gaucher disease-causing mutation (N370S). Intracellular enzyme activity increased approximately two-fold after cells had been incubated with isofagomine, and the increase in glucocerebrosidase activity was both dose-dependent and time-dependent. Western blotting demonstrated that there was a substantial increase in glucocerebrosidase protein in cells after isofagomine treatment. Immunocytochemistry revealed an improvement in the glucocerebrosidase trafficking pattern, which overlaps that of lysosome-associated membrane protein 2 in Gaucher fibroblasts cultivated with isofagomine, suggesting that the transport of mutant glucocerebrosidase is at least partially improved in the presence of isofagomine. The hydrophilic active-site-specific chaperones are less toxic to cultured cells. These results indicate that these hydrophilic small molecules are suitable candidates for further drug development for the treatment of Gaucher disease.

Inhibitors of sphingolipid metabolism enzymes

Sphingolipids are a family of lipids that play essential roles both as structural cell membrane components and in cell signalling. The cellular contents of the various sphingolipid species are controlled by enzymes involved in their metabolic pathways. In this context, the discovery of small chemical entities able to modify these enzyme activities in a potent and selective way should offer new pharmacological tools and therapeutic agents.

Genetic diseases of sphingolipid metabolism: pathological mechanisms and therapeutic options

Although diseases in the pathway of sphingolipid degradation have been known for decades, the first disease in the biosynthetic pathway was only reported in 2004, when a form of infantile-onset symptomatic epilepsy was described as a genetic defect in GM3 synthase. Presumably other diseases in the sphingolipid biosynthetic pathway will yet be discovered, although many may remain undetected due to their putative lethal phenotypes. In contrast, diseases are known for essentially every step in the pathway of SL degradation, caused by the defective activity of one or other of the lysosomal hydrolases in this pathway. Despite the fact that some of these storage disorders were first discovered in the 19th century, the cellular and biochemical events that cause pathology are still poorly delineated. In this review, we focus on recent advances in our understanding of how defects in the pathways of sphingolipid metabolism may lead to pathology. In addition, we discuss currently-available and emerging therapeutic options.

Alpha-1-C-octyl-1-deoxynojirimycin as a pharmacological chaperone for Gaucher disease

The most common lysosomal storage disorder, Gaucher disease, is caused by inefficient folding and trafficking of certain variants of lysosomal beta-glucosidase (beta-Glu, also known as beta-glucocerebrosidase). Recently, Sawker et al. reported that the addition of subinhibitory concentrations (10 microM) of the pharmacological chaperone N-nonyl-1-deoxynojirimycin (NN-DNJ) (10) to Gaucher patient-derived cells leads to a 2-fold increase in activity of mutant (N370S) enzyme [Proc. Natl. Acad. Sci. U.S.A.2002, 99, 15428]. However, we found that the addition of NN-DNJ at 10 microM lowered the lysosomal alpha-glucosidase (alpha-Glu) activity by 50% throughout the assay period in spite of the excellent chaperoning activity in N370S fibroblasts. Hence, we prepared a series of DNJ derivatives with an alkyl chain at the C-1alpha position and evaluated their in vitro inhibitory activity and potential as pharmacological chaperones for Gaucher cell lines. Among them, alpha-1-C-octyl-DNJ (CO-DNJ) (15) showed 460-fold stronger in vitro inhibitory activity than DNJ toward beta-Glu, while NN-DNJ enhanced in vitro inhibitory activity by 360-fold. Treatment with CO-DNJ (20 microM) for 4 days maximally increased intracellular beta-Glu activity by 1.7-fold in Gaucher N370 cell line (GM0037) and by 2.0-fold in another N370 cell line (GM00852). The addition of 20 microM CO-DNJ to the N370S (GM00372) culture medium for 10 days led to 1.9-fold increase in the beta-Glu activity without affecting the intracellular alpha-Glu activity for 10 days. Only CO-DNJ showed a weak beta-Glu chaperoning activity in the L444P type 2 variant, with 1.2-fold increase at 5-20 microM, and furthermore maximally increased the alpha-Glu activity by 1.3-fold at 20 microM. These experimental results suggest that CO-DNJ is a significant pharmacological chaperone for N370S Gaucher variants, minimizing the potential for undesirable side effects such as alpha-Glu inhibition.

Fabry disease: identification of 50 novel alpha-galactosidase A mutations causing the classic phenotype and three-dimensional structural analysis of 29 missense mutations

Fabry disease, an X-linked recessive inborn error of glycosphingolipid catabolism, results from the deficient activity of the lysosomal exoglycohydrolase, α-galactosidase A (EC 3.2.1.22; α-Gal A). The molecular lesions in the α-Gal A gene causing the classic phenotype of Fabry disease in 66 unrelated families were determined. In 49 families, 50 new mutations were identified, including: 29 missense mutations (N34K, T41I, D93V, R112S, L166G, G171D, M187T, S201Y, S201F, D234E, W236R, D264Y, M267R, V269M, G271S, G271V, S276G, Q283P, A285P, A285D, M290I, P293T, Q312H, Q321R, G328V, E338K, A348P, E358A, Q386P); nine nonsense mutations (C56X, E79X, K127X, Y151X, Y173X, L177X, W262X, Q306X, E338X); five splicing defects (IVS4-1G > A, IVS5-2A > G, IVS5 + 3A > G, IVS5 + 4A > G, IVS6-1G > C); four small deletions (18delA, 457delGAC, 567delG, 1096delACCAT); one small insertion (996insC); one 3.1 kilobase Alu-Alu deletion (which included exon 2); and one complex mutation (K374R, 1124delGAG). In 18 families, 17 previously reported mutations were identified, with R112C occurring in two families. In two classically affected families, affected males were identified with two mutations: one with two novel mutations, D264Y and V269M and the other with one novel (Q312H) and one previously reported (A143T) mutation. Transient expression of the individual mutations revealed that D264Y and Q312H were localised in the endoplasmic reticulum and had no detectable or markedly reduced activity, whereas V269M and A143T were localised in lysosomes and had approximately 10 per cent and approximately 35 per cent of expressed wild-type activity, respectively. Structural analyses based on the enzyme's three-dimensional structure predicted the effect of the 29 novel missense mutations on the mutant glycoprotein's structure. Of note, three novel mutations (approximately 10 per cent) were predicted not to significantly alter the glycoprotein's structure; however, they were disease causing. These studies further define the molecular heterogeneity of the α-Gal A mutations in classical Fabry disease, permit precise heterozygote detection and prenatal diagnosis, and provide insights into the structural alterations of the mutant enzymes that cause the classic phenotype.

High incidence of later-onset fabry disease revealed by newborn screening

The classic phenotype of Fabry disease, X-linked alpha -galactosidase A (alpha -Gal A) deficiency, has an estimated incidence of approximately 1 in 50,000 males. The recent recognition of later-onset variants suggested that this treatable lysosomal disease is more frequent. To determine the disease incidence, we undertook newborn screening by assaying the alpha-Gal A activity in blood spots from 37,104 consecutive Italian male neonates. Enzyme-deficient infants were retested, and "doubly screened-positive" infants and their relatives were diagnostically confirmed by enzyme and mutation analyses. Twelve (0.03%) neonates had deficient alpha-Gal A activities and specific mutations, including four novel missense mutations (M51I, E66G, A73V, and R118C), three missense mutations (F113L, A143T, and N215S) identified previously in later-onset patients, and one splicing defect (IVS5(+1G-->T)) reported in a patient with the classic phenotype. Molecular modeling and in vitro overexpression of the missense mutations demonstrated structures and residual activities, which were rescued/enhanced by an alpha-Gal A-specific pharmacologic chaperone, consistent with mutations that cause the later-onset phenotype. Family studies revealed undiagnosed Fabry disease in affected individuals. In this population, the incidence of alpha-Gal A deficiency was 1 in approximately 3,100, with an 11 : 1 ratio of patients with the later-onset : classic phenotypes. If only known disease-causing mutations were included, the incidence would be 1 in approximately 4,600, with a 7 : 1 ratio of patients with the later-onset : classic phenotypes. These results suggest that the later-onset phenotype of Fabry disease is underdiagnosed among males with cardiac, cerebrovascular, and/or renal disease. Recognition of these patients would permit family screening and earlier therapeutic intervention. However, the higher incidence of the later-onset phenotype in patients raises ethical issues related to when screening should be performed--in the neonatal period or at early maturity, perhaps in conjunction with screening for other treatable adult-onset disorders.