Neuronopathic Gaucher's disease: induced pluripotent stem cells for disease modelling and testing chaperone activity of small compounds

Emerging therapeutic targets for Gaucher disease

INTRODUCTION

Gaucher disease (GD) is an inherited metabolic disorder caused by mutations in the glucocerebrosidase (GBA1) gene. Although infusions of recombinant GBA ameliorate the systemic effects of GD, this therapy has no effect on the neurological manifestations. Patients with the neuronopathic forms of GD (nGD) are often severely disabled and die prematurely. The search for innovative drugs is thus urgent for the neuronopathic forms.

AREAS COVERED

Here we briefly summarize the available treatments for GD. We then review recent studies of the molecular pathogenesis of GD, which suggest new avenues for therapeutic development.

EXPERT OPINION

Existing treatments for GD are designed to target the primary consequence of the inborn defects of sphingolipid metabolism, that is, lysosomal accumulation of glucosylceramide (GlcCer). Here we suggest that targeting other pathways, such as those that are activated as a consequence of GlcCer accumulation, may also have salutary clinical effects irrespective of whether excess substrate persists. These pathways include those implicated in neuroinflammation, and specifically, receptor-interacting protein kinase-3 (RIP3) and related components of this pathway, which appear to play a vital role in the pathogenesis of nGD. Once available, inhibitors to components of the RIP kinase pathway will hopefully offer new therapeutic opportunities in GD.

Conformationally-locked N-glycosides: exploiting long-range non-glycone interactions in the design of pharmacological chaperones for Gaucher disease

Pyranoid-type glycomimetics having a cis-1,2-fused glucopyranose-2-alkylsulfanyl-1,3-oxazoline (Glc-PSO) structure exhibit an unprecedented specificity as inhibitors of mammalian β-glucosidase. Notably, their inhibitory potency against human β-glucocerebrosidase (GCase) was found to be strongly dependent on the nature of aglycone-type moieties attached at the sulfur atom. In the particular case of ω-substituted hexadecyl chains, an amazing influence of the terminal group was observed. A comparative study on a series of Glc-PSO derivatives suggests that hydrogen bond acceptor functionalities, e.g. fluoro or methyloxycarbonyl, significantly stabilize the Glc-PSO:GCase complex. The S-(16-fluorohexadecyl)-PSO glycomimetic turned out to be a more potent GCase competitive inhibitor than ambroxol, a non glycomimetic drug currently in pilot trials as a pharmacological chaperone for Gaucher disease. Moreover, the inhibition constant increased by one order of magnitude when shifting from neutral (pH 7) to acidic (pH 5) media, a favorable characteristic for a chaperone candidate. Indeed, the fluoro-PSO derivative also proved superior to ambroxol in mutant GCase activity enhancement assays in N370S/N370S Gaucher fibroblasts. The results presented here represent a proof of concept of the potential of exploiting long-range non-glycone interactions for the optimization of glycosidase inhibitors with chaperone activity.

Induced pluripotent stem cell (iPSC)-derived dopaminergic models of Parkinson's disease

iPSCs (induced pluripotent stem cells) are the newest tool used to model PD (Parkinson's disease). Fibroblasts from patients carrying pathogenic mutations that lead to PD have been reprogrammed into iPSCs, which can subsequently be differentiated into important cell types. Given the characteristic loss of dopaminergic neurons in the substantia nigra pars compacta of PD patients, iPSC-derived midbrain dopaminergic neurons have been generated to investigate pathogenic mechanisms in this important cell type as a means of modelling PD. iPSC-derived cultures studied so far have been made from patients carrying mutations in LRRK2 (leucine-rich repeat kinase 2), PINK1 [PTEN (phosphatase and tensin homologue deleted on chromosome 10)-induced putative kinase 1], PARK2 (encodes parkin) or GBA (β-glucocerebrosidase), in addition to those with SNCA (α-synuclein) multiplication and idiopathic PD. In some cases, isogenic control lines have been created to minimize inherent variability between lines from different individuals. Disruptions in autophagy, mitochondrial function and dopamine biology at the synapse have been described. Future applications for iPSC-derived models of PD beyond modelling include drug testing and the ability to investigate the genetic diversity of PD.

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.

Niemann-Pick Disease Type C: Induced Pluripotent Stem Cell-Derived Neuronal Cells for Modeling Neural Disease and Evaluating Drug Efficacy

Niemann-Pick disease type C (NPC) is a rare neurodegenerative disorder caused by recessive mutations in the NPC1 or NPC2 gene that result in lysosomal accumulation of unesterified cholesterol in patient cells. Patient fibroblasts have been used for evaluation of compound efficacy, although neuronal degeneration is the hallmark of NPC disease. Here, we report the application of human NPC1 neural stem cells as a cell-based disease model to evaluate nine compounds that have been reported to be efficacious in the NPC1 fibroblasts and mouse models. These cells are differentiated from NPC1 induced pluripotent stem cells and exhibit a phenotype of lysosomal cholesterol accumulation. Treatment of these cells with hydroxypropyl-β-cyclodextrin, methyl-β-cyclodextrin, and δ-tocopherol significantly ameliorated the lysosomal cholesterol accumulation. Combined treatment with cyclodextrin and δ-tocopherol shows an additive or synergistic effect that otherwise requires 10-fold higher concentration of cyclodextrin alone. In addition, we found that hydroxypropyl-β-cyclodextrin is much more potent and efficacious in the NPC1 neural stem cells compared to the NPC1 fibroblasts. Miglustat, suberoylanilide hydroxamic acid, curcumin, lovastatin, pravastatin, and rapamycin did not, however, have significant effects in these cells. The results demonstrate that patient-derived NPC1 neural stem cells can be used as a model system for evaluation of drug efficacy and study of disease pathogenesis.

Candidate molecules for chemical chaperone therapy of GM1-gangliosidosis

A growing body of evidence suggests that misfolding of a mutant protein followed by its aggregation or premature degradation in the endoplasmic reticulum is one of the main mechanisms that underlie inherited neurodegenerative diseases, including lysosomal storage diseases. Chemical or pharmacological chaperones are small molecules that bind to and stabilize mutant lysosomal enzyme proteins in the endoplasmic reticulum. A number of chaperone compounds for lysosomal hydrolases have been identified in the last decade. They have gained attention because they can be orally administrated, and also because they can penetrate the blood-brain barrier. In this article, we describe two chaperone candidates for the treatment of GM1-gangliosidosis. We also discuss the future direction of this strategy targeting other lysosomal storage diseases as well as protein misfolding diseases in general.

Stem cells on the brain: modeling neurodevelopmental and neurodegenerative diseases using human induced pluripotent stem cells

Seven years have passed since the initial report of the generation of induced pluripotent stem cells (iPSCs) from adult human somatic cells, and in the intervening time the field of neuroscience has developed numerous disease models using this technology. Here, we review progress in the field and describe both the advantages and potential pitfalls of modeling neurodegenerative and neurodevelopmental diseases using this technology. We include tables with information on neural differentiation protocols and studies that developed human iPSC lines to model neurological diseases. We also discuss how one can: investigate effects of genetic mutations with iPSCs, examine cell fate-specific phenotypes, best determine the specificity of a phenotype, and bring in vivo relevance to this in vitro technique.

Human stem cell models of neurodegeneration: a novel approach to study mechanisms of disease development

The number of patients with neurodegenerative diseases is increasing significantly worldwide. Thus, intense research is being pursued to uncover mechanisms of disease development in an effort to identify molecular targets for therapeutic intervention. Analysis of postmortem tissue from patients has yielded important histological and biochemical markers of disease progression. However, this approach is inherently limited because it is not possible to study patient neurons prior to degeneration. As such, transgenic and knockout models of neurodegenerative diseases are commonly employed. While these animal models have yielded important insights into some molecular mechanisms of disease development, they do not provide the opportunity to study mechanisms of neurodegeneration in human neurons at risk and thus, it is often difficult or even impossible to replicate human pathogenesis with this approach. The generation of patient-specific induced pluripotent stem (iPS) cells offers a unique opportunity to overcome these obstacles. By expanding and differentiating iPS cells, it is possible to generate large numbers of functional neurons in vitro, which can then be used to study the disease of the donating patient. Here, we provide an overview of human stem cell models of neurodegeneration using iPS cells from patients with Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, frontotemporal dementia, Huntington's disease, spinal muscular atrophy and other neurodegenerative diseases. In addition, we describe how further refinements of reprogramming technology resulted in the generation of patient-specific induced neurons, which have also been used to model neurodegenerative changes in vitro.

Targeted delivery of pharmacological chaperones for Gaucher disease to macrophages by a mannosylated cyclodextrin carrier

Efficient delivery of pharmacological chaperones for Gaucher disease to macrophages has been achieved.

New castanospermine glycoside analogues inhibit breast cancer cell proliferation and induce apoptosis without affecting normal cells

sp²-Iminosugar-type castanospermine analogues have been shown to exhibit anti-tumor activity. However, their effects on cell proliferation and apoptosis and the molecular mechanism at play are not fully understood. Here, we investigated the effect of two representatives, namely the pseudo-S- and C-octyl glycoside 2-oxa-3-oxocastanospermine derivatives SO-OCS and CO-OCS, on MCF-7 and MDA-MB-231 breast cancer and MCF-10A mammary normal cell lines. We found that SO-OCS and CO-OCS inhibited breast cancer cell viability in a concentration- and time-dependent manner. This effect is specific to breast cancer cells as both molecules had no impact on normal MCF-10A cell proliferation. Both drugs induced a cell cycle arrest. CO-OCS arrested cell cycle at G1 and G2/M in MCF-7 and MDA-MB-231cells respectively. In MCF-7 cells, the G1 arrest is associated with a reduction of CDK4 (cyclin-dependent kinase 4), cyclin D1 and cyclin E expression, pRb phosphorylation, and an overexpression of p21^Waf1/Cip1. In MDA-MB-231 cells, CO-OCS reduced CDK1 but not cyclin B1 expression. SO-OCS accumulated cells in G2/M in both cell lines and this blockade was accompanied by a decrease of CDK1, but not cyclin B1 expression. Furthermore, both drugs induced apoptosis as demonstrated by the increased percentage of annexin V positive cells and Bax/Bcl-2 ratio. Interestingly, in normal MCF-10A cells the two drugs failed to modify cell proliferation, cell cycle progression, cyclins, or CDKs expression. These results demonstrate that the effect of CO-OCS and SO-OCS is triggered by both cell cycle arrest and apoptosis, suggesting that these castanospermine analogues may constitute potential anti-cancer agents against breast cancer.

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 β-N-acetylglucosaminidase (human placenta) competitive inhibitor than the D-gluco (DNJNAc) and D-galacto (DGJNAc) stereoisomers.

Bicyclic derivatives of L-idonojirimycin as pharmacological chaperones for neuronopathic forms of Gaucher disease

New human β-glucocerebrosidase (GCase) ligands with rigid 1,6-anhydro-β-L-idonojirimycin cores have been designed with the aid of molecular modeling. Efficient pharmacological chaperones for the L444P (trafficking-incompetent) mutant GCase enzyme associated with type 2 and 3 Gaucher disease (GD) were identified.