Development of resistance to FGFR inhibition in urothelial carcinoma via multiple pathways in vitro

Alterations of fibroblast growth factor receptors (FGFRs) are common in bladder and other cancers and result in disrupted signalling via several pathways. Therapeutics that target FGFRs have now entered the clinic, but, in common with many cancer therapies, resistance develops in most cases. To model this, we derived resistant sublines of two FGFR-driven bladder cancer cell lines by long-term culture with the FGFR inhibitor PD173074 and explored mechanisms using expression profiling and whole-exome sequencing. We identified several resistance-associated molecular profiles. These included HRAS mutation in one case and reversible mechanisms resembling a drug-tolerant persister phenotype in others. Upregulated IGF1R expression in one resistant derivative was associated with sensitivity to linsitinib and a profile with upregulation of a YAP/TAZ signature to sensitivity to the YAP inhibitor CA3 in another. However, upregulation of other potential therapeutic targets was not indicative of sensitivity. Overall, the heterogeneity in resistance mechanisms and commonality of the persister state present a considerable challenge for personalised therapy. Nevertheless, the reversibility of resistance may indicate a benefit from treatment interruptions or retreatment following disease relapse in some patients. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Molecular profile of pure squamous cell carcinoma of the bladder identifies major roles for OSMR and YAP signalling

Pure squamous cell carcinoma (SCC) is the most common pure variant form of bladder cancer, found in 2–5% of cases. It often presents late and is unresponsive to cisplatin‐based chemotherapy. The molecular features of these tumours have not been elucidated in detail. We carried out whole‐exome sequencing (WES), copy number, and transcriptome analysis of bladder SCC. Muscle‐invasive bladder cancer (MIBC) samples with no evidence of squamous differentiation (non‐SD) were used for comparison. To assess commonality of features with urothelial carcinoma with SD, we examined data from SD samples in The Cancer Genome Atlas (TCGA) study of MIBC. TP53 was the most commonly mutated gene in SCC (64%) followed by FAT1 (45%). Copy number analysis revealed complex changes in SCC, many differing from those in samples with SD. Gain of 5p and 7p was the most common feature, and focal regions on 5p included OSMR and RICTOR. In addition to 9p deletions, we found some samples with focal gain of 9p24 containing CD274 (PD‐L1). Loss of 4q35 containing FAT1 was found in many samples such that all but one sample analysed by WES had FAT1 mutation or deletion. Expression features included upregulation of oncostatin M receptor (OSMR), metalloproteinases, metallothioneins, keratinisation genes, extracellular matrix components, inflammatory response genes, stem cell markers, and immune response modulators. Exploration of differentially expressed transcription factors identified BNC1 and TFAP2A, a gene repressed by PPARG, as the most upregulated factors. Known urothelial differentiation factors were downregulated along with 72 Kruppel‐associated (KRAB) domain‐containing zinc finger family protein (KZFP) genes. Novel therapies are urgently needed for these tumours. In addition to upregulated expression of EGFR, which has been suggested as a therapeutic target in basal/squamous bladder cancer, we identified expression signatures that indicate upregulated OSMR and YAP/TAZ signalling. Preclinical evaluation of the effects of inhibition of these pathways alone or in combination is merited.

Stage-stratified molecular profiling of non-muscle-invasive bladder cancer enhances biological, clinical, and therapeutic insight

Understanding the molecular determinants that underpin the clinical heterogeneity of non-muscle-invasive bladder cancer (NMIBC) is essential for prognostication and therapy development. Stage T1 disease in particular presents a high risk of progression and requires improved understanding. We present a detailed multi-omics study containing gene expression, copy number, and mutational profiles that show relationships to immune infiltration, disease recurrence, and progression to muscle invasion. We compare expression and genomic subtypes derived from all NMIBCs with those derived from the individual disease stages Ta and T1. We show that sufficient molecular heterogeneity exists within the separate stages to allow subclassification and that this is more clinically meaningful for stage T1 disease than that derived from all NMIBCs. This provides improved biological understanding and identifies subtypes of T1 tumors that may benefit from chemo- or immunotherapy.

Genomic Subtypes of Non-invasive Bladder Cancer with Distinct Metabolic Profile and Female Gender Bias in KDM6A Mutation Frequency

Bladder cancer incurs a higher lifetime treatment cost than other cancers due to frequent recurrence of non-invasive disease. Improved prognostic biomarkers and localized therapy are needed for this large patient group. We defined two major genomic subtypes of primary stage Ta tumors. One of these was characterized by loss of 9q including TSC1, increased KI67 labeling index, upregulated glycolysis, DNA repair, mTORC1 signaling, features of the unfolded protein response, and altered cholesterol homeostasis. Comparison with muscle-invasive bladder cancer mutation profiles revealed lower overall mutation rates and more frequent mutations in RHOB and chromatin modifier genes. More mutations in the histone lysine demethylase KDM6A were present in non-invasive tumors from females than males.

Abstract LB-323: The genomic landscape of non-muscle-invasive bladder cancer: implications for molecular classification and treatment

Non-muscle-invasive bladder cancers (NMIBC) and muscle-invasive bladder cancers (MIBC) show distinct molecular and clinical features and are considered to follow different pathogenesis pathways. MIBC commonly metastasise (>50%) and have poor prognosis whereas NMIBC, particularly low-stage low-grade tumors, rarely progress to invade muscle (<5%). Patients diagnosed with NMIBC frequently suffer disease recurrence, demanding long-term disease monitoring and repeated resection of recurrences. Large MIBC cohorts have been extensively interrogated on a genome-wide scale but relatively few NMIBC have been studied at this level. To address this we determined the mutational landscape of 82 non-muscle-invasive tumors (stage Ta grade 2) using whole-exome and targeted deep sequencing. Whole-exome sequencing identified an average of 124±79 synonymous and non-synonymous somatic mutations (single nucleotide substitutions and indels) per sample, giving mean and median somatic mutation rates of 2.41 and 1.64 per megabase, respectively. Overall, 47% of nucleotide substitutions were C>T transitions, followed by C>G transversions (24.8%). Similar to MIBC, APOBEC mutagenesis was the strongest source of mutation in NMIBC with 75% of samples showing up to 5-fold enrichment of the APOBEC mutation signature. Significantly mutated genes included genes implicated in epigenetic regulation and several genes that have not previously been reported as significantly mutated in bladder cancer. Comparison of mutation frequencies in NMIBC with those found in MIBC revealed both known differences (absence of TP53 mutations and high frequency of FGFR3, PIK3CA and STAG2 mutations in NMIBC) and novel findings including a higher frequency of mutations in chromatin-state regulators in NMIBC. Notably CDKN1A, RB1, ERCC2, ERBB3 and FBXW7, which are mutated in >10% of MIBC were not significantly mutated in TaG2 tumors, further delineating the distinct pathogenesis pathways of NMIBC and MIBC. Whole-genome expression array profiling and immunohistochemistry using a panel of markers were carried out to further examine the molecular features of NMIBC samples and define potentially clinically relevant subtypes. These data provide a detailed view of the genomic landscape of NMIBC that highlights chromatin modification as a key area for consideration in the development of potential future therapeutic approaches to the treatment of patients with non-muscle-invasive disease.

Citation Format: Carolyn D. Hurst, Olivia Alder, Fiona M. Platt, Alastair Droop, Lucy F. Stead, Julie E. Burns, George J. Burghel, Sunjay Jain, Leszek J. Klimczak, Helen Lindsay, Jo-An Roulson, Claire F. Taylor, Helene Thygesen, Angus J. Cameron, Anne J. Ridley, Helene R. Mott, Dmitry A. Gordenin, Margaret A. Knowles. The genomic landscape of non-muscle-invasive bladder cancer: implications for molecular classification and treatment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-323.

Frequent inactivating mutations of STAG2 in bladder cancer are associated with low tumour grade and stage and inversely related to chromosomal copy number changes

Inactivating mutations of STAG2 have been reported at low frequency in several cancers. In glioblastoma, the function of STAG2 has been related to maintenance of euploidy via its role in the cohesin complex. In a screen of a large series of bladder tumours and cell lines, we found inactivating mutations (nonsense, frameshift and splicing) in 67 of 307 tumours (21.8%) and 6 of 47 cell lines. Thirteen missense mutations of unknown significance were also identified. Inactivating mutation was associated with low tumour stage (P = 0.001) and low grade (P = 0.0002). There was also a relationship with female patient gender (P = 0.042). Examination of copy number profiles revealed an inverse relationship of mutation with both fraction of genome altered and whole chromosome copy number changes. Immunohistochemistry showed that in the majority of cases with inactivating mutations, STAG2 protein expression was absent. Strikingly, we identified a relatively large subset of tumours (12%) with areas of both positive and negative immunoreactivity, in only four of which a potentially function-altering mutation was detected. Regions of differential expression were contiguous and showed similar morphological phenotype in all cases. Microdissected positive and negative areas from one tumour showed an inactivating mutation to be present only in the negative area, suggesting intra-tumoral sub-clonal genomic evolution. Our findings indicate that loss of STAG2 function plays a more important role in non-invasive than that in muscle-invasive bladder cancer and suggest that cohesin complex-independent functions are likely to be important in these cases.

Putative tumour suppressor gene necdin is hypermethylated and mutated in human cancer

Background:

Necdin (NDN) expression is downregulated in telomerase-immortalised normal human urothelial cells. Telomerase-immortalised normal human urothelial cells have no detected genetic alterations. Accordingly, many of the genes whose expression is altered following immortalisation are those for which epigenetic silencing is reported.

Methods:

NDN expression was examined in normal tissues and tumour cell lines by quantitative real-time PCR and immunoblotting. Immunohistochemistry was performed on urothelial carcinoma (UC). Urothelial carcinoma and UC cell lines were subject to HumanMethylation27 BeadChip Array-based methylation analyses. Mutation screening was performed. The functional significance of NDN expression was investigated using retroviral-mediated downregulation or overexpression.

Results:

NDN protein was widely expressed in normal tissues. Loss of expression was observed in 38 out of 44 (86%) of UC cell lines and 19 out of 25 (76%) of non-UC cell lines. Loss of NDN protein was found in the majority of primary UC. Oncomine analysis demonstrated downregulation of expression in multiple tumour types. In UC, tumour-specific hypermethylation of NDN and key CpG sites where hypermethylation correlated with reduced expression were identified. Six novel mutations, including some of predicted functional significance, were identified in colorectal and ovarian cancer cell lines. Functional studies showed that NDN could suppress colony formation at low cell density and affect anchorage-independent growth and anoikis in vitro.

Conclusion:

NDN is a novel tumour suppressor candidate that is downregulated and hypermethylated or mutated in cancer.

Abstract 821: Subgroups of urothelial carcinoma of the bladder defined by genomic analysis

Urothelial carcinoma (UC) of the bladder is a heterogeneous disease and presents a significant challenge in disease management. The divergence in clinical behaviour of tumors of similar stage and grade indicates the presence of molecular subgroups. In this study we aimed to identify novel genomic subgroups of UC to provide improved subclassification at diagnosis. We assessed 160 bladder tumors comprising all stages and grades and including 49 high-stage T1 (T1G3) tumors for genome-wide copy number alterations and mutations in 8 key genes (AKT1, FGFR3, HRAS, KRAS, NRAS, PIK3CA, TP53, TSC1) implicated in UC. This revealed the existence of potential genomic subclasses of the “gold-standard” stage/grade groups of UC. The clinical management of patients with T1G3 tumors is particularly challenging as this subset of tumors exhibit highly divergent behaviour. Three major subgroups of T1G3 tumors were identified that differed with respect to copy number alterations and to FGFR3 and TP53 mutation status. One of these, which showed a prevalence of copy number losses, had the highest rate of stage progression/metastasis. We also identified novel regions of copy number alteration, concomitant molecular events, and relationships between molecular events and clinico-pathological features. Tumors harbouring FGFR3 mutations were found to be more chromosomally stable than their wild-type counterparts and FGFR3 mutation was mutually exclusive with overrepresentation of 8q in non-muscle-invasive tumors. In muscle-invasive (MI) tumors, losses of regions on 10q (including PTEN), 16q and 22q and gains on 10q, 11p, 12p, 19p and 19q were positively associated with metastasis. TP53 mutation in MI tumors was positively associated with losses on 16p, 2q, 4q, 11p, 10q, 13q, 14q, 16q and 19p and gains on 1p, 8q, 10q and 12q. Molecular alterations involving chromosome 9 were highly complex and copy number loss in the CDKN2A region was positively associated with deletions on 6p, 6q, 9p, 9q, 11p, 13q and 17p, and gains on 1q, 4q, 7p, 7q, 8p, 17q and 20q in MI tumors. Our findings add information to conventional histopathological classification and may lead to improved biological understanding and the development of robust prognostic biomarkers. Studies of larger numbers of tumors are underway to confirm the subgroups and relate findings to clinico-pathological data.

Citation Format: Carolyn D. Hurst, Fiona M. Platt, Claire F. Taylor, Margaret A. Knowles. Subgroups of urothelial carcinoma of the bladder defined by genomic analysis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 821. doi:10.1158/1538-7445.AM2013-821

Novel tumor subgroups of urothelial carcinoma of the bladder defined by integrated genomic analysis

PURPOSE

There is a need for improved subclassification of urothelial carcinoma (UC) at diagnosis. A major aim of this study was to search for novel genomic subgroups.

EXPERIMENTAL DESIGN

We assessed 160 tumors for genome-wide copy number alterations and mutation in genes implicated in UC. These comprised all tumor grades and stages and included 49 high-grade stage T1 (T1G3) tumors.

RESULTS

Our findings point to the existence of genomic subclasses of the "gold-standard" grade/stage groups. The T1G3 tumors separated into 3 major subgroups that differed with respect to the type and number of copy number events and to FGFR3 and TP53 mutation status. We also identified novel regions of copy number alteration, uncovered relationships between molecular events, and elucidated relationships between molecular events and clinico-pathologic features. FGFR3 mutant tumors were more chromosomally stable than their wild-type counterparts and a mutually exclusive relationship between FGFR3 mutation and overrepresentation of 8q was observed in non-muscle-invasive tumors. In muscle-invasive (MI) tumors, metastasis was positively associated with losses of regions on 10q (including PTEN), 16q and 22q, and gains on 10p, 11q, 12p, 19p, and 19q. Concomitant copy number alterations positively associated with TP53 mutation in MI tumors were losses on 16p, 2q, 4q, 11p, 10q, 13q, 14q, 16q, and 19p, and gains on 1p, 8q, 10q, and 12q. Significant complexity was revealed in events affecting chromosome 9.

CONCLUSIONS

These findings may lead to improved biologic understanding and the development of prognostic biomarkers. Novel regions of copy number alteration may reveal potential therapeutic targets.

High-resolution analysis of genomic alteration on chromosome arm 8p in urothelial carcinoma

Loss of chromosome arm 8p, sometimes in combination with amplification of proximal 8p, is found in urothelial carcinoma (UC) and other epithelial cancers and is associated with more advanced tumor stage. We carried out array comparative genomic hybridization on 174 UC and 33 UC cell lines to examine breakpoints and copy number. This was followed by a detailed analysis of the cell lines using fluorescence in situ hybridization (FISH) and, in some cases, M-FISH, to refine breakpoints and determine translocation partners, heterozygosity analysis, and analysis of expression of selected genes. We showed an overall pattern of 8p loss with reduced heterozygosity and reduced gene expression. Amplification was seen in some samples and shown in the cell line JMSU1 to correlate with overexpression of ZNF703, ERLIN2, PROSC, GPR124, and BRF2. Apart from the centromere, no single breakpoint was overrepresented, and we postulate that frequent complex changes without consistent breakpoints reflect the need for alterations of combinations of genes. The region around 2 Mb, which was homozygously deleted in one cell line and includes the gene ARHGEF10 and the micro-RNA hsa-mir-596, is one candidate tumor suppressor gene region.

Spectrum of phosphatidylinositol 3-kinase pathway gene alterations in bladder cancer

PURPOSE

The phosphatidylinositol 3-kinase (PI3K) pathway can be activated by alterations affecting several pathway components. For rational application of targeted therapies, detailed understanding of tumor biology and approaches to predict efficacy in individual tumors are required. Our aim was to assess the frequency and distribution of pathway alterations in bladder cancer.

EXPERIMENTAL DESIGN

We examined the pathway components (PIK3CA, PTEN, TSC1, RHEB, and LKB1) and putative upstream regulators (FGFR3 and RAS genes) for mutation, allelic loss, copy number alteration, and expression in bladder tumors and cell lines.

RESULTS

No mutations were found in RHEB and only a single mutation in LKB1. PIK3CA mutations were detected in 25% of tumors and 26% of cell lines with a significant excess of helical domain mutations (E542K and E545K). There was over-representation but not amplification of the gene. Loss of heterozygosity of the PTEN region and homozygous deletion were found in 12% and 1.4% of tumors, and reduced expression in 49%. Forty-six percent of cell lines showed alterations that implicated PTEN. Sixteen percent of tumors and 11% of cell lines showed TSC1 mutation, and 9q loss of heterozygosity was common (57%). Pathway alterations were independently distributed, suggesting that the mutation of two pathway members may have additive or synergistic effects through noncanonical functions.

CONCLUSIONS

PI3K pathway alterations are common in bladder cancer. The lack of redundancy of alterations suggests that single-agent PI3K-targeted therapy may not be successful in these cancers. This study provides a well-characterized series of cell lines for use in preclinical studies of targeted agents.

Integrated genomic and transcriptional analysis of the in vitro evolution of telomerase-immortalized urothelial cells (TERT-NHUC)

Much progress has been made in identifying the molecular genetic alterations that occur in bladder cancer. However, in many cases the genes targeted by these alterations are not known. Telomerase immortalized human urothelial cells (TERT-NHUC) are a useful resource for in vitro studies of genes involved in urothelial transformation. When cultured under standard conditions they remain genetically stable but when cultured under low-density conditions they exhibit genetic instability and acquire chromosomal alterations. TERT-NHUC from three donors were cultured at low plating density and examined at four time-points during a culture period of 600 days. Analyses included population doubling kinetics, array-based CGH (aCGH), chromosome counts, fluorescence in situ hybridization (FISH), mutation analysis, Affymetrix gene expression analysis, Western blotting for p16, anchorage-independent growth and tumorigenicity assays. Alterations acquired during continued culture of TERT-NHUC at low density (TERT-NHUC-L) included some observed in urothelial carcinoma (UC) cell lines and primary UC. Examination of gene expression in TERT-NHUC with distinct acquired genetic aberrations may pinpoint genes targeted by these alterations. Data from an aCGH study of UC cell lines and primary tumors were examined for changes in chromosomal regions that also showed alterations in TERT-NHUC-L. Loss of a region on 2q including BOK was identified in UC cell lines and primary tumors. DNER and FRAS1 were identified as potential candidate genes, whose expression is altered independently of the acquisition of any genetic event.

Bladder tumour-derived somatic TSC1 missense mutations cause loss of function via distinct mechanisms

More than 50% of transitional cell carcinomas of the bladder show loss of heterozygosity of a region spanning the TSC1 locus at 9q34 and mutations of TSC1 have been identified in 14.5% of tumours. These comprise nonsense mutations, splicing mutations, small deletions and missense mutations. Missense mutations are only rarely found in the germline in TSC disease. Therefore, we have examined six somatic missense mutations found in bladder cancer to determine whether these result in loss of function. We describe loss of function via distinct mechanisms. Five mutations caused mutually exclusive defects at mRNA and protein levels. Of these, two mutations caused pre-mRNA splicing errors that were predicted to result in premature protein truncation and three resulted in markedly reduced stability of exogenous TSC1 protein. Primary tumours with aberrant TSC1 pre-mRNA splicing were confirmed as negative for TSC1 expression by immunohistochemistry. Expression was also significantly reduced in a tumour with a TSC1 missense mutation resulting in diminished protein half-life. A single TSC1 missense mutation identified in a tumour with retained heterozygosity of the TSC1 region on chromosome 9 caused an apparently TSC2- and mTOR-independent localization defect of the mutant protein. We conclude that although TSC1 missense mutations do not play a major role in causation of TSC disease, they represent a significant proportion of somatic loss of function mutations in bladder cancer.

N-butyldeoxynojirimycin causes weight loss as a result of appetite suppression in lean and obese mice

AIM

To determine the mechanism of weight loss caused by high doses of N-butyldeoxynojirimycin (NB-DNJ) in healthy lean and leptin-deficient obese (ob/ob) mice.

METHODS

Healthy lean and obese mice were treated with NB-DNJ by the following methods: admixed with their diet, delivered by subcutaneously implanted mini-pumps or by intraperitoneal or intracerebroventricular (ICV) injection. Daily changes in body weight and food intake were recorded during the experimental period. The effect of NB-DNJ treatment on subcutaneous adipose tissue and on epididymal fat pads was measured.

RESULTS

Lean mice treated with NB-DNJ, admixed with their diet, lost weight in the form of adipose tissue. This resulted in a 40% reduction in skin thickness (control, 358 +/- 11 microm; NB-DNJ treated 203 +/- 6 microm) and a reduction in epididymal fat pad weights after 5 weeks of treatment at 2400 mg/kg/day (control, 0.0154 +/- 0.001; NB-DNJ treated, 0.0026 +/- 0.0005 as ratios of fat pad weight to total body weight). Following the depletion of adipose tissue mass, the mice grew normally and did not have any reduction in lean mass. Obese mice treated with NB-DNJ also lost weight or gained weight at a greatly reduced rate compared with non-treated controls. Body weights at 6 months of age were: lean control, 29.10 +/- 1.15 g; lean NB-DNJ treated, 22.73 +/- 0.29 g; obese control, 63.25 +/- 1.5 g; obese NB-DNJ treated from 5 weeks of age, 35.30 +/- 1.68 g; obese NB-DNJ treated from 12 weeks of age, 38.84 +/- 1.26 g. Both the lean and obese groups of mice treated with NB-DNJ ate up to 30% less than untreated controls. Daily food intake (powder diet) were: lean control, 4.15 +/- 0.54 g; obese control, 4.14 +/- 0.2 g; lean NB-DNJ treated 2.9 +/- 0.37 g; obese NB-DNJ treated, 2.88 +/- 0.47 g. Mice treated with the N-substituted galactose imino sugar analogue, N-butyldeoxygalactonojirimycin (NB-DGJ) did not lose weight. Mice experienced similar weight loss or lack of weight gain when fed a restricted diet that mimics the drug-induced level of food consumption. Delivery of 2 nmol NB-DNJ by ICV injection into lean mice also caused similar reductions in food intake. Food intake: saline vehicle, 4.30 +/- 0.12 g; NB-DNJ, 3.37 +/- 0.19 g; NB-DGJ, 4.03 +/- 0.16 g; 2-deoxyglucose, 4.7 +/- 0.15 g.

CONCLUSION

NB-DNJ causes weight loss as a result of reduced food consumption due to central appetite suppression.

Severe endothelial dysfunction in the aorta of a mouse model of Fabry disease; partial prevention by N-butyldeoxynojirimycin treatment

OBJECTIVE

Fabry disease results from alpha-gala-ctosidase A deficiency and is characterized by the lysosomal accumulation of globotriaosylceramide. Globotriaosylceramide storage predominantly affects endothelial cells, altering vascular wall morphology and vasomotor function. Our objective was to investigate aortic globotriaosylceramide levels, morphology and function in a mouse model of Fabry disease, and the effect of substrate reduction therapy, using the glycosphingolipid biosynthesis inhibitor N-butyldeoxynojirimycin.

METHODS AND RESULTS

Mice used were C57BL/6J and alpha-galactosidase A knockout (Fabry). We show progressive accumulation of aortic globotriaosylceramide throughout the lifespan of untreated Fabry mice (55-fold elevation at 2 months increasing to 187-fold by 19 months), localized to endothelial and vascular smooth-muscle cells; there was no effect on vascular wall morphology in young Fabry mice. In old mice, storage resulted in intimal thickening. Endothelial function declined with age in Fabry mouse aorta. Aortae from N-butyldeoxynojirimycin-treated Fabry mice at 19 months of age had reduced endothelial globotriaosylceramide storage, fewer morphological abnormalities and less severe vasomotor dysfunction compared with untreated littermates.

CONCLUSION

We provide evidence of a novel vascular phenotype in the Fabry mouse that has relevance to vascular disease in Fabry patients. N-Butyldeoxynojirimycin treatment partially prevented the phenotype in the Fabry mouse by reducing endothelial globotriaosylceramide storage.

MRS reveals additional hexose N-acetyl resonances in the brain of a mouse model for Sandhoff disease

Sandhoff disease, one of several related lysosomal storage disorders, results from the build up of N-acetyl-containing glycosphingolipids in the brain and is caused by mutations in the genes encoding the hexosaminidase beta-subunit. Affected individuals undergo progressive neurodegeneration in response to the glycosphingolipid storage. (1)H magnetic resonance spectra of perchloric acid extracts of Sandhoff mouse brain exhibited several resonances ca 2.07 ppm that were not present in the corresponding spectra from extracts of wild-type mouse brain. High-performance liquid chromatography and mass spectrometry of the Sandhoff extracts post-MRS identified the presence of N-acetylhexosamine-containing oligosaccharides, which are the likely cause of the additional MRS resonances. MRS of intact brain tissue with magic angle spinning also showed additional resonances at ca 2.07 ppm in the Sandhoff case. These resonances appeared to increase with disease progression and probably arise, for the most part, from the stored glycosphingolipids, which are absent in the aqueous extracts. Hence in vivo MRS may be a useful tool for detecting early-stage Sandhoff disease and response to treatment.

Substrate reduction reduces gangliosides in postnatal cerebrum-brainstem and cerebellum in GM1 gangliosidosis mice

II3NeuAc-GgOse4Cer (GM1) gangliosidosis is an incurable lysosomal storage disease caused by a deficiency in acid beta-galactosidase (beta-gal), resulting in the accumulation of ganglioside GM1 and its asialo derivative GgOse4Cer (GA1) in the central nervous system, primarily in the brain. In this study, we investigated the effects of N-butyldeoxygalacto-nojirimycin (N B-DGJ), an imino sugar that inhibits ganglioside biosynthesis, in normal C57BL/6J mice and in beta-gal knockout (beta-gal-/-) mice from postnatal day 9 (p-9) to p-15. This is a period of active cerebellar development and central nervous system (CNS) myelinogenesis in the mouse and would be comparable to late-stage embryonic and early neonatal development in humans. N B-DGJ significantly reduced total ganglioside and GM1 content in cerebrum-brainstem (C-BS) and in cerebellum of normal and beta-gal-/- mice. N B-DGJ had no adverse effects on body weight or C-BS/cerebellar weight, water content, or thickness of the external cerebellar granule cell layer. Sphingomyelin was increased in C-BS and cerebellum, but no changes were found for cerebroside (a myelin-enriched glycosphingolipid), neutral phospholipids, or GA1 in the treated mice. Our findings indicate that the effects of N B-DGJ in the postnatal CNS are largely specific to gangliosides and suggest that N B-DGJ may be an effective early intervention therapy for GM1 gangliosidosis and other ganglioside storage disorders.

New therapeutics for the treatment of glycosphingolipid lysosomal storage diseases

Glycosphingolipid lysosomal storage diseases are a small but challenging group of human disorders to treat. Although these appear to be monogenic disorders where the catalytic activity of enzymes in glycosphingolipid catabolism is impaired, the presentation and severity of disease is heterogeneous. Treatment is often restricted to palliative care, but in some disorders enzyme replacement does offer a significant clinical improvement of disease severity. An alternative therapeutic approach termed "substrate deprivation" or "substrate reduction therapy" (SRT) aims to reduce cellular glycosphingolipid biosynthesis to match the impairment in catalytic activity seen in lysosomal storage disorders. N-Alkylated imino sugars are nitrogen containing polyhydroxylated heterocycles that have inhibitory activity against the first enzyme in the pathway for glucosylating sphingolipid in eukaryotic cells, ceramide-specific glucosyltransferase. The use of N-alkylated imino sugars to establish SRT as an alternative therapeutic strategy is described in cell culture and gene knockout mouse disease models. One imino sugar, N-butyl-DNJ (NB-DNJ) has been used in clinical trials for type 1 Gaucher disease and has shown to be an effective and safe therapy for this disorder. The results of these trials and the prospects of improvement to the design of imino sugar compounds for treating Gaucher and other glycosphingolipid lysosomal storage disorders will be discussed.

Substrate deprivation: A new therapeutic approach for the glycosphingolipid lysosomal storage diseases

The glycosphingolipid (GSL) lysosomal storage diseases are a family of human metabolic diseases that, in their severest forms, cause death in early infancy, as a result of progressive neurodegeneration. They are caused by mutations in the genes encoding the glycohydrolases or the activator proteins that catabolise GSLs within lysosomes. In these diseases the GSL substrate of the defective enzyme accumulates in the lysosome, where it is stored and leads to cellular dysfunction and disease. The therapeutic options for treating these diseases are relatively limited; in fact, there are currently no available therapies for most of these disorders. The problem is further compounded by difficulties in delivering therapeutic agents to the central nervous system, which is where the pathology is frequently manifested. To date, research effort has mainly focused on strategies for augmenting enzyme concentrations to compensate for the underlying defect. These strategies include bone-marrow transplantation, enzyme-replacement therapy and gene therapy. Our group has been exploring the alternative strategy of substrate deprivation. This approach aims to balance the rate of GSL synthesis with the impaired rate of GSL breakdown. Studies using an asymptomatic mouse model of Tay-Sachs disease have shown that substrate deprivation prevents GSL storage. In a severe neurodegenerative mouse model of Sandhoff disease, substrate deprivation delayed the onset of symptoms and disease progression, and significantly increased life expectancy. The implications of this research for human therapy have been discussed.

Sustained therapeutic effects of oral miglustat (Zavesca, N-butyldeoxynojirimycin, OGT 918) in type I Gaucher disease

It has been shown that treatment with miglustat (Zavesca, N-butyldeoxynojirimycin, OGT 918) improves key clinical features of type I Gaucher disease after 1 year of treatment. This study reports longer-term efficacy and safety data. Patients who had completed 12 months of treatment with open-label miglustat (100-300 mg three times daily) were enrolled to continue with therapy in an extension study. Data are presented up to month 36. Liver and spleen volumes measured by CT or MRI were scheduled every 6 months. Biochemical and haematological parameters, including chitotriosidase activity (a sensitive marker of Gaucher disease activity) were monitored every 3 months. Safety data were also collected every 3 months. Eighteen of 22 eligible patients at four centres entered the extension phase and 14 of these completed 36 months of treatment with miglustat. After 36 months, there were statistically significant improvements in all major efficacy endpoints. Liver and spleen organ volumes were reduced by 18% and 30%, respectively. In patients whose haemoglobin value had been below 11.5 g/dl at baseline, mean haemoglobin increased progressively from baseline by 0.55 g/dl at month 12 (NS), 1.28 g/dl at month 24 (p =0.007), and 1.30 g/dl at month 36 (p =0.013). The mean platelet count at month 36 increased from baseline by 22 x 10(9)/L. No new cases of peripheral neuropathy occurred since previously reported. Diarrhoea and weight loss, which were frequently reported during the initial 12-month study, decreased in magnitude and prevalence during the second and third years. Patients treated with miglustat for 3 years show significant improvements in organ volumes and haematological parameters. In conclusion, miglustat was increasingly effective over time and showed acceptable tolerability in patients who continued with treatment for 3 years.

Central nervous system inflammation is a hallmark of pathogenesis in mouse models of GM1 and GM2 gangliosidosis

Mouse models of the GM2 gangliosidoses [Tay-Sachs, late onset Tay-Sachs (LOTS), Sandhoff] and GM1 gangliosidosis have been studied to determine whether there is a common neuro-inflammatory component to these disorders. During the disease course, we have: (i) examined the expression of a number of inflammatory markers in the CNS, including MHC class II, CD68, CD11b (CR3), 7/4, F4/80, nitrotyrosine, CD4 and CD8; (ii) profiled cytokine production [tumour necrosis factor alpha (TNF alpha), transforming growth factor (TGF beta 1) and interleukin 1 beta (IL1 beta)]; and (iii) studied blood-brain barrier (BBB) integrity. The kinetics of apoptosis and the expression of Fas and TNF-R1 were also assessed. In all symptomatic mouse models, a progressive increase in local microglial activation/expansion and infiltration of inflammatory cells was noted. Altered BBB permeability was evident in Sandhoff and GM1 mice, but absent in LOTS mice. Progressive CNS inflammation coincided with the onset of clinical signs in these mouse models. Substrate reduction therapy in the Sandhoff mouse model slowed the rate of accumulation of glycosphingolipids in the CNS, thus delaying the onset of the inflammatory process and disease pathogenesis. These data suggest that inflammation may play an important role in the pathogenesis of the gangliosidoses.

Glycosphingolipid lysosomal storage diseases: therapy and pathogenesis

Paediatric neurodegenerative diseases are frequently caused by inborn errors in glycosphingolipid (GSL) catabolism and are collectively termed the glycosphingolipidoses. GSL catabolism occurs in the lysosome and a defect in an enzyme involved in GSL degradation leads to the lysosomal storage of its substrate(s). GSLs are abundantly expressed in the central nervous system (CNS) and the disorders frequently have a progressive neurodegenerative course. Our understanding of pathogenesis in these diseases is incomplete and currently few options exist for therapy. In this review we discuss how mouse models of these disorders are providing insights into pathogenesis and also leading to progress in evaluating experimental therapies.

High-performance liquid chromatography analysis of ganglioside carbohydrates at the picomole level after ceramide glycanase digestion and fluorescent labeling with 2-aminobenzamide

The functional importance of glycolipids has emphasized the need for more sensitive methods of detection, characterization, and quantification than has often been possible using traditional thin-layer chromatographic techniques. We describe the use of ceramide glycanase and HPLC to identify and quantify gangliosides in which the carbohydrate is in Glcbeta1--> linkage with ceramide. Detection of released carbohydrate was by fluorescent labeling with 2-aminobenzamide at the reducing terminal prior to HPLC analysis. Under the conditions described, ceramide glycanase hydrolyzed all of the common gangliosides studied, offering a broad spectrum of specificity. Release and detection of carbohydrate were linear over a wide range (over two orders of magnitude) of micromolar glycolipid substrate concentrations. Use of an N-linked glycan as an internal standard allowed accurate quantification and a recovery of 93% was achieved. The method additionally maintained the sensitivity (chromatographic peaks containing 1 pmol were readily detected from tissue samples) and comparable resolution to related assays. This was shown by the separation, not only of isomeric carbohydrates from the "a" and "b" series, but also of ganglioside carbohydrate differing only by the presence of either N-acetyl- or N-glycolylneuraminic acid. Application of the method to neutral glycosphingolipids and to tissue samples, including 10-microl quantities of plasma, is illustrated. Glycan structures were confirmed by exoglycosidase digestion and/or matrix-assisted laser desorption/ionization mass spectrometry.

N -butyldeoxynojirimycin reduces growth and ganglioside content of experimental mouse brain tumours

Abnormalities in glycosphingolipid (GSL) biosynthesis have been implicated in the oncogenesis and malignancy of brain tumours. GSLs comprise the gangliosides and the neutral GSLs and are major components of the cell surface glycocalyx. N -butyldeoxynojirimycin (N B-DNJ) is an imino sugar that inhibits the glucosyltransferase catalysing the first step in GSL biosynthesis. The influence of N B-DNJ was studied on the growth and ganglioside composition of two 20-methylcholanthrene-induced experimental mouse brain tumours, EPEN and CT-2A, which were grown in vitro and in vivo. N B-DNJ (200 microM) inhibited the proliferation of the EPEN and CT-2A cells by 50%, but did not reduce cell viability. The drug, administered in the diet (2400 mg kg(-1)) to adult syngeneic C57BL/6 mice, reduced the growth and ganglioside content of subcutaneous and intracerebral EPEN and CT-2A tumours by at least 50% compared to the untreated controls. N B-DNJ treatment also shifted the relative distribution of tumour gangliosides in accordance with the depletion of metabolic substrates. Side effects of N B-DNJ treatment were generally mild and included reductions in body and spleen weights and intestinal distension. We conclude that N B-DNJ may inhibit tumour growth through an effect on ganglioside biosynthesis and may be useful as a new chemotherapy for brain tumours.

Inhibition of substrate synthesis as a strategy for glycolipid lysosomal storage disease therapy

The glycosphingolipid (GSL) lysosomal storage diseases are caused by mutations in the genes encoding the glycohydrolases that catabolize GSLs within lysosomes. In these diseases the substrate for the defective enzyme accumulates in the lysosome and the stored GSL leads to cellular dysfunction and disease. The diseases frequently have a progressive neurodegenerative course. The therapeutic options for treating these diseases are relatively limited, and for the majority there are no effective therapies. The problem is further compounded by difficulties in delivering therapeutic agents to the brain. Most research effort to date has focused on strategies for augmenting enzyme levels to compensate for the underlying defect. These include bone marrow transplantation (BMT), enzyme replacement and gene therapy. An alternative strategy that we have been exploring is substrate deprivation. This approach aims to balance the rate of GSL synthesis with the impaired rate of GSL breakdown. The imino sugar N-butyldeoxynojirimycin (NB-DNJ) inhibits the first step in GSL biosynthesis and has been used to evaluate this approach. Studies in an asymptomatic mouse model of Tay-Sachs disease have shown that substrate deprivation prevents GSL storage in the CNS. In a severe neurodegenerative mouse model of Sandhoff disease, substrate deprivation delayed the onset of symptoms and disease progression and significantly increased life expectancy. Combining NB-DNJ and BMT was found to be synergistic in the Sandhoff mouse model. A clinical trial in type I Gaucher disease has been undertaken and has shown beneficial effects. Efficacy was demonstrated on the basis of significant decreases in liver and spleen volumes, gradual but significant improvement in haematological parameters and disease activity markers, together with diminished GSL biosynthesis and storage as determined by independent biochemical assays. Further trials in type I Gaucher disease are in progress; studies are planned in patients with GSL storage in the CNS.

Substrate reduction therapy for glycosphingolipid storage disorders

Substrate reduction therapy is a novel approach to treating glycosphingolipid (GSL) lysosomal storage disorders. These diseases are caused by mutations in the genes coding for enzymes involved in GSL catabolism and are characterised by the accumulation of GSL substrates within the lysosomes of cells. The aim of substrate reduction therapy is to inhibit the rate of synthesis of GSLs to levels where the residual activity of the mutant catabolic enzyme is sufficient to prevent pathological storage. In this review we discuss the development of N-butyldeoxynojirimycin (NB-DNJ), an imino sugar that inhibits the ceramide-specific glucosyltransferase which catalyses the first committed step of GSL synthesis. This agent has been shown to slow accumulation of stored glycolipid in an in vitro model of Gaucher's disease and in knockout mouse models of Tay-Sachs and Sandhoff diseases. Furthermore, administration of NB-DNJ to Sandhoff mice delays the onset of neurological disease and also slows its progression. We discuss safety and efficacy data from the clinical trial of substrate reduction with NB-DNJ which has been undertaken in patients with Type 1 Gaucher's disease. This trial provides a proof-of-principle for the use of this approach in a wide range of GSL lysosomal storage diseases.

Enhanced survival in Sandhoff disease mice receiving a combination of substrate deprivation therapy and bone marrow transplantation

Sandhoff disease is a lysosomal storage disorder characterized by G(M2) ganglioside accumulation in the central nervous system (CNS) and periphery. It results from mutations in the HEXB gene, causing a deficiency in beta-hexosaminidase. Bone marrow transplantation (BMT), which augments enzyme levels, and substrate deprivation (using the glycosphingolipid biosynthesis inhibitor N-butyldeoxynojirimycin [NB-DNJ]) independently have been shown to extend life expectancy in a mouse model of Sandhoff disease. The efficacy of combining these 2 therapies was evaluated. Sandhoff disease mice treated with BMT and NB-DNJ survived significantly longer than those treated with BMT or NB-DNJ alone. When the mice were subdivided into 2 groups on the basis of their donor bone marrow-derived CNS enzyme levels, the high enzyme group exhibited a greater degree of synergy (25%) than the group as a whole (13%). Combination therapy may therefore be the strategy of choice for treating the infantile onset disease variants.

High-performance cation-exchange chromatography and pulsed amperometric detection for the separation, detection, and quantitation of N-alkylated imino sugars in biological samples

The use of imino sugars for the potential treatment of lysosomal glycolipid storage diseases and hepatitis virus infections requires accurate, quantitative measurement of these compounds in biological samples. We demonstrate here the versatility of cation-exchange chromatography and pulsed amperometric detection of a range of compounds that differ in both isometric structure and N-alkyl chain length. Although column retention appears dependent upon residual charge on the imine function, successful isocratic separation can be achieved by secondary hydrophobic interactions. A series of N-alkylated deoxynojirimycin compounds containing C(1-10) alkyl chains are readily separated and detected by pulsed amperometry after cation suppression. Using experimentally derived response factors for imino sugars and measurement of peak areas we have developed a reliable method for quantitatively determining concentrations in solution. A rapid protocol for the removal of protein and contaminants in biological samples is described. This has allowed the successful measurement of imino sugars in animal tissues and will be useful for understanding the factors involved in compound bioavailability and in the design of novel therapeutics.

N-butyldeoxygalactonojirimycin: a more selective inhibitor of glycosphingolipid biosynthesis than N-butyldeoxynojirimycin, in vitro and in vivo

N-Butyldeoxynojirimycin (NB-DNJ) inhibits the ceramide glucosyltransferase which catalyses the first step in glycosphingolipid (GSL) biosynthesis. It has the potential to be used for the treatment of the GSL lysosomal storage diseases and is currently in clinical trials for the treatment of type 1 Gaucher's disease. However, NB-DNJ is also a potent inhibitor of other enzymes, including alpha-glucosidase I and II, which could potentially cause side effects in patients receiving life-long therapy. Wetherefore evaluated a potentially more selective GSL biosynthesis inhibitor, N-butyldeoxygalactonojirimycin (NB-DGJ), in vitro and in vivo. The distribution and degree of GSL depletion in the liver of mice treated with NB-DGJ or NB-DNJ were equivalent. Mice treated with NB-DGJ had normal body weights and lymphoid organ sizes, whereas NB-DNJ-treated mice showed weight loss and partial lymphoid organ shrinkage. NB-DNJ inhibited glycogen catabolism in the liver, whereas NB-DGJ did not. NB-DNJ was also a potent inhibitor of sucrase and maltase in vitro but not of lactase, while NB-DGJ inhibited lactase but not sucrase or maltase. NB-DGJ is therefore more selective than NB-DNJ, and deserves to be evaluated for human therapy.

Mutations at critical N-glycosylation sites reduce tyrosinase activity by altering folding and quality control

Tyrosinase is a copper-containing enzyme that regulates melanin biosynthesis in mammals. Mutations at a single N-glycosylation sequon of tyrosinase have been reported to be responsible for oculocutaneous albinism type IA in humans, characterized by inactive tyrosinase and the total absence of pigmentation. To probe the role that each N-glycosylation site plays in the synthesis of biologically active tyrosinase, we analyzed the calnexin mediated folding of tyrosinase N-glycosylation mutants. We have determined that four of the six potential N-glycosylation sites, including that associated with albinism, are occupied. Analysis of the folding pathway and activity of 15 tyrosinase mutants lacking one or more of the occupied N-glycosylation sites shows that glycans at any two N-glycosylation sites are sufficient to interact with calnexin and give partial activity, but a specific pair of sites (Asn(86) and Asn(371)) is required for full activity. The mutants with less than two N-glycosylation sites do not interact with calnexin and show a complete absence of enzyme activity. Copper analysis of selected mutants suggests that the observed partial activity is due to two populations with differential copper content. By correlating the degree of folding with the activity of tyrosinase, we propose a local folding mechanism for tyrosinase that can explain the mechanism of inactivation of tyrosinase N-glycosylation mutants found in certain pigmentation disorders.

Imino sugars inhibit the formation and secretion of bovine viral diarrhea virus, a pestivirus model of hepatitis C virus: implications for the development of broad spectrum anti-hepatitis virus agents

One function of N-linked glycans is to assist in the folding of glycoproteins by mediating interactions of the lectin-like chaperone proteins calnexin and calreticulin with nascent glycoproteins. These interactions can be prevented by inhibitors of the alpha-glucosidases, such as N-butyl-deoxynojirimycin (NB-DNJ) and N-nonyl-DNJ (NN-DNJ), and this causes some proteins to be misfolded and retained within the endoplasmic reticulum (ER). We have shown previously that the NN-DNJ-induced misfolding of one of the hepatitis B virus (HBV) envelope glycoproteins prevents the formation and secretion of virus in vitro and that this inhibitor alters glycosylation and reduces the viral levels in an animal model of chronic HBV infection. This led us to investigate the effect of glucosidase inhibitors on another ER-budding virus, bovine viral diarrhea virus, a tissue culture surrogate of human hepatitis C virus (HCV). Here we show that in MDBK cells alpha-glucosidase inhibitors prevented the formation and secretion of infectious bovine viral diarrhea virus. Data also are presented showing that NN-DNJ, compared with NB-DNJ, exhibits a prolonged retention in liver in vivo. Because viral secretion is selectively hypersensitive to glucosidase inhibition relative to the secretion of cellular proteins, the possibility that glucosidase inhibitors could be used as broad-based antiviral hepatitis agents is discussed. A single drug against HBV, HCV, and, possibly, HDV, which together chronically infect more than 400 million people worldwide, would be of great therapeutic value.

Tyrosinase folding and copper loading in vivo: a crucial role for calnexin and alpha-glucosidase II

Tyrosinase is the key enzyme of melanin biosynthesis. It is a multiply glycosylated metalloenzyme, which has a long maturation time making it an ideal in vivo model system to probe protein folding and metal loading events. The use of NB-DNJ, an alpha-glucosidase I and II inhibitor has allowed us to dissect these processes. Here we show that tyrosinase folds through several inactive intermediates, at least two of which are recognised by the ER chaperone, calnexin. If the association with calnexin is prevented, more rapid folding occurs, the resulting protein fails to bind copper and is inactive. If dissociation from calnexin is inhibited, folding is prevented; the protein does not go through the normal secretory pathway and is targeted for degradation. Thus, tyrosinase folds off calnexin, giving alpha-glucosidase II a critical role, but the association with calnexin is essential to promote the correct folding which enables it to acquire copper.

Delayed symptom onset and increased life expectancy in Sandhoff disease mice treated with N-butyldeoxynojirimycin

Sandhoff disease is a neurodegenerative disorder resulting from the autosomal recessive inheritance of mutations in the HEXB gene, which encodes the beta-subunit of beta-hexosaminidase. GM2 ganglioside fails to be degraded and accumulates within lysosomes in cells of the periphery and the central nervous system (CNS). There are currently no therapies for the glycosphingolipid lysosomal storage diseases that involve CNS pathology, including the GM2 gangliosidoses. One strategy for treating this and related diseases is substrate deprivation. This would utilize an inhibitor of glycosphingolipid biosynthesis to balance synthesis with the impaired rate of catabolism, thus preventing storage. One such inhibitor is N-butyldeoxynojirimycin, which currently is in clinical trials for the potential treatment of type 1 Gaucher disease, a related disease that involves glycosphingolipid storage in peripheral tissues, but not in the CNS. In this study, we have evaluated whether this drug also could be applied to the treatment of diseases with CNS storage and pathology. We therefore have treated a mouse model of Sandhoff disease with the inhibitor N-butyldeoxynojirimycin. The treated mice have delayed symptom onset, reduced storage in the brain and peripheral tissues, and increased life expectancy. Substrate deprivation therefore offers a potentially general therapy for this family of lysosomal storage diseases, including those with CNS disease.

New therapeutic prospects for the glycosphingolipid lysosomal storage diseases

The glycosphingolipid (GSL) lysosomal storage diseases result from mutations in the genes that encode the enzymes required for glycosphingolipid catabolism within lysosomes. They are relatively rare diseases, but are frequently severe in terms of their pathology. Many involve progressive neurodegeneration, and in the most severe forms result in death in early infancy. The therapeutic options for treating these diseases are limited, and for the majority of these disorders there are currently no therapies available. To date, most research has focused on correcting the genetic lesion by gene therapy or by augmenting the enzyme activity deficient in these patients by introducing fully functional enzyme. This can be achieved by bone marrow transplantation or intravenous infusion of purified or recombinant enzyme (enzyme replacement). Gene therapy and enzyme replacement therapy are disease specific, and pharmacological approaches for the treatment of these disorders have not been fully explored. In this commentary, the problems associated with disease therapy are discussed, and a pharmacological agent (N-butyldeoxynojirimycin) is presented for the potential generic treatment of this family of disorders. Successful prevention of glycosphingolipid storage in a mouse model of Tay-Sachs disease suggests that this strategy merits clinical evaluation.

Inhibition of glycosphingolipid biosynthesis does not impair growth or morphogenesis of the postimplantation mouse embryo

Whole embryo culture (WEC) of organogenesis-stage mouse embryos was adapted for glycosphingolipid (GSL) metabolic studies to evaluate the hypothesis that de novo GSL biosynthesis is a prerequisite for growth and morphogenesis of the early postimplantation embryo. WEC supports the growth and development of postimplantation mouse embryos to stages that are indistinguishable from those achieved in vivo. N-Butyldeoxygalactonojirimycin (NB-DGJ) is an N-alkylated imino sugar that specifically inhibits biosynthesis of all glucosylceramide-based GSLs. NB-DGJ inhibited glucosylceramide and lactosylceramide biosynthesis nearly completely and inhibited ganglioside biosynthesis approximately 90% in both the embryo and visceral yolk sac. NB-DGJ also significantly reduced total ganglioside content in both the embryo and visceral yolk sac as estimated by the cholera toxin immunooverlay technique. A shift in expression from the structurally simple to the structurally complex gangliosides was also observed in NB-DGJ-treated embryos and yolk sacs. Despite causing major changes in GSL biosynthesis and composition, NB-DGJ had no effect on embryo viability, growth, or morphology. The findings suggest that de novo GSL biosynthesis may not be a prerequisite for the growth and morphogenesis of the organogenesis-stage mouse embryo.

Extensive glycosphingolipid depletion in the liver and lymphoid organs of mice treated with N-butyldeoxynojirimycin

The imino sugar N-butyldeoxynojirimycin is an inhibitor of the ceramide-specific glucosyltransferase that catalyzes the first step in glycosphingolipid biosynthesis. It results in extensive glycosphingolipid depletion in cells treated in vitro, without causing toxicity. However, we currently do not know the degree to which glycosphingolipids can be depleted in vivo in a mammalian species. We have therefore administered N-butyldeoxynojirimycin long term to young mice and have found that glycosphingolipid levels are reduced (50-70%) in all tissues examined, without resulting in any overt pathology. When the lymphoid tissues from these mice were examined, they were found to be 50% acellular relative to non-lymphoid tissues. These data implicate a role for glycosphingolipids in the biology of the immune system or indicate an additional as yet unknown activity of N-butyldeoxynojirimycin. Extensive glycosphingolipid depletion resulting from N-butyldeoxynojirimycin administration is therefore well tolerated in adult mice, and this compound may be in an invaluable tool for probing glycosphingolipid functions in vivo. In addition, this drug may be effective in clinical situations where glycosphingolipid depletion would be desirable, such as the in the treatment of the human glycosphingolipidoses.

The solution NMR structure of glucosylated N-glycans involved in the early stages of glycoprotein biosynthesis and folding

Glucosylated oligomannose N-linked oligosaccharides (Glc(x)Man9GlcNAc2 where x = 1-3) are not normally found on mature glycoproteins but are involved in the early stages of glycoprotein biosynthesis and folding as (i) recognition elements during protein N-glycosylation and chaperone recognition and (ii) substrates in the initial steps of N-glycan processing. By inhibiting the first steps of glycan processing in CHO cells using the alpha-glucosidase inhibitor N-butyl-deoxynojirimycin, we have produced sufficient Glc3Man7GlcNAc2 for structural analysis by nuclear magnetic resonance (NMR) spectroscopy. Our results show the glucosyl cap to have a single, well-defined conformation independent of the rest of the saccharide. Comparison with the conformation of Man9GlcNAc2, previously determined by NMR and molecular dynamics, shows the mannose residues to be largely unaffected by the presence of the glucosyl cap. Sequential enzymatic cleavage of the glucose residues does not affect the conformation of the remaining saccharide. Modelling of the Glc3Man9GlcNAc2, Glc2Man9GlcNAc2 and Glc1Man9GlcNAc2 conformations shows the glucose residues to be fully accessible for recognition. A more detailed analysis of the conformations allows potential recognition epitopes on the glycans to be identified and can form the basis for understanding the specificity of the glucosidases and chaperones (such as calnexin) that recognize these glycans, with implications for their mechanisms of action.

Inhibition of N-glycan processing in B16 melanoma cells results in inactivation of tyrosinase but does not prevent its transport to the melanosome

Tyrosinase is the key enzyme in melanin biosynthesis, catalyzing multiple steps in this pathway. The mature glycoprotein is transported from the Golgi to the melanosome where melanin biosynthesis occurs. In this study, we have investigated the effects of inhibitors of N-glycan processing on the synthesis, transport, and catalytic activity of tyrosinase. When B16 mouse melanoma cells were cultured in the presence of N-butyldeoxynojirimycin, an inhibitor of the endoplasmic reticulum-processing enzymes alpha-glucosidases I and II, the enzyme was synthesized and transported to the melanosome but almost completely lacked catalytic activity. The cells contained only 2% of the melanin found in untreated cells. Structural analysis of the N-glycans from N-butyldeoxynojirimycin-treated B16 cells demonstrated that three oligosaccharide structures (Glc3Man7-9) predominated. Removal of the glucose residues with alpha-glucosidases I and II failed to restore enzymatic activity, suggesting that the glucosylated N-glycans do not sterically interfere with the enzyme's active sites. The mannosidase inhibitor deoxymannojirimycin had no effect on catalytic activity suggesting that the retention of glucosylated N-glycans results in the inactivation of this enzyme. The retention of glucosylated N-glycans does not therefore result in misfolding and degradation of the glycoprotein, as the enzyme is transported to the melanosome, but may cause conformational changes in its catalytic domains.

Ultrastructural changes in the Golgi apparatus and secretory granules of HL-60 cells treated with the imino sugar N-butyldeoxynojirimycin

The imino sugar N-butyldeoxynojirimycin inhibits the N-linked oligosaccharide processing enzymes alpha-glucosidases I and II, and the ceramide specific glucosyltransferase which catalyses the first step in glucosphingolipid biosynthesis. We have studied the effects of this compound on the ultrastructure of HL-60 cells to identify novel activities of this compound. Treatment of HL-60 cells with this imino sugar results in several morphological changes within the cell, none of which result in cytotoxicity. The plasma membrane stains heavily with potassium ferrocyanide within 30 min following addition of the compound to the medium, and there is then a time dependent involvement of all other intracellular membranes. Secretory granules become enlarged and lose their dense core morphology and appear either empty and vacuolated or have low density contents. However, the most striking effect of NB-DNJ treatment is on the Golgi apparatus. The Golgi exhibits a time-dependent change from typical Golgi morphology to a structure almost completely devoid of cisternae and consisting predominantly of vesicles. All the observed changes are fully reversible on withdrawal of the compound.

Prevention of lysosomal storage in Tay-Sachs mice treated with N-butyldeoxynojirimycin

The glycosphingolipid (GSL) lysosomal storage diseases result from the inheritance of defects in the genes encoding the enzymes required for catabolism of GSLs within lysosomes. A strategy for the treatment of these diseases, based on an inhibitor of GSL biosynthesis N-butyldeoxynojirimycin, was evaluated in a mouse model of Tay-Sachs disease. When Tay-Sachs mice were treated with N-butyldeoxynojirimycin, the accumulation of GM2 in the brain was prevented, with the number of storage neurons and the quantity of ganglioside stored per cell markedly reduced. Thus, limiting the biosynthesis of the substrate (GM2) for the defective enzyme (beta-hexosaminidase A) prevents GSL accumulation and the neuropathology associated with its lysosomal storage.

N-butyldeoxynojirimycin-mediated inhibition of human immunodeficiency virus entry correlates with changes in antibody recognition of the V1/V2 region of gp120

The alpha-glucosidase inhibitor N-butyldeoxynojirimycin (NB-DNJ) is an inhibitor of human immunodeficiency virus (HIV) replication and HIV-induced syncytium formation in vitro. Although NB-DNJ appears to inhibit HIV entry at the level of post-CD4 binding (P.B. Fischer, M. Collin, G.B. Karlsson, W. James, T.D. Butters, S.J. Davis, S. Gordon, R.A. Dwek, and F.M. Platt, J. Virol. 69:5791-5797, 1995), the exact mechanism of action remains to be established. In this study we have examined the effect of NB-DNJ on the structure of recombinant gp120 (rgpl20), expressed in CHO cells, by using a panel of 40 monoclonal antibodies. The levels of binding of antibodies to rgp120 produced in the presence [rgpl20(+)] and absence [rgpl20(-)] of NB-DNJ were compared by enzyme-linked immunosorbent assay and surface plasmon resonance (BIAcore; Pharmacia). The results showed an increase in the binding to rgp120(+) of antibodies directed against the C1 and C2 regions and a decrease in the binding of antibodies directed against the V1/V2 loops compared with antibody binding to rgpl20(-). A decrease in the binding to rgpl20(+) of antibodies directed against discontinuous epitopes was also observed. No differences were seen in the binding of antibodies directed against the crown of the V3 loop and the C4 region of gp120. Treatment of rgpl20 with alpha-glucosidases I and II had no effect on the differential binding observed, whereas treatment with sialidase abolished the differences seen in the binding of antibodies directed against the C1 and C2 regions of gp120. In addition to these findings, rgpl20(+) showed increased sensitivity to proteases released by CHO cells during expression, as well as to exogenous thrombin. Taken together, the data presented in this paper suggest that production of gp120 in the presence of NB-DNJ affects the conformation of the Vl/V2 loops of gpl20, as well as the overall charge of the C1 and C2 regions. These effects may play a role in the previously described NB-DNJ-mediated inhibition of HIV entry at the level of post-CD4 binding.

N-butyldeoxynojirimycin-mediated inhibition of human immunodeficiency virus entry correlates with impaired gp120 shedding and gp41 exposure

The alpha-glucosidase inhibitor N-butyldeoxynojirimycin (NB-DNJ) is an inhibitor of human immunodeficiency virus (HIV) replication and HIV-induced syncytium formation in vitro. Although an NB-DNJ-mediated change in viral envelope N-glycan composition inhibits HIV entry at the level of post-CD4 binding, the exact mechanism of inhibition remains to be established. In this study we have examined the effects of NB-DNJ on virion envelope composition and CD4-induced gp120 shedding and gp41 exposure. Virion composition analysis revealed an NB-DNJ-mediated reduction of 15% in overall virion envelope glycoprotein content and a reduction of 26% in the proteolytic maturation of virion gp160. Taken together, these two effects resulted in a reduction of approximately 40% in virion gp120 content. CD4-induced shedding of gp120 from the surfaces of envelope-transfected Cos cells was undetectable when gp120 was expressed in the presence of NB-DNJ. Similarly, the shedding of virion-associated gp120 was reduced 7.4-fold. CD4-induced exposure of cryptic gp41 epitopes on the surfaces of HIV-expressing ACH-2 cells was also greatly impaired, and the exposure of virion-associated gp41 epitopes was reduced 4.0-fold. Finally, CD4-induced increases in the binding of antibodies to the V3 loop of ACH-2-cell-expressed envelope glycoproteins were reduced 25-fold when the glycoproteins were expressed in the presence of NB-DNJ. These results suggest that the NB-DNJ-mediated retention of glycosylated N-glycans inhibits HIV entry by a combined effect of a reduction in virion gp120 content and a qualitative defect within the remaining gp120, preventing it from undergoing conformational changes after CD4 binding.

The alpha-glucosidase inhibitor N-butyldeoxynojirimycin inhibits human immunodeficiency virus entry at the level of post-CD4 binding

The alpha-glucosidase inhibitor N-butyldeoxynojirimycin (NB-DNJ) is a potent inhibitor of human immunodeficiency virus (HIV) replication and syncytium formation in vitro. However, the exact mechanism of action of NB-DNJ remains to be determined. In this study we have examined the impairment of HIV infectivity mediated by NB-DNJ. By two independent HIV entry assays [PCR-based HIV entry assay and entry of Cocal(HIV) pseudotypes], the reduction in infectivity was found to be due to an impairment of viral entry. No effect of NB-DNJ treatment was seen on the kinetics of the interaction between gp120 and CD4 (surface plasmon resonance; BIAcore) or on the binding of virus particles to H9 cells (using radiolabeled virions). We therefore conclude that a major mechanism of action of NB-DNJ as an inhibitor of HIV replication is the impairment of viral entry at the level of post-CD4 binding, due to an effect on viral envelope components.

N-butyldeoxygalactonojirimycin inhibits glycolipid biosynthesis but does not affect N-linked oligosaccharide processing

We have previously reported that the imino sugar N-butyldeoxynojirimycin (NB-DNJ) inhibits glycolipid biosynthesis, in addition to its known activity as an inhibitor of the N-linked oligosaccharide processing enzyme alpha-glucosidase I. In an attempt to dissociate these two activities and identify an inhibitor which was more selective for the glycolipid biosynthetic pathway, several imino sugars have been N-alkylated and tested for inhibitory activity. The galactose analogue N-butyldeoxygalactonojirimycin (NB-DGJ) was found to be a potent inhibitor of glycolipid biosynthesis but in contrast to NB-DNJ had no effect on the maturation of N-linked oligosaccharides or on lysosomal glucocerebrosidase. The effect of increasing N-alkyl chain length on glycolipid inhibition was investigated. Nonalkylated DGJ, the N-methyl and N-ethyl derivatives, were noninhibitory. However, N-propylation resulted in partial inhibition while the N-butyl and N-hexyl derivatives resulted in maximal inhibition. Increasing alkyl chain length also resulted in increased potency of glucosyltransferase inhibition. In an in vitro Gaucher's disease model NB-DGJ was as effective as NB-DNJ in preventing glycolipid storage and may represent a more selective potential therapeutic agent than NB-DNJ for the management of this and other glycosphingolipidoses.