Genetic Polymorphisms Associated with Vincristine Pharmacokinetics and Vincristine-Induced Peripheral Neuropathy in Pediatric Oncology Patients

Simple Summary

Vincristine is a type of chemotherapy that is often used in the treatment of children with cancer. The main side effect of vincristine is nerve damage. Patients experience symptoms such as tingling, pain or muscle weakness. Some children are more sensitive to vincristine than others, which may depend on variations in genes and in the breakdown of vincristine by the body. In this study, we investigated the effect of variations in genes on nerve damage due to vincristine and breakdown of vincristine by the body. We found that nine variations in seven genes were associated with nerve damage due to vincristine, whereas three variations in three genes were associated with the breakdown of vincristine by the body. It is important that future studies try to replicate these findings. Our findings help us towards the goal of tailoring vincristine treatment to each child, with optimal therapeutic effect while limiting nerve damage.

Abstract

Vincristine (VCR) is an important component of curative chemotherapy for many childhood cancers. Its main side effect is VCR-induced peripheral neuropathy (VIPN), a dose limiting toxicity. Some children are more susceptible to VIPN, which is at least partially dependent on genetic factors and pharmacokinetics (PK). In this study, we identify and replicate genetic variants associated with VCR PK and VIPN. Patient samples from a randomized clinical trial studying the effect of administration duration of VCR on VIPN in 90 patients were used. PK sampling was conducted on between one and five occasions at multiple time points. A linear two-compartment model with first-order elimination was used, and targeted next-generation DNA sequencing was performed. Genotype–trait associations were analyzed using mixed-effect models or logistic regression analysis for repeated measures, or Poisson regression analysis in which the highest VIPN score per patient was included. Nine single-nucleotide polymorphisms (SNPs) in seven genes (NDRG1, GARS, FIG4, FGD4, SEPTIN9, CEP72, and ETAA1) were associated with VIPN. Furthermore, three SNPs in three genes (MTNR1B, RAB7A and SNU13) were associated with PK of VCR. In conclusion, PK of VCR and VIPN are influenced by SNPs; upfront identification of those that lead to an altered susceptibility to VIPN or VCR exposure could help individualize VCR treatment.

MO006INFLAMMASOME ACTIVATOR NLRP3 HYPOMETHYLATION IS ASSOCIATED WITH GLUCOCORTICOID RESISTANCE IN PATIENTS WITH IDIOPATHIC NEPHROTIC SYNDROME

Background and Aims

We have previously shown that the Nod-like receptor protein-3 (NLRP3) gene is over-expressed in leukocytes of many patients with chronic kidney disease, and studies have also shown that hypomethylation and overexpression of NLRP3 are associated with glucocorticoid resistance in acute lymphoblastic leukemia. Therefore, we hypothesized that hypomethylation of the NLRP3 promoter my cause glucocorticoid resistance in patients with Idiopathic Nephrotic Syndrome (INS) associated with minimal change disease (MCD) or focal glomerulosclerosis (FSGS).

Method

We assessed NLRP3 and Caspase 1 (CASP1) promoter methylation by SNuPE reaction in germline DNA from leukocytes of 14 glucocorticoid-resistant and 18 glucocorticoid-sensitive adult INS patients (discovery cohort) and 7 glucocorticoid-resistant and 14 glucocorticoid-sensitive pediatric INS patients with MCD/FSGS (validation cohort). The effects of NLRP3 inflammasome on glucocorticoid resistance were validated in vitro in human monocytic cell lines (THP-1 and U937).

Results

Methylation of CpG islands in the CASP1 promoter was undetectable in both groups whereas NLRP3 promoter methylation was significantly lower in glucocorticoid-resistant compared to glucocorticoid-sensitive in both adults and children.

The AUROC curve was 81.2% (p=0.0003) in adults and 73.5% (p=0.0002) in children demonstrating the capability of NLRP3 methylation to discriminate glucocorticoid-resistant versus glucocorticoid-sensitive.

Activation of the NLRP3 inflammasome by LPS/ATP reduced glucocorticoid receptor expression and increased glucocorticoid resistance in U937. Consistently, knockdown of NLRP3 in THP-1 increased sensitivity to glucocorticoids.

Conclusion

Our findings demonstrate a novel mechanism whereby INS patients develop resistance to glucocorticoids via leukocyte epigenetic changes of NLRP3 and reveal a new potential clinical biomarker to early detect this condition.

Preclinical dose-finding study with a liver-tropic, recombinant AAV-2/8 vector in the mouse model of galactosialidosis

Galactosialidosis (GS) is a lysosomal storage disease linked to deficiency of the protective protein/cathepsin A (PPCA). Similarly to GS patients, Ppca-null mice develop a systemic disease of the reticuloendothelial system, affecting most visceral organs and the nervous system. Symptoms include severe nephropathy, visceromegaly, infertility, progressive ataxia, and shortened life span. Here, we have conducted a preclinical, dose-finding study on a large cohort of GS mice injected intravenously at 1 month of age with increasing doses of a GMP-grade rAAV2/8 vector, expressing PPCA under the control of a liver-specific promoter. Treated mice, monitored for 16 weeks post-treatment, had normal physical appearance and behavior without discernable side effects. Despite the restricted expression of the transgene in the liver, immunohistochemical and biochemical analyses of other systemic organs, serum, and urine showed a dose-dependent, widespread correction of the disease phenotype, suggestive of a protein-mediated mechanism of cross-correction. A notable finding was that rAAV-treated GS mice showed high expression of PPCA in the reproductive organs, which resulted in reversal of their infertility. Together these results support the use of this rAAV-PPCA vector as a viable and safe method of gene delivery for the treatment of systemic disease in non-neuropathic GS patients.

Vacuolization and alterations of lysosomal membrane proteins in cochlear marginal cells contribute to hearing loss in neuraminidase 1-deficient mice

The neuraminidase-1 (Neu1) knockout mouse model is a phenocopy of the lysosomal storage disease (LSD) sialidosis, characterized by multisystemic and neuropathic symptoms, including hearing loss. We have characterized the auditory defects in Neu1(-/-) mice and found that hearing loss involves both conductive and sensorineural components. Auditory brainstem response (ABR) thresholds were significantly elevated in Neu1(-/-) mice at P21 (48-55 dB), and hearing loss appeared progressive (53-66 dB at P60). At these ages Neu1(-/-) mice accumulated cerumen in the external ear canal and had a thickened mucosa and inflammation in the middle ear. In cochleae of adult wild-type mice, Neu1 was expressed in several cell types in the stria vascularis, the organ of Corti, and spiral ganglion. Progressive morphological abnormalities such as extensive vacuolization were detected in the Neu1(-/-) cochleae as early as P9. These early morphologic changes in Neu1(-/-) cochleae were associated with oversialylation of several lysosomal associated membrane proteins (Lamps) in the stria vascularis. A marked increase in the expression and apical localization of Lamp-1 in marginal cells of the stria vascularis predicts exacerbation of lysosomal exocytosis into the endolymph. Consequently, the endolymphatic potential in Neu1(-/-) mice was reduced by approximately 20 mV at ages P31-P44, which would cause dysfunction of transduction in sensory hair cells. This study suggests a molecular mechanism that contributes to hearing loss in sialidosis and identifies potential therapeutic targets.

Protective protein/cathepsin A rescues N-glycosylation defects in neuraminidase-1

BACKGROUND

Neuraminidase-1 (NEU1) catabolizes the hydrolysis of sialic acids from sialo-glycoconjugates. NEU1 depends on its interaction with the protective protein/cathepsin A (PPCA) for lysosomal compartmentalization and catalytic activation. Murine NEU1 contains 4 N-glycosylation sites, 3 of which are conserved in the human enzyme. The expression of NEU1 gives rise to differentially glycosylated proteins.

METHODS

We generated single-point mutations in mouse NEU1 at each of the 4 N-glycosylation sites. Mutant enzymes were expressed in NEU1-deficient cells in the presence and absence of PPCA.

RESULTS

All 4 N-glycosylation variants were targeted to the lysosomal/endosomal compartment. All N-glycans, with the exception of the most C-terminal glycan, were important for maintaining stability or catalytic activity. The loss of catalytic activity caused by the deletion of the second N-glycan was rescued by increasing PPCA expression. Similar results were obtained with a human NEU1 N-glycosylation mutant identified in a sialidosis patient. The N-terminal N-glycan of NEU1 is indispensable for its function, whereas the C-terminal N-glycan appears to be non-essential. The omission of the second N-glycan can be compensated for by upregulating the expression of PPCA.

GENERAL SIGNIFICANCE

These findings could be relevant for the design of target therapies for patients carrying specific NEU1 mutations.

Structure determination of the human protective protein: twofold averaging reveals the three-dimensional structure of a domain which was entirely absent in the initial model

Mutations in the human 'protective protein' result in the human lysosomal storage disease galactosialidosis. The structure of the human 'protective protein' has been determined using X-ray crystallography to a resolution of 2.2 A. Initial phases were obtained from molecular replacement calculations. A very partial search model comprising 30% of the scattering mass, was constructed from the atomic model of the wheat serine carboxypeptidase. This truncated probe was used to find the position of two monomers in the asymmetric unit. Subsequently, 'bootstrapping' cycles, consisting of twofold averaging and model expansion, retrieved the electron density for residues initially missing. In particular, it proved possible to add a domain (more than 110 residues) to the initial partial search model. In total, 314 residues per asymmetric unit were added to the 588 residues of the initial model. Factors contributing to our success are discussed.

Systemic and neurologic abnormalities distinguish the lysosomal disorders sialidosis and galactosialidosis in mice

Neuraminidase initiates the hydrolysis of sialo-glycoconjugates by removing their terminal sialic acid residues. In humans, primary or secondary deficiency of this enzyme leads to two clinically similar neurodegenerative lysosomal storage disorders: sialidosis and galactosialidosis (GS). Mice nullizygous at the Neu1 locus develop clinical abnormalities reminiscent of early-onset sialidosis in children, including severe nephropathy, progressive edema, splenomegaly, kyphosis and urinary excretion of sialylated oligosaccharides. Although the sialidosis mouse model shares clinical and histopathological features with GS mice and GS patients, we have identified phenotypic abnormalities that seem specific for sialidosis mice. These include progressive deformity of the spine, high incidence of premature death, age-related extramedullary hematopoiesis, and lack of early degeneration of cerebellar Purkinje cells. The differences and similarities identified in these sialidosis and GS mice may help to better understand the pathophysiology of these diseases in children and to identify more targeted therapies for each of these diseases.

Functional amelioration of murine galactosialidosis by genetically modified bone marrow hematopoietic progenitor cells

Protective protein/cathepsin A (PPCA), a lysosomal carboxypeptidase, is deficient in the neurodegenerative lysosomal disorder galactosialidosis (GS). PPCA(-/-) mice display a disease course similar to that of severe human GS, resulting in nephropathy, ataxia, and premature death. Bone marrow transplantation (BMT) in mutant animals using transgenic BM overexpressing the corrective enzyme in either erythroid cells or monocytes/macrophages has proven effective for the improvement of the phenotype, and encouraged the use of genetically modified BM cells for ex vivo gene therapy of GS. Here, we established stable donor hematopoiesis in PPCA(-/-) mice that received hematopoietic progenitors transduced with a murine stem cell virus (MSCV)-based, bicistronic retroviral vector overexpressing PPCA and the green fluorescent protein (GFP) marker. We observed complete correction of the disease phenotype in the systemic organs up to 10 months after transplantation. PPCA(+) BM-derived cells were detected in all tissues, with the highest expression in liver, spleen, BM, thymus, and lung. In addition, a lysosomal immunostaining was seen in nonhematopoietic cells, indicating efficient uptake of the corrective protein by these cells and cross-correction. Expression in the brain occurred throughout the parenchyma but was mainly localized on perivascular areas. However, PPCA expression in the central nervous system was apparently sufficient to delay the onset of Purkinje cell degeneration and to correct the ataxia. The long-term expression and internalization of the PPCA by cells of systemic organs and the clear improvement of the neurologic phenotype support the use of this approach for the treatment of GS in humans. (Blood. 2002;99:3169-3178)

Processing of lysosomal beta-galactosidase. The C-terminal precursor fragment is an essential domain of the mature enzyme

Lysosomal beta-D-galactosidase (beta-gal), the enzyme deficient in the autosomal recessive disorders G(M1) gangliosidosis and Morquio B, is synthesized as an 85-kDa precursor that is C-terminally processed into a 64-66-kDa mature form. The released approximately 20-kDa proteolytic fragment was thought to be degraded. We now present evidence that it remains associated to the 64-kDa chain after partial proteolysis of the precursor. This polypeptide was found to copurify with beta-gal and protective protein/cathepsin A from mouse liver and Madin-Darby bovine kidney cells and was immunoprecipitated from human fibroblasts but not from fibroblasts of a G(M1) gangliosidosis and a galactosialidosis patient. Uptake of wild-type protective protein/cathepsin A by galactosialidosis fibroblasts resulted in a significant increase of mature and active beta-gal and its C-terminal fragment. Expression in COS-1 cells of mutant cDNAs encoding either the N-terminal or the C-terminal domain of beta-gal resulted in the synthesis of correctly sized polypeptides without catalytic activity. Only when co-expressed, the two subunits associate and become catalytically active. Our results suggest that the C terminus of beta-gal is an essential domain of the catalytically active enzyme and provide evidence that lysosomal beta-galactosidase is a two-subunit molecule. These data may give new significance to mutations in G(M1) gangliosidosis patients found in the C-terminal part of the molecule.

Transport of human lysosomal neuraminidase to mature lysosomes requires protective protein/cathepsin A

Human lysosomal N-acetyl-alpha-neuraminidase is deficient in two lysosomal storage disorders, sialidosis, caused by structural mutations in the neuraminidase gene, and galactosialidosis, in which a primary defect of protective protein/cathepsin A (PPCA) leads to a combined deficiency of neuraminidase and beta-D-galactosidase. These three glycoproteins can be isolated in a high molecular weight multi-enzyme complex, and the enzymatic activity of neuraminidase is contingent on its interaction with PPCA. To explain the unusual need of neuraminidase for an auxiliary protein, we examined, in transfected COS-1 cells, the effect of PPCA expression on post-translational modification, turnover and intracellular localization of neuraminidase. In pulse-chase studies, we show that the enzyme is synthesized as a 46 kDa glycoprotein, which is poorly phosphorylated, does not undergo major proteolytic processing and is secreted. Importantly, its half-life is not altered by the presence of PPCA. However, neuraminidase associates with the PPCA precursor shortly after synthesis, since the latter protein co-precipitates with neuraminidase using anti-neuraminidase antibodies. We further demonstrate by subcellular fractionation of transfected cells that neuraminidase segregates to mature lysosomes only when accompanied by wild-type PPCA, but not by transport-impaired PPCA mutants. These data suggest a novel role for PPCA in the activation of lysosomal neuraminidase, that of an intracellular transport protein.

A point mutation in the neu-1 locus causes the neuraminidase defect in the SM/J mouse

Lysosomal neuraminidase (sialidase) occurs in a high molecular weight complex with the glycosidase beta-galactosidase and the serine carboxypeptidase protective protein/cathepsin A (PPCA). Association of the enzyme with PPCA is crucial for its correct targeting and lysosomal activation. In man two genetically distinct storage disorders are associated with either a primary or a secondary deficiency of lysosomal neuraminidase: sialidosis and galactosialidosis. In the mouse the naturally occurring inbred strain SM/J presents with a number of phenotypic abnormalities that have been attributed to reduced neuraminidase activity. SM/J mice were originally characterized by their altered sialylation of several lysosomal glycoproteins. This defect was linked to a single gene, neu-1 , on chromosome 17, which was mapped by linkage analysis to the H-2 locus. In addition, these mice have an altered immune response that has also been coupled to a deficiency of the Neu-1 neuraminidase. Here we report the identification in SM/J mice of a single amino acid substitution (L209I) in the Neu-1 protein which is responsible for the partial deficiency of lysosomal neuraminidase. We propose that the reduced activity is caused by the enzyme's altered affinity for its substrate, rather than a change in substrate specificity or turnover rate. The mutant enzyme is correctly compartmentalized in lysosomes and maintains the ability to associate with its activating protein, PPCA. We propose that it is this mutation that is responsible for the SM/J phenotype.

The atomic model of the human protective protein/cathepsin A suggests a structural basis for galactosialidosis

Human protective protein/cathepsin A (PPCA), a serine carboxypeptidase, forms a multienzyme complex with beta-galactosidase and neuraminidase and is required for the intralysosomal activity and stability of these two glycosidases. Genetic lesions in PPCA lead to a deficiency of beta-galactosidase and neuraminidase that is manifest as the autosomal recessive lysosomal storage disorder galactosialidosis. Eleven amino acid substitutions identified in mutant PPCAs from clinically different galactosialidosis patients have now been modeled in the three-dimensional structure of the wild-type enzyme. Of these substitutions, 9 are located in positions likely to alter drastically the folding and stability of the variant protein. In contrast, the other 2 mutations that are associated with a more moderate clinical outcome and are characterized by residual mature protein appeared to have a milder effect on protein structure. Remarkably, none of the mutations occurred in the active site or at the protein surface, which would have disrupted the catalytic activity or protective function. Instead, analysis of the 11 mutations revealed a substantive correlation between the effect of the amino acid substitution on the integrity of protein structure and the general severity of the clinical phenotype. The high incidence of PPCA folding mutants in galactosialidosis reflects the fact that a single point mutation is unlikely to affect both the beta-galactosidase and the neuraminidase binding sites of PPCA at the same time to produce the double glycosidase deficiency. Mutations in PPCA that result in defective folding, however, disrupt every function of PPCA simultaneously.

Characterization of human lysosomal neuraminidase defines the molecular basis of the metabolic storage disorder sialidosis

Neuraminidases (sialidases) have an essential role in the removal of terminal sialic acid residues from sialoglycoconjugates and are distributed widely in nature. The human lysosomal enzyme occurs in complex with beta-galactosidase and protective protein/cathepsin A (PPCA), and is deficient in two genetic disorders: sialidosis, caused by a structural defect in the neuraminidase gene, and galactosialidosis, in which the loss of neuraminidase activity is secondary to a deficiency of PPCA. We identified a full-length cDNA clone in the dbEST data base, of which the predicted amino acid sequence has extensive homology to other mammalian and bacterial neuraminidases, including the F(Y)RIP domain and "Asp-boxes." In situ hybridization localized the human neuraminidase gene to chromosome band 6p21, a region known to contain the HLA locus. Transient expression of the cDNA in deficient human fibroblasts showed that the enzyme is compartmentalized in lysosomes and restored neuraminidase activity in a PPCA-dependent manner. The authenticity of the cDNA was verified by the identification of three independent mutations in the open reading frame of the mRNA from clinically distinct sialidosis patients. Coexpression of the mutant cDNAs with PPCA failed to generate neuraminidase activity, confirming the inactivating effect of the mutations. These results establish the molecular basis of sialidosis in these patients, and clearly identify the cDNA-encoded protein as lysosomal neuraminidase.

Three-dimensional structure of the human 'protective protein': structure of the precursor form suggests a complex activation mechanism

BACKGROUND

The human 'protective protein' (HPP) forms a multi-enzyme complex with beta-galactosidase and neuraminidase in the lysosomes, protecting these two glycosidases from degradation. In humans, deficiency of HPP leads to the lysosomal storage disease galactosialidosis. Proteolytic cleavage of the precursor form of HPP involves removal of a 2 kDa excision peptide and results in a carboxypeptidase activity. The physiological relevance of this activity is, as yet, unknown.

RESULTS

The crystal structure of the 108 kDa dimer of the precursor HPP has been elucidated by making extensive use of twofold density averaging. The monomer consists of a 'core' domain and a 'cap' domain. Comparison with the distantly related wheat serine carboxypeptidase dimer shows that the two subunits in the HPP dimer differ by 15 degrees in mutual orientation. Also, the helical subdomain forming part of the cap domains is very different. In addition, the HPP precursor cap domain contains a 'maturation' subdomain of 49 residues which fills the active-site cleft. Merely removing the 'excision' peptide located in the maturation subdomain does not render the catalytic triad solvent accessible.

CONCLUSIONS

The activation mechanism of HPP is unique among proteases with known structure. It differs from the serine proteases in that the active site is performed in the zymogen, but is blocked by a maturation subdomain. In contrast to the zinc metalloproteases and aspartic proteases, the chain segment physically rendering the catalytic triad solvent inaccessible in HPP is not cleaved off to form the active enzyme. The activation must be a multi-step process involving removal of the excision peptide and major conformational changes of the maturation subdomain, whereas the conformation of the enzymatic machinery is probably almost, or completely, unaffected.

Mouse model for the lysosomal disorder galactosialidosis and correction of the phenotype with overexpressing erythroid precursor cells

The lysosomal storage disorder galactosialidosis results from a primary deficiency of the protective protein/cathepsin A (PPCA), which in turn affects the activities of beta-galactosidase and neuraminidase. Mice homozygous for a null mutation at the PPCA locus present with signs of the disease shortly after birth and develop a phenotype closely resembling human patients with galactosialidosis. Most of their tissues show characteristic vacuolation of specific cells, attributable to lysosomal storage. Excessive excretion of sialyloligosaccharides in urine is diagnostic of the disease. Affected mice progressively deteriorate as a consequence of severe organ dysfunction, especially of the kidney. The deficient phenotype can be corrected by transplanting null mutants with bone marrow from a transgenic line overexpressing human PPCA in erythroid precursor cells. The transgenic bone marrow gives a more efficient and complete correction of the visceral organs than normal bone marrow. Our data demonstrate the usefulness of this animal model, very similar to the human disease, for experimenting therapeutic strategies aimed to deliver the functional protein or gene to affected organs. Furthermore, they suggest the feasibility of gene therapy for galactosialidosis and other disorders, using bone marrow cells engineered to overexpress and secrete the correcting lysosomal protein.

Organization of the gene encoding human lysosomal beta-galactosidase

Human beta-galactosidase precursor mRNA is alternatively spliced into an abundant 2.5-kb transcript and a minor 2.0-kb species. These templates direct the synthesis of the classic lysosomal beta-D-galactosidase enzyme and of a beta-galactosidase-related protein with no enzymatic activity. Mutations in the beta-galactosidase gene result in the lysosomal storage disorders GM1-gangliosidosis and Morquio B syndrome. To analyze the genetic lesions underlying these syndromes we have isolated the human beta-galactosidase gene and determined its organization. The gene spans greater than 62.5 kb and contains 16 exons. Promoter activity is located on a 236-bp Pst I fragment which works in a direction-independent manner. A second Pst I fragment of 851 bp located upstream from the first negatively regulates initiation of transcription. The promoter has characteristics of a housekeeping gene with GC-rich stretches and five potential SP1 transcription elements on two strands. We identified multiple cap sites of the mRNA, the major of which maps 53 bp upstream from the translation initiation codon. The portion of the human pre-mRNA undergoing alternative splicing is encoded by exons II-VII. Sequence analysis of equivalent mouse exons showed an identical genomic organization. However, translation of the corresponding differentially spliced murine transcript is interrupted in its reading frame. Thus, the mouse gene cannot encode a beta-galactosidase-related protein in a manner similar to the human counterpart. Differential expression of the murine beta-galactosidase transcript is observed in different mouse tissues.