UX007 for the treatment of long chain-fatty acid oxidation disorders: Safety and efficacy in children and adults following 24weeks of treatment

BACKGROUND

Long-chain fatty acid oxidation disorders (LC-FAOD) lead to accumulation of high concentrations of potentially toxic fatty acid intermediates. Newborn screening and early intervention have reduced mortality, but most patients continue to experience frequent hospitalizations and significant morbidity despite treatment. The deficient energy state can cause serious liver, muscle, and heart disease, and may be associated with an increased risk of sudden death. Triheptanoin is a medium odd-chain fatty acid. Anaplerotic metabolites of triheptanoin have the potential to replace deficient tricarboxylic acid (TCA) cycle intermediates, resulting in net glucose production as a novel energy source for the treatment of LC-FAOD.

STUDY DESIGN

A single-arm, open-label, multicenter Phase 2 safety and efficacy study evaluated patients with severe LC-FAOD evidenced by ongoing related musculoskeletal, cardiac, and/or hepatic events despite treatment. After a four-week run-in on current regimen, investigational triheptanoin (UX007) was titrated to a target dose of 25-35% of total daily caloric intake. Patients were evaluated on several age/condition-eligible endpoints, including submaximal exercise tests to assess muscle function/endurance (12-minute walk test; 12MWT) and exercise tolerance (cycle ergometry), and health related quality of life (HR-QoL). Results through 24weeks of treatment are presented; total study duration is 78weeks.

RESULTS

Twenty-nine patients (0.8 to 58years) were enrolled; most qualified based on severe musculoskeletal disease. Twenty-five patients (86%) completed the 24-week treatment period. At Week 18, eligible patients (n=8) demonstrated a 28% increase (LS mean=+181.9 meters; p=0.087) from baseline (673.4meters) in 12MWT distance. At Week 24, eligible patients (n=7) showed a 60% increase in watts generated (LS mean=+409.3W; p=0.149) over baseline (744.6W) for the exercise tolerance test. Improvements in exercise tests were supported by significant improvements from baseline in the adult (n=5) self-reported SF-12v2 physical component summary score (LS mean=+8.9; p<0.001). No difference from baseline was seen in pediatric parent-reported (n=5) scores (SF-10) at Week 24. Eighteen patients (62%) had treatment-related adverse events, predominantly gastrointestinal (55%), mild-to-moderate in severity, similar to that seen with prior treatment with medium chain triglyceride (MCT) oil. One patient experienced a treatment-related serious adverse event of gastroenteritis. One patient discontinued from study due to diarrhea of moderate severity; the majority of patients (25/29; 86%) elected to continue treatment in the extension period.

CONCLUSIONS

In patients with severe LC-FAOD, UX007 interim study results demonstrated improved exercise endurance and tolerance, and were associated with positive changes in self-reported HR-QoL.

Research challenges in central nervous system manifestations of inborn errors of metabolism

The Research Challenges in CNS Manifestations of Inborn Errors of Metabolism workshop was designed to address challenges in translating potential therapies for these rare disorders, and to highlight novel therapeutic strategies and innovative approaches to CNS delivery, assessment of effects and directions for the future in the treatment of these diseases. Therapies for the brain in inborn errors represent some of the greatest challenges to translational research due to the special properties of the brain, and of inborn errors themselves. This review covers the proceedings of this workshop as submitted by participants. Scientific, ethical and regulatory issues are discussed, along with ways to measure outcomes and the conduct of clinical trials. Participants included regulatory and funding agencies, clinicians, scientists, industry and advocacy groups.

Intrathecal administration of AAV vectors for the treatment of lysosomal storage in the brains of MPS I mice

Mucopolysaccharidosis type I (MPS I) is caused by an inherited deficiency of alpha-L-iduronidase (IDUA). The result is a progressive, lysosomal storage disease with central nervous system (CNS) as well as systemic involvement. To target gene therapy to the CNS, recombinant adeno-associated virus (AAV) vectors carrying IDUA sequence were administered to MPS I mice via injection into cerebrospinal fluid. In contrast to intravenous administration, this intrathecal administration was effective in generating widespread IDUA activity in the brain, with the cerebellum and olfactory bulbs having highest activities. In general, IDUA levels correlated with vector dose, although this correlation was obscured in cerebellum by particularly high variability. High doses of vector (4 x 10(10) particles) provided IDUA levels approaching or exceeding normal levels in the brain. Histopathology indicated that the number of cells with storage vacuoles was reduced extensively or was eliminated entirely. Elimination of storage material in Purkinje cells was particularly dramatic. A lower vector dose (2 x 10(9) particles) reduced both the number of storage cells and the extent of storage per cell, but the effect was not complete. Some perivascular cells with storage persisted, and this cell type appeared to be more resistant to treatment than neurons or glial cells. We conclude that intrathecal administration of AAV-IDUA delivers vector to brain cells, and that this route of administration is both minimally invasive and effective.

Intrathecal enzyme replacement therapy reduces lysosomal storage in the brain and meninges of the canine model of MPS I

Enzyme replacement therapy (ERT) has been developed for several lysosomal storage disorders, including mucopolysaccharidosis I (MPS I), and is effective at reducing lysosomal storage in many tissues and in ameliorating clinical disease. However, intravenous ERT does not adequately treat storage disease in the central nervous system (CNS), presumably due to effects of the blood-brain barrier on enzyme distribution. To circumvent this barrier, we studied whether intrathecal (IT) recombinant human alpha-L-iduronidase (rhIDU) could penetrate and treat the brain and meninges. An initial dose-response study showed that doses of 0.46-4.14 mg of IT rhIDU successfully penetrated the brain of normal dogs and reached tissue levels 5.6 to 18.9-fold normal overall and 2.7 to 5.9-fold normal in deep brain sections lacking CSF contact. To assess the efficacy and safety in treating lysosomal storage disease, four weekly doses of approximately 1 mg of IT rhIDU were administered to MPS I-affected dogs resulting in a mean 23- and 300-fold normal levels of iduronidase in total brain and meninges, respectively. Quantitative glycosaminoglycan (GAG) analysis showed that the IT treatment reduced mean total brain GAG to normal levels and achieved a 57% reduction in meningeal GAG levels accompanied by histologic improvement in lysosomal storage in all cell types. The dogs did develop a dose-dependent immune response against the recombinant human protein and a meningeal lymphocytic/plasmacytic infiltrate. The IT route of ERT administration may be an effective way to treat the CNS disease in MPS I and could be applicable to other lysosomal storage disorders.

Successful induction of immune tolerance to enzyme replacement therapy in canine mucopolysaccharidosis I

Immune responses can interfere with the effective use of therapeutic proteins to treat genetic deficiencies and have been challenging to manage. To address this problem, we adapted and studied methods of immune tolerance used in canine organ transplantation research to soluble protein therapeutics. A tolerization regimen was developed that prevents a strong antibody response to the enzyme alpha-l-iduronidase during enzyme replacement therapy of a canine model of the lysosomal storage disorder mucopolysaccharidosis I. The tolerizing regimen consists of a limited 60-day course of cyclosporin A and azathioprine combined with weekly i.v. infusions of low-dose recombinant human alpha-l-iduronidase. The canines tolerized with this regimen maintain a reduced immune response for up to 6 months despite weekly therapeutic doses of enzyme in the absence of immunosuppressive drugs. Successful tolerization depended on high plasma levels of cyclosporin A combined with azathioprine. In addition, the induction of tolerance may require mannose 6-phosphate receptor-mediated uptake because alpha-l-iduronidase and alpha-glucosidase induced tolerance with the drug regimen whereas ovalbumin and dephosphorylated alpha-l-iduronidase did not. This tolerization method should be applicable to the treatment of other lysosomal storage disorders and provides a strategy to consider for other nontoleragenic therapeutic proteins and autoimmune diseases.

Retrovirus-mediated transfer of the human alpha-L-iduronidase cDNA into human hematopoietic progenitor cells leads to correction in trans of Hurler fibroblasts

Hurler syndrome (mucopolysaccharidosis IH or MPS IH) is a congenital mucopolysaccharide storage disorder resulting from a genetic deficiency of alpha-L-iduronidase (IDUA), which is required for lysosomal degradation of glycosaminoglycans heparan sulfate and dermatan sulfate. Even though histocompatible bone marrow transplantation has been applied for the treatment of Hurler syndrome, gene therapy via autologous bone marrow transplantation (BMT) may be more beneficial for this disease. Two retroviral vectors containing a full-length human IDUA cDNA were constructed using Moloney murine leukemia virus (MoMLV)-based vector backbones. High-titer vector-producing clones containing the L-HuID-SN and MFG-HuID retroviral vectors were established. The efficiency of gene transfer into primitive human CD34+ hematopoietic cells using both retroviral vectors is in the range of 18-23%. The level of enzyme expression in transduced primary bone marrow cells was increased 40- to 50-fold compared with that of sham-transduced cells. Enzyme produced by the progeny of the transduced human CD34+ cells carrying IDUA cDNA corrected Hurler fibroblasts via mannose-6-phosphate receptors. These findings suggest that genetically modified hematopoietic progenitor cells can potentially be useful for gene therapy of Hurler syndrome.

A transcriptional repressor of c-myc

In murine plasmacytomas there is deregulated transcription of a translocated c-myc allele and undetectable transcription of the normal, unrearranged c-myc allele. Deregulated c-myc transcription probably contributes to the transformed phenotype of the tumour cells, whereas repression of the normal allele probably reflects the normal turn-off of c-myc in non-dividing plasma cells. We previously identified a plasmacytoma-specific protein which binds to the c-myc promoter region 290 base pairs 5' of the P1 transcription start site. This plasmacytoma repressor factor (myc-PRF; formerly myc-PCF) is not found in cell lines representing earlier B-cell stages during which c-myc is transcribed, so it could be a negative regulator of c-myc transcription in terminally differentiated B cells. Here we report that site-directed deletion of the binding site for this protein leads to a 30-fold increase in transcription of a stably transfected c-myc fusion construct in plasmacytoma cells but has no effect in L cells or 18-81 pre-B cells, which lack the protein. Myc-PRF interacts with another widely distributed protein, myc-CF1 (common factor 1), which binds nearby, and this association may be important in myc-PRF repression.

Strong transcriptional activation of translocated c-myc genes occurs without a strong nearby enhancer or promoter

We have studied the transcriptional activation of translocated c-myc genes in murine plasmacytomas in which the translocation juncture occurs within the first intron of c-myc and juxtaposes c-myc with the immunoglobulin C alpha gene segment. It has been widely suggested that a novel transcriptional enhancer element located near the C alpha gene segment might activate the translocated c-myc gene. We have carried out an extensive search for such an element and find no significant transcriptional enhancer activity in a 22 kb region encompassing the translocation junction, C alpha gene segment and regions 3' of C alpha. We also find that the cryptic promoter region of the translocated c-myc gene is a very weak promoter of transcription. Despite this evidence against the presence of strong transcriptional regulatory elements, the translocated c-myc gene locus is transcribed at high rates that are 25-greater than 100% of that measured for the highly active immunoglobulin genes in murine plasmacytomas. These data suggest the presence of a novel type of strong activator of transcription in the murine heavy chain locus.

A plasmacytoma-specific factor binds the c-myc promoter region

We used an electrophoretic mobility-shift assay to study proteins that bind to sequences in the 5' flanking region of the murine c-myc gene. By comparing the DNA-protein complexes formed with extracts from cells representing earlier stages of B-cell development with those from plasmacytomas, we identified a plasmacytoma-specific protein that binds to a region within the c-myc promoter. Five other regions of this promoter show extensive sequence-specific binding, but the binding is not clearly B-cell stage-specific. Methylation-interference and o-phenanthroline/copper-protection experiments identified a single plasmacytoma-specific protein binding site 290 base pairs 5' of the transcription start site P1. Homologues of a core sequence, d(AGAAAGGGAAAGGA), within the 25-base-pair binding site are found at three additional sites in the murine c-myc locus. The plasmacytoma-specific occurrence of this protein suggests that it may play a role in the transcriptional repression of the normal c-myc gene observed in plasmacytomas.

An active chromatin structure acquired by translocated c-myc genes

We used general sensitivity to DNase I digestion to analyze the chromatin structure of c-myc genes in seven murine plasmacytomas. In every case, the 3' portion of c-myc juxtaposed with C alpha displayed a much more DNase I-sensitive chromatin structure than untranslocated c-myc or, in one case analyzed, the reciprocally translocated 5' portion. Our data suggest the presence of regulatory sequences near the C alpha gene segment.