Current Pharmaceutical Biotechnology - Volume 12, Issue 6, 2011

This special topic issue published in the journal Current Pharmaceutical Biotechnology is devoted to Recent advances in treatment approaches of lysosomal storage diseases (LSDs). LSDs constitute a group of more than 50 genetic pathologies characterized by chronic and progressive accumulation of substances in lysosomes. Most of them are caused by genetic mutations in catabolic lysosomal hydrolases genes producing a loss or reduction of their enzymatic activities. For many years, since the identification of lysosomal storage diseases, it was assumed that storage per se was responsible for cell and tissue damage, and palliative treatment of signs and symptoms was the only option for patients. Research conducted in the recent years has produced a revolution in the field of LSDs. Nowadays, it is broadly accepted there are other concomitant molecular mechanisms that translate the primary insult into cell damage. These pathophysiological pathways are becoming a major focus of the investigation in lysosomal storage diseases. This knowledge would be of benefit to generate potential targets of therapy that could be applied as concomitant treatment. Symptomatic treatment was the only possible therapy until 1991, when the first enzyme replacement therapy became available for the treatment of Gaucher disease. Since then, much effort has been put into the development of different treatment approaches, acting at the different steps of the cascade of pathological events: DNA, protein, substrate deposits. In this issue, leading researchers in each of the particular LSDs chosen will give us an up-to-date review of the latest advances in terms of treatment of LSDs. We would be able to learn about the range of possibilities available now for treating each disease.

Gaucher disease is inherited as an autosomal recessive disorder. The absence of β-glucocerebrosidase whose purpose is to cleave the glucose from ceramide results in accumulation of glucocerebroside; storage of this glycolipid results in Gaucher disease. There is tremendous clinical heterogeneity: prediction of onset of symptoms (if at all), which organs will be affected, and the degree of severity of the signs and symptoms are areas of current research. Lysosomal storage diseases may be treatable by enzyme replacement therapy. Enzyme replacement for Gaucher disease has been attempted intermittently since the middle 1970s but was not successful until removal of sugars to expose the inner mannose residues allowed the targeting of the enzyme to macrophages via mannose receptors. The use of the recombinant imiglucerase (Cerezyme™) as intravenous therapy has been safe and effective for the visceral symptoms and signs of Gaucher disease in more than 5000 patients world-wide for more than 18 years. Nonetheless, beyond enzymes not being able to traverse the blood-brain barrer, dependence on a single modality is problematic since not all patients are responders, some develop adverse events, and supply may not be forthcoming for non-medical reasons. Thus, the availability of new enzymatic preparations, velaglucerase alfa (VPRIV™) and taliglucerase alfa (UPLYSO™), as well as alternative modalities such as substrate reduction and pharmacological chaperones, are important additions to the management portfolio of this disease.

Mucopolysaccharidosis (MPS) type II (Hunter syndrome, OMIM 309900) is an X-linked lysosomal storage disorder caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS). Major clinical manifestations include joint contractures, obstructive and restrictive airway disease, cardiac disease, skeletal deformities and often mental retardation. As with all the MPS disorders, mucopolysaccharidosis type II is a clinically heterogeneous disease in terms of the extent and rate of progression of organ impairment in affected individuals. Common causes of death, which usually occurs within the second decade of life, are obstructive airway disease and cardiac failure due to valvular dysfunction, pulmonary hypertension and myocardial disease. Patients with the more attenuated (so-called adult) form usually have a normal intelligence, but often have many complaints such as progressive loss of vision due to retinal dysfunction, spastic paresis due to myelon compression at the cranio-cerevical region, severe hip disease and cardiac complications. Clinical investigations that have been performed in the last years in a great number of patients have shown that many of these complications are still underdiagnosed and untreated. Until recently, no specific treatment was available for the affected patients; management mainly consisted of supportive care and treatment of complications. Enzyme replacement therapy with recombinant iduronate-2-sulphatase (idursulfase), however, has now been introduced. And it could be demonstrated that weekly intravenous infusions of idursulfase is able to improve many of the symptoms and signs of Hunter syndrome. This review will present the efficacy and safety data of the enzyme preparation and discuss benefits and limitations of this new therapeutic option.

The Neuronal Ceroid Lipofuscinoses (NCLs) are lysosomal storage diseases (LSDs) affecting the central nervous system (CNS), with generally with recessive inheritance. They are characterized by pathological lipofuscin-like material accumulating in cells. The clinical phenotypes at all onset ages show progressive loss of vision, decreasing cognitive and motor skills, epileptic seizures and premature death, with dementia without visual loss prominent in the rarer adult forms. Eight causal genes, CLN10/CTSD, CLN1/PPT1, CLN2/TPP1, CLN3, CLN5, CLN6, CLN7/MFSD8, CLN8, with more than 269 mutations and 49 polymorphisms (http://www.ucl.ac.uk/ncl) have been described. Other NCL genes are hypothesized, including CLN4 and CLN9; CLCN6, CLCN7 and possibly SGSH are under study. Some therapeutic strategies applied to other LSDs with significant systemic involvement would not be effective in NCLs due to the necessity of passing the blood brain barrier to prevent the neurodegeneration, repair or restore the CNS functionality. There are therapies for the NCLs currently at preclinical stages and under phase 1 trials to establish safety in affected children. These approaches involve enzyme replacement, gene therapy, neural stem cell replacement, immune therapy and other pharmacological approaches. In the next decade, progress in the understanding of the natural history and the biochemical and molecular cascade of events relevant to the pathogenesis of these diseases in humans and animal models will be required to achieve significant therapeutic advances.

Mucopolysaccharidoses (MPS) are a group of lysosomal storage diseases that are resulted from abnormal accumulation of glycosaminoglycans. Among the progressive multi-organ abnormalities often associated with MPS diseases, the deterioration of central nervous system (CNS) is the most challenging manifestations to be tackled, due to the impermeability of the blood-brain-barrier (BBB). Evolved with recent development in stem cell biotechnology and gene therapy, several novel experimental approaches have been investigated in animal models. In this review, we will address different approaches attempting to bypass the BBB for neuropathic MPS treatment using cell- and gene-based therapies. Several neurological findings in CNS pathophysiology emerged with therapeutic investigation will also be discussed.

Niemann-Pick disease type C is an autosomal recessive disorder caused by mutations in either one of the two genes, NPC1 or NPC2, which encode proteins involved in the regulation of normal transport and/or processing of free cholesterol. Several types of lipids including free cholesterol (unesterified), sphingosine, sphingomyelin, phospholipids and glycosphingolipids (glucosylceramide and gangliosides GM2 and GM3) are accumulated in lysosomes and late endosomes of cells, with pronounced concentrations in the liver and the spleen. The key laboratory diagnostic test for NP-C is filliping staining of cultured skin fibroblasts from the patient, to demonstrate free cholesterol accumulation in lysosomes secondary to impaired intracellular cholesterol transport. The symptomatology and rate of disease progression are strongly influenced by age at disease onset and different clinical forms have been described on this basis: Perinatal, Early-infantile (EI), late-infantile (LI), juvenile and adult forms. Clinical symptoms include progressive neurological deterioration and visceral organomegaly. Nowadays there is no fully effective treatment, only supportive measures for relief of specific manifestations of the disease. The intervention to slow disease progression is the most promising therapy. A number of experimental disease - specific therapies, based on the molecular pathology of NP-C, have been tested in cell culture and animal models including neurosteroids, cholesterol - binding agents, curcumin and Miglustat. This paper summarizes the recent developments that have been investigated for the treatment in patients and animal models with NPC. Current therapeutic approaches have been classified based on the targeting of cellular function, the anti - apoptotic cellular mechanisms and the stem cells therapy.

Pompe disease (PD) is a metabolic myopathy caused by the deficiency of the lysosomal hydrolase acid α- glucosidase (GAA) and characterized by generalized glycogen storage. Heterogeneous GAA gene mutations result in wide phenotypic variability, ranging from the severe classic infantile presentation to the attenuated intermediate and late-onset forms. Enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA) is at present the only approved treatment for PD, in addition to supportive and physical therapies. However, ERT shows limited efficacy in some patients and does not completely correct the disease phenotype. Recently, an improved knowledge of PD pathophysiology has provided clues to explain the limitations of ERT. A mechanical effect of lysosomal inclusions on muscle contractility has been proposed as a key factor of disease resulting in a severe loss of contractility. In addition, it has been shown that secondary abnormalities of housekeeping cellular functions, such as autophagy, have an important role in the pathogenesis of cell damage in PD. Abnormalities of intra-cellular trafficking of vesicles and membrane-bound proteins, such as the cation-independent mannose-6-phosphate receptor, may be deleterious for the efficacy of ERT. At present, new therapeutic strategies, in addition to ERT, are under investigation. An emerging strategy for the treatment of PD is pharmacological chaperone therapy, based on the use of chaperone molecules that assist the folding of mutated enzymes and improve their stability and lysosomal trafficking. Pre-clinical studies demonstrated a synergistic effect of pharmacological chaperones and ERT. Other approaches, also in a pre-clinical stage, include substrate reduction and gene therapy.

Fabry disease is an X-linked lysosomal storage disorder (LSD) due to deficiency of the enzyme α-galactosidase A (GLA). Absent or reduced enzyme activity leads to impaired catabolism of neutral glycosphingolipids, particularly globotriaosylceramide (Gb3), resulting in intracellular deposition of such lipids. Clinical manifestations in hemizygote males include angiokeratoma, hypohydrosis, acroparesthesia, abdominal pain, proteinuria, renal insufficiency, left ventricular hypertrophy and cerebrovascular accidents. Heterozygote women may present with mild to severe signs and symptoms. Since year 2001, enzyme replacement therapy (ERT) is the only specific treatment for Fabry disease. The beneficial effect of ERT on different organs/systems has been extensively evaluated, and an improvement in renal function, cardiac mass and quality of life has been reported. Different treatment approaches are currently on development. One of them implies the use of the active-site-specific chaperone 1-deoxygalactonojirimycin that acts facilitating folding of mutant GLA in the endoplasmic reticulum and increasing its lysosomal residual activity. Reduction of Gb3 deposits has been shown in lymphoblasts from Fabry patients with missense mutations and transgenic mouse model expressing a missense mutation GLA. Gene therapy has been also developed as a potential option for treatment of Fabry disease. This review will discuss these novel therapeutic options along with their advantages and limitations.

Mucopolysaccharosis III (MPS III) is a lysosomal storage disorder and belongs to the group of mucopolysaccharidoses. MPS III is caused by a deficiency of one of the four enzymes catalyzing the degradation of the glycosaminoglycan heparan sulfate. MPS III is clinically characterized by progressive dementia with distinct behavioral disturbances and relatively mild somatic disease. This review will summarize and discuss the available and potential future therapeutic options for patients with MPS III. This includes enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), substrate reduction therapy (SRT), chaperone-mediated therapy, and gene therapy. Although clinical efficacy has not yet been fully demonstrated for any of these therapies, it is likely that future developments will lead to disease- modifying treatment for this devastating disease.

Mucopolysaccharidosis IVA (MPS IVA), also known as Morquio A, is a rare, autosomal recessive disorder caused by a deficiency of the lysosomal enzyme N-acetylgalatosamine-6-sulfate-sulfatase (GALNS), which catalyzes a step in the catabolism of glycosaminoglycans (GAGs), keratan sulfate (KS) and chondroitin-6-sulfate (C6S). It leads to accumulation of the KS and C6S, mainly in bone and cornea, causing a systemic skeletal chondrodysplasia. MPS IVA has a variable age of onset and variable rate of progression. Common presenting features include elevation of urinary and blood KS, marked short stature, hypoplasia of the odontoid process, pectus carinatum, kyphoscoliosis, genu valgum, laxity of joints and corneal clouding; however there is no central nervous system impairment. Generally, MPS IVA patients with a severe form do not survive beyond the third decade of life whereas those patients with an attenuated form may survive over 70 years. There has been no effective therapy for MPS IVA, and care has been palliative. Enzyme replacement therapy (ERT) and hematopoietic stem cell therapy (HSCT) have emerged as a treatment for mucopolysaccharidoses disorders, including Morquio A disease. This review provides an overview of the clinical manifestations, diagnosis and symptomatic management of patients with MPS IVA and describes potential perspectives of ERT and HSCT. The issue of treating very young patients is also discussed.

Intrathecal enzyme replacement therapy has been proposed to treat central nervous system (CNS) disease due to mucopolysaccharidosis type I. Our research has shown that repeated injections of recombinant enzyme into the spinal fluid corrects enzyme deficiency and normalizes lysosomal storage in the canine model. The challenge is to translate the success in the animal where there are fewer study limitations to human patients where studies are more restricted. This review will explore what is known about the measurement of clinically-relevant outcomes of intrathecal enzyme replacement therapy for MPS I (including ongoing clinical trials), the challenges in translating therapies for the CNS in rare diseases, and new outcome measures that could aid translation of CNS therapies for MPS disorders.

Mucopolysaccharidosis VI is caused by accumulation of the glycosaminoglycan dermatan sulfate in all tissues due to decreased activity of the enzyme arylsulfatase B. Patients exhibit multisystemic signs and symptoms in a chronic and progressive manner, especially with changes in the skeleton, cardiopulmonary system, cornea, skin, liver, spleen and meninges. Patients usually have normal inteligence. In the past, treatment of mucopolysaccharidoses was limited to palliative medical care. The outcome for affected patients improved with the introduction of new technologies as hematopoietic stem cell transplantation, relegated to specific situations after enzyme replacement therapy (ERT) became available. The specific ERT for MPS VI, galsulfase (Naglazyme®, Biomarin Pharmaceutical) was approved in 2005 by FDA and in 2006 by EMEA, and three clinical studies including 56 patients have evaluated the efficacy and safety. Long-term follow up data with patients treated up to 5 years showed that ERT is well tolerated and associated with sustained improvements in the patients' clinical condition. Intrathecal ERT may be considered in situations of high neurosurgical risk but still it is experimental in humans, as is intra-articular ERT. It is possible that the full impact of this therapy will only be demonstrated when patients are identified and treated soon after birth, as it was shown that early introduction of ERT produced immune tolerance and improved enzyme effectiveness in the cat model. New insights on the pathophysiology of MPS disorders are leading to alternative therapeutic approaches, as gene therapy, inflammatory response modulators and substrate reduction therapy.