Research
METACHROMATIC LEUKODYSTROPHY
NETWORK PROJECT
WHAT IS METACHROMATIC LEUKODYSTROPHY?
The metachromatic leukodystrophy (MLD) is a severe and fatal genetic disease, caused by the lack of the enzyme arylsulfatase A (ASA) in lysosomes, organelles present in all the cells of the body. This deficit results in a progressive and irreversible accumulation of toxic cellular substances, which has devastating effects on the organism, mainly on the central nervous system. Affected children appear normal and healthy at birth, but then they gradually loose their vital capacities during next few years.
THE FIGHT AGAINST LEUKODYSTROPHY
The Brains for Brain Onlus Foundation has initiated a research Program lasting two years, for the treatment of MLD. This programt, involving the major European experts in the field, is divided into 8 projects which are independent but closely related, aimed at identifying new therapeutic approaches. The development of novel therapies is based on:
enzyme replacement therapy capable of reaching the brain
gene therapy
haematopoietic and neural stem cell transplantation
substrate reduction therapy
The discoveries and success of this research Program are essential not only for the children life, but also to address and treat neurological diseases in adults, such as, for example, Parkinson's disease and Alzheimer's disease, Multiple Sclerosis and Amyotrophic Lateral Sclerosis.
STRATEGY FOR THE FIGHT
CLINICAL HISTORY (PROJECT 1)
Detailed clinical data on the natural history of MLD are necessary for any clinical study evaluating therapies in MLD. For this reason project 1 has already designed MRI and motor scores specifically for MLD patients and will use these scores for a more detailed description of clinical history of MLD. The designed scoring system will describe clinical (gross and fine motor function, GMFCS and BFMF) and neuroimaging features and will focus on the evaluation of patients with late infantile MLD. An additional scoring system for the juvenile course will be established for cognitive, language functions and behaviour, relevant for the early course.
All this in order to allow a careful and detailed description of the clinical history of MLD on an international level.
MECHANISMS OF ENZYME REPLACEMENT THERAPY (PROJECT 2, 3, 4, 5)
Preclinical studies performed in a mouse model of metachromatic leukodystrophy have surprisingly shown that sulfatide storage in brain is reduced upon repeated intravenous injections of high doses of recombinant arylsulfatase A. This suggests that the enzyme may actually be able to cross the BBB even though unfortunately not yet able to reverse the process of neurodegeneration. The mechanisms and pathways behind this phenomenon are unknown.
Project 2 will examine the transcytosis of recombinant arylsulfatase A in a BBB cell culture model. This model is based on primary porcine brain endothelial cells. Recombinant arylsulfatase A will be added to the apical side of the culture system and the delivery to the basal site after various time periods and enzyme modifications will be determined. This cell culture system should allow to determine the rate of transcytosis and the pathways involved. It may yield clues to improving delivery of enzyme across the blood brain barrier.
Whereas project 2 is based on an in vitro cell culture system project 3 will add in vivo information to passage of ASA across the BBB.
Another possible route to deliver enzyme across the blood brain barrier is the paracellular route.
Project 4 will fuse arylsulfatase A to peptides which bind to proteins constituting the tight junctions between the endothelial cells of the BBB. The possible transfer of such proteins across the BBB can be tested in cell culture systems available in projects 2 and 4.
Another option for CNS delivery of recombinant arylsulfatase A may be the use of nanoparticles, ie particles of variable size 1-1000 nm (1 micron).
Recombinant enzyme will be coupled to nanoparticles within project 5 and tested for brain delivery in projects 2 and 3. Due to their small size, nanoparticles can infact "convey" the enzyme transport across the BBB by endocytosis or trans-cytosis mechanisms.
If expedient, results from project 2, 3, 4 and/or 5 can be tested for therapeutic efficacy in mouse models provided by project 6 in follow up projects.
DEVELOPING SUBSTRATE REDUCTION THERAPY (PROJECT 6)
So far research on MLD has largely ignored the development of therapies based on small molecules.
One of the options involving small molecules is substrate reduction.
Project 6 aims at the development of tools which shall allow screening for small molecules which can be useful to develop substrate reduction therapy for MLD. In particular, it will assess the capacity to reduce the synthesis of accumulating substrates. This new therapeutic approach is based on the use of substances that have the ability to selectively inhibit the synthesis of molecules that accumulate as a consequence of enzyme defect, reducing the imbalance between synthesis and degradation.
TRANSPLANTATION OF NEURAL STEM CELLS AND GENE THERAPY (PROJECTS 7, 8)
Subject of these two projects is the experimental assessment of a possible clinical application and therapeutic use of human neural stem cells. These cells, once over crossed the barrier, have the unique capacity of repairing the nerve damage caused by a genetic enzyme deficiency and the resulting accumulation of substrate characteristic of MLD. The neural stem cells therefore represent a promising new approach for the development of neuro repair and neuro protective therapies. Initially, it will investigate the expression of ASA in animal models affected by MLD and receiving intratechal or intracerebroventricular injection of neural stem cells. If the results of this preliminary study will be satisfactory the project will be then extended to a clinical trials on patients.
In particular while the principal aim of the project 7 is to investigate and assess the feasibility of transplantation of neural stem cells in a mouse model of MLD, the project 8 is focused on evaluating the safety and efficacy of haematopoietic stem cells gene therapy. Both these therapeutic approaches will assess the capability and safety of human stem cells to correct the MLD phenotype in vivo, either by replacing impaired oligodendrocytes, either by the cross correction of ASA deficiency, spontaneously or upon manipulation with therapeutic viral vectors.
HOW MUCH IT COSTS
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The project has a cost of 850,000 euros.
The Brains for Brain Foundation is able to grant 75% of the total budge corresponding to 600,000 Euros. It is necessary to approach additional sources to obtain the remaining 25% (about 250,000 Euros).