Sanfilippo disease type B (also called mucopolysaccharidosis type III, or MPS III) is a devastating neuro-degenerative genetic disorder of childhood that is fatal. There is no cure or effective treatment. MPS IIIB is caused by the lack of a lysosomal enzyme called NAGLU (alpha-N-acetylglucosaminidase) that is required to degrade heparan sulfate glycosaminoglycans (GAG). Bone marrow transplantation is not effective in treating MPS III because most cells normally synthesize and secrete NAGLU that has mannose 6-phosphate (M6P) sugars attached via post-translational modification, and M6P is essential to achieve adequate cellular uptake of the secreted enzyme via the M6P receptor. Unfortunately, human macrophages (the principal therapeutic cells in a bone marrow transplant) secrete NAGLU that lacks M6P. Encouraging preliminary data from the Dickson lab shows that recombinant human NAGLU fused to a small peptide fragment that consists of the receptor binding motif of the insulin-like growth factor 2 (IGF2) is able to enter cells using an alternativ uptake pathway - the IGF2 receptor - and has kinetic, pH, and functional characteristics similar to recombinant human NAGLU without the IGF2 fusion peptide. We therefore propose to bioengineer stem cells to secrete NAGLU fused to an IGF2 peptide fragment that will be secreted and taken up by cells missing NAGLU, thus correcting the cause of the disease when these modified stem cells are delivered clinically via injection. Feasibility criteria for this phae I STTR will determine whether our approach merits further commercial development for a new therapy to treat MPS IIIB and are defined below in our two proposed AIMS:
Aim 1 : Macrophage secretion of NAGLU-IGF2. Sanfilippo B syndrome is caused by deficiency of the enzyme, alpha-N-acetylglucosaminidase (NAGLU). NAGLU lacks M6P when produced from cells [12,13], and therefore represents a perfect test case for the IGF2 technology. We will use a lentiviral vector encoding murine Naglu-IGF2 or Naglu and a CMV promoter to overexpress the transgene in murine macrophages. We will deem this approach feasible for further development if: 1) macrophages are successfully transduced; 2) Naglu-IGF2 is secreted in adequate quantities; and 3) secreted Naglu-IGF2 is taken up by co-cultured Naglu-deficient cells via M6P receptors, traffics to lysosomes, and degrades heparan sulfate (NAGLU's substrate).
Aim 2 : Modifying murine stem cells to express Naglu-IGF2. This controlled, in vivo study in Sanfilippo B mice will test whether IGF2 can restore uptake of NAGLU from a bone marrow transplant. We will perform autologous stem cell transplantation using GFP-labeled murine stem cells harvested from bone marrow modified with a lentiviral vector bearing the Naglu-IGF2 coding sequence. Feasibility criteria for this aim will be deemed to have been attained if evidence of significant disease correction is observed. Our objective is to produce an effective treatment for MPS IIIB as rapidly and efficiently as possible. If successful, we will immediately proceed with a Phase II project that will propose IND-enabling studies.
We will develop a new treatment for a fatal neurodegenerative disorder of childhood called Sanfilippo B (or, alternatively, mucopolysaccharidosis IIIB or MPS IIIB). Sanfilippo B caused by lack of alpha-N-acetylglucosaminidase (NAGLU), but delivery of recombinant synthesized NAGLU will not correct the disease because when NAGLU is synthesized in cell culture, specific types of sugars that are required for NAGLU to function properly are not attached to the protein. To solve this roadblock and create an effective treatment for this catastrophic disease, we propose to modify stem cells to express NAGLU fused to the receptor binding motif of the insulin-like growth factor 2 (NAGLU-IGF2) because our preliminary data shows that this enzyme, which we have already synthesized and begun testing, can be taken up by cells via an alternative pathway (the IGF2 receptor pathway), traffics appropriately to the lysosomes, has biochemical and functional properties similar to normal NAGLU, and hence could reverse the terrible pathology caused by this disease.
| Ekins, Sean; Perlstein, Ethan O (2018) Doing it All - How Families are Reshaping Rare Disease Research. Pharm Res 35:192 |
