Efficacy of a Bicistronic Vector for Correction of Sandhoff Disease in a Mouse Model

Abstract

GM2 gangliosidoses are a family of severe neurodegenerative disorders resulting from a deficiency in the β-hexosaminidase A enzyme. These disorders include Tay-Sachs disease and Sandhoff disease, caused by mutations in the HEXA gene and HEXB gene, respectively. The HEXA and HEXB genes are required to produce the α and β subunits of the β-hexosaminidase A enzyme, respectively. Using a Sandhoff disease mouse model, we tested for the first time the potential of a comparatively lower dose (2.04 × 1013 vg/kg) of systemically delivered single-stranded adeno-associated virus 9 expressing both human HEXB and human HEXA cDNA under the control of a single promoter with a P2A-linked bicistronic vector design to correct the neurological phenotype. A bicistronic design allows maximal overexpression and secretion of the Hex A enzyme. Neonatal mice were injected with either this ssAAV9-HexB-P2A-HexA vector or a vehicle solution via the superficial temporal vein. An increase in survival of 56% compared with vehicle-injected controls and biochemical analysis of the brain tissue and serum revealed an increase in enzyme activity and a decrease in brain GM2 ganglioside buildup. This is a proof-of-concept study showing the “correction efficacy” of a bicistronic AAV9 vector delivered intravenously for GM2 gangliosidoses. Further studies with higher doses are warranted.

Natural History of Adult Patients with GM2 Gangliosidosis

“…Finally, gene therapy using adeno-associated viruses has shown some positive results in GM2 gangliosidosis mouse models and offers the most promising perspective. 15 In the near future, therapeutic approaches for GM2 gangliosidosis will undeniably emerge and evolve, and a better understanding of the disease's natural history is essential to their evaluation. This work intends to expand our understanding of GM2 gangliosidosis manifestations and evolution in adults to better predict its course and to determine the most reliable tools to evaluate future treatments.…”

“…3,4 Different therapeutic options, such as substrate reduction (eg, miglustat) or chaperone therapy (eg, pyrimethamine), have been attempted and can be used in selected patients with the aim of slowing or stabilizing the disease's evolution. [8][9][10][11][12][13][14][15] Other drugs currently being tested in other lysosomal storage diseases have the potential to be effective in GM2 gangliosidosis, whereas genetic therapies are under investigation in GM2 gangliosidosis animal models.…”

GM2 Gangliosidoses: Clinical Features, Pathophysiological Aspects, and Current Therapies

“…Novel approaches using bicistronic vectors have been developed [ 162 ]. As a proof-of-concept the bicistronic ssAAV9-HexBP2A-HexA vector was evaluated, which has a short P2A linker and the cDNA of HEXA and HEXB genes under the control of the chicken β-actin promoter [ 163 ]. A single administration of the vector into neonatal SD mice allowed a 56% extension of the lifespan compared to untreated animals.…”

“…A single administration of the vector into neonatal SD mice allowed a 56% extension of the lifespan compared to untreated animals. In addition, this vector allowed a significant increase in the enzyme activity and the reduction of GM2 gangliosides levels both in brain and serum [ 163 ]. Using similar bicistronic vector but with a bidirectional promoter to drive the transgene expression in opposite directions of the HEXA and HEXB subunits, recently Lahey et al, 2020 found an increase the survival from 138 for untreated SD mice to up to more than 600 days after of the IV administration of the vectors [ 41 ].…”

Metabolism of Glycosphingolipids and Their Role in the Pathophysiology of Lysosomal Storage Disorders

“…However, administration of only one of the two genes (i.e., HEXA and HEXB) may limit heterodimer formation due to the availability of proportionate amounts of subunits. Therefore, two novel vectors have been designed as a solution: an artificial hybrid HEX enzyme called HEXM and the other, a bicistronic vector carrying both HEXA and HEXB in the same cassette [168,185,186]. In vivo testing of these vectors has shown marked reduction of GM2 ganglioside storage and a significant increase in survival of SD mice.…”