545Myoblast transfer has been tried for treatment of DMD but the results have not been
satisfactory. Stem cells are promising for treating DMD because a small number of
cells are required to obtain a therapeutic effect but identifi cation of a stem cell popu-
lation that provides effi cient muscle regeneration is critical for the progression of
cell therapy for DMD. However, there are still unanswered questions regarding a
variety of stem cells with myogenic potential, numerous cytokines and growth fac-
tors acting solo or in an orchestrated manner.
Most attractive are molecular-based therapies that can express the missing dys-
trophin protein (exon skipping or mutation suppression) or a surrogate gene product
(utrophin). Duchenne muscular dystrophy gene that forms the basis of future gene
therapy of this disorder, was identifi ed in 1987 (Hoffman et al. 1987 ). Endogenous
gene expression of dystrophin should be restored to >20 % of normal levels for
improvement of muscular dystrophy symptoms. It is possible to block expression of
both chromosomal copies of the defective native gene by an antisense approach.
Normal protein can be expressed by a normal gene construct that is introduced and
contains divergent codons to prevent blocking by the antisense compound. Various
gene therapy approaches to DMD are shown in Table 16.2.
Other approaches to DMD include increasing the strength of muscles (myostatin
inhibitors), reducing muscle fi brosis and decreasing oxidative stress. Additional tar-
gets include inhibition of NF-κB to reduce infl ammation or promote skeletal muscle
blood fl ow and muscle contractility using phosphodiesterase inhibitors or nitric
oxide (NO) donors. The goal of treatment should be to fi nd a product at least as
effective as glucocorticoids with a lower side effect profi le or with a signifi cant
glucocorticoid sparing effect (Malik et al. 2012 ). Gene therapy still remains the
most promising approach. The most promising possibility for the treatment of DMD
might be a combination of approaches such as drugs, stem cell and gene therapy.
Antisense Oligonucleotide-Induced Exon-Skipping for DMD
Exon-skipping, induced by antisense oligonucleotides changes an out-of-frame
mutation into an in-frame mutation, aiming at conversion of a severe DMD pheno-
type into a mild phenotype by restoration of truncated dystrophin expression
(Nakamura and Takeda 2009 ). Many of the mutations associated with DMD can
Table 16.2 Gene therapy approaches to Duchenne muscular dystrophy
Viral vector-mediated gene transfer: retrovirus, lentivirus, adenoviral, AAV
Nonviral vectors: liposome-mediated gene transfer
Plasmid-mediated gene therapy: direct injection of plasmid DNA into the muscles
Electrotransfer of naked DNA in the skeletal muscles
Liposome-mediated gene transfer
Myoblast-mediated gene transfer
Repair of the dystrophin gene
Antisense approach
Pharmacological modulation of dystrophin gene
© Jain PharmaBiotechPersonalized Cell and Gene Therapies of Genetic Disorders