MUSCLE

No cure is currently available for most neuromuscular diseases (NMDs) and their treatment remains mainly symptomatic. The three most frequent are Duchenne Muscular Dystrophy (DMD), Spinal Muscular Atrophy (SMA), and Type 1 Myotonic Dystrophy (DM1). They affect between 1/6000 to 10 000 births, rely on very different pathophysiological mechanisms and are emblematic neuromuscular genetic disorders for which cellular and animal models are available and that have benefited of tremendous research efforts to develop therapies. Ongoing gene therapies for NMDs, approved or still in trials, rely on AAV viruses which currently constitute the best vector to introduce genetic material in muscles or motor neurons.

However, AAV-based vectors are not a panacea and their use imposes limitations:
i) a low transgene encapsidation capacity limited to 5kb
ii) ii) only a single treatment is possible because of the immunization consecutive to the first injection of the virus
iii) some individuals have pre-existing immunization against AAVs
iv) the viral dose to treat the muscles of newborn children or teenagers/adults are not the same and increasing the viral charge increases the risk to develop severe thrombotic microangiopathies that can be lethal.

Given the limitations imposed by AAVs vectors, future gene therapy treatments for NMDs will require the development of novel delivery vectors to efficiently deliver nucleic acids to targeted tissues and offering the possibility of repeated administration. In this line, we have developed Lipid Nanoparticles (LNPs) capable of delivering nucleic acids to muscle fibers with no limitation in size and without triggering an immune response.
The present project aims at:

1. Improving the in vivo efficiency of our LNPs by functionalizing LNPs with recombinant Fabs using CLIP chemistry or by including into LNPs a miniagrin protein we have shown to bind mouse and human muscle cells. Following GMP compatible standards, the technology acceleration platform TIBH will produce the recombinant proteins required to functionalize the LNPs.
2. Using cultured cells and animal models to establish the proof of concept that our LNPs can deliver therapeutic nucleic acids for DMD, SMA and DM1.
   • For DMD, LNPs offer the possibility to encapsulate the whole dystrophin mRNA to fully restore dystrophin function.
   • For DM1, two antisens-based strategies will be tested: blocking oligonucleotides and gapmers-oligonucleotides targeting DMPK mRNA to induce their RNaseH-dependent degradation.
   • For SMA, gene replacement or splicing modifying therapies efficiently rescue motoneurons but do not prevent persistent disabling muscle atrophy. 2 strategies will be tested: encapsulation of smn mRNA or of Nusinersen-like oligonucleotides targeting smn2 splicing.

To achieve these goals, we have gathered a consortium of 4 internationally renowned specialists with complementary skills. Pr Laurent Schaeffer is the director of a laboratory hosting 11 research teams working on neuromuscular diseases. His team develops therapeutic approaches for DMD and SMA. He is the coordinator of the RHU SMART partnering with Roche and aiming at developing pharmacological approaches to treat muscle atrophy in SMA patients. The present PEPR project is the result of a longstanding collaboration with Giovanna Lollo, a leader in the LNP field. Together, we have developed LNPs delivering nucleic acids to striated muscles. These LNPs are at the center of the project for optimization and establishment of proof of therapeutic concepts for DMD, DM1 and SMA. For DM1 and SMA in vivo evaluation, the best teams in France have been selected. Denis Furling is the director of the center for research in myology and the head of the team leading research on DM1 in France. Pr. Frederic Charbonnier is the head of the main research team working on the SMA mouse model in France and partner of the RHU SMART.