Systemic delivery of therapeutic nucleic acids into skeletal muscle by means of lipid-based vectors

Introduction : Lipid-based vectors are considered a promising tool when a systemic delivery is desirable. Although not as efficient as viral vectors, lipoplexes present some major advantages, as they are non immunogenic, non mutagenic, as well as easy and cheap to prepare. We had previously shown that skeletal muscles are poorly accessible to lipoplexes via intra-venous administration, whereas local intra-arterial delivery yielded good preliminary results. Objectives : Optimization of a lipid-based, systemic gene delivery system capable of introducing therapeutic nucleic acids into skeletal muscle. Methods : We use lipid-based vehicles containing the cationic lipid DODAC, formulated either as conventional or encapsulated PEG-ylated lipoplexes. Results : We injected lipoplexes in the femoral artery of adult rats in which muscle regeneration was chemically induced in the TA muscles. Using an encapsulated formulation (SPLP, developed by Protiva Bioteherapeutics) we obtained up to 10% of GFP+ve fibers after a single injection. High transfection levels were maintained for at least three weeks. At the same time, we showed that SPLPs only induced a slight delay in the process of muscle regeneration and did not lead to any germ-line transmission of the transgene. More recently we began to apply our delivery protocol to the development of an exon-skipping approach for the correction of mutations in the dystrophin gene. In particular, we are using DODACbased lipoplexes to deliver an exon 23-specific morpholino AO into the muscles of mdx mice. Our initial data showed the production of a significant amount (i.e., as abundant as the wild type or higher) of the desired skipped mRNA in the leg muscle groups of the injected limbs. The effect of the treatment on dystrophin production is presently being assessed. Conclusions : Our data indicate that both encapsulated and conventional lipoplexes have the potential to be used for the development of therapeutic protocols for muscle diseases.