Pathway IV ™ Gene Delivery

Executive Summary

Pathway IV ™ gene delivery is a novel, clinically practical procedure based upon intravenous (“IV”) delivery of plasmid DNA (“pDNA”) to targeted limb muscle. Once resident in muscle cells, the introduced DNA produces therapeutic proteins that can be active locally or secreted systemically. If the DNA encodes an antigenic protein, either antibody or cellular immune responses may be induced. A single dose can result in long-term gene expression, and the ease of repeat administration makes this platform technology ideal for treating chronic illnesses. This versatile platform has potential utility to treat a wide range of diseases, including muscular dystrophy, peripheral vascular ischemia, arthritis, anemia, multiple sclerosis, and cancer. [view brochure]

The Need: Delivery of Therapeutic Genes

One of the greatest challenges in the field of gene therapy to date has been the inability to efficiently deliver candidate therapeutic genes to target tissues. Direct injection of plasmid DNA into muscle and other tissues showed early promise in animal research models, but comparable success in human clinical studies has proved elusive. Formulation of pDNA with lipids and other compounds was attempted to increase delivery efficiency and cellular uptake with moderate success. More recently, precipitation of pDNA onto gold carrier particles has shown great promise for genetic vaccination, but this approach is generally limited to epidermal (skin) delivery where the DNA can be expressed for only a short timeframe.

The Solution: Pathway IV ™ Gene Delivery

Mirus researchers and collaborators at the University of Wisconsin – Madison discovered a simple, elegant method to overcome the delivery hurdle. As shown in the adjoining graphic, it relies upon elevating intravascular pressure to physically increase the permeability of the cellular walls of the blood vessel. When nucleic acids are injected intravascularly under normal physiological conditions, they are retained within the blood stream because these macromolecules are too large to be transported through the cell walls. Furthermore, they are quickly degraded by the nucleases in the blood stream. By transiently restricting blood flow and elevating the pressure, the DNA can pass through the blood vessel wall into adjoining muscle cells before this occurs.

In clinical practice this translates into a simple, practical procedure. With blood flow in an arm or leg temporarily occluded by a tourniquet, a pDNA solution is rapidly injected intravenously. This elevates the pressure within the occlusion zone, making the blood vessel wall more permeable and allowing the pDNA to migrate into the adjoining muscle cells. Blood flow is then restored to normal within a few minutes, with no adverse affects to the vasculature.

Preclinical work is ongoing to determine optimum dose levels, dosing frequency, plasmid construction, etc. for use in human clinical studies, the first of which are anticipated in 2008. Data from primate models suggest that a single dose is highly efficient at transfecting nearly all muscle groups within the treatment zone, with selected muscles showing DNA being taken up by up to 50% of the cells¹. The ability to target large numbers of cells within multiple muscle groups enables unprecedented levels of expression. Moreover, repeat dosing has been shown to be feasible and effective at boosting and prolonging gene expression, both of which are key to clinical utility for chronic diseases.

Applications

The therapeutic goal of nucleic acid delivery can be directed towards one of several desirable outcomes. For certain diseases, the goal is to deliver genes that encode a therapeutic protein to be retained within the target cells. Such is the case with muscular dystrophy, where intracellular expression of dystrophin has been shown to preserve muscle function. For other diseases, the goal is to encode a therapeutic protein in the host muscle cells for secretion into the bloodstream to elicit a systemic or body-wide effect – such is the case with erythropoietin, a treatment for anemia. A third approach is to deliver genes encoding an antigen, expression of which induces a therapeutically beneficial antibody or cellular immune response. For example, cancer researchers are actively investigating delivery of tumor antigens as a means to induce a therapeutic response against cancerous cells. Lastly, one could deliver other nucleic acids to muscle such as synthetic siRNA oligonucleotides or vectors that express siRNAs. Unlike gene delivery, the goal of which is to enhance gene expression, these sequences modulate a natural cellular process called RNA interference that leads to suppression of gene activity. This approach could be used to modulate inflammation or cellular responses that are the hallmark of diseases like arthritis.

The Pathway IV ™ Technology is an exciting new approach for nucleic acid delivery which has potential applicability for a wide range of uses. Mirus is actively exploring this potential, as well as investigating protocol modifications that would enable delivery to additional tissues such as joints and bone. [view brochure]

¹ Hagstrom J, et al. A Facile Non-Viral Method for Delivering Genes and siRNAs to Skeletal Muscle of Mammalian Limbs. Molecular Therapy, Vol. 10:2, 386-398; August 2004.