Peptide-addressed liposome -embedded therapeutic systems: PALETS delivering tools to alter protein expression and limit pathologic protein misfolding

Introduction: No known therapeutics improve quality of life or survival times of humans afflicted with neurodegenerative, protein misfolding diseases (NPMDs) like Alzheimer's, Parkinson's and prion diseases.  We and others developed new therapies for NPMDs  using RNA interference, a pathway that decreases levels of mRNA encoding proteins that misfold to cause NPMDs. Objectives: We developed a non-invasive therapeutic delivery system consisting of liposomes complexed with a peptide that delivers the nanoparticles across the blood-brain barrier to Acetylcholine-expressing cells. These peptide-addressed, liposome-embedded therapeutic systems (PALETS) deliver therapeutic cargo to the central nervous system. Methods: We assessed Prp siRNA PALET pharmacokinetics and pharmacodynamics by live animal imaging and flow cytometry.   We treated infected mice intravenously and/or intranasally with siRNA PALETS 3-9X and assessed for clinical prion disease by survival time, biochemistry, neuropathology and associated behavioral deficits. We assessed immune responses to PALETS by IgG ELISA. Results: PALETS efficiently deliver PrP siRNA to 47% of brain cells, decrease PrP expression 70% and extends survival and improve behavior of prion-infected mice. However, repeated immunization elicited a strong IgG antibody response to the delivery peptide. Conclusions: PrP siRNA PALETS extend survival time up to 22% in mice that remain immunotolerant to treatment.  PALETS hold promise as efficient delivery systems that can be sized to carry therapeutic cargo of interest, such as Cas9 and derivatives, without requiring truncated or spliced versions that greatly reduce efficiency, like adeno-associated viral vectors, for example. PALETS offer a flexible, non-viral therapeutic delivery system for a single dose somatic cell genome editing approach for treating monogenic NPMDs.