The potential of toxin-based drug delivery systems for enhanced nucleic acid therapeutic delivery

Abstract

Abstract.Introduction: The potential of gene replacement therapy has been underscored by the market authorisation of alipogene tiparvovec (Glybera) and GSK2696273 (Strimvelis) in the EU and recombinant adenovirus-p53 (Gendicine) in China. Common to these systems is the use of attenuated viruses for "drug" delivery. Whilst viral delivery systems are being developed for siRNA, their application to antisense delivery remains problematic. Non-viral delivery remains experimental, with some notable successes. However, stability and the "PEG dilemma", balancing toxicity and limited (often liver-tropic) PK-PD, with the membrane destabilising activity, necessary for nucleocytosolic access and transfection remain a problem. Areas Covered:Here we review the use of attenuated protein toxins as a delivery vehicle for nucleic acids, their relationship to the PEG-dilemma, and their biological properties with specific reference to their intracellular trafficking. Expert opinion:The possibility of using attenuated toxins as antisense and siRNA delivery systems has been demonstrated in vitro. Systems based upon attenuated anthrax toxin have been shown to have high activity (equivalent to nucleofection) and low toxicity whilst not requiring cationic "helpers" or condensing agents, divorcing these systems from the problems associated with the PEG dilemma. It remains to be seen whether these systems can operate safely, efficiently and reproducibly, in vivo or in the clinic. Key words.Antisense, Drug Delivery, Endocytosis, Gene Therapy, siRNA, Toxin. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 This paper covers:1) The deferential between the challenges associated with gene and siRNA / antisense delivery.2) Why this differential is important within the context of existing rate limits to nonviral therapy i.e. the PEG dilemma.3) The use of protein toxins as part of non-viral DNA delivery systems. 4) How toxins navigate the endomembrane system. 5) Recent successes using toxins to deliver siRNA and antisense oligonucleotides.

Polymers in the Delivery of siRNA for the Treatment of Virus Infections

“…Typically, siRNA therapeutics cross the cell membrane via the endocytic pathway and thus must escape the endosome before they can interact with the RISC complex in the cytoplasm. An effective delivery of siRNA must therefore be able to efficiently disrupt the endosome in order to deliver the siRNA to the cytoplasm prior to being transported to and degraded in a lysosome [82].…”

The Delivery of Personalised, Precision MedicinesviaSynthetic Proteins

“…In addition to the aforementioned limitations, target compartment accessibility is also a significant challenge. However, drugs based upon a molecule or supramolecular assembly that have evolved to reach normally inaccessible target compartments prove to be the exception [4]. This is pertinent to drug delivery as "third order", or organelle-specific targeting remains a significant challenge, which is exemplified by the problems associated with the delivery of nucleic acid based drugs [4].…”

“…However, drugs based upon a molecule or supramolecular assembly that have evolved to reach normally inaccessible target compartments prove to be the exception [4]. This is pertinent to drug delivery as "third order", or organelle-specific targeting remains a significant challenge, which is exemplified by the problems associated with the delivery of nucleic acid based drugs [4]. Although *Address correspondence to Dr Simon Richardson, Faculty of Engineering and Science, University of Greenwich, Central Avenue, Chatham, Kent, ME4 4TB UK.…”

“…Although *Address correspondence to Dr Simon Richardson, Faculty of Engineering and Science, University of Greenwich, Central Avenue, Chatham, Kent, ME4 4TB UK. Tel +44-208-331-8207; E-mails: rs73@Greenwich.ac.uk there are numerous studies highlighting the compartmentalisation of cells as a barrier to third order targeting [4], perhaps the most compelling evidence is the everyday use of a variety of transfection systems in research laboratories across the world.…”

“…As many of these targets reside within the nucleocytosolic compartment, a way into this compartment for non-membrane permeant molecules is critical. This is especially true for drugs based on nucleic acids which, by default, have no direct way of accessing the nucleocytosolic compartment [4]. Consequently, to be active, nucleic acid "gene" drugs need to cross several barriers that have evolved to limit both genomic plasticity as well as the expression of exogenous material.…”