Nanoparticulate System for Efficient Gene Transfer into Refractory Cell Targets

Hox transcription factor regulation of adult bone-marrow-derived cell behaviour during tissue repair and regeneration

INTRODUCTION

Bone marrow offers a valuable source of stem/progenitor cells that contribute to the repair of injured tissues. Failure in the function of these cells results in delayed or reduced tissue repair. Identification of factors that can correct these defects is critical to treating the underlying dysfunction. Notably, homeobox (Hox) transcription factors have been identified as having significant effects on BMDC behaviour, including differentiation, migration and adhesion in injured tissue, and may provide a basis for future therapies.

AREAS COVERED

Hox protein regulation of bone-marrow-derived cell (BMDC) differentiation, factors that influence BMDC behaviour in response to injury, the effects of the diabetic environment on BMDCs, methods that can be used to reprogramme BMDCs, and the use of Hox transcription factors to correct BMDC behaviour.

EXPERT OPINION

Hox gene therapy has been successfully employed to change cell behaviour using ex vivo 'reprogramming' strategies overexpressing selected Hox genes in BMDCs to direct the fate of these cells to the desired cell type, promoting tissue repair.

Polymers for viral gene delivery

BACKGROUND

The development of viral vectors capable of providing efficient gene transfer in diseased tissues without causing any pathogenic effects is pivotal for overcoming the many challenges facing gene therapy.

OBJECTIVE

Immune responses against viral vectors, inadequate gene expression and inefficient targeting to specific cells in vivo are some of the major problems limiting the clinical utility of viral gene therapy.

METHODS

This review will focus on recent progress in strategic polymer-based modifications to improve the performance and biocompatibility of a variety of viral vectors. We will discuss the preclinical development of four approaches involving injectable polymers, polyelectrolytes, polymer microspheres and polymer-virus conjugates.

RESULTS/CONCLUSION

Much progress has been made in creating 'hybrid' gene delivery vectors that combine the strengths of polymers and viruses. With further optimization, these hybrid vectors, which may be safer and more effective, are likely to succeed in clinical applications.

Nanovehicular intracellular delivery systems

This article provides an overview of principles and barriers relevant to intracellular drug and gene transport, accumulation and retention (collectively called as drug delivery) by means of nanovehicles (NV). The aim is to deliver a cargo to a particular intracellular site, if possible, to exert a local action. Some of the principles discussed in this article apply to noncolloidal drugs that are not permeable to the plasma membrane or to the blood-brain barrier. NV are defined as a wide range of nanosized particles leading to colloidal objects which are capable of entering cells and tissues and delivering a cargo intracelullarly. Different localization and targeting means are discussed. Limited discussion on pharmacokinetics and pharmacodynamics is also presented. NVs are contrasted to micro-delivery and current nanotechnologies which are already in commercial use. Newer developments in NV technologies are outlined and future applications are stressed. We also briefly review the existing modeling tools and approaches to quantitatively describe the behavior of targeted NV within the vascular and tumor compartments, an area of particular importance. While we list "elementary" phenomena related to different level of complexity of delivery to cancer, we also stress importance of multi-scale modeling and bottom-up systems biology approach.

Kinetic analysis of nanoparticulate polyelectrolyte complex interactions with endothelial cells

A non-toxic, nanoparticulate polyelectrolyte complex (PEC) drug delivery system was formulated to maintain suitable physicochemical properties at physiological pH. Toxicity, binding, and internalization were evaluated in relevant microvascular endothelial cells. PEC were non-toxic, as indicated by cell proliferation studies and propidium iodide staining. Inhibitor studies revealed that PEC were bound, in part, via heparan sulfate proteoglycans and internalized through macropinocytosis. A novel, flow cytometric, Scatchard protocol was established and showed that PEC, in the absence of surface modification, bind cells non-specifically with positive cooperativity, as seen by graphical transformations.

Gene therapy and wound healing

Wound repair involves the sequential interaction of various cell types, extracellular matrix molecules, and soluble mediators. During the past 10 years, much new information on signals controlling wound cell behavior has emerged. This knowledge has led to a number of novel therapeutic strategies. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trails indicates that a crucial aspect of the growth factor wound healing strategy is the effective delivery of these polypeptides to the wound site. A molecular approach in which genetically modified cells synthesize and deliver the desired growth factor in regulated fashion has been used to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. We have summarized the molecular and cellular basis of repair mechanisms and their failure, and we give an overview of techniques and studies applied to gene transfer in tissue repair.

Development of Improved Nanoparticulate Polyelectrolyte Complex Physicochemistry by Nonstoichiometric Mixing of Polyions with Similar Molecular Weights

Water-based, biodegradable polyelectrolyte complex dispersions (PECs) prepared by mixing oppositely charged polyions are advantageous drug delivery systems due to constituent biocompatibility and nanoparticulate architectures. Reaction phase environmental parameters dictate PEC physicochemical properties, and specifically, complexation between polyelectrolytes having significantly different molecular weights leads to formation of water-insoluble aggregates. Starting with this fact, four-component similar and dissimilar molecular weight PEC chemistries were applied and compared with and without frequency-induced dispergation. The goal was to define nanoparticulate PEC systems with desirable characteristics for use in biological systems. Results show PEC formulations from precursors with similar low molecular weights yielded dispersions with suitable physicochemical characteristics, as verified by photon correlation spectroscopy and TEM, presumably due to efficient ion pairing. Similar low molecular weight PECs fabricated with dispergation exhibited pH-independent stability, as validated by charge and size measurements. These physicochemical advantages lead to an ideal delivery platform.

Proteolytic surface functionalization enhances in vitro magnetic nanoparticle mobility through extracellular matrix

Steric barriers such as collagen I sharply limit interstitial delivery of macromolecular and nanoparticle (NP) based therapeutic agents. Collagenase-linked superparamagnetic NPs overcame these barriers and moved through in vitro extracellular matrix (ECM) at 90 microm h(-1), a rate similar to invasive cells, under the influence of a magnetic field. NP migration in ECM diminished linearly over 5 days. The collagenase-NP construct overcame two of the most significant barriers to nano- and microscale therapeutics deployment: proteolytic enzyme stability was maintained during a clinically useful time frame by immobilization on the NP surface and degradation of interstitial barriers to tissue biodistribution was enabled by the conjugated microbial protease.