Pulmonary gene delivery using polymeric nonviral vectors

Novel polyethylenimine-derived nanoparticles for in vivo gene delivery

INTRODUCTION

Branched and linear polyethylenimines (PEIs) are cationic polymers that have been used to deliver nucleic acids both in vitro and in vivo. Owing to the high cationic charge, the branched polymers exhibit high transfection efficiency, and particularly PEI of molecular weight 25 kDa is considered as a gold standard in gene delivery. These polymers have been extensively studied and modified with different ligands so as to achieve the targeted delivery.

AREAS COVERED

The application of PEI in vivo promises to take the polymer-based vector to the next level wherein it can undergo clinical trials and subsequently could be used for delivery of therapeutics in humans. This review focuses on the various recent developments that have been made in the field of PEI-based delivery vectors for delivery of therapeutics in vivo.

EXPERT OPINION

The efficacy of PEI-based delivery vectors in vivo is significantly high and animal studies demonstrate that such systems have a potential in humans. However, we feel that though PEI is a promising vector, further studies involving PEI in animal models are needed so as to get a detailed toxicity profile of these vectors. Also, it is imperative that the vector reaches the specific organ causing little or no undesirable effects to other organs.

Manipulation of Cell Physiology Enables Gene Silencing in Well-differentiated Airway Epithelia

The application of RNA interference-based gene silencing to the airway surface epithelium holds great promise to manipulate host and pathogen gene expression for therapeutic purposes. However, well-differentiated airway epithelia display significant barriers to double-stranded small-interfering RNA (siRNA) delivery despite testing varied classes of nonviral reagents. In well-differentiated primary pig airway epithelia (PAE) or human airway epithelia (HAE) grown at the air–liquid interface (ALI), the delivery of a Dicer-substrate small-interfering RNA (DsiRNA) duplex against hypoxanthine–guanine phosphoribosyltransferase (HPRT) with several nonviral reagents showed minimal uptake and no knockdown of the target. In contrast, poorly differentiated cells (2–5-day post-seeding) exhibited significant oligonucleotide internalization and target knockdown. This finding suggested that during differentiation, the barrier properties of the epithelium are modified to an extent that impedes oligonucleotide uptake. We used two methods to overcome this inefficiency. First, we tested the impact of epidermal growth factor (EGF), a known enhancer of macropinocytosis. Treatment of the cells with EGF improved oligonucleotide uptake resulting in significant but modest levels of target knockdown. Secondly, we used the connectivity map (Cmap) database to correlate gene expression changes during small molecule treatments on various cells types with genes that change upon mucociliary differentiation. Several different drug classes were identified from this correlative assessment. Well-differentiated epithelia treated with DsiRNAs and LY294002, a PI3K inhibitor, significantly improved gene silencing and concomitantly reduced target protein levels. These novel findings reveal that well-differentiated airway epithelia, normally resistant to siRNA delivery, can be pretreated with small molecules to improve uptake of synthetic oligonucleotide and RNA interference (RNAi) responses.