Polymer-mediated gene therapy: Recent advances and merging of delivery techniques

Abstract

The ability to safely and precisely deliver genetic materials to target sites in complex biological environments is vital to the success of gene therapy. Numerous viral and nonviral vectors have been developed and evaluated for their safety and efficacy. This study will feature progress in synthetic polymers as nonviral vectors, which benefit from their chemical versatility, biocompatibility, and ability to carry both therapeutic cargo and targeting moieties. The combination of synthetic gene carrying constructs with advanced delivery techniques promises new therapeutic options for treating and curing genetic disorders. This article is characterized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

FIGURE 1

Summary of gene delivery approaches (viral, physical, and chemical): (a) chemical systems involve cationic lipids or polymers which complex negatively charged nucleic acids; (b) biological systems utilize deactivated viral vectors; and (c) physical methods, such as electroporation and sonoporation, create temporary pores in the cell membrane using electronic pulses or ultrasound

FIGURE 2

Schematic diagram of gene delivery using polyplexes, with steps including cell entry, lysosomal escape, and nuclear entry

FIGURE 3

Branched PEI, poly(amidoamine) dendrimers, and comb polymers represent examples of polymer vectors with tunable nucleic acid binding and targeting capacity. Upper-left: chemical structures of linear polyethyleneimine (PEI) and poly-l-lysine, two widely used polymers in gene delivery research

FIGURE 4

Chemical structures of (a) trehalose-triazole “click” polymer (Srinivasachari, Liu, Zhang, Prevette, & Reineke, 2006) and (b) poly(glycoamidoamine) (Jiang, Lodge, & Reineke, 2018)

FIGURE 5

Cryo-TEM images of self-assembled micelleplexes with different poly(ethylene glycol) corona length (Jiang, Lodge, et al., 2018)

FIGURE 6

Examples of cationic conjugated polymers used for gene transfection: (a) polyfluorene (Yu, Liu, & Wang, 2008); (b) poly(phenylene ethynylene) (Jiang et al., 2013); and (c) poly(phenylene vinylene) (Li et al., 2016); Fluorescence microscopy shows colocalization of PPV/Cy5-labeled siRNA polyplex (red/green) with endosomes (blue; Lysotracker). Transfection efficiency of the PPV/Cy5-labeled siRNA polyplex, measured by fluorescence-activated cell sorting (FACS), exceeded that of PEI and Lipofectamine (Li et al., 2016)

FIGURE 7

Targeted gene delivery modalities. (a) Shielding with PEG or Tf can enhance targeting specificity of polyplexes. Surface shielding of polyplexes reduces nonspecific interactions (a1), while nonshielded polyplexes induce aggregation of erythrocytes (a2), suggesting increased nonspecific interactions. Nontreated control erythrocytes are shown in (a3) (Kircheis, Wightman, Kursa, Ostermann, & Wagner, 2002). (b) Synthesis of the PEI-PEG-TAT system for delivery of plasmid DNA (pDNA) encoding TRAIL as well as the drug DOX (Jiang et al., 2017). (c) Codelivery of the drug DOX and TRAIL-encoding plasmid DNA via redox sensitive Tf-targeted micelles, and hypothesized route following intravenous injection of drug/pDNA-loaded micelles in a syngeneic tumor model (Feng et al., 2018)

FIGURE 8

In vivo and ex vivo imaging of polyplex biodistribution. (a) in vivo time-dependent near infrared (NIR) imaging following injection with RPM-conjugated (IR820-bPEI-PEG-RPM) or nontargeted (IR820-SS-bPEI-PEG) polyplexes. (b) ex vivo images of organs collected 4 hr following intravenous injection with RPM-conjugated or nontargeted polyplexes. (c) in vivo imaging of HT-29 (RPM-positive cells, left) and HCT-116 (RPM-negative cells, right) in dual tumor bearing mice following injection with RPM-conjugated polyplexes (Lee et al., 2015)

FIGURE 9

(a) Structures of NLS and rNLS-comb polymers. (b) in vitro transfection performance of polyplexes in SKOV3 cells. (c) in vivo intramuscular gene delivery (with or without ultrasound mediation) in mice by NLS- and rNLS-based polyplexes (Parelkar et al., 2014)

FIGURE 10

In vivo and ex vivo imaging of tumor-bearing mice treated with nonconjugated (NC) or EGF-conjugated dendriplexes (EGF). (a) Upper panel: localization of EGFR-targeted and untargeted dendrimers via near infrared (NIR) fluorescence at 2 hr posttreatment. Lower panel: luminescence imaging of the localization of breast cancer tumor cells labeled with luciferase (MDA-MB-231-Luc), implanted subcutaneously, and following administration of 150 mg/kg D-luciferin. (b) Overlay of X-ray and ex vivo NIR fluorescence images of tumors treated with NC or EGF-conjugated dendriplexes. (c) Mean ± SD ex vivo fluorescence intensity of tumors 2 hr posttreatment with NC or EGF-conjugated dendriplexes (J. Li et al., 2016)

FIGURE 11

Targeted gene therapy in a PC3 tumor xenograft mouse model. (a) Tumor growth studies following intravenous injection with DAB-Lf dendriplex encoding TNF-α (■, green), TRAIL (●, red), IL-12 (▲, blue), all at 50 mg pDNA/injection. DAB-Lf (▼, brown), naked pTNFα (■, pale green), naked pTRAIL (●, orange), naked pIL-27 (▲, cyan), and nontreated tumors (●, black). (b) Relative mouse weight throughout the study. (c) Overall tumor response to treatment evaluated according to the Response Evaluation Criteria in Solid Tumors (RECIST). Red, progressive response; orange, stable response; yellow, partial response; green, complete response. (d) Time to disease progression. Y-axis indicates the percent of surviving animals. Animals were removed from the study when the tumor reaches 10 mm in diameter. Color coding in b and d are similar to a (Al Robaian et al., 2014)