Synthetic-polymer-assisted antisense oligonucleotide delivery: targeted approaches for precision disease treatment

Abstract

This review explores the recent advancements in polymer-assisted delivery systems for antisense oligonucleotides (ASOs) and their potential in precision disease treatment. Synthetic polymers have shown significant promise in enhancing the delivery, stability, and therapeutic efficacy of ASOs by addressing key challenges such as cellular uptake, endosomal escape, and reducing cytotoxicity. The review highlights key studies from the past decade demonstrating how these polymers improve gene silencing efficiencies, particularly in cancer and neurodegenerative disease models. Despite the progress achieved, barriers such as immunogenicity, delivery limitations, and scalability still need to be overcome for broader clinical application. Emerging strategies, including stimuli-responsive polymers and advanced nanoparticle systems, offer potential solutions to these challenges. The review underscores the transformative potential of polymer-enhanced ASO delivery in personalised medicine, emphasising the importance of continued innovation to optimise ASO-based therapeutics for more precise and effective disease treatments.

Keywords: antisense oligonucleotides; enhanced delivery; gene transfection; intracellular uptake; locked nucleic acid (LNA); nanoparticles; peptide nucleic acid (PNA); personalised therapy; phosphorodiamidate morpholino oligomer (PMO); phosphorothioate (PS); polyplexes; ribose substitutions; small interfering RNA (siRNA); synthetic polymers; tricyclo-DNA (tcDNA).

Figure 1

Common chemical modifications used in antisense oligonucleotides (ASOs). First-generation ASOs involve modifications in the natural phosphodiester linkage found in native oligonucleotides (ODNs). Second-generation ASOs introduce changes at the 2′-O-position of the ribose sugar and are commonly designed as gapmer ASOs. Third-generation ASOs encompass more advance chemistries, including locked nucleic acids (LNAs), phosphorodiamidate morpholino oligomers (PMOs), peptide nucleic acids (PNAs), tricyclo-DNA oligomers (tcDNA), and nucleotides with synthetic bases.

Figure 2

Mechanisms of action of ASOs. (A) RNase H-recruiting ASOs through formation of ASO–mRNA hybrids that can be recognised by RNase H. (B) Splice switching ASOs (ssASOs) modulate splicing processes by targeting pre-mRNA.

Figure 3

Schematic representation of poly(ʟ-lysine) (PLL). (a) Chemical structure of lysine monomers. (b) (i) Linear, (ii) dendritic, and (iii) hyper-branched architectures of PLL, and (iv) configuration of PLL.

Figure 4

Illustration of the delivery of ASO-loaded glucosylated-polyion complex micelles (Glu-PIC/Ms) to the brain. This figure was reproduced from [71] (© 2020 Hyun Su Min et al. Published by Wiley-VCH Verlag GmbH & Co. KGaA, distributed under the terms of the Creative Commons Attribution-Noncommercial 4.0 International License, https://creativecommons.org/licenses/by-nc/4.0/). This content is not subject to CC BY 4.0.

Figure 5

Structure of the cationic amino acids, ʟ-ornithine, ʟ-arginine, and ʟ-lysine.

Figure 6

(A) Chemical structure of PEGylated poly(ʟ-arginine)–chitosan derivatives (PEG-CS-PLR) polymers. (B) Expression of targeted RFP protein in siRNA-treated tumours and untreated tumours. (C) Molecular imaging of tumour-bearing mice after siRNA treatment with PEG-CS-PLR. Figure 6 was adapted from [95], Journal of Controlled Release, Volume 145, Issue 2, Noh, S. M.; Park, M. O.; Shim, G.; Han, S. E.; Lee, H. Y.; Huh, J. H.; Kim, M. S.; Choi, J. J.; Kim, K.; Kwon, I. C.; Kim, J.-S.; Baek, K.-H.; Oh, Y.-K., “Pegylated poly-ʟ-arginine derivatives of chitosan for effective delivery of siRNA”, Pages 159–164, Copyright (2010), with permission from Elsevier. This content is not subject to CC BY 4.0.

Figure 7

Polyamines frequently employed in ASO delivery systems include linear and branched poly(ethylene imine) (PEI and b-PEI respectively), poly(propylene imine) (PPI), poly(amidoamine) (PAMAM), and poly(vinyl amine) (PVAm); along with a representation of different particle types often used to deliver antisense and siRNA oligonucleotides.

Figure 8

Impact of unsaturated fatty acids on cellular membrane interactions. (A) Confocal microscopy images of HeLa pLuc/705 cells treated with 0.45 mg·mL⁻¹ calcein and PMO-LP SteA (control) or PMO-LP LenA at a concentration of 5 × 10⁻⁶ M for 4 h. (B) Cellular calcein fluorescence intensity determined by flow cytometry. (C) Haemoglobin levels after 60 min of incubation with PMO conjugates (2.5 × 10⁻⁶ M) at pH 7.4, 6.5, and 5.5. Figure 8 was reproduced from [127] (© 2019 Jasmin Kuhn et al. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, distributed under the terms of the Creative Commons Attribution 4.0 International License, https://creativecommons.org/licenses/by/4.0/).

Figure 9

Stability of dendriplexes composed of GEM91 and (A) PPI G4, (B) PPI-Mal G4, and (C) PPI-Mal-III G4. This figure was reprinted from [135], Biochemical and Biophysical Research Communications, Volume 427, Issue 1, J. Drzewińska; D. Appelhans; B. Voit; M. Bryszewska; B. Klajnert, “Poly(propylene imine) dendrimers modified with maltose or maltotriose protect phosphorothioate oligodeoxynucleotides against nuclease activity”, Pages 197–201, Copyright (2012), with permission from Elsevier. This content is not subject to CC BY 4.0.

Figure 10

(A) Depiction of the cationic homopolymer D. (B) Depiction of the polymers for traditional micelles and a scheme to show the binding with ASOs and the effect of acidification. (C) Depiction of the polymers for pH-responsive micelles and a depiction of binding with ASOs and the effect of acidification. Figure 10 was adapted with permission from [175], Copyright 2023 American Chemical Society. This content is not subject to CC BY 4.0.

Figure 11

pH-responsive PEGylated systems for antisense oligonucleotide delivery. Figure 11 was reprinted with permission from [222], Copyright 2012 American Chemical Society. This content is not subject to CC BY 4.0.