Ionic liquids: prospects for nucleic acid handling and delivery

Abstract

Operations with nucleic acids are among the main means of studying the mechanisms of gene function and developing novel methods of molecular medicine and gene therapy. These endeavours usually imply the necessity of nucleic acid storage and delivery into eukaryotic cells. In spite of diversity of the existing dedicated techniques, all of them have their limitations. Thus, a recent notion of using ionic liquids in manipulations of nucleic acids has been attracting significant attention lately. Due to their unique physicochemical properties, in particular, their micro-structuring impact and tunability, ionic liquids are currently applied as solvents and stabilizing media in chemical synthesis, electrochemistry, biotechnology, and other areas. Here, we review the current knowledge on interactions between nucleic acids and ionic liquids and discuss potential advantages of applying the latter in delivery of the former into eukaryotic cells.

Figure 1.

Examples of ILs, in particular, those used in studies on nucleic acids.

Figure 2.

Structural peculiarities and levels of organization found in ILs. A covalently bonded skeleton (A) is combined with easily replaceable side chains (B) and the ability to form Coulomb (C), stacking and van der Waals (D) interactions, as well as hydrogen bonds (E). Taken together, all these features provide ILs with their structuring impact (F) and capability to assemble into various nano- (G) and micro-scale patterns (H).

Figure 3.

Overview of common approaches to delivering genes into eukaryotic cells: physical methods (microinjection, hydroporation, particle bombardment, magnetofection, electroporation, photoporation, sonoporation), non-viral delivery systems (calcium phosphate, nanoparticles, liposomes, polymers, cell-penetrating peptides, self-delivering oligonucleotides), and virus-based delivery systems. Systems, in which IL application has been tested, are marked by a green star, whereas those in which IL potential can be realized are marked by an orange star.

Figure 4.

Stages of cationic-assisted gene delivery. (A) Cationic polymer is released from polyplexes and intercalates into the plasma membrane. (B) Cationic polymer is dispersed into internal cellular membranes via lipid recycling pathways, whereas polyplexes are endocytosed. (C) Cationic polymer in the endosomal membranes increases the membrane permeability and facilitates the release of genetic material into the cytosol. (D) Cationic polymer associated with the nuclear membrane via lipid recycling and/or cytosolic pathways enhances the membrane permeabilization, promotes the release of the genetic material through the leaky membrane or pores, and facilitates its transport into the nucleus. Adapted and reproduced with permission from (2).

Figure 5.

Production of recombinant AAV (rAAV). (A) The wild-type AAV genome is modified by replacing the viral genes rep and cap with a transgene expression cassette containing the transgene sequence, promoter and regulatory elements, which is inserted between the inverted terminal repeats (ITR). (B) This rAAV, together with helper plasmids and/or wild-type adenovirus, are introduced into permissive cells (usually HEK 293) that subsequently produce rAVV particles. Reproduced with permission from (181).

Figure 6.

Structures of ILs and IL-like compounds used in gene delivery. (A) Chloride and bromide derivatives of 1-methyl-3-[3,4-bis(alkoxy)benzyl]-4H-imidazolium (182). (B) 1-(2-Hydroxyethyl)alkylimidazolium (183) and (C) 1-alkyl-3-methylimidazolium (184) bromides (n = 14, 16, 18). (D) 1,3-dimethyl-4,5-dipentadecyl-2-(5-(trimethylammonio)pentyl)imidazolium iodide (185). (E) 1,5-Bis(1-imidazolilo-3-decyloxymethyl)pentane chloride (186). (F) Pyridinium amphiphiles (*, 85% cis-orientation; **, trans-orientation; ***, cis-orientation) (187). (G) IL-robed siRNA (188). (H) Hydroxyl-carrying (189) and (I) folic acid-conjugated (190) imidazolium copolymers. (J) Imidazolium-containing copolyesters (191). (K) Poly[3-butyl-1-vinylimidazolium L-proline] (192). (L) PEI and PMAS polymers functionalized by bis(dialkylamino)cyclopropenium chloride ILs (193). (M) Ammonium- and phosphonium-carrying styrenic homopolymers (194). (N) Ammonium block copolymers (195).

Figure 7.

Prospective fields of IL application in nucleic acid handling and delivery.