Influence of RNA Strand Rigidity on Polyion Complex Formation with Block Catiomers

Abstract

Polyion complexes (b-PICs) are prepared by mixing single- or double-stranded oligo RNA (aniomer) with poly(ethylene glycol)-b-poly(L-lysine) (PEG-PLL) (block catiomer) to clarify the effect of aniomer chain rigidity on association behaviors at varying concentrations. Here, a 21-mer single-stranded RNA (ssRNA) (persistence length: 1.0 nm) and a 21-mer double-stranded RNA (small interfering RNA, siRNA) (persistence length: 62 nm) are compared. Both oligo RNAs form a minimal charge-neutralized ionomer pair with a single PEG-PLL chain, termed unit b-PIC (uPIC), at low concentrations (<≈ 0.01 mg mL(-1)). Above the critical association concentration (≈ 0.01 mg mL(-1)), ssRNA b-PICs form secondary associates, PIC micelles, with sizes up to 30-70 nm, while no such multimolecular assembly is observed for siRNA b-PICs. The entropy gain associated with the formation of a segregated PIC phase in the multimolecular PIC micelles may not be large enough for rigid siRNA strands to compensate with appreciably high steric repulsion derived from PEG chains. Chain rigidity appears to be a critical parameter in polyion complex association.

Smart polymeric nanocarriers for small nucleic acid delivery

“…Above a critical association concentration (CAC), uPICs undergo secondary assembly into micellar PICs (mPICs). This two-step self-assembly is clearly demonstrated when single-strand RNA (ssRNA) (21-mer) is combined with PEG-poly(Llysine) (PEG-PLys) (MW of PEG (MW PEG ): 12,000, degree of polymerization of PLys (DP PLys ): ~40) ( Figure 4B) (20). At lower concentrations (< 0.01 mg/mL), the formation of small PICs with a hydrodynamic diameter (D H ) of ~10 nm is clearly observed, corresponding to the primary assembly step, i.e., uPICs.…”

“…The D H of oligonucleotideloaded mPICs prepared from PEG-PLys is reported to range from 40 to 80 nm with a narrow size-distribution (polydispersity index in dynamic light scattering, µ2/ Γ 2 < 0.1) (21,22). The smaller mPICs were constructed using PEG-PLys with shorter PLys segments, e.g., DP PLys = ~20 and ~40, whereas PEG-PLys with a longer PLys segment (DP PLys = ~80) generated the larger mPICs (20,22). Thus, the smaller mPICs are potentially highly efficient for permeation within solid tumor tissues, in contrast with lipid nanoparticles with a D H of ~90 nm (23).…”

Polyion complex micelle formation from double-hydrophilic block copolymers composed of charged and non-charged segments in aqueous media

“…35 Either 21-mer single-strand RNA or double-strand RNA (dsRNA) was mixed in an aqueous solution with PEG-PLys. The DP of the PLys segment was fixed at 40, and the molecular weight of the PEG segment was systematically varied in the range from 2k to 42k.…”

“…Thus, no significant increase in the positioning freedom in the PIC phase is expected to compensate for the increased steric repulsion of the PEG strands in the PIC micelle structure, and dsRNA/PEG-PLys remains as uPICs in aqueous media. 35 The formation of a stable uPIC structure from dsRNA is used to construct a palisade of block ionomers to pair with dsRNA (small interfering RNA) onto gold nanoparticles to create systemically injectable nanocarriers to deliver small interfering RNA therapeutics to target organs to treat cancer. 36,37 …”

Bulk and nanoscale polypeptide based polyelectrolyte complexes

“…[102] Interestingly, in a subsequent investigation, RNA strand rigidity was found to influence the formation of a unimer versus a PEC micelle. [103] Hayahsi et al found that double stranded RNA formed unimer PEC complexes, whereas single stranded RNA was able to form a PEC micelle. [103]…”