Balancing hydrophobic and electrostatic interactions in thermosensitive polyplexes for nucleic acid delivery

Abstract

For the design of newpolymeric-based drug delivery systems, understanding howmultiple functionalities in the polymer structure are influencing each other in particle formation is important. Therefore in this study, the balance between hydrophobic and electrostatic interactions has been investigated for thermosensitive plasmidDNA(pDNA)-loaded polyplexes.NPDtriblock copolymers consisting of a thermosensitive poly(N-isopropylacrylamide) (PNIPAM,N), a hydrophilic poly(ethylene glycol) (PEG, P) and a cationic poly(2-(dimethylamino)ethylmethacrylate) (PDMAEMA,D) blockwith different block lengthswere prepared using a hetero-functional PEGmacroinitiator. Cloud points of the thermosensitive polymers inHBS buffer (20mM HEPES, 150mM NaCl,pH7.4) were determined by light scattering and ranged between 33 °C and 34 °C for the different polymers. The binding and condensation properties of these thermosensitive polymers and pDNAwere studied taking nonthermosensitive PDpolymers as controls.The size, surface charge, and stability of the formed colloidal particles ('polyplexes') were studied as a function of polymer block lengths,N/P charge ratio, and temperature.TheNPDpolymers were able to self-assemble into polyplex nanostructureswith hydrodynamic sizes ranging between 150 and 205 nmat roomtemperature inHBS buffer as determined by dynamic light scattering. Polyplexes preparedwith a lowN/P charge ratio of 1 aggregated upon heating to 37 °C,whichwas not observed at higherN/P charge ratios.When the length of the cationicD blockwas relatively long compared to the thermosensitiveNblock, stable polyplexeswere formed at all N/P ratios and elevated temperatures. 1H-NMRstudies, static light scattering and æ-potential measurements further supported the stability of these polyplexes at 37 °C. Finally, the presence of thermosensitive blocks inNPD-based polyplexes resulted in better cytocompatibility compared to PD based polyplexeswith similar efficiencies of delivering its cargo into HeLa cells.