Pullulan-PEI-Histidine towards gene delivery: vector unpacking with respect to molecular weight and cytoplasmic histones

摘要

Introduction: Cationic polymers, one of the most important nonviral vectors have a number of advantages over viral vectors. However cationic surface charge, the key factor which determines the transfection efficiency, is also one of the limitations associated with it. Major limiting factors are cytotoxicity, biocompatibility and the release of the cargo from the vector intracellularly. The tightly formed nanoplexes gains entry into the cells, however it doesn't lead to good transfection if the DNA remains tightly bound to carrier. Schaffer et.al proved that unpacking of the ONA from the vectors is a major limiting step in the process of non-viral gene delivery. Earlier we reported the possible role of histones in unpacking in which a combination of all histones were used. In this work we attempted to evaluate the possible role played by the molecular weight of the polymers and which of the cytoplasmic histones aids more in vector unpacking. Histone 1 (H1) and histone 3 (H3) reported to be found in cytoplasm were used for the study. Materials and Methods: Pullulan a hydrophilic, nonionic polysaccharide was conjugated with PEI (10 and 25KDa) to which histidine was introduced to improve its transfection efficiency (PPE10H and PPE25H). The conjugation was extablished by variuos techniques including NMR. The particle size and zelapotential of nanoplexes was evaluated with DLS. The cellular uptake and transfection efficiency was done in C6 glioma cells. For vector unpacking studies, cellulose-DNA beads were used by which the displacement of the polymer was assessed. Labelled PPEH and histones (H 1 and H 3) were used to study the unpacking in cell lines. Results and Discussion: The derivatisation was established using techniques including NMR and Raman spectroscopy. The optimum size of PPE10H and PPE25H nanoplexes were 78.4 ± 0.72 and 101.6 ±2.3 respectively at 1:4 ratio with a zeta potential in the range 13-15 mV. The nanoplexes of both polymers demonstrated very high intracellular uptake and PPE10H had higher transfection efficiency in comparison with PEI10K and PPE10KH. Among the histones studied H3 was found to be more efficient in vector unpacking (Fig.1). In the absence of histone intact nanoplex is internalised as TRITC labeled PPE10H is found in the cytoplasm and tagged DNA in the nucleus. The nanoplex treated with H1 and H3 resulted in unpacking outside the cell and the labeled polymers are excluded from the entry into the cells (Fig. 1 B to E). However H1 is not as efficient as H3 in unpacking the DNA from the polyplex. The vector unpacking was higher with PPEH10K which might be the reason for better transfection efficacy which could be attributed to its low cationicity (Fig. 2). Figure 1. Intemalization of TRITC labeled PPE10KH nanoplex in C6 cells. Nanoplex alone (A), nanoplex treated with 500 ng histone H1 (B), 1 micro g histone H1 (C), 500 ng histone H3 (D) and 1 micro g histone H3 (E). Absence of TRITC labeled polymer in D & E indicate the better displacement of polymer with H3. Figure 2. Luciferase expression in C6 cells transfected by PPE10H and PEI complexes at ratios 1:3 and 1:4.~(**)p＜0.05 Conclusion: PPE1 OH was found to be a better transfecting agent. It was observed that H3 is more effiecient in displacing the plasmid DNA from the vector. The extent of cationicity also found to play a role in release of DNA from the vector in presence of histones.