Linear-PEI

Intravesical infusion of linear PEI/pDNA polyplexes was evaluated in patients with superficial bladder cancer where intravesical therapy with bacillus Calmette-Guerin had failed [6, 224]. Patients had low grade superficial bladder cancer, which expressed H19. The therapeutic pDNA contains H19 gene regulatory sequences that drive the expression of an intracellular toxin. Escalating doses of 2-20 mg plasmid per intravesical treatment were applied, with responders continuing to receive polyplexes once a month every month for 1 year. The treatment resulted in complete ablation of the marker tumor, without any new tumors in four of the 18 patients (22% overall complete response rate). Eight of the 18 patients (44%) had complete marker tumor ablation or a 50% reduction of the marker lesion. 

In a similar fashion, the cationic polymerization of 2-oxazolines has been extensively studied and was found to provide the first verified entry to linear-poly(alkyleneimine) architectures. These acylated polymers were first recognized as precursors to linear poly(ethyleneimines) in the early 1960s [25]. Hydrolysis experiments demonstrated that deacylation of these products to linear PEI was possible. The original polymerization mechanism proposed by Tomalia et al. 

Poly (ethylenimine) (PEI) has been demonstrated as an efficient gene delivery vehicle both in vitro and in vivo (161-163). Linear (22 kDa) and branched PEI formulations of varying molecular weights (0.6-800 kDa) have been reported. While polyplexes from higher molecular weight branched PEIs (70-800 kDa) were found to be more efficient in vitro but on intravenous administration the smaller and linear PEIs seem in general to be more efficient (171). However, questions as to the... 

ULTRA resins were prepared from varying molar ratios between dialdehydes and the linear PEI and with PEI of varying length (Fig. 10). In all cases resin micropellets of a defined size range were generated by polymer extrusion in the swollen state, followed by sieving. 

Poly(ethylene oxide)-/>-polyethyleneimine (PEO-6-PEI) Block copolymer, linear PEI segment Synthesis of carrier (Akiyama et al., 2000)... 

Figuer 9.1 Schematic illustration of various polycation structures used for preparation of polyplexes (A) linear (PEI) (B) randomly branched (PEI) (C) dendrimer (PAMAM) (D) block and graft copolymers (Pluronic-g-PEI and PEO-g-PEI modified with a targeting moiety by one PEO end) (E) nanoscale cross-linked network (PEO-c7-PEI). 

Shim and Kwon coupled acid-responsive amino ketal branches to secondary amines of 25 kDa linear PEI, thus showing distinct eGFP silencing at N/P (polymer nitrogen to siRNA phosphate) ratios of 100 and low toxicity compared to... 

Fig. 9 PCI-induced transfection utilizing branched and linear PEI as vector. HT116 colon carcinoma cells were treated with AlPcS (20 (tg/mL) for 18 h followed by a 4-h incubation with an plasmid encoding EGFP and complexed with 25 kDa branched or 22 kDa linear PEI at an N P ratio of 4 before light exposure. EGFP expression was measure by flow cytometry 2 days later. The photochemical treatment caused 40-60% cytotoxicity...

Linear PEI can be obtained by cationic ring-opening polymerization of 2-oxazoline, followed by alkaline hydrolysis of the resulting poly(N-formylethyleneimine)9). 

Owing to its regular structure, linear PEI may crystallize, and on stretched samples of high molecular weight PEI an x-ray crystallographic study could be performed. It seems to crystallize as arrays of double strand helices 12). Furthermore, two crystalline hydrates of linear PEI of Mn about 2000 have been reported 13). 

Poly(N-alkyl-ethylene imine) can be prepared by cationic ring-opening polymerization of N-alkylaziridines however, branched polymers are obtained by this way 19>. Linear poly-MEI may be obtained by N-methylation of linear PEI by the Clarke-Eschiweiler variation of the Leukart reaction, in which an excess of formic acid is used together with formaldehyde. The reaction may be performed either on PEI, or... 

Calorimetric data on the protonation of PVA, and linear PEI at various temperatures and ionic strengths have been published by St. Pierre et al.10). The very important point of this study is, that AH0 data allow a better evaluation of the polyelectrolyte effect. The following results are worth to be mentioned (Fig. 1). 

Linear PEI None Pol-III HI IV Partial liver resection Fisher rats Liver HGF Suppression of mRNA and protein, moderate suppression of hepatocyte proliferation (54)... 

Linear PEI None Pol-III U6 Intratumoral U87 human glioblas- toma SC1D mice Subcutaneous VEGF Efficient reduction of tumor vascularization (80)... 

Linear PEI None CMV-H1 Stereotaxic injection into lateral ventricles Normal brain Mice Brain TRal Inhibition of gene expression (55)... 

The properties and applications of linear PEI are described in the polyoxazoline chapter. 

Linear PEI have properties very different from those of branched PEI. They precipitate from water solution forming insoluble crystallohydrates. The structure of the latter determined by x-rays reveals a system of double-stranded helices stabilized by H bonds [180], Three hydrated forms have been identified hemihydrate, sesquihydrate, and dihydrate. 

Figure 1 Structures of polymers commonly used in biomaterials applications PGA (I), PLA (2), PAAs (3), linear PEI (4), PAMAMs (5) and chitosan (6) (see text for abbreviations)...

As shown in Fig. 2a, linear PEI Pa = 8-9) shows a significant acceleration of the reaction rate compared to the condensation reaction under similar conditions but without the addition of an... 

In our design of polyrotaxanes here, the respective numbers of threaded a-CDs and DMAEC groups per polyrotaxane were estimated to be around 23 and 40 for DMAEC-SS-PRx, 30 and 40 for DMAEC-PRx from their H-NMR spectra. The complexation of DMAEC-(SS)-PRXs with pDNA was compared with that of a linear PEI with a Mn of 22,000 (LPEI22k) in terms of gel electrophoresis. A band for free pDNA in the electrophoresis was disappeared upon complexation with a smaller quantity of amino groups in the polyplex with the polyrotaxane than with the LPEI. 

Enhanced transfection with larger vectors was also seen with lipid-DNA lipoplexes in CHO cells [113]. However, the opposite was found with linear PEI (L-PEI) in vivo. Smaller complexes led to higher levels of gene expression in adult and newborn mice, which correlated to their diffusivity through tissue [100]. In this study, L-PEI DNA complexes were shown to cross the endothelial cell barrier following intravenous administration and preferentially transfect pulmonary cells [92]. Cationic lipids, on the other hand, show some expression in pulmonary cells following intravenous administration but preferentially transfected endothelial cells [51,53,114,115], perhaps due to their reduced stability compared to polyplexes. 

Goula D, Remy JS, Erbacher P, Wasowicz M, I evi G, Abdalkan B, Demeneix BA. Size, diffusibility and transfection performance of linear PEI/DNA complexes in the mouse central nervous system. Gene Therapy 1998, 5, 712-717. 

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