Cor J. Snel

Steric stabilization of poly(2-(dimethylamino)ethyl methacrylate)-based polyplexes mediates prolonged circulation and tumor targeting in mice

Efficient tumor targeting of polymeric gene transfer systems (polyplexes) represents a major challenge. To establish tumor targeting after intravenous (IV) administration, the circulation lifetime of these systems should be sufficiently long. Since naked polyplexes are rapidly eliminated from the circulation after IV adminstration, strategies have to be developed to improve their pharmacokinetics.

Effect of Liposome Characteristics and Dose on the Pharmacokinetics of Liposomes Coated with Poly(amino acid)s

Long-circulating liposomes, such as PEG-liposomes, are frequently studied for drug delivery and diagnostic purposes. In our group, poly(amino acid) (PAA)-based coatings for long-circulating liposomes have been developed. These coatings provide liposomes with similar circulation times as compared to PEG-liposomes, but have the advantage of being enzymatically degradable. For PEG-liposomes it has been reported that circulation times are relatively independent of their physicochemical characteristics. In this study, the influence of factors such as PAA grafting density, cholesterol inclusion, surface charge, particle size, and lipid dose on the circulation kinetics of PAA-liposomes was evaluated after intravenous administration in rats. Prolonged circulation kinetics of PAA-liposomes can be maintained upon variation of liposome characteristics and the lipid dose given. However, the use of relatively high amounts of strongly charge-inducing lipids and a too large mean size is to be avoided. In conclusion, PAA-liposomes represent a versatile drug carrier system for a wide variety of applications.

Plasmid CpG Depletion Improves Degree and Duration of Tumor Gene Expression After Intravenous Administration of Polyplexes

PurposeTumor gene expression after the intravenous (i.v.) administration of current polymer-based gene delivery systems is generally low and short-lived. Immune stimulatory CpG dinucleotides, present within the plasmid DNA of the polyplexes are likely to contribute to this. The effect of CpG replacement on the levels of transgene expression was studied, after the i.v. administration of polyethylenimine (PEI) polyplexes.MethodsTumor transfection and immune stimulation of PEI polyplexes containing plasmid DNA encoding for luciferase and rich in CpG motifs was monitored and compared to polyplexes containing the same gene but devoid of CpG motifs. Lipoplexes based on 1,2-dioleyl-3-trimethylammonium-propane/dioleoylphosphatidylethanolamine liposomes were included as a control.ResultsThe replacement of CpGrich DNA by CpGfree DNA did neither affect the physical properties of the DNA complexes nor did it affect their in vitro transfection activity or cytotoxicity. The immune stimulation (interleukin-12) after i.v. administration of the PEI DNA complexes was low and unaffected by the presence of CpG motifs. The absence of CpG motifs within the different DNA complexes improved the degree and the duration of organ and tumor gene expression.ConclusionThe depletion of CpG dinucleotides within the plasmid DNA of polyplexes enhances the degree and duration of in vivo transgene expression.

Biodegradable, cationic methacrylamide-based polymers for gene delivery to ovarian cancer cells in mice

A series of cationic, methacrylamide polymers was tested for use as a biodegradable gene carrier in ovarian cancer. Tumor transfection activity of polyplexes consisting of a reporter gene and different methacrylamide polymers was assessed, after intraperitoneal injection in mice bearing an ovarian cancer xenograft. In this model, polyplexes based on poly(HPMA-DMAE) showed transfection activity similar to polyplexes based on the nondegradable and rather toxic polyethylenimine (PEI22). The tumor transfection activity of the pHPMA-DMAE polyplexes was remarkable considering their poor transfection activity in in vitro assays. Polyplexes based on pHPMA-DMAE were devoid of any cytotoxicity and mediated highest transfection activity at the highest N/P ratio investigated. Tumor cell gene expression after a single administration of these polyplexes rapidly declined within time, at a similar rate to that observed after injection with polyplexes based on PEI22. Incubation of the polyplexes with hyaluronic acid (HA), a polyanion accumulating in the ascitic fluid of ovarian cancer bearing mice, changed the physical characteristics of the pHPMA-DMAE and PEI22 polyplexes. The transfection activity of PEI22-based polyplexes, but not that of pHPMA-DMAE based polyplexes, was strongly impaired by HA. Differences in HA sensitivity might have contributed to the in vivo gene expression activities of pHPMA-DMAE- and PEI22-based polyplexes. pHPMA-DMAE-based polyplexes have potential for use in ovarian cancer therapy due to their considerable transfection activity, their low cytotoxicity, and their HA resistance.