Replacement of quaternary ammonium headgroups by tri-ornithine in cationic lipids for the improvement of gene delivery in vitro and in vivo.

Headgroups in cationic lipids play very important roles in determining transfection efficiency and toxicity in gene delivery. To better understand the influence of headgroups on gene delivery, a tri-peptide-based lipid was synthesized, wherein the usual quaternary ammonium was replaced by a tri-peptide. Though both the tri-peptide-based lipid (DAO3) and the quaternary ammonium-based lipid (DDCTMA) successfully mediated gene transfection, DAO3 was superior to DDCTMA in both in vitro and in vivo studies. Following their preparation into liposomes, the particle size, zeta potential, and DNA-binding capacity of the liposomes and lipoplexes were characterized to evaluate the efficiency of DAO3 compared to DDCTMA with regard to gene interactions. The expression of luciferase from pDNA mediated by DAO3 was 2-fold greater than than that with DDCTMA in Hep-2 cells, and DAO3/siRNA lipoplexes could silence about 60% luciferase in A549 cancer cells expressing firefly luciferase. DAO3/Luc-siRNA treatment exhibited 3-fold the efficiency of DDCTMA/Luc-siRNA in terms of in vivo luciferase RNAi with the bare density ratio of 0.54 at 48 h. Furthermore, DAO3 could mediate IGF-1R siRNA to inhibit tumor growth through silencing the expression of the IGF-1R protein, whereas DDCTMA showed nearly no effects. Most importantly, DAO3 had no obvious toxicity in vitro and in vivo, due to the biocompatibility of the peptide headgroups. In conclusion, these results demonstrated that the replacement of the quaternary ammonium headgroup by tri-ornithine may increase transfection efficiency and decrease toxicity.

Characterization of pRGO1, a plasmid from Propionibacterium acidipropionici, and its use for development of a host-vector system in propionibacteria.

The complete nucleotide sequence of pRGO1, a cryptic plasmid from Propionibacterium acidipropionici E214, was determined. pRGO1 is 6, 868 bp long, and its G+C content is 65.0%. Frame analysis of the sequence revealed six open reading frames, which were designated Orf1 to Orf6. The deduced amino acid sequences of Orf1 and Orf2 showed extensive similarities to an initiator of plasmid replication, the Rep protein, of various plasmids of gram-positive bacteria. The amino acid sequence of the putative translation product of orf3 exhibited a high degree of similarity to the amino acid sequences of DNA invertase in several bacteria. For the putative translation products of orf4, orf5, and orf6, on the other hand, no homologous sequences were found. The function of these open reading frames was studied by deletion analysis. A shuttle vector, pPK705, was constructed for shuttling between Escherichia coli and a Propionibacterium strain containing orf1 (repA), orf2 (repB), orf5, and orf6 from pRGO1, pUC18, and the hygromycin B-resistant gene as a drug marker. Shuttle vector pPK705 successfully transformed Propionibacterium freudenreichii subsp. shermanii IFO12426 by electroporation at an efficiency of 8 x 10(6) CFU/microg of DNA under optimized conditions. Transformation of various species of propionibacteria with pPK705 was also performed at efficiencies of about 10(4) to 10(7) CFU/microg of DNA. The vector was stably maintained in strains of P. freudenreichii subsp. shermanii, P. freudenreichii, P. pentosaceum, and P. freudenreichii subsp. freudenreichii grown under nonselective conditions. Successful manipulation of a host-vector system in propionibacteria should facilitate genetic studies and lead to creation of genes that are useful industrially.