A novel gene delivery system targeting Tie2 for cancer gene therapy.

UNLABELLED: The aim of this study was to explore a novel gene vector for targeting gene therapy. MATERIALS AND METHODS: We conjugated a peptide ligand (named GA3) for endothelial TEK tyrosine kinase (Tie2) with polyethylenimine (PEI) to construct a GA3-PEI complex and used the vector to transfer reporter and therapeutic gene in vitro and in vivo respectively. RESULTS: The results demonstrated the vehicle was able to transfer reporter genes specifically into lung cancer SPC-A1 cells and SPC-A1 xenografts highly expressing Tie2 and epithelial cells of bronchus, but not in heart, liver, spleen, kidney, lung alveolar and vascular tissues. In the gene therapy study, tumor growth was significantly inhibited in SPC-A1 xenograft-bearing mice treated with GA3-PEI/p53 complexes compared with control groups (p<0.05). CONCLUSION: Our results indicated that GA3-PEI is an efficient gene delivery system targeting Tie2.

Identification and characterization of a novel peptide ligand of Tie2 for targeting gene therapy.

Tyrosine kinase with immunoglobulin and epidermal growth factor homology domain-2 (Tie2) has been considered as a rational target for gene therapy in solid tumors. In order to identify a novel peptide ligand of Tie2 for targeted gene therapy, we screened a phage display peptide library and identified a candidate peptide ligand NSLSNASEFRAPY (designated GA5). Binding assays and Scatchard analysis revealed that GA5 could specifically bind to Tie2 with a dissociation constant of 2.1x10(-8)M. In addition, we showed that GA5 was internalized into tumor cells highly expressing Tie2. In the biodistribution assay, (125)I-GA5 was mainly accumulated in SPC-A1 xenograft tumors that express Tie2. In gene delivery studies, GA5-conjugated polyethylenimine vector could achieve greater transgene transduction than non-targeted vectors both in vitro and in vivo. Tumor growth inhibition was observed in SPC-A1 xenograft-bearing mice that received eight intratumoral injections of GA5-polyethylenimine/p53 complexes in 3 weeks. The difference in tumor volume between the experiment and control groups was significant (P<0.05). Our results showed that GA5 is a potentially efficient targeting element for cancer gene or molecular therapy.

Kinetics and subcellular localization of 5-ALA-induced PpIX in DHL cells via two-photon excitation fluorescence microscopy.

Two-photon excitation fluorescence (TPEF) microscopy was used to measure the 5-aminolevulinic acid (5-ALA)-induced PpIX fluorescence in follicular lymphoma DHL cells. Kinetics of 5-ALA-induced PpIX accumulation in DHL cells under various 5-ALA concentrations was studied. We found that during the course of continuous incubation with 5-ALA, the relationship between the DHL cell fluorescence signal and the incubation time showed a biphasic variation. Initially the PpIX signal increased with the incubation time and reached the maximal value at about 3 h, and then it decreased with time during the subsequent incubation period. By labeling the 5-ALA incubated DHL cells with different organelle-specific fluorescence probes: Rhodamine 123 (for mitochondria), DioC6(3) (for endoplasmic reticulum) and LysoTracker Green (for lysosomes) respectively, we found that 5-ALA-induced PpIX was primarily localized in endoplasmic reticulum and mitochondria; its concentration in the lysosome was much lower. The results suggested that 5-ALA could potentially be an effective photosensitizer in photodynamic purging of DHL cells. Two-photon excitation fluorescence microscope is a useful tool for studying 5-ALA-induced PpIX subcellular localization.

Large-scale cDNA transfection screening for genes related to cancer development and progression.

A large-scale assay was performed by transfecting 29,910 individual cDNA clones derived from human placenta, fetus, and normal liver tissues into human hepatoma cells and 22,926 cDNA clones into mouse NIH 3T3 cells. Based on the results of colony formation in hepatoma cells and foci formation in NIH 3T3 cells, 3,806 cDNA species (8,237 clones) were found to possess the ability of either stimulating or inhibiting cell growth. Among them, 2,836 (6,958 clones) were known genes, 372 (384 clones) were previously unrecognized genes, and 598 (895 clones) were unigenes of uncharacterized structure and function. A comprehensive analysis of the genes and the potential mechanisms for their involvement in the regulation of cell growth is provided. The genes were classified into four categories: I, genes related to the basic cellular mechanism for growth and survival; II, genes related to the cellular microenvironment; III, genes related to host-cell systemic regulation; and IV, genes of miscellaneous function. The extensive growth-regulatory activity of genes with such highly diversified functions suggests that cancer may be related to multiple levels of cellular and systemic controls. The present assay provides a direct genomewide functional screening method. It offers a better understanding of the basic machinery of oncogenesis, including previously undescribed systemic regulatory mechanisms, and also provides a tool for gene discovery with potential clinical applications.

A novel small peptide as a targeting ligand for receptor tyrosine kinase Tie2.

Tie2 is an endothelium-specific receptor tyrosine kinase known to play an important role in tumor angiogenesis. We sought to identify a small peptide ligand against Tie2 for developing a delivery targeting agent. We used hydrophobic analysis and comparative sequence/structure analysis to select a minimal peptide based on angiopoietin-2 amino acid sequence. The resulting peptide named GA3(WTIIQRREDGSVDFQRTWKEYK) was synthesized and labeled with iodine-125 at the C-terminal tyrosine residue to characterize its binding capability. In in vitro binding assays, GA3 can not only specifically bind to SMMC7721-Tie2 but also compete with angiopoietin-2 in binding. Via mouse tail vein injection, 125I-labeled GA3 was found to favorably accumulate in SPC-A1 xenograft tumor tissues which positively express Tie2. These results demonstrated that GA3 may be useful as a drug or gene delivery ligand for targeted chemotherapy, radiotherapy, and gene therapy.