The goal of cancer chemotherapy is to develop effective, safe, and well-tolerated medications. The over-expression of certain receptors on cancer cell membrane provides a basis for active targeting by not only specific interaction between drug delivery system and cells, but also facilitated cellular uptake via receptor-mediated endocytosis. In this study, LDV oligomers up to six LDV repeating units were synthesized via solid phase peptide synthesis method, and evaluated as drug carrier as well as targeting moiety to deliver doxorubicin (Dox) to human malignant melanoma cells (A375), which over-express integrin α 4 β 1 . Cells expressing different levels of integrin α 4 β 1 or modulated using integrin α 4 -specific siRNA knock-down technique were verified by western blot and PCR. Magnetic beads with tripeptides LDV, VDL, or LNV on the surface were used in the binding specificity studies. Results verified that LDV was the minimally required ligand sequence for the specific binding to integrin α 4 β 1 , of which the interaction depends on the amount of integrin and can be utilized for the design of targeted drug delivery. The studies on A375 cells uptake of FITC-labeled LDV oligomers examined the effects of EDTA, temperature, endocytosis inhibitor, and competitive ligand. Cellular uptake mechanism was revealed to be temperature-dependent, receptor-mediated endocytosis, involving the specific interaction between LDV and integrin α 4 β 1 . The internalization extent of LDV monomer was the highest and was also inhibited to the most by the addition of free LDV when compared to other LDV oligomers. Cytotoxicity profiles of Dox-conjugated LDV oligomers were obtained on wild-type A375, integrin α4 knock-down A375, and normal human epithelial keratinocytes (NHEK) using SRB assay. A significant decrease (3∼6 folds) in the cytotoxicity of oligo(LDV)-Dox on A375 cells were observed when the integrin α4 expression was knocked down by ∼50%. Cytotoxicity further decreased on NHEK, which has the lowest integrin α4 expression among three cell lines. In contrast to oligo(LDV)-Dox, free Dox was not able to differentiate between cancerous and normal cells. This result demonstrated the potential of oligo(LDV) as targeting ligand. However, increase of repeating LDV unit did not lead to any apparent trend in cytotoxicity capacity. To facilitate the intracellular Dox release, hydrazone bond (HYD) was introduced between LDV and Dox. In vitro Dox release profiles in pH 6.0, 7.4, and rat plasma proved the pH-sensitivity of LDV-HYD-Dox. Cytotoxicity studies showed an increased cytotoxic effect of LDV-HYD-Dox when compared with LDV-Dox on wild-type A375 (2.5 times), knock-down A375 (1.5 times); while no significant difference in cytotoxicity on NHEK was observed. In vivo animal study supported the in vitro findings on LDV-HYD-Dox, which showed a significant inhibition of tumor growth and longest mice life span when compared to free Dox, poly(L,D,V)-Dox, and LDV-Dox, with averagely only ¼ of the tumor size and almost twice the life span of that from the free Dox group. In conclusion, based on the concept of specific interaction between LDV and integrin α 4 β 1 , oligo(LDV)-Dox targeted drug delivery system was developed and proved to be effective in the delivery of Dox to melanoma cells.
| Identifer | oai:union.ndltd.org:pacific.edu/oai:scholarlycommons.pacific.edu:uop_etds-3398 |
| Date | 01 January 2009 |
| Creators | Zhong, Sha |
| Publisher | Scholarly Commons |
| Source Sets | University of the Pacific |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | University of the Pacific Theses and Dissertations |
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