| Many anti-tumor drugs are proved to be able to effectively inhibit the growth of tumor cells in ex vivo studies. The in vivo studies, however, show that their efficacy is not as effective as we anticipated in light of their performance in ex vivo. The side effect of drugs limits their translation from bench to bed. Fortunately, studies on drug vehicle are expected to help transport the drug to the targeted organs or cells, effectively and precisely, which minimizes the toxicity of drugs to the healthy part of human bodies. It’s known that nanomicelles as vehicles are already commonly used in establishing the drug delivery systems. In our study, we synthesized the amino-terminated4-arm star-shaped PLGA-PEG copolymer [4s-(PLGA-PEG-NH2)], and then, encapsulated the hydrophobic anti-tumor drug Doxorubicin (DOX) into the micelles self-assembled by the novel polymer to formulate drug-loaded micelles eventually. We characterized both physical and chemical properties of the novel polymers, and observed the morphology of the nanomicelles. Additionally, we contrast the uptake ability by HeLa cells of micelles prepared by our synthesized star-shaped copolymer with micelles assembled by linear copolymers which contain the same length PLGA and PEG segments. We also contrast toxicity of two types of micelles to HeLa cells. The results demonstrated that star-shaped PLGA-PEG copolymers we synthesized as drug carrier can perform better in improving the drugs’efficacy and minimizing their side effects than linear PLGA-PEG-PLGA.Consequently, the major contents of this thesis elaborating my experiments in three portions are shown as follows:1. The synthesis and characterization of4-arm star-shaped PLGA-PEG copolymer Two steps method is adopted by synthesizing the amino-terminated4-arm star-shaped PLGA-PEG block copolymer. First of all, the4-arm star-shaped PLGA was synthesized via the ring-opening polymerization of D,L-lactide and glycolide. Second, the amphiphilic4-arm star-shaped PLGA-PEG copolymer is synthesized by DCC crosslinking method. The structure and molecular weight of the polymer were demonstrated by1H NMR and GPC respectively. The results showed that structure of our synthesized copolymer is coincided with previous design. And the structures of PLGA and PEG segment within the polymers are not changed in the process of synthesis. 2. The preparation and characterization of4-arm star-shaped PLGA-PEG nanomicelles.DOX-loaded micelles are prepared by emulsion-solvent evaporation method. The hydrophobic model drug-DOX was prepared by desalt with TEA. First of all, a suspension was formed by DOX and our4-arm star-shaped PLGA-PEG-NH2through single emulsion method. When suspension is stable, we removed organic solvent in it by stirring overnight. Then,4-arm star-shaped PLGA-PEG-NH2micelles were achieved through centrifugation and lyophilization. Meanwhile, micelles formulated by linear PLGA-PEG-PLGA copolymers made up of the same length of PLGA and PEG segments were prepared in the same way. The contrast of these two types of micelles was preceded from the perspective of morphology, size, zeta-potential, drug loading, and encapsulation efficiency. The results demonstrated that the diameter, zeta potential, drug loading, encapsulation rate of the4-arm star-shaped PLGA-PEG micelles are between (120±4.1)nm,(-17.6±0.87)mv,(7.49±0.3)%, and (75.2±3.2)%respectively. However, as above, the parameters of the micelles self-assembled by linear PLGA and PEG are (91.28±2.3)nm,(-13.1±1.12)mv,(5.54±0.2)%,(57.3±2.8)%, respectively.3. The anti-tumor effect of DOX-loaded PLGA-PEG nanomicelles in ex vivo studiesThe anti-tumor effect of DOX-loaded PLGA-PEG nanomicelles was evaluated by HeLa cells. First of all, HeLa cells were incubated with DOX-loaded4s-PLGA-PEG nanomicelles, linear DOX-loaded PLGA-PEG-PLGA nanomicelles, and free DOX respectively, for6and12hours. The results showed that the uptake rate of DOX-loaded PLGA-PEG nanomicelles by HeLa cells are extremely higher than that of linear DOX-loaded PLGA-PEG-NH2nanomicelles and free DOX. In toxicity study of the effect, DOX-loaded4s-PLGA-PEG nanomicelles were shown better performance in decreasing the viability of the tumor cells. In conclusion, we successfully synthesized4-arm star-shaped PLGA-PEG block copolymer and formulated4-arm star-shaped PLGA-PEG block copolymer nanomicelles. The results of the studies demonstrated that4-arms star-shaped PLGA-PEG-NH2nanomicelles are more promising to be used as anti-tumor drug carrier in terms of their advantages in drug-laoding and cell-uptaken ability and better performance in inhibiting the growth of tumor cells comparing to linear PLGA-PEG-PLGA micelles. |
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