Characterization On Drug Delivery To Glioma Of Lactoferrin-conjugated Polymersome

Glioma is the most common malignant intracranial tumor, which has a poor prognosis. Blood-Brain Barrier (BBB) and Multidrug resistance (MDR) are the main hindrance preventing chemotherapeutics entering the brain and reaching the tumour. In order to improve the therapeutic efficacy for glioma, a novel active targeting nanocarrier, namely lactoferrin conjugated polymersome (Lf-PO) was designed and prepared, which was expected to get an access into tumour cells via low density lipoprotein receptor-related protein (LRP) that was expressed on both BBB and tumour cells. To further inhibit MDR, tetrandrine (Tet) was also encapsulated in this nanocarrier.In the 1st Chapter, the fluorescent probe DiR loaded polymersome was prepared from methoxyl polyethylene-polycaprolactone (MPEG-PCL) and carboxyl polyethylene-polycaprolactone (MPEG-PCL). And then lactoferrin was decorated onto the surface of the polymersome resulting in the final Lf-PO-DiR, which had an average diameter around 240 nm and zeta potential at-11 mV. Entrapment efficiency (EE) and drug loading capacity (DLC) for DiR were 33.3% and 1.4%, respectively. The average number of Lf molecules conjugated to the polymersome was about 37. Later on, glioma rat model was established through injection of C6 cells into the striatum. The model was validated at tissue level and cell level. Then the distribution of Lf-PO-DiR in glioma implanted rat was investigated by use of in-vivo imaging technology. The result indicated that Lf-PO-DiR could enter the brain and accumulate at the tumour site. According to the semiquantitative brain fluorescence intensity-time curve, AUCLf-PO-DiR was 2.6 times higher than AUCPO-DiR, confirming that Lf conjugation increased the glioma homing of Lf-PO-DiR.In the 2nd Chapter, polymersome encapsulating both doxorubicin and tetrandrine was prepared, which was subjected to Lf decoration to yield Lf-PO-Dox/Tet. Lf-PO-Dox/Tet's diameter was around 220 nm with zeta potential at-10 mV. EE and DLC for doxorubicin were 96.2% and around 4.0%; EE and DLC for tetrandrine were 93.9% and 1.5%. The number of Lf molecules on the polymersome surface was about 40. According to the results of MTT method, IC50 of Lf-PO-Dox/Tet against C6 cell was 8.4μg/mL, which was half that of PO-Dox/Tet. Fluorescencent imaging revealed that Lf-PO-Dox/Tet located in the cytoplasma and the nucleus while free doxorubicin mainly accumulated in the nucleus. This phenomenon indicated that polymersome could effectively encapsulate doxorubicin even in cytoplasma which facilitated its transcytosis towards the targeted site. The quantitative determination of cell uptake exhibited that after 12 h incubation uptake index (UI) of Lf-PO-Dox/Tet was 1.5 times that of PO-Dox/Tet and Lf-PO-Dox, and 3 times that of PO-Dox. These results illustrated both Lf and Tet improved cell uptake and intensified cell toxicity.In the 3rd Chapter, pharmacokinetics and pharmacodynamics of Lf-PO-Dox/Tet were investigated in glioma implanted rats. Plasma concentration-time curve was determined after i.v. injection of 4 different polymersomes. The results revealed that AUC for Lf-PO-Dox/Tet and Lf-PO-Dox was lower than that for PO-Dox/Tet and PO-Dox, but there were no significant differences of the k value between groups indicating that the long circulation function of polymersomes was not significantly influenced by Lf. Brain distribution indicated that Lf-PO-Dox/Tet could enter the brain and accumulate in the tumour site. For other organs, polymersomes accumulated most in spleen and liver and relatively less in heart and kidney. Pharmacodynamics was evaluated through comparation of tumor volume and survival time of glioma implanted rats. The results indicated that tumor volume of rats treated with Lf-PO-Dox/Tet was significantly smaller than other therapeutic groups, while the median survival time of rats treated with Lf-PO-Dox/Tet was longer than Lf-PO-Dox and significantly longer than the rest three therapeutic groups. The above results further confirmed that Lf-PO-Dox/Tet improved glioma uptake and therapeutic effects of doxrubicin.