Study On Polyelectrolyte Microcapsules With PH-controlled Spontaneous Antitumor Drug Deposition For Lung Targeting And Local Chemotherapy

Polyelectrolyte multilayer capsule, a promising candidate for multifunctional drug delivery system, has recently received increased interest. However, the loading amount of drugs is insufficient to carry out a large scale evaluation, such as animal experiments. The target-ability and security after intravenous injection of polyelectrolyte microcapsules (1～10μm) are unsatisfactory, restricting their studies in vivo. The lack of reports about animal experiments has greatly slowed down their development for drug delivery. Spontaneous deposition, a promising method for encapsulation, occurs in the case of electrostatic attraction between the drug molecules and an oppositely charged matrix inside the capsules, thus facilitating diffusion of molecules into the preformed capsules. This method greatly increases the encapsulation efficiency and shows specific advantages in drug loading of polyelectrolyte capsules. Nevertheless, we should notice that the deposited molecules are bound with the matrix tightly driven by electrostatic attraction, then how to control the spontaneous drug loading effect and release these active molecules is still a challenging and meaningful task. Moreover, the study on an animal experimental level is significant for the development of polyelectrolyte microcapsules as drug delivery vehicles.For this context, we constructed a novel polyelectrolyte multilayer capsule containing BSA gels (BSA-gel-capsule, abbreviated as BGC). This capsule not only had pH-controlled spontaneous deposition effect, but also possessed pH-responsive release property, based on the charge alterability of BSA varied with pH values. This method greatly increased the drug loading amount of polyelectrolyte microcapsules, assuring the drug loading sufficient enough for pharmacodynamics study. It presents new opportunities en route to the drug loading and release of polyelectrolyte microcapsules. Moreover, for the first time, we studied the passive lung targeting action after intravenous injection of BSA-gel-capsules. Afterwards, we further evaluated the in vitro and in vivo antitumor effects of DOX-loaded BGC, against the mice pulmonary melanoma model and the subcutaneous transplanted model of human breast cancer in nude mice, respectively. The results will provide a theoretical basis and experimental evidence for the application and development of polyelectrolyte microcapsules as drug delivery carriers.Firstly, BSA molecules were incorporated in CaCO3microparticles by co-precipitation to prepare CaCO3(BSA) particles. Because PAH/PSS are widely used in layer-by-layer technique, BSA-gel-capsules were then fabricated by layer-by-layer assembly of PAH/PSS on CaCO3(BSA) particles. The obtained BSA-gel-capsules were abbreviated as PAH/PSS-BGC. PAH/PSS-BGC displayed excellent pH-controlled loading and release properties for doxorubicine (DOX). At pH6.5, PAH/PSS-BGC showed pronounced accumulation effect of DOX into capsules. It greatly increased the loading amount of DOX in capsules, which was sufficient enough for pharmacodynamics study.Secondly, obvious lung targeting action after intravenous injection of PAH/PSS-BGC into mice was observed under the Maestro in-vivo imaging system. Based on this, the mice B16F10pulmonary melanoma model, which was commonly used for establishing an experimental lung cancer model, was employed to carry out the in vitro and in vivo antitumor studies of DOX-loaded PAH/PSS-BGC. The results showed that DOX-loaded PAH/PSS-BGC could effectively inhibit the growth of B16F10cells in vitro. After intravenous administration, DOX-loaded PAH/PSS-BGC showed more effective antitumor ability compared with free DOX. These results rendered feasible the intravenous administration and the in vitro and in vivo study of polyelectrolyte microcapsules.Thirdly, because both poly electrolytes PAH and PSS are non-biodegradable, chitosan (CTS) and alginate (ALG) were used instead of PAH and PSS to fabricate biocompatible BSA-gel-capsules. The obtained CTS/ALG BSA-gel-capsules were abbreviated as CTS/ALG-BGC. They showed similar properties as PAH/PSS-BGC:the spontaneous loading and release of DOX were pH-sensitive; the cytotoxicity against B16F10cells in vitro and the tumor-inhibition against pulmonary melanoma in vivo were remarkable. In addition, the study in this section still demonstrated that CTS/ALG-BGC could be internalized into cytoplasm in B16F10cells. DOX was mainly accumulated in the lung after intravenous injection of DOX-loaded CTS/ALG-BGC and then they were metabolized into the liver. Intravenous injection of CTS/ALG-BGC didn’t result in the death of mice. The results indicated that the security and the biocompatibility of CTS/ALG-BGC after intravenous injection were satisfactory, and CTS/ALG-BGC was more suitable for drug delivery than PAH/PSS-BGC.Finally, the application of DOX-loaded CTS/ALG-BGC in local chemotherapy for breast cancer was investigated. The results showed that both free DOX and DOX-loaded CTS/ALG-BGC could effectively inhibit the growth of MCF-7cells. However, the cytotoxicity of DOX-loaded CTS/ALG-BGC against MCF-7/ADR cells was significantly higher than free DOX, showing some reversal efficiency in the DOX resistant of MCF-7/ADR cells. The transplanted model of human breast cancer in nude mice was established after subcutaneous injection of MCF-7/ADR cells. Compared with intra-tumor injection of free DOX, the tumor-inhibition after intra-tumor injection of DOX-loaded capsules was more effective, because both concentration and retention time of DOX in tumor were higher after injection of DOX-loaded capsules.