| Cancer is one of the main threats to human health, which kills millions of people every year. Although chemotherapy plays an important role in treatment of cancer, common anticancer agents have lots of limitations, such as systemic cytotoxicity. Therefore, the targeted delivery and controlled release of anti-cancer drugs has become the research focus.Macromolecules have been widely investigated as drug carriers due to their flexible structures, as well as excellent physical, chemical and biological properties. Compared with common anticancer agents, nanoscale drug delivery systems for cancer therapy can improve treatment efficacy and reduce the side effects of anticancer drugs. Among all these macromolecules, poly (N-(2-hydroxypropyl)methacrylamide) (PHPMA) has recieved lots of attention owing to its non-toxic, non-immunogenic and water-soluble characteristics. In this thesis, our aim was to prepare a novel anti-cancer drug delivery system with highly tumor accumulation. We synthesized a series of well-defined copolymers of HPMA and its methacrylamide derivatives, and investigated the influences of the physico-chemical properties on their biological functions. Finally, a highly efficient anticancer drug delivery system with excellent prospects for clinical applications was obtained.Reduction-sensitive monomer N-methacryloyl-N’-(t-butyloxycarbonyl) cystamine (MABC) was synthesized. Di-block copolymers PEG-b-PMABC and tri-block copolymers were synthesized via RAFT polymerization by using a PEG macroRAFT agent. A new method of adjusting micelles’ size and surface charge was established by controlling the deprotection procedure of Boc-protected amino groups. Micelle sizes changed immediately after the addition of trifluoroacetic acid (TFA) due to the alteration of intra- or inter-molecular hydrogen bonds. When the di-block copolymers were substituted with tri-block copolymers, no sudden change of micelle size could be observed due to the restriction of polystyrene (PS) core. The zeta potentials of micelles were increasing during the whole incubation period due to the remove of Boc groups and the exposion of amino groups after adding TFA. The deprotection process was in an ordered manner from outside to inside of micelles.The tunable sizes (from 50 nm to 210 nm) and zeta potential changes (-16 mV to 60 mV) of micelles were obtained. For the first time, the influences of size and surface charge on the bio-functions of polymeric micelles were explored independently.The biological properties for these micelles were characterized by both in vitro and in vivo experiments. With the surface charge turning from negative to positive, the cellular uptake increased accordingly. The introduction of disulfide bonds can enhance the intracellular drug release. For micelles with the same size and surface properties, the alteration of surface charge from negative to positive brought about an obvious increase of both tumor and organs accumulation while the circulation time decreased accordingly. The negative charged micelles with small size showed strong penetrating ability in tumor. Positive charged micelles with large sizes showed strong interaction with blood vessels. The results have brought us a new way of designing efficient drug delivery systems. It is reasonable to infer that by exploring the most optimal size and surface charge, novel drug delivery systems with both tumor targeting and cancer cell endocytosis abilities could be obtained.For drug delivery systems, micelles with small sizes showed strong penetrating ability in tumor. However, tumor accumulation and retention abilities were unsatisfactory due to the small size of the conjugates. The prolonged blood circulation can be obtained by increasing the molecular weight of the conjugates. However, this may cause either a complicated synthesis process or activate the reticuloendothelial system (RES), increasing the risk of some undesired side effects. Therefore, to date, there are great demands in developing HPMA-based copolymer-drug conjugates with very low non-target tissue uptake and highly tumor accumulation. In this study, we used the multi-micelle aggregate (MMA) mechanism to achieve our objective. Water-soluble polymers with different components and structures were synthesized by RAFT copolymerization of HPMA and its methacrylamide derivatives. pH-sensitive polymer-DOX conjugates were synthesized by the post-polymerization modification technique. The influences of components and structures on the MMA ability were confirmed by DLS and TEM. Finally, a highly efficient anticancer drug delivery system was obtained. Investigation of the antitumor efficacy and toxicity of the polymer-DOX conjugates was performed on a 4T1 murine breast cancer model. All treated groups showed growth retardation compared with the control group. The highest tumor inhibition rate of all trested groups was 87.1%. During treatment, significant weight loss caused by free DOX was observed. However, no apparent signs of dehydration, locomotor impairment, muscle loss, anorexia, weight loss, or other symptoms associated with animal toxicity were observed in the groups treated with conjugates. Therefore, with the combination of this novel topological structure and appropriate targeting or tumor-penetrating moieties, highly-efficient anticancer drug delivery systems with excellent prospects for clinical application could be obtained. |
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