Preparation Of PH-responsive Drug Carriers Based On Chitosan

Cancer is a major cause of devastating health outcomes and economic constraintsin human life. Globally, cancer rates are increasing at a distressing rate. A hugeamount of research has already been carried out in the field of cancer, resulting in anumber of available treatment options. However， it is well known that mostanticarcinogens affect not only rapidly dividing cells such as those in tumors, but alsothose in highly proliferative normal tissues. This nonspecific drawback has limited theclinical application of most anticarc inogens. Hence, there has been a global quest todevelop safe and efficient drug carriers that can deliver anticarcinogen exclusively tothe intended site without provoking adverse reactions in disease therapy. To reach thegoal, people have researched many methods for cancer targetted therapy viacombining the nanotechnology and biotechnology. Among them, stimuli-sensitivepolymers especially pH-and thermo-sensitive polymers have been extensivelystudied for drug delivery, because pH and temperature are distinctive environmentalfactors inside the human body, and some disease states manifest themselves by achange in temperature and/or pH. In our paper, according to the feature that a lowerextracellular pH in most solid tumors than in the surrounding tissues and blood, wedesigned and prepared two pH-sensitive drug carrier for cancer targetted therapy.Chitosan is a linear, cationic polysaccharide which is a natural polymer，wesynthesized an amphiphilic polymer, carboxymethylchitosan-grafted-p(ethyleneglycol)-dodecylamine (CMC-g-PEG-DDA) via amidationreaction. Carboxymethyl chitosan (CMC) which contains–COOH groups and–NH2groups in the molecule has improved the solubility of chitosan. PEGylated chitosan may improve the solubility properties and the stability of the drug delivery system inthe blood by preventing the absorption of protein and uptake by reticuloendothelialsystems (RES). Dodecylamine (DDA), could encapsulate a large amount ofhydrophobic therapeutic agents, which can control the size of nanoparticles. Thecopolymer was prepared successfully via characterizing by1H NMR, FTIR and GPC.In addition, we studied the nature of its dissolution, the reaction medium wasdetermined as H2O and DMSO, and prepared polymer micelles by dialysis method.Polymer micelles’ sizes were by characterized dynamic light scattering (DLS), Themorphology were characterized by transmission electron microscopy (TEM).Theresults show that all the micelles were spherical in shape, dispersed evenly. And thesize was about220nm. Moreover, critical micelle concentration (CMC) wasdetermined based on I3/I1derived from emission spectrum afforded by fluorescencespectroscopy with pyrene as fluorescent probe. The CMC of CMC-g-PEG-DDA=2.8x10-3mg mL-1.In the third chapter, we prepared a pH-sensitive Polymer-Drug model drugsystem via using an acid-cleavable bond-hydrazone bond link amphiphilic polymerCMC-g-PEG-DDA and the anticancer drug doxorubicin. The products werecharacterized by1H NMR, DLS, TEM. The conjugates with a small diameter181nmcould form micelles in aqueous phase. In order to observe the release pattern of thedrug from the nanoparticles, DOX-loaded nanoparticles were immersed into buffersolutions of different pH (7.4and5.0) and free DOX released was determined as afunction of time. At pH=7.4, they were stable under physiological conditions for over48h(<5%). At pH=5.0, DOX was rapidly released from the nanoparticles (>70%).Finally, An MTT assay showed none of the conjugates showed significantcytotoxicity against the cells;85%–90%cells remained viable after4h incubation.In the fourth chapter, a novel organic-inorganic hybrid polymer micelles basedon chitosan have been synthesized and demonstrated to be robust nanocarriers forintracellular controlled release drug delivery. The polymer micelles of carboxymethyl chitosan-grafted-p(ethylene glycol)-dodecylamine(CMC-g-PEG-DDA) were readily mineralized in the presence of calcium chloride(CaCl2) and disodium hydrogen phosphate (Na2HPO4). Mineralization reduced thepolymer micelles’ size from239nm to138nm and formed a multi-core structure. Themineralized polymer micelles (MPM) exhibited enhanced serum stability. The DOXrelease from the DOX-loaded mineralized polymer micelles (MPM@DOX) atphysiological pH was efficiently inhibited, whereas at an endosomal pH (pH5.0),DOX release was facilitated due to the rapid dissolution of the CaP. These resultsindicate that mineralized polymer micelles have potential as robust carriers that canrelease DOX at specific sites under mild acidic conditions, such as in the extracellularmatrix of tumor tissue and in intracellular compartments of the cell.In summary, in this paper, we prepared two pH-sensitive drug delivery system,which have a stable under physiological conditions, and release drug on the tumor site.These system can improve drug utilization, reduce the toxic side effects, so haveprospects in the field of cancer treatment.