Polypeptide And Anti-cancer Drug Active Targeting Delivery System

Until now, chemotherapeutics is still the most efficiency method to treat cancer. Manytherapeutic anticancer drugs, while pharmacologically effective in cancer treatment, arelimited in their clinical applications due to their serious toxicities and multi-drug resistance(MDR) of tumors. Gene therapy is a kind of new way, but the committed step is how toefficiently deliver the gene to tumor cells. Herein, based on the theories of the chemicalproduct engineering and drug delivery system, a series of delivery vectors were designed anddeveloped as the targeted delivery systems according to the properties of the drug/gene.With regard to the properties of the anti-cancer drug and the weakly aicidic conditionsaround the tumor cells, the hydrophobic DOX was selected as the model drug in order todevelop novel targeted drug deliverers.1) a series of newly amphiphilic copolymers withrandom hydrophobic/pH-sensitive structure of poly(ethylene glycol) methyl ether-b-(polylactic acid-co-poly(β-amino esters))(MPEG-b-(PLA-co-PAE)) containing different segmentratios were designed and synthesized by Michael-type step polymerization. They couldself-assemble polymeric micelle in the aqueous solution. The core of the micelle wascomposed of the PLA segment, which could offer the space for the drug and diminish theinitial burst. PAE was a kind of poly alkali with pH-sensitivity, showing hydrophobic in theneutral or alkaline conditions for carrying drug. When the pH value was acidic circumstance,PAE segment was transformed to hydrophilic because of the protonation of the amino groups,leading to accelerated drug release rate from the micelle. MPEG was used as the outer shellon the surface of the micelle to protect the drug-loaded system.2) According to the systemabove and the previous work in our team, a novel triblock amphiphilic copolymers with threelayered structure by conjugated hydrophilic and hydrophobic segments on the sides ofpolypeptides, resulting in poly(ethylene glycol) methyl ether-b-polypeptides-b-cholesterol(mPEG-b-polypeptides-b-Chol), were designed and synthesized. During the process ofcopolymer self-assembled into polymeric micelles, the cholesterol with higherbiocompatibility was selected as the micellar core for loading drugs. The polypeptides withthree different topological structures (linear, Y-shape and fork-shape) containing same numberof histidines constructed the middle layer which was pH-sensitivity. MPEG segment was alsoused as the micellar shell to prevent aggregation of the durg-loaded systems. This kind oftriblock copolymer with high efficacy of the loading drug and well controlled release behaviorcould reduce the side-effects, enhance the bioavailability of the drug and remit the multi-drugresistance of the tumors. Based on the above systems, DOX-loaded micelles were developed by dialysis method. Many physicochemical properties of the micelles, such as particle size,zeta-potential, pH-sensitivity, morphology and criticle micelle concentration, were measuredby a variety of experimental techniques. The release mechanism was evaluated by themathematic model, and the relationship of the structure-property was also discussedpreliminary. The cytotoxicity of the polymers and the drug-loaded micelles were determinedby MTT assay.Gene therapy showed many advantages such as high efficacy, safety and well targeting.In this study, a series of amphiphilic copolymers with different topological structures (2-arm,3-arm and4-arm) were designed and synthesized by conjugating shielding PEG and targetingfolate domains with the polypeptides via NCL reaction.2-arm and4-arm polypeptides werecomposed of Stp and Sph, respectively.3-arm polypeptides were constructed by Stp or Sphbuilding block. Trityrosines were introduced in the different sites in the2-arm and3-armpolypeptides. Histidines were added in the every arm in the4-arm polypeptides. The polymerscould bind the gene via electrostatic interaction. The particle size and zeta potential ofgene/polymer polyplexes were evaluated by the DLS. The cellular internalization and thestability of the polyplexes were also measured under different conditions. The folatereceptor-targeted DNA and RNA transfection against KB cells were tested. The influences ofthe different building cationic blocks and trityrosines or histidines on the different sites werediscussed. All the results displayed that the polymers could deliver DNA and RNA efficiently,but the2-arm could be not available for the RNA targeted delivery. Therefore,2-armpolypeptides were modified by the C-R-C moieties on the terminus with the purpose ofenhanced gene binding capacity by the disulfide bond. The polypeptides were also conjugatedwith shielding PEG and targeting folate by NCL reaction. Comapred to the unmodified2-armpolymers, the RNA binding capacity of modifications was markedly enhanced and theaverage hydrodynamic size was obviously decreased. The results of the gene transfections andthe MTT assay demonstrated that the C-R-C moieties modified polymers were much usefulfor the RNA targeted delivery.In this work, a series of polymers designed and synthesized according to the propertiesof the drugs and requirements of controlled release and targeting delivery were used as theanticancer drug delivery carriers, which have potential applications in cancer drug targeteddelivery. The work provided new technique and method for designing and synthesizing thenovel targeted drug delivery system in the multiaspects and multiangles, combining with themethods and theories of chemical product engineering.