| Liposomes assembled of phospholipids are regarded as the most important nano drug carriers till now.Nevertheless,the defects of traditional liposomes should not be neglected,such as poor sensitivity,inferior functionalization,and low drug loading capacity.Recently,the novel functionalized phospholipids and their assembled liposomes including phospholipid analogues and phospholipid conjugates arouse more and more interests of researchers gradually.These kinds of novel phospholipid materials could partly or even completely substitute the traditional phospholipids to prepare liposomes or liposome-like vesicae.Compared with the traditional liposomes,these novel liposomes or liposome-like vesicae demonstrate many superiorities,such as the high sensitivity towards specific environments,high drug loading capacity as well as considerable stability.This thesis focuses on a series of novel functionalized phospholipids and their assemblies,then explores the application potential in the field of related diseases.The main contents are as follows:(1)A series of novel oxidation sensitive phosphatidylcholines(S-PC)were synthesized,which had thioether-contained structures substituted in both sn-1 and sn-2 positions.S-PC with different hydrophobic chain lengths were named as S14-PC,S16-PC and S18-PC.The critical micelle concentration(CMC)and calculated distribution coefficient(c Log P)were decreased with the increasing of chain length,and the tendency phase transition temperature(T_m)and theoretical solubility(Log S)was opposite.S-PC could be used to replace traditional phospholipids to prepare oxidation sensitive liposomes(S-LP).S-LP with different chain lengths showed similar average sizes(?120 nm)and zeta potentials(?-18 m V).Doxorubicin(DOX)could be encapsulated as a model drug into S-LP(DOX/S-LP)using ammonium sulfate gradient method.S-LP showed similar drug loading rates(8?9%)and encapsulation efficiencies(90?98%).Through the detection of the final oxidation products,the hydrophobic sulfur ether structures were confirmed to be transformed to hydrophilic sulfoxide structures.The detailed oxidation process could be observed by transmission electron microscope(TEM).The size distribution and turbidity also changed a lot.Besides,the release rate of DOX/S-LP was obviously accelerated in the oxidation environment.Under confocal laser scanning microscope,DOX/S-LP was observed to be uptaken by cancer cells via endocytosis pathway.Finally,the drug efficacy of DOX/S-LP was improved compared with traditional liposomes in both in vitro and in vivo evaluations.(2)A series of novel reduction sensitive phosphatidylcholines(SS-PC)were synthesized,which had disulfide bond-contained structures substituted in both sn-1 and sn-2positions.SS-PC with different hydrophobic chain lengths were named as SS13-PC,SS15-PC,SS17-PC,SS19-PC and SS21-PC.The critical micelle concentration(CMC)and calculated distribution coefficient(c Log P)were decreased with the increasing of chain length,and the tendency phase transition temperature(T_m)and theoretical solubility(Log S)was opposite.SS-PC could be used to replace traditional phospholipids to prepare reduction sensitive liposomes(SS-LP).The SS-LP with longer chain length showed smaller size(100?140 nm),but the zeta potentials(?-10 m V)had no relationship with the chain length.Doxorubicin(DOX)could be encapsulated as a model drug into SS-LP(DOX/SS-LP)using ammonium sulfate gradient method.SS-LP showed similar drug loading rates(?8%)and encapsulation efficiencies(90?95%).Through the detection of the final reduction products,the disulfide bonds were cleaved efficiently.The destroyed structure of SS-LP could be observed by transmission electron microscope(TEM).Besides,the release rate of DOX/SS-LP was obviously accelerated in the reduction environment.Under confocal laser scanning microscope,DOX/SS-LP was observed to be uptaken by cancer cells via endocytosis pathway.Finally,the drug efficacy of DOX/SS-LP was improved compared with traditional liposomes in both in vitro and in vivo evaluations.(3)Paclitaxel(PTX)encapsulated reduction sensitive liposomes(PTX/SS-LP)were designed and prepared based on SS-PC.PTX/SS-LP prepared by reverse-phase evaporation method showed the size distribution of 108.6±2.4 nm and zeta potential of-37.9±0.6 m V,and the drug loading and encapsulation efficiency were 4.5±0.1%and 94.8±0.4%,respectively.Besides,PTX/SS-LP demonstrated great store stability as well as rapid reduction response.After 20 m M dithiothreitol(DTT)treatment for 2 hours,the morphology,size distribution and chemical structure showed significant changes,which were attributed to the complete destroy of PTX/SS-LP.The destroy of liposomes made the encapsulated PTX released effectively.PTX/SS-LP could be uptaken by cancer cells via endocytosis pathway.Compared with commercial PTX-loaded liposomes,PTX/SS-LP demonstrated high reduction sensitivity,which could benefit the targeting controlled release of cargos as well as in vivo safety.Through the in vitro and in vivo evaluations,the efficacy and safety of PTX/SS-LP were confirmed.(4)The assembly of artesunate-phospholipid conjugate(dAPC)with substitutions in both sn-1 and sn-2 positions was prepared,and its anti-malarial activity was researched as well.We especially focused on the efficacy against Kelch 13 mediated artemisinin resistant malaria as well as the mechanism.dAPC could be prepared into self-assembly liposomes by a direct-dissolve method,which showed similar structural features with the liposomes prepared by traditional thin film dispersion-homogenization method.In the drug efficacy assay,dAPC assembly showed considerable anti-malarial activity against artemisinin-resistant parasites.The artemisinin-resistance mainly exists in the ring stage of life cycle.In this stage,dAPC assembly had significantly better efficacy than DHA after short-time drug pulse.Although dAPC shared the same anti-malaria mechanism with traditional artemisinin-based drugs,it demonstrated great stability and controlled release behavior,resulting the sustained potency while DHA inactivated rapidly.Besides,dAPC could solve the defect of short half-life of traditional artemisinins,which showed significantly extended circulation time in vivo.In conclusion,the oxidation and reduction sensitive phosphatidylcholines(S-PC and SS-PC)with substitutions in both sn-1 and sn-2 positions could be used to replace traditional phospholipids completely to prepare novel sensitive liposomes.The drug-loaded sensitive liposomes showed efficiently environment responsiveness.Both in vitro and in vivo evaluations demonstrated the improved efficacy compared with traditional liposomes.Besides,the similar synthetic method could be used to synthesize dAPC with artesunate substitutions in both sn-1and sn-2 positions.dAPC showed extremely high self-assembly ability and stability.It showed the great solubility and long half-life and much improved efficacy compared with the traditional artesunate injection.Therefore,dAPC as well as its self-assembly have great potential to replace traditional artesunate as an injection of medicine for severe malaria and artemisinin-resistant malaria. |
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