Construction Of A Size Switchable Drug Delivery System Response To The Enzyme Of Tumor

Chemotherapy is one of the most important means of cancer treatment.However,because of lacking of selectivity,chemotherapeutic drugs not only kill tumor cells,but also kill normal cells.Nanodrug delivery system can increase the accumulation of drugs in the tumor site,reduce the dosage and avoid the toxic side effects of drugs on normal tissues.Present studies have shown that the drug delivery targeted to tumors is a complex fivestep cascade process in vivo,which includes circulation in the blood compartments,accumulation in the tumor sites,penetration into the tumor tissue,internalization into tumor cells and intracellular drug release.Because of the existence of biological barriers of tumors,most of the nanodrug delivery systems are difficult to penetrate into deep tumor tissues effectively,leading to the inadequate drug delivery,which not only weaken the therapeutic effects of drugs greatly,but also cause tumor cells with insufficient drugs uptake to develop resistance,eventually leading to the failure of treatment.Recent studies have shown that the large-sized nanoparticles(100 nm<n<300 nm)have a long systemic circulation time,but the weak permeability of them prevent them from penetrating deep into the tumor tissues to exert efficacy.In contrast,small-sized nanoparticles(n<50 nm)have strong permeability to tumor tissues.However,they have a short circulation time in the blood and are easy to be cleared by bodies.The realization of the characteristics of long circulation and high permeability at the same time is one of the bottlenecs in the application of nanodrugs in vivo and the key to improve the antitumor effects of nanodrug delivery systems.It’s also a higher challenge to the construction of nanocarriers.To solve the bottleneck problems of tumor targeted delivery of nanodrug delivery systems,the size switchable "ball-and-rod" nanodrug delivery system was designed to realize the long circulation of drugs in vivo and the high permeability to tumor tissues.The small-sized "spherical" carriers(MSNs)were connected by the "rod-like" connection medium(star PEG)to assemble into the "ball-and-rod" carriers,MSNs-pp-PEG,which has a larger particle size under physiological conditions and could maintain long circulation in vivo to increase the opportunities of reaching to tumor tissues through the EPR effect.In the tumor tissues,particle size conversion was completed by enzymatic reaction,and the released nanocarriers with smaller sizes could penetrate into the tumor tissues effectively and exert the antitumor efficiency on the deep tumor site.The contents of this experiment were as follows:The first part is the preparation and characterization of MSNs-pp-PEG.The tetraethyl orthosilicate was used as a silicon source and the emulsion polymerization method was used to prepare mesoporous silica nanoparticles(MSNs)with uniform particle size and good dispersion.The particle size of MSNs was 39.8±2.8 nm and the transmission electron microscopy was used to characterize the particle size and microstructure of MSNs.The matrix metalloproteinase sensitive peptides(pp)and star PEG were connected.The pp-PEG was obtained and verified by nuclear magnetism.The pp-PEG and MSNs were assembled into larger-sized MSNs-pp-PEG with particle size of 100.7±13.6 nm.The peptide bonds of pp were broken under the action of matrix metalloproteinase and the particle size of MSNspp-PEG decreased to 41.9±3.4 nm.The second part is in vitro drug release and biological performance evaluation of nanocarriers.The drug loading efficiency of MSNs and MSNs-pp-PEG was 19.78±1.09%and 17.42±0.36%respectively.Dynamic dialysis method was used to investigate the drug release in vitro,and the drug release behaviors of them were almost the same,indicating that the connection of PEG did not affect the release of drugs.Hemolysis test and cytotoxicity test of blank nanocarriers confirmed the biological safety of the carriers.Cytotoxicity test of DOX-loaded nanocarriers confirmed that the uptake of nanodrugs by cells was size-dependent,and smaller-sized nanocarriers were easier to be internalized into tumor cells.The tumor multicellular spheres were cultured using agar-liquid cover method.The permeability experiment confirmed that after the action of MMP-2,the large-sized MSNs-pp-PEG showed similar permeability to the small-sized nanocarriers,which proved the occurrence of particle size conversion and the high permeability of small-sized nanocarriers after the particle size conversion.The third part is tumor growth inhibition experiment in vivo and permeability evaluation of nanocarriers.The distribution of Cy5.5-labled nanocarriers in tumors were assessed through in vivo imaging system,along with tumor slices were observed by confocal microscopy,to investigate the distribution of nanocarriers.Compared with the other control groups,MSNs-pp-PEG/Cy5.5 treatment group had the maximum accumulation at tumor sites,which indicated that the carriers with characters of long circulation and high permeability could achieve a good permeability and distribution in the tumor site.The in vivo antitumor effect of carriers was evaluated in the B16 tumor-bearing mice model.The tumor growth inhibition revealed that DOX treatment group had a weak antitumor effect with the tumor inhibition rate of 28.4%.The small-sized MSNs/DOX treatment group and invariable large-sized MSNs-PEG/DOX treatment group had a certain level of antitumor effect with the tumor inhibition rate of 50.1%and 42.6%respectively.MSNs-pp-PEG/DOX treatment group possessed a prominent antitumor effect with a pretty high tumor inhibition rate of 75.81%.Besides,survival analysis confirmed that MSNs-pp-PEG/DOX could prolong the survival times of tumor-bearing mice effectively.In conclusion,the "ball-and-rod" size switchable nanodrug delivery system,MSNspp-PEG,had a good tumor microenvironment responsiveness and increased the drug penetration at the tumor sites significantly.The nanodrug delivery system had a prominent antitumor effect.The project has provided a new design idea for the construction of multifunctional size switchable drug delivery system.