Research And Evaluation Of Novel Nanomaterials For Diagnosis And Chemotherapy Of Tumor

Malignant tumor,i.e.cancer,is currently one of the major diseases,and needs to be conquered urgently.It is widely recognized that the conquering cancer,which is a highly comprehensive system,requires the integration of multi-disciplinary and the effort of trans-disciplinary research team.So far,surgery is the primary means to cancer therapy,but the efficiency is greatly inhibited on lack of early accurate diagnosis and inherent uncertainties of surgery.Furthermore,chemotherapy and radiotherapy as the essential supplementary means for surgical operation can still significantly enhance the therapeutic efficiency of cancer,and even decline health level and life quality of patients due to great side-effect.Therefore,the techniques with high sensitivity are urgently needed to achieve early accurate diagnosis of tumors.In this case,magnetic resonance imaging(MRI)is an acknowledged powerful tool for cancer diagnosis,and the development of novel high-efficiency Ti-weighted contrast agents has been become a hot spot of radiology and material science in order to improve contrast enhancement effect.On the other hand,in order to inhibit toxicity and side effects of chemotherapy drugs,many kinds of new drug delivery systems have been explored based on the integration of multi-disciplinary and recent progress including nano-biomedicine especially.Moreover,many targeting and intelligent drug-loaded systems,which are specific response to tumor microenvironment,have been developed.In this thesis,the T1-weighted positive contrast nanoparticles for MRI and drug-loaded nano-carriers for chemotherapy had been developed,and the main findings are detailedly depicted as follows:(1)For magnetic contrast nanoparticles of Ti-weighted MRI,such as Gd2O3 and MnO nanoparticles,the ultrasmall size was controlled to achieve a high longitudinal relaxivity(r1)while surface modification strategy was also applied to contribute functionality and targeting potential toward tumor tissue,enhance in vivo stability,and other key issues.Based on the chelation between catechol groups in dopaime and the surface of Gd203 nanoparticles,dopamine-modified Gd2O3 nanoparticles with an average size of ca.3.7 nm has been achieved,and the longitudinal relaxivity(r1)was determined as 2.11 mM-1·s-1.Obviously,such surface modification introduced amino groups,which facilitated the attachment to cell membrane and provided the active sites of further derivatization to enhance functionality.Moreover,for the other kind of potential positive contrast agent,i.e.the MnO nanoparticles with an average size of ca.5nm,facile surface PEGylation has been carried out via the chelation mechanism between catechol group and transition metal to improve in vivo stability and biocompatibility of hydrophobic MnO nanoparticles.The key issue of this research was to realize the "trade-off" between high longitudinal relaxivity(r1)and good physiological stability because the surface PEG segment might inhibit the intimate contact between the protons in water molecules and the Mn on nanoparticle surface,and hence resulted in the decrease of longitudinal relaxivity.By changing the feeding ratio of MnO nanoparticles and dopa-terminated PEG monomethyl ether(mPEG),the in vivo stability and longitudinal relaxivity were optimized.Interestedly,surface PEGylation toward ultrasmall MnO nanoparticles produced the new nano-objects with an average size of ca.120 nm,which showed a passive targeting potential to tumor tissue.Furthermore,long in vivo circulation ability was verified while in vitro cell viability assay proved acceptable toxicity of PEGylated MnO nanoparticles against A549 cells for MRI application.In vivo MRI revealed that the PEGylated MnO nanoparticles could effectively enhance the signal intensity of liver and kidney.Based on the advantages of surface PEG modification and the stable conjugation of catechol-metal chelation,an as-synthesized graft copolymer containing the main chain of poly(aspartic acid)and many kinds of grafted moieties including dopa and mPEG and 6-maleimidocaproic acid was used to modify the MnO nanoparticles with a ultrasamll size of ca.5 nm,and hence conjugated with cRGD peptide to produce a novel T1-weighted MRI contrast agent of mPEG&cRGD-g-PAsp@MnO.The average size of as-fabricated positive contrast nano-agent was ca.100 nm and longitudinal relaxivity could reach 10.2 mM-1·S-1.For the mPEG&cRGD-g-PAsp@MnO,mPEG contributed high stability under storing and physiological conditions,and hence guaranteed long circulation time in vivo.Furthermore,the biodistribution experiment proved the integrated active and passive targeting function to tumor tissue and even cells,which was ascribed to the regulation of proper nanoscale and the introduction of cRGD.In addition,in vivo MRI showed the best time of contrast enhancement was 30?120 min and could sustain to 300 min.(2)For two typical chemotherapy drugs of paclitaxel(PTX)and camptothecin(CPT),nano-carriers have been designed and developed to achieve expected targeting delivery and on-site release based on the characteristics of tumor microenvironment together with reducing side-effect.As a result,PTX was encapsulated by a disulfide-containing carrier with specific response to intracellular reduction condition while CPT as guest was included by P-cyclodextrin(P-CD)in polymeric carrier to enhance the water-solubility as well as the physiological stability of active lactone form in CPT.Firstly,polycaprolactone-grafted bis(acryloyl)cystamine-ethanolamine copolymer(PCA-g-PCL)was synthesized,and then conjugated with carboxyl-terminated mPEGr(mPEG-COOH)via electrostatic interaction between N-H group in PCA-g-PCL and COOH group in mPEG-COOH to improve the stability of the assembled micelles in aqueous media.Such assembled micelles showed a spherical structure with an average size of ca.100 nm,suggesting a passive targeting potential to tumor tissue.Since the polymer precursor contained disulfide bonds,the assembled micelles inherited the response to intracellular high-concentration reduction condition.Moreover,the PTX-loaded micelles withe high encapsulation efficiency showed a predominant reduction-response release profiles.In the simulated intracellular condition containing 40 mM DTT,PTX could quickly and fully release from the micellar carrier within 9 h.Meanwhile,the leakage ratio of PTX was controlled below 30%in the simulated normal physiological condition in vivo.On the other hand,the amino-functionalized ?-CD was used to open the ring of poly(L-succinimide)(PSI)to produce a carrier precursor of ?-CD grafted ?,?-poly(aspartic acid)(?-CD-graft-PAsp).Thereafter,the ?-CD-graft-PAsp self-assembled as hollow nano-spheres with an apparent size of 20 nm and an internal hole of ca.17 nm.Moreover,the wall thickness was determined as ca.1.5 nm,which is well consistent with the size of two ?-CD molecules.It indicated that the surface of assembled hollow spheres was covered by ?-CD cavity.Obviously,the loading of CPT by the assembled hollow spheres significantly improves the stability of CPT in aqueous media and its lactone ring form under physiological condition.The in vitro cell assay showed almost no toxicity against L929 cells while the drug release experiment proved the sustained release profile of CPT from the assembled hollow spheres.Through the above research,the innovative points can be depicted as follows:? For the T1-weighted MRI application,novel positive contrast nano-agents have been developed,and,moreover,the surface modification strategy has been applied to regulate the functionality,to improve the stability in aqueous media,and to integrate active and passive targeting functions to tumor;? The nano-encapsulation strategy has been used to develop high-efficiency and low-toxic drug delivery systems for typical chemotherapy drugs,and the reduction-response property and the host-guest inclusion have been introduced to achieve the controlled intracellular release and sustaining release of anti-cancer drugs,to improve the stability and solubility of hydrophobic drugs in aqueous physiological media,and to contribute passive targeting potential to tumor.Consequently,based on the combination between medicine and material science,this thesis aims to the major challenge of clinic cancer treatment including early diagnosis and high-efficiency chemotherapy,and hence new T1-weighted contrast nano-agents and drug delivery nano-carriers with a great application potential have been developed and evaluated,which provides an essential scientific basis for the further profound study.