Synthesis And Application Of Metal-free Organic Nanomaterials For Image-guided Cancer Therapy

The desire for metal-free all-organic-composed nanoparticles（NPs）of appreciable biocompatibility to simultaneously diagnose and treat cancer is undeniably interminable.Hittherto,the landscape of available magnetic resonance imaging（MRI）contrast agents（CAs）and photothermal agents is dominated by metal-based nanoparticles（NPs）with attendant in vivo negatives.These metal CAs are considered unsafe as they have been linked to incurable nephrogenic systemic fibrosis and other neurological disorders,leading to the discontinuation of a good number of such CAs.The metal-based photothermal agents for cancer photothermal therapy（PTT）have particularly been associated with potential long-term toxicity.On the other hand,the clinically approved indocyanine green（ICG）for fluorescence imaging signal enhancement exhibit fast photodegradation upon repeated photoirradiation,coupled with its aggregation tendency and non-specific binding to protein molecules in typical biological environment.With these in mind,this thesis investigates the use of metal-free all-organic NPs to solve these problems with emphasis on the considerable tissue tolerance of such NPs.Moreover,the challenges that are currently faced by researchers in ameliorating these properties are also highlighted along with possible solutions and perspectives.First,considering the afore-mentioned drawbacks of metal-based CAs for tumor MRI,this thesis reports a self-assembled metal-free CA which is based on an organic nitroxide radical（4-carboxy-TEMPO）compartmentalized in chitosan（CS）,a natural polymer with an outstanding biocompatibility and biodegradability track record,alongside folate targeting for in vivo tumor MRI.This also uncovers an entirely new application for CS-TEMPO,which has hitherto been used in macro-sizes as initiators for grafting CS to various polymers.Significantly,the folic acid（FA）-modified metal-free CA（CS-TEMPO-FA;average size～113 nm）exhibit no acute toxicity,desirable pharmacokinetic profile,improved stability in highly reducing environment,high nitroxide loading(molecular relaxivity～18.56 m M^-1s^-1),and effective tumor targeting,thus ameliorating the non-specific uptake of CAs by normal cells.Moreover,when injected into 4T1 tumor-bearing mice,the CS-TEMPO-FA nanoparticles demonstrate commensurate contrast enhancement of the tumor region up to 1 h post-injection,a contrast enhancement domain hitherto unattained by TEMPO-based CAs.This work not only opens new application possibilities for CS-TEMPO but also establishes CS-TEMPO-FA as a potential alternative to metal-based CAs as well as an active folate-targeted metal-free CA for long-term longitudinal tumor MRI which improves the otherwise short in vivo lifetimes of typical organic radicals-based CAs.Second,an all-organic-composed theranostic nanosystem with outstanding biocompatibility for fluorescence image-guided tumor photothermal therapy,and as a potential alternative to metal-based photothermal agents is developed in this thesis.This is rationally achieved by compartmentalizing the clinically approved indocyanine green（ICG）in a glycol chitosan（GC）-polypyrrole（PP）nanocarrier to form hybrid ICG@GC-PP NPs（～65 nm）.The compartmentalization strategy,alongside the high photothermal conversion ability of PP jointly enhanced the otherwise low photostability of free ICG caused by the common’bleaching effect’.Advantageously,the proposed nanotheranostic platform（ICG@GC-PP）is endowed with an impeccable in vivo performance by the well-known biocompatibility track records of its individual tri organo-components（GC,PP and ICG）.As a proof of concept,ICG@GC-PP NPs enabled a sufficiently prolonged tumor diagnosis by fluorescence imaging up to 20 h post-injection.Furthermore,owing to the complementary heating performances of PP and ICG,tumor-bearing mice treated with the hybrid ICG@GC-PP NPs and one-time NIR irradiation showed total tumor recovery within 14 d post-treatment.It is therefore expected that leveraging the underlying benefits of this study will help to guide the development of new all-organic biocompatible systems for safer tumor theranostics.Third,combining the efficacious in vivo MRI and tumor PTT achieved above with the metal-free CAs and all-organic-composed photothermal agents,respectively,a nanoprobe whose impressive biocompatibility is synergistically contributed by its tetra-organo-components,is developed as a viable alternative to metal-based probes for MRI-guided tumor-targeted PTT.This reasonably involves a GC-linked PP nano-scaffold that provides abundant primary and secondary amino groups for amidation with the carboxyl groups in a nitroxide radical（TEMPO）and FA,to obtain GC-PP@TEMPO-FA NPs.Advantageously,the appreciably-benign GC-PP@TEMPO-FA features the effective compartmentalization of highly loaded TEMPO radicals in GC-PP NPs,prolonged nitroxide-systemic circulation times,appreciable water dispersibility,unprecedented in vivo nitroxide-reduction resistance,superlative biocompatibility,and ultimately achieves 17 hour commensurate MRI contrast enhancement;the first of its kind for nitroxide-based MRI CAs.Moreover,its GC component conveys plethora PP to tumor sites,where FA-mediated tumor targeting enables substantial NPs accumulation with consequential near-complete tumor regression within 16 days in an MRI-guided PTT.The present work therefore promotes the engineering of organic-based metal-free biocompatible NPs in synergism,in furtherance to tumor-targeted image-guided therapy.