Molecular Self-assembly And Disassembly Strategies Enabling Construction Of Multimodal Probes For In Vivo Imaging

Development of effective strategies that enables design of molecular imaging probes for high-sensitivity and high-resolution detection of biomarkers is indispensable for the biological research and clinical diagnosis of diseases.Molecular self-assembly and disassembly are ubiquitous in biology,playing essential roles in controlling mutual transformation between simple molecules and complex substances.Inspired by them,people have designed probes for bioapplications.With rationally designed molecular structures,biomolecule-mediated enhancement or attenuation of molecular interactions can be achieved,which can control transformation of probes between small molecules and nanostructures at the target tissues.Such an intelligent process leads to a switch in the imaging signals in the target tissues,allowing for the construction of biomolecule-activatable molecular imaging probes for in vivo imaging and disease detection.Though encouraging progresses have been made,molecular imaging via self-assembly and disassembly strategies still suffers form the following limitations:(1)self-assembled nanoprobes based polymers or inorganic nanomaterials generally have slow degradation and clearance rates,potentially causing long-term systemic toxicity;(2)current small-molecule-based self-assembling nanoprobes generally containsimple one imaging modality,incapable of in vivo imaging with high sensitivity and tissue penetration;(3)simultaneous introduction of multiple imaging groups and targeting groups into a small molecule probe would increase molecule weight,making it hard to synthesize and self-assembly.In this thesis,we focuse on the development of controllable self-assembly and disassembly strategies,allowing for the constuction of biomolecule responsive multimodal imaging probes for in vivo imaging analysis.On one hand,we develope co-assembly and disassembly strategy to build liver-targeted multimodal imaging probe for high-sensitivity and high spatial resolution imaging of acute hepatitis in vivo.On the other hand,we devcelope the in situ self-assembly strategy to design ALP-activateble multimodal imaging probes for in vivo imaging of tumor.The main contents include three parts:In the first part of the thesis,we develope the molecular co-assembly and disassembly strageties,successfully design a Fluorescence/MRI/19F-MRS trimodal nanoprobe(GdNPs-Gal)for rapid assessment of GSH loss in acute hepatitis.GdNPs-Gal is constructed by molecular co-assembly of a GSH-responsive Gd(?)-based MRI probe(1-Gd)and a liver-targeted probe(1-Gal),which initially shows high r1 relaxivity with low fluorescence and fluorine magnetic resonance spectroscopic(19F-MRS)signals.The introduce of ?-galactose(?-Gal)allows active delivery of the probes into liver tissues after system administration.Upon interaction with GSH,the disulfides in GdNPs-Gal can be cleaved to trigger disassembly of GdNPs-Gal,producing a substantial decline in r1 relaxivity with compensatory enhancements in fluorescence and 19F-MRS.By combining in vivo magnetic resonance imaging(1H-MRI)with ex vivo fluorescence imaging and 19F-MRS analysis,GdNPs-Gal efficiently detects hepatic GSH using three independent modalities.Using GdNPs-Gal,we noninvasively visualize LPS-induced liver inflammation and longitudinally monitor its remediation in mice after treatment with an anti-inflammatory drug,dexamethasone(DEX).In the second part of the thesis,we integrate the enzyme-mediated fluorogenic reaction and in-situ self-assembly strategies to construct a near-infrared(NIR)fluorescence and positron emission computed tomography(PET)bimodal probe(P-CyFF-68Ga)for in vivo bimodal imaging of malignant tumor with high sensitivity and high tissue penetration.As a small molecule,P-CyFF-68Ga easily acrosses blood vessels and diffuses into tumor tissues.After selectively recognized by the membrane-located ALP,P-CyFF-68Ga can be dephosphorylated and converted into fluorescent product,which subsequently self-assembles into fluorescent and radioactive nanoparticles(NPs).In situ assembled NPs are also prone to anchoring on the cell membrane,which facilitates the cellular uptake and localization in lysosomes through endocytosis.The increased molecular size and enhanced cellular uptake prolong the retention of NPs in tumor tissues,resulting in higher signal-to-background ratio.Strong NIR fluorescence and PET signal can be obtained in ALP over-expressed tumors,enabling noninvasive imaging of ALP activity in vivo.In the third part of the thesis,we rationally combine the enzyme-mediated fluorogenic reaction and in situ self-assembly strategies with fast bioorthogonal IEDDA reaction to design an activatable small-molecule probe(P-FFGd-TCO)for pretargeted multimodality imaging of ALP activity in vivo.P-FFGd-TCO,as a trans-cyclooctene(TCO)bearing fluorogenic and paramagnetic small-molecule probe,can be activated by ALP overexpressed on tumor cell membranes and then in situ self-assembles into fluorescent and magnetic nanoparticles(FMNPs-TCO).The on-site formed FMNPs-TCO helps to prolong retention near the ALP sites in tumor tissues,permitting to(1)amplify near-infrared(NIR)fluorescence(FL)and magnetic resonance imaging(MRI)signals,and(2)enrich TCOs to promote in vivo IEDDA ligation.Subsequent intravenous(i.v.)injection of a Gallium-68(68Ga)labeled tetrazine(Tz-68Ga)can readily conjugate the tumor-retained FMNPs-TCO to enhance radioactivity uptake in tumors via the fast IEDDA reaction.Hence,strong NIR FL,MRI and PET signals can be concomitantly achieved,allowing for pretargeted multimodality imaging of ALP activity in HeLa tumor-bearing mice with high-sensitivity and spatial-resolution.