Construction Of Liposome-based Activatable Near-infrared Fluorescent Probes And Their Application In Mouse Breast Cancer Imaging

Liposomes have excellent biocompatibility,which have been widely used in loading hydrophobic and hydrophilic drugs/dyes.Therefore,liposomes can be used as carriers for molecular imaging probes.Near-infrared fluorescent probes are playing an increasingly important role in tumor imaging due to high sensitivity,relatively high penetration depth and low autofluorescence interference.The application of liposome-based fluorescent probes in tumor imaging has become one of the research hotspots.However,most of the liposome-based fluorescent probes have high background signals during blood circulation,which results in low signal-to-background ratio(SBR)and low sensitivity in tumor imaging.Therefore,it is of great significance to develop liposome-based activatable fluorescent probes for high-sensitive tumor imaging.In this thesis,two activated fluorescence probes for high signal-to-background and high-sensitivity tumor imaging were constructed.Specifically,the following two projects were carried out in this thesis:(1)Construction of an activatable liposomal fluorescence probe based on fluorescence resonance energy transfer(FRET)and aggregation induced emission(AIE)and its application in tumor imaging In this part of the work,the hydrophobic AIE dye TPE-BIOH and the hydrophobic quencher BHQ were selected as FRET pairs,and the activatable liposomal fluorescence probe with FRET effect and AIE effect was constructed by loading TPE-BIOH and BHQ simultaneously into the lipid bilayer of liposomes.To optimize the molar ratio between TPE-BIOH and BHQ,TPE/BHQ-lipos with different TPE/BHQ ratio were prepared.At the same time,an always-on fluorescence probe TPE-lipo containing only TPE-BIOH was prepared as a control.According to the fluorescence spectra results,the FRET efficiency of optimized TPE/BHQ-lipo reached as high as 99%,and the fluorescence enhancement upon liposome rupture was up to 120-fold.Both TPE/BHQ-lipo and TPE-lipo were used to image 4T1 tumor-bearing mice and the results showed that the TPE/BHQ-lipo group showed a higher signal-to-noise ratio(4.1)at 24 h post injection,while the TPE-lipo group showed a lower signal-to-noise ratio(1.8).(2)Construction of an activatable liposomal fluorescence probe based on aggregation-caused quenching(ACQ)and its application in tumor imaging In this part of the work,an activatable liposomal fluorescence probe DiR-LP-C was constructed by loading hydrophobic near-infrared dye DiR into the hydrophilic interior through DMSO-assisted active loading method.At the same time,a control probe DiR-LP-B was prepared by loading DiR in the hydrophobic bilayer through passive loading.After comparision between the fluorescence spectra of DiR-LP-C and DiR-LP-B,it was found that DiR-LP-C showed higher self-quenching efficiency and higher fluorescence enhancement upon liposome rupture.For 4T1 cell uptake experiments,DiR-LP-C showed much faster and higher cellular uptake than DiR-LP-B.The two liposomal probes were then applied to 4T1 tumor-bearing mice,and the results showed that DiR-LP-B and DiR-LP-C have comparable fluorescence imaging capabilities in tumor imaging,with signal-to-background ratios of 5.3 and 5.2(48 h after injection).Further,photoacoustic imaging was performed on 4T1 tumorbearing mice,and the maximum photoacoustic imaging signal values of DiR-LP-C and DiR-LP-B were almost equivalent,but DiR-LP-C showed maximum tumor uptake at 1 h post injection(p.i.)while DiR-LP-B showed maximum tumor uptake at 2 h p.i.,which indicated that DiR-LP-C accumulated in tumor tissue faster than DiR-LP-B.In summary,to realize high-sensitive tumor imaging,two liposome-based activatable fluorescence probes were constructed through FRET effect,AIE effect,and ACQ effect,which improved the specificity and signal-to-noise ratio for 4T1 breast cancer fluorescence imaging.Our research offered new nano-probes with excellent biocompatability and high sensitivity for tumor fluorescence imaging.