Study On Fluorescent Molecules For Tumor Imaging And Treatment

In the contemporary world,cancer has become one of the most serious challenges to human health and life.Cancer cells grow and divide indefinitely,spreading throughout the body over time via the bloodstream or lymphatic system,which complicates treatment significantly.Therefore,early diagnosis and treatment of cancer can significantly reduce mortality rates.Among cancer diagnostic methods,tumour fluorescence imaging is non-invasive,as it does not require tissue sampling,thus greatly reducing patient harm.Clinical cancer treatments primarily include surgery,chemotherapy,radiotherapy,and photodynamic therapy.The integration of diagnostic and treatment methods has always been a focus of researchers and clinical practitioners.In this regard,fluorescent therapeutic probes with imaging and treatment capabilities have become indispensable tools in precision oncology.Currently,organic fluorescent therapeutic probes mainly consist of tumour microenvironment-responsive fluorescent prodrugs and phototherapy probes.Tumour microenvironment-responsive fluorescent prodrugs hold great clinical potential.These probes utilise tumour microenvironment stimuli to release chemotherapy drugs and fluorescent tags,enabling drug monitoring and tumour-specific imaging.Moreover,this strategy can effectively reduce damage to normal tissues caused by naked drugs.However,issues such as cellular drug resistance and inadequate drug accumulation in tumours may lead to suboptimal treatment outcomes.Additionally,current tumour microenvironment-responsive fluorescent probes are limited to closed-shell molecular systems.Therefore,designing new cancer diagnosis and treatment strategies and expanding the use of multifunctional organic luminescent radicals as tumour microenvironment-responsive fluorescent probes to address these issues is crucial.The combination of fluorescent molecules with photodynamic therapy（PDT）in phototherapy probes has attracted widespread attention among researchers.Photosensitizer（PS）molecules with fluorescent properties can generate reactive oxygen species（ROS）under specific light conditions,enabling tumour imaging and precise treatment.However,the photodynamic process of existing pure organic PSs relies heavily on the spin-forbidden triplet excited state and is significantly dependent on the oxygen concentration within cancer cells,limiting their effectiveness in hypoxic solid tumours.Recently,organic luminescent radicals with open-shell electronic structures have emerged in tumour imaging and PDT due to their unique characteristics of doublet emission and high photosensitivity.However,the limited variety of organic luminescent radicals,lack of specific recognition sites,issues like aggregation-caused quenching（ACQ）,and poor water solubility hinder their extensive application in tumour imaging and treatment.To address these challenges,this paper aims to achieve precise tumour imaging and treatment through the design of structurally simple fluorescent probes.Firstly,building on tumour microenvironment-responsive fluorescent prodrugs,a novel cancer diagnosis and treatment strategy is proposed.Molecular designs synthesised based on this strategy successfully circumvent issues such as restricted drug accumulation in tumours,adverse effects on normal cells,and drug resistance.Secondly,through rational molecular design,several new types of organic luminescent radicals are synthesised,expanding the repertoire of fluorescent probe materials with imaging and therapeutic functionalities,overcoming many limitations of organic luminescent radicals in biological applications.The main research content and achievements are outlined as follows:1.Following cellular carcinogenesis,significant changes occur in the intracellular microenvironment,such as a decrease in lysosomal pH from 4.5-6.0 to3.8-4.7.Therefore,we propose a novel cancer diagnosis and treatment strategy that involves activating a membranolytic blocks of fluorescent molecules at the low pH of cancer cell lysosomes.To achieve this,we successfully designed and synthesized a structurally simple fluorescent molecule called Lyso-Mito,which possesses structural inherent targeting and an ideal acid dissociation constant（p K_a=4.62）.Lyso-Mito targets cell lysosomes,facilitating drug accumulation.Moreover,Lyso-Mito undergoes protonation in the low pH environment of cancer cell lysosomes,accompanied by significant fluorescence changes that can accurately differentiate cancer cells.Protonated Lyso-Mito acts as a membranolytic molecule to disrupt cancer cell lysosomal membranes,releasing lysosomal enzymes and thereby causing mitochondrial damage,ultimately achieving selective cancer therapy.Furthermore,Lyso-Mito exhibits significant toxicity against drug-sensitive MCF-7 cells with a half-maximal inhibitory concentration(IC₅₀)of approximately15μg/m L,and it demonstrates excellent inhibitory effects against drug-resistant MCF-7/ADR cells(IC₅₀:50μg/m L).Thus,this strategy combining lysosomal acidity and membranolytic molecules offers a simple and effective approach,providing a more intelligent solution to overcome issues like drug efflux,adverse effects on normal cells,and drug resistance commonly encountered in traditional chemotherapy.2.To overcome the limitations of closed-shell molecular systems in tumour microenvironment-responsive fluorescent probes,we developed multifunctional organic luminescent radicals as tumour-specific imaging probes with optical,electrical,and magnetic properties.It is well-known that cysteine（Cys）is a typical tumour marker overexpressed in cancer.Therefore,we synthesized an organic luminescent radical,TTM^·-3NO2,which emits red light.By introducing a nitro group between the benzene rings of the radical molecule to increase the radical’s reactivity and serve as a Cys reduction site,TTM^·-3NO2 undergoes transformation from an open-shell to a closed-shell molecule upon reaction with Cys.This process results in the disappearance of specific optical and magnetic signals of TTM^·-3NO2and manifests changes in fluorescence,ultraviolet,and electron paramagnetic resonance（EPR）signals.TTM^·-3NO2 exhibits high sensitivity to Cys,with detection limits of 0.695μM（fluorescence）,0.013μM（UV）,and 7.808μM（EPR）.Subsequently,we dispersed TTM^·-3NO2 into its precursor HTTM-3NO₂ and encapsulated them into DSPE-PEG₂₀₀₀ to prepare nanoparticles（TTM^·-3NO2@NPs）,addressing the issue of ACQ while improving water solubility for biological imaging.TTM^·-3NO2@NPs can sensitively and specifically detect endogenous and exogenous Cys within cancer cells,achieving specific imaging of tumour tissues.3.Building on the previous chapter’s method of addressing the water insolubility and reducing ACQ effects of organic luminescent radicals,we successfully prepared two types of nanoparticles emitting near-infrared light（TTM-3PDMAC:HTTM-3PDMAC@NPs and TTM-PDMAC:HTTM-PDMAC@NPs）with maximum emission wavelengths of 785 nm and 730 nm in water.These nanoparticles,with sizes of 169.92 nm and 135.17 nm respectively,accumulate at tumour sites due to enhanced permeability and retention effects,enabling precise targeted delivery of drugs to tumours.Additionally,both nanoparticles can generate ROS through Type-I photodynamic processes,overcoming the inefficiency of traditional photosensitizers in hypoxic solid tumours.Experimental results demonstrate that ROS production by these nanoparticles results from the combined action of radicals and their precursors.Subsequently,we applied TTM-3PDMAC:HTTM-3PDMAC@NPs to PDT in tumour-bearing mice.After15 days of treatment,significant tumour regression was observed with negligible systemic toxicity in mice.This study expands the material system of PSs and provides a unique approach for designing and developing Type-I PSs based on organic luminescent radicals.4.To obtain water-soluble organic luminescent radicals,we modified the triphenylmethyl radical（TTM）with pyridinium salts and successfully synthesized a completely water-soluble organic luminescent radical called TTM-2PyPh,with a dissolution rate of 0.7 m M at room temperature.TTM-2PyPh emits deep red light with a fluorescence peak at 670 nm and a quantum yield of 3%.In vitro photodynamic experiments and cytotoxicity studies demonstrate that TTM-2PyPh can produce ROS through Type-I/II PDT processes,exhibiting excellent anticancer effects in both normoxic and hypoxic cellular environments.Due to the typically higher mitochondrial membrane potential in cancer cells compared to normal cells,TTM-2PyPh specifically targets tumour cell mitochondria.Moreover,mitochondria are the primary site of aerobic respiration in cells,containing higher oxygen levels.The specific targeting of tumour mitochondria by TTM-2PyPh prevents drug efflux while achieving efficient PDT.Subsequently,we applied TTM-2PyPh to PDT in tumour-bearing mice,resulting in significant tumour regression after 15 days of treatment with negligible systemic toxicity.Therefore,TTM-2PyPh holds tremendous potential in fluorescence-guided precise cancer therapy,providing new insights into the development of water-soluble organic luminescent radicals.