The Researches Of Functionalized Aptamers For Precise Tumor Identification And Targeted Therapy

As one of the important tools for precise targeting of diseases,aptamers have attracted more and more attention.Aptamers are a special class of functional nucleic acids that can recognize and bind targets with high specificity and affinity by folding into a unique tertiary structure,also known as "chemists’ antibodies".Compared with antibodies,aptamers have unique advantages,such as smaller size,lower cost,better synthesis reproducibility,easy modification and transformation,etc.,which make aptamers a better choice for the application of precision medicine in tumor.However,the nature of aptamers is oligonucleotide,which leads to the problems of weak blood circulation stability and rapid clearance in vivo.Therefore,how to functionalize the aptamers and provide effective universal solutions for the practical problems in the field of biomedical research is the starting point and foothold of this paper.In view of the current key and difficult problems faced by aptamers and their practical applications in the field of biomedicine,this paper designed a series of functional aptamer platforms to achieve accurate recognition and tumor targeted therapy in vivo.The details are as follows:1)In Chapter 2,in view of the problems that common drug combination cancer treatment strategies cannot accurately adjust their drug load ratio,pharmacokinetics and biodistribution,we developed a circular bivalent aptamer-drug conjugates(cb-Ap DCs)platform with precisely adjustable drug ratio,by modular combination and aptamer-drug conjugates monomer design.The design of this platform not only enhances the biological stability of aptamers and the specific recognition ability for target cells,but also realizes the precise ratio modification of different chemotherapeutic drugs and the activation and release of drugs triggered by esterases in target cells.Through a systematic investigation of cell cytotoxicity,we demonstrated that the cb-Ap DCs platform can achieve better synergistic growth inhibition of cancer cells after delivering a certain ratio of drugs to cells.The research content in this chapter is expected to provide technical support for the development of novel drug combination cancer treatment platforms.2)In Chapter 3,we designed a "photochemical crosslink locked"(PCCL)strategy to address the problems of the attenuation of biological binding affinity and the sensitivity of exonuclease in complex biological environment caused by the flexible conformation of aptamers.In this strategy,the small molecule compound8-methoxypsoralen is used to achieve covalent crosslink of thymine nucleotides between the double strands of aptamer terminal DNA by UV irradiation,so as to form the conformation stable aptamer PCCL-Apt.By comparing with unlocked aptamers,we systematically investigated the thermodynamic parameters,binding affinity,adaptability to physiological environment,and resistance of PCCL-Apt to interferences such as exonuclease,flow shear stress,and non-target proteins.Furthermore,the half-life of blood circulation and the ability of accumulation and penetration in tumors were explored through tumor-bearing mouse models,which further clarified the conformation-performance relationship of aptamers.An in-depth analysis of the conformation-performance relationship of aptamers is expected to facilitate the design and preparation of advanced aptamer diagnostic reagents,opening new avenues for biosensing and biomedical fields.3)In Chapter 4,in view of the limited therapeutic effect of aptamer-drug conjugates in complex physiological environments caused by the properties of aptamers(including flexible conformation,etc.),the conformation-stable aptamer-drug conjugates(PCCL-Ap DCs)were constructed by virtue of the PCCL strategy to achieve precise tumor targeted therapy.Through live cells and tumor-bearing mouse model studies,we demonstrated that PCCL-Ap DCs could achieve more efficient tumor growth inhibition than unlocked Ap DCs,and this strategy did not cause systemic toxicity.The research content of this chapter not only further explores the conformation-performance relationship of aptamers,but also opens up a road for conformation stable aptamers in the field of precision medicine,and is expected to solve the practical problems of aptamers chemistry in this field and promote its clinical application.4)In Chapter 5,we developed a flexible aptamer polymer coating bioorthogonal nanoreactor to address the difficulties in designing bioorthogonal reaction-activated prodrugs and their low efficiency of delivery and activation in vivo,by virtue of nanoconfined bioorthogonal cleavage reactions to improve the collision probability of bioorthogonal prodrug-activator.This nanoreactor further overcame the spatiotemporal dislocation of prodrug-activator in vivo caused by traditional pretargeted strategies.We designed a novel click-activated prodrug CA4 V,a flexible aptamer polymer poly XQ-2d,and the corresponding nanoreactor CA4V/ZIF-90@Tz COF@Apt to achieve efficient tumor target recognition and cellular internalization,controlled collapse of the partition layer ZIF-90,and excellent cytotoxicity.We also demonstrated the in vivo tumor suppressive effect of CA4V/ZIF-90@Tz COF@Apt through a tumor-bearing mouse model.The design of this nanoreactor can be extended to most click-activated prodrug systems,especially those containing two highly active species that require simultaneous delivery.The research content in this chapter not only provides an efficient approach to improve the therapeutic efficiency of bbioorthogonal cleavage reaction-activated prodrugs,but also opens a new avenue for designing activatable delivery and therapeutic strategies for precision cancer therapy.