Construction Of Chimeric Peptide Nano-drug Delivery System And Its Application In Tumor Precise Therapy

Tumors are considered to be one of the most complex diseases in recent decades due to their extremely high mortality rate and elusive characteristics.To this end,scientists have made great efforts to understand the mechanism of cancer development and find effective treatment strategies.With the rapid development of modern molecular biology and in-depth study of tumor biology,many tumor-specific physiological characteristics and peptides with special bioactivities have been discovered.These bioactive peptides can bind to overexpressed antibodies in tumor tissues,respond to overexpressed enzymes in tumor tissues,also directly target tumor cell suborgans,and have the ability to respond to and regulate tumor progression at the molecular and cellular levels.Because traditional drugs have the characteristics of low targeting efficiency,high toxic and side effects,and difficulty in crossing complex physiological obstacles to reach the lesion site,they often cause undesirable treatment results and serious side effects.The functional molecules(chimeric peptides)formed by combining these active peptides may be effective in improving the selectivity of drugs and reducing the dosage of drugs.Based on the above contents,some new types of chimeric peptide nanoparticles with self-assembly properties were designed in this paper.Compared with traditional nanoparticles,these nanoparticles can reassemble in the tumor microenvironment,change the structure and physicochemical properties of drugs,generate new functions and new biological effects,providing some new ideas for tumor treatment and imaging.The contents are as follows:1.Tumor acidity-responsive assembled chimeric peptide for enhanced tumor internalization and photodynamic therapyThe geometry of nanoparticles plays an important role in the internalization of cells.However,there were few reports on improving drug selectivity through morphological changes.By modifying the 2,3-dimethylmaleic anhydride group(DMA)on the AEAEAKAKAEAEAKAK peptide sequence,we designed a chimeric peptide that could respond to tumor extracellular acidity and has a geometric shape change.The chimeric peptide molecule could self-assemble into spherical nanoparticles under normal physiological conditions.However,in the acidic microenvironment of the tumor,the negatively charged acid-sensitive DMA group on the chimeric peptide would separate.Subsequently,the AEAEAKAKAEAEAKAK peptide without DMA can be reassembled into rod-shaped nanoparticles through the phenomenon of ion complementation.In vitro and in vivo studies had shown that this acid-triggered geometric transformation could accelerate the uptake of chimeric peptides by tumor cells,increase the accumulation of chimeric peptides in tumor tissues,enhance photodynamic therapy and minimize side effects.These results indicated that the method of changing the geometric shape through responsive peptide assembly may provide a new idea for targeted drug delivery.2.Tumor-triggered assembled chimeric peptide for dual-stage amplified magnetic resonance imaging and precise photodynamic therapyTraditional Gd³⁺-based contrast agent protons usually have the problems of low relaxation efficiency,fast metabolic clearance,and poor sensitivity.The second part mainly designed a chimeric peptide that responds to matrix metalloproteinase-2(MMP-2).The chimeric peptide could self-assemble into spherical nanoparticles under physiological conditions,enhancing the r₁ value of the contrast agent to 28.17 m M^-1s^-1.However,once it reaches the tumor site,the over-expressed MMP-2 in the tumor area could specifically hydrolyze the chimeric peptides,drive the formation of?-sheets between the chimeric peptides,and realize the transition from sphere to fiber.This transformation enhanced the accumulation of chimeric peptides in tumor tissues and the relaxation rate of contrast agents,resulting in a significant increase in r₁ to 51.52m M^-1s^-1,realizing double-amplification tumor MRI and precise photodynamic therapy.The strategy of specifically improving tumor MRI through this assembly strategy triggered by the tumor microenvironment should be able to show great application potential in tumor-targeted imaging and phototherapy.3.Tumor/Caspase-3 dual-response Mn O₂-chimeric peptide nanocomposite for oxygenated photodynamic therapyPhotodynamic therapy(PDT)can convert oxygen into reactive oxygen species under light conditions to kill tumor cells.Therefore,a large amount of oxygen will be consumed during the treatment,leading to a harsh tumor hypoxic environment and aggravating the development of tumors.In this chapter,we construct a tumor/Caspase-3dual-responsive Mn O₂-chimeric peptide nanocomposite(MPPa-DP).This composite material can release chimeric peptides(PPa-DP)at the tumor site,and appear responsive self-assembly in apoptotic cells,changing the photoactivity of drug molecules,realizing a new PDT strategy-aerobic PDT(the tumor tissue is in aerobic state before and after PDT).Under physiological conditions,this nanocomposite material has lower photoactivity.In the H₂O₂ enriched tumor microenvironment,the nanocomposite can react with overexpressed H₂O₂ to generate O₂,and release the highly active chimeric peptide PPa-DP,which increases the oxygen content of the tumor and is beneficial to the PDT of the tumor.Importantly,when PDT mediates cell apoptosis,PPa-DP can be hydrolyzed by the apoptotic enzyme caspase-3,which induces molecular aggregation of chimeric peptides,reduces photoactivity and O₂ consumption,and avoids residual oxygen consumption in apoptosis cell.Immunofluorescence and immunohistochemistry experiments showed that the nanocomposite could effectively down-regulate the expression of hypoxia markers HIF-1?and VEGF,which provides a new way for alleviating the adverse side effects caused by photodynamic therapy.4.p H/Caspase-3 dual-response assembled peptides for nuclear magnetic evaluation of p H and therapeutic responseAccurate,high-penetration,non-invasive diagnosis and real-time treatment feedback for disease control are of great significance.In the fourth part,we constructed a p H/caspase-3 dual-response multifunctional nuclear magnetic probe(PDDP)for the evaluation of p H and therapeutic response based on the content of chapter 3.First,under normal physiological conditions(p H 7.4),the carboxyl group on the side group of the DEVD peptide sequence is negatively charged.The high hydrophilicity and charge repulsion of these carboxylate radicals would facilitate the PDDP self-assemble into a smaller nanoparticle.However,with the decrease of p H,the carboxylate anion would gradually protonate into a neutral,hydrophobic carboxylic acid.Enhanced hydrophobicity and reduced electrostatic repulsion will drive the PDDP to reassemble into a larger nanoparticle.Importantly,this assembly process can be correlated with relaxation value of PDDP and could be used for nuclear magnetic evaluation of p H.Secondly,the DEVD sequence in PDDP can also be specifically hydrolyzed by the apoptosis marker,Caspase-3,resulting in a more robust aggregation and higher relaxation rate,enabling nuclear magnetic evaluation of caspase-3 enzyme.In vitro results demonstated that PDDP could effectively respond to p H and caspase-3 enzymes,changing their nanostructure and relaxation rate,and should be used for the evaluation of p H and caspase-3.