Tumor-triggered transformation of chimeric peptide for dual-stage-amplified magnetic resonance imaging and precise photodynamic therapy

Recent progress in quantitative analysis of self-assembled peptides

Self-assembled peptides have been among the important biomaterials due to its excellent biocompatibility and diverse functions. Over the past decades, substantial progress and breakthroughs have been made in designing self-assembled peptides with multifaceted biomedical applications. The techniques for quantitative analysis, including imaging-based quantitative techniques, chromatographic technique and computational approach (molecular dynamics simulation), are becoming powerful tools for exploring the structure, properties, biomedical applications, and even supramolecular assembly processes of self-assembled peptides. However, a comprehensive review concerning these quantitative techniques remains scarce. In this review, recent progress in techniques for quantitative investigation of biostability, cellular uptake, biodistribution, self-assembly behaviors of self-assembled peptide etc., are summarized. Specific applications and roles of these techniques are highlighted in detail. Finally, challenges and outlook in this field are concluded. It is believed that this review will provide technical guidance for researchers in the field of peptide-based materials and pharmaceuticals, and facilitate related research for newcomers in this field.

A dual-targeted Gd-based contrast agent for magnetic resonance imaging in tumor diagnosis

Enhanced magnetic resonance imaging (MRI) has important clinical value in the diagnosis of tumors. Much effort has been made to improve the relaxivity and specificity of contrast agents (CAs) in tumor diagnosis over the past few decades. However, there is still a lack of CAs which not only enhance the signal intensity of tumors rather than surrounding tissues in MRI but also maintain a high signal intensity prolonged for a long time. Herein, we synthesized a dual-targeted CA, RGD-(DOTA-Gd)-TPP (RDP), in which RGD is used to target the αvβ3 integrin receptor overexpressed in tumor cells and TPP is used to bind to a mitochondrion further. The structure of RDP was characterized and its properties, such as relaxivity and biosafety, were measured and in vitro and in vivo MRI assays were carried out. It has been proven that RDP has higher relaxivity of aqueous solution than Magnevist used in clinics. Moreover, RDP achieved higher signal intensity and a longer signal duration in tumor imaging. Therefore, RDP can be applied as the potential dual-targeted MRI CA for clinical tumor diagnosis.

Enzyme-Directed and Organelle-Specific Sphere-to-Fiber Nanotransformation Enhances Photodynamic Therapy in Cancer Cells

Employing responsive nanoplatforms as carriers for photosensitizers represents an effective strategy to overcome the challenges associated with photodynamic therapy (PDT), including poor solubility, low bioavailability, and high systemic toxicity. Drawing inspiration from the morphology transitions in biological systems, a general approach to enhance PDT that utilizes enzyme-responsive nanoplatforms is developed. The transformation of phosphopeptide/photosensitizer co-assembled nanoparticles is first demonstrated into nanofibers when exposed to cytoplasmic enzyme alkaline phosphatase. This transition is primarily driven by alkaline phosphatase-induced changes of the nanoparticles in the hydrophilic and hydrophobic balance, and intermolecular electrostatic interactions within the nanoparticles. The resulting nanofibers exhibit improved ability of generating reactive oxygen species (ROS), intracellular accumulation, and retention in cancer cells. Furthermore, the enzyme-responsive nanoplatform is expanded to selectively target mitochondria by mitochondria-specific enzyme sirtuin 5 (SIRT5). Under the catalysis of SIRT5, the succinylated peptide/photosensitizer co-assembled nanoparticles can be transformed into nanofibers specifically within the mitochondria. The resulting nanofibers exhibit excellent capability of modulating mitochondrial activity, enhanced ROS formation, and significant anticancer efficacy via PDT. Consequently, the enzyme-instructed in situ fibrillar transformation of peptide/photosensitizers co-assembled nanoparticles provides an efficient pathway to address the challenges associated with photosensitizers. It is envisaged that this approach will further expand the toolbox for enzyme-responsive biomaterials for cancer therapy.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Supramolecular self-assembled peptide-engineered nanofibers: A propitious proposition for cancer therapy

Cancer is a devastating disease that causes a substantial number of deaths worldwide. Current therapeutic interventions for cancer include chemotherapy, radiation therapy, or surgery. These conventional therapeutic approaches are associated with disadvantages such as multidrug resistance, destruction of healthy tissues, and tissue toxicity. Therefore, there is a paradigm shift in cancer management wherein nanomedicine-based novel therapeutic interventions are being explored to overcome the aforementioned disadvantages. Supramolecular self-assembled peptide nanofibers are emerging drug delivery vehicles that have gained much attention in cancer management owing to their biocompatibility, biodegradability, biomimetic property, stimuli-responsiveness, transformability, and inherent therapeutic property. Supramolecules form well-organized structures via non-covalent linkages, the intricate molecular arrangement helps to improve tissue permeation, pharmacokinetic profile and chemical stability of therapeutic agents while enabling targeted delivery and allowing efficient tumor imaging. In this review, we present fundamental aspects of peptide-based self-assembled nanofiber fabrication their applications in monotherapy/combinatorial chemo- and/or immuno-therapy to overcome multi-drug resistance. The role of self-assembled structures in targeted/stimuli-responsive (pH, enzyme and photo-responsive) drug delivery has been discussed along with the case studies. Further, recent advancements in peptide nanofibers in cancer diagnosis, imaging, gene therapy, and immune therapy along with regulatory obstacles towards clinical translation have been deliberated.

Research advances in peptide‒drug conjugates

Peptide‒drug conjugates (PDCs) are drug delivery systems consisting of a drug covalently coupled to a multifunctional peptide via a cleavable linker. As an emerging prodrug strategy, PDCs not only preserve the function and bioactivity of the peptides but also release the drugs responsively with the cleavable property of the linkers. Given the ability to significantly improve the circulation stability and targeting of drugs in vivo and reduce the toxic side effects of drugs, PDCs have already been extensively applied in drug delivery. Herein, we review the types and mechanisms of peptides, linkers and drugs used to construct PDCs, and summarize the clinical applications and challenges of PDC drugs.

Metal-Assembled Collagen Peptide Microflorettes as Magnetic Resonance Imaging Agents

Magnetic resonance imaging (MRI) is a medical imaging technique that provides detailed information on tissues and organs. However, the low sensitivity of the technique requires the use of contrast agents, usually ones that are based on the chelates of gadolinium ions. In an effort to improve MRI signal intensity, we developed two strategies whereby the ligand DOTA and Gd(III) ions are contained within Zn(II)-promoted collagen peptide (NCoH) supramolecular assemblies. The DOTA moiety was included in the assembly either via a collagen peptide sidechain (NHdota) or through metal–ligand interactions with a His-tagged DOTA conjugate (DOTA-His6). SEM verified that the morphology of the NCoH assembly was maintained in the presence of the DOTA-containing peptides (microflorettes), and EDX and ICP-MS confirmed that Gd(III) ions were incorporated within the microflorettes. The Gd(III)-loaded DOTA florettes demonstrated higher intensities for the T1-weighted MRI signal and higher longitudinal relaxivity (r1) values, as compared to the clinically used contrast agent Magnevist. Additionally, no appreciable cellular toxicity was observed with the collagen microflorettes loaded with Gd(III). Overall, two peptide-based materials were generated that have potential as MRI contrast agents.

Intracellular Enzyme-Instructed Self-Assembly of Peptides (IEISAP) for Biomedical Applications

Despite the remarkable significance and encouraging breakthroughs of intracellular enzyme-instructed self-assembly of peptides (IEISAP) in disease diagnosis and treatment, a comprehensive review that focuses on this topic is still desirable. In this article, we carefully review the advances in the applications of IEISAP, including the development of various bioimaging techniques, such as fluorescence imaging, photoacoustic imaging, magnetic resonance imaging, positron-emission tomography imaging, radiation imaging, and multimodal imaging, which are successfully leveraged in visualizing cancer tissues and cells, bacteria, and enzyme activity. We also summarize the utilization of IEISAP in disease treatments, including anticancer, antibacterial, and antiinflammation applications, among others. We present the design, action modes, structures, properties, functions, and performance of IEISAP materials, such as nanofibers, nanoparticles, nanoaggregates, and hydrogels. Finally, we conclude with an outlook towards future developments of IEISAP materials for biomedical applications. It is believed that this review may foster the future development of IEISAP with better performance in the biomedical field.

Enzyme-mediated intratumoral self-assembly of nanotheranostics for enhanced imaging and tumor therapy

Enzyme-mediated intratumoral self-assembled (EMISA) nanotheranostics represent a new class of smart agents for combined imaging and therapy of cancer. Cancer cells overexpress various enzymes that are essential for high metabolism, fast proliferation, and tissue invasion and metastasis. By conjugating small molecules that contain an enzyme-specific cleavage site to appropriate chemical linkers, it is possible to induce self-assembly of nanostructures in tumor cells having the target enzyme. This approach of injecting small theranostic molecules that eventually become larger nanotheranostics in situ avoids some of the major limitations that are encountered when injecting larger, pre-assembled nanotheranostics. The advantage of EMISA nanotheranostics include the avoidance of nonspecific uptake and rapid clearance by phagocytic cells, increased cellular accumulation, reduced drug efflux and prolonged cellular exposure time, all of which lead to an amplified imaging signal and therapeutic efficacy. We review here the different approaches that can be used for preparing EMISA-based organic, inorganic, or organic/inorganic hybrid nanotheranostics based on noncovalent interactions and/or covalent bonding. Imaging examples are shown for fluorescence imaging, nuclear imaging, photoacoustic imaging, Raman imaging, computed tomography imaging, bioluminescent imaging, and magnetic resonance imaging. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Biology-Inspired Nanomaterials > Peptide-Based Structures.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Engineered Exosomes-Based Photothermal Therapy with MRI/CT Imaging Guidance Enhances Anticancer Efficacy through Deep Tumor Nucleus Penetration

Exosomes, as natural nanovesicles, have become a spotlight in the field of cancer therapy due to their reduced immunogenicity and ability to overcome physiological barriers. However, the tumor targeting ability of exosomes needs to be improved before its actual application. Herein, a multiple targeted engineered exosomes nanoplatform was constructed through rare earth element Gd and Dy-doped and TAT peptide-modified carbon dots (CDs:Gd,Dy-TAT) encapsulated into RGD peptide engineered exosomes (Exo-RGD), which were used to enhance the effect of cancer imaging diagnosis and photothermal therapy. In vitro and in vivo experiments showed that the resulting CDs:Gd,Dy-TAT@Exo-RGD could effectively accumulate at cancer site with an increased concentration owing to the targeting peptides modification and exosomes encapsulation. The tumor therapy effects of mice treated with CDs:Gd,Dy-TAT@Exo-RGD were heightened compared with mice from the CDs:Gd,Dy control group. After intravenous injection of CDs:Gd,Dy-TAT@Exo-RGD into tumor-bearing mice, the temperature of tumors rose to above 50 °C under NIR irradiation and the localized hyperpyrexia induced by CDs could remarkably ablate tumors. The survival rate of the mice was 100% after 60 days. In addition, the CDs:Gd,Dy-TAT@Exo-RGD exhibited higher MRI/CT imaging contrast enhancement of tumor sites than that of CDs:Gd,Dy. Our study identified that engineered exosomes are a powerful tool for encapsulating multiple agents to enhance cancer theranostic efficiency and provide insight into precise personalized nanomedicine.

Self-assembly of peptide nanofibers for imaging applications

Pathological stimuli-responsive self-assembly of peptide nanofibers enables selective accumulation of imaging agent cargos in the stimuli-rich regions of interest. It provides enhanced imaging signals, biocompatibility, and tumor/disease accessibility and retention, thereby promoting smart, precise, and sensitive tumor/disease imaging both in vitro and in vivo. Considering the remarkable significance and recent encouraging breakthroughs of self-assembled peptide nanofibers in tumor/disease diagnosis, this reivew is herein proposed. We emphasize the recent advances particularly in the past three years, and provide an outlook in this field.

Supramolecular peptide nano-assemblies for cancer diagnosis and therapy: from molecular design to material synthesis and function-specific applications

Peptide molecule has high bioactivity, good biocompatibility, and excellent biodegradability. In addition, it has adjustable amino acid structure and sequence, which can be flexible designed and tailored to form supramolecular nano-assemblies with specific biomimicking, recognition, and targeting properties via molecular self-assembly. These unique properties of peptide nano-assemblies made it possible for utilizing them for biomedical and tissue engineering applications. In this review, we summarize recent progress on the motif design, self-assembly synthesis, and functional tailoring of peptide nano-assemblies for both cancer diagnosis and therapy. For this aim, firstly we demonstrate the methodologies on the synthesis of various functional pure and hybrid peptide nano-assemblies, by which the structural and functional tailoring of peptide nano-assemblies are introduced and discussed in detail. Secondly, we present the applications of peptide nano-assemblies for cancer diagnosis applications, including optical and magnetic imaging as well as biosensing of cancer cells. Thirdly, the design of peptide nano-assemblies for enzyme-mediated killing, chemo-therapy, photothermal therapy, and multi-therapy of cancer cells are introduced. Finally, the challenges and perspectives in this promising topic are discussed. This work will be useful for readers to understand the methodologies on peptide design and functional tailoring for highly effective, specific, and targeted diagnosis and therapy of cancers, and at the same time it will promote the development of cancer diagnosis and therapy by linking those knowledges in biological science, nanotechnology, biomedicine, tissue engineering, and analytical science.

A novel strategy for site selective spin-labeling to investigate bioactive entities by DNP and EPR spectroscopy

A novel specific spin-labeling strategy for bioactive molecules is presented for eptifibatide (integrilin) an antiplatelet aggregation inhibitor, which derives from the venom of certain rattlesnakes. By specifically labeling the disulfide bridge this molecule becomes accessible for analytical techniques such as Electron Paramagnetic Resonance (EPR) and solid state Dynamic Nuclear Polarization (DNP). The necessary spin-label was synthesized and inserted into the disulfide bridge of eptifibatide via reductive followed by insertion by a double Michael addition under physiological conditions. This procedure is universally applicable for disulfide containing biomolecules and is expected to preserve their tertiary structure with minimal change due to the small size of the label and restoring of the previous disulfide connection. HPLC and MS analysis show the successful introduction of the spin label and EPR spectroscopy confirms its activity. DNP-enhanced solid state NMR experiments show signal enhancement factors of up to 19 in ¹³C CP MAS experiments which corresponds to time saving factors of up to 361. This clearly shows the high potential of our new spin labeling strategy for the introduction of site selective radical spin labels into biomolecules and biosolids without compromising its conformational integrity for structural investigations employing solid-state DNP or advanced EPR techniques.

Intracellular Self-Assembly of Peptide Conjugates for Tumor Imaging and Therapy

Intracellular self-assembly (ISA) is a versatile and powerful strategy for in situ constructing sophisticated and functional supramolecular nanostructures, which has been widely applied in biomedicine and biomedical engineering. Among the common building blocks for ISA, peptides have attracted increasingly attention due to their intrinsic bioactivity, biocompatibility, and biodegradability. Particularly, by conjugating functional motifs (e.g., probes or drugs) to peptides to yield the peptide conjugates, the latter show enhanced stability and efficiency, and probably new functions. In recent years, employing ISA of peptide conjugates for tumor imaging and treatment has achieved great progresses. Therefore, the recent progress of ISA of peptide conjugates is summarized in this progress report. Moreover, several examples of ISA of peptide conjugates for other important imaging or therapeutic applications are also introduced. Finally, a brief perspective on remaining challenges and potential directions for future research in this area is presented.

Biomaterials based on noncovalent interactions of small molecules

Unlike conventional materials that covalent bonds connecting atoms as the major force to hold the materials together, supramolecular biomaterials rely on noncovalent intermolecular interactions to assemble. The reversibility and biocompatibility of supramolecular biomaterials render them with diverse range of functions and lead to rapid development in the past two decades. This review focuses on the noncovalent and enzymatic control of supramolecular biomaterials, with the introduction to various triggering mechanism to initiate self-assembly. Representative applications of supramolecular biomaterials are highlighted in four categories: tissue engineering, cancer therapy, drug delivery, and molecular imaging. By introducing various applications, we intend to show enzymatic control and noncovalent interactions as a powerful tool for achieving spatiotemporal control of biomaterials both invitro and in vivo for biomedicine.

Enzymatic Noncovalent Synthesis

Enzymatic reactions and noncovalent (i.e., supramolecular) interactions are two fundamental nongenetic attributes of life. Enzymatic noncovalent synthesis (ENS) refers to a process where enzymatic reactions control intermolecular noncovalent interactions for spatial organization of higher-order molecular assemblies that exhibit emergent properties and functions. Like enzymatic covalent synthesis (ECS), in which an enzyme catalyzes the formation of covalent bonds to generate individual molecules, ENS is a unifying theme for understanding the functions, morphologies, and locations of molecular ensembles in cellular environments. This review intends to provide a summary of the works of ENS within the past decade and emphasize ENS for functions. After comparing ECS and ENS, we describe a few representative examples where nature uses ENS, as a rule of life, to create the ensembles of biomacromolecules for emergent properties/functions in a myriad of cellular processes. Then, we focus on ENS of man-made (synthetic) molecules in cell-free conditions, classified by the types of enzymes. After that, we introduce the exploration of ENS of man-made molecules in the context of cells by discussing intercellular, peri/intracellular, and subcellular ENS for cell morphogenesis, molecular imaging, cancer therapy, and other applications. Finally, we provide a perspective on the promises of ENS for developing molecular assemblies/processes for functions. This review aims to be an updated introduction for researchers who are interested in exploring noncovalent synthesis for developing molecular science and technologies to address societal needs.

Peptide-Based Nanoassemblies in Gene Therapy and Diagnosis: Paving the Way for Clinical Application

Nanotechnology approaches play an important role in developing novel and efficient carriers for biomedical applications. Peptides are particularly appealing to generate such nanocarriers because they can be rationally designed to serve as building blocks for self-assembling nanoscale structures with great potential as therapeutic or diagnostic delivery vehicles. In this review, we describe peptide-based nanoassemblies and highlight features that make them particularly attractive for the delivery of nucleic acids to host cells or improve the specificity and sensitivity of probes in diagnostic imaging. We outline the current state in the design of peptides and peptide-conjugates and the paradigms of their self-assembly into well-defined nanostructures, as well as the co-assembly of nucleic acids to form less structured nanoparticles. Various recent examples of engineered peptides and peptide-conjugates promoting self-assembly and providing the structures with wanted functionalities are presented. The advantages of peptides are not only their biocompatibility and biodegradability, but the possibility of sheer limitless combinations and modifications of amino acid residues to induce the assembly of modular, multiplexed delivery systems. Moreover, functions that nature encoded in peptides, such as their ability to target molecular recognition sites, can be emulated repeatedly in nanoassemblies. Finally, we present recent examples where self-assembled peptide-based assemblies with "smart" activity are used in vivo. Gene delivery and diagnostic imaging in mouse tumor models exemplify the great potential of peptide nanoassemblies for future clinical applications.

Systematic overview of soft materials as a novel frontier for MRI contrast agents

Magnetic resonance imaging (MRI) is a well-known diagnostic technique used to obtain high quality images in a non-invasive manner. In order to increase the contrast between normal and pathological regions in the human body, positive (T1) or negative (T2) contrast agents (CAs) are commonly intravenously administered. The most efficient class of T1-CAs are based on kinetically stable and thermodynamically inert gadolinium complexes. In the last two decades many novel macro- and supramolecular CAs have been proposed. These approaches have been optimized to increase the performance of the CAs in terms of the relaxivity values and to reduce the administered dose, decreasing the toxicity and giving better safety and pharmacokinetic profiles. The improved performances may also allow further information to be gained on the pathological and physiological state of the human body. The goal of this review is to report a systematic overview of the nanostructurated CAs obtained and developed by manipulating soft materials at the nanometer scale. Specifically, our attention is centered on recent examples of fibers, hydrogels and nanogel formulations, that seem particularly promising for overcoming the problematic issues that have recently pushed the European Medicines Agency (EMA) to withdraw linear CAs from the market.

Gd(iii)-nanostructurated Constrast Agents (CAs) for Magnetic Resonance Imaging (MRI) can be designed and developed by manipulating soft material, including fibers, hydrogels and nanogels, in the nanometer scale.

In situ self-assembled biosupramolecular porphyrin nanofibers for enhancing photodynamic therapy in tumors

Due to the complicated environment and high tissue hydraulic pressure in tumors that easily pumps the nanomedicines back to the systemic circulation, the concentration of released photosensitizers (PSs) retained in a tumor by a traditional nano-delivery system is very low, causing an unsatisfactory photodynamic therapy (PDT) effect. Therefore, we prepared a pH/H₂O₂-responsive nano-system (ZnP-OC-M) through modified porphyrin PS units with a long-unsaturated oleoyl chloride chain, and by the further introduction of hydrophilic hydroxyl groups and MnO₂ through a cis-addition reaction between the unsaturated double bonds of oleoyl chloride and dilute KMnO₄ solution. Making use of the sensitivity of MnO₂ to the H₂O₂ in the acid environment of tumor cells, ZnP-OC-M selectively realized responsive disintegration and O₂ generation. More importantly, the rich amphiphilic PS units were shedded simultaneously and spontaneously completed the self-assembly into nanofibers in situ by helical stacking, which displayed a 1.85-fold higher retention effect of PSs in vivo compared with free PS groups and showed a great tumor inhibition effect in enhancing PDT. This nanosystem effectively solves the problem of the low retention abilities leading to a poor PS concentration in a tumor, prolonging the treatment time window efficiently after only a single administration and achieving the purpose of PDT enhancement.

Magnetic Nanoparticles as MRI Contrast Agents

Iron oxide nanoparticles (IONPs) have emerged as a promising alternative to conventional contrast agents (CAs) for magnetic resonance imaging (MRI). They have been extensively investigated as CAs due to their high biocompatibility and excellent magnetic properties. Furthermore, the ease of functionalization of their surfaces with different types of ligands (antibodies, peptides, sugars, etc.) opens up the possibility of carrying out molecular MRI. Thus, IONPs functionalized with epithelial growth factor receptor antibodies, short peptides, like RGD, or aptamers, among others, have been proposed for the diagnosis of various types of cancer, including breast, stomach, colon, kidney, liver or brain cancer. In addition to cancer diagnosis, different types of IONPs have been developed for other applications, such as the detection of brain inflammation or the early diagnosis of thrombosis. This review addresses key aspects in the development of IONPs for MRI applications, namely, synthesis of the inorganic core, functionalization processes to make IONPs biocompatible and also to target them to specific tissues or cells, and finally in vivo studies in animal models, with special emphasis on tumor models.

Self-Amplified Photodynamic Therapy through the 1 O2 -Mediated Internalization of Photosensitizers from a Ppa-Bearing Block Copolymer

Nanocarriers are employed to deliver photosensitizers for photodynamic therapy (PDT) through the enhanced penetration and retention effect, but disadvantages including the premature leakage and non-selective release of photosensitizers still exist. Herein, we report a 1 O2 -responsive block copolymer (POEGMA-b-P(MAA-co-VSPpaMA) to enhance PDT via the controllable release of photosensitizers. Once nanoparticles formed by the block copolymer have accumulated in a tumor and have been taken up by cancer cells, pyropheophorbide a (Ppa) could be controllably released by singlet oxygen (1 O2 ) generated by light irradiation, enhancing the photosensitization. This was demonstrated by confocal laser scanning microscopy and in vivo fluorescence imaging. The 1 O2 -responsiveness of POEGMA-b-P(MAA-co-VSPpaMA) block copolymer enabled the realization of self-amplified photodynamic therapy by the regulation of Ppa release using NIR illumination. This may provide a new insight into the design of precise PDT.

Tumor Microenvironment-Responsive Theranostic Nanoplatform for in Situ Self-Boosting Combined Phototherapy through Intracellular Reassembly

Through rational design, in vivo supramolecular construction of nanodrugs could precisely proceed in the lesion areas, which may apparently improve the theranostic performance of nanomaterials. Herein, a tumor microenvironment-responsive theranostic nanoplatform (Ce6-GA@MnO₂-HA-PEG) has been constructed to achieve in vivo supramolecular construction and enhance the therapeutic efficacy of combined phototherapy through intracellular reassembly. Under the tumor microenvironment, such nanoplatform could undergo the process of decomposition-reassembly and form in situ photothermal assemblies. The generation of assemblies would endow this nanoplatform with the capacity of photothermal therapy. Meanwhile, this nanoplatform could alleviate hypoxia and improve the therapeutic efficacy of photodynamic therapy. The results of in vitro and in vivo experiments reveal that tumors can be ablated efficiently by the designed nanoplatform under laser irradiation. In addition, fluorescence imaging and magnetic resonance imaging can be activated by the decomposition of MnO₂ to realize tumor imaging in vivo. Therefore, this multifunctional nanoplatform exhibits the capacity for boosting dual-modal imaging-guided combined phototherapy through intracellular reassembly, which may propose a new thought in cancer theranostics.

Tumor Microenvironment-Responsive Nanoshuttles with Sodium Citrate Modification for Hierarchical Targeting and Improved Tumor Theranostics

Enhancement of permeability and the retention effect is one of the main pathways for the accumulation of nanomaterials in tumor sites, but poor cellular internalization and rapid clearance of nanomaterials always hamper the efficacy of imaging diagnosis and treatment. With the consideration of both high tumor accumulation and cellular internalization, positively charged nanomaterials can adhere to the tumor cell membrane by an electrostatic force, which is conducive to cellular internalization, but they are easily recognized and cleared during blood circulation. However, negatively charged nanomaterials show an enhanced stealth-like effect and possess a long blood circulation time, which is conducive to tumor accumulation. Therefore, in this work, on the basis of the shielding effect of citrate ions to positive charge and the protonation under an acidic tumor microenvironment, pH-sensitive sodium citrate-modified polyaniline nanoshuttles (NSs) with negative charge during blood circulation but positive charge in tumor sites are designed. With this hierarchical targeting strategy, the blood circulation half-life increases from 4.35 to 7.33 h, and the retention rate of NSs in tumors increases from 5.29 to 8.57% ID/g. Because the retention rate of NSs is increased, the magnetic resonance imaging resolution and signal intensity are significantly improved. A synergistic treatment of tumors is further achieved by means of photothermal therapy with laser irradiation and chemotherapy via heat-stimulated drug release.

Au Hollow Nanorods-Chimeric Peptide Nanocarrier for NIR-II Photothermal Therapy and Real-time Apoptosis Imaging for Tumor Theranostics

The strategy that combines photodynamic therapy (PDT) and photothermal therapy (PTT) is widely used to achieve strong antitumor efficiency. Since light in the NIR-II window possesses ideal penetration ability, developing NIR-II PTT and NIR-II light triggered photosensitizer release for combined PDT and PTT is very promising in nanomedicine.

Methods: We develop a novel nanocarrier (termed AuHNRs-DTPP) by conjugating photosensitizer contained chimeric peptide (DTPP) to Au hollow nanorods (AuHNRs). AuHNRs was obtained by a Te-templated method with the assistance of L-cysteine. The chimeric peptide PpIX-PEG8-GGK(TPP)GRDEVDGC (DTPP) was obtained through a solid-phase peptide synthesis (SPPS) method.

Results: Under the 1064 nm laser irradiation, the nanocarrier can accumulate heat quickly for efficient PTT, and then release activated photosensitizer for real-time apoptosis imaging. Thereafter, supplementary PDT can be conducted to kill tumor cells survived from the PTT, and meanwhile the normal tissue can be protected from photo-toxicity.

Conclusion: This designed AuHNRs-DTPP nanocarrier with remarkable therapy effect, real-time apoptosis imaging ability and reduced skin damage is of great potential in nanomedicine application.

Reasonably retard O2 consumption through a photoactivity conversion nanocomposite for oxygenated photodynamic therapy

Photodynamic therapy (PDT) brings excellent treatment outcome while also causing poor tumor microenvironment and prognosis due to the uncontrolled oxygen consumption. To solve this issue, a novel PDT strategy, oxygenated PDT (maintain the tumor oxygenation before and after PDT) was carried out by a tumor and apoptosis responsive photoactivity conversion nanocomposite (MPPa-DP). Under physiological conditions, this nanocomposite has a low photoactivity. While at H₂O₂-rich tumor microenvironment, the nanocomposite could react with overexpressed H₂O₂ to produce O₂ and release high photoactivity chimeric peptide PPa-DP for oxygenated tumor and PDT. Importantly, when the PDT mediates cell apoptosis, the photoactivity of PPa-DP be effectively quenched and the O₂ consumption appeared retard, which avoided further consumption of residual O₂ on apoptotic cells. In vitro and vivo studies revealed that this nanocomposite could efficiently change photoactivity, reasonable control O₂ consumption and increase residual O₂ content of tumor after PDT.

Peptide-based building blocks as structural elements for supramolecular Gd-containing MRI contrast agents

Magnetic resonance imaging (MRI) is one of the most important clinic diagnostic tool used to obtain high-quality body images. The administration of low-molecular-weight Gd complex-based MRI contrast agents (CAs) permits to increase the ¹ H relaxation rate of nearby water molecules, thus modulating signal intensity and contrast enhancement. Even if highly accurate, MRI modality suffers from its low sensitivity. Moreover, low-molecular-weight CAs rapidly equilibrate between the intravascular and extravascular spaces after their administration. In order to improve their sensitivity and limit the extravasation phenomenon, several macromolecular and supramolecular multimeric gadolinium complexes (dendrimers, polymers, carbon nanostructures, micelles, and liposomes) have been designed until now. Because of their biocompatibility, low immunogenicity, low cost, and easy synthetic modification, peptides are attractive building blocks for the fabbrication of novel materials for biomedical applications. We report on the state of the art of supramolecular CAs obtained by self-assembly of three different classes of building blocks containing a peptide sequence, a gadolinium complex, and, if necessary, a third functional portion achieving the organization process.