ROS-responsive nanoparticles based on amphiphilic hyperbranched polyphosphoester for drug delivery: Light-triggered size-reducing and enhanced tumor penetration

Advanced Biomaterials Derived from Functional Polyphosphoesters: Synthesis, Properties, and Biomedical Applications

Polyphosphoesters (PPEs) represent an innovative class of biodegradable polymers, with the phosphate ester serving as the core repeating unit of their polymeric backbone. Recently, biomaterials derived from functionalized PPEs have garnered significant interest in biomedical applications because of their commendable biocompatibility, biodegradability, and the capacity for functional modification. This review commences with a brief overview of synthesis methodologies and the distinctive properties of PPEs, including thermoresponsiveness, degradability, stealth effect, and biocompatibility. Subsequently, the review delves into the latest applications of PPEs-based nanocarriers for drug or gene delivery and PPEs-based polymeric prodrugs and scaffolds in the biomedical field, presenting several illustrative examples for each application. By encapsulating the advancements of recent years, this review aims to offer an enhanced understanding and serve as a reference for the synthesis and biomedical applications of functional PPEs.

Dual pH/redox-responsive size-switchable polymeric nano-carrier system for tumor microenvironment DTX release

Innovation chemotherapeutic nano drug delivery systems (NDDSs) with various pharmacological achievement have become one of the hopeful therapeutic strategies in cancer therapy. This study focused on low pH, and high levels of glutathione (GSH) as two prominent characteristics of the tumor microenvironment (TME) to design a novel TME-targeted pH/redox dual-responsive P (AMA-co-DMAEMA)-b-PCL-SS-PCL-b-P (AMA-co-DMAEMA) nanoparticles (NPs) for deep tumor penetration and targeted anti-tumor therapy. The positively charged NPs exhibit strong electrostatic interactions with negatively charged cell membranes, significantly enhancing cellular uptake. Moreover, these NPs possess the unique size-shrinkable property, transitioning from 98.24 ± 27.78 to 45.56 ± 20.62 nm within the TME. This remarkable size change fosters an impressive uptake of approximately 100% by MDA-MB-231 cells within just 30 min, thereby greatly improving drug delivery efficiency. This size switchability enables passive targeting through the enhanced permeability and retention (EPR) effect, facilitating deep penetration into tumors. The NPs also demonstrate improved pH/redox-triggered drug release (∼70% at 24 h) within the TME and exhibit no toxicity in cell viability test. The cell cycle results of treated cells with docetaxel (DTX)-loaded NPs revealed G2/M (84.6 ± 1.16%) arrest. The DTX-loaded NPs showed more apoptosis (62.6 ± 3.7%) than the free DTX (51.8 ± 3.2%) in treated cells. The western blot and RT-PCR assays revealed that apoptotic genes and proteins expression of treated cells were significantly upregulated with the DTX-loaded NPs vs. the free DTX (Pvalue<.001). In conclusion, these findings suggest that this novel-engineered NPs holds promise as a TME-targeted NDDS.

Biomaterials with cancer cell-specific cytotoxicity: challenges and perspectives

Significant advances have been made in materials for biomedical applications, including tissue engineering, bioimaging, cancer treatment, etc. In the past few decades, nanostructure-mediated therapeutic strategies have been developed to improve drug delivery, targeted therapy, and diagnosis, maximizing therapeutic effectiveness while reducing systemic toxicity and side effects by exploiting the complicated interactions between the materials and the cell and tissue microenvironments. This review briefly introduces the differences between the cells and tissues of tumour or normal cells. We summarize recent advances in tumour microenvironment-mediated therapeutic strategies using nanostructured materials. We then comprehensively discuss strategies for fabricating nanostructures with cancer cell-specific cytotoxicity by precisely controlling their composition, particle size, shape, structure, surface functionalization, and external energy stimulation. Finally, we present perspectives on the challenges and future opportunities of nanotechnology-based toxicity strategies in tumour therapy.

Fabrication of polymeric sorafenib coated chitosan and fucoidan nanoparticles: Investigation of anticancer activity and apoptosis in colorectal cancer cells

The most prevalent form of colon cancer also ranks high among cancer-related deaths globally. Traditional chemotherapy drugs do not provide sufficient therapeutic efficacy, and advanced colon cancer demonstrates considerable resistance to chemotherapy. As an oral kinase inhibitor, sorafenib (SOR) suppresses the growth of tumour cells, the formation of new blood vessels, and the death of cancer cells. Unfortunately, sorafenib's limited bioavailability, rapid metabolism, and poor solubility have severely limited its clinical use. We developed nanoparticles targeting P-selectin and SOR, with fucoidan (FU) as a ligand. The SOR-CS-FU-NPs were developed by coating polylactide-co-glycolide nanoparticles with chitosan and FU through electrostatic interaction. The SOR-CS-FU-NPs exhibited an average particle diameter of 209.98 ± 1.25 nm and a polydisperse index (PDI) of 0.229 ± 0.022. The SOR-CS-FU nanoparticles exhibited a continuous release pattern for up to 120 h. The SOR-CS-FU nanoparticles exhibited cytotoxicity 8 times greater than free SOR in HCT116 colorectal cancer cells. The cellular absorption of Rhodamine-CS-FU-NPs was three times more than that of free Rhodamine and 19 times greater than that of Rhodamine-CS-NPs. Enhanced reactive oxygen species (ROS) generation and mitochondrial membrane potential damage were also shown in SOR-CS-FU-NPs. An investigation of cell death found that SOR-CS-FU-NPs had an apoptosis index that was 7.5 times greater than free SOR. After that, the SOR-CS-FU-NPs demonstrated a more significant inhibition of cell migration, leading to a wound closure of about 5 %. No toxicity was shown in the non-cancer VERO cell line when exposed to the developed NPs. Taken together, these results provide strong evidence that biocompatible SOR-CS-FU-NPs fabricated effective carriers for the targeted delivery of dasatinib to colorectal cancer.

Fabrication of folic acid-modified bovine serum albumin cloaked dual-drug loaded hollow mesoporous silica nanoparticles for pH-responsive and targeted delivery of gastric cancer therapy

Combination therapy is a highly successful way to address the limitations of using a single treatment method and improve therapy's overall efficacy. In this study, we developed a unique hollow mesoporous silica nanoparticle (HMSN) coated with folic acid (FA)-modified bovine serum albumin (FA-BSA). This nanoparticle, referred to as HFB, was designed to target cancer cells and release dual therapeutic drugs, Indocyanine green (ICG) and Paclitaxel (PTX), in response to specific stimuli termed as HFB@IP. The BSA protein acts as a "gatekeeper" to prevent early drug releases and cargo leakage by detaching from BSA in reaction to GSH. The FA facilitates the targeted transport of the drug into cancer cells that express folate receptors (FR), enhancing the effectiveness of chemo-photodynamic treatment (PDT). The drug nanocarrier demonstrated in vitro pH/redox-triggered drug release from HFB@IP due to breaking the imine bonds between aldehyde-functionalized HMSN (CHO-HMSN) and FA-BSA with the disulfide bond inside BSA. In addition, various biological assessments, including cell uptake experiments, demonstrated that HFB@IP effectively targets SGC-7901 cells and induces apoptosis in vitro. Further, it exhibits remarkable efficiency in synergistically killing cancer cells through chemo-photodynamic therapy, as indicated by a combination index (CI) of 0.328. The results showed that combining HMSN with biodegradable stimuli-responsive BSA molecules could offer a promising approach for precise chemo-photodynamic therapy in treating gastric cancer, allowing for the controlled release of drugs as necessary.

Customizing biomimetic surface attributes of dendritic lipopeptide nanoplatforms for extended circulation

The pressing demand for innovative approaches to create delivery systems with heightened drug loading and prolonged circulation has spurred numerous efforts, yielding some successes but accompanied by constraints. Our study proposes employing dendritic lipopeptide with precisely balanced opposing charges to extend blood residency for biomimetic nanoplatforms. Neutrally mixed-charged zwitterionic nanoparticles (NNPs) achieved a notable 19 % simvastatin loading content and kept stable even after one-month storage at 4 °C. These nanoplatforms demonstrated low cytotoxicity in NIH-3T3 and L02 cells and negligible hemolysis (<5 %). NNPs inhibited protein adhesion (>95 %) from positively and negatively charged sources through surface hydration. In comparison to positively charged CNPs, NNPs demonstrated an 86 % decrease in phagocytic rate by BMDMs, highlighting their efficacy. Importantly, NNPs showed prolonged circulation compared to CNPs and free simvastatin. These findings highlight the potential of this biomimetic nanoplatform for future therapeutic applications with enhanced drug loading and circulation traits.

Enhancing drug penetration in solid tumors via nanomedicine: Evaluation models, strategies and perspectives

Effective tumor treatment depends on optimizing drug penetration and accumulation in tumor tissue while minimizing systemic toxicity. Nanomedicine has emerged as a key solution that addresses the rapid clearance of free drugs, but achieving deep drug penetration into solid tumors remains elusive. This review discusses various strategies to enhance drug penetration, including manipulation of the tumor microenvironment, exploitation of both external and internal stimuli, pioneering nanocarrier surface engineering, and development of innovative tactics for active tumor penetration. One outstanding strategy is organelle-affinitive transfer, which exploits the unique properties of specific tumor cell organelles and heralds a potentially transformative approach to active transcellular transfer for deep tumor penetration. Rigorous models are essential to evaluate the efficacy of these strategies. The patient-derived xenograft (PDX) model is gaining traction as a bridge between laboratory discovery and clinical application. However, the journey from bench to bedside for nanomedicines is fraught with challenges. Future efforts should prioritize deepening our understanding of nanoparticle-tumor interactions, re-evaluating the EPR effect, and exploring novel nanoparticle transport mechanisms.

Recent advances of polymeric nanoplatforms for cancer treatment: smart delivery systems (SDS), nanotheranostics and multidrug resistance (MDR) inhibition

Nanotheranostics is a promising field that combines the benefits of diagnostic and treatment into a single nano-platform that not only administers treatment but also allows for real-time monitoring of therapeutic response, decreasing the possibility of under/over-drug dosing. Furthermore, developing smart delivery systems (SDSs) for cancer theranostics that can take advantage of various tumour microenvironment (TME) conditions (such as deformed tumour vasculature, various over-expressed receptor proteins, reduced pH, oxidative stress, and resulting elevated glutathione levels) can aid in achieving improved pharmacokinetics, higher tumour accumulation, enhanced antitumour efficacy, and/or decreased side effects and multidrug resistance (MDR) inhibition. Polymeric nanoparticles (PNPs) are being widely investigated in this regard due to their unique features such as small size, passive/active targeting possibility, better pharmaceutical kinetics and biological distribution, decreased adverse reactions of the established drugs, inherent inhibitory properties to MDR efflux pump proteins, as well as the feasibility of delivering numerous therapeutic substances in just one design. Hence in this review, we have primarily discussed PNPs based targeted and/or controlled SDSs in which we have elaborated upon different TME mediated nanotheranostic platforms (NTPs) including active/passive/magnetic targeting platforms along with pH/ROS/redox-responsive platforms. Besides, we have elucidated different imaging guided cancer therapeutic platforms based on four major cancer imaging techniques i.e., fluorescence/photo-acoustic/radionuclide/magnetic resonance imaging, Furthermore, we have deliberated some of the most recently developed PNPs based multimodal NTPs (by combining two or more imaging or therapy techniques on a single nanoplatform) in cancer theranostics. Moreover, we have provided a brief update on PNPs based NTP which are recently developed to overcome MDR for effective cancer treatment. Additionally, we have briefly discussed about the tissue biodistribution/tumour targeting efficiency of these nanoplatforms along with recent preclinical/clinical studies. Finally, we have elaborated on various limitations associated with PNPs based nanoplatforms.

Hyperbranched Polymers: Recent Advances in Photodynamic Therapy against Cancer

Hyperbranched polymers are a class of three-dimensional dendritic polymers with highly branched architectures. Their unique structural features endow them with promising physical and chemical properties, such as abundant surface functional groups, intramolecular cavities, and low viscosity. Therefore, hyperbranched-polymer-constructed cargo delivery carriers have drawn increasing interest and are being utilized in many biomedical applications. When applied for photodynamic therapy, photosensitizers are encapsulated in or covalently incorporated into hyperbranched polymers to improve their solubility, stability, and targeting efficiency and promote the therapeutic efficacy. This review will focus on the state-of-the-art studies concerning recent progress in hyperbranched-polymer-fabricated phototherapeutic nanomaterials with emphases on the building-block structures, synthetic strategies, and their combination with the codelivered diagnostics and synergistic therapeutics. We expect to bring our demonstration to the field to increase the understanding of the structure-property relationships and promote the further development of advanced photodynamic-therapy nanosystems.

Synergistic chemo-photo anticancer therapy by using reversible Diels-Alder dynamic covalent bond mediated polyprodrug amphiphiles and immunoactivation investigation

Highly efficient endocytosis and multi-approach integrated therapeutic tactics are important factors in oncotherapy. With the aid of thermally reversible furan-maleimide dynamic covalent bonds and the "polyprodrug amphiphiles" concept, thermo- and reduction-responsive PEG(-COOH)Fu/MI(-SS-)CPT copolymers were fabricated by the Diels-Alder (D-A) coupling of hydrophilic Fu(-COOH)-PEG and hydrophobic MI(-SS-)-CPT building blocks. The copolymers could self-assemble to form composite nanoparticles with a photothermal conversion reagent (IR780) and maintain excellent stability. In the in vitro simulated environments, the composite nanoparticles could detach Fu(-COOH)-PEG chains by a retro-D-A reaction upon near-infrared light (NIR) irradiation and reduce the size to facilitate endocytosis. Once in the intracellular environment, glutathione (GSH) could trigger a cascade reaction to release active CPT drugs to achieve chemotherapy, which could be further promoted by NIR light induced photothermal therapy. The in vivo mouse tumor model experiments demonstrated that these nanoparticles had an excellent therapeutic effect on solid tumors and inhibited their recurrence. Not only that, the synergistic chemical and optical therapy induced body immune response was also systematically evaluated; the maturation of dendritic cells, the proliferation of T cells, the increase of high mobility group box protein 1, and the decrease of immunosuppressive regulatory T cells confirmed that such synergistic therapy could effectively provide immune protection to the body. We believe such in situ generation of small-sized therapeutic units brought by a dynamically reversible D-A reaction could expand the pathway to design next generation drug delivery systems possessing superior design philosophy and excellent practice effects compared to currently available ones.

Phototriggered structures: Latest advances in biomedical applications

Non-invasive control of the drug molecules accessibility is a key issue in improving diagnostic and therapeutic procedures. Some studies have explored the spatiotemporal control by light as a peripheral stimulus. Phototriggered drug delivery systems (PTDDSs) have received interest in the past decade among biological researchers due to their capability the control drug release. To this end, a wide range of phototrigger molecular structures participated in the DDSs to serve additional efficiency and a high-conversion release of active fragments under light irradiation. Up to now, several categories of PTDDSs have been extended to upgrade the performance of controlled delivery of therapeutic agents based on well-known phototrigger molecular structures like o-nitrobenzyl, coumarinyl, anthracenyl, quinolinyl, o-hydroxycinnamate and hydroxyphenacyl, where either of one endows an exclusive feature and distinct mechanistic approach. This review conveys the design, photochemical properties and essential mechanism of the most important phototriggered structures for the release of single and dual (similar or different) active molecules that have the ability to quickly reason of the large variety of dynamic biological phenomena for biomedical applications like photo-regulated drug release, synergistic outcomes, real-time monitoring, and biocompatibility potential.

Chlorin e6: A Promising Photosensitizer in Photo-Based Cancer Nanomedicine

Conventional cancer treatment modalities are often associated with major therapeutic limitations and severe side effects. Photodynamic therapy is a localized noninvasive mode of treatment that has given a different direction to cancer research due to its effectivity against a wide range of cancers and minimal side effects. A photosensitizer is the key component of photodynamic therapy (PDT) that generates cytotoxic reactive oxygen species to eradicate cancer cells. As the therapeutic effectivity of PDT greatly depends upon the photosensitizer, great efforts have been made to search for an ideal photosensitizer. Chlorin e6 is a FDA approved second generation photosensitizer that meets the desired clinical properties for PDT. It is known for its high reactive oxygen species (ROS) generation ability and anticancer potency against many types of cancer. Hydrophobicity is a major drawback of Ce6 that leads to its poor biodistribution and rapid clearance from the circulatory system. To overcome this drawback, researchers have designed and fabricated several types of nanosystems, which can enhance Ce6 solubility and thereby enhance its bioavailability. These nanosystems also improve tumor accumulation of Ce6 by selectively targeting the cancer cells through passive and active targeting. In addition, Ce6 has been employed in many combination therapies like chemo-photodynamic therapy, photoimmunotherapy, and combined photodynamic-photothermal therapy. A combination therapy is more curative than a single therapy due to the synergistic effects of individual therapies. Ce6-based nanosystems for combination therapies have shown excellent results in various studies and provide a promising platform for cancer treatment.

Supramolecular Theranostic Nanomedicine for In Situ Self-Boosting Cancer Photochemotherapy

Although traditional nanomedicines have enhanced the therapeutic efficacy and improved the survival quality of cancer patients, random drug release and drug resistance are deep-rooted problems hindering their clinical application. A precise nanoplatform combing chemotherapy and photodynamic therapy (PDT) is developing as a new therapeutic strategy to overcome the above challenges. Herein, a novel supramolecular nanomedicine is ingeniously constructed for in situ self-boosting cancer photochemotherapy. Hydrophilic polyethylene glycol (PEG) chains or β-cyclodextrin (β-CD) hosts are first conjugated onto tetraphenyl porphyrin (TCPP) to improve the solubility of TCPP and decrease their π-π stacking interactions, guaranteeing a high-efficiency PDT. Then, two camptothecin (CPT) molecules are linked together via a reactive oxygen species (ROS)-responsive thioketal bond, which averts the premature burst release of CPT and realizes in situ drug release at the tumor site where PDT is performed, resulting in an enhanced chemotherapy. Benefiting from the collaboration of host-guest complexation between β-CD and CPT, multiple intermolecular hydrogen bonds of β-CD, π-π stacking interactions among CPT and TCPP as well as PEG shell protection, a prolonged blood circulation time, and a selective tumor accumulation are acquired, which facilitate the synergistic photochemotherapy and bring a pre-eminent antitumor response with a low systemic toxicity.

H2O2-responsive polymer prodrug nanoparticles with glutathione scavenger for enhanced chemo-photodynamic synergistic cancer therapy

The combination of chemotherapy and photodynamic therapy (PDT) based on nanoparticles (NPs) has been extensively developed to improve the therapeutic effect and decrease the systemic toxicity of current treatments. However, overexpressed glutathione (GSH) in tumor cells efficiently scavenges singlet oxygens (¹O₂) generated from photosensitizers and results in the unsatisfactory efficacy of PDT. To address this obstacle, here we design H₂O₂-responsive polymer prodrug NPs with GSH-scavenger (Ce6@P(EG-a-CPBE) NPs) for chemo-photodynamic synergistic cancer therapy. They are constructed by the co-self-assembly of photosensitizer chlorin e6 (Ce6) and amphiphilic polymer prodrug P(EG-a-CPBE), which is synthesized from a hydrophilic alternating copolymer P(EG-a-PD) by conjugating hydrophobic anticancer drug chlorambucil (CB) via an H₂O₂-cleavable linker 4-(hydroxymethyl)phenylboronic acid (PBA). Ce6@P(EG-a-CPBE) NPs can efficiently prevent premature drug leakage in blood circulation because of the high stability of the PBA linker under the physiological environment and facilitate the delivery of Ce6 and CB to the tumor site after intravenous injection. Upon internalization of Ce6@P(EG-a-CPBE) NPs by tumor cells, PBA is cleaved rapidly triggered by endogenous H₂O₂ to release CB and Ce6. Ce6 can effectively generate abundant ¹O₂ under 660 nm light irradiation to synergistically kill cancer cells with CB. Concurrently, PBA can be transformed into a GSH-scavenger (quinine methide, QM) under intracellular H₂O₂ and prevent the depletion of ¹O₂, which induces the cooperatively strong oxidative stress and enhanced cancer cell apoptosis. Collectively, such H₂O₂-responsive polymer prodrug NPs loaded with photosensitizer provide a feasible approach to enhance chemo-photodynamic synergistic cancer treatment.

Multifunctional nanoparticle for cancer therapy

Cancer is a complex disease associated with a combination of abnormal physiological process and exhibiting dysfunctions in multiple systems. To provide effective treatment and diagnosis for cancer, current treatment strategies simultaneously focus on various tumor targets. Based on the rapid development of nanotechnology, nanocarriers have been shown to exhibit excellent potential for cancer therapy. Compared with nanoparticles with single functions, multifunctional nanoparticles are believed to be more aggressive and potent in the context of tumor targeting. However, the development of multifunctional nanoparticles is not simply an upgraded version of the original function, but involves a sophisticated system with a proper backbone, optimized modification sites, simple preparation method, and efficient function integration. Despite this, many well-designed multifunctional nanoparticles with promising therapeutic potential have emerged recently. Here, to give a detailed understanding and analyzation of the currently developed multifunctional nanoparticles, their platform structures with organic or inorganic backbones were systemically generalized. We emphasized on the functionalization and modification strategies, which provide additional functions to the nanoparticle. We also discussed the application combination strategies that were involved in the development of nanoformulations with functional crosstalk. This review thus provides an overview of the construction strategies and application advances of multifunctional nanoparticles.

Applications and challenges of ultra-small particle size nanoparticles in tumor therapy

With the development of nanotechnology, nanomedicines are widely used in tumor therapy. However, biological barriers in the delivery of nanoparticles still limit their application in tumor therapy. As one of the most fundamental properties of nanoparticles, particle size plays a crucial role in the process of the nanoparticles delivery process. It is difficult for large size nanoparticles with fixed size to achieve satisfactory outcomes in every process. In order to overcome the poor penetration of larger size, nanoparticles with ultra-small particle size are proposed, which are more conducive to deep tumor penetration and uniform drug distribution. In this review, the latest progresses and advantages of ultra-small nanoparticles are systematically summarized, the perspectives and challenges of ultra-small nanoparticles strategy for cancer treatment are also discussed.

K. ZHENG ET AL.Gold-nanoparticle-based multistage drug delivery system for antitumor therapy

Nanoparticles can promote the accumulation of drugs in tumors. However, they find limited clinical applications because they cannot easily penetrate the stroma of cancer tissues, and it is difficult to control drug release. We developed a multiresponse multistage drug-delivery nanogel with improved tumor permeability and responsiveness to the tumor microenvironment for the controlled delivery of anticancer agents. For this purpose, ∼100 nm multistage drug delivery nanogels with pH, redox, near-infrared stimulation, and enzyme responsiveness were grown in situ using 20 nm gold nanoparticles (AuNPs) via an emulsion-aiding crosslinking technique with cysteine crosslinker. An alginate cysteine AuNP (ACA) nanocarrier can efficiently load the cationic drug doxorubicin (DOX) to produce a multistage drug delivery nanocarrier (DOX@ACA). DOX@ACA can maintain the slow release of DOX and reduce its toxicity. In cancer tissues, the high pH and reductase microenvironment combined with the in vitro delivery of alginate and near-infrared light drove drug release. The developed nanoparticles effectively inhibited cancer cells, and in vivo evaluations showed that they effectively enhanced antitumor activity while having negligible in vivo toxicity to major organs.

Light-Activated Reactive Oxygen Species-Responsive Nanocarriers for Enhanced Photodynamic Immunotherapy of Cancer

Exploring polymeric nanoplatforms combined with reactive oxygen species (ROS) responsiveness with mitochondria targeting has emerged as an effective strategy for enhanced photodynamic therapy (PDT). Amphiphilic copolymers were synthesized by reacting acrylamide thioketal (TK) linkers with amino-terminated triphenylphosphonium-polyethylene glycol and dodecylamine for encapsulating chlorin e6 (Ce6) via self-assembly. Then, anionic cladding with tumor targeting deshelled in tumor acidic microenvironments was surface-anchored by electrostatic forces (BioPEGDMA@RM). After sequential targeting to the mitochondria of cancerous cells, BioPEGDMA@RM could be light-activated with Ce6 released upon ROS cleavage of TK linkages. It was found that Ce6-loaded BioPEGDMA@RM exhibited higher cytotoxicity on CT26 cells and performed stronger ability on the production of ROS than that without TK linkers. Moreover, a minimum illumination of 3 and 5 min could be required for achieving the maximum release of Ce6 and high in vitro cytotoxicity for Ce6-loaded BioPEGDMA@RM, respectively. Furthermore, Ce6-loaded BioPEGDMA@RM showed 1.29-fold and 1.21-fold higher tumor inhibition on BALB/c nude mice and Kunming mice and stimulated immunologic reactions with more generation of IFN-γ and TNF-α and activation of CD3⁺, CD4⁺, and CD8⁺ T-lymphocytes and DCs than that of Ce6-loaded nanoparticles without TK bonds. This work provided an academic reference for the development of ROS-responsive drug delivery systems for advanced PDT efficiency.

Enhancing the therapeutic efficacy of nanoparticles for cancer treatment using versatile targeted strategies

Poor targeting of therapeutics leading to severe adverse effects on normal tissues is considered one of the obstacles in cancer therapy. To help overcome this, nanoscale drug delivery systems have provided an alternative avenue for improving the therapeutic potential of various agents and bioactive molecules through the enhanced permeability and retention (EPR) effect. Nanosystems with cancer-targeted ligands can achieve effective delivery to the tumor cells utilizing cell surface-specific receptors, the tumor vasculature and antigens with high accuracy and affinity. Additionally, stimuli-responsive nanoplatforms have also been considered as a promising and effective targeting strategy against tumors, as these nanoplatforms maintain their stealth feature under normal conditions, but upon homing in on cancerous lesions or their microenvironment, are responsive and release their cargoes. In this review, we comprehensively summarize the field of active targeting drug delivery systems and a number of stimuli-responsive release studies in the context of emerging nanoplatform development, and also discuss how this knowledge can contribute to further improvements in clinical practice.

Reactive Oxygen Species Responsive Cleavable Hierarchical Metallic Supra-Nanostructure

A reactive oxygen species (ROS) responsive cleavable hierarchical metallic supra-nanostructure (HMSN) is reported. HMSN structured with thin branches composed of primary gold (Au) nanocrystals and silver (Ag) nano-linkers is synthesized by a one-pot aqueous synthesis with a selected ratio of Au/Ag/cholate. ROS responsive degradability of HMSN is tested in the presence of endogenous and exogeneous ROS. Significant ROS-responsive structural deformation of HMSN is observed in the ROS exposure with hydrogen peroxide (H2 O2 ) solution. The ROS responsiveness of HMSN is significantly comparable with negligible structural changes of conventional spherical gold nanoparticles. The demonstrated ROS responsive degradation of HMSN is further confirmed in various in vitro ROS conditions of each cellular endogenous ROS and exogeneous ROS generated by photodynamic therapy (PDT) or X-ray radiation. Then, in vivo ROS responsive degradability of HMSN is further evaluated with intratumoral injection of HMSN and exogeneous ROS generation via PDT in a mouse tumor model. Additional in vivo biodistribution and toxicity of intravenously administrated HMSN at 30-day post-injection are investigated for potential in vivo applications. The observed ROS responsive degradability of HMSN will provide a promising option for a type of ROS responsive-multifunctional nanocarriers in cancer treatment and various biomedical applications.

Nano-drug delivery system with enhanced tumour penetration and layered anti-tumour efficacy

The low delivery efficiency of nano-drugs and limited tumour penetration are still huge challenges in treating solid tumours. Herein, we developed a pH-responsive nano-drug delivery system, CALS/PDMA@DOX, with a size conversion-layered delivery function. The system is composed of a pH-responsive cationic liposome loaded with DOX (CALS) and a polyamidoamine dendrimer loaded with DOX (PAMAM@DOX) modified with 2,3-dimethylmaleic anhydride (PDMA@DOX) using electrostatic adsorption. In the tumour microenvironment, the positively-charged large-size CALS and the positively-charged small-size PAMAM@DOX were dissociated to exert anti-tumour effects. CALS preferentially targeted tumour angiogenesis endothelial cells. Because of its small size and positive charge, PAMAM@DOX showed excellent tumour penetration. Significant tumour suppression by the system in vivo was confirmed in a 4T1 tumour xenograft mouse model. This pH-triggered size-switching layered delivery nanosystem is a safe and effective cancer treatment delivery platform that improves drug permeability and therapeutic efficacy.

Functional Nanoparticles for Enhanced Cancer Therapy

Cancer is the leading cause of death in people worldwide. The conventional therapeutic approach is mainly based on chemotherapy, which has a series of side effects. Compared with traditional chemotherapy drugs, nanoparticle-based delivery of anti-cancer drugs possesses a few attractive features. The application of nanotechnology in an interdisciplinary manner in the biomedical field has led to functional nanoparticles achieving much progress in cancer therapy. Nanoparticles have been involved in the diagnosis and targeted and personalized treatment of cancer. For example, different nano-drug strategies, including endogenous and exogenous stimuli-responsive, surface conjugation, and macromolecular encapsulation for nano-drug systems, have successfully prevented tumor procession. The future for functional nanoparticles is bright and promising due to the fast development of nanotechnology. However, there are still some challenges and limitations that need to be considered. Based on the above contents, the present article analyzes the progress in developing functional nanoparticles in cancer therapy. Research gaps and promising strategies for the clinical application are discussed.

Multifunctional Magnetic CuS/Gd2O3 Nanoparticles for Fluorescence/Magnetic Resonance Bimodal Imaging-Guided Photothermal-Intensified Chemodynamic Synergetic Therapy of Targeted Tumors

Chemodynamic therapy (CDT), which consumes endogenous hydrogen peroxide (H₂O₂) to generate reactive oxygen species (ROS) and causes oxidative damage to tumor cells, shows tremendous promise for advanced cancer treatment. However, the rate of ROS generation based on the Fenton reaction is prone to being restricted by inadequate H₂O₂ and unattainable acidity in the hypoxic tumor microenvironment. We herein report a multifunctional nanoprobe (BCGCR) integrating bimodal imaging and photothermal-enhanced CDT of the targeted tumor, which is produced by covalent conjugation of bovine serum albumin-stabilized CuS/Gd₂O₃ nanoparticles (NPs) with the Cy5.5 fluorophore and the tumor-targeting ligand RGD. BCGCR exhibits intense near-infrared (NIR) fluorescence and acceptable r₁ relaxivity (∼15.3 mM^-1 s^-1) for both sensitive fluorescence imaging and high-spatial-resolution magnetic resonance imaging of tumors in living mice. Moreover, owing to the strong NIR absorbance from the internal CuS NPs, BCGCR can generate localized heat and displays a high photothermal conversion efficiency (30.3%) under 980 nm laser irradiation, which enables photothermal therapy and further intensifies ROS generation arising from the Cu-induced Fenton-like reaction for enhanced CDT. This synergetic effect shows such an excellent therapeutic efficacy that it can ablate xenografted tumors in vivo. We believe that this strategy will be beneficial to exploring other advanced nanomaterials for the clinical application of multimodal imaging-guided synergetic cancer therapies.

Light-responsive biomaterials for ocular drug delivery

Light-responsive biomaterials can be used for the delivery of therapeutic drugs and nucleic acids, where the tunable/precise delivery of payload highlights the potential of such biomaterials for treating a variety of conditions. The translucency of eyes and advances of laser technology in ophthalmology make light-responsive delivery of drugs feasible. Importantly, light can be applied in a non-invasive fashion; therefore, light-triggered drug delivery systems have great potential for clinical impact. This review will examine various types of light-responsive polymers and the chemistry that underpins their application as ophthalmic drug delivery systems.

Applications of the ROS-Responsive Thioketal Linker for the Production of Smart Nanomedicines

Reactive oxygen species (ROS)-sensitive drug delivery systems (DDS) specifically responding to altered levels of ROS in the pathological microenvironment have emerged as an effective means to enhance the pharmaceutical efficacy of conventional nanomedicines, while simultaneously reducing side effects. In particular, the use of the biocompatible, biodegradable, and non-toxic ROS-responsive thioketal (TK) functional group in the design of smart DDS has grown exponentially in recent years. In the design of TK-based DDS, different technological uses of TK have been proposed to overcome the major limitations of conventional DDS counterparts including uncontrolled drug release and off-target effects. This review will focus on the different technological uses of TK-based biomaterials in smart nanomedicines by using it as a linker to connect a drug on the surface of nanoparticles, form prodrugs, as a core component of the DDS to directly control its structure, to control the opening of drug-releasing gates or to change the conformation of the nano-systems. A comprehensive view of the various uses of TK may allow researchers to exploit this reactive linker more consciously while designing nanomedicines to be more effective with improved disease-targeting ability, providing novel therapeutic opportunities in the treatment of many diseases.

Reactive Oxygen Species (ROS)-Responsive Biomaterials for the Treatment of Bone-Related Diseases

Reactive oxygen species (ROS) are the key signaling molecules in many physiological signs of progress and are associated with almost all diseases, such as atherosclerosis, aging, and cancer. Bone is a specific connective tissue consisting of cells, fibers, and mineralized extracellular components, and its quality changes with aging and disease. Growing evidence indicated that overproduced ROS accumulation may disrupt cellular homeostasis in the progress of bone modeling and remodeling, leading to bone metabolic disease. Thus, ROS-responsive biomaterials have attracted great interest from many researchers as promising strategies to realize drug release or targeted therapy for bone-related diseases. Herein, we endeavor to introduce the role of ROS in the bone microenvironment, summarize the mechanism and development of ROS-responsive biomaterials, and their completion and potential for future therapy of bone-related diseases.

Recent advances in nanomedicines for photodynamic therapy (PDT)-driven cancer immunotherapy

Cancer immunotherapy has made tremendous clinical progress in advanced-stage malignancies. However, patients with various tumors exhibit a low response rate to immunotherapy because of a powerful immunosuppressive tumor microenvironment (TME) and insufficient immunogenicity of tumors. Photodynamic therapy (PDT) can not only directly kill tumor cells, but also elicit immunogenic cell death (ICD), providing antitumor immunity. Unfortunately, limitations from the inherent nature and complex TME significantly reduce the efficiency of PDT. Recently, smart nanomedicine-based strategies could subtly modulate the pharmacokinetics of therapeutic compounds and the TME to optimize both PDT and immunotherapy, resulting in an improved antitumor effect. Here, the emerging nanomedicines for PDT-driven cancer immunotherapy are reviewed, including hypoxia-reversed nanomedicines, nanosized metal-organic frameworks, and subcellular targeted nanoparticles (NPs). Moreover, we highlight the synergistic nanotherapeutics used to amplify immune responses combined with immunotherapy against tumors. Lastly, the challenges and future expectations in the field of PDT-driven cancer immunotherapy are discussed.

Tumor microenvironment and nanotherapeutics: intruding the tumor fort

Over recent years, advancements in nanomedicine have allowed new approaches to diagnose and treat tumors. Nano drug delivery systems exploit the enhanced permeability and retention (EPR) effect and enter the tumor tissue's interstitial space. However, tumor barriers play a crucial role, and cause inefficient EPR or the homing effect. Mounting evidence supports the hypothesis that the components of the tumor microenvironment, such as the extracellular matrix, and cellular and physiological components collectively or cooperatively hinder entry and distribution of drugs, and therefore, limit the theragnostic applications of cancer nanomedicine. This abnormal tumor microenvironment plays a pivotal role in cancer nanomedicine and was recently recognized as a promising target for improving nano-drug delivery and their therapeutic outcomes. Strategies like passive or active targeting, stimuli-triggered nanocarriers, and the modulation of immune components have shown promising results in achieving anticancer efficacy. The present review focuses on the tumor microenvironment and nanoparticle-based strategies (polymeric, inorganic and organic nanoparticles) for intruding the tumor barrier and improving therapeutic effects.

Photosensitive drug delivery systems for cancer therapy: Mechanisms and applications

Over the past three decades, various photosensitive nanoparticles have been developed as potential therapies in human health, ranging from photodynamic therapy technologies that have already reached clinical use, to drug delivery systems that are still in the preclinical stages. Many of these systems are designed to achieve a high spatial and temporal on-demand drug release via phototriggerable mechanisms. This review examines the current clinical and experimental applications in cancer treatment of photosensitive drug release systems, including nanocarriers such as liposomes, micelles, polymeric nanoparticles, and hydrogels. We will focus on the three main physicochemical mechanisms of imparting photosensitivity to a delivery system: i) photochemical reactions (oxidation, cleavage, and polymerization), ii) photoisomerization, iii) and photothermal reactions. Photosensitive nanoparticles have a multitude of different applications including controlled drug release, resulting from physical/conformational changes in the delivery systems in response to light of specific wavelengths. Most of the recent research in these delivery systems has primarily focused on improving the efficacy and safety of cancer treatments such as photodynamic and photothermal therapy. Combinations of multiple treatment modalities using photosensitive nanoparticulate delivery systems have also garnered great interest in combating multi-drug resistant cancers due to their synergistic effects. Finally, the challenges and future potential of photosensitive drug delivery systems in biomedical applications is outlined.

Photo-responsive polymeric nanocarriers for target-specific and controlled drug delivery

Conventional drug delivery systems often have several pharmacodynamic and pharmacokinetic limitations related to their low efficacy and bad safety. It is because these traditional systems cannot always be selectively addressed to their therapeutic target sites. Currently, target-specific and controlled drug delivery is one of the foremost challenges in the biomedical field. In this context, stimuli-responsive polymeric nanomaterials have been recognized as a topic of intense research. They have gained immense attention in therapeutics - particularly in the drug delivery area - due to the ease of tailorable behavior in response to the surroundings. Light irradiation is of particular interest among externally triggered stimuli because it may be specifically localized in a contact-free manner. Light-human body interactions may sometimes be harmful due to photothermal and photomechanical reactions that lead to cell death by photo-toxicity and/or photosensitization. However, these limitations may also be overcome by the use of photo-responsive polymeric nanostructures. This review summarizes recent developments in photo-responsive polymeric nanocarriers used in the field of drug delivery systems, including nanoparticles, nanogels, micelles, nanofibers, dendrimers, and polymersomes, as well as their classification and mechanisms of drug release.

Improving Targeted Delivery and Antitumor Efficacy with Engineered Tumor Necrosis Factor-Related Apoptosis Ligand-Affibody Fusion Protein

Tumor necrosis factor-related apoptosis ligand (TRAIL) is a promising protein candidate for selective apoptosis of a variety of cancer cells. However, the short half-life and a lack of targeted delivery are major obstacles for its application in cancer therapy. Here, we propose a simple strategy to solve the targeting problem by genetically fusing an anti-HER2 affibody to the C-terminus of the TRAIL. The fusion protein TRAIL-affibody was produced as a soluble form with high yield in recombinant Escherichia coli. In vitro studies proved that the affibody domain promoted the cellular uptake of the fusion protein in the HER2 overexpressed SKOV-3 cells and improved its apoptosis-inducing ability. In addition, the fusion protein exhibited higher accumulation at the tumor site and greater antitumor effect than those of TRAIL in vivo, indicating that the affibody promoted the tumor homing of the TRAIL and then improved the therapeutic efficacy. Importantly, repeated injection of high-dose TRAIL-affibody showed no obvious toxicity in mice. These results demonstrated that the engineered TRAIL-affibody is promising to be a highly tumor-specific and targeted cancer therapeutic agent.

Fabrication of polymer-based self-assembly nanocarriers loaded with a crizotinib and gemcitabine: potential therapeutics for the treatment of endometrial cancer

Combination therapy in cancer therapy has been widely used for its positive attributes, such as minimizing the undesirable side effects of chemotherapies and enhancing the therapeutic effects on different cancers. Compared with free drugs crizotinib (CRZ) and gemcitabine (GEM), CRZ@GEM-NPs could remarkably improve the cytotoxicity for endometrial cancer (EC) cells (Ishikawa cells and KLE cells) after treatment with MTT assay. In this study, CRZ and GEM were conjugated to tri-block copolymer poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL, known as NPs). The fabricated nanoparticles were characterized by the high-resolution transmission electron microscopy (HR-TEM), and the particles size and zeta potential were investigated by the dynamic light scattering analysis. Further, the morphological features of the EC cell lines were examined by the biochemical staining assays. Morphological changes in endometrial cells morphology revealed by nuclear fragmentation and nuclear condensation (the hallmarks of apoptosis) were noted upon treatment with CRZ@GEM-NPs to the Ishikawa and KLE cancer cells. In addition, resulting in the highest ratio of apoptosis and mitochondrial membrane potential shows the cell death through the mitochondrial membrane potential. In vivo, systemic toxicity studies showed no histological changes and substantial blood biochemical with the near-normal appearance of the organs upon treatment with CRZ@GEM-NPs. Overall, the targeted combination suitable therapeutic framework may be a promising candidate for improved EC therapy.

An Organic Nanotherapeutic Agent Self-Assembled from Cyanine and Cu (II) for Combined Photothermal and Chemodynamic Therapy

Although the combination of photothermal/chemodynamic therapy (PTT/CDT) based on various inorganic nanomaterials has promising anticancer effects, poor biocompatibility and biodegradability of inorganic nanoplatforms pose obstacles to their use in clinic. On the contrary, nanoscale metal-organic particles are considered to be a promising platform because of their biocompatibility and efficient metabolism. Herein, HA@Cy-Cu NPs are prepared using the coordination-driven assembly of cyanine dyes with Cu²⁺ ions. HA@Cy-Cu NPs demonstrate excellent synergistic PTT/CDT, a high photothermal conversion efficiency (43%), and enhanced photostability. Moreover, Cu²⁺ in the NPs can be reduced to Cu⁺ by glutathione (GSH) and can transform H₂ O₂ to •OH, which down-regulates intracellular GSH levels and up-regulates significant oxidative damage. Therefore, promising in vivo tumor ablation is observed at a low dose of HA@Cy-Cu, suggesting that the combination of PTT/CDT greatly improved the antitumor performance. HA@Cy-Cu can further improve organic nano-systems for anti-tumor therapy by integrating PTT and CDT.

NIR-triggerable ROS-responsive cluster-bomb-like nanoplatform for enhanced tumor penetration, phototherapy efficiency and antitumor immunity

The restricted tumor penetration has been regarded as the Achilles' Heels of most nanomedicines, largely limiting their efficacy. To address this challenge, a cluster-bomb-like nanoplatform named CPIM is prepared, which for the first time combines size-transforming and transcytosis strategies, thus enhancing both passive and active transport. For passive diffusion, the "cluster-bomb" CPIM (135 nm) releases drug-loaded "bomblets" (IR780/1-methyl-tryptophan (1 MT) loaded PAMAM, <10 nm) in response to the high reactive-oxygen-species (ROS) concentration in tumor microenvironment (TME), which promotes intratumoral diffusion. Besides, IR780 generates ROS upon NIR irradiation and intensifies this responsiveness; therefore, there exists a NIR-triggered self-destructive behavior, rendering CPIM spatiotemporal controllability. For active transport, the nanoplatform is proven to be delivered via transcytosis with/without NIR irradiation. Regarding the anti-cancer performance, CPIM strengthens the photodynamic therapy (PDT)/photothermal therapy (PTT) activity of IR780 and IDO pathway inhibition effect of 1 MT, thus exhibiting a strongest inhibitory effect on primary tumor. CPIM also optimally induces immunogenic cell death, reverses the "cold" TME to a "hot" one and evokes systemic immune response, thus exerting an abscopal and anti-metastasis effects. In conclusion, this work provides a facile, simple yet effective strategy to enhance the tumor penetration, tumor-killing effect and antitumor immunity of nanomedicines.

Acid-Sensitive Supramolecular Nanoassemblies with Multivalent Interaction: Effective Tumor Retention and Deep Intratumor Infiltration

It remains a conundrum to reconcile the contradiction between effective tumor retention and deep intratumor infiltration for nanotherapeutics due to the sophisticated drug delivery journey. Herein, we reported an acid-sensitive supramolecular nanoassemblies (DCD SNs) based on the multivalent host-gest inclusions of two polymer conjugates for conquering diverse physiological blockages and amplifying therapeutic efficacy. The multiple inclusions of repetitive units on the hydrophilic polymer backbone reinforced the binding affinity and induced robust self-assembly, ameliorating instability of the self-assemblies and facilitating to prolong the drug retention time. By virtue of the acid-sensitive Schiff base linkages, the supramolecular nanoassembly could respond to the unique tumor microenvironment (TME), dissociate, and transform into smaller particles (∼30 nm), thereby efficiently traversing the complicated extracellular matrix and irregular blood vessels to achieve deep intratumor infiltration. The acid-sensitive DCD SNs can absorb a large number of protons in the acidic lysosomal environment, causing the proton sponge effect, which was conducive to their escape from endolysosomes and accelerated lysosomal disruption, so that the active chemotherapeutic doxorubicin (DOX) could enter the nucleus well and exert severe DNA damage to induce apoptosis. This versatile supramolecular nanoplatform is anticipated to be a promising candidate to overcome the limitations of insufficient stability within the circulation and weak intratumor penetration.

Moderating hypoxia and promoting immunogenic photodynamic therapy by HER-2 nanobody conjugate nanoparticles for ovarian cancer treatment

Photodynamic therapy (PDT) and immunotherapy have been often adopted for ovarian cancer therapy, yet their application is limited by the high recurrence rate and toxic side effects. Intriguingly, nanoparticles contribute to enhancing the performance of PDT. Here, we investigated the synthesis of HER-2-Nanobody (Nb)-conjugated human serum albumin (HSA) incorporated with chlorin (Ce6) and catalase (CAT) (Nb@HCC), and analyzed the synergic effect of Nb@HCC-mediated PDT and immunotherapy for SK-OV-3 tumors. The Ce6 and CAT were incorporated into HSA to construct the HCC nanoparticles. HER-2-Nanobody was the purified bacterial crude extract, and conjugated with HCC to prepare Nb@HCC via heterodisulfide. The effects of Nb@HCC with near infrared ray (NIR) irradiation on moderating hypoxia and hypoxia inducible factor-1α(HIF-1α) expression were evaluated in the SK-OV-3 cells and tumor tissues. A SK-OV-3 tumor-bearing model was developed, where the synergistic effect of Nb@HCC-mediated PDT and anti-CTLA-4 therapy was investigated. Nb@HCC with a 660 nm laser irradiation could induce massive reactive oxygen species and trigger apoptosis in SK-OV-3 cells. Nb@HCC and PDT promoted danger-associated molecular patterns (DAMPs), which indicated immunogenic cell death and maturation of dendritic cells in the SK-OV-3 cells. Irradiated by NIR, Nb@HCC alleviated the hypoxia and decreased the expression of HIF-1α. The Nb@HCC-mediated PDT and anti-CTLA-4 therapy synergically inhibited the progression of distant tumor, and induced T cell infiltration. Biosafety tests suggested that Nb@HCC would not cause damage to the major organs with less toxicity and side effects. To conclude, a combination of Nb@HCC-mediated PDT and anti-CTLA-4 therapy could inhibit the progression of distant tumor to attain remarkable therapeutic outcomes.

Photo cleavable thioacetal block copolymers for controlled release

We present a new light cleavable polymer containing o-nitrobenzene thioacetal groups in the main chain. By conjugation to a PEG block, we synthesized block copolymers capable of forming nanoparticles in aqueous solution. We studied drug encapsulation and release using the model drug Nile Red. Irradiation with UV-A light (365 nm) leads to efficient degradation of the polymers and associated burst release of the payload. Unlike other thioacetal and thioketal polymers, these polymers are stable to reactive oxygen species (ROS), preventing non-triggered release. Moreover, the nanocarriers showed low cytotoxicity in cell viability experiments.

The o-nitrobenzene thioacetal group selectively cleaves upon UV-A irradiation. When incorporated in a block-copolymer, these photoactive groups can be used for controlled release of molecular cargo from polymer nanoparticles.

Emerging strategies against tumor-associated fibroblast for improved the penetration of nanoparticle into desmoplastic tumor

The therapeutic effect of nanoparticles is limited in solid tumors, especially desmoplastic tumors, because the tumor matrix hinders the delivery of nanoparticles. As the most abundant cells in the tumor stroma, tumor-associated fibroblasts (TAFs) produce a dense extracellular matrix, which leads to higher tissue fluid pressure, thereby creating a physical barrier for nanoparticle delivery. Therefore, researchers focused on eliminating TAFs to combat desmoplastic tumors. In recent years, a series of methods for TAFs have been developed. In this paper, we first introduced the biological mechanism of TAFs hindering the penetration of nanoparticles. Then, the different methods of eliminating TAFs were summarized, and the mechanism of nanomedicine in eliminating TAFs was highlighted. Finally, the problems and future development directions for TAFs treatment were discussed from the perspective of the treatment of desmoplastic tumors.