Tumor-pH-Responsive Dissociable Albumin-Tamoxifen Nanocomplexes Enabling Efficient Tumor Penetration and Hypoxia Relief for Enhanced Cancer Photodynamic Therapy

Strategies to enhance the penetration of nanomedicine in solid tumors

Nanomedicine was previously regarded as a promising solution in the battle against cancer. Over the past few decades, extensive research has been conducted to exploit nanomedicine for overcoming tumors. Unfortunately, despite these efforts, nanomedicine has not yet demonstrated its ability to cure tumors, and the research on nanomedicine has reached a bottleneck. For a significant period of time, drug delivery strategies have primarily focused on targeting nanomedicine delivery to tumors while neglecting its redistribution within solid tumors. The uneven distribution of nanomedicine within solid tumors results in limited therapeutic effects on most tumor cells and significantly hampers the efficiency of drug delivery and treatment outcomes. Therefore, this review discusses the challenges faced by nanomedicine in penetrating solid tumors and provides an overview of current nanotechnology strategies (alleviating penetration resistance, size regulation, tumor cell transport, and nanomotors) that facilitate enhanced penetration of nanomedicine into solid tumors. Additionally, we discussed the potential role of nanobionics in promoting effective penetration of nanomedicine.

Phototherapy in cancer treatment: strategies and challenges

Phototherapy has emerged as a promising modality in cancer treatment, garnering considerable attention for its minimal side effects, exceptional spatial selectivity, and optimal preservation of normal tissue function. This innovative approach primarily encompasses three distinct paradigms: Photodynamic Therapy (PDT), Photothermal Therapy (PTT), and Photoimmunotherapy (PIT). Each of these modalities exerts its antitumor effects through unique mechanisms-specifically, the generation of reactive oxygen species (ROS), heat, and immune responses, respectively. However, significant challenges impede the advancement and clinical application of phototherapy. These include inadequate ROS production rates, subpar photothermal conversion efficiency, difficulties in tumor targeting, and unfavorable physicochemical properties inherent to traditional phototherapeutic agents (PTs). Additionally, the hypoxic microenvironment typical of tumors complicates therapeutic efficacy due to limited agent penetration in deep-seated lesions. To address these limitations, ongoing research is fervently exploring innovative solutions. The unique advantages offered by nano-PTs and nanocarrier systems aim to enhance traditional approaches' effectiveness. Strategies such as generating oxygen in situ within tumors or inhibiting mitochondrial respiration while targeting the HIF-1α pathway may alleviate tumor hypoxia. Moreover, utilizing self-luminescent materials, near-infrared excitation sources, non-photoactivated sensitizers, and wireless light delivery systems can improve light penetration. Furthermore, integrating immunoadjuvants and modulating immunosuppressive cell populations while deploying immune checkpoint inhibitors holds promise for enhancing immunogenic cell death through PIT. This review seeks to elucidate the fundamental principles and biological implications of phototherapy while discussing dominant mechanisms and advanced strategies designed to overcome existing challenges-ultimately illuminating pathways for future research aimed at amplifying this intervention's therapeutic efficacy.

Targeting tumor angiogenesis and metabolism with photodynamic nanomedicine

Photodynamic therapy (PDT) holds considerable promise as a tumor treatment modality, characterized by its targeted action, compatibility with other therapeutic approaches, and non - invasive features. PDT can achieve remarkable spatiotemporal precision in tumor ablation through the generation of reactive oxygen species (ROS). Nevertheless, despite its potential in tumor treatment, PDT encounters multiple challenges in practical applications. PDT is highly oxygen - dependent, and thus the effectiveness of PDT can be markedly influenced by tumor hypoxia. The co-existence of abnormal vasculature and metabolic deregulation gives rise to a hypoxic microenvironment, which not only sustains tumor survival but also undermines the therapeutic efficacy of PDT. Consequently, targeting tumor angiogenesis and metabolism is essential for revitalizing PDT. This review emphasizes the mechanisms and strategies for revitalizing PDT in tumor treatment, predominantly concentrating on interfering with tumor angiogenesis and reprogramming tumor cell metabolism. Lastly, the outlining future perspectives and current limitations of PDT are also summarized. This could provide new insights and methodologies for overcoming the challenges associated with PDT in tumor treatment, ultimately advancing the field of PDT.

Hypoxia-responsive liposome enhances intracellular delivery of photosensitizer for effective photodynamic therapy

Liposomes, especially polyethylene glycol (PEG)-modified long-circulating liposomes, have been approved for market use, due to good biocompatibility, passive tumor targeting, and sustained drug release. PEG-modified long-circulating liposomes address issues such as poor stability and rapid clearance by the reticuloendothelial system. However, they still face challenges like hindering drug uptake by tumor cells and preventing tumor penetration. Inspired by the hypoxic tumor microenvironment, we constructed a hypoxia-responsive liposome (PAO-L) to enhance the intracellular uptake and photodynamic therapy (PDT) effect of chlorin e6 (Ce6). The intelligent hypoxia-cleavable PEG-AZO-OA (PAO) was prepared by coupling PEG and octadecylamine (OA) to hypoxia-sensitive azobenzene-4,4'-dicarboxylic acid (AZO) through amide reaction. The synthesized PAO was further incorporated into Ce6-loaded liposomes to enhance the circulation stability, while promote the tumor penetration and internalization by the responsive shedding of PEG from liposome surface upon reaching the hypoxic tumor tissue. PAO-L mediated PDT significantly inhibited the growth of B16F10 and 4T1 tumors, as well as lung metastasis of 4T1 breast cancer. The excellent therapeutic effect and good tolerability make PAO-L a promising candidate for enhanced PDT.

The Latest Applications of Carbon-Nitride-Based Materials for Combination Treatment of Cancer

Carbon-nitride-based (CN-based) materials have shown great potential in combination therapy in recent years. Due to their outstanding biocompatibility, ease of modification, and adjustable band-gap position, CN-based materials can be applied as photosensitizers in photodynamic therapy (PDT) and light-driven water-splitting catalysts in gas therapy. After doping with other elements, the photocatalytic performance of CN-based materials will be enhanced, and more interesting functions will be obtained. In addition, the large specific surface area also promotes CN-based materials as drug carriers combined with other therapeutic modalities to achieve combination therapy. This Review analyzes and summarizes the latest research on CN-based materials in combined therapies, such as PDT with photothermal therapy (PTT), PDT with sonodynamic therapy (SDT), PDT with drug therapy, PDT with gene therapy, gas therapy with PDT, and bioimaging-guided combined therapy. In particular, the applications of CN-based materials in gas and gene combination therapy are summarized for the first time. Finally, the current challenges faced by CN-based materials in combination therapy are further discussed.

Bovine serum albumin-bound homologous targeted nanoparticles for breast cancer combinatorial therapy

Breast cancer, the most common lethal cancer among women, is characterized by the uncontrolled growth of abnormal cells in breast tissue. Therefore, synergistic anticancer strategies are essential, particularly for maximizing drug delivery to tumor sites. Herein, bovine serum albumin (BSA)-bound nanoparticles encapsulating the photosensitizer chlorin e6 (Ce6) (BC) with a CuO2 core (BC/CuO2 NPs) were developed for cuproptosis-promoted cancer photodynamic therapy (PDT). The cancer cell membrane (CC) was then coated onto the surfaces to produce BC/CuO2@CC NPs for breast cancer combinatorial therapy. BSA serves dual functions as both a stabilizing scaffold for metal peroxide nanomaterials and a molecular connector for Ce6. The BC/CuO2@CC NPs group showed the stronger internalization capability than the other groups. BC/CuO2@CC NPs could effectively induce the greatest degree of apoptosis and death ratio (81.77 %), and lead to cuproptosis by downregulating the expression of DLAT, LIAS, and FDX1 protein in vitro. The intra-tumoral accumulation of BC/CuO2@CC NPs was 8.3- and 7.7-fold higher than that of Ce6 and BC/CuO2@CC NPs at 24 h postinjection, respectively. Moreover, synergistic efficacy of cuproptosis and PDT not only inhibited tumor growth but also prevented liver metastases. Thus, our work may be a novel approach for efficient and targeted cancer treatment.

Hypoxia Reversion and STING Pathway Activation through Large Mesoporous Nanozyme for Near-Infrared-II Light Amplified Tumor Polymetallic-Immunotherapy

cGAS/STING pathway, which is highly related to tumor hypoxia, is considered as a potential target for remodeling the immunosuppressive microenvironment of solid tumors. Metal ions, such as Mn2+, activate the cGAS/STING pathway, but their efficacy in cancer therapy is limited by insufficient effect on immunogenic tumor cell death of a single ion. Here, we evaluate the association between tumor hypoxia and cGAS/STING inhibition and report a polymetallic-immunotherapy strategy based on large mesoporous trimetal-based nanozyme (AuPdRh) coordinated with Mn2+ (Mn2+@AuPdRh) to activate cGAS/STING signaling for robust adaptive antitumor immunity. Specifically, the inherent CAT-like activity of this polymetallic Mn2+@AuPdRh nanozyme decomposes the endogenous H2O2 into O2 to relieve tumor hypoxia induced suppression of cGAS/STING signaling. Moreover, the Mn2+@AuPdRh nanozyme displays a potent near-infrared-II photothermal effect and strong POD-mimic activity; and the generated hyperthermia and •OH radicals synergistically trigger immunogenic cell death in tumors, releasing abundant dsDNA, while the delivered Mn2+ augments the sensitivity of cGAS to dsDNA and activates the cGAS-STING pathway, thereby triggering downstream immunostimulatory signals to kill primary and distant metastatic tumors. Our study demonstrates the potential of metal-based nanozyme for STING-mediated tumor polymetallic-immunotherapy and may inspire the development of more effective strategies for cancer immunotherapy.

Targeted Delivery of Catalase and Photosensitizer Ce6 by a Tumor-Specific Aptamer Is Effective against Bladder Cancer In Vivo

Photodynamic therapy (PDT) is often applied in a clinical setting to treat bladder cancer. However, current photosensitizers report drawbacks such as low efficacy, low selectivity, and numerous side effects, which have limited the clinical values of PDT for bladder cancer. Previously, we developed the first bladder cancer-specific aptamer that can selectively bind to and be internalized by bladder tumor cells versus normal uroepithelium cells. Here, we use an aptamer-based drug delivery system to deliver photosensitizer chlorine e6 (Ce6) into bladder tumor cells. In addition to Ce6, we also incorporate catalase into the drug complex to increase local oxygen levels in the tumor tissue. Compared with free Ce6, an aptamer-guided DNA nanotrain (NT) loaded with Ce6 and catalase (NT-Catalase-Ce6) can specifically recognize bladder cancer cells, produce oxygen locally, induce ROS in tumor cells, and cause mitochondrial apoptosis. In an orthotopic mouse model of bladder cancer, the intravesical instillation of NT-Catalase-Ce6 exhibits faster drug internalization and a longer drug retention time in tumor tissue compared with that in normal urothelium. Moreover, our modified PDT significantly inhibits tumor growth with fewer side effects such as cystitis than free Ce6. This aptamer-based photosensitizer delivery system can therefore improve the selectivity and efficacy and reduce the side effects of PDT treatment in mouse models of bladder cancer, bearing a great translational value for bladder cancer intravesical therapy.

Design strategies for enhancing antitumor efficacy through tumor microenvironment exploitation using albumin-based nanosystems: A review

The tumor microenvironment (TME) is a complex and dynamic system that plays a crucial role in regulating cancer progression, treatment response, and the emergence of acquired resistance mechanisms. The TME is usually featured by severe hypoxia, low pH values, high hydrogen peroxide (H2O2) concentrations, and overproduction of glutathione (GSH). The current development of intelligent nanosystems that respond to TME has shown great potential to enhance the efficacy of cancer treatment. As one of the functional macromolecules explored in this field, albumin-based nanocarriers, known for their inherent biocompatibility, serves as a cornerstone for constructing diverse therapeutic platforms. In this paper, we present a comprehensive overview of the latest advancements in the design strategies of albumin nanosystems, aiming to enhance cancer therapy by harnessing various features of solid tumors, including tumor hypoxia, acidic pH, the condensed extracellular matrix (ECM) network, excessive GSH, high glucose levels, and tumor immune microenvironment. Furthermore, we highlight representative designs of albumin-based nanoplatforms by exploiting the TME that enhance a broad range of cancer therapies, such as chemotherapy, phototherapy, radiotherapy, immunotherapy, and other tumor therapies. Finally, we discuss the existing challenges and future prospects in direction of albumin-based nanosystems for the practical applications in advancing enhanced cancer treatments.

Photothermal-driven micro/nanomotors: From structural design to potential applications

Micro/nanomotors (MNMs) that accomplish autonomous movement by transforming external energy into mechanical work are attractive cargo delivery vehicles. Among various propulsion mechanisms of MNMs, photothermal propulsion has gained considerable attention because of their unique advantages, such as remote, flexible, accurate, biocompatible, short response time, etc. Moreover, besides as a propulsion source, the light has been extensively investigated as an excitation source in bioimaging, photothermal therapy (PTT), photodynamic therapy (PDT) and so on. Furthermore, the geometric topology and morphology of MNMs have a tremendous impact on improving their performance in motion behavior under NIR light propulsion, environmental suitability and functional versatility. Hence, this review article provides a comprehensive overview of structural design principles and construction strategies of photothermal-driven MNMs, and their emerging nanobiomedical applications. Finally, we further provide an outlook towards prospects and challenges during the development of photothermal-driven MNMs in the future. STATEMENT OF SIGNIFICANCE: Photothermal-driven micro/nanomotors (MNMs) that are regarded as functional cargo delivery tools have gained considerable attention because of unique advantages in propulsion mechanisms, such as remote, flexible, accurate and fully biocompatible light manipulation and extremely short light response time. The geometric topology and morphology of MNMs have a tremendous impact on improving their performance in motion behavior under NIR light propulsion, environmental suitability and functional versatility of MNMs. There are no reports about the review focusing on photothermal-driven MNMs up to now. Herein, we systematically review the latest progress of photothermal-driven MNMs including design principle, fabrication strategy of various MNMs with different structures and nanobiomedical applications. Moreover, the summary and outlook on the development prospects and challenges of photothermal-driven MNMs are proposed, hoping to provide new ideas for the future design of photothermal-driven MNMs with efficient propulsion, multiple functions and high biocompatibility.

Self-reported and self-facilitated theranostic oxygen nano-economizer for precise and hypoxia alleviation-potentiated photodynamic therapy

Photodynamic therapy (PDT) has been extensively investigated for cancer treatment by virtue of singlet oxygen-induced oxidative damage to tumors. Nevertheless, the therapeutic efficiency of PDT is still limited by the low singlet oxygen yield attributed to the improper irradiation duration and the tumor hypoxic microenvironment. To tackle these challenges, we elaborately design a theranostic oxygen nano-economizer to self-report the optimal irradiation duration and alleviate tumor hypoxia simultaneously, which is engineered by fluorescent 9,10-anthracenyl bis (benzoic acid) (DPA)-MOF, tetrakis (4-carboxyphenyl) porphyrin (TCPP), triphenyl phosphine (TPP) and redox-responsive lipid-PEG (DSPE-SS-PEG2k). Upon laser irradiation, the fluorescence of DPA-MOF could be quenched, thereby self-reporting the optimal irradiation duration for sufficient PDT. The decoration of DSPE-SS-PEG2k and TPP endows the theranostic oxygen nano-economizer with a tumor-specific response and mitochondrial targeting capability, respectively. Notably, singlet oxygen generated from TCPP reduces oxygen consumption by disrupting the entire oxidative phosphorylation (OXPHOS) pathway in the mitochondria of tumor cells, further improving the level of singlet oxygen in a self-facilitated manner for hypoxia alleviation-potentiated PDT. As expected, such a self-reported and self-facilitated theranostic oxygen nano-economizer exhibits potent antitumor activity in the 4T1 tumor-bearing mouse model. This study offers a theranostic paradigm for precise and hypoxia alleviation-potentiated cancer therapy.

Repurposing Tamoxifen for Tumor Microenvironment Priming and Enhanced Tumor-Targeted Drug Delivery

The dense stromal matrix in fibrotic tumors hinders tumor-targeted drug delivery. Tamoxifen (TMX), an estrogen receptor modulator that is clinically used for the treatment of breast cancer, has been shown to reprogram the tumor microenvironment (TME) and to alleviate desmoplasia. We here investigated if TMX, administered in free and nano-formulated form, can be repurposed as a TME remodeling agent to improve tumor accumulation of nano-formulations in pancreatic ductal adenocarcinoma and triple-negative breast cancer mouse models, evaluated using clinical-stage Cy7-labeled core-crosslinked polymeric micelles (CCPM). Under control conditions, we found higher levels of Cy7-CCPM in PANC-1 tumors (16.7 % ID g-1 at 48 h post i.v. injection) than in 4T1 tumors (11.0 % ID g-1). In both models, free and nano-formulated TMX failed to improve CCPM delivery. These findings were congruent with the results from histopathological immunofluorescence analysis of tumor tissue, which indicated that TMX treatment did not significantly change vascularization, perfusion, macrophage infiltration, collagen density, and collagen fiber thickness. Altogether, our results demonstrate that in PANC-1 and 4T1 mouse models, TMX treatment does not contribute to beneficial TME priming and enhanced tumor-targeted drug delivery.

Multi-target responsive nanoprobe with cellular-level accuracy for spatiotemporally selective photodynamic therapy

Photodynamic therapy is known for its non-invasiveness to significantly reduce undesired side effects on patients. However, the infiltration and invasiveness of tumor growth are still beyond the specificity of traditional light-controlled photodynamic therapy (PDT), which lacks cellular-level accuracy to tumor cells, possibly leading to "off-target" damage to healthy tissues such as the skin or immune cells infiltrated. Here, upconversion nanoparticles (UCNPs) were co-encapsulated with manganese dioxide (MnO2) by amphiphilic polymers poly(styrene-co-methyl acrylate) (PSMA) and further coated with photosensitizer (riboflavin)-loaded mesoporous silica (C@S/V). The C@S/V nanoprobes exhibited shielded upconversion luminescence in normal conditions (pH 7.4, no hydroperoxide (H2O2)) under 980-nm irradiation and thus minimal reactive oxygen production from riboflavin. However, the excess H2O2 (1 mM) and acidic environment (pH 5.5) could decompose the MnO2 within the C@S/V, resulting in remarkable enhancement of upconversion luminescence and a favorable hypoxia-relieving condition for PDT, providing a spatiotemporal signal for therapy initiation. The C@S/V nanoprobes were applied to the co-culture of normal cells (HEK293) and pancreatic cancer cells (Panc02) and performed a selective killing on Panc02 under the 980-nm irradiation. By using the "double-safety" strategy, a responsive C@S/V nanoprobe was designed by the selective activation of acidic and H2O2-rich conditions and 980-nm irradiation for spatiotemporally selective photodynamic therapy with cellular-level accuracy.

NIR-dye bridged human serum albumin reassemblies for effective photothermal therapy of tumor

Human serum albumin (HSA) based drug delivery platforms that feature desirable biocompatibility and pharmacokinetic property are rapidly developed for tumor-targeted drug delivery. Even though various HSA-based platforms have been established, it is still of great significance to develop more efficient preparation technology to broaden the therapeutic applications of HSA-based nano-carriers. Here we report a bridging strategy that unfastens HSA to polypeptide chains and subsequently crosslinks these chains by a bridge-like molecule (BPY-Mal2) to afford the HSA reassemblies formulation (BPY@HSA) with enhanced loading capacity, endowing the BPY@HSA with uniformed size, high photothermal efficacy, and favorable therapeutic features. Both in vitro and in vivo studies demonstrate that the BPY@HSA presents higher delivery efficacy and more prominent photothermal therapeutic performance than that of the conventionally prepared formulation. The feasibility in preparation, stability, high photothermal conversion efficacy, and biocompatibility of BPY@HSA may facilitate it as an efficient photothermal agents (PTAs) for tumor photothermal therapy (PTT). This work provides a facile strategy to enhance the loading capacity of HSA-based crosslinking platforms in order to improve delivery efficacy and therapeutic effect.

Biomimetic biomineralization nanoplatform-mediated differentiation therapy and phototherapy for cancer stem cell inhibition and antitumor immunity activation

Growing evidence suggests that the presence of cancer stem cells (CSCs) is a major challenge in current tumor treatments, especially the transition from non-CSCs to differentiation of CSCs for evading conventional therapies and driving metastasis. Here we propose a therapeutic strategy of synergistic differentiation therapy and phototherapy to induce differentiation of CSCs into mature tumor cells by differentiation inducers and synergistic elimination of them and normal cancer cells through phototherapy. In this work, we synthesized a biomimetic nanoplatform loaded with IR-780 and all-trans retinoic acid (ATRA) via biomineralization. This method can integrate aluminum ions into small-sized protein carriers to form nanoclusters, which undergo responsive degradation under acidic conditions and facilitate deep tumor penetration. With the help of CSC differentiation induced by ATRA, IR-780 inhibited the self-renewal of CSCs and cancer progression by generating hyperthermia and reactive oxygen species in a synergistic manner. Furthermore, ATRA can boost immunogenic cell death induced by phototherapy, thereby strongly causing a systemic anti-tumor immune response and efficiently eliminating CSCs and tumor cells. Taken together, this dual strategy represents a new paradigm of targeted eradication of CSCs and tumors by inducing CSC differentiation, improving photothermal therapy/photodynamic therapy and enhancing antitumor immunity.

Porous SiO2-Based Reactor with Self-Supply of O2 and H2O2 for Synergistic Photo-Thermal/Photodynamic Therapy

Purpose

Although the combined photo-thermal (PTT) and photodynamic therapy (PDT) of tumors have demonstrated promise as effective cancer therapy, the hypoxic and insufficient H₂O₂ supply of tumors seriously limits the efficacy of PDT, and the acidic environment reduces the catalytic activity of nanomaterial in the tumor microenvironment. To develop a platform for efficiently addressing these challenges, we constructed a nanomaterial of Aptamer@dox/GOD-MnO₂-SiO₂@HGNs-Fc@Ce6 (AMS) for combination tumor therapy. The treatment effects of AMS were evaluated both in vitro and in vivo.

Methods

In this work, Ce6 and hemin were loaded on graphene (GO) through π-π conjugation, and Fc was connected to GO via amide bond. The HGNs-Fc@Ce6 was loaded into SiO₂, and coated with dopamine. Then, MnO₂ was modified on the SiO₂. Finally, AS1411-aptamer@dox and GOD were fixed to gain AMS. We characterized the morphology, size, and zeta potential of AMS. The oxygen and reactive oxygen species (ROS) production properties of AMS were analyzed. The cytotoxicity of AMS was detected by MTT and calcein-AM/PI assays. The apoptosis of AMS to a tumor cell was estimated with a JC-1 probe, and the ROS level was detected with a 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) probe. The anticancer efficacy in vivo was analyzed by the changes in the tumor size in different treatment groups.

Results

AMS was targeted to the tumor cell and released doxorubicin. It decomposed glucose to produce H₂O₂ in the GOD-mediated reaction. The generated sufficient H₂O₂ was catalyzed by MnO₂ and HGNs-Fc@Ce6 to produce O₂ and free radicals (•OH), respectively. The increased oxygen content improved the hypoxic environment of the tumor and effectively reduced the resistance to PDT. The generated •OH enhanced the ROS treatment. Moreover, AMS depicted a good photo-thermal effect.

Conclusion

The results revealed that AMS had an excellent enhanced therapy effect by combining synergistic PTT and PDT.

Albumin-based near-infrared phototheranostics for frequency upconversion luminescence/photoacoustic dual-modal imaging-guided photothermal therapy

Engineering versatile phototheranostics for multimodal diagnostic imaging and effective therapy has great potential in cancer treatment. However, developing an inherently versatile molecule is a huge challenge. In this work, a near-infrared organic dye (NRh) was synthesized and further bound with bovine serum albumin (BSA) to construct facile "one-for-all" phototheranostics (NRh-BSA NPs), which exhibited enhanced frequency upconversion luminescence (FUCL, λ_ex/em = 850/825 nm) and excellent photoacoustic (PA) and photothermal properties (λ^'_ex = 808 nm). Additionally, the BSA-modified phototheranostics NRh-BSA NPs showed specific accumulation in the tumor region through passive targeting. Based on the FUCL/PA dual modal imaging-guidance, the NRh-BSA NPs not only can guarantee the accuracy of imaging of the U87MG tumor sites, but also can improve the therapeutic effect on ablating tumors without recurrence by photothermal therapy (PTT). Collectively, our work proposed a novel strategy to construct versatile phototheranostics with the unique FUCL/PA imaging-guided technique for accurate cancer theranostics.

Design of Disintegrable Nanoassemblies to Release Multiple Small-Sized Nanoparticles

The therapeutic and diagnostic effects of nanoparticles depend on the efficiency of their delivery to targeted tissues, such as tumors. The size of nanoparticles, among other characteristics, plays a crucial role in determining their tissue penetration and retention. Small nanoparticles may penetrate deeper into tumor parenchyma but are poorly retained, whereas large ones are distributed around tumor blood vessels. Thus, compared to smaller individual nanoparticles, assemblies of such nanoparticles due to their larger size are favorable for prolonged blood circulation and enhanced tumor accumulation. Upon reaching the targeted tissues, nanoassemblies may dissociate at the target region and release the smaller nanoparticles, which is beneficial for their distribution at the target site and ultimate clearance. The recent emerging strategy that combines small nanoparticles into larger, biodegradable nanoassemblies has been demonstrated by several groups. This review summarizes a variety of chemical and structural designs for constructing stimuli-responsive disintegrable nanoassemblies as well as their different disassembly routes. These nanoassemblies have been applied as demonstrators in the fields of cancer therapy, antibacterial infection, ischemic stroke recovery, bioimaging, and diagnostics. Finally, we summarize stimuli-responsive mechanisms and their corresponding nanomedicine designing strategies, and discuss potential challenges and barriers towards clinical translation.

Mesopore-encaged active MnOx in nano-silica selectively suppresses lung cancer cells by inducing autophagy

Autophagy induced by nanomaterials is one of the intracellular catabolic pathways that degrade and recycle the biomacromolecules and damaged organelles in cells and has emerged as a very promising pharmacological target critical to future drug development and anti-cancer therapy. Herein, we developed mesopore-encaged highly-dispersed active cluster-like MnOx in nanosilica entitled MnO-MS, with a size of around 130 nm. Our studies show that MnO-MS could not only obviously induce autophagy in both stable GFP-LC3 HeLa cells and GFP-LC3-mCherry HeLa cells but also could selectively inhibit lung cancer A549 cell growth at 11.19 μg mL^-1 (IC₅₀) while exhibiting little cytotoxicity in normal cells. Encouraged by these interesting results, a further mechanistic study reveals that reactive oxygen species (ROS) were excited by the active MnOx in nanosilica, leading to the disruption of mitochondrial membrane potential (MMP), enhancement of ATG5A/ATG16L/ATG4B/Beclin1, and finally, inhibition of the mTOR signaling pathways. Collectively, these findings indicate that MnO-MS-induced cell death via autophagy pathways in cancer cells. Furthermore, MnO-MS significantly inhibited tumor growth with minimal side effects in vivo, and it is envisioned that MnO-MS can be further developed as a potential autophagy inducer for the treatment of lung cancers.

Manipulate tumor hypoxia for improved photodynamic therapy using nanomaterials

Due to its low adverse effects, minimal invasiveness, and outstanding patient compliance, photodynamic therapy (PDT) has drawn a great deal of interest, which is achieved through incomplete reduction of O₂ by a photosensitizer under light illumination that produces amounts of reactive oxygen species (ROS). However, tumor hypoxia significantly hinders the therapeutic effect of PDT so that tumor cells cannot be eliminated, which results in tumor cells proliferating, invading, and metastasizing. Additionally, O₂ consumption during PDT exacerbates hypoxia in tumors, leading to several adverse events after PDT treatment. In recent years, various investigations have focused on conquering or using tumor hypoxia by nanomaterials to amplify PDT efficacy, which is summarized in this review. This comprehensive review's objective is to present novel viewpoints on the advancement of oxygenation nanomaterials in this promising field, which is motivated by hypoxia-associated anti-tumor therapy.

A positive self-amplified H2O2 and acidity circulation for boosting CDT-PTT-starvation therapy

The therapeutic application of chemodynamic therapy (CDT) is severely limited by the insufficient intracellular H₂O₂ and acidity in tumor. Herein, an acid-sensitive nanoplatform (ZIF67-ICG/TAM@GOx) to promote H₂O₂ and acidity enhancement through intracellular cyclic amplification for enhanced CDT is rationally designed. Notably, the acidic conditions of the tumor microenvironment (TME) can turn on the switch of the nanoplatform, setting free the loaded tamoxifen (TAM) and indocyanine green (ICG). The mitochondrial respiration inhibitor TAM and the superoxide dismutase-mimicking ZIF67 synergistically lead to an increase in the content of O₂ and H₂O₂, accelerating the depletion of β-d-glucose by GOx to generate gluconate and H₂O₂. The gluconate in turn boosts the acidity to facilitate the collapse of nanoparticles, further significantly promoting the accumulation of intracellular H₂O₂ through a positive circulation. Consequently, the amplificated endogenous H₂O₂ is catalyzed by Co²⁺ to liberate hydroxyl radicals (•OH). Besides, ICG-mediated photothermal therapy (PTT) and GOx-induced starvation therapy along with CDT realize the synergistic cancer treatment. Importantly, in vitro and in vivo experiments verified that the nanoplatform performed superior specificity and excellent therapeutic responses. The smart nanoplatform overcomes H₂O₂ and acidity deficiency simultaneously for intensive CDT, providing new prospects for the development of biocompatible cancer synergistic therapy strategies.

Anti-Hypoxia Nanoplatforms for Enhanced Photosensitizer Uptake and Photodynamic Therapy Effects in Cancer Cells

Photodynamic therapy (PDT) holds great promise in cancer eradication due to its target selectivity, non-invasiveness, and low systemic toxicity. However, due to the hypoxic nature of many native tumors, PDT is frequently limited in its therapeutic effect. Additionally, oxygen consumption during PDT may exacerbate the tumor's hypoxic condition, which stimulates tumor proliferation, metastasis, and invasion, resulting in poor treatment outcomes. Therefore, various strategies have been developed to combat hypoxia in PDT, such as oxygen carriers, reactive oxygen supplements, and the modulation of tumor microenvironments. However, most PDT-related studies are still conducted on two-dimensional (2D) cell cultures, which fail to accurately reflect tissue complexity. Thus, three-dimensional (3D) cell cultures are ideal models for drug screening, disease simulation and targeted cancer therapy, since they accurately replicate the tumor tissue architecture and microenvironment. This review summarizes recent advances in the development of strategies to overcome tumor hypoxia for enhanced PDT efficiency, with a particular focus on nanoparticle-based photosensitizer (PS) delivery systems, as well as the advantages of 3D cell cultures.

Prospects for hypoxia-based drug delivery platforms for the elimination of advanced metastatic tumors: From 3D modeling to clinical concepts

Hypoxia is a unique characteristic of the solid tumor microenvironment. Hypoxia contributes to multi-drug resistance, metastasis and cancer relapse through numerous molecular pathways, but at the same time provides an opportunity for the development of novel drugs or modalities specifically targeting hypoxic tumor regions. Given the high significance of tumor hypoxia in therapeutic results, we here discuss a variety of hypoxia-adopted strategies, and their potential and utility in the treatment of deep-seated hypoxic tumor cells. We discuss the merits and demerits of these approaches, as well as their combination with other approaches such as photodynamic therapy. We also survey the currently available 3D hypoxia modeling systems, in particular organoid-based microfluidics. Finally, we discuss the potential and the current status of preclinical tumor hypoxia approaches in clinical trials for advanced cancer. We believe that multi-modal imaging and therapeutic hypoxia adopted drug delivery platforms could provide better efficacy and safety profiles, and more importantly personalized therapy. Determining the hypoxia status of tumors could offer a second chance for the clinical translation of hypoxia-based agents, such as hypoxia activated prodrugs (HAPs) from bench to bedside.

A tumor pH-responsive autocatalytic nanoreactor as a H2O2 and O2 self-supplying depot for enhanced ROS-based chemo/photodynamic therapy

Combining the internal force-driven chemodynamic therapy (CDT) and the external energy-triggered photodynamic therapy (PDT) holds great promise to achieve an advanced anticancer effect based on reactive oxygen species (ROS). However, the insufficient oxy-substrates supply in tumor microenvironment, like hydrogen peroxide (H₂O₂) and oxygen (O₂), is the Achilles heel that greatly restricts the efficacy of this ROS-based treatment. Herein, the construction of a copper peroxide-based tumor pH-responsive autocatalytic nanoreactor (CESAR), via an albumin-mediated biomimetic mineralization strategy is described. The decoration of human serum albumin endows the nanoreactor good hydrophilicity and biocompatibility, which is highly desired for the metal-based materials. Upon exposure to acidic tumor microenvironment, CESAR presents a pH-triggered disintegration with Cu²⁺, H₂O₂ and O₂ generated instantly. The generated H₂O₂ complements the hyperoxide deficiency and initiates a localized Fenton-like reaction with the assistance of Cu²⁺ for highly toxic hydroxyl radicals (•OH) production for improving CDT. The evolved O₂ gas enables hypoxia relief for enhanced Ce6-mediated PDT. This H₂O₂/O₂ self-supplying strategy significantly amplifies the tumor oxidative damage and gains an optimal treatment outcome, which offers a new paradigm for optimizing the tumor therapeutic options limited by oxide or hyperoxide deficiency, not only for CDT/PDT, but also other oxy-substrates involved strategies. STATEMENT OF SIGNIFICANCE: The shortage of oxy-substrates in the tumor microenvironment remains a great challenge for ROS-based cancer therapy. Herein, we introduce human serum albumin as a scaffold to stabilize copper peroxide nanomaterials for constant production of H₂O₂ and O₂ to enhance chemodynamic/photodynamic therapy. The tumor pH-triggered H₂O₂/O₂ production and Cu²⁺ release are confirmed, assuring the strategy of a highly precise, effective way to destroy tumor without any side effects. This work lends new and exciting insights into the engineering design of autocatalytic oxy-substrates self-supply nanoreactor for overcoming the bottlenecks, like the oxy-substrates deficiency of CDT/PDT and the poor stability of metal peroxides, to achieve highly effective chemodynamic/photodynamic therapy.

Dual-Stage Irradiation of Size-Switchable Albumin Nanocluster for Cascaded Tumor Enhanced Penetration and Photothermal Therapy

The triple-negative breast cancer (TNBC) microenvironment makes a feature of aberrant vasculature, high interstitial pressure, and compact extracellular matrix, which combine to reduce the delivery and penetration of therapeutic agents, bringing about incomplete elimination of cancer cells. Herein, employing the tumor penetration strategy of size-shrinkage combined with ligand modification, we constructed a photothermal nanocluster for cascaded deep penetration in tumor parenchyma and efficient eradication of TNBC cells. In our approach, the photothermal agent indocyanine green (ICG) is laded in human serum albumin (HSA), which is cross-linked by a thermally labile azo linker (VA057) and then further modified with a tumor homing/penetrating tLyP-1 peptide (HP), resulting in a TNBC-targeting photothermal-responsive size-switchable albumin nanocluster (ICG@HSA-Azo-HP). Aided by the enhanced permeability and retention effect and guidance of HP, the ca. 149 nm nanoclusters selectively accumulate in the tumor site and then, upon mild irradiation with the 808 nm laser, disintegrate into 11 nm albumin fractions that possess enhanced intratumoral diffusion ability. Meanwhile, HP initiates the CendR pathway among the nutrient-deficient tumor cells and facilitates the transcellular delivery of the nanocluster and its disintegrated fractions for subsequent therapy. By employing this size-shrinkage and peptide-initiated transcytosis strategy, ICG@HSA-Azo-HP possesses excellent penetration capabilities and shows extensive penetration depth in three-dimensional multicellular tumor spheroids after irradiation. Moreover, with a superior photothermal conversion effect, the tumor-penetrating nanocluster can implement effective photothermal therapy throughout the tumor tissue under a second robust irradiation. Both in vivo orthotopic and ectopic TNBC therapy confirmed the efficient tumor inhibition of ICG@HSA-Azo-HP after dual-stage irradiation. The synergistic penetration strategy of on-demanded size-shrinkage and ligand guidance accompanied by clinically feasible NIR irradiation provides a promising approach for deep-penetrating TNBC therapy.

Semiconductor quantum dots for photodynamic therapy: Recent advances

Photodynamic therapy is a promising cancer treatment that induces apoptosis as a result of the interactions between light and a photosensitizing drug. Lately, the emergence of biocompatible nanoparticles has revolutionized the prospects of photodynamic therapy (PDT) in clinical trials. Consequently, a lot of research is now being focused on developing non-toxic, biocompatible nanoparticle-based photosensitizers for effective cancer treatments using PDT. In this regard, semiconducting quantum dots have shown encouraging results. Quantum dots are artificial semiconducting nanocrystals with distinct chemical and physical properties. Their optical properties can be fine-tuned by varying their size, which usually ranges from 1 to 10 nm. They present many advantages over conventional photosensitizers, mainly their emission properties can be manipulated within the near IR region as opposed to the visible region by the former. Consequently, low intensity light can be used to penetrate deeper tissues owing to low scattering in the near IR region. Recently, successful reports on imaging and PDT of cancer using carbon (carbon, graphene based) and metallic (Cd based) based quantum dots are promising. This review aims to summarize the development and the status quo of quantum dots for cancer treatment.

Light-triggered photodynamic nanomedicines for overcoming localized therapeutic efficacy in cancer treatment

Photodynamic nanomedicines have significantly enhanced the therapeutic efficacy of photosensitizers (PSs) by overcoming critical limitations of PSs such as poor water solubility and low tumor accumulation. Furthermore, functional photodynamic nanomedicines have enabled overcoming oxygen depletion during photodynamic therapy (PDT) and tissue light penetration limitation by supplying oxygen or upconverting light in targeted tumor tissues, resulting in providing the potential to overcome biological therapeutic barriers of PDT. Nevertheless, their localized therapeutic effects still remain a huddle for the effective treatment of metastatic- or recurrent tumors. Recently, newly designed photodynamic nanomedicines and their combination chemo- or immune checkpoint inhibitor therapy enable the systemic treatment of various metastatic tumors by eliciting antitumor immune responses via immunogenic cell death (ICD). This review introduces recent advances in photodynamic nanomedicines and their applications, focusing on overcoming current limitations. Finally, the challenges and future perspectives of the clinical translation of photodynamic nanomedicines in cancer PDT are discussed.

Engineering prodrug nanomicelles as pyroptosis inducer for codelivery of PI3K/mTOR and CDK inhibitors to enhance antitumor immunity

Aberrant activation of oncogenic signaling pathways in tumors can promote resistance to the antitumor immune response. However, single blockade of these pathways is usually ineffective because of the complex crosstalk and feedback among oncogenic signaling pathways. The enhanced toxicity of free small molecule inhibitor combinations is considered an insurmountable barrier to their clinical applications. To circumvent this issue, we rationally designed an effective tumor microenvironment-activatable prodrug nanomicelle (PNM) for cancer therapy. PNM was engineered by integrating the PI3K/mTOR inhibitor PF-04691502 (PF) and the broad spectrum CDK inhibitor flavopiridol (Flav) into a single nanoplatform, which showed tumor-specific accumulation, activation and deep penetration in response to the high glutathione (GSH) tumoral microenvironment. The codelivery of PF and Flav could trigger gasdermin E (GSDME)-based immunogenic pyroptosis of tumor cells to elicit a robust antitumor immune response. Furthermore, the combination of PNM-induced immunogenic pyroptosis with anti-programmed cell death-1 (αPD-1) immunotherapy further boosted the antitumor effect and prolonged the survival time of mice. Collectively, these results indicated that the pyroptosis-induced nanoplatform codelivery of PI3K/mTOR and CDK inhibitors can reprogram the immunosuppressive tumor microenvironment and efficiently improve checkpoint blockade cancer immunotherapy.

Engineered extracellular vesicles as intelligent nanosystems for next-generation nanomedicine

Extracellular vesicles (EVs), as natural carriers of bioactive cargo, have a unique micro/nanostructure, bioactive composition, and characteristic morphology, as well as fascinating physical, chemical and biochemical features, which have shown promising application in the treatment of a wide range of diseases. However, native EVs have limitations such as lack of or inefficient cell targeting, on-demand delivery, and therapeutic feedback. Recently, EVs have been engineered to contain an intelligent core, enabling them to (i) actively target sites of disease, (ii) respond to endogenous and/or exogenous signals, and (iii) provide treatment feedback for optimal function in the host. These advances pave the way for next-generation nanomedicine and offer promise for a revolution in drug delivery. Here, we summarise recent research on intelligent EVs and discuss the use of "intelligent core" based EV systems for the treatment of disease. We provide a critique about the construction and properties of intelligent EVs, and challenges in their commercialization. We compare the therapeutic potential of intelligent EVs to traditional nanomedicine and highlight key advantages for their clinical application. Collectively, this review aims to provide a new insight into the design of next-generation EV-based theranostic platforms for disease treatment.

Targeted delivery of maytansine to liver cancer cells via galactose-modified supramolecular two-dimensional glycomaterial

A two-dimensional (2D) glycomaterial for targeted delivery of maytansine to liver cancer cells was developed. Host-guest interaction between a galactosyl dye and human serum albumin (HSA) produces supramolecular galactoside-HSA conjugates, which are then used to coat 2D MoS₂. The 2D glycomaterial was shown to be capable of the targeted delivery of maytansine to a liver cancer cell line that highly expresses a galactose receptor, resulting in greater cytotoxicity than maytansine alone.

Albumin-Based Therapeutics Capable of Glutathione Consumption and Hydrogen Peroxide Generation for Synergetic Chemodynamic and Chemotherapy of Cancer

A nanoscale therapeutic system with good biocompatibility was facilely fabricated by the coassembly of human serum albumin and glucose oxidase (GOD), where the former was pretreated with metal ions through a chelating agent or the chemotherapeutic prodrug oxaliplatin (Oxa(IV)). Among different chelating metal ions used, Mn²⁺ ion was selected to produce hydroxyl radical (•OH) efficiently through Fenton-like reaction, while GOD loaded in the system was able to generate a large amount of hydrogen peroxide for promoting efficient conversion into highly toxic •OH. In the meanwhile, the conversion of the Oxa(IV) prodrug into chemotherapeutic Oxa(II) was beneficial for the consumption of glutathione, thereby enhancing the chemodynamic therapy (CDT) efficacy. Based on the combined chemotherapy and CDT, the treatment with this system leads to superior antitumor outcome.

Recent advances in upconversion nanoparticle-based nanocomposites for gas therapy

Gas therapy has attracted wide attention for the treatment of various diseases. However, a controlled gas release is highly important for biomedical applications. Upconversion nanoparticles (UCNPs) can precisely convert the long wavelength of light to ultraviolet/visible (UV/Vis) light in gas therapy for the controlled gas release owing to their unique upconversion luminescence (UCL) ability. In this review, we mainly summarized the recent progress of UCNP-based nanocomposites in gas therapy. The gases NO, O2, H2, H2S, SO2, and CO play an essential role in the physiological and pathological processes. The UCNP-based gas therapy holds great promise in cancer therapy, bacterial therapy, anti-inflammation, neuromodulation, and so on. Furthermore, the limitations and prospects of UCNP-based nanocomposites for gas therapy are also discussed.

Recent Progress of Novel Nanotechnology Challenging the Multidrug Resistance of Cancer

Multidrug resistance (MDR) of tumors is one of the clinical direct reasons for chemotherapy failure. MDR directly leads to tumor recurrence and metastasis, with extremely grievous mortality. Engineering a novel nano-delivery system for the treatment of MDR tumors has become an important part of nanotechnology. Herein, this review will take those different mechanisms of MDR as the classification standards and systematically summarize the advances in nanotechnology targeting different mechanisms of MDR in recent years. However, it still needs to be seriously considered that there are still some thorny problems in the application of the nano-delivery system against MDR tumors, including the excessive utilization of carrier materials, low drug-loading capacity, relatively narrow targeting mechanism, and so on. It is hoped that through the continuous development of nanotechnology, nano-delivery systems with more universal uses and a simpler preparation process can be obtained, for achieving the goal of defeating cancer MDR and accelerating clinical transformation.

Recent Advances in Strategies for Addressing Hypoxia in Tumor Photodynamic Therapy

Photodynamic therapy (PDT) is a treatment modality that uses light to target tumors and minimize damage to normal tissues. It offers advantages including high spatiotemporal selectivity, low side effects, and maximal preservation of tissue functions. However, the PDT efficiency is severely impeded by the hypoxic feature of tumors. Moreover, hypoxia may promote tumor metastasis and tumor resistance to multiple therapies. Therefore, addressing tumor hypoxia to improve PDT efficacy has been the focus of antitumor treatment, and research on this theme is continuously emerging. In this review, we summarize state-of-the-art advances in strategies for overcoming hypoxia in tumor PDTs, categorizing them into oxygen-independent phototherapy, oxygen-economizing PDT, and oxygen-supplementing PDT. Moreover, we highlight strategies possessing intriguing advantages such as exceedingly high PDT efficiency and high novelty, analyze the strengths and shortcomings of different methods, and envision the opportunities and challenges for future research.

Smart transformable nanoparticles for enhanced tumor theranostics

The physical morphologies of nanoparticles, especially size and shape, always significantly influence their biological behaviors. In the past, nanoparticles with constant physical morphologies have been widely investigated and applied in tumor theranostics. With the increased in-depth knowledge of tumors and physiological microenvironments, nanoparticles are required to self-adjust their physical morphologies during their circulation in varying physiological microenvironments and when reaching tumor site that possess distinct microenvironments. Therefore, smart transformable nanomaterials, which can alter their morphologies under different physiological conditions, show great potential in advanced tumor theranostics. This review summarizes the influence of nanoparticles' physical morphologies on their biological behaviors under different physiological conditions, highlights the designs of transformable nanoparticles serving as a guideline for their construction, intensively discusses the recent biomedical applications of these smart transformable nanoparticles for tumor theranostics, and also proposes future challenges and perspectives in the development of smart transformable nanoparticles for tumor theranostics.

ZnS@BSA Nanoclusters Potentiate Efficacy of Cancer Immunotherapy

Although immunotherapy such as immune checkpoint inhibitors has shown promising efficacy in cancer treatment, the responsiveness among patients is relatively limited. Activation of the cyclic guanosine monophosphate-adenosine monophosphate synthase/interferon gene stimulator (cGAS/STING) signaling pathway to upregulate innate immunity has become an emerging strategy for enhancing tumor immunotherapy. Herein, ZnS@BSA (bovine serum albumin) nanoclusters synthesized via a self-assembly approach are reported, where the released zinc ions under acidic tumor microenvironment significantly enhance cGAS/STING signals. Meanwhile, intracellular zinc ions can produce reactive oxygen species, which is further facilitated by the generated H₂ S gas from ZnS@BSA via specifically inhibiting catalase in hepatocellular carcinoma cells. It is found that the nanoclusters activate the cGAS/STING signals in mice, which promotes the infiltration of CD8⁺ T cells at the tumor site and cross-presentation of dendritic cells, leading to an improved immunotherapy efficacy against hepatocellular carcinoma.

Conquering the Hypoxia Limitation for Photodynamic Therapy

Photodynamic therapy (PDT) has aroused great research interest in recent years owing to its high spatiotemporal selectivity, minimal invasiveness, and low systemic toxicity. However, due to the hypoxic nature characteristic of many solid tumors, PDT is frequently limited in therapeutic effect. Moreover, the consumption of O₂ during PDT may further aggravate the tumor hypoxic condition, which promotes tumor proliferation, metastasis, and invasion resulting in poor prognosis of treatment. Therefore, numerous efforts have been made to increase the O₂ content in tumor with the goal of enhancing PDT efficacy. Herein, these strategies developed in past decade are comprehensively reviewed to alleviate tumor hypoxia, including 1) delivering exogenous O₂ to tumor directly, 2) generating O₂ in situ, 3) reducing tumor cellular O₂ consumption by inhibiting respiration, 4) regulating the TME, (e.g., normalizing tumor vasculature or disrupting tumor extracellular matrix), and 5) inhibiting the hypoxia-inducible factor 1 (HIF-1) signaling pathway to relieve tumor hypoxia. Additionally, the O₂ -independent Type-I PDT is also discussed as an alternative strategy. By reviewing recent progress, it is hoped that this review will provide innovative perspectives in new nanomaterials designed to combat hypoxia and avoid the associated limitation of PDT.

Size-Adjustable Nano-Drug Delivery Systems for Enhanced Tumor Retention and Penetration

Over the past decades, nano-drug delivery systems have shown great potential in improving tumor treatment. And the controllability and design flexibility of nanoparticles endow them a broad development space. The particle size is one of the most important factors affecting the potency of nano-drug delivery systems. Large-size (100–200 nm) nanoparticles are more conducive to long circulation and tumor retention, but have poor tumor penetration; small-size (<50 nm) nanoparticles can deeply penetrate tumor but are easily cleared. Most of the current fixed-size nanoparticles are difficult to balance the retention and penetration, while the proposal of size-adjustable nano-drug delivery systems offers a solution to this paradox. Many endogenous and exogenous stimuli, such as acidic pH, upregulated enzymes, temperature, light, catalysts, redox conditions, and reactive oxygen species, can trigger the in situ transformation of nanoparticles based on protonation, hydrolysis, click reaction, phase transition, photoisomerization, redox reaction, etc. In this review, we summarize the principles and applications of stimuli-responsive size-adjustable strategies, including size-enlargement strategies and size-shrinkage strategies. We also propose the challenges faced by size-adjustable nano-drug delivery systems, hoping to promote the development of this strategy.

Nanomaterials targeting tumor associated macrophages for cancer immunotherapy

Tumor-associated macrophages (TAMs) play an important role in regulating tumor growth, invasion and metastasis, and constitute approximately 50% of tumor mass. TAMs can exist in two different subtypes, M1-polarized phenotype (pro-inflammatory and immunostimulatory) and M2-polarized phenotype (immunosuppressive myeloid cells). M2 macrophages can suppress CD8⁺ T cells to support tumor survival. A number of biological strategies aimed at engineering macrophages to modulate the tumor immune microenvironment remain at the forefront of cancer research. Here, we review the different therapeutic strategies that have been developed based on nanotechnology to modulate macrophage functions, such as inhibition of macrophage recruitment to tumor, depletion of M2-polarized macrophages, reprograming of M2-polarized macrophages to M1-polarized macrophages, and blocking of the CD47-signal-regulatory protein alpha (CD47-SIRPα) pathway. Furthermore, we also discuss how to image TAMs with nanoparticles to unravel novel treatment options and observe their responses to the various therapies. Overall, macrophage-mediated immune modulation based on nanotechnology can be further investigated to be effectively developed as an immunoadjuvant therapy against different cancers.

An intelligent responsive macrophage cell membrane-camouflaged mesoporous silicon nanorod drug delivery system for precise targeted therapy of tumors

Macrophage cell membrane-camouflaged nanocarriers can effectively reduce immune cell clearance and actively target tumors. In this study, a macrophage cell membrane-camouflaged mesoporous silica nanorod (MSNR)-based antitumor drug carrier equipped with a cationic polymer layer was developed. As drug carriers, these MSNRs were loaded with the thermosensitive phase change material L-menthol (LM), the chemotherapy drug doxorubicin (DOX) and the fluorescent molecule indocyanine green (ICG). The rod-like shape of the MSNRs was shown to enhance the penetration of the drug carriers to tumors. In the weakly acidic tumor microenvironment, the cationic polymer exhibited a proton sponge effect to trigger macrophage cell membrane coating detachment, promoting tumor cell uptake. Following nanocarrier uptake, ICG is heated by near-infrared (NIR) irradiation to make LM undergo a phase transition to release DOX and generate a synergistic effect of thermochemotherapy which kills tumor cells and inhibits tumor growth together with reactive oxygen species (ROS) produced by ICG. Overall, this nanohybrid drug delivery system demonstrates an intelligent cascade response, leads to tissue-cell specific targeting and improves drug release accuracy, thus proving to be an effective cancer therapy.

Effective tumor vessel barrier disruption mediated by perfluoro-N-(4-methylcyclohexyl) piperidine nanoparticles to enhance the efficacy of photodynamic therapy

BACKGROUND

Currently, limited tumor drug permeation, poor oxygen perfusion and immunosuppressive microenvironments are the most important bottlenecks that significantly reduce the efficacy of photodynamic therapy (PDT). The main cause of these major bottlenecks is the platelet activation maintained abnormal tumor vessel barriers. Thus, platelet inhibition may present a new way to most effectively enhance the efficacy of PDT. However, to the best of our knowledge, few studies have validated the effectiveness of such a way in enhancing the efficacy of PDT both in vivo and in vitro. In this study, perfluoro-N-(4-methylcyclohexyl) piperidine-loaded albumin (PMP@Alb) nanoparticles were discovered, which possess excellent platelet inhibition ability. After PMP@Alb treatment, remarkably enhanced intra-tumoral drug accumulation, oxygen perfusion and T cell infiltration could be observed owing to the disrupted tumor vessel barriers. Besides, the effect of ICG@Lip mediated PDT was significantly amplified by PMP@Alb nanoparticles. It was demonstrated that PMP@Alb could be used as a useful tool to improve the efficacy of existing PDT by disrupting tumor vessel barriers through effective platelet inhibition.

Diagnostic and therapeutic nanoenzymes for enhanced chemotherapy and photodynamic therapy

Nanozymes, as a kind of artificial mimic enzymes, have superior catalytic capacity and stability. As lack of O2 in tumor cells can cause resistance to drugs, we designed drug delivery liposomes (MnO2-PTX/Ce6@lips) loaded with catalase-like nanozymes of manganese dioxide nanoparticles (MnO2 NPs), paclitaxel (PTX) and chlorin e6 (Ce6) to consume tumor's native H2O2 and produce O2. Based on the catalysis of MnO2 NPs, a large amount of oxygen was produced by MnO2-PTX/Ce6@lips to burst the liposomes and achieve a responsive release of the loaded drug (paclitaxel), and the released O2 relieved the chemoresistance of tumor cells and provided raw materials for photodynamic therapy. Subsequently, MnO2 NPs were decomposed into Mn2+ in an acidic tumor environment to be used as contrast agents for magnetic resonance imaging. The MnO2-PTX/Ce6@lips enhanced the efficacy of chemotherapy and photodynamic therapy (PDT) in bearing-tumor mice, even achieving complete cure. These results indicated the great potential of MnO2-PTX/Ce6@lips for the modulation of the TME and the enhancement of chemotherapy and PDT along with MRI tracing in the treatment of tumors.

Dual-step irradiation strategy to sequentially destroy singlet oxygen-responsive polymeric micelles and boost photodynamic cancer therapy

Nanotechnology provides a powerful tool to overcome many disadvantages of small-molecule photosensitizers for photodynamic cancer therapy, such as hydrophobicity, rapid blood clearance, low accumulation in tumor tissue and low cell penetration, etc. The occurrence of quench in photosensitizer-loaded nanoparticle greatly downregulates the ability to generate singlet oxygen with light irradiation. Stimuli-responsive nanocarriers can improve the efficacy of PDT to a certain extent. However, insufficient release of photosensitizer from either endogenous or exogenous stimuli responsive nanocarriers in the short period of light irradiation restricts full usage of the photosensitizer delivered into cancer cells. We here report a dual-step light irradiation strategy to enhance the efficacy of cancer PDT. Ce6 as a photosensitizer is loaded in singlet oxygen-sensitive micelles (Ce6-M) via self-assembly of amphiphilic polymer mPEG2000-TK-C16. After co-incubation of Ce6-M with cancer cells or i.v. injection of Ce6-M, cancer cells or tumor tissues are irradiated with light for a short time to trigger Ce6 release, and 2 h later, re-irradiated for relatively long time. The sufficient release of Ce6 in the period between twice light irradiation significantly improves the generation of singlet oxygen, leading to more efficient cancer therapeutic effects of dual-step irradiation than that of single-step irradiation for the same total irradiation time.

Recent progress in sono-photodynamic cancer therapy: From developed new sensitizers to nanotechnology-based efficacy-enhancing strategies

Many sensitizers have not only photodynamic effects, but also sonodynamic effects. Therefore, the combination of sonodynamic therapy (SDT) and photodynamic therapy (PDT) using sensitizers for sono-photodynamic therapy (SPDT) provides alternative opportunities for clinical cancer therapy. Although significant advances have been made in synthesizing new sensitizers for SPDT, few of them are successfully applied in clinical settings. The anti-tumor effects of the sensitizers are restricted by the lack of tumor-targeting specificity, incapability in deep intratumoral delivery, and the deteriorating tumor microenvironment. The application of nanotechnology-based drug delivery systems (NDDSs) can solve the above shortcomings, thereby improving the SPDT efficacy. This review summarizes various sensitizers as sono/photosensitizers that can be further used in SPDT, and describes different strategies for enhancing tumor treatment by NDDSs, such as overcoming biological barriers, improving tumor-targeted delivery and intratumoral delivery, providing stimuli-responsive controlled-release characteristics, stimulating anti-tumor immunity, increasing oxygen supply, employing different therapeutic modalities, and combining diagnosis and treatment. The challenges and prospects for further development of intelligent sensitizers and translational NDDSs for SPDT are also discussed.

A Tumor-Microenvironment-Responsive Nanocomposite for Hydrogen Sulfide Gas and Trimodal-Enhanced Enzyme Dynamic Therapy

Recently, enzyme dynamic therapy (EDT) has drawn much attention as a new type of dynamic therapy. However, the selection of suitable nanocarriers to deliver chloroperoxidase (CPO) and enhancement of the level of hydrogen peroxide (H2 O2 ) in the tumor microenvironment (TME) are critical factors for improving the efficiency of EDT. In this study, a rapidly decomposing nanocomposite is designed using tetra-sulfide-bond-incorporating dendritic mesoporous organosilica (DMOS) as a nanocarrier, followed by loading CPO and sodium-hyaluronate-modified calcium peroxide nanoparticles (CaO2 -HA NPs). The nanocomposite can effectively generate singlet oxygen (1 O2 ) for tumor therapy without any exogenous stimulus via trimodal-enhanced EDT, including DMOS-induced depletion of glutathione (GSH), H2 O2 compensation from CaO2 -HA NPs in mildly acidic TME, and oxidative stress caused by overloading of Ca2+ . As tetra-sulfide bonds are sensitive to GSH, DMOS can generate hydrogen sulfide (H2 S) gas as a new kind of H2 S gas nanoreactor. Additionally, the overloading of Ca2+ can cause tumor calcification to accelerate in vivo tumor necrosis and promote computed tomography imaging efficacy. Therefore, a novel H2 S gas, EDT, and Ca2+ -interference combined therapy strategy is developed.

An Albumin-Based Therapeutic Nanosystem for Photosensitizer/Protein Co-Delivery to Realize Synergistic Cancer Therapy

Oxygen-dependent photodynamic therapy (PDT) is hindered by the limited availability of endogenous oxygen in solid tumors and low tumor accumulation of photosensitizers. Herein, we developed a biocompatible cancer-targeted therapeutic nanosystem based on cRGD conjugated bovine serum albumin (CBSA) co-loaded with a photosensitizer (chlorin e6, Ce6) and a therapeutic protein (cytochrome c, Cytc) for synergistic photodynamic and protein therapy. The nanosystem (Ce6/Cytc@CBSA) can target αVβ3 integrin overexpressed cancer cells to improve tumor accumulation due to incorporation of cRGD. In the intracellular environment, Ce6 is released to produce toxic singlet oxygen upon near-infrared irradiation. At the same time, the therapeutic protein, Cytc, can induce programmed cell death by activating the downstream caspase pathway. Most importantly, Cytc with the catalase-like activity accelerates O2 generation by decomposing excess H2O2 in cancer cells, thereby relieving the PDT-induced hypoxia to enhance therapeutic efficacy. Both in vitro and in vivo studies reveal the significantly improved antitumor effects of the combined photodynamic/protein therapy, indicating that Ce6/Cytc@CBSA shows great potential in synergetic cancer treatments.

Protein-Based Nanomedicine for Therapeutic Benefits of Cancer

Proteins, a type of natural biopolymer that possess many prominent merits, have been widely utilized to engineer nanomedicine for fighting against cancer. Motivated by their ever-increasing attention in the scientific community, this review aims to provide a comprehensive showcase on the current landscape of protein-based nanomedicine for cancer therapy. On the basis of role differences of proteins in nanomedicine, protein-based nanomedicine engineered with protein therapeutics, protein carriers, enzymes, and composite proteins is introduced. The cancer therapeutic benefits of the protein-based nanomedicine are also discussed, including small-molecular therapeutics-mediated therapy, macromolecular therapeutics-mediated therapy, radiation-mediated therapy, reactive oxygen species-mediated therapy, and thermal effect-mediated therapy. Lastly, future developments and potential challenges of protein-based nanomedicine are elucidated toward clinical translation. It is believed that protein-based nanomedicine will play a vital role in the battle against cancer. We hope that this review will inspire extensive research interests from diverse disciplines to further push the developments of protein-based nanomedicine in the biomedical frontier, contributing to ever-greater medical advances.

A cyclic nano-reactor achieving enhanced photodynamic tumor therapy by reversing multiple resistances

BACKGROUND

Photodynamic therapy (PDT) is a clinically implemented modality to combat malignant tumor, while its efficacy is largely limited by several resistance factors from tumor microenvironment (TME), such as hypoxia, anti-oxidant systems, and ATP-dependent tumor adaptive resistances. The aim of this work is to construct a multifunctional nanoplatform to remodel multiple resistant TME for enhanced PDT.

RESULTS

Here, a targeting nano-reactor was facilely constructed to reverse the multiple resistances of PDT by incorporating glucose oxidase (GOx) and chlorin e6 (Ce6) into poly (D, L-lactic-co-glycolic acid) (PLGA)/ metal-organic framework (MOF) core-shell nanoassembly, with surface deposition of hyaluronic acid (HA) stabilized MnO2. The nano-reactor could selectively target tumor cells by virtue of surface HA modification, and once internalization, a few reactions were initiated to modulate TME. Glucose was consumed by GOx to inhibit ATP generation, and the produced H2O2 was catalyzed by MnO2 to generate O2 for tumor hypoxia alleviation and photodynamic sensitization, and glutathione (GSH) was also effectively depleted by MnO2 to suppress the tumor antioxidant defense. Consequently, the nano-reactor achieved robust PDT with amplified tumor therapy via intravenous injection.

CONCLUSIONS

This nano-reactor offers a multifunctional nanoplatform to sensitize TME-limited tumor treatment means via reversing multiple resistances.

Novel Fe(III)-Polybasic acid coordination polymer nanoparticles with targeted retention for photothermal and chemodynamic therapy of tumor

The development of Fe-coordination polymer-based nanoparticles, with safe and high anti-tumor effects, for the treatment of tumor is facing challenges such as limited resources and poor targeting. In this study, we prepared Fe-polyhydroxy coordination polymer nanoparticles (TA-Fe@MNPs), based on tartaric acid (TA)-Fe(III) coordination polymer as the new photothermal agent, mannose (M) as the target, and bovine serum albumin (BSA) and polyethyleneimine (PEI) as the carrier materials, and investigated them for targeting the multifunctional therapy of tumors. The TA-Fe@MNPs synthesized via a simple coordination of Fe³⁺ with TA, bovine serum albumin, and polyethyleneimine under ambient conditions exhibited an appropriate size (~125 nm), electrically neutral surfaces, good biocompatibility, and low normal cell toxicity. The TA-Fe@MNPs are the first to exhibit a remarkable photothermal performance. They also showed a pH-sensitive Fenton-like response that was further enhanced via glutathione response. Interestingly, after a single injection, the TA-Fe@MNPs could be retained at the tumor site for 36 h with an effective photothermal dose, which was attributed to the reduced protein adsorption and slow elimination in tumor cells with the aid of M modification and carrier materials, while that for the TA-Fe@NPs did so for only 2 h. Tumor ablation was demonstrated by in vivo photothermal and chemokinetic therapy using TA-Fe@MNPs, and their safety was evident from the weight changes and blood parameters. These results indicated that the TA-Fe@MNPs, as new photothermal and CDT agents, have the potential to be used in clinical tumor therapy nanoplatforms.

Synergistic Combination of Bioactive Hydroxyapatite Nanoparticles and the Chemotherapeutic Doxorubicin to Overcome Tumor Multidrug Resistance

Multidrug resistance (MDR) is one of the biggest obstacles in cancer chemotherapy. Here, a remarkable reversal of MDR in breast cancer through the synergistic effects of bioactive hydroxyapatite nanoparticles (HAPNs) and doxorubicin (DOX) is shown. DOX loaded HAPNs (DHAPNs) exhibit a 150-fold reduction in IC₅₀ compared with free DOX for human MDR breast cancer MCF-7/ADR cells, and lead to almost complete inhibition of tumor growth in vivo without obvious side effects of free DOX. This high efficacy and specificity could be attributed to multiple action mechanisms of HAPNs. In addition to acting as the conventional nanocarriers to facilitate the cellular uptake and retention of DOX in MCF-7/ADR cells, more importantly, drug-free HAPNs themselves are able to prevent drug being pumped out of MDR cells through targeting mitochondria to induce mitochondrial damage and inhibit ATP production and to trigger sustained mitochondrial calcium overload and apoptosis in MDR cancer cells while not affecting normal cells. The results demonstrate that this simple but versatile bioactive nanoparticle provides a practical approach to effectively overcome MDR.