Self-Monitoring Artificial Red Cells with Sufficient Oxygen Supply for Enhanced Photodynamic Therapy

The role of reactive oxygen species in tumor treatment

Reactive oxygen species (ROS) are by-products of aerobic metabolism and can also act as signaling molecules to participate in multiple regulation of biological and physiological processes. The occurrence, growth and metastasis of tumors, and even the apoptosis, necrosis and autophagy of tumor cells are all closely related to ROS. However, ROS levels in the body are usually maintained at a stable status. ROS produced by oxidative stress can cause damage to cell lipids, protein and DNA. In recent years, ROS have achieved satisfactory results on the treatment of tumors. Therefore, this review summarizes some research results of tumor treatments from the perspective of ROS in recent years, and analyzes how to achieve the mechanism of inhibition and treatment of tumors by ROS or how to affect the tumor microenvironment by influencing ROS. At the same time, the detection methods of ROS, problems encountered in the research process and solutions are also summarized. The purpose of this review is to provide a clearer understanding of the ROS role in tumor treatment, so that researchers might have more inspiration and thoughts for cancer prevention and treatment in the next stage.

This review provides a clear understanding of the ROS role in tumor treatment and some thoughts for potential cancer prevention.

Fighting Hypoxia to Improve PDT

Photodynamic therapy (PDT) has drawn great interest in recent years mainly due to its low side effects and few drug resistances. Nevertheless, one of the issues of PDT is the need for oxygen to induce a photodynamic effect. Tumours often have low oxygen concentrations, related to the abnormal structure of the microvessels leading to an ineffective blood distribution. Moreover, PDT consumes O2. In order to improve the oxygenation of tumour or decrease hypoxia, different strategies are developed and are described in this review: 1) The use of O2 vehicle; 2) the modification of the tumour microenvironment (TME); 3) combining other therapies with PDT; 4) hypoxia-independent PDT; 5) hypoxia-dependent PDT and 6) fractional PDT.

Improving cancer therapy through the nanomaterials-assisted alleviation of hypoxia

Hypoxia, resulting from the imbalance between oxygen supply and consumption is a critical component of the tumor microenvironment. It has a paramount impact on cancer growth, metastasis and has long been known as a major obstacle for cancer therapy. However, none of the clinically approved anticancer therapeutics currently available for human use directly tackles this problem. Previous clinical trials of targeting tumor hypoxia with bioreductive prodrugs have failed to demonstrate satisfactory results. Therefore, new ideas are needed to overcome the hypoxia barrier. The method of modulating hypoxia to improve the therapeutic activity is of great interest but remains a considerable challenge. One of the emerging concepts is to supply or generate oxygen at the tumor site to increase the partial oxygen pressure and thereby reverse the hypoxia and its effects. In this review, we present an overview of the recent progress in the development of novel nanomaterials for the alleviation of hypoxic microenvironment. Two main strategies for hypoxia augmentation, i) direct delivery of O₂ into the tumor, and ii) in situ O₂ generations in the tumor microenvironment through different methods such as catalytic decomposition of endogenous hydrogen peroxide (H₂O₂) and light-triggered water splitting are discussed in detail. At present, these emerging nanomaterials are in their early phase and expected to grow rapidly in the coming years. Despite the promising start, there are several challenges needed to overcome for successful clinical translation.

Insight into the efficiency of oxygen introduced photodynamic therapy (PDT) and deep PDT against cancers with various assembled nanocarriers

Photodynamic therapy (PDT) has been used in the treatment of cancers and other benign diseases for several years in clinic. However, the hypoxia of tumors and the penetration limitation of excitation light to tissues can dramatically reduce the efficacy of PDT to cancers. To overcome these drawbacks, various assembled nanocarriers such as nanoparticles, nanocapsules, nanocrystals, and so on were introduced. The assembled nanocarriers have the ability of loading photosensitizers, delivering O₂ into tumors, generating O₂ in situ in tumors, as well as turning near-infrared (NIR) light, X-rays, and chemical energy into ultraviolet or visible light. Therefore, it is easy for the nanocarriers to improve the hypoxia microenvironment or increase the treatment depth of cancers, which will improve the efficiency of PDT to some degree. In recent years, a number of investigations were focused on these subjects. We will summarize the advances of nanocarriers in PDT, especially in O₂ introduction PDT and deep PDT. The perspectives, challenges, and potential in translation of PDT will also be discussed. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Biology-Inspired Nanomaterials > Lipid-Based Structures Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Fenton Reaction-Assisted Photodynamic Therapy for Cancer with Multifunctional Magnetic Nanoparticles

Tumor hypoxia and the short half-life of reactive oxygen species (ROS) with small diffusion distance have greatly limited the therapeutic effect of photodynamic therapy (PDT). Here, a multifunctional nanoplatform is developed to enhance the PDT effect through increasing the oxygen concentration in tumor cells by the Fenton reaction and reducing the distance between the ROS and the target site by mitochondrial targeting. Fe₃O₄@Dex-TPP nanoparticles are first prepared by coprecipitation in the presence of triphenylphosphine (TPP)-grafted dextran (Dex-TPP) and Fe²⁺/Fe³⁺, which have a magnetic resonance imaging effect. Next, the photosensitizers of protoporphyrin IX (PpIX) and glutathione-responsive mPEG-ss-COOH are grafted on Fe₃O₄@Dex-TPP to form Fe₃O₄@Dex/TPP/PpIX/ss-mPEG nanoparticles. After the nanoparticles are internalized, part of Fe₃O₄ are decomposed into Fe²⁺/Fe³⁺ in the acidic lysosome and then Fe²⁺/Fe³⁺ diffused into the cytoplasm, and subsequently, Fe²⁺ reacted with the overproduced H₂O₂ to produce O₂ and ^•OH. The undecomposed nanoparticles enter the cytoplasm by photoinduced internalization and targeted to the mitochondria, leading to ROS direct generation around the mitochondria. Simultaneously, the produced O₂ by the Fenton reaction can serve as a raw material for PDT to continuously exert PDT effect. As a result, the Fenton reaction-assisted PDT can significantly improve the therapeutic efficacy of tumors.

Gold nanorods functionalized by a glutathione response near-infrared fluorescent probe as a promising nanoplatform for fluorescence imaging guided precision therapy

Theranostics nanoplatforms offer opportunities for imaging-guided precision therapy and hold great potential for clinical applications. In most reported works, the imaging unit has a lack of site selectivity, and is always kept in the "on" modality regardless of whether it is in normal tissues or tumor sites, increasing the risk of unsafe treatment. Herein, we designed a near-infrared (NIR) fluorescence-guided theranostics nanoplatform by integrating the functions of tumor-response and photodynamic therapy (PDT)/photothermal therapy (PTT). A novel NIR fluorescent dye, CyPT, with excellent optical and PDT/PTT properties, was synthesized and linked onto the gold nanorods (AuNRs) to form CyPT-AuNRs nanohybrids via a sulfur-sulfur bond that can be broken by glutathione (GSH) with high selectivity and sensitivity. In normal cells where the concentration of GSH is low, the fluorescence of CyPT is quenched by the AuNRs. By contrast, the high level of GSH in tumor cells leads to the breaking of the sulfur-sulfur bond, resulting in the release of CyPT and the accomplishment of a "off-on" fluorescence response. Followed by precise NIR tumor-imaging diagnosis, the PDT and PTT treatment which rely on the released CyPT and AuNRs, respectively, can be effectively performed. The CyPT-AuNRs nanoplatform has been successfully applied to the treatment of tumor xenograft models and no distinct damage has been observed in the nearby normal tissues. This versatile nanoplatform has potential for use in targeted tumor imaging and precision therapy.

Luminescent, Oxygen-Supplying, Hemoglobin-Linked Conjugated Polymer Nanoparticles for Photodynamic Therapy

Photodynamic therapy (PDT) is a promising method for cancer treatment. Two parameters that influence the efficacy of PDT are the light source and oxygen supply. Herein, we prepared a system for PDT using hemoglobin (Hb)-linked conjugated polymer nanoparticles (CPNs), which can luminesce and supply oxygen. Hb catalyzes the activation of luminol, the conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) nanoparticles can absorb the chemiluminescence of luminol through chemiluminescence resonance energy transfer (CRET) and then sensitize the oxygen supplied by Hb to produce reactive oxygen species that kill cancer cells. This system could be used for the controlled release of an anticancer prodrug. The system does not need an external light source and circumvents the insufficient level molecular oxygen under hypoxia. This work provides a proof-of-concept to explore smart and multifunctional nanoplatforms for phototherapy.

Biomorphic Engineering of Multifunctional Polylactide Stomatocytes toward Therapeutic Nano-Red Blood Cells

Morphologically discrete nanoarchitectures, which mimic the structural complexity of biological systems, are an increasingly popular design paradigm in the development of new nanomedical technologies. Herein, engineered polymeric stomatocytes are presented as a structural and functional mimic of red blood cells (RBCs) with multifunctional therapeutic features. Stomatocytes, comprising biodegradable poly(ethylene glycol)-block-poly(D,L-lactide), possess an oblate-like morphology reminiscent of RBCs. This unique dual-compartmentalized structure is augmented via encapsulation of multifunctional cargo (oxygen-binding hemoglobin and the photosensitizer chlorin e6). Furthermore, stomatocytes are decorated with a cell membrane isolated from erythrocytes to ensure that the surface characteristics matched those of RBCs. In vivo biodistribution data reveal that both the uncoated and coated nano-RBCs have long circulation times in mice, with the membrane-coated ones outperforming the uncoated stomatoctyes. The capacity of nano-RBCs to transport oxygen and create oxygen radicals upon exposure to light is effectively explored toward photodynamic therapy, using 2D and 3D tumor models; addressing the challenge presented by cancer-induced hypoxia. The morphological and functional control demonstrated by this synthetic nanosystem, coupled with indications of therapeutic efficacy, constitutes a highly promising platform for future clinical application.

Effect of photodynamic therapy with (17R,18R)-2-(1-hexyloxyethyl)-2-devinyl chlorine E6 trisodium salt on pancreatic cancer cells in vitro and in vivo

AIM

To investigate the antitumor effects and underlying mechanisms of (17R,18R)-2-(1-hexyloxyethyl)-2-devinyl chlorine E6 trisodium salt (YLG-1)-induced photodynamic therapy (PDT) on pancreatic cancer in vitro and in vivo.

METHODS

YLG-1 is a novel photosensitizer extracted from spirulina. Its phototoxicity, cellular uptake and localization, as well as its effect on reactive oxygen species (ROS) production, apoptosis, and expression of apoptosis-associated proteins were detected in vitro. An in vivo imaging system (IVIS), the Lumina K imaging system, and mouse models of subcutaneous Panc-1-bearing tumors were exploited to evaluate the drug delivery pathway and pancreatic cancer growth in vivo.

RESULTS

YLG-1 was localized to the mitochondria, and the appropriate incubation time was 6 h. Under 650 nm light irradiation, YLG-1-PDT exerted a potent cytotoxic effect on pancreatic cancer cells in vitro, which could be abolished by the ROS scavenger N-acetyl-L-cysteine (NAC). The death mode caused by YLG-1-PDT was apoptosis, accompanied by upregulated Bax and cleaved Caspase-3 and decreased Bcl-2 expression. The results from the IVIS images suggested that the optimal administration route was intratumoral (IT) injection and that the best time to conduct YLG-1-PDT was 2 h post-IT injection. Consistent with the results in vitro, YLG-1-PDT showed great growth inhibition effects on pancreatic cancer cells in a mouse model.

CONCLUSION

YLG-1 is a potential photosensitizer for pancreatic cancer PDT via IT injection, the mechanisms of which are associated with inducing ROS and promoting apoptosis.

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

Despite the promises of applying nano-photosensitizers (nano-PSs) for photodynamic therapy (PDT) against cancer, severe tumor hypoxia and limited tumor penetration of nano-PSs would lead to nonoptimized therapeutic outcomes of PDT. Therefore, herein a biocompatible nano-PS is prepared by using tamoxifen (TAM), an anti-estrogen compound, to induce self-assembly of chlorin e6 (Ce6) modified human serum albumin (HSA). The formed HSA-Ce6/TAM nanocomplexes, which are stable under neutral pH with a diameter of ≈130 nm, would be dissociated into individual HSA-Ce6 and TAM molecules under the acidic tumor microenvironment, owing to the pH responsive transition of TAM from hydrophobic to hydrophilic. Upon systemic administration, such HSA-Ce6/TAM nanoparticles exhibit prolonged blood circulation and high accumulation in the tumor, where it would undergo rapid pH responsive dissociation to enable obviously enhanced intratumoral penetration of HSA-Ce6. Furthermore, utilizing the ability of TAM in reducing the oxygen consumption of cancer cells, it is found that HSA-Ce6/TAM after systemic administration could efficiently attenuate the tumor hypoxia status. Those effects acting together lead to remarkably enhanced PDT treatment. This work presents a rather simple approach to fabricate smart nano-PSs with multiple functions integrated into a single system via self-assembly of all-biocompatible components, promising for the next generation cancer PDT.

Real-Time Imaging of Free Radicals for Mitochondria-Targeting Hypoxic Tumor Therapy

Free radicals have emerged as new-type and promising candidates for hypoxic tumor treatment, and further study of their therapeutic mechanism by real-time imaging is of great importance to explore their biomedical applications. Herein, we present a smart free-radical generator AuNC-V057-TPP for hypoxic tumor therapy; the AuNC-V057-TPP not only exhibits good therapeutic effect under both hypoxic and normoxic conditions but also can monitor the release of free radicals in real-time both in vitro and in vivo. What is more, with the mitochondria-targeting ability, the AuNC-V057-TPP is demonstrated with improved antitumor efficacy through enhanced free radical level in mitochondria, which leads to mitochondrial membrane damage and ATP production reduction and finally induces cancer cell apoptosis.

Lipid-Polymer Bilaminar Oxygen Nanobubbles for Enhanced Photodynamic Therapy of Cancer

Hypoxia in solid tumors may be a hindrance to effective treatments of tumors in achieving their therapeutic potential, especially for photodynamic therapy (PDT) which requires oxygen as the supplement substrate. Oxygen delivery using perfluorocarbon emulsions or lipid oxygen microbubbles has been developed as the agents to supply endogenous oxygen to fuel singlet oxygen generation in PDT. However, such methods suffer from premature oxygen release and storage issues. To address these limitations, we designed lipid-polymer bilaminar oxygen nanobubbles with chlorin e6 (Ce6) conjugated to the polymer shell as a novel oxygen self-supplement agent for PDT. The resultant nanobubbles possessed excellent stability to reduce the risk of premature oxygen release and were stored as freeze-dried powders to avoid shelf storage issues. In vitro and in vivo experimental results demonstrated that the nanobubbles exhibited much higher cellular uptake rates and tumor targeting efficiency compared to free Ce6. Using the oxygen nanobubbles for PDT, a significant enhancement of therapeutic efficacy and survival rates was achieved on a C6 glioma-bearing mice model with no noticeable side effects, owing to the greatly enhanced singlet oxygen generation powered by oxygen encapsulated nanobubbles.

Nitric oxide as an all-rounder for enhanced photodynamic therapy: Hypoxia relief, glutathione depletion and reactive nitrogen species generation

A glutathione (GSH)-sensitive supramolecular nitric oxide (NO) nanogenerator is developed as an all-rounder for enhanced photodynamic therapy (PDT). By integrating GSH-sensitive NO prodrug into the system via LEGO-like host-guest interaction, the nanocarrier could not only deplete intracellular GSH, but also relieve hypoxia at tumor sites through NO mediated blood vessel relaxation. Furthermore, reactive nitrogen species (RNS) with enhanced biocidal activity could be produced by the reaction between NO and reactive oxygen species (ROS), generated from α-cyclodextrin (α-CD) conjugated S-nitrosothiol and light-activated chlorin e6 (Ce6) respectively. Due to multiple combined effects between NO and PDT, the NO acts as the loaded gunpowder inside a 'grenade', 'explosively' amplifying the therapeutic effects that the light responsive 'fuse' Ce6 could exert. The present work may well serve as an inspiration for future creative approaches of photodynamic cancer therapy.

Oxygen-independent combined photothermal/photodynamic therapy delivered by tumor acidity-responsive polymeric micelles

Tumor hypoxia strikingly restricts photodynamic therapy (PDT) efficacy and limits its clinical applications in cancer therapy. The ideal strategy to address this issue is to develop oxygen-independent PDT systems. Herein, the rationally designed tumor pH-responsive polymeric micelles are devised to realize oxygen-independent combined PDT and photothermal therapy (PTT) under near-infrared light (NIR) irradiation. The triblock copolymer, poly(ethylene glycol)-b-poly(ε-caprolactone)-b-poly(2-(piperidin-1-yl)ethyl methacrylate) (PEG-b-PCL-b- PPEMA), was prepared to co-encapsulate cypate and singlet oxygen donor (diphenylanthracene endoperoxide, DPAE) via self-assembly to obtain the micellar delivery system (C/O@N-Micelle). C/O@N-Micelle showed remarkable tumor accumulation and improved cellular internalization (2.1 times) as the pH value was changed from 7.4 during blood circulation to 6.8 in tumor tissues. The micelles could produce a potent hyperthermia for PTT of cypate under 808 nm NIR irradiation, which simultaneously induced thermal cycloreversion of DPAE generating abundant singlet oxygen for PDT without participation of tumor oxygen. Finally, the photothermally triggered PDT and PTT combination achieved efficient tumor ablation without remarkable systemic toxicity in an oxygen-independent manner. This work represents an efficient strategy for oxygen-independent combined PDT and PTT of cancers under NIR irradiation through co-encapsulation of cypate and DPAE into tumor pH-responsive polymeric micelles.

Biomimetic O2-Evolving metal-organic framework nanoplatform for highly efficient photodynamic therapy against hypoxic tumor

Improving the supply of O₂ and the circulation lifetime of photosensitizers for photodynamic therapy (PDT) in vivo would be a promising approach to eliminate hypoxic tumors. Herein, by taking advantage of the significant gas-adsorption capability of metal-organic frameworks (MOFs), a biomimetic O₂-evolving photodynamic therapy (PDT) nanoplatform with long circulating properties was fabricated. Zirconium (IV)-based MOF (UiO-66) was used as a vehicle for O₂ storing, then conjugated with indocyanine green (ICG) by coordination reaction, and further coated with red blood cell (RBC) membranes. Upon 808 nm laser irradiation, the initial singlet oxygen (¹O₂) generated by ICG would decompose RBC membranes. At the same time, The photothermal property of ICG could facilitate the burst release of O₂ from UiO-66. Subsequently, the generated O₂ could significantly improve the PDT effects on hypoxic tumor. Owing to the advantages of long circulation and O₂ self-sufficient, the designed nanotherapeutic agent can improve the efficiency of treatment against hypoxia tumor via PDT. Hence, this study presents a new paradigm for co-delivery of O₂ and photosensitizers, and provides a new avenue to eliminate hypoxic tumors.

Tumor-targeted hybrid protein oxygen carrier to simultaneously enhance hypoxia-dampened chemotherapy and photodynamic therapy at a single dose

Hypoxia is a characteristic feature of solid tumors and an important causation of resistance to chemotherapy and photodynamic therapy (PDT). It is challenging to develop efficient functional nanomaterials for tumor oxygenation and therapeutic applications.

Methods: Through disulfide reconfiguration to hybridize hemoglobin and albumin, tumor-targeted hybrid protein oxygen carriers (HPOCs) were fabricated, serving as nanomedicines for precise tumor oxygenation and simultaneous enhancement of hypoxia-dampened chemotherapy and photodynamic therapy. Based on encapsulation of doxorubicin (DOX) and chlorin e6 (Ce6) into HPOCs to form ODC-HPOCs, the mechanism and therapeutic efficacy of oxygen-enhanced chemo-PDT was investigated in vitro and in vivo.

Results: The precise oxygen preservation and release of the HPOC guaranteed sufficient tumor oxygenation, which is able to break hypoxia-induced chemoresistance by downregulating the expressions of hypoxia-inducible factor-1α (HIF-1α), multidrug resistance 1 (MDR1) and P-glycoprotein (P-gp), resulting in minimized cellular efflux of chemodrug. Moreover, the oxygen supply is fully exploited for upgrading the generation of reactive oxygen species (ROS) during the photodynamic process. As a result, only a single-dose treatment of the HPOCs-based chemo-PDT exhibited superior tumor suppression. The combination therapy was guided by in vivo fluorescence/photoacoustic imaging with nanoparticle tracking and oxygen monitoring.

Conclusion: This well-defined HPOC as a versatile nanosystem is expected to pave a new way for breaking multiple hypoxia-induced therapeutic resistances to achieve highly effective treatment of solid tumors.

Intraparticle FRET for Enhanced Efficiency of Two-Photon Activated Photodynamic Therapy

Photodynamic therapy (PDT) still faces two main problems on cancer therapy. One is how to improve PDT efficiency against hypoxic environment of tumors. The other one is how to overcome the limit of short wavelength light to increase PDT treatment depth. In this work, an intraparticle fluorescence resonance energy transfer (FRET) platform is designed to address these problems together. The nanoparticles are doped with multicomponents, such as catalase, two-photon dyes, and traditional photosensitizers, with a simple "one-pot" and green method. On the one hand, catalase can catalyze intracellular H₂ O₂ into O₂ and promote PDT efficiency. One the other hand, photosensitizers can be excited indirectly by two-photon lasers through an intraparticle FRET mechanism, which results in deeper tissue penetration for PDT. These properties are verified through the material induced cytotoxicity in light or in dark and in vivo blocking blood-vessel experiment.

Theranostic Nanoparticles for Tracking and Monitoring Disease State

The development of novel nanoparticles consisting of both diagnostic and therapeutic components has increased over the past decade. These "theranostic" nanoparticles have been tailored toward one or more types of imaging modalities and have been developed for optical imaging, magnetic resonance imaging, ultrasound, computed tomography, and nuclear imaging comprising both single-photon computed tomography and positron emission tomography. In this review, we focus on state-of-the-art theranostic nanoparticles that are capable of both delivering therapy and self-reporting/tracking disease through imaging. We discuss challenges and the opportunity to rapidly adjust treatment for individualized medicine.

Nanotechnology for Cancer Therapy Based on Chemotherapy

Chemotherapy has been widely applied in clinics. However, the therapeutic potential of chemotherapy against cancer is seriously dissatisfactory due to the nonspecific drug distribution, multidrug resistance (MDR) and the heterogeneity of cancer. Therefore, combinational therapy based on chemotherapy mediated by nanotechnology, has been the trend in clinical research at present, which can result in a remarkably increased therapeutic efficiency with few side effects to normal tissues. Moreover, to achieve the accurate pre-diagnosis and real-time monitoring for tumor, the research of nano-theranostics, which integrates diagnosis with treatment process, is a promising field in cancer treatment. In this review, the recent studies on combinational therapy based on chemotherapy will be systematically discussed. Furthermore, as a current trend in cancer treatment, advance in theranostic nanoparticles based on chemotherapy will be exemplified briefly. Finally, the present challenges and improvement tips will be presented in combination therapy and nano-theranostics.

Indocyanine green-incorporating nanoparticles for cancer theranostics

Indocyanine green (ICG) is a near-infrared dye that has been used in the clinic for retinal angiography, and defining cardiovascular and liver function for over 50 years. Recently, there has been an increasing interest in the incorporation of ICG into nanoparticles (NPs) for cancer theranostic applications. Various types of ICG-incorporated NPs have been developed and strategically functionalised to embrace multiple imaging and therapeutic techniques for cancer diagnosis and treatment. This review systematically summaries the biodistribution of various types of ICG-incorporated NPs for the first time, and discusses the principles, opportunities, limitations, and application of ICG-incorporated NPs for cancer theranostics. We believe that ICG-incorporated NPs would be a promising multifunctional theranostic platform in oncology and facilitate significant advancements in this research-active area.

Near-Infrared Upconversion Mesoporous Cerium Oxide Hollow Biophotocatalyst for Concurrent pH-/H2 O2 -Responsive O2 -Evolving Synergetic Cancer Therapy

Tumor hypoxia is typically presented in the central region of solid tumors, which is mainly caused by an inadequate blood flow and oxygen supply. In the conventional treatment of hypoxic human tumors, not only the oxygen-dependent photodynamic therapy (PDT), but also antitumor drug-based chemotherapy, is considerably limited. The use of direct oxygen delivering approach with oxygen-dependent PDT or chemotherapy may potentiate the reactive oxygen species (ROS)-mediated cytotoxicity of the drug toward normal tissues. Herein, a synergetic one-for-all mesoporous cerium oxide upconversion biophotocatalyst is developed to achieve intratumorally endogenous H₂ O₂ -responsive self-sufficiency of O₂ and near-infrared light controlled PDT simultaneously for overcoming hypoxia cancer. Furthermore, the sufficient O₂ plays an important role in overcoming the chemotherapeutic drug-resistant cancer caused by hypoxia, therefore inducing tumor cell apoptosis significantly.

PL-W18O49-TPZ Nanoparticles for Simultaneous Hypoxia-Activated Chemotherapy and Photothermal Therapy

The combination of W₁₈O₄₉ and tirapazamine (TPZ) core has been first introduced into the preparation of poly(ε-caprolactone)-poly(ethylene glycol) (PL) surrounded nanoparticles (NPs). The aim of using W₁₈O₄₉ is employing its capability of reacting with the absorbed O₂ to generate reactive oxygen species (ROS) when exposed to a long-wavelength laser at 808 nm to increase skin penetration and body tolerance. In this work, we have demonstrated that W₁₈O₄₉ unit gives rise to more hypoxic tumor microenvironment and activates the prodrug TPZ to achieve hypoxia-activated chemotherapy, which could be monitored by the intracellular ROS/hypoxia detection and in vivo positron emission tomography imaging. In addition, the successful introduction of W₁₈O₄₉ into PL-W₁₈O₄₉-TPZ NPs could render the photothermal therapy under the irradiation of an 808 nm laser. As a result, in vivo antitumor results have clearly shown that PL-W₁₈O₄₉-TPZ NPs could efficiently erase the solid tumor tissues by means of simultaneous hypoxia-activated chemotherapy and photothermal therapy. In comparison to the costly small-molecule photosensitizer chlorine e6 used in hypoxia-activated chemotherapy, W₁₈O₄₉ NPs have two advantages of large-scale preparation and additional photothermal therapy effect, which could provide new insight into future clinical applications.

Multifunctional Bi2WO6 Nanoparticles for CT-Guided Photothermal and Oxygen-free Photodynamic Therapy

The consumption of oxygen in photodynamic therapy (PDT) significantly exacerbates the degree of hypoxia in tumors, which not only impedes the therapeutic effect of PDT, but also drives local tumor recurrence. To relieve the PDT-induced hypoxia and improve the therapeutic outcome of PDT in cancer treatment, herein we reported a class of Bi₂WO₆ nanoparticles (NPs) as a robust multifunctional platform, which integrates the abilities for contrast-enhanced computed tomography (CT) imaging, photothermal therapy, and PDT in an oxygen-free manner. The as-obtained Bi₂WO₆ NPs with a mean diameter of 5.2 nm are stable in phosphate-buffered saline and an in vivo microenvironment-mimicking buffer. The location of the solid tumor could be accurately positioned using Bi₂WO₆-enhanced CT with higher spatial resolution. After being irradiated with an 808 nm laser, these Bi₂WO₆ NPs could realize CT-guided local photothermal ablation of the tumor. Meanwhile, ^•OH radicals were generated simultaneously from the treatment without consuming an oxygen molecule, which enabled these Bi₂WO₆ NPs to exert photodynamic killing effect in an oxygen-free manner during cancer therapy. Remarkable tumor suppression was observed in mice bearing the HeLa xenograft, supporting the promising application of these multifunctional Bi₂WO₆ NPs in the combat against cancers through synergistic photothermal and oxygen-free PDT treatment.

Fluorinated polymeric micelles to overcome hypoxia and enhance photodynamic cancer therapy

Perfluoroalkyl groups-containing polymeric micelles were constructed to transport oxygen, overcome the hypoxia of tumours and enhance photodynamic cancer therapy.

Near-infrared light triggered photothermal therapy and enhanced photodynamic therapy with a tumor-targeting hydrogen peroxide shuttle

Tumor-targeting oxygen self-carrying nanoparticles are developed for PTT and enhanced PDT to completely eradicate tumors.

Oxygen Self-Sufficient Amphiphilic Polypeptide Nanoparticles Encapsulating BODIPY for Potential Near Infrared Imaging-guided Photodynamic Therapy at Low Energy

Near infrared (NIR) imaging-guided photodynamic therapy (PDT) is remarkable for its high-efficiency in "see and treat" field. However, hypoxia of cancer cell limits PDT dues to the low singlet oxygen yield. Here MnO₂ conjugated multifunctional polypeptide nanoparticles encapsulating photosensitizer BODIPY has been prepared via a one-step reaction, which can generate oxygen in cancer cytoplasm where rich of H₂O₂, following singlet oxygen by photosensitizer under NIR light irradiation. In vitro studies on HepG2 and 4T1 cancer cells revealed that the as-prepared nanoparticles obviously increase the cell suppression rate under hypoxia conditions, even exposed to an extremely low light energy density (25 mW/cm²). Meanwhile, excellent NIR fluorescence property of BODIPY enabled the nanoparticles to light up the cancer cells for real-time imaging. These results suggest the promises of biocompatible and biodegradable nanoparticles has potential application on efficient NIR imaging-guided photodynamic therapy.

Recent Progress in Near Infrared Light Triggered Photodynamic Therapy

Nowadays, photodynamic therapy (PDT) is under the research spotlight as an appealing modality for various malignant tumors. Compared with conventional PDT treatment activated by ultraviolet or visible light, near infrared (NIR) light-triggered PDT possessing deeper penetration to lesion area and lower photodamage to normal tissue holds great potential for in vivo deep-seated tumor. In this review, recent research progress related to the exploration of NIR light responsive PDT nanosystems is summarized. To address current obstacles of PDT treatment and facilitate the effective utilization, several innovative strategies are developed and introduced into PDT nanosystems, including the conjugation with targeted moieties, O₂ self-sufficient PDT, dual photosensitizers (PSs)-loaded PDT nanoplatform, and PDT-involved synergistic therapy. Finally, the potential challenges as well as the prospective for further development are also discussed.

Nanoparticle design strategies for enhanced anticancer therapy by exploiting the tumour microenvironment

Nanovehicles can efficiently carry and deliver anticancer agents to tumour sites. Compared with normal tissue, the tumour microenvironment has some unique properties, such as vascular abnormalities, hypoxia and acidic pH. There are many types of cells, including tumour cells, macrophages, immune and fibroblast cells, fed by defective blood vessels in the solid tumour. Exploiting the tumour microenvironment can benefit the design of nanoparticles for enhanced therapeutic effectiveness. In this review article, we summarized the recent progress in various nanoformulations for cancer therapy, with a special emphasis on tumour microenvironment stimuli-responsive ones. Numerous tumour microenvironment modulation strategies with promising cancer therapeutic efficacy have also been highlighted. Future challenges and opportunities of design consideration are also discussed in detail. We believe that these tumour microenvironment modulation strategies offer a good chance for the practical translation of nanoparticle formulas into clinic.

Dual-stimuli responsive and reversibly activatable theranostic nanoprobe for precision tumor-targeting and fluorescence-guided photothermal therapy

The integrated functions of diagnostics and therapeutics make theranostics great potential for personalized medicine. Stimulus-responsive therapy allows spatial control of therapeutic effect only in the site of interest, and offers promising opportunities for imaging-guided precision therapy. However, the imaging strategies in previous stimulus-responsive therapies are ‘always on' or irreversible ‘turn on' modality, resulting in poor signal-to-noise ratios or even ‘false positive' results. Here we show the design of dual-stimuli-responsive and reversibly activatable nanoprobe for precision tumour-targeting and fluorescence-guided photothermal therapy. We fabricate the nanoprobe from asymmetric cyanine and glycosyl-functionalized gold nanorods (AuNRs) with matrix metalloproteinases (MMPs)-specific peptide as a linker to achieve MMPs/pH synergistic and pH reversible activation. The unique activation and glycosyl targetibility makes the nanoprobe bright only in tumour sites with negligible background, while AuNRs and asymmetric cyanine give synergistic photothermal effect. This work paves the way to designing efficient nanoprobes for precision theranostics.

A number of nanomaterials for dual diagnostic and therapeutic application have a number of limitations including poor signal-to-noise ratio. Here, the authors developed dual stimuli-responsive and reversibly activatable nanoprobes for tumour targeting and fluorescence-guided photothermal therapy.

Catalase-loaded cisplatin-prodrug-constructed liposomes to overcome tumor hypoxia for enhanced chemo-radiotherapy of cancer

Aiming at improved therapeutic efficacies, the combination of chemotherapy and radiotherapy (chemo-radiotherapy) has been widely studied and applied in clinic. However, the hostile characteristics of tumor microenvironment such as hypoxia often limit the efficacies in both types of cancer therapies. Herein, catalase (CAT), an antioxidant enzyme, is encapsulated inside liposomes constituted by cisplatin (IV)-prodrug-conjugated phospholipid, forming CAT@Pt (IV)-liposome for enhanced chemo-radiotherapy of cancer. After being loaded inside liposomes, CAT within CAT@Pt (IV)-liposome shows retained and well-protected enzyme activity, and is able to trigger decomposition of H₂O₂ produced by tumor cells, so as to produce additional oxygen for hypoxia relief. As the result, treatment of CAT@Pt (IV)-liposome induces the highest level of DNA damage in cancer cells after X-ray radiation compared to the control groups. In vivo tumor treatment further demonstrates a remarkably improved therapeutic outcome in chemo-radiotherapy with such CAT@Pt (IV)-liposome nanoparticles. Hence, an exquisite type of liposome-based nanoparticles is developed in this work by integrating cisplatin-based chemotherapy and catalase-induced tumor hypoxia relief together for combined chemo-radiotherapy with great synergistic efficacy, promising for clinical translation in cancer treatment.

Modulating tumor hypoxia by nanomedicine for effective cancer therapy

Hypoxia, a characteristic feature of tumors, is indispensable to tumor angiogenesis, metastasis, and multi drug resistance. Hypoxic avascular regions, deeply embedded inside the tumors significantly hinder delivery of therapeutic agents. The low oxygen tension results in resistance to the current applied anti-cancer therapeutics including radiotherapy, chemotherapy, and photodynamic therapy, the efficacy of which is firmly tied to the level of tumor oxygen supply. However, emerging data indicate that nanocarriers/nanodrugs can offer substantial benefits to improve the efficacy of current therapeutics, through modulation of tumor hypoxia. This review aims to introduce the most recent advances made in nanocarrier mediated targeting of tumor hypoxia. The first part is dedicated to the approaches by which nanocarriers could be designed to target/leverage hypoxia. These approaches include i) inhibiting Hypoxia Inducer Factor (HIF-1α); ii) hypoxia activated prodrugs/linkers; and iii) obligate anaerobe mediated targeting of tumor hypoxia. The second part, details novel nanosystems proposed to modulate tumor hypoxia through tumor oxygenation. These methods seek to lessen tumor hypoxia through vascular normalization, or reoxygenation therapy. The reoxygenation of tumor could be accomplished by: i) generation of oxygen filled nanocarriers; ii) natural/artificial oxygen nanocarriers; and iii) oxygen generators. The efficacy of each approach and their potential in cancer therapy is further discussed.

Photosensitizer Decorated Red Blood Cells as an Ultrasensitive Light-Responsive Drug Delivery System

Red blood cells (RBCs) have been widely explored as a natural drug delivery system (DDS) owing to their inherent biocompatibility and large internal cavities to load various types of functional molecules. Herein, we uncover that a photosensitizer, chlorin e6 (Ce6), could be decorated into the membrane of RBCs upon simple mixing, without affecting the membrane integrity and stability in dark. Upon light irradiation with a rather low power density, the singlet oxygen generated by Ce6 would lead to rather efficient disruption of RBC membrane. With doxorubicin (DOX), a typical chemotherapy drug, as the model, we engineer a unique type of light-responsive RBC-based DDS by decorating Ce6 on the cell membrane and loading DOX inside cells. The light triggered cell membrane breakdown would thus trigger instant release of DOX, enabling light-controlled chemotherapy with great specificity. Beyond that our RBC system could also be utilized for loading of larger biomolecules such as enzymes, whose release as well as catalytic function is also controlled by light. Our work thus presents a unique type of biocompatible cell-based DDS that can be precisely controlled by mild external stimuli, promising not only for cancer therapy but also for other potential applications in biotechnologies.

Manipulating tumor hypoxia toward enhanced photodynamic therapy (PDT)

This mini-review summarizes various methods for overcoming or utilizing hypoxia for enhanced PDT.

Reactive oxygen species generating systems meeting challenges of photodynamic cancer therapy

The reactive oxygen species (ROS)-mediated mechanism is the major cause underlying the efficacy of photodynamic therapy (PDT). The PDT procedure is based on the cascade of synergistic effects between light, a photosensitizer (PS) and oxygen, which greatly favors the spatiotemporal control of the treatment. This procedure has also evoked several unresolved challenges at different levels including (i) the limited penetration depth of light, which restricts traditional PDT to superficial tumours; (ii) oxygen reliance does not allow PDT treatment of hypoxic tumours; (iii) light can complicate the phototherapeutic outcomes because of the concurrent heat generation; (iv) specific delivery of PSs to sub-cellular organelles for exerting effective toxicity remains an issue; and (v) side effects from undesirable white-light activation and self-catalysation of traditional PSs. Recent advances in nanotechnology and nanomedicine have provided new opportunities to develop ROS-generating systems through photodynamic or non-photodynamic procedures while tackling the challenges of the current PDT approaches. In this review, we summarize the current status and discuss the possible opportunities for ROS generation for cancer therapy. We hope this review will spur pre-clinical research and clinical practice for ROS-mediated tumour treatments.

Encapsulation of indocyanine green into cell membrane capsules for photothermal cancer therapy

Although indocyanine green (ICG) has promising applications in photothermal therapy (PPT) because of its low toxicity and high efficiency in inducing heat and singlet oxygen formation in response to near-infrared light with a wavelength of approximately 800nm, its clinical application has been restricted because of its rapid body clearance and poor water stability. Therefore, cell membrane capsules (CMCs) derived from mammalian cells were used to encapsulate negatively charged ICG by temporarily permeating the plasma membrane and resealing using positively charged doxorubicin hydrochloride (DOX). The resulting CMCs@DOX/ICG exhibited a spherical shape, with a diameter of approximately 800nm. The DOX and ICG encapsulation was confirmed by the UV-vis spectrum; a very small amount of DOX (0.8μg) and a very high amount of ICG (∼110μg) were encapsulated in 200μg CMCs. Encapsulation in the CMCs leads to sustained release of ICG, especially in the presence of positively charged DOX. The temperature enhancement and generation of ROS by ICG encapsulated in CMCs were confirmed upon laser irradiation in vitro, leading to cell death. CMCs@DOX/ICG also can significantly enhance the retention of ICG in a tumor after intratumoral injection in vivo. As a result, combination treatment with CMCs@DOX/ICG and laser irradiation demonstrated much better anticancer efficacy than that of free DOX/ICG and CMCs@ICG. The encapsulation of ICG into CMCs, especially with the assistance of DOX, significantly slows down the body clearance of ICG, with a retained PPT effect against tumors, an important step forward in the practical application of ICG in cancer therapy.

STATEMENT OF SIGNIFICANCE

In this study, cell membrane capsules (CMCs) derived from mammalian cells were used to encapsulate negatively charged indocyanine green (ICG) by temporarily permeating the plasma membrane and resealing, in the presence of positively charged doxorubicin hydrochloride (DOX). The resulting CMCs@DOX/ICG exhibited a spherical shape, with a diameter of approximately 800nm. Encapsulation in the CMCs leads to sustained release of ICG and thus slower clearance inside body, especially in the presence of positively charged DOX. The system provides a better photothermal effect against tumors, an important step forward in the practical application of ICG in cancer therapy.

Oxygen Nanocarrier for Combined Cancer Therapy: Oxygen-Boosted ATP-Responsive Chemotherapy with Amplified ROS Lethality

Oxygen nanocarrier (A/D-ONC) with a polymeric core entrapping hemoglobin and a cationic lipid shell absorbing a DOX-intercalating DNA duplex is developed. After endocytosis oxygenated A/D-ONC donates O2 to cancer cells that acts therapeutically by: (1) increasing intracellular ATP content that promotes DOX release, thereby converting ATP to the trigger of detrimental chemotherapy; (2) by synchronously increasing the ROS amount to amplify the lethality to cancer cells.

Water-soluble benzylidene cyclopentanone based photosensitizers for in vitro and in vivo antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy (aPDT) has been proposed to cope with the increasing antibiotic resistance among pathogens. As versatile pharmacophores, benzylidene cyclopentanone based photosensitizers (PSs) have been used in various bioactive materials. However, their reports as aPDT agents are very limited, and relationships between their chemical structures and antibacterial abilities have not been systematically discussed. Here, nine water-soluble benzylidene cyclopentanone PSs modified by polyethylene glycol (PEG), carboxylate anionic or pyridyl cationic agents are studied for aPDT. It is found that the binding/uptake abilities and aPDT effects of these PSs toward bacterial cells vary significantly when adjusting the number and position of their terminal charged groups. Though the comparable (also best) binding/uptake amounts are achieved by both cationic PS P3 and anionic PS Y1, only Y1 exhibits much more excellent aPDT activities than other PSs. Antibacterial mechanisms reveal that, relative to the favorable cell wall-binding of cationic PS P3, the anionic PS Y1 can accumulate more in the spheroplast/protoplast of methicillin-resistant Staphylococcus aureus (MRSA), which ensures its high efficient aPDT abilities both in vitro and in vivo. This study suggests the great clinical application potential of Y1 in inactivation of MRSA.