Advanced nanotechnology for hypoxia-associated antitumor therapy

Bioengineered nanomaterials for dynamic diagnostics in vivo

In vivo diagnostics obtains real-time physiological information directly from the site of interest in a patient's body, providing more accurate disease diagnosis compared with ex vivo diagnostics. Particularly, in vivo dynamic diagnostics allows the continuous monitoring of physiological signals over a period of time, offering deeper insights into disease pathogenesis and progression. However, achieving in situ dynamic diagnostics in deep tissues presents challenges related to energy and signal penetration as well as dynamic monitoring. Bioengineered nanomaterials serve as an ideal platform for in vivo dynamic diagnostics, leveraging energy conversion and biofunctionalization to enable continuous acquisition of physiological information across temporal and spatial scales. In this review, with reference to the studies from the last five years, we summarize the fundamental components that are essential for dynamic diagnosis in vivo. Firstly, an input energy source with high tissue penetration is needed, such as near-infrared (NIR) light, X-rays, magnetic field and ultrasound. Secondly, a nanomaterial class that is responsive to such an energy source to provide a readable output signal is chosen. Thirdly, bioengineered nanoprobes are designed to exhibit spatial, temporal or spatiotemporal changes in the output signal. Finally, different methods are used to analyse the output signal of nanoprobes, such as detecting changes in optical, radiation, magnetic and ultrasound signals. This review also discusses the obstacles and potential solutions for advancing these bioengineered nanomaterials toward clinical translational applications.

Oxygen-Releasing Nanodroplets Relieve Intratumoral Hypoxia and Potentiate Photodynamic Therapy in 3D Head and Neck Cancer Spheroids

Hypoxia in solid tumors, including head and neck cancer (HNC), contributes to treatment resistance, aggressive tumor phenotypes, and poorer clinical outcomes. Perfluorocarbon nanodroplets have emerged as promising drugs to alleviate tumor hypoxia. These versatile nanocarriers can also encapsulate and deliver various therapeutic agents, offering a multifunctional approach to cancer treatment. However, a detailed characterization of hypoxia alleviation, particularly the duration of hypoxia treatment drug residence, has not been thoroughly investigated. In this study, we developed and characterized perfluoropentane nanodroplets (PFP NDs) for the codelivery of oxygen and the photoactivatable drug benzoporphyrin derivative (BPD) to hypoxic HNC spheroids. The PFP NDs exhibited excellent stability, efficient oxygen loading/release, and biocompatibility. Using 3D multicellular tumor spheroids of FaDu and SCC9 HNC cells, we investigated the spatiotemporal dynamics of hypoxia within these spheroids and the ability of oxygenated PFP NDs to alleviate hypoxia. Our results showed that oxygen-loaded PFP NDs effectively penetrated the core of tumor spheroids, significantly reducing hypoxia, as evidenced by the downregulation of hypoxia-inducible factors HIF-1α and HIF-2α. Importantly, we demonstrated sustained hypoxia alleviation for up to 3 h post-treatment with PFP NDs. BPD-loaded PFP NDs successfully delivered the photosensitizer into the spheroid core in a time-dependent manner. Furthermore, we evaluated the efficacy of oxygen-dependent treatment modality, namely, photodynamic therapy (PDT) with BPD and oxygen-loaded PFP NDs compared to free BPD. The NDs formulation exhibited superior PDT outcomes, which were attributed to improved oxygen availability during the treatment. This study provides comprehensive evidence for the potential of PFP NDs as a codelivery platform to overcome hypoxia-mediated treatment resistance and enhance PDT efficacy in HNC. Our findings pave the way for further investigation of this promising approach in more complex in vivo models, potentially leading to improved therapeutic strategies for hypoxic solid tumors.

Combating chemoresistance: Current approaches & nanocarrier mediated targeted delivery

Chemoresistance, a significant challenge in effective cancer treatment needs clear elucidation of the underlying molecular mechanism for the development of novel therapeutic strategies. Alterations in transporter pumps, oncogenes, tumour suppressor genes, mitochondrial function, DNA repair processes, autophagy, epithelial-mesenchymal transition (EMT), cancer stemness, epigenetic modifications, and exosome secretion lead to chemoresistance. Despite notable advancements in targeted cancer therapies employing both small molecules and macromolecules success rates remain suboptimal due to adverse effects like drug efflux, target mutation, increased mortality of normal cells, defective apoptosis, etc. This review proposes an advanced nanotechnological technique precisely targeting molecular determinants of chemoresistance which holds promise for enhancing cancer treatment efficacy. Further, the review explores various cancer hallmarks and pathways implicated in chemoresistance, current therapeutic modalities, and their limitations. It advocates the combination of nanoparticle-conjugated conventional drugs and natural compounds to specifically target molecular pathways that can potentially reverse or minimize chemoresistance incidences in cancer patients.

Core-Shell Structured Metal-Organic Frameworks for pH-Triggered Combination Photodynamic/Chemotherapy-Based Cancer Treatment

The use of hypoxia-activated prodrugs is a promising strategy to address the limitations of photodynamic therapy (PDT) caused by a hypoxic tumor microenvironment. However, the controlled release of these hypoxia-activated prodrugs during PDT remains a challenge. In this study, we present a metal-organic framework (MOF) with a core-shell structure that can achieve a high PDT efficacy and on-demand release of hypoxia-activated prodrugs (AQ4N) for hypoxic tumor therapy. The nanocomposites were created by assembling zeolitic imidazolate frameworks (ZIF-8) onto the surface of AQ4N-encapsulated porphyrinic MOF, followed by surface functionalization with folic acid-conjugated polyethylene glycol. AQ4N is entrapped in the mesopores of MOFs, and it shows acidic environment-triggered release due to the degradation of the ZIF-8. When exposed to laser, porphyrinic MOFs can produce reactive oxygen species for PDT. At the same time, PDT exacerbates hypoxia at the tumor site, leading to the bioreduction of AQ4N to AQ4 for enhanced anticancer activity. This work presents a practical approach to improve the tumor-targeting and therapeutic efficiency of hypoxic tumors.

ROS-responsive self-assembly nanoplatform overcomes hypoxia for enhanced photodynamic therapy

Photodynamic therapy (PDT) has emerged as a promising treatment for malignant tumours in recent decades due to its impressive spatiotemporal selectivity, minimal invasiveness, and few adverse effects. Despite these advancements, there remain significant challenges in effectively delivering photosensitizers to tumours and overcoming tumour hypoxia to maximize the therapeutic benefits of PDT. Ongoing research efforts are focused on developing innovative strategies to overcome the above-mentioned challenges, such as nanoplatforms and combination therapy approaches. Hence, reactive oxygen species (ROS)-responsive polymeric micelles are promising candidates to enhance the distribution and retention of photosensitizers within tumours. Additionally, efforts to alleviate tumour hypoxia may further improve the anti-tumour effects of PDT. In this study, we designed ROS-responsive polymeric micelles (TC@PTP) co-loaded with a Tapp-COF, a porphyrin derivative, and capsaicin for PDT of melanoma. These ROS-responsive nanocarriers, constructed from thioketal (TK)-linked amphiphilic di-block copolymers (PEG5K-TK-PLGA5K), could accumulate in the tumor microenvironment and release drugs under the action of ROS. Capsaicin, acting as a biogenic respiratory inhibitor, suppressed mitochondrial respiration and the hypoxia-inducible factor 1 (HIF-1) signaling pathway, thereby increasing oxygen levels at the tumour site. These PDT-triggered ROS-responsive nanoparticles effectively alleviated the tumour hypoxic microenvironment and enhanced anti-tumour efficacy. With superior biocompatibility and tumour-targeting abilities, the platform holds great promise for advancing anti-tumour combination therapy.

The use of methylene blue to control the tumor oxygenation level

BACKGROUND

Hypoxia is a characteristic feature of many tumors. It promotes tumor proliferation, metastasis, and invasion and can reduce the effectiveness of many types of cancer treatment.

OBJECTIVE

The aim of this study was to investigate the pharmacokinetics of methylene blue (MB) and its impact on the tumor oxygenation level at mouse Lewis lung carcinoma (LLC) model using spectroscopic methods.

APPROACH

The pharmacokinetics of MB were studied qualitatively and quantitatively using video fluorescence imaging and fluorescence spectroscopy. The degree of hemoglobin oxygenation in vivo was examined by calculating hemoglobin optical absorption from the measured diffuse reflectance spectra. The distribution of MB fluorescence and the lifetime of NADH were analyzed using laser scanning microscopy and fluorescence lifetime imaging microscopy (FLIM) to assess cellular metabolism.

RESULTS

After intravenous administration of MB at 10-20 mg/kg, it quickly transitioned in the tumor to a colorless leucomethylene blue, with maximum accumulation in the tumor occurring after 5-10 min. A concentration of 10 mg/kg resulted in a relative increase of the tumor oxygenation level for small tumors (volume 50-75 mm3) and normal tissue 120 min after the introduction of MB. A shift in tumor metabolism towards oxidative phosphorylation (according to the lifetime of the NADH coenzyme) was measured using FLIM method after intravenous administration of 10 mg/kg of MB. Intravenous administration of MB at 20 mg/kg results in a long-term decrease in oxygenation, which persisted for at least 120 min after the administration and did not return to its initial level.

CONCLUSIONS

Administration of MB at 10 mg/kg shown to increase tumor oxygenation level, potentially leading to more effective antitumor therapy. However, at higher doses (20 mg/kg), MB may cause long-term decrease in oxygenation.

Self-Disassembling and Oxygen-Generating Porphyrin-Lipoprotein Nanoparticle for Targeted Glioblastoma Resection and Enhanced Photodynamic Therapy

The dismal prognosis for glioblastoma multiform (GBM) patients is primarily attributed to the highly invasive tumor residual that remained after surgical intervention. The development of precise intraoperative imaging and postoperative residual removal techniques will facilitate the gross total elimination of GBM. Here, a self-disassembling porphyrin lipoprotein-coated calcium peroxide nanoparticles (PLCNP) is developed to target GBM via macropinocytosis, allowing for fluorescence-guided surgery of GBM and improving photodynamic treatment (PDT) of GBM residual by alleviating hypoxia. By reducing self-quenching and enhancing lysosome escape efficiency, the incorporation of calcium peroxide (CaO2) cores in PLCNP amplifies the fluorescence intensity of porphyrin-lipid. Furthermore, the CaO2 core has diminished tumor hypoxia and improves the PDT efficacy of PLCNP, enabling low-dose PDT and reversing tumor progression induced by hypoxia aggravation following PDT. Taken together, this self-disassembling and oxygen-generating porphyrin-lipoprotein nanoparticle may serve as a promising all-in-one nanotheranostic platform for guiding precise GBM excision and empowering post-operative PDT, providing a clinically applicable strategy to combat GBM in a safe and effective manner.

Recent advances in the colorimetric and fluorescence analysis of bioactive small-molecule compounds based on the enzyme-like activity of nanomaterials

Nanomaterials with enzyme-like activity have been widely used in the construction of colorimetric and fluorescence sensors due to their advantages of cost-effectiveness, high stability, good biocompatibility, and ease of modification. Furthermore, the colorimetric and fluorescence sensors, which are effective approaches for detecting bioactive small-molecule compounds, have been extensively explored due to their simple operation and high sensitivity. Recent significant researches have focused on designing various sensors based on nanozymes with peroxidase- and oxidase-like activity for the colorimetric and fluorescence analysis of different analytes. In this review, recent developments (from 2018 to present) in the colorimetric and fluorescent analysis of bioactive small-molecule compounds based on the enzyme-like activity of nanomaterials were summarized. In addition, the challenges and design strategies in developing colorimetric and fluorescent assays with high performance and specific sensing were discussed.

Overview and countermeasures of cancer burden in China

Cancer is one of the leading causes of human death worldwide. Treatment of cancer exhausts significant medical resources, and the morbidity and mortality caused by cancer is a huge social burden. Cancer has therefore become a serious economic and social problem shared globally. As an increasingly prevalent disease in China, cancer is a huge challenge for the country's healthcare system. Based on recent data published in the Journal of the National Cancer Center on cancer incidence and mortality in China in 2016, we analyzed the current trends in cancer incidence and changes in cancer mortality and survival rate in China. And also, we examined several key risk factors for cancer pathogenesis and discussed potential countermeasures for cancer prevention and treatment in China.

A Versatile G-Quadruplex (G4)-Coated Upconverted Metal-Organic Framework for Hypoxic Tumor Therapy

Given the complexity of the tumor microenvironment, multiple strategies are being explored to tackle hypoxic tumors. The most efficient strategies combine several therapeutic modalities and typically requires the development of multifunctional nanocomposites through sophisticated synthetic procedures. Herein, the G-quadruplex (G4)-forming sequence AS1411-A (d[(G2 T)4 TG(TG2 )4 A]) is used for both its anti-tumor and biocatalytic properties when combined with hemin, increasing the production of O2 ca. two-fold as compared to the parent AS1411 sequence. The AS1411-A/hemin complex (GH) is grafted on the surface and pores of a core-shell upconverted metal-organic framework (UMOF) to generate a UMGH nanoplatform. Compared with UMOF, UMGH exhibits enhanced colloidal stability, increased tumor cell targeting and improved O2 production (8.5-fold) in situ. When irradiated by near-infrared (NIR) light, the UMGH antitumor properties are bolstered by photodynamic therapy (PDT), thanks to its ability to convert O2 into singlet oxygen (1 O2 ). Combined with the antiproliferative activity of AS1411-A, this novel approach lays the foundation for a new type of G4-based nanomedicine.

Cascade strategy for glucose oxidase-based synergistic cancer therapy using nanomaterials

Nanomaterial-based cancer therapy faces significant limitations due to the complex nature of the tumor microenvironment (TME). Starvation therapy is an emerging therapeutic approach that targets tumor cell metabolism using glucose oxidase (GOx). Importantly, it can provide a material or environmental foundation for other diverse therapeutic methods by manipulating the properties of the TME, such as acidity, hydrogen peroxide (H2O2) levels, and hypoxia degree. In recent years, this cascade strategy has been extensively applied in nanoplatforms for ongoing synergetic therapy and still holds undeniable potential. However, only a few review articles comprehensively elucidate the rational designs of nanoplatforms for synergetic therapeutic regimens revolving around the conception of the cascade strategy. Therefore, this review focuses on innovative cascade strategies for GOx-based synergetic therapy from representative paradigms to state-of-the-art reports to provide an instructive, comprehensive, and insightful reference for readers. Thereafter, we discuss the remaining challenges and offer a critical perspective on the further advancement of GOx-facilitated cancer treatment toward clinical translation.

Immunogenic Radiation Therapy for Enhanced Antitumor Immunity via a Core-Shell Nanosensitizer-Mediated Immunosuppressive Tumor Microenvironment Modulation

Due to the immunosuppressive tumor microenvironment (TME) and weak radiation absorption, the immune response triggered by radiation therapy (RT) is limited. Herein, a core-shell nanosensitizer UiO@MnS (denoted as UM) was genuinely constructed for the amplification of RT efficacy and induction of immunogenicity via integrating MnS-reprogrammed TME with Hf-based UiO-sensitized RT. The acid-sensitive MnS would produce H2S under acidic TME to improve oxygenation through inhibition mitochondrial respiration and reducing metabolic oxygen consumption, leading to decreased HIF-1α expression and enhanced radiosensitization. In addition, the generated H2S inhibited the catalase activity to increase the H2O2 level, which subsequently enhanced the Mn2+-mediated Fenton-like reaction, resulting in G2/M cell cycle arrest to improve the cellular sensitivity for radiation. This impressive tumor oxygenation, cell cycle arrest, and radiosensitization procedure boosted RT efficacy and resulted in strong antitumor immunogenicity. Taken together, combining the immunosuppressive TME modulation with a sensitizing radiation strategy shows great promise for magnifying immunogenic RT outputs.

pH/GSH dual-responsive supramolecular nanomedicine for hypoxia-activated combination therapy

Moderate oxygen (O2) supply and uneven distribution of oxygen at the tumor site usually hinder the therapeutic efficacy of hypoxia-activated prodrugs. In this report, we designed a ferrocene-containing supramolecular nanomedicine (PFC/GOD-TPZ) with the PEG corona and disulfide-bond cross-linked core to co-encapsulate 4-di-N-oxide tirapazamine (TPZ) and glucose oxidase (GOD). The PEG corona of PFC/GOD-TPZ could be weakly acidic tumor pH-responsively detached for an enhanced cellular internalization, while the disulfide-bond cross-linked core could be cleavaged by intracellular glutathione (GSH) to present a GSH-triggered drug-release behavior. Subsequently, the cascade reactions, including catalytic reactions among the released GOD, glucose, and O2 to generate H2O2 and the subsequent Fenton reaction between ferrocene and H2O2, occurred. With the depletion of O2, the non-toxic TPZ was activated and converted into the cytotoxic therapeutic agent benzotriazinyl (BTZ) radical under the exacerbated hypoxic microenvironment. Collectively, the PFC/GOD-TPZ provides a promising strategy for effective combination therapy of GOD-mediated starvation therapy, chemodynamic therapy (CDT), and hypoxia-activated chemotherapy (CT).

Nano-engineering nanomedicines with customized functions for tumor treatment applications

Nano-engineering with unique "custom function" capability has shown great potential in solving technical difficulties of nanomaterials in tumor treatment. Through tuning the size and surface properties controllablly, nanoparticles can be endoewd with tailored structure, and then the characteristic functions to improve the therapeutic effect of nanomedicines. Based on nano-engineering, many have been carried out to advance nano-engineering nanomedicine. In this review, the main research related to cancer therapy attached to the development of nanoengineering nanomedicines has been presented as follows. Firstly, therapeutic agents that target to tumor area can exert the therapeutic effect effectively. Secondly, drug resistance of tumor cells can be overcome to enhance the efficacy. Thirdly, remodeling the immunosuppressive microenvironment makes the therapeutic agents work with the autoimmune system to eliminate the primary tumor and then prevent tumor recurrence and metastasis. Finally, the development prospects of nano-engineering nanomedicine are also outlined.

Reprogramming of the tumor microenvironment using a PCN-224@IrNCs/D-Arg nanoplatform for the synergistic PDT, NO, and radiosensitization therapy of breast cancer and improving anti-tumor immunity

The low X-ray attenuation coefficient of tumor soft tissue and the hypoxic tumor microenvironment (TME) during radiation therapy (RT) of breast cancer result in RT resistance and thus reduced therapeutic efficacy. In addition, immunosuppression induced by the TME severely limits the antitumor immunity of radiation therapy. In this paper, we propose a PCN-224@IrNCs/D-Arg nanoplatform for the synergistic radiosensitization, photodynamic, and NO therapy of breast cancer that also boosts antitumor immunity (PCN = porous coordination network, IrNCs = iridium nanocrystals, D-Arg = D-arginine). The local tumors can be selectively ablated via reprogramming the tumor microenvironment (TME), photodynamic therapy (PDT) and NO therapy, and the presence of the high-Z element Ir that sensitizes radiotherapy. The synergistic execution of these treatment modalities also resulted in adapted antitumor immune response. The intrinsic immunomodulatory effects of the nanoplatform also repolarize macrophages toward the M1 phenotype and induce dendritic cell maturation, activating antitumor T cells to induce immunogenic cell death as demonstrated in vitro and in vivo. The nanocomposite design reported herein represents a new regimen for the treatment of breast cancer through TME reprogramming to exert a synergistic effect for effective cancer therapy and antitumor immunity.

Development of the Cu/ZIF-8 MOF Acid-Sensitive Nanocatalytic Platform Capable of Chemo/Chemodynamic Therapy with Improved Anti-Tumor Efficacy

Recently, the combination of chemotherapy and chemodynamic therapy (CDT) has become a desirable strategy in the treatment of cancer. However, a satisfactory therapeutic outcome is often difficult to achieve due to the deficiency of endogenous H₂O₂ and O₂ in the tumor microenvironment. In this study, a CaO₂@DOX@Cu/ZIF-8 nanocomposite was prepared as a novel nanocatalytic platform to enable the combination of chemotherapy and CDT in cancer cells. The anticancer drug doxorubicin hydrochloride (DOX) was loaded onto calcium peroxide (CaO₂) nanoparticles (NPs) to form CaO₂@DOX, which was then encapsulated in a copper zeolitic imidazole ester MOF (Cu/ZIF-8) to form CaO₂@DOX@Cu/ZIF-8 NPs. In the mildly acidic tumor microenvironment, CaO₂@DOX@Cu/ZIF-8 NPs rapidly disintegrated, releasing CaO₂, which reacted with water to generate H₂O₂ and O₂ in the tumor microenvironment. The ability of CaO₂@DOX@Cu/ZIF-8 NPs to combine chemotherapy and CDT was assessed by conducting cytotoxicity, living dead staining, cellular uptakes, H&E staining, and TUNEL assays in vitro and in vivo. The combination of chemotherapy and CDT of CaO₂@DOX@Cu/ZIF-8 NPs had a more favorable tumor suppression effect than the nanomaterial precursors, which were not capable of the combined chemotherapy/CDT.

Tumor microenvironment-regulating nanomedicine design to fight multi-drug resistant tumors

The tumor microenvironment (TME) is a very cunning system that enables tumor cells to escape death post-traditional antitumor treatments through the comprehensive effect of different factors, thereby leading to drug resistance. Deep insights into TME characteristics and tumor resistance encourage the construction of nanomedicines that can remodel the TME against drug resistance. Tremendous interest in combining TME-regulation measurement with traditional tumor treatment to fight multidrug-resistant tumors has been inspired by the increasing understanding of the role of TME reconstruction in improving the antitumor efficiency of drug-resistant tumor therapy. This review focuses on the underlying relationships between specific TME characteristics (such as hypoxia, acidity, immunity, microorganisms, and metabolism) and drug resistance in tumor treatments. The exciting antitumor activities strengthened by TME regulation are also discussed in-depth, providing solutions from the perspective of nanomedicine design. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Biomedical engineered nanomaterials to alleviate tumor hypoxia for enhanced photodynamic therapy

Photodynamic therapy (PDT), as a highly selective, widely applicable, and non-invasive therapeutic modality that is an alternative to radiotherapy and chemotherapy, is extensively applied to cancer therapy. Practically, the efficiency of PDT is severely hindered by the existence of hypoxia in tumor tissue. Hypoxia is a typical hallmark of malignant solid tumors, which remains an essential impediment to many current treatments, thereby leading to poor clinical prognosis after therapy. To address this issue, studies have been focused on modulating tumor hypoxia to augment the therapeutic efficacy. Although nanomaterials to relieve tumor hypoxia for enhanced PDT have been demonstrated in many research articles, a systematical summary of the role of nanomaterials in alleviating tumor hypoxia is scarce. In this review, we introduced the mechanism of PDT, and the involved therapeutic modality of PDT for ablation of tumor cells was specifically summarized. Moreover, current advances in nanomaterials-mediated tumor oxygenation via oxygen-carrying or oxygen-generation tactics to alleviate tumor hypoxia are emphasized. Based on these considerable summaries and analyses, we proposed some feasible perspectives on nanoparticle-based tumor oxygenation to ameliorate the therapeutic outcomes, which may provide some detailed information in designing new oxygenation nanomaterials in this burgeneous field.

Probing the Role of Connecting Bonds and Modifying Chains in the Rational Design of Prodrug Nanoassemblies

Prodrug-based self-assembled nanoparticles combined with the merits of nanotechnology and prodrugs strategies have gradually become a research trending topic in the field of drug delivery. These prodrugs usually consist of parent drugs, connecting bonds, and modifying chains. The influences of the connecting bonds and modifying chains on the pharmaceutical characteristics, in vivo delivery fate, and antitumor activity of prodrug nanoassemblies remain elusive. Herein, three docetaxel (DTX) prodrugs were designed using sulfur bonds (thioether bond or disulfide bond) as connecting bonds and fatty alcohols (straight chain or branched chain) as modifying chains. Interestingly, the difference between connecting bonds and modifying chains deeply influenced the colloidal stability, redox responsive drug release, cytotoxicity, pharmacokinetic properties, tumor accumulation, and antitumor effect of prodrug nanoassemblies. DTX conjugated with branched chain fatty alcohols via disulfide bonds (HUA-SS-DTX) significantly improved the antitumor efficiency of DTX and reduced the systematic toxicity. Our study elaborates on the vital role of connecting bonds and modifying chains in the rational design of prodrug nanoassemblies.

Hypoxia responsive phytonanotheranostics: A novel paradigm towards fighting cancer

Hypoxia enhances tumor aggressiveness, thereby reducing the efficacy of anticancer therapies. Phytomedicine, which is nowadays considered as the new panacea owing to its dynamic physiological properties, is often plagued by shortcomings. Incorporating these wonder drugs in nanoparticles (phytonanomedicine) for hypoxia therapy is a new prospect in the direction of cancer management. Similarly, the concept of phytonanotheranostics for the precise tumor lesion detection and treatment monitoring in the hypoxic scenario is going on a rampant speed. In the same line, smart nanoparticles which step in for "on-demand" drug release based on internal or external stimuli are also being explored as a new tool for cancer management. However, studies regarding these smart and tailor-made nanotheranostics in the hypoxic tumor microenvironment are very limited. The present review is an attempt to collate these smart stimuli-responsive phytonanotherapeutics in one place for initiating future research in this upcoming field for better cancer treatment.

An Enhanced Photothermal Therapeutic Iridium Hybrid Platform Reversing the Tumor Hypoxic Microenvironment

As hypoxia is closely associated with tumor progression, proliferation, invasion, metastasis, and strong resistance to therapy, regulating and overcoming the hypoxia tumor microenvironment are two increasingly important aspects of tumor treatment. Herein, we report a phototherapeutic platform that uses the organic photosensitizer diketopyrrolopyrrole (DPP) derivative and inorganic iridium salts (IrCl₃) with photothermal activity and the capacity to decompose H₂O₂ efficiently. The characterization of their photophysical properties proved that DPP-Ir nanoparticles are capable of remarkable near-infrared (NIR) absorption, and compared to DPP nanoparticles, the photothermal conversion efficiency (PCE) increases from 42.1% in DPP nanoparticles to 67.0% in DPP-Ir nanoparticles. The hybrid nanoparticles utilize the catalytic decomposition of endogenous H₂O₂ to produce oxygen for the downregulation of the hypoxia-inducible factor 1 subunit alpha (HIF-1α) protein, which could reverse the tumor hypoxic microenvironment. Benefiting from the excellent optical properties and good biocompatibility, the hybrid platform exhibits efficient photothermal therapeutic effects as well as good biological safety. In conclusion, such a hybrid platform could improve photothermal therapy against cancer.

Hypoxia-Responsive Molecular Probe Lighted up by Peptide Self-Assembly for Cancer Cell Imaging

Hypoxia is a characteristic feature of most solid tumors, which promotes the proliferation, metastasis, and invasion of tumors and stimulates the resistance of cancer treatments, leading to the serious consequences of tumor recurrence. The exploration of hypoxia detection technology will aid tumor diagnosis and treatment. Fluorescence imaging technology is an accurate and efficient hypoxia detection technology. It has attracted significant research interest, but designing novel fluorescence probes, especially stimuli-responsive probes with high sensitivity and low toxicity is still challenging. In this work, we report a hypoxia-responsive molecular bioprobe lighted up by peptide self-assembly, which contains aggregationinduced emission (AIE) fluorescent molecule TPE, hypoxia-responsive azo group (-N═N-), the self-assembling peptide GFFY, and targeting ligand RGD. The resulting peptide derivative TPE-GFFY-N═N-EERGD forms supramolecular nanofibers but emit weak fluorescence because the azobenzene moiety can effectively quench the fluorescence of the TPE dye. However, the fluorescence-quenched nanofibers could be lighted up dramatically when the azo group is reduced. More importantly, this "turn-on" supramolecular fluorescence bioprobe enables effective detecting tumor hypoxia due to the overexpressed azoreductase in the tumor microenvironment. This work affords a paradigm of designing environmentsensitive fluorescent molecular probes for tumor hypoxia imaging.

Acceptor Planarization and Donor Rotation: A Facile Strategy for Realizing Synergistic Cancer Phototherapy via Type I PDT and PTT

Tumor hypoxia seriously impairs the therapeutic outcomes of type II photodynamic therapy (PDT), which is highly dependent upon tissue oxygen concentration. Herein, a facile strategy of acceptor planarization and donor rotation is proposed to design type I photosensitizers (PSs) and photothermal reagents. Acceptor planarization can not only enforce intramolecular charge transfer to redshift NIR absorption but also transfer the type of PSs from type II to type I photochemical pathways. Donor rotation optimizes photothermal conversion efficiency (PCE). Accordingly, three 3,6-divinyl-substituted diketopyrrolopyrrole (DPP) derivatives, 2TPAVDPP, TPATPEVDPP, and 2TPEVDPP, with different number of rotors were prepared. Experimental results showed that three compounds were excellent type I PSs, and the corresponding 2TPEVDPP nanoparticles (NPs) with the most rotors possessed the highest PCE. The photophysical properties of 2TPEVDPP NPs are particularly suitable for in vivo NIR fluorescence imaging-guided synergistic PDT/PTT therapy. The proposed strategy is helpful for exploiting type I phototherapeutic reagents with high efficacy for synergistic PDT and PTT.

Robust radiosensitization of hemoglobin-curcumin nanoparticles suppresses hypoxic hepatocellular carcinoma

Background

Radioresistance inducing by hypoxic microenvironment of hepatocellular carcinoma is a major obstacle to clinical radiotherapy. Advanced nanomedicine provides an alternative to alleviate the hypoxia extent of solid tumor, even to achieve effective synergistic treatment when combined with chemotherapy or radiotherapy.

Results

Herein, we developed a self-assembled nanoparticle based on hemoglobin and curcumin for photoacoustic imaging and radiotherapy of hypoxic hepatocellular carcinoma. The fabricated nanoparticles inhibited hepatoma migration and vascular mimics, and enhanced the radiosensitivity of hypoxic hepatoma cells in vitro via repressing cell proliferation and DNA damage repair, as well as inducing apoptosis. Benefit from oxygen-carrying hemoglobin combined with polyphenolic curcumin, the nanoparticles also effectively enhanced the photoacoustic contrast and the efficacy of radiotherapy for hepatocellular carcinoma in vivo.

Conclusions

Together, the current study offered a radiosensitization platform for optimizing the efficacy of nanomedicines on hypoxic radioresistant tumor.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01316-w.

Research advances in NQO1-responsive prodrugs and nanocarriers for cancer treatment

NAD(P)H: quinine oxidoreductase (NQO1) is a class of flavoprotein enzymes commonly expressed in eukaryotic cells. It actively participates in the metabolism of various quinones and their in vivo bioactivation through electron reduction reactions. The expression level of NQO1 is highly upregulated in many solid tumor cells compared with that in normal cells. NQO1 has been considered a candidate molecular target because of its overexpression and bioactivity in different tumors. NQO1-responsive prodrugs and nanocarriers have recently been identified as effective objectives for achieving controlled drug release, reducing adverse reactions and improving clinical efficacy. This review systematically introduces the research advances in applying NQO1-responsive prodrugs and nanocarriers to cancer treatment. It also discusses the existing problems and the developmental prospects of these two antitumor drug delivery systems.

Autocatalytic oncotherapy nanosystem with glucose depletion for cascade amplification of hypoxia-activated chemotherapy and H2O2-dependent chemodynamic therapy

Hypoxia-activated prodrug is an appealing oncotherapy strategy, but limited by insufficient tumor hypoxia. Moreover, standalone prodrug fails to treat tumor satisfactorily due to tumor complexity. Herein, a nanosystem (TPZ@FeMSN-GOX) was...

Dynamic nano-assemblies based on two-dimensional inorganic nanoparticles: Construction and preclinical demonstration

Dynamic drug delivery systems (DDSs) have the ability of transforming their morphology and functionality in response to the biological microenvironments at the disease site and/or external stimuli, show spatio-temporally controllable drug delivery, and enhance the treatment efficacy. Due to the large surface area and modification flexibility, two-dimensional (2D) inorganic nanomaterials are being increasingly exploited for developing intelligent DDSs for biomedical applications. In this review, we summarize the engineering methodologies used to construct transformable 2D DDSs, including changing compositions, creating defects, and surface dot-coating with polymers, biomolecules, or nanodots. Then we present and discuss dynamic inorganic 2D DDSs whose transformation is driven by the diseased characteristics, such as pH gradient, redox, hypoxia, and enzyme in the tumor microenvironment as well as the external stimuli including light, magnetism, and ultrasound. Finally, the limitations and challenges of current transformable inorganic DDSs for clinical translation and their in vivo safety assessment are discussed.

The synthesis of a nanodrug using metal-based nanozymes conjugated with ginsenoside Rg3 for pancreatic cancer therapy

Nanozymes have limited applications in clinical practice due to issues relating to their safety, stability, biocompatibility, and relatively low catalytic activity in the tumor microenvironment (TME) in vivo. Herein, we report a synergistic enhancement strategy involving the conjugation of metal-based nanozymes (Fe@Fe3O4) with natural bioactive organic molecules (ginsenoside Rg3) to establish a new nanodrug. Importantly, this metal-organic nanocomposite drug ensured the stability and biosafety of the nanozyme cores and the cellular uptake efficiency of the whole nanodrug entity. This nanodrug is based on integrating the biological characteristics and intrinsic physicochemical properties of bionics. The glycoside chain of Rg3 forms a hydrophilic layer on the outermost layer of the nanodrug to improve the biocompatibility and pharmacokinetics. Additionally, Rg3 can activate apoptosis and optimize the activity and status of normal cells. Internal nanozymes enter the TME and release Fe3+ and Fe2+, and the central metal Fe(0) continuously generates highly active Fe2+ under the conditions of the TME and in the presence of Fe3+, maintaining the catalytic activity. Therefore, these nanozymes can effectively produce reactive oxygen species and oxygen in the TME, thereby promoting the apoptosis of cancer cells. Thus, we propose the use of a new type of metal-organic nanocomposite material as a synergistic strategy against cancer.

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.

Recent advances in peptide-based nanomaterials for targeting hypoxia

Hypoxia is a prominent feature of many severe diseases such as malignant tumors, ischemic strokes, and rheumatoid arthritis. The lack of oxygen has a paramount impact on angiogenesis, invasion, metastasis, and chemotherapy resistance. The potential of hypoxia as a therapeutic target has been increasingly recognized over the last decade. In order to treat these disease states, peptides have been extensively investigated due to their advantages in safety, target specificity, and tumor penetrability. Peptides can overcome difficulties such as low drug/energy delivery efficiency, hypoxia-induced drug resistance, and tumor nonspecificity. There are three main strategies for targeting hypoxia through peptide-based nanomaterials: (i) using peptide ligands to target cellular environments unique to hypoxic conditions, such as cell surface receptors that are upregulated in cells under hypoxic conditions, (ii) utilizing peptide linkers sensitive to the hypoxic microenvironment that can be cleaved to release therapeutic or diagnostic payloads, and (iii) a combination of the above where targeting peptides will localize the system to a hypoxic environment for it to be selectively cleaved to release its payload, forming a dual-targeting system. This review focuses on recent developments in the design and construction of novel peptide-based hypoxia-targeting nanomaterials, followed by their mechanisms and potential applications in diagnosis and treatment of hypoxic diseases. In addition, we address challenges and prospects of how peptide-based hypoxia-targeting nanomaterials can achieve a wider range of clinical applications.

A co-delivery nanoplatform for a lignan-derived compound and perfluorocarbon tuning IL-25 secretion and the oxygen level in tumor microenvironments for meliorative tumor radiotherapy

A hypoxic environment in tumors hampers the therapeutic efficacy of radiotherapy. Moreover, radiotherapy, a localized treatment technique, can barely control tumor metastases. Herein, poly(lactic-co-glycolic acid) was used to encapsulate perfluorocarbon (PFC) for increasing the oxygen level and a lignan-derived compound (Q1) for enhancing IL-25 secretion from fibroblasts, thereby boosting the radiotherapeutic effect on local and distant tumors. The prepared co-delivery nanoplatform, PFC-Q1@PLGA, has a nano-scale size of around 160 nm and a negative zeta potential (about -13 mV). PFC-Q1@PLGA treatment leads to an arrest of the G2 phase (4n) in the cell cycle and reduces the mitochondria membrane potential. A high expression level of IL-25 in fibroblasts is detected after the cells are treated with PFC-Q1@PLGA, which increases the late apoptosis percentage of 4T1 cells after treatment with IL-25-containing conditional medium from fibroblasts. The oxygen level in tumors is significantly promoted to about 52.3% after injection of oxygen-saturated PFC-Q1@PLGA (O₂), which is confirmed from the functional magnetic resonance images of the tumor site in mice. The in vivo study demonstrates that the injection of PFC-Q1@PLGA (O₂) into local tumors significantly enhances the radiotherapeutic effect on local tumors and also inhibits the growth of remote tumors by an enhanced abscopal effect. This study presents a novel radiotherapy strategy to enable synergistic whole-body therapeutic responses after localized treatment with PFC-Q1@PLGA (O₂).

Hypoxia boosts aerobic glycolysis of carcinoma：a complex process for tumor development

Hypoxia, a common feature in malignant tumors, is mainly caused by insufficient oxygen supply. Hypoxia is closely related to cancer development, affecting cancer invasion and metastasis, energy metabolism and other pathological processes, and is not conducive to cancer treatment and prognosis. Tumor cells exacerbate metabolic abnormalities to adapt to the hypoxic microenvironment, especially to enhance aerobic glycolysis. Glycolysis leads to an acidic microenvironment in cancer tissues, enhancing cancer metastasis, deterioration and drug resistance. Therefore, hypoxia is a therapeutic target that cannot be ignored in cancer treatment. The adaptation of tumor cells to hypoxia is mainly regulated by hypoxia inducible factors (HIFs), and the stability of HIFs is improved under hypoxic conditions. HIFs can promote the glycolysis of tumors by regulating glycolytic enzymes, transporters, and participates in regulating the TCA (tricarboxylic acid) cycle. In addition, HIFs indirectly affect glycolysis through its interaction with non-coding RNAs. Therefore, targeting hypoxia and HIFs are important tumor therapies.

The targetable nanoparticle BAF312@cRGD-CaP-NP represses tumor growth and angiogenesis by downregulating the S1PR1/P-STAT3/VEGFA axis in triple-negative breast cancer

Background

Overexpressed vascular endothelial growth factor A (VEGFA) and phosphorylated signal transducer and activator of transcription 3 (P-STAT3) cause unrestricted tumor growth and angiogenesis of breast cancer (BRCA), especially triple-negative breast cancer (TNBC). Hence, novel treatment strategy is urgently needed.

Results

We found sphingosine 1 phosphate receptor 1 (S1PR1) can regulate P-STAT3/VEGFA. Database showed S1PR1 is highly expressed in BRCA and causes the poor prognosis of patients. Interrupting the expression of S1PR1 could inhibit the growth of human breast cancer cells (MCF-7 and MDA-MB-231) and suppress the angiogenesis of human umbilical vein endothelial cells (HUVECs) via affecting S1PR1/P-STAT3/VEGFA axis. Siponimod (BAF312) is a selective antagonist of S1PR1, which inhibits tumor growth and angiogenesis in vitro by downregulating the S1PR1/P-STAT3/VEGFA axis. We prepared pH-sensitive and tumor-targeted shell-core structure nanoparticles, in which hydrophilic PEG2000 modified with the cyclic Arg-Gly-Asp (cRGD) formed the shell, hydrophobic DSPE formed the core, and CaP (calcium and phosphate ions) was adsorbed onto the shell; the nanoparticles were used to deliver BAF312 (BAF312@cRGD-CaP-NPs). The size and potential of the nanoparticles were 109.9 ± 1.002 nm and − 10.6 ± 0.056 mV. The incorporation efficacy for BAF312 was 81.4%. Results confirmed BAF312@cRGD-CaP-NP could dramatically inhibit tumor growth and angiogenesis in vitro and in MDA-MB-231 tumor-bearing mice via downregulating the S1PR1/P-STAT3/VEGFA axis.

Conclusions

Our data suggest a potent role for BAF312@cRGD-CaP-NPs in treating BRCA, especially TNBC by downregulating the S1PR1/P-STAT3/VEGFA axis.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00904-6.

Enzyme/GSH dual-responsive biodegradable nanohybrid for spatiotemporally specific photodynamic and hypoxia-augmented therapy against tumors

Photodynamic therapy (PDT) efficacy has been severely limited by the hypoxia in tumor microenvironment. A multitherapy modality was developed, integrating the advantages of each therapy and a nanocarrier: PDT and PDT-induced hypoxia-activated chemotherapy. Following PDT-induced hypoxia augmented in the periphery of the tumors, chemotherapy was locally activated. To this end, new indocyanine green (IR820) and a hypoxia-activated prodrug tirapazamine (TPZ) were loaded in glutathione (GSH) decomposable mesoporous organic silica nanoparticles (GMONs), tethered by hyaluronic acid (HA). This nanohybrid showed a tendency to accumulate and be retained in tumors, due to passive and active targeting. The IR820 produced singlet oxygen (¹O₂) under near-infrared (NIR) laser irradiation and concomitantly tumorous abnormality exacerbated hypoxia. TPZ-mediated hypoxia-activated chemotherapy acted to kill more tumor cells. In vivo results indicated that the tumor inhibition rate of dual-loaded nanohybrids was up to 76% under NIR laser irradiation. The immunofluorescence staining of tumor slices demonstrated that the superficial part of tumors experienced exacerbated hypoxia with laser irradiation, resulting in TPZ exerting powerful chemotherapy effects. This nanohybrid is expected to be valuable as spatiotemporally specific therapy for cancer.

Magnetothermally Triggered Free-Radical Generation for Deep-Seated Tumor Treatment

Tumor hypoxia and the tissue penetration limitation of excitation light hamper the widespread clinical use of photodynamic therapy. The development of new therapeutic strategies that can generate oxygen-independent free radicals without penetration depth limitation is of great demand. Herein, a novel magnetothermodynamic strategy for deep-seated tumor therapy is reported. In this system, a radical initiator (AIPH) was loaded into porous hollow iron oxide nanoparticles (PHIONs). Under the induction of an alternating magnetic field (AMF), PHIONs can generate heat to trigger the release and decomposition of AIPH, resulting in the generation of oxygen-independent alkyl radicals. The resulting alkyl radicals can effectively kill cancer cells under hypoxic conditions. More importantly, this magnetothermally triggered free-radical generator exhibits significant therapeutic efficacy for orthotopic liver tumors in a rat model. This magnetothermodynamic therapy strategy with the advantages of oxygen independence and no limitation of penetration depth holds great promise in deep-seated solid tumor treatment.

An Alternating Irradiation Strategy-Driven Combination Therapy of PDT and RNAi for Highly Efficient Inhibition of Tumor Growth and Metastasis

Hypoxia and hypoxia induced overexpression of vascular endothelial growth factor (VEGF) not only seriously affects the treatment effects of photodynamic therapy (PDT) but also promotes tumor metastasis. Herein, an alternating irradiation strategy (referred to as alternate use of low/high dose of light [ALHDL] irradiation)-driven combination therapy of PDT and RNA interference (RNAi) is developed to synergistically inhibit tumor growth and metastasis. A cationic amphipathic peptide (ALS) served as a carrier in the co-delivery system of photochlor (HPPH) and siVEGF (ALSH/siVEGF). At the beginning of ALHDL-driven ALSH/siVEGF treatment, short-term LDL irradiation can facilitate the tumor penetration, cellular uptake, and endosome escape of ALSH/siVEGF. Moreover, accompanied by HDL-mediated rapid cell apoptosis and LDL-mediated efficient VEGF silencing, the joint use of PDT and RNAi achieved remarkable antitumor effects both in vitro and in vivo. Importantly, benefited from the excellent performance of ALHDL in slowing the rapid deterioration of the anoxic environment of tumors, and ALSH/siVEGF treatment-mediated highly improved VEGF silencing efficacy and inhibitory effect on angiogenesis, the liver and lung metastases of HeLa cells have been successfully suppressed. Together, this study clearly indicates that ALHDL-driven combination therapy of PDT and RNAi is a highly effective modality for inhibition of tumor growth and metastasis.

Recoverable peroxidase-like Fe3O4@MoS2-Ag nanozyme with enhanced antibacterial ability

Antibacterial agents with enzyme-like properties and bacteria-binding ability have provided an alternative method to efficiently disinfect drug-resistance microorganism. Herein, a Fe₃O₄@MoS₂-Ag nanozyme with defect-rich rough surface was constructed by a simple hydrothermal method and in-situ photodeposition of Ag nanoparticles. The nanozyme exhibited good antibacterial performance against E. coli (~69.4%) by the generated ROS and released Ag⁺, while the nanozyme could further achieve an excellent synergistic disinfection (~100%) by combining with the near-infrared photothermal property of Fe₃O₄@MoS₂-Ag. The antibacterial mechanism study showed that the antibacterial process was determined by the collaborative work of peroxidase-like activity, photothermal effect and leakage of Ag⁺. The defect-rich rough surface of MoS₂ layers facilitated the capture of bacteria, which enhanced the accurate and rapid attack of •OH and Ag⁺ to the membrane of E. coli with the assistance of local hyperthermia. This method showed broad-spectrum antibacterial performance against Gram-negative bacteria, Gram-positive bacteria, drug-resistant bacteria and fungal bacteria. Meanwhile, the magnetism of Fe₃O₄ was used to recycle the nanozyme. This work showed great potential of engineered nanozymes for efficient disinfection treatment.

Functional Transdermal Nanoethosomes Enhance Photodynamic Therapy of Hypertrophic Scars via Self-Generating Oxygen

Photodynamic therapy (PDT) is a new therapeutic strategy for hypertrophic scars (HSs), and nanoethosomes (ES) have attracted considerable attention as an efficient transdermal delivery system for PDT of HSs (HS-PDT). However, the delivery of photosensitizers and the hypoxic microenvironment of HSs limit HS-PDT efficacy. Consequently, functional transdermal ES (A/A-ES) that are loaded with the photosensitizer, 5-aminolevulinic acid (ALA), and immobilized nanoenzyme Au nanoclusters (ANCs) within the ES surface have been developed that exhibit superior co-delivery characteristics and produce catalase that enhances HS-PDT efficacy. The unique structure of A/A-ES enables them to co-deliver ALA and ANCs into the HS tissue and to efficiently decompose the endogenous hydrogen peroxide in the HS to generate oxygen. The findings from in vitro and in vivo experiments demonstrated that A/A-ES efficiently co-delivered ALA and ANCs into the HS tissue and that they improved the hypoxic microenvironment of the HS. Systematic assessments reveal that A/A-ES enhance HS-PDT efficacy and that they are highly effective at improving the morphology and promoting HS fibroblast apoptosis and the rearrangement of collagen. These works give rise to an effective treatment option for HSs that integrates the transdermal co-delivery of ALA and nanoenzymes, thereby enabling them to exert their respective beneficial effects, and they highlight the enhancement of HS-PDT efficacy via self-generating oxygen.

Perfluorocarbons Therapeutics in Modern Cancer Nanotechnology for Hypoxiainduced Anti-tumor Therapy

With an estimated failure rate of about 90%, immunotherapies that are intended for the treatment of solid tumors have caused an anomalous rise in the mortality rate over the past decades. It is apparent that resistance towards such therapies primarily occurs due to elevated levels of HIF-1 (Hypoxia-induced factor) in tumor cells, which are caused by disrupted microcirculation and diffusion mechanisms. With the advent of nanotechnology, several innovative advances were brought to the fore; and, one such promising direction is the use of perfluorocarbon nanoparticles in the management of solid tumors. Perfluorocarbon nanoparticles enhance the response of hypoxia-based agents (HBAs) within the tumor cells and have been found to augment the entry of HBAs into the tumor micro-environment. The heightened penetration of HBAs causes chronic hypoxia, thus aiding in the process of cell quiescence. In addition, this technology has also been applied in photodynamic therapy, where oxygen self-enriched photosensitizers loaded perfluorocarbon nanoparticles are employed. The resulting processes initiate a cascade, depleting tumour oxygen and turning it into a reactive oxygen species eventually to destroy the tumour cell. This review elaborates on the multiple applications of nanotechnology based perfluorocarbon formulations that are being currently employed in the treatment of tumour hypoxia.

Tumor targeted self-synergistic nanoplatforms for arsenic-sensitized photodynamic therapy

Development of antitumor agents with high efficiency and low toxicity is one of the most important goals for biomedical research. However, most traditional therapeutic strategies were limited due to their non-specificity and abnormal tumor microenvironments, causing a poor therapeutic efficiency and severe side effects. In this paper, a tumor targeted self-synergistic nanoplatform (designated as PAO@PCN@HA) was developed for chemotherapy sensitized photodynamic therapy (PDT) against hypoxic tumors. The efficient drug loading of phenylarsine oxide (PAO) in porphyrinic metal organic framework of PCN-224 as well as the surface modification of hyaluronic acid (HA) improved the targeted drug delivery and reduced the side effects of PAO at the therapeutic dose. Particularly, PAO as an arsenical-based chemotherapeutic agent could not only induce cell apoptosis by generating reactive oxygen species (ROS), but also regulate tumor microenvironments to improve the PDT effect of PCN-224 by mitigating hypoxia and consuming cellular GSH. Both in vitro and in vivo investigations confirmed an effective self-synergy of PAO@PCN@HA in hypoxic tumor therapy with a low systemic toxicity. This integration of microenvironment adjustment with tumor targeted self-synergistic mechanism might provide a new insight for the development of arsenic-based antitumor strategy for clinical applications.

Nanostructured manganese dioxide for anticancer applications: preparation, diagnosis, and therapy

Nanostructured manganese dioxide (MnO₂) has attracted extensive attention in the field of anticancer applications. As we all know, the tumor microenvironment is usually characterized by a high glutathione (GSH) concentration, overproduced hydrogen peroxide (H₂O₂), acidity, and hypoxia, which affect the efficacy of many traditional treatments such as chemotherapy, radiotherapy, and surgery. Fortunately, as one kind of redox-active nanomaterial, nanostructured MnO₂ has many excellent properties such as strong oxidation ability, excellent catalytic activity, and good biodegradability. It can be used effectively in diagnosis and treatment when it reacts with some harmful substances in the tumor site. It can not only enhance the therapeutic effect but also adjust the tumor microenvironment. Therefore, it is necessary to present the recent achievements and progression of nanostructured MnO₂ for anticancer applications, including preparation methods, diagnosis, and treatment. Special attention was paid to photodynamic therapy (PDT), bioimaging and cancer diagnosis (BCD), and drug delivery systems (DDS). This review is expected to provide helpful guidance on further research of nanostructured MnO₂ for anticancer applications.

Recent advances in strategies for overcoming hypoxia in photodynamic therapy of cancer

The selectivity of photodynamic therapy (PDT) derived from the tailored accumulation of photosensitizing drug (photosensitizer; PS) in the tumor microenvironment (TME), and from local irradiation, turns it into a "magic bullet" for the treatment of resistant tumors without sparing the healthy tissue and possible adverse effects. However, locally-induced hypoxia is one of the undesirable consequences of PDT, which may contribute to the emergence of resistance and significantly reduce therapeutic outcomes. Therefore, the development of strategies using new approaches in nanotechnology and molecular biology can offer an increased opportunity to eliminate the disadvantages of hypoxia. Emerging evidence indicates that wisely designed phototherapeutic procedures, including: (i) ROS-tunable photosensitizers, (ii) organelle targeting, (iii) nano-based photoactive drugs and/or PS delivery nanosystems, as well as (iv) combining them with other strategies (i.e. PTT, chemotherapy, theranostics or the design of dual anticancer drug and photosensitizers) can significantly improve the PDT efficacy and overcome the resistance. This mini-review addresses the role of hypoxia and hypoxia-related molecular mechanisms of the HIF-1α pathway in the regulation of PDT efficacy. It also discusses the most recent achievements as well as future perspectives and potential challenges of PDT application against hypoxic tumors.

Nanoenzymes in disease diagnosis and therapy

This feature article highlights various nanoenzymes and their bio-applications in disease diagnosis and therapy. Current challenges and future trends of nanoenzymes are also discussed.