Catalase-Loaded TaOx Nanoshells as Bio-Nanoreactors Combining High-Z Element and Enzyme Delivery for Enhancing Radiotherapy

Metal-based NanoEnhancers for Future Radiotherapy: Radiosensitizing and Synergistic Effects on Tumor Cells

Radiotherapy is one of the major therapeutic strategies for cancer treatment. In the past decade, there has been growing interest in using high Z (atomic number) elements (materials) as radiosensitizers. New strategies in nanomedicine could help to improve cancer diagnosis and therapy at cellular and molecular levels. Metal-based nanoparticles usually exhibit chemical inertness in cellular and subcellular systems and may play a role in radiosensitization and synergistic cell-killing effects for radiation therapy. This review summarizes the efficacy of metal-based NanoEnhancers against cancers in both in vitro and in vivo systems for a range of ionizing radiations including gamma-rays, X-rays, and charged particles. The potential of translating preclinical studies on metal-based nanoparticles-enhanced radiation therapy into clinical practice is also discussed using examples of several metal-based NanoEnhancers (such as CYT-6091, AGuIX, and NBTXR3). Also, a few general examples of theranostic multimetallic nanocomposites are presented, and the related biological mechanisms are discussed.

Albumin-Assisted Synthesis of Ultrasmall FeS2 Nanodots for Imaging-Guided Photothermal Enhanced Photodynamic Therapy

Current mainstream cancer treatment methods have their limitations. New approaches are thus desired to assist our battle against cancer. Herein, multifunctional ultrasmall FeS₂ nanodots with the size of 7 nm are synthesized by biomineralization and used for imaging-guided combined tumor therapy. Bovine serum albumin (BSA), which acts as the reaction template to induce the mineralization of FeS₂ nanomaterials under alkaline conditions, could also be used as a drug delivery system for coupling photosensitive molecule such as Chlorin e6 (Ce6). Taking advantage of the near-infrared (NIR) absorbance and the high r₂ relaxivity of the synthesized ultrasmall FeS₂ nanodots, as well as the Ce6 fluorescence, in vivo trimodal imaging of optical/magnetic resonance/photoacoustics was carried out, showing efficient tumor accumulation of FeS₂@BSA-Ce6 after intravenous injection. In vitro and in vivo photothermal and photodynamic therapy were then conducted for synergistic tumor therapy and did not cause any apparent toxicity to the treated animals. Our work thus provides a new kind of ultrasmall FeS₂ multifunctional nanodot modified by albumin via a simple method, promising for combination phototherapy as well as cancer theranostics.

A smart copper-phthalocyanine framework nanoparticle for enhancing photodynamic therapy in hypoxic conditions by weakening cells through ATP depletion

Hypoxic tumor treatment by synergistic of photodynamic therapy and ATP deprivation.

Manganese Dioxide Coated WS2 @Fe3 O4 /sSiO2 Nanocomposites for pH-Responsive MR Imaging and Oxygen-Elevated Synergetic Therapy

Recently, the development of multifunctional theranostic nanoplatforms to realize tumor-specific imaging and enhanced cancer therapy via responding or modulating the tumor microenvironment (TME) has attracted tremendous interests in the field of nanomedicine. Herein, tungsten disulfide (WS₂ ) nanoflakes with their surface adsorbed with iron oxide nanoparticles (IONPs) via self-assembly are coated with silica and then subsequently with manganese dioxide (MnO₂ ), on to which polyethylene glycol (PEG) is attached. The obtained WS₂ -IO/S@MO-PEG appears to be highly sensitive to pH, enabling tumor pH-responsive magnetic resonance imaging with IONPs as the pH-inert T2 contrast probe and MnO₂ as the pH-sensitive T1 contrast probe. Meanwhile, synergistic combination tumor therapy is realized with such WS₂ -IO/S@MO-PEG, by utilizing the strong near-infrared light and X-ray absorbance of WS₂ for photothermal therapy (PTT) and enhanced cancer radiotherapy (RT), respectively, as well as the ability of MnO₂ to decompose tumor endogenous H₂ O₂ and relieve tumor hypoxia to further overcome hypoxia-associated radiotherapy resistance. The combination of PTT and RT with WS₂ -IO/S@MO-PEG results in a remarkable synergistic effect to destruct tumors. This work highlights the promise of developing multifunction nanocomposites for TME-specific imaging and TME modulation, aiming at precision cancer synergistic treatment.

Sequential delivery of bismuth nanoparticles and doxorubicin by injectable macroporous hydrogels for combined anticancer kilovoltage X-ray radio- and chemo-therapy

Sequential delivery systems are required to maximize synergistic anticancer therapeutic effects in combined X-ray radio- and chemo-therapy.

Octopod PtCu Nanoframe for Dual-Modal Imaging-Guided Synergistic Photothermal Radiotherapy

Heavy atom nanoparticles have high X-ray absorption capacity and near infrared (NIR) photothermal conversion efficiency, which could be used as radio-sensitizers. We hypothesized that concave PtCu octopod nanoframes (OPCNs) would be an efficient nanoplatform for synergistic radio-photothermal tumor ablation.

Methods: In this study, we newly exploited a folic acid-receptor (FR) mediated photothermal radiotherapy nanoagent base on OPCNs. OPCNs were synthesized with a hydrothermal method and then modified with polyethylene glycol (PEG) and folic acid (FA). A series of physical and chemical characterizations, cytotoxicity, targeting potential, endocytosis mechanism, biodistribution, systematic toxicological evaluation, pharmacokinetics, applications of OPCNs-PEG-FA for in vitro and in vivo infrared thermal imaging (ITI)/photoacoustic imaging (PAI) dual-modal imaging and synergistic photothermal radiotherapy against tumor were carried out.

Results: The OPCNs-PEG-FA demonstrated good biocompatibility, strong NIR absorption and X-ray radio-sensitization, which enabling it to track and visualize tumor in vivo via ITI/PAI dual-modal imaging. Moreover, the as-synthesized OPCNs-PEG-FA exhibited remarkable photothermal therapy (PTT) and radiotherapy (RT) synergistic tumor inhibition when treated with NIR laser and X-ray.

Conclusion: A novel multifunctional theranostic nanoplatform based on OPCNs was designed and developed for dual-modal image-guided synergistic tumor photothermal radiotherapy.

Nanoparticle-triggered in situ catalytic chemical reactions for tumour-specific therapy

This tutorial review highlights the progress and future development of nanoparticle-triggered in situ catalytic chemical reactions for tumour-specific therapy.

Cancer Radiosensitizers

Radiotherapy (RT) is a mainstay treatment for many types of cancer, although it is still a large challenge to enhance radiation damage to tumor tissue and reduce side effects to healthy tissue. Radiosensitizers are promising agents that enhance injury to tumor tissue by accelerating DNA damage and producing free radicals. Several strategies have been exploited to develop highly effective and low-toxicity radiosensitizers. In this review, we highlight recent progress on radiosensitizers, including small molecules, macromolecules, and nanomaterials. First, small molecules are reviewed based on free radicals, pseudosubstrates, and other mechanisms. Second, nanomaterials, such as nanometallic materials, especially gold-based materials that have flexible surface engineering and favorable kinetic properties, have emerged as promising radiosensitizers. Finally, emerging macromolecules have shown significant advantages in RT because these molecules can be combined with biological therapy as well as drug delivery. Further research on the mechanisms of radioresistance and multidisciplinary approaches will accelerate the development of radiosensitizers.

Engineering of inorganic nanoparticles as magnetic resonance imaging contrast agents

Magnetic resonance imaging (MRI) is a highly valuable non-invasive imaging tool owing to its exquisite soft tissue contrast, high spatial resolution, lack of ionizing radiation, and wide clinical applicability. Contrast agents (CAs) can be used to further enhance the sensitivity of MRI to obtain information-rich images. Recently, extensive research efforts have been focused on the design and synthesis of high-performance inorganic nanoparticle-based CAs to improve the quality and specificity of MRI. Herein, the basic rules, including the choice of metal ions, effect of electron motion on water relaxation, and involved mechanisms, of CAs for MRI have been elucidated in detail. In particular, various design principles, including size control, surface modification (e.g. organic ligand, silica shell, and inorganic nanolayers), and shape regulation, to impact relaxation of water molecules have been discussed in detail. Comprehensive understanding of how these factors work can guide the engineering of future inorganic nanoparticles with high relaxivity. Finally, we have summarized the currently available strategies and their mechanism for obtaining high-performance CAs and discussed the challenges and future developments of nanoparticulate CAs for clinical translation in MRI.

Au@Pt nanoparticles as catalase mimics to attenuate tumor hypoxia and enhance immune cell-mediated cytotoxicity

Hypoxic tumor microenvironment (TME) is closely linked to tumor progression, heterogeneity and immune suppression. Therefore, the development of effective methods to overcome hypoxia and substantially enhance the immunotherapy efficacy remains a desirable goal. Herein, we engineered a biocompatible Au core/Pt shell nanoparticles (Au@Pt NPs) to reoxygenate the TME by reacting with endogenous H₂O₂. Treatment with Au@Pt NPs appeared to improve oxygen in intracellular environments and decrease hypoxia-inducible factor-1α expression. Furthermore, the integration of high catalytic efficiency of Au@Pt NPs with cytokine-induced killer (CIK) cell immunotherapy, could lead to significantly improve the effect of CIK cell-mediated cytotoxicity. These results suggest great potential of Au@Pt NPs for regulation of the hypoxic TME and enhance immune cell mediated anti-tumor immunity.

Cisplatin-conjugated gold nanoparticles as a theranostic agent for head and neck cancer

BACKGROUND

The purpose of this study was to develop a nanoplatform, which simultaneously acts as radiosensitizer, drug carrier, and tumor imaging agent for head and neck cancer.

METHODS

We synthesized 20 nm gold nanoparticles, coated with glucose and cisplatin (CG-GNPs). Their penetration into tumor cells and their cellular toxicity were evaluated in vitro. In vivo experiments were conducted to evaluate their impact on tumor growth and their imaging capabilities.

RESULTS

The CG-GNPs showed efficient penetration into tumor cells and similar cellular toxicity as cisplatin alone. Combined with radiation, CG-GNPs led to greater tumor reduction than that of radiation alone and radiation with free cisplatin. The CG-GNPs also demonstrated efficient tumor imaging capabilities.

CONCLUSION

Our CG-GNPs have a great potential to increase antitumor effect, overcome resistance to chemotherapeutics and radiation, and allow imaging-guided therapy.

Synthesis of BSA-Coated BiOI@Bi2 S3 Semiconductor Heterojunction Nanoparticles and Their Applications for Radio/Photodynamic/Photothermal Synergistic Therapy of Tumor

Developing an effective theranostic nanoplatform remains a great challenge for cancer diagnosis and treatment. Here, BiOI@Bi₂ S₃ @BSA (bovine serum albumin) semiconductor heterojunction nanoparticles (SHNPs) for triple-combination radio/photodynamic/photothermal cancer therapy and multimodal computed tomography/photoacoustic (CT/PA) bioimaging are reported. On the one hand, SHNPs possess strong X-ray attenuation capability since they contain high-Z elements, and thus they are anticipated to be a very competent candidate as radio-sensitizing materials for radiotherapy enhancement. On the other hand, as a semiconductor, the as-prepared SHNPs offer an extra approach for reactive oxygen species generation based on electron-hole pair under the irradiation of X-ray through the photodynamic therapy process. This X-ray excited photodynamic therapy obviously has better penetration depth in bio-tissue. What's more, the SHNPs also possess well photothermal conversion efficiency for photothermal therapy, because Bi₂ S₃ is a thin band semiconductor with strong near-infrared absorption that can cause local overheat. In vivo tumor ablation studies show that synergistic radio/photodynamic/photothermal therapy achieves more significant therapeutic effect than any single treatment. In addition, with the strong X-ray attenuation and high near-infrared absorption, the as-obtained SHNPs can also be applied as a multimodal contrast agent in CT/PA imaging.

Tantalum Sulfide Nanosheets as a Theranostic Nanoplatform for Computed Tomography Imaging-Guided Combinatorial Chemo-Photothermal Therapy

Near-infrared (NIR)-absorbing metal-based nanomaterials have shown tremendous potential for cancer therapy, given their facile and controllable synthesis, efficient photothermal conversion, capability of spatiotemporal-controlled drug delivery, and intrinsic imaging function. Tantalum (Ta) is among the most biocompatible metals and arouses negligible adverse biological responses in either oxidized or reduced forms, and thus Ta-derived nanomaterials represent promising candidates for biomedical applications. However, Ta-based nanomaterials by themselves have not been explored for NIR-mediated photothermal ablation therapy. In this work, we report an innovative Ta-based multifunctional nanoplatform composed of biocompatible tantalum sulfide (TaS2) nanosheets (NSs) for simultaneous NIR hyperthermia, drug delivery, and computed tomography (CT) imaging. The TaS2 NSs exhibit multiple unique features including (i) efficient NIR light-to-heat conversion with a high photothermal conversion efficiency of 39%. (ii) high drug loading (177% by weight), (iii) controlled drug release triggered by NIR light and moderate acidic pH, (iv) high tumor accumulation via heat-enhanced tumor vascular permeability, (v) complete tumor ablation and negligible side effects, and (vi) comparable CT imaging contrast efficiency to the widely clinically used agent iobitridol. We expect that this multifunctional NS platform can serve as a promising candidate for imaging-guided cancer therapy and selection of cancer patients with high tumor accumulation.

X-Ray responsive nanoparticles with triggered release of nitrite, a precursor of reactive nitrogen species, for enhanced cancer radiosensitization

Remotely and locally triggered release of therapeutic species by X-ray irradiation is highly desired to enhance the efficacy of radiotherapy. However, the development of such X-ray responsive nanosystems remains a challenge, especially in response to high energy clinically relevant X-ray radiation. Herein, we report novel nitroimidazole ligated gold nanoparticles (AuNPs) that synergistically function to release nitrite, an important precursor for nitric oxide and reactive nitrogen species that sensitize cancer cells, upon radiation with clinically used 6 MeV X-rays, while no release was detected without radiation. These functional AuNPs were prepared with surface-grafted nitroimidazole as the nitrite-releasing agent, cell-penetrating peptide (CPP) to induce nucleus localization, and poly(ethylene glycol) for water solubility. In vitro radiotherapy using such nanoparticles showed enhanced sensitivity of hypoxic cancer cells to X-ray radiation, presumably due to the generation of both reactive oxygen and nitrogen species. The dose modifying factor (DMF) was found to be 0.71 for the dual-functionalized nanoparticle, which indicates that significant lower X-ray doses are required to achieve the same therapeutic effects. Thus, X-ray triggered nitrite release from gold-nitroimidazole nanosystems offers a novel strategy to sensitize cancer cells for improved radiotherapy.

Endogenous Catalytic Generation of O2 Bubbles for In Situ Ultrasound-Guided High Intensity Focused Ultrasound Ablation

High intensity focused ultrasound (HIFU) surgery generally suffers from poor precision and low efficiency in clinical application, especially for cancer therapy. Herein, a multiscale hybrid catalytic nanoreactor (catalase@MONs, abbreviated as C@M) has been developed as a tumor-sensitive contrast and synergistic agent (C&SA) for ultrasound-guided HIFU cancer surgery, by integrating dendritic-structured mesoporous organosilica nanoparticles (MONs) and catalase immobilized in the large open pore channels of MONs. Such a hybrid nanoreactor exhibited sensitive catalytic activity toward H₂O₂, facilitating the continuous O₂ gas generation in a relatively mild manner even if incubated with 10 μM H₂O₂, which finally led to enhanced ablation in the tissue-mimicking PAA gel model after HIFU exposure mainly resulting from intensified cavitation effect. The C@M nanoparticles could be accumulated within the H₂O₂-enriched tumor region through enhanced permeability and retention effect, enabling durable contrast enhancement of ultrasound imaging, and highly efficient tumor ablation under relatively low power of HIFU exposure in vivo. Very different from the traditional perfluorocarbon-based C&SA, such an on-demand catalytic nanoreactor could realize the accurate positioning of tumor without HIFU prestimulation and efficient HIFU ablation with a much safer power output, which is highly desired in clinical HIFU application.

Enhanced Radiotherapy using Bismuth Sulfide Nanoagents Combined with Photo-thermal Treatment

Nanotechniques that can improve the effectiveness of radiotherapy (RT) by integrating it with multimodal imaging are highly desirable. Results In this study, we fabricated Bi2S3 nanorods that have attractive features such as their ability to function as contrast agents for X-ray computed tomography (CT) and photoacoustic (PA) imaging as well as good biocompatibility. Both in vitro and in vivo studies confirmed that the Bi2S3 nanoagents could potentiate the lethal effects of radiation via amplifying the local radiation dose and enhancing the anti-tumor efficacy of RT by augmenting the photo-thermal effect. Furthermore, the nanoagent-mediated hyperthermia could effectively increase the oxygen concentration in hypoxic regions thereby inhibiting the expression of hypoxia-inducible factor (HIF-1α). This, in turn, interfered with DNA repair via decreasing the expression of DNA repair-related proteins to overcome radio-resistance. Also, RT combined with nanoagent-mediated hyperthermia could substantially suppress tumor metastasis via down-regulating angiogenic factors. Conclusion In summary, we constructed a single-component powerful nanoagent for CT/PA imaging-guided tumor radiotherapy and, most importantly, explored the potential mechanisms of nanoagent-mediated photo-thermal treatment for enhancing the efficacy of RT in a synergistic manner.

Enzymes as key features in therapeutic cell mimicry

Cell mimicry is a nature inspired concept that aims to substitute for missing or lost (sub)cellular function. This review focuses on the latest advancements in the use of enzymes in cell mimicry for encapsulated catalysis and artificial motility in synthetic bottom-up assemblies with emphasis on the biological response in cell culture or more rarely in animal models. Entities across the length scale from nano-sized enzyme mimics, sub-micron sized artificial organelles and self-propelled particles (swimmers) to micron-sized artificial cells are discussed. Although the field remains in its infancy, the primary aim of this review is to illustrate the advent of nature-mimicking artificial molecules and assemblies on their way to become a complementary alternative to their role models for diverse biomedical purposes.

Erythrocyte-Membrane-Enveloped Perfluorocarbon as Nanoscale Artificial Red Blood Cells to Relieve Tumor Hypoxia and Enhance Cancer Radiotherapy

Hypoxia, a common feature within many types of solid tumors, is known to be closely associated with limited efficacy for cancer therapies, including radiotherapy (RT) in which oxygen is essential to promote radiation-induced cell damage. Here, an artificial nanoscale red-blood-cell system is designed by encapsulating perfluorocarbon (PFC), a commonly used artificial blood substitute, within biocompatible poly(d,l-lactide-co-glycolide) (PLGA), obtaining PFC@PLGA nanoparticles, which are further coated with a red-blood-cell membrane (RBCM). The developed PFC@PLGA-RBCM nanoparticles with the PFC core show rather efficient loading of oxygen, as well as greatly prolonged blood circulation time owing to the coating of RBCM. With significantly improved extravascular diffusion within the tumor mass, owing to their much smaller nanoscale sizes compared to native RBCs with micrometer sizes, PFC@PLGA-RBCM nanoparticles are able to effectively deliver oxygen into tumors after intravenous injection, leading to greatly relieved tumor hypoxia and thus remarkably enhanced treatment efficacy during RT. This work thus presents a unique type of nanoscale RBC mimic for efficient oxygen delivery into solid tumors, favorable for cancer treatment by RT, and potentially other types of therapy as well.

Tumor-selective catalytic nanomedicine by nanocatalyst delivery

Tumor cells metabolize in distinct pathways compared with most normal tissue cells. The resulting tumor microenvironment would provide characteristic physiochemical conditions for selective tumor modalities. Here we introduce a concept of sequential catalytic nanomedicine for efficient tumor therapy by designing and delivering biocompatible nanocatalysts into tumor sites. Natural glucose oxidase (GOD, enzyme catalyst) and ultrasmall Fe₃O₄ nanoparticles (inorganic nanozyme, Fenton reaction catalyst) have been integrated into the large pore-sized and biodegradable dendritic silica nanoparticles to fabricate the sequential nanocatalyst. GOD in sequential nanocatalyst could effectively deplete glucose in tumor cells, and meanwhile produce a considerable amount of H₂O₂ for subsequent Fenton-like reaction catalyzed by Fe₃O₄ nanoparticles in response to mild acidic tumor microenvironment. Highly toxic hydroxyl radicals are generated through these sequential catalytic reactions to trigger the apoptosis and death of tumor cells. The current work manifests a proof of concept of catalytic nanomedicine by approaching selectivity and efficiency concurrently for tumor therapeutics.The specific metabolism of cancer cells may allow for selective tumor therapeutics. Here, the authors show that a suitable combination of an enzyme and iron nanoparticles loaded on dendritic silica induces apoptosis of cancer cells in response to the glucose-reliant and mild acidic microenvironment.

Emerging Nanotechnology and Advanced Materials for Cancer Radiation Therapy

Radiation therapy (RT) including external beam radiotherapy (EBRT) and internal radioisotope therapy (RIT) has been widely used for clinical cancer treatment. However, owing to the low radiation absorption of tumors, high doses of ionizing radiations are often needed during RT, leading to severe damages to normal tissues adjacent to tumors. Meanwhile, the RT efficacies are limited by different mechanisms, among which the tumor hypoxia-associated radiation resistance is a well-known one, as there exists hypoxia inside most solid tumors while oxygen is essential to enhance radiation-induced DNA damages. With the development in nanotechnology, there have been great interests in using nanomedicine strategies to enhance radiation responses of tumors. Nanomaterials containing high-Z elements to absorb radiation rays (e.g. X-ray) can act as radio-sensitizers to deposit radiation energy within tumors and promote treatment efficacy. Nanoscale carriers are able to deliver therapeutic radioisotopes into tumors for internal RIT, or chemotherapeutic drugs for synergistically combined chemo-radiotherapy. As uncovered in recent studies, the tumor microenvironment could be modulated by various nanomedicine approaches to overcome hypoxia-associated radiation resistance. Herein, the authors will summarize the applications of nanomedicine for RT cancer treatment, and pay particular attention to the latest development of 'advanced materials' for enhanced cancer RT.

Quantitatively Intrinsic Biomimetic Catalytic Activity of Nanocerias as Radical Scavengers and Their Ability against H2O2 and Doxorubicin-Induced Oxidative Stress

Artificial enzymes as radical scavengers show great potentials in treatments of various diseases induced by oxidative stress. Herein, the quantitative analysis indicates that the intrinsic activity of nanocerias for the degradation of radicals is determined by the concentration of surface defects as well as their morphological features. The surface Ce³⁺ fraction of the CeO₂ nanozymes with a similar morphology can be used as a descriptor to index their catalytic activity as radical scavengers. Defect-abundant porous nanorods of ceria (PN-CeO₂) with a large surface area (141 m²/g) and high surface Ce³⁺ fraction (32.8%) deliver an excellent catalytic capability for the degradation of radicals, which is 15.5 times higher than that of Trolox. Results indicate that PN-CeO₂ not only provides more surface catalytic centers but also supplies the active site with higher activity. Oxidative stress induced by doxorubicin (Dox), an essential medicine for a wide range of tumors, was used as the model system to evaluate the radical degradation ability of PN-CeO₂. Both in vitro cellar (H9c2 cells) and in vivo animal models revealed that PN-CeO₂ did not affect the cell and rat growth and was able to alleviate the Dox-induced oxidative stress. Results suggest that the artificial PN-CeO₂ nanozymes have potentials to function as an adjuvant medicine during tumor chemotherapy.

One-Pot Synthesis of Multiple Protein-Encapsulated DNA Flowers and Their Application in Intracellular Protein Delivery

Inspired by biological systems, many biomimetic methods suggest fabrication of functional materials with unique physicochemical properties. Such methods frequently generate organic-inorganic composites that feature highly ordered hierarchical structures with intriguing properties, distinct from their individual components. A striking example is that of DNA-inorganic hybrid micro/nanostructures, fabricated by the rolling circle technique. Here, a novel concept for the encapsulation of bioactive proteins in DNA flowers (DNF) while maintaining the activity of protein payloads is reported. A wide range of proteins, including enzymes, can be simultaneously associated with the growing DNA strands and Mg2 PPi crystals during the rolling circle process, ultimately leading to the direct immobilization of proteins into DNF. The unique porous structure of this construct, along with the abundance of Mg ions and DNA molecules present, provides many interaction sites for proteins, enabling high loading efficiency and enhanced stability. Further, as a proof of concept, it is demonstrated that the DNF can deliver payloads of cytotoxic protein (i.e., RNase A) to the cells without a loss in its biological function and structural integrity, resulting in highly increased cell death compared to the free protein.

Harnessing the Power of Nanotechnology for Enhanced Radiation Therapy

Radiotherapy has emerged as one of the first lines of treatment in oncology. The past few decades have seen dramatic changes in the delivery of radiation therapy, with dose fractionation and treatment planning being the major focuses of research. Although effective, such empirical approaches are hardly optimal, and instances of patient mortality and tumor relapse are not rare. In this Perspective, we review the emerging technologies for optimization of radiosensitization, hypoxia modulation, and combinatorial therapeutic regimes for improved treatment outcomes in preclinical tumor models, with a focus on nanotechnology-mediated approaches. Such an approach is expected to open more productive avenues in the advancement of radiation therapy compared to simply modulating the radiation dose delivered to the tumor.

Design of TPGS-functionalized Cu3BiS3 nanocrystals with strong absorption in the second near-infrared window for radiation therapy enhancement

Integrating radiation therapy with high-depth photothermal therapy in the second near-infrared (NIR) window is highly required for efficient treatment of deep-seated tumor cells. Here, we constructed a multifunctional nano-theranostic with bimetallic chalcogenide nanocrystals (NCs) functionalized with amphiphilic d-α-tocopherol polyethylene glycol 1000 succinate (TPGS-Cu₃BiS₃). Benefiting from the strong absorbance of both X-ray and NIR light in the second NIR window, TPGS-Cu₃BiS₃ CNs can not only deposit more radiation dose to trigger enhanced radiation damage in vivo, but also conduct photo-induced hyperthermia for thermal ablation in the second NIR window and effective improvement of tumor oxygenation to overcome the hypoxia-associated radio-resistance of tumors. Moreover, copper ions on the surface of TPGS-Cu₃BiS₃ NCs are capable of catalyzing the Fenton-like and Haber-Weiss reactions to produce highly reactive hydroxyl radicals, leading to the increase in the level of oxygen radicals and further enhance cancer cell destruction. Apart from their therapeutic application, by means of X-ray computer tomography imaging as well as multispectral optoacoustic tomography imaging, TPGS-Cu₃BiS₃ NCs also have the potential as a nano-theranostic to offer remarkable therapeutic outcome for deep-seated tumor cells in imaging-guided synergistically enhanced radiation therapy.

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.

Designing Core-Shell Gold and Selenium Nanocomposites for Cancer Radiochemotherapy

Radiotherapy is an important regime for treating malignant tumors. There is interest in the development of radiosensitizers to increase the local treatment efficacy under a relatively low and safe radiation dose. In this study, we designed Au@Se-R/A nanocomposites (Au@Se-R/A NCs) as nano-radiosensitizer to realize synergistic radiochemotherapy based on the radiotherapy sensitization property of Au nanorods (NRs) and antitumor activity of Se NPs. In vitro studies show that the combined treatment of A375 melanoma cells in culture with NCs and X-ray induces cell apoptosis through alteration in expression of p53 and DNA-damaging genes and triggers intracellular ROS overproduction, leading to greatly enhanced anticancer efficacy. Further studies using clinically used radiotherapy equipment demonstrate that the combined treatment of NCs and X-ray significantly inhibits the tumor growth in vivo and shows negligible acute toxicity to the major organs. Taken together, this study provides a strategy for clinical translation application of nanomedicne in cancer radiochemotherapy.

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.

A Hybrid Nanomaterial for the Controlled Generation of Free Radicals and Oxidative Destruction of Hypoxic Cancer Cells

Anticancer modalities based on oxygen free radicals, including photodynamic therapy and radiotherapy, have emerged as promising treatments in the clinic. However, the hypoxic environment in tumor tissue prevents the formation of oxygen free radicals. Here we introduce a novel strategy that employs oxygen-independent free radicals generated from a polymerization initiator for eradicating cancer cells. The initiator is mixed with a phase-change material and loaded into the cavities of gold nanocages. Upon irradiation by a near-infrared laser, the phase-change material is melted due to the photothermal effect of gold nanocages, leading to the release and decomposition of the loaded initiator to generate free radicals. The free radicals produced in this way are highly effective in inducing apoptosis in hypoxic cancer cells.

Ultrasmall Semimetal Nanoparticles of Bismuth for Dual-Modal Computed Tomography/Photoacoustic Imaging and Synergistic Thermoradiotherapy

Multifunctional nanomaterials with integrated diagnostic and therapeutic functions, combination therapy to enhance treatment efficacy, as well as low toxicity have drawn tremendous attentions. Herein, we report a multifunctional theranostic agent based on peptide (LyP-1)-labeled ultrasmall semimetal nanoparticles of bismuth (Bi-LyP-1 NPs). Ultrasmall Bi NPs (3.6 nm) were facilely synthesized using oleylamine as the reducing agent and exhibited a higher tumor accumulation after being conjugated with the tumor-homing peptide LyP-1. The abilities to absorb both ionizing radiation and the second near-infrared (NIR-II) window laser radiation ensured that Bi-LyP-1 NPs are capable of dual-modal computed tomography/photoacoustic imaging and efficient synergistic NIR-II photothermal/radiotherapy of tumors. Moreover, Bi-LyP-1 NPs could be rapidly cleared from mice through both renal and fecal clearance and almost completely cleared after 30 days. Such multifunctional nanoparticles as efficient cancer theranostic agents, coupled with fast clearance and low toxicity, shed light on the future use of semimetal nanoparticles for biomedicine.

Mitochondrion-Anchoring Photosensitizer with Aggregation-Induced Emission Characteristics Synergistically Boosts the Radiosensitivity of Cancer Cells to Ionizing Radiation

The first mitochondrion-anchoring photosensitizer that specifically generates singlet oxygen (¹ O₂ ) in mitochondria under white light irradiation that can serve as a highly effective radiosensitizer is reported here, significantly sensitizing cancer cells to ionizing radiation. An aggregation-induced emission luminogen (AIEgen), namely DPA-SCP, is rationally designed with α-cyanostilbene as a simple building block to reveal AIE, diphenylamino (DPA) group as a strong electron donating group to benefit red emission and efficient light-controlled ¹ O₂ generation, as well as a pyridinium salt as the targeting moiety to ensure specific mitochondrial localization. The AIE signature endows DPA-SCP with the capacity to visualize mitochondria in a fluorescence turn-on mode. It is found that under optimized experimental condition, DPA-SCP with white light does not lead to apoptosis/death of cancer cells, whereas provides an elevated ¹ O₂ environment in the mitochondria. More importantly, increasing intracellular level of ¹ O₂ originated from mitochondria is demonstrated to be a generic method to enhance the radiosensitivity of cancer cells with a supra-additive synergistic effect of "0 + 1 > 1." Noteworthy is that "DPA-SCP + white light" achieves a high SER10 value of 1.62, which is much larger than that of the most popularly used radiosensitizers, gold nanoparticles (1.19), and paclitaxel (1.32).

Drug-Loaded Mesoporous Tantalum Oxide Nanoparticles for Enhanced Synergetic Chemoradiotherapy with Reduced Systemic Toxicity

Combining chemotherapy and radiotherapy (chemoradiotherapy) has been widely applied in many clinical practices, showing promises in enhancing therapeutic outcomes. Nontoxic nanocarriers that not only are able to deliver chemotherapeutics into tumors, but could also act as radiosensitizers to enhance radiotherapy would thus be of great interest in the development of chemoradiotherapies. To achieve this aim, herein mesoporous tantalum oxide (mTa₂ O₅ ) nanoparticles with polyethylene glycol (PEG) modification are fabricated. Those mTa₂ O₅ -PEG nanoparticles could serve as a drug delivery vehicle to allow efficient loading of chemotherapeutics such as doxorubicin (DOX), whose release appears to be pH responsive. Meanwhile, owing to the interaction of Ta with X-ray, mTa₂ O₅ -PEG nanoparticles could offer an intrinsic radiosensitization effect to increase X-ray-induced DNA damages during radiotherapy. As a result, DOX-loaded mTa₂ O₅ -PEG (mTa₂ O₅ -PEG/DOX) nanoparticles can offer a strong synergistic therapeutic effect during the combined chemoradiotherapy. Furthermore, in chemoradiotherapy, such mTa₂ O₅ -PEG/DOX shows remarkably reduced side effects compared to free DOX, which at the same dose appears to be lethal to animals. This work thus presents a new type of mesoporous nanocarrier particularly useful for the delivery of safe and effective chemoradiotherapy.

Theranostic Liposomes with Hypoxia-Activated Prodrug to Effectively Destruct Hypoxic Tumors Post-Photodynamic Therapy

Photodynamic therapy (PDT), a noninvasive cancer therapeutic method triggered by light, would lead to severe tumor hypoxia after treatment. Utilizing a hypoxia-activated prodrug, AQ4N, which only shows toxicity to cancer cells under hypoxic environment, herein, a multipurpose liposome is prepared by encapsulating hydrophilic AQ4N and hydrophobic hexadecylamine conjugated chlorin e6 (hCe6), a photosensitizer, into its aqueous cavity and hydrophobic bilayer, respectively. After chelating a ⁶⁴Cu isotope with Ce6, the obtained AQ4N-⁶⁴Cu-hCe6-liposome is demonstrated to be an effective imaging probe for in vivo positron emission tomography, which together with in vivo fluorescence and photoacoustic imaging uncovers efficient passive homing of those liposomes after intravenous injection. After being irradiated with the 660 nm light-emitting diode light, the tumor bearing mice with injection of AQ4N-hCe6-liposome show severe tumor hypoxia, which in turn would trigger activation of AQ4N, and finally contributes to remarkably improved cancer treatment outcomes via sequential PDT and hypoxia-activated chemotherapy. This work highlights a liposome-based theranostic nanomedicine that could utilize tumor hypoxia, a side effect of PDT, to trigger chemotherapy, resulting in greatly improved efficacy compared to conventional cancer PDT.

TaOx decorated perfluorocarbon nanodroplets as oxygen reservoirs to overcome tumor hypoxia and enhance cancer radiotherapy

Cancer radiotherapy (RT) is a clinically used tumor treatment strategy applicable for a wide range of solid tumors. However, during RT treatment of tumors, only a small portion of applied ionizing irradiation energy is absorbed by the tumor, in which the largely hypoxic microenvironment also limits the anti-tumor efficacy of RT. In this work, we rationally fabricate polyethylene glycol (PEG) stabilized perfluorocarbon (PFC) nano-droplets decorated with TaOx nanoparticles (TaOx@PFC-PEG) as a multifunctional RT sensitizer. The obtained TaOx@PFC-PEG nanoparticles on one hand can absorb X-ray by TaOx to concentrate radiation energy within tumor cells, on the other hand after saturating PFC with oxygen will act as an oxygen reservoir to gradually release oxygen and improve tumor oxygenation. As the result, remarkably enhanced in vivo RT treatment is achieved with TaOx@PFC-PEG nanoparticles in our mouse tumor model experiments. Our work thus presents a new nanotechnology strategy to enhance RT-induced tumor treatment by simultaneously concentrating radiation energy within tumors and improving tumor oxygenation, using one multifunctional agent.