A Comprehensive Review: Versatile Imaging Probe Based on Chemical Materials for Biomedical Applications

Imaging probe and contrast agents play significant role in combating cancer. Based on special chemical materials, imaging probe can convert cancer symptoms into information-rich images with high sensitivity and signal amplification, accompanying with detection, diagnosis, drug delivery and treatment. In the paper, some inorganic and organic chemical materials as imaging probe, including Ultrasound imaging (US), Optical imaging (OP), Photoacoustic imaging (PA), X-ray Computed Tomography (CT), Magnetic Resonance imaging (MRI), Radionuclide imaging (RNI) probe, as well as multi-modality imaging probe for diagnosis and therapy of tumour were introduced. The sophisticated and comprehensive chemical materials as imaging probe were highlighted in detail. Meanwhile, the advantages and disadvantages of the imaging probe were compared. In order to provide some reference and help researchers for construction imaging probe for tumour diagnosis and treatment, it attempts to exhaustively cover the whole field. Finally, the prospect and challenge for imaging probe were discussed.

Topochemical-like bandgap regulation engineering: A bismuth thiooxide nanocatalyst for breast cancer phototherapy

The physical property tuning of nanomaterials is of great importance in energy, medicine, environment, catalysis, and other fields. Topochemical synthesis of nanomaterials can achieve precise control of material properties. Here, we synthesized a kind of element-doped bismuth-based nanomaterial (BOS) by topochemical-like synthesis and used it for the phototherapy of tumors. In this study, we employed bismuth fluoride nanoflowers as a template and fabricated element-doped bismuth oxide nanoflowers by reduction conditions. The product is consistent with the precursor in crystal structure and nanomorphology, realizing topochemical-like synthesis under mild conditions. BOS can generate reactive oxygen species, consume glutathione, and perform photothermal conversion under 730 nm light irradiation. In vitro and in vivo studies demonstrate that BOS could suppress tumor growth by inducing apoptosis and ferroptosis through phototherapy. Therefore, this study offers a general regulation method for tuning the physical properties of nanomaterials by using a topochemical-like synthesis strategy.

ZnAl2O4:Er3+ Upconversion Nanophosphor for SPECT Imaging and Luminescence Modulation via Defect Engineering

This work reports an "all-in-one" theranostic upconversion luminescence (UCL) system having potential for both diagnostic and therapeutic applications. Despite considerable efforts in designing upconversion nanoparticles (UCNPs) for multimodal imaging and tumor therapy, there are few reports investigating dual modality SPECT/optical imaging for theranostics. Especially, research focusing on in vivo biodistribution studies of intrinsically radiolabeled UCNPs after intravenous injection is of utmost importance for the potential clinical translation of such formulations. Here, we utilized the gamma emission from 169Er and 171Er radionuclides for the demonstration of radiolabeled ZnAl2O4:171/169Er3+ as a potent agent for dual-modality SPECT/optical imaging. No uptake of radio nanoformulation was detected in the skeleton after 4 h of administration, which evidenced the robust integrity of ZnAl2O4:169/171Er3+. Combining the therapeutics using the emission of β- particulates from 169Er and 171Er will be promising for the radio-theranostic application of the synthesized ZnAl2O4:169/171Er3+ nanoformulation. Cell toxicity studies of ZnAl2O4:1%Er3+ nanoparticles were examined by an MTT assay in B16F10 mouse melanoma cell lines, which demonstrated good biocompatibility. In addition, we explored the mechanism of UCL modulation via defect engineering by Bi3+ codoping in the ZnAl2O4:Er3+ upconversion nanophosphor. The UCL color tuning was successfully achieved from the red to the green region as a function of Bi3+ codoping concentrations. Further, we tried to establish a correlation of UCL tuning with the intrinsic oxygen and cation vacancy defects as a function of Bi3+ codoping concentrations with the help of electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) studies. This study contributes to building a bridge between nature of defects and UC luminescence that is crucial for the design of advanced UCNPs for theranostics.

[18F]-Radiolabelled Nanoplatforms: A Critical Review of Their Intrinsic Characteristics, Radiolabelling Methods, and Purification Techniques

A wide range of nano-objects is found in many applications of our everyday life. Recognition of their peculiar properties and ease of functionalization has prompted their engineering into multifunctional platforms that are supposed to afford efficient tools for the development of biomedical applications. However, bridging the gap between bench to bedside cannot be expected without a good knowledge of their behaviour in vivo, which can be obtained through non-invasive imaging techniques, such as positron emission tomography (PET). Their radiolabelling with [18F]-fluorine, a technique already well established and widely used routinely for PET imaging, with [18F]-FDG for example, and in preclinical investigation using [18F]-radiolabelled biological macromolecules, has, therefore, been developed. In this context, this review highlights the various nano-objects studied so far, the reasons behind their radiolabelling, and main in vitro and/or in vivo results obtained thereof. Then, the methods developed to introduce the radioelement are presented. Detailed indications on the chemical steps involved are provided, and the stability of the radiolabelling is discussed. Emphasis is then made on the techniques used to purify and analyse the radiolabelled nano-objects, a point that is rarely discussed despite its technical relevance and importance for accurate imaging. The pros and cons of the different methods developed are finally discussed from which future work can develop.

Recent advances in lanthanide-doped up-conversion probes for theranostics

Up-conversion (or anti-Stokes) luminescence refers to the phenomenon whereby materials emit high energy, short-wavelength light upon excitation at longer wavelengths. Lanthanide-doped up-conversion nanoparticles (Ln-UCNPs) are widely used in biomedicine due to their excellent physical and chemical properties such as high penetration depth, low damage threshold and light conversion ability. Here, the latest developments in the synthesis and application of Ln-UCNPs are reviewed. First, methods used to synthesize Ln-UCNPs are introduced, and four strategies for enhancing up-conversion luminescence are analyzed, followed by an overview of the applications in phototherapy, bioimaging and biosensing. Finally, the challenges and future prospects of Ln-UCNPs are summarized.

How do bismuth-based nanomaterials function as promising theranostic agents for the tumor diagnosis and therapy?

The complexity of tumor microenvironment and the diversity of tumors seriously affect the therapeutic effect, the focus, therefore, has gradually been shifted from monotherapy to combination therapy in clinical research in order to improve the curative effect. The synergistic enhancement interactions among multiple monotherapies majorly contribute to the birth of the multi-mode cooperative therapy, whose effect of the treatment is clearly stronger than that of any single therapy. In addition, the accurate diagnosis of the tumour location is also crucial to the treatment. Bismuth-based nanomaterials (NMs) hold great properties as promising theranostic platforms based on their many unique features that include low toxicity, excellent photothermal conversion efficiency as well as high ability of X-ray computed tomography imaging and photoacoustic imaging. In this review, we will introduce briefly the main features of tumor microenvironment first and its effect on the mechanism of nanomedicine actions and present the recent advances of bismuth-based NMs for diagnosis and photothermal therapy-based combined therapies using bismuth-based NMs are presented, which may provide a new way for overcoming drug resistance and hypoxia. At the end, further challenges and outlooks regarding this promising field are discussed accompanied with some design tips for bismuth-based NMs, hoping to provide researchers some inspirations to design safe and effective nanotherapeutic agents for the clinical treatments of cancers.

Tumor Microenvironment Modulation Platform Based on Composite Biodegradable Bismuth-Manganese Radiosensitizer for Inhibiting Radioresistant Hypoxic Tumors

Solid tumors possess a unique internal environment with high-level thiols (mainly glutathione), over-expressed H₂ O₂ , and low oxygen partial pressure, which severely restrict the radiotherapy (RT) efficacy. To overcome the imperfections of RT alone, there is vital to design a multifunctional radiosensitizer that simultaneously achieves multimodal therapy and tumor microenvironment (TME) regulation. Bismuth (Bi)-based nanospheres are wrapped in the MnO₂ layer to form core-shell-structured radiosensitizer (Bi@Mn) that can effectively load docetaxel (DTX). The solubility of Bi@Mn-DTX is further improved via folic acid-modified amphiphilic polyethylene glycol (PFA). Bi@Mn-DTX-PFA can specifically respond to the TME to realize multimodal therapy. Primarily, the outer MnO₂ layer responds with H₂ O₂ and glutathione to release oxygen and generate •OH, thereby alleviating hypoxia and achieving chemodynamic therapy (CDT). Afterward, the strong coordination between Bi³⁺ and deprotonated thiol groups in glutathione allows the mesoporous Bi-containing core bonding with glutathione to form a water-soluble complex. These actions conduce Bi@Mn-DTX-PFA degradation, further releasing DTX to implement chemotherapy (CHT). In addition, the degradation in vivo and tumor enrichment of Bi@Mn-PFA are explored via T₁ -weighted magnetic resonance and computed tomography imaging. The biodegradable composite Bi@Mn-DTX-PFA can simultaneously modulate the TME and achieve multimodal treatment (RT/CDT/CHT) for hypoxic tumors.

Biodegradable BiOCl platform for oxidative stress injury-enhanced chemodynamic/radiation therapy of hypoxic tumors

Various physiological characteristics of the tumor microenvironment (TME), such as hypoxia, overexpression of glutathione (GSH) and hydrogen peroxide (H₂O₂), and mild acidity, can severely reduce the efficacy of many cancer therapies. Altering the redox balance of the TME and increasing oxidative stress can accordingly enhance the efficacy of tumor therapy. Herein, we developed a bismuth-based Cu²⁺-doped BiOCl nanotherapeutic platform, BCHN, able to self-supply H₂O₂ for TME-regulated chemodynamic therapy (CDT) combined with sensitized radiotherapy (RT). BCHN released H₂O₂ and consumed GSH to degrade the composite in the slightly acidic TME, and generated hydroxyl radicals (•OH) via a Fenton-like reaction catalyzed by copper ions, to achieve oxidative stress-enhanced CDT. The Fenton-like reaction also catalyzed H₂O₂ to produce O₂ to relieve tumor hypoxia, and combined with the X-ray-blocking property of bismuth to realize TME-enhanced radiotherapy. Synergistic CDT/RT has previously been shown to effectively inhibit tumor cell proliferation and achieve effective tumor control. The current results demonstrated a highly efficient multifunctional bio-degradable nanoplatform for oncotherapy. STATEMENT OF SIGNIFICANCE: Tumor microenvironment-modulated synergy of radiotherapy and chemodynamic therapy is conducive to rapid tumor ablation. Based on this principle, we fabricated a biodegradable BiOCl-based nanocomposite, BCHN. By supplying H₂O₂, a Fenton-like reaction generated •OH and O₂ catalyzed by copper ions, and consumed glutathione to biodegrade the composite. Overall, these actions increased tumor oxidative stress and realized the synergistic anti-tumor actions of chemodynamic therapy combined with bismuth-based sensitization radiotherapy. This strategy thus provides a unique approach to oncology therapy.

Hetero-Core-Shell BiNS-Fe@Fe as a Potential Theranostic Nanoplatform for Multimodal Imaging-Guided Simultaneous Photothermal-Photodynamic and Chemodynamic Treatment

Photothermal/photodynamic therapy (PTT/PDT) and synergistic therapeutic strategies are often sought after, owing to their low side effects and minimal invasiveness compared to chemotherapy and surgical treatments. However, in spite of the development of the most PTT/PDT materials with good tumor-inhibitory effect, there are some disadvantages of photosensitizers and photothermal agents, such as low stability and low photonic efficiency, which greatly limit their further application. Therefore, in this study, a novel bismuth-based hetero-core-shell semiconductor nanomaterial BiNS-Fe@Fe with good photonic stability and synergistic theranostic functions was designed. On the one hand, BiNS-Fe@Fe with a high atomic number exhibits good X-ray absorption, enhanced magnetic resonance (MR) T₂-weighted imaging, and strong photoacoustic imaging (PAI) signals. In addition, the hetero-core-shell provides a strong barrier to decline the recombination of electron-hole pairs, inducing the generation of a large amount of reactive oxygen species (ROS) when irradiated with visible-NIR light. Meanwhile, a Fenton reaction can further increase ROS generation in the tumor microenvironment. Furthermore, an outstanding chemodynamic therapeutic potential was determined for this material. In particular, a high photothermal conversion efficiency (η = 37.9%) is of significance and could be achieved by manipulating surface decoration with Fe, which results in tumor ablation. In summary, BiNS-Fe@Fe could achieve remarkable utilization of ROS, high photothermal conversion law, and good chemodynamic activity, which highlight the multimodal theranostic potential strategies of tumors, providing a potential viewpoint for theranostic applications of tumors.

Pnictogen Semimetal (Sb, Bi)-Based Nanomaterials for Cancer Imaging and Therapy: A Materials Perspective

Innovative multifunctional nanomaterials have attracted tremendous interest in current research by facilitating simultaneous cancer imaging and therapy. Among them, antimony (Sb)- and bismuth (Bi)-based nanoparticles are important species with multifunction to boost cancer theranostic efficacy. Despite the rapid development, the extensive previous work treated Sb- and Bi-based nanoparticles as mutually independent species, and therefore a thorough understanding of their relationship in cancer theranostics was lacking. We propose here that the identical chemical nature of Sb and Bi, being semimetals, provides their derived nanoparticles with inherent multifunction for near-infrared laser-driven and/or X-ray-based cancer imaging and therapy as well as some other imparted functions. An overview of recent progress on Sb- and Bi-based nanoparticles for cancer theranostics is provided to highlight the relationship between chemical nature and multifunction. The understanding of Sb- and Bi-based nanoparticles in this way might shed light on the further design of smart multifunctional nanoparticles for cancer theranostics.

A biodegradable bismuth–gadolinium-based nano contrast agent for accurate identification and imaging of renal insufficiency in vivo

A biodegradable gadolinium-doped mesoporous bismuth-based nanomaterial is used to diagnose kidneys with dysfunction accurately via magnetic resonance imaging in vivo.

Recent Advances on Rare Earth Upconversion Nanomaterials for Combined Tumor Near-Infrared Photoimmunotherapy

Cancer has been threatening the safety of human life. In order to treat cancer, many methods have been developed to treat tumor, such as traditional therapies like surgery, chemotherapy, radiotherapy, as well as new strategies like photodynamic therapy, photothermal therapy, sonodynamic therapy, and other emerging therapies. Although there are so many ways to treat tumors, these methods all face the dilemma that they are incapable to cope with metastasis and recurrence of tumors. The emergence of immunotherapy has given the hope to conquer the challenge. Immunotherapy is to use the body's own immune system to stimulate and maintain a systemic immune response to form immunological memory, resist the metastasis and recurrence of tumors. At the same time, immunotherapy can combine with other treatments to exhibit excellent antitumor effects. Upconversion nanoparticles (UCNPs) can convert near-infrared (NIR) light into ultraviolet and visible light, thus have good performance in bioimaging and NIR triggered phototherapy. In this review paper, we summarize the design, fabrication, and application of UCNPs-based NIR photoimmunotherapy for combined cancer treatment, as well as put forward the prospect of future development.

Bismuth-Based Mesoporous Nanoball Carrying Sorafenib for Computed Tomography Imaging and Synergetic Chemoradiotherapy of Hepatocellular Carcinoma

Sorafenib (SOR), a multi-kinase inhibitor for advanced hepatocellular carcinoma (HCC), reveals a limited therapeutic effect due to a lack of selectivity and evident drug resistance. In the present study, bismuth-based mesoporous nanomaterial (NBOF) is loaded with SOR and then coated with polyethylene glycol and folic acid conjugates (P-FA) to form an NBOF@SOR-P-FA nanocarrier system. The system achieves significantly enhanced anti-cancer efficacy by combining chemotherapy with radiotherapy. To evaluate the effect of synergistic treatment, cytotoxicity detection, Live/Dead staining, apoptotic assay, and Western blot analysis are performed. The results suggest that NBOF@SOR-P-FA significantly inhibits HCC cell proliferation and promotes cell apoptosis. Also, the NBOF@SOR-P-FA exhibits excellent biocompatibility by hemolysis and serum biochemical tests and produces a substantially enhanced contrast efficiency as compared to iohexol by computed tomography imaging. More importantly, the profound suppression of tumor growth and potentiation of apoptosis are observed in a mouse subcutaneous tumor model. Collectively, these results indicate that the bismuth-based nanotheranostic platform could enhance the therapeutic effect of sorafenib and serve as an innovative method for HCC treatment.

X-ray and NIR light dual-triggered mesoporous upconversion nanophosphor/Bi heterojunction radiosensitizer for highly efficient tumor ablation

Developing a multi-functional radiosensitizer with high efficiency and low toxicity remains challenging. Herein, we report a mesoporous heterostructure radiosensitizer (UCNP@NBOF-FePc-PFA) containing Lu-based upconversion nanophosphor (UCNP) and Bi-based nanomaterial loaded with iron phthalocyanine for X-ray and NIR light dual-triggered tri-modal tumor therapy. NaLuF₄:Yb,Tm, a Lu-based UCNP, offers radiosensitization and upconversion luminescence for optical bio-imaging. However, Bi has a higher X-ray mass attenuation coefficient than Lu. Thus, after stepwise fabrication, Na_0.2Bi_0.8O_0.35F_1.91:Yb (NBOF) was assembled with the UCNP to form a mesoporous heterostructure composite. This enhanced the radiosensitization effect and drug load to realize multi-modal tumor therapy. After coating it with folate-conjugated amphiphilic PEG (PFA), UCNP@NBOF-FePc-PFA realized tumor photothermal/photodynamic/radio-therapy. The structure of UCNP@NBOF-FePc-PFA was well characterized. Different properties triggered by X-ray and NIR light were evaluated. Finally, a highly efficient tumor ablation effect was demonstrated in vitro and in vivo. Consequently, this kind of nanocomposite provides a unique strategy for designing a theranostic platform for oncotherapy. STATEMENT OF SIGNIFICANCE: The synergy of enhanced radiotherapy and photothermal/photodynamic therapy is found to improve tumor therapeutic efficacy. On that basis, a heterostructure nanohybrid containing Lu-based UCNP and Bi-based mesoporous material is synthesized. The heterostructure nanohybrid can be loaded with FePc and decorated with folate-modified amphiphilic PEG to form a multi-functional theranostic nano-platform. The platform exhibits upconversion luminescence capacity, X-ray attenuation property, photothermal effect, and X-ray and NIR dual-light triggered ROS generation capability. These features can not only enable upconversion luminescence/CT bioimaging of living beings but also be applied to the photothermal/photodynamic/radio- synergistic tumor ablation. To sum up, the nanomaterial offers a novel method for the construction of a new theranostic platform.

Mesoporous Bi-Containing Radiosensitizer Loading with DOX to Repolarize Tumor-Associated Macrophages and Elicit Immunogenic Tumor Cell Death to Inhibit Tumor Progression

Tumor-associated macrophages (TAMs) were a major component of tumor, which comprised up to 50% of tumor mass, and correlated with poor prognosis in more than 80% of cases. TAMs were resistant to radiotherapy and chemotherapy, and radiation could further activate TAMs to promote tumor progression. Herein, we explored a kind of Bi-based mesoporous upconversion nanophosphor (UCNP) loaded with doxorubicin (UCNP-DOX) to elicit immunogenic tumor cell death and repolarize TAMs to an antitumor M1-like type for strengthening the tumor-specific antitumor immune effects of X-ray radiotherapy. The repolarization effect of UCNP-DOX with X-ray was confirmed in THP-1 cell line, in vivo mouse model, and hydrothorax of a non-small-cell lung carcinoma patient. Moreover, the UCNP-DOX and X-ray radiation could elicit immunogenic tumor necrosis, presenting more tumor antigens for tumor-specific immune response. In a cell co-incubation system, activated macrophages could significantly inhibit cancer colony formation, migration, and invasion. After treatment, xenografted tumor in mice was also found to be significantly regressed and presented substantial CD8-positive T cells. This study opens the door to further enhance the abscopal effects and inhibit the metastasis in radiotherapy.

Ultrafast Synthesizing Bismuth Mesoporous Nanolitchi Radiosensitizer Loading High Dose DOX for CT-Guided Enhanced Chemoradiotherapy

Radiotherapy and chemotherapy are both common clinical treatment methods. The combination of the two treatments can decrease tumor recurrence. In this study, bismuth-based mesoporous litchi-shaped Na_0.2Bi_0.8O_0.35F_1.91:20%Yb (NBOF) nanoparticles (NPs) have been reported as a radiosensitizer and as a nanovehicle for loading and slow-releasing doxorubicin (DOX). After assembling with amphiphilic poly(ethylene glycol) (PEG), NBOF-DOX-PEG qualified with excellent aqueous dispersibility and the enhanced tumor radiation and chemo-synergistic therapy characteristics. The formation of NBOF revealed the oxygen element in NBOF came from H₂O and air in the synthesis and post-treatment process, and the size of NBOF could be adjusted by changing the concentration of doped Yb ion. The average size of NBOF was ca. 80 nm. Brunauer-Emmett-Teller results demonstrated the mesoporous structure of NBOF. So DOX could be loaded in NBOF and the optimized loading content was 39%. Then, NBOF-PEG exhibited a strong computed tomography signal whitening ability and enhanced radiotherapy effect. Combined with the chemotherapy ability of DOX, NBOF-DOX-PEG NPs presented remarkable synergistic tumor elimination ability. Meanwhile, NBOF-DOX-PEG NPs qualified for excellent biosafety. Our study not only proved the combined chemo- and radiotherapy for enhancing therapeutic effect but also supplied a functional Bi-based mesoporous nanovehicle for constructing an intelligent theranostic platform.