Activating TiO2 Nanoparticles: Gallium-68 Serves as a High-Yield Photon Emitter for Cerenkov-Induced Photodynamic Therapy

Radionuclide-Activated Luminescence for Cancer Theranostics

Within dielectric media, charged particles emitted from medical radionuclides induce polarization of surrounding molecules, which subsequently generate Cerenkov luminescence (CL) upon returning to their ground state. This CL emission confers clinically approved radiotracers with distinctive potential for applications in phototheranostics. However, the utility of CL in vivo has been severely constrained by its ultraviolet-weighted emission spectrum and extremely low photon flux, particularly in living imaging and triggering photodynamic therapy. Certain optical probes, encompassing fluorescent agents and nanoparticle scintillators, can be activated by radionuclides to generate red-shifted emissions with amplified luminescence intensity compared to CL. This phenomenon, termed radionuclide-activated luminescence (RL), represents a promising strategy for enhancing radionuclide-induced tumor phototheranostic outcomes. This review systematically summarizes the advances in RL technology, highlighting the development of various RL probes and their innovative applications in laser-free optical bioimaging and cancer phototherapy. It further delves into the confronting challenges and prospects of RL technology, aiming to provide a comprehensive overview and practical insights to advance the integration of radiotheranostics and phototheranostics in clinical practice.

Impact of UV-Irradiated Mesoporous Titania Nanoparticles (mTiNPs) on Key Onco- and Tumor Suppressor microRNAs of PC3 Prostate Cancer Cells

BACKGROUND

Mesoporous titanium dioxide nanoparticles (mTiNPs) are known for their chemical stability, non-toxicity, antimicrobial and anticancer effects, as well as for their photocatalytic properties. When this material is subjected to UV radiation, its electronic structure shifts, and during that process, reactive oxygen species are generated, which in turn exert apoptotic events on the cancer cells.

OBJECTIVES

We evaluated the cytotoxic effects of UV-irradiated mTiNPs on prostate cancer (PCa) cell line PC3 with the aim of demonstrating that the interaction between UV-light and mTiNPs positively impacts the nanomaterial's cytotoxic efficiency. Moreover, we assessed the differential expression of key oncomiRs and tumor suppressor (TS) miRNAs, as well as their associated target genes, in cells undergoing this treatment.

METHODS

PBS-suspended mTiNPs exposed to 290 nm UV light were added at different concentrations to PC3 cells. Cell viability was determined after 24 h with a crystal violet assay. Then, the obtained IC50 concentration of UV-nanomaterial was applied to a new PC3 cell culture, and the expression of a set of miRNAs and selected target genes was evaluated via qRT-PCR.

RESULTS

The cells exposed to photo-activated mTiNPs required 4.38 times less concentration of the nanomaterial than the group exposed to non-irradiated mTiNPs to achieve the half-maximal inhibition, demonstrating an improved cytotoxic performance of the UV-irradiated mTiNPs. Moreover, the expression of miR-18a-5p, miR-21-5p, and miR-221-5p was downregulated after the application of UV-mTiNPs, while TS miR-200a-5p and miR-200b-5p displayed an upregulated expression. Among the miRNA target genes, PTEN was found to be upregulated after the treatment, while BCL-2 and TP53 were underexpressed.

CONCLUSIONS

Our cytotoxic outcomes coincided with previous reports performed in other cancer cell lines, strongly suggesting UV-irradiated mTiNPs as a promising nano-therapeutic approach against PCa. On the other hand, to the best of our knowledge, this is the first report exploring the impact of UV-irradiated mTiNPs on key onco- and TS microRNAs in PCa cells.

Radionuclide-labelled nanoparticles for cancer combination therapy: a review

Radionuclide therapy (RT) is widely used to advanced local cancers. However, its therapeutic efficacy is limited to the radiation resistance of cancer cells. Combination therapy aims to circumvent tumor resistance, and the combination of RT with photothermal therapy (PTT), photodynamic therapy (PDT), chemotherapy (CMT), and immunotherapy has shown promising treatment outcomes. Nanotechnology holds promise in advancing combination therapy by integrating multiple therapies on a nanostructure platform. This is due to the increased surface area, passive/active targeting capabilities, high payload capacity, and enriched surface of nanomedicines, offering significant advantages in treatment sensitivity and specificity. In the first part of this review, we categorize radionuclide therapy. The second part summarizes the latest developments in combination therapies, specifically focusing on the integration of RT with PTT, PDT, CMT and immunotherapy. The last part provides an overview of the challenges and potential opportunities related to radionuclide-labelled nanoparticles for cancer combination therapy.

Engineering photodynamics for treatment, priming and imaging

Photodynamic therapy (PDT) is a photochemistry-based treatment approach that relies on the activation of photosensitizers by light to locally generate reactive oxygen species that induce cellular cytotoxicity, in particular for the treatment of tumours. The cytotoxic effects of PDT are depth-limited owing to light penetration limits in tissue. However, photodynamic priming (PDP), which inherently occurs during PDT, can prime the tissue microenvironment to adjuvant therapies beyond the direct PDT ablative zone. In this Review, we discuss the underlying mechanisms of PDT and PDP, and their application to the treatment of cancer, outlining how PDP can permeabilize the tumour vasculature, overcome biological barriers, modulate multidrug resistance, enhance immune responses, increase tumour permeability and enable the photochemical release of drugs. We further examine the molecular engineering of photosensitizers to improve their pharmacodynamic and pharmacokinetic properties, increase their molecular specificity and allow image guidance of PDT, and investigate engineered cellular models for the design and optimization of PDT and PDP. Finally, we discuss alternative activation sources, including ultrasound, X-rays and self-illuminating compounds, and outline key barriers to the clinical translation of PDT and PDP.

Nanoscale Radiotheranostics for Cancer Treatment: From Bench to Bedside

In recent years, the application of radionuclides-containing nanomaterials in cancer treatment has garnered widespread attention. The diversity of nanomaterials allows researchers to selectively combine them with appropriate radionuclides for biomedical purposes, addressing challenges faced by peptides, small molecules, or antibodies used for radionuclide labeling. However, with advantages come challenges, and nanoradionuclides still encounter significant issues during clinical translation. This review summarized the recent progress of nanosized radionuclides for cancer treatment or diagnosis. The discussion began with representative radionuclides and the methods of incorporating them into nanomaterial structures. Subsequently, new combinations of nanomaterials and radionuclides, along with their applications, were introduced to demonstrate their future trends. The benefits of nanoradionuclides included optimized pharmacokinetic properties, enhanced disease-targeting efficacy, and synergistic application with other treatment techniques. Besides, the basic rule of this section was to summarize how these nanoradionuclides can truly impact the diagnosis and therapy of various cancer types. In the last part, the focus was devoted to the nanoradionuclides currently applicable in clinics and how to address the existing issues and problems based on our knowledge.

131I Induced In Vivo Proteolysis by Photoswitchable azoPROTAC Reinforces Internal Radiotherapy

Photopharmacology, incorporating photoswitches such as azobenezes into drugs, is an emerging therapeutic method to realize spatiotemporal control of pharmacological activity by light. However, most photoswitchable molecules are triggered by UV light with limited tissue penetration, which greatly restricts the in vivo application. Here, this study proves that 131I can trigger the trans-cis photoisomerization of a reported azobenezen incorporating PROTACs (azoPROTAC). With the presence of 50 µCi mL-1 131I, the azoPROTAC can effectively down-regulate BRD4 and c-Myc levels in 4T1 cells at a similar level as it does under light irradiation (405 nm, 60 mW cm-2). What's more, the degradation of BRD4 can further benefit the 131I-based radiotherapy. The in vivo experiment proves that intratumoral co-adminstration of 131I (300 µCi) and azoPROTC (25 mg kg-1) via hydrogel not only successfully induce protein degradation in 4T1 tumor bearing-mice but also efficiently inhibit tumor growth with enhanced radiotherapeutic effect and anti-tumor immunological effect. This is the first time that a radioisotope is successfully used as a trigger in photopharmacology in a mouse model. It believes that this study will benefit photopharmacology in deep tissue.

Imaging and Downstaging Bladder Cancer with the 177Lu-Labeled Bioorthogonal Nanoprobe

Efforts on bladder cancer treatment have been shifting from extensive surgery to organ preservation in the past decade. To this end, we herein develop a multifunctional nanoagent for bladder cancer downstaging and bladder-preserving therapy by integrating mucosa penetration, reduced off-target effects, and internal irradiation therapy into a nanodrug. Specifically, an iron oxide nanoparticle was used as a carrier that was coated with hyaluronic acid (HA) for facilitating mucosa penetration. Dibenzocyclooctyne (DBCO) was introduced into the HA coating layer to react through bioorthogonal reaction with azide as an artificial receptor of bladder cancer cells, to improve the cellular internalization of the nanoprobe labeled with 177Lu. Through magnetic resonance imaging, the targeted imaging of both nonmuscle-invasive bladder cancer (NMIBC) and muscle-invasive bladder cancer (MIBC) was realized after intravesical instillation of the multifunctional probe, both NMIBC and MIBC were found downstaged, and the metastasis was inhibited, which demonstrates the potential of the multifunctional nanoprobe for bladder preservation in bladder cancer treatment.

The effect of polymer coating on nanoparticles' interaction with lipid membranes studied by coarse-grained molecular dynamics simulations

Nanoparticles' (NPs) permeation through cell membranes, whether it happens via passive or active transport, is an essential initial step for their cellular internalization. The NPs' surface coating impacts the way they translocate through the lipid bilayer and the spontaneity of the process. Understanding the molecular details of NPs' interaction with cell membranes allows the design of nanosystems with optimal characteristics for crossing the lipid bilayer: computer simulations are a powerful tool for this purpose. In this work, we have performed coarse-grained molecular dynamics simulations and free energy calculations on spherical titanium dioxide NPs conjugated with polymer chains of different chemical compositions. We have demonstrated that the hydrophobic/hydrophilic character of the chains, more than the nature of their terminal group, plays a crucial role in determining the NPs' interaction with the lipid bilayer and the thermodynamic spontaneity of NPs' translocation from water to the membrane. We envision that this computational work will be helpful to the experimental community in terms of the rational design of NPs for efficient cell membrane permeation.

Self-Illuminating In Situ Hydrogel with Immune-Adjuvant Amplify Cerenkov Radiation-Induced Photodynamic Therapy

Cerenkov radiation-induced photodynamic therapy (CR-induced PDT) has shown the potential to overcome the light penetration limitation in conventional PDT. In addition, the tumor-associated antigens (TAAs) produced by PDT can initiate an antitumor immune process but only show a limited immunotherapeutic effect without the use of immunotherapeutic agents. Herein, a CR-induced PDT hydrogel (R837/89Zr-HG-PpIX) has been developed by in situ formation of a hyaluronic acid (HA)-based hydrogel integrated with internal light source 89Zr, photosensitizer protoporphyrin IX (PpIX), and immune adjuvant imiquimod (R837). The obtained R837/89Zr-HG-PpIX hydrogel with long-term tumor retention and low radiation leakage can provide long-lasting photodynamic therapy without phototoxicity in normal tissues. In addition, the loaded R837 improves the immunogenicity of TAAs released after PDT, resulting in considerably enhanced immune responses. At relatively low radioactivity, R837/89Zr-HG-PpIX shows significant inhibition in subcutaneous H22 tumor-bearing BALB/c mice and orthotopic VX2 liver tumor-bearing rabbits. Furthermore, the combination of such a CR-induced PDT hydrogel with anti-PD-L1 exhibits the abscopal effect to inhibit the growth of distant tumors. Therefore, the proposed in situ formed CR-induced PDT hydrogel with long-term photodynamic-immunotherapy provides an effective strategy for deep tumor therapy.

Selective Intracellular Delivery of Antibodies in Cancer Cells with Nanocarriers Sensing Endo/Lysosomal Enzymatic Activity

The differential enzymatic activity in the endo/lysosomes of particular cells could trigger targeted endosomal escape functions, enabling selective intracellular protein delivery. However, this strategy may be jeopardized due to protein degradation during endosomal trafficking. Herein, using custom made fluorescent probes to assess the endosomal activity of cathepsin B (CTSB) and protein degradation, we found that certain cancer cells with hyperacidified endosomes grant a spatiotemporal window where CTSB activity surpass protein digestion. This inspired the engineering of antibody-loaded polymeric nanocarriers having CTSB-activatable endosomal escape ability. The nanocarriers selectively escaped from the endo/lysosomes in the cells with high endosomal CTSB activity and delivered active antibodies to intracellular targets. This study provides a viable strategy for cell-specific protein delivery using stimuli-responsive nanocarriers with controlled endosomal escape.

A comprehensive review on singlet oxygen generation in nanomaterials and conjugated polymers for photodynamic therapy in the treatment of cancer

A key role in lessening humanity's continuous fight against cancer could be played by photodynamic therapy (PDT), a minimally invasive treatment employed in the medical care of a range of benign disorders and malignancies. Cancerous tissue can be effectively removed by using a light source-excited photosensitizer. Singlet oxygen and reactive oxygen species are produced via the photosensitizer as a result of this excitation. In the recent past, researchers have put in tremendous efforts towards developing photosensitizer molecules for photodynamic treatment (PDT) to treat cancer. Conjugated polymers, characterized by their efficient fluorescence, exceptional photostability, and strong light absorption, are currently under scrutiny for their potential applications in cancer detection and treatment through photodynamic and photothermal therapy. Researchers are exploring the versatility of these polymers, utilizing sophisticated chemical synthesis and adaptable polymer structures to create new variants with enhanced capabilities for generating singlet oxygen in photodynamic treatment (PDT). The incorporation of photosensitizers into conjugated polymer nanoparticles has proved to be beneficial, as it improves singlet oxygen formation through effective energy transfer. The evolution of nanotechnology has emerged as an alternative avenue for enhancing the performance of current photosensitizers and overcoming significant challenges in cancer PDT. Various materials, including biocompatible metals, polymers, carbon, silicon, and semiconductor-based nanomaterials, have undergone thorough investigation as potential photosensitizers for cancer PDT. This paper outlines the recent advances in singlet oxygen generation by investigators using an array of materials, including graphene quantum dots (GQDs), gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), titanium dioxide (TiO2), ytterbium (Yb) and thulium (Tm) co-doped upconversion nanoparticle cores (Yb/Tm-co-doped UCNP cores), bismuth oxychloride nanoplates and nanosheets (BiOCl nanoplates and nanosheets), and others. It also stresses the synthesis and application of systems such as amphiphilic block copolymer functionalized with folic acid (FA), polyethylene glycol (PEG), poly(β-benzyl-L-aspartate) (PBLA10) (FA-PEG-PBLA10) functionalized with folic acid, tetra(4-hydroxyphenyl)porphyrin (THPP-(PNIPAM-b-PMAGA)4), pyrazoline-fused axial silicon phthalocyanine (HY-SiPc), phthalocyanines (HY-ZnPcp, HY-ZnPcnp, and HY-SiPc), silver nanoparticles coated with polyaniline (Ag@PANI), doxorubicin (DOX) and infrared (IR)-responsive poly(2-ethyl-2-oxazoline) (PEtOx) (DOX/PEtOx-IR NPs), particularly in NIR imaging-guided photodynamic therapy (fluorescent and photoacoustic). The study puts forward a comprehensive summary and a convincing justification for the usage of the above-mentioned materials in cancer PDT.

Molecularly generated light and its biomedical applications

Molecularly generated light, referred to here as "molecular light", mainly includes bioluminescence, chemiluminescence, and Cerenkov luminescence. Molecular light possesses unique dual features of being both a molecule and a source of light. Its molecular nature enables it to be delivered as molecules to regions deep within the body, overcoming the limitations of natural sunlight and physically generated light sources like lasers and LEDs. Simultaneously, its light properties make it valuable for applications such as imaging, photodynamic therapy, photo-oxidative therapy, and photobiomodulation. In this review article, we provide an updated overview of the diverse applications of molecular light and discuss the strengths and weaknesses of molecular light across various domains. Lastly, we present forward-looking perspectives on the potential of molecular light in the realms of molecular imaging, photobiological mechanisms, therapeutic applications, and photobiomodulation. While some of these perspectives may be considered bold and contentious, our intent is to inspire further innovations in the field of molecular light applications.

Internal Light Sources-Mediated Photodynamic Therapy Nanoplatforms: Hope for the Resolution of the Traditional Penetration Problem

Photodynamic therapy (PDT) is an alternative cancer treatment technique with a noninvasive nature, high selectivity, and minimal adverse effects. The indispensable light source used in PDT is a critical factor in determining the energy conversion of photosensitizers (PSs). Traditional light sources are primarily concentrated in the visible light region, severely limiting their penetration depth and making them prone to scattering and absorption when applied to biological tissues. For that reason, its efficacy in treating deep-seated lesions is often inadequate. Self-exciting PDT, also known as auto-PDT (APDT), is an attractive option for circumventing the limited penetration depth of traditional PDT and has acquired significant attention. APDT employs depth-independent internal light sources to excite PSs through resonance or radiative energy transfer. APDT has considerable potential for treating deep-tissue malignancies. To facilitate many researchers' comprehension of the latest research progress in this field and inspire the emergence of more novel research results. This review introduces internal light generation mechanisms and characteristics and provides an overview of current research progress based on the recently reported APDT nanoplatforms. The current challenges and possible solutions of APDT nanoplatforms are also presented and provide insights for future research in the final section of this article.

Prodrug-based strategy with a two-in-one liposome for Cerenkov-induced photodynamic therapy and chemotherapy

Cerenkov radiation induced photodynamic therapy (CR-PDT) can tackle the tissue penetration limitation of traditional PDT. However, co-delivery of radionuclides and photosensitizer may cause continuous phototoxicity in normal tissues during the circulation. 5-aminolevulinic acid (ALA) which can intracellularly transform into photosensitive protoporphyrin IX (PpIX) is a cancer-selective photosensitizer with negligible side effect. However, the hydrophilic nature of ALA and the further conversion of PpIX to photoinactive Heme severely hinder the therapeutic benefits of ALA-based PDT. Herein, we developed an 89Zr-labeled, pH responsive ALA and artemisinin (ART) co-loaded liposome (89Zr-ALA-Liposome-ART) for highly selective cancer therapy. 89Zr can serve as the internal excitation source to self-activate PpIX for CR-PDT, and the photoinactive Heme can activate the chemotherapeutic effect of ART. The 89Zr-ALA-Liposome-ART exhibited excellent tumor inhibition capability in subcutaneous 4T1-tumor-bearing Balb/c mice via CR-PDT and chemotherapy. Combined with anti-PD-L1, the 89Zr-ALA-Liposome-ART elicited strong antitumor immunity to against tumor recurrence.

Beyond External Light: On-Spot Light Generation or Light Delivery for Highly Penetrated Photodynamic Therapy

External light sources, such as lasers, light emitting diodes (LEDs) and lamps, are widely applied in photodynamic therapy (PDT); however, their use is severely limited by the nature of shallow tissue penetration depth. The recent exploration of light delivery or local generation on tumor sites has attracted much attention, owing to the fact that these systems are significantly endowed with high tissue penetration. In this review, we briefly introduced the principle of "on-spot light generation or delivery systems" in PDT. These systems are divided into different categories: (1) implantable luminescence, (2) mechanoluminescence, (3) electrochemiluminescence, (4) Cerenkov luminescence, (5) chemiluminescence, and (6) bioluminescence. Finally, their applications, advantages, and disadvantages in PDT will be appropriately summarized and further discussed in detail. We believe that this review will provide general guidance for the further design of light generation or delivery systems and clinical studies for PDT-mediated cancer treatments with unparalleled merits.

Theranostics through Utilizing Cherenkov Radiation of Radioisotope Zr-89 with a Nanocomposite Combination of TiO2 and MnO2

Cherenkov radiation (CR) derived from the decay of diagnostic and therapeutic radionuclides is currently being studied by the scientific community to determine if these emissions can be harnessed for cancer detection and therapy. While Cherenkov luminescence imaging (CLI) has been studied in the preclinical and clinical settings, Cherenkov radiation-induced cancer therapy (CRICT) is a relatively new area of research that harnesses the emitted photons to kill cancer cells through free radical generation and DNA damage. Nanoparticles seem well suited for developing a theranostic platform that would allow researchers to visualize therapy delivery and also generate the reactive oxygen species necessary to kill cancer cells. Herein, we report the preparation of an ⁸⁹Zr-TiO₂-MnO₂ nanocomposite that incorporates transferrin onto the nanoparticle surface to enhance cancer cell growth inhibition. The incorporation of the positron emission tomography (PET) radioisotope ⁸⁹Zr (half-life: 3.3 days) allowed for the detection of the nanoparticle using PET and for the creation of Cherenkov emissions that interacted with the nanoparticle surface to generate free radicals for therapy delivery. After preparation, these systems were observed to be stable in various media and provided excellent tumor growth control after being intratumorally injected into mice bearing CT-26 tumors. These results demonstrate that a therapeutically efficient CRICT platform can be generated using commercially available and affordable materials.

Added Value of Scintillating Element in Cerenkov-Induced Photodynamic Therapy

Cerenkov-induced photodynamic therapy (CR-PDT) with the use of Gallium-68 (68Ga) as an unsealed radioactive source has been proposed as an alternative strategy to X-ray-induced photodynamic therapy (X-PDT). This new strategy still aims to produce a photodynamic effect with the use of nanoparticles, namely, AGuIX. Recently, we replaced Gd from the AGuIX@ platform with Terbium (Tb) as a nanoscintillator and added 5-(4-carboxyphenyl succinimide ester)-10,15,20-triphenylporphyrin (P1) as a photosensitizer (referred to as AGuIX@Tb-P1). Although Cerenkov luminescence from 68Ga positrons is involved in nanoscintillator and photosensitizer activation, the cytotoxic effect obtained by PDT remains controversial. Herein, we tested whether free 68Ga could substitute X-rays of X-PDT to obtain a cytotoxic phototherapeutic effect. Results were compared with those obtained with AGuIX@Gd-P1 nanoparticles. We showed, by Monte Carlo simulations, the contribution of Tb scintillation in P1 activation by an energy transfer between Tb and P1 after Cerenkov radiation, compared to the Gd-based nanoparticles. We confirmed the involvement of the type II PDT reaction during 68Ga-mediated Cerenkov luminescence, id est, the transfer of photon to AGuIX@Tb-P1 which, in turn, generated P1-mediated singlet oxygen. The effect of 68Ga on cell survival was studied by clonogenic assays using human glioblastoma U-251 MG cells. Exposure of pre-treated cells with AGuIX@Tb-P1 to 68Ga resulted in the decrease in cell clone formation, unlike AGuIX@Gd-P1. We conclude that CR-PDT could be an alternative of X-PDT.

Advanced techniques for performing photodynamic therapy in deep-seated tissues

Photodynamic therapy (PDT) is a promising localized cancer treatment modality. It has been used successfully to treat a range of dermatological conditions with comparable efficacy to conventional treatments. However, some drawbacks limit the clinical utility of PDT in treating deep-seated tumors. Notably, the penetration limitation of UV and visible light, commonly applied to activate photosensitizers, makes PDT incompetent in treating deep-seated tumors. Development in light delivery technologies, especially fiber optics, led to improved clinical strategies for accessing deep tissues for irradiation. However, PDT efficacy issues remained partly due to light penetration limitations. In this review, we first summarized the current PDT applications for deep-seated tumor treatment. Then, the most recent progress in advanced techniques to overcome the light penetration limitation in PDT, including using functional nanomaterials that can either self-illuminate or be activated by near-infrared (NIR) light and X-rays as transducers, and implantable light delivery devices were discussed. Finally, current challenges and future opportunities of these technologies were discussed, which we hope may inspire the development of more effective techniques to enhance PDT efficacy against deep-seated tumors.

Combining Radiotherapy (RT) and Photodynamic Therapy (PDT): Clinical Studies on Conventional RT-PDT Approaches and Novel Nanoparticle-Based RT-PDT Approaches under Preclinical Evaluation

Radiotherapy (RT) is the primary standard of care for many locally advanced cancers. Often times, however, the efficacy of RT is limited due to radio-resistance that cancer cells develop. Photodynamic therapy (PDT) has gained importance as an alternative local therapy. Because its mechanism involves minimal acquired resistance, PDT is a useful adjunct to RT. This review discusses recent advances in combining RT with PDT for cancer treatment. In the first part of this review, we will discuss clinical trials on RT + PDT combination therapies. All these approaches suffer from the same inherent limitations as any current PDT methods; (i) visible light has a short penetration depth in human tissue (<∼10 mm), and (ii) it is difficult to illuminate the entire tumor homogeneously by external/interstitial laser irradiation. To address these limitations, scintillating nanoparticle-mediated RT-PDT approaches have been explored in which nanoparticles convert X-rays (RT) into visible light (PDT); high-energy X-rays can reach deep into the body to irradiate cancers uniformly and precisely. The second part of this review will discuss recent efforts in developing and applying nanoparticles for RT-PDT applications.

Application of Cherenkov radiation in tumor imaging and treatment

Cherenkov radiation (CR) is the characteristic blue glow that is generated during radiotherapy or radioisotope decay. Its distribution and intensity naturally reflect the actual dose and field of radiotherapy and the location of radioisotope imaging agents in vivo. Therefore, CR can represent a potential in situ light source for radiotherapy monitoring and radioisotope-based tumor imaging. When used in combination with new imaging techniques, molecular probes or nanomedicine, CR imaging exhibits unique advantages (accuracy, low cost, convenience and fast) in tumor radiotherapy monitoring and imaging. Furthermore, photosensitive nanomaterials can be used for CR photodynamic therapy, providing new approaches for integrating tumor imaging and treatment. Here the authors review the latest developments in the use of CR in tumor research and discuss current challenges and new directions for future studies.

Secure transplantation by tissue purging using photodynamic therapy to eradicate malignant cells

The field of photodynamic therapy (PDT) for treating various malignant neoplasms has been given researchers' attention due to its ability to be a selective and minimally invasive cancer therapy strategy. The possibility of tumor cell infection and hence high recurrence rates in cancer patients tends to restrict autologous transplantation. So, the photodynamic tissue purging process, which consists of selective photoinactivation of the malignant cells in the graft, is defined as a compromising strategy to purify contaminated tissues before transplantation. In this strategy, the direct malignant cells' death results from the reactive oxygen species (ROS) generation through the activation of a photosensitizer (PS) by light exposure in the presence of oxygen. Since new PS generations can effectively penetrate the tissue, PDT could be an ideal ex vivo tissue purging protocol that eradicates cancer cells derived from various malignancies. The challenge is that the applied pharmacologic ex vivo tissue purging should efficiently induce tumor cells with minor influence on normal tissue cells. This review aims to provide an overview of the current status of the most effective PDT strategies and PS development concerning their potential application in ex vivo purging before hematopoietic stem cell or ovarian tissue transplantation.

Activation of nano-photosensitizers by Y-90 microspheres to enhance oxidative stress and cell death in hepatocellular carcinoma

While radioembolization with yttrium-90 (Y-90) microspheres is a promising treatment for hepatocellular carcinoma (HCC), lower responses in advanced and high-grade tumors present an urgent need to augment its tumoricidal efficacy. The purpose of this study was to determine whether clinically used Y-90 microspheres activate light-responsive nano-photosensitizers to enhance hepatocellular carcinoma (HCC) cell oxidative stress and cytotoxicity over Y-90 alone in vitro. Singlet oxygen and hydroxyl radical production was enhanced when Y-90 microspheres were in the presence of several nano-photosensitizers compared to either alone in cell-free conditions. Both the SNU-387 and HepG2 human HCC cells demonstrated significantly lower viability when treated with low activity Y-90 microspheres (0.1-0.2 MBq/0.2 mL) and a nano-photosensitizer consisting of both titanium dioxide (TiO2) and titanocene (TC) labelled with transferrin (TiO2-Tf-TC) compared to Y-90 microspheres alone or untreated cells. Cellular oxidative stress and cell death demonstrated a linear dependence on Y-90 at higher activities (up to 0.75 MBq/0.2 mL), but was significantly more accentuated in the presence of increasing TiO2-Tf-TC concentrations in the poorly differentiated SNU-387 HCC cell line (p < 0.0001 and p = 0.0002 respectively) but not the well-differentiated HepG2 cell line. Addition of TiO2-Tf-TC to normal human hepatocyte THLE-2 cells did not increase cellular oxidative stress or cell death in the presence of Y-90. The enhanced tumoricidal activity of nano-photosensitizers with Y-90 microspheres is a potentially promising adjunctive treatment strategy for certain patient subsets. Applications in clinically relevant in vivo HCC models are underway.

Molecular dynamics simulations of cRGD-conjugated PEGylated TiO2 nanoparticles for targeted photodynamic therapy

The conjugation of high-affinity cRGD-containing peptides is a promising approach in nanomedicine to efficiently reduce off-targeting effects and enhance the cellular uptake by integrin-overexpressing tumor cells. Herein we utilize atomistic molecular dynamics simulations to evaluate key structural-functional parameters of these targeting ligands for an effective binding activity towards α_Vβ₃ integrins. An increasing number of cRGD ligands is conjugated to PEG chains grafted to highly curved TiO₂ nanoparticles to unveil the impact of cRGD density on the ligand's presentation, stability, and conformation in an explicit aqueous environment. We find that a low density leads to an optimal spatial presentation of cRGD ligands out of the "stealth" PEGylated layer around the nanosystem, favoring a straight upward orientation and spaced distribution of the targeting ligands in the bulk-water phase. On the contrary, high densities favor over-clustering of cRGD ligands, driven by a concerted mechanism of enhanced ligand-ligand interactions and reduced water accessibility over the ligand's molecular surface. These findings strongly suggest that the ligand density modulation is a key factor in the design of cRGD-targeting nanodevices to maximize their binding efficiency into over-expressed α_Vβ₃ integrin receptors.

Cherenkov Luminescence in Tumor Diagnosis and Treatment: A Review

Malignant tumors rank as a leading cause of death worldwide. Accurate diagnosis and advanced treatment options are crucial to win battle against tumors. In recent years, Cherenkov luminescence (CL) has shown its technical advantages and clinical transformation potential in many important fields, particularly in tumor diagnosis and treatment, such as tumor detection in vivo, surgical navigation, radiotherapy, photodynamic therapy, and the evaluation of therapeutic effect. In this review, we summarize the advances in CL for tumor diagnosis and treatment. We first describe the physical principles of CL and discuss the imaging techniques used in tumor diagnosis, including CL imaging, CL endoscope, and CL tomography. Then we present a broad overview of the current status of surgical resection, radiotherapy, photodynamic therapy, and tumor microenvironment monitoring using CL. Finally, we shed light on the challenges and possible solutions for tumor diagnosis and therapy using CL.

Minimizing adverse effects of Cerenkov radiation induced photodynamic therapy with transformable photosensitizer-loaded nanovesicles

Background

Photodynamic therapy (PDT) is a promising antitumor strategy with fewer adverse effects and higher selectivity than conventional therapies. Recently, a series of reports have suggested that PDT induced by Cerenkov radiation (CR) (CR-PDT) has deeper tissue penetration than traditional PDT; however, the strategy of coupling radionuclides with photosensitizers may cause severe side effects.

Methods

We designed tumor-targeting nanoparticles (¹³¹I-EM@ALA) by loading 5-aminolevulinic acid (ALA) into an ¹³¹I-labeled exosome mimetic (EM) to achieve combined antitumor therapy. In addition to playing a radiotherapeutic role, ¹³¹I served as an internal light source for the Cerenkov radiation (CR).

Results

The drug-loaded nanoparticles effectively targeted tumors as confirmed by confocal imaging, flow cytometry, and small animal fluorescence imaging. In vitro and in vivo experiments demonstrated that ¹³¹I-EM@ALA produced a promising antitumor effect through the synergy of radiotherapy and CR-PDT. The nanoparticles killed tumor cells by inducing DNA damage and activating the lysosome-mitochondrial pathways. No obvious abnormalities in the hematology analyses, blood biochemistry, or histological examinations were observed during the treatment.

Conclusions

We successfully engineered a nanocarrier coloaded with the radionuclide ¹³¹I and a photosensitizer precursor for combined radiotherapy and PDT for the treatment of breast cancer.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01401-0.

Deep-Tissue Activation of Photonanomedicines: An Update and Clinical Perspectives

Simple Summary

Photodynamic therapy (PDT) is a light-activated treatment modality, which is being clinically used and further developed for a number of premalignancies, solid tumors, and disseminated cancers. Nanomedicines that facilitate PDT (photonanomedicines, PNMs) have transformed its safety, efficacy, and capacity for multifunctionality. This review focuses on the state of the art in deep-tissue activation technologies for PNMs and explores how their preclinical use can evolve towards clinical translation by harnessing current clinically available instrumentation.

Abstract

With the continued development of nanomaterials over the past two decades, specialized photonanomedicines (light-activable nanomedicines, PNMs) have evolved to become excitable by alternative energy sources that typically penetrate tissue deeper than visible light. These sources include electromagnetic radiation lying outside the visible near-infrared spectrum, high energy particles, and acoustic waves, amongst others. Various direct activation mechanisms have leveraged unique facets of specialized nanomaterials, such as upconversion, scintillation, and radiosensitization, as well as several others, in order to activate PNMs. Other indirect activation mechanisms have leveraged the effect of the interaction of deeply penetrating energy sources with tissue in order to activate proximal PNMs. These indirect mechanisms include sonoluminescence and Cerenkov radiation. Such direct and indirect deep-tissue activation has been explored extensively in the preclinical setting to facilitate deep-tissue anticancer photodynamic therapy (PDT); however, clinical translation of these approaches is yet to be explored. This review provides a summary of the state of the art in deep-tissue excitation of PNMs and explores the translatability of such excitation mechanisms towards their clinical adoption. A special emphasis is placed on how current clinical instrumentation can be repurposed to achieve deep-tissue PDT with the mechanisms discussed in this review, thereby further expediting the translation of these highly promising strategies.

Light-Sensitive Phenacyl Crosslinked Dextran Hydrogels for Controlled Delivery

Stimuli-responsive soft materials enable controlled release of loaded drug molecules and biomolecules. Controlled release of potent chemotherapeutic or immunotherapeutic agents is crucial to reduce unwanted side effects. In an effort to develop controlled release strategies that can be triggered by using Cerenkov luminescence, we have developed polymer hydrogels that can release bovine serum albumin and immunoglobulin G by using light (254 nm-375 nm) as a trigger. We describe the synthesis and photochemical characterization of two light sensitive phenacyl bis-azide crosslinkers that are used to prepare transparent self-supporting hydrogel patches. One crosslinker was designed to optimize the overlap with the Cerenkov luminescence emission window, bearing an π-extended phenacyl core, resulting in a high quantum yield (14 %) of photocleavage when irradiated with 375 nm light. We used the extended phenacyl crosslinker for the preparation of protein-loaded dextran hydrogel patches, which showed efficient and selective dosed release of bovine serum albumin or immunoglobulin G after irradiation with 375 nm light. Cerenkov-triggered release is as yet inconclusive due to unexpected side-reactivity. Based on the high quantum yield, efficient release and large overlap with the Cerenkov window, we envision application of these photosensitive soft materials in radiation targeted drug release.

Acidity-Activated Charge Conversion of 177Lu-Labeled Nanoagent for the Enhanced Photodynamic Radionuclide Therapy of Cancer

Nanomaterials in combination with radionuclide therapy (RNT) provide new opportunities for cancer treatment. However, nanomaterials with efficient tumor accumulation have been less exploited for effective radionuclide-based therapy. Here, we report glycol chitosan-based nanoparticles (GCP-NPs) with acidic pH-dependent surface charge conversion for efficient radionuclide-based combination therapy. The nanoplatform can change the surface charge of nanoparticles from slight negative to positive in the acidic tumor microenvironment, which facilitates cellular internalization and penetration and thus improves the tumor accumulation efficiency of nanomaterials. Radiolabeling of GCP-NPs with ^99mTc enables in vivo radioactive imaging in the mouse subcutaneous tumor model, showing 8.1-fold enhanced tumor uptake relative to pH-insensitive control nanoparticles (termed as GCOP-NPs). Afterward, therapeutic radioisotope ¹⁷⁷Lu-labeled GCP-NPs (¹⁷⁷Lu-GCP-NPs) that utilize RNT synergistic with photodynamic therapy (PDT) derived from conjugated pyropheophorbide-a within nanoparticles endow superior antitumor efficacy in living cells and tumor-bearing mouse model. More importantly, the combination of RNT and PDT using ¹⁷⁷Lu-GCP-NPs can effectively inhibit lung metastasis and eliminate splenomegaly, which is not possible for individual RNT or PDT. Therefore, this study proposes a facile radionuclide-based combination therapy strategy toward complete cancer remission.

Strategies to Improve Photodynamic Therapy Efficacy of Metal-Free Semiconducting Conjugated Polymers

Photodynamic therapy (PDT) is a noninvasive therapy for cancer and bacterial infection. Metal-free semiconducting conjugated polymers (SCPS) with good stability and optical and electrical properties are promising photosensitizers (PSs) for PDT compared with traditional small-molecule PSs. This review analyzes the latest progress of strategies to improve PDT effect of linear, planar, and three-dimensional SCPS, including improving solubility, adjusting conjugated structure, enhancing PS-doped SCPs, and combining therapies. Moreover, the current issues, such as hypoxia, low penetration, targeting and biosafety of SCPS, and corresponding strategies, are discussed. Furthermore, the challenges and potential opportunities on further improvement of PDT for SCPs are presented.

Ligand Engineering of Titanium-Oxo Nanoclusters for Cerenkov Radiation-Reinforced Photo/Chemodynamic Tumor Therapy

The therapeutic effect of general photodynamic therapy (PDT) is gravely limited by the poor penetration depth of exogenous light radiation. In recent years, Cerenkov radiation (CR) has been exploringly applied to overcome this critical defect. However, the currently reported type I photosensitizers for CR-induced PDT (CRIT) are only TiO₂ nanoparticle-based agents with numerous fatally intrinsic drawbacks. Herein, we developed NH₂-Ti₃₂O₁₆ nanocluster (NTOC)-derived ultrasmall nanophotosensitizers (NPSs, denoted as TDPs) via innovate ligand engineering. The introduced dopamine (DA) ligands not only facilitate the water solubility and photocatalytic properties of NPSs but also involve the tumor-targeting behavior through the binding affinity with DA receptors on cancer cells. Under CR irradiation, TDPs enable efficient hydroxyl radical (·OH) generation benefiting from the enhanced separation of hole (h⁺)-electron (e^-) pairs, where the h⁺ will react with H₂O to execute type I PDT and the transferred e^- can realize the augmentation of Ti³⁺ to substantially promote the therapeutic index of chemodynamic therapy. This study provides an easy but feasible strategy for constructing versatile NPSs with an ultrasmall framework structure, propounding a refreshing paradigm for implementing efficient CR-induced combined therapy (CRICT) and spurring the development of CR and titanium-familial nanoplatforms in the fields of photocatalysis and nanocatalytic medicine.

Progress in Nanocarriers Codelivery System to Enhance the Anticancer Effect of Photodynamic Therapy

Photodynamic therapy (PDT) is a promising anticancer noninvasive method and has great potential for clinical applications. Unfortunately, PDT still has many limitations, such as metastatic tumor at unknown sites, inadequate light delivery and a lack of sufficient oxygen. Recent studies have demonstrated that photodynamic therapy in combination with other therapies can enhance anticancer effects. The development of new nanomaterials provides a platform for the codelivery of two or more therapeutic drugs, which is a promising cancer treatment method. The use of multifunctional nanocarriers for the codelivery of two or more drugs can improve physical and chemical properties, increase tumor site aggregation, and enhance the antitumor effect through synergistic actions, which is worthy of further study. This review focuses on the latest research progress on the synergistic enhancement of PDT by simultaneous multidrug administration using codelivery nanocarriers. We introduce the design of codelivery nanocarriers and discuss the mechanism of PDT combined with other antitumor methods. The combination of PDT and chemotherapy, gene therapy, immunotherapy, photothermal therapy, hyperthermia, radiotherapy, sonodynamic therapy and even multidrug therapy are discussed to provide a comprehensive understanding.

Molecular Probes for Autofluorescence-Free Optical Imaging

Optical imaging is an indispensable tool in clinical diagnostics and fundamental biomedical research. Autofluorescence-free optical imaging, which eliminates real-time optical excitation to minimize background noise, enables clear visualization of biological architecture and physiopathological events deep within living subjects. Molecular probes especially developed for autofluorescence-free optical imaging have been proven to remarkably improve the imaging sensitivity, penetration depth, target specificity, and multiplexing capability. In this Review, we focus on the advancements of autofluorescence-free molecular probes through the lens of particular molecular or photophysical mechanisms that produce long-lasting luminescence after the cessation of light excitation. The versatile design strategies of these molecular probes are discussed along with a broad range of biological applications. Finally, challenges and perspectives are discussed to further advance the next-generation autofluorescence-free molecular probes for in vivo imaging and in vitro biosensors.

One-pot synthesis of 68Ga-doped ultrasmall gold nanoclusters for PET/CT imaging of tumors

Gold nanoclusters (AuNCs) have attracted much attention for tumor theranostics in recent years because of their ability of renal clearance and to escape the reticuloendothelial system (RES) sequestration. In this study, we presented a novel method to synthesize ⁶⁸Ga-doped (labeled) AuNCs by simultaneous reduction of ⁶⁸GaCl₃ and HAuCl₄ by glutathione. As synthesized ⁶⁸Ga-doped, glutathione-coated AuNCs (⁶⁸Ga-GSH@AuNCs) were ultrasmall in size (<2 nm), highly stable under physiological conditions and renally clearable, and had high efficiency for tumor targeting. To demonstrate the universality of this ⁶⁸Ga labeling method and further enhance tumor targeting efficiency, arginine-glycine-aspartate (RGD)-containing peptide was introduced as co-reductant to synthesize RGD peptide and glutathione co-coated, ⁶⁸Ga-labeled AuNCs (⁶⁸Ga-RGD-GSH@AuNCs). Introduction of RGD peptide did not interfere the synthesis process but significantly enhanced the tumor targeting efficiency of the AuNCs. Our study demonstrated that it was feasible to label AuNCs with gallium-68 by direct reduction of the radioisotope and HAuCl₄ with reductant peptides, holding a great potential for clinical translation for PET/CT detection of tumors.

Light Technology for Efficient and Effective Photodynamic Therapy: A Critical Review

Photodynamic therapy (PDT) is a cancer treatment with strong potential over well-established standard therapies in certain cases. Non-ionising radiation, localisation, possible repeated treatments, and stimulation of immunological response are some of the main beneficial features of PDT. Despite the great potential, its application remains challenging. Limited light penetration depth, non-ideal photosensitisers, complex dosimetry, and complicated implementations in the clinic are some limiting factors hindering the extended use of PDT. To surpass actual technological paradigms, radically new sources, light-based devices, advanced photosensitisers, measurement devices, and innovative application strategies are under extensive investigation. The main aim of this review is to highlight the advantages/pitfalls, technical challenges and opportunities of PDT, with a focus on technologies for light activation of photosensitisers, such as light sources, delivery devices, and systems. In this vein, a broad overview of the current status of superficial, interstitial, and deep PDT modalities-and a critical review of light sources and their effects on the PDT process-are presented. Insight into the technical advancements and remaining challenges of optical sources and light devices is provided from a physical and bioengineering perspective.

A Cationic Micelle as In Vivo Catalyst for Tumor-Localized Cleavage Chemistry

The emerging strategies of accelerating the cleavage reaction in tumors through locally enriching the reactants is promising. Yet, the applications are limited due to the lack of the tumor-selectivity for most of the reactants. Here we explored an alternative approach to leverage the rate constant by locally inducing an in vivo catalyst. We found that the desilylation-induced cleavage chemistry could be catalyzed in vivo by cationic micelles, and accelerated over 1400-fold under physiological condition. This micelle-catalyzed controlled release platform is demonstrated by the release of a 6-hydroxyl-quinoline-2-benzothiazole derivative (HQB) in two cancer cell lines and a NIR dye in mouse tumor xenografts. Through intravenous injection of a pH-sensitive polymer micelles, we successfully applied this strategy to a prodrug activation of hydroxyl camptothecin (OH-CPT) in tumors. Its "decaging" efficiency is 42-fold to that without cationic micelles-mediated catalysis. This micelle-catalyzed desilylation strategy unveils the potential that micelle may act beyond a carrier but a catalyst for local perturbing or activation.

Oxygen-Carrying Polymer Nanoconstructs for Radiodynamic Therapy of Deep Hypoxic Malignant Tumors

Radiodynamic therapy (RDT) is an emerging non-invasive anti-cancer treatment based on the generation of the reactive oxygen species (ROS) at the lesion site following the interaction between X-rays and a photosensitizer drug (PS). The broader application of RDT is impeded by the tumor-associated hypoxia that results in low availability of oxygen for the generation of sufficient amounts of ROS. Herein, a novel nanoparticle drug formulation for RDT, which addresses the problem of low oxygen availability, is reported. It consists of poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) co-loaded with a PS drug verteporfin (VP), and the clinically approved oxygen-carrying molecule, perfluorooctylbromide (PFOB). When triggered by X-rays (4 Gy), under both normoxic and hypoxic conditions, PLGA-VP-PFOB nanoconstructs (NCs) induced a significant increase of the ROS production compared with matching PLGA-VP nanoparticles. The RDT with NCs effectively killed ~60% of human pancreatic cancer cells in monolayer cultures, and almost completely suppressed the outgrowth of tumor cells in 2-weeks clonogenic assay. In a 3D engineered model of pancreatic cancer metastasis to the liver, RDT with NCs destroyed ~35% of tumor cells, demonstrating an exceptional efficiency at a tissue level. These results show that PLGA-VP-PFOB is a promising agent for RDT of deep-seated hypoxic tumors.

Solutions to the Drawbacks of Photothermal and Photodynamic Cancer Therapy

Phototherapy such as photothermal therapy and photodynamic therapy in cancer treatment has been developed quickly over the past few years for its noninvasive nature and high efficiency. However, there are still many drawbacks in phototherapy that prevent it from clinical applications. Thus, scientists have designed different systems to overcome the issues associated with phototherapy, including enhancing the targeting ability of phototherapy, low-temperature photothermal therapy, replacing near-infrared light with other excitation sources, and so on. This article discusses the problems and shortcomings encountered in the development of phototherapy and highlights possible solutions to address them so that phototherapy may become a useful cancer treatment approach in clinical practice. This article aims to give a brief summary about current research advancements in phototherapy research and provides a quick guideline toward future developments in the field.

Radiolabelling of nanomaterials for medical imaging and therapy

Nanomaterials offer unique physical, chemical and biological properties of interest for medical imaging and therapy. Over the last two decades, there has been an increasing effort to translate nanomaterial-based medicinal products (so-called nanomedicines) into clinical practice and, although multiple nanoparticle-based formulations are clinically available, there is still a disparity between the number of pre-clinical products and those that reach clinical approval. To facilitate the efficient clinical translation of nanomedicinal-drugs, it is important to study their whole-body biodistribution and pharmacokinetics from the early stages of their development. Integrating this knowledge with that of their therapeutic profile and/or toxicity should provide a powerful combination to efficiently inform nanomedicine trials and allow early selection of the most promising candidates. In this context, radiolabelling nanomaterials allows whole-body and non-invasive in vivo tracking by the sensitive clinical imaging techniques positron emission tomography (PET), and single photon emission computed tomography (SPECT). Furthermore, certain radionuclides with specific nuclear emissions can elicit therapeutic effects by themselves, leading to radionuclide-based therapy. To ensure robust information during the development of nanomaterials for PET/SPECT imaging and/or radionuclide therapy, selection of the most appropriate radiolabelling method and knowledge of its limitations are critical. Different radiolabelling strategies are available depending on the type of material, the radionuclide and/or the final application. In this review we describe the different radiolabelling strategies currently available, with a critical vision over their advantages and disadvantages. The final aim is to review the most relevant and up-to-date knowledge available in this field, and support the efficient clinical translation of future nanomedicinal products for in vivo imaging and/or therapy.

PET imaging facilitates antibody screening for synergistic radioimmunotherapy with a 177Lu-labeled αPD-L1 antibody

Rationale: The low response rate of immunotherapy, such as anti-PD-L1/PD-1 and anti-CTLA4, has limited its application to a wider population of cancer patients. One widely accepted view is that inflammation within the tumor microenvironment is low or ineffective for inducing the sufficient infiltration and/or activation of lymphocytes. Here, a highly tumor-selective anti-PD-L1 (αPD-L1) antibody was developed through PET imaging screening, and it was radiolabeled with Lu-177 for PD-L1-targeted radioimmunotherapy (RIT) and radiation-synergized immunotherapy. Methods: A series of αPD-L1 antibodies were radiolabeled with zirconium-89 for PET imaging to screen the most suitable antibodies for RIT. Mice were divided into an immunotherapy group, a RIT group and a radiation-synergized immunotherapy group to evaluate the therapeutic effect. Alterations in the tumor microenvironment after treatment were assessed using flow cytometry and immunofluorescence microscopy. Results: Radiation-synergistic RIT can achieve a significantly better therapeutic effect than immunotherapy or RIT alone. The dosages of the radiopharmaceuticals and αPD-L1 antibodies were reduced, the infiltration of CD4⁺ and CD8⁺ T cells in the tumor microenvironment was increased, and no side effects were observed. This radiation-synergistic RIT strategy successfully showed a strong synergistic effect with αPD-L1 checkpoint blockade therapy, at least in the mouse model. Conclusions: PET imaging of ⁸⁹Zr-labeled antibodies is an effective method for antibody screening. RIT with a ¹⁷⁷Lu-labeled αPD-L1 antibody could successfully upregulate antitumor immunity in the tumor microenvironment and turn "cold" tumors "hot" for immunotherapy.

Covalent Organic Polymer as a Carborane Carrier for Imaging-Facilitated Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is an atomic targeted radiotherapy that shows fantastic suppression impact on locally intrusive threatening tumors. One key factor for effective BNCT is to aggregate an adequate concentration (>20 ppm) of ¹⁰B in the cytoplasm of the tumor. Carborane-loaded polymer nanoparticles are promising because of their outstanding biocompatibility and plasma steadiness. In this study, a new class of carborane-loaded nanoscale covalent organic polymers (BCOPs) was prepared by a Schiff base condensation reaction, and their solubility was greatly improved in common solvents via alkyl chain engineering and size tailoring. The obtained BCOP-5T was further functionalized by biocompatible 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene-glycol)-2000] (DSPE-PEG, molecular weight 2000) to form stable aqueous-phase nanoparticles with a hydrodynamic diameter of around 100 nm. After chelating with radioactive copper-64, DSPE-BCOP-5T was tracked by positron emission tomography (PET) imaging and showed significant accumulation in the tumor. DSPE-BCOP-5T + neutron radiation showed remarkable tumor suppression in 4T1 tumor-bearing mice (murine breast cancer). No obvious physical tissue damage and abnormal behavior were observed, demonstrating that the boron delivery was successful and tumor-selective. To conclude, this study presents a theranostic COP-based platform with a well-defined composition, good biocompatibility, and satisfactory tumor accumulation, which is promising for PET imaging, drug delivery, and BNCT.

Mechanisms for Tuning Engineered Nanomaterials to Enhance Radiation Therapy of Cancer

Engineered nanomaterials that produce reactive oxygen species on exposure to X- and gamma-rays used in radiation therapy offer promise of novel cancer treatment strategies. Similar to photodynamic therapy but suitable for large and deep tumors, this new approach where nanomaterials acting as sensitizing agents are combined with clinical radiation can be effective at well-tolerated low radiation doses. Suitably engineered nanomaterials can enhance cancer radiotherapy by increasing the tumor selectivity and decreasing side effects. Additionally, the nanomaterial platform offers therapeutically valuable functionalities, including molecular targeting, drug/gene delivery, and adaptive responses to trigger drug release. The potential of such nanomaterials to be combined with radiotherapy is widely recognized. In order for further breakthroughs to be made, and to facilitate clinical translation, the applicable principles and fundamentals should be articulated. This review focuses on mechanisms underpinning rational nanomaterial design to enhance radiation therapy, the understanding of which will enable novel ways to optimize its therapeutic efficacy. A roadmap for designing nanomaterials with optimized anticancer performance is also shown and the potential clinical significance and future translation are discussed.

Can Cerenkov Light Really Induce an Effective Photodynamic Therapy?

Photodynamic therapy (PDT) is a promising therapeutic strategy for cancers where surgery and radiotherapy cannot be effective. PDT relies on the photoactivation of photosensitizers, most of the time by lasers to produced reactive oxygen species and notably singlet oxygen. The major drawback of this strategy is the weak light penetration in the tissues. To overcome this issue, recent studies proposed to generate visible light in situ with radioactive isotopes emitting charged particles able to produce Cerenkov radiation. In vitro and preclinical results are appealing, but the existence of a true, lethal phototherapeutic effect is still controversial. In this article, we have reviewed previous original works dealing with Cerenkov-induced PDT (CR-PDT). Moreover, we propose a simple analytical equation resolution to demonstrate that Cerenkov light can potentially generate a photo-therapeutic effect, although most of the Cerenkov photons are emitted in the UV-B and UV-C domains. We suggest that CR-PDT and direct UV-tissue interaction act synergistically to yield the therapeutic effect observed in the literature. Moreover, adding a nanoscintillator in the photosensitizer vicinity would increase the PDT efficacy, as it will convert Cerenkov UV photons to light absorbed by the photosensitizer.

Dopamine-Decorated TiO2 Nanoparticles in Water: A QM/MM vs an MM Description

Nanoparticle functionalization is a modern strategy in nanotechnology to build up devices for several applications. Modeling fully decorated metal oxide nanoparticles of realistic size (few nanometers) in an aqueous environment is a challenging task. In this work, we present a case study relevant for solar-light exploitation and for biomedical applications, i.e., a dopamine-functionalized TiO₂ nanoparticle (1700 atoms) in bulk water, for which we have performed an extensive comparative investigation with both MM and QM/MM approaches of the structural properties and of the conformational dynamics. We have used a combined multiscale protocol for a more efficient exploration of the complex conformational space. On the basis of the results of this study and of some QM and experimental data, we have defined strengths and limitations of the existing force field parameters. Our findings will be useful for an improved modeling and simulation of many other similar hybrid bioinorganic nanosystems in an aqueous environment that are pivotal in a broad range of nanotechnological applications.

Animal heat activated cancer therapy by a traditional catalyst TiO2-Pd/graphene composites

Cancer therapy is one of the most important challenges in clinical medicine. So far different methods have been developed for cancer therapy, such as radiation therapy, surgery, chemotherapy and photodynamic therapy. Here we propose a new concept for cancer therapy, i.e., killing the cancer cells simply via reactive oxygen species (ROS) generated by TiO₂-Pd/graphene composites. Activated by animal heat of 37 °C, the electrons in the valence band can be excited to the conduction band of TiO₂ via the energy levels of Pd species and graphene, generating ROS without light irradiation or electric excitation. The tumors in BALB/c mice are successfully regressed at animal heat without any other external conditions, such as radiation, UV, visible and IR irradiation. Our results suggest that the design of animal heat activated cancer therapy is a feasible concept for practical applications of cancer treatments.

Dandelion-Inspired Hierarchical Upconversion Nanoplatform for Synergistic Chemo-Photodynamic Therapy In Vitro

Herein, inspired by the structure of a dandelion, we develop a fresh preparation of an upconversion nanoplatform (UCNPs@C₆₀-DOX-FA). The target part folic acid (FA) modified with β-CD-NH₂ can enhance dispersibility and afford the nanoplatform to arrive at the tumor and enter cancer cells easily. After the mouse breast cancer (4T1) cell incubation with the nanoplatform, the abundant glutathione (GSH) in cells cuts the -S-S- bonds like scissors, just as dandelion encountering wind, and the drug doxorubicin (DOX) flows into the nucleus for chemotherapy. Meanwhile, the photodynamic therapy (PDT) effect is enhanced with the decrease content of GSH, which promotes the reactive oxygen species to accumulation. The synergistic chemotherapy and PDT are outstanding in killing 4T1 cells. The rest part UCNPs@C₆₀ possesses excellent biocompatibility and low cytotoxicity. As for cancer diagnosis, UCNPs can be used as a visual imaging agent. Benefited by the delicate structure, all of the functional parts of the nanoplatform go and coordinate well. On account of an FA ligand and the -S-S- bond, the nanoplatform works very well in 4T1 cells while it is able to avoid damage to normal cells since the FA receptors and GSH have overexpression in the 4T1 cells. Thus, this work shows an accessible strategy to design a dandelion-like hierarchical nanoplatform for potential bioimaging-guided synergistic chemo-photodynamic therapy.