Terbium-Rose Bengal Coordination Nanocrystals-Induced ROS Production under Low-Dose X-rays in Cultured Cancer Cells for Photodynamic Therapy

X-ray-triggered scintillators (Sc) and photosensitizers (Ps) have been developed for X-ray-induced photodynamic therapy (X-PDT) to selectively destruct deep tissue tumors with a low X-ray dose. This study designed terbium (Tb)-rose bengal (RB) coordination nanocrystals (T-RBNs) by a solvothermal treatment, aiming to reduce photon energy dissipation between Tb³⁺ and RB and thus increase the reactive oxygen species (ROS) production efficiency. T-RBNs synthesized at a molar ratio of [RB]/[Tb] = 3 exhibited a size of 6.8 ± 1.2 nm with a crystalline property. Fourier transform infrared analyses of T-RBNs indicated successful coordination between RB and Tb³⁺. T-RBNs generated singlet oxygen (¹O₂) and hydroxyl radicals (^•OH) under low-dose X-ray irradiation (0.5 Gy) via scintillating and radiosensitizing pathways. T-RBNs produced ∼8-fold higher ROS amounts than bare RB and ∼3.6-fold higher ROS amounts than inorganic nanoparticle-based controls. T-RBNs did not exhibit severe cytotoxicity up to 2 mg/mL concentration in cultured luciferase-expressing murine epithelial breast cancer (4T1-luc) cells. Furthermore, T-RBNs were efficiently internalized into cultured 4T1-luc cells and induced DNA double strand damage, as evidenced by an immunofluorescence staining assay with phosphorylated γ-H₂AX. Ultimately, under 0.5 Gy X-ray irradiation, T-RBNs induced >70% 4T1-luc cell death via simultaneous apoptosis/necrosis pathways. Overall, T-RBNs provided a promising Sc/Ps platform under low-dose X-PDT for advanced cancer therapy.

Enhancement of Light and X-ray Charging in Persistent Luminescence Nanoparticle Scintillators Zn2SiO4:Mn2+, Yb3+, Li. ACS Appl Mater Interfaces 2023;15:21228-21238. [PMID: 37078901 DOI: 10.1021/acsami.3c00664]

Persistent luminescence nanoparticle scintillators (PLNS) have been attempted for X-ray-induced photodynamic therapy (X-PDT) because persistent luminescence after ceasing radiation can make PLNS use less cumulative irradiation time and dose to generate the same amount of reactive oxygen species (ROS) compared with conventional scintillators to combat cancer cells. However, excessive surface defects in PLNS reduce the luminescence efficiency and quench the persistent luminescence, which is fatal to the efficacy of X-PDT. Herein, the PLNS of SiO₂@Zn₂SiO₄:Mn²⁺, Yb³⁺, Li⁺ was designed by the energy trap engineering and synthesized by a simple template method, which has excellent X-ray and UV-excited persistent luminescence and continuously tunable emission spectra from 520 to 550 nm. Its luminescence intensity and afterglow time are more than 7 times that of the reported Zn₂SiO₄:Mn²⁺ used for X-PDT. By loading a Rose Bengal (RB) photosensitizer, an effective persistent energy transfer from the PLNS to photosensitizer is observed even after the removal of X-ray irradiation. The X-ray dose of nanoplatform SiO₂@Zn₂SiO₄:Mn²⁺, Yb³⁺, Li⁺@RB in X-PDT of HeLa cancer cells was reduced to 0.18 Gy compared to the X-ray dose of 1.0 Gy for Zn₂SiO₄:Mn for X-PDT. This indicates that the Zn₂SiO₄:Mn²⁺, Yb³⁺, Li⁺ PLNS have great potential for X-PDT applications.

Recent Progress and Trends in X-ray-Induced Photodynamic Therapy with Low Radiation Doses

The prominence of photodynamic therapy (PDT) in treating superficial skin cancer inspires innovative solutions for its congenitally deficient shadow penetration of the visible-light excitation. X-ray-induced photodynamic therapy (X-PDT) has been proven to be a successful technique in reforming the conventional PDT for deep-seated tumors by creatively utilizing penetrating X-rays as external excitation sources and has witnessed rapid developments over the past several years. Beyond the proof-of-concept demonstration, recent advances in X-PDT have exhibited a trend of minimizing X-ray radiation doses to quite low values. As such, scintillating materials used to bridge X-rays and photosensitizers play a significant role, as do diverse well-designed irradiation modes and smart strategies for improving the tumor microenvironment. Here in this review, we provide a comprehensive summary of recent achievements in X-PDT and highlight trending efforts using low doses of X-ray radiation. We first describe the concept of X-PDT and its relationships with radiodynamic therapy and radiotherapy and then dissect the mechanism of X-ray absorption and conversion by scintillating materials, reactive oxygen species evaluation for X-PDT, and radiation side effects and clinical concerns on X-ray radiation. Finally, we discuss a detailed overview of recent progress regarding low-dose X-PDT and present perspectives on possible clinical translation. It is expected that the pursuit of low-dose X-PDT will facilitate significant breakthroughs, both fundamentally and clinically, for effective deep-seated cancer treatment in the near future.

Nanoscintillator-Based X-Ray-Induced Photodynamic Therapy

Photodynamic therapy (PDT) is an emerging treatment option for cancer. In PDT, photosensitizers are delivered to tumors and stimulated by light to generate reactive oxygen species (ROS)-most importantly singlet oxygen (¹O₂)-to damage tumor cells or induce tissue ischemia. PDT is associated with a low level of systemic toxicity because photosensitizers are usually pharmaceutically inactive in the dark and photoirradiation is applied only to tumor areas in the procedure. Additionally, PDT can be applied repeatedly without cumulative toxicity or incurring resistance, and may stimulate systemic anti-tumor immunity. However, PDT's clinical use has been restricted due to the limited penetration of visible light through tissues. X-rays possess superior tissue penetration capability and are exploited in X-ray-induced photodynamic therapy to overcome this limitation. Herein we have demonstrated this principle with a novel LiGa₅O₈:Cr (LGO:Cr)-based nanoscintillator which emits near-infrared X-ray luminescence to both guide external beam therapy and induce PDT with the photosensitizer (2,3-naphthalocyanine) encapsulated in a mesoporous silica shell of the nanoscintillator.

Antiangiogenesis Combined with Inhibition of the Hypoxia Pathway Facilitates Low-Dose, X-ray-Induced Photodynamic Therapy

X-ray-induced photodynamic therapy (XPDT) is overwhelmingly superior in treating deep-seated cancers. However, limitations remain, owing to a combination of the poor scintillation performance of the nanoscintillator, low energy transfer efficiency of the therapeutic nanoplatform, and hypoxic environment presented in the tumor tissue. Collectively, these reduce the curative effect of XPDT. Here, we report a highly efficient, low-dose XPDT realized by systematic optimization from scintillation efficiency, nanoplatform structure, to therapeutic approach. We developed a biocompatible, codoped CaF₂ nanoscintillator that emitted sufficiently green radioluminescence that was bright enough to be seen by the naked eye. Using dendrimers as a framework, we built a nanoplatform featuring a dual-core-satellite architecture, which enabled both procedurally and spatially separate dual-loading of therapeutic agents. This strategy allowed for the fabrication of a combined XPDT and antiangiogenic therapy, resulting in a therapeutic system capable of simultaneous tumor attacks. After exposure to ultralow dose radiation, XPDT resulted in marked tumor reduction while the antiangiogenic drug effectively blocked tumor vascularization exacerbated by XPDT-mediated hypoxia, rendering a pronounced synergy effect. This system also showed high biosafety, as the agents adopted had been used clinically and both Ca and F elements were widespread in the human body. Taken together, the findings presented here provided a reference for the construction of complex, multiloading architecture in coordination with structural complexity and functional diversification. This work provided a safer and more robust application of the combined XPDT and antiangiogenesis in future clinical treatment settings.

Terbium-Based AGuIX-Design Nanoparticle to Mediate X-ray-Induced Photodynamic Therapy

X-ray-induced photodynamic therapy is based on the energy transfer from a nanoscintillator to a photosensitizer molecule, whose activation leads to singlet oxygen and radical species generation, triggering cancer cells to cell death. Herein, we synthesized ultra-small nanoparticle chelated with Terbium (Tb) as a nanoscintillator and 5-(4-carboxyphenyl succinimide ester)-10,15,20-triphenyl porphyrin (P1) as a photosensitizer (AGuIX@Tb-P1). The synthesis was based on the AGuIX@ platform design. AGuIX@Tb-P1 was characterised for its photo-physical and physico-chemical properties. The effect of the nanoparticles was studied using human glioblastoma U-251 MG cells and was compared to treatment with AGuIX@ nanoparticles doped with Gadolinium (Gd) and P1 (AGuIX@Gd-P1). We demonstrated that the AGuIX@Tb-P1 design was consistent with X-ray photon energy transfer from Terbium to P1. Both nanoparticles had similar dark cytotoxicity and they were absorbed in a similar rate within the cells. Pre-treated cells exposure to X-rays was related to reactive species production. Using clonogenic assays, establishment of survival curves allowed discrimination of the impact of radiation treatment from X-ray-induced photodynamic effect. We showed that cell growth arrest was increased (35%-increase) when cells were treated with AGuIX@Tb-P1 compared to the nanoparticle doped with Gd.