Radioluminescent Nanoparticles Research Articles

Combining Pr3+-Doped Nanoradiosensitizers and Endogenous Protoporphyrin IX for X-ray-Mediated Photodynamic Therapy of Glioblastoma Cells.

Glioblastoma multiforme is an aggressive type of brain cancer with high recurrence rates due to the presence of radioresistant cells remaining after tumor resection. Here, we report the development of an X-ray-mediated photodynamic therapy (X-PDT) system using NaLuF4:25% Pr3+ radioluminescent nanoparticles in conjunction with protoporphyrin IX (PPIX), an endogenous photosensitizer that accumulates selectively in cancer cells. Conveniently, 5-aminolevulinic acid (5-ALA), the prodrug that is administered for PDT, is the only drug approved for fluorescence-guided resection of glioblastoma, enabling dual detection and treatment of malignant cells. NaLuF4:Pr3+ nanoparticles were synthesized and spectroscopically evaluated at a range of Pr3+ concentrations. This generated radioluminescent nanoparticles with strong emissions from the 1S0 excited state of Pr3+, which overlaps with the Soret band of PPIX to perform photodynamic therapy. The spectral overlap between the nanoparticles and PPIX improved treatment outcomes for U251 cells, which were used as a model for the thin tumor margin. In addition to sensitizing PPIX to induce X-PDT, our nanoparticles exhibit strong radiosensitizing properties through a radiation dose-enhancement effect. We evaluate the effects of the nanoparticles alone and in combination with PPIX on viability, death, stress, senescence, and proliferation. Collectively, our results demonstrate this as a strong proof of concept for nanomedicine.

Radioluminescent nanoparticles and deep-tissue photodynamic therapy to enhance radiotherapy efficacy

Radioluminescent nanoparticles and deep-tissue photodynamic therapy to enhance radiotherapy efficacy

Wireless Optogenetic Modulation of Cortical Neurons Enabled by Radioluminescent Nanoparticles.

While offering high-precision control of neural circuits, optogenetics is hampered by the necessity to implant fiber-optic waveguides in order to deliver photons to genetically engineered light-gated neurons in the brain. Unlike laser light, X-rays freely pass biological barriers. Here we show that radioluminescent Gd2(WO4)3:Eu nanoparticles, which absorb external X-rays energy and then downconvert it into optical photons with wavelengths of ∼610 nm, can be used for the transcranial stimulation of cortical neurons expressing red-shifted, ∼590-630 nm, channelrhodopsin ReaChR, thereby promoting optogenetic neural control to the practical implementation of minimally invasive wireless deep brain stimulation.

Investigating the reactive oxygen species production of Rose Bengal and Merocyanine 540-loaded radioluminescent nanoparticles.

Radioluminescent nanomaterials have garnered significant attention in the past decade due to their potential to perform X-ray mediated photodynamic therapy (X-PDT). Many of these materials are assumed to produce singlet oxygen based on a single assay. Herein we demonstrate that multiple assays are required to confidently determine whether singlet oxygen or other reactive oxygen species are being produced through type I or type II PDT mechanisms. Rose Bengal and Merocyanine 540 photosensitizers were loaded into mesoporous silica-coated NaLuF4:Dy3+,Gd3+ nanoparticles and the combination of ABDA, DPBF, and NaN3 assays along with electron paramagnetic resonance were employed to determine that superoxide and hydroxyl radicals were exclusively produced from this system under X-ray excitation. Knowledge of the correct PDT mechanism is crucial for informing what types of disease may be best suited for treatment using PDT nanosystems.

Development of dispersible radioluminescent silicate nanoparticles through a sacrificial layer approach

X-rays offer low tissue attenuation with high penetration depth when used in medical applications and when coupled with radioluminescent nanoparticles, offer novel theranostic opportunities. In this role, the ideal scintillator requires a high degree of crystallinity for an application relevant radioluminescence, yet a key challenge is the irreversible aggregation of the particles at most crystallization temperatures. In this communication, a high temperature multi-composite reactor (HTMcR) process was successfully developed to recrystallize monodisperse scintillating particulates by employing a core-multishell architecture. The core–shell morphology of the particles consisted of a silica core over-coated with a rare earth (Re = Y3+, Lu3+, Ce3+) oxide shell. This core–shell assembly was then encapsulated within a poly(divinylbenzene) shell which was converted to glassy carbon during the annealing & crystallization of the silica/rare earth oxide core–shell particle. This glassy carbon acted as a delamination layer and prevented the irreversible aggregation of the particles during the high temperature crystallization step. A subsequent low temperature annealing step in an air environment removed the glassy carbon and resulted in radioluminescent nanoparticles. Two monodisperse nanoparticle systems were synthesized using the HTMcR process including cerium doped Y2Si2O7 and Lu2Si2O7 with radioluminescence peaks at 427 and 399 nm, respectively. These particles may be employed as an in vivo light source for a noninvasive X-ray excited optogenetics.

Radioluminescent nanoparticles for radiation-controlled release of drugs

The present work demonstrates a novel concept for intratumoral chemo-radio combination therapy for locally advanced solid tumors. For some locally advanced tumors, chemoradiation is currently standard of care. This combination treatment can cause acute and long term toxicity that can limit its use in older patients or those with multiple medical comorbidities. Intratumoral chemotherapy has the potential to address the problem of systemic toxicity that conventional chemotherapy suffers, and may, in our view, be a better strategy for treating certain locally advanced tumors. The present study proposes how intratumoral chemoradiation can be best implemented. The enabling concept is the use of a new chemotherapeutic formulation in which chemotherapy drugs (e.g., paclitaxel (PTX)) are co-encapsulated with radioluminecsnt nanoparticles (e.g., CaWO4 (CWO) nanoparticles (NPs)) within protective capsules formed by biocompatible/biodegradable polymers (e.g., poly(ethylene glycol)-poly(lactic acid) or PEG-PLA). This drug-loaded polymer-encapsulated radioluminescent nanoparticle system can be locally injected in solution form into the patient's tumor before the patient receives normal radiotherapy (e.g., 30–40 fractions of 2–3 Gy daily X-ray dose delivered over several weeks for locally advanced head and neck tumors). Under X-ray irradiation, the radioluminescent nanoparticles produce UV-A light that has a radio-sensitizing effect. These co-encapsulated radioluminescent nanoparticles also enable radiation-triggered release of chemo drugs from the polymer coating layer. The non-toxic nature (absence of dark toxicity) of this drug-loaded polymer-encapsulated radioluminescent nanoparticle (“PEG-PLA/CWO/PTX”) formulation was confirmed by the MTT assay in cancer cell cultures. A clonogenic cell survival assay confirmed that these drug-loaded polymer-encapsulated radioluminescent nanoparticles significantly enhance the cancer cell killing effect of radiation therapy. In vivo study validated the efficacy of PEG-PLA/CWO/PTX-based intratumoral chemo-radio therapy in mouse tumor xenografts (in terms of tumor response and mouse survival). Results of a small-scale NP biodistribution (BD) study demonstrate that PEG-PLA/CWO/PTX NPs remained at the tumor sites for a long period of time (> 1 month) following direct intratumoral administration. A multi-compartmental pharmacokinetic model (with rate constants estimated from in vitro experiments) predicts that this radiation-controlled drug release technology enables significant improvements in the level and duration of drug availability within the tumor (throughout the typical length of radiation treatment, i.e., > 1 month) over conventional delivery systems (e.g., PEG-PLA micelles with no co-encapsulated CaWO4, or an organic liquid, e.g., a 50:50 mixture of Cremophor EL and ethanol, as in Taxol), while it is capable of maintaining the systemic level of the chemo drug far below the toxic threshold limit over the entire treatment period. This technology thus has the potential to offer a new therapeutic option that has not previously been available for patients excluded from conventional chemoradiation protocols.

Low dose photodynamic therapy harmonizes with radiation therapy to induce beneficial effects on pancreatic heterocellular spheroids.

Photodynamic therapy (PDT) has seen long standing interest as a therapy for resistant cancers, but the main Achilles’ heel for its successful clinical exploitation is the use of poorly penetrating visible light. This limitation could be overcome by using radioluminescent nanoparticles, which can be excited during radiation therapy (RT) with penetrating X-rays. When infused in tumors, X-ray activated-nanoscintillators act as internal light sources and excite nearby photosensitizers. Recent studies demonstrated that it is realistic to achieve low dose PDT with current nanoscintillators. However, as the origin of enhanced RT efficacy with nanoscintillators may have varying origins, we aimed to answer the basic question: Is a combination of low-dose PDT beneficial to the RT efficacy in clinically relevant models of cancer?Pancreatic cancer (PanCa) remains a lethal disease for which RT is part of the palliative care and for which PDT demonstrated promising results in clinical trial. We thus evaluated the combination of low-dose PDT and RT delivered in absence of nanoscintillators on various heterocellular spheroid models that recapitulate the clinical heterogeneity of PanCa. Although therapeutic effects emerged at different timepoints in each model, the RT/PDT combination uniformly achieved favorable outcomes. With RT providing stunted tumor growth while PDT drove adjuvant apoptotic and necrotic cell death, the combination produced significantly smaller and less viable PanCa spheroids.In conclusion, the beneficial RT/PDT treatment outcomes encourage the further development of nanoscinitillators for X-ray-activated PDT. Assessment of such combination treatments should encompass multiparametric and temporally-spaced assessment of treatment effects in preclinical cancer models.

Radioluminescence studies of colloidal oleate-capped β-Na(Gd,Lu)F4:Ln3+ nanoparticles (Ln = Ce, Eu, Tb).

We report on the synthesis, characterization, and radioluminescence quantification of several new varieties of nanoparticles with the general composition β-NaLnF4, incorporating known luminescent activator/sensitizer pairs. Using Monte Carlo modeling to complement luminescence measurements, we have calculated the radioluminescence yields and intrinsic conversion efficiencies of colloidally-dispersed nanoparticles by comparison to an organic liquid scintillator. While five of the compositions had low to modest radioluminescence yields relative to bulk materials, colloidal β-Na(Lu0.65Gd0.2Tb0.15)F4 displayed a strong output of 39 460 photons per MeV absorbed, comparable to some of the best non-hygroscopic bulk crystal scintillators and X-ray phosphors such as Gd2O2S:Tb. Measurements of β-Na(Lu0.65Gd0.2Tb0.15)F4 powder samples revealed persistent luminescence as well as stable charge trapping, warranting further investigation.

Polymer‐Coated Radioluminescent Nanoparticles for Quantitative Imaging of Drug Delivery

Some theranostic nanoparticle (NP) drug delivery systems are capable of measuring drug release rates in situ. This can provide quantitative information regarding drug biodistribution, and drug dose that is delivered to cells or tissues. Here, X‐ray excited optical luminescent (XEOL) NPs coated with poly(glycolide)‐poly(ethylene glycol) (XGP) are used measure the amount of drug released into cells. The photoactive drug protoporphyrin IX (PpIX) is loaded into XGP and is able to attenuate the XEOL NP emission. Measuring an increase in XEOL intensity as PpIX is released enables the measurement of drug release into glioblastoma cells (GBM). Biodistribution studies in a BALB/c mouse GBM intracranial xenograft model show significant XGP accumulation at the site of the GBM xenograft within the brain, and not in adjacent healthy brain tissues. There is no uptake of XGP in the heart or kidneys, the primary organs associated with drug and gadolinium ion toxicity. NP toxicity is tested with U‐138MG GBM in vitro, and NPs show low cytotoxicity at concentrations of 100 μg/mL. In vivo dose escalation studies in BALB/c mice show no adverse effects at doses up to 75 mg/kg. These theranostic NPs offer an approach to quantitatively measure drug release into cells.

MO‐D‐141‐07: X‐Ray Activated Gold Nanoparticles for Tumor‐Specific Molecular Imaging

Purpose: X‐ray radiography and computed tomography are commonly used anatomical imaging modalities still have significant shortcomings in sensitivity and specificity. Molecular imaging based on tumor‐specific nanoparticles that can probe biochemical processes in vivo can provide characterization and identification of benign and malignant lesions on the cellular level. In particular, radioluminescent nanoparticles (RLNPs) are the ideal platform for X‐ray‐mediated imaging and synergistic therapy during radiation treatment. These unique particles can emit visible light under X‐ray irradiation. However, existing RLNPs based on lanthanides may cause toxicity in vivo. Here we report new intriguing radioluminescent properties of a new type of nanoparticles made by arranging a small number of gold atoms. The objective of this work is to examine practical aspects of a new imaging modality: light emission and spectral emission characteristics. Methods: Bare gold nanoparticles (4 and 1.8 nm) and conjugated gold nanoparticles with size less than 2 nm (25 atoms size) were synthesized. Imaging was performed by irradiating the samples with X‐ray (30–80 kVp, 10–30 mA) while acquiring 10 s frames with an EMCCD camera (Princeton Instruments, 300–900 nm). The samples were further characterized by using a custom PMT‐based system. The spectral properties of the emission were measured under both optical and X‐ray excitation using a sensitive spectrometer. Results: It was found that tested gold nanoparticles had different responses to x‐ray excitation. Au25‐BSA is the most promising candidate for x‐ray luminescence imaging, with up to 4‐6‐fold increase in the optical signal compared to the controls. Conclusion: In this work, it was first time demonstrated the optical detection of small atom number gold nanoparticles excited by x‐ray source. Development of a new optical imaging probes will allow us to take advantage of the desirable features of optical molecular imaging and achieve substantially improved spatiotemporal resolution, sensitivity and specificity for tumor detection.

Radioluminescent nanophosphors enable multiplexed small-animal imaging

We demonstrate the ability to image multiple nanoparticle-based contrast agents simultaneously using a nanophosphor platform excited by either radiopharmaceutical or X-ray irradiation. These radioluminescent nanoparticles emit optical light at unique wavelengths depending on their lanthanide dopant, enabling multiplexed imaging. This study demonstrates the separation of two distinct nanophosphor contrast agents in gelatin phantoms with a recovered phosphor separation correlation of −0.98. The ability to distinguish the two nanophosphors and a Cerenkov component is then demonstrated in a small animal phantom. Combined with the high-resolution potential of low-scattering X-ray excitation, this imaging technique may be a promising method to probe molecular processes in living organisms.

Magnetic and optical properties of multifunctional core-shell radioluminescence nanoparticles.

When X-rays irradiate radioluminescence nanoparticles, they generate visible and near infrared light that can penetrate through centimeters of tissue. X-ray luminescence tomography (XLT) maps the location of these radioluminescent contrast agents at high resolution by scanning a narrow X-ray beam through the tissue sample and collecting the luminescence at every position. Adding magnetic functionality to these radioluminescent particles would enable them to be guided, oriented, and heated using external magnetic fields, while their location and spectrum could be imaged with XLT and complementary magnetic resonance imaging. In this work, multifunctional monodispersed magnetic radioluminescent nanoparticles were developed as potential drug delivery carriers and radioluminescence imaging agents. The particles consisted of a spindle-shaped magnetic γ-Fe2O3 core and a radioluminescent europium-doped gadolinium oxide shell. Particles with solid iron oxide cores displayed saturation magnetizations consistent with their ~13% core volume, however, the iron oxide quenched their luminescence. In order to increase the luminescence, we partially etched the iron oxide core in oxalic acid while preserving the radioluminescent shell. The core size was controlled by the etching time which in turn affected the particles' luminescence and magnetic properties. Particles with intermediate core sizes displayed both strong magnetophoresis and luminescence properties. They also served as MRI contrast agents with relaxivities of up to 58 mM-1s-1 (r2) and 120 mM-1s-1 (r2*). These particles offer promising multimodal MRI/fluorescence/X-ray luminescence contrast agents. Our core-shell synthesis technique offers a flexible method to control particle size, shape, and composition for a wide range of biological applications of magnetic/luminescent nanoparticles.

Limited-angle x-ray luminescence tomography: methodology and feasibility study

X-ray luminescence tomography (XLT) has recently been proposed as a new imaging modality for biological imaging applications. This modality utilizes phosphor nanoparticles which luminesce near-infrared light when excited by x-ray photons. The advantages of this modality are that it uniquely combines the high sensitivity of radioluminescent nanoparticles and the high spatial localization of collimated x-ray beams. Currently, XLT has been demonstrated using x-ray spatial encoding to resolve the imaging volume. However, there are applications where the x-ray excitation may be limited by geometry, where increased temporal resolution is desired, or where a lower dose is mandatory. This paper extends the utility of XLT to meet these requirements by incorporating a photon propagation model into the reconstruction algorithm in an x-ray limited-angle (LA) geometry. This enables such applications as image-guided surgery, where the ability to resolve lesions at depths of several centimeters can be the key to successful resection. The hybrid x-ray/diffuse optical model is first formulated and then demonstrated in a breast-sized phantom, simulating a breast lumpectomy geometry. Both numerical and experimental phantoms are tested, with lesion-simulating objects of various sizes and depths. Results show localization accuracy with median error of 2.2 mm, or 4% of object depth, for small 2–14 mm diameter lesions positioned from 1 to 4.5 cm in depth. This compares favorably with fluorescence optical imaging, which is not able to resolve such small objects at this depth. The recovered lesion size has lower size bias in the x-ray excitation direction than the optical direction, which is expected due to the increased optical scatter. However, the technique is shown to be quite invariant in recovered size with respect to depth, as the standard deviation is less than 2.5 mm. Sensitivity is a function of dose; radiological doses are found to provide sufficient recovery for µg ml−1 concentrations, while therapy dosages provide recovery for ng ml−1 concentrations. Experimental phantom results agree closely with the numerical results, with positional errors recovered within 8.6% of the effective depth for a 5 mm object, and within 5.2% of the depth for a 10 mm object. Object-size median error is within 2.3% and 2% for the 5 and 10 mm objects, respectively. For shallow-to-medium depth applications where optical and radio-emission imaging modalities are not ideal, such as in intra-operative procedures, LAXLT may be a useful tool to detect molecular signatures of disease.