Development of neutron-activated samarium-153-loaded polystyrene microspheres as a potential theranostic agent for hepatic radioembolization

Development of samarium-doped phosphate glass microspheres for internal radiotheranostic applications

Internal radiotherapy delivers radioactive sources inside the body, near to or into malignant tumours, which may be particularly effective when malignancies are not responding to external beam radiotherapy. A pure beta emitter, 90Y, is currently used for internal radiotherapy. However, theranostic radionuclide-doped microspheres can be developed by incorporating 153Sm, which emits therapeutic beta and diagnostic gamma energies. This study investigated the production of high concentrations of samarium-content doped phosphate-based glass microspheres. The glass P60 (i.e. 60P2O5-25CaO-15Na2O) was mixed with Sm2O3 at ratios of 75:25 (G75:Sm25), 50:50 (G50:Sm50) and 25:75 (G25:Sm75) and processed via flame spheroidisation. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) confirmed the microsphere uniformity with significantly high samarium content up to 44 % in G25:Sm75. Via X-ray diffraction (XRD) analysis, samarium-doped microspheres appeared to be glass-ceramic in nature. Mass-loss, size and pH changes were performed over 28 days, revealing a significant increase in samarium microsphere stability. After 15 min of neutron activation (neutron flux 3.01 × 1013 n.cm-2.s-1), the specific activity of the microspheres (G75:Sm25, G50:Sm50 and G25:Sm75) was 0.28, 0.54 and 0.58 GBq.g-1, respectively. Therefore, the samarium microspheres produced in this study provide great potential for improving internal radiotherapy treatment for liver cancer by avoiding complex procedures and using less microspheres with shorter irradiation time.

Development and physicochemical characterization of a biodegradable microspheres formulation loaded with samarium-153 and doxorubicin for chemo-radioembolization of liver tumours

Transarterial chemoembolization (TACE) and transarterial radioembolization (TARE) are promising treatments for unresectable liver tumours. Some recent studies suggested that combining TACE and TARE in one treatment course might improve treatment efficacy through synergistic cytotoxicity effects. Nonetheless, current formulations do not facilitate a combination of chemo- and radio-embolic agents in one delivery system. Therefore, this study aimed to synthesise a hybrid biodegradable microsphere loaded with both radioactive agent, samarium-153 (153 Sm) and chemotherapeutic drug, doxorubicin (Dox) for potential radio-chemoembolization of advanced liver tumours. 152 Sm and Dox-loaded polyhydroxybutyrate-co-3-hydroxyvalerate (PHBV) microspheres were prepared using water-in-oil-in-water solvent evaporation method. The microspheres were then sent for neutron activation in a neutron flux of 2 × 1012  n/cm2 /s. The physicochemical properties, radioactivity, radionuclide purity, 153 Sm retention efficiency, and Dox release profile of the Dox-153 Sm-PHBV microspheres were analysed. In addition, in vitro cytotoxicity of the formulation was tested using MTT assay on HepG2 cell line at 24 and 72 h. The mean diameter of the Dox-153 Sm-PHBV microspheres was 30.08 ± 2.79 μm. The specific radioactivity was 8.68 ± 0.17 GBq/g, or 177.69 Bq per microsphere. The 153 Sm retention efficiency was more than 99%, tested in phosphate-buffered saline (PBS) and human blood plasma over 26 days. The cumulative release of Dox from the microspheres after 41 days was 65.21 ± 1.96% and 29.96 ± 0.03% in PBS solution of pH 7.4 and pH 5.5, respectively. The Dox-153 Sm-PHBV microspheres achieved a greater in vitro cytotoxicity effect on HepG2 cells (85.73 ± 3.63%) than 153 Sm-PHBV (70.03 ± 5.61%) and Dox-PHBV (74.06 ± 0.78%) microspheres at 300 μg/mL at 72 h. In conclusion, a novel biodegradable microspheres formulation loaded with chemotherapeutic drug (Dox) and radioactive agent (153 Sm) was successfully developed in this study. The formulation fulfilled all the desired physicochemical properties of a chemo-radioembolic agent and achieved better in vitro cytotoxicity on HepG2 cells. Further investigations are needed to evaluate the biosafety, radiation dosimetry, and synergetic anticancer properties of the formulation.

Evaluation of Therapeutic Efficacy and Imaging Capabilities of 153Sm2O3-Loaded Polystyrene Microspheres for Intra-Tumoural Radionuclide Therapy of Liver Cancer Using Sprague-Dawley Rat Model

Introduction: Neutron-activated samarium-153-oxide-loaded polystyrene ([¹⁵³Sm]Sm₂O₃-PS) microspheres has been developed in previous study as a potential theranostic agent for hepatic radioembolization. In this study, the therapeutic efficacy and diagnostic imaging capabilities of the formulation was assessed using liver cancer Sprague-Dawley (SD) rat model. Methods: Twelve male SD rats (150-200 g) that implanted with N1-S1 hepatoma cell line orthotopically were divided into two groups (study versus control) to monitor the tumour growth along 60 days of treatment. The study group received an intra-tumoural injection of approximately 37 MBq of [¹⁵³Sm]Sm₂O₃-PS microspheres, while control group received an intra-tumoural injection of 0.1 mL of saline solution. A clinical single photon emission computed tomography/computed tomography (SPECT/CT) system was used to scan the rats at Day 5 post-injection to investigate the diagnostic imaging capabilities of the microspheres. All rats were monitored for change in tumour volume using a portable ultrasound system throughout the study period. Histopathological examination (HPE) was performed after the rats were euthanized at Day 60. Results: At Day 60, no tumour was observed on the ultrasound images of all rats in the study group. In contrast, the tumour volumes in the control group were 24-fold larger compared to baseline. Statistically significant difference was observed in tumour volumes between the study and control groups (p < 0.05). The SPECT/CT images clearly displayed the location of [¹⁵³Sm]Sm₂O₃-PS in the liver tumour of all rats at Day 5 post-injection. Additionally, the [¹⁵³Sm]Sm₂O₃-PS microspheres was visible on the CT images and this has added to the benefits of ¹⁵³Sm as a CT contrast agent. The HPE results showed that the [¹⁵³Sm]Sm₂O₃-PS microspheres remained concentrated at the injection site with no tumour cells observed in the study group. Conclusions: Neutron-activated [¹⁵³Sm]Sm₂O₃-PS microspheres demonstrated excellent therapeutic and diagnostic imaging capabilities for theranostic treatment of liver cancer in a SD rat model. Further studies with different animal and tumour models are planned to validate this finding.

SIRT in 2025

Selective internal radiation therapy represents an endovascular treatment option for patients with primary liver malignancies, in different clinical stages. Potential applications of this treatment are in early-stage hepatocellular carcinoma, as a curative option, or in combination with systemic treatments in intermediate and advanced-stages. This review, based on existing literature and ongoing trials, will focus on the future of this treatment in patients with hepatocellular carcinoma, in combination with systemic treatments, or with the use of new devices and technological developments; it will also describe new potential future indications and structural and organizational perspectives.