Radioactive Microspheres for Medical Applications

The Use of Microspheres for Cancer Embolization Therapy: Recent Advancements and Prospective

Embolization therapy involving biomaterials has improved the therapeutic strategy for most liver cancer treatments. Developing biomaterials as embolic agents has significantly improved patients' survival rates. Various embolic agents are present in liquid agents, foam, particulates, and particles. Some of the most applied embolic agents are microparticles, such as microspheres (3D micrometer-sized spherical particles). Microspheres with added functionalities are currently being developed for effective therapeutic embolization. Their excellent properties of high surface area and capacity for being loaded with radionuclides and alternate active or therapeutic agents provide an additional advantage to overcome limitations from traditional cancer treatments. Microspheres (non-radioactive and radioactive) have been widely used and explored for localized cancer treatment. Non-radioactive microspheres exhibit improved clinical performance as drug delivery vehicles in chemotherapy due to their controlled and sustained drug release to the target site. They offer better flow properties and are beneficial for the ease of delivery via injection procedures. In addition, radioactive microspheres have also been exploited for use as an embolic platform in internal radiotherapy as an alternative to cancer treatment. This short review summarizes the progressive development of non-radioactive and radioactive embolic microspheres, emphasizing material characteristics. The use of embolic microspheres for various modalities of therapeutic arterial embolization and their impact on therapeutic performance are also discussed.

DEVELOPMENT AND ESTIMATION OF HUMAN DOSIMETRY OF A NEW 47SC-RISEDRONATE FOR RADIOPHARMACEUTICAL APPLICATION

Bisphosphonate risedronate (2-(3-pyridinyl)-1-hydroxyethane diphosphonic acid) was radiolabeled with scandium-47 (47Sc) as potential therapeutic radiopharmaceutical for skeletal metastases. Its time-dependent biodistribution in mice was measured and its human dosimetry was derived. The labelling process was performed at 95 °C for 30 min. The stability of the radio-conjugate was tested in human serum at 37 °C and its biodistribution was studied in balb/c mice. The radiochemical yield of ≥90% was obtained corresponding to a specific activity of 277 MBq/mg. The radio-conjugate showed good stability in human serum up to 48 h. A high bone uptake by 48 h post-injection was achieved, which suggests that 47Sc-risedronate may be therapeutically beneficial for the palliation of painful bone metastasis. The estimated absorbed dose coefficient and the time-integrated activity coefficient (ã (rs, TD)) in the bone were 1.35 mGy/MBq and 31.04 (Bq-h/Bq), respectively. The absorbed doses to non-osseous normal organs were much lower than that to the bone.

Cenosphere-Based Zeolite Precursors of Lutetium Encapsulated Aluminosilicate Microspheres for Application in Brachytherapy

Coal fly ash hollow aluminosilicate microspheres (cenospheres) of stabilized composition (glass phase-95.4; (SiO₂/Al₂O₃)_glass-3.1; (Si/Al)_at. = 2.6) were used to fabricate lutetium-176 encapsulated aluminosilicate microspheres as precursors of radiolabeled microspheres applied for selective irradiation of tumors. To incorporate Lu³⁺ ions into cenosphere's aluminosilicate material, the following strategy was realized: (i) chemical modification of cenosphere globules by conversion of aluminosilicate glass into zeolites preserving a spherical form of cenospheres; (ii) loading of zeolitized microspheres with Lu³⁺ by means of ion exchange 3Na⁺ ↔ Lu³⁺; (iii) Lu³⁺ encapsulation in an aluminosilicate matrix by solid-phase transformation of the Lu³⁺ loaded microspheres under thermal treatment at 1273-1473 K. Two types of zeolitized products, such as NaX (FAU) and NaP1 (GIS) bearing microspheres having the specific surface area of 204 and 33 m²/g, accordingly, were prepared and their Lu³⁺ sorption abilities were studied. As revealed, the Lu³⁺ sorption capacities of the zeolitized products are about 130 and 70 mg/g Lu³⁺ for NaX and NaP1 microspheres, respectively. It was found that the long-time heating of the Lu³⁺-loaded zeolite precursors at 1273 K in a fixed bed resulted in the crystallization of monoclinic Lu₂Si₂O₇ in both zeolite systems, which is a major component of crystalline constituents of the calcined microspheres. The fast heating-cooling cycle at 1473 K in a moving bed resulted in the amorphization of zeolite components in both precursors and softening glass crystalline matter of the NaX-bearing precursor with preserving its spherical form and partial elimination of surface open pores. The NaX-bearing microspheres, compared to NaP1-based precursor, are characterized by uneven Lu distribution over the zeolite-derived layer. The precursor based on gismondin-type zeolite provides a near-uniform Lu distribution and acceptable Lu content (up to 15 mol.% Lu₂O₃) in the solid phase.

Preliminary evaluation of indigenous 90 Y-labelled microspheres for therapy of hepatocellular carcinoma

Background & objectives:

Yttrium-90 (⁹⁰Y)-based radioembolization has been employed to treat hepatocellular carcinoma (HCC) as commercial radioactive glass and polymeric resin microspheres. However, in India and other Asian countries, these preparations must be imported and are expensive, validating the need for development of indigenous alternatives. This work was aimed to develop an economically and logistically favourable indigenous alternative to imported radioembolizing agents for HCC therapy.

Methods:

The preparation of ⁹⁰Y-labelled Biorex 70 microspheres was optimized and in vitro stability was assessed. Hepatic tumour model was generated in Sprague-Dawley rats by orthotopic implantation of N1S1 rat HCC cell line. In vivo localization and retention of the ⁹⁰Y-labelled Biorex 70 microspheres was assessed for seven days, and impact on N1S1 tumour growth was studied by histological examination and biochemical assays.

Results:

Under optimal conditions, >95% ⁹⁰Y-labelling yield of Biorex70 resin microspheres was obtained, and these showed excellent in vitro stability of labelling (>95%) at seven days. In animal studies, ⁹⁰Y-labelled Biorex 70 microspheres were retained (87.72±1.56% retained in liver at 7 days). Rats administered with ⁹⁰Y-labelled Biorex 70 microspheres exhibited lower tumour to liver weight ratio, reduced serum alpha-foetoprotein level and greater damage to tumour tissue as compared to controls.

Interpretation & conclusions:

⁹⁰Y-labelled Biorex 70 microspheres showed stable retention in the liver and therapeutic effect on tumour tissue, indicating the potential for further study towards clinical use.

Carboxylate microsphere-induced cellular toxicity in human lung fibroblasts

Carboxylate microspheres (CMs) are mainly used in industrial, biomedical and various household products. In this study, we assessed the cytotoxic effects of CMs on human MRC-5 lung fibroblasts by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Oxidative stress was determined by measurements of reactive oxygen species and antioxidant (superoxide dismutase and catalase) levels and proinflammatory cytokines quantified by enzyme-linked immunosorbent assay. Morphological changes were examined by light microscopy, confocal microscopy and transmission electron microscopy. The lung fibroblasts were exposed to increasing concentrations of CMs (0.1–1000 μmol/L) for 24 h. The results showed significant changes in cell morphology with induction of cytotoxicity and oxidative stress observed in 10–1000 μmol/L concentrations of CM-treated fibroblasts. Ultrastructural examination revealed the presence of CMs inside the cytoplasm of treated lung fibroblasts. CMs also induced elevated interleukin (IL)-1, IL-6, IL-8, IL-10 and tumor necrosis factor α levels at higher concentrations. We have demonstrated that CMs significantly reduce cell viability in a dose-dependant manner in lung fibroblasts at 0.1–1000 μmol/L doses. The findings suggest that high doses of CMs have the potential to induce cellular toxicity to the lung in vitro.

A starch-based microparticulate system dedicated to diagnostic and therapeutic nuclear medicine applications

The aim of this work was to develop a new microparticulate system able to form a complex with radionuclides with a high yield of purity for diagnostic or therapeutic applications. Owing to its properties potato starch was chosen as starting material and modified by oxidization and coupling of a ligand (polyamine) enabling modified starch to chelate radionuclides. The choice of suitable experiments was based on a combination of a Rechtschaffner experimental design and a surface response design to determine the influence of experimental parameters and to optimize the final product. Starch-based microparticle formulations from the experimental plans were compared and characterized through particle size analysis, scanning electron microscopy, elemental analysis and, for the most promising formulations, by in vitro labeling stability studies and determination of free polyamine content or in vivo imaging studies. The mechanism of starch-based microparticle degradation was identified by means of size measurements. The results of the Rechtschaffner design showed the positive qualitative effect of the temperature and the duration of coupling reaction whereas surface response analysis clearly showed that, by increasing the oxidization level and starch concentration, the nitrogen content in the final product is increased. In vitro and in vivo characterization led to identification of the best formulation. With a size around 30 μm, high radiochemical purity (over 95%) and a high signal-to-noise ratio (over 600), the new starch-based microparticulate system could be prepared as ready-to-use kits and sterilized without modification of its characteristics, and thus meet the requirement for in vivo diagnostic and therapeutic applications.