Biodistribution of Nanoradiopharmaceuticals in Internal Organs

Conjugation of nanomedicine and radiopharmacy treats a new research and technology area that is named nanoradiopharmacy. It has great advantages in disease diagnosis and control and subsequent therapy, due to the ability to develop molecular diagnostics for the early detection of disease as well as the ability to develop increasingly personalized and individualized treatments. Nanostructured materials attracted considerable attention because of their high surface area to volume ratio resulting from their nanoscale dimensions. This class of sorbents is expected to have a potential impact on enhancing the efficacy of radioisotope generators for diagnostic and therapeutic applications in nuclear medicine. Radiolabelled nanoparticles represent a novel class of radiopharmaceutical agents with great potential in cancer research. The radiolabelled nanoparticles can be used for specific tumour imaging or for effective tumour treatment by specific radiation. Various kinds of nanoradiopharmaceuticals, such as Tc-99m nanogels, have been industrialized and applied for disease diagnosis purposes. But, nanoradiopharmacy like other technologies has its own limitations that must be considered. Nanoparticles have several orders of magnitude larger than classical drugs and represent an important advancement in drug therapy because they can be assembled as multimolecular complexes including not only pharmacologically-active molecules, but also molecules for selective targeting to specific tissues. The Liver and spleen have important roles in nanoparticles pharmacokinetics. The spleen has a mechanism for sequestrating nanoparticles. A preferential accumulation in the liver and in the spleen was observed by researchers. It was found that unmodified nanoparticles disappear from the blood in seconds or minutes after their injection. Renal filtration has a significant role in this process if their size is smaller than 15 nm, whereas for nanoparticles larger than 40 nm, their disappearance from the blood is mainly dependent on their accumulation in cells of the reticuloendothelial system. This significantly reduces nanoparticle half-life and represents a major barrier for the implementation of their clinical use. Nanoparticle uptake is mainly operated by liver Kupffer cells, but splenic macrophages also have a significant role. Splenic capture can be used to selectively deliver old drugs to the spleen. Additionally, researchers found that spleen capture is a limiting factor in nanoparticle pharmacokinetics and that it has to be overridden in order to optimize its therapeutic effects. In most cases after injection of nanoradiopharmaceuticals, due to the pharmacokinetics role the radioactivity is detected in the liver and spleen. Hence, increasing the internal radiation dose in liver and spleen may initiate the creation of some kind of diseases for the liver and spleen. Radiation induced toxicities in non-tumourous liver tissues are associated with the development of numerous symptoms or have serious chronic side effects. (author)