Abstract
Recent progress in functionalized lanthanide oxide (Ln2O3) nanoparticles for tumor targeting, medical imaging, and therapy is reviewed. Among the medical imaging techniques, magnetic resonance imaging (MRI) is an important noninvasive imaging tool for tumor diagnosis due to its high spatial resolution and excellent imaging contrast, especially when contrast agents are used. However, commercially available low-molecular-weight MRI contrast agents exhibit several shortcomings, such as nonspecificity for the tissue of interest and rapid excretion in vivo. Recently, nanoparticle-based MRI contrast agents have become a hot research topic in biomedical imaging due to their high performance, easy surface functionalization, and low toxicity. Among them, functionalized Ln2O3 nanoparticles are applicable as MRI contrast agents for tumor-targeting and nontumor-targeting imaging and image-guided tumor therapy. Primarily, Gd2O3 nanoparticles have been intensively investigated as tumor-targeting T1 MRI contrast agents. T2 MRI is also possible due to the appreciable paramagnetic moments of Ln2O3 nanoparticles (Ln = Dy, Ho, and Tb) at room temperature arising from the nonzero orbital motion of 4f electrons. In addition, Ln2O3 nanoparticles are eligible as X-ray computed tomography contrast agents because of their high X-ray attenuation power. Since nanoparticle toxicity is of great concern, recent toxicity studies on Ln2O3 nanoparticles are also discussed.
Highlights
Medical imaging plays an important role in the pre-detection, diagnosis, and treatment of tumors [1]
Lanthanide oxide (Ln2 O3 ) nanoparticles (Ln = Gd, Tb, Dy, and Ho) are of special interest because they have appreciable magnetic moments at room temperature, which is useful for magnetic resonance imaging (MRI) [12,13,14,15], and high X-ray attenuation power, which is useful for X-ray computed tomography (CT) [16,17,18]
Among the various methods currently available for the synthesis of ultrasmall Ln2 O3 nanoparticles, the synthesis in a polyol solvent is preferred for biomedical applications because ultrasmall nanoparticles are obtained and subsequent surface coating of the nanoparticles with hydrophilic and biocompatible ligands can be performed in one pot [17,31]
Summary
Medical imaging plays an important role in the pre-detection, diagnosis, and treatment of tumors [1]. MR images and are ideal candidates for tumor-targeting T1 MRI contrast agents Their r1 value is optimal at ultrasmall nanoparticle size (1.0–2.5 nm) [24,25]. The accumulation amount and specificity to tumors can be enhanced by active targeting, which is commonly achieved by modifying contrast agents with tumor-targeting ligands that can selectively bind to receptors overexpressed on tumor-cell membranes. Anticancer drugs can be attached to nanoparticle surfaces for chemotherapy In this type of treatment, most anticancer drugs cannot differentiate between tumor and normal cells, causing toxic side effects [35,36]. Nanoparticle synthesis methods, surface-modification, tumortargeting ligand conjugation, and various experimental analyses for Ln2 O3 nanoparticles are introduced Physicochemical properties, such as particle diameters and magnetic properties, and imaging properties, including relaxivities, are discussed. This review provides an overview of the recent progress in functionalized Ln2 O3 nanoparticles applied in tumor imaging and therapy
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