Radioiodine 131 ((131)I) has been used worldwide for the ablation of remnant thyroidal tissue after surgery or as the first-line treatment for Graves' disease. Although the use of (131)I is becoming increasingly prevalent, there is evidence suggesting that this treatment is associated with side effects such as salivary gland dysfunction and an increased risk of leukemia. This article aims to review the potential use of radioprotective agents and the side effects induced by (131)I therapy. Several synthetic and natural compounds have been investigated in preclinical and clinical studies. The protective agents reduced the toxicity of (131)I, mainly in the salivary glands, and mitigated the genetic damage through different mechanisms. There are limited clinical studies evaluating the use of radioprotective agents in patients undergoing radioiodine therapy. However, lemon candies, lemon juice and sugarless chewing gum have been proposed to be beneficial for minimizing the side effects of radioiodine within the salivary glands.

The high expression of the human epidermal growth factor receptor 2 (HER2) and the accessibility of its extracellular domain make it an ideal target for the targeted delivery of anti-tumor drugs as well as imaging agents. In this study, the heptapeptide leucine-threonine-valine-serine-proline-tryptophan-tyrosine (LTVSPWY) as a new small peptide for an anti-HER2 target was labeled by incorporating Tc to the cysteine-based ligands CGGG (Cys-Gly-Gly-Gly) and CSSS (Cys-Ser-Ser-Ser) linked to this peptide. BothTc-labeled peptides were evaluated for HER2 bindings as well as pharmacokinetics and tumor targeting. CGGG- and CSSS-LTVSPWY peptides were labeled with Tc using a gluconate ligand exchange. Cellular specific binding, affinities, and internalization of both peptides to the HER2 receptor were evaluated in the SKOV-3 cell line. Specific targeting of both peptides to the HER2 receptor was assessed in three cell lines with different levels of HER2 expression. Studies were performed in SKOV-3 tumor bearing mice for tumor targeting. Both peptides were labeled withTc with more than 99% efficiency and showed favorable stability in solution and serum. The HER2 binding affinities of both the radiolabeled peptides were inhibited up to 60% by the unlabeled peptide, as well as with trastuzumab antibody. We observed nanomolar binding affinities for both radiolabeled peptides. The tumor uptakes were 4.95 ± 4.84% and 3.84 ± 2.53% for the CSSS and CGGG chelators, respectively, at 1 h after injection. However, tumor uptakes were similar for both peptides at 4 h postinjection, although a higher tumor to background ratio and lower radioactivity retention in the kidney were observed for CSSS, leading to a clearer tumor image with injection of this peptide. These small new peptides were selectively targeted to the HER2 receptor, and introduction of a serine residue into the chelator improved the pharmacokinetics of Tc labeled LTVSPWY for clear tumor imaging in animals.

AS1411, a 26-base guanine-rich oligonucleotide aptamer, has high affinity to nucleolin, mainly on tumor cell surfaces. In this study, a modified AS1411 was labeled with (99m)Tc and evaluated as a potential tumor-targeting agent for imaging. The AS1411 aptamer was conjugated with HYNIC and labeled with (99m)Tc in the presence a co-ligand. Radiochemical purity and stability testing of the (99m)Tc-HYNIC-AS1411 aptamer were carried out with thin layer chromatography and a size-exclusion column in normal saline and human serum. Cellular nucleolin-specific binding, cellular internalization in DU-145 cells, as high levels of nucleolin expression, were performed. Additionally, biodistribution in normal mice and DU-145 tumour-bearing mice was assessed. Radiolabeling of the aptamer resulted in a reasonable yield and radiochemical purity after purification. The aptamer was stable in normal saline and human serum, and cellular experiments demonstrated specific binding of the AS1411 aptamer to the nucleolin protein. Based on biodistribution assessment of (99m)Tc-HYNIC-AS1411, rapid blood clearance was seen after injection and it appears that the excretion route was via the urinary system at 1 h post-injection. Tumours also showed a higher accumulation of radioactivity with this labeled aptamer. (99m)Tc-AS1411 can be a potential tool for the molecular imaging of nucleolin-overexpressing cancers.

BackgroundOvarian cancer is a serious threat for women health and the early diagnosis of this cancer might improves the survival rate of patients. The use of the targeted radiopharmaceuticals could be a non-invasive and logical method for tumor imaging. The aim of this study was to radiolabel GE11 peptide as a new specific probe for imaging of ovarian tumor.MethodsHYNIC-SSS-GE11 peptide was labeled with 99mTc using tricine as a coligand. The 99mTc-tricine-HYNIC-SSS-GE11 peptide was evaluated for specific cellular binding in three cell lines with different levels of EGFR expression. Tumor targeting was assessed in SKOV3 tumor bearing mice.ResultsBy using tricine as a coligand, labeling yield was more than 98% and the stability of the radiolabelled peptide in human serum up to 4 h was 96%. The in vitro cell uptake test showed that this radiolabeled peptide had a good affinity to SKOV3 cells with dissociation constant of 73 nM. The in vivo results showed a tumor/muscle ratio of 3.2 at 4 h following injection of 99mTc-tricine-HYNIC-SSS-GE11 peptide.ConclusionsResults of this study showed that 99mTc-tricine-HYNIC-SSS-GE11 peptide could be a promising tool for diagnosis and staging of ovarian cancer.Graphical Abstract 99mTc-tricine-HYNIC-SSS-GE11, a novl targeted agent for ovarian tumor imaging

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