Internal radiation therapy: a neglected aspect of nuclear medicine in the molecular era

Radioactive Iodine in Differentiated Carcinoma of Thyroid: An Overview

Thyroid cancer is the fifth most prevalent cancer in women and the fastest-growing malignancy. Although surgery is still the basis of treatment, internal radiation therapy (Brachytherapy) with radioactive iodine-131, which functions by releasing beta particles with low tissue penetration and causing DNA damage, is also a potential option. The three basic aims of RAI therapy in well-differentiated thyroid tumors are ablation of the remnant, adjuvant therapy, and disease management. Radioactive iodine dose is selected in one of two ways, empiric and dosimetric, which relies on numerous criteria. The dosage for ablation is 30-100 mCi, 30-150 mCi for adjuvant therapy, and 100-200 mCi for treatment. The RAI treatment effectively aids in the treatment to achieve complete removal of the disease and increase survival. The present review intends to emphasize the significance of radioactive iodine in the management of differentiated thyroid cancer and put forward the current breakthroughs in therapy.

Changes in Serum Alkaline Phosphatase, Calcium, and Parathyroid Hormone with Different Doses of Iodine Therapy:

Background: Despite the benefits of radioactive iodine (RAI) therapy as an adjunctive treatment for thyroid cancer, it can be associated with several side effects. The main purpose of this study was to determine the changes in serum alkaline phosphatase (ALP), calcium (Ca), and parathyroid hormone (PTH) at different doses of RAI therapy among patients who were referred to the nuclear medicine department of Namazi Hospital, Shiraz. Materials and Methods: This cross-sectional study was conducted on 60 patients with papillary thyroid cancer who underwent RAI therapy at different doses of 100, 150, and 200 mCi. The ALP, Ca, and PTH levels of patients were measured before and 60 days after RAI therapy. Results: Our study revealed that RAI therapy at all doses significantly increased ALP level in comparison with baseline amounts (P≤0.05). However, changes in PTH and Ca levels were not significant among patients who received different doses of RAI (P˃0.05). Conclusion: RAI therapy could affect important hormones and enzymes such as ALP and PTH. This issue can be considered in diagnostic and therapeutic prescriptions of RAI for the treatment of thyroid cancer.[GMJ.2022;11:e2397].

Ionizing Radiation from Radiopharmaceuticals and the Human Gut Microbiota: An Ex Vivo Approach

This study aimed to determine the effect of three widely used radiopharmaceuticals with intestinal excretion on selected relevant bacteria that are part of the human gut microbiota, using an ex vivo approach. Fecal samples obtained from healthy volunteers were analyzed. Each sample was divided into four smaller aliquots. One served as the non-irradiated control. The other three were homogenized with three radiopharmaceutical solutions ([¹³¹I]NaI, [^99mTc]NaTcO₄, and [²²³Ra]RaCl₂). Relative quantification of each taxa was determined by the 2^−ΔΔC method, using the ribosomal gene 16S as an internal control (primers 534/385). Twelve fecal samples were analysed: three controls and nine irradiated. Our experiment showed fold changes in all analyzed taxa with all radiopharmaceuticals, but results were more significant with I-131, ranging from 1.87–83.58; whereas no relevant differences were found with Tc-99m and Ra-223, ranging from 0.98–1.58 and 0.83–1.97, respectively. This study corroborates limited existing research on how ionizing radiation changes the gut microbiota composition, providing novel data regarding the ex vivo effect of radiopharmaceuticals. Our findings justify the need for future larger scale projects.

131I-Caerin 1.1 and 131I-Caerin 1.9 for the treatment of non-small-cell lung cancer

Objective

To investigate the effect of the ¹³¹I-labeled high-affinity peptides Caerin 1.1 and Caerin 1.9 for the treatment of A549 human NSCLC cells.

Methods

① 3-[4,5-Dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and plate clone formation assays were performed to confirm the in vitro anti-tumor activity of Caerin 1.1 and Caerin 1.9. ② Chloramine-T was used to label Caerin 1.1 and Caerin 1.9 with ¹³¹I, and the Cell Counting Kit 8 assay was performed to analyze the inhibitory effect of unlabeled Caerin 1.1, unlabeled Caerin 1.9, ¹³¹I-labeled Caerin 1.1, and ¹³¹I-labeled Caerin 1.9 on the proliferation of NSCLC cells. An A549 NSCLC nude mouse model was established to investigate the in vivo anti-tumor activity of unlabeled Caerin 1.1, unlabeled Caerin 1.9, ¹³¹I-labeled Caerin 1.1, and ¹³¹I-labeled Caerin 1.9.

Results

① Caerin 1.1 and Caerin 1.9 inhibited the proliferation of NSCLC cells in vitro in a concentration-dependent manner. The half-maximal inhibitory concentration was 16.26 µg/ml and 17.46 µg/ml, respectively, with no significant intergroup difference (P>0.05). ② ¹³¹I-labeled Caerin 1.1 and ¹³¹I-labeled Caerin 1.9 were equally effective and were superior to their unlabeled versions in their ability to inhibit the proliferation and growth of NSCLC cells (P>0.05).

Conclusions

¹³¹I-labeled Caerin 1.1 and ¹³¹I-labeled Caerin 1.9 inhibit the proliferation and growth of NSCLC cells and may become potential treatments for NSCLC.

Radiotherapy and Its Impact on the Nervous System of Cancer Survivors

Radiotherapy is routinely used for the treatment of nearly all brain tumors, but it may lead to progressive and debilitating impairments of cognitive function. The growing evidence supports the fact that radiation exposure to CNS disrupts diverse cognitive functions including learning, memory, processing speed, attention and executive functions. The present review highlights the types of radiotherapy and the possible mechanisms of cognitive deficits and neurotoxicity following radiotherapy. The review summarizes the articles from Scopus, PubMed, and Web of science search engines. Radiation therapy uses high-powered x-rays, particles, or radioactive seeds to kill cancer cells, with minimal damage to healthy cells. While radiotherapy has yielded relative success in the treatment of cancer, patients are often plagued with unwanted and even debilitating side effects from the treatment, which can lead to dose reduction or even cessation of treatment. Little is known about the underlying mechanisms responsible for the development of these behavioral toxicities; however, neuroinflammation is widely considered as one of the major mechanisms responsible for radiotherapy-induced toxicities. The present study reviews the different types of radiotherapy available for the treatment of various types of cancers and their associated neurological complications. It also summarizes the doses of radiations used in the variety of radiotherapy, and their early and delayed side effects. Special emphasis is given to the effects of various types of radiations or late side effects on cognitive impairments.

Effects of nuclear factor‑κB on the uptake of 131iodine and apoptosis of thyroid carcinoma cells

Thyroid carcinoma is primarily treated by surgery combined with radioactive ¹³¹iodine (¹³¹I) treatment; however, certain patients exhibit resistance to ¹³¹I treatment. Previous research indicated that nuclear factor-κB (NF-κB) was associated with resistance to ¹³¹I in cancer cells. The present study aimed to investigate the effects of NF-κB on ¹³¹I uptake and apoptosis in thyroid carcinoma cells. TPC-1 and BCPAP cell lines were employed as research models in the present study, and the expression of NF-κB was inhibited by RNA interference (RNAi). The ability of TPC-1 and BCPAP cells to uptake ¹³¹I was measured and the cell viability was detected by an MTT assay. Finally, the expression of the apoptosis-associated proteins X-linked inhibitor of apoptosis (XIAP), cellular inhibitor of apoptosis protein 1 (cIAP1) and caspase-3 in TCP-1 and BCPAP cells was determined by western blotting. Western blotting results demonstrated that the expression levels of NF-κB in TPC-1 and BCPAP cells were successfully downregulated by RNAi (P<0.05), while analysis of ¹³¹I uptake revealed no significant alterations in the ¹³¹I uptake ability of cells following RNAi (P>0.05). MTT experiments demonstrated that the inhibition of NF-κB expression in combination with radiation (¹³¹I treatment) led to a marked reduction in cell viability (P<0.05). Furthermore, western blot analysis revealed that the inhibition of NF-κB expression downregulated the expression levels of XIAP and cIAP1 (P<0.05), while the expression levels of caspase-3 were upregulated, indicating that the observed reduction in cell viability following NF-κB inhibition may be due to an increased level of apoptosis. Although NF-κB inhibition did not affect the ¹³¹I uptake of thyroid cancer cells, this inhibition may increase the apoptotic effects of radioactive ¹³¹I.