Retinoic acid therapy in patients with radioiodine negative differentiated thyroid cancer and clinical or biochemical evidence of disease: An initial experience

Molecular mechanisms of radioactive iodine refractoriness in differentiated thyroid cancer: Impaired sodium iodide symporter (NIS) expression owing to altered signaling pathway activity and intracellular localization of NIS

The advanced, metastatic differentiated thyroid cancers (DTCs) have a poor prognosis mainly owing to radioactive iodine (RAI) refractoriness caused by decreased expression of sodium iodide symporter (NIS), diminished targeting of NIS to the cell membrane, or both, thereby decreasing the efficacy of RAI therapy. Genetic aberrations (such as BRAF, RAS, and RET/PTC rearrangements) have been reported to be prominently responsible for the onset, progression, and dedifferentiation of DTCs, mainly through the activation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT signaling pathways. Eventually, these alterations result in a lack of NIS and disabling of RAI uptake, leading to the development of resistance to RAI therapy. Over the past decade, promising approaches with various targets have been reported to restore NIS expression and RAI uptake in preclinical studies. In this review, we summarized comprehensive molecular mechanisms underlying the dedifferentiation in RAI-refractory DTCs and reviews strategies for restoring RAI avidity by tackling the mechanisms.

The effect of retinoic acid in the ability of cold solid thyroid nodule to take up radioactive iodine: A preliminary study

One of the treatment options for benign thyroid nodules is radioactive iodine (RAI). However, this treatment is more effective for hot/warm solid thyroid nodules. Cold thyroid solid nodules are characterized by the lack of iodine uptake compared to normal thyroid tissue. Oral retinoic acid (RA) is a synthetic derivative of Vitamin A. The effect of RA on the uptake of RAI is still controversial. The aim of this study was to evaluate the effect of RA in the ability of a cold solid thyroid nodule to take up RAI. Individuals with a cold solid thyroid nodule based on ultrasonography and thyroid scintigraphy were included. Participants with liver dysfunction, smokers, and pregnant patients were excluded from the study. Each participant underwent thyroid uptake scintigraphy twice (pre- and post-RA consumption) using 35–37 MBq NaI-131. Participants consumed RA at a dose of 1 mg/kg body weight (BW) followed with 1.5 mg/kg BW. This study was approved by Dr. Hasan Sadikin General Hospital Ethic Committee. A total of 12 cold thyroid solid nodules were evaluated. The mean percentage of the nodule uptake value pre- and post-intervention was 1.11% and 0.62%, respectively (P = 0.004), while normal thyroid tissue uptake values pre- and post-intervention were 27.57% and 13.40%, respectively (P = 0.002). The percentage alteration of nodules and normal thyroid tissue uptake value were 42.4% and 51.5% lower, respectively (P = 0.354). This study showed that RA reduces the ability of cold solid thyroid nodule, as well as normal thyroid tissue, to take up RAI.

Family of microRNA-146 Regulates RARβ in Papillary Thyroid Carcinoma

Retinoic acid is a promising tool in adjuvant cancer therapies, including refractory thyroid cancer, and its biological role is mediated by the retinoic acid receptor beta (RARβ). However, expression of RARβ is lowered in papillary thyroid carcinoma (PTC), contributing to promotion of tumor growth and inefficiency of retinoic acid and radioactive iodine treatment. The causes of aberrant RARB expression are largely unknown. We hypothesized that the culpable mechanisms include the action of microRNAs from the miR-146 family, previously identified as significantly upregulated in PTC tumors. To test this hypothesis, we assessed the expression of RARB as well as miR-146a-5p and miR-146b-5p in 48 PTC tumor/normal tissue pairs by Taqman assay to reveal that the expression of RARB was 3.28-fold decreased, and miR-146b-5p was 28.9-fold increased in PTC tumors. Direct interaction between miRs and RARB was determined in the luciferase assay and further confirmed in cell lines, where overexpression of miR-146a-5p and miR-146b-5p caused a 31% and 33% decrease in endogenous RARB mRNA levels. Inhibition of miR-146a and miR-146b resulted in 62.5% and 45.4% increase of RARB, respectively, and a concomitant decrease in proliferation rates of thyroid cancer cell lines, analyzed in xCELLigence system.We showed that two microRNAs of the miR-146 family directly regulate RARB. Inhibition of miRs resulted in restoration of RARB expression and decreased rates of proliferation of thyroid cancer cells. By restoring RARB levels, microRNA inhibitors may become part of an adjuvant therapy in thyroid cancer patients.

All-trans-retinoic acid promotes iodine uptake via up- regulating the sodium iodide symporter in medullary thyroid cancer stem cells

Recently, the main therapy of medullary thyroid cancer (MTC) is surgical, but by which way there is a poor prognosis with a mean survival of only 5 years. In some cases, some researchers found that it is the medullary thyroid cancer stem cells (MTCSCs) that cause metastasis and recurrence. This study aimed to eradicate MTCSCs through administration of all-trans-retinoic acid (ATRA). Here we demonstrate that MTCSCs possess stem- like properties in serum-free medium. The ABCG2, OCT4 and sodium iodide symporter (NIS) were changed by ATRA. Additionally, we found that ATRA can increase the expression of NIS in vivo. All the data suggested that ATRA could increase the iodine uptake of MTCSCs through NIS.