Cornelia Schmutzler

Redifferentiation Therapy with Retinoids: Therapeutic Option for Advanced Follicular and Papillary Thyroid Carcinoma

Abstract. During the course of tumor progression the differentiated morphologic and functional characteristics of differentiated thyroid carcinomas (DTC) disappear. This corresponds to more aggressive growth, metastatic spread, and loss of iodine uptake. Experimental data give strong evidence that differentiated functions of iodine metabolism can be reinduced by retinoic acids. Results of a study performed in patients with advanced DTC are presented. Twenty patients with DTC (eight follicular, seven papillary, five oxyphilic) were selected for treatment with retinoic acid 1.5 mg/kg body weight/day over 5 weeks. All patients had advanced tumor stages with prior operative and radioiodine treatment. Extensive tumor invasion, distant metastatic spread, or insufficient or no radioiodine uptake precluded any conventional therapeutic option. The aim was to assess the changes under retinoid treatment. Iodine uptake increased in eight patients (three follicular, three papillary, two oxyphilic). Thyroglobulin (TG) as parameter for tumor mass and differentiation increased in 12 (63%) patients, decreased in 6 (32%), and did not change in 1 (5%). Retinoids do have an effect on differentiation status of DTC, reinducing iodine uptake in 50% of patients. TG levels do not always parallel a response in iodine uptake.

Endocrine disruptors and the thyroid gland--a combined in vitro and in vivo analysis of potential new biomarkers.

Background There is growing evidence that, in addition to the reproductive system, the hypothalamic–pituitary–thyroid axis is a target of endocrine-disrupting compounds (EDCs). However, this is not reflected adequately in current screening and assessment procedures for endocrine activity that to date determine only general parameters of thyroid function. Objective and Methods We used several in vitro and ex vivo assays in an attempt to identify suitable biomarkers for antithyroid action testing a selected panel of putative EDCs. Results In vitro we detected stimulation or inhibition of iodide uptake into FRTL-5 rat thyroid cells, inhibition of thyroid hormone binding to transthyretin, agonistic or antagonistic effects in a thyroid hormone receptor–dependent reporter assay, and inhibition of thyroid peroxidase using a novel assay system based on human recombinant thyroperoxidase that might be suitable for routine screening for potential EDCs. In rats, chronic application of several EDCs led to changes in thyroid morphology, alterations of thyrotropin and thyroid hormone serum levels as well as alterations in peripheral thyroid hormone–regulated end points such as malic enzyme and type I 5′-deiodinase activity. Conclusions As the effects of EDCs do not reflect classic mechanisms of hormone-dependent regulation and feedback, we believe multitarget and multimodal actions of EDCs affect the hypothalamic–pituitary–thyroid axis. These complex effects require a diverse approach for screening, evaluation, and risk assessment of potential antithyroid compounds. This approach involves novel in vitro or cell-based screening assays in order to assess thyroid hormone synthesis, transport, metabolism, and action as well as in vivo assays to measure thyroid hormone–regulated tissue-specific and developmental end points in animals.

FUNCTIONAL RETINOID AND THYROID HORMONE RECEPTORS IN HUMAN THYROID-CARCINOMA CELL LINES AND TISSUES

Thyroid carcinomas no longer accessible to radio‐iodide or TSH‐suppressive T4 therapy, due to loss of thyroid‐specific functions, might be sufficiently re‐differentiated by retinoic acid (RA) to be treated by conventional methods again. To help evaluate the feasibility of RA re‐differentiation therapy in thyroid carcinomas, we examined the functionality of RA receptors (RARs/RXRs), central RA signal mediators, in human thyroid‐carcinoma cell lines as model systems. [3H]‐RA binding assays with nuclear extracts from follicular thyroid‐carcinoma cell lines FTC‐133 and ‐238 revealed high‐affinity binding sites for RA. Electrophoretic mobility shift and supershift assays using a DR2 (“direct repeat” 2) RA response element demonstrated DNA‐binding of RARα, RARγ, RXRα and RXRβ in nuclear extracts of FTC‐133 and anaplastic HTh74 cells. Use of a DR5 RA response element revealed no difference in DNA binding. In supershift assays with a DR4 T3 response element, we found DNA‐binding by TRα1, TRα2, and TRβ. Northern‐blot analysis showed low expression of RXRβ mRNA in FTC‐133 and of TRα1 mRNA in FTC‐133 and FTC‐238 cells. Using RT‐PCR, we detected mRNA for RARα, RARβ, RARγ, RXRα, and RXRβ in the 4 cell lines and in human thyroid‐carcinoma samples. RARβ mRNA was reduced in FTC‐238 cells and RXRβ mRNA was decreased in anaplastic C643 cells and 9 of 12 tumor samples. Differential RA regulation of RA‐receptor‐mRNA expression was observed in the various cell lines. Thus, RA and T3 nuclear receptors are present in thyroid‐carcinoma cell lines or tissues, albeit with cell‐line and tumor‐dependent variations; in the cell lines, they were shown to be functional with respect to DNA and/or ligand binding. Int. J. Cancer 76:368–376, 1998.© 1998 Wiley‐Liss, Inc.

Retinoic acid-mediated down-regulation of ENO1/MBP-1 gene products caused decreased invasiveness of the follicular thyroid carcinoma cell lines.

Retinoic acid (RA) acts as an anti-proliferative and redifferentiation agent in the therapy of thyroid carcinoma. Our previous studies demonstrated that pretreatment of follicular thyroid carcinoma cell lines FTC-133 and FTC-238 resulted in decreased in vitro proliferation rates and reduced tumor cell growth of xenotransplants. In addition to the previous results, we found that RA led to decreased vitality and invasiveness of FTC-133 and FTC-238 cells as they reacted with reduction of intracellular ATP levels and number of migrated cells respectively. However, the molecular mechanisms by which RA mediates these effects are not well understood. Two-dimensional (2D) screening of the proteins related to ATP metabolism and western blot analysis revealed alpha-enolase (ENO1) to be down-regulated in FTC-133 and FTC-238 cells after RA treatment. 2D gel detection and mass spectrometric analysis revealed that ENO1 existed as three separate protein spots of distinct pIs (ENO1-A1-A3). Comparative 2D difference gel electrophoresis analysis of fluorescently labeled protein samples of RA-treated and untreated FTC-133 demonstrated a selective down-regulation of ENO1-A1 which we identified as a phosphoprotein. RA caused the dephosphorylation of ENO1-A1. Both, RA-mediated and specific knock-down of ENO1/MBP-1 resulted in the reduction of MYC oncoprotein, and simultaneously decreased proliferation rates of FTC-133 and FTC-238 cell lines. In summary, the RA-mediated down-regulation of the ENO1 gene products and MYC oncoprotein provides a novel molecular mechanism facilitating the anti-proliferative effect of RA in human thyroid carcinoma cells and suggests new pathways for supportive RA therapies.

Selenoproteine im Knochen, Gastrointestinaltrakt und in der Schilddrüse des Menschen

Summary□Basis: Selenium is an essential trace element, which is incorporated as selenocysteine (secys) into specific proteins in a regulated fashion. In the presence of a hairpin loop structure within the 3′ untranslated region of the mRNA the opal stop codon UGA is coding for selenocysteine. Selenoprotein functions are dependent on secys incorporation. Members of the family of deiodinases as well as the family of glutathione peroxidases, selenoprotein P and thioredoxin reductase are selenoproteins.□Discussion: Bone, the intestine and the thyroid rely on antioxidant systems against potential cell and DNA damage through endogenous and environmental peroxides and reactive oxygen species (ROS) potentially promoting inflammation and tumorigenesis. Optimized cell defense through antioxidant selenoproteins requires optimal selenium supplementation of the organism. We have analyzed the expression of selenoproteins in these tissues, thus providing molecular tools to further elucidate optimal selenium supply on a cellular level.□Conclusion: Clinical intervention studies that focus on the development of disease must confirm the relevance of optimized selenium supply for the pathogenesis, prevention and therapy of metabolic bone disease as well as chronic (autoimmune) inflammation and tumorigenesis in the thyroid and intestine.