Mario A. Pisarev

Abstract: Although thyroid gland function is mainly under the control of pituitary TSH, other factors may also play a role in this process. Iodine is not used only by the thyroid to synthesize thyroid hormones but also directly influences a number of parameters such as thyroid proliferation and function. Thyroid autoregulation has been related to intraglandular content of an unknown putative iodocompound. The thyroid is capable of producing different iodolipids such as 6-iododeltalactone (ILδ) and 2-iodohexadecanal (2-IHDA). Data from different laboratories have shown that these iodolipids can inhibit several thyroid parameters suggesting that these compounds may be the intermediates in the thyroid autoregulation process.

To review advances in understanding of the relationships between the thyroid gland and endocrine function of the pancreas. Recent advances reviewed here are the association of certain thyroid diseases with diabetes mellitus, the possible contribution of insulin resistance to thyroid pathology, insulin and glucose metabolism in states of thyroid dysfunction and insulin requirements in diabetic patients with thyroid disease. Appreciation of associations between the functions of the thyroid gland and endocrine pancreas provides certain insights into clinical management of these conditions.

Background: We have demonstrated that the administration of δ-iodolactone (i.e., 5-iodo-delta lactone) of arachidonic acid (IL-δ), a mediator in thyroid autoregulation, prevents goiter induction by methylmercaptoimidazol (MMI) in rats. Other studies have shown that transforming growth factor beta-1 (TGF-β1) mimics some of the actions of excess iodide, but its participation in autoregulation is disputed. The present studies were performed to test the hypotheses that IL-δ decreases thyroid growth by inhibition of cell proliferation and/or by stimulation of apoptosis due to oxidative stress, that TGF-β is stimulated by an excess of iodide and by IL-δ, and that c-Myc and c-Fos expression are upregulated during goiter induction and downregulated during goiter inhibition. Methods: Rats were treated with MMI alone or together with iodide or IL-δ. Thyroid weight, cell number, cell proliferation, apoptosis, and oxidative stress were determined. Proliferating cell nuclear antigen (PCNA), TGF-β1, TGF-β3, c-Myc, and c-Fos were measured by Western blot. Results: MMI caused a progressive increase in thyroid weight accompanied by an increase in cell number, asymmetry of the ploidy histograms, and PCNA, c-Fos, and c-Myc expression. In addition, an early increase of apoptosis was observed. Peroxides as well as glutathione peroxidase and catalase activities were also increased in goitrous animals. The inhibitory action of IL-δ on goiter formation was accompanied by the inhibition of cell proliferation evidenced by a significant decrease in cell number, PCNA expression, and asymmetry of the ploidy histograms. A transient stimulation of apoptosis after 7 days of treatment was also observed. MMI administration stimulated TGF-β1 but not TGF-β3 synthesis. IL-δ alone caused a slight increase of TGF-β3 but not TGF-β1, whereas potassium iodide (KI) stimulated both isoforms and MMI reversed KI effect on TGF-β1 expression but not on TGF-β3. Conclusions: The goiter inhibitory action of IL-δ is due to the inhibition of cell proliferation and the transient stimulation of apoptosis. This latter action does not involve oxidative stress. TGF-β1 does not play a role in the autoregulatory pathway mediated by IL-δ. Iodide stimulates TGF-β3 without the need of being organified. These results suggest that there may be more than one pathway involved in the autoregulatory mechanism.

Transforming growth factor beta (TGF-β) exists in nature as three isoforms. They exert their effects by binding to a type II receptor located at the cell membrane. The TGF-β-type II receptor complex then recruits type I receptor, and this new complex stimulates the phosphorylation of Smads 2 and 3, which are subsequently transferred to the nucleus, where they regulate gene transcription. The thyroid gland expresses the TGF-β1 gene mRNA and synthesizes the protein, which under physiologic conditions regulates thyroid growth and function. Different studies have demonstrated that TGF-β1 inhibits cell proliferation and a number of functional parameters. These include cyclic adenosine monophosphate (AMP) formation, iodine uptake and organification, hormone secretion, and the expression of thyroglobulin, thyroid peroxidase, and Na⁺/I⁻ symporter. The expression of the TGF-β1 gene and protein may be stimulated by iodine under normal conditions. Since TGF-β1 mimics some of the inhibitory actions of iodine, its participation in thyroid autoregulation has been proposed; however, this concept is still debated. In thyroid tumors, the inhibitory action of TGF-β1 on cell proliferation is progressively lost as the tumor becomes more undifferentiated. The alterations in the signaling pathway of TGF-β1 are not the same in tumors from different species. Even within the same species, such as the pig thyroid, the results may be different depending on whether monolayers or follicular suspensions are employed. The data suggest that it is not entirely possible to apply the results obtained in animal studies to normal or pathological human thyroid tissue. More studies are required to provide the information needed to develop treatments, based on targeting the signaling pathway of TGF-β1, for undifferentiated thyroid cancer and other thyroid diseases.

Undifferentiated thyroid cancer (UTC) is a very aggressive tumor with no effective treatment, since it lacks iodine uptake and does not respond to radio or chemotherapy. The prognosis of these patients is bad, due to the rapid growth of the tumor and the early development of metastasis. Boron neutron capture therapy (BNCT) is based on the selective uptake of certain boron non-radioactive compounds by a tumor, and the subsequent irradiation of the area with an appropriate neutron beam. 10B is then activated to 11B, which will immediately decay releasing alpha particles and 7Li, of high linear energy transfer (LET) and limited reach. Clinical trials are being performed in patients with glioblastoma multiforme and melanoma. We have explored its possible application to UTC. Our results demonstrated that a cell line of human UTC has a selective uptake of borophenylalanine (BPA) both in vitro and after transplantation to nude mice. Treatment of mice by BNCT led to a complete control of growth and cure of 100% of the animals. Moreover dogs with spontaneous UTC also have a selective uptake of BPA. At the present we are studying the biodistribution of BPA in patients with UTC before its application in humans.

Undifferentiated thyroid carcinoma (UTC) is an aggressive tumor with a poor prognosis due to the lack of an effective treatment. Boron neutron capture therapy (BNCT) is based on the selective uptake of boron by the tumor and its activation by a neutron beam, releasing lithium-7 and an alpha particle that will kill the tumor cells by their high linear energy transfer (LET). In previous studies we have shown a selective uptake of borophenylalanine (10BPA) in a human UTC cell line (ARO) and in NIH nude mice implanted with this cell line. When these animals were injected with BPA and irradiated with an appropriated neutron beam, we observed a 100% of tumor growth control and a 50% of histological cure when the initial tumor volume was 50 mm3 or less. Further studies with BOPP (tetrakis-carborane carboxylate ester of 2,4-bis-(alpha, beta-dihydroxyethyl)-deutero-porphyrin IX) showed that when this porphyrin was injected 5-7 days before BPA, and the animals were sacrificed 60 min after the i.p. injection of BPA, a significant increase in boron uptake by the tumor was found (45-38 ppm with both compounds vs. 20 ppm with BPA alone). The application of BNCT using the combination of boron compounds showed a 100% of complete remission in tumors with initial volumes under 50 mm3. Dogs suffer spontaneous UTC, with a similar biological behavior to the human tumor, and a selective uptake of BPA. These results open the possibility of applying BNCT to UTC.

Undifferentiated thyroid carcinoma (UTC) is a rapidly growing, highly invasive malignant tumor that currently lacks any effective treatment. Boron neutron capture therapy (BNCT) has been investigated recently for some types of tumors including glioblastoma multiforme and malignant melanoma. In previous studies we have shown the selective uptake of p-boronophenylalanine (BPA) by undifferentiated thyroid cancer cells in vitro and in vivo, as well as the histologic cure of 50% of the nude mice transplanted with human UTC cells when treated with BPA and an appropriate neutron beam. The present studies were performed to further optimize this treatment through the investigation of a boronated porphyrin, both alone and in combination with BPA. In vitro studies with cells in culture showed that BOPP (tetrakis-carborane carboxylate ester of 2,4-bis-(alpha,beta-dihydroxyethyl)-deutero-porphyrin IX) is localized intracellularly, with a highest concentration in the 11500g (mitochondrial-enriched pellet) fraction. When BOPP was administered alone to NIH nude mice transplanted with UTC human cells, no significant tumor uptake or selectivity in our in vivo model was observed. In contrast, when BOPP was injected 5-7 days before BPA and the animals were sacrificed 60 min after administration of BPA, a significant increase in boron uptake by the tumor was found (38-45 ppm with both compounds vs 20 ppm with BPA alone). On day 5 the tissue boron selectivity ratios were tumor/blood similar to 3.8 and tumor/distal skin similar to 1.8. Other important ratios were tumor/thyroid similar to 6.6 and tumor/lung similar to 2.9. These results open the possibility of improving the efficacy of BNCT for the treatment of this so far "orphan" tumor.