Richard Wahl

Chemotherapy and Chemoprevention by Thiazolidinediones

Thiazolidinediones (TZDs) are synthetic ligands of Peroxisome-Proliferator-Activated Receptor gamma (PPARγ). Troglitazone, rosiglitazone, and pioglitazone have been approved for treatment of diabetes mellitus type II. All three compounds, together with the first TZD ciglitazone, also showed an antitumor effect in preclinical studies and a beneficial effect in some clinical trials. This review summarizes hypotheses on the role of PPARγ in tumors, on cellular targets of TZDs, antitumor effects of monotherapy and of TZDs in combination with other compounds, with a focus on their role in the treatment of differentiated thyroid carcinoma. The results of chemopreventive effects of TZDs are also considered. Existing data suggest that the action of TZDs is highly complex and that actions do not correlate with cellular PPARγ expression status. Effects are cell-, species-, and compound-specific and concentration-dependent. Data from human trials suggest the efficacy of TZDs as monotherapy in prostate cancer and glioma and as chemopreventive agent in colon, lung, and breast cancer. TZDs in combination with other therapies might increase antitumor effects in thyroid cancer, soft tissue sarcoma, and melanoma.

Induction of iodide uptake in transformed thyrocytes: a compound screening in cell lines.

PurposeRetinoic acid presently is the most advanced agent able to improve the efficacy of radioiodine therapy in differentiated thyroid carcinoma. In order to identify compounds with higher efficacy a panel of pharmacologically well-characterized compounds with antitumour action in solid cancer cell lines was screened.MethodsThe effects of the compounds on iodide uptake, cell number, proliferation and apoptosis were evaluated.ResultsIn general, compounds were more effective in cell lines derived from more aggressive tumours. The effectiveness in terms of number of responsive cell lines and maximal increase in iodide uptake achieved decreased in the order: APHA > valproic acid ≈ sirolimus ≈ arsenic trioxide > retinoic acid ≈ lovastatin > apicidine ≈ azacytidine ≈ retinol ≈ rosiglitazone ≈ bortezomib.ConclusionWe hypothesize that testing of cells from primary tumours or metastases in patients may be a way to identify compounds with optimum therapeutic efficacy for individualized treatment.

The current role of targeted therapies to induce radioiodine uptake in thyroid cancer

Targeted therapy pinpointing specific alteration in cancer cells has gained an important role in the treatment of cancer. Compounds that re-induce thyroid-specific functions could be particularly useful in differentiated thyroid cancers by rendering them susceptible to radioiodine treatment, which is relatively specific and has few adverse effects. This review describes the rationale for radioiodine treatment, considering the targets of compounds with differentiation-inducing effects, and the impact of these drugs on the expression of thyroid-specific proteins and on iodine-uptake. We survey the results from the clinical trials thus far performed. We conclude that although retinoids, thiazolidinediones, histone deacetylase inhibitors and DNA methyltransferase inhibitors do increase the expression of thyroid-specific proteins, their clinical efficacy is limited. The relatively low rate of remissions in clinical trials with re-differentiating compounds could be due to low levels of the target, heterogeneity of iodine uptake into the tumor, poor correlation of radioiodine uptake and clinical remission, and/or the slow onset of the therapeutic effect. Although the mode of action is not clear, the combination of tyrosine kinase inhibitors and RAI treatment could improve clinical responses in non-radioiodine avid metastatic thyroid carcinoma.

Is transketolase like 1 a target for the treatment of differentiated thyroid carcinoma? A study on thyroid cancer cell lines.

SummaryRadioactive iodine-refractory [18F] fluorodeoxy-glucose-positron emission tomography-positive thyroid carcinomas represent especially aggressive tumors. Targeting glucose metabolism by the transketolase isoenzyme transketolase like 1 (TKTL-1) which is over-expressed in various neoplasms, may be effective. The correlation of TKTL-1 expression and the response to oxythiamine as the currently best-characterized inhibitor of transketolases was studied in differentiated thyroid cancer cell lines. We determined TKTL-1 expression, proliferation, glucose uptake and GLUT-1 expression in non-treated thyroid cells and recorded the effect of oxythiamine on iodide uptake and on thymidine uptake. TKTL 1 was highest expressed in cell lines derived from more invasive tumors but the expression level was not strongly correlated to proliferation rate, to GLUT-1 expression or to the response to oxythiamine. Oxythiamine showed only a weak effect in the TKTL-1 expressing cell lines. Over-expression of TKTL-1 is not an indicator for responsiveness to oxythiamine. More specific inhibitors should be tested.

Thyroid Autoimmunity: Role of Anti-thyroid Antibodies in Thyroid and Extra-Thyroidal Diseases

Autoimmune diseases have a high prevalence in the population, and autoimmune thyroid disease (AITD) is one of the most common representatives. Thyroid autoantibodies are not only frequently detected in patients with AITD but also in subjects without manifest thyroid dysfunction. The high prevalence raises questions regarding a potential role in extra-thyroidal diseases. This review summarizes the etiology and mechanism of AITD and addresses prevalence of antibodies against thyroid peroxidase, thyroid-stimulating hormone receptor (TSHR), and anti-thyroglobulin and their action outside the thyroid. The main issues limiting the reliability of the conclusions drawn here include problems with different specificities and sensitivities of the antibody detection assays employed, as well as potential confounding effects of altered thyroid hormone levels, and lack of prospective studies. In addition to the well-known effects of TSHR antibodies on fibroblasts in Graves’ disease (GD), studies speculate on a role of anti-thyroid antibodies in cancer. All antibodies may have a tumor-promoting role in breast cancer carcinogenesis despite anti-thyroid peroxidase antibodies having a positive prognostic effect in patients with overt disease. Cross-reactivity with lactoperoxidase leading to induction of chronic inflammation might promote breast cancer, while anti-thyroid antibodies in manifest breast cancer might be an indication for a more active immune system. A better general health condition in older women with anti-thyroid peroxidase antibodies might support this hypothesis. The different actions of the anti-thyroid antibodies correspond to differences in cellular location of the antigens, titers of the circulating antibodies, duration of antibody exposure, and immunological mechanisms in GD and Hashimoto’s thyroiditis.

Antitumor effects of arsenic trioxide in transformed human thyroid cells.

BACKGROUND To improve radioiodine treatment of metastasized differentiated thyroid carcinomas, substances that increase iodide uptake are needed. Many tumors are not responsive to retinoic acid as a differentiating agent. Therefore, identification of other differentiating substances is needed. Arsenic trioxide (ATO) was investigated for its potential to increase iodide uptake. METHODS The action of ATO on proliferation, differentiation, and apoptosis was evaluated in follicular and papillary thyroid carcinoma cell lines. To get insight into the mode of action of ATO, coincubations with inhibitors of the phosphoinositide 3 (PI3) kinase pathway (V-Akt Murine Thymoma Viral Oncogene Homolog 1, Akt inhibitors) were performed; glutathione (GSH) levels were determined, as well as synergistic effects of ATO with inhibitors of GSH metabolism, inductors of oxidative stress. As a potential additional target of the pleiotropic action of ATO, its effect on glucose uptake was investigated. The expression of sodium iodide symporter, pendrin, phospho-Akt, and glucose transporter 1 was studied to reveal a potential effect of ATO on the transcription of specific genes. RESULTS ATO reduced proliferation, increased iodide uptake and apoptosis, and, as an additional new mechanism, decreased glucose uptake in transformed thyrocytes. The pharmacological reduction of the amount of reduced GSH was effective in enhancing the differentiating action of ATO, whereas the combination of ATO with Akt-1 inhibitors reduced cell number but did not increase differentiation. CONCLUSIONS Our study suggests a new therapeutic option for postoperative treatment of radioiodine nonresponsive differentiated thyroid carcinomas.

Effects of retinoids on porcine thyrocytes under different culture conditions.

The purpose of the paper was to study the morphological effects of retinoids on non-transformed cells such as thyrocytes. The formation of follicles was studied in primary cultures of porcine thyrocytes by adding retinol and thyroid stimulating hormone (TSH) to cells grown in the absence of TSH to form monolayers. The proliferation and apoptosis of thyrocytes were studied in cells both grown adherent to plastic surfaces and in suspension. Standard medium with traces of retinol and the same medium without retinol were used. Retinol alone was added to thyrocytes grown in the absence of TSH (TSH ⊕ culture) or both retinol and TSH were added to cultures after stimulation with TSH (TSH ⊕ culture). The concentration was varied from 0 to 80 μM for retinol and from 0 to 13 μM for retinoic acid. At a concentration of 13 μM, the effect of retinol was similar to that of retinoic acid. At concentrations higher than 40 μM, retinol reduced the formation of thyroglobulin-immunoreactive follicles, whereas up to 13 μM retinoic acid had no obvious influence on follicle formation. The retinoids induced apoptosis under all experimental conditions. In contrast, a significant decrease in proliferation and in the formation of thyroglobulin-immunoreactive follicles was observed only in adherent cells cultured in customary medium. The decrease in functional follicles after treatment with retinol suggests a de-differentiating effect of retinoids on normal thyrocytes and is in contrast with the differentiating effect of retinoids observed in cancer cells.

Effects of retinol on follicular porcine thyrocytes in culture

Retinoids influence proliferation and differentiation in transformed thyroid cell lines. Retinoids are able to damage cells by destabilizing lysosomal membranes and induce apoptosis in certain cell lines. In normal thyrocytes retinol modulates iodine metabolism. At concentrations higher than 50×10–6 M retinoids are cytotoxic for normal (not transformed) thyroid cells. The mechanism of this cytotoxicity is unknown. We studied the effect of 7–80×10–6 M retinol on porcine follicular thyrocytes in culture. In order to differentiate between membrane-destabilizing effects and apoptosis we investigated cultures after incubation with retinol by light- and electron-microscopy and by labeling of potential nicks in the DNA helix by terminal deoxynucleotidyltransferase-dUTP mediated DNA nick end labeling. We conclude that the observed cytotoxicity is caused mainly by the induction of apoptosis.

Remodelling of the Myocyte at a Molecular Level — Relationship Between Myosin Isoenzyme Population and Sarcoplasmic Reticulum

There is increasing evidence that the molecular structure of the myocyte is variable, critically depending on the functional load to which the heart is subjected on a long-term basis. The potential of the myocyte to adapt its functionally important structural elements to a given load represents an important means by which the heart can cope with a variety of loads ranging from those arising during physical exercise or increased blood pressure (1). Although such remodelling of the myocyte is of great functional relevance, only little is known at present in terms of the trigger reactions involved at the cellular or molecular level. In view of the great number of variable elements of the myocyte, it is unlikely that for each one there is a selective trigger signal. Rather, it can be assumed that a given stimulus affects a number of functionally coherent structures of the myocyte in a concerted manner. An understanding of mechanisms involved in the remodelling is the prerequisite not only for a rational description of myocardial performance but also for tracing the causes of pathological processes such as decompensation of the pressure loaded heart issuing in pump failure.

MECHANISMS IN ENDOCRINOLOGY: Impact of isolated TSH levels in and out of normal range on different tissues

Routine treatment of thyroid cancer (TC) includes long-term suppression of TSH. The necessity of this treatment in low- and intermediate-risk patients as well as the extent of TSH suppression is currently under discussion. A literature search was performed to illustrate the role of TSH in extrathyroidal cells and to identify potential reasons for different effects of exogenously suppressed and endogenously low TSH levels. Although adverse effects of subnormal and supranormal TSH blood levels on heart and brain have not been consistently found, studies show a clear negative effect of suppressed TSH levels on bone mineral density. Experimental data also support an important role of TSH in the immune system. The ability of levothyroxine (l-T4) to regulate TSH levels and triiodothyronine levels in a physiological manner is limited. Reduction of circadian changes in TSH levels, decrease of thyroid hormone-binding proteins, prevention of potential compensatory increases of TSH levels (e.g., in old age), and unresponsiveness of TSH-producing cells to TRH on l-T4 treatment might cause adverse effects of suppressed TSH levels. In view of the adverse effects of aggressive TSH suppression, achieving the suggested levels of TSH between 0.9 and 1 mU/l in the treatment of low-to-intermediate risk TC patients appears justified.