Heng-Yuan Tang

Acting via a Cell Surface Receptor, Thyroid Hormone Is a Growth Factor for Glioma Cells

Recent evidence suggests that the thyroid hormone L-thyroxine (T4) stimulates growth of cancer cells via a plasma membrane receptor on integrin alphaVbeta3. The contribution of this recently described receptor for thyroid hormone and receptor-based stimulation of cellular mitogen-activated protein kinase [MAPK; extracellular signal-regulated kinase 1/2 (ERK1/2)] activity, to enhancement of cell proliferation by thyroid hormone was quantitated functionally and by immunologic means in three glioma cell lines exposed to T4. At concentrations of 1 to 100 nmol/L, T4 caused proliferation of C6, F98, and GL261 cells, measured by accumulation of proliferating cell nuclear antigen (PCNA) and radiolabeled thymidine incorporation. This effect was inhibited by the T4 analogue, tetraiodothyroacetic acid, and by an alphaVbeta3 RGD recognition site peptide, both of which block T4 binding to integrin alphaVbeta3 but are not agonists. Activation of MAPK by T4 was similarly inhibited by tetraiodothyroacetic acid and the RGD peptide. The thyroid hormone 3,5,3-triiodo-L-thyronine (T3) and T4 were equipotent stimulators of PCNA accumulation in C6, F98, and GL261 cells, but physiologic concentrations of T3 are 50-fold lower than those of T4. In conclusion, our studies suggest that glioblastoma cells are thyroid hormone dependent and provide a molecular basis for recent clinical observations that induction of mild hypothyroidism may improve duration of survival in glioblastoma patients. The present experiments infer a novel cell membrane receptor-mediated basis for the growth-promoting activity of thyroid hormone in such tumors and suggest new therapeutic approaches to the treatment of patients with glioblastoma.

Pharmacodynamic Modeling of Anti-Cancer Activity of Tetraiodothyroacetic Acid in a Perfused Cell Culture System

Unmodified or as a poly[lactide-co-glycolide] nanoparticle, tetraiodothyroacetic acid (tetrac) acts at the integrin αvβ3 receptor on human cancer cells to inhibit tumor cell proliferation and xenograft growth. To study in vitro the pharmacodynamics of tetrac formulations in the absence of and in conjunction with other chemotherapeutic agents, we developed a perfusion bellows cell culture system. Cells were grown on polymer flakes and exposed to various concentrations of tetrac, nano-tetrac, resveratrol, cetuximab, or a combination for up to 18 days. Cells were harvested and counted every one or two days. Both NONMEM VI and the exact Monte Carlo parametric expectation maximization algorithm in S-ADAPT were utilized for mathematical modeling. Unmodified tetrac inhibited the proliferation of cancer cells and did so with differing potency in different cell lines. The developed mechanism-based model included two effects of tetrac on different parts of the cell cycle which could be distinguished. For human breast cancer cells, modeling suggested a higher sensitivity (lower IC50) to the effect on success rate of replication than the effect on rate of growth, whereas the capacity (Imax) was larger for the effect on growth rate. Nanoparticulate tetrac (nano-tetrac), which does not enter into cells, had a higher potency and a larger anti-proliferative effect than unmodified tetrac. Fluorescence-activated cell sorting analysis of harvested cells revealed tetrac and nano-tetrac induced concentration-dependent apoptosis that was correlated with expression of pro-apoptotic proteins, such as p53, p21, PIG3 and BAD for nano-tetrac, while unmodified tetrac showed a different profile. Approximately additive anti-proliferative effects were found for the combinations of tetrac and resveratrol, tetrac and cetuximab (Erbitux), and nano-tetrac and cetuximab. Our in vitro perfusion cancer cell system together with mathematical modeling successfully described the anti-proliferative effects over time of tetrac and nano-tetrac and may be useful for dose-finding and studying the pharmacodynamics of other chemotherapeutic agents or their combinations.

The pro-apoptotic action of stilbene-induced COX-2 in cancer cells: Convergence with the anti-apoptotic effect of thyroid hormone

Constitutively expressed cyclooxygenase-2 (COX-2) is a marker of tumor cell aggressiveness. Inducible COX-2 has also been described in cancer cells and localizes in the cancer cell nucleus, where formation of a complex of mitogen-activated protein kinase (MAPK) and COX-2 is antecedent to p53-dependent apoptosis. The stilbene resveratrol is a model pharmacologic activator of this pro-apoptotic mechanism. Physiological concentrations of thyroid hormone are anti-apoptotic in several types of tumor cells. A mechanism by which the hormone is anti-apoptotic is disruption of the nuclear MAPK-COX-2 complex. We review here the apoptosis-relevant effects of resveratrol and thyroid hormone and then speculate about the significance of convergence of these actions in cancer cells in the intact organism. Clinical activity of resveratrol may be modulated by normal tissue levels of endogenous thyroid hormone, and hypothyroidism in the cancer patient—whether spontaneous or induced by chemotherapeutic agents—may permit full expression of the apoptotic activity of the administered stilbene. Chronic pharmacologic inhibition of COX-2 may oppose the pro-apoptotic effect of resveratrol.

Abstract 3979: In vitro modeling of pharmacodynamics of resveratrol-induced anti-proliferation in breast cancer cells

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DCnnWe and others have shown that resveratrol, a naturally-occurring stilbene, induces p53-dependent apoptosis in human and animal cancer cell lines. The molecular basis of induction of apoptosis by resveratrol includes activation and nuclear translocation of mitogen-activated protein kinase (MAPK; ERK1/2) and MAPK-mediated Ser-15 phosphorylation of p53 (pSer15-p53). In this study, we used a newly developing perfusion bellows cell culture system to investigate resveratrol-induced apoptosis in the human estrogen receptor (ER)-negative breast cancer MDA-MB-231 cells. The cell culture system is a disposable bioreactor capable of high density cell culture for studies of anti-cancer drugs. Bellows-induced alternate flow of culture medium and air through porous matrices where cells are grown provides a relatively low shear, high aeration, foam-free culture environment. Medium level is raised and lowered to submerge and expose matrices to create a dynamic interface between air and media on the cell surface. Anchorage-dependent cells are grown on plastic flakes in the system; the flakes facilitate harvesting of whole cells for analysis. After 6 days incubation, the IC50 of resveratrol-induced apoptosis was 0.1 μM. Short term incubation with 10 μM resveratrol for 6 days inhibited cell proliferation by 75%. Using an injection system to pump media with different concentrations of resveratrol (0.5 μM to 100 μM), we were able to reproduce the resveratrol-induced anti-proliferation effect in the perfusion bellows culture system. Incubating the cells in either acidic or alkaline condition did not affect anti-proliferation induced by resveratrol. The effect of resveratrol-induced apoptosis is based on increasing transcription of pro-apoptotic p53-dependent genes such as PIG3, c-fos, c-jun and BAD. The aim of the present study is to establish the pharmacodynamics of resveratrol in the suppression or elimination of human breast cancer cells. With the use of the perfusion bellows cell culture system we will provide an efficient, convenient and financially beneficial method for determining optimal regimens for the effective suppression and elimination of these cancer cells.nnNote: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.nnCitation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3979.