Effects of Anticancer Agent P-bi-TAT on Gene Expression Link the Integrin Thyroid Hormone Receptor to Expression of Stemness and Energy Metabolism Genes in Cancer Cells

Chemically modified forms of tetraiodothyroacetic acid (tetrac), an L-thyroxine derivative, have been shown to exert their anticancer activity at plasma membrane integrin αvβ3 of tumor cells. Via a specific hormone receptor on the integrin, tetrac-based therapeutic agents modulate expression of genes relevant to cancer cell proliferation, survival and energy metabolism. P-bi-TAT, a novel bivalent tetrac-containing synthetic compound has anticancer activity in vitro and in vivo against glioblastoma multiforme (GBM) and other types of human cancers. In the current study, microarray analysis was carried out on a primary culture of human GBM cells exposed to P-bi-TAT (10⁻⁶ tetrac equivalent) for 24 h. P-bi-TAT significantly affected expression of a large panel of genes implicated in cancer cell stemness, growth, survival and angiogenesis. Recent interest elsewhere in ATP synthase as a target in GBM cells caused us to focus attention on expression of genes involved in energy metabolism. Significantly downregulated transcripts included multiple energy-metabolism-related genes: electron transport chain genes ATP5A1 (ATP synthase 1), ATP51, ATP5G2, COX6B1 (cytochrome c oxidase subunit 6B1), NDUFA8 (NADH dehydrogenase (ubiquinone) FA8), NDUFV2I and other NDUF genes. The NDUF and ATP genes are also relevant to control of oxidative phosphorylation and transcription. Qualitatively similar actions of P-bi-TAT on expression of subsets of energy-metabolism-linked genes were also detected in established human GBM and pancreatic cancer cell lines. In conclusion, acting at αvβ3 integrin, P-bi-TAT caused downregulation in human cancer cells of expression of a large number of genes involved in electron transport and oxidative phosphorylation. These observations suggest that cell surface thyroid hormone receptors on αvβ3 regulate expression of genes relevant to tumor cell stemness and energy metabolism.

How thyroid hormone works depends upon cell type, receptor type, and hormone analogue: implications in cancer growth

The classical molecular mechanism of thyroid hormone involves the intranuclear interaction of 3,5,3'-triiodo-L-thyronine (T3) with thyroid hormone-specific nuclear proteins and consequent specific gene expression. This mechanism prevails in normal cells. What we emphasize here is that how thyroid hormone acts depends upon the types of cell or cell-like structure, e.g., platelet, under consideration, and that cancer cells, dividing endothelial cells, phagocytes, and platelets respond to the liganding of L-thyroxine (T4) by plasma membrane integrin αvβ3. In intact tumor cells, T4 at the integrin can modulate the transcription of a substantial number of specific genes relevant to cancer cell proliferation, cell metabolism, and cancer cell anti-apoptosis defense. T4 may also regulate the interactions of the integrin in the endothelial cell plasma membrane with adjacent vascular growth factor receptors, modulating angiogenesis. T4 activates platelets via αvβ3 transferred from the megakaryocyte. It is also possible that, in addition to T4, reverse T3 (rT3) may have actions in cancer cells at the thyroid hormone receptor on αvβ3.

In vitro effects of tetraiodothyroacetic acid combined with X-irradiation on basal cell carcinoma cells

We investigated radiosensitization in an untreated basal cell carcinoma (TE.354.T) cell line and post-pretreatment with tetraiodothyroacetic acid (tetrac) X 1 h at 37°C, 0.2 and 2.0 µM tetrac. Radioresistant TE.354.T cells were grown in modified medium containing fibroblast growth factor-2, stem cell factor-1 and a reduced calcium level. We also added reproductively inactivated (30 Gy) “feeder cells” to the medium. The in vitro doubling time was 34.1 h, and the colony forming efficiency was 5.09 percent. These results were therefore suitable for clonogenic radiation survival assessment. The 250 kVp X-ray survival curve of control TE.354.T cells showed linear-quadratic survival parameters of α_X-ray = 0.201 Gy⁻¹ and β_X-ray = 0.125 Gy⁻². Tetrac concentrations of either 0.2 or 2.0 µM produced α_X-ray and β_X-ray parameters of 2.010 and 0.282 Gy⁻¹ and 2.050 and 0.837 Gy⁻², respectively. The surviving fraction at 2 Gy (SF₂) for control cells was 0.581, while values for 0.2 and 2.0 µM tetrac were 0.281 and 0.024. The SF₂ data show that tetrac concentrations of 0.2 and 2.0 µM sensitize otherwise radioresistant TE.354.T cells by factors of 2.1 and 24.0, respectively. Thus, radioresistant basal cell carcinoma cells may be radiosensitized pharmacologically by exposure to tetrac.

Triiodothyronine [T3]-induced hypothyroxinemia: Response and survival in a compassionate care cancer patient population

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Background: Increased survival under chemically induced hypothyroidism has been reported in cancer patients with poor prognosis, but the associated morbidity can deter patient compliance. Acting via a receptor site upon the plasma membrane avβ3 integrin, L-thyroxine (T4) in physiological concentrations non-genomically activates mitogenesis and neo-angiogenesis of cancer cells and proliferating vascular endothelium. Occlusion of the receptor by tetraiodothyroacetic acid (tetrac), a T4 derivative, induces apoptosis, inhibits angiogenesis and enhances chemotherapy and radiation. 3, 5, 3’-Triiodo-L-thyronine (T3) in physiological concentrations is significantly less mitogenic than T4 and inhibits pituitary release of thyrotropin (TSH). Absence of TSH, but with T3 support, depletes circulating T4 without resultant hypothyroidism. Methods: 21 cancer patients at dispersed clinical sites with stage 4 solid tumors and projected limited survival received T3 [n=10] only or with methimazole (MT) [n=9]. Serum TSH, free T4 (FT4) and T3 concentrations were obtained initially, then monthly. FT4 levels below lower normal range were achieved in all patients within 3 to 12 weeks. Results: See Table. Conclusions: T3 treatment with resultant hypothyroxinemia in poor prognosis cancer patients was associated with favorable response rates in 17/19 subjects. Two others with aggressive tumors had extended survival on long-term T3. [Table: see text] [Table: see text] [Table: see text]

Abstract 3447: Tetrac (tetraiidothyroacetic acid) decreases in vitro x-ray survival of a human medullary thyroid cancer cell line under oxic and hypoxic conditions

In 2009 we showed that 2 µM tetrac given for 1 hour at 37oC prior to 250 kVP x-irradiation sensitized GL261 murine brain tumor cells. Radiosensitization was accomplished by increasing the alpha component in the linear-quadratic equation of cell survival (Cell Cycle, 8:2586-91). In 2011, we showed that tetrac also sensitized U87MG human brain tumor cells to 250 kVp x-rays (Cell Cycle, 10: 352-57). Again radiosensitization was accomplished by an increase in the αx-ray component. Tetrac also inhibited the repair of DNA double strand breaks in U87MG cells. However, tetrac which binds to the αvβ3 integrin receptor and inhibitssignaling from the αvβ3 receptor, penetrates the cell and has a thyromimetic effect which offsets radiosensitization. In this regard, we synthesized a nanoparticle tetrac formulation termed Nano-T. Nano-T also binds to the αvβ3 receptor but does notpenetrate the cell. Nano-T causes radiosensitization in vitro in H522 lung cancer cells, producing an added benefit compared to tetrac. We have also shown that daily treatment of in vivo human-MTC (h-MTC) solid tumors in mice with Nano-T for 20 days produced significant growth inhibition. It is our intent to combine Nano-T with ionizing radiation in vivo, and we have begun by studying the effects of tetrac on h-MTC cells in vitro. These h-MTC cells are show an in vitro cell culture doubling time of 96.2 hours and a clonogenicity of 3.16%. We irradiated cells in exponential growth with 250 kVp X-rays. Below we give the LQ survival parameters, and the surviving fraction at 2 Gy (SF2). Table 1. Initial Results of 250 kVp Single Dose X-irradiation on h-MTC CellsIn Vitro without and with Tetrac ≤ α SF2 Tetrac Oxygen (Gy-1 x 10-1) (Gy-2 x 10-2) Enhancment Enhancement Factor Factor Without Tetrac Oxic Cells - 0.033 0.0256 0.901 2.55 Hypoxic Cells 0.030 0.0023 0.922 With Tetrac Oxic Cells 0.472 0.0495 0.330 2.84 2.60 Hypoxic Cells 0.013 0.0256 0.803 2.84 First, h-MTC cells irradiated as oxic or hypoxic, exponentially growing cells are very radioresistant suggesting a large capacity to repair radiation damage. Second, tetrac sensitized both oxic and hypoxic h-MTC cells. These characteristics speak to our proposed Nano-T in treatment of h-MTC tumors in vivo. Nano-T should increase the radiosensitivity of both oxic and hypoxic cells and should also decrease the repair of radiation damage in conventional fractionated radiation therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3447. doi:1538-7445.AM2012-3447

Abstract C146: In human lung carcinoma cells that contain estrogen receptor-α(ER), thyroid hormone-induced proliferation initiated at an integrin requires ER

We examined the molecular basis of thyroid hormone-induced proliferation of two estrogen receptor-α (ER)-expressing human lung cancer cell lines, non-small cell carcinoma NCI-H522 and small cell carcinoma NCI-H510A. At a physiologic total L-thyroxine (T4) concentration (10[−7] M) and supraphysiologic 3,5,3'-triiodo-L-thyronine (T3) levels, thyroid hormone significantly increased proliferating cell nuclear antigen (PCNA) content of both cell lines. Neutralizing antibody to integrin αvβ3 and integrin-binding Arg-Gly-Asp (RGD) peptide inhibited cell proliferation stimulated by thyroid hormone. Tetraiodothyroacetic acid (tetrac) blocks binding of T4 and T3 to the hormone receptor on αvβ3 and inhibited thyroid hormone-induced cancer cell proliferation. Thus, the thyroid hormone effect is initiated nongenomically at the cell surface thyroid hormone receptor we have described on integrin αvβ3. The thyroid hormone isoforms also caused serine phosphorylation of ER in NCI-H522 and NCI-H510A cells. The ER antagonist, ICI 182,780 (fulvestrant) inhibited stimulation by T4 and T3 of ER phosphorylation, of PCNA accumulation and of radiolabeled thymidine incorporation by the cells. These results are consistent with existence of crosstalk between the plasma membrane receptor for iodothyronines and ER in these lung cancer cells. We conclude that endogenous T4 is a growth factor for ER-containing lung cancer cells and this hormonal action is subject to inhibition by tetrac and by fulvestrant.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C146.

Overlapping nongenomic and genomic actions of thyroid hormone and steroids

Nuclear receptors for thyroid hormone and steroids are members of a receptor superfamily with similar molecular organization, but discrete transcriptional functions that define genomic actions of these nonpeptide hormones. Nongenomic actions of thyroid hormone and estrogens and androgens are initiated outside the nucleus, at receptors in the plasma membrane or in cytoplasm; these actions are largely regarded to be unique to the respective hormones. However, there is an increasing number of descriptions of overlapping nongenomic and genomic effects of thyroid hormone and estrogens and testosterone. These effects are concentrated in tumor cells, where, for example, estrogens and thyroid hormone have similar mitogen-activate protein kinase (MAPK)-dependent proliferative actions on ERα-positive human breast cancer cells, and where dihydrotestosterone also can stimulate proliferation. Steroids and thyroid hormone have similar anti-apoptotic effects in certain tumors. But thyroid hormone and steroids also have overlapping or interacting nongenomic and genomic actions in heart and brain cells. These various effects of thyroid hormone and estrogens and androgens are reviewed here and their possible clinical consequences are enumerated.

Abstract 2673: Tetraiodothyroacetic acid (tetrac) produces an increase in the unirradiated steady-state levels of DNA double strand breaks (DSBs) and inhibition of repair of DSBs after x-irradiation in human U87MG brain tumor cells

INTRODUCTION. We measured the steady-state levels and post-x-irradiation repair of DNA DSBs by neutral comet assay in human U87MG glioblastoma cells in vitro in the absence and presence of tetrac. The results provide a mechanistic basis for our previous observations of radiosensitization and inhibition of cellular recovery after x-irradiation in murine GL261 cells by tetrac (A.H. Hercbergs et al., Cell Cycle 8:2586-2591, 2009).

METHODS. U87MG cells on plastic slides were exposed to 2 nM tetrac for 1 h at 37°C. The slides were then placed on crushed ice and irradiated with doses from 0 to 75 Gy. Slides were then immersed in lysing solution at 50°C for 2 h. Slides were washed and placed in a gel electrophoresis unit. Electrophoresis was carried out at 0.66 V/cm for 25 min. Cells were stained with ethidium bromide and image analysis was carried out on an epifluorescence microscope at a total magnification of 400X, using an excitation filter of 515-535 nm and a barrier filter at 590 nm. We calculated the mean tail moment (TM) expressed in arbitrary units. TM was calculated with a CCD camera and software. Approximately 350 comets were analyzed per condition.

RESULTS. We first demonstrated that human U87MG cells responded to tetrac exposure in a manner similar to that seen in murine GL261 cells. That is, we observed both radiosensitization and inhibition of radiation repair in cellular studies with both GL261 and U87MG cells. For radiosensitization. we observed a factor of approximately 2.2 in U87MG cells which is quite similar to that seen in GL261 cells. We demonstrated that DSB repair in U87 MG cells was inhibited by 2 nM tetrac by a factor of 72.5%, compared to repair observed in control U87MG cells. Again, this finding is similar to that obtained in murine glioma cells. We then demonstrated that exposure of non-irradiated U87MG cells (0 Gy) to tetrac increased the steady-state levels of DSBs, as indicated by a change in TM from 6.0 to 13.1, yielding a sensitization factor of 2.2. However, in graded single doses, tetrac did not affect the slope of the mean tail moment. Lastly, flow cytometric studies on control and tetrac-treated U87MG cells indicated these changes were not due to alteration in the cell cycle distribution of cells.

CONCLUSIONS. These studies provide a linkage between cellular results, i.e., radiosensitization and inhibition of repair in fractionated repair studies, and biochemical endpoints that include increased numbers of DSBs in cells in the unirradiated state and decreased repair of DSBs in fractionated radiation experiments in tetrac-exposed cells. These studies suggest additional studies of possible inhibition of the activity of ATM kinase in tetrac-treated cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2673. doi:10.1158/1538-7445.AM2011-2673

Identification and functions of the plasma membrane receptor for thyroid hormone analogues

Integrin αvβ3 is a heterodimeric structural protein of the plasma membrane that bears a cell surface receptor for thyroid hormone. The functions of this receptor are distinct from those of the classical nuclear receptor (TR) for thyroid hormone. The integrin is expressed primarily by cancer cells, dividing endothelial and vascular smooth muscle cells, and osteoclasts. The hormone receptor on αvβ3 enables L-thyroxine (T(4)) and 3, 5, 3'-triiodo-L-thyronine (T(3)) to stimulate cancer cell proliferation and angiogenesis and to regulate the activity of certain membrane ion pumps. Bound to the receptor, the hormone ligand also stimulates protein trafficking within the cell. A deaminated derivative of T(4), tetraiodothyroacetic acid (tetrac), blocks binding and actions of T(4) and T(3) at the receptor on αvβ3; tetrac also has anti-proliferative actions at the integrin thyroid hormone receptor beyond the effects of antagonizing actions of agonist thyroid hormone analogues at the receptor. The structure-activity relationships of hormone analogues at the receptor have been computer-modeled and indicate that the receptor includes a site that binds T(3) and a site that binds both T(4) and T(3). Mathematical modeling of the kinetics of hormone-binding also suggests the existence of two sites. Cell proliferation is modulated from the T(4)/T(3) site. Tetrac has been re-formulated as a nanoparticle (nanotetrac) that acts exclusively at the αvβ3 receptor and does not enter cells. Nanotetrac disrupts expression of genes in multiple cancer cell survival pathways. The tetrac formulations block human cancer cell proliferation in vitro and in tumor xenografts. Nanotetrac and tetrac inhibit the pro-angiogenic actions in vitro of vascular endothelial growth factor, basic fibroblast factor, and other growth factors. Thus, the receptor described on integrin αvβ3 for T(4) and T(3), the function of which is materially affected by tetrac and nanotetrac, provides insight into tumor cell biology and vascular biology.

Propylthiouracil-induced chemical hypothyroidism with high-dose tamoxifen prolongs survival in recurrent high grade glioma: a phase I/II study

BACKGROUND

High-dose tamoxifen has had disappointing results as a palliative therapy in recurrent glioma. Insulin-like growth factor 1 (IGF-1) is a thyroid hormone modulated naturally occurring antagonist of tamoxifen-induced cytotoxicity. Thyroid function was suppressed to reduce IGF-1 levels in glioma patients and high-dose tamoxifen administered.

MATERIALS AND METHODS

Propylthiouracil was used to induce chemical hypothyroidism in 22 patients with recurrent glioma. Tamoxifen was started within one month and given in escalating doses from 40 mg twice a day up to 80 mg 3 times a day. No significant toxicity developed.

RESULTS

Eleven out of 22 patients became hypothyroid. No patients experienced symptoms of clinical hypothyroidism. Median survival was significantly longer in the hypothyroid group (10.1 months versus 3.1 months); p = 0.03. There was a significant decrease in blood levels of IGF-1 (p = 0.02). in hypothyroid patients.

CONCLUSION

Patients treated for recurrent high-grade gliomas with high-dose tamoxifen had significantly longer survival when chemical hypothyroidism was induced with propylthiouracil.

Hypofractionated radiation therapy and concurrent cisplatin in malignant cerebral gliomas. Rapid palliation in low performance status patients

Twenty-eight patients with high-grade cerebral gliomas (16 biopsy-proven and 12 diagnosed clinically and by computed tomography scan) were treated with altered fraction radiation and concomitant cisplatin (C-DDP). Twenty cases (Groups IA and IB) whose Karnofsky performance status (KPS) was 60% or less received hypofractionation and C-DDP. All these patients had received high-dose Decadron (Merck Sharp & Dohme, West Point, PA), and their conditions were not improving or progressively deteriorating. The first 11 patients (Group IA) received from 600 cGy twice weekly to 3600 cGy over 3 weeks combined with C-DDP IV at 40 mg/M2 every 2 weeks for two courses. The nine subsequent patients (Group IB) received from 600 cGy weekly to 3600 cGy over 5 to 6 weeks with C-DDP IV at 40 mg/M2 every 1 to 2 weeks for four courses. The target volume in all cases was confined to the tumor as defined on computed tomography (CT) scan with a 2 cm to 3 cm margin. The C-DDP at 40 mg/M2 was administered immediately (within 5 minutes after radiation). Eight cases (Group II) with a KPS of more than 60% were treated with hyperfractionation, i.e., from 200 cGy twice daily to 4800 cGy in just under 3 weeks. The C-DDP was administered every 2 weeks for a total of two courses, as for Group IA. In Group I, 15 of 20 (75%) patients experienced rapid improvement in their performance status, which usually becoming evident within 1 to 2 weeks from the initiation of treatment, and progressed over time. Four patients with a KPS of 10% improved their KPS to over 60%. This regimen was both well tolerated and logistically very convenient both for the patients and attending staff. Follow-up CT scans in three of 16 evaluable patients in the hypofractionated group showed complete tumor resolution. Median survival for Group IA was 7 months, for Group IB was 12 months, and overall was eight months. The Group II median survival was 9 months. This experience suggests that hypofractionated radiation in combination with C-DDP may offer rapid palliation with improvement in functional status in severely compromised patients with malignant glioma.