Tetraiodothyroacetic Acid (Tetrac) and Nanoparticulate Tetrac Arrest Growth of Medullary Carcinoma of the Thyroid

Context: Tetraiodothyroacetic acid (tetrac) blocks angiogenic and tumor cell proliferation actions of thyroid hormone initiated at the cell surface hormone receptor on integrin alpha v beta 3. Tetrac also inhibits angiogenesis initiated by vascular endothelial growth factor and basic fibroblast growth factor. Objective: We tested antiangiogenic and antiproliferative efficacy of tetrac and tetrac nanoparticles (tetrac NP) against human medullary thyroid carcinoma (h-MTC) implants in the chick chorioallantoic membrane (CAM) and h-MTC xenografts in the nude mouse. Design: h-MTCcells were implanted in the CAM model (n = 8 per group); effects of tetrac and tetrac NP at 1 mu g/CAM were determined on tumor angiogenesis and tumor growth after 8 d. h-MTC cells were also implanted sc in nude mice (n = 6 animals per group), and actions on established tumor growth of unmodified tetrac and tetrac NP ip were determined. Results: In the CAM, tetrac and tetrac NP inhibited tumor growth and tumor-associated angiogenesis. In the nude mouse xenograft model, established 450-500 mm(3) h-MTC tumors were reduced in size over 21 d by both tetrac formulations to less than the initial cell mass (100 mm(3)). Tumor tissue hemoglobin content of xenografts decreased by 66% over the course of administration of each drug. RNA microarray and quantitative real-time PCR of tumor cell mRNAs revealed that both tetrac formulations significantly induced antiangiogenic thrombospondin 1 and apoptosis activator gene expression. Conclusions: Acting via a cell surface receptor, tetrac and tetrac NP inhibit growth of h-MTC cells and associated angiogenesis in CAM and mouse xenograft models. (J Clin Endocrinol Metab 95: 1972-1980, 2010)