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 alphavbeta3. 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-MTC cells were implanted in the CAM model (n = 8 per group); effects of tetrac and tetrac NP at 1 microg/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.

Tetraidothyroacetic acid (tetrac) and tetrac nanoparticles inhibit growth of human renal cell carcinoma xenografts

Renal cell carcinoma is the most lethal of the common urologic malignancies, with no available effective therapeutics. Tetrac (tetraiodothyroacetic acid) is a deaminated analogue of L-thyroxine (T(4)) that blocks the pro-angiogenesis actions of T(4) and 3, 5, 3'-triiodo-L-thyronine as well as other growth factors at the cell surface receptor for thyroid hormone on integrin alphavbeta3. Since this integrin is expressed on cancer cells and also on endothelial and vascular smooth cells, the possibility exists that Tetrac may act on both cell types to block the proliferative effects of thyroid hormone on tumor growth and tumor-related angiogenesis. To test this hypothesis, we determined the effect of Tetrac on tumor cell proliferation and on related angiogenesis of human renal cell carcinoma (RCC). We used two models: tumor cell implants in the chick chorioallantoic membrane (CAM) system and xenografts in nude mice. To determine the relative contribution of the nuclear versus the plasma membrane action of Tetrac, we compared the effects of unmodified Tetrac to Tetrac covalently linked to poly (lactide-co-glycolide) as a nanoparticle (Tetrac NP) that acts exclusively at the cell surface through the integrin receptor. In the CAM model, Tetrac and Tetrac NP (both at 1 microg/CAM) arrested tumor-related angiogenesis and tumor growth. In the mouse xenograft model, Tetrac and Tetrac NP promptly reduced tumor volume (p<0.01) when administered daily for up to 20 days. Animal weight gain was comparable in the control and treatment groups. Overall, the findings presented here provide evidence for the anti-angiogenic, and anti-tumor actions of Tetrac and Tetrac NP and suggest their potential utility in the treatment of renal cell carcinoma.

Mini-review: Cell surface receptor for thyroid hormone and nongenomic regulation of ion fluxes in excitable cells

Thyroid hormone has been shown experimentally to affect cellular ion fluxes. For example, thyroid hormone-induced modulation has been described of cellular sodium current (I(Na)), inward rectifying potassium current (IKir) and sodium pump (Na, K-ATPase) and of calcium pump (Ca(2+)-ATPase) activities. Certain of these actions appear to reflect nongenomic mechanisms of hormone action that are initiated at the plasma membrane receptor for iodothyronines described on integrin alphavbeta3. One such action is the recent demonstration of enhancement by the hormone of I(Na) in neurons. Nongenomic actions of thyroid hormone initiated at the plasma membrane may be specifically inhibited by tetraiodothyroacetic acid (tetrac), a deaminated thyroid hormone analogue. Important behavioral changes are associated with clinical states of excessive or deficient thyroid function. The molecular basis for these changes has not been established. It is proposed that nongenomic actions of thyroid hormone in neurons-such as that on sodium current-underlie certain of these behaviors. The contribution of such nongenomic actions of the hormone to animal behavioral paradigms possibly relevant to thyroid hormone actions in human subjects may be tested in vivo with tetrac.

Chronic relapsing thrombotic thrombocytopenic purpura: role of therapy with cyclosporine

Relapsing thrombotic thrombocytopenic purpura (TTP) is a rare disorder with most individuals experiencing 1 to 5 relapses. We report a patient with 18 episodes of thrombotic thrombocytopenic purpura (TTP), the highest number of relapses thus far described. The last 11 episodes were treated with regimens containing cyclosporine. The patient's medical record was reviewed for pertinent clinical, laboratory, and treatment data. We summarized various parameters for each episode and compared characteristics of relapses treated with vs. without cyclosporine. The initial episode of TTP was unusual in that it failed to respond to plasmapheresis, glucocorticoids, and fresh frozen plasma (FFP). It remitted only following splenectomy. Episodes 2-7 responded to FFP plus prednisone. Episode 8 failed to respond to prednisone plus FFP but remitted promptly with cyclosporine plus prednisone. Subsequently, 2 relapses responded to cyclosporine alone, 2 to cyclosporine plus FFP, 4 to cyclosporine plus prednisone +/- FFP, and 2 to cyclosporine, FFP, prednisone, and plasma exchange. There was no difference in remission duration, or in severity or duration of relapses treated with vs. without cyclosporine. Use of cyclosporine, however, significantly decreased the requirement for prednisone and the length of maintenance therapy; thus it is effective mainly as an adjunctive therapy for TTP.