Abstract 87: Apigenin further enhances Akti1/2-induced radioactive iodine uptake (RAIU) and rescues TGF-β1-reduced RAIU in PCCl3 rat thyroid cells.

Abstract Background: Na+/I− Symporter (NIS) is a glycoprotein expressed on the basolateral membrane of thyroid follicular cells and it facilitates iodide uptake from circulating blood. In thyroid cancer, NIS-mediated RAIU serves as the basis for therapeutic ablation of post-thyroidectomy remnants. However, patients with advanced thyroid cancer do not benefit from radioiodine therapy due to reduced or absence of NIS expression/function. Thus, it is of clinical importance to investigate the underlying mechanisms of NIS modulation such that strategies to selectively upregulate NIS expression/ function can be devised. Approach: Clinical and experimental evidences suggest an inverse correlation between Epithelial-to-mesenchymal transition (EMT) and NIS-mediated RAIU in thyroid cancer. To investigate if there is a functional role for EMT in decreasing RAIU, we determined the expression levels of 83 EMT-associated genes in PCCl3 rat thyroid cell lines treated with DMSO (control), Akti1/2 (small molecule inhibitor of pAkt1/2 known to increase RAIU) or TGF-β1 (cytokine known to decrease RAIU) using SABiosciences RT2 profiler EMT PCR array and subjected the results to Ingenuity Pathway Analysis (IPA). To mimic clinical conditions, cells were subjected to ≈5-day Thyroid Stimulating Hormone (TSH) withdrawal followed by acute stimulation by TSH for 24h. Cells were then treated for 24h with reagents in the presence of TSH followed by RNA extraction or RAIU assay or protein isolation. Results: From IPA analysis, we predicted apigenin, a plant derived flavonoid could potentially increase radioactive iodide uptake. Indeed, in-vitro RAIU assays and western blots revealed that apigenin (20μM) further enhances Akti1/2 (10μM)-induced RAIU up to 2-fold by increasing iodide influx and not by increasing NIS protein levels or decreasing iodide efflux in thyroid cells. pAkt inhibition was permissive for apigenin to increase RAIU. Apigenin (20μM) also rescued TGF-β1 (10ng/ml)-reduced RAIU up to 85%. Apigenin is known to affect many kinases and the molecular mechanism of action of apigenin in increasing RAIU is currently under investigation using candidate approach. Conclusion: Apigenin is the only compound reported so far that consistently further increases Akti1/2-induced RAIU. Apigenin promises to reveal novel molecular mechanisms of NIS modulation in thyroid. Apigenin also serves as a potential candidate for dietary supplement in combination with other drugs for future efficacy studies related to radioiodide therapy of thyroid cancer. Citation Format: Aparna Lakshmanan, Sissy Meihua Jhiang. Apigenin further enhances Akti1/2-induced radioactive iodine uptake (RAIU) and rescues TGF-β1-reduced RAIU in PCCl3 rat thyroid cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 87. doi:10.1158/1538-7445.AM2013-87