Thornton, C. E. M. | Search bioRxiv

bioRxiv2020

New mechanisms of radioiodide uptake revealed via a novel high throughput drug screening approach in thyroid cancer

New combinatorial drug strategies are urgently needed to improve radioiodide (RAI) uptake and efficiently ablate thyroid cancer cells, thereby addressing recurrent and metastatic disease. Cellular iodide uptake is accomplished solely by the sodium iodide symporter (NIS), but the complexity of NIS functional regulation and a lack of amenable high-throughput screening assays has impeded progress. We utilised mutated yellow fluorescent protein (YFP) as a surrogate biosensor of intracellular iodide for [~]1200 FDA-approved drugs, allowing us to appraise the impact of 73 leading compounds at 10 doses on 125I uptake in thyroid cancer cell lines. Subsequent mechanistic analysis suggests three predominant modes of drug action: Firstly, a number of drugs inhibited specific regulation of NIS function by the protein VCP. Secondly, some drugs enhanced transcriptional or post-transcriptional regulation of NIS expression. Thirdly, several drugs strongly implicated proteasomal degradation and the unfolded protein response in the cellular processing of NIS. Exploiting these mechanistic insights, multiple compounds gave striking increases in radioiodide uptake when combined with the drug SAHA. Importantly, our new drug combination strategies were also effective in human primary thyrocytes, suggesting they target endogenous NIS physiology. In patients with papillary thyroid cancer, genes involved in proteostasis were remarkably altered and predicted significantly worse outcome, but only in those patients who received RAI therapy. Collectively, we therefore propose a new model of intracellular NIS processing, and identify key nodes which may now be druggable in patients with aggressive thyroid cancer. SUMMARYOur data identify FDA-approved drugs that enhance radioiodide uptake outside of the canonical pathways of NIS processing, leading to a new mechanistic understanding of endogenous NIS function which is subverted in cancer.

cancer biology↗

bioRxiv2019

Pharmacologically targeting a novel pathway of sodium iodide symporter trafficking to enhance radioiodine uptake

Radioiodine treatment fails [≥]25% of patients with thyroid cancer and has been proposed as a potential treatment for breast cancer. Cellular iodide uptake is governed by the sodium iodide symporter (NIS), which is frequently mislocalized in thyroid and breast tumours. However, the trafficking of NIS to the plasma membrane (PM) is ill-defined. Through mass spectrometry, co-immunoprecipitation, cell surface biotinylation and proximity ligation assays we identify two proteins which control NIS subcellular trafficking: ADP-ribosylation factor 4 (ARF4) and valosin-containing protein (VCP). HiLo microscopy revealed ARF4 enhanced NIS trafficking in co-incident PM vesicles, governed by a C-terminal VXPX motif, whilst papillary thyroid cancers (PTC) demonstrate repressed ARF4 expression. In contrast, VCP, the central protein in ER-associated degradation, specifically bound NIS and decreased its PM localization. Five chemically distinct allosteric VCP inhibitors all overcame VCP-mediated repression of NIS function. In mice, two re-purposed FDA-approved VCP inhibitors significantly enhanced radioiodine uptake into thyrocytes, whilst human primary thyrocytes showed similar increases. Critically, PTC patients with high tumoural VCP expression who received radioiodine had strikingly worse disease-free survival. These studies now delineate the mechanisms of NIS trafficking, and for the first time open the therapeutic possibility of systemically enhancing radioiodine uptake in patients via FDA-approved drugs.\n\nOne Sentence SummaryNovel NIS interactors ARF4 and VCP alter NIS trafficking in vitro, and FDA-approved VCP inhibitors can significantly enhance radioiodine uptake.

cancer biology↗