ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2019) 65 OC4.1 | DOI: 10.1530/endoabs.65.OC4.1

A high-throughput yellow fluorescent protein (YFP) cell-based screen identifies autophagy modulators to increase the effectiveness of radioiodine therapy

Martin Read1, Katie Baker1, Alice Fletcher1, Caitlin Thornton1, Mohammed Alshahrani1, Hannah Nieto1, Rashida Khan1, Jamie Webster2, Peter Haggie3, Alan Verkman3, Luke Alderwick4, Kristien Boelaert1, Vicki Smith1 & Christopher McCabe1

1Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, UK; 2Protein Expression Facility, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK; 3Division of Nephrology, Department of Medicine, UCSF, San Francisco, USA; 4Institute of Microbiology and Infection, School of Biosciences, University of Birmingham, Birmingham, UK

New targeted drug strategies are urgently needed to improve radioiodine uptake and efficiently ablate thyroid cancer cells thereby minimising the risk of recurrent disease. High-throughput screening (HTS) offers a promising approach to identify new candidate drugs that will induce sodium iodide symporter (NIS) function to promote iodide uptake. However, significant progress has been limited by a lack of thyroid cell-based assays amenable to HTS. Here, we constructed a thyroid cancer cell reporter consisting of a modified version of the yellow fluorescent protein (YFP) as a biosensor of intracellular iodide. We then screened the Prestwick Chemical Library (1200 drugs; 95% approved; 10 mM dose; n=2) with iodide uptake monitored by quenching of YFP fluorescence. Preliminary results showed that the YFP cell-based assay was sensitive towards iodide uptake (Z-factor=0.82) with cell viability >75% for most drugs (1033/1200; AlamarBlue). Normalization of the primary screen dataset using an interquartile mean well-based method identified 48 hit candidate drugs which increased iodide uptake >2 S.D. above mean. Of particular interest, categorisation of top hits revealed a high proportion of drugs that modulate autophagy (18/48; 37.5%) - a key process for maintaining cellular homeostasis by degrading/recycling intracellular material. Secondary screening confirmed the role of autophagy modulators in enhancing iodide uptake after ranking 73 leading compounds based on their pharmacologic (AUC, EMAX and EC50) and specificity of response (NIS+ve vs. NIS-ve YFP-thyroid cells) at ten different drug doses (0.1–50 μM). Subsequent treatment of primary human thyrocytes with the repurposed drug prestw-138 further demonstrated greater radioiodine (125I) uptake (˜3.5-fold; P<0.05). In summary, we have performed high-throughput screening and identified autophagy modulators as well as other repurposed drugs that induce iodide uptake. We propose that these drugs either alone or in combination with existing therapies might offer new therapeutic strategies to improve the treatment of thyroid cancer.