Abstract 3915: RNAseq analysis reveals differentiation gene drivers as potential therapeutic targets in anaplastic thyroid cancer
Authors: Kopec Kaci , Jarboe Tara , Guo Michael , DeSouza Nicole R. , Singh Sarnath , Moscatello Augustine , Islam Humayun K. , Geliebter Jan , Tiwari Raj K. 
Published: April 2023

Abstract
Papillary thyroid cancer (PTC) is a well-differentiated and highly treatable cancer with a 5-year survival rate of almost 99%. In contrast, anaplastic thyroid cancer (ATC) lacks differentiation and loses its thyroid-like functions, including lack of response to radioiodine therapy. Due to ATC’s aggressive metastatic phenotype, it is always diagnosed as stage IV with a 5 year survival rate of less than 3%. ATC lacks targetable genetic lesions making it a difficult cancer to treat, therefore RNAseq analysis was performed in an effort to investigate the differentially expressed genes between ATC to PTC. Exploration of differential gene expression between ATC and PTC was undertaken to further elucidate the differences in expression that drive the aggressive nature of ATC phenotype. RNA was isolated from human thyroid cancer cell lines T238 (ATC) and K1 (PTC) and RNA sequencing was conducted by Azenta Life Sciences. Our analysis resulted in 4,931 significant differentially expressed genes between ATC and PTC. Looking at the gene ontology analysis, pathways involving cell differentiation, proliferation, and migration revealed 90, 70, and 47 genes differentially expressed in ATC vs PTC respectively. These pathways putatively give rise to ATC’s aggressive phenotype when compared to PTC, therefore, we narrowed down the focus from 4,931 genes to 207. Through RNAseq analysis, Homeobox D4 (HOXD4) was observed to significantly increase in ATC (7.69 log2 fold change) compared to PTC. HOXD4 is a transcription factor that plays a crucial role in cell differentiation and has been associated with a worse prognosis in cancers such as ovarian serous carcinoma. As loss of differentiation is essential to ATC’s refractory nature and therapeutic resistance, targeting pathways involved in differentiation can be crucial in making ATC amenable to therapy. Other differentiation regulatory genes identified include BLK and LAMA5. BLK (3.95 log2 fold change) is a Src family tyrosine kinase proto-oncogene that is not only involved in cell proliferation but also differentiation. LAMA5 (4.76 log2 fold change) is an extracellular glycoprotein that has been linked to differentiation, migration and metastasis. Validation of the RNAseq results was completed via western blot analysis of multiple ATC and PTC cells lines. We found that HOXD4 expression was higher in ATC cell lines T238, 8505C, and SW1736 than PTC cell lines K1, TPC1, and BCPAP. Further validation was carried out by immunohistochemistry of human thyroid tissue. Preliminary IHC on ATC, PTC, and normal thyroid patient samples showed ATC has significantly increased HOXD4 expression (27.5%) compared to PTC (8.7%) and normal thyroid tissue (2.3%). Ongoing studies in the laboratory to identify novel genetic drivers of cell differentiation and proliferation so as to discover a therapeutic target to fulfill an unmet clinical need is underway.
Citation Format: Kaci Kopec, Tara Jarboe, Michael Guo, Nicole R. DeSouza, Sarnath Singh, Augustine Moscatello, Humayun K. Islam, Jan Geliebter, Raj K. Tiwari. RNAseq analysis reveals differentiation gene drivers as potential therapeutic targets in anaplastic thyroid cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3915.