Undergraduate Researcher University of Maryland Frederick, Maryland, United States
Introduction: BRAFV600E is a common mutation in the MAP kinase (MAPK) pathway that contributes to life threatening forms of thyroid cancer including advanced papillary and anaplastic thyroid cancer (PTC and ATC). Despite the FDA-approved drug combination therapy of MAPK inhibitors including dabrafenib (BRAFi) and trametinib (MEKi), patients exhibit de novo resistance or develop resistance over time. BRAF-mutant forms of thyroid cancer have variations in incidence and severity between males and females, suggesting the role of sex hormones and their receptors in thyroid cancer progression and severity. The Schweppe Lab has recently observed an induction of androgen receptor (AR) gene and protein expression in cells that are resistant or sensitive to BRAFi. In this project, we evaluated the role of AR in resistance to BRAFi using genetic and pharmacologic approaches.
Materials and
Methods: BRAFi-sensitive (CUTC5) and -resistant (CUTC60) thyroid cancer cell lines were transduced with an AR-overexpressing lentivirus (AR GC-E2325) or an empty vector control lentivirus (EV). Cells were treated with dabrafenib or corresponding vehicle. Western blotting was used to monitor AR overexpression levels. The CellTiter-Glo assay was used to measure cell growth and viability over 3 to 6 days. The Incucyte Scratch Wound assay was used to measure collective cell invasion. Subcellular fractionation was performed to monitor AR nuclear localization.
Results, Conclusions, and Discussions: Exogenous expression of AR results in a 12% increase in cell growth in CUTC5 cells in absence of drug. Initial experiments showed that exogenous AR expression promotes resistance to BRAFi. However, this effect was lost in subsequent experiments. BRAFi increases endogenous and exogenous AR nuclear accumulation, suggesting increased AR transcriptional activity in response to BRAFi. Finally, exogenous overexpression increases invasion in the CUTC60 cells.
The increase in cell growth by exogenous AR expression indicates that AR may be an important mediator of thyroid cancer progression. BRAFi induction of AR gene and protein expression, along with nuclear accumulation suggests that AR may mediate resistance to BRAF-directed therapies in thyroid cancer. Our data further indicates that thyroid cancer cells may rapidly adapt to exogenous AR expression, which will be evaluated in future studies. Overall, androgen signaling may contribute to thyroid tumor progression and response to BRAF-directed therapies.
Acknowledgements (Optional): I would like to express gratitude for the resources provided by the Schweppe laboratory, to Rebecca Schweppe and Vibha Sharma, the University of Colorado Cancer Center's Cancer Research Experience for Undergraduates (CREU) as part of the NCI grant 1R25CA240122.
