Anaplastic Thyroid Cancer: Identification of Candidate Therapeutics and Mechanisms of Disease Progression
Abstract
Malignancies derived from follicular cells of the thyroid can be divided into well-differentiated thyroid cancer (WDTC), poorly differentiated thyroid cancer and anaplastic (undifferentiated) thyroid cancer (ATC). While the majority of thyroid cancers are well-differentiated in nature and have an excellent prognosis, ATC is rare, nonresponsive to conventional therapies, and is nearly universally fatal. In this study, I employed high-throughput screening of kinase inhibitors to identify candidate drugs to control ATC and expanded these studies to include a focus on studying the underlying progression from WDTC to ATC. Two compounds, lestaurtinib (JAK2 inhibitor) and flavopiridol (pan-CDK inhibitor) were selected from the high-throughput screen for follow-up studies. Our first study showed that lestaurtinib demonstrated a potent antiproliferative effect and impeded cell migration and colony formation in addition to causing cell cycle arrest following drug treatment. Ex vivo, we used the chick chorioallantoic membrane model to demonstrate that lestaurtinib resulted in a significant decrease in endpoint tumour volume and tumour vascularity, together highlighting an antiproliferative and potentially antiangiogenic effect. In our second study, we found that flavopiridol treatment in vitrohad an antiproliferative effect and induced cell cycle arrest. In vivo, flavopiridol decreased tumour volume and tumour growth over time using a patient-derived xenograft model of ATC. Finally, we sought to determine whether the introduction of a canonical PIK3CA (E545K) mutation, characteristically found at a higher mutation frequency in ATC, would contribute to disease progression when expressed in a BRAF-mutant WDTC cell line. In vitro, we demonstrated that the PIK3CA mutation resulted in an increase in cell proliferation and the ability of cells to form colonies and migrate. When we compared both cell lines for their tumourigenic capabilities in vivo using a patient-derived xenograft model, we found that while the average tumour volume was higher in the PIK3CA group, the difference was not significant. Collectively, this thesis identified two candidate therapeutic agents with potential to improve patient outcomes and identified PIK3CA as a driver of thyroid cancer progression.