Abstract A55: DCLK1 mediates tumor stemness and platinum resistance in high-grade serous epithelial ovarian cancer

Background: Ovarian cancer is the fifth leading cause of cancer death in the United States, with an anticipated 13,000 deaths in the United States in 2017. High-grade serous (HGSOC) sub-type is both the most common and the most lethal histopathology. As more than 85% of patients present with metastatic disease, the 5-year overall survival remains dismal at only 30%. It is known that human cancers are initiated and maintained by self-renewing stem cells. Cancer stem cell related protein Doublecortin-like kinase 1 (DCLK1) is a major regulator of stemness and EMT, promoting drug resistance, tumor dormancy, progression, and metastasis in solid tumors. The molecular mechanisms of DCLK1 in tumorigenesis and drug resistance remain limited but DCLK1 expression is increased in cancer, especially in the drug-resistant setting. Results: Our lab has made the discovery that DCLK1 is overexpressed in HGSOC where it regulates tumor progression, tumor stemness, and EMT via noncoding RNA regulation of downstream oncogenic pathways. Our study involved assessment of DCLK1 expression in tissue culture and xenografts created from primary patient-derived cell lines (PDACs). Expression of the DCLK1 protein was assessed by immunoblot analysis in lysates of cell lines representing HGSOC and PDACs obtained from the ascites of patients at the University of Oklahoma at the time of diagnosis, prior to initiation of chemotherapy. FTE-187, FTE-188, and OSE cells were used as normal controls. Elevated levels of DCLK1 expression were observed in the panel of HGSOC cell lines and in PDAC lines. Our in vitro studies confirmed DCLK1 upregulation in the tissue and stroma of PDAC lines and our in vivo studies with PDAC xenografts revealed that siRNA knockdown of DCLK1 negatively regulated tumor suppressor miRNAs including mi-143/145, let-7a, and miR-200a-c resulting in downregulation of pluripotency, EMT, and proangiogenic markers including OCT4, SOX2, KLF4, NANOG, LIN28B, NOTCH, KRAS, and c-MYC. This was most pronounced in the setting of platinum resistance. For this, lysates from paired cells lines with known platinum-sensitive and platinum-resistant variants were assessed (Tyk-nu/Tyk-nu CPR and A2780/A2780.cp). An increase in DCLK1 expression was observed in both of the platinum-resistant lines compared to the platinum-sensitive lines. This was confirmed in PDACs where clinical platinum status correlated with DCLK1 expression, suggesting the role of DCLK1 in inherent platinum-resistant tumor clones. Conclusions: Our data implicate DCLK1 in ovarian cancer pathogenesis and platinum resistance and indicate that DCLK1 knockdown via may suppress malignant progression and resensitize tumors to platinum chemotherapy. These data could have a significant impact on future therapeutic strategies involving DCLK1 inhibitors in treating platinum-resistant patients. Given the high recurrence rate and inevitable development of platinum-resistant disease, such compounds have high potential to impact clinical outcomes in this lethal malignancy. Citation Format: Katherine M. Moxley, JiHee Ha, Daniel Andrade, Courtney Houchen, Danny Dhanasekaran. DCLK1 mediates tumor stemness and platinum resistance in high-grade serous epithelial ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A55.