Abstract LB-142: Identification of STK33 as a cancer stemness kinase and regulator of Nanog function

In recent years evidence has accumulated in support of the cancer stem cell (CSC) model in cancer chemotherapy resistance, highlighting the urgency and necessity of identifying CSC targets for developing novel cancer therapeutics. A number of studies have suggested that Nanog is a crucial factor that can confer stemness properties to a portion of the heterogeneous cancer cell population. Although latent in normal somatic cells, aberrant expression of Nanog has been reported in many types of human cancers. Importantly, the expression levels of Nanog are often positively correlated with treatment resistance and poor survival of cancer patients. Various studies have shown that upregulation of Nanog expression enhances the tumorigenicity both in vivo and in vitro whereas repression or ablation of Nanog inhibits tumor initiation. Thus, expression of the stemness factor Nanog is linked to tumor progression, therapeutic resistance, relapse and metastasis. However, Nanog is considered a non-druggable target. Here we provide data to support a role for STK33 (Serine Threonine Kinase 33) as a novel regulator of Nanog and as a potential therapeutic target. Ectopic STK33 expression promotes stemness phenotypes of cancer cells and increases expression levels of CSC drivers including Nanog, KLF4, and SOX2. On the other hand, knockdown of STK33 inhibits expression of Nanog and results in a reduction of the stemness phenotype. STK33 directly interacts with Nanog and appears to promote its stabilization through phosphorylation, resulting in increased Nanog transcriptional activity. Moreover, BBI-503 (Amcasertib), a first-in-class cancer stemness inhibitor, potently inhibits STK33, which led to inhibition of phosphorylation of Nanog. Collectively, our data demonstrate STK33 is a critical element in the signaling network that governs the stemness of cancer cells, and as a promising therapeutic target for cancer. Citation Format: Susan L. Tran, Yudai Furuta, Chen Zhu, Ao Yang, Xiangao Sun, Harry A. Rogoff, Chiang J. Li. Identification of STK33 as a cancer stemness kinase and regulator of Nanog function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-142. doi:10.1158/1538-7445.AM2017-LB-142