Abstract 2328: Targeting self-renewal in human colorectal cancer by inhibiting SUMOylation

Abstract

Abstract Colorectal cancer is the third most commonly diagnosed cancer and the second leading cause of cancer death in the US. It is well recognized that cancer stem cells (CSCs) are responsible for treatment resistance, tumor metastasis and relapse, which cause treatment failure. SUMOylation is known to be important for pluripotency and is dysregulated in cancers to drive tumor growth and metastasis. Therefore, we investigate the role of SUMOylation in colorectal cancer CSC maintenance and self-renewal. In this study, we established that aldehyde dehydrogenase 1 (ALDH1) activity is a valid marker of colorectal CSCs, because ALDH+ cells in HT29 displayed CSC properties including self-renewal, clonal formation and tumor initiation in NSG xenograft mouse model, while ALDH- cells did not. Profiling ALDH+ and ALDH- cells showed that SUMO-activating enzyme (SAE) is highly enriched in ALDH+ cells along with enhanced global SUMOylation. Overexpression of the catalytic subunit of SAE, SAE2, increased the population of ALDH+ cells while knockdown of SAE2 decreased the population of ALDH+ cells. This result suggests that increased SAE level promotes stemness in colorectal cells. To characterize CSC maintenance and self-renewal quantitatively, we performed limited dilution assays in vitro with sphere initiation and in vivo using mouse xenograft models. In in vitro assays, we observed 4-fold reduction in CSC self-renewal frequency in SAE2 knockdown cells compared to control cells in the colorectal cancer cell line HT29. In four colorectal cancer patient-derived primary culture cells, the frequency was 2∼6 fold lower in SAE2 knockdown groups than control. In the in vivo experiment, SAE2 knockdown group showed 12-fold reduction in self-renewal frequency of HT29 cells. These data demonstrate that silencing of SAE2 causes a significant decrease in stemness of colorectal cancer cells, both in HT29 cell line and primary human tumors. Mechanistic analysis regarding how SUMOylation regulate colorectal cancer CSC is underway and will be discussed. In conclusion, our study indicates that SUMOylation, in particular the SAE, is an important regulator of colorectal CSC maintenance and self-renewal. Therefore, the data suggests that targeting SAE is a potential strategy to inhibit colorectal CSC. Citation Format: Li Du, Yuan Chen. Targeting self-renewal in human colorectal cancer by inhibiting SUMOylation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2328. doi:10.1158/1538-7445.AM2015-2328