Abstract 6068: Restoring the balance between WNT and retinoic acid signaling to promote differentiation of cancer stem cells in treatment of colorectal cancer

Abstract

Abstract Given that the stem cell (SC) marker ALDH is a key component of the retinoic acid (RA) signaling pathway and since APC mutation leads to increased WNT signaling and overpopulation of ALDH+ SCs in colorectal cancer (CRC), we hypothesized that human CRC evolves due to an imbalance between dysregulated RA and WNT signaling. Herein, we investigated how to target the link between these two pathways to restore proper WNT and RA signaling, and promote differentiation of CSCs along the neuroendocrine cell (NEC) lineage. Accordingly, we conducted in vitro experiments to determine if restoring wt-APC in APC-mutant CRC cells reduces Wnt/β-catenin signaling, increases sensitivity to retinoids, reduces cell proliferation, reduces expression of stem cell markers, reduces the number of ALDH+ cells, and enhances NEC maturation. We utilized Nanostring profiling, TCF reporter assay, western blot, and fluorescence activated cell sorting analyses to ascertain the effects of restoring WNT in HT29 CRC cells. We found that induction of wt-APC expression decreased WNT/β-catenin signaling and reduced protein expression of WNT-target genes. Notably, inducing wt-APC decreased ATRA-induced expression of the WNT target gene CYP26A1 (by 50%), which is predicted to increase RA signaling by lowering the degradation of RA. Indeed, wt-APC increased sensitivity of CRC cells to ATRA-induced inhibition of cell proliferation in a dose-dependent manner. Expression of ALDH1A1 decreased 3-fold by ATRA treatment and inducing wt-APC furthered the decrease by an additional 2-fold. Furthermore, we found an increase in the protein expression of several NEC markers including CHGA, GLP2R, NSE (ENO2), and SSTR1, and an increased number of GLP2R+ NECs upon inducing wt-APC. Thus, the link between WNT and RA signaling at the level of CYP26A1, provides a mechanism that can explain how mutant APC leads to decreased maturation of ALDH+ SCs along the NEC lineage and an increased number of ALDH+ SCs. Therefore, discovering ways to increase differentiation of SCs along the NEC lineage in vivo might lead to new more effective treatment strategies involving retinoids for CRC patients. Citation Format: Caroline O. Facey, Victoria O. Hunsu, Brian T. Osmond, Lynn M. Opdenaker, Bruce M. Boman. Restoring the balance between WNT and retinoic acid signaling to promote differentiation of cancer stem cells in treatment of colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6068.