Abstract 2457: Restoring the balance between WNT and retinoic acid signaling to promote differentiation of cancer stem cells in treatment of colorectal cancer

Abstract

Abstract Dysregulated WNT signaling caused by mutation in the APC gene occurs in 80-90% of all colorectal cancer (CRC) cases. Progressive overpopulation of ALDH+ stem cells occurs during development of CRC in familial adenomatous polyposis (FAP) patients. Given that ALDH is a key member of the retinoic acid signaling (RA) pathway, we hypothesize that human CRC is caused by an imbalance between dysregulated WNT and RA signaling. Herein, we aim to restore proper WNT and RA signaling and identify a common link or target to induce differentiation of CSCs along the neuroendocrine cell (NEC) lineage. Accordingly, to determine the effects of restoring wt-APC in APC-mutant HT29 CRC cells, we conducted in vitro experiments to examine Wnt/β-catenin signaling, sensitivity to retinoids, cell proliferation, expression of stem cell markers, quantification of ALDH+ stem cells, and NEC maturation. We utilized Nanostring profiling, TCF reporter assay, western blot, and fluorescence activated cell sorting analyses to ascertain these effects. 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, in turn, increase RA signaling by lowering degradation of RA. Indeed, inducing wt-APC increased sensitivity of CRC cells to ATRA-induced apoptosis and inhibition of cell proliferation in a dose-dependent manner. Expression of ALDH1A1 decreased (3-fold) with ATRA treatment and inducing wt-APC extended the decrease by an additional 2-fold. Furthermore, upon inducing wt-APC, 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. We also discovered a very highly regulated protein network of 248 proteins and identified a cell signaling mechanism that links the WNT and retinoic acid pathways via CYP26A1. Thus, by inducing wt-APC expression and exogenously activating RA signaling, we found a way to increase differentiation of SCs along the NEC (and other) lineage(s). Translating this strategy in vivo might lead to new, more effective treatments involving retinoids for CRC patients. Citation Format: Caroline O. B. Facey, Victoria O. Hunsu, Brian T. Osmond, Chi Zhang, 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 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2457.