This item is non-discoverable
Targeting cancer stem cell differentiation in colorectal cancer
Date
2025
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
The goal of this dissertation is to sensitize human colorectal cancer (CRC) to the differentiation-inducing effects of retinoic acid (RA) agents by suppressing WNT signaling. We previously reported a mechanism that functionally links the RA and WNT signaling pathways, which are both involved in CRC development, and that APC mutation causes a WNT: RA imbalance that leads to incomplete differentiation and stem cell (SC) overpopulation. This dissertation further investigates the interplay between both pathways and evaluates the therapeutic potential of combining RA and anti-WNT agents. We hypothesized that therapeutically inhibiting therapeutically inhibiting WNT signaling would sensitize CRC cells to the anti-tumor effects of retinoid agents and would also enhance the ability of retinoids to induce growth suppression and differentiation of CRC stem cells. Multiple in vitro and in vivo were employed, including the use of CRC cell lines, organoid cultures, CRISR/CaS9 mediated gene editing, and patient-derived xenograft (PDX) models. We tested: 1). anti-WNT agents (sulindac & piroxicam) that decrease WNT signaling in vitro and the in vivo anti-tumor activity in humans and animals harboring APC germline mutations, combined with 2). RA agents (All-trans-RA, 13-cis RA, 9-cis RA) and RA metabolism blocking agents (CYP26A1 inhibitors Liarozole and talarozole), which inhibit proliferation and induce differentiation of CRC cell lines. The key findings show that the combined effect of anti-WNT agents and RA agents inhibit CRC cell proliferation both dose and time-dependently and also shows synergistic responses most pronounced in HCT116 cells. Drug combinations, particularly 9-cis RA with sulindac, decrease the proportion of aldehyde dehydrogenase-positive SCs and increase neuroendocrine cell differentiation in beta-catenin but not APC, mutant CRC cells. Gene expression analyses revealed that sulindac modulates the expression of WNT-regulating elements (WREs) and enhances the retinoid-induced transcriptional changes with upregulated genes in HCT116 cells involved in cellular differentiation. Knockout of RARĪ± in HT29 cells resulted in lower sensitivity to ATRA, slower division rates, and increased ALDH+ SCs. Treating CRC organoid cultures with WNT: RA-based drug combinations lead to greater anti-tumor activity as compared to individual agents. Triple drug combinations significantly reduced tumor volume in PDX models. Thus, inhibiting WNT signaling effectively sensitizes CRC cells to the anti-tumor effects of retinoids. These combination findings have important clinical significance and offers a promising approach for designing new drug combinations against CRC.
Description
Keywords
Retinoic acid, Colorectal cancer, Stem cell, Organoid cultures, Patient-derived xenograft