Targeting SNAI1-Mediated Colorectal Cancer Chemoresistance and Stemness by Sphingosine Kinase 2 Inhibition

Background: Epithelial-to-mesenchymal transition (EMT), cancer stem cells (CSCs), and colorectal cancer (CRC) therapy resistance are closely associated. Prior reports have demonstrated that sphingosine-1-phosphate (S1P) supports stem cells and maintains the CSC phenotype. We hypothesized that the EMT inducer SNAI1 drives S1P signaling to amplify CSC self-renewal capacity and chemoresistance. Methods: CRC cell lines with or without ectopic expression of SNAI1 were used to study the role of S1P signaling as mediators of cancer stemness and 5-fluorouracil (5FU) chemoresistance. The therapeutic ability of sphingosine kinase 2 (SPHK2) was assessed using siRNA and ABC294640, a SPHK2 inhibitor. CSCs were isolated from patient-derived xenografts (PDXs) and assessed for SPHK2 and SNAI1 expression. Results: Ectopic SNAI1 expressing cell lines demonstrated elevated SPHK2 expression and increased SPHK2 promoter activity. SPHK2 inhibition with siRNA or ABC294640 ablated in vitro self-renewal and sensitized cells to 5FU. CSCs isolated from CRC PDXs express increased SPHK2 relative to the non-CSC population. Combination ABC294640/5FU therapy significantly inhibited tumor growth in mice and enhanced 5FU response in therapy-resistant CRC patient- derived tumor organoids (PDTOs). Conclusions: SNAI1/SPHK2 signaling mediates cancer stemness and 5FU resistance, implicating S1P as a therapeutic target for CRC. The S1P inhibitor ABC294640 holds potential as a therapeutic agent to target CSCs in therapy refractory CRC.