Abstract 122: Novel role of SLC22A3 in serotonin transport and subsequent regulation of the pancreatic cancer stemness machinery

Abstract Cancer stem cells (CSCs) are a small subpopulation within tumors that possess self-renewal and differentiation capabilities, driving tumor recurrence, therapy resistance, disease aggressiveness, and metastasis. In pancreatic cancer (PC), the mechanisms governing CSC self-renewal remain poorly understood, despite their critical role in malignancy. Emerging evidence indicates that normal embryonic and adult progenitor stem cells share molecular characteristics with CSCs, suggesting that early pluripotency programs may be reactivated during oncogenesis, contributing to cancer aggressiveness. In this study, we investigated novel stemness regulators that drive CSC self-renewal in PC. By performing computational analyses of gene signatures shared between embryonic stem cells, CSCs, and PC cells using publicly available datasets, we identified several putative stemness-associated genes, including SLC22A3/OCT3. Our results reveal that SLC22A3/OCT3 is highly expressed in CSC sub-type population and pancreatic tumor tissues and organoids derived from Kras; PdxCre (KC) and Kras; p53; PdxCre (KPC) mouse models, while its expression is minimal or absent in normal pancreatic tissues. Functional studies demonstrated that knockdown (KD) of SLC22A3/OCT3 in PC cell lines significantly reduced spheroid size in serum-free 3D cultures, indicating a decline in the CSC population. Flow cytometry further confirmed a marked reduction in the side population (SP) fraction in SLC22A3/OCT3 KD clones compared to controls. In vivo, SLC22A3/OCT3 depletion led to reduced tumor burden and impaired oncogenic dedifferentiation, a hallmark of CSCs in PC. SLC22A3/OCT3, a transmembrane transporter, facilitates the uptake and efflux of organic cations, including monoamine neurotransmitters such as serotonin, dopamine, and norepinephrine. Interestingly, serotonin supplementation increased stemness potential in PC cells, but this effect was absent in SLC22A3/OCT3 KD clones, implicating serotonin transport as a key mechanism in CSC regulation. Mechanistically, we propose that SLC22A3/OCT3 regulates serotonin transport in pancreatic CSCs, activating downstream pathways that enhance transcription factor binding and upregulate self-renewal and pluripotency-related genes. This process may involve serotonin-mediated epigenetic modifications, including serotonylation, to maintain CSC stemness and drive pancreatic tumor aggressiveness. Our findings highlight SLC22A3/OCT3 as a critical regulator of serotonin-driven stemness in PC. Understanding its role in CSC biology may provide novel insights into pancreatic cancer pathogenesis and open avenues for the development of targeted therapies aimed at disrupting CSC-mediated tumor progression. Citation Format: Nivedeta Krishna Kumar, Bhuvaneshwari Seshadri, Venkatesh Varadharaj, Neelanjana Gayen, Palanisamy Nallasamy, Zahraa Wajih Alsafwani, Kirtana Arikath, Annant Bir Kaur, Surinder Batra, Moorthy Ponnusamy. Novel role of SLC22A3 in serotonin transport and subsequent regulation of the pancreatic cancer stemness machinery [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 122.