Abstract A12: L1CAM defines the regenerative origin of metastasis initiating cells in colorectal cancer

Metastatic cancers relapse due to the emergence of stemlike clones capable of reversible quiescence, tumour reinitiation, and therapy resistance termed metastasis-initiating cells (MICs). The origins of MICs and their relationship to primary tumor-initiating cells are not known, largely due to a lack of representative models of MICS. To directly scrutinize MICs in patient metastases, we established organoid cultures from therapy-resistant, residual colorectal cancer (CRC) liver metastases of patients undergoing cancer surgery. We identify the neuronal cell adhesion molecule L1 (L1CAM) as a critical mediator and marker of colorectal cancer (CRC) MICs. L1CAM+ cells are quiescent in well-structured neoplastic glands in vivo, but when dissociated from their epithelial niche, drive organoid regeneration and xenograft tumor reinitiation. FACS-sorted L1CAM+ cells preferentially regenerate heterogeneous organoids containing both L1CAM+ and L1CAM- progeny. Single-cell mRNA sequencing of 10,000 cells from four patient-derived organoids reveals that L1CAMhigh MICs in human CRC organoids partially overlap with a subset of LGR5high cancer stem cells (CSCs). The number of LGR5-expressing cells decreases, while the number of L1CAM-expressing cells increases in metastases in comparison with primary tumors in patients. We show that L1CAM is required for organoid formation, intestinal epithelial repair following colitis in vivo, regeneration of orthotopic rectal tumors, and metastatic colonization of the liver, but is dispensable for intestinal epithelial homeostasis or tumor initiation. Mechanistically, disruption of intercellular epithelial contacts inhibits an E-cadherin-REST signaling axis and enables transcriptional derepression of L1CAM. Our work underscores the distinct requirements of the CSCs that initiate tumor growth and MICs that drive lethal metastatic relapse. We identify the loss of epithelial integrity, an obligatory step of metastasis, as a crucial molecular driver of the transcriptional plasticity required for the emergence of prometastatic traits. Further, we define L1CAM as a crucial vulnerability of MICs that could be exploited therapeutically to treat patients with metastatic cancer. Citation Format: Karuna Ganesh, Harihar Basnet, Yasemin Kaygusuz, Ashley Laughney, Lan He, Roshan Sharma, Kevin O9Rourke, Vincent Reuter, Yun-Han Huang, Ignas Masilionis, Mesruh Turkekul, Ekrem Er, Katja Manova-Todorova, Leonard Saltz, Martin Weiser, Julio Garcia-Aguilar, Richard Koche, Scott Lowe, Dana Peer, Jinru Shia, Joan Massague. L1CAM defines the regenerative origin of metastasis initiating cells in colorectal cancer [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A12.