Abstract

Introduction: Gastrointestinal cancers’ liver metastases or peritoneal carcinomatosis frequently do not coexist. They are associated to specific types of cancers, like “adenoma-to-carcinoma” and “serrated” colon cancers respectively. Pre-metastatic niches, circulating cell clusters, and polyclonal cooperation, show these are non-cell autonomously regulated processes. In vivo visualization of this cell interaction requires high-resolution intra-vital imaging, which is bounded to superficial and small spatial and short observational windows, in syngeneic murine models of experimental metastases. Method: In search for a model to observe differences of cancer cell interactions in vivo, we followed in real-time the engraftment of two ontologically divergent human colon cancer cell lines, SW620 and RKO -that match with the combinatorial genotypic features of the adenoma-to-carcinoma and serrated pathways respectively-, in a zebrafish xenograft model. Whole organism prolonged imaging allowed unbiased observation of engraftment mechanisms distant to the injection site. Results: SW620 cells formed tumors in the the caudal hematopoietic tissue when injected into the blood stream of 2dpf zebrafish larvae, while RKO cells were unable to engraft through this route. Engraftment was dependent on the formation of intravascular cell clusters by active cell adhesion of SW620 cells, while RKO did not cluster and their deformability precluded their entrapment in any vascular territory. Contrarily, RKO cells engrafted and invaded the surrounding tissues when injected into the brain ventricles, while SW620 cells remained confined to the ventricles with progressive decrease in the volume they occupied. RKO cells migrated through the neural tube lumen, and established invasive secondary colonies in distal locations. When both cell lines were implanted together at this site, they behaved as predicted by the differential adhesion hypothesis. The SW620 cells expressed high levels of E-cadherin, absent in RKO, which expressed high levels of CD44 involved in cell-ECM interaction and chemoattraction. Loss-of-function experiments of these adhesive features are underway.