EP532 - Innate and Shared ST6GAL1 in Colorectal Adenocarcinoma Migration and Metastasis

Purpose/Background: Colorectal cancer (CRC) can be a highly morbid and fatal disease, especially when presenting at an advanced stage. We have previously shown that ST6GAL1, a glycosyltransferase that adds alpha 2,6-sialic acid to N-glycans, is important in treatment response. We hypothesized that innate and exosome-shared ST6GAL1 may increase CRC migration and metastasis.

Methods/Interventions: We isolated exosomes from SW620 cells and assessed for ST6GAL1 via Western blot. We performed soft agar assay to test ability of SW620 cells with ST6GAL1 or ST6GAL1 knockdown (KD) to perform anchorage independent growth. We tested human colorectal cancer SW620 cell migration in a transwell assay when co-cultured with cells that produce exosomes containing ST6GAL1 versus no cells. We developed an orthotopic needle injection animal model of colorectal cancer using CT26 cells with or without ST6GAL1 overexpression (OE) and assessed for differences in animal survival.

Results/Outcomes: Exosomes from SW620 control vector (CV) cells contain ST6GAL1 (Fig A). When SW620 CV cells were compared with ST6GAL1 KD cells in the soft agar assay, we found decreased colony formation in the KD cells (Fig. B). Culturing ST6GAL1 KD cells in transwell inserts demonstrated increased migration when co-cultured with ST6GAL1 CV cells, and therefore exposed to ST6GAL1 CV exosomes, compared with no co-cultured cells (Fig. C). In the orthotopic needle injection model, survival was worse in mice with CT26 ST6GAL1 OE tumors compared with CV (Fig. D). There were no liver metastases, but there were 2 animals with lung metastases but no differences between the genotypes. When considering the cause of death, the mice grossly and on computed tomography imaging demonstrated large primary tumors, cachexia, and large bowel dilation indicative of obstruction.

Conclusion/Discussion: Expression of ST6GAL1 was sufficient to improve anchorage independent growth, a key feature of metastatic cancer cells. Exposure to ST6GAL1 containing exosomes increased migration of human CRC cells in vitro. In an animal model of CRC, the presence of ST6GAL1 was associated worse survival. ST6GAL1 expressing cells can transfer the enzyme in exosome cargo to cells without ST6GAL1, increasing cell migration. These data together indicate that innate and exosome-shared ST6GAL1 protein contribute to increased migration of tumor cells in CRC.

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