Increased Src kinase activity is known to correlate with cancer progression and poor prognosis, indicating that Src plays a central role in cell migration and invasion. In this study, we investigated the effects of saracatinib, a Src kinase inhibitor, under anoikis-resistant conditions in colorectal cancer cells.

Wild-type and 5-fluorouracil-resistance acquired SNU-C5 colorectal cancer cells were cultured in both monolayer and spheroid systems under fetal bovine serum (FBS) or growth factor (GF) supplemented conditions. Cell viability assay, flow cytometry, wound healing assay, spheroid formation and morphometric analysis, and Western blotting were performed using both adherent cells and spheroids.

Saracatinib significantly reduced cell viability and migration in both cell lines, predominantly through the induction of apoptosis. Spheroid formation was less efficient under GF-supplemented conditions than under FBS-supplemented conditions. The anti-cancer effects of saracatinib were mediated through inhibition of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated protein kinase (ERK), or epidermal growth factor receptor (EGFR) signaling pathways. Although most cancer stem cell (CSC) markers were suppressed by saracatinib, expression of sex determining region Y-box-2 (Sox2) was paradoxically increased in monolayer cultures. Upon re-treatment with saracatinib, Sox2-upregulated cells formed larger spheroids under GF-supplemented conditions compared with wild-type cells.

Saracatinib exerts anti-cancer effects in colorectal cancer cells by downregulating MAPKs, EGFR, and CSC-associated markers. However, paradoxical upregulation of Sox2 influenced spheroid formation under GF-supplemented conditions, suggesting that Sox2 may contribute to drug resistance or recurrence in colorectal cancers.

Chitosan oligosaccharide (COS) is the major degradation product of chitosan by enzymatic processes. COS, with complete water solubility, exerts significant biological effects, including anti-cancer activity. We investigated the anti-tumor effects of COS on colorectal cancer as effective therapeutic methods with low side effects are lacking.

COS was obtained from low molecular weight chitosan by an enzymatic method and the anti-cancer effects were measured by cell viability assay, flow cytometry analysis, Western blotting, and xenograft.

COS suppressed the proliferation of SNU-C5 cells compared to other colorectal cancer cells, but higher concentrations were required in the xenograft model. Co-treatment with 5-fluorouracil (5-FU) and COS enhanced the anti-cancer effects of 5-FU in SNU-C5 cells in vitro and in vivo. Flow cytometry revealed that COS induced cell cycle arrest at the G0/G1 phase without 5-FU or at the S and G2/M phases with 5-FU but did not affect cell death pathways. COS increased extracellular signal-regulated protein kinase (ERK) activation with or without 5-FU, whereas 5-FU treatment increased p53 activation. A low-dose of an ERK inhibitor suppressed COS-induced ERK activation and resulted in higher proliferation compared with COS.

These results suggest that COS might enhance the anti-cancer effects of 5-FU in SNU-C5 colorectal cancer cells by activating ERK.