Saquayamycin B-1 Suppresses Proliferation, Invasion, and Migration by Inhibiting PI3K/AKT Signaling Pathway in Human Colorectal Cancer Cells

Moromycin B (Mor B), saquayamycin B-1 (Saq B-1), saquayamycin B (Saq B), and landomycin N (Lan N), four angucyclines produced by the marine-derived actinomycete Streptomyces sp., are a class of polyketone compounds containing benzanthracene. Here, the structure-activity relationship of these four compounds was analyzed in human colorectal cancer (CRC) cells. Saq B-1, which showed the strongest cytotoxicity with an IC50 of 0.18-0.84 mu M for CRC cells in MTT assays, was employed to test underlying mechanisms of action in SW480 and SW620 cells (two invasive CRC cell lines). Our results showed that Saq B-1 inhibited CRC cell proliferation in a dose- and time-dependent manner. Notably, lower cytotoxicity was measured in normal human hepatocyte cells (QSG-7701). Furthermore, we observed proapoptosis, antimigration, and anti-invasion activities of Saq B-1 in CRC cells. At the same time, the protein and mRNA expression of important markers related to the epithelial-mesenchymal transition (EMT) and apoptosis changed, including N-cadherin, E-cadherin, and Bcl-2, in Saq B-1-treated CRC cells. Surprisingly, the PI3K/AKT signaling pathway was shown to be involved in Saq B-1-induced apoptosis, and in inhibiting invasion and migration. Computer docking models also suggested that Saq B-1 might bind to PI3K alpha. Collectively, these results indicate that Saq B-1 effectively inhibited growth and decreased the motor ability of CRC cells by regulating the PI3K/AKT signaling pathway, which provides more possibilities for the development of drugs in the treatment of CRC.