Autophagy Inhibition Enhances SPCA-1 Cell Proliferation Inhibition Induced by By-1 from the Stout Camphor Medicinal Mushroom, Taiwanofungus camphoratus (Agaricomycetes)

Abstract

Taiwanofungus camphoratus has been reported to have antitumor effects against various cancer cells. The aim of this study was to investigate the direct inhibitory effect of By-1 (3-isobutyl-l-methoxy-4-[4'-(3-methylbut-2-enyloxy)phenyl]-1H-pyrrole-2,5-dione), a compound from spent broth from submerged cultures of T. camphoratus, on human lung adenocarcinoma cells and to determine the molecular mechanism underlying this effect. The growth-inhibitory assay and colony formation assay showed that cell viability was significantly decreased. A By-1 concentration of 300 μmol/L caused 73.55% cell death and at a concentration of 240 μmol/L led to a 58% reduction in the number of colonies. The wound-healing assay showed that the distance of migration was 0.3 times shorter than that of untreated cells. Flow cytometry revealed that By-1 could suppress DNA synthesis, cause cell cycle arrest at the S phase, and induce apoptosis in a reactive oxygen species-dependent manner. Furthermore, the expression of caspase-3 and P53 was 4 times higher than that in untreated cells, and the antiapoptotic protein Bcl-2 was decreased 2 times compared with the protein in untreated cells. It is interesting to note that apoptosis and autophagy were both induced during treatment with By-1, and autophagy inhibition decreased cell proliferation. By-1 potently inhibited the growth of SPCA-1 cells by inducing cell cycle arrest and apoptosis. The combination of proapoptosis agents and antiautophagy agents could effectively enhance anticancer efficacy, which may be a new strategy in treating non-small cell lung cancer.