Human squamous cell carcinoma of the tongue and colon undergoes apoptosis upon phagocytosis of Saccharomyces cerevisiae, the baker's yeast, in vitro.

The present study was carried out to evaluate the effect of phagocytosis of killed yeast on the induction of apoptosis in two human solid tumors of the gastrointestinal (GI): the squamous cell carcinomas of the tongue (SCCA) are (SCC-4 and SCC-9) and the adenocarcinomas of the colon (ADENOCA) are (Caco-2 and DLD-1). Cancer cells were cultured with heat killed Saccharomyces cerevisiae, baker's and brewer's yeast, at ratio of yeast to cancer cells = 10:1. The percentage of tumor cells that had attached/phagocytosed yeast and oxidative burst was determined by using oxidative sensitive dye (DCFH-DA) and flow cytometry. SCC-4 and colon Caco-2 cells demonstrated initial high levels of phagocytosis that peaked (35.8-52.8%) at 2 hr. The oral SCC-9 and colon DLD-1 cells demonstrated low phagocytic activity (7-12%). Phagocytosis was not associated with oxidative burst. Upon phagocytosis of yeast, cancer cells underwent apoptosis that was maximized at 4 hr. Yeast-induced apoptosis was significant in SCC-4 (45%), as compared with SCC-9 cells (17%), and Caco-2 (76%), as compared with DLD cells (12%). Apoptosis in cancer cells was inhibited by caspase inhibitor, Z-VAD-FMK; this suggests that caspases may be involved in apoptosis of the GI cancers. This data may have clinical implications for the treatment of solid tumors.