Baker’s Yeast Sensitizes Metastatic Breast Cancer Cells to Paclitaxel In Vitro

Our earlier studies have demonstrated that phagocytosis of baker’s yeast (Saccharomyces cerevisiae) induces apoptosis in different cancer cell lines in vitro and in vivo. This study aimed to examine how baker’s yeast sensitizes murine and human breast cancer cells (BCC) to paclitaxel in vitro. This sensitizing effect makes lower concentrations of chemotherapy more effective at killing cancer cells, thereby enhancing the capacity of treatment. Three BCC lines were used: the metastatic murine 4T1 line, the murine Ehrlich ascites carcinoma (EAC) line, and the human breast cancer MCF-7 line. Cells were cultured with different concentrations of paclitaxel in the presence or absence of baker’s yeast. Cell survival and the IC(50) values were determined by MTT assay and trypan blue exclusion method. Percent of DNA damage, apoptosis, and cell proliferation were examined by flow cytometry. Yeast alone and paclitaxel alone significantly decreased 4T1 cell viability postculture (24 and 48 hours), caused DNA damage, increased apoptosis, and suppressed cell proliferation. Baker’s yeast in the presence of paclitaxel increased the sensitivity of 4T1 cells to chemotherapy and caused effects that were greater than either treatment alone. The chemosensitizing effect of yeast was also observed with murine EAC cells and human MCF-7 cells, but to a lesser extent. These data suggest that dietary baker’s yeast is an effective chemosensitizer and can enhance the apoptotic capacity of paclitaxel against breast cancer cells in vitro. Baker’s yeast may represent a novel adjuvant for chemotherapy treatment.