Putative probiotics decrease cell viability and enhance chemotherapy effectiveness in human cancer cells: role of butyrate and secreted proteins

Recent advances have highlighted probiotic role in preventing colorectal cancer, by promoting differentiation, inhibiting proliferation, and inducing apoptosis in colonocytes. Here, three ascertained probiotics (L. rhamnosus GG ATCC 53103, L. reuterii DSM 17938 and L. johnsonii LC1) and four food-isolated putative probiotics (L. plantarum S2, L. plantarum O2, L. pentosus S3, L. rhamnosus 14E4) were investigated for their ability to adhere to HT29 cancer cells and to inhibit their and the chemoresistant counterpart (HT29-dx cells) proliferation. Three putative probiotics (S2, S3 and 14E4) were able to decrease viability of both sensitive and chemo-resistant HT-29 cells. Supposing this effect related to secreted metabolites (namely short chain fatty acids (SCFA), exopolysaccharides (EPS) and extracellular proteins) we tested the efficacy of extracellular extracts and butyrate with or without the chemotherapeutic agent doxorubicin (DOXO) (10 µM, 4 h). Increased production of mitochondrial reactive oxygen species (ROS) in HT29 and HT29-dx cells was observed. Moreover, cell exposure to DOXO (10 µM, 24 h) and extracellular extracts (48 h) reduced cell viability. Comparative phenotypic and secretome analyses on the effective/non effective strains, revealed quantitative/qualitative differences in EPS content and protein profiles, suggesting that P40, phage-tail-like and capsid-like proteins may be also involved. These results suggest that food-isolated bacteria releasing bioactive compounds (butyrate, EPS and peculiar proteins) may control cancer cell proliferation and improve their response to chemotherapy.