Cell-Free Supernatants from Probiotic Lactobacillus casei and Lactobacillus rhamnosus GG Decrease Colon Cancer Cell Invasion In Vitro

Probiotics have been shown to have a preventative role in colorectal carcinogenesis but research concerning their prophylactic potential in the later stages of colorectal cancer, specifically metastasis is limited. This study explored the potential of cell-free supernatants (CFS) from 2 probiotic Lactobacillus sp., Lactobacillus casei and Lactobacillus rhamnosus GG, to inhibit colon cancer cell invasion by influencing matrix metalloproteinase-9 (MMP-9) activity and levels of the tight junction protein zona occludens-1 (ZO-1) in cultured metastatic human colorectal carcinoma cells. HCT-116 cells were treated with CFS from L. casei, L. rhamnosus, or Bacteroides thetaiotaomicron (a gut commensal); or with uninoculated bacterial growth media. Treatment with CFS from both Lactobacillus sp. decreased colorectal cell invasion but treatment with CFS from B. thetaiotaomicron did not. CFS from both Lactobacillus sp. decreased MMP-9 and increased ZO-1 protein levels. L. rhamnosus CFS also lowered MMP-9 activity. To begin elucidating the secreted bacterial factor conveying these responses, Lactobacillus sp. CFS were fractionated into defined molecular weight ranges and cell invasion assessed. Fractionation revealed that the inhibitory activity was contained primarily in the >100 kDa and 50-100 kDa fractions, suggesting the inhibitory compound may be a macromolecule such as a protein, nucleic acid, or a polysaccharide.