Probiotic Lactobacillus casei Inhibits Oral Squamous Cell Carcinoma Growth and Induces Apoptosis In Vitro

Oral squamous cell carcinoma (OSCC) is a significant cause of mortality. Probiotic bacteria like Lactobacillus casei have shown anti-cancer and immune-modulatory properties. This study aimed to investigate the anti-proliferative effects of L. casei on OSCC and its apoptotic mechanisms.

Human head and neck squamous cell carcinoma (HNSCC) cells of the oral cavity (HNO97 cell line) were exposed to L. casei at concentrations of 1 × 10⁸ CFU/ml and 5 × 10⁷ CFU/ml, and the viability of HNO97 cells was assessed by MTT assay. Bacterial attachment was studied by live confocal microscopy, and apoptosis was confirmed by Nexin staining. The underlying mechanisms of apoptosis were studied by examining the expression of the TRAIL gene and its encoding protein, TNF-related apoptosis-inducing ligand (TRAIL) by RT-PCR and ELISA, respectively.

L. casei adhered to HNO97 cells and demonstrated an anti-proliferative effect, reducing cell viability of L. casei-treated HNO97 cells by 50%. Compared to untreated cells (90%), only ∼45% of L. casei-treated cells remained live and intact, with 20.5%-31.5% of cells in the late apoptotic stage. Further, the cell growth inhibition was accompanied by the upregulation of the TRAIL gene, which surprisingly did not corroborate with the expression of TRAIL protein in the HNO97 cells.

L. casei exhibits anti-proliferative and apoptotic effects on OSCC. The TRAIL gene upregulation without translation into TRAIL protein suggests a potential caspase-independent mechanism of apoptosis. Further exploration is needed to understand the inhibitory effects of L. casei and its potential as a therapeutic probiotic in OSCC treatment.