Screening of Health-Associated Oral Bacteria for Anticancer Properties in vitro

Abstract

While extensive literature exists about the role of oral bacterial pathogens like <i>Porphyromonas gingivalis</i> and <i>Fusobacterium nucleatum</i> in oral squamous cell carcinoma (OSCC), the role of health-associated species has been largely unexplored. In this study, we assessed the effect of <i>Streptococcus mitis, Rothia mucilaginosa, Neisseria flavescens, Haemophilus parainfluenzae, Lautropia mirabilis</i>, and <i>Veillonella parvula</i> on proliferation and expression of marker genes (IL-6, TNF-α, MMP3, CD36, CCD1, and NANOG) in OSCC cell lines CAL27, SCC25, and SCC4. <i>Porphyromonas gingivalis</i> was included as a pathogenic control. Both bacterial lysates (3 concentrations) and live cells (3 MOIs) were tested. <i>S. mitis, H. parainfluenzae</i>, and <i>N. flavescens</i> resulted in substantial, dose-dependent reduction of proliferation, which was found to be mediated by H₂O₂ for the former and intracellular infection in the latter two species. However, only <i>H. parainfluenzae</i> showed differential antiproliferative effect against the cancer cell lines vs. the normal control (TIGKs). In the gene expression assays, the health-associated species mostly downregulated CD36, a gene that plays an important role in tumor growth and metastasis, while <i>P. gingivalis</i> upregulated it. IL6 and TNF expression, on the other hand, was upregulated by almost all species, particularly the Gram-negatives including <i>P. gingivalis</i>. The effect on other genes was less evident and varied significantly by cell line. This exploratory study is the first insight into how health-associated bacteria may interact with OSCC. Further studies to explore whether the observed effects may have implications for the prevention or treatment of oral cancer are warranted.