Oral Administration of Porphyromonas gingivalis, a Major Pathogen of Chronic Periodontitis, Promotes Resistance to Paclitaxel in Mouse Xenografts of Oral Squamous Cell Carcinoma

Abstract

Chemotherapy is not a first-line therapy for oral squamous cell carcinoma (OSCC), which is the most common type of oral cancer, because most OSCC shows resistance to chemotherapeutic reagents. Inflammatory signals are suggested to be associated with chemoresistance as well as carcinogenesis in many different cancers, and thus chronic periodontitis, the most common chronic inflammatory disease of the oral cavity, could modulate responsiveness to chemotherapeutic agents used against oral cancer. This study was performed to define the role of chronic periodontitis in oral cancer progression and to determine the responsiveness of oral cancer to a chemotherapeutic reagent. First, we quantified the tumor growth rate and changes in serum cytokine profiles of mice administered Porphyromonas gingivalis, a major pathogen of chronic periodontitis. Compared with uninfected mice, the mice that were chronically administered P. gingivalis showed increased resistance to paclitaxel and a decreased tumor growth rate. In addition, P. gingivalis-treated mice exhibited higher serum levels of interleukin-6 (IL-6) than uninfected mice. Furthermore, the sensitivity of tumor xenografts to paclitaxel in mice administered P. gingivalis was dramatically increased when the mice were administered ibuprofen, an anti-inflammatory drug which supports the modulatory effect of periodontal pathogen-induced inflammation in chemoresistance.

Keywords: Porphyromonas gingivalis; chemoresistance; chronic periodontitis; cytokine; ibuprofen; oral cancer; paclitaxel.

Figure 1

Comparisons of the tumor volume and growth rate between P. gingivalis-treated and/or paclitaxel-treated mice. (A) Photographs of OSCC xenografts in mice and representative images of H & E-stained sections of tumor masses (×200 magnification). Tumor volumes (B) were measured twice per week after the subcutaneous implantation of tumor cells, and the growth rate of the tumor masses (C) was calculated. Data are presented as the mean ± standard deviation.

Figure 2

Comparisons of the serum cytokines in tumor xenografts from mice that were administered P. gingivalis and/or paclitaxel. Data are presented as the mean ± standard deviation. Significance was assessed using ANOVA. * P < 0.05.

Figure 3

Comparisons of tumor volume and growth rate between P. gingivalis-treated and/or paclitaxel-treated mice administered ibuprofen. Tumor volumes (A) were measured twice per week after the subcutaneous implantation of tumor cells, and ibuprofen was administered in drinking water. The growth rate of the tumor masses (B) was calculated. Data are presented as the mean ± standard deviation. Significance was assessed using ANOVA. * P < 0.05.

Figure 4

Comparisons of the serum cytokines in ibuprofen-treated mice that were administered P. gingivalis and/or paclitaxel. Data are presented as the mean ± standard deviation. Significance was assessed using ANOVA. * P < 0.05.