Effects of Photobiomodulation on Response to Gemcitabine in SCC-25 Cells

Objectives: Potential antitumor effects of photobiomodulation therapy include enhancement of pro-apoptotic pathways and synergy with chemotherapeutic drugs such as cisplatin. Using a cell model, we evaluated the combinatorial effect of PBMT on anti-cancer properties in response to gemcitabine. We hypothesized that PBMT would create a synergistic effect on reducing cellular viability when combined with gemcitabine.
Methods: Dose-response curves for gemcitabine in SCC-25 cells (oral squamous carcinoma cell line) were determined to identify appropriate concentrations ranges. SCC-25 cells were treated for 72 hr with increasing concentrations of gemcitabine (0, 10, 20, 50 nM). Media and treatments were replaced every 24 hr and PBMT was performed in combination at 24 hr intervals using a 660nm diode laser in a continuous wave mode 75mW laser probe at 3 J/cm². At 72 hr, MTT assay was performed to assess cellular viability. Calcein and propidium iodide fluorescent staining were used to evaluate late-stage apoptosis. All data were quantified on a microplate reader and analyzed using two-way ANOVA with Tukey post hoc analysis.
Results: PBMT alone did not induce changes to cellular viability when compared to non-treated controls. Gemcitabine resulted in reduction of cellular viability in a dose-dependent manner and showed significant reduction to MTT viability at 50 nM (p<0.05). The addition of PBMT did not result in differences in response to chemotherapeutic treatments at 72 hr for overall cell viability. Preliminary data using calcein and propidium iodide staining demonstrated a trend towards decreasing the ratio of late-stage apoptotic cells in response to gemcitabine.
Conclusions: Changes to overall viability of SCC-25 cells were not observed in combinatorial use of PBMT with gemcitabine. However, our data confirms that PBMT did not interfere with the overall effectiveness of gemcitabine. Future studies are necessary to evaluate combinatorial effects of PBMT using normal oral mucosal cells.