Low-level laser therapy can produce increased aggressiveness of dysplastic and oral cancer cell lines by modulation of Akt/mTOR signaling pathway

Low-level laser therapy (LLLT) is a non-thermal phototherapy used in several medical applications, including wound healing, reduction of pain and amelioration of oral mucositis. Nevertheless, the effects of LLLT upon cancer or dysplastic cells have been so far poorly studied. Head and neck cancer patients receiving LLLT for oral mucositis, for example, might have remaining tumor cells that could be stimulated by LLLT. This study demonstrated that LLLT (GaAlAs - 660 nm or 780 nm, 40 mW, 2.05, 3.07 or 6.15 J/cm²) can modify oral dysplastic cells (DOK) and oral cancer cells (SCC9 and SCC25) growth by modulating the Akt/mTOR/CyclinD1 signaling pathway; LLLT significantly modified the expression of proteins related to progression and invasion in all the cell lines, and could aggravate oral cancer cellular behavior, increasing the expression of pAkt, pS6 and Cyclin D1 proteins and producing an aggressive Hsp90 isoform. Apoptosis was detected for SCC25 and was related to pAkt levels. Translocation of pAkt seen through Immunofluorescence from cytoplasm of control SCC9 cells (A) to nuclei of red (D) and infrared (G) laser irradiated cells. B, E and H: pAkt staining in control, red and infrared laser groups, respectively. C, F and I: nuclear DAPI in control, red and infrared groups, respectively.