Objective: This study evaluated the function and structural consequences of direct exposure of murine hepatoma MH-22a cells to polychromatic polarized light, to determine potential risk of malignancy following irradiation.
Background data: Visible (VIS) and infrared (IR) light have been actively used for prevention and treatment of complications developed after conventional tumor therapy. However, the safety associated with this irradiation has not been determined.
Materials and methods: Polychromatic light (480-3400 and 385-750 nm), were used at different doses (4.8-38.4 J/cm(2)) to determine the viability, proliferation, and actin cytoskeleton in vitro by flow cytometry and confocal microscopy. Tumorogenic properties of cells were studied in vivo after transplantation in C3HA mice.
Results: Polychromatic light of a wide range of doses did not change the viability and proliferation of cells. After transplantation of cells irradiated with VIS-IR light (4.8 and 9.6 J/cm(2)) and VIS light (38.4 J/cm(2)) the tumor volume was lower in the treated group than in the control group in vivo. Transplantability of the irradiated cells also decreased, whereas survival of tumor-bearing mice increased. Three cell populations with different cytoskeleton structure were identified. After irradiation, the reorganized part of the actin cytoskeleton changed its localization to the submembranous area.
Conclusions: A decrease of tumorigenicity in cells irradiated with polychromatic light used in non-damaging doses correlated with an increase in the number of cells with reorganized actin in the submembranous area. The results of the present study argue in favor of the oncological safety of polychromatic VIS-IR light (480-3400 nm).