The effect of radiation with polychromatic visible and infrared light on the tumorigenicity of murine hepatoma 22A cells and their sensitivity to lysis by natural killers

Abstract

The tumorigenicity of murine hepatoma cells (MH-22a) and their sensitivity to lysis by natural killers (NKs) have been studied after exposure to polychromatic visible and infrared light (VIS-IR, 480–3400 nm, 40 mW/cm2), similar to the terrestrial solar spectrum without its minor UV component, with the aim of clarifying the participation of this important environmental and physiotherapeutic factor in regulation of antitumor protective system. MH-22 cells were exposed in vitro to VIS-IR light and their sensitivity to lytic activity of NKs was evaluated. It was found that, after exposure to VIS-IR light at a dose of 4.8 J/cm2, the sensitivity of MH-22a cells to lysis by NKs increased by 1.5–2 times, while after exposure at a dose of 9.6 J/cm2 it did not change at all the ratios of the NKs-number (effectors) to that of hepatoma cells — targets (1 : 5–1 : 50). An increase of the hepatoma cell sensitivity to NKs was accompanied by structural changes of cell surface: the capability of supramembranous glycoproteins (glycocalyx) to sorb the vital dye alcian blue (AB) was significantly lower than in the case of unexposed cells of the control group. However, no changes in AB sorption was revealed in hepatoma cells exposed to light at a dose of 9.6 J/cm2. The tumorigenicity of photoirradiated MH-22a cells has been studied in the experiments in vitro. For 25 days after transplantation of light-exposed hepatoma cells to C3HA syngene mice, the tumor volume proved to be smaller after exposure to light at both doses of 4.8 and 9.6 J/cm2 than in the control group (by 4–4.5 times and 2.5–4 times, respectively), which correlated with an increase of sensitivity to lysis by NKs and with a decrease of AB sorption after light exposure only at a dose of 4.8 J/cm2. Using the flow-cytometry method, we could show that VIS-IR light at the doses used did not interfere with the distribution of hepatoma cells over the cell-cycle phases and, thus, deceleration of the tumor growth was not associated with a cytostatic effect of the VIS-IR light. To evaluate the effect of polychromatic light on growth of the preformed tumors, a 5-day course of daily light exposure of C3HA tumor-bearing mice was performed on the 10th day after subcutaneous transplantation of 2 × 105 cells of syngene hepatoma, when tumors developed in all (100%) animals. As in the case of transplantation of light-exposed cells, irradiation of tumor-bearing mice at doses 4.8–9.6 J/cm2 resulted in a deceleration of tumor growth (by 2.1–2.9 and 2,2 times, respectively) for 4 weeks compared with unirradiated mice.