The radioprotective potential of histamine on healthy tissue has been previously demonstrated. The aims of this work were to investigate the combinatorial effect of histamine or its receptor ligands and gamma radiation in vitro on the radiobiological response of 2 breast cancer cell lines (MDA-MB-231 and MCF-7), to explore the potential molecular mechanisms of the radiosensitizing action and to evaluate the histamine-induced radiosensitization in vivo in a triple negative breast cancer model. Results indicate that histamine significantly increased the radiosensitivity of MDA-MB-231 and MCF-7 cells. This effect was mimicked by the H1R agonist 2-(3-(trifluoromethyl)phenyl)histamine and the H4R agonists (Clobenpropit and VUF8430) in MDA-MB-231 and MCF-7 cells, respectively. Histamine and its agonists enhanced radiation-induced oxidative DNA damage, DNA double-strand breaks, apoptosis and senescence. These effects were associated with increased production of reactive oxygen species, which correlated with the inhibition of catalase, glutathione peroxidase and superoxide dismutase activities in MDA-MB-231 cells. Histamine was able also to potentiate in vivo the anti-tumoral effect of radiation, increasing the exponential tumor doubling time. We conclude that histamine increased radiation response of breast cancer cells, suggesting that it could be used as a potential adjuvant to enhance the efficacy of radiotherapy.
Keywords: 3F-MPHA, 2-(3-(trifluoromethyl)phenyl)histamine; 8-OHdG, 8-hydroxy-2′-deoxyguanosine; BSA, bovine seroalbumine; BrdU, 5-bromo-2′-deoxyuridine; Clob, clobenpropit; DCFH-DA, dichlorodihydrofluorescein diacetate; Dapi, 4′-6-diamidino-2-phenylindole; ER, estrogen receptor; FBS, fetal bovine serum; GPx, glutathione peroxidase; Gy, gray; H1R, histamine receptor 1; H2O2, hydrogen peroxide; H2R, histamine receptor 2; H3R, histamine receptor 3; H4R, histamine receptor 4; HA, histamine; IgG, immunoglobuline G; PBS, phosphate buffer saline; ROS, reactive oxygen species; SEM, standard error of mean; SF, surviving fraction; SOD, superoxide dismutase; TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labeling; U, unit; apoptosis; breast cancer; cell proliferation; histamine; ionizing radiation; radio-potentiation; reactive oxygen species; sc, subcutaneous; γH2AX, phosphorylated histone H2AX.