THE POTENTIATION OF THE RADIOPROTECTIVE EFFICACY OF TWO MEDICAL COUNTERMEASURES, GAMMA-TOCOTRIENOL AND AMIFOSTINE, BY A COMBINATION PROPHYLACTIC MODALITY

Abstract

This study was designed to evaluate the possible potentiation of survival protection afforded by relatively low-dose amifostine prophylaxis against total body irradiation in combination with a protective, less toxic agent, gamma-tocotrienol (GT3). Mice were administered amifostine and/or GT3, then exposed to 9.2 Gy ⁶⁰Co γ-irradiation and monitored for survival for 30 days. To investigate cytokine stimulation, mice were administered amifostine or GT3; serum samples were collected and analyzed for cytokines. Survival studies show single treatments of GT3 or amifostine significantly improved survival, compared to the vehicle, and combination treatments resulted in significantly higher survival compared to single treatments. In vivo studies with GT3 confirmed prior work indicating GT3 induces granulocyte colony-stimulating factor (G-CSF). This approach, the prophylactic combination of amifostine and GT3, which act through different mechanisms, shows promise and should be investigated further as a potential countermeasure for acute radiation syndrome.

Figure 1.

Efficacy of single GT3 (25 or 50 mg/kg) or amifostine (30 or 50 mg/kg) administrations or combination treatment on mouse survival after exposure to 9.2 Gy ⁶⁰Co γ-radiation (0.6 Gy/min). Mice (n = 16 per treatment group) were administered GT3 24 h prior to and/or amifostine 15 min prior to radiation exposure. Mice were then observed for survival for 30 days post-irradiation. (A) All mice received GT3 50 mg/kg and/or amifostine (30 or 50 mg/kg) prior to irradiation. * Indicates a significant difference compared to vehicle control treated mice; # indicates there is a significant difference compared to amifostine (30 mg/kg) treated mice (p < 0.05). (B) All mice received GT3 (25 mg/kg) and/or amifostine (30 or 50 mg/kg) * indicates a significant difference compared to vehicle control treated mice; # indicates there is a significant difference compared to GT3 (25 mg/kg) treated mice; $ indicates there is a significant difference compared to amifostine (50 mg/kg) treated mice; @ indicates there is a significant difference compared to amifostine (30 mg/kg) treated mice (p < 0.05). For both panels, the two combination treatment groups overlap at 100% survival; all statistical symbols above the line correspond to GT3 50 mg/kg + Amifostine 50 mg/kg, and all those below correspond with GT3 50 mg/kg + 30 mg/kg.

Figure 2.

G-CSF levels in mice serum 24 h after GT3 treatment (25 or 50 mg/kg). Mice were administered GT3 or vehicle (sc) and serum samples were collected at 24 h and analyzed using Luminex (n = 6). * Indicates that the two groups are significantly different (p < 0.05).

Figure 3.

Cytokines induced in the mouse serum at various time points after amifostine administration (sc). Serum samples were collected at various time points (4, 8, 24, and 48 h) after amifostine injection. Samples were stored at −80°C until analysis with Luminex (n = 6). * Indicates that the treatment group is significantly different (p < 0.05).