The Direct Biologic Effects of Radioactive 125 I Seeds on Pancreatic Cancer Cells PANC-1,at Continuous Low-Dose Rates

Abstract

The relative biologic effectiveness of model 6711 ¹²⁵I seeds (Ningbo Junan Pharmaceutical Technology Company, Ningbo, China) and their effects on growth, cell cycle, and apoptosis in human pancreatic cancer cell line PANC-1 were examined in the present study. PANC-1 cells were exposed to the absorbed doses of 1, 2, 4, 6, 8, and 10 Gy either with ¹²⁵I seeds (initial dose rate, 2.59 cGy/h) or with ⁶⁰Co γ-ray irradiation (dose rate, 221 cGy/min), respectively. Significantly greater numbers of apoptotic PANC-1 cells were detected following the continuous low-dose-rate (CLDR) irradiation of ¹²⁵I seeds, compared with cells irradiated with identical doses of ⁶⁰Co γ-ray. The D₀ for ⁶⁰Co γ-ray and ¹²⁵I seed irradiation were 2.30 and 1.66, respectively. The survival fraction after ¹²⁵I seed irradiation was significantly lower than that of ⁶⁰Co γ-ray, with a relative biologic effectiveness of 1.39. PANC-1 cells were dose dependently arrested in the S-phase by ⁶⁰Co γ-rays and in the G2/M phase by ¹²⁵I seeds, 24 hour after irradiation. CLDR irradiation by ¹²⁵I seeds was more effective in inducing cell apoptosis in PANC-1 cells than acute high-dose-rate ⁶⁰Co γ irradiation. Interestingly, CLDR irradiation by ¹²⁵I seeds can cause PANC-1 cell-cycle arrest at the G2/M phase and induce apoptosis, which may be an important mechanism underlying ¹²⁵I seed–induced PANC-1 cell inhibition.