Nucleosomes indicate the in vitro radiosensitivity of irradiated bronchoepithelial and lung cancer cells

Nucleosomes, which are typical cell death products, are elevated in
the serum of cancer patients and are known to rapidly increase
during radiotherapy. As both normal and malignant cells are damaged
by irradiation, we investigated to which extent both cell types
contribute to the release of nucleosomes. We cultured monolayers of
normal bronchoepithelial lung cells (BEAS-2B, n = 18) and
epithelial lung cancer cells (EPLC, n = 18), exposed them to
various radiation doses (0, 10 and 30 Gy) and observed them for 5
days. Culture medium was changed every 24 h. Subsequently,
nucleosomes were determined in the supernatant by the Cell Death
Detection-ELISA(plus) ( Roche Diagnostics). Additionally, the cell
number was estimated after harvesting the cells in a second
preparation. After 5 days, the cell number of BEAS-2B cultures in
the irradiated groups (10 Gy: median 0.03 x 10(6) cells/culture,
range 0.02-0.08 x 10(6) cells/culture; 30 Gy: median 0.08 x 10(6)
cells/culture, range 0.02-0.14 x 10(6) cells/culture) decreased
significantly (10 Gy: p = 0.005; 30 Gy p = 0.005; Wilcoxon test)
compared to the non-irradiated control group (median 4.81 x 10(6)
cells/culture, range 1.50-9.54 x 10(6) cells/culture).
Consistently, nucleosomes remained low in the supernatant of
nonirradiated BEAS-2B. However, at 10 Gy, BEAS-2B showed a
considerably increasing release of nucleosomes, with a maximum at
72 h ( before irradiation: 0.24 x 10(3) arbitrary units, AU, range
0.13-4.09 x 10(3) AU, and after 72 h: 1.94 x 10(3) AU, range
0.11-5.70 x 10(3) AU). At 30 Gy, the release was even stronger,
reaching the maximum earlier (at 48 h, 11.09 x 10(3) AU, range
6.89-18.28 x 10(3) AU). In non-irradiated EPLC, nucleosomes
constantly increased slightly. At 10 Gy, we observed a considerably
higher release of nucleosomes in EPLC, with a maximum at 72 h
(before irradiation: 2.79 x 10(3) AU, range 2.42-3.80 x 10(3) AU,
and after 72 h: 7.16 x 10(3) AU, range 4.30-16.20 x 10(3) AU),
which was more than 3.5 times higher than in BEAS-2B. At 30 Gy, the
maximum (6.22 x 10(3) AU, range 5.13-9.71 x 10(3) AU) was observed
already after 24 h. These results indicate that normal
bronchoepithelial and malignant lung cancer cells contribute to the
release of nucleosomes during irradiation in a dose-and
time-dependent manner with cancer cells having a stronger impact at
low doses. Copyright (C) 2004 S. Karger AG, Basel.