Colon-cancer cellular model for the study of the radioresistance modulation

CERDA, MB; BRACALENTE C; IBA&241EZ ILL; TROPER I; MOLINARI B; PODHAJCER O; DURAN H; POLICASTRO L

Congreso; XLVI Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

The radioresistance of tumors is one of the main causes that lead to the failure of radiation treatment against cancer. The aim of this study was to evaluate the intrinsic radiosensitivity of several colon human cancer cell lines for future studies related to the modulation of radiation response by silencing the expression of radioresistant associated genes. We characterized the intrinsic radiosensitivity of HT-29, Caco-2, and LoVo cells by their survival curves and their capacity of induction and rejoining DNA double strand breaks (DSBs) after exposure to gamma radiation. Survival curves were obtained by clonogenic assay and were fitted to the linear-quadratic model (S=exp(-.áD+âD2)). The analysis of the survival curves parameters showed significant increasing á values:  HT-29 (á=0.47+0.07;) Caco-2 (á=0.86+0.17) than LoVo (á= 1.41+0.13) cell lines, and the loss of the quadratic component of survival curves (â=0) for this last cell line. To evaluate damage and repair of DNA after exposure to gamma radiation (2 Gy), we evaluated the phosphorylation of the histone protein H2AX (ãH2AX) by immunohistochemical assay at 30 min and 6 h post-irradiation. The number of ãH2AX foci has been shown to be directly proportional to the number of DSBs and their dephosphorylation has been correlated with repair of DSBs. The quantification of the number of foci per nucleus showed a significant decrease in foci number at 6 h  post-irradiation. Repair of damage of DNA is 65+% for HT-29, 40+% for Caco-2 cells and 20+% for LoVo cells. Moreover, we analyzed foci size at 30 min post irradiation as a measure of initial damage. After a dose of 2Gy foci size increased 33% in HT-29 cells, 66% en Caco-2 and 132% en LoVo cells. This results showed that this cells have high, middle and low levels of radioresistance,  to gamma radiation (HT-29>Caco-2>LoVo), and they could be a useful model to study the modulation of radioresistance.