Abstract 1077: Galectin-1 is implicated in G1/S-checkpoint control following irradiation - possible explanation of Galectin-1 mediated radioresistance

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Purpose: The purpose of the conducted study was to examine a possible therapeutic relevance of Galectin 1 (Gal-1), a beta-galactoside binding protein. Gal-1 is overexpressed in high grade gliomas and leads to increased radioresistance in glioma cell culture models. Inhibition of Gal-1 increases radiosensitivity and thus is a potential therapeutic target for radiation sensitization. P53 has been shown to negatively regulate Gal-1, hence radiosensitivity could possibly be cell cycle mediated. Experimental Design: We used flow cytometry based cell cycle analysis to investigate cell cycle distribution of LN 229 glioma cells following irradiation. LN229 control cell lines and shRNA mediated Gal-1 knockdown LN 229 cell line were exposed to 6 Gy of irradiation and cell cycle analysis was performed. Furthermore Western blot analysis was carried out, probing for multiple proteins implicated in cell proliferation. The phosphorylation status of a variety of phosphorylation sites of p53, Chk1/2 and AKT were examined. Additionally p53-Gal-1 double-knockdown cell lines were created and clonogenic survival assays as well as AnnexinV apoptosis assays were conducted to analyze the influence on radiation sensitivity. Results: The results of the flow cytometry based cell cycle analysis show significant differences between the LN 229 control cell line and the Gal-1 knockdown cell line after irradiation. 24 h after irradiation 77 % of the control line cells are in G1 whereas only 60 % of the Gal-1 knockdown cells are in G1. Previous data has identified differences in the phosphorylation status of Akt in control vs. Gal-1 knockdown glioma cell lines. Phosphorylation of Akt is induced after irradiation. Western blot analysis indicates a reduction of phosphorylated Chk1/2 in Gal1 knockdown cell lines after irradiation. The phosphorylation state of the p53 phosphorylation site, correlating with Chk1/2 activity, exhibit anticipated results. P53-Gal-1 double-knockdown cell lines demonstrate significantly reduced clonogenic survival compared to control cell lines. Conclusions: The finding that less Gal-1 knockdown cells are in G1 phase after irradiation and that there is a reduction in phosphorylated Chk1/2 leads to the conclusion that Gal-1 knockdown abrogates G1 arrest through a Chk1/2 mediated pathway. That means in reverse that Gal-1 can mediate cell cycle arrest, thus potentially can explain Gal-1 mediated radioresistance. Further analysis of Chk1/2 independent phosphorylation sites of p53 is going to be conducted. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1077.