Abstract 2836: Downregulation of galectin-1 by OTX-008, a novel calyx[4]arene, is associated with galectin-1 oxidation followed by proteosomal degradation in human head and neck tumor cell lines

Abstract

Abstract Background. Galectin-1 is a multifunctional protein involved in various aspects of tumorigenesis and has been described as a promising cancer target. It has been previously shown that galectin-1 has high sensitivity to oxidative inactivation. During oxidation, galectin-1 may forms disulfide bridges resulting in profound conformational changes, which prevent galectin-1 dimerization and ligand recognition. OTX-008 is a non-peptide chemical antagonist designed to bind galectin-1. We previously showed that OTX-008 displays direct antiproliferative effects and inhibits galectin-1 expression in cancer cell lines (AACR 2011, Abstract n°685). The aim of the present study was to further the understanding on the molecular mechanism implicated on galectin-1 downregulation mediated by OTX-008 in cancer cells. Material and Methods. Proliferative SQ20B cancer cells were exposed to 3µM OTX-008 during 48h with or without i) 10µM N-acetylcysteine (an antioxidant agent), ii) 1mM Tempol (an antioxidant agent), iii) 10µM co-enzyme Q10 (a naturally occurring antioxidant agent), iv) 55µM α-mercaptoethanol (a strong reducing agent), or v) 10nM bortezomib (a proteasome inhibitor). Effects on galectin-1 protein levels were assessed by western blot analysis. Results. The head and neck SQ20B human cancer cell line is sensitive to OTX-008 (GI50 = 3µM). In this cell line, 48h-exposure to OTX-008 inhibits galectin-1 protein level (40% inhibition respect to control cells) without effect on galectin-1 mRNA levels. It has been described that galectin-1 oxidation represents a mechanism by which galectin-1 activity is regulated. SQ20B cells were exposed to OTX-008 for 48h with or without co-treatment with well-known antioxidant or reducing agents. Interestingly, these agents counteract the effects of OTX-008 on galectin-1 expression (galectin-1 protein levels by densitometry analysis: control SQ20B 100%, OTX-008 60%, N-acetylcystein+OTX-008 110%, Tempol+OTX-008 120%, co-enzyme Q10 +OTX-008 140% and α-mercaptoethanol+OTX-008 120%), suggesting that oxidation plays a key role in galectin-1 down-expression by OTX-008 in SQ20B cells. We further observed that pre-treatment with bortezomib abrogated the decrease in galectin-1 protein levels by OTX-008, pointing out that oxidized galectin-1 is recognized and degradated by the proteasome system. Conclusion. Our findings show that OTX-008 mechanism of action involves galectin-1 oxidation followed by proteosomal degradation in SQ20B cells. The mechanism by which OTX-008 can enhance the oxidation of galectin-1 will require further investigations. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2836. doi:1538-7445.AM2012-2836