Abstract 3373: Overexpression of EcSOD-ΔHBD suppresses breast cancer metastasis

Abstract

Abstract A critical event in the process of cancer invasion and metastasis is the remodeling of the extracellular matrix (ECM). Heparanase participates in this event by degrading the heparan sulfate (HS) component of the cell surface and the ECM. The expression level of heparanase correlates with an aggressive phenotype and greater metastasis potential in most cancers. Therefore, a variety of heparanase inhibitors, including low molecular weight heparin (LMWH) have been developed as anticancer agents. An overlooked yet interesting effect of LMWH administration is an increase in the circulating level of extracellular superoxide dismutase (EcSOD), which may play a role in its anti-cancer function. We have previously shown that overexpression of EcSOD enhanced the inhibitory effect of LMWH on breast carcinoma growth, clonogenic survival, and invasion in vitro, partly by attenuating heparanase expression and preventing HS degradation. To further understand the role of EcSOD in breast cancer progression in vivo, we performed an experimental lung metastasis study in which MDA-MB231.luc cells were introduced intravenously into athymic nude mice and colonization of the cells to the lungs was monitored by bioluminescent imaging. Overexpression of EcSOD via intramuscular injection of adenovirus vector resulted in a significant reduction in lung colonization compared to the empty vector (AdEmpty) infected group by more than two fold. Strikingly, a ten fold suppression of lung metastasis was observed when a truncated form of EcSOD that has a deletion in its heparin binding domain, EcSODΔHBD was introduced. Furthermore, EcSOD also significantly prolonged the survival of the animals from 58 days in AdEmpty group to 78 days in the AdEcSOD group and 99 days in the AdEcSOD⊗HBD group. In addition to studying the lung colonization, we also determined he effect of EcSOD on a spontaneous metastasis using a yngeneic model whereby a highly aggressive mouse mammary carcinoma cell line, 4T1.luc was injected into the mammary fat pad of immuno-competent BALB/c mice. Bioluminescent imaging analysis indicated that when all animals in the AdEmpty group showed secondary metastasis, only 71% and 63% of mice infected with AdEcSOD and AdEcSODΔHBD, respectively, developed secondary metastasis. Moreover, both EcSOD and EcSODΔHBD prolonged the survival of the animals from 44 days in the AdEmpty group to 69 days in the AdEcSOD group to 77 days in the AdEcSODΔHBD group. These results clearly indicate that EcSOD plays an important role in suppressing breast cancer metastasis and that the EcSODΔHBD that remains in the circulation system is more efficient than the full length protein. Most significantly, this is the first study demonstrating the biological function of the truncated EcSOD. 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 3373.