Abstract 1470: Enhancing radiation therapy by simultaneous inhibition of thioredoxin- and glutathione-dependent metabolism

Abstract

Cancer cells have been shown to be in a constant state of metabolic oxidative stress, concurrent with an elevated level of reactive oxygen species (ROS). In order to facilitate survival in the face of increased steady-sate levels of ROS, cancer cells rely on glutathione (GSH) and thioredoxin (Trx) dependent metabolism. We have recently demonstrated that the simultaneous inhibition of GSH using Buthionine sulphoximine [(BSO), a GHS synthesis inhibitor] and thioredoxin reductase using auronofin [(Au), a thioredoxin reductase inhibitor] effectively chemo-radio-sensitized lung cancer cells via a mechanism involving oxidative stress. In this work we extend this observation to demonstrate that Au 2 mg/kg and BSO 450 mg/kg, given prior to ionizing radiation (6 Gy x 2 doses) can significantly delay tumor growth rate for mice treated with radiation alone in H292 lung cancer xenografts. In addition, we demonstrate through clonogenic survival assays that the combination of Au (250-500 nM) and BSO (100 μM) radio-sensitizes two breast cancer cell lines in vitro, and more importantly the combination of Au and BSO given by intraperitoneal injection prior to radiation decreases the percent of breast cancer stem/progenitor cells in vivo. The rate limiting substrate for GSH synthesis is cysteine, whose level is controlled by the xc- cystine/glutamate antiporter. Sulfasazine (SSZ) has been shown to be a potent inhibitor of the xc- cystine/glutamate antiporter. We demonstrate that SSZ (0.1-0.5 mM) decreases total GSH (up to 90%) levels in a dose dependent manner in both Mia PaCa-2 and PANC-1 human pancreatic cell lines. The combination of Au (250 nM for 3 hours) with SSZ (0.2 mM for 24 hours) demonstrates an 80% and 30% decrease in clonogenic cell survival in MiaPaCa-2 and PANC-1 pancreatic cells that is inhibited by treatment with the thiol antioxidant, 15 mM N-acetylcysteine. These results indicate that inhibition of hydroperoxide metabolism using pharmacologically relevant agents to simultaneously disrupt GSH and Trx system, can sensitize multiple cancer cell lines to radiation. These results support the hypothesis that standard of care radiotherapy protocols could be enhanced using SSZ, Au, and/or BSO. Supported by The Iowa Center for Research by Undergraduates, R21CA139182, R01CA133114 and a Breast Cancer Research Group Seed Grand from the Holden Comprehensive Cancer Center.

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 1470. doi:1538-7445.AM2012-1470