Temozolomide toxicity operates in a xCT/SLC7a11 dependent manner and is fostered by ferroptosis

Abstract

// Tina Sehm 1 , Manfred Rauh 2 , Kurt Wiendieck 3 , Michael Buchfelder 1 , IIker Y. Eyüpoglu 1, * , Nicolai E. Savaskan 1, 4, * 1 Translational Cell Biology & Neurooncology Lab, Department of Neurosurgery, Universitätsklinikum Erlangen, Medical School of The Friedrich Alexander University of Erlangen-Nürnberg (FAU), Erlangen, Germany 2 Department of Pediatrics and Adolescent Medicine, Universitätsklinikum Erlangen, Medical School of The Friedrich Alexander University of Erlangen-Nürnberg (FAU), Erlangen, Germany 3 Department of Spinal Colum Therapies, Kliniken Dr. Erler, Nürnberg, Germany 4 BiMECON Ent. Berlin, Germany * Both authors have contributed as senior author to this work Correspondence to: Nicolai E. Savaskan, email: [e-mail] , [e-mail] Keywords: brain tumor, cell death, ferroptosis, glioma niche, apoptosis Received: March 08, 2016      Accepted: August 24, 2016      Published: September 06, 2016 ABSTRACT The glutamate exchanger xCT (SLC7a11) is causally linked with the malignancy grade of brain tumors and represents a key player in glutamate, cystine and glutathione metabolism. Although blocking xCT is not cytotoxic for brain tumors, xCT inhibition disrupts the neurodegenerative and microenvironment-toxifying activity of gliomas. Here, we report on the use of various xCT inhibitors as single modal drugs and in combination with the autophagy-inducing standard chemotherapeutic agent temozolomide (Temodal/Temcad®, TMZ). xCT overexpressing cells (xCT OE ) are more resistant to the FDA and EMA approved drug sulfasalazine (Azulfidine/Salazopyrin/Sulazine®, SAS) and RNAi-mediated xCT knock down (xCT KD ) in gliomas increases the susceptibility towards SAS in rodent gliomas. In human gliomas, challenged xCT expression had no impact on SAS-induced cytotoxicity. Noteworthy, other xCT inhibitors such as erastin and sorafenib showed enhanced efficacy on xCT KD gliomas. In contrast, cytotoxic action of TMZ operates independently from xCT expression levels on rodent gliomas. Human glioma cells with silenced xCT expression display higher vulnerability towards TMZ alone as well as towards combined TMZ and SAS. Hence, we tested the partial xCT blockers and ferroptosis inducing agents erastin and sorafenib (Nexavar®, FDA and EMA-approved drug for lung cancer). Noteworthy, xCT OE gliomas withstand erastin and sorafenib-induced cell death in a concentration-dependent manner, whereas siRNA-mediated xCT knock down increased susceptibility towards erastin and sorafenib. TMZ efficacy can be potentiated when combined with erastin, however not by sorafenib. Moreover, gliomas with high xCT expression are more vulnerable towards combinatorial treatment with erastin-temozolomide. These results disclose that ferroptosis inducers are valid compounds for potentiating the frontline therapeutic agent temozolomide in a multitoxic approach.