Abstract B37: Development of a monoclonal antibody targeting xCT/SLC7A11 expressed in metastatic cancer cells
Authors: Salameh Ahmad , Caldeira Jerri , Rolih Valeria , Bolli Elisabetta , Conti Laura , Perrine Michael 
Published: March 2020

Abstract
The cystine-glutamate antiporter xCT (SLC7A11), the light chain of the antiporter system Xc–, regulates cysteine intake and stimulates the conversion of cysteine and subsequent glutathione (GSH) synthesis, which normally protects cells from oxidative and chemical insults. xCT expression is reported to be low in normal cells but elevated in numerous cancer types, including but not limited to colorectal, breast, pancreatic, and non-small cell lung cancer. Cancer cells have adopted xCT as a means of protection from chemotherapeutic agents and to meet their increased biosynthetic and bioenergetic needs. Additionally, high levels of xCT expression have been reported to correlate with poor patient survival. Thus, our published work and the work of others have established xCT as a novel target for the treatment of metastatic cancer. We have utilized our virus-like particle (VLP) technology and knowledge of xCT to create novel therapeutic monoclonal antibodies that will bind and inhibit the function of xCT expressed on metastatic cancer cells. We bioengineered the presentation of the extracellular domain three (ECD3) of the xCT protein on the surface of our VLP platform and immunized mice to identify biologically active anti-xCT antibodies. We identified 15 subclones that were then selected based upon affinity and avidity to the VLP presenting the ECD3 peptide, the ECD3 peptide itself, and the whole xCT protein, via ELISA. Supernatants were also analyzed using immunofluorescence, to determine the ability to bind xCT expressed on HT-29 cells (human colorectal cancer cell line), MDA-BM-231 cells (human breast cancer cell line), and 4T1 spheroids (mouse breast cancer cell line). One potential candidate, mAb M5, demonstrated specific and high-affinity binding to xCT-expressing cancer cells. mAb M5 was further evaluated in an NSG mouse transplantable model (MDA-MB-231 cells), where primary tumor formation and lung metastases formation were measured. NSG mice were injected subQ with MDA-MB-231 cells and subsequently treated with the mAb M5. We observed that intraperitoneal injections of mAb M5 were able to reduce primary tumor formation and the number of lung metastases when compared to control mice. We also demonstrated in vitro that mAb M5 was able to significantly inhibit spheroid adhesion/spreading. Additionally, mAb M5 was shown in vitro to significantly reduce the uptake of FITC-cystine, which is indicative of xCT inhibition. Therefore, mAb M5 represents a potential therapeutic candidate for multiple metastatic cancer types by inhibiting the function of xCT.
Citation Format: Ahmad Salameh, Jerri Caldeira, Valeria Rolih, Elisabetta Bolli, Laura Conti, Michael Perrine. Development of a monoclonal antibody targeting xCT/SLC7A11 expressed in metastatic cancer cells [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B37.