Abstract PO3-24-05: Cysteine metabolism related ferroptosis sensitivity in trastuzumab resistant HER2 positive breast cancer

Abstract Background Trastuzumab has shown great effectiveness in HER2 positive breast cancer treatment, but about 50% patients would undergo resistance during or after treatment. Although previous research has suggested several potential reasons for trastuzumab resistance, the metabolic reprogramming during resistance formation remains largely unclear. Here we identified aberrant ferroptosis associated cysteine metabolism in trastuzumab resistant HER2 positive breast cancer, which might become a novel target for overcoming resistance. Methods Trastuzumab sensitive HER2 positive breast cancer cell SKBR3 and resistant JITM1 were obtained for transcriptomics, proteomics, metabolomics and epigenomics analysis. Gene silencing was mediated by siRNAs. CUT&Tag was applied to compare H3K4me3 and H3K27me3 binding regions. DNA methylation levels and different methylated regions were evaluated by WGBS-seq. CRISPRi with dCas9-DNMT3A was applied to regulate specific DNA methylation in CpG islands. Lipid ROS was measured by flow cytometry with BODIPY-C11. Results Joint analyses of transcriptomics and proteomics according to ferroptosis pathways revealed downregulated glutathione metabolism, glutamate transmembrane and homocysteine metabolism processes, as well as upregulated fatty acid metabolism and iron metabolism pathways in JIMT1. Metabolomics verified that JIMT1 increased cysteine metabolism and decreased glutathione metabolism. SLC7A11 expression and GSH/GSSG ratio were increased in JIMT1, while no difference was observed in free cysteine. JIMT1 featured significant higher UGC codon usage bias and increased cysteinyl-tRNA synthetase. The abundance of H3K4me3 other than H3K27me3 in SLC7A11 promoter region was found increased in JIMT1, and the 5-mC level of CpG islands in SLC7A11 promoter region was shown decreased. Using dCas9-DNMT3A, the methylation of SLC7A11 promoter was enhanced and SLC7A11 expression was reduced in JIMT1. Inhibition of SLC7A11 by siRNAs, CRISPRi or Erastin all indicated a higher ferroptosis sensitivity in JIMT1. Conclusion Trastuzumab resistant HER2 positive breast cancer features aberrant cysteine metabolism resulting from altered H3K4me3 modification and DNA methylation in SLC7A11 promoter region. This might provide novel targets for further anti-HER2 treatment. Citation Format: Yongmei Yin, Yijia Hua, Ningjun Duan, Chunxiao Sun, Fan Yang. Cysteine metabolism related ferroptosis sensitivity in trastuzumab resistant HER2 positive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-24-05.