Abstract 3698: Epigenetic modification induced reprogramming of PUFAs-associated metabolism during trastuzumab resistance formation of HER2-positive breast cancer
Authors: Yin Yongmei , Duan Ningjun , Hua Yijia , Hu Shuang 
Published: April 2023

Abstract
Background: Secondary trastuzumab resistance seriously affects the treatment of HER2-positive breast cancer. Although studies have demonstrated several potential reasons that cause trastuzumab resistance, we still have poor knowledge about the changes in cell itself as well as its interaction with tumor microenvironment (TME) components during resistance formation. Here we suggested that altered histone modification reprograms polyunsaturated fatty acids (PUFAs) metabolism, which reduces cellular PUFAs and stimulates prostaglandin E2 (PGE2) production. Excessive PGE2 may further affect both cancer cells as well as immune cells in TME.
Materials and Methods: Secondary trastuzumab-resistant cell line SKBR3_HR was generated from sensitive SKBR3 cells by raising trastuzumab concentration gently from 1ug/ml to 20ug/ml in 30 weeks. Cell viabilities were measured by CCK8 test. CUT&Tag with anti-H3K4me3 and anti-H3K27me3 antibodies were applied to make sequencing libraries. Total RNA and protein were collected for transcriptome and proteome analysis. Activity scores of metabolism processes were defined and calculated as the relative gene expression value averaged over all genes in this pathway in certain cell types. Oxidized PUFAs and PGE2 were assessed by flow cytometry with BODIPY-C11 and ELISA, respectively.
Results: SKBR3_HR cells showed similar viability as primary resistant JIMT1 cells and were significantly higher than original SKBR3 cells. Pathway analysis indicated reduced PUFAs synthesis and activated arachidonic acid metabolism. As a consequence, oxidized PUFAs decreased while PGE2 accumulated heavily in SKBR3_HR cells, which may promote tumor and vascular endothelial cell proliferation but interrupt immune cell activity in TME. Transcriptional activity of two critical PUFAs synthesis-related genes, FASN and SCD, were reduced in resistant cells, while two key genes in arachidonic acid metabolism, PTGS1 and PTGES, were activated. H3K4me3 and H3K27me3 play opposite but critical rules in transcriptional regulation. During resistance formation, changes happened on 3256 H3K27me3 peaks as well as 316 H3K4me3 peaks. In detail, although little H3K27me3 changes were found at the promoter regions of four genes (FASN, SCD, PTGS1 and PTGES), reduced H3K4me3 levels may inhibit FASN and SCD expression while raised levels could stimulate PTGS1 and PTGES transcription.
Conclusions: Combining the transcriptome and histone modification data, we have a deeper understanding of the cellular adaptions to trastuzumab. Altered trimethylation of H3K4 but not H3K27 remodels the expressions of FASN, SCD, PTGS1 and PTGES, drives the reprogramming of PUFAs-associated metabolism, and finally reduces cellular PUFAs while stimulates PGE2 production. High PGE2 level may affect the activities of tumor and TME-related cells.
Citation Format: Yongmei Yin, Ningjun Duan, Yijia Hua, Shuang Hu. Epigenetic modification induced reprogramming of PUFAs-associated metabolism during trastuzumab resistance formation of HER2-positive breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3698.