32P - Epigenetic reprogramming induced prostaglandin E2 accumulation via overactivated arachidonic acid metabolism during trastuzumab resistance formation of HER2-positive breast cancer

Background

Secondary trastuzumab resistance seriously affects HER2-positive breast cancer treatment. However, we still lack knowledge about changes in tumor cells and their interaction with tumor microenvironment (TME) components during resistance formation. This study aimed to uncover metabolism pathway changes during trastuzumab resistance formation and potential epigenetic variations that are relevant to these processes.

Methods

Induced secondary trastuzumab-resistant SKBR3_HR cell line together with the original trastuzumab-sensitive SKBR3 cell line were applied in this study. Total RNA was collected for transcriptome analysis. Anti-H3K4me3, K27me3 and K27ac antibodies were chosen for CUT&Tag sequencing library preparation. Total genome DNA was prepared for Micro-C sequencing library preparation. Activity score of metabolism pathway was calculated as relative gene expression value averaged over all genes in this pathway in certain cell types. Extracellular prostaglandin E2 (PGE2) was measured by ELISA.

Results

SKBR3_HR cells showed higher trastuzumab tolerance than SKBR3 cells. Upregulation of arachidonic acid metabolism, which was characterized by two overexpressed genes, PTGS1 and PTGES, was observed in SKBR3_HR cells, resulting in PGE2 accumulation in culture medium. Variations of 1519 H3K27me3 peaks and 256 H3K4me3 peaks at promoters were observed during resistance formation. Little H3K27me3 but considerable raised H3K4me3 levels at PTGS1 and PTGES gene promoters may stimulate their transcription.692 altered active enhancers were measured during resistance formation. Meanwhile, 2741 and 7007 DNA loops were lost and gained. New DNA loops formation between PTGS1 gene promoter and enhancers nearby, indicating a positive synergy regulatory on PTGS1 gene expression together with promoter modifications.

Conclusions

During trastuzumab resistance formation, promoter H3K4me3, active enhancers and DNA loops together regulate PTGS1 and PTGES expression, activate arachidonic acid metabolism, and eventually stimulate PGE2 accumulation.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

National Natural Science Foundation of China (81972484), National Natural Science Foundation of China (82203488).

Disclosure

All authors have declared no conflicts of interest.