Abstract A012: ZFTA-RELA fusion epigenetically enhances glutathione biosynthesis in pediatric supratentorial ependymoma

Abstract

Pediatric brain tumors are the leading cause of childhood cancer mortality with ependymomas being the third most common brain tumor in children. Supratentorial ependymoma (ST-EPN) is a malignant aggressive pediatric brain tumor arising in the brain hemispheres. These tumors are chemotherapy resistant, and the current standard treatments—surgical resection and radiation—are ineffective. More than 70% of ST-EPN tumors are driven by the oncogenic ZFTA-RELA fusion protein formed between the putative chromatin modifier, ZFTA, and the central NF-kB pathway regulator, RELA. Many oncogenes actively drive aberrant metabolic pathways and alter the epigenetic landscape, making them hallmarks of cancer. An unbiased metabolic screen found that ZFTA-RELA upregulates glutathione biosynthesis, a key pathway for combating oxidative stress. We treated ZFTA-RELA fusion and non-fusion cell lines with hydrogen peroxide, an oxidative stress inducer and found that ZFTA-RELA fusion cell lines were relatively resistant to oxidative stress. We also performed a proteomic screen and found key GSH biosynthesis proteins (GCLM, SLC7A11) are upregulated in ZFTA-RELA fusion cells compared to wildtype controls. Additionally, the histone acetyl transferase complex, CBP/p300, and activating H3K27ac are co-localized and enriched with ZFTA-RELA at key glutathione biosynthesis genes. Using a CBP/p300 specific proteolysis targeting chimera (PROTAC) degrader, CBPD-409, in ZFTA-RELA cell models, we found a reduction in key glutathione biosynthesis proteins, glutathione levels, and global H3K27ac. We completed RNA sequencing on a ZFTA-RELA fusion patient cell line treated with vehicle or CBPD-409 and found a downregulation in 54/93 signature ZFTA-RELA driven genes. Additional work will aim to characterize CBPD-409 in ZFTA-RELA mouse models in vivo and further dissect the mechanism by which ZFTA-RELA rewires CBP/p300 and H3K27ac to enhance glutathione biosynthesis and downstream oncogenic transcriptional programs.