DIPG-20. Copper chelation therapy targets S-adenosylmethionine (SAM) metabolism and epigenetic regulators in diffuse intrinsic pontine glioma (DIPG)

Abstract

DIPG is an incurable pediatric brain cancer of the ventral pons characterized by its complex epigenetic profile. Up to 81% of patients present with mutation H3K27M, resulting in the global reduction of H3K27 trimethylation and increased H3K27 acetylation, deregulating gene expression through an aberrant pattern of epigenetic modification. These alterations affect many cellular and metabolic mechanisms, complicating the search for effective targeted therapeutic strategies. Copper is highly abundant in the pons and is essential for normal brain function and development. However, excess copper accumulation is implicated in several neurological diseases and cancers. Incidentally, recent investigations have indicated the H3-H4 dimer can interact with copper acting as a reductase enzyme. Copper chelation therapy is clinically approved for pediatric patients with Wilson’s Disease, improving their neurological symptoms, and is being trialed in several cancers. We therefore hypothesized copper chelation may represent an effective therapeutic strategy for DIPG. Copper chelator tetraethylenepentamine (TEPA) decreased cell growth and induced apoptosis in DIPG cell lines. To understand these results, unbiased RNA-seq and metabolomics analyses were performed, revealing downregulation of EZH2, DNMT1 and DNMT3B, upregulation of KDM6B and the disruption of key enzymes in the S-adenosylmethionine (SAM)-cycle. Importantly, TEPA downregulated SAM, which donates methyl groups for methylation, S-adenosylhomocysteine, its post-methylation product and α-ketoglutarate, a co-factor for KDM6B. Western blots confirmed the reduced expression of EZH2, DNMT1 and DNMT3B, with further blots examining the chromatin cell fraction revealing modulation of H3K27 trimethylation through copper or TEPA stimulation, and reduction of H3K27 acetylation by TEPA. Importantly, in vitro combinations with Panobinostat were synergistic, while in vivo investigations demonstrated TEPA improved survival in an orthotopic patient derived xenograft (PDX) model, showing complete tumor regression in 25% of treated mice. This study indicates a novel use for copper chelators as epigenetic drugs, and their potential as therapeutics for DIPG.

PRMT5 maintains tumor stem cells to promote pediatric high-grade glioma tumorigenesis

“…This approach has been attempted successfully with other epigenetic regulatory drugs in preliminary preclinical experiments. 49 A similar combinatory approach with a PRMT5 inhibitor could also be attempted.…”