(P 395) INTEGRATED EPIGENETIC ANALYSES IDENTIFY A MULTI-SARCOMA DNA METHYLATION SIGNATURE OF TUMOR PROGRESSION AND METASTASIS

Objective: There is a critical need to improve the treatment, prevention, and monitoring of metastatic disease to improve outcomes of sarcoma patients. Epigenetic mechanisms of metastasis represent a promising area for prognostic patient surveillance of rare tumors. The objective of this study is to identify epigenetic mechanisms and signatures of sarcoma metastasis using preclinical platforms and patient datasets. ~70% of MPNSTs have loss-of-function mutations in the histone methyltransferase Polycomb Repressive Complex 2 (PRC2), a master epigenetic regulator of cancer progression. Using preclinical models and patient samples, we recently determined that PRC2 loss is a critical driver of MPNST metastasis through enzymatic restructuring of the tumor microenvironment (TME). Since PRC2 also plays non-canonical roles in DNA methylation, we hypothesized that wide-spread epigenetic plasticity is associated with tumor metastasis.

Methods: Using epigenetic and genomic patient datasets, we identified a DNA methylation signature of sarcoma progression and metastasis in multiple sarcoma subtypes. We first used three independent DNA methylation and RNAseq datasets from patient neurofibromas and MPNSTs to examine changes associated with MPNST progression. Subsequent studies examined DNA methylation profiles and scRNASeq datasets from osteosarcoma (OS), rhabdomyosarcoma (RMS), and synovial sarcoma (SS) patients.

Results: We determined that loss of H3K27me3 is associated with a global DNA hypermethylation signature in MPNST patients. Alterations in IL-17D DNA methylation and RNA expression correlate with the progression of NF1-associated MPNSTs. IL-17D is a poorly understood member of the pro-inflammatory IL-17 cytokine superfamily that regulates crosstalk between cancer cells and the TME. Further studies identified similar changes in IL-17D DNA methylation in OS, RMS, and SS patients, suggesting that IL-17D DNA methylation can predict progression of multiple sarcoma subtypes. Analysis of scRNAseq datasets determined that expression of IL-17D mRNA occurs in both tumor cells and surrounding stromal populations.

Conclusion: We identified an IL-17D DNA methylation signature that is associated with H3K27me3 loss, progression/metastasis, and survival in patients with MPNSTs. Furthermore, changes in IL-17D DNA methylation are associated with metastasis in multiple sarcoma subtypes including osteosarcoma, rhabdomyosarcoma, and synovial sarcoma. To our knowledge, this is the first analysis of IL-17 expression and methylation patterns in sarcoma data sets. These findings have broad implications for NF1-associated MPNST progression, disease monitoring, and therapeutic development, with potential ramifications for additional sarcoma subtypes. These results identify critical epitgenetic cross-talk in metastatic processes and may have broad implications for the clinical management and surveillance of sarcoma.