Faculty Bibliography

As oxygen is essential for many metabolic pathways, tumour hypoxia may impair cancer cell proliferation^1-4. However, the limiting metabolites for proliferation under hypoxia and in tumours are unknown. Here, we assessed proliferation of a collection of cancer cells following inhibition of the mitochondrial electron transport chain (ETC), a major metabolic pathway requiring molecular oxygen ⁵ . Sensitivity to ETC inhibition varied across cell lines, and subsequent metabolomic analysis uncovered aspartate availability as a major determinant of sensitivity. Cell lines least sensitive to ETC inhibition maintain aspartate levels by importing it through an aspartate/glutamate transporter, SLC1A3. Genetic or pharmacologic modulation of SLC1A3 activity markedly altered cancer cell sensitivity to ETC inhibitors. Interestingly, aspartate levels also decrease under low oxygen, and increasing aspartate import by SLC1A3 provides a competitive advantage to cancer cells at low oxygen levels and in tumour xenografts. Finally, aspartate levels in primary human tumours negatively correlate with the expression of hypoxia markers, suggesting that tumour hypoxia is sufficient to inhibit ETC and, consequently, aspartate synthesis in vivo. Therefore, aspartate may be a limiting metabolite for tumour growth, and aspartate availability could be targeted for cancer therapy.

Epigenetic patterns on the level of DNA methylation have already been shown to separate clinically relevant subgroups of meningiomas. We here set out to identify potential prognostic implications of epigenetic modification on the level of histones with focus on H3K27 trimethylation (H3K27me3). H3K27me3 was assessed by immunohistochemistry on 232 meningiomas from 232 patients. In 194 cases, trimethylation was detected in tumor cells. In 25 cases, staining was limited to vessels while all tumor cells were negative. Finally, 13 cases yielded equivocal staining patterns. Reduced abundance of H3K27me3 in cases with staining limited to vessels was confirmed by mass spectrometry on a subset of cases. Lack of staining for H3K27me3 in all tumor cells was significantly associated with more rapid progression (p = 0.009). In line, H3K27me3-negative cases were associated with a DNA methylation pattern of the more aggressive types among the recently introduced DNA methylation groups. Also, NF2 and SUFU mutations were enriched among cases with complete lack of H3K27me3 staining in tumor cells (p < 0.0001 and p = 0.029, respectively). H3K27me3 staining pattern added significant prognostic insight into WHO grade II cases and in the compound subset of WHO grade I and II cases (p = 0.04 and p = 0.007, respectively). However, it did not further stratify within WHO grade III cases. Collectively, these data indicate that epigenetic modifications beyond DNA methylation are involved in the aggressiveness of meningioma. It also suggests that H3K27me3 immunohistochemistry might be a useful adjunct in meningioma diagnostics, particularly for cases with WHO grade II histology or at the borderline between WHO grade I and II.

CNS-PNET is no longer regarded a single disease but encompassed many distinct molecular entities. After removal of the term from the 2016 WHO classification of CNS tumours, diagnostic and therapeutic uncertainty remains. Through a world-wide collaboration, tumour samples from patients with the "historic" diagnosis of CNS-PNET were re-evaluated by DNA methylation profiling (n=405) and blinded neuropathological panel review (n=256). Clinical data on treatment and outcome were pooled with data on previously published patients. The given numbers represent preliminary data of the ongoing project. The re-evaluation by DNA methylation identified many distinct entities as expected, including high grade glioma (HGG, n=70), embryonal tumors with multilayered rosettes (ETMR, n=57) and CNS-neuroblastoma with FOXR2 alteration (CNS-NB-FOXR2, n=42) as the most frequent molecular diagnostic categories. Poor clinical outcome was confirmed for patients with HGG (5y-PFS 12%/5y-OS 12%, n=24), and ETMR (5y-PFS 12%/5y-OS 18%, n=62), while most patients with CNS-NBFOXR2 survived (5y-PFS 52%/5y-OS 96%, n=31). Seven of 12 relapses/progressions of CNS-NB-FOXR2 occurred in radiotherapy-naive patients. Classification into other newly described and less common entities included HGNET-MN1 (n=19), HGNET-BCOR (n=11), and EFT-CIC (n=13). Independent neuropathological review demonstrated that samples of these entities presented as non-embryonal tumours. Furthermore, marked clinical differences exist (HGNET-MN1: 5y-PFS 25%/5y-OS 95%, n=22; HGNETBCOR: 5y-PFS 0%/5y-OS 44%, n=16; CNS-EFT-CIC: 5y-PFS 40%/5y-OS 60%, n=10). Our results show that implementation of DNA methylation profiling together with histopathological analysis will improve prospective diagnostic accuracy and facilitates the retrospective outcome analysis of treatment protocols used for this variety of biologically distinct entities