Untargeted Metabolomic Characterization of Glioblastoma Intra-Tumor Heterogeneity Using OrbiSIMS

Glioblastoma (GBM) is an incurable brain cancer with
a median survival
of less than two years from diagnosis. The standard treatment of GBM
is multimodality therapy comprising surgical resection, radiation,
and chemotherapy. However, prognosis remains poor, and there is an
urgent need for effective anticancer drugs. Since different regions
of a single GBM contain multiple cancer subpopulations (“intra-tumor
heterogeneity”), this likely accounts for therapy failure as
certain cancer cells can escape from immune surveillance and therapeutic
threats. Here, we present metabolomic data generated using the Orbitrap
secondary ion mass spectrometry (OrbiSIMS) technique to investigate
brain tumor metabolism within its highly heterogeneous tumor microenvironment.
Our results demonstrate that an OrbiSIMS-based untargeted metabolomics
method was able to discriminate morphologically distinct regions (viable,
necrotic, and non-cancerous) within single tumors from formalin-fixed
paraffin-embedded tissue archives. Specifically, cancer cells from
necrotic regions were separated from viable GBM cells based on a set
of metabolites including cytosine, phosphate, purine, xanthine, and
8-hydroxy-7-methylguanine. Moreover, we mapped ubiquitous metabolites
across necrotic and viable regions into metabolic pathways, which
allowed for the discovery of tryptophan metabolism that was likely
essential for GBM cellular survival. In summary, this study first
demonstrated the capability of OrbiSIMS for in situ investigation
of GBM intra-tumor heterogeneity, and the acquired information can
potentially help improve our understanding of cancer metabolism and
develop new therapies that can effectively target multiple subpopulations
within a tumor.

胶质母细胞瘤（Glioblastoma, GBM）是一种无法治愈的脑癌，确诊后的中位生存期不足两年。目前胶质母细胞瘤的标准治疗方案为涵盖手术切除、放射治疗与化学治疗的多模式疗法，但患者预后仍较差，因此亟需开发有效的抗癌药物。由于单颗胶质母细胞瘤的不同区域存在多种癌症亚群，即肿瘤内异质性（intra-tumor heterogeneity），这一特征可能是治疗失败的原因——部分癌细胞能够逃脱免疫监视与治疗威胁。本研究采用轨道阱二次离子质谱（Orbitrap secondary ion mass spectrometry, OrbiSIMS）技术生成代谢组学数据，以探究高度异质性肿瘤微环境中的脑肿瘤代谢特征。研究结果显示，基于OrbiSIMS的非靶向代谢组学方法可区分福尔马林固定石蜡包埋组织档案中单颗肿瘤内形态学各异的区域：存活区、坏死区与非癌区域。具体而言，可通过包括胞嘧啶、磷酸盐、嘌呤、黄嘌呤与8-羟基-7-甲基鸟嘌呤在内的一组代谢物，将坏死区的癌细胞与存活的胶质母细胞瘤细胞区分开来。此外，我们将坏死区与存活区的普遍存在代谢物映射至代谢通路中，进而发现色氨酸代谢可能对胶质母细胞瘤细胞的存活至关重要。综上，本研究首次证实了OrbiSIMS技术可用于胶质母细胞瘤肿瘤内异质性的原位研究，所获得的信息或有助于加深我们对癌症代谢的理解，并开发出可有效靶向肿瘤内多种亚群的新型治疗方案。