Proteomic Analysis of Spatial Heterogeneity Identifies HMGB2 as Putative Biomarker of Tumor Progression in Adult-Type Diffuse Astrocytomas

Simple Summary Adult-type astrocytomas usually present heterogeneous aspects under the microscope, reflecting their progression over time from grade 2 or 3 to grade 4, the highest possible grade. We identified a number of proteins and molecular pathways dysregulated in the high-grade areas of astrocytomas, which are involved in tumor evolution that could be targeted to avoid or detain glioma progression to higher grades. We identified HMGB2 as a potential biomarker of glioma evolution and predictive of response to treatment in more than 300 adult-type gliomas, using molecular profiling and immunohistochemistry, which are highly accessible for most pathology laboratories. HMGB2 expression increased even before histological markers of evolution appeared in grades 2 and 3 astrocytomas, and it was associated with poor survival. In glioblastomas, high HMGB2 expression identified tumors with better response to the standard treatment and could be used as additional inclusion/exclusion criterion to enroll patients in future clinical trials of new treatments.Abstract Although grading is defined by the highest histological grade observed in a glioma, most high-grade gliomas retain areas with histology reminiscent of their low-grade counterparts. We sought to achieve the following: (i) identify proteins and molecular pathways involved in glioma evolution; and (ii) validate the high mobility group protein B2 (HMGB2) as a key player in tumor progression and as a prognostic/predictive biomarker for diffuse astrocytomas. We performed liquid chromatography tandem mass spectrometry (LC-MS/MS) in multiple areas of adult-type astrocytomas and validated our finding in multiplatform-omics studies and high-throughput IHC analysis. LC-MS/MSdetected proteomic signatures characterizing glioma evolution towards higher grades associated with, but not completely dependent, on IDH status. Spatial heterogeneity of diffuse astrocytomas was associated with dysregulation of specific molecular pathways, and HMGB2 was identified as a putative driver of tumor progression, and an early marker of worse overall survival in grades 2 and 3 diffuse gliomas, at least in part regulated by DNA methylation. In grade 4 astrocytomas, HMGB2 expression was strongly associated with proliferative activity and microvascular proliferation. Grounded in proteomic findings, our results showed that HMGB2 expression assessed by IHC detected early signs of tumor progression in grades 2 and 3 astrocytomas, as well as identified GBMs that had a better response to the standard chemoradiation with temozolomide.