Brain Tumor Microenvironment and Angiogenesis in Melanoma Brain Metastases

Abstract

BackgroundHigh tumor-infiltrating lymphocytes (TILs) and hemorrhage are important prognostic factors in patients who have undergone craniotomy for melanoma brain metastases (MBM) before 2011 at the University of Pittsburgh Medical Center (UPMC). We have investigated the prognostic or predictive role of these histopathologic factors in a more contemporary craniotomy cohort from the University of North Carolina at Chapel Hill (UNC-CH). We have also sought to understand better how various immune cell subsets, angiogenic factors, and blood vessels may be associated with clinical and radiographic features in MBM.MethodsBrain tumors from the UPMC and UNC-CH patient cohorts were (re)analyzed by standard histopathology, tumor tissue imaging, and gene expression profiling. Variables were associated with overall survival (OS) and radiographic features.ResultsThe patient subgroup with high TILs in craniotomy specimens and subsequent treatment with immune checkpoint inhibitors (ICIs, n=7) trended to have longer OS compared to the subgroup with high TILs and no treatment with ICIs (n=11, p=0.059). Bleeding was significantly associated with tumor volume before craniotomy, high melanoma-specific expression of basic fibroblast growth factor (bFGF), and high density of CD31+αSMA- blood vessels. Brain tumors with high versus low peritumoral edema before craniotomy had low (17%) versus high (41%) incidence of brisk TILs. Melanoma-specific expression of the vascular endothelial growth factor (VEGF) was comparable to VEGF expression by TILs and was not associated with any particular prognostic, radiographic, or histopathologic features. A gene signature associated with gamma delta (gd) T cells was significantly higher in intracranial than same-patient extracranial metastases and primary melanoma. However, gdT cell density in MBM was not prognostic.ConclusionsICIs may provide greater clinical benefit in patients with brisk TILs in MBM. Intratumoral hemorrhage in brain metastases, a significant clinical problem, is not merely associated with tumor volume but also with underlying biology. bFGF may be an essential pathway to target. VEGF, a factor principally associated with peritumoral edema, is not only produced by melanoma cells but also by TILs. Therefore, suppressing low-grade peritumoral edema using corticosteroids may harm TIL function in 41% of cases. Ongoing clinical trials targeting VEGF in MBM may predict a lack of unfavorable impacts on TIL density and/or intratumoral hemorrhage.

Re‐thinking therapeutic development for CNS metastatic disease

“…This analysis showed that melanoma brain metastases are characterized by (a) decreased immune infiltration and (b) increased expression of genes in the metabolic pathway of oxidative phosphorylation (OXPHOS). The observed decrease in T‐cell infiltration was consistent with previous characterization of melanoma brain metastases by other methods 67,68 and may contribute to the decreased clinical activity of anti‐PD1 immunotherapy in patients with CNS metastases. The increase in expression of OXPHOS genes in the clinical brain metastases was recapitulated by directly injecting human melanoma cells into brain tissue (compared with subcutaneous injection), strongly supporting that this phenomenon is induced by the brain TME.…”

The clinical significance of adenomatous polyposis coli (APC) and catenin Beta 1 (CTNNB1) genetic aberrations in patients with melanoma

“…We analyzed the expression of β-catenin across different cellular compartments within the brain (i.e., melanoma, reactive glia, TILs, normal brain parenchyma) using the Wilcoxon matched-pairs signed-rank test, as we have previously described [26]. We investigated the correlation between protein expression of various proteins by melanoma cells and TIL density using the Kendall rank correlation statistic.…”

“…We dichotomized protein expression of β-catenin in melanoma cells by IHC as high expression (2+, 3+) or low/absent expression (0, 1+) by IHC. We then performed an OS analysis to assess the prognostic significance of β-catenin in MBM using the Kaplan-Meier method, as we have previously described [26]. We performed statistical analysis using Prism 8 (GraphPad Software, version 8.3.1, San Diego CA).…”

“…Under the UNC-CH IRB-approved protocol 16-2959, we analyzed tumor specimens corresponding to patients who underwent craniotomy for melanoma brain metastases (MBM) at UNC-CH. We have recently reported information about patient demographics, histopathologic data, and OS defined from craniotomy to the last followup, and status at last follow-up (alive or deceased) [26].…”

“…We performed single-color immunohistochemistry (IHC) for β-catenin in 5 μm-thick sections obtained from formalinfixed, paraffin-embedded melanoma craniotomy tissues placed on positively charged glass slides, as we have previously described [26]. Briefly, slides were dried, then baked at 60 °C for 90 min, followed by heat-induced epitope retrieval using HIER Buffer L (Thermo Scientific, TA-135-HBL, Thermo Fisher Scientific, MA).…”