In situ expression of hypoxia inducible factor 2-alpha in gliomas.

Abstract

e13534 Background: Hypoxia, a driver of malignancy, is fundamental to glioblastoma (GBM). Of the hypoxia inducible transcription factors (HIFs), HIF-2a is expressed in GBM tumor cells, responds to prolonged hypoxia, and is a prime candidate for HIF therapeutic targeting. PT2385 is a novel, orally available, first-in-class, HIF-2a inhibitor with a brain:plasma ratio of 0.9 in rats. To establish HIF-2a as a therapeutic target in GBM, in situ expression needs to be described. Methods: Twenty-two paraffin-embedded gliomas (grade II-IV) underwent immunohistochemistry for HIF-2a. After rehydration, a hot Tris EDTA pH 9.0 solution retrieved epitopes, non-specific sites were blocked, and HIF-2a antibody (Santa Cruz, sc-13596) was added. A horseradish peroxidase detection system identified staining. Representative samples were digitally scanned. Localization and quantification of HIF-2a was independently verified by a neuropathologist. Patient survival and molecular genetics were retrospectively collected with Institutional Review Board approval. Results: HIF-2a expression was not detected in the 4 Grade II and 2 Grade III gliomas.Of the 16 GBMs, HIF-2a was expressed in 13 specimens (81%) - highly in 7 ( > 10% cells positive), intermediate in 6 ( < 10% cells positive), and minimally in 3. Recurrent disease stained highly for HIF-2a. Staining was specific to tumor cells and occasionally monocytic cells, clustering in perivascular and perinecrotic regions. Amongst the 16 GBMs, median patient age and survival was 58 and 13.9 months. The two longest survivors harbored positive prognostic genetics (six-year survival with a 1p/19q co-deletion and ten-year survival with MGMT gene methylation). Twelve of 16 patients received chemoradiation. Survival was not correlated with HIF-2a. Conclusions: This first in situ description of HIF-2a demonstrates expression is absent in low-grade gliomas, present in the majority of GBMs, and high in recurrent GBMs. HIF-2a abundance varies with clustering in perivascular and perinecrotic niches. Survival did not appear to be correlated with HIF-2a in this small cohort though well-known prognostic genetic mutations and treatment heterogeneity limit firm conclusions. Preclinical studies with PT2385 are in progress.