Matthias Preusser

Assessment of BRAF V600E mutation status by immunohistochemistry with a mutation-specific monoclonal antibody

Activating mutations of the serine threonine kinase v-RAF murine sarcoma viral oncogene homolog B1 (BRAF) are frequent in benign and malignant human tumors and are emerging as an important biomarker. Over 95% of BRAF mutations are of the V600E type and specific small molecular inhibitors are currently under pre-clinical or clinical investigation. BRAF mutation status is determined by DNA-based methods, most commonly by sequencing. Here we describe the development of a monoclonal BRAF V600E mutation-specific antibody that can differentiate BRAF V600E and wild type protein in routinely processed formalin-fixed and paraffin-embedded tissue. A total of 47 intracerebral melanoma metastases and 21 primary papillary thyroid carcinomas were evaluated by direct sequencing of BRAF and by immunohistochemistry using the BRAF V600E mutation-specific antibody clone VE1. Correlation of VE1 immunohistochemistry and BRAF sequencing revealed a perfect match for both papillary thyroid carcinomas and melanoma metastases. The staining intensity in BRAF V600E mutated tumor samples ranged from weak to strong. The generally homogenous VE1 staining patterns argue against a clonal heterogeneity of the tumors investigated. Caution is essential when only poorly preserved tissue is available for VE1 immunohistochemical analysis or when tissues with only little total BRAF protein are analyzed. Immunohistochemistry using antibody VE1 may substantially facilitate molecular analysis of BRAF V600E status for diagnostic, prognostic, and predictive purposes.

Delta-like 4 Notch Ligand Regulates Tumor Angiogenesis, Improves Tumor Vascular Function, and Promotes Tumor Growth In vivo

The vascular endothelial growth factor (VEGF) plays a key role in tumor angiogenesis. However, clinical trials targeting the VEGF pathway are often ineffective, suggesting that other factors/pathways are also important in tumor angiogenesis. We have previously shown that the Notch ligand Delta-like 4 (DLL4) is up-regulated in tumor vasculature. Here, we show that DLL4, when expressed in tumor cells, functions as a negative regulator of tumor angiogenesis by reducing the number of blood vessels in all five types of xenografts, but acts as a positive driver for tumor growth in two of them (human glioblastoma and prostate cancer). The growth of in vivo models was not related to the effects on growth in vitro. DLL4 expressed in the tumor cells activated Notch signaling in host stromal/endothelial cells, increased blood vessel size, and improved vascular function within tumors. The promotion of tumor growth was, to some extent, due to a reduction of tumor hypoxia and apoptosis. DLL4-expressing tumor cells responded to anti-VEGF therapy with bevacizumab. A soluble form of DLL4 (D4ECD-Fc) blocked tumor growth in both bevacizumab-sensitive and bevacizumab-resistant tumors by disrupting vascular function despite increased tumor vessel density. In addition, we show that DLL4 is up-regulated in tumor cells and tumor endothelial cells of human glioblastoma. Our findings provide a rational basis for the development of novel antiangiogenic strategies via blockade of DLL4/Notch signaling and suggest that combined approaches for interrupting both DLL4 and VEGF pathways may improve antiangiogenic therapy.

Immunohistochemistry Is Highly Sensitive and Specific for the Detection of V600E BRAF Mutation in Melanoma

This study investigated the sensitivity and specificity of immunohistochemical (IHC) analysis using an anti-BRAF antibody to detect the presence of the BRAF V600E mutation in patients with metastatic melanoma. A total of 100 patients with American Joint Committee on Cancer stage IIIC unresectable or stage IV melanoma and who underwent tumor DNA BRAF mutation testing were selected. Paraffin-embedded, formalin-fixed melanoma biopsies were analyzed for the BRAF mutation status by independent, blinded observers using both conventional DNA molecular techniques and IHC with the novel BRAF V600E mutant-specific antibody, VE1. The antibody had a sensitivity of 97% (37/38) and a specificity of 98% (58/59) for detecting the presence of a BRAF V600E mutation. Of the BRAF-mutated cases, none of the non-V600E cases (including V600K) stained positive with the antibody (0/11). There were 5 cases with discordant BRAF mutation results. Additional molecular analysis confirmed the immunohistochemically obtained BRAF result in 3 cases, suggesting that the initial molecular testing results were incorrect. Two of these patients would not have received a BRAF inhibitor on the basis of the initial false-negative mutation testing result. Two cases remained discordant. The reported IHC method is an accurate, rapid, and cost-effective method for detecting V600E BRAF mutations in melanoma patients. Clinical use of the V600E BRAF antibody should be a valuable supplement to conventional mutation testing and allow V600E mutant metastatic melanoma patients to be triaged rapidly into appropriate treatment pathways.

Anti-O6-methylguanine-methyltransferase (MGMT) immunohistochemistry in glioblastoma multiforme: observer variability and lack of association with patient survival impede its use as clinical biomarker.

Silencing of O6‐methylguanine‐DNA methyltransferase (MGMT) protein expression because of MGMT gene promoter hypermethylation is considered to be associated with postoperative chemoradiotherapy benefits in glioblastoma multiforme (GBM) patients. The objective of this study was to clarify the usability of MGMT immunohistochemistry (IHC) as a clinical biomarker.

Immunohistochemical testing of BRAF V600E status in 1,120 tumor tissue samples of patients with brain metastases

Brain metastases (BM) are frequent and carry a dismal prognosis. BRAF V600E mutations are found in a broad range of tumor types and specific inhibitors targeting BRAF V600E protein exist. We analyzed tumoral BRAF V600E-mutant protein expression using the novel mutation-specific antibody VE1 in a series of 1,120 tumor specimens (885 BM, 157 primary tumors, 78 extra-cranial metastases) of 874 BM patients. In 85 cases, we performed validation of immunohistochemical results by BRAF exon 15 gene sequencing. BRAF V600E protein was expressed in BM of 42/76 (55.3%) melanomas, 1/15 (6.7%) ovarian cancers, 4/72 (5.5%) colorectal cancers, 1/355 (0.3%) lung cancers, 2/6 thyroid cancers and 1/2 choriocarcinomas. BRAF V600E expression showed high intra-tumoral homogeneity and was similar in different tumor manifestations of individual patients. VE1 immunohistochemistry and BRAF exon 15 sequencing were congruent in 68/70 (97.1%) cases, but VE1 immunostaining identified small BRAF V600E expressing tumor cell aggregates in 10 cases with inconclusive genetic results. Melanoma patients with BRAF V600E mutant protein expressing tumors were significantly younger at diagnosis of the primary tumor and at operation of BM than patients with non-mutated tumors. In conclusion, expression of BRAF V600E mutant protein occurs in approximately 6% of BM and is consistent in different tumor manifestations of the same patient. Thus, BRAF V600E inhibiting therapies seem feasible in selected BM patients. Immunohistochemical visualization of V600E-mutant BRAF protein is a promising tool for patient stratification. An integrated approach combining both, VE1 immunohistochemistry and genetic analysis may increase the diagnostic accuracy of BRAF mutation analysis.

Programmed death ligand 1 expression and tumor-infiltrating lymphocytes in glioblastoma

BACKGROUND Immune checkpoint inhibitors targeting programmed cell death 1 (PD1) or its ligand (PD-L1) showed activity in several cancer types. METHODS We performed immunohistochemistry for CD3, CD8, CD20, HLA-DR, phosphatase and tensin homolog (PTEN), PD-1, and PD-L1 and pyrosequencing for assessment of the O6-methylguanine-methyltransferase (MGMT) promoter methylation status in 135 glioblastoma specimens (117 initial resection, 18 first local recurrence). PD-L1 gene expression was analyzed in 446 cases from The Cancer Genome Atlas. RESULTS Diffuse/fibrillary PD-L1 expression of variable extent, with or without interspersed epithelioid tumor cells with membranous PD-L1 expression, was observed in 103 of 117 (88.0%) newly diagnosed and 13 of 18 (72.2%) recurrent glioblastoma specimens. Sparse-to-moderate density of tumor-infiltrating lymphocytes (TILs) was found in 85 of 117 (72.6%) specimens (CD3+ 78/117, 66.7%; CD8+ 52/117, 44.4%; CD20+ 27/117, 23.1%; PD1+ 34/117, 29.1%). PD1+ TIL density correlated positively with CD3+ (P < .001), CD8+ (P < .001), CD20+ TIL density (P < .001), and PTEN expression (P = .035). Enrichment of specimens with low PD-L1 gene expression levels was observed in the proneural and G-CIMP glioblastoma subtypes and in specimens with high PD-L1 gene expression in the mesenchymal subtype (P = 5.966e-10). No significant differences in PD-L1 expression or TIL density between initial and recurrent glioblastoma specimens or correlation of PD-L1 expression or TIL density with patient age or outcome were evident. CONCLUSION TILs and PD-L1 expression are detectable in the majority of glioblastoma samples but are not related to outcome. Because the target is present, a clinical study with specific immune checkpoint inhibitors seems to be warranted in glioblastoma.

Brain tumour cells interconnect to a functional and resistant network

Astrocytic brain tumours, including glioblastomas, are incurable neoplasms characterized by diffusely infiltrative growth. Here we show that many tumour cells in astrocytomas extend ultra-long membrane protrusions, and use these distinct tumour microtubes as routes for brain invasion, proliferation, and to interconnect over long distances. The resulting network allows multicellular communication through microtube-associated gap junctions. When damage to the network occurred, tumour microtubes were used for repair. Moreover, the microtube-connected astrocytoma cells, but not those remaining unconnected throughout tumour progression, were protected from cell death inflicted by radiotherapy. The neuronal growth-associated protein 43 was important for microtube formation and function, and drove microtube-dependent tumour cell invasion, proliferation, interconnection, and radioresistance. Oligodendroglial brain tumours were deficient in this mechanism. In summary, astrocytomas can develop functional multicellular network structures. Disconnection of astrocytoma cells by targeting their tumour microtubes emerges as a new principle to reduce the treatment resistance of this disease.

Immunohistochemical Detection of the BRAF V600E-mutated Protein in Papillary Thyroid Carcinoma

The V600E mutation of the B-type Raf kinase (BRAF) gene is a common event in papillary thyroid carcinoma (PTC) and seems to play a key role in the development and progression of this disease. We evaluated the expression of the mutated BRAF V600E protein in 144 cases of PTC using a novel mutation-specific antibody. Seventy-six PTCs (52.8%) showed unequivocal diffuse cytoplasmic expression of the mutated BRAF protein, and the T1799A point mutation was confirmed by sequencing analysis in selected cases. No statistical difference in V600E BRAF protein expression was seen between microcarcinomas and macrocarcinomas. Further, no significant correlation of V600E expression with clinicopathologic parameters of aggressiveness such as lymph node metastasis, peritumoral infiltration, or perithyroidal infiltration was found. BRAF V600E protein expression was significantly more common in tumors with tall cell or oncocytic features but was less common in tumors with follicular growth pattern. Diffuse sclerosing, solid and follicular variants did not show the mutated BRAF protein. Immunohistochemical detection of the mutated V600E BRAF protein in PTC may facilitate mutational analysis in the clinical setting. Our data show that the expression of the mutated BRAF V600 protein and thus the corresponding BRAF mutation seems not to be per se a marker of aggressiveness but is already seen in clinically indolent microcarcinomas. Nevertheless, the investigation of BRAF V600E protein expression might be of clinical interest especially in therapy-resistant disease, as new therapeutics inhibiting the mutated protein are clinically available.

Prospects of immune checkpoint modulators in the treatment of glioblastoma

Glioblastoma is the most common primary brain tumour in adults. Prognosis is poor: even with the current gold-standard first-line treatment—maximal safe resection and combination of radiotherapy with temozolomide chemotherapy—the median overall survival time is only approximately 15–17 months, because the tumour recurs in virtually all patients, and no commonly accepted standard treatment for recurrent disease exists. Several targeted agents have failed to improve patient outcomes in glioblastoma. Immunotherapy with immune checkpoint inhibitors such as ipilimumab, nivolumab, and pembrolizumab has provided relevant clinical improvements in other advanced tumours for which conventional therapies have had limited success, making immunotherapy an appealing strategy in glioblastoma. This Review summarizes current knowledge on immune checkpoint modulators and evaluates their potential role in glioblastoma on the basis of preclinical studies and emerging clinical data. Furthermore, we discuss challenges that need to be considered in the clinical development of drugs that target immune checkpoint pathways in glioblastoma, such as specific properties of the immune system in the CNS, issues with radiological response assessment, and potential interactions with established and emerging treatment strategies.

Brain metastases: pathobiology and emerging targeted therapies

Brain metastases (BM) are common in cancer patients and are associated with high morbidity and poor prognosis, even after intensive multimodal therapy including resection, radiotherapy (stereotactic radiosurgery or whole brain radiotherapy) and chemotherapy. However, advances in the understanding of the pathobiology of BM and the development of molecular targeted agents hold promise for improved prophylaxis and therapy of BM. Here we provide a comprehensive review of the current concepts on mechanisms of the brain-metastatic cascade involving hematogenous dissemination of tumor cells, attachment to microvessel endothelial cells, extravasation into the brain, interaction with the local microenvironment, angiogenesis and intraparenchymal proliferation. Transendothelial migration depends on adhesion molecules such as integrins, selectins and chemokines. Tumor cells invade the brain by degrading extracellular matrix components using heparanase and matrix metalloproteinases. Astrocytes and microglial cells exert not only anti-, but also pro-neoplastic effects on brain-invading tumor cells. Some tumor types (e.g. melanoma) show prominent cooption of preexisting vasculature, while other tumor types (e.g. lung cancer) tend to show early angiogenesis after brain invasion. In this article we also critically summarize the data on currently studied targeted therapeutics in BM especially in the context of recent preclinical data. The most promising agents for BM patients include anti-angiogenic drugs, inhibitors of v-RAF murine sarcoma viral oncogene homolog B1 (BRAF) for BRAF V600E mutated melanoma and inhibitors of epithelial growth factor receptor for non-small cell lung cancer. Molecular analysis of the BRAF V600E status of melanoma BM using DNA-based methods or immunohistochemistry may soon enter the routine neuropathological practice.