Overexpression of Receptor Tyrosine Kinase EphB4 Triggers Tumor Growth and Hypoxia in A375 Melanoma Xenografts: Insights from Multitracer Small Animal Imaging Experiments.

Christin Neuber,Frank Hofheinz,Ralf Bergmann,Sebastian Meister,Hans-Jürgen Pietzsch,Birgit Belter,Jens Pietzsch

doi:10.3390/molecules23020444

Christin Neuber, Frank Hofheinz + Show 5 more

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https://doi.org/10.3390/molecules23020444

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Abstract

Experimental evidence has associated receptor tyrosine kinase EphB4 with tumor angiogenesis also in malignant melanoma. Considering the limited in vivo data available, we have conducted a systematic multitracer and multimodal imaging investigation in EphB4-overexpressing and mock-transfected A375 melanoma xenografts. Tumor growth, perfusion, and hypoxia were investigated by positron emission tomography. Vascularization was investigated by fluorescence imaging in vivo and ex vivo. The approach was completed by magnetic resonance imaging, radioluminography ex vivo, and immunohistochemical staining for blood and lymph vessel markers. Results revealed EphB4 to be a positive regulator of A375 melanoma growth, but a negative regulator of tumor vascularization. Resulting in increased hypoxia, this physiological characteristic is considered as highly unfavorable for melanoma prognosis and therapy outcome. Lymphangiogenesis, by contrast, was not influenced by EphB4 overexpression. In order to distinguish between EphB4 forward and EphrinB2, the natural EphB4 ligand, reverse signaling a specific EphB4 kinase inhibitor was applied. Blocking experiments show EphrinB2 reverse signaling rather than EphB4 forward signaling to be responsible for the observed effects. In conclusion, functional expression of EphB4 is considered a promising differentiating characteristic, preferentially determined by non-invasive in vivo imaging, which may improve personalized theranostics of malignant melanoma.

Highlights

Cutaneous malignant melanoma, an aggressive tumor entity with steadily increasing incidence, tends to metastasize early and, once in a metastatic stage, represents a fatal neoplasm with scarce therapeutic options
Malignant melanoma is characterized by high vascularization and elevated expression of both vascular endothelial growth factors (VEGF) and VEGF receptors (VEGFR) which strongly correlates with melanoma progression and poor clinical outcome [4,10,11,12,13]
Using a combination of non-invasive small animal positron emission tomography (PET), magnetic resonance imaging (MRI), and optical imaging in vivo, together with ex vivo imaging modalities, we systematically investigated the functional relevance of EphB4 overexpression in A375 melanoma xenografts as model

Summary

Introduction

An aggressive tumor entity with steadily increasing incidence, tends to metastasize early and, once in a metastatic stage (stage IV), represents a fatal neoplasm with scarce therapeutic options. This results in a 5 year survival below 10% and accounts for up to 90% of skin cancer deaths despite its relatively low frequency that amounts to only 5% of all invasive skin cancer cases [1,2]. New therapeutic concepts, especially for malignant melanoma, are urgently needed

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