| Samenvatting: | <p><strong>Background</strong></p>
Metastasis to the brain is a major challenge with poor prognosis. The blood-brain barrier (BBB) is a significant impediment to effective treatment, being intact during the early stages of tumour development and heterogeneously permeable at later stages. Intravenous injection of tumour necrosis factor (TNF) selectively induces BBB permeabilisation at sites of brain micrometastasis, in a TNF type-1 receptor (TNFR1) dependent manner. Here, to enable clinical translation, we have developed a TNFR1-selective agonist variant of human TNF that induces BBB permeabilisation, whilst minimising potential toxicity.
<p><strong>Methods</strong></p>
A library of human TNF muteins (mutTNF) were generated and assessed for binding specificity to mouse and human TNFR1/2, endothelial permeabilising activity in vitro, potential immunogenicity and circulatory half-life. The permeabilising ability of the most promising variant was assessed in vivo in a model of brain metastasis.
<p><strong>Results</strong></p>
The primary mutTNF variant showed similar affinity for human TNFR1 than wild-type human TNF, similar affinity for mouse TNFR1 as wild-type mouse TNF, undetectable binding to human/mouse TNFR2, low potential immunogenicity and permeabilisation of an endothelial monolayer. Circulatory half-life was similar to mouse/human TNF and BBB permeabilisation was induced selectively at sites of micrometastases in vivo, with a time window of ≥24h and enabling delivery of agents within a therapeutically-relevant range (0.5-150kDa), including the clinically approved therapy, trastuzumab.
<p><strong>Conclusions</strong></p>
We have developed a clinically-translatable mutTNF that selectively opens the BBB at micrometastatic sites, whilst leaving the rest of the cerebrovasculature intact. This approach will open a window for brain metastasis treatment that currently does not exist.
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