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TNF-alpha downregulates vascular endothelial Flk-1 expression in human melanoma xenograft model
Chandrakala Menon1, Malini Iyer, Indira Prabakaran
1Harrison Department of Surgical Research, School of Medicine, University of Pennsylvania, Philadelphia 19104, USA.
Abstract:
High-dose TNF with melphalan has significant antitumor activity in regional perfusion of the limbs and liver in human malignancies. TNF is believed to target tumor vasculature, but the precise molecular mechanism is unknown. The present study demonstrates that TNF downregulates the VEGF receptor, fetal liver kinase-1 (Flk-1), on tumor endothelium in a human melanoma xenograft model. NIH1286 human melanoma cells were transduced with a 720-bp fragment of the human VEGF(121) gene to develop well-vascularized tumors that served as an amplified system for measuring Flk-1 expression changes. We injected 5 x 10(6) cells subcutaneously, each of two distinct single cell clones (NIH1286/3 and NIH1286/15), into athymic nude mice to produce tumors approximately 10 mm in size. Each animal then received either BSA or TNF in BSA by tail vein. Tumors harvested at different time points post-TNF were analyzed for Flk-1 mRNA and protein expression. Data obtained showed that intravascular TNF downregulated Flk-1 expression in tumor endothelial cells. This effect could contribute to the antitumor activity of TNF known to target tumor vasculature.
Insights
Tumor necrosis factor (TNF) downregulates fetal liver kinase-1 (Flk-1) in tumor blood vessels. This mechanism may explain TNF
Area of Science:
- Oncology
- Molecular Biology
- Immunology
Background:
- High-dose tumor necrosis factor (TNF) combined with melphalan shows antitumor effects in human cancers.
- TNF's impact on tumor vasculature is recognized, but the exact molecular pathways remain unclear.
Purpose of the Study:
- To investigate the molecular mechanism by which TNF affects tumor vasculature.
- To determine if TNF influences the expression of vascular endothelial growth factor receptor (VEGF receptor) fetal liver kinase-1 (Flk-1) on tumor endothelial cells.
Main Methods:
- Human melanoma cells engineered to express VEGF were implanted in mice to create well-vascularized tumors.
- Mice received either bovine serum albumin (BSA) or TNF intravenously.
- Tumor samples were analyzed for Flk-1 mRNA and protein expression at various time points after TNF administration.
Main Results:
- Intravascular administration of TNF led to a significant downregulation of Flk-1 expression in tumor endothelial cells.
- This downregulation was observed at both the mRNA and protein levels.
Conclusions:
- TNF reduces Flk-1 expression on tumor endothelium, suggesting a role in targeting tumor vasculature.
- This finding provides a molecular explanation for the antitumor activity of TNF in regional perfusion therapies.