Gillian Tozer

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  Tumour Microcirculation, Vascular Targeting and Biomarkers: insight from pre-clinical models
  Gillian Tozer

  Since clinical approval in 2004 of the vascular endothelial growth factor (VEGFA) blocking antibody, bevacizumab (Avastin), for treatment of colorectal cancer, a substantial number of additional anti-angiogenic compounds are now available for cancer treatment. Although these compounds are primarily targeted against the angiogenic process itself, they undoubtedly have additional effects on already established tumour blood vessels. In addition, a number of so-called tumour vascular disrupting agents (VDAs), which are specifically designed to target established tumour blood vessels, are in clinical trials. Despite this success, resistance to treatment is a major problem, with lack of predictive biomarkers to select those patients most likely to benefit from vascular targeted treatments a major limitation and biomarkers of response technically challenging.

  
  

  VEGFA exists as multiple isoforms generated through alternative splicing and proteolysis. Recent retrospective analyses of data from several large phase III clinical trials have found an association between high concentrations of soluble VEGFA isoforms in plasma and poor prognosis, but also improved response to bevacizumab, making them potential predictive biomarkers. Using mouse fibrosarcoma cells genetically modified to express single isoforms of VEGFA, we have investigated the role of individual VEGFA isoforms in tumour vascularisation, patterning and function, metastasis and response to VEGFA pathway inhibitors and VDAs. Notably, soluble VEGFA-120 was associated with increased metastasis to the lung and a good response to the anti-VEGFA blocking antibody, B20-4.1.1. (the mouse equivalent of bevacizumab). Expression of VEGFA-120 was associated with highly permeable and dilated blood vessels in the primary tumour and a modified extracellular matrix, which could account for the increased metastasis. Analytical methods for measuring vascular and metabolic parameters in intravital microscopy and magnetic resonance imaging/spectroscopy (MRI/MRS) of tumours will be discussed.