155P - Effect of Bevacizumab on Tumour 5-Fluorouracil Concentration and Microcirculatory Parameters Obtained by Dynamic Contrast-Enhanced MRI in a Hepatocellular Carcinoma Xenograft Model

Abstract

ABSTRACT Introduction Vascular endothelial growth factor (VEGF) is expressed by tumours to promote angiogenesis. Clinical trials of anti-VEGF therapy combined with chemotherapy demonstrate improvement in survival. We investigate the effect of bevacizumab (bev), a humanized monoclonal antibody that inhibits VEGF-A, on tumour 5-fluorouracil (5FU) concentration in a hepatocellular carcinoma (HCC) xenograft model, together with changes in tumour microcirculatory parameters obtained by dynamic contrast-enhanced (DCE) MRI. Methods 48 immunodeficient mice implanted with subcutaneous HCC xenografts were first injected with bev (1mg/kg or 10mg/kg) or omalizumab (control). 1 day later, they received 5FU and were sacrificed. Tumour and plasma 5FU concentration was measured by liquid chromatography-mass spectrometry. A subset of 17 mice underwent DCE MRI with gadolinium contrast at baseline and one day after bev/omalizumab injection. Scans employed a three-dimensional spoiled gradient recalled sequence with tracer concentration estimated using variable flip-angle technique. Data analysis employed a conventional two-compartment tracer kinetic model. Results Tumour 5FU concentration (µg/g) was significantly lower 1 day after bev (10mg/kg) compared to control (8.4 vs 21.6, p = 0.027). However, there was no significant difference in plasma 5FU concentration between the bev and control groups. Following bev (10mg/kg), DCE MRI measurements of tumour intravascular blood volume reduced by 38.3% (p = 0.01); there was no significant change in DCE-MRI parameters in the control group. Following bev (1mg/kg), tumour permeability-surface area product (ml/100ml/min) correlated with tumour 5FU concentration (r2 = 0.84, p = 0.01). Conclusion Bev causes vascular shutdown consistent with its anti-angiogenic mode of action. Reduced tumour 5FU concentration suggests that the reported synergism between anti-VEGF and chemotherapy may not be attributable to improved drug delivery at this early time point. DCE-MRI may play a role as a biomarker for tumour drug concentration following anti-VEGF therapy. Disclosure All authors have declared no conflicts of interest.