Evaluation of vascular permeability and intratumoral level of IFN-alpha in 4 T1 tumor-bearing mice treated with 5-FU. (a) Fluorescent microscopy of 4 T1 tumor cryosections demonstrating a FITC-dextran 2000 kDa accumulation in untreated (left) and 5-FU treated (right) tumors. FITC-dextran 2000 kDa (green) was intravenously-administrated and 2 h later tumors were processed as described in methods. FITC, fluorescein isothiocyanate. H&E, hematoxylin and eosin staining of cryosections. The 5-FU exhibited morphological changes in tumor sections, microvessel density was significantly lower than that in the untreated control, large patchy necrosis was visualized. (b) The diagram shows the data from three tumors, evaluating ten sections per tumor. (c) IFN-alpha response to intratumoral SFV/EnhLuc injections in tumor-bearing mice treated and untreated with 5-FU. The IFN-alpha level is expressed in % relative to tumors non-treated with 5-FU and virus. Two groups of mice (n = 6) were treated and non-treated with 5-FU, respectively, then a half of each group of mice was subjected to intratumoral injections of SFV/EnhLuc. The IFN-alpha response was measured in tumor homogenates after 18 h of virus injection. NS – non-significant differences; * - significant differences (p < 0.05), mean ± SD; bar 200 μm.