Intensity of doxorubicin fluorescence (I) plotted against distance from the nearest blood vessel (μm) is shown for HCT-8Ea and Ra (A) and HCT-8E11/1R1 (C) xenografts. Mean values are shown for ~160 areas of interest from 20 tumours in 10 mice. Upper curves represent drug penetration through HCT-8R tumors, middle curves represent pre-treatment with bortezomib, while lower curves represent controls. Growth curves for HCT-8Ea/Ra (B) and HCT-8E11/1R1 (D) xenografts following single treatments with doxorubicin (8 mg/kg) with or without prior bortezomib (1 mg/kg). Greater growth delay was observed for the loosely packed HCT-81R1 tumour xenografts than their tightly packed HCT-8E11 counterparts (p = 0.0012) with similar results for HCT-8Ra and HCT-8Ea derived xenografts (p = 0.004). Bortezomib pre-treatment did not significantly enhance doxorubicin treatment efficacy in tumour xenografts derived from HCT-8Ea and E11 cell lines (p = 0.45 and p = 0.09 respectively). Data represent means and SEM for 10-12 mice.