RI-BPI effectively distributes to lymphomas after parenteral administration. (A) The serum concentration of RI-BPI^biotin and L-BPI^biotin was determined after the intraperitoneal administration of 500 μg to mice carrying SU-DHL4 xenografts. Serum was taken at several time points (x-axis), and the concentration of biotinylated peptides was determined by chemical reaction with avidin-HRP (y-axis). (B) Histochemistry of the SU-DHL4 xenografts injected with RI-BPI^biotin and L-BPI^biotin performed at similar time points as in panel A. The presence of peptide was detected using Texas Red–avidin conjugates followed by fluorescence microscopy. Slides were mounted with permanent mounting medium (Vectashield Hard set; Vector Laboratories, Burlingame, CA) to prevent photobleaching. Slides were viewed with a fluorescent microscope (AxioSkop 2; Carl Zeiss, Jena, Germany) using a Plan-neofluar lens at a 10×/0.50 air objective and a 25×/0.80 oil objective. Images were acquired using a color camera (AxioCam; Carl Zeiss), and were processed using Axiovision software (Carl Zeiss).