In vivo effects of alphastatin. In vivo effects of alphastatin on (A) the volume and (B) histologic appearance of CT26 tumors grown in Balb/C mice. Data are shown as mean ± SEM. (B) Tumors were excised from control (i,iii) or alphastatin-treated (ii,iv) mice and general morphology/histology was examined at low magnification (i-ii, bar = 100 μm) or stained with an antimurine CD31 antibody and viewed at higher magnification (iii-iv, bar = 50 μm). Cells in control tumors exhibited a compact regular morphology (i) with many patent vessels in the viable regions (white arrows; i) lined with a continuous single layer of endothelial cells (iii). By contrast, alphastatin-treated tumors exhibited an irregular overall morphology with increased levels of necrosis (N; ii,iv) and large distended vessels found in areas of viable tumor as well as in areas of necrosis (as in ii,iv) showing a central thrombosis (T; ii,iv) and lined with patchy incomplete endothelial cells (arrows; iv). (C) No effect of alphastatin injections was evident on the vascular endothelium of nonmalignant murine tissue in vivo. CD31⁺ cells lining vessels in a range of nonmalignant tissues (arrows); lungs (i,iv), liver (ii,v), and kidneys (iii,vi) from mice were unaffected by alphastatin treatment (iv-vi) and resembled those from control (i-iii) mice. Bar in vi = 50 μm.