Direct evidence that the VEGF-specific antibody bevacizumab has antivascular effects in human rectal cancer

Abstract

The effects of vascular endothelial growth factor (VEGF) blockade on the vascular biology of human tumors are not known. Here we show here that a single infusion of the VEGF-specific antibody bevacizumab decreases tumor perfusion, vascular volume, microvascular density, interstitial fluid pressure and the number of viable, circulating endothelial and progenitor cells, and increases the fraction of vessels with pericyte coverage in rectal carcinoma patients. These data indicate that VEGF blockade has a direct and rapid antivascular effect in human tumors.

Figure 1

Effect of treatment on tumors in patients who completed entire combined treatment regimen, and surgery. (a) Endoscopic and pathological evaluation of rectal tumors. Surgical specimens showed grade II tumor regression in patients 1–5 and grade III in patient 6, by Mandard criteria (see Supplementary Note). Endoscopic image (instead of surgical specimen) was taken for patient 6, 3.5 weeks before surgery. BV, bevacizumab. (b) Representative functional CT images of blood perfusion before treatment (day 0), after bevacizumab (day 12) and after completion of treatment (day 104) in patient 5. (c) Tumor FDG uptake before treatment (pretreatment), 12 d after bevacizumab treatment and 6–7 weeks after completion of all neoadjuvant therapy (presurgery). Sagittal projections of FDG-PET scans for patient 1 are shown. Tumor is outlined in box, posterior to bladder.

Figure 2

Effect of a single injection of bevacizumab on tumor vasculature and FDG uptake. Parameters were obtained pretreatment and after one bevacizumab infusion. (a–c) Blood perfusion (a), blood volume (b) and permeability–surface area product (PS; c). Significant decreases after treatment are indicated by solid lines (P < 0.05 by t-test). Blood flow and blood volume decreased significantly in four of the patients. (d) Microvascular density. All patients showed significant decreases after treatment (P < 0.05 by t-test). (e) Fraction of vessels with pericyte coverage. The difference in the fraction of vessels positive for α-smooth muscle actin (α-SMA) in patient 2 was identified as an outlier by the Extreme Studentized Deviate test. Paired t-test analyses of the mean values that included and excluded the data of patient 2 had P < 0.09 and 0.001, respectively. (f) Mean tumor IFP decreased significantly after bevacizumab (P < 0.01 by paired t-test). (g) Tumor FDG uptake before treatment, on day 12 and presurgery (day 93), normalized for muscle values. On day 12 after bevacizumab treatment, a 40% decrease was observed in patient 3, and no change in the other patients. Lower levels were found in all patients before surgery except for patient 5, who had low levels throughout the treatment. In comparison to pretreatment and day 12 values, the median standard uptake value was significantly lower on day 93 (P < 0.01; Supplementary Table 1). (h) Circulating progenitor/stem cells (AC133⁺; left) and viable CECs (right) in peripheral blood. Samples were run to acquire 50,000 events in the mononuclear/lymphocyte gate. For both cell populations, bevacizumab induced a significant decrease in mean values (P < 0.05 by Wilcoxon signed-rank test). Key in b applies to a,c, g–i.