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CTA Combined with CT Perfusion for Assessing the Efficacy of Anti-angiogenic Therapy in Rabbit VX2 Tumors

Posted Feb 29, 2012 Updated Apr 10, 2023
By Han Wang MD PhD , Lin-Feng Zheng MD PhD , Yan Feng MD , Xue-Qian Xie MD , Xiaoming Yang MD PhD , Gui-Xiang Zhang MD PhD
11 min read

Rationale and Objectives

The aim of this study was to validate the feasibility of assessing the efficacy of antiangiogenic therapy on VX2 tumors using three-dimensional computed tomographic (CT) angiography (CTA) combined with CT perfusion.

Materials and Methods

Forty rabbits with VX2 tumors were randomly assigned to four groups according to different doses of antiangiogenic drug, which were administered intraperitoneally daily for 14 days. In each group, 10 animals were scanned using three-dimensional CTA and CT perfusion on days 1 and 2 after the latest administration of the drug. Tumor masses were sectioned, stained by immunohistochemistry, and processed for correlation between CT imaging and histology.

Results

The numbers of new tumor vessels from CTA were significantly different among the four groups ( P < .001). As the dose of the drug increased, blood flow and blood volume on CT perfusion increased linearly, but the mean transit time and permeability surface-area product decreased linearly ( P < .001). Immunohistochemical analyses showed that microvascular density decreased, while both luminal vascular number and mature vessel number increased linearly as the drug dose increased ( P < .001). CT manifestations were correlated well with histologic findings ( P < .05).

Conclusions

It is feasible to assess the efficacy of antiangiogenic therapy on VX2 tumors using three-dimensional CTA combined with CT perfusion. Three-dimensional CTA can display the morphologic changes of tumor vessels, while CT perfusion can predict the functional changes of tumor vessels after antiangiogenic therapy.

Neovascularization is an essential process for the growth, invasion, and metastasis of solid tumors . Antiangiogenic therapy represents a promising strategy for tumor therapy. Our understanding of the molecular mechanisms that underlie angiogenesis has advanced significantly over the past decade, leading to the development of a number of new drugs that inhibit angiogenesis .

These forms of antiangiogenic therapies have created a need for efficient, noninvasive, and reliable ways to monitor tumor angiogenesis and to assess the efficacy of antiangiogenic therapy. Microvascular density (MVD), particularly measured in the most neovascular area (the “hot spot”) of a tumor, is currently an ideal histologic method in assessing the efficacy of antiangiogenic therapy . However, the measurement of MVD is not pragmatic in clinical practice, because of its invasiveness and the inconvenience of obtaining tumor tissues with repeated tumor biopsies.

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Materials and methods

Animal and Tumor Models

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Antiangiogenic Therapy

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CT Imaging Studies

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CTA

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CT perfusion

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Histopathology and Immunohistochemistry

Histopathology

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Immunohistochemistry

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Image Analysis

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Histopathologic and Immunohistochemical Analyses

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Figure 1, Microscope images show the two categories of luminal vessel in tumor: (a) mature vessel, with a complete endothelial cell wall (arrow) and layers of smooth muscle cells (star) , and (b) immature tumor vessels, with an incomplete layer of endothelial cell wall (arrow) . CD31 stain, original magnification 400×.

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Statistical Analysis

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Results

Numbers of New Tumor Vessel Branches on CTA

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Table 1

Numbers of New Vessel Branches in Tumors From Each Group ( n = 10)

Group Number of New Tumor Vessel Branches LSD A 22.3 ± 2.1 B 13.9 ± 1.6P < .001 C 10.8 ± 1.2P < .001 D 7.0 ± 1.3P < .001 ANOVA_P_ < .001

ANOVA, analysis of variance; LSD, least significant difference.

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Morphologic Features of Tumor Vessels after Antiangiogenic Therapy on CTA

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Figure 2, Reconstructed computed tomographic angiographic images (a–d) showing new tumor vessels (arrows) as well as preexisting tumor feeder arteries (arrowheads) in groups a to d , respectively. The numbers of new tumor vessels of negative control group (group a ) are greater than those of antiangiogenic drug–treated groups (groups b, c , and d ). As the dose of administrated drug increased, the numbers of new tumor vessels reduced. Among the three treated groups, the new tumor vessels of group b were more prominent than those of groups c and d .

Figure 3, Reconstructed computed tomographic angiographic maximum intensity projection images (a–d) presenting new tumor vessels (arrows) as well as preexisting tumor feeder arteries (arrowheads) in groups a to d , respectively. The characteristics of tumor vessels among different groups are similar to those shown in Figure 2 .

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Efficacy of Antiangiogenic Therapy with Different Doses of Endostatin on CT Perfusion Maps

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Figure 4, Computed tomographic (CT) perfusion maps of tumors among the four animal groups. Rows A to D represent groups A to D, respectively. In each row, image (a) is the contrast-enhancement CT image of the largest size cross-section of tumor, and images (b) to (e) are the perfusion map images, including (b) blood flow, (c) blood volume, (d) mean transit time, and (e) permeability surface of the same cross-section. The elliptical dashed lines and arrows highlight the tumor area. The color spectrum indicates the value of the perfusion parameter, ranging from high (red) to low (blue) .

Table 2

Values of BF, BV, MTT, and PS of Tumors, as Calculated on CT Perfusion Maps ( n = 10)

Group BF (mL/min/100 g) BV (mL/100 g) MTT (seconds) PS (mL/min/100 g) LSD A 38.9 ± 2.7 13.6 ± 1.7 29.8 ± 2.9 56.6 ± 12.1 B 53.2 ± 5.9 26.9 ± 3.7 25.0 ± 1.6 47.7 ± 11.3P < .001 C 78.5 ± 7.0 33.0 ± 3.3 20.6 ± 1.7 38.9 ± 12.3P < .001 D 95.3 ± 9.7 41.5 ± 5.7 17.5 ± 1.8 31.6 ± 11.5P < .001 Analysis of variance_P_ < .001P < .001P < .001P < .001

ANOVA, analysis of variance; BF, blood flow; BV, blood volume; CT, computed tomographic; LSD, least significant difference; MTT, mean transit time; PS, permeability surface-area product.

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Immunohistochemistry

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Figure 5, Immunohistochemical staining of tumor tissue sections for the specific endothelial antigen CD31 (a–d) shows the tumor tissues of groups a to d , respectively. The luminal microvascular structures (arrows) in tumors increased as the dose of endostatin increased. Original magnification 100×.

Table 3

MVD, LVN, MVN, IVN, and the Percentage of MVN in LVN of Each Group ( n = 10)

Group MVD LVN MVN IVN MVN in LVN (%) LSD A 40.7 ± 3.4 1.3 ± 0.6 0.2 ± 0.1 1.2 ± 0.5 11.1 ± 2.1 B 30.8 ± 4.1 3.2 ± 0.7 0.5 ± 0.2 2.7 ± 1.2 13.3 ± 1.3P < .001 C 20.2 ± 2.8 6.0 ± 1.4 0.8 ± 0.4 5.7 ± 1.6 14.7 ± 2.7P < .001 D 16.7 ± 1.6 8.7 ± 1.5 1.2 ± 0.5 7.6 ± 1.3 15.0 ± 2.8P < .001 ANOVA_P_ < .001P < .001P < .001P < .001P = .002

ANOVA, analysis of variance; IVN, immature vessel number; LSD, least significant difference; LVN, luminal vascular number; MVD, microvascular density; MVN, mature vessel number.

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CT Imaging and Histologic Correlations

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Table 4

Pearson’s Correlations ( P Values) and Associated Significance Levels Between the CT Perfusion Parameters and Histologic Findings ( n = 10)

BF BV MTT PS MVD −0.814 (<.001) −0.861 (<.001) 0.976 (<.001) 0.825 (<.001) LVN 0.992 (<.001) 0.950 (<.001) −0.747 (<.001) −0.362 (.022) MVN 0.912 (<.001) 0.929 (<.001) −0.596 (<.001) −0.194 (.230)

BF, blood flow; BV, blood volume; CT, computed tomographic; LVN, luminal vascular number; MTT, mean transit time; MVD, microvascular density; MVN, mature vessel number; PS, permeability surface-area product.

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Discussion

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Conclusions

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Acknowledgments

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Academic Radiology, Volume 19, Issue 3
Journals General Radiology
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