Analysis of the microvasculature of rat transplanted tumors using the synchrotron radiation microangiography system: Effects of tumor microvasculature and microcirculation of radiotherapy and angiogenesis-related factors *
The purpose of this study was to establish an in vivo experimental system using monochromatic synchrotron radiation microangiography（MSRA）, with which we could observe morphological changes in tumor microvasculature. In addition, using this experimental system, we also investigated the morphological and dynamic changes occurring in the tumor microenvironment under the influence of an angiogenesis activator, an inhibitor, and irradiation. Using male athymic rats into which N-nitrosomethylurea-induced mammary adenocarcinomas had been transplanted in the inferior epigastric wall, microangiography was performed with the SPring-8 BL20B2 beamline. At two weeks after tumor transplantation, the rats ware divided into the following four different procedure groups of five rats each:a non-treated（NT）group, a radiation therapy（RT）group, an anti-VEGFR neutralizing antibody（AI）administered group, and a b-FGF（AP）administered group. In all groups, changes in tumor microvasculature were assessed four weeks after the tumor transplantation. The morphological changes in tumor microvessels were analyzed with a scoring system which involved the assignment of a special score to a typical finding, and microvessel density（MVD）was evaluated with binary data originating from image analyzing software. The MVD from binary analysis was compared with the MVD from histological analysis to evaluate the correlation between two groups. The circulatory dynamics of the tumor were assessed by the time-density-curve obtained from an angiographic dynamic study. The minimal detectable vessel diameter was 20 to 30μm. Compared to the NT group, the AP group showed a higher total tumor vessel score and a higher MVD. The AI group had a lower total score and lower MVD, and the RT group had a higher total score and lower MVD than the NT group. A statistically significant correlation was found between the binary MVD and histological MVD in both the marginal and central areas of the transplanted tumor（p＝0.004 and 0.02, respectively）. The time-density curve of the AP group revealed a rapid increase in the first pass curve with a peak and then a gradual decrease. The AI and RT groups showed on initial rapid increase without peak and continued gradual increase thereafter. This experimental system could make possible in vivo observation of tumor microvessels with a minimal diameter about 20 to 30μm which have not been identified before, and also provides methodology for the quantitative assessment of morphological changes in tumor vessels before and after administration of irradiation or angiogenesis related molecules. （Accepted on September 27，2004）
