Influence of the site of human gallbladder xenograft (Mz-ChA-1) on angiogenesis at the distant site.

We reported that orthotopic xenograft of human gallbladder cancer (Mz-ChA-2) produced a greater amount of endogenous angiogenic inhibitory factors, however, only TGFbeta1 suppressed angiogenesis and tumor growth at the distant site (intracranium). The aim of this study was to confirm the validity of our previous findings that the site of the primary tumor would influence the angiogenesis in the distant site in a different xenograft of human gallbladder cancer (Mz-ChA-1). The growth rates, histology of the ectopic (flank) and orthotopic (gallbladder) xenografts, the plasma level of TGFbeta1, micro-circulation and angiogenesis in the distant site (intracranium) were estimated by size-measurement, hematoxylin and eosin staining, ELISA, intravital fluorescence microscopic observation and cranial window gel assay for angiogenesis. All experiments were performed in severe combined immunodeficient (SCID) mice. Orthotopic tumors grew faster and were less necrotic than ectopic tumors. Angiogenesis, vessel diameters, vessel density and leukocyte-rolling count in the distant site were significantly decreased in orthotopic tumor-bearing mice compared to those in either ectopic or no tumor-bearing mice. The plasma level of TGFbeta1 was significantly elevated in mice bearing orthotopic tumor as compared with ectopic and no tumor-bearing mice. Angiogenesis at the distant site was inhibited by the orthotopic xenograft of Mz-ChA-1 by the greatest amount of TGFbeta1 production. The results of the present study together with our previous study imply that the primary tumor microenvironment is conducive to the angiogenesis at a distant site by the production of the endogenous angiogenesis inhibitor TGFbeta1.