Zhang 22-6

Several microcirculation patterns in tumors have been reported, including vasculogenic mimicry (VM), mosaic vessels (MV) and endothelium-dependent vessels. To investigate the sources of blood supply during different tumor stages, we studied the correlation between expression of vasculogenic mimicry (VM), mosaic vessels (MV) and endothelium-dependent vessels in a mouse melanoma xenograph. Sixty C57 mice were divided into 12 groups (5 mice per group) and inoculated with B16 melanoma cells. Eleven days later, the average tumor size was approximately 0.2 to 0.3 cm. From days 11 to 22, one group per day was randomly sacrificed, and the density of vasculogenic mimicry, mosaic vessels and endothelium-dependent vessels was measured in tumor tissue sections. Immunohistochemical dual-staining and electronic microscopy were also used to confirm the vessel types. All three types of microcirculation patterns were observed during tumor development. In the early stage of tumor growth, vasculogenic mimicry is the main pattern of blood supply. As the area of tumor tissue expands and the number of endothelium increase, vasculogenic mimicry is replaced by endothelium-dependent vessels. Mosaic vessels might be the interim state between vasculogenic mimicry and endothelium-dependent vessels. The number of endothelium-dependent vessels correlated with the size of the tumor (r=0.718, P=0.009), while the number of vasculogenic mimicry was inversely correlated (r=0.77, P=0.003). In conclusion, the number of vasculogenic mimicry decreased and the number of endothelial-dependent vessels increased during tumor growth. Introduction To maintain development and rapid growth, tumors need a sufficient blood supply (1). Besides the well-studied angiogenesis, recent studies have revealed several new patterns by which tumor tissues nourish themselves, including the pattern of mosaic vessels from both endothelium and tumor cells (2,3), and the pattern of vessels lined exclusively with tumor cells mimicking the presence and function of endothelial cells. This last process is termed vasculogenic mimicry (4,5). Three patterns of microcirculation were reported to participate in tumor blood supply. However, it is unclear how these patterns are involved in tumor growth. To answer this question, we monitored blood supply patterns during different stages of growth of melanoma xenografts in C57 mice. The results demonstrate that there are specific microcirculation pattern traits in different stages of tumor growth. Vasculogenic mimicry is the dominant blood supply pattern in the early stage characterized by rapid tumor growth (6). When the tumor mass expands, endothelial cells differentiate and proliferate, and the mosaic vessels appear as a transitional pattern. Consequently, endothelium-dependent vessels replace vasculogenic mimicry and mosaic vessels to become the major pattern of blood supply in the late stage of tumor growth (7,8). Materials and methods Animals. Sixty C57/6J 6-8 week-old black mice including 30 males and 30 females were purchased from the Animal Base of Union Drug Institute (Beijing). The average weight of these mice was 21 g. Cell strain. A single cell suspension of B16 malignant melanoma was provided by the Tianjin Cancer Hospital Department of Biochemistry and stored in liquid nitrogen. Before injection, the suspension was incubated for 20-30 sec in a 43 ̊C water bath and centrifuged at 1000 gps for 10 min. The supernatant was absorbed by an asepsis tampon, and the pellet was diluted with 1-2 ml 0.9% NaCl solution to ensure a final cell density of 3-5x106 cells/ml. Tumor-bearing animal model. All 60 C57BL/6J mice were divided randomly into 12 groups (5 mice per group). A week later, mice were inoculated with a single cell suspension of ONCOLOGY REPORTS 15: 15-20, 2006 15 Microcirculation patterns in different stages of melanoma growth SHIWU ZHANG1, HUA GUO1, DANFANG ZHANG1, WENZHI ZHANG3, XIULAN ZHAO2, ZHIYONG REN4 and BAOCUN SUN1,2 1Department of Pathology, TianJin Cancer Hospital, 2Department of Pathology, TianJin Medical University, 3Department of Molecular Pathology, TianJin Huanhu Hospital, TianJin 300060, P.R. China; 4Department of Biochemistry and Molecular Biology, The University of Texas, M.D. Anderson Cancer Center, Houston, TX 77030, USA Received June 22, 2005; Accepted August 3, 2005 _________________________________________ Correspondence to: Dr Baocun Sun, Department of Pathology, Tianjin Cancer Hospital, Tianjin Medical University, Tianjin