Endothelial-like cells derived directly from human tumor xenografts Gangadharan B. Sajithlal 1 , Terence F. McGuire 1 , Jie Lu 1 , Donna Beer-Stolz 2 and Edward V. Prochownik 1,3,4 1 Section of Hematology/Oncology, Children’s Hospital of Pittsburgh, Pittsburgh, PA 2 The Center for Biological Imaging, The University of Pittsburgh Medical Center, Pittsburgh, PA 3 Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 4 The University of Pittsburgh Cancer Institute, Pittsburgh, PA Tumor-associated endothelial cells (TAECs) harboring various genomic abnormalities have been described in human cancers although their origins remain obscure. We generated 4 human cancer cell lines tagged with multiple markers, grew them as xenografts, and characterized their TAECs. Depending on their tumor of origin, 5–40% of TAECs reproducibly expressed all tags. Tagged TAECs (tTAECS) were morphologically, immunologically and functionally similar, although not identical, to normal endothelial cells (ECs) and contained only human chromosomes. tTAECs underwent a senescent-like proliferative arrest after several in vitro passages, but could be immortalized by telomerase, thus allowing us to show that the retention of the EC phenotype was of long-term duration. In contrast, nonimmortalized tTAECs could be propagated in vivo where they incorporated into the tumor neo-vasculature. Although consistent with previous reports that some tumor cells may undergo ‘‘vasculogenic mimicry’’ (VM), the tumor-derived endothelial-like cells described here appear distinctly different. Moreover, their properties and behaviors are more durable than expected for cells undergoing VM, are not the result of fusions between ECs and tumor cells, and are cell autonomous. These findings could have significant implications for therapies that target tumor angiogenesis. A major determinant of a tumor’s growth and metastatic potential is the extent and integrity of its blood supply. 1–4 The tumor neovasculature is widely believed to have 2 dis- tinct extratumoral origins. The first, arising through a process termed ‘‘angiogenesis,’’ originates from the sprouting of new capillaries from pre-existing vessels in geographical proximity to the tumor. The second, known as ‘‘vasculogenesis,’’ arises from the recruitment into the tumor bed of bone marrow- derived hematopoietic/endothelial progenitors (hemangio- blasts) or mesodermal/endothelial progenitors (mesangio- blasts) and their subsequent differentiation into endothelial cells (ECs). 2–5 As a rule, the tumor vasculature is neither structurally nor functionally normal 6,7 but is nonetheless con- sidered an excellent target for cancer chemotherapy due to its presumed genomic stability. 8,9 Recent observations, however, have challenged the notion that the tumor neovasculature is genetically normal. Tumor- associated endothelial cells (TAECs) and other vascular components occasionally show loss of heterozygosity or even the same chromosomal translocations as the tumor cells themselves. 10–12 Although the origins of these ECs have not been rigorously determined, potential sources include tumor cell-EC fusions, phagocytic uptake of tumor cell nuclei or chromosomes by ECs and the direct trans-dif- ferentiation of tumor cells to ECs. 12,13 Somewhat related to the latter is ‘‘vasculogenic mimicry’’ (VM), a process by which tumor cells, particularly those of an aggressive nature, form structures resembling blood vessels. These can some- times be shown to contain plasma and blood cells and to communicate with the true endothelium-lined tumor vascu- lature. 14–17 Cells undergoing VM may be quite heterogene- ous and display varying amounts and degrees of EC- and/ or mesenchymal-like differentiation and marker expres- sion. 16,18–24 Although VM has been defined and studied under a vari- ety of conditions, 14,19–24 a common feature appears to be tu- mor cell de-differentiation and a tendency to express embry- onal and EC-specific markers. 18,19,22,24 This raises questions as to which tumor cells actually undergo this transition, how closely related to true ECs they really are, and how long and under what other circumstances the state persists. Moreover, the precise relationship between the observed molecular Key words: vasculogenic mimicry, angiogenesis, vasculogenesis, endothelial cells, epithelial-mesenchymal transition Additional Supporting Information may be found in the online version of this article. Grant sponsor: NIH; Grant number: CA105033; Grant sponsor: The Research Advisory Committee of Children’s Hospital of Pittsburgh DOI: 10.1002/ijc.25251 History: Received 28 Sep 2009; Revised 11 Jan 2010; Accepted 3 Feb 2010; Online 16 Feb 2010 Correspondence to: Edward V. Prochownik, Section of Hematology/Oncology, Children’s Hospital of Pittsburgh of UPMC, Rangos Research Center, Rm. 5124, 530 45th St, Pittsburgh, PA 15201, USA, Tel.: 412-692-9110 (L), Fax: þ412-692-5228, E-mail: procev@chp.edu Cancer Cell Biology Int. J. Cancer: 127, 2268–2278 (2010) V C 2010 UICC International Journal of Cancer IJC