title: Distinct contributions of angiogenesis and vascular co-option during the initiation of primary microtumors and micrometastases.
abstract: Primary tumors and metastases have been thought to initiate avascularly as multicellular aggregates and later induce angiogenesis or initiate vascularly by co-opting pre-existing host blood vessels without inducing angiogenesis. These two distinct concepts of microtumor vascularization have raised significant controversies. To clarify intratumoral vascularization and tumor cell behaviors at single-cell level during the earliest stage of microtumor initiation, we established primary and metastatic microtumor models in Tg(flk1:EGFP) transgenic zebrafish. We found that tumor cells preferred to initiate avascularly as multicellular aggregates and only later (50-100 cells in size) induced angiogenesis in blood-supply-sufficient microenvironments. In blood-supply-deficient microenvironments, less tumor cells (20-30 cells per fish) managed to co-opt and migrate along host vessels, whereas more tumor cells (100-300 cells per fish) could immediately induce angiogenesis without obvious cell migration. In a metastatic model, we clearly observed that tumor cells co-opted, migrated along and proliferated on the surface of host vessels at an early stage after they extravasated from host vessels and induced angiogenesis later when micromatastases comprised only 15-30 tumor cells. Moreover, the inducement of neovessels accelerated the growth of micromatastases in size, meanwhile, decreased the migration of tumor cells on the surface of host vessels. These results suggest that vessel co-option and angiogenesis have distinct contributions during the initiation of microtumors. Microtumors initiated reasonably through co-opting host vessels or inducing angiogenesis, depending on the differences of local microenvironments and cell numbers in microtumors. The results in this study may have important implications for the therapeutic application of antiangiogenic strategies.
authors.affiliation: State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, West China Medical School, Sichuan University, Chengdu, People's Republic of China.
authors.forename: Chengjian
authors.initials: C
authors.lastname: Zhao
authors.forename: Hanshuo
authors.initials: H
authors.lastname: Yang
authors.forename: Huanshan
authors.initials: H
authors.lastname: Shi
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Wang
authors.forename: Xiancheng
authors.initials: X
authors.lastname: Chen
authors.forename: Yike
authors.initials: Y
authors.lastname: Yuan
authors.forename: Shuo
authors.initials: S
authors.lastname: Lin
authors.forename: Yuquan
authors.initials: Y
authors.lastname: Wei
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D051379:Mice; D055806:Microvessels / Q000473:pathology*; D008954:Models, Biological; D009362:Neoplasm Metastasis; D009374:Neoplasms, Experimental / Q000098:blood supply* / Q000473:pathology*; D009389:Neovascularization, Pathologic; D014407:Tumor Cells, Cultured; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000502:physiology; D015027:Zebrafish
chemical_list: C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D040301:Vascular Endothelial Growth Factor Receptor-2