Vascular mimicry: Triggers, molecular interactions and in vivo models.

Vascular mimicry is induced by a wide array of genes with functions related to cancer stemness, hypoxia, angiogenesis and autophagy. Vascular mimicry competent (VM-competent) cells that form de novo blood vessels are common in solid tumors facilitating tumor cell survival and metastasis. VM-competent cells display increased levels of vascular mimicry selecting for stem-like cells in an O2-gradient-dependent manner in deeply hypoxic tumor regions, while also aiding in maintaining tumor cell metabolism and stemness. Three of the principal drivers of vascular mimicry are EphA2, Nodal and HIF-1α, however, directly or indirectly many of these molecules affect VE-Cadherin (VE-Cad), which forms gap-junctions to bind angiogenic blood vessels together. During vascular mimicry, the endothelial-like functions of VM-competent cancer stem cells co-opt VE-Cad to bind cancer cells together to create cancer cell-derived blood conducting vessels. This process potentially compensates for the lack of access to blood and nutrient in avascular tumors, simultaneously providing nutrients and enhancing cancer invasion and metastasis. Current evidence also supports that vascular mimicry promotes cancer malignancy and metastasis due to the cooperation of oncogenic signaling molecules driving cancer stemness and autophagy. While a number of currently used cancer therapeutics are effective inhibitors of vascular mimicry, developing a new class of vascular mimicry specific inhibitors could allow for the treatment of angiogenesis-resistant tumors, inhibit cancer metastasis and improve patient survival. In this review, we describe the principal vascular mimicry pathways in addition to emphasizing the roles of hypoxia, autophagy and select proangiogenic oncogenes in this process.