Melanoma vasculogenic mimicry is strongly related to reactive oxygen species level.

The concept of 'vasculogenic mimicry' (VM) was introduced to describe the unique ability of highly invasive tumor cells to form capillary-like structures (CLS) and matrix-rich patterned network in three-dimensional culture that mimic embryonic vasculogenic network. Recently, we have shown that CLS formation requires apoptotic cell death through activation of caspase-3-dependent mechanism. In this study, to identify some molecular determinants driving aggressive melanoma cells to express a latent 'angiogenic program' that recapitulates the early events of CLS formation, we focused on the involvement of antioxidants (AOs) in the process of melanoma VM. We have studied the effects of resveratrol, (-)-epigallocathechin gallate, N-acetyl-cysteine (NAC) and Trolox on the ability of melanoma cells to form/destroy CLS. We observed that the formation of CLS was strongly related to reactive oxygen species level. In vivo animal experiments confirmed the involvement of reactive oxygen species level in melanoma VM. To understand the molecular mechanisms of this phenomenon, we specifically looked for induction of apoptosis and vascular endothelial growth factor (VEGF) release. Western blot analysis revealed that the level of VEGF, VEGF receptors (VEGF-Rs) and active caspase-3 dramatically decreased in cells treated with AOs. Here, we also report further experiments designed to determine whether the crosstalk between AOs and apoptosis exists in melanoma VM.

The involvement of apoptosis in melanoma vasculogenic mimicry.

During development, the formation and remodeling of the primary vascular network occurs by vasculogenesis and angiogenesis. In 1999, the concept of vasculogenic mimicry was introduced to describe the unique ability of highly aggressive tumor cells to form a capillary-like structure and a matrix-rich patterned network in three-dimensional culture that mimic the embryonic vasculogenic network. In this study, we examined the ability of melanoma cells derived from patients with disseminated melanoma to engage in vasculogenic mimicry in order to identify key parameters in the complexity of the formation of capillary-like structure. We showed that disseminated melanoma as well as uveal and cutaneous melanoma adopts a vascular-related phenotype and engages in vasculogenic mimicry: the main geometrical features of capillary-like structure are determined during the first step of the vascular network assembly. We provided experimental evidence that capillary-like structure formation requires apoptotic cell death through activation of a caspase-dependent mechanism: a broad range caspase inhibitor zVAD-fmk and a caspase-3 inhibitor DEVD blocked capillary-like structure formation. Apoptosis occurs before capillary-like structure formation but not after capillary-like structures have assembled. These observations may provide a better understanding of the mechanisms involved in melanoma vasculogenic mimicry.