The Generation of Vasculogenic Mimicry Patterns in Uveal Melanoma: Reversion From an Invasive to Non–Invasive Genotype and Phenotype

Abstract

Purpose: : The detection of laminin–rich vasculogenic mimicry patterns (VMP) in histological sections of primary uveal melanoma is associated with death from metastatic uveal melanoma. We hypothesized that melanoma cells forming VMPs would feature genotypic and phenotypic characteristics associated with metastatic behavior.

Methods: : Gene expression (Affymetrix Test3 Arrays, 6 replicates per assay) between poorly invasive OCM1a primary uveal melanoma cells, highly invasive M619 primary uveal melanoma cells, and highly invasive metastatic MUM2B melanoma cells was determined in in 3D culture conditions after VM patterns were generated. The ability of VM forming cells to replicate and invade were studied in novel halo culture conditions, and the morphological characteristics of these cells documented by phase contrast microscopy. In vitro morphological characteristics were compared with the appearance of VMPs in human tumor tissue sections and by immunohistochemistry with a uveal melanoma tissue microarray.

Results: : Unexpectedly, differentially up–regulated in VMP–forming M619 and MUM2B included GDF15 (a differentiation gene, 14.6x increase) and p21 (2.7x increase) and genes down–regulated in VMP–forming cells included versican and CD44 (both associated with invasion), VE–cadherin and endoglin (associated with the endothelial cell phenotype), and cyclin E2 (p < 1E16 for all expression differentials). Highly invasive melanoma MUM2B cells changed shape from epithelioid to spindle A cells and failed to replicate after forming VMPs in vitro. In human tissue samples, tumor cells adjacent to or embedded within VMPs assume a spindle A ("indolent") melanoma phenotype. By tissue microarray, the percent of Ki67+ tumor cells adjacent to VM patterns is significantly less than Ki67+ cells spatially removed from VM patterns (p < 0.0001).

Conclusions: : The formation of VM patterns by highly invasive melanoma cells is accompanied by a reversion of the genotype and morphological appearance to non–invasive, low proliferative melanoma cells, and is consistent with the developmental biology concept of pattern–formation best described as "regional specialization." Facilitation of metastasis by melanoma cells VM patterns involves mechanisms other than behaviors associated with an invasive tumor cell phenotype.

Keywords: melanoma • pathobiology • extracellular matrix