Increased Resistance of Vasculogenic Mimicry-Forming Uveal Melanoma Cells against Cytotoxic Agents in Three-Dimensional Cultures

Vasculogenic mimicry (VM) patterns are present in a wide variety of malignant tumors, represent the formation of perfusion pathways by tumor cells, and their presence in tumors is associated with adverse outcome (Maniotis et al., 1999; Folberg et al., 2000; Hendrix et al., 2003; Folberg and Maniotis, 2004; Dome et al., 2007). Mechanisms by which VM may contribute to adverse outcome are not well understood. Previous observations in our laboratory indicated that VM-forming tumor cells have increased resistance to herpes simplex virus-mediated oncolysis in three-dimensional (3D) uveal melanoma cultures (Valyi-Nagy et al., 2010). To determine whether VM-forming tumor cell subpopulations also have increased resistance against cytotoxic drugs, traditional two-dimensional (2D) and extracellular matrix (ECM, Matrigel)-containing 3D cultures of C918 uveal melanoma cells were established. In 2D cultures, C918 cells grew in monolayers. In 3D cultures, C918 cells formed a number of morphologically distinct tumor cell subpopulations that included cells that grew in monolayers on the Matrigel surface, cells that formed VM patterns, and cells that formed monolayers on the bottom of the culture dish. Following exposure to cisplatin or cadmium chloride, VM-forming tumor cells demonstrated prolonged survival relative to other tumor cell subpopulations in 3D cultures and cells grown in 2D. As presented in detail below, these findings suggest that increased drug resistance is a mechanism by which VMforming tumor cells contribute to adverse outcome.