Linearly Patterned Programmed Cell Necrosis Induced by Chronic Hypoxia Plays a Role in Melanoma Angiogenesis

Background: Highly aggressive tumors are exposed to hypoxia and increased tumor interstitial fluid pressure (IFP) conditions which is resistant to blood supply. Physiological responses of the organism may reduce IFP through induction of orderly cell death. Specific aims: This study demonstrates that orderly cell death provided spatial structure for early angiogenesis in the hypoxic, high-IFP tumor microenvironment and the participation of linearly patterned programmed cell necrosis (LPPCN) in nascent melanoma angiogenesis. Methods: Animal model, laser capture microdissection, wound healing and transwell assays, three-dimensional cultures, zymography assays, western-blotting analysis, immunohistochemistry and RT-PCR were performed. Results: This study demonstrated a special form of cell death occurring in groups of malignant tumor cells which arrayed in lines. Both features of apoptosis and necrosis can be found in this cell death pattern and were termed as LPPCN. Its role as a stimulus of tumor angiogenesis was investigated using human melanoma samples and an animal model. Computer image analysis showed that LPPCN and tumor microvessels had identical spatial distributions. It can be induced by chronic hypoxia, high IFP and subsequent calcium influx. Higher number of tumor associated macrophages (TAM) and VEGF expression were found in the tumor with LPPCN. Based on the tumor-bearing animal model, it was found that block of caspase pathway inhibited LPPCN, microvessel density and vasculogenic mimicry (VM). Conclusions: LPPCN formation may play an important role in tumor angiogenesis due to stimulation of macrophage infiltration and HIF-1α regulation, and that inhibition of LPPCN may be a novel therapeutic strategy against tumor angiogenesis and metastasis.