Anti-angiogenic effects of VEGF stimulation on endothelium deficient in phosphoinositide recycling

Anti-angiogenic therapies have generated significant interest for their potential to combat tumor growth. However, the ability of tumors to overproduce pro-angiogenic ligands and overcome targeted inhibitory therapies has hampered this approach. A novel way to circumvent this problem might be to target the re-synthesis of critical substrates consumed during intracellular transduction of pro-angiogenic signals in endothelial cells, thus harnessing the tumors own production of excess stimulatory ligands to deplete adjacent host endothelial cells of the capacity to respond to these signals. Here we show using zebrafish and human endothelial cells in vitro that endothelial cells deficient in CDP-diacylglycerol synthase 2 are uniquely sensitive to increased VEGF stimulation due to a reduced capacity to re-synthesize phosphoinositides, including phosphatidylinositol 4,5-bisphosphate (PIP2) a key substrate for VEGF signal transduction, resulting in VEGF-exacerbated defects in angiogenesis and angiogenic signaling. Using murine tumor allograft models we show that either systemic or endothelial cell specific suppression of phosphoinositide recycling results in reduced tumor growth and reduced tumor angiogenesis. Our results suggest that inhibition of phosphoinositide recycling may provide a useful anti-angiogenic approach, and highlights the general potential of targeting the resynthesis of rate limiting signaling substrates as a valuable therapeutic strategy.