VHL and clear cell renal carcinoma: Glycine, an essential precursor for de novo purine nucleotide synthesis significantly decreased in HIF-1α silenced and combined HIF-1α+2α silenced tumors consistent with a previous cell study using Von Hippel-Lindau (VHL) modified human clear cell renal cell carcinoma cells, with HIF-1α, HIF-2α and combined HIF-1α and HIF-2α downregulated [13].