CDC6 and cancer: The high demand or “addiction” of cancer cells to exogenously provided methionine is not caused by the cancer cells’ inability to synthesize methionine but rather by their high demands of methionine-derived metabolites [32], including processes involving Cdc6 and prereplication complexes [33], nucleoside metabolism and polyamine synthesis [34], and cell cycle arrest in G1 involving p38 mitogen-activated protein kinase [35].