The MAP kinase pathway is activated by ligand binding to a transmembrane receptor, which switches Ras on via GEF (Guanine nucleotide Exchange Factor) that counteracts GAP (GTPase Activating Protein) activity. Ras-GTP in turn activates the downstream signaling intermediates (kinases), which are activated by sequential phosphorylation. Which drug CANNOT be used to target cancer cells that have elevated receptor activation? A. Antibodies that block the ligand-binding domain of receptor
B. Small molecule inhibitors that bind the ATP-binding pocket of kinases
C. Small molecule inhibitors that interfere with GAP activity
D. Small molecule inhibitors that interfere with Ras binding to the downstream kinase
E. Antibodies specific for ligand to prevent receptor binding