Kinases mediate various fundamental regulations in living cells.ATP-competitive kinase inhibitors have been essential pharmacological tools and are widely used to identify signaling pathways, which make these compounds great candidates for use as therapeutic agents.However, the discrepancies found between their in vitro and in vivo responses have hampered their development as drugs.By using a FRET (fluorescent resonance energy transfer) based probe, CKAR, we analyzed how protein complexes and activation states modulate sensitivity towards PKC inhibitors.We found that intermolecular or intramolecular protein interactions could protect PKC from certain PKC inhibitors.