PTPA and lung carcinoma: The combination of triptolide and hydroxycamptothecin induces the apoptosis of human lung cancer cells by increasing PP2A activity, activating p38, ERK, and MAPK cascade reactions and by inhibiting the Akt survival pathway through mechanisms that involve PP2A activation, which synergistically enhances the effect of triptolide on A549 lung adenocarcinoma cells.169