CASP9 and nasopharyngeal carcinoma: As shown in Fig. 2e, triptolide decreased expression of caspase-9 and increased expression of p53, cleaved caspase-3 and cleaved PARP-1 in EBV-positive HONE1/Akata, HK1/Akata, C666–1 and EBV-negative NPC CNE1cells.