Role of mitogen-activated protein kinase in Zn-BC-AM PDT-induced apoptosis in nasopharyngeal carcinoma cells

Photodynamic therapy (PDT) with a recently developed photosensitizer Zn-BC-AM was found to effectively induce apoptosis in a welldifferentiated nasopharyngeal carcinoma (NPC) HK-1 cell line. Sustained activation of p38 mitogen-activated protein kinase (MAPK) and cjun N-terminal kinase (JNK) as well as a transient increase in activation of extracellular signal-regulated kinase (ERK) were observed immediately after Zn-BC-AM PDT. A commonly used p38 MAPK/JNK pharmacological inhibitor PD169316 was found to reduce PDTinduced apoptosis of HK-1 cells. PD169316 also prevented the loss of Bcl-2 and Bcl-xL in PDT-treated HK-1 cells. However, inhibition of JNK with SP600125 had no effect on Zn-BC-AM PDT-induced apoptosis while inhibition of ERK with PD98059 or p38 MAPK with SB203580 significantly increased Zn-BC-AM PDT-induced apoptosis. Further study showed that knockdown of the p38b isoform with siRNA also increased Zn-BC-AM PDT-induced apoptosis, indicating that the anti-apoptotic effect of PD169316 in PDT-treated HK-1 cells was probably independent of p38 MAPK or JNK activation. Taken together, the results suggest that inhibition of p38b and ERK may enhance the therapeutic efficacy of Zn-BC-AM PDTon NPC cells. It should be noted that data only based on the use of PD169316 should be interpreted in caution.