ABSTRACT
BACKGROUND: Growing evidence suggests that tobacco can affect the responsiveness of cancer cells to treatment, particularly those of head and neck cancer. This article describes the effects of nicotine on the signaling of the death pathway, resulting in a decreased cytotoxicity of various anticancer agents such as cisplatin and gamma-radiation. METHODS: Colony-forming assays (CFA), using the head and neck cancer cell lines UMSCC10b and UMSCC5 and DNA fragmentation assays, were used to determine the effect of nicotine on cytotoxicity of various anticancer agents, whereas PCR and a JNK activity test were used to study the effect of nicotine on message expression levels and activity of the JNK signaling pathway. RESULTS: Nicotine consistently reduced the cytotoxic effect of DNA-damaging agents, such as cisplatin, UV, and gamma radiation, in UMSCC10b cells, increasing their IC(50) values by twofold, 1.7-fold, and 1.8-fold, respectively. These results were confirmed in a second squamous cell carcinoma cell line (UMSCC5), demonstrating an increase in IC(50) values for cDDP by twofold and 1.9-fold in the UMSCC10b andUMSCC5, respectively. In addition, nicotine reduced the DNA fragmentation 48 h after cDDP exposure in UMSCC10b and UMSCC5 cell lines by 30% and 33%, respectively. The latter, however, was not the result of an effect of nicotine on either the uptake of cDDP or repair of the cDDP-DNA-adducts. To further substantiate the adverse effect of nicotine, the JNK and gadd153 signaling pathways were studied. JNK activity was decreased by 1.8-fold, as well as the expression of its downstream target c-jun (1.9-fold), when tumor cells were exposed to cisplatin in the presence of nicotine. In addition, the gadd153 message was affected and reduced by 1.8-fold. CONCLUSIONS: Nicotine adversely affects the cytotoxicity of DNA-damaging agents. Nicotine does not interfere with the repair of the damage but directly affects the signaling of the death pathway, reducing the signaling of the JNK1 pathway. The latter results in a decrease in efficacy of the anticancer treatment in tumors exposed to nicotine.
