Pioglitazone prevents smoking carcinogen-induced lung tumor development in mice.

Pioglitazone (PGZ), a synthetic peroxisome proliferator-activated receptor gamma (PPARγ) ligand, is known to have anti-tumor activity by inducing tumor cell apoptosis. However, it is unknown whether it can be used to prevent smoking carcinogen-induced lung tumor development. We induced mouse lung tumors using smoking carcinogen 4- methylnitrosamino-l-3-pyridyl-butanone (NNK). PGZ was given at two early stages before the tumor formation. The role and the functional mechanism of PGZ were investigated in the development of mouse pulmonary tumors. The tumor development was monitored and PPARγ activity and endogenous PPARγ ligands 15(S)-HETE, 13(S)-HODE were determined. The application of PGZ before alveolar hyperplasia formation (Group NPa) and at the early phase of alveolar hyperplasia formation (Group NPb) significantly prevented the lung tumor development especially in Group NPb mice (all p < 0.05). PGZ not only prevented the NNK-mediated reduction of endogenous ligands 15(S)-HETE and 13(S)-HODE, but also increased 13(S)-HODE level in Group NPb mice. PPARγ transcriptional activity was increased in NNKstimulated lung tissues when PGZ was given. The in vivo results were confirmed in the human lung cancer cells, which showed that PGZ induced lung cancer cell apoptosis through up-regulating nuclear PPARγ expression, inducing PPARγ transcriptional activity and increasing the levels of PPARγ ligands in NNK-treated cells. The early application of PGZ is able to prevent NNK-induced lung tumor development through maintaining the level of endogenous PPARγ ligands 15(S)-HETE and 13(S)-HODE and activation of PPARγ.

4-Methylnitrosamino-1-3-pyridyl-1-butanone (NNK) promotes lung cancer cell survival by stimulating thromboxane A2 and its receptor.

The role of thromboxane A(2) (TxA(2)) in smoking-associated lung cancer is poorly understood. This study was conducted to study the role of TxA(2) in smoking carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-promoted cell survival and growth in human lung cancer cells. We found that NNK increased TxA(2) synthase (TxAS) expression and thromboxane B(2) (TxB(2)) generation in cultured lung cancer cells, the result of which was supported by the increased level of TxAS in lung cancer tissues of smokers. Both TxAS-specific inhibitor furegrelate and TxA(2) receptor antagonist SQ29548 completely blocked NNK-mediated cell survival and growth via inducting apoptosis. TxA(2) receptor agonist U46619 reconstituted a near-full survival and growth response to NNK when TxAS was inhibited, affirming the role of TxA(2) receptor in NNK-mediated cell survival and growth. Suppression of cyclic adenosine monophosphate response element binding protein (CREB) activity by its small interference RNA blocked the effect of NNK. Phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) also had a positive role. Altogether, our results have revealed that NNK stimulates TxA(2) synthesis and activates its receptor in lung cancer cells. The increased TxA(2) may then activate CREB through PI3K/Akt and extracellular ERK pathways, thereby contributing to the NNK-promoted survival and growth of lung cancer cells.

Haem oxygenase-1 plays a central role in NNK-mediated lung carcinogenesis.

The tobacco-specific nitrosamine, 4-(N-methyl-N-nitrosoamino)-1-(3-pyridyl)-1-butanone (NNK), is a potent lung cancer inducer. However, how NNK induces lung cancer is still largely unknown. Haem oxygenase (HO)-1 was evaluated in 30 pairs of lung cancer tumour samples and matched nontumour tissues from patients with a history of cigarette smoking. Expression of HO-1, p21(Cip1/Waf1/Cid1) (p21), B-cell lymphoma (Bcl)-2 family members, mitogen-activated protein kinase and nuclear factor (NF)-kappaB was also studied in lung cancer cells treated with NNK. The levels of HO-1 and p21 were significantly increased in lung tumour tissues. There was a positive relationship between these two proteins in the tumour. NNK stimulated lung cell proliferation and elevated the levels of HO-1, p21, inhibitor of apoptosis protein (c-IAP)2 and Bcl-2, but downregulated Bad. These effects of NNK were blocked by zinc protoporphyrin-XII, an HO-1 inhibitor. The NNK-mediated expression of HO-1 was governed by NF-kappaB and extracellular signal-regulated kinase 1/2, since blocking either of these prevented the stimulatory effect of NNK on HO-1, as well as molecules downstream of HO-1, such as p21, c-IAP2, Bcl-2 and Bad. In conclusion, haem oxygenase-1 plays a central role in NNK-mediated cell proliferation by promoting the expression of p21(Cip1/Waf1/Cid1), inhibitor of apoptosis protein 2 and B-cell lymphoma-2 but inhibiting the activity of Bad. Nuclear factor-kappaB and extracellular signal-regulated kinase 1/2 function upstream of haem oxygenase-1. Therefore, haem oxygenase-1 is likely to be a potential target in the treatment of smoking-related lung cancer.