Inhibition of benzo(a)pyrene-induced lung tumorigenesis in A/J mice by dietary N-acetylcysteine conjugates of benzyl and phenethyl isothiocyanates during the postinitiation phase is associated with activation of mitogen-activated protein kinases and p53 activity and induction of apoptosis.
Recent studies in cell culture have shown that isothiocyanates (ITCs) induce apoptosis via activation of mitogen-activated protein (MAP) kinases and p53 pathways, suggesting a potential for ITCs or their conjugates to inhibit tumorigenesis during the postinitiation phase. To evaluate whether ITC compounds administered after carcinogen treatment inhibit lung tumorigenesis, we investigated in A/J mice the effects of the N-acetylcysteine (NAC) conjugates of benzyl (BITC-NAC) and phenethyl ITC (PEITC-NAC) in the diet (15 micromol/g) administered after a single dose of 20 micromol benzo(a)pyrene [B(a)P]. The formation of lung adenomas was examined 140 days after B(a)P dosing. Both the BITC-NAC and PEITC-NAC-treated groups showed a significant reduction in lung tumor multiplicity from 6.1 +/- 3.1 tumors/mouse in the B(a)P group fed the control diet to 3.7 +/- 2.9 and 3.4 +/- 2.7 tumors/mouse (P = 0.018 and 0.006, respectively). To investigate the mechanisms of tumor inhibition, lung tissues were obtained at 21, 84, and 140 days at interim sacrifices during the bioassay. These tissues showed a significant increase in apoptosis as determined by in situ end-labeling for both ITC-NAC-treated groups. The MAP kinase pathway was activated in the ITC-NAC-treated groups. The activation of c-Jun NH(2)-terminal kinase was higher in the BITC-NAC and PEITC-NAC groups when compared with B(a)P-treated control. The phosphorylation of p38 and extracellular signal-regulated kinases (ErKs) 1 and 2 was also induced by these treatments. To determine the downstream target of MAP kinases, activator protein-1 (AP-1) and nuclear factor-kappaB activities were evaluated by gel shift assay. The AP-1 binding activity was remarkably increased in lung tissue from both the BITC-NAC and PEITC-NAC groups. No change in nuclear factor-kappaB binding activity was found, however. Phosphorylation of p53 was also higher than the constitutive levels in both ITC-NAC-treated groups, but no induction of p53 expression was detected. This study demonstrates the chemopreventive efficacy of the NAC conjugates of PEITC and BITC administered in the diet after a single dose of B(a)P for lung tumorigenesis and provides the first in vivo evidence that activation of MAP kinases, AP-1 transcription factors, p53 phosphorylation, and the induction of apoptosis may be involved in the chemopreventive activity of these compounds.
Yang
Yang-Ming
YM
Division of Carcinogenesis and Molecular Epidemiology, American Health Foundation, Valhalla, New York 10595, USA.
Conaway
C Clifford
CC
Chiao
J W
JW
Wang
Chung-Xiou
CX
Amin
Shantu
S
Whysner
John
J
Dai
Wei
W
Reinhardt
Joel
J
Chung
Fung-Lung
FL
D000111:Acetylcysteine / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D016588:Anticarcinogenic Agents / Q000737:chemistry / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001564:Benzo(a)pyrene / Q000037:antagonists & inhibitors / Q000633:toxicity; D002273:Carcinogens / Q000037:antagonists & inhibitors / Q000633:toxicity; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics; D004789:Enzyme Activation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D017879:Isothiocyanates / Q000737:chemistry / Q000494:pharmacology*; D008168:Lung / Q000187:drug effects / Q000473:pathology; D008175:Lung Neoplasms / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D051379:Mice; D008805:Mice, Inbred A; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D018808:Transcription Factor AP-1 / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein
D016588:Anticarcinogenic Agents; D002273:Carcinogens; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D017879:Isothiocyanates; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D018808:Transcription Factor AP-1; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D001564:Benzo(a)pyrene; C058305:phenethyl isothiocyanate; C031403:benzyl isothiocyanate; D020928:Mitogen-Activated Protein Kinases; D000111:Acetylcysteine