Zebularine suppresses the apoptotic potential of 5-fluorouracil via cAMP/PKA/CREB pathway against human oral squamous cell carcinoma cells.
OBJECTIVE
During tumorigenesis, tumor suppressor and tumor-related genes are commonly silenced by aberrant DNA methylation in their promoter regions, which is one of the important determinants of susceptibility to 5-fluorouracil (5-FU) in oral squamous cell carcinoma (OSCC) cells. Here, we examine the chemotherapeutic efficacy of epigenetic agents on 5-FU cytotoxicity.


METHODS
We investigated the effect of a DNA methyltransferase (DNMT) inhibitor, zebularine (Zeb), on the chemosensitivity of 5-FU and cisplatin (CDDP) by MTT and TUNEL methods, and compared the molecular mechanism of action with those of a GSK3beta inhibitor, LiCl, and an Hsp90 inhibitor, 17-AAG.


RESULTS
A significant apoptotic effect by a combination of Zeb or 17-AAG was found in CDDP treatment; however, considerable suppression of 5-FU-induced apoptosis was observed after incubation with Zeb, 17-AAG, or LiCl. Zeb's suppressive effects were associated with activation of the cAMP/PKA/CREB pathway, differing from mechanisms of 17-AAG and LiCl. Suppression of 5-FU-induced apoptosis by Zeb was not associated with increased Bcl-2 and Bcl-xL expressions dependent on transcription factor CREB, and with the expression level of thymidylate synthase.


CONCLUSIONS
In the present study, we identified a more detailed mechanism of action by which Zeb suppresses 5-FU-induced apoptosis. These results indicate that combination therapies have to be carefully investigated due to potential harmful effects in the clinical application of DNMT inhibitors.
Suzuki
Maiko
M
Department of Microbiology and Immunology, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Japan.
Shinohara
Fumiaki
F
Endo
Manabu
M
Sugazaki
Masaki
M
Echigo
Seishi
S
Rikiishi
Hidemi
H
D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D016227:Benzoquinones / Q000494:pharmacology; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003562:Cytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000037:antagonists & inhibitors; D005472:Fluorouracil / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D047029:Lactams, Macrocyclic / Q000494:pharmacology; D018021:Lithium Chloride / Q000494:pharmacology; D009062:Mouth Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
D000276:Adjuvants, Immunologic; D000964:Antimetabolites, Antineoplastic; D000970:Antineoplastic Agents; D016227:Benzoquinones; C115163:CREB1 protein, human; D017362:Cyclic AMP Response Element-Binding Protein; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D016328:NF-kappa B; D019253:Proto-Oncogene Proteins c-bcl-2; C112765:tanespimycin; D003562:Cytidine; C009131:pyrimidin-2-one beta-ribofuranoside; D004248:DNA (Cytosine-5-)-Methyltransferases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D017868:Cyclic AMP-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride; D002945:Cisplatin; D005472:Fluorouracil