TY - JOUR
T1 - Valproic acid induces p21 and topoisomerase-II (α/β) expression and synergistically enhances etoposide cytotoxicity in human glioblastoma cell lines
AU - Das, Chandra M.
AU - Aguilera, Dolly
AU - Vasquez, Hernan
AU - Prasad, Preethi
AU - Zhang, Ming
AU - Wolff, Johannes E.
AU - Gopalakrishnan, Vidya
N1 - Funding Information:
Acknowledgments We thank Drs. Joya Chandra, Peter Zage, Neeta Kang, and Jason Long for their technical help and critical reading of the manuscript. This work was supported in part by funds from The Children’s Brain Tumor Foundation to VG.
PY - 2007/11
Y1 - 2007/11
N2 - Object: Etoposide, a topoisomerase-II inhibitor promotes DNA damage and apoptosis of cancer cells. In this study, we have examined the ability of the histone deacetylase inhibitor, valproic acid (VPA) to modulate gene expression and sensitize glioblastoma cell lines to the cytotoxic effects of etoposide in vitro. Methods: The effect of VPA and etoposide alone or a combination of the two drugs on the growth of three different glioblastoma cell lines (U87, LN18, and U251) were measured by MTT assays. Drug treated cells were analyzed for their cell cycle profile, gene expression, differentiation status, and induction of apoptosis by flow-cytometry, western blotting, immunofluorescence assays, and caspase activity measurements. Results: We observed that while VPA and etoposide independently inhibited the growth of U87, U251, and LN18 cells, exposure of tumor cells to both drugs significantly enhanced the cytotoxicity of etoposide in all cell lines. VPA promoted a G1 accumulation of U87, while an increase in the G2/M population of U251 and LN18 cells was observed upon exposure to the drug. Treatment with etoposide resulted in a G2/M arrest of U87, U251, and LN18 cells, whereas, exposure to both drugs increased the fraction of cells with a G2/M and sub-G1 DNA content. Further, VPA and not etoposide, promoted acetylation of histone H4 and induced the expression of the cyclin-dependent kinase inhibitor (CDKI), p21/WAF1. VPA also up-regulated the expression of the α and β isoforms of topoisomerase-II, as well as the glial differentiation marker, glial fibrillary acidic protein. Finally, a significant increase in caspase-3 activity and apoptosis was observed in the presence of both VPA and etoposide compared to either agent alone. Conclusion: Our study demonstrates that VPA sensitizes U87, U251, and LN18 cells to the cytotoxic effects of etoposide in vitro by inducing differentiation and up-regulating the expression of p21/WAF1 and both isoforms of topoisomerase-II.
AB - Object: Etoposide, a topoisomerase-II inhibitor promotes DNA damage and apoptosis of cancer cells. In this study, we have examined the ability of the histone deacetylase inhibitor, valproic acid (VPA) to modulate gene expression and sensitize glioblastoma cell lines to the cytotoxic effects of etoposide in vitro. Methods: The effect of VPA and etoposide alone or a combination of the two drugs on the growth of three different glioblastoma cell lines (U87, LN18, and U251) were measured by MTT assays. Drug treated cells were analyzed for their cell cycle profile, gene expression, differentiation status, and induction of apoptosis by flow-cytometry, western blotting, immunofluorescence assays, and caspase activity measurements. Results: We observed that while VPA and etoposide independently inhibited the growth of U87, U251, and LN18 cells, exposure of tumor cells to both drugs significantly enhanced the cytotoxicity of etoposide in all cell lines. VPA promoted a G1 accumulation of U87, while an increase in the G2/M population of U251 and LN18 cells was observed upon exposure to the drug. Treatment with etoposide resulted in a G2/M arrest of U87, U251, and LN18 cells, whereas, exposure to both drugs increased the fraction of cells with a G2/M and sub-G1 DNA content. Further, VPA and not etoposide, promoted acetylation of histone H4 and induced the expression of the cyclin-dependent kinase inhibitor (CDKI), p21/WAF1. VPA also up-regulated the expression of the α and β isoforms of topoisomerase-II, as well as the glial differentiation marker, glial fibrillary acidic protein. Finally, a significant increase in caspase-3 activity and apoptosis was observed in the presence of both VPA and etoposide compared to either agent alone. Conclusion: Our study demonstrates that VPA sensitizes U87, U251, and LN18 cells to the cytotoxic effects of etoposide in vitro by inducing differentiation and up-regulating the expression of p21/WAF1 and both isoforms of topoisomerase-II.
KW - Adjuvant
KW - Etoposide
KW - Glioblastoma
KW - HDAC inhibitor
KW - Topoisomerase-II
KW - Valproic acid
KW - p21
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U2 - 10.1007/s11060-007-9402-7
DO - 10.1007/s11060-007-9402-7
M3 - Article
C2 - 17534580
AN - SCOPUS:35448999681
SN - 0167-594X
VL - 85
SP - 159
EP - 170
JO - Journal of neuro-oncology
JF - Journal of neuro-oncology
IS - 2
ER -