Phenylbutyrate sensitizes human glioblastoma cells lacking wild-type p53 function to ionizing radiation.
OBJECTIVE
Histone deacetylase (HDAC) inhibitors induce growth arrest, differentiation, and apoptosis in cancer cells. Phenylbutyrate (PB) is a HDAC inhibitor used clinically for treatment of urea cycle disorders. Because of its low cytotoxicity, cerebrospinal fluid penetration, and high oral bioavailability, we investigated PB as a potential radiation sensitizer in human glioblastoma cell lines.


METHODS
Four glioblastoma cell lines were selected for this study. Phenylbutyrate was used at a concentration of 2 mM, which is achievable in humans. Western blots were used to assess levels of acetylated histone H3 in tumor cells after treatment with PB. Flow cytometry was used for cell cycle analysis. Clonogenic assays were performed to assess the effect of PB on radiation sensitivity. We used shRNA against p53 to study the role of p53 in radiosensitization.


RESULTS
Treatment with PB alone resulted in hyperacetylation of histones, confirmed by Western blot analysis. The PB alone resulted in cytostatic effects in three cell lines. There was no evidence of G(1) arrest, increase in sub-G(1) fraction or p21 protein induction. Clonogenic assays showed radiosensitization in two lines harboring p53 mutations, with enhancement ratios (+/- SE) of 1.5 (+/- 0.2) and 1.3 (+/- 0.1), respectively. There was no radiopotentiating effect in two cell lines with wild-type p53, but knockdown of wild-type p53 resulted in radiosensitization by PB.


CONCLUSIONS
Phenylbutyrate can produce p21-independent cytostasis, and enhances radiation sensitivity in p53 mutant human glioblastoma cells in vitro. This suggests the potential application of combined PB and radiotherapy in glioblastoma harboring mutant p53.
Lopez
Carlos A
CA
Department of Radiation Oncology, University of Michigan, Ann Arbor, MI 48109-0010, USA. carlopez@umich.edu
Feng
Felix Y
FY
Herman
Joseph M
JM
Nyati
Mukesh K
MK
Lawrence
Theodore S
TS
Ljungman
Mats
M
D000107:Acetylation / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects / Q000528:radiation effects; D049109:Cell Proliferation / Q000187:drug effects; D016193:G1 Phase / Q000187:drug effects / Q000528:radiation effects; D005909:Glioblastoma / Q000201:enzymology / Q000235:genetics / Q000532:radiotherapy*; D056572:Histone Deacetylase Inhibitors; D006657:Histones / Q000378:metabolism; D006801:Humans; D010654:Phenylbutyrates / Q000494:pharmacology*; D011836:Radiation Tolerance / Q000187:drug effects* / Q000235:genetics; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
D056572:Histone Deacetylase Inhibitors; D006657:Histones; D010654:Phenylbutyrates; D011838:Radiation-Sensitizing Agents; D016159:Tumor Suppressor Protein p53; C075773:4-phenylbutyric acid