Growth inhibitory effects and radiosensitization induced by fatty aromatic acids on human cervical cancer cells

Phase II trial of the histone deacetylase inhibitor vorinostat (Zolinza, suberoylanilide hydroxamic acid, SAHA) in patients with recurrent and/or metastatic head and neck cancer

This phase II trial was initiated to assess the efficacy and safety of oral vorinostat (Zolinza, suberoylanilide hydroxamic acid, SAHA) in patients with recurrent and/or metastatic head and neck cancer. Eligible patients must have recurrent and/or metastatic head and neck cancer unresponsive to or intolerant of conventional chemotherapy. Patients must have measurable disease, adequate hematologic, hepatic, and renal function, and be able to swallow capsules. Four or more weeks must have elapsed since prior chemotherapy, radiation therapy, major surgery or investigational anticancer therapy, and patients must have recovered from prior toxicities. Study endpoints included response rate, duration of stable disease and progression-free survival. Thirteen patients were enrolled (9 males); 1 withdrew consent prior to starting therapy. Twelve patients received oral vorinostat 400 mg once daily and were evaluable for response. The median age was 54 years (range 40-82). All patients had received prior chemotherapy (including 10 with platinum- or taxane-based combination therapy), and 9 had prior radiation therapy. No confirmed partial or complete responses were observed. One unconfirmed partial response was seen. Three patients had stable disease ranging from 9 to 26 weeks. Nine patients discontinued due to progressive disease, two withdrew consent, and one discontinued therapy for grade 3 anorexia. Grades 3-4 drug-related toxicities included thrombocytopenia (n=3), anorexia (n=2), and dehydration (n=2). Oral vorinostat 400 mg qd was generally well tolerated but did not demonstrate efficacy as defined by tumor response in this small group of heavily pre-treated patients.

Phenylbutyrate sensitizes human glioblastoma cells lacking wild-type p53 function to ionizing radiation

PURPOSE

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 AND MATERIALS

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.

Histone deacetylase inhibitors radiosensitize human melanoma cells by suppressing DNA repair activity

PURPOSE

Histone deacetylase (HDAC) inhibitors have emerged recently as promising anticancer agents. They arrest cells in the cell cycle and induce differentiation and cell death. The antitumor activity of HDAC inhibitors has been linked to their ability to induce gene expression through acetylation of histone and nonhistone proteins. However, it has recently been suggested that HDAC inhibitors may also enhance the activity of other cancer therapeutics, including radiotherapy. The purpose of this study was to evaluate the ability of HDAC inhibitors to radiosensitize human melanoma cells in vitro.

EXPERIMENTAL DESIGN

A panel of HDAC inhibitors that included sodium butyrate (NaB), phenylbutyrate, tributyrin, and trichostatin A were tested for their ability to radiosensitize two human melanoma cell lines (A375 and MeWo) using clonogenic cell survival assays. Apoptosis and DNA repair were measured by standard assays.

RESULTS

NaB induced hyperacetylation of histone H4 in the two melanoma cell lines and the normal human fibroblasts. NaB radiosensitized both the A375 and MeWo melanoma cell lines, substantially reducing the surviving fraction at 2 Gy (SF2), whereas it had no effect on the normal human fibroblasts. The other HDAC inhibitors, phenylbutyrate, tributyrin, and trichostatin A had significant radiosensitizing effects on both melanoma cell lines tested. NaB modestly enhanced radiation-induced apoptosis that did not correlate with survival but did correlate with functional impairment of DNA repair as determined based on the host cell reactivation assay. Moreover, NaB significantly reduced the expression of the repair-related genes Ku70 and Ku86 and DNA-dependent protein kinase catalytic subunit in melanoma cells at the protein and mRNA levels. Normal human fibroblasts showed no change in DNA repair capacity or levels of DNA repair proteins following NaB treatment. We also examined gamma-H2AX phosphorylation as a marker of radiation response to NaB and observed that compared with controls, gamma-H2AX foci persisted long after ionizing exposure in the NaB-treated cells.

CONCLUSIONS

HDAC inhibitors radiosensitize human tumor cells by affecting their ability to repair the DNA damage induced by ionizing radiation and that gamma-H2AX phosphorylation can be used as a predictive marker of radioresponse.

Antitumor histone deacetylase inhibitors suppress cutaneous radiation syndrome: Implications for increasing therapeutic gain in cancer radiotherapy

Radiotherapy is an effective treatment for head and neck, skin, anogenital, and breast cancers. However, radiation-induced skin morbidity limits the therapeutic benefits. A low-toxicity approach to selectively reduce skin morbidity without compromising tumor killing by radiotherapy is needed. We found that the antitumor agents known as histone deacetylase (HDAC) inhibitors (phenylbutyrate, trichostatin A, and valproic acid) could suppress cutaneous radiation syndrome. The effects of HDAC inhibitors in promoting the healing of wounds caused by radiation and in decreasing later skin fibrosis and tumorigenesis were correlated with suppression of the aberrant expression of radiation-induced transforming growth factor β and tumor necrosis factor α. Our findings implicate that the inhibition of HDAC may provide a novel strategy to increase the therapeutic gain in cancer radiotherapy by not only inhibiting tumor growth but also protecting normal tissues.