Background Histone modifications and DNA methylation are two major factors in epigenetic phenomenon. Unlike the histone deacetylase inhibitors, which are known to exert radiosensitizing effects, there have only been a few studies thus far concerning the role of DNA methyltransferase (DNMT) inhibitors as radiosensitizers. The principal objective of this study was to evaluate the effects of DNMT inhibitors on the radiosensitivity of human cancer cell lines, and to elucidate the mechanisms relevant to that process. Methods A549 (lung cancer) and U373MG (glioblastoma) cells were exposed to radiation with or without six DNMT inhibitors (5-azacytidine, 5-aza-2'-deoxycytidine, zebularine, hydralazine, epigallocatechin gallate, and psammaplin A) for 18 hours prior to radiation, after which cell survival was evaluated via clonogenic assays. Cell cycle and apoptosis were analyzed via flow cytometry. Expressions of DNMT1, 3A/3B, and cleaved caspase-3 were detected via Western blotting. Expression of γH2AX, a marker of radiation-induced DNA double-strand break, was examined by immunocytochemistry. Results Pretreatment with psammaplin A, 5-aza-2'-deoxycytidine, and zebularine radiosensitized both A549 and U373MG cells. Pretreatment with psammaplin A increased the sub-G1 fraction of A549 cells, as compared to cells exposed to radiation alone. Prolongation of γH2AX expression was observed in the cells treated with DNMT inhibitors prior to radiation as compared with those treated by radiation alone. Conclusions Psammaplin A, 5-aza-2'-deoxycytidine, and zebularine induce radiosensitivity in both A549 and U373MG cell lines, and suggest that this effect might be associated with the inhibition of DNA repair.

Several studies have shown solid evidence for the potential value of targeting epidermal growth factor receptor (EGFR) signaling to enhance the antitumor activity of radiation. However, therapeutic resistance has emerged as an important clinical issue. Here, we investigated whether strategies for targeting EGFR-associated downstream signaling would radiosensitize a panel of non-small cell lung cancer cell lines. Inhibition of K-RAS using RNA interference attenuated downstream signaling and increased radiosensitivity of A549 and H460 cells, whereas inhibition of EGFR did not. A549 cells harboring a K-RAS mutation at codon V12 were radiosensitized by small interfering RNA (siRNA) targeting this codon. H460 cells having mutation at codon V61 was radiosensitized by siRNA targeting of this mutation. K-RAS siRNA did not radiosensitize H1299 cells possessing wild-type K-RAS. Inhibition of the phosphoinositide 3-kinase (PI3K)-AKT-mammalian target of rapamycin pathway led to significant radiosensitization of the two cell lines, whereas selective inhibition of extracellular signal-regulated kinase signaling did not. Inhibitors targeting the PI3K-AKT-mTOR pathway also abrogated G 2 arrest following irradiation and induced γH2AX foci formation. A dual inhibitor of class I PI3K and mammalian target of rapamycin effectively increased the radiosensitivity of A549 and H460 cells. Inhibition of PI3K-AKT signaling was associated with the downregulation of DNA-PKs. Although apoptosis was the primary mode of cell death when cells were pretreated with LY294002 or AKT inhibitor VIII, cells pretreated with rapamycin or PI-103 showed mixed modes of cell death, including apoptosis and autophagy. Our results suggest possible mechanisms for counteracting EGFR prosurvival signaling implicated in radioresistance and offer an alternative strategy for overcoming resistance to EGFR inhibitors used in combination with irradiation.

Our study demonstrated the therapeutic potential of DSF against BTICs from AT/RT and suggested the possibility of ALDH inhibition for clinical application.

To evaluate the mechanism of the development of therapeutic resistance after temozolomide treatment, we focused on changes in O(6)-methylguanine DNA methyltransferase (MGMT) and mismatch repair (MMR) between initial and recurrent glioblastomas. Tissue samples obtained from 24 paired histologically confirmed initial and recurrent adult glioblastoma patients who were initially treated with temozolomide were used for MGMT and MMR gene promoter methylation status and protein expression analysis using methylation-specific multiplex ligation probe amplification (MS-MLPA), methylation-specific polymerase chain reaction (MSP), and immunohistochemical staining. There was a significant decrease in the methylation ratio of the MGMT promoter determined by MS-MLPA, which was not detectable with MSP, and MGMT protein expression changes were not remarkable. However, there was no epigenetic variability in MMR genes, and a relatively homogeneous expression of MMR proteins was observed in initial and recurrent tumors. We conclude that the development of reduced methylation in the MGMT promoter is one of the mechanisms for acquiring therapeutic resistance after temozolomide treatment in glioblastomas.

Radiation-induced glioblastoma multiforme (GBM) is a rare complication of radiotherapy. The authors report such a case occurring 10 years after treatment of cerebellar medulloblastoma. The patient was a 15-year-old boy who had undergone a gross-total removal of a medulloblastoma and received radiation therapy at the age of 5 years. He had experienced no tumor recurrences for 10 years until a new enhancing mass was found at the original site of the medulloblastoma. Following its resection the new lesion was found to be a GBM and there was no evidence of a medulloblastoma. The second tumor developed at the same site as the previous one after a sufficient latent period and fulfilled the criteria for a radiation-induced neoplasm. The original tumor cells expressed synaptophysin without p53 overexpression, a characteristic feature of medulloblastomas. In contrast, cells from the later tumor expressed glial fibrillary acidic protein and p53 but not synaptophysin. A sequence analysis of the p53 gene showed deletion at codon 233 and a C to G transition at codon 278 in the GBM but no mutation in the medulloblastoma. A GBM specimen revealed no amplification of the epidermal growth factor receptor compared with a normal control specimen. In conclusion, the clinical features of a radiation-induced GBM are similar to that of the primary GBM, whereas its genetic alterations render it a secondary GBM. These findings indicate that radiation-induced GBM should be considered a distinct clinical entity.

• DCE MR imaging provides candidate prognostic marker of GBM after standard treatment. • Cumulative histogram was applied to include entire non-enhancing T2 high SI lesions. • The 99th percentile value of Ktrans was the most likely potential biomarker.

PurposeHomeobox (HOX) genes are essential developmental regulators that should normally be in the silenced state in an adult brain. The aberrant expression of HOX genes has been associated with the prognosis of many cancer types, including glioblastoma (GBM). This study examined the identity and role of HOX genes affecting GBM prognosis and treatment resistance.Materials and MethodsThe full series of HOX genes of five pairs of initial and recurrent human GBM samples were screened by microarray analysis to determine the most plausible candidate responsible for GBM prognosis. Another 20 newly diagnosed GBM samples were used for prognostic validation. In vitro experiments were performed to confirm the role of HOX in treatment resistance. Mediators involved in HOX gene regulation were searched using differentially expressed gene analysis, gene set enrichment tests, and network analysis.ResultsThe underexpression of HOXA11 was identified as a consistent signature for a poor prognosis among the HOX genes. The overall survival of the GBM patients indicated a significantly favorable prognosis in patients with high HOXA11 expression (31±15.3 months) compared to the prognoses in thosewith low HOXA11 expression (18±7.3 months, p=0.03). When HOXA11 was suppressed in the GBM cell lines, the anticancer effect of radiotherapy and/or temozolomide declined. In addition, five candidate mediators (TGFBR2, CRIM1, TXNIP, DPYSL2, and CRMP1) that may confer an oncologic effect after HOXA11 suppression were identified.ConclusionThe treatment resistance induced by the underexpression of HOXA11 can contribute to a poor prognosis in GBM. Further investigation will be needed to confirm the value of HOXA11 as a potential target for overcoming the treatment resistance by developing chemo- or radiosensitizers.

DSF and RT combination therapy has additive therapeutic effects on AT/RT by potentiating programmed cell death, including apoptosis and autophagy of AT/RT cells. We suggest that DSF can be applied as a radiosensitizer in AT/RT treatment.