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DNMT (DNA methyltransferase) inhibitors radiosensitize human cancer cells by suppressing DNA repair activity.

Kim HJ, Kim JH, Chie EK, Young PD, Kim IA, Kim IH - Radiat Oncol (2012)

Bottom Line: 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.Pretreatment with psammaplin A, 5-aza-2'-deoxycytidine, and zebularine radiosensitized both A549 and U373MG cells.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.

ABSTRACT

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.

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The effect of zebularine on radiation-induced G2/M arrest in A549 cells. A549 cells were treated with 800 uM zebularine for 18 hours and then irradiated with 6 Gy. A549 cells were accumulated in G2/M phase after radiation. This radiation-induced G2/M arrest was abrogated by zebularine pretreatment at 6-12 hours, but this abrogation disappeared at 24 hours.
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Figure 4: The effect of zebularine on radiation-induced G2/M arrest in A549 cells. A549 cells were treated with 800 uM zebularine for 18 hours and then irradiated with 6 Gy. A549 cells were accumulated in G2/M phase after radiation. This radiation-induced G2/M arrest was abrogated by zebularine pretreatment at 6-12 hours, but this abrogation disappeared at 24 hours.

Mentions: Cell cycle and apoptosis were evaluated by flow cytometry. Both cell lines evidenced a G2/M delay after radiation treatment alone. Although the effects of combining DNMT inhibitors and radiation vary between cell lines, we noted no significant differences in cell cycle phase distribution patterns between cells treated with radiation alone and those treated with a combination of radiation combined with DNMT inhibitors (Figure 3). However, in the A549 cells, radiation-induced G2/M arrest was abrogated by zebularine pretreatment at 6-12 hours, but this abrogation disappeared at 24 hours (Figure 3 and 4).


DNMT (DNA methyltransferase) inhibitors radiosensitize human cancer cells by suppressing DNA repair activity.

Kim HJ, Kim JH, Chie EK, Young PD, Kim IA, Kim IH - Radiat Oncol (2012)

The effect of zebularine on radiation-induced G2/M arrest in A549 cells. A549 cells were treated with 800 uM zebularine for 18 hours and then irradiated with 6 Gy. A549 cells were accumulated in G2/M phase after radiation. This radiation-induced G2/M arrest was abrogated by zebularine pretreatment at 6-12 hours, but this abrogation disappeared at 24 hours.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3375186&req=5

Figure 4: The effect of zebularine on radiation-induced G2/M arrest in A549 cells. A549 cells were treated with 800 uM zebularine for 18 hours and then irradiated with 6 Gy. A549 cells were accumulated in G2/M phase after radiation. This radiation-induced G2/M arrest was abrogated by zebularine pretreatment at 6-12 hours, but this abrogation disappeared at 24 hours.
Mentions: Cell cycle and apoptosis were evaluated by flow cytometry. Both cell lines evidenced a G2/M delay after radiation treatment alone. Although the effects of combining DNMT inhibitors and radiation vary between cell lines, we noted no significant differences in cell cycle phase distribution patterns between cells treated with radiation alone and those treated with a combination of radiation combined with DNMT inhibitors (Figure 3). However, in the A549 cells, radiation-induced G2/M arrest was abrogated by zebularine pretreatment at 6-12 hours, but this abrogation disappeared at 24 hours (Figure 3 and 4).

Bottom Line: 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.Pretreatment with psammaplin A, 5-aza-2'-deoxycytidine, and zebularine radiosensitized both A549 and U373MG cells.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea.

ABSTRACT

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.

Show MeSH
Related in: MedlinePlus