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Updated: Mar 30, 2026
Assays for Validating Histone Acetyltransferase Inhibitors
Published on: August 6, 2020
Isotype-Specific Inhibition of Histone Deacetylases: Identification of Optimal Targets for Radiosensitization
Jin Ho Kim1,2, Sung Ho Moon1, Mina No3
1Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea.
Purpose:
Histone deacetylase (HDAC) inhibitors radiosensitize tumor cells. To elucidate mechanisms underlying radiosensitization by HDAC inhibition, understanding of differential contributions of HDAC isotypes is needed. The aim of this study was to investigate involvement of known HDAC isotypes in modulation of cellular radiosensitivity.
Materials And Methods:
Because pharmacologic HDAC inhibitors lack isotype-specificity, RNA interference against 11 HDAC isotypes was used to inhibit HDAC in an isotype-specific manner. Radiation cell survival was evaluated using a clonogenic assay in SQ20B cells transfected with small interfering RNA specifically targeting HDAC isotypes. Immunocytochemistry was performed for detection of γH2AX foci. Protein expression was measured using Western blotting.
Results:
Among 11 HDAC isotypes tested, specific inhibition of 7 isotypes (HDAC1, HDAC3, HDAC4, HDAC6, HDAC7, HDAC10, and HDAC11) enhanced radiation lethality in SQ20B cells. Radiosensitization by inhibition of these HDAC isotypes was accompanied by delay of DNA double strand break repair. Radiosensitivity of SQ20B cells was not altered by selective inhibition of the remaining four isotypes (HDAC2, HDAC5, HDAC8, and HDAC9). Inhibition of HDAC isotypes resulted in downregulation of various proteins involved in pro-survival and DNA damage repair pathways.
Conclusion:
Isotype-specificity exists in HDAC inhibition-induced radiosensitization. Different HDAC isotypes are differentially involved in modulation of cellular radiosensitivity.
Insights
Specific inhibition of seven histone deacetylase (HDAC) isotypes enhanced tumor cell radiosensitivity and delayed DNA repair. This highlights isotype-specific roles in HDAC inhibitor-induced radiosensitization.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Research
Background:
- Histone deacetylase (HDAC) inhibitors are known to radiosensitize tumor cells.
- Understanding the specific roles of different HDAC isotypes is crucial for elucidating radiosensitization mechanisms.
Purpose of the Study:
- To investigate the involvement of specific HDAC isotypes in modulating cellular radiosensitivity.
- To determine which HDAC isotypes contribute to radiosensitization induced by HDAC inhibitors.
Main Methods:
- Utilized RNA interference (RNAi) for isotype-specific inhibition of 11 HDAC isotypes in SQ20B cells.
- Assessed radiation cell survival via clonogenic assays and DNA double-strand break repair using γH2AX foci detection.
- Analyzed protein expression changes using Western blotting.
Main Results:
- Specific inhibition of HDAC1, HDAC3, HDAC4, HDAC6, HDAC7, HDAC10, and HDAC11 enhanced radiation lethality.
- Radiosensitization correlated with delayed DNA double-strand break repair.
- Downregulation of pro-survival and DNA repair proteins was observed following HDAC isotype inhibition.
Conclusions:
- HDAC inhibition-induced radiosensitization exhibits isotype-specificity.
- Different HDAC isotypes play distinct roles in regulating cellular radiosensitivity and DNA repair.
