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Targeted Degradation of Histone Deacetylase 8 Using Proteolysis Targeting Chimeras Technology: A Promising Approach
Jiranan Chotitumnavee1, Peeratchai Seemaung1, Rapeewan Settacomkul2
1Department of Pharmacology, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
Introduction:
Histone deacetylase 8 (HDAC8) plays a role in glioblastoma progression, making it a promising therapeutic target. While HDAC8 inhibitors (HDAC8is) suppress glioblastoma growth and prolong survival in animal models, they do not eliminate HDAC8. In contrast, HDAC8-targeting proteolysis-targeting chimera (PROTAC), a selective HDAC8 degrader, induces proteasomal degradation of HDAC8 and thus eliminates all of its functions.
Purpose:
In this study, we investigated the antitumor activity and underlying mechanisms of a previously reported HDAC8 PROTAC in glioblastoma cells.
Methods:
Cytotoxicity in glioblastoma-derived U-87 MG, A172 and T98G cells and primary human astrocytes (PHA) was assessed via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assays. Live-cell imaging was performed using an Incucyte® Live-Cell Analysis System. Cell proliferation, cell cycle distribution, and apoptosis were analyzed using flow cytometry. HDAC8 and key regulators of cell cycle and apoptosis were quantified via Western blotting.
Results:
HDAC8 PROTAC effectively degraded HDAC8 and exhibited cytotoxic and antiproliferative effects in human glioblastoma cells, while demonstrating minimal toxicity in PHA. It induced S-phase arrest and reduced Cdk1, Cdk2, Cdk4, Cdk6, and cyclin B1 expression. It elevated caspase-3/7 activation, downregulated Bcl-2, induced apoptosis, and upregulated key endoplasmic reticulum (ER) stress response proteins, including BiP, XBP1s, CHOP, and p-JNK in U-87 MG glioblastoma cells. The HDAC8 PROTAC demonstrated stronger antitumor activity than HDAC8i and pan-HDACi vorinostat. Moreover, the HDAC8 PROTAC showed selective toxicity toward glioblastoma cells compared to primary human astrocytes.
Conclusion:
HDAC8 PROTAC selectively suppressed glioblastoma cell growth and viability by arresting the cell cycle and inducing ER stress-mediated apoptosis via the IRE1α/XBP1s-JNK-CHOP pathway. Hence, HDAC8 PROTAC is a potential therapeutic agent for glioblastoma treatment.
Insights
A novel HDAC8 PROTAC effectively degrades HDAC8, selectively killing glioblastoma cells by halting cell division and triggering apoptosis. This targeted approach shows promise for glioblastoma treatment.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Histone deacetylase 8 (HDAC8) is implicated in glioblastoma progression and represents a potential therapeutic target.
- HDAC8 inhibitors (HDAC8is) can suppress tumor growth but do not eliminate HDAC8.
- Proteolysis-targeting chimeras (PROTACs) offer a novel approach by inducing targeted protein degradation.
Purpose of the Study:
- To investigate the antitumor activity and mechanisms of an HDAC8-targeting PROTAC in glioblastoma cells.
- To compare the efficacy of the HDAC8 PROTAC with traditional HDAC8 inhibitors.
Main Methods:
- Assessed cytotoxicity in glioblastoma cell lines (U-87 MG, A172, T98G) and primary human astrocytes (PHA) using MTT assays.
- Analyzed cell proliferation, cell cycle distribution, and apoptosis via flow cytometry.
- Quantified HDAC8 and related protein expression using Western blotting.
Main Results:
- The HDAC8 PROTAC effectively degraded HDAC8, exhibiting potent cytotoxic and antiproliferative effects in glioblastoma cells with minimal toxicity to PHA.
- It induced S-phase arrest, reduced key cell cycle regulators (Cdk1, Cdk2, Cdk4, Cdk6, cyclin B1), and triggered apoptosis.
- The PROTAC upregulated endoplasmic reticulum (ER) stress markers (BiP, XBP1s, CHOP, p-JNK) and demonstrated superior antitumor activity compared to HDAC8i and vorinostat.
Conclusions:
- HDAC8 PROTAC selectively inhibits glioblastoma growth by inducing cell cycle arrest and ER stress-mediated apoptosis through the IRE1α/XBP1s-JNK-CHOP pathway.
- The selective toxicity and potent antitumor effects position HDAC8 PROTAC as a promising therapeutic candidate for glioblastoma.
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