Combination BET Family Protein and HDAC Inhibition Synergistically Elicits Chondrosarcoma Cell Apoptosis Through RAD51-Related DNA Damage Repair

Abstract

Songwei Huan,1,* Tao Gui,1,* Qiutong Xu,1,* Songkuan Zhuang,2 Zhenyan Li,1 Yuling Shi,3 Jiebin Lin,3 Bin Gong,1 Guiqiang Miao,1 Manseng Tam,4 Huan-Tian Zhang,1 Zhengang Zha,1 Chunfei Wu3 1Institute of Orthopedic Diseases and Department of Bone and Joint Surgery, The First Affiliated Hospital, Jinan University, Guangzhou 510630, Guangdong, People’s Republic of China; 2School of Life Science, Xiamen University, Xiamen, Fujian 361005, People’s Republic of China; 3Department of Orthopedics, The Third Affiliated Hospital, Guangzhou University of Chinese Medicine, Guangzhou, Guangdong 510405, People’s Republic of China; 4IAN WO Medical Center, Macao Special Administrative Region, People’s Republic of China*These authors contributed equally to this workCorrespondence: Zhengang Zha; Chunfei Wu Tel [phone]; Tel [phone]Fax [phone]; Email [email protected]; [email protected]: Chondrosarcoma is the second-most common type of bone tumor and has inherent resistance to conventional chemotherapy. Present study aimed to explore the therapeutic effect and specific mechanism(s) of combination BET family protein and HDAC inhibition in chondrosarcoma.Methods: Two chondrosarcoma cells were treated with BET family protein inhibitor (JQ1) and histone deacetylase inhibitors (HDACIs) (vorinostat/SAHA or panobinostat/PANO) separately or in combination; then, the cell viability was determined by Cell Counting Kit-8 (CCK-8) assay, and the combination index (CI) was calculated by the Chou method; cell proliferation was evaluated by 5-ethynyl-2′-deoxyuridine (EdU) incorporation and colony formation assay; cell apoptosis and reactive oxygen species (ROS) level were determined by flow cytometry; protein expressions of caspase-3, Bcl-XL, Bcl-2, γ-H2AX, and RAD51 were examined by Immunoblotting; DNA damage was determined by comet assay; RAD51 and γ-H2AX foci were observed by immunofluorescence.Results: Combined treatment with JQ1 and SAHA or PANO synergistically suppressed the growth and colony formation ability of the chondrosarcoma cells. Combined BET and HDAC inhibition also significantly elevated the ROS level, followed by the activation of cleaved-caspase-3, and the downregulation of Bcl-2 and Bcl-XL. Mechanistically, combination treatment with JQ1 and SAHA caused numerous DNA double-strand breaks (DSBs), as evidenced by the comet assay. The increase in γ-H2AX expression and foci formation also consistently indicated the accumulation of DNA damage upon cotreatment with JQ1 and SAHA. Furthermore, RAD51, a key protein of homologous recombination (HR) DNA repair, was found to be profoundly suppressed. In contrast, ectopic expression of RAD51 partially rescued SW 1353 cell apoptosis by inhibiting the expression of cleaved-caspase-3.Conclusion: Taken together, our results disclose that BET and HDAC inhibition synergistically inhibit cell growth and induce cell apoptosis through a mechanism that involves the suppression of RAD51-related HR DNA repair in chondrosarcoma cells.Keywords: chondrosarcoma, JQ1, HDAC, apoptosis, RAD51, DNA repair

Keywords

• chondrosarcoma
• jq1
• hdac
• apoptosis
• rad51
• dna repair