Abstract 1884: Dual targeting of cell cycle checkpoint and histone deacetylase overcomes bortezomib resistance in multiple myeloma
Authors: Tabayashi Takayuki , Tanaka Yuka , Takahashi Yasuyuki , Kimura Yuta , Tomikawa Tatsuki , Anan Tomoe , Sagawa Morihiko , Watanabe Reiko , Tokuhira Michihide , Kizaki Masahiro 
Published: August 2018

Abstract
Although the introduction of novel agents, such as proteasome inhibitors, immunomodulatory drugs, and histone deacetylase inhibitors (HDACi) has improved the clinical outcomes of the patients with multiple myeloma (MM), most patients eventually relapse and develop drug resistance. Proteasome inhibitor, bortezomib (BTZ), is a key drug for the treatment of MM, and the prognosis of the patients with BTZ resistance is very poor. Therefore, novel therapeutic approaches to overcome BTZ resistance are urgently needed. WEE1 is a cell cycle checkpoint kinase and a key regulator of DNA damage surveillance pathways. In response to extrinsically induced DNA damage, WEE1 induces cell cycle arrest, allowing for the damaged DNA to be repaired before the cell undergoes DNA replication, and prevents cells from mitotic lethality. WEE1 is overexpressed in various cancers, and relates to poor prognosis. In addition, the inhibition of WEE1 has been shown to induce cancer cells to premature mitotic entry leading to apoptotic cell death, suggesting that combining WEE1 inhibitor with DNA damaging agent is effective in cancer therapy. Resent research has shown that HDACi increase reactive oxygen species production resulting in increased DNA damage and impaired DNA repair. These data suggest that the combination of WEE1 inhibitor and HDACi might be an attractive therapeutic option against this incurable hematological malignancy. In the present study, we investigated the efficacy of WEE1 inhibitor MK-1775, a potent and highly-selective small molecule inhibitor of WEE1, in combination with HDACi in various MM cells. MTS assays showed that single agent MK-1775 inhibited the proliferation of various MM cell lines, including BTZ-resistant cell line, in a dose- (0 to 10 μM) and time- (0 to 72 h) dependent manner. In combination with vorinostat which is a pan-HDACi, MK-1775 inhibited the proliferation of BTZ-resistant MM cells more effectively than single agent. Furthermore, the combination of vorinostat and MK-1775 was able to re-sensitize BTZ-resistant MM cells to BTZ. Assays for apoptotic cell death demonstrated that MK-1775 induces both early and late apoptosis in MM cells. Western blotting analysis was performed to investigate the molecular mechanisms of MK-1775-induced cell death, showing that MK-1775 inhibited the expression of the target molecules of Bcl-2 and MCL1, and CDK1 phosphorylation. Moreover, the marked increase in PARP and Caspase 3 cleavage, and histone H2AX expression was observed following treatment with MK-1775 in combination with vorinostat. These findings suggest that the combination of MK-1775 and vorinostat induces synergistically DNA damage and promotes premature mitotic entry resulting in apoptotic cell death in MM cells. In conclusion, our data suggest that WEE1 in combination with HDACi might be a promising molecular target for the treatment of BTZ-resistant MM.
Citation Format: Takayuki Tabayashi, Yuka Tanaka, Yasuyuki Takahashi, Yuta Kimura, Tatsuki Tomikawa, Tomoe Anan, Morihiko Sagawa, Reiko Watanabe, Michihide Tokuhira, Masahiro Kizaki. Dual targeting of cell cycle checkpoint and histone deacetylase overcomes bortezomib resistance in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1884.