Indirubin-3’-Monoxime Acts as a Novel Proteasome Inhibitor: Therapeutic Application in Multiple Myeloma

Abstract

Multiple myeloma (MM) is still an incurable malignancy of plasma cells. Proteasome inhibitors (PIs) work as the backbone agent and have greatly improved the outcome in majority of newly diagnosed patients with myeloma. However, drug resistance remains the major obstacle causing treatment failure in clinical practice. Indirubin-3’-monoxime (Id-3) is one of the derivatives of Indirubin, a traditional Chinese medicine that has reported to be effective in the treatment of chronic myeloid leukemia and some solid tumors. In this study, we demonstrated the anti-MM activity of Id-3 in both drug sensitive and bortezomib-resistance human MM cell lines and patient-derived cells. Moreover, combination with Id-3 could sensitize MM cells to bortezomib-induced apoptosis. Mechanistically, Id-3 acts as a multifaceted regulator of cell death, which induces DNA damage and cell cycle arrest as well as abrogates NF-κB activation in MM cells. Id-3 efficiently down-regulates USP7 expression, resulting in destabilization of NEK2 and suppression of NF-κB signaling. Importantly, proteasome complex subunits PSME3 (PA28γ) and PSME4 (PA200) were down-regulated in MM cells treated with Id-3. Knockdown of PSME3 or PSME4 by shRNA caused proteasome inhibition and paraprotein accumulation, as well as sensitized MM cells to bortezomib-mediated growth arrest. Clinical data analysis demonstrated that PSME3 and PSME4 are over-expressed in relapsed/refractory MM and associated with inferior overall survival. Taken together, our study indicate that Id-3 is a novel agent triggering proteasome inhibition and represents a promising therapeutic strategy to improve patient outcome in MM. Funding: This work was supported by the Natural Science Foundation of China (8217011925, 81570181, 81920108006), the Non-profit Central Research Institute Fund of the Chinese Academy of Medical Sciences (2018PT31006, 2018RC320012), the Chinese Academy of Medical Sciences (CAMS) Innovation Fund for Medical Sciences CAMS- 2017-I2M-1-005, 2016-I2M-3-023). National Program on Key Basic Research Project 2018ZX09733003. Declaration of Interest: Dr. Kenneth. C. Anderson is the consultant: Pfizer, Amgen, Astrazeneca, Janssen, Precision Biosciences, Mana and Window. Founder/Stock Shareholder: C4 Therapeutics, Oncopep, Raqia and NextRNA. Other authors declared no competing financial interests in relation to the work described. Ethical Approval: The study was approved by the Medical Ethical Committee of the Institute of Hematology & Blood Diseases Hospital, State Key Laboratory of Experimental Hematology, Chinese Academy of Medical Science & Peking Union Medical College, Tianjin, China.