Status of proteasome inhibitors in the treatment of multiple myeloma

Multiple myeloma (MM) is a hematological malignancy caused by the clonal expansion ofbone marrow plasmacytes.It accounts for 10 ％ of all hematological malignancies.The proteasome,an intracellular enzyme complex that degrades ubiquitin-tagged proteins to regulate protein levels within the cell,plays an important role in maintaining cellular homeostasis.Proteasome inhibitors proved to be significantly effective in the clinical treatment of MM.In recent years,the application of the proteasome inhibitor has led to increased survival rates in MM patients.Bortezomib is the first proteasome inhibitor that has been approved by the US Food and Drug Administration due to its ability to reversibly inhibit the 26 s proteasome functions.Despite the fact that Bortezomib improves medical treatment,many patients experience difficulty responding to this drug and some patients who do respond eventually relapse.These results have led researchers to investigate new proteasome inhibitors with mechanisms different from those of Bortezomib.Some drugs that bind to the active site of the proteasome and irreversibly inhibit the complex have recently been developed and are currently being tested in advanced clinical trials.Here,we will elaborate on the proteasome inhibitors targeting MM and focus on newly discovered inhibitors that may overcome the resistance to Bortezomib. Key words: Mutiple myeloma;  Proteasome inhibitor;  Drug resistance