cancers Review Proteasome Inhibitors for the Treatment of Multiple Myeloma Shigeki Ito Hematology & Oncology, Department of Internal Medicine, Iwate Medical University School of Medicine, Yahaba-cho 028-3695, Japan;
[email protected]; Tel.: +81-19-613-7111 Received: 27 December 2019; Accepted: 19 January 2020; Published: 22 January 2020 Abstract: Use of proteasome inhibitors (PIs) has been the therapeutic backbone of myeloma treatment over the past decade. Many PIs are being developed and evaluated in the preclinical and clinical setting. The first-in-class PI, bortezomib, was approved by the US food and drug administration in 2003. Carfilzomib is a next-generation PI, which selectively and irreversibly inhibits proteasome enzymatic activities in a dose-dependent manner. Ixazomib was the first oral PI to be developed and has a robust efficacy and favorable safety profile in patients with multiple myeloma. These PIs, together with other agents, including alkylators, immunomodulatory drugs, and monoclonal antibodies, have been incorporated into several regimens. This review summarizes the biological effects and the results of clinical trials investigating PI-based combination regimens and novel investigational inhibitors and discusses the future perspective in the treatment of multiple myeloma. Keywords: multiple myeloma; proteasome inhibitors; bortezomib; carfilzomib; ixazomib 1. Introduction Multiple myeloma (MM) remains an incurable disease. Over the last ten years, the availability of new drugs, such as the proteasome inhibitors (PIs), the immunomodulatory drugs (IMiDs), the monoclonal antibodies (MoAbs), and the histone deacetylase inhibitors, have greatly advanced the treatment and improved the survival of patients with MM [1–3]. Proteasome inhibition has emerged as a crucial therapeutic strategy in the treatment of MM.