Development of proteasome inhibitors in oncology and autoimmune diseases.

The proteasome is a multicatalytic protease complex that mediates the controlled degradation of intracellular proteins, including key components of pathways that contribute to cancer cell growth and immune cell signaling. Validation for the proteasome as a therapeutic target in oncology was provided by bortezomib, a proteasome inhibitor that was approved for the treatment of multiple myeloma in 2003. Since that time, a number of structurally and mechanistically distinct proteasome inhibitors have entered clinical development in oncology. In this review, the chemical properties, preclinical antitumor activities and early clinical trials of these next-generation proteasome inhibitors are described and the potential for future proteasome inhibitor development in autoimmune indications is discussed.

Potent activity of carfilzomib, a novel, irreversible inhibitor of the ubiquitin-proteasome pathway, against preclinical models of multiple myeloma.

The proteasome has emerged as an important target for cancer therapy with the approval of bortezomib, a first-in-class, reversible proteasome inhibitor, for relapsed/refractory multiple myeloma (MM). However, many patients have disease that does not respond to bortezomib, whereas others develop resistance, suggesting the need for other inhibitors with enhanced activity. We therefore evaluated a novel, irreversible, epoxomicin-related proteasome inhibitor, carfilzomib. In models of MM, this agent potently bound and specifically inhibited the chymotrypsin-like proteasome and immunoproteasome activities, resulting in accumulation of ubiquitinated substrates. Carfilzomib induced a dose- and time-dependent inhibition of proliferation, ultimately leading to apoptosis. Programmed cell death was associated with activation of c-Jun-N-terminal kinase, mitochondrial membrane depolarization, release of cytochrome c, and activation of both intrinsic and extrinsic caspase pathways. This agent also inhibited proliferation and activated apoptosis in patient-derived MM cells and neoplastic cells from patients with other hematologic malignancies. Importantly, carfilzomib showed increased efficacy compared with bortezomib and was active against bortezomib-resistant MM cell lines and samples from patients with clinical bortezomib resistance. Carfilzomib also overcame resistance to other conventional agents and acted synergistically with dexamethasone to enhance cell death. Taken together, these data provide a rationale for the clinical evaluation of carfilzomib in MM.