Proteasome inhibition for treatment of leishmaniasis, Chagas disease and sleeping sickness.

Chagas disease, leishmaniasis and sleeping sickness affect 20 million people worldwide and lead to more than 50,000 deaths annually. The diseases are caused by infection with the kinetoplastid parasites Trypanosoma cruzi, Leishmania spp. and Trypanosoma brucei spp., respectively. These parasites have similar biology and genomic sequence, suggesting that all three diseases could be cured with drugs that modulate the activity of a conserved parasite target. However, no such molecular targets or broad spectrum drugs have been identified to date. Here we describe a selective inhibitor of the kinetoplastid proteasome (GNF6702) with unprecedented in vivo efficacy, which cleared parasites from mice in all three models of infection. GNF6702 inhibits the kinetoplastid proteasome through a non-competitive mechanism, does not inhibit the mammalian proteasome or growth of mammalian cells, and is well-tolerated in mice. Our data provide genetic and chemical validation of the parasite proteasome as a promising therapeutic target for treatment of kinetoplastid infections, and underscore the possibility of developing a single class of drugs for these neglected diseases.

Use of proteasome inhibitors.

Proteasome inhibitors are indispensable research tools in immunology and cell biology. With numerous proteasome inhibitors available commercially, choosing the appropriate compound for a biological experiment may be challenging, especially for a novice. This unit provides an overview of the proteasome inhibitors commonly used in research. It discusses how to select an appropriate highly specific inhibitor, its concentration, and length of exposure for mammalian cell culture experiments. In addition, assays that can be used to confirm proteasome inhibition are discussed.

Discovery and development of second-generation proteasome inhibitors.

Proteasome inhibition is a validated therapeutic strategy for the treatment of B-cell neoplasms. The peptide boronate based inhibitor bortezomib has become an important tool in the armamentarium for the treatment of multiple myeloma (MM) and has spurred the development of new agents that target the catalytic activities of the proteasome. Five of these agents, representing three distinct chemical classes, have reached clinical testing. These compounds have properties similar to and distinct from bortezomib. Here, the preclinical activity and clinical development of these agents are reviewed with special attention given to comparisons with bortezomib.

Comparative mechanisms of action of proteasome inhibitors.

The proteasome has emerged as an important target for therapeutic intervention. In preclinical studies, proteasome inhibitors (PIs) induced apoptosis and inhibited tumor growth, supporting their potential role in the treatment of various tumor types, especially hematologic malignancies. Bortezomib (Velcade), the first clinically validated PI, reversibly binds to the chymotrypsin-like (ChT-L) active sites in the 20S proteasome and potently inhibits cell growth and proliferation in human tumor cell lines and in multiple myeloma (MM) and mantle cell lymphoma. However, the adverse event profile and intravenous administration of bortezomib have underscored the need for the development of PIs with selective actions on different proteasome subunits, which would have different binding kinetics and routes of administration. The most advanced next-generation PI is carfilzomib, an epoxyketone that differs structurally and mechanistically from bortezomib. In preclinical studies, carfilzomib demonstrates sustained inhibition of proteasomal ChT-L activity and greater selectivity than bortezomib. It is thought that the selectivity of carfilzomib for the ß5 subunit contributes to its greater cytotoxic response and improved tolerability profile relative to bortezomib. Furthermore, in preclinical studies, carfilzomib did not exhibit the same magnitude of off-target activity against non-proteasomal proteases that is observed with bortezomib. Variations in the binding profiles of some of the next-generation PIs may translate into key differences in pharmacokinetic and toxicity profiles, and thus may be clinically relevant in the treatment of MM.