title: Targeted inhibition of the immunoproteasome is a potent strategy against models of multiple myeloma that overcomes resistance to conventional drugs and nonspecific proteasome inhibitors.
abstract: Proteasome inhibition is a validated strategy for therapy of multiple myeloma, but this disease remains challenging as relapses are common, and often associated with increasing chemoresistance. Moreover, nonspecific proteasome inhibitors such as bortezomib can induce peripheral neuropathy and other toxicities that may compromise the ability to deliver therapy at full doses, thereby decreasing efficacy. One novel approach may be to target the immunoproteasome, a proteasomal variant found predominantly in cells of hematopoietic origin that differs from the constitutive proteasome found in most other cell types. Using purified preparations of constitutive and immunoproteasomes, we screened a rationally designed series of peptidyl-aldehydes and identified several with relative specificity for the immunoproteasome. The most potent immunoproteasome-specific inhibitor, IPSI-001, preferentially targeted the beta1(i) subunit of the immunoproteasome in vitro and in cellulo in a dose-dependent manner. This agent induced accumulation of ubiquitin-protein conjugates, proapoptotic proteins, and activated caspase-mediated apoptosis. IPSI-001 potently inhibited proliferation in myeloma patient samples and other hematologic malignancies. Importantly, IPSI-001 was able to overcome conventional and novel drug resistance, including resistance to bortezomib. These findings provide a rationale for the translation of IPSIs to the clinic, where they may provide antimyeloma activity with greater specificity and less toxicity than current inhibitors.
authors.affiliation: Department of Lymphoma and Myeloma, Division of Cancer Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX 77030-4009, USA.
authors.forename: Deborah J
authors.initials: DJ
authors.lastname: Kuhn
authors.forename: Sally A
authors.initials: SA
authors.lastname: Hunsucker
authors.forename: Qing
authors.initials: Q
authors.lastname: Chen
authors.forename: Peter M
authors.initials: PM
authors.lastname: Voorhees
authors.forename: Marian
authors.initials: M
authors.lastname: Orlowski
authors.forename: Robert Z
authors.initials: RZ
authors.lastname: Orlowski
mesh_terms: D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001667:Binding, Competitive; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D002478:Cells, Cultured; D002872:Chromosome Deletion; D002882:Chromosomes, Human, Pair 13 / Q000235:genetics; D003907:Dexamethasone / Q000494:pharmacology; D004151:Dipeptides / Q000138:chemical synthesis / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004357:Drug Synergism; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology*; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D011480:Protease Inhibitors / Q000138:chemical synthesis / Q000494:pharmacology*; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014471:Umbilical Veins / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
chemical_list: D000893:Anti-Inflammatory Agents; D001897:Boronic Acids; D004151:Dipeptides; C541163:IPSI-001; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D012333:RNA, Messenger; D000069286:Bortezomib; D003907:Dexamethasone