Targeting proteasome ubiquitin receptor Rpn13 in multiple myeloma

Abstract

Proteasome inhibitor bortezomib is an effective therapy for relapsed and newly diagnosed multiple myeloma (MM); however, dose-limiting toxicities and the development of resistance can limit its long-term utility. Recent research has focused on targeting ubiquitin receptors upstream of 20S proteasome, with the aim of generating less toxic therapies. Here we show that 19S proteasome-associated ubiquitin receptor Rpn13 is more highly expressed in MM cells than in normal plasma cells. Rpn13-siRNA (small interfering RNA) decreases MM cell viability. A novel agent RA190 targets Rpn13 and inhibits proteasome function, without blocking the proteasome activity or the 19S deubiquitylating activity. CRISPR/Cas9 Rpn13-knockout demonstrates that RA190-induced activity is dependent on Rpn13. RA190 decreases viability in MM cell lines and patient MM cells, inhibits proliferation of MM cells even in the presence of bone marrow stroma and overcomes bortezomib resistance. Anti-MM activity of RA190 is associated with induction of caspase-dependent apoptosis and unfolded protein response-related apoptosis. MM xenograft model studies show that RA190 is well tolerated, inhibits tumor growth and prolongs survival. Combining RA190 with bortezomib, lenalidomide or pomalidomide induces synergistic anti-MM activity. Our preclinical data validates targeting Rpn13 to overcome bortezomib resistance, and provides the framework for clinical evaluation of Rpn13 inhibitors, alone or in combination, to improve patient outcome in MM.

RA190, a Proteasome Subunit ADRM1 Inhibitor, Suppresses Intrahepatic Cholangiocarcinoma by Inducing NF-KB-Mediated Cell Apoptosis

“…Overexpression of ADRM1 was found in some malignancies [14][15][16][17][18], and high expression of ADRM1 indicated poor prognosis in ovarian cancer [17] and gastric carcinoma [18]. However, to our knowledge, its expression and roles in ICC have not been studied previously.…”

“…RA190, which can covalently bind to cysteine 88 of ADRM1 in the 19S regulatory particle of proteasome, inhibits proteasome function, resulting in higher-molecular weight polyubiquitylated protein accumulation [14,19]. In HCT116 cells, RA190 can also bind with UCH37, a deubiquitinating enzyme interacting with ADRM1, to suppress proteasome function [35].…”

“…RA190 can covalently bind to ADRM1 in the 19S regulatory particle, resulting in inhibition of proteasome function and accumulation of higher-molecular weight polyubiquitylated proteins [14,19]. Since ADRM1 also mediates the degradation of IκBα [27], we hypothesized that RA190 could impede proteasome function and induce the accumulation of highermolecular weight polyubiquitylated proteins and phosphorylated IκBα (p-IκBα) in ICC cells.…”

“…Recently, a ubiquitin receptor ADRM1 [13] was found to be overexpressed in several malignancies [14][15][16][17][18]. However, the role of ADRM1 in these tumors has not been explored fully.…”

“…Moreover, knockdown of ADRM1 suppresses tumor growth in different malignancies [15][16][17][18]. RA190, a novel specific inhibitor of ADRM1, was found to have a significant suppressive effect on multiple myeloma [14,19]. However, the expression of ADRM1 in ICC and the effect and mechanism of action of targeting ADRM1 in ICC remain unclear.…”