The novel β2-selective proteasome inhibitor LU-102 synergizes with bortezomib and carfilzomib to overcome proteasome inhibitor resistance of myeloma cells

• Published in: Haematologica (Roma) Vol. 100; no. 10; pp. 1350 - 1360
• Main Authors: Kraus, Marianne, Bader, Juergen, Geurink, Paul P, Weyburne, Emily S, Mirabella, Anne C, Silzle, Tobias, Shabaneh, Tamer B, van der Linden, Wouter A, de Bruin, Gerjan, Haile, Sarah R, van Rooden, Eva, Appenzeller, Christina, Li, Nan, Kisselev, Alexei F, Overkleeft, Herman, Driessen, Christoph
• Format: Journal Article
• Language: English
• Published: Italy Ferrata Storti Foundation 01.10.2015
• Subjects: Animals; Antineoplastic Agents - pharmacology; Bortezomib - pharmacology; Cell Line, Tumor; Disease Models, Animal; Drug Resistance, Neoplasm; Drug Synergism; Humans; Mice; Multiple Myeloma - drug therapy; Multiple Myeloma - pathology; Oligopeptides - pharmacology; Proteasome Inhibitors - pharmacology; Xenograft Model Antitumor Assays
• ISSN: 0390-6078; 1592-8721
• DOI: 10.3324/haematol.2014.109421

Proteasome inhibitor resistance is a challenge for myeloma therapy. Bortezomib targets the β5 and β1 activity, but not the β2 activity of the proteasome. Bortezomib-resistant myeloma cells down-regulate the activation status of the unfolded protein response, and up-regulate β2 proteasome activity. To improve proteasome inhibition in bortezomib-resistant myeloma and to achieve more efficient UPR activation, we have developed LU-102, a selective inhibitor of the β2 proteasome activity. LU-102 inhibited the β2 activity in intact myeloma cells at low micromolar concentrations without relevant co-inhibition of β1 and β5 proteasome subunits. In proteasome inhibitor-resistant myeloma cells, significantly more potent proteasome inhibition was achieved by bortezomib or carfilzomib in combination with LU-102, compared to bortezomib/carfilzomib alone, resulting in highly synergistic cytotoxic activity of the drug combination via endoplasmatic reticulum stress-induced apoptosis. Combining bortezomib/carfilzomib with LU-102 significantly prolonged proteasome inhibition and increased activation of the unfolded protein response and IRE1-a activity. IRE1-α has recently been shown to control myeloma cell differentiation and bortezomib sensitivity (Leung-Hagesteijn, Cancer Cell 24:3, 289-304). Thus, β2-selective proteasome inhibition by LU-102 in combination with bortezomib or carfilzomib results in synergistic proteasome inhibition, activation of the unfolded protein response, and cytotoxicity, and overcomes bortezomib/carfilzomib resistance in myeloma cells in vitro.