Fig. 1.

Design, rationale, and characterization of noncovalent β5i selective inhibitors. (A) Structures of DPLG3, PKS2086, and inactive congener PKS2032. (B) IC₅₀ values of the compounds against β5i and β5c of human proteasomes and mouse proteasomes, the latter noted by an asterisk (*). Data are shown as mean ± SEM (n ≥ 3). (C) Selectivity indexes of ONX0914 and DPLG3 after 1- and 24-h preincubation with human c-20S and i-20S. “Reported” refers to data from ref. 10. Data are shown as mean ± SD (n = 2). (D) Inhibition of pan-β5 (β5i and β5c) activities in B lymphoma Karpas 1106P cells (β5i-dominant) and (E) hepatoma HepG2 cells (expressing β5c only) by DPLG3, PKS2086, and inactive congener PKS2032. Bortezomib was used as positive control. Pan-β5 activity was recorded with suc-LLVY-aminoluciferin, measuring luminescence of the hydrolysis product, aminoluciferin. (F) Assessment of DPLG3’s toxicity for PBMCs, mouse bone marrow macrophages (values of EC₅₀ > 100 µM), and Karpas cells (EC₅₀ = 5.53 µM). Data in D–F are means ± SEM (n ≥ 3).