Figure 3.

Cytotoxicity of the immunoproteasome-selective proteasome inhibitors in hematological malignancies. (A) Comparison of IC₅₀ values of LU005i determined 48 h after the continuous treatment in various hematological malignancies. Data represent geometric mean ± geometric SD, statistical significance was obtained with ANOVA and Tukey’s multiple comparison test, where * represents p < 0.05 and **** represents p < 0.0001. Line represents a 2.5 µM dose, to which the inhibitor retains its selectivity. (B) Correlation between the activities of constitutive vs. the immunoproteasome β5 subunits and the cytotoxicity of LU005i in 15 AML, 3 B-ALL, 17 CLL, 6 MM and 5 PCL samples. Correlation and statistical significance were obtained using Spearman’s rank correlation. (C) Comparison of IC₅₀ values of LU035i determined 48 h after the continuous treatment in various hematological malignancies, data represent geometric mean ± geometric SD. In samples, where the IC₅₀ value was not reached, it was arbitrarily given an IC₅₀ = 100 µM. Statistical significance was obtained with ANOVA and Tukey’s multiple comparison test, where ** represents p < 0.01 and **** represents p < 0.0001. Line represents a 5 µM dose, to which the inhibitor retains its selectivity. (D) Correlation between the activities of constitutive vs. the immunoproteasome β5 subunits and the cytotoxicity of LU035i in 17 CLL samples. Correlation and statistical significance were obtained using Spearman’s rank correlation. (E) Dose-response curves of AMO-1 and AMO-1 PSMB5 knock-out cells to LU035i determined 48 h after the treatment. Data represent mean ± SD of three independent experiments. (F–H) Dose-response curves of three B-CLL samples to LU035i alone or in combination with 1 µM LU025c determined 48 h after the treatment. Data represent mean ± SD of tetraplicate. AML = acute myeloid leukemia, B-ALL = B-cell acute lymphoblastic leukemia, B-CLL = B-cell chronic lymphocytic leukemia, MM = multiple myeloma, PCL = plasma-cell leukemia, PBMC = peripheral blood mononuclear cells; LU005i = proteasome β5i + β2i + β1i selective inhibitor; LU035i = proteasome β5i selective inhibitor; LU025c = proteasome β5c selective inhibitor; i = immunoproteasome, c = constitutive proteasome.