14-3-3ε expression level influences PI sensitivity and protein load in primary MM cells. (A) CD138⁺ cells from bone marrow aspirates of 11 patients with MM were assessed for 14-3-3ε (YWHAE) mRNA expression and sensitivity to PIs. YWHAE mRNA expression was assessed by quantitative polymerase chain reaction and presented as cycle threshold (CT) values (a higher value indicates lower mRNA expression). Cell viability was assessed by CTG after 24 hours of treatment in the presence of different concentrations of BTZ or CFZ, and IC₅₀ values were calculated by GraphPad Prism 8. Pearson correlation analysis showed a significant correlation between 14-3-3ε mRNA expression level and IC₅₀ for BTZ and CFZ treatment. (B) Comparison of BTZ and CFZ IC₅₀ average between the 2 groups of patients with MM with high and low 14-3-3ε expression, respectively, using an unpaired Student t test. (C) Comparison of YWHAE levels in secretory and nonsecretory patients based on their M-spike levels. (D) YWHAE levels in secretory vs nonsecretory patients in a Chinese cohort of patients with MM (n = 27). (E) CD138⁺ cells from bone marrow aspirates were assessed for del17p status by FISH. M-protein levels in patients with del17p (n = 21) vs without del17p (n = 249) are reported in the graph. (F) PFS in del17p MM patients with different M protein levels undergoing BTZ-based therapy.