Targeting IL-6 and DKK1 overcomes BTZ-drug resistance in vivo. (A) Cleavage of PARP as the apoptotic marker in MM cells treated with or without anti-DKK1, anti-IL-6, combined with BTZ for 24 hours (n = 3). (B) Quantification of apoptotic MM cells treated with BTZ (0-10 nM) with or without anti-DKK1 or anti-IL-6 for 24 hours (n = 3). (C) Tumor growth of BTZ-resistant (BR) MM.1S cells stably expressing CKAP4-shRNA (CKAP4 KD) or NT Ctrl (3 × 10⁶ cells/mouse, n = 12) in NSG mice receiving BTZ (0.5 mg/kg) at week 3 after inoculation for another 4 weeks. (D) Survival rate of mice at the time point of tumor diameter over 15 mm (n = 12). (E) Immunohistochemistry staining in tissues from xenograft of different mice groups to detect CKAP4 level and apoptosis using a terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling kit. Scale bar, 100 μm. (F) Experiment design and treatment schedule in a mice intra-bone (i.b.) model harboring BR-MM.1S cells (n = 12). (G) Quantification of the percentage of CD138⁺ plasma cells in bone marrow biopsies using flow cytometry. (H) Representative micro-computed tomography images of mouse femurs bearing BR MM.1S cells and treated with IgG, anti-DKK1, and anti-IL-6 neutralizing antibodies (0.5 mg/kg) in presence of BTZ (0.5 mg/kg) (n = 8). (I) Measurement of the percentage of bone volume to total volume (BV/TV) and trabecular number in the metaphyseal regions of the mice femurs in the IgG, anti-DKK1, anti-IL-6 and anti-DKK1⁺ anti-IL-6 neutralizing antibodies groups were analyzed (n = 8).