Fig. 3. Reversible PI tolerance is mediated by epigenetic alterations and can be eliminated with combination and intermittent therapies.

a Hierarchical clustering heatmap of the 239 differentially expressed epigenetic regulators in relapsed and reversed MM patient cells. b Gene ontology analysis of the BP of the differentially expressed epigenetic regulators. c MM1.S-tolerant cells were treated with DMSO, LBH589 (10 nM), or SAHA (2 μM) for 20 h. Cell viability was detected by MTS assay 24 h after the addition of bortezomib. The IC₅₀ of different cells was quantified. d Treatment schedule for administration of bortezomib, SAHA, or vehicle. NOD-SCID mice were inoculated with 1 × 10⁷ MM1.S cells by subcutaneous injection in the right flank. Mice were then administered bortezomib intravenously or SAHA intraperitoneally once tumours were measurable. e Effect of different treatments on myeloma cell growth in vivo. Calliper measurements to estimate the tumour volume, using the following formula: 4π/3 × (width/2)² × (length/2). f Tumours were obtained from sacrificed mice and were incubated with BCMA and Annexin V antibodies. Flow cytometric assays for Annexin V-positive cells in tumours are shown. *P < 0.05; **P < 0.01; two-tailed t test. Data are represented as mean ± SD.