1. Table S1. HTS positive hits.

2. Figure S1. Isogenic bortezomib (Btz) resistant mouse and human cell models. The indicated human (MM.1S and U266) and mouse (595sp and 589bm) were exposed to increasing concentrations of Btz for greater than 6 months in culture, eventually giving rise to Btz resistant cell populations. The indicated cell lines were exposed to increasing concentrations of Btz for 24 (human) or 48 (mouse) hours, at which time cell viability was measured. The parental, sensitive cell lines show EC50 values between 5- 10 nM, whereas EC50s for resistant cell lines ranged from 60-200 nM.

3. Figure S2. HTS assay Z’ factor calculation. The Z’ factor, a statistical measure of assay performance, was calculated using Btz as a positive control/test compound in the sensitive 595 BzS cells. The assay Z’ factor at an Effective Concentration 60 (EC60) of Btz was calculated at 0.49. Z’ factor values greater than 0.40 are considered acceptable for HTS assays, as they demonstrate statistical significance of the given effect size.

4. Figure S3. VRC2 gene expression signatures predict p53 pathway activation. Treatment of human MM1.S BzR cell lines over 24 hours shows downstream evidence of p53 pathway activation through CCND1 inhibition by Ingenuity Pathway Analysis (see Figure 2A). Molecules in orange are predicted as activated and those in blue are inhibited. Orange lines lead to activation, blue lines lead to inhibition, yellow lines are findings inconsistent between the input dataset and the database, and gray lines have no effect prediction. Solid lines are known direct effects and dashed lines are predicted effects based on the literature.

5. VRC2 (hrs): 0 2 4 6 8 Nutlin A B Figure S4. VRC2 induces p53 pathway activation. (A) Wild-type p53 expressing NCI- H929 cells were treated with 500nM VRC2 for the indicated time points. Western blots are shown. The MDM2 inhibitor, Nutlin3a (5μM), was included as a positive control. (B) NCI-H929 cells were treated with VRC2 (500nM) and mRNA levels of the p53 target genes P21, PUMA, and NOXA were measured by qPCR. Nutlin3a (5μM) and the DNA- damaging topoisomerase inhibitor, CPT-11 (33μM), were included as positive controls. P21 PUMA NOXA p53 Ran

6. Figure S5. Nutlin3a restores sensitivity to proteasome inhibitors in resistant MM cells. (A) PI resistant MM.1S VR cells were treated with increasing concentrations of Btz (left) or carfilzomib (right) in the presence or absence of Nutlin3a (5μM) for 24 hours. Cell viability data are shown. Nutlin3a had no effect at this time point as a single agent, and therefore any separation of the dose curves is an indication of a superadditive/synergistic drug interaction. Parental MM.1s, which are highly sensitive to both Btz and Crflz were included for comparison. (B) PI resistant mouse 595sp VR cells were treated as in (A) for 48 hours. Cell viability data are shown. AB