Stewart, A. Keith

Abstract Bortezomib is highly effective in the treatment of multiple myeloma; however, emergent drug resistance is common. Consequently, we employed CRISPR targeting 19,052 human genes to identify unbiased targets that contribute to bortezomib resistance. Specifically, we engineered an RPMI8226 multiple myeloma cell line to express Cas9 infected by lentiviral vector CRISPR library and cultured derived cells in doses of bortezomib lethal to parental cells. Sequencing was performed on surviving cells to identify inactivated genes responsible for drug resistance. From two independent whole-genome screens, we selected 31 candidate genes and constructed a second CRISPR sgRNA library, specifically targeting each of these 31 genes with four sgRNAs. After secondary screening for bortezomib resistance, the top 20 “resistance” genes were selected for individual validation. Of these 20 targets, the proteasome regulatory subunit PSMC6 was the only gene validated to reproducibly confer bortezomib resistance. We confirmed that inhibition of chymotrypsin-like proteasome activity by bortezomib was significantly reduced in cells lacking PSMC6. We individually investigated other members of the PSMC group (PSMC1 to 5) and found that deficiency in each of those subunits also imparts bortezomib resistance. We found 36 mutations in 19S proteasome subunits out of 895 patients in the IA10 release of the CoMMpass study (https://themmrf.org). Our findings demonstrate that the PSMC6 subunit is the most prominent target required for bortezomib sensitivity in multiple myeloma cells and should be examined in drug-refractory populations. Mol Cancer Ther; 16(12); 2862–70. ©2017 AACR.

Key Points PVD is an active combination in relapsed lenalidomide-refractory MM patients. PVD with weekly bortezomib offers a simpler, more convenient, and well-tolerated regimen option.

Abstract FAM46C is one of the most recurrently mutated genes in multiple myeloma; however its role in disease pathogenesis has not been determined. Here we demonstrate that wild-type (WT) FAM46C overexpression induces substantial cytotoxicity in multiple myeloma cells. In contrast, FAM46C mutations found in multiple myeloma patients abrogate this cytotoxicity, indicating a survival advantage conferred by the FAM46C mutant phenotype. WT FAM46C overexpression downregulated IRF4, CEBPB, and MYC and upregulated immunoglobulin (Ig) light chain and HSPA5/BIP. Furthermore, pathway analysis suggests that enforced FAM46C expression activated the unfolded protein response pathway and induced mitochondrial dysfunction. CRISPR-mediated depletion of endogenous FAM46C enhanced multiple myeloma cell growth, decreased Ig light chain and HSPA5/BIP expression, activated ERK and antiapoptotic signaling, and conferred relative resistance to dexamethasone and lenalidomide treatments. Genes altered in FAM46C-depleted cells were enriched for signaling pathways regulating estrogen, glucocorticoid, B-cell receptor signaling, and ATM signaling. Together these results implicate FAM46C in myeloma cell growth and survival and identify FAM46C mutation as a contributor to myeloma pathogenesis and disease progression via perturbation in plasma cell differentiation and endoplasmic reticulum homeostasis. Cancer Res; 77(16); 4317–27. ©2017 AACR.

Key Points IMiDs inhibit TrxR-mediated intracellular decomposition of H2O2 and caused oxidative stress in MM cells. MM cells with lower antioxidative capacity were more vulnerable to lenalidomide-induced H2O2 accumulation and its associated cytotoxicity.

AbstractA population pharmacokinetic (PK) model and exposure–response (E‐R) analysis was developed using data collected from 5 phase 1b/2 and 2 phase 3 studies in subjects with multiple myeloma. Subjects receiving intravenous infusion on 2 consecutive days each week for 3 weeks (days 1, 2, 8, 9, 15, and 16) in each cycle at doses ranging from 15 to 20/56 mg/m2 (20 mg/m2 in cycle 1 and, if tolerated, escalated to 56 mg/m2 on day 8 of cycle 1). The population PK analysis indicated that among all the covariates tested, the only statistically significant covariate was body surface area on carfilzomib clearance; however, this covariate was unlikely to be clinically significant. Despite inclusion of different populations (relapsed or relapsed/refractory), treatments (carfilzomib monotherapy or combination therapy), infusion lengths (2 to 10 minutes or 30 minutes), and different doses, the E‐R analysis of efficacy showed that after adjusting for baseline characteristics, higher area under the concentration–time curve was associated with improved overall response rate (ORR), from 15 to 20/56 mg/m2. No positive relationships between maximum concentration and ORR were identified, indicating that ORR would not be expected to be impacted by infusion length. For safety end points, no statistically significant relationship between exposure and increasing risk of adverse events was identified. The results of an E‐R analysis provided strong support for a carfilzomib dose at 20/56 mg/m2 as a 30‐minute infusion for monotherapy and combination therapy. This article illustrates an example of application of E‐R analysis to support labeling dose recommendation in the absence of extensive clinical data.

Purpose To determine the effects of carfilzomib, lenalidomide, and dexamethasone (KRd) versus lenalidomide and dexamethasone (Rd) on health-related quality of life (HR-QoL) in the Carfilzomib, Lenalidomide, and Dexamethasone Versus Lenalidomide and Dexamethasone for the Treatment of Patients With Relapsed Multiple Myeloma (ASPIRE) trial. Methods Patients with relapsed multiple myeloma were randomly assigned to receive KRd or Rd. The European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire C30 and myeloma-specific module were administered at baseline; day 1 of cycles 3, 6, 12, and 18; and after treatment. The Global Health Status/Quality of Life (GHS/QoL) scale and seven subscales (fatigue, nausea and vomiting, pain, physical functioning, role functioning, disease symptoms, and adverse effects of treatment) were compared between groups using a mixed model for repeated measures. The percentages of responders with ≥ 5- or 15-point GHS/QoL improvement at each cycle were compared between groups. Results Baseline questionnaire compliance was excellent (94.1% of randomly assigned patients). KRd patients had higher GHS/QoL scores versus Rd patients over 18 treatment cycles (two-sided P < .001). The minimal important difference was met at cycle 12 (5.6 points) and approached at cycle 18 (4.8 points). There was no difference between groups for the other prespecified subscales from ASPIRE. A higher proportion of KRd patients met the GHS/QoL responder definition (≥ 5-point improvement) with statistical differences at cycle 12 (KRd v Rd patients, 25.5% v 17.4%, respectively) and 18 (KRd v Rd patients, 24.2% v 12.9%, respectively). Conclusion KRd improves GHS/QoL without negatively affecting patient-reported symptoms when compared with Rd. These data further support the benefit of KRd in patients with relapsed multiple myeloma.

Key Points The incidence of mutations within the MAPK pathway, the CRBN pathway, and TP53 is significantly increased in drug-refractory MM. Mutations in CRBN might contribute to IMiD resistance in drug-refractory MM.

Key Points KRd has a favorable benefit-risk profile compared with Rd, regardless of baseline cytogenetic risk status, in patients with relapsed MM. KRd improves but does not abrogate the poor prognosis associated with high-risk cytogenetics in patients with relapsed MM.