Therapeutically targeting CD138, a define multiple myeloma (MM) antigen, is not yet approved for patients. We here developed and determined the preclinical efficacy of VIS832, a novel therapeutic monoclonal antibody (MoAb) with differentiated CD138 target binding to BB4 that is anti-CD138 MoAb scaffold for indatuximab ravtansine (BT062). VIS832 demonstrated enhanced CD138-binding avidity and significantly improved potency to kill MM cell lines and autologous patient MM cells regardless of resistance to current standard-of-care therapies, via robust antibody-dependent cellular cytotoxicity and phagocytosis mediated by NK and macrophage effector cells, respectively. Specifically, CD38-targeting daratumumab-resistant MM cells were highly susceptible to VIS832 which, unlike daratumumab, spares NK cells. Superior maximal cytolysis of VIS832 vs. daratumumab corresponded to higher CD138 vs. CD38 levels in MM cells. Furthermore, VIS832 acted synergistically with lenalidomide or bortezomib to deplete MM cells. Importantly, VIS832 at a sub-optimal dose inhibited disseminated MM1S tumors in vivo as monotherapy (P < 0.0001), and rapidly eradicated myeloma burden in all mice concomitantly receiving bortezomib, with 100% host survival. Taken together, these data strongly support clinical development of VIS832, alone and in combination, for the therapeutic treatment of MM in relapsed and refractory patients while pointing to its potential therapeutic use earlier in disease intervention.

Purpose: p21-activated kinase 4 (PAK4) plays a significant biological and functional role in a number of malignancies, including multiple myeloma (MM). On the basis of our promising findings in MM, we here characterize PAK4 expression and role in WM cells, as well effect of dual PAK4-NAMPT inhibitor (KPT-9274) against WM cell growth and viability. Experimental Design: We have analyzed mRNA and protein expression levels of PAK4 in WM cells, and used loss-of-function approach to investigate its contribution to WM cell viability. We have further tested the in vitro and in vivo effect of KPT-9274 against WM cell growth and viability. Results: We report here high-level expression and functional role of PAK4 in WM, as demonstrated by shRNA-mediated knockdown; and significant impact of KPT-9274 on WM cell growth and viability. The growth inhibitory effect of KPT-9274 was associated with decreased PAK4 expression and NAMPT activity, as well as induction of apoptosis. Interestingly, in WM cell lines treated with KPT-9274, we detected a significant impact on DNA damage and repair genes. Moreover, we observed that apart from inducing DNA damage, KPT-9274 specifically decreased RAD51 and the double-strand break repair by the homologous recombination pathway. As a result, when combined with a DNA alkylating agents bendamustine and melphalan, KPT-9274 provided a synergistic inhibition of cell viability in WM cell lines and primary patient WM cells in vitro and in vivo. Conclusions: These results support the clinical investigation of KPT-9274 in combination with DNA-damaging agent for treatment of WM.

Therapeutic targeting of CDK7 has proven beneficial in pre-clinical studies, yet the off-target effects of currently available CDK7 inhibitors make it difficult to pinpoint the exact mechanisms behind MM cell death mediated by CDK7 inhibition. Here, we show that CDK7 expression positively correlates with E2F and MYC transcriptional programs in multiple myeloma (MM) patient cells; and its selective targeting counteracts E2F activity via perturbation of the CDKs/Rb axis and impairs MYC-regulated metabolic gene signatures translating into defects in glycolysis and reduced levels of lactate production in MM cells. CDK7 inhibition using the covalent small molecule inhibitor YKL-5-124 elicits a strong therapeutic response with minimal effects on normal cells, and causes in vivo tumor regression increasing survival in several MM mouse models including a genetically engineered mouse model of MYC-dependent MM. Through its role as a critical cofactor and regulator of MYC and E2F activity, CDK7 is therefore a master regulator of oncogenic cellular programs supporting MM growth and survival, and a valuable therapeutic target providing rationale for development of YKL-5-124 for clinical use.

Purpose: We investigated both the clinical utilities and the prognostic impacts of the clonotypic peptide mass spectrometry (MS)-EasyM, a blood-based minimal residual disease (MRD) monitoring protocol in multiple myeloma. Experimental Design: A total of 447 sequential serum samples from 56 patients with multiple myeloma were analyzed using EasyM. Patient-specific M-protein peptides were sequenced from diagnostic samples; sequential samples were quantified by EasyM to monitor the M-protein. The performance of EasyM was compared with serum immunofixation electrophoresis (IFE), bone marrow multiparameter flow cytometry (MFC), and next-generation flow cytometry (NGF) detection. The optimal balance of EasyM sensitivity/specificity versus NGF (10−5 sensitivity) was determined and the prognostic impact of MS-MRD status was investigated. Results: Of the 447 serum samples detected and measured by EasyM, 397, 126, and 92 had time-matching results for comparison with serum IFE, MFC-MRD, and NGF-MRD, respectively. Using a dotp >0.9 as the MS-MRD positive, sensitivity was 99.6% versus IFE and 100.0% versus MFC and NGF. Using an MS negative cutoff informed by ROC analysis (<1.86% of that at diagnosis), EasyM sensitivity remained high versus IFE (88.3%), MFC (85.1%), and NGF (93.2%), whereas specificity increased to 90.4%, 55.8%, and 93.2%, respectively. In the multivariate analysis, older diagnostic age was an independent predictor for progression-free survival [PFS; high risk (HR), 3.15; 1.26–7.86], the best MS-MRD status (MS-MRD negative) was independent predictor for both PFS (HR, 0.25; 0.12–0.52) and overall survival (HR, 0.16; 0.06–0.40). Conclusions: EasyM is a highly sensitive and minimal invasive method of MRD monitoring in multiple myeloma; MS-MRD had significant predictive ability for survival outcomes.

Single-cell analysis is of significant importance in delineating the exact phylogeny of the subclonal population and in discovering subtle diversification. So far, studies of intratumor heterogeneity and clonal evolution in multiple myeloma (MM) were largely focused on the bulk tumor population level. We performed quantitative multigene fluorescence in situ hybridization (QM-FISH) in 129 longitudinal samples of 57 MM patients. All the patients had newly diagnosed and relapsed paired samples. An expanded cohort of 188 MM patients underwent conventional FISH (cFISH) to validate the cytogenetic evolution in bulk tumor level. Forty-three of 57 patients (75.4%) harbored 3 or 4 cytogenetic clones at diagnosis. We delineated the phylogeny of the subclonal tumor population and derived the evolutionary architecture in each patient. Patients with clonal stabilization had a significantly improved overall survival (OS) than those with other evolutionary patterns (median OS, 71.2 months vs 39.7 months vs 35.2 months vs 25.5 months, for stable, differential, branching, and linear patterns, respectively; P = .001). A high degree of consistency and complementarity across QM-FISH and cFISH was observed in the evaluation of cytogenetic evolution patterns in MM. Survival after relapse was greater influenced by the presence of high-risk aberrations at relapse (hazard ratio = 2.07) rather than present at diagnosis (hazard ratio = 1.55). This study shows that QM-FISH is a valuable tool to elucidate the clonal architecture at the single-cell level. Clonal evolution pattern is of prognostic significance, highlighting the need for repeated cytogenetic evaluation in relapsed MM.