CD20-Targeting Immunotherapy Promotes Cellular Senescence in B-Cell Lymphoma

The CD20-targeting monoclonal antibody rituximab is an established component of immunochemotherapeutic regimens against B-cell lymphomas, where its coadministration with conventional anticancer agents has significantly improved long-term outcome. However, the cellular mechanisms by which rituximab exerts its antilymphoma activity are only partially understood. We show here that rituximab induces typical features of cellular senescence, a long-term growth arrest of viable cells with distinct biologic properties, in established B-cell lymphoma cell lines as well as primary transformed B cells. In addition, rituximab-based immunotherapy sensitized lymphoma cells to senescence induction by the chemotherapeutic compound adriamycin (a.k.a. doxorubicin), and, to a lesser extent, by the antimicrotubule agent vincristine. Anti-CD20 treatment further enhanced secretion of senescence-associated cytokines, and augmented the DNA damage response signaling cascade triggered by adriamycin. As the underlying prosenescence mechanism, we found intracellular reactive oxygen species (ROS) levels to be elevated in response to rituximab, and, in turn, the ROS scavenger N-acetylcysteine to largely abrogate rituximab-mediated senescence. Our results, further supported by gene set enrichment analyses in a clinical data set of chronic lymphocytic leukemia patient samples exposed to a rituximab-containing treatment regimen, provide important mechanistic insights into the biologic complexity of anti-CD20-evoked tumor responses, and unveil cellular senescence as a hitherto unrecognized effector principle of the antibody component in lymphoma immunochemotherapy. Mol Cancer Ther; 15(5); 1074-81. ©2016 AACR.

Frequent induction of chromosomal aberrations in in vivo skin fibroblasts after allogeneic stem cell transplantation: hints to chromosomal instability after irradiation

Background

Total body irradiation (TBI) has been part of standard conditioning regimens before allogeneic stem cell transplantation for many years. Its effect on normal tissue in these patients has not been studied extensively.

Method

We studied the in vivo cytogenetic effects of TBI and high-dose chemotherapy on skin fibroblasts from 35 allogeneic stem cell transplantation (SCT) patients. Biopsies were obtained prospectively (n = 18 patients) before, 3 and 12 months after allogeneic SCT and retrospectively (n = 17 patients) 23–65 months after SCT for G-banded chromosome analysis.

Results

Chromosomal aberrations were detected in 2/18 patients (11 %) before allogeneic SCT, in 12/13 patients (92 %) after 3 months, in all patients after 12 months and in all patients in the retrospective group after allogeneic SCT. The percentage of aberrant cells was significantly higher at all times after allogeneic SCT compared to baseline analysis. Reciprocal translocations were the most common aberrations, but all other types of stable, structural chromosomal aberrations were also observed. Clonal aberrations were observed, but only in three cases they were detected in independently cultured flasks. A tendency to non-random clustering throughout the genome was observed. The percentage of aberrant cells was not different between patients with and without secondary malignancies in this study group.

Conclusion

High-dose chemotherapy and TBI leads to severe chromosomal damage in skin fibroblasts of patients after SCT. Our long-term data suggest that this damage increases with time, possibly due to in vivo radiation-induced chromosomal instability.

Multiple myeloma cells modify VEGF/IL-6 levels and osteogenic potential of bone marrow stromal cells via Notch/miR-223

Bone marrow mesenchymal stromal cells (BMMSCs) represent a crucial component of multiple myeloma (MM) microenvironment supporting its progression and proliferation. Recently, microRNAs have become an important point of interest for research on micro-environmental interactions in MM with some evidence of tumor supportive roles in MM. In this study, we examined the role of miR-223 for MM support in BMMSCs of 56 patients with MM (MM-BMMSCs). miR-223 expression in MM-BMMSCs was reduced by the presence of MM cells in vitro in a cell-contact dependent manner compared to mono-cultured MM-BMMSCs. Co-cultivation of MM cells and MM-BMMSCs induced activation of notch amongst others via jagged-2/notch-2 leading to increased expression of Hes1, Hey2, or Hes5 in both cell types. Cultivation of MM-BMMSCs with increasing levels of recombinant jagged-2 reduced miR-223 and increased Hes1 levels in a concentration-dependent manner. Transient reduction of miR-223 levels increased VEGF and IL-6 expression and secretion by MM-BMMSCs. In addition, reduction of miR-223 degraded the osteogenic differentiation potential of MM-BMMSCs. Inhibition of notch signaling induced apoptosis in both MM cells and MM-BMMSCs. Furthermore, it increased miR-223 levels and reduced expression of VEGF and IL-6 by both cell types. These data provide first evidence that miR-223 participates in different MM supporting pathways in MM-BMMSCs inlcuding regulation of cytokine secretion and expression as well as osteogenic differentiation of MM-BMMSCs. More insights on the role of miR-223 in MM-BMMSCs and in cellular interactions between MM cells and MM-BMMSCs could provide starting points for a more efficient anti-myeloma treatment by targeting of notch signaling. © 2015 Wiley Periodicals, Inc.

Apoptosis Susceptibility Prolongs the Lack of Memory B Cells in Acute Leukemic Patients After Allogeneic Hematopoietic Stem Cell Transplantation

Long-term survival after allogeneic hematopoietic stem cell transplantation requires intact immunosurveillance, which is hampered by lymphoid organ damage associated with conditioning therapy, graft-versus-host disease, and immunosuppression. Our study aimed to identify the mechanisms contributing to sustained low memory B cell numbers after transplantation. Peripheral B and T cell subset recovery and functional marker expression were investigated in 35 acute leukemic patients up to 1 year after transplantation. Apoptosis of B cells after CD40/TLR-9, CD40/BCR, and CD40/BCR/TLR-9-dependent stimulation and drug efflux capacity were analyzed. One half of the patients suffered from infections after day 180. All patients had strongly diminished CD27(+) memory B cells despite already normalized total B cell numbers and fully recovered CD27(-)IgD(-) memory B cells, putatively of extra-follicular origin. Circulating memory follicular helper T cells were reduced in the majority of patients as well. Naïve B cells exhibited a decreased expression of CXCR5, which mediates follicular B cell entry. Additionally, a lower HLA-DR expression was found on naïve B cells, impairing antigen presentation. Upon CD40/TLR-9-dependent activation, B cells underwent significantly increased apoptosis paralleled by an aberrant up-regulation of Fas-L on activated T cells and Fas on resting B cells. Significantly increased B cell apoptosis was also observed after CD40/BCR and CD40/BCR/TLR-9-dependent activation. Drug efflux capacity of naïve B cells was diminished in cyclosporin A-treated patients, additionally contributing to an apoptosis-prone phenotype. We conclude that B cell survival and migration and T cell communication defects are contributing candidates for an impaired germinal center formation of memory B cells after allogeneic hematopoietic stem cell transplantation. Follow-up studies should evaluate effectiveness of revaccinations on the cellular level and should address the long-term sequelae of B cell defects after transplantation.

Anti-CD22 and anti-CD79B antibody drug conjugates are active in different molecular diffuse large B-cell lymphoma subtypes

Antibody drug conjugates (ADCs), in which cytotoxic drugs are linked to antibodies targeting antigens on tumor cells, represent promising novel agents for the treatment of malignant lymphomas. Pinatuzumab vedotin is an anti-CD22 ADC and polatuzumab vedotin an anti-CD79B ADC that are both linked to the microtubule-disrupting agent monomethyl auristatin E (MMAE). In the present study, we analyzed the activity of these agents in different molecular subtypes of diffuse large B-cell lymphoma (DLBCL) both in vitro and in early clinical trials. Both anti-CD22-MMAE and anti-CD79B-MMAE were highly active and induced cell death in the vast majority of activated B-cell-like (ABC) and germinal center B-cell-like (GCB) DLBCL cell lines. Similarly, both agents induced cytotoxicity in models with and without mutations in the signaling molecule CD79B. In line with these observations, relapsed and refractory DLBCL patients of both subtypes responded to these agents. Importantly, a strong correlation between CD22 and CD79B expression in vitro and in vivo was not detectable, indicating that patients should not be excluded from anti-CD22-MMAE or anti-CD79B-MMAE treatment because of low target expression. In summary, these studies suggest that pinatuzumab vedotin and polatuzumab vedotin are active agents for the treatment of patients with different subtypes of DLBCL.

Efficacy of Prophylactic Low–Molecular Weight Heparin for Ambulatory Patients With Advanced Pancreatic Cancer: Outcomes From the CONKO-004 Trial

Purpose

Advanced pancreatic cancer (APC), in addition to its high mortality, accounts for the highest rates of venous thromboembolic events (VTEs). Enoxaparin, a low–molecular weight heparin, is effective in prevention and treatment of VTEs. Some small studies have indicated that this benefit might extend to patients with cancer.

Patients and Methods

Patients with histologically proven APC were randomly assigned to ambulant first-line chemotherapy and prophylactic use of enoxaparin or chemotherapy alone to investigate the probable reduction in symptomatic VTEs and the impact on survival.

Results

A total of 312 patients were recruited as one of the protocol end points was reached. Within the first 3 months, the numbers of symptomatic VTEs were as follows: 15 of 152 patients in the observation group and two of 160 patients in the enoxaparin group (hazard ratio [HR], 0.12; 95% CI, 0.03 to 0.52; χ2 P = .001). The numbers of major bleeding events were as follows: five of 152 patients in the observation arm and seven of 160 patients in the enoxaparin arm (HR, 1.4; 95% CI, 0.35 to 3.72; χ2 P = 1.0). Overall cumulative incidence rates of symptomatic VTEs were 15.1% (observation) and 6.4% (enoxaparin; HR, 0.40; 95% CI, 0.19 to 0.83; P = .01). Progression-free (HR, 1.06; 95% CI, 0.84 to 1.32; P = .64) and overall survival (HR, 1.01; 95% CI, 0.87 to 1.38; P = .44) did not differ between groups.

Conclusion

This study demonstrates the high efficacy and feasibility of primary pharmacologic prevention of symptomatic VTEs in outpatients with APC. Treatment efficacy was not affected by simultaneous treatment with enoxaparin in this trial setting.

Quantitative detection of DNMT3A R882H mutation in acute myeloid leukemia

Background

DNMT3A mutations represent one of the most frequent gene alterations detectable in acute myeloid leukemia (AML) with normal karyotype. Although various recurrent somatic mutations of DNMT3A have been described, the most common mutation is located at R882 in the methyltransferase domain of the gene. Because of their prognostic significance and high stability during disease evolution, DNMT3A mutations might represent highly informative biomarkers for prognosis and outcome of disease.

Methods

We describe an allele-specific PCR with a Blocking reagent for the quantitative detection of DNMT3A R882H mutation providing the possibility to analyze the quantitative amount of mutation during the course of disease. Next, we analyzed 62 follow-up samples from 6 AML patients after therapy and allogeneic stem cell transplantation (alloSCT).

Results

We developed an ASB-PCR assay for quantitative analysis of R882H DNMT3A mutation. After optimization of blocker concentration, a R882H-positive plasmid was constructed to enhance the accuracy of the sensitivity of quantitative detection. The assay displayed a high efficiency and sensitivity up to 10⁻³. The reproducibility of assay analyzed using follow-up samples showed the standard deviation less than 3.1 %. This assay displayed a complete concordance with sequencing and endonuclease restriction analysis. We have found persistence of DNMT3A R882H mutations in complete remission (CR) after standard cytoreduction therapy that could be indicating presence of DNMT3A mutation in early pre-leukemic stem cells that resist chemotherapy. The loss of correlation between NPM1 and DNMT3A in CR could be associated with evolution of pre-leukemic and leukemic clones. In patients with CR with complete donor chimerism after alloSCT, we have found no DNMT3A R882H. In relapsed patients, all samples showed an increasing of both NPM1 and DNMT3A mutated alleles. This suggests at least in part the presence of NPM1 and DNMT3A mutations in the same cell clone.

Conclusion

We developed a rapid and reliable method for quantitative detection of DNMT3A R882H mutations in AML patients. Quantitative detection of DNMT3A R882H mutations at different time points of AML disease enables screening of follow-up samples. This could provide additional information about the role of DNMT3A mutations in development and progression of AML.

Flow cytometric maturity score as a novel prognostic parameter in patients with acute myeloid leukemia

The European LeukemiaNet (ELN) classification is widely accepted for risk stratification of patients with acute myeloid leukemia (AML). In order to establish immunophenotypic features that predict prognosis, the expression of single AML blast cell antigens has been evaluated with partly conflicting results; however, the influence of immunophenotypic blast maturity is largely unknown. In our study, 300 AML patients diagnosed at our institution between January 2003 and April 2012 were analyzed. A flow cytometric maturity score was developed in order to distinguish "mature" AML (AML-ma) from "immature" AML (AML-im) by quantitative expression levels of early progenitor cell antigens (CD34, CD117, and TdT). AML-ma showed significantly longer relapse-free survival (RFS) and overall survival (OS) than AML-im (p < 0.001). Interestingly, statistically significant differences in RFS and OS were maintained within the "intermediate-risk" group according to ELN (RFS, 7.0 years (AML-ma) vs. 3.3 years (AML-im); p = 0.002; OS, 5.1 years (AML-ma) vs. 3.0 years (AML-im); p = 0.022). Our novel flow cytometric score easily determines AML blast maturity and can predict clinical outcome. It remains to be clarified whether these results simply reflect an accumulation of favorable molecular phenotypes in the AML-ma subgroup or whether they rely on biological differences such as a higher proportion of leukemia stem cells and/or a higher degree of genetic instability within the AML-im subgroup.

Allogeneic stem cell transplantation for refractory acute myeloid leukemia: a single center analysis of long-term outcome

For patients with refractory acute myeloid leukemia (AML), allogeneic stem cell transplantation (alloSCT) represents the only curative approach. We here analyzed the long-term outcome of 131 consecutive patients with active AML, which was either primary refractory or unresponsive to salvage chemotherapy, transplanted at our center between 1997 and 2013. After a median follow-up of 48 months for the surviving patients, disease-free survival (DFS) at 5 yr post alloSCT was 26% (94% CI: 17-35). Relapses, most of which occurred within the first 2 yr from transplant, were the predominant cause of treatment failure affecting 48% (95%CI: 40-58) of patients, whereas non-relapse mortality was 26% (95%CI: 20-36) at 5 yr and thereafter. A marrow blast count ≥20% before alloSCT was an independent prognosticator associated with an inferior DFS (HR: 1.58, P = 0.027), whereas the development of chronic graft-versus-host disease (cGvHD) predicted an improved DFS (HR 0.21, P < 0.001) and a decreased relapse incidence (HR: 0.18, P = 0.026), respectively. These results indicate that alloSCT represents a curative treatment option in a substantial proportion of patients with refractory AML. A pretransplant blast count <20% before alloSCT and the development of cGvHD are the most important predictors of long-term disease control.

Up-regulated MSI2 is associated with more aggressive chronic myeloid leukemia

A better understanding of events triggering chronic myeloid leukemia progression is critical for optimized clinical management of chronic myeloid leukemia (CML). We sought to validate that increased expression of Musashi 2 (MSI2), a post-transcription regulator, is associated with progression and prognosis. Screening of 152 patients with CML showed that MSI2 was significantly decreased among patients with CML in chronic phase (CP) at diagnosis (p < 0.0001), but found no significant difference between the normal control group and treated patients with CML in CP. Moreover MSI2 was significantly increased (p < 0.0001) in patients with advance disease (AD) CML. Furthermore, our human hematopoietic cell line data imply that MSI2 and BCR-ABL1 mRNA expression are correlated. However, these data cast a doubt on earlier reports that MSI2 effects HES1 expression via NUMB-NOTCH signaling.

BCR-ABL1(+) acute myeloid leukemia: clonal selection of a BCR-ABL1(-) subclone as a cause of refractory disease with nilotinib treatment

The presence of a Philadelphia chromosome with a corresponding BCR-ABL1 rearrangement is the hallmark of chronic myeloid leukemia, but is considered a very rare event in de novo acute myeloid leukemia (AML). Here, we report the first case in which a dominant Philadelphia chromosome-positive subclone was detected upon relapse in a formerly Philadelphia chromosome-negative MLL-AF6(+) AML. Due to refractory disease under salvage chemotherapy, the patient was started on nilotinib treatment. As a result, the Philadelphia chromosome-positive subclone was eradicated within 1 month; however, disease progressed and was again dominated by the Philadelphia chromosome-negative founding clone, demonstrating rapid clonal expansion under nilotinib-induced selection pressure.

Impact of early remission by induction therapy on allogeneic stem cell transplantation for acute myeloid leukemia with an intermediate-risk karyotype in first complete remission

For patients with acute myeloid leukemia (AML) early achievement of remission during induction treatment is an important predictor for long-term outcome irrespective of the type of consolidation therapy employed. Here, we retrospectively examined the prognostic impact of early remission (ER) vs. delayed remission (DR) in a cohort of 132 AML patients with an intermediate-risk karyotype undergoing allogeneic stem cell transplantation (alloSCT) in first complete remission (CR1). In contrast to patients showing DR, patients achieving ER had a significantly higher 3-yr overall survival (OS) and disease-free survival (DFS) of 76% vs. 54% (P = 0.03) and 76% vs. 53% (P = 0.03). Likewise, 3 yr after alloSCT the cumulative incidence of relapse (CI-R) was significantly lower in the ER subgroup as compared to patients achieving DR, that is, 10% vs. 35% (P = 0.004), whereas non-relapse mortality (NRM) did not differ significantly. Multivariate analysis identified DR as an independent prognosticator for an inferior DFS (HR 3.37, P = 0.002) and a higher CI-R (HR 3.55, P = 0.002). Taken together, these data may indicate that the rapid achievement of remission predicts a favorable outcome in patients with intermediate-risk AML undergoing alloSCT in CR1. In turn, the adverse effect of DR may not be fully overcome by alloSCT.

Gene expression profiling of peripheral blood mononuclear cells during treatment with a gene-modified allogeneic tumor cell vaccine in advanced renal cell cancer: tumor-induced immunosuppression and a possible role for NF-κB

Tumor-induced immunosuppression remains a major challenge for immunotherapy of cancer patients. To further elucidate why an allogeneic gene-modified [interleukin-7 (IL-7)/CD80-cotransfected] renal cell cancer (RCC) vaccine failed to induce clinically relevant TH-1-polarized immune responses, peripheral blood mononuclear cells from enrolled study patients were analyzed by gene expression profiling (GEP) both prior and after vaccination. At baseline before vaccination, a profound downregulation of gene signatures associated with antigen presentation, immune response/T cells, cytokines/chemokines and signaling/transcription factors was observed in RCC patients as compared to healthy controls. Vaccination led to a partial reversion of preexisting immunosuppression, however, GEP indicated that an appropriate TH-1 polarization could not be achieved. Most interestingly, our results suggest that the nuclear factor-kappa B signaling pathway might be involved in the impairment of immunological responsiveness and the observed TH-2 deviation. In summary, our data suggest that GEP might be a powerful tool for the prediction of immunosuppression and the monitoring of immune responses within immunotherapy trials.

Dendritic cell-mediated survival signals in Eμ-Myc B-cell lymphoma depend on the transcription factor C/EBPβ

The capacity of dendritic cells (DCs) to regulate tumour-specific adaptive immune responses depends on their proper differentiation and homing status. Whereas DC-associated tumour-promoting functions are linked to T-cell tolerance and formation of an inflammatory milieu, DC-mediated direct effects on tumour growth have remained unexplored. Here we show that deletion of DCs substantially delays progression of Myc-driven lymphomas. Lymphoma-exposed DCs upregulate immunomodulatory cytokines, growth factors and the CCAAT/enhancer-binding protein β (C/EBPβ). Moreover, Eμ-Myc lymphomas induce the preferential translation of the LAP/LAP* isoforms of C/EBPβ. C/EBPβ(-/-) DCs are unresponsive to lymphoma-associated cytokine changes and in contrast to wild-type DCs, they are unable to mediate enhanced Eμ-Myc lymphoma cell survival. Antigen-specific T-cell proliferation in lymphoma-bearing mice is impaired; however, this immune suppression is reverted by the DC-restricted deletion of C/EBPβ. Thus, we show that C/EBPβ-controlled DC functions are critical steps for the creation of a lymphoma growth-promoting and -immunosuppressive niche.

Access to follicular dendritic cells is a pivotal step in murine chronic lymphocytic leukemia B-cell activation and proliferation

In human chronic lymphocytic leukemia (CLL) pathogenesis, B-cell antigen receptor signaling seems important for leukemia B-cell ontogeny, whereas the microenvironment influences B-cell activation, tumor cell lodging, and provision of antigenic stimuli. Using the murine Eμ-Tcl1 CLL model, we demonstrate that CXCR5-controlled access to follicular dendritic cells confers proliferative stimuli to leukemia B cells. Intravital imaging revealed a marginal zone B cell-like leukemia cell trafficking route. Murine and human CLL cells reciprocally stimulated resident mesenchymal stromal cells through lymphotoxin-β-receptor activation, resulting in CXCL13 secretion and stromal compartment remodeling. Inhibition of lymphotoxin/lymphotoxin-β-receptor signaling or of CXCR5 signaling retards leukemia progression. Thus, CXCR5 activity links tumor cell homing, shaping a survival niche, and access to localized proliferation stimuli.

SIGNIFICANCE

CLL and other indolent lymphoma are not curable and usually relapse after treatment, a process in which the tumor microenvironment plays a pivotal role. We dissect the consecutive steps of CXCR5-dependent tumor cell lodging and LTβR-dependent stroma-leukemia cell interaction; moreover, we provide therapeutic solutions to interfere with this reciprocal tumor-stroma cross-talk.

Transformation and additional malignancies are leading risk factors for an adverse course of disease in marginal zone lymphoma

BACKGROUND

Marginal zone lymphoma (MZL) is a non-Hodgkin lymphoma that occurs as extra nodal, nodal, or splenic. While MZL is generally considered an indolent disease, a substantial percentage of patients follow an unfavorable course. The objective of this retrospective analysis was to identify predictors for a reduced overall survival (OS), or conversely an increased OS.

PATIENTS AND METHODS

One hundred and ninety-seven MZL patients were analyzed. Apart from assessing previously published risk factors, concomitant morbidity at diagnosis, transformation into aggressive lymphoma, and occurrence of additional malignancies were evaluated.

RESULTS

Next to the known risk factors, i.e. above 60 years of age and elevated serum lactate dehydrogenase (LDH), we demonstrate that transformation into aggressive lymphoma, as well as additional malignancies, are important independent risk factors for a shortened OS in a multivariate analysis, irrespective of the MZL localization. Impressively, in the group of patients lacking LDH elevation, transformation, and/or additional malignancies, only 1 of 63 patients died during follow-up compared with 37 of 87 patients in the high-risk group (HR = 22.8; 95% confidence interval 3.1-167.0; P = 0.002).

CONCLUSIONS

Our analysis proposes novel risk factors and warrants for a continuous follow-up to detect the occurrence of transformation and additional malignancies early on.

Second-line oxaliplatin, folinic acid, and fluorouracil versus folinic acid and fluorouracil alone for gemcitabine-refractory pancreatic cancer: outcomes from the CONKO-003 trial

PURPOSE

To assess the efficacy of a second-line regimen of oxaliplatin and folinic acid-modulated fluorouracil in patients with advanced pancreatic cancer who have experienced progression while receiving gemcitabine monotherapy.

PATIENTS AND METHODS

A randomized, open-label, phase III study was conducted in 16 institutions throughout Germany. Recruitment ran from January 2004 until May 2007, and the last follow-up concluded in December 2012. Overall, 168 patients age 18 years or older who experienced disease progression during first-line gemcitabine therapy were randomly assigned to folinic acid and fluorouracil (FF) or oxaliplatin and FF (OFF). Patients were stratified according to the presence of metastases, duration of first-line therapy, and Karnofsky performance status.

RESULTS

Median follow-up was 54.1 months, and 160 patients were eligible for the primary analysis. The median overall survival in the OFF group (5.9 months; 95% CI, 4.1 to 7.4) versus the FF group (3.3 months; 95% CI, 2.7 to 4.0) was significantly improved (hazard ratio [HR], 0.66; 95% CI, 0.48 to 0.91; log-rank P = .010). Time to progression with OFF (2.9 months; 95% CI, 2.4 to 3.2) versus FF (2.0 months; 95% CI, 1.6 to 2.3) was significantly extended also (HR, 0.68; 95% CI, 0.50 to 0.94; log-rank P = .019). Rates of adverse events were similar between treatment arms, with the exception of grades 1 to 2 neurotoxicity, which were reported in 29 patients (38.2%) and six patients (7.1%) in the OFF and FF groups, respectively (P < .001).

CONCLUSION

Second-line OFF significantly extended the duration of overall survival when compared with FF alone in patients with advanced gemcitabine-refractory pancreatic cancer.

Notch pathway inhibition controls myeloma bone disease in the murine MOPC315.BM model

Despite evidence that deregulated Notch signalling is a master regulator of multiple myeloma (MM) pathogenesis, its contribution to myeloma bone disease remains to be resolved. Notch promotes survival of human MM cells and triggers human osteoclast activity in vitro. Here, we show that inhibition of Notch through the γ-secretase inhibitor XII (GSI XII) induces apoptosis of murine MOPC315.BM myeloma cells with high Notch activity. GSI XII impairs murine osteoclast differentiation of receptor activator of NF-κB ligand (RANKL)-stimulated RAW264.7 cells in vitro. In the murine MOPC315.BM myeloma model GSI XII has potent anti-MM activity and reduces osteolytic lesions as evidenced by diminished myeloma-specific monoclonal immunoglobulin (Ig)-A serum levels and quantitative assessment of bone structure changes via high-resolution microcomputed tomography scans. Thus, we suggest that Notch inhibition through GSI XII controls myeloma bone disease mainly by targeting Notch in MM cells and possibly in osteoclasts in their microenvironment. We conclude that Notch inhibition is a valid therapeutic strategy in MM.