A p53 score derived from TP53 CRISPR/Cas9 HMCLs predicts survival and reveals major role of BAX in BH3 mimetics response

To establish a strict p53-dependent gene expression profile, TP53-/- clones were derived from TP53+/+ and TP53-/mut t(4;14) human myeloma cell lines (HMCLs) using CRISPR/Cas9 technology. From the 17 dysregulated genes shared between the TP53-/- clones from TP53+/+ HMCLs, we established a functional p53 score, involving 13 genes specifically downregulated upon p53 silencing. This functional score segregated clones and myeloma cell lines, as well as other cancer cell lines according to their TP53 status. The score was efficient to identify myeloma patient samples with biallelic TP53 inactivation and was predictive of overall survival in MMRF-coMMpass and CASSIOPEA cohorts. At the functional level, we showed that among the 13 genes, p53-regulated BAX expression correlated to, and directly impacted, the MCL1 BH3 mimetic S63845 sensitivity of myeloma cells by decreasing MCL1-BAX complexes. However, resistance to S63845 was overcome by combining MCL1 and BCL2 BH3 mimetics which displayed synergistic efficacy. BH3 mimetics combination was efficient in 97% of patient samples with or without del17p. Nevertheless, scRNAseq analysis showed that myeloma cells surviving to the combination had lower p53 score, showing that myeloma cells with higher p53 score were more sensitive to BH3 mimetics. Taken together, we established a functional p53 score that identifies myeloma cells with biallelic TP53 invalidation, demonstrated that p53-regulated BAX is critical for optimal cell response to BH3 mimetics, and showed that MCL1 and BCL2 BH3 mimetics combination may be of interest for patients with biallelic TP53 invalidation, for whom there is still an unmet medical need.

BCLXL PROTAC degrader DT2216 targets secondary plasma cell leukemia addicted to BCLXL for survival

Secondary plasma cell leukemia (sPCL) is a rare form of aggressive plasma cell malignancy arising mostly at end-stage refractory multiple myeloma and consequently presenting limited therapeutic options. We analyzed 13 sPCL for their sensitivity to BH3 mimetics targeting either BCL2 (venetoclax) or BCLXL (A1155463) and showed that 3 sPCL were efficiently killed by venetoclax and 3 sPCL by A1155463. Accordingly, BH3 profiling of 2 sPCL sensitive to BCLXL inhibition confirmed their high BCLXL primed profile. While targeting BCLXL using BH3 mimetics induces platelets on-target drug toxicity, the recent development of DT2216, a clinical-stage BCLXL proteolysis targeting chimera PROTAC compound, provides an alternative strategy to target BCLXL. Indeed, DT2216 specifically degrades BCLXL via VHL E3 ligase, without inducing thrombocytopenia. We demonstrated in human myeloma cell lines and sPCL that sensitivity to DT2216 strongly correlated with the sensitivity to A1155463. Interestingly, we showed that low doses of DT2216 (nM range) were sufficient to specifically degrade BCLXL after 48 hours of treatment, consistent with VHL expression, in all cell lines but irrespectively to DT2216 sensitivity. In myeloma cells, DT2216 induced apoptotic cell death and triggered BAX and BAK activation. In conclusion, our study demonstrated that patients with sPCL addicted to BCLXL, a small but a very challenging group, could potentially receive therapeutic benefit from DT2216. Clinical trials of DT2216 in this subset of sPCL patients are warranted.

Restoring Apoptosis with BH3 Mimetics in Mature B-Cell Malignancies

Apoptosis is a highly conserved mechanism enabling the removal of unwanted cells. Mitochondrial apoptosis is governed by the B-cell lymphoma (BCL-2) family, including anti-apoptotic and pro-apoptotic proteins. Apoptosis evasion by dysregulation of anti-apoptotic BCL-2 members (BCL-2, MCL-1, BCL-XL) is a common hallmark in cancers. To divert this dysregulation into vulnerability, researchers have developed BH3 mimetics, which are small molecules that restore effective apoptosis in neoplastic cells by interfering with anti-apoptotic proteins. Among them, venetoclax is a potent and selective BCL-2 inhibitor, which has demonstrated the strongest clinical activity in mature B-cell malignancies, including chronic lymphoid leukemia, mantle-cell lymphoma, and multiple myeloma. Nevertheless, mechanisms of primary and acquired resistance have been recently described and several features such as cytogenetic abnormalities, BCL-2 family expression, and ex vivo drug testing have to be considered for predicting sensitivity to BH3 mimetics and helping in the identification of patients able to respond. The medical need to overcome resistance to BH3 mimetics supports the evaluation of innovative combination strategies. Novel agents including MCL-1 targeting BH3 mimetics are currently evaluated and may represent new therapeutic options in the field. The present review summarizes the current knowledge regarding venetoclax and other BH3 mimetics for the treatment of mature B-cell malignancies.

Interactions between cancer-associated fibroblasts and tumor cells promote MCL-1 dependency in estrogen receptor-positive breast cancers

Selective inhibition of BCL-2 is expected to enhance therapeutic vulnerability in luminal estrogen receptor-positive breast cancers. We show here that the BCL-2 dependency of luminal tumor cells is nevertheless mitigated by breast cancer-associated fibroblasts (bCAFs) in a manner that defines MCL-1 as another critical therapeutic target. bCAFs favor MCL-1 expression and apoptotic resistance in luminal cancer cells in a IL-6 dependent manner while their own, robust, survival also relies on MCL-1. Studies based on ex vivo cultures of human luminal breast cancer tissues further argue that the contribution of stroma-derived signals to MCL-1 expression shapes BCL-2 dependency. Thus, MCL-1 inhibitors are beneficial for targeted apoptosis of breast tumor ecosystems, even in a subtype where MCL-1 dependency is not intrinsically driven by oncogenic pathways.

BCL2-Family Dysregulation in B-Cell Malignancies: From Gene Expression Regulation to a Targeted Therapy Biomarker

BCL2-family proteins have a central role in the mitochondrial apoptosis machinery and their expression is known to be deregulated in many cancer types. Effort in the development of small molecules that selectively target anti-apoptotic members of this family i.e., Bcl-2, Bcl-xL, Mcl-1 recently opened novel therapeutic opportunities. Among these apoptosis-inducing agents, BH3-mimetics (i.e., venetoclax) led to promising preclinical and clinical activity in B cell malignancies. However, several mechanisms of intrinsic or acquired resistance have been described ex vivo therefore predictive markers of response as well as mechanism-based combinations have to be designed. In the present study, we analyzed the expression of the BCL2-family genes across 10 mature B cell malignancies through computational normalization of 21 publicly available Affimetrix datasets gathering 1,219 patient samples. To better understand the deregulation of anti- and pro-apoptotic members of the BCL2-family in hematological disorders, we first compared gene expression profiles of malignant B cells to their relative normal control (naïve B cell to plasma cells, n = 37). We further assessed BCL2-family expression according to tissue localization i.e., peripheral blood, bone marrow, and lymph node, molecular subgroups or disease status i.e., indolent to aggressive. Across all cancer types, we showed that anti-apoptotic genes are upregulated while pro-apoptotic genes are downregulated when compared to normal counterpart cells. Of interest, our analysis highlighted that, independently of the nature of malignant B cells, the pro-apoptotic BH3-only BCL2L11 and PMAIP1 are deeply repressed in tumor niches, suggesting a central role of the microenvironment in their regulation. In addition, we showed selective modulations across molecular subgroups and showed that the BCL2-family expression profile was related to tumor aggressiveness. Finally, by integrating recent data on venetoclax-monotherapy clinical activity with the expression of BCL2-family members involved in the venetoclax response, we determined that the ratio (BCL2+BCL2L11+BAX)/BCL2L1 was the strongest predictor of venetoclax response for mature B cell malignancies in vivo.

Whole-exon sequencing of human myeloma cell lines shows mutations related to myeloma patients at relapse with major hits in the DNA regulation and repair pathways

Background

Human myeloma cell lines (HMCLs) are widely used for their representation of primary myeloma cells because they cover patient diversity, although not fully. Their genetic background is mostly undiscovered, and no comprehensive study has ever been conducted in order to reveal those details.

Methods

We performed whole-exon sequencing of 33 HMCLs, which were established over the last 50 years in 12 laboratories. Gene expression profiling and drug testing for the 33 HMCLs are also provided and correlated to exon-sequencing findings.

Results

Missense mutations were the most frequent hits in genes (92%). HMCLs harbored between 307 and 916 mutations per sample, with TP53 being the most mutated gene (67%). Recurrent bi-allelic losses were found in genes involved in cell cycle regulation (RB1, CDKN2C), the NFκB pathway (TRAF3, BIRC2), and the p53 pathway (TP53, CDKN2A). Frequency of mutations/deletions in HMCLs were either similar to that of patients (e.g., DIS3, PRDM1, KRAS) or highly increased (e.g., TP53, CDKN2C, NRAS, PRKD2). MAPK was the most altered pathway (82% of HMCLs), mainly by RAS mutants. Surprisingly, HMCLs displayed alterations in epigenetic (73%) and Fanconi anemia (54%) and few alterations in apoptotic machinery. We further identified mutually exclusive and associated mutations/deletions in genes involved in the MAPK and p53 pathways as well as in chromatin regulator/modifier genes. Finally, by combining the gene expression profile, gene mutation, gene deletion, and drug response, we demonstrated that several targeted drugs overcome or bypass some mutations.

Conclusions

With this work, we retrieved genomic alterations of HMCLs, highlighting that they display numerous and unprecedented abnormalities, especially in DNA regulation and repair pathways. Furthermore, we demonstrate that HMCLs are a reliable model for drug screening for refractory patients at diagnosis or at relapse.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0679-0) contains supplementary material, which is available to authorized users.

Repression of Mcl-1 and disruption of the Mcl-1/Bak interaction in myeloma cells couple ER stress to mitochondrial apoptosis

As myeloma cells actively produce and secrete immunoglobulins, they are prone to ER stress, which if unresolved leads to apoptosis. We found that myeloma cell death induced by the ER stressor Thapsigargin was highly variable, ranging from 2 to 89%. Induction of ATF4 and CHOP was observed in myeloma cells under Thapsigargin independently of cell death. The decrease in Mcl-1 was associated with protein translation inhibition and identified as a crucial factor in Thapsigargin sensitivity, since it was the only Bcl-2 family protein differentially modified between sensitive and resistant myeloma cells. Bak but not Bax was found to contribute to Thapsigargin-induced apoptosis. Appropriately, a basal Mcl-1/Bak interaction was demonstrated in Thapsigargin-sensitive cells. Of note, the only pro-apoptotic protein freed from Mcl-1 under Thapsigargin was Bak, whereas Mcl-1/Noxa or Mcl-1/Bim complexes were simultaneously increased. Thus, the disruption of the basal Mcl-1/Bak complex in Thapsigargin-sensitive cells seemed to be an essential event in cell death induction, probably favored by the induced Noxa and Bim BH3-only proteins. These findings underscore the implication of the Mcl-1/Bak axis in myeloma cell death triggered by Thapsigargin.

BCL-B (BCL2L10) is overexpressed in patients suffering from multiple myeloma (MM) and drives an MM-like disease in transgenic mice

Luciano et al. generate transgenic mice expressing the Bcl-B gene under the control of the VH promoter and Eµ enhancer and show that these mice recapitulate the characteristic features of human MM.

Multiple myeloma (MM) evolves from a premalignant condition known as monoclonal gammopathy of undetermined significance (MGUS). However, the factors underlying the malignant transformation of plasmocytes in MM are not fully characterized. We report here that Eµ-directed expression of the antiapoptotic Bcl-B protein in mice drives an MM phenotype that reproduces accurately the human disease. Indeed, with age, Eµ-bcl-b transgenic mice develop the characteristic features of human MM, including bone malignant plasma cell infiltration, a monoclonal immunoglobulin peak, immunoglobulin deposit in renal tubules, and highly characteristic bone lytic lesions. In addition, the tumors are serially transplantable in irradiated wild-type mice, underlying the tumoral origin of the disease. Eµ-bcl-b plasmocytes show increased expression of a panel of genes known to be dysregulated in human MM pathogenesis. Treatment of Eµ-bcl-b mice with drugs currently used to treat patients such as melphalan and VELCADE efficiently kills malignant plasmocytes in vivo. Finally, we find that Bcl-B is overexpressed in plasmocytes from MM patients but neither in MGUS patients nor in healthy individuals, suggesting that Bcl-B may drive MM. These findings suggest that Bcl-B could be an important factor in MM disease and pinpoint Eµ-bcl-b mice as a pertinent model to validate new therapies in MM.

Curcumin induces cell death of the main molecular myeloma subtypes, particularly the poor prognosis subgroups

Multiple myeloma (MM), a plasma cell malignancy, remains incurable despite the development of new therapies. Curcumin anti-tumor effects were previously characterized in multiple myeloma, however only few MM cell lines were included in these studies. Since myeloma is a heterogeneous disease it is important to address the impact of myeloma molecular heterogeneity in curcumin cell death induction. In the present study, a large panel of human myeloma cell lines (HMCLs) (n = 29), representing the main molecular MM subgroups, was screened for curcumin sensitivity. We observed that curcumin cell death induction was heterogeneous, of note 16 HMCLs were highly sensitive to curcumin (LD₅₀ < 20.5 μM), 6 HMCLs exhibited intermediate LD₅₀ values (20.5 μM ≤ LD₅₀ < 32.2 μM) and only 7 HMCLs were weakly sensitive (35 < LD₅₀ < 56 μM). Cell lines harboring the t(11;14) translocation were less sensitive (median LD50 32.9 μM) than non-t(11;14) (median LD50 17.9 μM), which included poor prognosis t(4;14) and t(14;16) cells. Interestingly, curcumin sensitivity was not dependent on TP53 status. For the first time we showed that primary myeloma cells were also sensitive, even those displaying del(17p), another poor prognosis factor. We also unravel the contribution of anti-apoptotic Bcl-2 family molecules in curcumin response. We found that down-regulation of Mcl-1, an essential MM survival factor, was associated with curcumin-induced cell death and its knockdown sensitized myeloma cells to curcumin, highlighting Mcl-1 as an important target for curcumin-induced apoptosis. Altogether, these results support clinical trials including curcumin in association with standard therapy.

Abstract B16: The pro-apoptotic effect of dexamethasone mediated by GILZ and Bim up-regulation is related to genetic heterogeneity of multiple myeloma

Multiple myeloma (MM) is heterogeneous with respect to its causative molecular abnormalities and the treatment response of patients. Briefly, MM that are hyperdiploid or have a t(11;14) translocation have a better prognosis than those with t(4;14) or t(14;16) translocations. Dexamethasone (Dex) is widely used in all phases of MM treatment as induction, consolidation or maintenance. However, the mechanism of Dex sensitivity still remains elusive.

In the present study, we analyzed the ability of Dex to induce cell death by Apo-2.7 staining in 33 human myeloma cell lines (HMCLs) representative of the molecular subsets carrying t(11;14), t(4;14) or t(14;16) translocations, which deregulate CCND1, MMSET and c-MAF, respectively. The mechanisms controlling Dex-induced apoptosis were evaluated by analyzing glucocorticoid receptor (GR), glucocorticoid-induced leucin zipper (GILZ) and Bcl-2 protein family expression in the different MM molecular subtypes. Transient knock-down of glucocorticoid-responsive proteins were performed to define their role in the pro-apoptotic effect of Dex.

We first demonstrated that direct pro-apoptotic effect of Dex was related to the genetic heterogeneity of MM, since sensitive cell lines were restricted to t(14;16) and t(4;14) subgroups. We next demonstrated by transcriptomic Affymetrix analysis that GR expression was heterogeneous among the different molecular subtypes of HMCLs. MAF subgroup significantly expressed higher levels of GR than all other subgroups (p=0.02). This result was also confirmed on 300 newly diagnosed MM patients (p&lt;.0001). We also demonstrated that Dex sensitivity was associated with its ability to down-regulate MAF protein level and its well-known target CCND2. This result was in agreement with the fact that elevated levels of MAF were associated not only with t(14;16) translocation but also with MMSET over-expression, which is a characteristic of t(4;14) subgroup. We next demonstrated that Dex induced an up-regulation of GILZ, a glucocorticoid-responsive molecule, in dex-sensitive and insensitive HMCLs. Nevertheless, resistant HMCLs, which expressed low levels of GR, failed to up-regulate GILZ to the same extent than sensitive HMCLs, suggesting that GR levels could be an important limiting factor for GILZ up-regulation. Of note, GILZ silencing induced a strong reduction of Dex-induced cell death. These results suggest that transactivation has a pivotal role in the induction of cell death by Dex in myeloma cells. Dex also induced an up-regulation of Bim isoforms and a down-regulation of Bcl-xL in all sensitive cell lines. We further demonstrated that Bim up-regulation is required for the apoptotic program in response to Dex. Finally, the silencing of GILZ impaired the up-regulation of Bim and the down-regulation of Bcl-xL under Dex treatment.

In conclusion, Dex exerted a direct anti-tumor effect on HMCLs of t(14;16) and t(4;14) molecular subgroups while t(11;14) subgroup was insensitive to it. This result suggested that conventional therapeutic approaches should be re-evaluated within molecular subgroups of MM patients to favor potential molecular subtype therapy based on rational preclinical data. Finally, while Dex interferes with multiple pathways, we begin to unravel its complex mechanism of action demonstrating that transactivation, inducing GILZ up-regulation, plays a pivotal role in Dex induced cell death through the regulation of the Bcl-2 protein network.

Citation Format: Charlotte Kervoëlen, Emmanuelle Ménoret, Patricia Gomez-Bougie, Régis Bataille, Philippe Moreau, Catherine Pellat-Deceunynck, Martine Amiot. The pro-apoptotic effect of dexamethasone mediated by GILZ and Bim up-regulation is related to genetic heterogeneity of multiple myeloma. [abstract]. In: Proceedings of the AACR Special Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(17 Suppl):Abstract nr B16.

RITA (Reactivating p53 and Inducing Tumor Apoptosis) is efficient against TP53abnormal myeloma cells independently of the p53 pathway

Background

The aim of this study was to evaluate the efficacy of the p53-reactivating drugs RITA and nutlin3a in killing myeloma cells.

Methods

A large cohort of myeloma cell lines (n = 32) and primary cells (n = 21) was used for this study. This cohort contained cell lines with various TP53 statuses and primary cells with various incidences of deletion of chromosome 17. Apoptosis was evaluated using flow cytometry with Apo2.7 staining of the cell lines or via the loss of the myeloma-specific marker CD138 in primary cells. Apoptosis was further confirmed by the appearance of a subG1 peak and the activation of caspases 3 and 9. Activation of the p53 pathway was monitored using immunoblotting via the expression of the p53 target genes p21, Noxa, Bax and DR5. The involvement of p53 was further studied in 4 different p53-silenced cell lines.

Results

Both drugs induced the apoptosis of myeloma cells. The apoptosis that was induced by RITA was not related to the TP53 status of the cell lines or the del17p status of the primary samples (p = 0.52 and p = 0.80, respectively), and RITA did not commonly increase the expression level of p53 or p53 targets (Noxa, p21, Bax or DR5) in sensitive cells. Moreover, silencing of p53 in two TP53^mutated cell lines failed to inhibit apoptosis that was induced by RITA, which confirmed that RITA-induced apoptosis in myeloma cells was p53 independent. In contrast, apoptosis induced by nutlin3a was directly linked to the TP53 status of the cell lines and primary samples (p < 0.001 and p = 0.034, respectively) and nutlin3a increased the level of p53 and p53 targets in a p53-dependent manner. Finally, we showed that a nutlin3a-induced DR5 increase (≥1.2-fold increase) was a specific and sensitive marker (p < 0.001) for a weak incidence of 17p deletion within the samples (≤19%).

Conclusion

These data show that RITA, in contrast to nutlin3a, effectively induced apoptosis in a subset of MM cells independently of p53. The findings and could be of interest for patients with a 17p deletion, who are resistant to current therapies.

Apoptotic machinery diversity in multiple myeloma molecular subtypes

Multiple myeloma (MM) is a plasma-cell (PC) malignancy that is heterogeneous in its clinical presentation and prognosis. Monoclonal gammopathy of undetermined significance (MGUS) consistently preceded development of MM. The presence of primary IgH translocations and the universal overexpression of cyclin D genes led to a molecular classification of MM patients into different disease subtypes. Since Bcl-2 family proteins determine cell fate, we analyzed a publicly available Affymetrix gene expression of 44 MGUS and 414 newly diagnosed MM patients to investigate (1) the global change of Bcl-2 family members in MM versus MGUS (2) whether the four major subtypes defined as hyperdiploid, CyclinD1, MAF, and MMSET, display specific apoptotic machineries. We showed that among the main anti-apoptotic members (Bcl-2, Bcl-x_L, and Mcl-1), Mcl-1 up-regulation discriminated MM from MGUS, in agreement with the prominent role of Mcl-1 in PC differentiation. Surprisingly, the expression of multi-domain pro-apoptotic Bak and Bax were increased during the progression of MGUS to MM. The combined profile of Bcl-2, Bcl-x_L, and Mcl-1 was sufficient to distinguish MM molecular groups. While specific pro-apoptotic members expression was observed for each MM subtypes, CyclinD1 subgroup, was identified as a particular entity characterized by a low expression of BH3-only (Puma, Bik, and Bad) and multi-domain pro-apoptotic members (Bax and Bak). Our analysis supports the notion that MM heterogeneity is extended to the differential expression of the Bcl-2 family content in each MM subgroup. The influence of Bcl-2 family profile in the survival of the different patient groups will be further discussed to establish the potential consequences for therapeutic interventions. Finally, the use of distinct pro-survival members in the different steps of immune responses to antigen raises also the question of whether the different Bcl-2 anti-apoptotic profile could reflect a different origin of MM cells.

Abstract C48: Dual targeting of myeloma cells by 2-deoxy-D-glucose and ABT-199 combination respectively through the down-regulation of Mcl-1 and binding to Bcl-2

Multiple myeloma (MM) is a heterogeneous but incurable plasma cell malignancy which still requires new therapeutic approaches. Several molecular subsets of MM have been defined based on genetic and chromosomal aberrations. Briefly, t(4;14) or t(14;16) translocations and TP53 deletion are most frequent poor-risk genetic features of MM, while t(11;14) confers a neutral prognostic value. Because cancer cells have a high glycolytic metabolism, we investigated the efficiency of 2-deoxy-d-glucose (2-DG), a competitive inhibitor of hexokinase, to kill myeloma cells. For this purpose we used 28 human myeloma cell lines (HMCL) representative of these different molecular subsets. Cell death induced by 2-DG was assessed by Apo-2.7 staining. Investigation of the underlying apoptotic mechanisms was evaluated by analyzing, by western blotting, modulation of the UPR response and implication of the Bcl-2 protein family. Finally, the possibly synergistic effect of the combination of 2-DG and ABT-199 was investigated.

Cell death induced by 2DG was very heterogeneous among HMCLs, ranging from 5% to 96%. Of note, HMCLs carrying t(4;14) showed a trend to be more sensitive to 2DG (p=0.06) while HMCLs carrying t(11;14) appeared to be more resistant (p=0.08). Interestingly, 2-DG not only strongly inhibited the glycolytic activity of HMCLs but also interfered with N-glycosylation. Indeed, addition of D-mannose, an N-linked glycosylation precursor, partly reversed 2-DG-induced cell death. However, the D-mannose efficiency was also heterogeneous among HMCLs, suggesting that the inhibition of N-glycosylation was not the only mechanism of 2-DG-induced cell death.

An up-regulation of GRP78, CHOP and ATF-4 expression was induced by 2-DG in both sensitive and resistant HMCLs, suggesting that 2DG-induced cell death was independent from the UPR response. Finally, 2-DG uniformly induced Mcl-1 down-regulation in HMCLs, but only those dependent on Mcl-1 for survival were killed by 2-DG. Preliminary results indicate that proteosomal degradation could be involved as part of a more complex mechanism. Of note, most of t(11;14) HMCLs were resistant to Mcl-1 down-regulation but highly sensitive to ABT-199, which targets Bcl-2 and efficiently kills t(11;14) HCMLs depending on this pathway for survival. Because 2-DG uniformly down-regulated Mcl-1, we combined it with ABT-199 in ABT-199-resistant HMCLs i.e., in HMCLs expressing a Bcl-2/Mcl-1 gene expression ratio lower to the threshold required for ABT-199 response. The combination of 2-DG and suboptimal ABT-199 dosage indeed strongly synergized in both t(4;14) and t(14;16) HMCLs.

This study highlights the fact that dual targeting of Mcl-1 by 2-DG and Bcl-2 by ABT-199, in MM cell lines or primary samples, is highly efficient to induce apoptosis whatever the molecular subtype, including those with the poorest prognostic value. ABT-199 is presently under evaluation in a phase I clinical trial in relapsed MM patients and the present study provides a biological rationale for evaluating 2-DG in combination with ABT-199 in MM patients.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C48.

Citation Format: Maxime Halliez, Sophie Maïga, Cyrille Touzeau, Patricia Gomez-Bougie, Steven Le Gouill, Catherine Pellat-Deceunynck, Martine Amiot. Dual targeting of myeloma cells by 2-deoxy-D-glucose and ABT-199 combination respectively through the down-regulation of Mcl-1 and binding to Bcl-2. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C48.

Abstract C28: Dexamethasone-induced apoptosis in multiple myeloma cells is restricted to t(14;16) and t(4;14) molecular subgroups due to a combined down-regulation of MAF and an up-regulation of Bim

Multiple myeloma (MM) is heterogeneous with respect to its causative chromosomal abnormalities and the treatment response of patients. Briefly, MM patients with chromosomal hyperdiploidy or those carrying a t(11.14) translocation have a better prognosis than those with a t(4;14) or t(14;16) translocation. Dexamethasone (Dex) is widely used in all phases of the treatment of MM as induction, consolidation or maintenance. However, the mechanisms of sensitivity and resistance to Dex still remain elusive. In the present study, we analyzed the ability of Dex to induce cell death by Apo-2.7 staining in 33 human myeloma cell lines (HMCLs) representative of the molecular subsets i.e., carrying a t(11;14), t(4;14) or t(14;16) translocation, which deregulates the expression of CCND1, MMSET, and c-MAF respectively. The mechanisms controlling Dex-induced apoptosis were evaluated by analyzing the nuclear translocation of glucocorticoid receptor (GR), signalling pathways and modulation of Bcl-2 protein family in the different MM molecular subtypes. We first demonstrated by transcriptomic analysis (Affymetrix) that GR expression was heterogeneous among the different molecular subtypes of HMCLs and patients. Indeed, t(14;16) c-MAF subgroup significantly expressed higher levels of GR than all other subgroups in both HMCLs (Kruskall-Wallis p&lt;.02) and primary MM cells from patients at diagnosis (n=309, Kruskall-Wallis p&lt;.0001). We further demonstrated that the direct pro-apoptotic effect of Dex was related to the genetic heterogeneity of MM, since sensitive HMCLs were restricted to t(14;16) and t(4;14) subgroups. Dex-induced apoptosis was associated with caspase 6 and 3 activation. We next demonstrated that Dex sensitivity depended on its ability to induce the down-regulation of c-MAF protein, which led to a decrease in CCND2 expression, a well-known target gene of c-MAF. The down-regulation of c-MAF mainly occurred by the increase of its proteasomal degradation. Altogether, these results were in agreement with the elevated levels of c-MAF found not only in t(14;16) translocated primary cells and HMCLs but also in t(4;14) translocated cells and HMCLs. While Bim expression (all isoforms) was up-regulated in most of cell lines by Dex irrespectively of its capacity to induce apoptosis, we demonstrated by Bim silencing that its up-regulation was required for initiating Dex-induced apoptotic program. Of note, by a long-term culture in the presence of low doses of Dex, we generated a Dex-resistant t(14;16) which was characterized by a decreased expression of GR. Dex treatment of this Dex-resistant HMCL neither induced any down-regulation of c-MAF nor any up-regulation of Bim, showing that a minimal expression level of GR was the first limiting step to induce a death response. In the present study, we demonstrated that Dex exerted a direct anti-tumor effect on myeloma cells from t(14;16) and t(4;14) molecular subgroups by controlling c-MAF level while those belonging to the t(11;14) subgroup were insensitive to Dex. This result highlights the fact that conventional therapeutic approaches could be re-evaluated in concert with the definition of molecular subgroups of MM patients to favor molecular subtype-specific therapy based on rational preclinical data.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C28.

Citation Format: Charlotte Kervoëlen, Emmanuelle Ménoret, Patricia Gomez-Bougie, Régis Bataille, Catherine Pellat-Deceunynck, Martine Amiot. Dexamethasone-induced apoptosis in multiple myeloma cells is restricted to t(14;16) and t(4;14) molecular subgroups due to a combined down-regulation of MAF and an up-regulation of Bim. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C28.

Paradoxical effect of lenalidomide on cytokine/growth factor profiles in multiple myeloma

Background:

Lenalidomide is an active immunomodulatory and antiproliferative agent in multiple myeloma. However, the molecular mechanisms driving these activities are not yet fully elucidated. Therefore, we investigated the modulation of the cytokine/growth factor patterns of myeloma cells under LEN treatment.

Methods:

Lenalidomide effect on myeloma cell proliferation was investigated in a myeloma cell line collection (n=23) by ³H-thymidine incorporation. Modulation of the cytokine/growth factor patterns of myeloma cells under LEN treatment was analysed by real-time quantitative PCR.

Results:

Lenalidomide inhibits the proliferation of two-thirds of myeloma cell lines independently of their genetic background. We demonstrated that LEN increased TNF-α and IL-8 inflammatory cytokines and insulin-like growth factor-1 (IGF-1) growth factor in both sensitive and resistant myeloma cells to LEN.

Conclusion:

Lenalidomide favours a uniform TNF-α and IL-8 inflammatory and IGF-1 secretory profile of myeloma cells, an observation that raises important questions for therapeutic approaches incorporating the agent.

Cell death via DR5, but not DR4, is regulated by p53 in myeloma cells

Myeloma cells are sensitive to TRAIL through the two death receptors DR4 and DR5. Because p53 directly modulates expression of death receptors, we investigated here whether p53 can modulate myeloma sensitivity to TRAIL. We found that p53 affects the sensitivity of myeloma cells to the DR5 agonistic human antibody lexatumumab but not the DR4 antibody mapatumumab. TP53 wild-type myeloma cells overexpressed DR5 in correlation with sensitivity to lexatumumab. Both nongenotoxic (nutlin-3a) and genotoxic (melphalan) p53-inducing stresses increased DR5 expression only in TP53 wild-type cells and synergistically increased lexatumumab efficiency yet did not increase DR4 expression, nor sensitivity to mapatumumab. Silencing of p53 strongly decreased DR5 expression and induced resistance to nutlin-3a and lexatumumab but did not modulate DR4 expression or sensitivity to mapatumumab. Increase of lexatumumab efficiency induced by nutlin-3a was related to a p53-dependent increase of DR5 expression. In primary myeloma cells, nutlin-3a increased DR5 expression and lexatumumab efficiency but did not increase mapatumumab efficiency. Taken together, our findings indicate that p53 controls the sensitivity of myeloma through DR5 but not DR4 and suggest that a subset of patients with multiple myeloma may benefit from DR5 therapy.

Noxa controls Mule-dependent Mcl-1 ubiquitination through the regulation of the Mcl-1/USP9X interaction

The level of the Mcl-1 pro-survival protein is highly regulated, and the down-regulation of Mcl-1 expression favors the apoptotic process. Mcl-1 physically interacts with different BH3-only proteins; particularly, Noxa is involved in the modulation of Mcl-1 expression. In this study, we demonstrated that Noxa triggers the degradation of Mcl-1 at the mitochondria according to the exclusive location of Noxa at this compartment. The Noxa-induced degradation of Mcl-1 required the E3 ligase Mule, which is responsible for the polyubiquitination of Mcl-1. Because the USP9X deubiquitinase was recently demonstrated to be involved in Mcl-1 protein turnover by preventing its degradation through the removal of conjugated ubiquitin, we investigated whether Noxa affected the deubiquitination process. Interestingly, Noxa over-expression caused a decrease in the USP9X/Mcl-1 interaction associated with an increase in the Mcl-1 polyubiquitinated forms. Additionally, Noxa over-expression triggered an increase in the Mule/Mcl-1 interaction in parallel with the decrease in Mule/USP9X complex formation. Taken together, these modifications result in the degradation of Mcl-1 by the proteasome machinery. The implication of Noxa in the regulation of Mcl-1 proteasomal degradation adds complexity to this process, which is governed by multiple interactions.

ABT-737 induces apoptosis in mantle cell lymphoma cells with a Bcl-2high/Mcl-1low profile and synergizes with other antineoplastic agents

PURPOSE

Mantle cell lymphoma (MCL) is considered to be incurable. ABT-737 is a BH3 mimetic that targets Bcl-2, which is overexpressed in MCL and implicated in drug resistance. The present work investigated the antitumor effect of ABT-737.

EXPERIMENTAL DESIGN

Six MCL cell lines and primary MCL cells (n = 13) were used. Sensitivity to ABT-737 was assessed, and expression levels of Bcl-2 and Mcl-1 were analyzed. Finally, ABT-737 was combined with other cytotoxic agents to promote tailored therapy.

RESULTS

MINO and GRANTA-519 cell lines were highly sensitive to ABT-737 [the median lethal dose (LD₅₀) = 20 and 80 nmol/L, respectively], whereas other cell lines were resistant. In primary MCL cells, 46% of patients' samples were sensitive to ABT-737. The analysis of protein expression levels revealed that both sensitive cell lines and primary MCL cells could be characterized by a Bcl-2(high)/Mcl-1(low) profile, whereas resistant MCL cells contained high levels of Mcl-1. ABT-737 induced a rapid disruption of both Bcl-2/Bax and Bcl-2/Bik complexes. In addition, silencing of Mcl-1 by siRNA sensitized MCL cell lines to ABT-737. Similarly, flavopiridol, which induces Mcl-1 downregulation, in combination with ABT-737 led to a synergistic anti-MCL effect in ABT-737-resistant cell lines. This synergy was also observed when ABT-737 was combined with either bortezomib or cytarabine.

CONCLUSIONS

The present work shows that ABT-737 induces strong apoptosis in MCL cells expressing a Bcl-2(high)/Mcl-1(low) profile. In ABT-737-resistant MCL cells, downregulation of Mcl-1 overcomes Mcl-1-induced resistance and synergizes ABT-737 effects. Our results strongly support the use of ABT-737 according to the Bcl-2/Mcl-1 tumor cell profiles in the treatment of MCL.

Mcl-1(128-350) fragment induces apoptosis through direct interaction with Bax

Mcl-1 full-length (Mcl-1(1-350)), a tightly regulated protein, plays an important role in protecting cells against apoptosis. Cleavage of Mcl-1 at Asp127 by caspase (Mcl-1(C1)) contributes to the regulation of Mcl-1 expression, but its pro-apoptotic function remains controversial. Here, we reported that Mcl-1(128-350) expression induced caspase-dependent apoptosis. We demonstrated that Mcl-1(128-350) but not Mcl-1(1-350) interacts with Bax. This interaction required an intact BH3 Mcl-1(128-350) domain and leads to Bax activation and translocation to mitochondria. The silencing of Bax, but not of Bak, prevented Mcl-1(128-350) induced apoptosis. In conclusion, Mcl-1(128-350) exerts a pro-apoptotic function governed by its capacity to interact with Bax.

Reciprocal protection of Mcl-1 and Bim from ubiquitin-proteasome degradation

Survival of multiple myeloma cells is essentially dependent on Mcl-1 protein that neutralizes the pro-apoptotic function of Bim and prevents activation of death effectors. To clarify the relationship between Mcl-1 and Bim, we generated cell lines silenced for Mcl-1 (shMcl-1) or Bim (shBim). We demonstrate that Mcl-1 and Bim proteins are concomitantly down-regulated in either shBim or shMcl-1 cells. We show that the down-regulation of either Mcl-1 in shBim or Bim in shMcl-1 cells is not due to a transcriptional event, but results from post-translational regulation. Indeed, the multi-ubiquitinated forms of Mcl-1 or Bim are increased in shBim and shMcl-1 cells, respectively, indicating proteasome degradation. Since Mcl-1/Bim complexes are predominant in myeloma cells the down-regulation of Mcl-1 by shRNA leads to unliganded Bim sensitive to degradation and reciprocally for unliganded Mcl-1 in shBim cells. Finally, our results support that the interaction between Mcl-1 and Bim confers to themselves mutual protection.

Noxa Up-regulation and Mcl-1 Cleavage Are Associated to Apoptosis Induction by Bortezomib in Multiple Myeloma

Targeting the ubiquitin-proteasome pathway has emerged as a potent anticancer strategy. Bortezomib, a specific proteasome inhibitor, has been approved for the treatment of relapsed or refractory multiple myeloma. Multiple myeloma cell survival is highly dependent on Mcl-1 antiapoptotic molecules. In a recent study, proteasome inhibitors induced Mcl-1 accumulation that slowed down their proapoptotic effects. Consequently, we investigated the role of Bcl-2 family members in bortezomib-induced apoptosis. We found that bortezomib induced apoptosis in five of seven human myeloma cell lines (HMCL). Bortezomib-induced apoptosis was associated with Mcl-1 cleavage regardless of Mcl-1L accumulation. Furthermore, RNA interference mediated Mcl-1 decrease and sensitized RPMI-8226 HMCL to bortezomib, highlighting the contribution of Mcl-1 in bortezomib-induced apoptosis. Interestingly, an important induction of Noxa was found in all sensitive HMCL both at protein and mRNA level. Concomitant to Mcl-1 cleavage and Noxa induction, we also found caspase-3, caspase-8, and caspase-9 activation. Under bortezomib treatment, Mcl-1L/Noxa complexes were highly increased, Mcl-1/Bak complexes were disrupted, and there was an accumulation of free Noxa. Finally, we observed a dissociation of Mcl-1/Bim complexes that may be due to a displacement of Bim induced by Noxa. Thus, in myeloma cells, the mechanistic basis for bortezomib sensitivity can be explained mainly by the model in which the sensitizer Noxa can displace Bim, a BH3-only activator, from Mcl-1, thus leading to Bax/Bak activation.

Mcl-1L cleavage is involved in TRAIL-R1– and TRAIL-R2–mediated apoptosis induced by HGS-ETR1 and HGS-ETR2 human mAbs in myeloma cells

We evaluated the ability of 2 human mAbs directed against TRAILR1 (HGS-ETR1) and TRAILR2 (HGS-ETR2) to kill human myeloma cells. HGS-ETR1 and HGS-ETR2 mAbs killed 15 and 9 human myeloma cell lines (HMCLs; n = 22), respectively. IL-6, the major survival and growth factor for these HMCLs, did not prevent their killing. Killing induced by either HGS-ETR1 or HGS-ETR2 was correlated with the cleavage of Mcl-1L, a major molecule for myeloma survival. Mcl-1L cleavage and anti-TRAILR HMCL killing were dependent on caspase activation. Kinetic studies showed that Mcl-1L cleavage occurred very early (less than 1 hour) and became drastic once caspase 3 was activated. Our data showed that both the extrinsic (caspase 8, Bid) and the intrinsic (caspase 9) pathways are activated by anti–TRAIL mAb. Finally, we showed that the HGS-ETR1 and, to a lesser extent, the HGS-ETR2 mAbs were able to induce the killing of primary myeloma cells. Of note, HGS-ETR1 mAb was able to induce the death of medullary and extramedullary myeloma cells collected from patients at relapse. Taken together, our data clearly encourage clinical trials of anti–TRAILR1 mAb in multiple myeloma, especially for patients whose disease is in relapse, at the time of drug resistance.

Melphalan-induced apoptosis in multiple myeloma cells is associated with a cleavage of Mcl-1 and Bim and a decrease in the Mcl-1/Bim complex

Multiple myeloma (MM) is a rapidly fatal plasma-cell malignancy that evolves mainly in the bone marrow. Melphalan is widely used to treat patients with MM but as yet its mechanisms of action are poorly documented. In the current study, we demonstrate that melphalan induces a drastic downregulation of Mcl-1L, Bcl-x(L) and BimEL in human melphalan-sensitive myeloma cells while the most potent proapoptotic isoforms, BimL and S, are affected to a lesser extent. Moreover, Mcl-1L and BimEL disappearance is associated with the generation of proapoptotic cleaved forms generated by a caspase cleavage. In myeloma cells, we have previously shown that Mcl-1 neutralizes the proapoptotic function of Bim and therefore, prevents the activation of death effectors. In this study, we demonstrate that melphalan disrupts the Mcl-1/Bim complex whereas the Bcl-2/Bim complex is not modified. The disappearance of full length Mcl-1 allows the release of Bim isoforms, particularly L and S, which can exert their proapoptotic function and leads to Bax activation and cytochrome c release. Thus, we can hypothesize that the cleaved 26 kDa proapoptotic Mcl-1 and the 19 and 12 kDa of Bim, generated during melphalan treatment could contribute to the amplification loop of apoptosis.

Endogenous association of Bim BH3-only protein with Mcl-1, Bcl-xL and Bcl-2 on mitochondria in human B cells

Bim is an essential regulator of lymphoid system homeostasis and appears essential for B cell apoptosis induction. The mechanism by which Bim isoforms are held in an inactive form remains poorly documented in normal B cells. In the current study, we demonstrated that in normal tonsil B cells the three major Bim isoforms are strongly associated with the anti-apoptotic Bcl-2 family members Mcl-1, Bcl-2 and Bcl-x(L). On the other hand, only a weak association of BimEL and L with the dynein LC8 chain has been found. In addition, there is no free Bim in normal B cells. Moreover, subcellular fractionation demonstrated that Bim and the anti-apoptotic counterparts are localized preferentially in the mitochondria-rich fraction. The fact that most Bim was found in this fraction supports the hypothesis that it is sequestered by anti-apoptotic molecules in mitochondria where its pro-apoptotic activity is controlled. Of interest, BimS is essentially complexed to Mcl-1 and the Mcl-1/Bim complex is the most abundant among the three types of complexes. This supports the idea that this complex is critical for the control of B cell death. In conclusion, these results favor a model in which Bim release from anti-apoptotic proteins is a critical event for initiation of apoptosis.

The imbalance between Bim and Mcl-1 expression controls the survival of human myeloma cells

Multiple myeloma is a fatal B cell malignancy characterized by the accumulation of plasma cells within the bone marrow. IL-6 is a major survival factor for myeloma cells. Bcl-2 protein family regulates pathways to apoptosis that are activated upon growth factor deprivation. Pro-apoptotic proteins that have only a single Bcl-2 homology domain, BH3-only, are potent inducers of apoptosis. In myeloma cells, Mcl-1 has been shown to be a major anti-apoptotic protein that appears to regulate cell survival through the JAK/STAT pathway. In this study, we examined the regulation of the BH3-only protein Bim and its interaction with Mcl-1. The three major Bim isoforms are expressed in myeloma cells and are negatively regulated by IL-6. Blockade of IL-6 signaling induces an up-regulation of Bim concomitant to Mcl-1 down-regulation. Of major interest, Bim is found strongly associated with Mcl-1 in viable myeloma cells while this interaction is disrupted under apoptosis induction. Of note, while Bim is also found strongly associated to Bcl-2, this interaction is not changed under apoptosis induction. Thus, in myeloma cells, Mcl-1 neutralizes Bim through complex formation and therefore prevents apoptosis. Under apoptosis induction, the disappearance of Mcl-1 allows Bim to exercise its pro-apoptotic function and to activate Bax.