Bioactive Compounds from Herbal Medicine Targeting Multiple Myeloma

Multiple myeloma (MM) is one of the most widespread hematological cancers. It is characterized by a clonal proliferation of malignant plasma cells in the bone marrow and by the overproduction of monoclonal proteins. In recent years, the survival rate of patients with multiple myeloma has increased significantly due to the use of transplanted stem cells and of the new therapeutic agents that have significantly increased the survival rate, but it still cannot be completely cured and therefore the development of new therapeutic products is needed. Moreover, many patients have various side effects and face the development of drug resistance to current therapies. The purpose of this review is to highlight the bioactive active compounds (flavonoids) and herbal extracts which target dysregulated signaling pathway in MM, assessed by in vitro and in vivo experiments or clinical studies, in order to explore their healing potential targeting multiple myeloma. Mechanistically, they demonstrated the ability to promote cell cycle blockage and apoptosis or autophagy in cancer cells, as well as inhibition of proliferation/migration/tumor progression, inhibition of angiogenesis in the tumor vascular network. Current research provides valuable new information about the ability of flavonoids to enhance the apoptotic effects of antineoplastic drugs, thus providing viable therapeutic options based on combining conventional and non-conventional therapies in MM therapeutic protocols.

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A Deptor Inhibitor Induces Its Degradation with Resulting Anti-Myeloma Cytotoxicity in Vitro and In Vivo

Blood ◽

10.1182/blood-2019-121480 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 1821-1821

Author(s):

Mario I Vega ◽

Yijiang Shi ◽

Patrick Frost ◽

Sara Huerta-Yepez ◽

Alan Lichtenstein

Keyword(s):

Multiple Myeloma ◽

Cell Lines ◽

Therapeutic Target ◽

Cytotoxic Effect ◽

Plasma Cells ◽

Conflicts Of Interest ◽

Inhibition Of Proliferation ◽

Induction Of Apoptosis

Multiple myeloma (MM) is a hematological disorder characterized by a proliferation of malignant monoclonal plasma cells in the bone marrow (BM) and / or in extramedullary sites. Despite recent progress in OS rates, MM remains an incurable disease and most patients will relapse and require treatment. Deptor is a component of mTOR complexes and a constitutive inhibitor of their activities. It is known that the inhibition of Deptor results in the inhibition of the proliferation and induction of apoptosis in MM cells. In addition, high levels of Deptor are predictive of a poor response to conventional therapies, indicating that Deptor expression are important as a prognostic marker for patients with myeloma and is a possible therapeutic target. Our group previously identified a drug which prevents mTOR-Deptor binding (NSC126405) and induces cellular cytotoxicity in MM (Shi Y, et al 2016). In this study, we developed a new related chemical inhibitor (43 M) capable of inducing the inhibition of the mTOR / Deptor interaction and results in the negative regulation of Deptor that leads to the inhibition of proliferation and induces apoptosis in several MM cell lines. The cytotoxic effect of 43 M is not dependent of caspase activation and induces the activation of p70 and AKT (T308). This leads to the induction of apoptosis in MM cell lines and tumor cells derived from MM patients. The degradation of Deptor induced by 43 M is dependent on the proteasome complex since it was prevented in the presence of MG132. In vivo, 43 M prevents the expression of Deptor in a xenograft tumor, and delayed tumor growth and interestingly, induces the eradication of tumors in 40% of mice in a murine model of MM, without significant toxic implications. Recent studies show that Deptor expression protects MM cells against Bortezomib treatment, suggesting that anti-Deptor drugs can synergize with proteasome inhibitors (PIs). However, the combination of 43 M + Bortezomib was not synergistic, and was antagonistic in vitro. These results are probably due to the prevention of the proteasomal degradation of Deptor, suggesting a possible use of the 43 M inhibitor in MM in the absence of the current PIs. This study describes for the first time the possible role of Deptor as a therapeutic target using a chemical inhibitor capable of degrading and inducing a cytotoxic effect in MM cell lines. In addition, Deptor is reported as an important therapeutic target in an in vivo MM model. Shi Y, Daniels-Wells TR, Frost P, Lee J, Finn RS, Bardeleben C, Penichet ML, Jung ME, Gera J, Lichtenstein A. Cytotoxic Properties of a DEPTOR-mTOR Inhibitor in Multiple Myeloma Cells. Cancer Res. 2016 Oct 1;76(19):5822-5831 Disclosures No relevant conflicts of interest to declare.

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IL-32 is a metabolic regulator promoting survival and proliferation of malignant plasma cells

10.1101/2021.02.22.431638 ◽

2021 ◽

Author(s):

Kristin Roseth Aass ◽

Robin Mjelle ◽

Martin H. Kastnes ◽

Synne S. Tryggestad ◽

Luca M. van den Brink ◽

...

Keyword(s):

Multiple Myeloma ◽

Oxidative Phosphorylation ◽

Plasma Cells ◽

Inflammatory Diseases ◽

Mitochondrial Respiratory Chain ◽

Gene Signature ◽

Growth And Survival ◽

Novel Concept

AbstractIL-32 is a non-classical cytokine expressed in cancers, inflammatory diseases and infections. IL-32 can have both extracellular and intracellular functions, and its receptor is not identified. We here demonstrate that endogenously expressed, intracellular IL-32 binds to components of the mitochondrial respiratory chain and promotes oxidative phosphorylation. Knocking out IL-32 in malignant plasma cells significantly reduced survival and proliferation in vitro and in vivo. High throughput transcriptomic and MS-metabolomic profiling of IL-32 KO cells revealed that loss of IL-32 leads to profound perturbations in metabolic pathways, with accumulation of lipids, pyruvate precursors and citrate, indicative of reduced mitochondrial function. IL-32 is expressed in a subgroup of multiple myeloma patients with an inferior prognosis. Primary myeloma cells expressing IL-32 were characterized by a plasma cell gene signature associated with immune activation, proliferation and oxidative phosphorylation. We propose a novel concept for regulation of metabolism by an intracellular cytokine and identify IL-32 as an endogenous growth and survival factor for malignant plasma cells. IL-32 is a potential prognostic biomarker and a treatment target in multiple myeloma.

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Identification of the Cysteine Protease Legumain as a Potential Chronic Hypoxia-Specific Multiple Myeloma Target Gene

Cells ◽

10.3390/cells11020292 ◽

2022 ◽

Vol 11 (2) ◽

pp. 292

Author(s):

Ada-Sophia Clees ◽

Verena Stolp ◽

Björn Häupl ◽

Dominik C. Fuhrmann ◽

Frank Wempe ◽

...

Keyword(s):

Multiple Myeloma ◽

Cysteine Protease ◽

Chronic Hypoxia ◽

Plasma Cells ◽

Hematologic Malignancy ◽

Low Oxygen ◽

Clonal Proliferation ◽

Temporal Adaptation ◽

Specific Regulation

Multiple myeloma (MM) is the second most common hematologic malignancy, which is characterized by clonal proliferation of neoplastic plasma cells in the bone marrow. This microenvironment is characterized by low oxygen levels (1–6% O2), known as hypoxia. For MM cells, hypoxia is a physiologic feature that has been described to promote an aggressive phenotype and to confer drug resistance. However, studies on hypoxia are scarce and show little conformity. Here, we analyzed the mRNA expression of previously determined hypoxia markers to define the temporal adaptation of MM cells to chronic hypoxia. Subsequent analyses of the global proteome in MM cells and the stromal cell line HS-5 revealed hypoxia-dependent regulation of proteins, which directly or indirectly upregulate glycolysis. In addition, chronic hypoxia led to MM-specific regulation of nine distinct proteins. One of these proteins is the cysteine protease legumain (LGMN), the depletion of which led to a significant growth disadvantage of MM cell lines that is enhanced under hypoxia. Thus, herein, we report a methodologic strategy to examine MM cells under physiologic hypoxic conditions in vitro and to decipher and study previously masked hypoxia-specific therapeutic targets such as the cysteine protease LGMN.

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A novel BCMA/CD3 bispecific T-cell engager for the treatment of multiple myeloma induces selective lysis in vitro and in vivo

Leukemia ◽

10.1038/leu.2016.388 ◽

2016 ◽

Vol 31 (8) ◽

pp. 1743-1751 ◽

Cited By ~ 86

Author(s):

S Hipp ◽

Y-T Tai ◽

D Blanset ◽

P Deegen ◽

J Wahl ◽

...

Keyword(s):

Multiple Myeloma ◽

Bone Marrow ◽

T Cell ◽

Plasma Cells ◽

Ex Vivo ◽

Xenograft Model ◽

Selective Lysis ◽

Bispecific T Cell Engager

Abstract B-cell maturation antigen (BCMA) is a highly plasma cell-selective protein that is expressed on malignant plasma cells of multiple myeloma (MM) patients and therefore is an ideal target for T-cell redirecting therapies. We developed a bispecific T-cell engager (BiTE) targeting BCMA and CD3ɛ (BI 836909) and studied its therapeutic impacts on MM. BI 836909 induced selective lysis of BCMA-positive MM cells, activation of T cells, release of cytokines and T-cell proliferation; whereas BCMA-negative cells were not affected. Activity of BI 836909 was not influenced by the presence of bone marrow stromal cells, soluble BCMA or a proliferation-inducing ligand (APRIL). In ex vivo assays, BI 836909 induced potent autologous MM cell lysis in both, newly diagnosed and relapsed/refractory patient samples. In mouse xenograft studies, BI 836909 induced tumor cell depletion in a subcutaneous NCI-H929 xenograft model and prolonged survival in an orthotopic L-363 xenograft model. In a cynomolgus monkey study, administration of BI 836909 led to depletion of BCMA-positive plasma cells in the bone marrow. Taken together, these results show that BI 836909 is a highly potent and efficacious approach to selectively deplete BCMA-positive MM cells and represents a novel immunotherapeutic for the treatment of MM.

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Characterization of Nonrandom Chromosomal Gains and Losses in Multiple Myeloma by Comparative Genomic Hybridization

Blood ◽

10.1182/blood.v91.8.3007.3007_3007_3010 ◽

1998 ◽

Vol 91 (8) ◽

pp. 3007-3010 ◽

Cited By ~ 103

Author(s):

Juan C. Cigudosa ◽

Pulivarthi H. Rao ◽

M. Jose Calasanz ◽

M. Dolores Odero ◽

Joseph Michaeli ◽

...

Keyword(s):

Multiple Myeloma ◽

Comparative Genomic Hybridization ◽

Plasma Cells ◽

Comparative Genomic ◽

Genomic Hybridization ◽

Banding Analysis ◽

Chromosomal Changes ◽

Gains And Losses

Clonal chromosomal changes in multiple myeloma (MM) and related disorders are not well defined, mainly due to the low in vivo and in vitro mitotic index of plasma cells. This difficulty can be overcome by using comparative genomic hybridization (CGH), a DNA-based technique that gives information about chromosomal copy number changes in tumors. We have performed CGH on 25 cases of MM, 4 cases of monoclonal gammopathy of uncertain significance, and 1 case of Waldenstrom's macroglobulinemia. G-banding analysis of the same group of patients demonstrated clonal chromosomal changes in only 13 (43%), whereas by CGH, the number of cases with clonal chromosomal gains and losses increased to 21 (70%). The most common recurrent changes detected by CGH were gain of chromosome 19 or 19p and complete or partial deletions of chromosome 13. +19, an anomaly that has so far not been detected as primary or recurrent change by G-banding analysis of these tumors, was noted in 2 cases as a unique change. Other recurrent changes included gains of 9q, 11q, 12q, 15q, 17q, and 22q and losses of 6q and 16q. We have been able to narrow the commonly deleted regions on 6q and 13q to bands 6q21 and 13q14-21. Gain of 11q and deletion of 13q, which have previously been associated with poor outcome, can thus be detected by CGH, allowing the use of this technique for prognostic evaluation of patients, without relying on the success of conventional cytogenetic analysis.

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GS-9219 - A Novel Prodrug of the Acyclic Nucleotide PMEG Has Antitumor Activity Against Naive and Melphalan-Refractory Spontaneous Myeloma in Pet Dogs.

Blood ◽

10.1182/blood.v110.11.1508.1508 ◽

2007 ◽

Vol 110 (11) ◽

pp. 1508-1508

Author(s):

Douglas H. Thamm ◽

Daniel B. Tumas ◽

Hans Reiser ◽

Grushenka H.I. Wolfgang ◽

Ilene D. Kurzman ◽

...

Keyword(s):

Multiple Myeloma ◽

Complete Remission ◽

Plasma Cells ◽

Safety Data ◽

Leukemia Cell ◽

Pet Dogs ◽

Naturally Occurring ◽

Treatment Naïve

Abstract Multiple myeloma is an important hematopoietic cancer in humans and pet dogs. While clinical remission can be achieved using currently available antineoplastic agents, eventual drug resistant relapse is common. GS-9219, a novel double prodrug of the anti-proliferative nucleotide analog 9-(2-phosphonylmethoxyethyl) guanine (PMEG), has been shown to have potent cytotoxic activity in vitro in human lymphoblasts and leukemia cell lines and in vivo in naturally occurring non-Hodgkin’s lymphoma in dogs (naive and refractory). We hypothesized that malignant plasma cells in multiple myeloma similarly would possess the intracellular enzymatic machinery necessary for the activation of GS-9219. To generate proof-of-concept, activity and safety data in multiple myeloma, a pilot study with GS-9219 monotherapy was initiated in pet dogs with naturally occurring chemotherapy-naive or refractory multiple myeloma. Three dogs with spontaneously occurring IgA myeloma (1 naive, 2 melphalan-refractory) have been treated with GS-9219 as a 30-minute intravenous infusion weekly for 2 weeks at 1 mg/kg, then every 3 weeks for another 3 treatments at 0.8 mg/kg (total of five GS-9219 doses). To date, major anti-tumor responses have been observed in all 3 multiple myeloma dogs treated with GS-9219. Two dogs are in complete remission as indicated by normalization of serum paraprotein and complete resolution of hypercalcemia, peripheral cytopenias and bone marrow plasmacytosis. The third currently has a strong partial response (normal marrow and >95% reduction in serum paraprotein). The only significant toxicity noted throughout the study was a single episode of transient neutropenia in one dog which resolved and, after a one week delay, treatment was continued without issue. Assessment of durability of response is currently ongoing, with all dogs remaining in remission to date; one dog has remained in complete remission for more than 5 months following completion of the treatment regimen. In conclusion, GS-9219 has significant anti-tumor activity in spontaneous melphalan-refractory or treatment-naive canine multiple myeloma.

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CD38-Targeted Immunochemotherapy Of Multiple Myeloma: Preclinical Evidence For Its Combinatorial Use In Lenalidomide and Bortezomib Refractory/Intolerant MM Patients

Blood ◽

10.1182/blood.v122.21.277.277 ◽

2013 ◽

Vol 122 (21) ◽

pp. 277-277 ◽

Cited By ~ 3

Author(s):

Inger S. Nijhof ◽

Willy A. Noort ◽

Jeroen Lammerts van Bueren ◽

Berris van Kessel ◽

Joost M. Bakker ◽

...

Keyword(s):

Multiple Myeloma ◽

Research Funding ◽

Plasma Cells ◽

Cell Lysis ◽

In Vitro Assays ◽

Human Antibody ◽

Myeloma Cells ◽

Clinical Phase

Abstract Multiple myeloma (MM) remains an incurable malignancy of clonal plasma cells. Although the new generation of immunomodulatory agents, such as lenalidomide (LEN), and the potent proteasome inhibitor bortezomib (BORT) have significantly improved the overall survival of MM patients, all chemotherapy strategies are eventually hampered by the development of drug-resistance. The outcome of patients who are refractory to thalidomide, lenalidomide (LEN) and bortezomib (BORT) is very poor. Set out with the idea that targeted immunotherapy with human antibodies may offer new perspectives for MM patients, we have recently developed daratumumab (DARA), a CD38 human antibody with broad-spectrum killing activity, mainly via ADCC (antibody dependent cellular cytotoxicity) and CDC (complement dependent cytotoxicity). In our previous preclinical studies and in current clinical phase I/II trials, DARA induces marked anti-MM activity. Based on these encouraging results, we now explored the potential activity of DARA for patients who are refractory to LEN- and/or BORT. In a recently developed human-mouse hybrid model that allows the in vivo engraftment and outgrowth of patient-derived primary myeloma cells in immune deficient Rag2-/-gc-/- mice, single dose DARA treatment appeared to effectively inhibit the malignant expansion of primary MM cells derived from a LEN- and BORT-refractory patient, indicating the potential efficacy of DARA even in LEN/BORT refractory patients. To substantiate the conclusions of these in vivo data, we conducted in vitro assays, in which full BM-MNCs from LEN (n=11) and LEN/BORT (n=8) refractory patients were treated with DARA alone or the combination of DARA with LEN or BORT to induce MM cell lysis. As expected, LEN alone induced no or little lysis of MM cells in the LEN-refractory patients and also BORT was not able to induce any lysis in the BORT-refractory patients. On the contrary, DARA induced substantial levels of MM cell lysis in all LEN and LEN/BORT-refractory patients. This lysis was significantly enhanced by combination with LEN or BORT. The combination of DARA and BORT improved MM lysis by additive mechanisms. However, LEN improved DARA-mediated lysis of MM cells in a synergistic manner through the activation of effector cells involved in DARA-mediated ADCC. In conclusion, our results demonstrate that DARA is also effective against multiple myeloma cells derived from LEN- and BORT-refractory patients. Especially LEN seems to improve responses in a synergistic manner. Our results provide a rationale for clinical evaluation of DARA in combination with LEN to achieve more effective results in LEN- and BORT-refractory patients. Disclosures: Lammerts van Bueren: Genmab: Employment. Bakker:Genmab: Employment. Parren:Genmab: Employment. van de Donk:Celgene: Research Funding. Lokhorst:Genmab A/S: Consultancy, Research Funding; Celgene: Honoraria; Johnson-Cilag: Honoraria; Mudipharma: Honoraria.

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Structural and Ultrastructural Analysis of the Multiple Myeloma Cell Niche and a Patient-Specific Model of Plasma Cell Dysfunction

Microscopy and Microanalysis ◽

10.1017/s1431927621013805 ◽

2021 ◽

pp. 1-11

Author(s):

Katrina A. Harmon ◽

Sara Roman ◽

Harrison D. Lancaster ◽

Saeeda Chowhury ◽

Elizabeth Cull ◽

...

Keyword(s):

Multiple Myeloma ◽

Cancer Progression ◽

Plasma Cells ◽

Myeloma Cell ◽

Specific Model ◽

Patient Specific ◽

Multiple Myeloma Cell ◽

Cell Niche

Multiple myeloma (MM) is a deadly, incurable malignancy in which antibody-secreting plasma cells (PCs) become neoplastic. Previous studies have shown that the PC niche plays a role cancer progression. Bone marrow (BM) cores from MM and a premalignant condition known as monoclonal gammopathy of unknown significance (MGUS) patients were analyzed with confocal and transmission electron microscopy. The BM aspirates from these patients were used to generate 3D PC cultures. These in vitro cultures were then assayed for the molecular, cellular, and ultrastructural hallmarks of dysfunctional PC at days 1 and 5. In vivo, evidence of PC endoplasmic reticulum stress was found in both MM and MGUS BM; however, evidence of PC autophagy was found only in MM BM. Analysis of in vitro cultures found that MM PC can survive and maintain a differentiated phenotype over an unprecedented 5 days, had higher levels of paraprotein production when compared to MGUS-derived cultures, and showed evidence of PC autophagy as well. Increased fibronectin deposition around PC associated with disease severity and autophagy dysregulation was also observed. 3D cultures constructed from BM aspirates from MGUS and MM patients allow for long-term culture of functional PC while maintaining their distinct morphological phenotypes.

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MCL1 Inhibitors in Multiple Myeloma

Blood ◽

10.1182/blood-2019-121104 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. SCI-12-SCI-12

Author(s):

Karin Vanderkerken ◽

Kim De Veirman ◽

Ken Maes ◽

Eline Menu ◽

Elke De Bruyne

Keyword(s):

Multiple Myeloma ◽

Bone Marrow ◽

Plasma Cells ◽

Conflicts Of Interest ◽

Therapeutic Option ◽

Therapy Resistance ◽

Bone Marrow Microenvironment ◽

Molecular Heterogeneity

Apoptosis plays a key role, not only in normal homeostasis but also in protection against genomic instability. Protection against apoptosis is a hallmark of cancer and is mainly regulated by the overexpression of anti-apoptotic proteins such as Bcl-2, Bcl-Xl or Mcl-1. This results in increased survival of the tumor cells and resistance to therapy. This presentation will focus on MCL-1 (myeloid cell leukemia 1), its expression and its role as potential target in multiple myeloma (MM). MCL1 gene regions are one the most amplified gene regions in several human cancers and Mcl-1 activity is often associated with therapy resistance and relapse. Mcl-1 binds to and sequesters the pro-apoptotic BH3 proteins, thereby preventing apoptosis. Mcl-1 is overexpressed on MM cells from newly diagnosed patients compared to normal plasma cells and in MM cells at relapse. This overexpression is furthermore associated with a shorter survival of these patients. Increased Mcl-1 expression can result either from genetic lesions or by induction through interaction with the bone marrow microenvironment. Its expression is correlated with the molecular heterogeneity of the myeloma patients; while the CCDN1 group has high BCL2 and low MCL-1 expression; the MMSET and MAF group has high MCL-1 and low BCL2 expression. Unlike Bcl-2 and Bcl-Xl, Mcl-1 has a large unstructured aminoterminus and its activity is mainly dependent on posttranslational modifications. The bone marrow microenvironment, by producing high levels of interleukin 6, also induces the upregulation of Mcl-1. Furthermore, our group recently demonstrated that not only stromal cells in the bone marrow microenvironment, but also MDSC (myeloid derived suppressor cells) induce survival of MM cells by increasing Mcl-1 levels through the AMPK pathway. As such, these data suggest the potential therapeutic benefit of targeting Mcl-1 in MM patients. Developing the first-generation inhibitors appeared to be challenging, especially in view of the occurrence of unwanted off target effects. Recent preclinical data with new, selective Mcl-1 inhibitors show promising anti-tumor effects both in vitro and in in vivo myeloma models, either alone or in combination with the Bcl-2 selective inhibitor, venetoclax, especially as it was demonstrated that high levels of MCL-1 are associated with venetoclax resistance in MM. In addition, it was also shown that proteasome inhibition can trigger Mcl-1 accumulation, further pointing to the importance of Mcl-1 inhibition. Induction of NOXA, as an inhibitor of Mcl-1, is also suggested as a therapeutic option, especially in combinations with other drugs. Clinically, following preclinical results, several new Mcl-1 inhibitors have entered phase I trials. Most of them are still recruiting patients, and as such too early to have results. Disclosures No relevant conflicts of interest to declare.

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Mcl-1 Is Overexpressed in Multiple Myeloma and Correlates with Disease Severity.

Blood ◽

10.1182/blood.v104.11.1419.1419 ◽

2004 ◽

Vol 104 (11) ◽

pp. 1419-1419

Author(s):

Soraya Wuilleme-Toumi ◽

Nelly Robillard ◽

Patricia Gomez-Bougie ◽

Philippe Moreau ◽

Steven Le Gouill ◽

...

Keyword(s):

Multiple Myeloma ◽

Bone Marrow ◽

Disease Severity ◽

Cell Lines ◽

Plasma Cells ◽

Myeloma Cell ◽

Lymphocytic Leukemia ◽

Myeloma Cells

Abstract Multiple Myeloma (MM) is a fatal malignancy of B-cell origin characterized by the accumulation of plasma cells within the bone marrow. The expression of the pro-survival members of the Bcl-2 family has been shown to be a key process in the survival of myeloma cells. More particularly, Mcl-1 expression turned out to be critical for their survival. Indeed, knockdown of Mcl-1 by antisenses induces apoptosis in myeloma cells. Finally, Mcl-1 was found to be the only anti-apoptotic Bcl-2 family member which level of expression was modified by cytokine treatment of myeloma cells. For these reasons, we have evaluated the expression of Mcl-1 in vivo in normal, reactive and malignant plasma cells (PC) i.e., myeloma cells from 55 patients with MM and 20 human myeloma cell lines using flow cytometry. We show that Mcl-1 is overexpressed in MM in comparison with normal bone marrow PC. Forty-seven percent of patients with MM at diagnosis (p=.017) and 80% at relapse (p=.014 for comparison with diagnosis) overexpress Mcl-1. Of note, only myeloma cell lines but not reactive plasmocytoses have abnormal Mcl-1 expression, although both plasmocyte expansion entities share similar high proliferation rates (>20%). Of interest, Bcl-2 as opposed to Mcl-1, does not discriminate malignant from normal PC. This shows that the overexpression of Mcl-1 is clearly related to malignancy rather than to proliferation. It will be important to know whether the overexpression of Mcl-1 is related to an abnormal response to cytokines like Interleukin-6 or to mutations of the promoter of the Mcl-1 gene as already described in B chronic lymphocytic leukemia. Finally, level of Mcl-1 expression is related to disease severity, the highest values being correlated with the shortest event-free survival (p=.01). In conclusion, Mcl-1 which has been shown to be essential for the survival of human myeloma cells in vitro is overexpressed in vivo in MM and correlates with disease severity. Mcl-1 represents a major therapeutical target in MM.

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