Growth Inhibition Of Myeloma Cells Research Articles

Geldanamycin and Its Derivatives Inhibit the Growth of Myeloma Cells and Reduce the Expression of the MET Receptor.

Introduction. Geldanamycin (GA) is an ansamycin antibiotic that exhibits potent anti-neoplastic properties. The aim of this study was to assess the impact of GA and its derivatives on the growth and invasiveness of myeloma cell lines and CD138+ cells derived from the bone marrow of patients with multiple myeloma.Materials and methods. We evaluated cell proliferation, survival, apoptosis, cell cycle of myeloma cells, and the expression of cell surface proteins after incubation with geldanamycin or its derivatives.Results. GA and its analogs have an effect on myeloma cells by inhibiting their growth in a time and dose-dependent manner. Myeloma cell lines demonstrated decreased proliferation after incubation with 10 nM of GA or 100 nM GA analogs. The first significant effects of GA on U266 cells was observed after 24 hours. After 24 hours, U266 cells incubated with 100 nM GA were in both early and late stages of apoptosis; 17AEP and 17DMAG caused apoptosis of similar intensity to GA. It has been observed that GA and its derivatives cause caspase-3 activation. Analysis of the activity of AKT and MAP 42/44 kinases was performed by incubating U266 cells for 24 and 48 hours in100 nM of GA and its derivatives. After 24 hours incubation, no significant changes in protein expression were observed, while after 48 hours, the strongest changes were seen in AKT protein expression after incubation with GA and 17AEP-GA. In studies of the cell cycle, it was found that 100 nM 17AEP-GA and 17-DMAP-GA cause cell cycle abnormalities. We observed a nearly two-fold increase in U266 cells in the G1 phase and a simultaneous decrease in the percentage of cells in the G2/M phase, indicating that cells were halted in the G1 phase. In the case of the INA6 cells, proliferation was halted in both the G1 and G2/M phases.Conclusions. GA and the analogues that we tested can inhibit myeloma cell growth by induction of apoptosis and blockage of cell cycle progression, and have an effect on the down-regulation of the MET receptor. The GA derivatives tested, despite their modifications still retain strong anticancer properties. Specifically, two analogues of GA, 17AEP-GA and 17DMAG due to their properties can be more effective and safer chemotherapeutic agents than 17AAG, which is currently used and described in literature.

Sphingolipids As a Novel Target For The Treatment Of Multiple Myeloma

IntroductionMultiple Myeloma (MM) is the second most common hematological malignancy in the United States and accounts for ∼10,600 deaths annually. MM remains an incurable disease and almost all patients will eventually relapse and become refractory to currently available therapeutic agents. There is an unmet need for better understanding of the disease's molecular pathways and identifying novel therapeutic targets. Sphingolipid metabolism is being increasingly recognized as a key pathway in cancer biology. In particular, sphingosine kinases (SK1 and SK2) provide a potential site for manipulation of the ceramide / sphingosine 1-phosphate (S1P) rheostat that regulates the balance between tumor cell proliferation and apoptosis, as well as tumor sensitivity to drugs. Currently, very little is known about sphingolipid metabolism in MM. We herein for the first time provide a detailed analysis of sphingolipid metabolism in MM and demonstrate the potential of targeting SK2 for the treatment of MM. MethodsWe first quantified sphingolipid metabolites and sphingolipid metabolizing genes in myeloma cell lines, in freshly isolated human primary CD138+ myeloma cells, and in a publically available gene expression dataset from MM patients. We then tested the anti-myeloma activity of SK2-specific shRNA and determined the efficacy of a selective SK2 inhibitor (ABC294640) in killing myeloma cell lines and primary human myeloma cells in vitro. The mechanistic pathway of apoptosis was analyzed by immunoblotting and flowcytometry. MM cell lines stably expressing luciferase and eGFP were generated for xenograft experiments and for in vitro co-cultures with stromal cells. ResultsFrom the publically available GSE6477 microarray data set, we found that one third of the genes involved in sphingolipid metabolism were significantly different in CD138+ MM cells from newly diagnosed MM patients compared to normal individuals, including SK2 and S1P receptors. In 5 MM cell lines compared to immortalized B cells (IBC), 19 key sphingolipid metabolites were measured, and we found that ceramides were significantly reduced whereas S1P was significantly increased. mRNA analyses of 11 sphingolipid metabolizing genes including S1P receptors in 7 MMs showed that SK1, SK2, and alkaline ceramidases were significantly increased compared to IBC. Furthermore, we isolated CD138+ myeloma cells from 21 MM patients and found that 13 of the patients had higher SK2 expression in CD138+ MM cells compared to CD138-cells. These data demonstrated abnormal sphingolipid metabolism and dys-regulated SK2 in myeloma cells.We generated SK2-specific shRNA and found that SK2 shRNA down-regulated SK2 mRNA, inhibited proliferation, and induced death in myeloma cells, suggesting that SK2 is important in myeloma cell survival. We then tested the efficacy of ABC294640 (the most-advanced, non-lipid SK2 inhibitor) in 6 MM cell lines. ABC294640 inhibited myeloma cell growth with an IC50s of ∼30 μM, including steroid-resistant and doxorubicin-resistant myeloma cells. ABC294640 inhibited MM cell growth as early as 6 hours after exposure and induced apoptotic cell death as demonstrated by Annexin V staining, PARP cleavage and caspase 9 activation. ABC294640 inhibited primary human CD138+MM cells with the same efficacy as with MM cell lines, demonstrating the potential of ABC294640 for the treatment of MM. Additionally, we found that blocking S1P receptors with FTY720 (a S1PR agonist with receptor degradation) induced apoptosis in MM cells.We performed extensive mechanistic and signaling pathway analyses and found that ABC294640 inhibited Mcl-1 and C-Myc expression, but had no effects on Bcl2. Furthermore, ABC294640 induced cell death by directing Mcl-1 to proteosomal degradation.MM is dependent on the bone marrow niche microenvironment for survival and progression. We found that ABC294640 was effective in inducing apoptosis in MM cells even in the presence of stromal cells. Finally, we are currently testing the in vivo effect of ABC294640 alone and in combination with bortezomib, thalidomide and dexamethasone in MM xenograft model transplanted with MM cells stably expressing luciferase. Our early preliminary results were encouraging. ConclusionOur data demonstrate that sphingolipid metabolism is abnormal and provides an attractive target in the treatment of refractory/relapsed MM. Disclosures:Costa:Otsuka: Research Funding.

Selective Inhibition Of The PI3K-Alpha Isoform Blocks Myeloma Cell Growth and Survival

IntroductionBoth, the phosphoinositide-3kinase (PI3K)/AKT pathway as well as its nutrient-dependent downstream target, the mToR (mammalian target of rapamycin) kinase, are essential for the growth and survival of malignant plasma cells. PI3K exists in four isotypes (α - δ), the role of each of these isotypes in multiple myeloma (MM), however, is not defined. Therefore, we evaluated systematically the in vitroanti-myeloma activity of NVP-BYL719 (Novartis), a newly developed inhibitor highly selective for the PI3K α isoform, and compared it with the activity of other inhibitors targeting the PI3K/AKT/mToR signaling network at different sites. Since inhibition of mToRC1 may lead to PI3K activation by a feedback loop, we looked also at combinations of NVP-BYL719 and rapalogs. Materials and MethodsAn MTS based growth assay was used to measure growth inhibition of NVP-BYL719 in comparison to different inhibitors (the pan-PI3K inhibitors Ly294002 and NVP-BKM120, the dual PI3K/mToR inhibitor NVP-BEZ235, and the allosteric mToR inhibitors rapamycin and everolimus) on six human malignant plasma cell lines and two non-myeloma cell lines, K562 and Raji. Western blot analysis was used to confirm inhibitor activity and specificity. In addition, combinations of PI3K and mToR inhibitors were tested and antagonistic/synergistic activity was calculated with the CalcuSynTM(Biosoft) software. ResultsThe selective PI3K alpha inhibitor NVP-BYL719 inhibited myeloma cell growth at a dose level (IC50 < 10 µM in 5/6 cell lines), where non-MM cell lines were not affected. Only cell line U266 was showed moderate sensitivity. The levels of the PI3K isoforms αwere comparable in all tested MM cell , as shown by Western blot. NVP-BYL719 blocked phosphorylation of AKT and of protein S6, an mToR downstream target. Of note, whenever rapamycin was combined with a PI3K inhibitor including NVP-BYL719, synergistic growth inhibition was seen, even in combination with the dual PI3K/mToR inhibitor NVP-BEZ235. ConclusionsHere, the PI3Kα isoform is reported as being essential for the growth of myeloma cells. This provides the rationale for the therapeutic exploration of such isoform specific PI3K inhibitors in MM allowing dose intensification with less toxicity. Allosteric mToR inhibitors, already active in early clinical trials in MM patients may provide interesting combination partners for these PI3K-inhibitors. Disclosures:Guenther:Novartis: Consultancy. Gramatzki:Novartis: Consultancy.

Sphingolipids as a novel target for the treatment of multiple myeloma.

e19534 Background: Multiple myeloma (MM) is the second most common hematological malignancy in the United States and accounts for ~10,600 deaths annually. MM remains an incurable disease and almost all patients will eventually relapse and become refractory to currently available therapeutic agents. There is an unmet need for better understanding the disease’s molecular pathways and for identifying novel therapeutic targets. Sphingolipid metabolism is being increasingly recognized as a key pathway in tumor cell proliferation and in tumor sensitivity to anticancer drugs. We hypothesize that altered sphingolipid metabolism plays an important role in the pathogenesis of MM, thus providing a novel target in the treatment of MM. Methods: We first assayed sphingolipid metabolism including sphingolipid metabolites and sphingolipid metabolizing genes in myeloma cell lines, in freshly isolated human primary CD138+myeloma cells, and in publically available dataset. We then tested the efficacy of the selective SK2 inhibitor (ABC294640) and the SK2 shRNA in killing myeloma cells in vitro. Results: 1) Compared to immortalized B cells, the levels of pro-apoptotic ceramides were decreased whereas the proliferative sphingosine 1-phosphate (S1P) was increased in myeloma cell lines. 2) The expression of several key sphingolipid-metabolizing genes including sphingosine kinase (SK) 1 and 2 was altered in freshly isolated human primary bone marrow myeloma cells and in publically available microarray dataset. 3) The selective SK2 inhibitor (ABC294640) induces apoptotic cell death and inhibits myeloma cell growth with an IC50of ~20 μM in 9 myeloma cell lines. 4) Interestingly, OPM-1 myeloma cell line was extremely sensitive to ABC294640 with an IC50of &lt;5 µM whereas U266 myeloma cell line was resistant to ABC294640. SK2 shRNA induced apoptotic cell death in OPM-1, but not in U266 cells. We are currently investigating the molecular mechanisms underlying the resistance of U266 myeloma cells to ABC294640. Conclusions: Our data demonstrated that sphingolipid metabolism provides an attractive target in the treatment of refractory/relapased multiple myeloma.

Abstract 5194: Pim2 is required for maintaining Multiple Myeloma cell proliferation through modulating mTORC1 pathway.

Abstract Multiple Myeloma (MM) is the second most common hematological malignancy. Despite the advances of therapeutic regimens over the last decade, nearly all patients eventually relapse, highlighting the need for additional therapeutic agents. Pim kinases, a family of serine/threonine kinase, are reported to be oncogenic and required for the maintenance of hematological malignancies. Here, consistent with previous reports, we show that Pim2 kinase expression is most highly elevated in MM. Importantly, shRNA knockdown of Pim2 leads to a significant inhibition of MM cell growth, suggesting that Pim2 is critical in maintaining MM malignancy. We developed a potent and specific small molecule inhibitor for the Pim kinases. Inhibition of Pim2 by this molecule suppresses MM cell growth. We find that Pim inhibitor treatment results in the suppression of cell proliferation, but not induction of apoptosis, in all MM cell lines tested. Further, we identified mTORC1 signaling, which is critical for cell proliferation, as significantly repressed by Pim2 inhibition. The two major mTORC1 downstream effectors: P70S6K and 4EBP1 are rapidly dephosphorylated upon Pim inhibitor treatment of MM cells. We are currently investigating the potential signaling modules that may mediate Pim2’s regulation on mTORC1 pathway. Taken together, our findings strongly support Pim2 as a promising therapeutic target in MM, given its distinct expression in MM and essential role in maintaining proliferation. Citation Format: Jing Lu, Tatiana Zavorotinskaya, Yumin Dai, Xiaohong Niu, Joseph Castillo, Janet Sim, Jianjun Yu, Kevin Shannon, Pablo Garcia. Pim2 is required for maintaining Multiple Myeloma cell proliferation through modulating mTORC1 pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5194. doi:10.1158/1538-7445.AM2013-5194

Small Molecule MIRA-1 Induces p53-Independent Apoptosis in Multiple Myeloma Cells Through Activation of the p38 MAPK Signaling Pathway.

Abstract 2937Mutation of p53, a tumor suppressor protein, is relatively rare (∼10% in newly diagnosed patients) in multiple myeloma (MM). However, p53 mutations/deletions are important risk factors for predicting the resistant to chemotherapy and no treatment is currently available for this subgroup of patients. MIRA-1, a novel class of small molecules with the ability to restore wild type conformation and function to mutant p53, induces apoptosis in different types of solid tumors harboring mutant p53. However, its effect on MM cells is not known. In this study we examined the ability of MIRA-1 to induce cytotoxic and apoptotic response in MM cells and inhibit tumor growth in MM mouse xenograft model. In addition, we explored the molecular mechanisms of MIRA-1-induced apoptosis in MM cells.Treatment of MM cells with MIRA-1 resulted in a time- and dose-dependent decrease in survival and increase in apoptosis of MM cells harboring either wild type (MM.1S, H929) or mutant (U266, 8226, and LP1) p53 suggesting that MIRA-induced apoptosis in MM cells is independent of p53 status. The IC50 of MIRA-1 observed in these cells was ranged between 10 and 15 μM. In addition, MIRA-1 elicited a dose-dependent inhibition of myeloma cell growth in seven primary MM samples with an average IC50of 10 μM. Two of the seven patient samples harbors p53 mutations/deletions. In contrast, MIRA-1 did not have a significant inhibitory effect on the survival of bone marrow or peripheral blood mononuclear cells obtained from three healthy donors at the concentrations (10–20 μM) that induced apoptosis of MM cells, indicating a preferential killing of myeloma cells by this drug. Apoptosis induced by MIRA-1 in MM cells harbouring either wild type or mutant p53 was associated with time- and dose-dependent activation of caspas-8, caspase-3 and PARP with subsequent up-regulation of a pro-apoptotic protein, Noxa and down-regulation of an anti-apoptotic protein, Mcl-1. Interestingly, MIRA-1 did not significantly modulate the level of p53 expression, although immunoprecipitation studies confirmed the restoration of wild type conformation of mutant p53 in LP1 and 8226 cells. Importantly, genetic knockdown of p53 using siRNA against wild type or mutant p53 had only a little effect on apoptosis induction by MIRA-1 in MM.1S or LP1 cells, respectively, confirming that apoptosis induction by MIRA-1 in MM cells is independent of p53. Furthermore, the combination of MIRA-1 with current anti-myeloma agents, dexamethasone or doxorubicin displayed synergistic cytotoxic response in MM.1S or LP1 cells (CI<1; p<0.05).To delineate the molecular mechanisms of apoptosis in MM cells induced by MIRA-1, we performed RT2 profiler PCR array analysis for the differential expression of 84 genes related to mitogen activated protein kinase (MAPK) signaling pathway. A significant number of genes of the MAPK family including MAP3K: MAP3K2 (MEKK2), MAP3K4 (MEKK4), PAK1; MAP2K: MAP2K5 (MEK5); and MAPK: MAPK11 (p38bMAPK) as well as transcription factors such as c-Jun, c-FOS, EGR1, and MKNK1, whose expression is induced by MAPK signaling, were up-regulated by more than 2-fold in MIRA-1-treated 8226 cells. On the other hand, expression of the scaffolding/anchoring genes, MAPK8IP2 (JIP-1) was down-regulated by ∼2-fold. Up-regulations of c-Jun, c-Fos, and EGR1 at their protein levels were further confirmed by Western blot analysis of MM.1S and 8226 cells treated with MIRA-1. Importantly, Western blot analysis revealed that treatment of MIRA-1 resulted in a time- and dose-dependent increase of phosphorylated p38 MAPK level in both MM.1S and 8226 cells. Taken together, our data indicates that activation of the MAPK signaling pathway is, at least in part, associated with MIRA-1-induced apoptosis of MM cells.Finally, we evaluated anti-tumorigenic potential of MIRA-1 in MM xenograft SCID mouse models. 8266 cells were inoculated into SCID mice and the mice received i.p. injections of either 100 μL PBS (control) or 10 mg/kg MIRA-1 once daily for 18 days after tumor formation was evident. Administration of MIRA-1 resulted in significant inhibition of tumor growth (p<0.05) and increase in survival (p=0.007) of the mice with no apparent toxicity.Our study for the first time demonstrates potent in vitro and in vivo anti-myeloma activity of MIRA-1 and thus providing a framework for clinical evaluation of MIRA-1 either alone or in combination with current anti-myeloma agents. Disclosures:Reece:Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Merck: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Otsuka: Honoraria, Research Funding; Millennium Pharmaceuticals: Research Funding.

Blockade of XBP1 splicing by inhibition of IRE1α is a promising therapeutic option in multiple myeloma

AbstractMultiple myeloma (MM) cells are characterized by high protein synthesis resulting in chronic endoplasmic reticulum (ER) stress, which is adaptively managed by the unfolded protein response. Inositol-requiring enzyme 1α (IRE1α) is activated to splice X-box binding protein 1 (XBP1) mRNA, thereby increasing XBP1s protein, which in turn regulates genes responsible for protein folding and degradation during the unfolded protein response. In this study, we examined whether IRE1α-XBP1 pathway is a potential therapeutic target in MM using a small-molecule IRE1α endoribonuclease domain inhibitor MKC-3946. MKC-3946 triggered modest growth inhibition in MM cell lines, without toxicity in normal mononuclear cells. Importantly, it significantly enhanced cytotoxicity induced by bortezomib or 17-AAG, even in the presence of bone marrow stromal cells or exogenous IL-6. Both bortezomib and 17-AAG induced ER stress, evidenced by induction of XBP1s, which was blocked by MKC-3946. Apoptosis induced by these agents was enhanced by MKC-3946, associated with increased CHOP. Finally, MKC-3946 inhibited XBP1 splicing in a model of ER stress in vivo, associated with significant growth inhibition of MM cells. Taken together, our results demonstrate that blockade of XBP1 splicing by inhibition of IRE1α endoribonuclease domain is a potential therapeutic option in MM.

Abstract 214: High expression of CKS1B antagonizes MLN4924, a nedd8-activating enzyme inhibitor, that induces myeloma cell growth inhibition through decreased neddylation of SCF complex

Abstract Background: MLN4924 binds to the NEDD8-activating enzyme (NAE), and promotes neddylation of SCF (Skp1-Cul1 / Cdc53-F-box protein) complex resulting in inhibition of proteasomal degradation of several substrates. CKS1B acts as an adaptor of SCF complexes involved in cell cycle progression and DNA damage repair in many cancers, including multiple myeloma (MM). In this study, we investigate the functional role of CKS1B expression on MLN4924 in myeloma and determine whether CKS1B can be used as a potential biomarker for sensitivity to MLN4924 treatment in MM. Methods: Three myeloma cell lines, KMS12, KMS28PE, and OCI-MY5 in which CKS1B was artificially over-expressed (CKS1B-OE) as well as their empty vector (EV) controls were treated with MLN4924 at different concentrations. The IC50 and growth inhibition of cells were analyzed via a fluorencent screeing assay. APC-labeled annexinV and PI were assessed by flow cytometry to detect apoptosis and cell cycle changes. The expression of Cullin-NEDD8 and a series of ubiquitined SCF substrates were analyzed by non-reducing western blot. Results: MLN4924 effectively inhibited cell growth and induced cell apoptosis in both CKS1B-OE and EV MM cells. However, MM cells transfected with EV were more sensitive than those transfected with CKS1B-OE as evidenced by the IC50 values (KMS28PE OE vs. EV 99: 65 nM; KMS12 OE vs. EV 125: 72 nM; and OCI-MY5 OE vs. EV 106:89 nM). The cell viabilities at 100 nM were 49.6% vs. 26.7%, 54.5% vs. 34.2%, and 53.6% vs. 36.8% in CKS1B-OE versus EV KMS28PE, KMS12, and OCI-MY5 cells (P&amp;lt;0.05). Western blots showed that over-expression of CKS1B significantly decreased expression of cullin1, nedd8, and the conjugated complex of cullin-nedd8 in MLN4924 treated cells (100 nM, 24h) compared with EV in all tested three cell lines. We also found that high expression of CKS1B was negatively correlated with SCF substrates including p21, CDT-1, p27 and CDT-1. MLN4924 induced a dose-dependent accumulation of these substrates in all three MM cell lines. Conclusion: High expression of CKS1B induces SCF substrate ubiquitination and degradation in MM cells. The NAE inhibitor MLN4924 induces cell apoptosis through decreased neddylation of SCF complex resulting in increase of p27, p21, CDT-1 and p130. CKS1B can be used as a marker of drug resistance to MLN4924, suggesting that a combination of MLN4924 with other drugs will be necessary to treat myeloma patients with high endogenous expression of CKS1B. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 214. doi:1538-7445.AM2012-214

Blockade of XBP1 Splicing by Inhibition of IRE1α Is a Promising Therapeutic Option in Multiple Myeloma

Abstract 133Multiple myeloma (MM) cells are characterized by high protein synthesis resulting in chronic endoplasmic reticulum (ER) stress, which is adaptively managed by the unfolded protein response (UPR). Therefore blockade of UPR could provide a novel therapeutic option in MM. Upon UPR, inositol-requiring enzyme 1α (IRE1α) is activated by auto-phosphorylation, resulting in activation of its endoribonuclease domain to cleave XBP1 mRNA from XBP1 unspliced form (XBP1u: inactive) to generate the XBP1 spliced form (XBP1s: active). XBP1s protein in turn regulates genes responsible for protein folding and degradation, playing a pro-survival signaling role in the UPR. In this study, we specifically examined whether IRE1α-XBP1 pathway is a potential therapeutic target in MM. We first examined the biologic significance of IRE1α by knockdown using lentiviral shRNA and observed significant growth inhibition in IRE1α knockdown cells. We next examined the impact of inhibition of XBP1 splicing using a novel small molecule IRE1α endoribonuclease domain inhibitor MKC-3946 (MannKind, Valencia CA). MKC-3946 blocked not only the basal level, but also inducible (by tunicamycin) XBP1s, evidenced by RT-PCR analysis in RPMI8226 cells, without affecting phosphorylation of IRE1α. Importantly, MKC-3946 also inhibited XBP1s in primary tumor cells from MM patients. We also confirmed functional inhibition of XBP1s, with target genes including SEC61A1, p58IPK, and ERdj4 downregulated by MKC-3946 treatment. Importantly, MKC-3946 triggered growth inhibition in MM cell lines, without toxicity in normal mononuclear cells. Furthermore, it significantly enhanced cytotoxicity induced by bortezomib or 17-AAG in RPMI8226 and INA6 cells, as well as primary tumor cells from MM patients. Both bortezomib and 17-AAG induced ER stress with XBP1s, which was markedly blocked by MKC-3946. Moreover, apoptosis induced by bortezomib or 17-AAG was enhanced by MKC-3946, associated with increased CHOP mRNA and protein, a proapoptotic factor triggered by ER stress. We next demonstrated that XBP1s was induced by bortezomib in INA6 cells co-cultured with bone marrow (BM) stromal cells, which was inhibited by MKC-3946, associated with enhanced cytotoxicity induced by the combination. Finally, MKC-3946 inhibited XBP1s in a model of in vivo ER stress induced by tunicamycin. To evaluate the anti-MM effect of MKC-3946, we used the subcutaneous RPMI8226 xenograft model in mice. MKC-3946 significantly reduced MM tumor growth in the treatment versus control group, associated with prolonged overall survival. We also confirmed that MKC-3946 treatment significantly inhibited XBP1s in excised tumors, assessed by RT-PCR. In order to examine the activity of MKC-3946 on MM cell growth in the context of the human BM microenvironment in vivo, we used the SCID-hu model, in which INA6 cells are directly injected into a human bone chip implanted subcutaneously in SCID-mice. MKC-3946 treatment significantly inhibited tumor growth compared with vehicle control. Moreover, XBP1s in excised tumor cells was inhibited, evidenced by RT-PCR. In conclusion, these data demonstrate that blockade of XBP1s by MKC-3946 triggers MM cell growth inhibition in vivo and prolongs host survival. Taken together, our results demonstrate that blockade of XBP1 splicing by inhibition of IRE1α endoribonuclease domain is a potential novel therapeutic option in MM. Disclosures:Tam:MannKind Corporation: Employment, Equity Ownership. Zeng:MannKind Corporation: Employment, Equity Ownership. Patterson:MannKind Corporation: Employment, Equity Ownership. Richardson:Bristol Myers Squibb: Membership on an entity’s Board of Directors or advisory committees; Novartis: Membership on an entity’s Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity’s Board of Directors or advisory committees; Celgene: Membership on an entity’s Board of Directors or advisory committees; Millennium: Membership on an entity’s Board of Directors or advisory committees. Munshi:Millennium: Membership on an entity’s Board of Directors or advisory committees; Celgene: Membership on an entity’s Board of Directors or advisory committees; Novartis: Membership on an entity’s Board of Directors or advisory committees. Anderson:Millennium: Membership on an entity’s Board of Directors or advisory committees; Onyx: Membership on an entity’s Board of Directors or advisory committees; MannKind: Membership on an entity’s Board of Directors or advisory committees.

Characterization of Pim Protein Kinases and Evaluation of Small Molecule Inhibitors in Multiple Myeloma

Abstract 2909Multiple myeloma (MM) is a plasma cell malignancy and is the second most common hematological neoplasm in the Western World. Despite the discovery of several highly effective chemotherapy agents, MM remains an incurable disease, suggesting the urgent need for better understanding the disease’s pathogenesis and for developing therapeutic agents that target novel molecular pathways. Pim (proviral insertion in murine lymphoma) kinases (Pim-1, -2 and -3) are constitutively active, oncogenic serine/threonine protein kinases that promote early transformation and tumor progression in hematological malignancies and in solid tumors including prostate cancer and colon cancer. In the current study, we characterized Pim expression and investigated the therapeutic potential of small molecule Pim kinase inhibitors in the treatment of MM. We found that Pim kinases are highly expressed in several MM cell lines (NCIH929, OPM-1, RPMI8226, U266 and MM1.R). Furthermore, Pim kinases were up-regulated in freshly isolated primary CD138+ myeloma cells (n = 4) when compared to CD138− cells (panel A). The predominant Pim kinase isoform (Pim-1, -2 or -3) varies among MM cell lines and among different patients. Two Pim kinase inhibitors, SMI-4a (selective small molecule Pim-1 and Pim-3 inhibitor) and 10058-F4 (Pim-3 and Pim-1 inhibitor) effectively inhibited myeloma cell growth, including steroid resistant MM1.R myeloma cells, with IC50s in the ∼10 mM range. Both SMI-4a and 10058-F4 induced apoptotic cell death in myeloma cells as measured by Annexin-V staining, caspase-9 activation and PARP cleavage in a dose dependent manner. To further dissect their mechanisms of action, we investigated the effects of SMI-4a and 10058-F4 on several cellular signaling pathways that are critical to the survival, cell cycle progression and proliferation of MM cells. Our data indicated that both SMI-4a and 10058-F4 reduce c-Myc protein expression levels and down-regulate the antiapoptotic Mcl-1 protein in MM cells (panel B). Our data also showed that MM cells treated with SMI-4a or 10058-F4 significantly reduced mTOR signaling as indicatd by decreased phosphorylation of 4E-BP1 and Cp70 S6 kinase α, the two common mTOR substrates. However, SMI-4a and 10058-F4 had no effect on the cell cycle regulation protein (p27Kip1) or heat shock protein 90. In summary, our data demonstrate that Pim inhibitors affect the survival and proliferation of myeloma cells and represent a potentially effective, novel strategy for the treatment of MM. We are currently performing in vivo studies to evaluate the therapeutic effects of Pim inhibitor in MM animal models (i.e, XPB-1s transgenic mouse model and NOD/SCID xenograft mouse model).This work was supported by MUSC Hollings Cancer Center Startup Fund, Hollings Cancer Center ACS IRG, and ASCO Conquer Cancer Foundation Career Development Award [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Deregulated Cellular Iron Metabolism Factors Mediate Iron Overload in Myeloma Cells and Osteoclasts, and Promote Myeloma Growth and Bone Disease,

Abstract 3941Iron overload is a significant clinical feature in multiple myeloma (MM) and has been implicated in osteoporosis. MM patients also frequently suffer from anemia presumably due to elevated hepcidin secretion and dysfunctional erythropoiesis. The aims of the study were to shed light on molecular mechanisms associated with iron overload in MM cells and study the effect of the novel iron chelator, Dp44mT, on MM cell growth, osteoclastogenesis and MM bone disease in vitro and in vivo. In our clinical global gene expression profiling (GEP) data the main iron transporter gene TFRC (transferrin receptor) was >3 folds higher (p<0.0001) in newly diagnosed MM cells (n=556) than normal plasma cells (n=25) while the iron exporter ferroportin was downregulated in MM cells by >4 folds (p<0.0001). Deregulated TFRC and ferroportin expression were more profound in the molecularly classified proliferation (PR) subtype. Osteoclasts which are known to have abundant mitochondria due to high energy consumption express excessive TFRC (>5 folds higher than highly proliferating MM cells). In primary MM cell-osteoclast cocultures (n=8) TFRC expression was upregulated in cocultured MM cells than baseline MM cells (p<0.03) while ferroportin was lower in cocultured osteoclasts than control osteoclasts (p<0.04). Our GEP, qRT-PCR and immunohistochemistry analyses revealed expression of hepcidin by osteoclasts but not MM cells. Hepcidin was not detected in conditioned media from osteoclasts cultured alone or cocultured with MM cells using ELISA, suggesting an autocrine role of hepcidin in maintaining excess iron in osteoclasts. In vitro, Dp44mT dose dependently inhibited growth of MM cell lines (n=3) at low nanomolar levels (IC50 at 3±0.8 nM, p<0.03, 48 hrs). In contrast, known chelators such as Deferoxamine and Deferasirox inhibited myeloma cell growth at 10–50 micromoles range. At 1nM Dp44mT also suppressed formation of multinucleated osteoclasts by 87% (p<0.001) and bone resorbing activity of mature osteoclasts on dentine slices by 94% (p<0.03). Dp44mT induced upregulation of BMP2 expression in osteoblast precursors and promoted osteoblast differentiation. In vivo, SCID-rab mice engrafted with luciferase-expressing U266 MM line (6 mice/group) or the Hg MM line (maintained through in vivo passaging, 10 mice/group) were subcutaneously treated with vehicle or Dp44mT (1 mg/kg/day) for 2–3 weeks. Using live-animal imaging, Dp44mT reduced growth of U266 cells by 3 folds from pretreatment levels (p<0.01) while in control group tumor burden was increased by 52 folds from pretreatment levels (p<0.002). Dp44mT also inhibited growth of Hg MM cells determined by measurement of circulating human immunoglobulins in mice sera (p<0.01). Osteoclasts numbers were lower by 36% (p<0.003) while osteoblasts numbers were higher by 59% (p<0.017) in myelomatous bones from hosts treated with Dp44mT than control vehicle. Our data suggest that interaction of myeloma cells with osteoclasts alters expression of distinct iron metabolism associated factors which elicit iron overload in both cell types, resulting in increased myeloma cell proliferation and osteoclast activity. This study also suggests that Dp44mT is an effective iron chelator with marked anti-MM activity. Disclosures:Barlogie:Celgene, Genzyme, Novartis, Millennium: Consultancy, Honoraria, Patents & Royalties. Shaughnessy:Myeloma Health, Celgene, Genzyme, Novartis: Consultancy, Employment, Equity Ownership, Honoraria, Patents & Royalties.

Arsenic trioxide-mediated growth inhibition of myeloma cells is associated with an extrinsic or intrinsic signaling pathway through activation of TRAIL or TRAIL receptor 2

Arsenic trioxide (ATO) is a well-known inhibitor of cell proliferation. Preclinical and clinical studies showed that ATO has anti-myeloma effects. However, the underlying mechanism remains elusive. In this study, the molecular mechanisms of ATO-induced myeloma apoptosis were explored on four myeloma cell lines of wild type or mutant p53 status and also on six primary myeloma cells. ATO induced potent inhibition of myeloma cell growth and myeloma cell apoptosis compared with controls. Further investigation showed that ATO down-regulated c-Myc and phosphorylated (p)-Rb while up-regulating p53, p21Cip1, and p27Kip1 proteins, resulting in G0/G1 or G2/M cell cycle arrest. ATO treatment increased mRNA levels of interferon regulatory factor-1 and TRAIL, as well as protein levels of caspase 8 and cleaved caspase 3, indicating the involvement of the extrinsic apoptotic pathway in the mutated p53 myeloma cells. ATO also activated caspases 3 and 9, indicating involvement of the intrinsic apoptotic pathway in the wild type p53 myeloma cells. More importantly, these molecular changes induced by ATO-treated myeloma cells are very similar to the baseline expression pattern of hyperdiploid myeloma, which has a relative good prognosis with high expression of TRAIL and interferon related genes. Together, our data suggest that ATO induces apoptosis in MM through either extrinsic or intrinsic signaling pathway, depending on the p53 genetic background. These observations may be employed as prognostic tools and lead to novel therapies in primary myelomas.

Small Molecule RITA Induces Apoptosis In Multiple Myeloma Cells through Activation of the p53 Pathway and Induction of ER-Stress response

AbstractAbstract 790TP53 mutations or deletions are relatively rare in multiple myeloma (MM). Thus, restoration of p53 tumor suppressor function in MM by blocking the inhibitory role of MDM2 is a promising and applicable therapeutic strategy. RITA (Reactivation of p53 and Induction of Tumor-cell Apoptosis), binds to p53, prevents the p53-MDM2 interaction and induces accumulation of p53 in solid tumors and leukemic cells. However, whether RITA exerts anti-myeloma activity is not known. Therefore, we examined the apoptotic effect of RITA and molecular mechanisms of RITA-induced apoptosis in MM cells. Treatment of MM cells with RITA caused a dose-dependent inhibition of survival and an increase in apoptosis of cells harboring wild type (MM.1S, H929) but not mutant (U266, LP1) or null p53 (8226R5) suggesting that RITA-induced apoptosis in MM cells is p53-dependent. MM cells were sensitive to low doses of RITA, killing about 80% of MM.1S or H929 cells at 2 or 6 μM, respectively. In addition, RITA elicited a dose-dependent inhibition of myeloma cell growth in 4 of the 5 primary MM samples tested. Importantly, RITA did not have a significant inhibitory effect on the survival of bone marrow or peripheral blood mononuclear cells obtained from 5 healthy donors at the concentrations that induced apoptosis of MM cells, indicating a preferential killing of myeloma cells by this drug. Furthermore, the combination of RITA with an MDM2 antagonist, nutlin displayed a strong synergism on the killing of H929 or MM.1S cells (CI=0.56-0.82). Western blot analysis showed that RITA induced an increase in the expression of p53 only in cells harboring wild type p53 but not mutant p53. The activation of p53 induced by RITA was mediated through modulation of multiple apoptotic regulatory proteins, including up-regulation of a pro-apoptotic protein Noxa, down-regulation of an anti-apoptotic protein Mcl-1 and activation of caspase-8 and -3. RITA-induced caspase-mediated apoptosis was followed by extrinsic pathway as shown by decrease in the percentage of annexin V-positive cells (p<0.05) as well as inhibition of cleavage of PARP and caspase-3 and/or caspase-8 activation in MM.1S or H929 cells when treated with either pan-caspase inhibitor, Z-VAD-FMK or caspase-8 specific inhibitor, Z-IETD-FMK. To further delineate the mechanisms of apoptosis, we performed gene expression profiling and identified up-regulation of transcription factors including JUN, DDIT3, ATF3 and ATF4, and down-regulation of survival factors, MYC and IGF1R in RITA-induced MM.1S cells, which were validated by qRT-pCR. Up-regulations of DDIT3, ATF3 and ATF4 are thought to be associated with the induction of endoplasmic reticulum (ER)-stress response. To examine whether apoptosis induction by RITA in MM cells is mediated through ER-stress response pathway, cells were treated with either an inhibitor of ER-stress-induced apoptosis, salubrinal, or a specific inhibitor of c-Jun N-terminal kinase (JNK), SP600125. Treatment of MM.1S or H929 cells with these inhibitors resulted in a significant inhibition of apoptosis induced by RITA as evidenced by inhibition of cleavage of caspase-3 and PARP, and decrease in the percentage of annexin V-positive cells (p<0.05). However, the above phenomenon was not observed in MM cells harboring mutant or null p53. Taken together, our results identify RITA as a promising agent in treatment of MM with two potential mechanisms of action: 1) activation of the p53 apoptotic pathway through up-regulation of Noxa and down-regulation of Mcl-1; and 2) p53-mediated induction of the ER-stress response pathways that may inhibit MM proliferation or survival. Our data provide the rationale for the clinical evaluation of RITA as a potential novel therapeutic intervention in MM. Disclosures:No relevant conflicts of interest to declare.

TRAIL as the ATO-Target Gene Uniquely Activated In the Hyperdiploid Subtype of Myeloma with Prognostic Relevance, Resulting In Better Prognosis

AbstractAbstract 1904Arsenic trioxide (ATO) is a well-known inhibitor of cell proliferation in certain forms of malignancy and has been successfully used in the treatment of acute promyelocytic leukemia. Preclinical and clinical studies showed that ATO has anti-myeloma effects both as a single agent and in the combination therapy; however, the underlying mechanism remains elusive. In this study, the molecular mechanisms of ATO-induced myeloma apoptosis were explored on four myeloma cell lines OPM2, U266, RPMI8226, and KMS28PE of wild type or mutant p53 status and six primary myeloma cells. Gene expression profiling (GEP) of CD138+ bone marrow plasma cells from 22 healthy individuals (NPC), 44 patients with monoclonal gammopathy of undetermined significance (MGUS), and 351 newly diagnosed MM patients were published previously (Zhan et al. Blood. 2006;108:2020-8. Shaughnessy et al. Blood. 2007;109:2276-84.); and GEP from 9 myeloma cell lines were used in this study from the unpublished data of the University of Utah. Cell growth and viability were assayed by trypan blue dye exclusion. Cell cycle and apoptosis were analyzed by flow cytometry using CellQuest software and Vybrant Apoptosis Assay Kit. Alterations of the signaling pathways induced by ATO were tested by real-time PCR and western blot. GEP was performed by using the Affymetrix U133Plus2.0 microarray. ATO induced potent inhibition of myeloma cell growth and myeloma cell apoptosis, compared with controls. Further investigation showed that ATO down-regulated c-Myc and phosphorylated (p)-Rb while up-regulating p53, p21Cip1, and p27Kip1 proteins, resulting in G0/G1 or G2/M cell cycle arrest. ATO treatment increased mRNA levels of interferon regulatory factor-1 and TRAIL, as well as protein levels of caspase 8 and cleaved caspase 3, indicating involvement of the extrinsic apoptotic pathway in the mutated p53 myeloma cells. ATO also activated caspases 3 and 9, indicating involvement of the intrinsic apoptotic pathway in the wild type p53 myeloma cells. The usage of ATO and TRAIL agonist together has a synergistic effect, indicated by a combination index of less than 1. More importantly, these molecular changes induced by ATO-treated myeloma cells are very similar to the baseline expression pattern of hyperdiploid myeloma, which has a relative good prognosis with high expression of TRAIL and interferon related genes. Together, our data suggest that ATO induces apoptosis in MM through either extrinsic or intrinsic signaling pathway depending on the p53 genetic background. These observations may be employed as prognostic tools and lead to novel therapies in primary myelomas. AcknowledgmentsThis work was supported by grants from National Natural Science Foundation of China (30973450 to JS), start-up funds from Shanghai Tenth People's Hospital (JS), institutional start-up funds from the University of Utah School of Medicine and the Huntsman Cancer Institute (FZ), the National Institutes of Health grant RO1 (CA115399 to GT, FZ) and Senior Award from the Multiple Myeloma Research Foundation (FZ). Disclosures:Zhan:University of Utah: Employment, patent Submission.

Antimyeloma Action of the Multikinase Inhibitor TG02

AbstractAbstract 4062Multiple myeloma (MM) is the second most common hematologic malignancy and remains incurable, despite recent advances in its treatment. Therefore, studies to develop new therapies are still necessary. MM is characterized by genetic instability with numerous chromosomal abnormalities and deregulation of several signalling pathways. Cell cycle control is also dysfunctional in this pathology, and altered functioning of cyclins has been indicated as a universal alteration in MM. Cyclins exert their action by controlling the activity of the cyclin-dependent kinases (CDKs). Therefore, CDKs represent promising novel therapeutic targets for MM. Several other kinases have important functions in MM, one of which - BMK or ERK5 - plays a key role in the proliferation and survival of the myelomatous clone. In this study we describe the preclinical activity of a novel multi-kinase inhibitor, TG02, in MM. This compound combines cell cycle regulatory and transcriptional CDK inhibition with activity against other oncogenic kinases, such as ERK5, JAK2, TYK2, FLT3 and TYRO3. Functional potency was assessed using MTT-based proliferation assays in a panel of MM cell lines. Maximal cytotoxicity was observed in the MM1S cell line with an IC50 value after 24 hours of 64 nM. There were cell lines with a more resistant phenotype, like OPM2, with an IC50 value after 24 hours of 4.7 μ M (although this was reduced to low nM by prolonged exposure). TG02 also inhibited the protective effect of the bone marrow microenvironment as it was able to induce growth inhibition of MM cells grown in direct coculture with bone marrow stromal cells (BMSC). To delineate the underlying mechanism of cytotoxicity induced by this compound, we performed cell cycle and apoptosis assays. There was a slight accumulation of cells in the G2-M phase of the cell cycle but the more marked effect was an increase in Annexin V-staining, indicative of apoptosis, which was detected as early as six hours after treatment of MM1S cells with 100 nM TG02. This process was associated with depletion of the anti-apoptotic proteins Mcl-1 and Bcl-XL, and cleavage of caspases-8,-9,-3 and -7 and PARP. Treatment with TG02 also induced a fall in mitochondrial membrane potential and the release of cytochrome c and AIF into the cytosol. We have also analyzed some substrates of the different kinases that TG02 targets, such as Rb (phosphorylated at Ser-807 by CDK2) and RNA pol II (phosphorylated by CDK9). TG02 dephosphorylated these two proteins in MM1S cells. TG02 was tested for in vivo anti-tumor activity using the human OPM2 MM xenograft model. In this model we observed that TG02 was able to decrease tumor volumes, and synergized with bortezomib. In conclusion, these results show a potent anti-myeloma activity of the multi-kinase inhibitor TG02, and supports additional preclinical studies together with its clinical development for the treatment of MM. Disclosures:Meshow:Charles River: Employment. Cheatham:Charles River: Employment. Burrows:Tragara Pharmaceutical: Employment.

Acadesine Inhibits Proliferation and Induces Apoptosis In Multiple Myeloma Cells, and Synergizes with Standard of Care Antimyeloma Agents

AbstractAbstract 5023Multiple myeloma (MM) is a malignancy characterized by the accumulation of plasma cells. The disease represents the second most common hematologic malignancy and remains incurable, despite recent advances in its treatment. Therefore, studies to develop new therapies are still necessary, particularly in patients with bad prognostic factors, such as 17p deleted/p53 mutated patients. In this study we describe the preclinical activity of 5-Aminoimidazole-4-carboxamide-1–4-ribofuranoside (AICAR or acadesine) in multiple myeloma. Acadesine is an analog of AMP that is widely used as an activator of AMP-kinase (AMPK), a protein that regulates the responses of the cell to energy changes.Acadesine induces apoptosis in different cell types including CLL, mantle cell lymphoma (MCL) and splenic marginal zone B-cell lymphoma (SMZL) cells and tumor cell lines, without affecting primary T lymphocytes. Thus, acadesine is a promising drug for the treatment of B-cell neoplasms. A clinical phase I/II study of acadesine is currently being performed in CLL patients.We studied the effects of acadesine on the MTT metabolization of several multiple myeloma cell lines (MM1S, MM1R, RPMI-8266, RPMI-LR5, U266, U266-LR7, U266 Dox4, MM144, MGG, SJR, OPM-2, NCIH-929). Acadesine inhibited MM cell growth and induced apoptosis, with IC50 values in the micromolar range, and independently of the p53 mutational status.Cancer treatment, including myeloma, is generally based on combinations of drugs with different mechanisms of action. Thus, we studied the effect of acadesine in double combinations with drugs used in myeloma therapy, such as dexamethasone, melphalan, doxorubicin, bortezomib, and lenalidomide. Analyses of these data using the Chou and Talalay method indicated that acadesine was synergistic with dexamethasone (CI values of 0.60), and particularly with lenalidomide (CI values of 0.42). These promising results with double combinations promoted the investigation of triple combinations in the MM1S cell line. Triple combination of acadesine plus dexamethasone plus lenalidomide or bortezomib notably improved the efficacy of the respective double combinations, being the combination of acadesine plus lenalidomide plus dexamethasone especially efficient.Further studies to determinate the mechanism of action, and in vivo studies in MM1S xenograph are ongoing. Disclosures:de Frias:Advancell: Employment. Campàs:Advancell: Employment.

Arsenic Trioxide-Mediated Growth Inhibition of Myeloma Cells Is Associated with An Extrinsic Signaling Pathway Involved in Caspase 3 and Caspase 8.

Abstract 4899Arsenic trioxide (ATO) is a well-known inhibitor of cell proliferation in certain forms of malignancy and has been successfully used in the treatment of acute promyelocytic leukemia. Preclinical and clinical studies showed that ATO has anti-myeloma effects both as a single agent and in the combination therapy; however, the underlying molecular mechanism remains elusive. This study was performed to evaluate the molecular mechanism underlying its anti-myeloma activities. Cells from OPM2, U266, RPMI8226 myeloma cell lines and patients diagnosed with myeloma (n=6) were cultured with various concentrations of ATO for 4 days. Cell growth and viability were assayed by trypan blue dye exclusion. Cell cycle and apoptosis were analyzed by flow cytometry using CellQuest software and Vybrant Apoptosis Assay Kit. Alterations of the signaling pathways induced by ATO were tested by real-time PCR and western blot. ATO induced potent inhibition of myeloma cell growth compared with untreated control cells. Further investigation showed that ATO down-regulated c-Myc and phosphorylated (p)-Rb, while it up-regulated p53, p21Clip1, and p27Kip1 proteins, resulting in G2/M cell cycle arrest and cell growth inhibition. ATO treatment increased mRNA levels of interferon regulatory factor-1 (IRF-1) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), as well as protein levels of caspase 8 and cleaved caspase 3, indicating involvement of the extrinsic apoptotic pathway. No significant change was detected in the expression levels of Bax, Bcl-xL caspase 9 and Bcl-2, indicating that the intrinsic signaling pathway was not involved. A pan-caspase inhibitor abrogated ATO-induced apoptosis of myeloma cells. Our data suggest that ATO induces apoptosis in MM cells most likely through an extracellular signaling pathway. DisclosuresNo relevant conflicts of interest to declare.

Preclinical Approach to Sensitize Multiple Myeloma Cells: Combination of the MEK Inhibitor PD0325901 with ABT-737 or Mevinolin.

Abstract 1842Poster Board I-868Multiple myeloma (MM) is a plasma cell malignancy incurable with existing conventional therapies. However, the increased understanding of the molecular mechanisms underlying the growth, progression and drug resistance of MM cells is allowing the development of novel therapies based on target-specific drugs. These agents have shown promising results in pre-clinical trials and some are already in early phase of clinical investigation. However, limitations of this approach are represented by the existence of cross-talking signals among different pathways which results in ineffective inhibition of a single pathway. Therefore, targeted therapy based on the multiple inhibition of key signal transduction pathways represents the present focus of translational research. We have already demonstrated (Haematologica 2008;93[suppl.2]:P195) the potent growth-inhibitory effects of the specific MEK inhibitor PD0325901 and the marked pro-apoptotic activity of the Bcl2/BclXL inhibitor ABT-737 (kindly provided by Abbott Laboratories) on MM cell lines and primary CD138+ cells from MM patients at different disease stages (smoldering, diagnosis, relapse, refractory/resistant). Since it has already been reported that the inhibitor of the mevalonate pathway, Mevinolin, strikingly induces apoptosis by regulating different pathways, including the MEK/ERK module, we aimed in the present study to analyze the impact of the simultaneous inhibition of both pathways on apoptosis and cell growth of MM cell lines and primary samples. We exposed the KMS18, KMS27 and ARH-77 MM cell lines to increasing concentrations of PD0325901 (1–100 nM) and ABT-737 (1–100 nM) or Mevinolin (1–100 μM), alone and in combination. When used as single agents the inhibition of cell-growth was dose-dependent, while if used in combination it was synergistic, with combination indexes (CI) of 0.12 and 0.15 for PD0325901 plus ABT-737 and the same plus Mevinolin, respectively (Chou-Talalay method). We then investigated the effects of these agents on apoptosis, as determined by the sub-G1 DNA peak, and found that PD0325901 mainly showed cytostatic effects, while ABT-737 and Mevinolin needed high concentrations to affect apoptosis. The simultaneous exposure to PD0325901 plus ABT-737 or Mevinolin at lower concentrations, induced apoptosis with highly synergistic effects, as demonstrated by a CI of 0.2 (KMS18) and 0.17 (KMS27) for PD0325901 plus ABT-737 and of 0.135 (KMS18) and 0.128 (KMS27) for PD0325901 plus Mevinolin. Similarly, mitochondrial membrane depolarization was greatly induced with the combination approach. Preliminary experiments performed on primary MM samples confirmed the pro-apoptotic synergistic activity of combination strategies. On the contrary, when we used the MEK-inhibitor resistant MM cell line ARH-77, the effects of ABT-737 and Mevinolin were not potentiated by MEK inhibition with PD0325901. In conclusion, we demonstrated that the simultaneous disruption of the MEK/ERK and Bcl2/BclXL or Mevalonate signalling is effective on apoptosis induction and growth inhibition of MM cells at a greater degree than single agent therapy. Additional ongoing studies on primary samples from MM patients at different stages of the disease will help to determine the feasibility and efficacy of these combinations for clinical use. Disclosures:Petrucci:Celgene: Honoraria; Janssen Cilag: Honoraria.

Myeloma cell growth inhibition is augmented by synchronous inhibition of the insulin-like growth factor-1 receptor by NVP-AEW541 and inhibition of mammalian target of rapamycin by Rad001

Multiple myeloma is still incurable. Myeloma cells become resistant to common drugs and patients eventually die of tumour progression. Therefore, new targets and drugs are needed immediately. NVP-AEW541 is a new, orally bioavailable small molecule inhibitor of the insulin-like growth factor-1 receptor (IGF-1R). Here, we show that NVP-AEW541 inhibits cell growth in myeloma cells at low concentrations in a time-dependent and a dose-dependent manner. Further experiments using the annexin-V-fluorescein isothiocyanate/propidium iodide assay revealed induction of apoptosis in common myeloma cell lines, but not in peripheral blood mononuclear cell from healthy donors. Stimulation of myeloma cells with IGF-1 led to a vast increase of cell growth and this was blocked by low doses of NVP-AEW541. Stimulation of myeloma cells with conditioned medium obtained from a 48-h-old HS-5 stromal cell culture was only partly blocked by NVP-AEW541. Western blotting experiments revealed that NVP-AEW541 decreased the phosphorylation status of P70S6 kinase and 4E-BP-1 but not of mammalian target of rapamycin (mTOR). Combined inhibition of IGF-1R and mTOR using the novel mTOR inhibitor Rad001 led to additive/synergistic increase of cell growth inhibition in multiple myeloma cells, which was accompanied by a stronger dephosphorylation of P70S6 kinase and 4E-BP-1. Taken together, we show that the combined inhibition of IGF-1R and mTOR by combining NVP-AEW541 and Rad001 is highly effective in multiple myeloma and might represent a potential new treatment strategy.

The CXCR4 Antagonist AMD3100 Stimulates the Proliferation of Myeloma Cells.

AMD3100, an antagonist of the chemokine receptor CXCR4, is about to be used clinically for the peripheral mobilization of hematopoietic stem cells, especially in patients with lymphoma and multiple myeloma. However, AMD3100 has been shown to activate a G protein coupled with CXCR4 and thus acts as a partial CXCR4 agonist in vitro. Although stromal cell-derived factor-1 (SDF-1) alone has minimal or negligible effects on the growth and survival of myeloma cells in vitro, many reports are consistent with the SDF-1/CXCR4 axis being involved in the progression of myeloma. Therefore, it is necessary to address the question of whether AMD3100 functions as a partial agonist for CXCR4 in myeloma cells, before it is released for wide clinical application. In this study, we explored whether AMD3100 affects the proliferation and survival of myeloma cells in vitro. As demonstrated previously, AMD3100 markedly inhibited the SDF-1 induced chemotaxis of myeloma cells, including three cell lines (RPMI8226, U266, and ARH77 cells), and CD138+ primary human myeloma cells. AMD3100 also induced internalization of CXCR4. SDF-1 alone did not stimulate the proliferation of these myeloma cells, nor did it rescue the cells from apoptosis induced by serum deprivation. By contrast, AMD3100 at 10−5M enhanced the proliferation of all three myeloma cell lines in serum-free condition by up to 2-folds in 3-day cultures, which was abrogated by pretreating the cells with pertussis toxin (PTX). This phenomenon was also observed with CD138+ primary human myeloma cells. In addition, AMD3100 enhanced the proliferation of U266 and ARH77 cells induced by interleukin-6 (IL-6). AMD3100 partially inhibited the apoptosis induced by serum deprivation, and the anti-apoptotic effect of AMD3100 was further enhanced in the presence of IL-6. AMD3100 on its own induced the phosphorylation of Akt and ERK1/2 but not Stat3 and p38/MAPK in RPMI8226 and U266 cells. The phosphorylation was also inhibited by pretreating the cells with PTX. The signal blocking agents wortmannin, PD98056, SB203580, and rapamycin did not affect the AMD3100-induced proliferation of RPMI8226 cells. LY294002 at concentrations not inhibiting spontaneous proliferation (5 μM or less) did not affect AMD3100-induced proliferation of the cells. AG490 inhibited spontaneous proliferation and AMD3100-induced proliferation of the cells in a dose-dependent manner. Accordingly, the signal-blocking effects were unclear. However, these results show that AMD3100 partially overcame the strong growth inhibition of myeloma cells induced by AG490. Our results indicate that AMD3100 can induce the phosphorylation of signaling molecules and stimulate the proliferation of myeloma cells, through signaling via G-protein pathway.