Citations

Abstract BAFF is a member of the tumor necrosis factor (TNF) family and plays a role in B cell survival including MM cells. We have previously established a role for BAFF in localization and survival of MM cells in the bone marrow (BM) microenvironment. (Cancer Res2006; 66(13): 6675–82). Here we validate the role of BAFF in MM patients and demonstrate the in vivo activity of anti-BAFF antibody in a SCID-hu MM model. We first performed gene expression profiling (GEP) on CD 138+ plasma cells isolated from 90 MM patients and 11 healthy controls using the Affymetrix U133A arrays. GEP analysis demonstrated increased BCMA expression (p<0.0001, student T test) on newly diagnosed and relapsed MM versus normal plasma cells. Flow cytometry performed on MM patient cells demonstrated the presence of all 3 receptors on CD 138+ cells. ELISA assays confirmed increased plasma BAFF levels in 51 MM plasma (mean: 1049 pg/ml; range: 176–4252 pg/ml) compared to 11 normal donors (mean: 461pg/ml; range: 317–652pg/ml) [p<0.001]. To understand the functional significance that BAFF might play in the biology of MM, we studied the effects of recombinant BAFF (rh-BAFF) on MM cells directly and in the context of its BM microenvironment. Our data demonstrate that rh-BAFF confers a survival advantage to MM cells and protects them against dexamethasone-induced cytotoxicity. Importantly, anti-apoptotic proteins Bcl2 and XIAP were upregulated, as were growth and survival signals belonging to the AKT and MAPKinase pathways. Because of the survival advantage conferred by BAFF on MM cells we evaluated the use of a clinical grade-neutralizing antibody to BAFF. To evaluate the in vivo activity of anti-Baff in MM we used the SCID-hu model, where MM cells grow in the context of human BM microenvironment. A cohort of SCID-hu mice bearing INA-6 MM cells, were treated i.p. weekly with anti-BAFF neutralizing antibody (10 mg/kg, n=3) or control isotype (10 mg/kg, n=3), respectively, for four weeks. Serum levels of soluble human IL-6 receptor (shuIL-6R) released by MM cells into the murine serum were monitored as a measure of MM growth. At the end of treatment we observed a significant (p=0.048) reduction in shuIL-6R level. This translated into a survival advantage of 3.1 weeks in the anti-BAFF treated animals versus the control group (p= 0.02). We also evaluated in vivo effects of anti-BAFF on the bone compartment by radiographic analysis and tartrate-resistant acid phosphatase (TRAP) staining of human bone implants. Our results demonstrate a decrease in radiologically evident lytic lesions in the anti-BAFF treated animals. This was accompanied by a significant decrease in TRAP + osteoclasts in bone sections from treated mice when compared to control mice. Our data therefore suggests that anti-BAFF antibody may impact MM cell growth directly and/or via effects on the BM microenvironment by impacting bone resorption. Taken together, these data show a role for BAFF mediating MM cell survival and its in vivo anti-tumor activities provide a preclinical rational for its clinical evaluation in MM.

Abstract PS-341 (bortezomib, Velcade™) is a promising novel agent for treatment of advanced multiple myeloma (MM); however, 65% of patients with relapsed refractory disease in a phase II study did not respond. Lysophosphatidic acid (LPA) is a phospholipid which mediates tumor cell migration and invasion. Recent studies have shown that inhibition of LPAAT-β inhibits both Ras/Raf/Erk and PI3K/Akt signaling cascades. We have previously shown that lysophosphatidic acid acyltransferase (LPAAT)-β inhibitor CT-32615 triggers caspase-dependent apoptosis, and can overcome resistance to conventional therapeutics (ie, dexamethasone, doxorubicin, melphalan) in MM cells. In this study, we determined whether CT-32615 could also overcome resistance to PS-341. We first characterized molecular mechanisms of resistance to PS-341 in DHL-4 lymphoma cells. DHL-4 cells express low levels of caspase-3 and caspase-8; furthermore, no cleavage in caspase-8, caspase-9, caspase-3, poly ADP-ribose polymerase (PARP), or DNA fragmentation factor (DFF) 45 is triggered by PS-341 treatment. We have previously shown that PS-341 treatment triggers phosphorylation of c-Jun NH2-terminal kinase (JNK), which subsequently induces caspase-dependent apoptosis; conversely, JNK inhibition blocks PS-341-induced apoptosis. Here we show that PS-341 does not induce phosphorylation of SEK-1, JNK, and c-Jun in DHL-4 cells, suggesting that it does not trigger a stress response. Importantly, CT-32615 inhibits growth of DHL-4 cells in a time- and dose-dependent fashion: a transient G2/M cell cycle arrest induced by CT-32615 is mediated via downregulation of cdc25c and cdc2. CT-32615 triggers swelling and cell membrane destruction in DHL-4 cells, without caspase/PARP cleavage or TUNEL-positivity, suggesting a necrotic response. Our studies therefore demonstrate that LPAAT-β inhibitor CT-32615 triggers necrosis even in PS-341-resistant DHL-4 cells, providing the framework for its evaluation to overcome clinical PS-341 resistance and improve patient outcome.

Abstract NF-κB is a transcriptional factor promoting tumor cell growth and inhibition of apoptosis via regulating expression of proteins modulating cell cycle and anti-apoptosis. NF-κB is constitutively associated with an inhibitor (IκB), which is phosphorylated by IκB kinase (IKK) upon cell stimulation (ie, TNFα) and subsequently degraded by ubiquitin-proteasome pathway, thereby allowing NF-κB to translocate to nucleus. We have previously shown that an IKK inhibitor PS-1145 partially (20–50%) inhibits MM cell proliferation; however, it inhibits both IL-6 secretion from BMSCs triggered by MM cell adhesion and proliferation of MM cells adherent to BMSCs. Targeting IKKβ is therefore a possible therapeutic option for inhibition of MM cell growth in the bone marrow microenvironment by downregulating NF-κB activity. In this study, we further delineated the biologic significance of IKK inhibition in MM cells using IKKβ specific inhibitor MLN120B (Millennium Pharmaceuticals, Cambridge, MA). MLN120B induced 60–90% growth inhibition in cells from the MM cell lines RPMI8226, RPMI/Dox40, RPMI/LR5, U266, and INA-6; on the other hand, it induced only 25–30% inhibition in MM.1S and MM.1R cells, assessed by 72 h tritiated-thymidine uptake. Importantly, neither IL-6 nor IGF-1 overcomes the growth inhibitory effect of MLN120B in both MM.1S and U266 cells. Interestingly, MLN120B significantly augmented TNFα-induced cytotoxicity in MM.1S cells. We next examined whether MLN120B could enhance the cytotoxicity of other agents. MLN120B augmented growth inhibition triggered by doxorubicin and melphalan in RPMI8226 and IL-6 dependent INA-6 cell line. We therefore studied growth inhibitory effect of MLN120B in the presence of bone marrow stromal cells (BMSCs). MLN120B inhibited 70–80% of constitutive IL-6 secretion from BMSCs, without toxicity. Importantly, MLN120B almost completely blocked stimulation of MM.1S, U266 and INA-4 cell growth and IL-6 secretion from BMSCs induced by binding of tumor cells to BMSCs. Finally, MLN120B overcame the protective effect of BMSCs, cell adhesion mediated drug resistance, against dexamethasone in MM.1S cells. Taken together, our data demonstrate that an IKKβ inhibitor induces cytotoxicity in MM cells in the BM milieu, providing the framework for clinical trials of these novel agents to improve patient outcome in MM.

Abstract Angiogenesis or formation of new blood vessels from existing blood vessels, in contrast to vasculogenesis or de novo formation of new vessels, plays an important role in the progression and spread of most cancers. Multiple myeloma (MM) is characterized by increased microvessel density (MVD), a quantitative estimate of angiogenesis, which correlates with stage of disease. MVD increases with progression from MGUS to smoldering MM to newly diagnosed MM and relapsed MM. It is a powerful prognostic factor, predicting for overall survival. To further elucidate the biological basis for the prognostic value of increased angiogenesis in MM, we studied the interactions of MM cells with endothelial cells using HUVECS as a model system. Co-culture of MM cells (MM1.S, OPM2, U266) with HUVECS induced tumor cell proliferation. Enhanced tumor cell proliferation correlated with the number of HUVECs and was greater than that triggered by co-culture with patient bone marrow stromal cells. When HUVECs were fixed prior to co-culture there was a significant decrease in the tumor cell proliferation. Addition of HUVEC conditioned media to the MM cell lines also induced proliferation. Importantly, HUVECS protected against anti-MM agents including conventional agents (Dexamethasone, Doxorubicin, Melphalan) and novel drugs (Revlimid™). The protective effect afforded by co-culture was lost on HUVEC fixation. Intracellular signaling events following MM cell-endothelial cell contact were studied to understand the mechanisms of the proliferative and protective effects. Western blotting demonstrated activation of the JAK/STAT, PI3K/Akt and the MAPK pathways, mediating proliferation and survival. Ongoing studies focused on understanding cytokine as well as adhesion-mediated interactions between the endothelial cells and the MM cells will identify targets for new therapeutic approaches in MM.

Abstract Interleukin-6 (IL-6) and insulin-like growth factor-1 (IGF-1) mediate growth of MM cells via activation of the mitogen-activated protein kinase (MAPK), JAK2/STAT3, and phosphatidylinositol 3′-kinase/Akt kinase (PI3-K/Akt) signaling cascades. We have previously demonstrated the in vitro and in vivo activity of Revlimid™ (CC-5013), an immunomodulatory analog (IMiD) of thalidomide, in MM. In the present study, we have examined the anti-MM activity of rapamycin, a specific mTOR inhibitor, combined with Revlimid™. This combination was highly synergistic at 0.1nmol/L of rapamycin with 0.1mmol/L of Revlimid™, and remained synergistic at higher concentrations. Based on the Chou-Talalay method, combination indices of < 1 were noted for all dose ranges of Revlimid™ and rapamycin, suggesting strong synergism. Importantly, this combination was able to overcome drug resistance when tested against MM cell lines resistant to conventional (doxorubicin, melphalan, dexamethasone) chemotherapy. Moreover, the combination, but not rapamycin alone, was able to overcome the growth advantage conferred on MM cells by IL-6, IGF-1, or adherence to bone marrow stromal cells (BMSCs). Cytotoxicity triggered by a combination of rapamycin with Revlimid™ resulted in apoptosis of MM cells. Furthermore, differential signaling cascades, including the MAPK and PI3-K/Akt pathways, were targeted by these drugs individually and in combination, suggesting the molecular mechanism by which they interfere with MM growth and survival. These studies therefore provide the framework for the clinical evaluation of targeted agents like mTOR inhibitors combined with immunomodulatory agents like Revlimid™ to improve patient outcome in MM.

A critical role for vascular endothelial factor (VEGF) has been demonstrated in multiple myeloma (MM) pathogenesis. Here, we characterized the effect of the small-molecule VEGF receptor inhibitor pazopanib on MM cells in the bone marrow milieu. Pazopanib inhibits VEGF-triggered signaling pathways in both tumor and endothelial cells, thereby blocking in vitro MM cell growth, survival, and migration, and inhibits VEGF-induced up-regulation of adhesion molecules on both endothelial and tumor cells, thereby abrogating endothelial cell-MM cell binding and associated cell proliferation. We show that pazopanib is the first-in-class VEGF receptor inhibitor to inhibit in vivo tumor cell growth associated with increased MM cell apoptosis, decreased angiogenesis, and prolonged survival in a mouse xenograft model of human MM. Low-dose pazopanib demonstrates synergistic cytotoxicity with conventional (melphalan) and novel (bortezomib and immunomodulatory drugs) therapies. Finally, gene expression and signaling network analysis show transcriptional changes of several cancer-related genes, in particular c-Myc. Using siRNA, we confirm the role of c-Myc in VEGF production and secretion, as well as angiogenesis. These preclinical studies provide the rationale for clinical evaluation of pazopanib, alone and in combination with conventional and novel therapies, to increase efficacy, overcome drug resistance, reduce toxicity, and improve patient outcome in MM.

AbstractCyclin-dependent kinase (CDK) inhibitors have the potential to induce cell-cycle arrest and apoptosis in cancer cells. Seliciclib (CYC202 or R-roscovitine) is a potent CDK inhibitor currently undergoing phase-2 clinical testing in lung and B-cell malignancies. Here we studied the in vitro cytotoxic activity of seliciclib against multiple myeloma (MM) cells. Our data demonstrate that seliciclib has potent cytotoxicity against MM cells that are both sensitive and resistant to conventional therapy as well as primary MM cells from patients. Cell-cycle and Western blot analysis confirmed apoptosis. Importantly, seliciclib triggered a rapid down-regulation of Mcl-1 transcription and protein expression independent of caspase cleavage. Adherence of MM cells to bone marrow stromal cells (BMSCs) induced increased Mcl-1 expression associated with signal transducer and activator of transcription 3 (STAT3) phosphorylation, which was inhibited in a time- and dose-dependent manner by seliciclib. Furthermore, seliciclib inhibited interleukin 6 (IL-6) transcription and secretion triggered by tumor cell binding to BMSCs. Up-regulation of Mcl-1 expression in cocultures was only partially blocked by neutralizing antibody to IL-6, suggesting alternative mechanisms of Mcl-1 modulation by seliciclib. Finally, combination studies of seliciclib with doxorubicin and bortezomib show in vitro synergism, providing the rationale for testing these drug combinations to improve patient outcome in MM.

AbstractPrevious studies have demonstrated the in vitro and in vivo activity of CC-5013 (Revlimid), an immunomodulatory analog (IMiD) of thalidomide, in multiple myeloma (MM). In the present study, we have examined the anti-MM activity of rapamycin (Rapamune), a specific mTOR inhibitor, combined with CC-5013. Based on the Chou-Talalay method, combination indices of less than 1 were obtained for all dose ranges of CC-5013 when combined with rapamycin, suggesting strong synergism. Importantly, this combination was able to overcome drug resistance when tested against MM cell lines resistant to conventional chemotherapy. Moreover, the combination, but not rapamycin alone, was able to overcome the growth advantage conferred on MM cells by interleukin-6 (IL-6), insulin-like growth factor-1 (IGF-1), or adherence to bone marrow stromal cells (BMSCs). Combining rapamycin and CC-5013 induced apoptosis of MM cells. Differential signaling cascades, including the mitogen-activated protein kinase (MAPK) and the phosphatidylinositol 3′-kinase/Akt kinase (PI3K/Akt) pathways, were targeted by these drugs individually and in combination, suggesting the molecular mechanism by which they interfere with MM growth and survival. These studies, therefore, provide the framework for clinical evaluation of mTOR inhibitors combined with IMiDs to improve patient outcome in MM.

AbstractGenetic heterogeneity between individuals confounds the comparison of gene profiling of multiple myeloma (MM) cells versus normal plasma cells (PCs). To overcome this barrier, we compared the gene expression profile of CD138+ MM cells from a patient bone marrow (BM) sample with CD138+ PCs from a genetically identical twin BM sample using microarray profiling. Two hundred and ninety-six genes were up-regulated and 103 genes were down-regulated at least 2-fold in MM cells versus normal twin PCs. Highly expressed genes in MM cells included cell survival pathway genes such as mcl-1, dad-1, caspase 8, and FADD-like apoptosis regulator (FLIP); oncogenes/transcriptional factors such as Jun-D, Xbp-1, calmodulin, Calnexin, and FGFR-3; stress response and ubiquitin/proteasome pathway–related genes and various ribosomal genes reflecting increased metabolic and translational activity. Genes that were down-regulated in MM cells versus healthy twin PCs included RAD51, killer cell immunoglobulin-like receptor protein, and apoptotic protease activating factor. Microarray results were further confirmed by Western blot analyses, immunohistochemistry, fluorescent in situ hybridization (FISH), and functional assays of telomerase activity and bone marrow angiogenesis. This molecular profiling provides potential insights into mechanisms of malignant transformation in MM. For example, FGFR3, xbp-1, and both mcl-1 and dad-1 may mediate transformation, differentiation, and survival, respectively, and may have clinical implications. By identifying genes uniquely altered in MM cells compared with normal PCs in an identical genotypic background, the current study provides the framework to identify novel therapeutic targets.