INA-6 Multiple Myeloma Cells Research Articles

Abstract 692: The BET inhibitor INCB054329 is synergistic with JAK1 inhibition in models of multiple myeloma

Abstract Bromodomain and Extra Terminal (BET) protein inhibitors have emerged as a potentially effective therapeutic option for multiple tumor types, through their ability to regulate expression of genes necessary for proliferation and survival. For example, multiple myeloma (MM) cells have been shown to be highly sensitive to BET inhibition due in large part to the ability of BET proteins to control transcription of c-myc, an oncogene known to be dysregulated in MM. Likewise, some inflammatory response and cytokine signaling pathways associated with MM (eg. IL-6/JAK/STAT pathway) have also been shown to be reliant on BET proteins. Therefore, inhibition of both BET proteins and the JAK/STAT signaling pathway may be beneficial to MM patients. Here we assess the in vitro and in vivo effects of combining clinical compounds that target BET proteins and JAK in multiple myeloma cell lines. Studies were performed using the potent pan-BET inhibitor INCB054329 and selective JAK1 inhibitors. When tested in cell proliferation assays, the combination of BET and JAK1 inhibitors displayed strong synergistic effects in the IL-6 dependent INA-6 MM cell line in vitro. Western blots also revealed that several pharmacodynamic (PD) markers including c-MYC, PIM-2 and phospho-STAT3 were further repressed with the combination than with single agents alone. Likewise, the c-MYC and p-STAT3 PD markers could also be increasingly repressed in vivo by combined administration of BET and JAK1 inhibitors in the INA-6 mouse xenograft model. In vivo efficacy experiments in the INA-6 model resulted in enhanced, synergistic tumor growth inhibition in the BET/JAK inhibitor cohort as compared with the single drug cohorts. Interestingly, the cytokine independent MM1.S cell line was also sensitive to the BET/JAK inhibitor combination in vivo, while being far less sensitive to JAK1 inhibition as a monotherapy. In the MM1.S model, the c-MYC and p-STAT3 PD markers also behaved as seen in the INA-6 model. Our data indicate that the pharmacological inhibition of BET proteins and JAK1 yields strong combinatorial effects in MM cell lines both in vitro and in vivo. Therefore, dual inhibition of BET proteins and the JAK/STAT signaling pathway may offer a novel therapeutic approach and suggest a potential clinical utility for this drug combination in MM. Citation Format: Matthew C. Stubbs, Xuesong M. Liu, Xiaoming Wen, Jun Li, Valerie Dostalik, Sybil O'Connor, Eian Caulder, Margaret Favata, Mark Rupar, Yu Li, Beth Rumberger, Thomas Maduskuie, Richard Sparks, Nikoo Falahatpisheh, Padmaja Polam, Kris Vaddi, Timothy Burn, Andrew P. Combs, Wenqing Yao, Reid Huber, Gregory Hollis, Peggy Scherle, Phillip CC Liu. The BET inhibitor INCB054329 is synergistic with JAK1 inhibition in models of multiple myeloma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 692. doi:10.1158/1538-7445.AM2015-692

Anti‐c‐MET Nanobody® – a new potential drug in multiple myeloma treatment

c-MET is the tyrosine kinase receptor of the hepatocyte growth factor (HGF). HGF-c-MET signaling is involved in many human malignancies, including multiple myeloma (MM). Recently, multiple agents have been developed directed to interfere at different levels in HGF-c-MET signaling pathway. Nanobodies are therapeutic proteins based on the smallest functional fragments of heavy-chain-only antibodies. In this study, we wanted to determine the anticancer effect of a novel anti-c-MET Nanobody in MM. We examined the effects of an anti-c-MET Nanobody on thymidine incorporation, migration, adhesion of MM cells, and osteoblastogenesis in vitro. Furthermore, we investigated the effects of the Nanobody on HGF-dependent c-MET signaling by Western blotting. We show that the anti-c-MET Nanobody effectively inhibited thymidine incorporation of ANBL-6 MM cells via inhibition of an HGF autocrine growth loop and thymidine incorporation in INA-6 MM cells induced by exogenous HGF. HGF-induced migration and adhesion of INA-6 were completely and specifically blocked by the Nanobody. Furthermore, the Nanobody abolished the inhibiting effect of HGF on bone morphogenetic protein-2-induced alkaline phosphatase activity and the mineralization of human mesenchymal stem cells. Finally, we show that the Nanobody reduced phosphorylation of tyrosine residues in c-MET, MAPK, and Akt. We also compared the Nanobody with anti-c-MET monoclonal antibodies and revealed the similar or better effect. The anti-c-MET Nanobody inhibited MM cell migration, thymidine incorporation, and adhesion, and blocked the HGF-mediated inhibition of osteoblastogenesis. The anti-c-MET Nanobody might represent a novel therapeutic agent in the treatment of MM and other cancers driven by HGF-c-MET signaling.

Decorin is down‐regulated in multiple myeloma and MGUS bone marrow plasma and inhibits HGF‐induced myeloma plasma cell viability and migration

Decorin is a stromal-produced small leucine-rich proteoglycan known to attenuate tumour pro-survival, migration, proliferation and angiogenic signalling pathways. Recent studies have shown that decorin interacts with the hepatocyte growth factor (HGF) receptor c-Met, a potential key pathway in multiple myeloma (MM). Decorin levels in paired peripheral blood and bone marrow plasma samples from healthy volunteers (HV) (n=23), and patients with monoclonal gammopathy of undetermined significance (MGUS) (n=41) and MM (n=19) were determined by ELISA. Further, the ability of decorin to inhibit HGF-induced effects on MM cell lines were analysed in vitro using cell viability and Transwell migration assays. We found that decorin concentrations were significantly higher (P<0.05) in bone marrow (BM) plasma from HVs (median 35.2ng/mL; range, 15.3-99.1) compared with MGUS (median 22.5ng/mL; range, 11.1-59.5) and patients with MM (median 21.5ng/mL; range, 10.6-35.9). Decorin levels were higher in BM plasma than in peripheral blood in all groups, with a BM/PB ratio of 3.9, 3.4 and 2.5 for HV, MGUS and MM, respectively. A positive correlation (Spearman's ρ=0.51, P<0.05) was found between simultaneously measured levels of HGF and decorin in BM plasma in HVs, but not in MGUS or MM samples. Functionally, decorin inhibited HGF-induced migration and viability of INA-6 and ANBL-6 MM cell lines, independent of c-Met down-regulation. Our results show that decorin is down-regulated in MGUS and MM bone marrow plasma and that it inhibits HGF-induced viability and migration of myeloma cell lines in vitro.

Targeting Brouton’s Tyrosine Kinase with PCI-32765 Blocks Growth and Survival of Multiple Myeloma and Waldenström Macroglobulinemia Via Potent Inhibition of Osteoclastogenesis, Cytokines/Chemokine Secretion, and Myeloma Stem-Like Cells in the Bone Marrow Microenvironment

Abstract 883▪▪This icon denotes a clinically relevant abstractSpecific expression of Bruton’s tyrosine kinase (Btk) in osteoclasts (OC), but not osteoblasts (OB), suggests its role in regulating osteoclastogenesis. Although Btk is critical in B cell maturation and myeloid function, it has not been characterized in plasma cell malignancies including multiple myeloma (MM) and Waldenström Macroglobulinemia (WM). We here investigate effects of PCI-32765, an oral, potent, and selective Btk inhibitor with promising clinical activity in B-cell malignancies, on OC differentiation and function within MM bone marrow (BM) microenvironment, as well as on MM and WM cancer cells. We further define molecular targets of Btk signaling cascade in OCs and MM in the BM milieu. In CD14+ OC precursor cells, RANKL and M-CSF stimulate phosphorylation of Btk in a time-dependent fashion; conversely, PCI-32765 abrogates RANKL/M-CSF-induced activation of Btk and downstream PLCγ2. Importantly, PCI-32765 decreased number of multinucleated OC (>3 nuclei) by tartrate-resistant acid phosphatase (TRAP) staining and the secretion of TRAP5b (ED50 = 17 nM), a specific mature OC marker. It increased size of OCs and number of nuclei per OC, with significantly defective bone resorption activity as evidenced by diminished pit formation on dentine slices. Moreover, lack of effect of Dexamethasone on OC activity was overcome by combination of Dexamethasone with PCI-32765. PCI-32765 significantly reduced cytokine and chemokine secretion from OC cultures, including MIP1α, MIP1β, IL-8, TGFβ1, RANTES, APRIL, SDF-1, and activin A (ED50 = 0.1–0.48 nM). It potently decreased IL-6, SDF-1, MIP1α, MIP1β, and M-CSF in CD138-negative cell cultures from active MM patients, associated with decreased TRAP staining in a dose-dependent manner. In MM and WM cells, immunoblotting analysis confirmed a higher Btk expression in CD138+ cells from majority of MM patients (4 out of 5 samples) than MM cell lines (5 out of 9 cell lines), whereas microarray analysis demonstrated a higher expression of Btk and its downstream signaling components in WM cells than in CD19+ normal bone marrow cells. PCI-32765 significantly inhibits SDF-1-induced adhesion and migration of MM cells. It further blocked cytokine expression (MIP1a, MIP-1β) at mRNA level in MM and WM tumor cells, correlated with inhibition of Btk-mediated pPLCγ2, pERK and NF-kB activation. Importantly, PCI-32765 inhibited growth and survival triggered by IL-6 and coculture with BM stromal cells (BMSCs) or OCs in IL-6-dependent INA6 and ANBL6 MM cells. Furthermore, myeloma stem-like cells express Btk and PCI-32765 (10–100 nM) blocks their abilities to form colonies from MM patients (n=5). In contrast, PCI-32765 has no adverse effects on Btk-negative BMSCs and OBs, as well as Btk-expressing dendritic cells. Finally, oral administration of PCI-32765 (12 mg/kg) in mice significantly suppresses MM cell growth (p< 0.03) and MM cell-induced osteolysis on implanted human bone chips in a humanized myeloma (SCID-hu) model. Together, these results provide compelling evidence to target Btk in the BM microenvironment against MM and WM., strongly supporting clinical trials of PCI-32765 to improve patient outcome in MM and WM. Disclosures:Chang:Pharmacyclics Inc: Employment. Buggy:Pharmacyclics, Inc.: Employment, Equity Ownership. Elias:Pharmacyclics Inc: Consultancy. Treon:Millennium: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Genentech: Honoraria. Richardson:Millennium: Membership on an entity’s Board of Directors or advisory committees; Celgene: Membership on an entity’s Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity’s Board of Directors or advisory committees; Novartis: Membership on an entity’s Board of Directors or advisory committees; Bristol Myers Squibb: 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 Pharmaceuticals, Inc.: Consultancy; Celgene: Consultancy; Novartis: Consultancy; Onyx: Consultancy; Merck: Consultancy; Bristol-Myers Squibb: Consultancy; Actelion: Equity Ownership, Membership on an entity’s Board of Directors or advisory committees.

PI3K/p110δ is a novel therapeutic target in multiple myeloma

In this study, we demonstrate expression and examined the biologic sequelae of PI3K/p110delta signaling in multiple myeloma (MM). Knockdown of p110delta by small interfering RNA caused significant inhibition of MM cell growth. Similarly, p110delta specific small molecule inhibitor CAL-101 triggered cytotoxicity against LB and INA-6 MM cell lines and patient MM cells, associated with inhibition of Akt phosphorylation. In contrast, CAL-101 did not inhibit survival of normal peripheral blood mononuclear cells. CAL-101 overcame MM cell growth conferred by interleukin-6, insulin-like growth factor-1, and bone marrow stromal cell coculture. Interestingly, inhibition of p110delta potently induced autophagy. The in vivo inhibition of p110delta with IC488743 was evaluated in 2 murine xenograft models of human MM: SCID mice bearing human MM cells subcutaneously and the SCID-hu model, in which human MM cells are injected within a human bone chip implanted subcutaneously in SCID mice. IC488743 significantly inhibited tumor growth and prolonged host survival in both models. Finally, combined CAL-101 with bortezomib induced synergistic cytotoxicity against MM cells. Our studies therefore show that PI3K/p110delta is a novel therapeutic target in MM and provide the basis for clinical evaluation of CAL-101 to improve patient outcome in MM.

CCL3 Impairs Osteoblast Function Via Downregulation of Osteocalcin.

Abstract 739A common feature of bone disease in cancer is hyperactivity of osteoclasts (OC). However, osteoblast (OB) inhibition is critical to the development of osteolytic lesions. Tumor-OC interactions have been extensively studied, the mechanism of OB inhibition however still remains elusive. Several chemokines are upregulated in the multiple myeloma (MM)/bone microenvironment. CCL3 (MIP-1αa), in particular, mediates MM cell migration and stimulates OC differentiation, directly, by stimulating precursor cell fusion, and indirectly, by inducing OB secretion of RANKL. Here, we investigate whether CCL3 interferes with OB differentiation and activity. In vitro osteoblastogenesis consists of differentiation of alkaline phosphatase (ALP) positive cells, followed by secretion and mineralization of the extracellular matrix. We observed that ALP-positive cells express both CCL3 receptors, CCR1 and CCR5, late in differentiation (40% and 32%, respectively, isotype control 9%). No significant CCL3 secretion was detected in OB culture supernatant, suggesting that paracrine CCL3 may primarily affect matrix mineralization. Indeed, exogenous CCL3 (25 to 100 ng/ml) did not modify OB number, instead it decreased calcium deposition (10% decrease at 25ng/ml, 33% decrease at 50 and 100 ng/ml, p<0.05). We next assessed the expression levels of proteins critical to matrix formation and mineralization including osteopontin, bone-sialoprotein and osteocalcin. Osteopontin expression was not affected by CCL3, while both bone-sialoprotein and osteocalcin were downregulated. Importantly, either continuous exposure to CCL3 or 24h stimulation of mature OB impaired RNA expression of osteocalcin (30% to 80%) and bone-sialoprotein (26% to 60%) but not ALP, confirming that CCL3 interferes with OB function rather than formation. We also observed a correlation between osteocalcin expression by IHC on BM biopsies and CCL3 levels in BM serum of MM patients. These data suggest that MM-derived CCL3 interferes with bone mineralization by inhibiting osteocalcin expression. Using neutralizing antibodies against CCL3 we restored both osteocalcin and bone sialoprotein RNA expression levels in the presence of CCL3. Importantly, pretreatment with a small molecule CCR1 inhibitor, MLN3897 (Millennium Pharmaceuticals) completely abrogated the inhibition on osteocalcin and partially reversed bone-sialoprotein expression, suggesting CCR1 as the main mediator of CCL3 effects. We further verified these results in an in-vivo setting of MM bone disease, using the SCID-hu model. CB17 SCID mice bearing a human fetal bone implant were engrafted with CCL3-expressing INA6 MM cells and treated orally with MLN3897 for a total of 49 doses. After 4 weeks of treatment the bones were harvested and stained for TRAP activity, hematoxylin-eosin and osteocalcin. The number of OC/400x field was significantly reduced in the treated group (2.7 vs 1.9, p<0.05), thus confirming in vivo the anti-osteoclastogenic effect of CCR1 inhibition. Moreover, in the presence of INA6 MM cells osteocalcin levels were downregulated compared to non-injected bones and treatment with the CCR1 inhibitor partially restored osteocalcin expression. These results suggest a new role for the CCL3/CCR1 pathway in the development of osteolytic lesions in MM, as inhibitor of OB function other than OC growth factor. Targeting this pathway represents a promising strategy for the treatment of bone disease. Disclosures: Veiby:Millennium Pharmaceuticals: Employment. Anderson:Millennium: Research Funding. Raje:Astrazeneca, Novartis, Celgene: Research Funding.

Citron Rho Interacting Kinase (CRIK) Regulates Survival in IL-6 Dependent Multiple Myeloma Cells.

Abstract 1825Poster Board I-851 PurposeRecent advances in understanding of the molecular alterations that occur at the genetic and epigenetic levels in Multiple Myeloma (MM) have led to major leaps in identifying molecular pathways that regulate progression and resistance to therapeutic agents. However, despite great scientific advances at the genomic level, studies to identify signaling pathways deregulated at the functional proteomic level in MM are limited. We have previously demonstrated that Citron Rho Interacting Kinase (CRIK) is overexpressed in primary multiple myeloma (MM) cells, as compared to the normal plasma cell counterpart, using an antibody-based protein microarray technique. We therefore sought to investigate the functional role of CRIK in MM cells. MethodsWe determined the protein expression level of 512 polypeptides in 12 samples of newly diagnosed patients with MM using high-throughput proteomic analysis with antibody-based protein microarray. Primary CD138+ sorted MM cells were obtained from the bone marrow of patients after informed consent. MM.1S, RPMI8226, and INA6 MM cell lines were used in this study. Protein expression has been studied by immunoblotting. Gene expression analysis has been assessed using the Affymetrix U133A platform. Lentivirus was used to knockdown CRIK in MM cell lines (MM.1S, RPMI8226, INA6). DNA synthesis, cell survival, cell cycle profiling and apoptosis were assessed by thymidine uptake, MTT, PI and Annexin/PI staining and flow cytometric analysis, respectively. ResultsOverexpression of CRIK has been confirmed in primary CD138+ tumor cells isolated from bone marrow of 12 patients with MM, as compared to normal plasma cells obtained from healthy donors. We found that CRIK-knockdown exerted an anti-proliferative and pro-apoptotic effect only in IL-6-dependent MM cell line INA6; in contrast, no effect on proliferation and survival was observed in MM1.S and RPMI8226. Indeed, INA6 CRIK-knockdown cells were characterized by a reduction in the proliferation rate, associated with decreased S-phase and G2/M phase cell cycle arrest. Moreover, induction of cytotoxicity was also demonstrated in CRIK knockdown cells compared to scramble probe transfected or non-transfected cells. We also showed that CRIK knockdown led to cytokinesis in INA6, indicating a possible mechanism for inhibition of proliferation of these cells. We next correlated CRIK gene expression level (CIT) with prognosis using previously published gene expression datasets and found that CRIK correlated with poor prognosis. ConclusionIn this study, we show that MM cells express a high level of CRIK, and that inhibition of this protein leads to significant inhibition of proliferation and survival of IL-6 dependent MM cells. Moreover, CRIK protein expression correlated with poor survival in patients with MM. DisclosuresAnderson:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Ghobrial:Millennium: Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau.

XmAb®5592 Fc-Engineered Humanized Anti-HM1.24 Monoclonal Antibody Has Potent in Vitro and In Vivo Efficacy against Multiple Myeloma.

Abstract 609HM1.24/CD317 or BST2, a cell surface protein highly expressed on malignant plasma cells, represents a potential target of immunotherapy for multiple myeloma (MM). Here we characterized XmAb®5592, a novel Fc-engineered and humanized anti-HM1.24 antibody (Ab), and studied mechanisms of its anti-MM activity. XmAb®5592, with double amino acid substitution in Fc region of the wild type IgG1, has approximately 40-fold and 10-fold increases in affinity for Fc gamma receptor III (FcγRIIIa) and (FcγRIIa), respectively, expressed on effector cells including NK cells. The Fv region of XmAb®5592 was humanized and engineered to achieve high affinity and specificity of binding to HM1.24-expressing target cells. XmAb®5592 reacts against a panel of MM cell lines (n=19) which are both sensitive or resistant to current anti-MM conventional and novel therapies. Importantly, it triggers 10-100-fold higher antibody-dependent cell-mediated cytotoxicity (ADCC) against these MM cell lines than a native/non Fc-engineered version (anti-HM1.24 IgG1) of the Ab. Specifically, the maximum specific lysis of MM1S, MM1R, and RPMI8226 target cells induced by XmAb®5592 is at a concentration of 0.001-0.01 μg/ml, whereas the IgG1 analog did not induce maximum cell lysis until 0.1 μg/ml. The maximum 100% specific lysis of INA-6 target cells occurred at 0.1 μg/ml of XmAb5592, in contrast to 60% maximum lysis induced by10 μg/ml of the IgG1 analog. Since the bone marrow (BM) microenvironment induces resistance in MM cells to conventional therapies, we next asked whether XmAb®5592 induced ADCC against MM cells even in the presence of BM stromal cells (BMSCs). Importantly, XmAb®5592 triggered significant ADCC against MM1S, MM1R, and INA-6 MM cells in the context of BMSCs. XmAb5592 also reacts against patient MM cells, and triggers robust ADCC against CD138-purified patient MM cells in assays using NK effector cells from normal donors. Furthermore, cross-linked XmAb5592 inhibited RMPI 8226 cell growth in the absence of effector cells. The in vivo efficacy of XmAb®5592 was next evaluated in murine subcutaneous (sc) xenograft murine models using RPMI 8226 cells. Administration of XmAb5592 (9mg/kg, ip, 2x/week for 4 weeks) led to a significant reduction in growth of established tumors in vivo compared to a non-engineered IgG1 anti-HM1.24 analog. At termination of the study. 7/15 mice were tumor free in the XmAb- treated group versus only 1/15 tumor free mice in the IgG1 analog treated group. An anti-HM1.24 antibody with Fc region engineered to completely ablate binding to FcγRs (knock-out) behaved equivalent to the PBS vehicle control in these studies, again underlining the significance of interaction with FcγR for anti-tumor efficacy. These results therefore suggest that XmAb5592, an anti-HM1.24 antibody engineered for improved effector function and antitumor potency in vitro and in vivo, is a promising next-generation immunotherapeutic for MM. Disclosures:Muchhal:Xencor: Employment. Horton:Xencor: Employment. Nguyen:Xencor: Employment. Karki:Xencor: Employment. Desjarlais:Xencor: Employment. Munshi:Millennium Pharmaceuticals: Honoraria, Speakers Bureau. Richardson:Keryx Biopharmaceuticals: Honoraria. Anderson:Millennium Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Restoration of Bone Balance Via Activin a Inhibition Results in Anti-Myeloma Activity

A distinct feature of multiple myeloma (MM) is the tight interaction between malignant plasma cells and their bone microenvironment, creating a niche suitable for MM growth. In particular, MM cells inhibit osteoblast (OB) differentiation and stimulate osteoclast (OC) function, resulting in imbalanced bone remodeling and osteolytic bone disease. Here we studied a novel cytokine, activin A, identified from a broad range of cytokines, in the development of MM bone disease. We next asked whether activin A inhibition could restore bone balance and suppress tumor growth. Activin, a member of the TNF-α superfamily, is a pleiotropic cytokine involved in bone remodeling. Here, we observed, that MM patients with multiple osteolytic lesions had a 4-fold increase in activin A expression levels in bone marrow plasma compared to MM patients with one or less osteolytic lesions and non-MM patients (average 123.6 ± 136 vs 26.4 ± 21.4 vs 30.6 ± 25.1 pg/ml respectively, p<0.05). Interestingly, our data demonstrate that the main source of activin in the MM niche are bone marrow stromal cells (BMSCs), followed by OCs, and OBs (average levels in 72h culture supernatant are 1884, 1300, 299 pg/ml, respectively). In contrast, MM cells did not secrete activin, but stimulated its secretion in coculture by BMSC (by 1.3 to 2 fold increase). Activin A stimulated OC differentiation in synergy with RANKL and M-CSF via induction of a three-fold increase in precursor cell proliferation. Moreover, activin A had a potent inhibitory effect on OB differentiation as verified by ALP activity (reduced by 30% compared to control, p<0.05) and OB function, assessed with alizarin red (80% inhibition, p< 0.01). To test the role of targeting activin A with therapeutic intent, we used both a neutralizing antibody and a soluble receptor fusion, RAP-011 (Acceleron Pharma Inc., Cambridge). In effect, both strategies enhanced OB differentiation and activity (5 fold increase in calcium deposition at day 21, p<0.05). This was confirmed by quantitative-PCR analysis of ALP and osteocalcin gene expression. Importantly, RAP-011 promoted OB differentiation even in the presence of INA6 MM cells and reversed the inhibitory effects of the stroma-dependent MOLP5 MM cells as well as patient derived MM cells on OB. Enhanced OB differentiation by RAP-011 resulted in inhibition of MM cell proliferation compared to BMSCs and mature OB. These data thus suggest that manipulating the bone niche may result in reduced tumor growth. To further verify if these results translated in reduced tumor growth in vivo, we used the SCID-hu mouse model consisting of INA6 MM cells injected in a subcutaneously implanted fetal human bone. RAP-011 treatment resulted in a decrease in the number of osteolytic lesions assessed by CT imaging accompanied by improved bone density. These effects translated in reduced MM cell growth, analyzed by soluble human IL6 receptor levels, in the treated group compared to the control (p<0.02). These data therefore suggest that activin A is involved in development of MM bone disease and can be effectively targeted by a novel clinical grade compound. RAP-011 demonstrated bone-anabolic effects via inhibition of OC formation and stimulation of OB differentiation resulting in restoration of bone balance within the MM niche, which translated in in-vivo inhibition of MM cell growth. These effects of RAP-011 support the use of the human ACE-011 as an attractive approach for the treatment of MM.

CCR1 Inhibition Targets Osteoclast-Myeloma Adhesion and Exerts in Vivo Anti-Osteoclast Activity

Among the components of the tumor microenvironment, osteoclasts (OC) and bone marrow stromal cells (BMSC) play a key role in stimulating multiple myeloma (MM) cell proliferation via cell-to-cell contact and cytokine secretion. In a vicious loop, MM cells promote OC development and impair osteoblasts (OB) differentiation shaping the microenvironment to support tumor growth and chemoresistance. These effects translate in osteolytic lesions that negatively affect patient quality of life and survival. CCL3 is involved in the pathogenesis of MM bone disease. Indeed, high bone marrow plasma levels of CCL3 correlate with osteolytic lesions in MM and CCL3 has a pro-osteoclastogenic effect. We have previously shown that inhibition of CCL3 receptor, CCR1, results in impaired osteoclastogenesis and blocks the proliferative advantage conferred by OCs to MM cells in vitro. (Vallet et al, Blood 2007) Here, we extend our studies and demonstrate in an in-vivo SCID-hu mouse model the anti-OC effects of MLN3897, a small molecule CCR1 inhibitor (Millennium Pharmaceuticals, Cambridge). CB17 SCID mice bearing a human fetal bone implant engrafted with INA6 MM cells were treated orally with MLN3897 for a total of 49 doses. After 4 weeks of treatment the bones were harvested and stained for TRAP activity and hematoxylin-eosin. The number of OC/400x field was significantly reduced in the treated group (2.7 vs 1.9, p<0.05), thus confirming in vivo the anti-osteoclastogenic effect of CCR1 inhibition. Although a 2-fold inhibition of tumor growth in the treated group was noted, this difference did not reach statistical significance. Our previous data suggested that CCR1 inhibition impaired OC-MM cell adhesion with subsequent reduced MM cell proliferation. Here, we observed a specific effect of CCR1 inhibition on MM cell/OC adhesion rather than BMSCs and fibronectin. Interestingly, these effects translated in anti-proliferative effects of the CCR1 inhibitor in OC-MM cells coculture with no effects in BMSCs-MM coculture, suggesting a specific inhibitory effect on the OC compartment. Ongoing studies to characterize the underlying mechanism of CCR1 inhbition on OC-MM cell adhesion will be presented. Combination approaches to study whether forced OB differentiation by the proteasome inhibitor, bortezomib, will improve BMSC sensitivity to CCR1 inhibition are being studied. These data confirm the specific in vivo anti-OC effects of CCR1 inhibition and will highlight the role of novel combinations by using anti-OC agents like MLN3897 and anabolic drugs like Bortezomib.

Promoting Osteoblastogenesis Using a Novel Dkk-1 Neutralizing Antibody in the Treatment of Multiple Myeloma Related Bone Disease

Treatment of bone disease in multiple myeloma (MM) has largely focussed on the osteoclast axis while the osteoblast axis has been underexploited. Dkk1, an inhibitor of the wingless int (wnt) pathway, is important in osteoblastogenesis. Increased expression of Dkk1 in a subset of MM patients and its association with lytic bone disease opens up the potential of targeting the osteoblast axis. The aim of this study was to test the effect of a Dkk-1 neutralizing chimeric antibody (Mab B3) on osteoblasts (OB), osteoclasts (OC) and MM cells in the context of the bone microenvironment. First, we tested the expression of Dkk1 in plasma and bone marrow of 16 MM patients and 10 MM cell lines. Dkk1 levels were >18 ng/mL in 2 out of 16 patients; levels were comparable in blood and bone marrow plasma. In contrast, very little Dkk1 (2–9 ng/ml) was produced by bone marrow stromal cells (BMSC). One out of 10 MM cell lines (INA-6) expressed low concentrations of Dkk1 in the supernatant. Next, we tested the effect of Mab B3 on MM cell lines, in the presence or absence of BMSC, and on OB and OC from MM patient derived bone marrow. The effects on OC were evaluated by TRAP staining and pit formation. Effects on OB were assayed by alkaline phosphatase staining and alizarin red assays for calcium deposition. Mab B3 treatment did not demonstrate direct cytotoxic effects on MM cell lines negative for Dkk1. Mab B3, however, enhanced OB differentiation and calcium deposition in a dose dependent manner and inhibited OC differentiation and function, as evidenced by a decrease in number of multinucleated TRAP+ cells and a decrease in pit formation. Ongoing studies are addressing the effect of Mab B3 on MM cells in the context of OC and OB. Mab B3 is also undergoing in vivo testing in a SCID-hu model bearing INA-6 MM cells. These studies and the underlying mechanism of action of Mab B3 will be presented. Our preliminary data suggests that Mab B3 has anabolic bone effects; a corresponding human monoclonal antibody may be useful for the treatment of MM related bone disease. Future studies will evaluate Mab B3 in combination with catabolic agents such as bisphosphonates with the goal of restoring normal bone homeostatsis.

Anti-DKK1 mAb (BHQ880) as a Potential Therapeutic for Multiple Myeloma.

Decreased activity of osteoblasts (OB) contributes to osteolytic lesions in multiple myeloma (MM). Dickkopf-1 (DKK1) is a soluble Wnt inhibitor produced by MM cells that inhibits osteoblastogenesis in the bone marrow (BM) microenvironment. DKK1, also present in MM patient plasma, has been shown to inhibit the differentiation of osteoblast precursor cells in vitro, and its plasma level correlates with focal bone lesions in MM. Therefore, we have evaluated DKK1 as a target in MM in the context of the BM microenvironment. We first analyzed the effects of a DKK1 neutralizing antibody (BHQ880) on OB differentiation. Anti-DKK1 Ab was able to increase differentiation of mesenchymal stem cells (MSCs) to OB and reduce IL-6 levels following MSC differentiation to OB. While OB activity in MSCs cultured with osteoblast differentiation media was reduced in the presence of INA-6 MM cells, treatment with DKK1 neutralizing antibody was able to restore OB activity in a dose-dependent manner, overcoming the negative effect of MM cells. We did not observe a direct effect of this Ab on growth or survival of human MM cell lines. However, when a panel of MM cell lines was cultured with BM stromal cells (BMSC), the Ab induced significant growth inhibitory effects on MM cells, associated with downregulation of IL-6 produced by MSCs. To evaluate the in vivo bone and antitumor effects of anti-DKK1 Ab treatment on MM cells in the human microenvironment, we used a SCID-hu murine model, using INA-6 MM cells. In this model we observed a direct correlation between the level of soluble human DKK1 in murine blood and the tumor growth. Following treatment with BHQ880, by bone histology analysis, we observed increased trabecular bone and numbers of OBs in the retrieved bone chip from BHQ880 treated mice compared to control mice, one month after initial dose. We also found an increase in human osteocalcin in the serum of BHQ880-treated mice compared to the controls, suggesting an increase in OB activity. Interestingly, we observed suppression of myeloma growth, measured by changes in serum level of soluble huIL6sR, 4 weeks following BHQ880 treatment of the mice. These results support DKK1 as an important therapeutic target in myeloma and provide the rationale for clinical evaluation of this molecule in MM to improve bone disease and to inhibit MM growth.

Multiple Myeloma Cell-Osteoblast Interaction Results in Impaired Bone Formation.

Osteolytic bone disease is a common complication of multiple myeloma (MM) resulting from uncoupled bone remodeling due to enhanced bone resorption and reduced bone formation. Bone formation is a complex process requiring functionally mature osteoblasts (OB). Mesenchymal stem cells differentiate into mature OB and following an active period of bone matrix synthesis lasting 1–2 weeks, they finally differentiate into inactive bone-lining cells or osteocytes. Although several studies have demonstrated that MM cells inhibit osteoblastogenesis via secretion of DKK1, a Wnt-pathway antagonist, the functional sequelae of interaction of mature OB with MM cells remains to be elucidated. Here, we studied the morphological and functional consequences induced by MM cells interacting with mature OB. Mature OB were generated from MM patients' bone marrow mononuclear cells by cultivation in differentiation media consisting of αMEM with 20% fetal bovine serum, β-glycerol phosphate (2.16 mg/ml), ascorbic acid (0.05 mg/ml) and dexamethasone (10 nM). These mature OBs were alkaline phosphatase (ALP) positive and secreted and mineralized bone matrix, as demonstrated by Alizarin Red staining. MM cell lines INA6 and MM1.S were co-cultured with mature OB at a 5:1 ratio for 2, 4 and 7 days in OB differentiation media and bone marrow stromal cells (BMSC) were used as negative controls. After 4 days of co-culture, we observed phenotypic changes featured by acquisition of a spindle-like shape with reduced ALP staining in OB. In contrast, OB alone were intensely ALP-positive and cuboidal-shaped cells. Co-culture with INA-6 MM cells induced a reduction in ALP enzymatic activity in a time-dependent manner by 28% (± 10%) at day 2 and 72% (± 5%) at day 4 (p<0.05), respectively, whereas co-culture with MM1.S induced a 38% (± 5%) reduction after 4 days. Other MM cell lines induced similar effects. We then verified OB activity by assessing osteocalcin release and matrix mineralization. Importantly, osteocalcin secretion was completely abrogated in the presence of INA6, while MM1.S reduced it by 50% as early as day 2 (p<0.05). Moreover, Alizarin red staining demonstrated an impairment of matrix mineralization after 7 days of co-culture. Reduced OB function in the presence of MM cells was further confirmed by downregulation of Type-I collagen expression in OB. These effects were associated with only modest (10%) OB apoptosis as demonstrated by APO2.7 staining after 4 days of co-culture compared to OB alone. These phenotypic and functional sequelae on OB were not induced by co-culture supernatants, suggesting the requirement for direct MM cell/OB contact. These results therefore suggest that MM cell/mature OB interactions result in inhibition of bone formation by inactivation of mature OB. Ongoing studies are characterizing the mechanism by which MM cells induce OB inactivation and whether these changes affect the OC compartment. These studies of MM cell-OB interactions will form the basis for evaluation of novel agents with anabolic effects on the bone in the future.

The MEK1/2 Inhibitor AZD6244 (ARRY-142886) Downregulates Constitutive and Adhesion-Induced c-MAF Oncogene Expression and Its Downstream Targets in Human Multiple Myeloma.

Human multiple myeloma (MM), an incurable plasma cell tumor, is highly dependent on its bone marrow (BM) microenvironment which secretes cytokines and growth factors (i.e., IL-6, IGF-1, BAFF) for myeloma cell growth, survival, and resistance to chemotherapeutic drugs. Studies of interactions of MM and BMSCs have demonstrated that activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) mediates these processes. Recently, gene expression profiling studies have revealed that the c-MAF oncogene, which is overexpressed in approximately 50% of myeloma cell lines and patient MM cells, not only stimulates cell cycle progression but also promotes pathological interactions between tumor and BMSCs. In this study, we examined effects of the MEK1/2 inhibitor AZD6244 (ARRY-142886) on the c-MAF signaling and adhesion-induced c-MAF expression in MM cells. We first demonstrated that AZD6244 inhibits growth of INA6, MM1S, MM1R and MCCAR MM cells in a dose-dependent manner (see also Abstract #553572, ASH 2006). We next found that AZD6244 significantly downregulates c-MAF mRNA and c-MAF protein expression in these MM lines, as early as 2h and this was sustained until 24h after drug treatment. Hypoxia-induced factor 2α (HIF-2α), a pro-angiogenic mediator, which regulates c-MAF gene expression and is regulated by ERK1/2, was significantly inhibited in AZD6244-treated MM cell lines. Since three c-MAF target genes, integrin β7, the C-C chemokines receptor-1 (CCR1), and cyclin D2, were recently identified in MM, we next asked whether the expression of these genes was concomitantly inhibited by AZD6244 in INA6 MM cells that lacks c-MAF translocation. Integrin β7 and CCR1 were inhibited by AZD6244 in a time-dependent manner, whereas cyclin D2 was not expressed in INA6 MM cells. Importantly, downregulation of c-MAF and integrin β7 by AZD6244 is associated with decreased MM cell adhesion to BMSCs and reduced VEGF secretion. Although the role of CCR1 in MM pathophysiology remains elusive, AZD6244 significantly decreased the expression of CCR1 as well as its cognate ligand MIP-1α in INA6 MM cells, which might inhibit a potential autocrine loop in MM cells. We next determined whether MM adhesion to BMSCs could upregulate the c-MAF pathway in MM cells, in the presence or absence of AZD6244. Adhesion of INA6 MM cells to BMSCs strongly induced ERK1/2 and STAT3 activation and augmented expression of c-MAF and its downstream targets (cyclin D2 and integrin β7). The induction of c-MAF and its downstream targets was also seen, although with less extent, in IL-6-induced INA6 MM cells. Conversely, AZD6244 inhibited adhesion-induced c-MAF and its target protein expression (cyclin D2, integrin β7) in INA6 MM cells. AZD6244 further blocked autocrine and paracrine VEGF secretion in a dose-dependent manner. In conclusion, these results confirm a role for c-MAF in the pathological interactions between MM cells and BMSCs and define an important role of the MEK/ERK activation in the ~40% of c-MAF-overexpressing myeloma cells that lack c-MAF translocations. Moreover, this study strongly supports AZD6244 (ARRY-142886) as a promising targeted therapeutic intervention in MM.

The In Vivo Activity of Neutralizing B Cell-Activating Factor (BAFF) Antibody in the Treatment of Multiple Myeloma (MM).

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 Res 2006; 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.

BCL3 is induced by IL-6 via Stat3 binding to intronic enhancer HS4 and represses its own transcription

BCL3 is a proto-oncogene affected by chromosomal translocations in some patients with chronic lymphocytic leukemia. It is an IkappaB family protein that is involved in transcriptional regulation of a number of NF-kappaB target genes. In this study, interleukin (IL)-6-induced BCL3 expression and its effect on survival of multiple myeloma (MM) cells were examined. We demonstrate the upregulation of BCL3 by IL-6 in INA-6 and other MM cell lines. Sequence analysis of the BCL3 gene locus revealed four potential signal transducer and activator of transcription (Stat) binding sites within two conserved intronic enhancers regions: one located within enhancer HS3 and three within HS4. Chromatin immunoprecipitation experiments showed increased Stat3 binding to both enhancers upon IL-6 stimulation. Silencing Stat3 expression by small interfering RNA (siRNA) abrogated BCL3 expression by IL-6. Using reporter gene assays, we demonstrate that BCL3 transcription depends on HS4. Mutation of the Stat motifs within HS4 abolished IL-6-dependent BCL3 induction. Furthermore, BCL3 transcription was inhibited by its own gene product. This repressive feedback is mediated by NF-kappaB sites within the promoter and HS3. Finally, we show that overexpression of BCL3 increases apoptosis, whereas BCL3-specific siRNA does not affect the viability of INA-6 cells suggesting that BCL3 is not essential for the survival of these cells.

A clinically relevant SCID-hu in vivo model of human multiple myeloma

AbstractWe developed a novel in vivo multiple myeloma (MM) model by engrafting the interleukin 6 (IL-6)-dependent human MM cell line INA-6 into severe combined immunodeficiency (SCID) mice previously given implants of a human fetal bone chip (SCID-hu mice). INA-6 cells require either exogenous human IL-6 (huIL-6) or bone marrow stromal cells (BMSCs) to proliferate in vitro. In this model, we monitored the in vivo growth of INA-6 cells stably transduced with a green fluorescent protein (GFP) gene (INA-6GFP+ cells). INA-6 MM cells engrafted in SCID-hu mice but not in SCID mice that had not been given implants of human fetal bone. The level of soluble human IL-6 receptor (shuIL-6R) in murine serum and fluorescence imaging of host animals were sensitive indicators of tumor growth. Dexamethasone as well as experimental drugs, such as Atiprimod and B-B4-DM1, were used to confirm the utility of the model for evaluation of anti-MM agents. We report that this model is highly reproducible and allows for evaluation of investigational drugs targeting IL-6-dependent MM cells in the human bone marrow (huBM) milieu. (Blood. 2005;106:713-716)

A Clinically Relevant SCID-hu in Vivo Model of Human Multiple Myeloma.

Human multiple myeloma (MM) xenografts in immunodeficient mice have limitations as a model for the human disease since they lack the human bone marrow (huBM) microenvironment. In contrast, murine models harboring a huBM microenvironment with implantation of patient MM cells in the huBM recapitulate the in vivo pathophysiology of MM and have significant advantages over conventional murine models for pre-clinical evaluation of investigational drugs. However, there are significant limitations in using patient MM cells in such models since i) not all patient MM samples engraft in the huBM; ii) only a fraction of engrafted specimens produce measurable paraprotein and/or osteolytic lesions; and iii) a limited number of MM cells can be harvested from an individual patient, thus limiting the number of mice that can be injected with cells from the same patient. To overcome these limitations, we have developed a novel murine model of MM by engrafting INA-6, a cytokine-dependent human MM cell line into SCID mice previously implanted with a human fetal bone chip (SCID-hu mice). INA-6 cells require either exogenous IL-6 or interaction with the bone marrow stromal cells (BMSCs) to proliferate in vitro. In this model, we monitored the in vivo growth of INA-6 cells stably transfected with a green fluorescent protein (GFP) expression vector (INA-6GFP+). Serum soluble human IL-6 receptor (shuIL-6R) and fluorescence imaging of host animals were sensitive indicators of tumor burden with time dependent increase. Fluorescence imaging was able to detect the myeloma cell growth earlier than measurement of sIL-6R levels. INA-6 MM cells grew in SCID-hu mice, but not in SCID mice injected subcutaneously or intravenously without the human fetal bone. We have further confirmed the feasibility of this model in monitoring the response to therapeutic agents such as dexamethasone by detecting reduction in the intensity of the fluorescent lesions as well as shuIL-6R in SCID-hu mice following anti-MM treatment. This highly reproducible model therefore allows for evaluation of investigational drugs targeting MM cells in the huBM milieu.

In the presence of bone marrow stromal cells human multiple myeloma cells become independent of the IL-6/gp130/STAT3 pathway

AbstractThe interleukin 6/glycoprotein 130/signal transducer and activator of transcription 3 (IL-6/gp130/STAT3) pathway has been reported to play an important role in the pathogenesis of multiple myeloma (MM) and for survival of MM cells. However, most data concerning the role of IL-6 and IL-6–triggered signaling pathways were obtained from experiments performed with MM cell lines and without considering the bone marrow microenvironment. Thus, the precise role of IL-6 and its intracellular signaling pathways for survival of human MM cells is still unclear. Here we show that treatment of human MM cells (IL-6–dependent MM cell line INA-6 and primary MM cells) with the IL-6 receptor antagonist Sant7 or with an anti-gp130 monoclonal antibody (mAb) induced apoptosis if the cells were cultured in the absence of bone marrow stromal cells (BMSCs). In contrast, apoptosis could not be observed if the MM cells were cocultured with BMSCs. The analysis of intracellular pathways revealed that Sant7 and anti-gp130 mAb were effectively inhibiting the phosphorylation of gp130 and STAT3 in the absence and presence of BMSCs, whereas ERK1 and ERK2 (ERK1,2) phosphorylation was only slightly affected. In contrast, treatment with the farnesyl transferase inhibitor, FPT III, induced apoptosis in MM cells in the absence or presence of BMSCs and led to a complete inhibition of the Ras/mitogen-activated protein kinase pathway. These observations indicate that the IL-6/gp130/STAT3 pathway is not essential for survival of human myeloma cells if they are grown in the presence of cells from the bone marrow microenvironment. Furthermore, we provide evidence that farnesyl transferase inhibitors might be useful for the development of novel therapeutic strategies for the treatment of MM.