ALBERT

Description: 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

Description: Abstract 4915 Multiple studies have highlighted the critical role of mutation and loss of p53 function in multiple myeloma (MM) when acquiring a more aggressive phenotype and refractoriness to treatment. Therefore, agents capable of overcoming p53 mutational status are important in the context of MM therapeutics. We have previously reported the in vitro and in vivo anti-MM activity of the multi-targeted small molecule inhibitor RGB-286638. Using a human MM cell xenograft model in SCID mice we demonstrated that RGB-286638 inhibited tumor growth and prolonged survival. Our data confirmed suppression of CDK1/cyclin B, CDK4, 6/Cyclin D1, D3, and CDK2/Cyclin E complexes in MM.1S MM cells containing wt-p53, which was correlated with rapid downregulation of Rb phosphorylation, resulting in effective G2/M cell cycle blockage and increased sub-G1phase. RGB-286638 induced dose and time-dependent inhibition of RNA pol II phosphorylation as an early event promptly followed by p53 induction. Moreover, RGB-286638 treatment was associated with p53 phosphorylation at ser 15, indicative of DNA damage followed by apoptosis, evidenced by caspases 8, 9 and 3 cleavage and confirmed by Annexin V/PI staining. All together these data suggested that RGB-286638-induced RNA pol II inhibition triggers cytotoxicity in MM cells via p53-dependent apoptosis. Interestingly, RGB-286638 demonstrated cytotoxic activity even in p53-deficient conventional drug-resistant RPMI 8226/Dox 40 MM cells. RGB-286638 treatment of RPMI 8226/Dox40 MM cells showed increased PARP response associated with enhanced NAD depletion followed by increased ATP consumption. Furthermore, concomitant assessment of RGB-286638-induced ATP depletion versus cytotoxicity demonstrated more than 60% ATP loss preceded cell death in RPMI 8226/Dox40 but not in MM.1S. This data suggests the role of either p53-mediated apoptosis (when active) or PARP-induced NAD/ATP depletion and bioenergetic crisis (when absent). Interestingly, the knockdown of p53 did not rescue MM.1S cells from RGB 286638-induced death, suggesting the existence of alternative p53-independent pathways through which RGB-286638 exerts its cytotoxic activity. Ongoing studies are addressing the molecular effects of p53 silencing in MM cells. In addition, dissecting the mechanism of RGB-286638 p53-independent cytotoxicity in MM cells will provide insights for future therapeutic strategies in patients with aggressive MM and associated mutated/deleted-p53. Disclosures Loferer: GPC Biotech AG: Employment. Munshi:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis : Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Anderson:Millenium: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Raje:Celgene: Research Funding; Novartis: Research Funding; AstraZeneca: Research Funding.

Description: Hsp90 inhibitor has shown promising anti-tumor activity through the destabilization and eventual degradation of Hsp90 client proteins critical for cell survival. In this study, we examined the in vitro effects of Hsp90 inhibitor on the phenotype and function of human T lymphocytes and NK cells. We observed no significant effects of Hsp90 inhibitor treatment on cell survivals. However, Hsp90 inhibitor treatment for 24 hours led to irreversible down-regulation of expression of critical T-cell surface antigens including CD3, CD4, CD8, CD28, CD154 (CD40L) and TCRab. Among the antigens evaluated, expression of CD4 antigen was most significantly downregulated (untrt vs. trt = 326 vs. 88 in Mean Fluorescence Intensity) following Hsp90 inhibitor treatment. Decreased CD3+ T lymphocytes proliferation (untrt vs. trt = 222839 cpm vs. 111102 cpm, 3[H]-thymidine incorporation) and reduced IFN-g secretion (untrt vs. trt = 77 vs. 48 pg/ml) was observed upon stimulation with allogeneic dendritic cells following 24 hrs treatments of T cells with Hsp90 inhibitor. Furthermore, CD3+ T-cell proliferation in response to mitogen stimulation, as measured by flow cytometry using CFSE was decreased following Hsp90 inhibitor treatment (untrt vs. trt = 41% vs. 3%, CFSE). Specifically, the CD4+CD28+ (untrt vs. trt = 32% vs. 1%) and CD8+CD28+ (untrt vs. trt = 27% vs. 17%) activated T-cell subpopulations displayed a significant decrease in proliferation in response to mitogen. Similarly, NK cells displayed decreased activation receptor expression including CD2, CD11a, CD94, NKp30, NKp44, NKp46, and KARp50.3 and reduced cytotoxic activity against multiple myeloma cells (untrt vs. trt = 49% vs. 11% against MM1S cells, 65% vs. 8% against ARP cells) following Hsp90 inhibitor treatment. These studies demonstrate that Hsp90 inhibitor treatment significantly affects phenotype and function of human T-lymphocytes as well as NK cells, and suggest the need to monitor immune functions in patients being treated with Hsp90 inhibitor in our future studies.

Description: Abstract 1809 Poster Board I-835 Bone marrow infiltration by myeloma cells and osteolytic bone lesions are the major features of Multiple Myeloma. Magnetic Resonance Imaging (MRI) has been used in MM not only to image bone marrow (BM) and to identify lytic bone disease but to also evaluate therapeutic response and prognosis. Gadolinium (Gd)-based contrast agents are frequently used to enhance MRI resolution. We evaluated effect of the most common Gd-containing agent, Omniscan, on myeloma cells. We observed that Omniscan induced both time and dose dependent MM cell growth in vitro (8-20 fold increase relative to control). Importantly, the presence of BMSC enhanced the effect of Omniscan on growth of both MM cell lines and primary MM cells. However, Omniscan was not able to overcome cytotoxic effects of conventional and novel agents in MM. This growth promoting effects were not observed on normal BM stromal cells. Evaluating the molecular mechanism of action of Omniscan on MM cells, we observed time dependent ERK1/2 phosphorylation as well as reversal of growth promoting effects of Omniscan by specific inhibition of ERK signaling; however, Omniscan had no effect on STAT3 and AKT signaling pathways. Next, we investigated in vivo effect of Omniscan in a murine xenograft model of MM. Following detection of tumor, mice were treated with either iv Omniscan or PBS. Treatment with Omniscan significantly induced MM tumor growth compared to control mice (1042 ±243 mm3 vs 502 ±137 mm3 respectively; p=0.0001). Finally in autopsies in 8 MM patients with repeated exposure to Omniscan, we quantified gadolinium in various tissues using Inductively-coupled mass spectrometry. We observed massive quantities of gadolinium accumulation in tissues of these MM patients regardless of their renal function. These results, confirming both in vitro and in vivo growth promoting effects of Gd-containing contrast agent on MM, suggest the need for further analysis of the mechanism of its action on myeloma cells and careful analysis of its clinical impact in MM patients undergoing MRI evaluation. Disclosures No relevant conflicts of interest to declare.

Description: Abstract 1786 Poster Board I-812 Background Multiple Myeloma (MM) is characterized by a clonal proliferation of antibody producing malignant plasma cells. Complete or partial monoallelic deletion of chromosome 13, is commonly observed in tumor cells of patients with monoclonal gammopathy of unknown significance and in over 50% of MM patients, as well as chronic lymphocytic leukemia (CLL) and mantle cell lymphoma. Recurrent loss of a minimal common region (MCR) of 10 megabases at 13q14, in MM and CLL suggests the MCR harbors a tumor suppressor gene(s) (TSG) with biological and clinical relevance. Within this MCR resides the Ret Finger Protein 2 (RFP2) encoding gene, which produce an E3 ubiquitin ligase located in the endoplasmic reticulum (ER). Because of its copy number-dependent expression, its strong and unique promoter, and its associated inferior survival with reduced expression in MM, RFP2 represents a candidate TSG. Nevertheless, its role and targets have not yet been established. Here we describe a functional analysis of RFP2 in MM cells. Methods: The MMS1 MM cell line lacks chromosome 13 deletion. To study the effects of loss of RFP2 in this line we used the PLKO- GFP lentiviral vector to stably transduce a RFP2 shRNA. Flow cytometer selected cell lines exhibit significantly reduced expression of RFP2 relative transduced shRNA controls or to the parental line. Cell growth rate was measured using trypan blue counting, soft agar colony formation and thymidine incorporation. Cell cycle analysis and apoptosis were measured by flow cytometry after staining with PI or Annexin-V PE and 7AAD, respectively. Intracellular signal modulation was demonstrated by Western blotting. Results At day six post transduction, 75-95% of MMS1 cells were GFP positive. RFP2 downregulation induced an impairment of cell growth with a G2 phase arrest and a profound apoptosis (over 50% at day six as compared with less than 15% of controls). This effect was mediated through ER stress evidenced by upregulation of p-eIF2a and Bip, and the induction of Caspase-8, 9 and 3 cleavage. RFP2 complementation did not produce by itself a significant growth promoting effect, but was able to rescue the knockdown-induced growth retardation. The above described presence of ER stress, combined with the previous reports that RFP2 has E3 ubiquitin ligase activity prompted us to assess total protein ubiquitination. Concordant with its effects on ER stress, RFP2 downregulation was associated with significantly higher levels of poly-ubiquitinated proteins. Subsequently, we were able to document a significant reduction (60% inhibition) in 20S proteasome activity in RFP2 down regulated cells. Proteasome inhibition by RFP2 down regulation was confirmed in other MM cell lines and was partially abrogated by restoring RFP2 levels by overexpression. Importantly, RFP2 down regulated cells were more sensitive to bortezomib; indeed proteasome inhibition was synergistic with RFP2 downregulation in MM cells. The above results prompted us to study the mechanism whereby RFP2 impacts survival and proliferation of MM cells. Inhibition of the NF-kappa-B (NFκB) pathway is a hallmark of proteasome-related growth retardation and apoptosis and is a key pathway in MM. We show that NFkB luciferase reporter assay was associated with significant activity reduction with RFP2 downregulation. To define the mechanism of this process, we examined the level of NFkB related proteins in nuclear and cytoplasmic fractions. Interestingly, the most prominent effect observed in RFP2 down regulated cells was increased levels of IkBá in the nucleus. Altogether, these results support our supposition that the effects of RFP2 downregulation are mediated through an inhibition of the NFkB pathway that is associated with increased nuclear IkBa as well as a decrease in 20S proteasome activity. Conclusions RFP2 is a gene mapping to a deletion hotspot at 13q14 and reduced RNA expression is associated with poor survival in MM. Functional studies revealed that shRNA mediated knockdown of RFP2 in MM causes growth retardation and apoptosis, mediated by ER stress and a G2 arrest, mediated by proteasome inhibition and reduced NFkB activity. Although RFP2 did not prove itself to be a tumor suppressor gene in our studies, targeting RFP2 may represent a novel therapeutic approach in MM and other lymphoid malignancies. Disclosures No relevant conflicts of interest to declare.

Description: Cell membrane protein CS1 is highly expressed by tumor cells from the majority of multiple myeloma (MM) patients (〉95%) regardless of cytogenetic abnormalities and response to current treatments. Furthermore, CS1 is detected in MM patient sera and correlates with active MM. However, its role in MM pathophysiology is undefined. In the present study, we first generated CS1 null OPM2 MM cells using lentiviral CS1 short interfering RNA. Specific CS1 knockdown was confirmed by depletion of CS1 mRNA and membrane protein, whereas CS1 was expressed in parental OPM2 and OPM2 cells infected with control lentiviral vector (cntOPM2). Immunoblotting of phopho-site of multiple kinase screen analysis showed decreased phosphorylation of ERK1/2, AKT, and STAT3 in CS1null OPM2 cells vs. cntOPM2 cells. Serum deprivation markedly blocked survival at earlier time points in CS1null OPM2 cells vs. cntOPM2 cells. Earlier apoptosis in CS1null OPM2 cells correlated with earlier activation of caspases, PARP cleavage, and increased proapoptotic proteins BNIP3, BIK. CS1 knockdown further delayed development of OPM2 tumor and prolonged survival in mice. CS1null OPM2 cells failed to grow tumors in the majority of mice (n=8) at 5 weeks after cell inoculation, whereas cntOPM2 cells formed tumors within 1.5 weeks in all animals (n=8). Interestingly, CS1 was expressed in tumors that developed late in mice injected with CS1null OPM2 cells. Concomitantly, we overexpressed CS1 in CS1-low expressing U266 cells by transfecting an expressing plasmid pflagCS1 or control vector. Enforced CS1 expression enhanced U266 cell growth and survival. In contrast to the majority of U266 cells (〉95%) that grow in suspension in standard tissue culture flasks, all U266CS1 cells exhibited adherent growth and homotypic adhesion. Importantly, overexpressed CS1 increased adhesion of U266 and MM1S cells to BMSCs. Furthermore, U266CS1 cells formed more and larger colonies in methylcellulose than U266 cells. Interestingly, tumors that developed in mice injected with U266 cells expressed significantly higher levels of CS1 than injected U266 cells; moreover, exercised tumors grew in an adherent manner in vitro. Overlapping differentially expressed genes in U266CS1 vs. U266 and CS1null OPM2 vs. cntOPM2 was next analyzed by gene expression profiling. Importantly, c-maf pathway was significantly upregulated in U266CS1 vs. U266 cells and downregulated in CS1null OPM2 vs. cntOPM2 cells, as evidenced by differentially expressed c-maf and its target genes, i.e., cyclin D2, integrin αE/β7 at both mRNA and protein levels. Myeloma cell adhesion-induced VEGF secretion by BMSCs was greater with U266CS1 than U266 cells. Finally, immunoblotting showed upregulation of c-maf and cyclin D2 in U266 tumors overexpressing CS1. These studies provide direct evidence of the role of CS1 in myeloma pathogenesis, define molecular mechanisms regulating its effects, and further support novel therapies targeting CS1 in MM.

Description: Background: Waldenstrom Macroglobulinemia (WM) is characterized by widespread involvement of the bone marrow (BM), and lymphadenopathy in 20% of the patients, implying continuous trafficking of WM cells into and out of the BM and lymph nodes. The normal process of B-cell homing is regulated by cytokines, chemokines, and adhesion molecules. One of the most extensively studied chemokines in migration is stromal derived factor SDF-1 and its receptor CXCR4. Here we study the role of chemokine receptors, and the SDF-1/CXCR4 axis on migration and adhesion in WM. Methods: Flow cytometry for CXC and CC chemokine receptors (CXCR1, CXCR2, CXCR3, CXCR4, CXCR5, CCR2, CCR4, CCR5, CCR6 and CCR7), and adhesion molecules (VLA-4 and LFA-1) on WM cell lines (BCWM.1 and WM-WSU) and patient samples was performed. Migration was determined using the transwell migration assay (Costar, NY). Cells were placed in the upper chambers of the migration assay with 1% FCS medium in the presence of serial concentrations of SDF-1 in the lower chambers. After 4 hours of incubation, cells that migrated to the lower chambers were counted. Similarly, adhesion was determined using an adhesion assay (EMD Biosciences, San Diego, CA) with 96-well plated coated with fibronectin. Immunoblotting for proteins downstream of CXCR4 was performed. The CXCR4 inhibitor AMD3100 (10–100uM, Sigma, MO) and Gi protein inhibitor pertussis toxin PTX (10–200ng/ml, Sigma, MO) were used to inhibit CXCR4 signaling. Results: The following chemokine receptors were expressed on patient CD19+WM cells with over 30% expression: CXCR1 (mean 60%), CXCR2 (mean 47%), CXCR4 (mean 47%), CXCR5 (mean 69%), CCR4 (mean 54%) and CCR6 (mean 61%). Similar expression was observed on WM cell lines. We next determined the effect of SDF-1 on migration and signaling pathways in WM. SDF-1 (10–100nM) induced migration in a bell-shaped curve with 30nM inducing maximum migration (110% compared to control). SDF-1 30nM induced a rapid activation of signaling pathways downstream of CXCR4 including pERK1/2, pAKT, and pPKC at 1 min, with maximum activation at 5min. The CXCR4 inhibitor AMD3100 inhibited migration of BCWM.1 in the presence of 30nM SDF-1, with AMD3100 10uM inhibiting migration at 59% of control, and 20 to 50uM leading to a plateau in inhibition of migration at 54% of control. AMD3100 inhibited pERK and pPKC activation, downstream of CXCR4 in a dose-dependent fashion. Similar results were observed using PTX, with inhibition of migration of WM cells at 50% compared to control. To determine the role of SDF-1 on adhesion, we first demonstrated that WM cells from patients and cell lines expressed high levels of surface VLA-4 expression (mean 95% surface expression). WM cells had an increase in adhesion to fibronectin (VLA-4 ligand) compared to BSA control. AMD3100 10uM inhibited adhesion to fibronectin (63 % of control), indicating that the SDF-1/CXCR4 axis regulates adhesion. Conclusion: CXCR4 is highly expressed on WM cells and regulates migration and adhesion, indicating a potential role in regulating WM trafficking into the BM and lymph nodes. These studies provide the preclinical framework to study CXCR4 inhibitors in the regulation of homing and adhesion in WM.

Description: Background: Bortezomib (VELCADE®, Bz) is approved for the treatment of patients (pts) with multiple myeloma (MM). Lenalidomide (Revlimid®, Len) plus dexamethasone (Dex) is approved for the treatment of relapsed MM pts following ≥1 prior therapy. Len/Bz±Dex is active and well tolerated in relapsed/refractory MM, and Len/Dex and Bz/Dex are active in front-line MM. The aims of this phase l/ll study were to determine the maximum tolerated dose of Len/Bz/Dex (RVD) and to assess safety and efficacy in previously untreated MM pts. Methods: Pts received Len 15–25 mg on days 1–14, Bz 1.0–1.3 mg/m2 on days 1, 4, 8, 11, and Dex 40/20 mg (cycles 1–4/5–8) on days 1, 2, 4, 5, 8, 9, 11, 12, for up to eight 21-day cycles, initially at four planned dose levels (Len/Bz: 15/1.0, 15/1.3, 20/1.3, 25/1.3). Dose-escalation proceeded (three-pt cohorts) depending on dose-limiting toxicities (DLTs; Grade (G) ≥3 non-hematologic toxicity; G4 thrombocytopenia with platelets 1 occasion despite transfusion support; G4 neutropenia for 〉5 days and/or resulting in neutropenic fever; inability to receive cycle 2/day 1 dose due to drug-related toxicity). Based on safety data, dose level 4M (Len/Bz 25/1.3) was added with a reduced Dex (20/10 mg) starting dose. Pts with G≥2 peripheral neuropathy (PNY) were excluded. Responses were assessed by modified European Group for Blood and Marrow Transplantation (EBMT) and Uniform Criteria. Pts with at least partial response (≥PR) could proceed to autologous stem cell transplant (ASCT) after ≥4 cycles. Results: 68 pts have been enrolled to date: 33 in phase l, including 17 pts at the maximum planned dose (MPD, dose level 4M) and 35 in phase ll (at MPD). Data are available for 66 pts (median age 58 yrs, 55% men, 67% IgG MM, 50% with ISS stage II/III). Pts have received a median of 10 cycles; 46 have completed all 8 cycles, 39 have discontinued/completed therapy. Two DLTs of G3 hyperglycemia due to high-dose Dex were seen at dose level 4. Dose reductions in cycle 2 and beyond have occurred in overall/dose levels 1–4 for: Len 16/8 pts, Bz 23/8 pts, and Dex 19/15 pts. Toxicities to date have been manageable, including all G3/4 hematological toxicities (3–15%), G3 hypophosphatemia (8%) and deep vein thrombosis/pulmonary embolism (5%, with daily aspirin), with no G4 PNY, and no treatment-related mortality. The overall response rate (ORR; ≥ PR) is 98%, including 71% ≥ VGPR and 36% CR/nCR; at MPD, ORR is 100%. Efficacy was independent of baseline cytogenetics or ISS stage (Table). ORR and ≥ VGPR rates were similar regardless of the absence or presence of deletion 13q or translocation 4;14; ORR rates ranged from 86% to 100% and ≥ VGPR rates ranged from 57% to 75%. Pts from all three ISS categories achieved ORR ranging from 97% to 100% and ≥ VGPR ranging from 51% to 80%; of note, the 10 pts with ISS stage III disease had an ORR of 100% and ≥ VGPR rate of 80%. Median stem cell collection in 21/23 pts was 6.2 × 106 CD34+ cells/kg after a median of 6 cycles of therapy; 15 pts have proceeded to ASCT, with the transplant course in each case reported as unremarkable. Two of 23 pts (9%) have had difficulty with mobilization. After a median follow-up of 8 months, median time to progression, progression-free survival, and overall survival have not been reached. Conclusions: RVD produces high quality responses and is well tolerated in newly diagnosed MM pts, regardless of their cytogenetic status or ISS stage. MPD has been reached at Len 25 mg, Bz 1.3 mg/m2, and Dex 20 mg, with phase ll enrollment now complete and 100% ORR reported at the MPD. Stem cell mobilization has been successful in almost all pts, with transplant course in pts otherwise unremarkable. Updated efficacy and ASCT data will be presented at the meeting. Responses by cytogenetic status (normal, abnormal [deletion 13q or t(4;14)]), and ISS stage Normal Abnormal No Del 13q With Del 13q No t(4;14) With t(4;14) * pts with available data n* (63) 39 24 52 7 49 10 ≥ PR 100% 96% 100% 86% 98% 100% P 0.381 0.119 1.00 ≥ VGPR 69% 79% 75% 57% 73% 70% P 0.560 0.375 1.00 ISS I ISS II ISS III n* (64) 33 21 10 ≥ PR 97% 100% 100% P 0.385 ≥ VGPR 51% 57% 80% P 0.421

Description: Multiple myeloma (MM) is a cancer of plasma cells with complex molecular characteristics that evolves from monoclonal gammopathy of undetermined significance, a highly prevalent premalignant condition. MM is the second most frequent hematologic cancer in the United States, and it remains incurable, thereby highlighting the need for new therapeutic approaches, particularly those targeting common molecular pathways involved in disease progression and maintenance, shared across different MM subtypes. Here we report that Wnt/β-catenin is one such pathway. We document the involvement of β-catenin in cell-cycle regulation, proliferation, and invasion contributing to enhanced proliferative and metastatic properties of MM. The pleiotropic effects of β-catenin in MM correlate with its transcriptional function, and we demonstrate regulation of a novel target gene, Aurora kinase A, implicating β-catenin in G2/M regulation. β-catenin and Aurora kinase A are present in most MM but not in normal plasma cells and are expressed in a pattern that parallels progression from monoclonal gammopathy of undetermined significance to MM. Our data provide evidence for a novel functional link between β-catenin and Aurora kinase A, underscoring a critical role of these pathways in MM disease progression.