ALBERT

Description: Introduction: Secondary CNS dissemination (SCNSL) is a rare but lethal event in pts with diffuse large B-cell lymphoma (DLBCL). It can occur both at presentation, in pts with systemic disease, or at relapse, during or after primary therapy. Following the experience from primary CNS lymphoma, pts with SCNSL are currently treated with high-dose-methotrexate-based chemo and autologous transplant (ASCT). However, this strategy is associated with poor control of extra-CNS disease, and only 1/3 of pts proceed to ASCT and recover from this event. Thus, we designed a multicenter phase II trial addressing an intensified chemoimmunotherapy consolidated by ASCT in HIV-neg pts with SCNSL (NCT02329080). Methods: Inclusion criteria were: histologically confirmed DLBCL; CNS involvement at presentation (concomitant to systemic disease) or relapse (isolated or concomitant to systemic lymphoma); age 18-70 ys; ECOG-PS ≤3; no prior treatment with high-dose methotrexate. Registered pts received 3 courses of MATRIX followed by 3 courses of RICE combined with intrathecal chemo and consolidated by BCNU-thiotepa/ASCT. The primary endpoint was 1-yr PFS. The Fleming design was used; to detect a difference in 1-yr PFS from 50% (P0) to 65% (P1), 69 pts were required (one-sided, type I error 5%, power 80%), with a dropout of 10%, 76 pts were needed. If ≥41 pts were progression-free at 1 yr, the strategy would be considered effective. Results: Between 3/2015 and 8/2018, 79 pts were enrolled at 24 centers in 4 countries; 75 pts (median age 58, range 23-70; 38 males) were assessable. CNS involvement was recorded at presentation in 32 (43%) pts and at relapse in 43 (isolated site in 15, concomitant to systemic relapse in 28). CNS sites were brain parenchyma in 34 (45%) pts, brain + eyes in 10 (13%), brain + CSF in 13 (17%), brain + CSF + eyes in 6 (8%), CSF/meninges in 8 (11%), spinal cord in 2 (3%), and eyes in 2 (3%). Median time to CNS involvement was 5 months (range 1-61) in the 43 pts registered at relapse; 20 (47%) of them had refractory disease. 320 (71%) of the 450 planned chemo courses were delivered; 64 (85%) pts received intrathecal chemo. 78 SAEs were recorded in 42 pts, mostly due to FN and infections (64) or bleeding (5); 74 (95%) SAEs were followed by recovery. The 4 lethal SAEs (TRM= 5%) and the 5 transient interruptions occurred during MATRIX. Dose reductions were indicated in 33 (10%) courses. Most common g4 toxicities were thrombocytopenia in 118 (37%) courses, neutropenia in 113 (35%) and infections in 9 (3%). Stem cells collection was successful (median of 6.75M/kg; range: 2.4 - 45) in 42 (88%) of the 48 pts referred for leukapheresis. 55 (73%; 95%CI 63-83%) pts achieved a response after 2 courses of MATRIX; 19 (95%) of the 20 pts who had a CR after 2 MATRIX maintained the response after RICE; 9 (26%) of the 35 pts who had a PR after 2 MATRIX achieved a CR after RICE. Conversely, only 3 of 16 pts with PD/SD after 2 MATRIX achieved a response from RICE. 49 pts (65%; 95%CI 54-76%) achieved a response after MATRIX-RICE induction, and 36 responders received ASCT; 13 responders did not receive ASCT due to insufficient mobilization (n=4), PD due to treatment delay (5), frailty (2), neurological decline (1), and consent withdrawal (1). 45 pts (60%; 95%CI 50-70%) had responsive disease after the whole treatment. At 1 year from registration, 41 pts were progression free (efficacy threshold ≥41). At a median follow-up of 25 (12-47) months, 31 pts are progression free, with a 2-yr PFS of 42 ± 6% for the whole series and 75 ± 7% for the 36 transplanted pts (Fig. A & B). Sites of relapse/progression were CNS in 10 pts, extra-CNS organs in 9 and both in 18. Overall, 33 pts are alive, with a 2-yr OS of 42 ± 6% for the whole series and 82 ± 7% for transplanted pts. Causes of death were lymphoma (35) and toxicity (4); 3 pts died without evidence of disease due to neurological decline, PTE and sudden death. Pts with CNS disease at presentation had the best outcome (Fig. C), whereas CSF/meningeal disease (Fig. D) and age 〉60 ys were independently associated with poor outcome. Conclusions: MATRIX-RICE followed by ASCT achieved the primary endpoint in this very-poor-prognosis population, without major safety concerns. Survival figures of transplanted pts seem a little better than reported in prior trials, whereas pts with MATRIX-refractory disease had no benefit from crossing to RICE. The best survival figures were recorded in chemo-naïve pts treated at presentation and in pts without CSF/meningeal disease. Figure Disclosures Ferreri: Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Roche: Research Funding. Doorduijn:Roche: Honoraria, Research Funding. Nassi:Merck: Consultancy; Takeda: Consultancy; Janssen: Consultancy. McKay:Janssen: Honoraria, Speakers Bureau; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MSD: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Epizyme: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Davies:ADCT Therapeutics: Honoraria, Research Funding; Karyopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; MorphoSys AG: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bayer: Research Funding; Janssen: Honoraria, Research Funding; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; GSK: Research Funding; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Research Funding; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta Pharma: Honoraria, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BioInvent: Research Funding. Fox:Celgene: Consultancy; Gilead: Consultancy; AbbVie: Consultancy; Janssen: Consultancy; Sunesis: Consultancy; Takeda Pharmaceuticals: Consultancy; Atara Biotherapeutics: Consultancy; Adienne: Other: Travel Support. Osborne:Gilead: Membership on an entity's Board of Directors or advisory committees; NIL: Employment; NIL: Other: leadership; NIL: Other: Stock & other ownership interests; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau; MSD: Membership on an entity's Board of Directors or advisory committees. Liberati:Incyte: Consultancy; Novartis: Other: Clinical trial support; Janssen: Honoraria; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Clinical trial support; Roche: Other: Clinical trial support; Amgen: Membership on an entity's Board of Directors or advisory committees, Other: Clinical trial support; Celgene: Honoraria, Other: Clinical trial support; Bristol-Myers Squibb: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees; Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees. Zambello:Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Zucca:Celltrion Helathcare: Membership on an entity's Board of Directors or advisory committees; AstraZenaca: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Research Funding; Merck: Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees, Other: Travel Grant, Research Funding; Kite, A Gilead Company: Membership on an entity's Board of Directors or advisory committees; Abbvie: Other: Travel Grant. Cwynarski:Adienne: Consultancy; Takeda: Consultancy, Other: conference and travel support , Speakers Bureau; Roche,: Consultancy, Other: conference and travel support, Speakers Bureau; Autolus: Consultancy; KITE: Consultancy; Gilead: Consultancy, Other: conference and travel support, Speakers Bureau; Celgene: Consultancy; Atara: Consultancy; Janssen: Other: conference and travel support, Speakers Bureau.

Description: Multiple myeloma (MM) is a plasma cell malignancy which remains incurable despite novel therapeutic approaches targeting both myeloma cells and their bone marrow milieu (BMM). MM cells express estrogen receptors (ER) belonging to both α and β isotypes and selective ER modulators or pure anti-estrogens have demonstrated therapeutic activity against this malignancy. GPER, formerly known as GPR30, is an orphan membrane-associated ER previously described to mediate non-genomic effects of estrogens and whose involvement in the pathophysiology of solid tumors is currently emerging. Here, we studied the expression pattern of GPER and the biological effects triggered by GPER activation using the synthetic compound G-1 ((±)-1-[(3aR*,4S*,9bS*)-4-(6-Bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H cyclopenta[c]quinolin-8-yl] ethanone), a selective GPER agonist (Tocris). We detected GPER expression in 9 out of 9 MM cell lines either at mRNA and protein level, as assessed by qRT-PCR and western blotting, respectively. By analysis of our microarray dataset based on plasma cells from 4 normal donors, 11 MGUS, 133 MM and 9 plasma cell leukemias (PCLs), we observed that GPER mRNA levels progressively declined during MM progression, since lower levels were found in PCL and MM samples as compared to healthy controls or MGUS. Interestingly, adhesion of MM cells to bone marrow stromal cells (BMSCs) reduced GPER mRNA levels, supporting a potential role of the BMM in regulating GPER expression. To address the relevance of GPER in modulating MM cell proliferation and/or death mechanisms, first we tested the GPER agonist G-1 in vitro. We found that G-1 inhibited, in a dose-dependent manner, proliferation of IL-6 dependent (INA-6) and independent (MM1R, MM1S, U266, RPMI-8226, NCI-H929, OPM2) MM cell lines, with an IC50 ranging from 2 to 5 microM, while did not affect the survival of peripheral blood mononuclear cells from healthy donors. G-1 treatment caused cell cycle arrest by increasing cells in G0 phase; moreover, it induced a significant and dose-dependent apoptotic cell death in all MM cell lines tested, as assessed by Annexin V/7AAD staining and western blot analysis of active caspases 3, 7 and 9. G-1 promoted the expression of autophagic markers like Beclin-1 and LC3A/B, the cytosolic punctate pattern of LC3B and down-regulated p62/SQSTM-1 expression, indicating functional involvement of GPER in autophagy. Moreover, GPER transduced rapid non-genomic signaling through MAPKs, since G-1-mediated GPER activation triggered phosphorylation of ERK1/2 already after 15’ treatment in MM1S and U266 cells. Importantly, i.p. injection of G-1 (2mg/kg) in SCID mice significantly reduced the growth of subcutaneous MM1S xenografts, as compared to vehicle-treated animals. We next evaluated whether G-1-induced effects could be associated to modulation of miRNA levels in MM cells. Indeed, we found that G-1 up-regulated the tumor suppressor miR-29b; this effect was likely a consequence of the down-regulation of the miR-29b transcriptional inhibitor Sp1, whose mRNA and protein levels were reduced after G-1 treatment. Consistently, an inverse correlation between GPER and Sp1 mRNA levels in MM patient plasma cells could be gathered from our microarray dataset. In addition, miR-29b canonical targets, like CDK6 and MCL-1, were down-regulated at protein level in G-1-treated MM cell lines. Finally, we demonstrated that G-1 synergizes with established miR-29b-inducing compounds, like bortezomib and vorinostat, in the inhibition of MM cell survival. Taken together, our results indicate that the GPER agonist G-1 is a novel powerful anti-tumor compound enriching the repertoire of investigative anti-MM agents, and further strengthen the role of miR-29b as effector of anti-MM drugs. Disclosures No relevant conflicts of interest to declare.

Description: Abstract 330 Background: Our previous study demonstrated that inhibition of nicotinamide phosphoribosyltransferase (Nampt) acts by severely depleting intracellular NAD+ content and thus eliciting mitochondrial dysfunction and autophagic MM cell death. The proteasome inhibitor Bortezomib induces anti-MM activity by affecting a variety of signaling pathways. However, as with other agents, dose-limiting toxicities and the development of resistance limit its long-term utility. Here, we demonstrate that combining Nampt inhibitor and bortezomb induces synergistic anti-MM cell death both in vitro using MM cell lines or patient CD138+ MM cells and in vivo in a human plasmacytoma xenograft mouse model. Material and Methods: We utilized MM.1S, MM.1R, RPMI-8226, and U266 human MM cell lines, as well as purified tumor cells from patients relapsing after prior therapies. Cell viability and apoptosis assays were performed using Annexin V/PI staining. Intracellular NAD+ level and proteasome activity were quantified after 12, 24, and 48h exposure to single/combination drugs by specific assays. In vitro angiogenesis was assessed by Matrigel capillary-like tube structure formation assay. Immunoblot analysis was performed using antibodies to caspase-8, caspase-9, caspase-3, PARP, Bcl-2, and tubulin. CB-17 SCID male mice (n = 28; 7 mice/EA group) were subcutaneously inoculated with 5.0 × 106 MM.1S cells in 100 microliters of serum free RPMI-1640 medium. When tumors were measurable (3 weeks after MM cell injection), mice were treated for three weeks with vehicle alone, FK866 (30mg/kg 4 days weekly), Bortezomib (0.5 mg/kg twice weekly), or FK866 (30 mg/kg) plus Bortezomib (0.5 mg/kg). Statistical significance of differences observed in FK866, Bortezomib or combination-treated mice was determined using a Student t test. Isobologram analysis was performed using “CalcuSyn” software program. A combination index 〈 1.0 indicates synergism. Results/Discussion: Combining FK866 and Bortezomib induces synergistic anti-MM activity in vitro against MM cell lines (P

Description: Key Points Overall, our results suggest that NOTCH2 and FLT3 aberrant splicing is a common event in AML that correlates with disease status and may correlate with disease outcomes. Selected variants of NOTCH2 and FLT3 transcripts were detected in a significant number of AML patients and could be useful as disease markers.

Description: Abstract 2920 Background: Nicotinamide adenine dinucleotide (NAD+) is a coenzyme crucially involved in several cellular functions, including energy metabolism, reactive oxygen species scavenging, DNA repair, and gene expression. Intracellular NAD+ stores are continuously replenished through pathways whose activity depends on the tissue and availability of substrates. Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme in the NAD+ salvage pathway from nicotinamide. During neoplastic transformation, Nampt is upregulated to compensate for increased metabolic demands. It promotes myeloid and lymphoid differentiation and increases specific cytokine production (TNF- α, IL-6 and VEGF). Importantly, cancer and leukaemia cells appear to be more sensitive to Nampt inhibitor drugs than normal cells. The reasons for this selectivity are not fully understood, but may include aberrant metabolic demands and increased reliance on NAD+-dependent enzymes. Promising results obtained with Nampt inhibitors (such as FK866) in preclinical cancer models suggest that Nampt activity represents an innovative therapeutic target for novel anticancer agents. Methods: A panel of eighteen different MM cell lines, both sensitive and resistant to conventional and novel anti-myeloma drugs, as well as patient MM cells were used in the study. The mechanism of action of FK866 was investigated by Annexin-V/propidium iodide staining, thymidine incorporation, Western-blotting, and with lentivirus-mediated shRNAs. For the autophagy assay, EGFP-LC3+ cells were treated with FK866 and the number of GFP-LC3 punctae was analyzed and quantified by fluorescence microscopy and flow cytometry, respectivley. Intracellular NAD+ content was measured using a biochemical assay. Angiogenesis was measured in vitro using Matrigel capillary-like tube structure formation assay. Results: To study the role of Nampt in MM cells, we performed a protein analysis of this enzyme in eighteen MM cell lines. Nampt is constitutively activated in all cell lines tested. Moreover, patient MM cells highly express this enzyme whereas normal cells lack this protein. Indeed, the Nampt inhibitor FK866 decreased MM cell line viability in a dose and time dependent manner, with an IC50 ranging from 3–30nM. Similar results were observed in patient MM cells. Importantly, FK866 did not inhibit viability of normal peripheral blood mononuclear cells. Tritiated thymidine uptake assay confirmed the antiproliferative effects of FK866 in MM cell lines and patient cells. To examine the mechansim of action, we showed that intracellular NAD+ levels decreased with FK866 treatment at 24 and 48 hours. Furthermore, knock-down of Nampt by small interfering RNAs caused significant inhibition of MM cell growth. FK866 triggered anti-MM activity in our models of MM in the bone marrow (BM) microenvironment, confirming its ability to overcome the proliferative advantage conferred by the BM milieu. FK866 treatment also inhibited angiogenesis via suppression of pivotal MM pathways PI3K/AKT and ERK. In further studies to delineate its mechanisms of action, no activation of apoptosis was observed in treated-cells. Instead FK866 treatment resulted in a marked increase in autophagy, evidenced by autophagic vacuoles in the cytoplasm and proteolitic processing of endogenous LC3-I to LC3-II. FK866 inhibited mTOR signaling and triggered increased formation of EGFP-LC3 punctae, confirming involvement of autophagic cell death. Finally, combined FK866 with bortezomib (CI 〈 0.6), melphalan (CI 〈 0.9), and dexamethasone (CI 〈 0.8), induced synergistic cytotoxicity against MM cells. Conclusion: Our data therefore show a pivotal role of Nampt in MM cell growth, survival and drug resistance. The ability of FK866 to inhibit Nampt activity strongly supports its clinical evaluation to improve patient outcome in MM. Disclosures: Hideshima: Acetylon: Consultancy. Anderson:Celgene: Membership on an entity's Board of Directors or advisory committees; Millennium: Membership on an entity's Board of Directors or advisory committees; Onyx: Membership on an entity's Board of Directors or advisory committees; Merck: 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; Novartis: Membership on an entity's Board of Directors or advisory committees; Acetylon: Membership on an entity's Board of Directors or advisory committees.

Description: Malignant cells have a higher nicotinamide adenine dinucleotide (NAD+) turnover rate than normal cells, making this biosynthetic pathway an attractive target for cancer treatment. Here we investigated the biologic role of a rate-limiting enzyme involved in NAD+ synthesis, Nampt, in multiple myeloma (MM). Nampt-specific chemical inhibitor FK866 triggered cytotoxicity in MM cell lines and patient MM cells, but not normal donor as well as MM patients PBMCs. Importantly, FK866 in a dose-dependent fashion triggered cytotoxicity in MM cells resistant to conventional and novel anti-MM therapies and overcomes the protective effects of cytokines (IL-6, IGF-1) and bone marrow stromal cells. Nampt knockdown by RNAi confirmed its pivotal role in maintenance of both MM cell viability and intracellular NAD+ stores. Interestingly, cytotoxicity of FK866 triggered autophagy, but not apoptosis. A transcriptional-dependent (TFEB) and independent (PI3K/mTORC1) activation of autophagy mediated FK866 MM cytotoxicity. Finally, FK866 demonstrated significant anti-MM activity in a xenograft-murine MM model, associated with down-regulation of ERK1/2 phosphorylation and proteolytic cleavage of LC3 in tumor cells. Our data therefore define a key role of Nampt in MM biology, providing the basis for a novel targeted therapeutic approach.

Description: Genomic instability is not only a hallmark of cancer, but potentially a primary mechanism for its occurrence. DNA repair mechanisms play a protective role during DNA damage induced by both normal metabolic activities and environmental factors such as reactive oxygen species (ROS), UV light and γ-irradiation. Genes related to DNA repair are usually considered as tumor suppressors. However, incomplete repair may induce severe genomic instability, leading eventually to transformation. Apurinic/apyrimidinic endonuclease 1 (APEX1), a gene involved in DNA repair with an important role in the base excision repair pathway, leads to transformation of normal cells in vitro. To investigate the role of APEX1 in tumor initiation in vivo, we generated a novel transgenic zebrafish model to overexpress APEX1 in fish. Specifically, pDestTol2A2_ubi:loxP-EGFP-loxP-APEX1-mCherry plasmid was injected into single cell embryos derived from the TP53 mutant line Tp53M214K/M214K to generate a stable conditional inducible transgenic zebrafish line: Tg:APEX1fl/- mCherry Tp53M214K/M214K. To activate APEX1 expression in vivo, this line was mated with Tg:HSP70-Cre+/+ fish. Compound zebrafish Tg: APEX1fl/- mCherry,Tp53+/M214K ,HSP70-Cre+/- carrying a Cre-activatable APEX1 knock-in allele were heated at 24hpf, and induction of APEX1 expression was monitored by downstream reporter - mCherry expression. Ten to twelve months post-fertilization, Tg:APEX1fl/- mCherry,Tp53+/M214K ,HSP70-Cre+/- fish developed abnormal swelling. Flow cytometry analysis of fish kidney marrow and peripheral blood showed dramatically increased precursor populations in scatter analysis. Histopathologic analysis showed that multiple organs were infiltrated with malignant lymphoblastic cells. None of the control fish Tg: GFP,Tp53+/M214K ,HSP70-Cre+/- developed tumors during their life span. Zebrafish with T-ALL have heterozygous Tp53+/M214K background, but the expression of p21, mdm2 and bax in Tp53+/M214K fish is exactly the same as in Tp53+/+ fish; and Tp53+/M214K zebrafish themselves have not developed tumors during their life span. RNA from lymphoblastic cells was evaluated by qRT-PCR and showed increased expression of CD3, LCK and Tal indicating a T-cell acute lymphoblastic leukemia/lymphoma (T-ALL). We have performed whole genomic DNA sequencing in extracted DNA from fish tumor cells and compared it with their normal counterpart and observed multiple copy number changes and mutations. We have now begun to see the development of other tumors in other organs including the eye and the testis. To uncover the molecular mechanism of tumorigenesis induced by APEX1, we have performed Mass Spectrometry analysis on APEX1 pulled down from 293T and AG08498 cells ectopically expressing APEX1. Besides verified binding proteins, such as PCNA, we also identified Ku70 and Ku80 binding to APEX1 directly. Further immunoflurescent staining and confocal microscopy of 293T cells also found co-localization of APEX1 and Ku70/Ku80. Those two proteins initiate Non-Homologous End Joining (NHEJ) repair and start the error-prone double strand repair and DNA damage. These results indicate that excessive repair activity may induce DNA damage and genomic instability. In summary, this is the first demonstration where overexpression of a DNA repair gene is responsible for induction of genomic instability leading to malignant transformation. It provides new insight into the process of tumorigenesis and development of both therapy as well as preventive strategies. Disclosures Zon: FATE Therapeutics: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Scholar Rock: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: Founder.

Description: Genomic instability is a hallmark of several types of solid and hematologic malignancies, including multiple myeloma (MM). Although structural and numerical chromosomal abnormalities are common features of MM cells, the underlying molecular basis of MM genomic instability is still largely unknown. To this aim, we have investigated the activity of non-homologous end joining (NHEJ), which represents the most important mechanism of double-strand breaks (DSBs) repair, in MM cells. First, we developed and validated a dual gene plasmid-based assay utilizing Luciferase (LUC) as a test gene which measures end joining, and Alkaline Phosphatase (SEAP) as a reporter gene to control for transfection efficiency, in either intact cells (in vivo assay) or in cell free extracts (in vitro assay). The first one is a chemiluminescent assay which allows for direct measurement of LUC and SEAP in the supernatant of the cells 24h after electroporation with the plasmid, while the cell free extract method is a customized TaqMan® approach based on a quantitative evaluation of the plasmid rejoining. Both assays revealed a significant increase in NHEJ in all 6 MM cell lines tested compared to normal peripheral blood mononuclear cells (PB-ND) and bone marrow stromal cells (BMSC). We further confirmed the hyper-activation of the NEHJ pathway by analyzing the binding activity of ku86, a key NHEJ-related protein involved in the recognition of the broken DNA ends and in the initiation of the DSBs repair process. Six out of 9 MM cell lines showed a significant increase in ku86-binding activity respect to normal cells. We also found a higher phosphorylation at Ser 2056 of DNA-PK, a ku86-partner whitch plays a key role in NHEJ. Next, we evaluated the NHEJ activity in 35 patient samples using the cell free assay. Interestingly, level of NHEJ activity divided patients into two different groups: one with an NHEJ activity similar to normal cells and the other to the MM cell lines. Preliminary correlation analysis between NHEJ activity and the clinical features of the patients indicated that the MGUS and Smoldering MM subgroup fall into the normal cluster while relapsed/refractory disease to the cell lines one. Finally, using the French (IFM) and the Arkansas (GSE2658) dataset, we demonstrate a significant association between NHEJ pathway-related gene expression and overall survival by the Globaltest analysis. We were also able to find a common NHEJ signature of 6 genes whose expression significantly correlates with patient survival in both the datasets. In conclusion, our data indicate an aberrant activation of NHEJ in MM, highlighting its role in the progression of the disease and suggesting this pathway as an important new prognostic marker in myeloma. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 452 The critical role of the human bone marrow microenvironment (HuBMM) in the pathogenesis of Multiple Myeloma (MM) has recently allowed the design of novel therapeutical approaches targeting not only MM cells but also their specific HuBMM. However, the lack of adequate mouse models, capable to recapitulate a HuBMM, has restrained large scale in vivo screening of investigational drugs. In fact, only the SCID-hu model, in which human MM cells are grown in human fetal bone chips previously implanted in SCID mice, addresses this specific requirement. However the poor availability of human fetal bone chips, the allogeneic nature of the fetal BM milieu versus MM cells and the heterogeneity of implanted human bone chips are important restrains of this system. Here we report the development of a novel in vivo model of human MM (SCID-synth-hu), which is based on the implant of a three-dimensional (3-D) poly-ε-caprolactone polymeric scaffold (PCLS) into SCID mice as recipient to allow growth of MM cells in a reconstituted HuBMM. This biosynthetic scaffold has been designed to resemble the micro-architecture of a normal human adult bone and was characterized by 3-D interconnected large and small pores suitable for engraftment of bone marrow-derived cells. Human bone marrow stromal cells (BMSCs) were collected from BM aspirates from MM patients and firstly used for coating 3D internal surface of PCLSs. We performed in vitro dynamic seeding of BMSCs into PCLSs using a suspension of 106 cells in 500 μl of growth medium. Before implantation, PCLSs were incubated in complete medium at 37°C, in 5% CO2 for 24 hours, in order to allow cell adhesion on 3D surfaces. Then, PCLSs were implanted subcutaneously into SCID mice. CD138+ immune-selected primary MM cells, obtained by MM patient with a different disease status, were directly injected into PCLSs, which have been previously coated with allogeneic BMSCs 2–3 weeks after the in vivo implant. By this experimental approach, we achieved engraftment of primary MM cells in PCLSs within a non autologous bone marrow milieu. In a subsequent series of experiments, bone marrow mononuclear cells (BMMCs), obtained by Ficoll gradient separation and containing primary unselected CD138+ and their autologous BMSCs, were directly seeded in vitro into PCLSs which were implanted in SCID mice after 24 hours of incubation. At different time points, H&E and CD138 or κ/λ staining demonstrated engraftment and filling of 3-D spaces by primary MM cells within the autologous bone marrow milieu in PCLSs retrieved from SCID-synth-hu mice. Neo-synthesized extracellular matrix and angiogenesis were also shown by H&E and immune histochemical staining in retrieved PCLSs. Angiogenesis mostly occurred within areas of MM infiltration, suggesting its role in our system. In vivo MM growth was monitored by ELISA measuring of human monotypic immunoglobulins (Igs) in mouse sera 4 to 10 weeks after cell injection. To demonstrate the usefulness of our SCID-synth-hu model as an experimental platform for in vivo testing of investigational drugs, mice bearing human MM implants were treated intraperitoneally with bortezomib plus dexamethasone (Bort+Dex). As expected, SCID-synth-hu mice treated with Bort+Dex exhibited a significant decrease of monotypic light chains in mice sera and induction of apoptosis of MM cells in retrieved PCLSs, as compared to untreated control mice. Our experimental findings demonstrate that the SCID-synth-hu is the first experimental system which allows the in vivo expansion of human primary MM cells within their autologous adult HuBMM. The unlimited availability and the low cost of PCLSs, as well as the potential for dissecting the biological events within the HuBMM, represent a clear improvement over the available preclinical in vivo models of MM. We conclude that the SCID-synth-hu is a unique tool for large scale in vivo preclinical screening of novel agents targeting MM in its autologous HuBMM, and a novel resource for translational research in the experimental treatment of this still incurable disease. Disclosures: No relevant conflicts of interest to declare.