Boise, Lawrence

Abstract Waldenstrom macroglobulinemia (WM) and its precursor IgM gammopathy are distinct disorders characterized by clonal mature IgM-expressing B-cell outgrowth in the bone marrow. Here, we show by high-dimensional single-cell immunogenomic profiling of patient samples that these disorders originate in the setting of global B-cell compartment alterations, characterized by expansion of genomically aberrant extrafollicular B cells of the nonmalignant clonotype. Alterations in the immune microenvironment preceding malignant clonal expansion include myeloid inflammation and naïve B- and T-cell depletion. Host response to these early lesions involves clone-specific T-cell immunity that may include MYD88 mutation–specific responses. Hematopoietic progenitors carry the oncogenic MYD88 mutations characteristic of the malignant WM clone. These data support a model for WM pathogenesis wherein oncogenic alterations and signaling in progenitors, myeloid inflammation, and global alterations in extrafollicular B cells create the milieu promoting extranodal pattern of growth in differentiated malignant cells. Significance: These data provide evidence that growth of the malignant clone in WM is preceded by expansion of extrafollicular B cells, myeloid inflammation, and immune dysfunction in the preneoplastic phase. These changes may be related in part to MYD88 oncogenic signaling in pre–B progenitor cells and suggest a novel model for WM pathogenesis. This article is highlighted in the In This Issue feature, p. 549

AbstractVenetoclax (Ven) is a selective small‐molecule inhibitor of BCL‐2 that exhibits antitumoral activity against MM cells with t(11;14) translocation. We evaluated the safety and efficacy of Ven and dexamethasone (VenDex) combination in patients with t(11;14) positive relapsed/refractory (R/R) multiple myeloma (MM). This open‐label, multicenter study had two distinct phases (phase one [P1], phase two [P2]). Patients in both phases received VenDex (oral Ven 800 mg/day + oral Dex 40 mg [20 mg for patients ≥75 years] on days 1, 8, and 15, per 21–day cycle). The primary objective of the P1 VenDex cohort was to assess safety and pharmacokinetics. Phase two further evaluated efficacy with objective response rate (ORR) and very good partial response or better. Correlative studies explored baseline BCL2 (BCL‐2) and BCL2L1 (BCL‐XL) gene expression, cytogenetics, and recurrent somatic mutations in MM. Twenty and 31 patients in P1 and P2 with t(11;14) positive translocation received VenDex. P1/P2 patients had received a median of 3/5 lines of prior therapy, and 20%/87% were refractory to daratumumab. Predominant grade 3/4 hematological adverse events (AEs) with ≥10% occurrence included lymphopenia (20%/19%), neutropenia (15%/7%), thrombocytopenia (10%/10%), and anemia (5%/16%). At a median follow‐up of 12.3/9.2 months, ORR was 60%/48%. The duration of response estimate at 12 months was 50%/61%, and the median time to progression was 12.4/10.8 months. In biomarker evaluable patients, response to VenDex was independent of concurrent del(17p) or gain(1q) and mutations in key oncogenic signaling pathways, including MAPK and NF‐kB. VenDex demonstrated efficacy and manageable safety in heavily‐pre‐treated patients with t(11;14) R/R MM.

Background Venetoclax (Ven) is a selective, small molecule inhibitor of anti-apoptosis protein Bcl-2 that has antitumoral activity against multiple myeloma (MM), notably those with translocation t(11;14). Dexamethasone (d) has shown to enhance the expression of BCL-2 and pro-apoptotic protein Bim, shifting its binding towards Bcl-2 and sensitizing MM cells to Ven. This Phase 1/2 open-label trial is evaluating the safety and efficacy of the combination of Ven+d as a therapeutic approach to improve clinical outcomes in patients with t(11;14) Relapsed/Refractory (R/R) MM. Methods This ongoing study (NCT01794520) has 2 distinct phases. Phase 1 (P1) consisted of separate dose escalation, safety expansion, and Ven+d combination cohorts. The phase 2 (P2) portion is an expansion cohort of Ven+d to further evaluate its efficacy. The safety and efficacy of the Ven+d cohorts from P1 and P2 are reported here. Eligible patients (pts) were adults with t(11;14) R/R MM ≥18 years of age. Key eligibility criteria for the Ven+d cohort in P1 included prior treatment with a proteasome inhibitor (PI) and an immunomodulatory drug (IMID), and an ECOG score ≤1. In P2, eligibility included an ECOG score ≤2, disease progression on or within 60 days from the last dose on previous treatment and having received at least two lines of therapy with a PI, IMID, daratumumab, and glucocorticoids. Additional inclusion criteria for both phases included measurable disease and adequate bone marrow function in all pts, and the presence of t(11;14) determined by fluorescence in-situ hybridization. In both phases, pts received oral Ven 800 mg/day + oral d 40 mg (20 mg for pts ≥75 years of age) on days 1, 8, and 15 of each 21-day cycle. In P1, preliminary efficacy was assessed as the overall response rate (ORR), time to progression (TTP), progression free survival (PFS), and duration of response (DOR) of Ven+d based on the 2011 International Uniform Response Criteria for MM. Efficacy in P2 further evaluated ORR, very good partial response (VGPR) or better, PFS, DOR, TTP, and overall survival (OS) using 2016 IMWG response criteria. Results In P1, as of 15thApril, 2019, 20 pts were enrolled (17 [85%] male; median age, 63 years [range, 46-77]). The median number of prior therapies received was 2.5 (range: 1-7). Nineteen pts (95%) discontinued the study (18 due to progressive disease and 1 underwent transplant). The treatment-emergent adverse events (TEAEs) are summarized in the Table. Most frequent TEAEs were insomnia (45%), hypophosphatemia (40%), hyperglycemia (35%), diarrhea (35%), and thrombocytopenia (30%). Predominant Grade 3 or 4 TEAEs included neutropenia (21%), lymphopenia (29%), and hypophosphatemia (20%). The most common serious TEAE was tumor lysis syndrome (TLS) (10%). No deaths were reported in the treatment-emergent period. ORR was achieved by 13 (65%) and ≥VGPR was achieved by 6 (30%) pts respectively. Partial response (PR) was observed in 7 (35%) pts and stable disease (SD) in 4 (20%) pts. Median time to first response was 1.4 mos (95% CI: 0.7, 2.8). The DOR was 13.1 mos (95% CI: 10.9, 21.9). Median PFS and TTP were both 12.4 mos (95% CI 3.6, 20.9). In P2, as of March 18, 2019, 31 pts were enrolled (18 [58%] male; median age, 65 years [range, 48-80]). The median number of prior therapies received were 5 (range: 1-9). Eight (26%) pts discontinued the study (6 deaths, 1 withdrew consent, 1 due to physician's decision). The most frequent TEAEs reported were diarrhea (32%), nausea (26%) and lymphopenia (32%). The most frequent Grade 3 or 4 TEAEs were lymphopenia (32%), thrombocytopenia (11%), and hypertension (10%). Most common serious TEAE was sepsis (10%). Six (19%) deaths were reported (5 due to progressive disease and 1 due to adverse event). In the intention to treat population, the median TTR was 0.7 mos (range: 0.6-1.5). ORR was achieved by 14 (45%) and >VGPR was observed in 8 (26%) pts. PR was observed in 6 (13%) pts and SD in 8 (26%) pts. Median PFS, DOR, and OS were not reached at the time of data analysis. The 9-mo estimates for PFS, DOR, and OS were 57% (95% CI: 19% 82%), 66% (95% CI: 16%, 91%), and 71% (95% CI: 44%, 87%) respectively. Conclusion In both phases of this study, Ven+d was efficacious and demonstrated tolerable safety in pts with t(11;14) R/R MM. These results support further investigation of Ven combinations in this pt population. This combination is also being investigated in the ongoing Phase 3 trial M13-494 (CANOVA) in t(11;14) positive R/R MM. Disclosures Kaufman: Takeda: Consultancy; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy; Bristol-Myers Squibb: Consultancy; Incyte: Consultancy; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria; AbbVie: Consultancy; Winship Cancer Institute of Emory University: Employment; Amgen: Consultancy; TG Therapeutics: Consultancy. Gasparetto:Celgene: Consultancy, Honoraria, Other: Travel, accommodations, or other expenses paid or reimbursed ; Janssen: Consultancy, Honoraria, Other: Travel, accommodations, or other expenses paid or reimbursed ; BMS: Consultancy, Honoraria, Other: Travel, accommodations, or other expenses paid or reimbursed . Schjesvold:Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; MSD: Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; SkyliteDX: Honoraria. Moreau:Takeda: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Celgene: Consultancy, Honoraria. Facon:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees. Boise:Genentech Inc.: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Honoraria, Research Funding. Alzate:AbbVie Inc: Employment, Other: Stock/stock options. Macartney:AbbVie Inc: Employment, Other: Stock/stock options. Pesko:AbbVie: Employment, Other: Stock/stock options. Salem:AbbVie: Employment, Other: Stock/stock options. Ross:AbbVie: Employment, Other: Stock/stock options. Hong:Genentech Inc.: Employment, Equity Ownership; Roche: Equity Ownership. Maciag:AbbVie: Employment, Other: Stock/stock options. Pauff:AbbVie Inc: Employment, Other: may own stock or stock options. Kumar:Takeda: Research Funding; Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding. OffLabel Disclosure: Venetoclax is a BCL-2 inhibitor that is FDA-approved in some indications. This presentation will focus on venetoclax for treatment in multiple myeloma, which is not an approved indication.

Abstract Waldenström Macroglobulinemia (WM) is a disorder of lymphoplasmacytoid cells that inhabit lymph nodes and the bone marrow. WM cells are characterized by secretion of monoclonal pentameric IgM. These cells are CD19+, CD20+, CD22+, CD38+, CD138+/- and phenotypically resemble IgM plasmablasts or plasma cells. In addition, 91% of WM cases carry an activating mutation of MyD88 (L265P). Mature resting B cells can be driven to differentiate to IgM secreting plasmablasts and plasma cells with similar phenotypes using the TLR4 ligand lipopolysaccharide (LPS). We have demonstrated that LPS (+ cytokine)-differentiated cells become Bcl-xL dependent during this process, rendering them sensitive to the Bcl-xL/Bcl-2 inhibitor ABT-737. For this reason, we hypothesized that activation of MyD88 in WM cells could drive Bcl-xL dependence in a similar manner conferring ABT-737 sensitivity. We treated three WM cell lines, BCWM.1, MWCL-1 and RPCI-WM1 which all harbor the MyD88 (L265P) mutation with ABT-737. We found varying levels of resistance to ABT-737 with an IC50 > 2 μM for all three lines as compared with the ABT-737 sensitive multiple myeloma cell line MM.1s which has an IC50 of 0.4 μM. The RPCI-WM1 cell line was the most insensitive to ABT-737-induced apoptosis with no apoptosis above baseline up to 1.6 μM of drug. Since the WM cell lines were not sensitive to direct inhibition of intrinsic survival regulators, we then examined the sensitivity of these cell lines to other activators of the intrinsic apoptosis pathway. Two of the three cell lines were moderately sensitive to bortezomib with IC50 ≈ 5 nM as compared with the sensitive multiple myeloma cell line MM.1s with an IC50 of 2 nM. The RPCI-WM1 cell line was insensitive to bortezomib with no apoptosis above baseline up to 20 nM bortezomib. Similarly, we found that two of the cell lines were moderately sensitive to arsenic trioxide with an IC50 ≈ 6 μM as compared with the multiple myeloma cell line MM1.s (IC50 ≈ 4 μM). The RPCI-WM1 cell line was insensitive to ATO as well with an IC50 > 20 μM. Given the lack of sensitivity of the three WM cell lines we tested to Bcl-xL/Bcl-2 inhibition with ABT-737 treatment, and that RPCI-WM1 appears insensitive to multiple inducers of intrinsic apoptosis, we examined the expression levels of Bcl-2 family members in these cells. Both BCWM.1 cells and MWCL-1 cells expressed Bim mRNA at very low levels with MWCL-1 expressing no detectable Bim at the protein level. Surprisingly, more moderate levels of Bim were detected in RPCI-WM1 cells. These findings were confirmed at the mRNA level by qRT-PCR. Bcl-xL and Mcl-1 were detectable in all three lines at moderate levels while Bcl-2 which was only expressed at significant levels in MWCL-1 cells and undetectable in BCWM.1 cells. We examined the expression levels of the Bax and Bak in these cells and remarkably there was no detectable Bax and very small amounts of Bak protein in RPCI-WM1 cells. Consistent with a defect in gene expression, Bax mRNA was also low in RPCI-WM1. This was not due to copy number variation, as determined by array-CGH in both the initial patient isolate and the established cell line. Additionally, no loss of Bax, Bak or Bim (Bcl2l11) was observed in SNP array analysis of 46 patients with WM. Interestingly, Bak mRNA levels in RPCI-WM1 were similar to the other WM lines, suggesting a defect in translation or post-translational regulation is responsible for the low protein expression. These results lead us to conclude that these WM cell lines are not sensitive to Bcl-xL/ Bcl-2 inhibition despite activation of MyD88. We have further shown that there are multiple and distinct differences in Bcl-2 family protein expression that lead to this insensitivity. While low levels of Bim combined with expression of Mcl-1 confer resistance to ABT-737 in MWCL-1 and BCWM.1, the lack of Bax and Bak confers resistance to intrinsic apoptotic stimuli in general in RPCI-WM1. Moreover, the loss of Bax and Bak protein expression occur through distinct mechanisms. These WM cell lines demonstrate that sensitivity to agents that kill through the intrinsic apoptotic pathway may vary within a disease that is characterized by a single activating mutation and suggests that additional heterogeneous events regulate the expression of Bcl-2 family proteins in WM. Disclosures: Leleu: CELGENE: Honoraria; JANSSEN: Honoraria. Lonial:Millennium: Consultancy; Celgene: Consultancy; Novartis: Consultancy; BMS: Consultancy; Sanofi: Consultancy; Onyx: Consultancy. Boise:Onyx Pharmaceuticals: Consultancy.

Abstract Abstract 132 Multiple myeloma (MM), an incurable neoplasia of terminally differentiated plasma cells, are critically dependent on their interactions with bone marrow stromal cells (BMSC) for essential survival signals, growth and immunosuppressive factors. Very little is known about the specific BM cell type or the molecular elements in these interactions, an understanding of which could provide novel targets that could be interdicted to enhance conventional chemotherapy. A potential MM surface protein that could be involved in these interactions is CD28, based on its known pro-survival role in T cells. Clinical studies have shown that expression of CD28 in multiple myeloma highly correlates (p=0.006) with myeloma tumoral expansion. Moreover, CD28+ MM cells invariably express the CD28 ligand CD86. A survival role for MM-CD28 might involve interactions with BM cells that express B7 (CD80/CD86) such as dendritic cells (DCs, that are known to be closely associated with MM cells in the BM) or with CD86+ MM cells themselves. We had previously shown (ASH2008, #I-769) that blocking CD28-CD86 interactions between myeloma cells with high affinity B7 ligand CTLA4Ig (Abatacept®) sensitized myeloma cells to chemotherapy. Now we show that myeloma cells co-cultured with myeloid DCs in vitro derive both direct and indirect survival signals from DCs, and this can be partially blocked by commercially available reagents. Our data show that flow cytometric analysis of mononuclear cells (MNC) from BM aspirates of myeloma patients with increased CD138+ plasma cell populations (9-58%), show an increased CD11b+ (myeloid) population (20-37%) as well, which is in contrast to healthy transplant donor controls (12-15% CD11b+, 4–6% CD138+). Moreover, a larger fraction (11-47%) of the myeloma CD138+ plasma cells expressed CD28 compared to healthy control (3.3-7.7%). Also, when we analyzed gene expression datasets (NCBI #GSE5900 and GSE4204) from plasma cells (PC) of normal donors, monoclonal gammopathy of undetermined significance (MGUS), smoldering myeloma (SM) and newly diagnosed multiple myeloma (MM), we found a progressive increase in patients showing CD28 expression with increasing severity of disease (normal<MGUS<SM<MM) (Fig 1A). When we sorted the highest scoring MM group (n=538) into 8 genetic subgroups as defined earlier, CD28 expression was found to peak in the MF subgroup (typically associated with poor survival in myeloma patients) (Zhan et al. 2006, Blood 108, pp. 2020) relative to total population (p<0.0001) (Fig 1B). Antibody mediated activation of MM-CD28 over 48 hrs increased viability of myeloma cell line MM.1S cultured under serum starvation (3.7%) or with drugs ATO (1.9%), melphalan (18%) or dexamethasone (3.3%) to 66%, 21%, 33% and 11% respectively. Viability of MM.1S cells or primary CD138+ plasma cells (isolated from myeloma BM aspirates) cultured under serum starvation was enhanced >3 fold (p<0.001) when co-cultured with monocyte derived DCs, and in MM.1S this was partially reversed when either MM-CD28 or DC-B7 was blocked (Fig 2). Similar protection of MM.1S was also observed against a gradient of dexamethasone or melphalan. CD28 activation was accompanied by rapid tyrosine phosphorylation of CD28, association of p85 (PI3K), activation of Vav-1 and increase in CD28 associated tyrosine kinase activity, as shown by immunoprecipitation, western and kinase activity assays. We had previously shown that MM-CD28 interaction drive DC production of pro-survival factor IL-6 and immunosuppressive factor IDO via DC-B7 “backsignaling” (ASH2008 #I-769). Now we show that MM induced DC production of IL-6 (8 ng/ml) was partially inhibited in presence of CD28 blocking αCD28(Fab) fragments (3 ng/ml) or with protein kinase C (PKC) inhibitor Bisindolylmaleimide-I (2.1ng/ml). Activity of the immunosuppressive enzyme IDO in these co-cultures was completely inhibited in the presence of a novel IDO inhibitor from Incyte corporation, and this helped partially reverse IDO mediated suppression of T-cell proliferation in proliferation assays using co-culture supernatants. In conclusion, our data characterizes CD28-B7 pathway and DCs in the BM as vital for myeloma survival and also as possible targets to include in future strategies in the treatment of myeloma. FIGURE 1 FIGURE 1. FIGURE 2 FIGURE 2. Disclosures: Boise: University of Chicago: Patents & Royalties.

Key PointsCD28 delivers a pro-survival signal to MM cells via regulation of PI3K/Akt, FoxO3a, and Bim. Blockade of CD28:CD80/CD86 in vivo resensitizes MM cells to chemotherapy and significantly reduces tumor burden.

Abstract Interactions between the malignant plasma cells of multiple myeloma and stromal cells within the bone marrow microenvironment are essential for myeloma cell survival, mirroring the same dependence of normal bone marrow-resident long-lived plasma cells on specific marrow niches. These interactions directly transduce prosurvival signals to the myeloma cells and also induce niche production of supportive soluble factors. However, despite their central importance, the specific molecular and cellular components involved remain poorly characterized. We now report that the prototypic T cell costimulatory receptor CD28 is overexpressed on myeloma cells during disease progression and in the poor-prognosis subgroups and plays a previously unrecognized role as a two-way molecular bridge to support myeloid stromal cells in the microenvironment. Engagement by CD28 to its ligand CD80/CD86 on stromal dendritic cell directly transduces a prosurvival signal to myeloma cell, protecting it against chemotherapy and growth factor withdrawal-induced death. Simultaneously, CD28-mediated ligation of CD80/CD86 induces the stromal dendritic cell to produce the prosurvival cytokine IL-6 (involving novel cross-talk with the Notch pathway) and the immunosuppressive enzyme IDO. These findings identify CD28 and CD80/CD86 as important molecular components of the interaction between myeloma cells and the bone marrow microenvironment, point to similar interaction for normal plasma cells, and suggest novel therapeutic strategies to target malignant and pathogenic (e.g., in allergy and autoimmunity) plasma cells.