Chanan‐Khan, Asher

Abstract Abstract 2699 Myeloid differentiation factor 88 (MYD88) is an adaptor protein that plays a key role in mediating innate immune response. Upon activation of toll-like (TLRs) or IL-1b receptors, MYD88 activates a signaling cascade that culminates in activation of NF-kB and expression of proinflammatory genes. Activating mutations in MYD88 have been reported in non-Hodgkin's lymphoma (NHL) tumors, including diffuse large B cell and marginal zones lymphoma. The most common MYD88 mutation described thus far is a single base pair mismatch resulting in an amino acid switch from lysine to proline at position 265 (MYD88L265P). MYD88L265P functions as a constitutively active MYD88 protein resulting in dysregulated NF-kB and STAT3 signaling. This mutation has recently been reported to be present in lymphomoplasmacytic lymphoma/Waldenstrom macroglobulinemia (LPL/WM) at a high frequency, ∼ 90% (Xu et al, ASH, #261, 2011). The discovery of MYD88L265P in a high percentage of LPL/WM tumors, and other subtypes of NHL, provides the basis for the identification and targeting of MYD88 dependent pathways. Additionally, the ability of this mutation to drive NF-kB-mediated cytokine expression combined with our finding that LPL/WM patients have elevated serum cytokines suggests that the MYD88 mutation may play a significant role in LPL/WM pathogenesis. We first wanted to confirm the incidence of the MYD88L265P mutation in LPL/WM and other subtypes of indolent lymphoma. Using Sanger sequencing we found that 57% (n=58) of LPL, 4% of MALT (n=23), 5% of nodal marginal zone (n=34), and 6% of splenic marginal zone (n=34) lymphomas harbor the MYD88L265P mutation, with all but 1 case being heterozygous. When we specifically looked at the LPL cases with WM, we found that 70% of WM tumors have the MYD88L265P mutation. In a validation cohort of WM (n=41), we found a similar mutation rate of 68%. Additionally, the WM cell line MWCL1 and the IgM secreting cell line BCWM.1 also harbor the MYD88L265P mutation. The prevalence of the MYD88L265P mutation in NHL, specifically WM and LPL, suggests that it may be a novel driver of lymphoma pathogenesis and a potential therapeutic target. However, it is not yet clear if this mutation correlates with activation of signaling pathways, or cell growth and survival in LPL/WM. To address these questions we first explored the possibility that the MYD88 signaling pathway is constitutively active in cells that express MYD88L265P. Upon activation of TLRs or IL-1b receptors, MYD88 forms a homodiamer and recruits IRAK1/4 and TRAF6 into a complex resulting in association and phosphorylation of TAK1 followed by activation of NF-kB. Using three cell lines that express MYD88L265P (BCWM, MWCL1, and OCI-Ly3), we looked for complex formation of MYD88, IRAK1/4, TRAF6, and TAK1. Immunoprecipitation of either endogenous IRAK1 or TAK1 revealed constitutive association with both TRAF6 and MYD88. We also detected phosphorylation of TAK1, and taken together, these data suggest that the MYD88 pathway is activated in cells that harbor the MYD88L265P mutation. We next wanted to confirm the significance of the MYD88 pathway on lymphoma cell growth. Using our cell lines we tested the effect of IRAK1/4, TAK1, and NF-kB inhibitors on cell proliferation. All MYD88L265P expressing cell lines were sensitive to the TAK1 and NF-kB inhibitors in a dose dependent manner (0–10 uM), however, we only saw inhibition of cell proliferation with the IRAK1/4 inhibitor at the highest dose (10 uM) in the BCWM cell line. These data suggest that cell proliferation is dependent on the MYD88 signaling pathway, with some variation being detected between cell line models and inhibitors. Because the MYD88 pathway has also been shown to drive cytokine secretion we next tested the impact of the IRAK1/4, TAK1, and NF-kB inhibitors on expression of IL-10. Using drug doses that were shown to inhibit cell proliferation, but not impact survival, we found that all three inhibitors reduced the level of IL-10 secreted by each of cell lines. In summary, our data confirm the high incidence on the MYD88L265P mutation in LPL/WM, we find that the MYD88 signaling pathway is constitutively activated in cells the harbor the mutation, and we show that cell proliferation and cytokine secretion are dependent on MYD88 signaling targets. These studies highlight the biologic significance of the MYD88L265P mutation in LPL/WM and suggest that the MYD88 signaling pathway may be a novel therapeutic target. Disclosures: No relevant conflicts of interest to declare.

Abstract BACKGROUND: Consistent with the advanced age at diagnosis (median age ~70 years), most patients with CLL have co-existent health problems. These co-morbidities influence the ability of many CLL patients to tolerate aggressive chemotherapy-based treatment and can also contribute to treatment-related side effects. The recent development of novel signaling inhibitors, particularly the Bruton's tyrosine kinase inhibitor ibrutinib, has been a major treatment advance for patients with CLL. While these agents generally have favorable toxicity profiles relative to standard chemotherapy-based treatments, they are chronic therapies which patients typically stay on for an extended period. Preliminary data suggests ibrutinib may be associated with an increased risk of atrial fibrillation (Afib). In one randomized trial comparing ibrutinib to ofatumumab in patient with relapsed CLL, incident grade 3+ Afib occurred in 3% of ibrutinib treated patients compared to 0% of ofatumumab treated patients (NEJM 371:213). Despite these observations, the baseline frequency of Afib in patients with CLL is not well described - particularly incident atrial fibrillation acquired during the course of the disease. METHODS: We used the Mayo Clinic CLL database to evaluate the prevalence of Afib at the time of CLL diagnosis as well as the incidence of Afib during follow-up. All patients with a new diagnosis of CLL after January 1995 who were seen at Mayo within 12 months of diagnosis were included in the analysis. Afib was identified by chart review and by billing search using ICD9 codes. Data on co-morbid conditions associated with risk of Afib was also abstracted (e.g. hypertension, coronary artery disease [CAD], valvular heart disease, cardiomyopathy, diabetes mellitus, pulmonary disease). RESULTS: A total of 2444 patients with newly diagnosed and previously untreated CLL were seen at Mayo Clinic within 12 months of diagnosis between 1/1995 and 4/2015.Median age at diagnosis was 65 years and 1626 (66.5%) patients were men. A history of Afib was present at the time of CLL diagnosis in 148 (6.1%) patients. Four additional patients had Afib documented in the record but the precise date of onset (e.g. prior to or after CLL diagnosis date) could not be determined. Age, male sex and history of CAD, valvular heart disease, cardiomyopathy, hypertension, and diabetes were associated with a greater likelihood of having a history of Afib at the time of CLL diagnosis (all p<0.01). Among the 2292 patients without a history of Afib at CLL diagnosis, 139 (6.1%) had incident Afib during the course of follow-up for their CLL. The incidence of Afib among patients without a history of Afib at diagnosis was approximately 1%/year (Figure 1A). Considering both Afib present at the time of CLL diagnosis or acquired during the course of the disease, 291 (11.9%) of the 2444 patients in this cohort experienced Afib (median follow-up: 59 months). Among patients without Afib at the time of CLL diagnosis, the following characteristics at the time of CLL diagnosis were associated with an increased risk of incident Afib on multivariate analysis: older age (age 65-74 HR=2.4, p<0.001; age ≥75 HR=3.6, p<0.001), male sex (HR=1.8, p=0.004); valvular heart disease (HR=2.4, p=0.007), and hypertension (HR=1.5; p=0.02). A predictive model for acquired Afib was subsequently constructed based on the independent factors in the Cox regression model. An individual weighted risk score was assigned to each independent factor based on the regression coefficients of the HRs. The Afib risk score (range 0-7) was defined as the sum of the scores of these independent factors. The risk of incident Afib among patients with risk scores of 0-1, 2-3, 4, and 5+ is shown in Figure 1B. Rates for these 4 groups were significantly different (p<0.001), with the 10-year Afib rates (95% C.I.) for those with a score of 0-1, 2-3, 4, and 5+: 4% (2-6%), 9% (6-13%), 17% (11-23%), and 33% (20-43%), respectively. CONCLUSIONS: A history of Afib is present in approximately 1 out of every 16 patients with newly diagnosed CLL. Among patients without Afib at diagnosis, the incidence rate of Afib is ~1%/year. The risk of incident Afib in newly diagnosed CLL patients can be predicted based on age, sex, and co-morbid health conditions present at diagnosis. These data provide context to help interpret data on the frequency of Afib in CLL patients treated with ibrutinib and other novel agents. Disclosures Shanafelt: Janssen: Research Funding; Polyphenon E Int'l: Research Funding; Glaxo-Smith_Kline: Research Funding; Cephalon: Research Funding; Genentech: Research Funding; Hospira: Research Funding; Celgene: Research Funding; Pharmactckucs: Research Funding. Ding:Merek: Research Funding. Kay:Tolero Pharm: Research Funding; Hospira: Research Funding; Genentech: Research Funding; Pharmacyclics: Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract Background: The anti-apoptotic proteins BCL-2 and MCL-1 promote multiple myeloma (MM) cell survival. Bortezomib (BTZ) can inhibit MCL-1 activity by stabilizing the MCL-1 antagonist, NOXA. Venetoclax is an orally bioavailable, highly selective BCL-2 inhibitor, which enhances BTZ efficacy in MM xenograft models. This Phase 1 study evaluates venetoclax with BTZ and dexamethasone (Dex) in patients (pts) with relapsed/refractory MM. Methods: Objectives include safety, pharmacokinetics, preliminary efficacy and maximum therapeutic dose of venetoclax with BTZ and Dex. A fixed dose of venetoclax ranging from 50 to 800 mg PO daily, according to dose cohort assignment, was given in combination in cycles (C) 1-11 and alone in C12 and beyond. Dose escalation decisions were made using the continual reassessment method. Pts received BTZ (1.3 mg/m2 SC, days [D] 1, 4, 8, 11) and Dex (20 mg PO, D1, 2, 4, 5, 8, 9, 11, 12) in cycles (C)1-8 (21D), then BTZ + Dex (D1, 8, 15, 22) in C9-11 (35D). Results: Forty-one pts were enrolled as of June 15, 2015 (pts in each cohort: 50 mg, n=3; 100 mg, n=5; 200 mg, n=6; 300 mg, n=7; 400 mg, n=6; 500 mg, n=7; 600 mg, n=5; 800 mg, n=2). Median age was 65 (38-79); 15/26 F/M. 14 were ISS stage I, 11 stage II, 11 stage III, 5 missing. Median (range) number of prior lines of therapy was 5 (1-15). Thirty-five pts had received prior BTZ (10 refractory), 34 prior lenalidomide (22 refractory); 29 had undergone stem cell transplantation. Based on FISH analysis, 5 pts had MM with t(11;14); 3 with t(4;14), 20 with del 17p, and 10 with del 13q. Treatment-emergent AEs occurring in ≥20% of pts were constipation (37%), diarrhea (37%), thrombocytopenia (32%), asthenia (29%), insomnia (29%), anemia (27%), peripheral neuropathy (27%), dyspnea (24%), peripheral edema (22%), and nausea (20%). Grade 3/4 AEs in ≥10% of pts were thrombocytopenia (20%), and anemia (17%). SAEs occurred in 18 pts; SAEs in ≥2 pts were cardiac failure, embolism, pyrexia, respiratory failure, sepsis, thrombocytopenia (n=2 each, no SAEs were venetoclax-related). Twenty-nine pts have discontinued treatment: 23 due to PD, 2 due to AEs [adenocarcinoma; cardiac and respiratory decompensation attributed to Dex (DLT at 300 mg)], and 4 withdrew consent. Three deaths occurred (all due to PD). No TLS occurred. In preliminary PK analyses (n=41), dose-normalized venetoclax exposure when given with BTZ+Dex was similar when compared to venetoclax monotherapy in MM as well as CLL and NHL pts. Forty of 41 pts were evaluable for efficacy. All responses occurred in BTZ sensitive or naïve pts. Median (range) duration or response was 5.9 (0-14.1) months in all pts, 8.5 (2.3-11.4) months in BTZ naïve pts, and 4.7 (0-14.1) months in BTZ-sensitive pts. Conclusions: Venetoclax with BTZ and Dex has an acceptable safety profile in heavily pretreated MM pts; no new safety signals were identified compared to other venetoclax studies. These early data suggest the combination of proteasome and BCL-2 inhibition resulted in anti-tumor activity. Responses were observed only in pts naïve or sensitive to prior BTZ (ORR = 100% and 58%, respectively) and occurred in all dose cohorts. The study is currently enrolling pts in the 1000 mg dose escalation cohort. Figure 1. Figure 1. Disclosures Moreau: Celgene, Janssen, Takeda, Novartis, Amgen: Membership on an entity's Board of Directors or advisory committees. Off Label Use: Venetoclax is an investigational drug that is not yet approved in this indication. Roberts:AbbVie and Genentech: Research Funding; Walter and Eliza Hall Institute of Medical Research: Employment. Agarwal:Amgen, Millennium: Consultancy; Celgene, Onyx: Speakers Bureau; AbbVie: Research Funding. 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; Millenium: Membership on an entity's Board of Directors or advisory committees; Onyx: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Pierre Fabre: Membership on an entity's Board of Directors or advisory committees. Kumar:Skyline, Noxxon: Honoraria; Celgene, Millennium, Onyx, Janssen, Noxxon, Sanofi, BMS, Skyline: Consultancy; Celgene, Millennium, Onyx, Novartis, Janssen, Sanofi: Research Funding. Touzeau:AbbVie: Research Funding. Darden:AbbVie: Employment, Equity Ownership. Morris:AbbVie: Employment, Equity Ownership. Ross:AbbVie: Employment, Equity Ownership. Salem:AbbVie: Employment, Equity Ownership. Munasinghe:AbbVie: Employment, Equity Ownership. Zhu:AbbVie: Employment, Equity Ownership. Leverson:AbbVie: Employment, Equity Ownership. Maciag:AbbVie: Employment, Equity Ownership. Enschede:AbbVie: Employment, Equity Ownership. Verdugo:AbbVie: Employment, Equity Ownership. Humerickhouse:AbbVie: Employment, Equity Ownership. Harrison:Celgene: Honoraria, Research Funding; Janssen: Research Funding, Speakers Bureau; AbbVie: Research Funding.

Abstract Introduction: The Food and Drug Administration (FDA) approved ibrutinib in February 2014 based on results from a pivotal phase 2 clinical trial that enrolled 85 patients with relapsed/refractory CLL. A subsequent phase 3 trial confirmed the superior progression-free survival (PFS) and overall survival (OS) of ibrutinib compared to ofatumumab in 391 CLL patients. However, there is no information on the efficacy and safety of ibrutinib in CLL patients treated outside the context of clinical trials. Additionally, it is unclear if the reasons for discontinuation of ibrutinib differ in routine clinical practice from those described in patients treated on clinical trials. We conducted a retrospective study to evaluate these aspects in a large cohort of CLL patients treated with ibrutinib off-protocol. Methods: After IRB approval, CLL patients seen at Mayo Clinic, Rochester, MN, and treated with commercial ibrutinib from November 2013 through July 2015 were evaluated. The baseline characteristics, time to therapy discontinuation, reasons for discontinuation and survival following discontinuation were abstracted. Results: One hundred thirty-five patients with CLL were treated during the study interval; 124 received ibrutinib for relapsed/refractory CLL and 11 received ibrutinib for treatment-naïve CLL with TP53 disruption (either del17p on FISH or TP53 mutation). Patients with relapsed/refractory CLL (n=124) Patients were high-risk, with a median of 3 prior therapies (range, 1-15), 81% had unmutated IGHV, and 38% had either del11q or del17p on FISH testing. After a median follow-up of 6.4 months, 101 remain on ibrutinib therapy. The estimated proportion of patients continuing ibrutinib at 6 months was 84% (95% CI: 77-92%) and at 12 months was 70% (95% CI: 59-83%). Of the 23 who discontinued ibrutinib therapy, 8 discontinued for progressive disease (2 progressive CLL; 6 Richter's transformation). The remaining 15 discontinued therapy for reasons other than progression, including: infection (n=3), bleeding (n=3), diarrhea (n=1), atrial fibrillation (n=1), rash (n=1), immune thrombocytopenia (n=1), renal dysfunction (n=1), severe edema (n=1), MDS (n=1) and physician preference (n=2). Table 1 shows the reasons for discontinuation of ibrutinib in patients treated on clinical trials (Maddocks, JAMA Oncology, 2015) compared to the current cohort of patients. The estimated cumulative incidence of discontinuation of ibrutinib therapy due to CLL progression/Richter's transformation at 6 and 12 months was 9% (95% CI: 4-17%) and 12% (95% CI: 5-23%), respectively. The estimated cumulative incidence of ibrutinib discontinuation due to reasons other than progression at 6 and 12 months was 10% (95% CI: 5-17%) and 22% (12-34%), respectively (Figure). The median survival after discontinuation of ibrutinib for patients who had CLL progression was 3.5 months, not reached in patients who developed Richter's transformation and not reached in those patients who discontinued ibrutinib due to reasons other than progression. Patients with treatment-naïve CLL (n=11) All patients had evidence of TP53 disruption (9 had del17p, 3 had TP53 mutation, and 1 had both). After a median follow-up of 2.8 months, no patient has had progression of CLL, and 2 patients have discontinued ibrutinib therapy for reasons other than CLL progression (atrial fibrillation, n=2). The estimated proportion of patients continuing ibrutinib at 6-months was 71% (95% CI: 45-100%). All 11 are still alive, and no patient has undergone allogeneic stem cell transplantation. Conclusion: This is the first study that describes the outcomes of a large cohort of CLL patients treated with ibrutinib outside the context of clinical trials. Patients treated in routine practice appear more likely to discontinue ibrutinib for reasons other than progression of disease, compared to those participating in clinical trials. Our results confirm the poor survival of CLL patients who progress on ibrutinib. Table 1. Comparative analysis of reasons for discontinuation of ibrutinib in patients with relapsed/refractory CLL: Characteristic Current Study (%) Maddocks (JAMA Oncology 2015) (%) No. of patients 124 308 Median follow-up (months) 6.4 20 Reasons for Discontinuation Progression of disease CLL 2 (2) 13 (4) Richter's transformation 6 (5) 15 (5) Non-progression of disease Infection 3 (2) 28 (9) Other 12 (10) 17 (5) Figure 1. Figure 1. Disclosures Ding: Merek: Research Funding. Kay: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, Research Funding; Hospira: Research Funding; Genentech: Research Funding; Pharmacyclics: Research Funding; Tolero Pharm: Research Funding. Shanafelt:Cephalon: Research Funding; Celgene: Research Funding; Glaxo-Smith_Kline: Research Funding; Polyphenon E Int'l: Research Funding; Hospira: Research Funding; Janssen: Research Funding; Pharmactckucs: Research Funding; Genentech: Research Funding.

Abstract Introduction In 2 large phase 3 trials of patients (pts) with relapsed or refractory (R/R) CLL/SLL, single-agent ibrutinib (ibr) was superior to ofatumumab (ofa) (RESONATE; Byrd. NEJM 2013) and ibr + BR was superior to placebo + BR (HELIOS; Chanan-Khan. ASCO 2015). Both studies evaluated ibr in different pt populations with different relevant comparators (eg, ofa in pts who had relapsed following prior anti-CD20-based chemoimmunotherapy [CIT] and/or with del17p, and BR in pts eligible for CIT). In the absence of head-to-head evaluations of single-agent ibr vs BR or single-agent ibr vs ibr + BR, indirect comparisons can be used for hypothesis testing by potentially providing insights on the relative efficacy of treatments. As such, an indirect comparative analysis of data from RESONATE and HELIOS was performed. Recognizing biases inherent in cross-trial comparisons, including lack of randomization across trials and consequent differences in distributions of important confounding variables (eg, pt characteristics, prognostic factors), we used pt-level data from both studies to risk adjust for confounders using accepted multivariate statistical approaches. Methods In RESONATE, pts received 420 mg oral ibr daily until disease progression or unacceptable toxicity or intravenous ofa for up to 24 weeks. The primary end point was IRC-assessed PFS, with secondary end points of OS and ORR. In HELIOS, pts received BR (≤ 6 cycles) with either 420 mg oral ibr daily or placebo until disease progression or unacceptable toxicity. Pts with del17p were excluded. The primary end point was IRC-assessed PFS, with secondary end points of ORR and OS. Per protocol amendment in both studies, pts in comparator arms could switch to ibr upon IRC-confirmed progression. The current exploratory analysis was based on the latest available data from each trial (median time on study: RESONATE, 19 months; HELIOS, 17 months) using investigator assessments, but excluding del17p pts from RESONATE. Analyses were performed using data from both the overall CLL/SLL population and only the CLL pts. Separate multivariate Cox proportional hazards models were constructed for PFS and OS, including treatment and clinically relevant prognostic variables as covariates (age, gender, Rai staging, ECOG score, del11q status, refractory status, number of prior lines of therapy, bulky disease, IgVH status). Adjusted HRs and 95% CIs are presented vs single-agent ibr, along with predicted survival curves derived from the multivariate Cox regressions. Results RESONATE and HELIOS enrolled populations with notable differences making naïve comparison flawed. Because HELIOS enrolled only CIT-eligible pts, the trial included younger pts who had received fewer lines of therapy, as well as lower proportions of pts with purine analog refractory disease, del11q, or Rai stage 4 disease. These factors have been previously reported to influence outcomes in pts with R/R CLL/SLL and thus were included as covariates in the statistical models. Other baseline factors (gender, ECOG score, bulky disease, and IgVH status) were not notably different between the trials, but were found to impact PFS and OS and thus were included as additional covariates. In the overall CLL/SLL population, PFS and OS were comparable for single-agent ibr vs ibr + BR, and were significantly improved for single-agent ibr vs BR (Figure 1). Results for only the CLL pts were similar to those shown in Figure 1 for both PFS (ibr + BR vs single-agent ibr: 1.03 [0.61-1.75], p = 0.9042; BR vs single-agent ibr: 7.52 [4.72-11.99], p < 0.0001; single-agent ibr reduced the risk of progression/death by 87% vs BR) and OS (ibr + BR vs single-agent ibr: 1.20 [0.59-2.43], p = 0.6197; BR vs single-agent ibr: 2.24 [1.14-4.40], p = 0.0197; single-agent ibr reduced the risk of death by 55% vs BR). Conclusions The adjusted indirect comparisons reported here suggest superiority of single-agent ibr over BR for PFS and OS in patients with R/R CLL/SLL. The comparisons also suggest that the addition of BR to ibr did not improve PFS or OS compared with single-agent ibr. However, as median PFS has not been reached for either ibr arm, it is too early to draw firm conclusions. Longer follow-up in the ibr arms of these studies will be required to give an indication of whether CIT adds any benefit to ibrutinib for PFS and OS. Overall, these findings provide support for single-agent ibr as an appropriate choice for all pts with previously treated CLL/SLL. Disclosures Hillmen: Roche Pharmaceuticals: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Gilead: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Celgene: Research Funding; Pharmacyclics LLC, an AbbVie Company: Honoraria, Research Funding. Fraser:Janssen: Honoraria, Research Funding, Speakers Bureau; Hoffman LaRoche: Consultancy, Honoraria; Celgene: Honoraria, Research Funding. Jones:Acerta Pharma BV: Research Funding. Rule:Roche: Consultancy, Other: Travel reimbursement; J&J: Consultancy, Other: Travel reimbursement, Research Funding; Celgene: Consultancy, Other: Travel reimbursement; Gilead: Research Funding. Dilhuydy:Roche: Honoraria, Other: Travel reimbursement; Janssen: Honoraria, Other: Travel reimbursement; Mundipharma: Honoraria. Jaeger:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Cymbalista:Karyopharm: Honoraria; Roche: Honoraria; Gilead: Honoraria; Janssen: Honoraria, Research Funding. Sun:Janssen/J&J: Employment, Equity Ownership. Ninomoto:Pharmacyclics LLC, an AbbVie Company: Employment. Mahler:Janssen: Employment, Other: Travel reimbursement. Cheng:Pharmacyclics LLC, an AbbVie Company: Employment. Diels:Janssen: Employment. Clow:Pharmacyclics LLC, an AbbVie Company: Employment. Salman:Janssen/J&J: Employment, Equity Ownership. James:Pharmacyclics LLC, an AbbVie Company: Employment. Howes:Janssen/J&J: Employment, Equity Ownership.

Abstract Introduction Ibrutinib has become a new standard of care in patients with previously treated CLL/SLL based on the phase 3 RESONATE study (Byrd, et al. NEJM 2014) and other trials evaluating ibrutinib mainly as a single agent in CLL. The first randomized, double-blind, placebo-controlled phase 3 study (HELIOS) investigating ibrutinib in combination with bendamustine and rituximab (BR) was recently reported (Chanan-Khan, et al. ASCO 2015), with ibrutinib significantly extending progression-free survival and reducing the risk of progression/death by 80%. The study design provides an opportunity to examine the overall safety and management of adverse events (AEs) with ibrutinib and placebo in a blinded manner that previously has not been possible. Here we examine the safety and management of AEs with ibrutinib + BR vs placebo + BR in HELIOS. Methods Patients with active CLL/SLL following ≥ 1 prior line of systemic therapy were randomized 1:1 to receive BR (≤ 6 cycles) with either ibrutinib 420 mg daily or placebo (n = 289 in each group). Safety was a secondary end point. Results Median exposure to ibrutinib and placebo was 14.7 and 12.8 months, respectively. Rates of infection in the ibrutinib + BR and placebo + BR arms were similar (all-grade, 70.4%; grade ≥ 3, 26.8% vs all-grade, 70.0%; grade ≥ 3, 22.6%, respectively) but exposure-adjusted analysis reveals an overall lower rate of infections with ibrutinib + BR vs placebo + BR (10.3/100 vs 11.2/100 patient-months), with similar rates of grade ≥ 3 infections (2.4/100 patient-months each arm). Rates of all-grade (grade 3/4) anemia were 22.3% (3.5%) with ibrutinib + BR and 28.9% (8.0%) with placebo + BR. Patients also required fewer transfusions with ibrutinib + BR (23%) vs placebo + BR (29%), the majority of which were red blood cell transfusions. Similar proportions of patients used growth factors in both arms (54% vs 52%, respectively). Grade 3/4 neutropenia was reported at similar rates in both arms (53.7% vs 50.5%, respectively); however, fewer patients discontinued due to treatment-related neutropenia with ibrutinib + BR (1.0%) vs placebo + BR (2.8%). Rates of thrombocytopenia were slightly higher with ibrutinib + BR (30.7%) than placebo + BR (24.0%), but rates of grade 3/4 events were similar between arms (15.0% each arm). Atrial fibrillation (AF) was observed more frequently in patients on ibrutinib + BR than placebo + BR (7.3% vs 2.8% overall and 2.8% vs 0.7% grade 3/4, respectively). However, only 4 patients with grade 3/4 AF discontinued therapy in the ibrutinib arm. No patients with grade 1/2 AF discontinued treatment. One-third of patients held ibrutinib treatment to manage AF, with all restarting at the same dose (420 mg). Median (range) time to onset was 3.0 (0.3-17.5) months with ibrutinib + BR and 2.4 (0.6-18.9) months with placebo + BR. Importantly, in those with a prior history of AF or abnormal heart rhythm, only 7/25 receiving ibrutinib + BR and 2/22 receiving placebo + BR developed AF/atrial flutter on study. The rates of any-grade bleeding were 31.0% and 14.6%, respectively, with the majority being grade 1 (77.5% and 69.0%, respectively). Low rates of grade 3/4 major bleeding were observed in the ibrutinib + BR (2.1%) and placebo + BR (1.7%) arms. Many patients (41.8% ibrutinib + BR, 41.1% placebo + BR) were receiving concomitant anticoagulant/antiplatelet medication. A low rate of treatment-related lymphocytosis was observed in both arms (7.0% ibrutinib + BR, 5.9% placebo + BR). The majority of cases resolved within 2 weeks. Conclusions In this randomized, double-blind, placebo-controlled trial, the addition of ibrutinib to BR was well tolerated and did not significantly impact the safety profile of BR. In addition, ibrutinib was associated with reduced rates of anemia and transfusional support. Consistent with its known toxicity profile, patients in the ibrutinib + BR arm had higher rates of bleeding (mostly grade 1 or 2) and AF; however, few patients discontinued therapy as a result of these AEs. A prior history of AF or abnormal heart rhythm did not lead to recurrent episodes in the majority of cases. Taken together, the results from HELIOS establish the significant efficacy of ibrutinib and also the overall positive risk-benefit profile of ibrutinib + BR. Disclosures Cramer: Janssen: Other: Travel grant, Research Funding, Speakers Bureau; Hoffman LaRoche: Other: Travel grant, Research Funding, Speakers Bureau; Astellas: Other: Travel grant; Glaxo Smith Klein/Novartis: Research Funding; Gilead: Other: Travel grant, Research Funding; Mundipharma: Other: Travel grant. Demirkan:Celgene: Other: Travel reimbursement; Amgen: Consultancy. Fraser:Hoffman LaRoche: Consultancy, Honoraria; Janssen: Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria, Research Funding. Santucci Silva:Janssen: Other: Travel reimbursement, Research Funding; GSK: Research Funding; Celgene: Research Funding; Merck: Research Funding; Novartis: Other: Travel reimbursement; Hoffman LaRoche: Other: Travel reimbursement, Research Funding. Janssens:Roche: Consultancy, Speakers Bureau; Mundipharma: Speakers Bureau; Janssen: Consultancy. Goy:Allos, Biogen Idec, Celgene, Genentech, and Millennium. Gilead: Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau. Mayer:Janssen: Research Funding. Dilhuydy:Roche: Honoraria, Other: Travel reimbursement; Janssen: Honoraria, Other: Travel reimbursement; Mundipharma: Honoraria. Bartlett:Medimmune: Research Funding; Novartis: Research Funding; Pfizer: Research Funding; Genentech: Research Funding; ImaginAB: Research Funding; Astra Zeneca: Research Funding; Pharmacyclics: Research Funding; Janssen: Research Funding; Gilead: Consultancy; Seattle Genetics: Consultancy, Research Funding; Millenium: Research Funding; Celgene: Research Funding. Rule:Roche: Consultancy, Other: Travel reimbursement; Gilead: Research Funding; Celgene: Consultancy, Other: Travel reimbursement; J&J: Consultancy, Other: Travel reimbursement, Research Funding. Sun:Janssen/J&J: Employment, Equity Ownership. Phelps:Janssen/J&J: Employment, Equity Ownership. Mahler:Janssen: Employment, Other: Travel reimbursement. Salman:Janssen/J&J: Employment, Equity Ownership. Howes:Janssen/J&J: Employment, Equity Ownership. Hallek:AbbVie: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Roche: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Gilead: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Pharmacyclics: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Celgene: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Boehringher Ingelheim: Honoraria, Other: Speakers Bureau and/or Advisory Boards; Mundipharma: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Janssen: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding.

Abstract Introduction Recent results from the HELIOS phase 3 study in relapsed/refractory CLL/SLL demonstrated that the addition of ibrutinib to chemoimmunotherapy with bendamustine/rituximab (BR) leads to an 80% reduction in risk of progression or death compared with placebo + BR (Chanan-Khan et al. ASCO 2015). In addition to prolongation of progression-free survival (PFS; median not reached vs 13.3 months; hazard ratio: 0.203, 95% confidence interval: 0.150-0.276, p<0.0001), overall response rate (ORR) and rates of complete response (CR) or CR with incomplete marrow recovery (CRi) were significantly improved with ibrutinib + BR (ORR: 82.7% vs 67.8%; CR/CRi: 10.4% vs 2.8%). Here we report additional analyses on the quality of response with ibrutinib combined with BR. Methods In total, 578 patients (pts) with relapsed/refractory CLL/SLL requiring treatment were randomized 1:1 (289 per arm) to receive BR (≤ 6 cycles) with either ibrutinib (420 mg daily) or placebo. Purine analog refractoriness (yes vs no) and number of prior therapies (1 vs > 1) were stratification factors. Pts with deletion 17p (del17p; > 20% of cells) were excluded. All pts were required to have ≥ 1 abnormal lymph node (LN; defined as a measurable lesion > 1.5 cm). The primary end point was independent review committee (IRC)-assessed PFS. In this analysis, individual parameters of response (LN, spleen, overall radiology, absolute lymphocyte count [ALC], complete blood count [CBC], and bone marrow [BM]) were evaluated. Minimal residual disease (MRD) was assessed by flow cytometry using an 8-color panel (Rawstron AC, et al. Leukemia. 2007;21:956-964); MRD samples were collected at confirmation of suspected CR (bone marrow) and every 3 months thereafter (peripheral blood). Rate of MRD-negative response was defined as the proportion of pts who reached negative disease status (< 0.01%, ie, < 1 CLL cell/10,000 leukocytes) in any sample. Reported MRD rates are based on the intent-to-treat (ITT) population. Results The ORR assessed by the IRC was 82.7% with ibrutinib + BR vs 67.8% with placebo + BR (p < 0.0001), and was consistent with ORR reported by the treating physician (investigator assessed) (ORR: 86.2% vs 68.9%, p < 0.0001). However, rates of CR/CRi were higher by investigator assessment (21.4%, ibrutinib + BR vs 5.9%, placebo + BR) than IRC (10.4% vs 2.8%). The IRC employed an independent evaluation of radiological scans including stringent evaluation of LN and volumetric assessment of spleen size-the main reasons for the difference in CR/CRi rates between investigator and IRC assessment. At baseline, similar proportions of pts in each arm had bulky disease defined as LN > 5 cm (54%-58%) or abnormal spleen (~40%) as assessed by IRC. Complete resolution of previous CLL/SLL manifestations as assessed by the IRC was achieved more often in the ibrutinib + BR arm in comparison with placebo + BR for LN (34.6% vs 15.2%), spleen (56.7% vs 37.0%), overall radiology (21.1% vs 9.0%), and BM (19.7% vs 5.9%). Rates of normalization of ALC (> 90%) and CBC (> 70%) were high and similar in the 2 arms. MRD was assessed in 120 pts treated with ibrutinib + BR and 57 pts treated with placebo + BR and was negative in 37 pts and 14 pts, respectively, which corresponds with an MRD-negative response rate of 12.8% vs 4.8% for ibrutinib + BR vs placebo + BR (p = 0.0011). Investigator-determined responses by different levels of MRD are shown in Table 1. The percentage of pts with an MRD level < 1% was higher with ibrutinib + BR vs placebo + BR (32.2% vs 11.8%). Moreover, the percentage of pts with an MRD level < 0.1% was higher for ibrutinib + BR vs placebo + BR (24.6% vs 7.6%) suggesting that the depth of response with ibrutinib + BR was superior. Kaplan-Meier plots by MRD level (Figure 1) show that a lower MRD level was associated with a longer PFS. However, pts in the ibrutinib + BR arm had a more sustained response at every MRD level compared with pts in the placebo + BR arm. Conclusions Pts treated with ibrutinib + BR showed not only a higher ORR, but also a greater depth of response, with more CRs and a higher rate of resolution of LN, spleen, and BM involvement. Furthermore, the rate and depth of MRD negativity was improved, and appeared to last longer in pts treated with ibrutinib + BR compared with pts receiving placebo + BR. With a median follow up of 17 months in the ibrutinib + BR arm, no MRD-negative pts and few MRD-positive pts had progressed, thus evaluating a trend in PFS with MRD negativity is currently limited in this arm. Disclosures Cramer: Gilead: Other: Travel grant, Research Funding; Glaxo Smith Klein/Novartis: Research Funding; Astellas: Other: Travel grant; Mundipharma: Other: Travel grant; Janssen: Other: Travel grant, Research Funding, Speakers Bureau; Hoffman LaRoche: Other: Travel grant, Research Funding, Speakers Bureau. Off Label Use: Combination of bendamustine, obinutuzumab and ibrutinib for treatment of CLL. Fraser:Hoffman LaRoche: Consultancy, Honoraria; Janssen: Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria, Research Funding. Demirkan:Amgen: Consultancy; Celgene: Other: Travel reimbursement. Santucci Silva:Merck: Research Funding; Celgene: Research Funding; GSK: Research Funding; Janssen: Other: Travel reimbursement, Research Funding; Hoffman LaRoche: Other: Travel reimbursement, Research Funding; Novartis: Other: Travel reimbursement. Janssens:Mundipharma: Speakers Bureau; Roche: Consultancy, Speakers Bureau; Janssen: Consultancy. Goy:Allos, Biogen Idec, Celgene, Genentech, and Millennium. Gilead: Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau. Mayer:Janssen: Research Funding. Dilhuydy:Roche: Honoraria, Other: Travel reimbursement; Janssen: Honoraria, Other: Travel reimbursement; Mundipharma: Honoraria. Bartlett:Millenium: Research Funding; Medimmune: Research Funding; Novartis: Research Funding; Pfizer: Research Funding; Genentech: Research Funding; ImaginAB: Research Funding; Astra Zeneca: Research Funding; Pharmacyclics: Research Funding; Janssen: Research Funding; Gilead: Consultancy; Seattle Genetics: Consultancy, Research Funding; Celgene: Research Funding. Rule:Roche: Consultancy, Other: Travel reimbursement; J&J: Consultancy, Other: Travel reimbursement, Research Funding; Celgene: Consultancy, Other: Travel reimbursement; Gilead: Research Funding. Sun:Janssen/J&J: Employment, Equity Ownership. Phelps:Janssen/J&J: Employment, Equity Ownership. Mahler:Janssen: Employment, Other: Travel reimbursement. Salman:Janssen/J&J: Employment, Equity Ownership. Schaffer:Janssen: Employment. Balasubramanian:Pharmacyclics LLC, an AbbVie Company: Equity Ownership; Janssen: Employment, Equity Ownership. Howes:Janssen/J&J: Employment, Equity Ownership. Hallek:AbbVie: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Celgene: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Pharmacyclics: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Gilead: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Boehringher Ingelheim: Honoraria, Other: Speakers Bureau and/or Advisory Boards; Roche: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Mundipharma: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Janssen: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding.

Abstract Introduction Ibrutinib is a first-in-class, once-daily, oral, covalent inhibitor of BTK that has excellent single-agent activity in patients with previously treated CLL/SLL, based on results of published clinical studies. In the HELIOS trial, addition of ibrutinib to BR resulted in an 80% reduction in disease progression or death and confirmed for the first time, in a randomized setting, the benefit of ibrutinib-based therapy compared with standard chemoimmunotherapy (CIT) in previously treated patients (Chanan-Khan et al. ASCO 2015). In patients with CLL or SLL, deletion 17p (del17p) and 11q (del11q), complex karyotype, unmutated IgVH, and elevated ZAP70 are known high-risk prognostic factors. The current analysis reports on the efficacy of ibrutinib + BR vs placebo + BR in patients in the HELIOS trial with relevant high-risk biomarkers. Methods HELIOS is a randomized, double-blind, placebo-controlled, phase 3 study. Patients with active CLL/SLL following ≥ 1 prior therapy were randomized 1:1 to receive BR (≤ 6 cycles) with either ibrutinib (420 mg daily) (n = 289) or placebo (n = 289). Patients with del17p (> 20% of cells) were excluded. Ninety patients in the placebo arm with independent review committee (IRC)-confirmed progressive disease crossed over to ibrutinib, per protocol amendment. The primary end point was IRC-assessed progression-free survival (PFS), and overall survival (OS) was a secondary end point. A total of 287 patients in each arm had data available for at least 1 biomarker, and this population was used for the biomarker analyses. Correlation of biological risk factors at baseline with PFS and OS was analyzed using Kaplan-Meier analysis and curves compared using log-rank tests. Hazard ratios (HRs) were estimated using univariate Cox proportional hazards models. Results At a median follow-up of 17 months, IRC-assessed PFS was significantly longer with ibrutinib + BR vs placebo + BR in the overall study population (median not reached vs 13.3 months, respectively; HR: 0.203; 95% CI: 0.150-0.276; p < 0.0001). All subgroups of patients, including those with adverse prognostic parameters, e.g., del11q, complex karyotype, unmutated IgVH and elevated ZAP70 levels, had a significantly longer PFS with the addition of ibrutinib to BR as compared with placebo + BR (Table 1). As expected, each of these adverse prognostic parameters had a negative impact on PFS in the placebo + BR arm, e.g., the median PFS was shortest in patients with complex karyotype [8.5 months vs 13.8 months in patients without complex karyotype] and in patients with unmutated IgVH (11.3 months vs 22.1 months in patients with mutated IgVH). Interestingly, in the ibrutinib + BR arm, the adverse impact of these risk factors could not be detected (median PFS not reached irrespective of presence of risk factors). For example, in Figure 1 showing the PFS curves stratified by both del11q status and treatment, the outcome for patients in the ibrutinib + BR arm with del11q was similar to those without, with a trend toward better outcome in the del11q patients (e.g., longer PFS - not reached vs 24.9 months), unlike for patients in the placebo + BR arm (11.01 months vs 13.86 months). In patients with del11q, unmutated IgVH, or elevated ZAP70, there were also statistically significant benefits in OS for those receiving ibrutinib + BR vs placebo + BR (del11q: HR: 0.326, 95% confidence interval [CI], 0.122-0.870; p = 0.025; unmutated IgVH: HR: 0.515, 95% CI, 0.298-0.890: p = 0.017; elevated ZAP70, HR 0.536, 95% CI, 0.289-0.994: p = 0.048). Addition of ibrutinib also increased PFS in patient subgroups with other cytogenetic or clinical prognostic markers (such as del13q or bulky disease) compared with placebo. Conclusions All subgroups of patients, irrespective of adverse risk factors, such as del11q, complex karyotype, elevated ZAP70, and unmutated IgVH, benefit from the addition of ibrutinib to BR compared with placebo + BR. The negative impact of these known risk factors is apparent in patients in the placebo + BR arm, but is not seen in patients in the ibrutinib + BR arm. These results suggest that ibrutinib + BR is a suitable treatment regimen for all patients with previously treated CLL/SLL, including those with high-risk prognostic markers. Disclosures Cramer: Janssen: Other: Travel grant, Research Funding, Speakers Bureau; Hoffman LaRoche: Other: Travel grant, Research Funding, Speakers Bureau; Mundipharma: Other: Travel grant; Glaxo Smith Klein/Novartis: Research Funding; Astellas: Other: Travel grant; Gilead: Other: Travel grant, Research Funding. Fraser:Janssen: Honoraria, Research Funding, Speakers Bureau; Hoffman LaRoche: Consultancy, Honoraria; Celgene: Honoraria, Research Funding. Santucci Silva:Janssen: Other: Travel reimbursement, Research Funding; GSK: Research Funding; Celgene: Research Funding; Merck: Research Funding; Novartis: Other: Travel reimbursement; Hoffman LaRoche: Other: Travel reimbursement, Research Funding. Dilhuydy:Roche: Honoraria, Other: Travel reimbursement; Janssen: Honoraria, Other: Travel reimbursement; Mundipharma: Honoraria. Goy:Allos, Biogen Idec, Celgene, Genentech, and Millennium. Gilead: Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau. Mato:Celgene: Consultancy, Other: Travel, Accommodations, Expenses, Research Funding; Gilead: Consultancy, Other: Travel, Accommodations, Expenses; Pharmacyclics LLC, an AbbVie Company: Consultancy, Other: Travel, Accommodations, Expenses; TA Therapeutics: Research Funding. Damle:Janssen: Employment. Phelps:Janssen/J&J: Employment, Equity Ownership. Mahler:Janssen: Employment, Other: Travel reimbursement. Salman:Janssen/J&J: Employment, Equity Ownership. Schaffer:Janssen: Employment. Howes:Janssen/J&J: Employment, Equity Ownership. Balasubramanian:Pharmacyclics LLC, an AbbVie Company: Equity Ownership; Janssen: Employment, Equity Ownership.

Abstract Background: The clinical impact of ibrutinib is irrefutable and has been hailed as a revolutionary treatment for several cancers, including mantle cell lymphoma (MCL). Despite high response rates noted with ibrutinib therapy in MCL (ORR, 68%), complete responses are low and durability of remission is suboptimal in MCL vs. CLL or Waldenstrom macroglobulinemia (WM) patients (Cheah et al Ann Oncol 2015). This relative lack of efficacy may be due to MCL cells having a higher proliferation rate and being less indolent in nature than CLL or WM cells. Tumor cells with a high proliferation index rely on optimally functioning protein metabolism/homeostasis systems. In MCL, this observation has been fortuitously exploited with the use of bortezomib, a 20S proteasome inhibitor. Indeed the ubiquitin proteasome system is a validated target and consists of several individual components whose function in MCL has yet to be mapped out. We have recently reported that inhibition of the 19S proteasomal deubiquitinating enzymes (DUBs), USP14 and UCHL5; with the small molecule inhibitor b-AP15 is lethal to drug-resistant WM tumor cells. This intriguing observation, prompted us to define the role of USP14/UCHL5 and their inhibition in a diverse panel of B-cell lymphoma cell lines, including MCL models as well as ibrutinib-resistant MCL cells. Materials: b-AP15 (and its clinical grade analog, VLX1570) was obtained from Vivolux AB and bortezomib from Sellekchem. Human NHL (DLBCL, MCL, Burkitt), Hodgkin lymphoma (HL), multiple myeloma (MM) cell lines as well as established drug-resistant subclones were used in drug-sensitivity screening experiments (total n=25). Results: USP14 and UCHL5 mRNA expression was queried in the CCLE database (Broad-Novartis) and showed highest expression in plasma cell and B-lymphoid tumor cell types. This was also observed at the protein level, wherein analysis of The Human Protein Atlas database revealed moderate to high intensity staining for USP14 and UCHL5 localizing to the cytoplasmic/membranous and nuclear compartments in high-grade NHL tissues. Next, we examined B-lymphoid tumor cell sensitivity to pharmacologic inhibition of USP14/UCHL5 with either b-AP15 or VLX1570 (72hr fluorescein diacetate hydrolysis assay or CellTiter Glo). We observed that MCL cells, including those resistant to ibrutinib (Jeko/IR cell line) were highly sensitive to VLX1570 (median IC50 12 - 25nM). In contrast, MM cells were not as sensitive (IC50's ranging between 58 - 90nM). Nine DLBCL cell lines exposed to equivalent time/concentrations of b-AP15 showed a median IC50 of 311nM (range, 70 - 910nM) and 3 HL models exhibited an IC50 of 531nM (range, 420 - 783nM). No difference in sensitivity to VLX1570 was noted between ABC-type vs. GCB-type DLBCL models. These functional results aligned with prior genomic inquiry where USP14 and UCHL5 gene expression was noted to be higher in MCL cell lines compared to DLBCL and non-hematologic cancer models analyzed (FDR=0.0019, p=0.001), suggesting their more central role in maintaining MCL tumor viability. Indeed MCL tumor survival (particularly ibrutinib-resistant cells) appears linked to USP14/UCHL5 function as treatment of Jeko/IR cells with VLX1570 (250nM, 12hrs) caused marked apoptosis (71.8% annexin-V+ staining) and cleavage of PARP-1. Moreover, the combination of ibrutinib and VLX1570 synergistically induced MCL cell death (median CI: 0.3). Mechanistic studies demonstrated that VLX1570 modulates several proteins critical for MCL survival including cyclin-D1, Myc and CXCR4/CD184. Reduction in cyclin-D1 was also noted to coincide with cell cycle arrest of VLX1570-treated MCL cells. Altogether, these findings suggest that VLX1570 modulates critical cellular signaling pathways utilized by MCL tumor cells, particularly those that are involved in resistance to ibrutinib. Conclusions: MCL remains a challenging malignancy to treat with no effective treatments for ibrutinib-relapsed disease. Our data supports the role of the proteasome-associated DUBs, USP14 and UCHL5, as critical factors involved in ibrutinib-resistant MCL tumor survival. VLX1570 is a potentially effective agent for the treatment of ibrutinib-resistant MCL. Disclosures Gullbo: Vivolux AB: Other: Shareholder. Linder:Vivolux AB: Other: Shareholder.

Abstract Background In the U.S. over 14,000 new cancer cases occur annually in people under 21 years of age; approximately 21% of cases are acute lymphoblastic leukemia (ALL) and ∼ 30% classify as Burkitt lymphoma (BL). Most cases of ALL and BL are due to malignant B-cells that have acquired disease-defining oncogenic lesions that facilitate their rapid proliferation. To maintain a state of homeostasis, the malignant cells rely heavily on the ability of the internal degradation and recycling systems to match the high rate of protein turnover. As such, the ubiquitin proteasome system (UPS) is central in this operation where it prevents buildup of misfolded proteins while also regulating the availability of anti-apoptotic proteins such as BCL2 and MCL1. These observations coupled with the observation that UPS disruption leads to cellular demise have resulted in the development of several proteasome inhibitors (PI). These PI have primarily been examined in adult B-cell malignancies. The feasibility of a bortezomib-containing regimen for use in pediatric malignancies has been examined by the TACL consortium and demonstrated a 73% response rate in relapsed/refractory ALL patients. However, a major limitation of bortezomib-based therapy is an increased incidence of peripheral neuropathy (PN), which was also noted in the TACL study. As such, more potent and reportedly less toxic PI have been developed that seem to carry considerably lower risk for development of PN. Such agents that maintain a high response rate and carry reduced long-term adverse effects are highly desirable in pediatric age patients. Aim Investigation of the novel proteasome inhibitors carfilzomib and MLN9708 (Millennium Pharmaceuticals) in preclinical models of pediatric B-lymphocytic cancer. Methods Representative preclinical models of BL (Raji cell line) and B-ALL (ALL-1 cells) were used in this study. Proteasomal activity was measured using synthetic fluorogenic peptide substrates. Cell viability was measured by MTS assay. Apoptosis was determined by annexin-v/PI staining and mitochondrial membrane permeability (MOMP) was assessed using TMRM followed by flow cytometry. Protein profiling was performed via immunoblot. Results In an effort to understand the effect of carfilzomib and MLN9708 in our pediatric cancer models, we first assessed their ability to inhibit proteasomal activity. While chymotrypsin-like activity, which is the target of both PIs, is inhibited by more than 90% in both cell lines, inhibition (∼ 35%) of caspase-like function conferred by the b1 subunit was more significantly pronounced in MLN9708 treated Raji and ALL-1 cells. Next we performed an MTS assay to determine the growth inhibitory effects of these PI in vitro. Both PI inhibited the growth of the Raji and ALL-1 cells in a dose dependent manner. Carfilzomib showed a more potent effect (IC50 ∼1nM in both cell lines) as compared to MLN9708 (IC50 ∼30nM in ALL-1 cells and ∼50nM in Raji cells). To further understand mechanisms of growth inhibition we examined both tumor cell lines for induction of apoptosis along with corresponding markers. As compared to Raji cells, we observed ALL-1 cells to be more sensitive to the effects of both PI, albeit with MLN9708 (50nM) inducing more cell death (65%) as compared to carfilzomib (10nM, 50% cell death). Further, we observed altered MOMP, cleavage of caspases 9, 3 and PARP-1 were found to occur in both cell lines in presence of carfilzomib or MLN9708. These changes indicate the apoptotic effects of novel PI in ALL-1 and Raji cells are via mitochondrial destabilization and caspase activation. As inhibition of the UPS aids NOXA and BIM (pro-apoptotic BCL2 proteins) mediated cell death, we examined the expression of BCL2 family proteins changes in Raji and ALL-1 cells in response to novel PI. Indeed protein levels of both BCL2 and MCL1 were reduced in carfilzomib and MLN9708 treated cells. Reduced BCL2 expression was more pronounced in ALL-1 cells as compared to Raji cells and downregulation was noted to be dose-dependent. Summary Our data show that both carfilzomib and MLN9708 potently inhibit the viability of malignant ALL and BL cells in vitro. We conclude that PI are promising anti-neoplastic therapeutics that target not only the UPS but also modulate the expression of critical anti-apoptotic proteins. Data from mechanistic studies conducted herein underscore the need for further research in in vivo models of these diseases. Disclosures: Foran: Celgene: Research Funding.