Coleman, Morton

Abstract Background: Patients with relapsed indolent NHL (iNHL) have limited standard treatment options. Lenalidomide combined with rituximab (R 2) has shown complimentary clinical activity and is a tolerable regimen in both untreated and relapsed or refractory (R/R) patients with iNHL (RELEVANCE : N Engl J Med 2018;379:934 and AUGMENT: J Clin Oncol. 2019;37:1188). Methods: MAGNIFY is a multicenter, phase 3b trial in patients with R/R follicular lymphoma (FL) grades 1-3b, transformed FL (tFL), marginal zone lymphoma (MZL), or mantle cell lymphoma (MCL; NCT01996865) exploring optimal lenalidomide duration. In the induction phase, lenalidomide 20 mg PO on days 1-21 of a 28-day cycle + rituximab IV at 375 mg/m 2/week cycle 1 and then every 8 weeks starting with cycle 3 (R 2) are administered for 12 cycles. Patients with stable disease, partial response, or complete response/complete response unconfirmed (CR/CRu) were randomized 1:1 to R 2 vs rituximab maintenance for 18 months. Data presented here are the complete analysis from the induction phase in efficacy-evaluable patients with FL grades 1-3a or MZL (FL grade 3b, tFL, and MCL not included). The focus of this interim analysis was overall response rate (ORR) by 1999 IWG criteria in the induction intention-to-treat population. Results: As of March 5, 2021, 394 patients (318 [81%] FL gr1-3a; 76 [19%] MZL) were enrolled. The median follow-up was 40.6 mo (range, 0.6-79.6). Median age was 66 y (range, 35-91), 328 (83%) had stage III/IV disease, with a median of 2 prior therapies (94% prior rituximab-containing). ORR was 71% (n = 279) with 42% (n = 164) CR/CRu (Table). All patients have completed R 2 induction (n = 232, 59%) or discontinued study treatment (n = 162, 41%). 141 patients (36%) prematurely discontinued both lenalidomide and rituximab, primarily due to adverse events (AEs) (n = 54, 14%) or progressive disease (n = 42, 11%). The majority of patients who have completed induction have been randomized and entered maintenance (n = 217). Median duration of response in the induction period was not reached (95% CI, 43.9 mo-NR), and median progression-free survival in the induction safety population (n = 393) was 50.5 mo (95% CI, 39.5-NR). Efficacy results are reported in the table by histology subgroups (FL vs MZL), and rituximab-refractory, double-refractory, and early relapse statuses. Most common all-grade AEs were 47% fatigue, 43% neutropenia, 37% diarrhea, 30% nausea, and 30% constipation. Grade 3/4 AEs occurring in ≥ 5% of patients included 37% neutropenia (10 patients [3%] had febrile neutropenia), 8% leukopenia, 6% thrombocytopenia, 5% anemia, and 5% fatigue. Conclusions: These data represent complete analysis of all patients in the induction phase of MAGNIFY which continue to support that R 2 is active with a tolerable safety profile in patients with R/R FL grade 1-3a and MZL, including rituximab-refractory, double-refractory, and early relapse patients. Figure 1 Figure 1. Disclosures Lansigan: Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees. Andorsky: Abbvie: Consultancy, Research Funding; Celgene/BMS: Consultancy, Research Funding; Epizyme: Research Funding. Coleman: immunomedics: Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company; Abbvie: Research Funding; Bristol Myers: Research Funding; Celgene: Research Funding; Genentech: Research Funding; Gilead: Research Funding; BeiGene: Research Funding; Innocare: Research Funding; Merck: Research Funding; Pfizer: Research Funding; Roche: Research Funding. Yacoub: Dynavex: Current equity holder in publicly-traded company; Cara: Current equity holder in publicly-traded company; Ardelyx: Current equity holder in publicly-traded company; Agios: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; ACCELERON PHARMA: Membership on an entity's Board of Directors or advisory committees; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; Seattle Genetics: Honoraria, Speakers Bureau; Hylapharm: Current equity holder in publicly-traded company. Melear: TG Therapeutics: Speakers Bureau; Astrazeneca: Speakers Bureau; Janssen: Speakers Bureau. Fanning: Sanofi: Speakers Bureau; Genmab: Membership on an entity's Board of Directors or advisory committees; TG Pharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Genentech: Membership on an entity's Board of Directors or advisory committees; Takeda: Speakers Bureau; ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees; BMS: Speakers Bureau. Kolibaba: TG Therapeutics: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company; Atara Biotechm: Consultancy; McKesson Specialty Health: Consultancy; Sunitomo Dainippon Pharma: Consultancy; Tolero Pharma: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Nowakowski: Incyte: Consultancy; Kymera Therapeutics: Consultancy; TG Therapeutics: Consultancy; Blueprint Medicines: Consultancy; Nanostrings: Research Funding; Curis: Consultancy; Selvita: Consultancy; Zai Labolatory: Consultancy; Daiichi Sankyo: Consultancy; Bantham Pharmaceutical: Consultancy; Karyopharm Therapeutics: Consultancy; Ryvu Therapeutics: Consultancy; Genentech: Consultancy, Research Funding; Kyte Pharma: Consultancy; Roche: Consultancy, Research Funding; Celgene/Bristol Myers Squibb: Consultancy, Research Funding; MorphoSys: Consultancy. Gharibo: BMS: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Ahn: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company; ADC therapeutics: Current equity holder in publicly-traded company. Li: BMS: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding. Sharman: BeiGene: Consultancy; TG Therapeutics: Consultancy; Lilly: Consultancy; Centessa: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics LLC, an AbbVie Company: Consultancy; AstraZeneca: Consultancy; BMS: Consultancy; AbbVie: Consultancy.

Background: Lenalidomide combined with rituximab (R2) has shown complimentary clinical activity and is a tolerable regimen in both untreated and relapsed or refractory (R/R) patients with indolent non-Hodgkin lymphoma. Patients with advanced age at diagnosis are considered to be high risk, supporting post-hoc subgroup analyses by age, with a focus on patients aged ≥ 70 years from the MAGNIFY study. Methods: MAGNIFY is a multicenter, phase IIIb trial in patients with R/R follicular lymphoma (FL) grades 1-3b, transformed FL (tFL), marginal zone lymphoma (MZL), or mantle cell lymphoma (MCL; NCT01996865) exploring optimal lenalidomide duration. Lenalidomide 20 mg on days 1-21 of a 28-day cycle + rituximab 375 mg/m2/week cycle 1 and then every 8 weeks starting with cycle 3 (R2) are administered for 12 cycles followed by 1:1 randomization in patients with stable disease, partial response, or complete response/complete response unconfirmed (CR/CRu) to R2 vs rituximab maintenance for 18 months. Data presented here focus on induction R2 in efficacy-evaluable FL grade 1-3a and MZL patients (FL grade 3b, tFL, and MCL not included) receiving ≥ 1 treatment with baseline/postbaseline assessments. The primary end point is progression-free survival (PFS) by 1999 International Working Group criteria. Post-hoc analyses were performed by analyzing data from patients aged ≥ 70 years at time of study entry. Results: As of November 30, 2019, 393 patients have enrolled and 152 (39%) were aged ≥ 70 years. Baseline characteristics including histology, disease status, and prior treatments of patients ≥ 70 and the overall population are shown in the table. Median PFS in the ≥ 70 subgroup was 36.0 months (95% CI, 28.3-NR). Overall response rate and CR/CRu were 75% and 38%, with a median duration of response that was not reached (95% CI, 27.1-NR). Efficacy results for the overall population are shown in the table. In patients ≥ 70 the most common (≥ 20%) any-grade treatment emergent adverse events (TEAEs) were fatigue (44%), neutropenia (41%), diarrhea (34%), constipation (34%), and nausea (27%). Neutropenia (35%) was the only grade 3/4 TEAE occurring in > 10% of patients (febrile neutropenia occurred in 3 patients [2%]). TEAEs led to lenalidomide dose reduction in 69 patients (46%) and discontinuation in 40 patients (26%). Seventy-eight patients ≥ 70 (51%) completed all 12 cycles of induction treatment, and 72 (47%) have entered the maintenance phase. Sixty-one patients ≥ 70 (40%), compared to 35% of patients in overall population, prematurely discontinued both lenalidomide and rituximab, due to TEAEs (n = 26; 17%), progressive disease (n = 15; 10%), patient withdrawal (n = 12; 8%), death (n = 5; 3%), and other reasons (n = 3; 2%). Neutropenia was the only TEAE leading to discontinuation of lenalidomide in more than 2 patients (n = 10; 7%). Conclusions: Similar to findings in the overall population, R2 treatment in advanced-age patients with R/R FL and MZL resulted in encouraging efficacy, and with close attention to dose reduction there is a tolerable safety profile. Table Disclosures Lansigan: BMS Steering Committee for MAGNIFY Program: Membership on an entity's Board of Directors or advisory committees; Spectrum Pharma: Consultancy, Research Funding; BMS: Consultancy; Seattle Genetics: Consultancy. Andorsky:AstraZeneca: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; CTI: Research Funding. Coleman:Novartis Pharmaceuticals: Research Funding; Merck Sharp & Dohme Corp.: Research Funding; Boston BIoMedical, Inc.: Research Funding; BeiGene: Research Funding; Acerta: Research Funding; Innocare: Research Funding; ARCUS Biosciences: Research Funding; AstraZeneca Pharmaceuticals, LP (Acerta Pharma BV Trials): Research Funding; AstraZeneca Pharmaceuticals, LP: Research Funding; BMS (Celgene Corporation): Research Funding; Eli Lilly and Company: Research Funding; EMD Serono Research and Development Institute Inc.: Research Funding; Genetech (F. Hoffman-LaRoche Ltd): Research Funding; Hutchinson MediPharma, LTD: Research Funding; Incyte Corporation: Research Funding; Ipsen Group: Research Funding; Karyopharma Therapeutics, Inc.: Research Funding; Klus Pharma, Inc.: Research Funding; MeiPharma, Inc.: Research Funding; Seattle Genetics: Research Funding. Yacoub:Novartis: Honoraria, Speakers Bureau; Agios: Speakers Bureau; Incyte: Speakers Bureau; Hylapharm: Current equity holder in private company; Cara therapeutics: Current equity holder in publicly-traded company; Ardelyx: Current equity holder in publicly-traded company; Dynavax: Current equity holder in publicly-traded company. Melear:AstraZeneca: Speakers Bureau; Janssen: Speakers Bureau. Fanning:Prisma Health: Current Employment; Abbvie: Consultancy; TG Therapeautics: Consultancy; Bristol Myers Squibb: Consultancy, Speakers Bureau; Takeda: Consultancy, Speakers Bureau; Sanofi Aventis: Speakers Bureau. Kolibaba:Compass Oncology: Ended employment in the past 24 months; Atara Biotech: Consultancy; TG Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sumitomo Dainippon Pharma Oncology: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company; AbbVie: Research Funding; Acerta: Research Funding; Celgene: Research Funding; Genentech: Research Funding; Gilead: Research Funding; Pharmacyclics: Research Funding; Seattle Genetics: Research Funding; Verastem: Honoraria; Janssen: Research Funding; Novartix: Research Funding. Reynolds:IHA Hematology/Oncology Consultants: Current Employment. Nowakowski:Ryvu: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other; Nanostrings: Research Funding; Seattle Genetics: Consultancy; Curis: Consultancy; MorphoSys: Consultancy, Research Funding; Roche: Consultancy, Research Funding; Kymera: Consultancy; Denovo: Consultancy; Kite: Consultancy; Celgene/BMS: Consultancy, Research Funding. Gharibo:Bayer: Ended employment in the past 24 months; Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Ahn:BMS: Current Employment, Current equity holder in publicly-traded company. Li:BMS: Current Employment, Current equity holder in publicly-traded company. Rummel:Celgene: Consultancy, Honoraria; Janssen: Honoraria; Amgen GmbH: Honoraria; Roche: Honoraria; Novartis Pharma GmbH: Honoraria. Sharman:Bristol Meyers Squibb: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Roche: Consultancy, Research Funding; Acerta: Consultancy, Research Funding; TG Therapeutics: Consultancy, Research Funding; BeiGene: Research Funding; Genentech: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Pharmacyclics: Consultancy, Research Funding; AstraZeneca: Consultancy, Research Funding.

Background: Relapse is expected when treating patients with follicular lymphoma (FL) and marginal zone lymphoma (MZL), with a shortened response associated with each relapse. Lenalidomide combined with rituximab (R2) has shown enhanced activity, with a recently reported median progression free-survival (PFS) of 39.4 months in patients with relapsed/refractory (R/R) indolent non-Hodgkin lymphoma, including those with FL and MZL (AUGMENT; J Clin Oncol. 2019;37:1188). Methods: MAGNIFY is a multicenter, phase IIIb trial in patients with R/R FL grades 1-3b, transformed FL (tFL), MZL, or mantle cell lymphoma (MCL; NCT01996865) in which optimal lenalidomide duration is being explored. Patients received 12 cycles of R2 (lenalidomide 20 mg/d, d1-21/28 + rituximab 375 mg/m2 weekly in cycle 1 and then on day 1 of cycles 3, 5, 7, 9, and 11) followed by 1:1 randomization in patients with stable disease, partial response, or complete response/complete response unconfirmed (CR/CRu) to R2 versus rituximab maintenance for 18 months. Data presented here focus on induction R2 in efficacy-evaluable MZL patients compared with the overall population of FL grades 1-3a+MZL (not including FL grade 3b, tFL, or MCL) receiving ≥ 1 treatment with baseline/post-baseline assessments. The primary end point is progression-free survival (PFS) by 1999 International Working Group criteria. Results: As of November 30, 2019, 393 patients with FL grades 1-3a and MZL enrolled; 76 (19%) had MZL. The median age of MZL patients was 68 years (range, 46-90), 68 (89%) had stage III/IV disease, and 72 (95%) had prior rituximab-containing therapy. Overall response rate was 68% with 39% CR/CRu, and median duration of response was 38.6 months (95% CI, 29.4-not reached [NR]). The median PFS was 41.2 months (95% CI, 38.4-NR). Efficacy results for MZL subtypes and the overall population (FL grades 1-3a + MZL) are shown in the table. Forty-two patients (55%) have completed 12 cycles of R2, and 41 (54%) have been randomized and entered maintenance. Twenty-eight patients (37%) prematurely discontinued both lenalidomide and rituximab, primarily due to adverse events (AEs; n = 11; 14%) and progressive disease (n = 6; 8%). The most common (≥ 20%) all-grade AEs were neutropenia (49%), diarrhea (37%), anemia (25%), thrombocytopenia (24%), and constipation (24%). Most common (≥ 10%) grade 3/4 AEs were neutropenia (41%; 1 patient [1%] had febrile neutropenia), thrombocytopenia (13%), and leukopenia (11%). Conclusions: R2 is active with a tolerable safety profile in patients with R/R MZL. The efficacy and safety profile of R2 in MZL patients were similar to results observed in the overall MAGNIFY population. Disclosures Coleman: Seattle Genetics: Research Funding; EMD Serono Research and Development Institute Inc.: Research Funding; Innocare: Research Funding; ARCUS Biosciences: Research Funding; AstraZeneca Pharmaceuticals, LP (Acerta Pharma BV Trials): Research Funding; AstraZeneca Pharmaceuticals, LP: Research Funding; BMS (Celgene Corporation): Research Funding; Eli Lilly and Company: Research Funding; Genetech (F. Hoffman-LaRoche Ltd): Research Funding; Hutchinson MediPharma, LTD: Research Funding; Ipsen Group: Research Funding; Karyopharma Therapeutics, Inc.: Research Funding; Klus Pharma, Inc.: Research Funding; MeiPharma, Inc.: Research Funding; Merck Sharp & Dohme Corp.: Research Funding; Novartis Pharmaceuticals: Research Funding; Incyte Corporation: Research Funding; Boston BIoMedical, Inc.: Research Funding; BeiGene: Research Funding; Acerta: Research Funding. Andorsky:CTI: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AstraZeneca: Research Funding. Yacoub:Roche: Other: Support of parent study and funding of editorial support; Dynavax: Current equity holder in publicly-traded company; Ardelyx: Current equity holder in publicly-traded company; Incyte: Speakers Bureau; Hylapharm: Current equity holder in private company; Cara Therapeutics: Current equity holder in publicly-traded company; Agios: Honoraria, Speakers Bureau; Novartis: Speakers Bureau. Melear:Janssen: Speakers Bureau; AstraZeneca: Speakers Bureau. Fanning:Takeda: Consultancy, Speakers Bureau; Bristol Myers Squibb: Consultancy, Speakers Bureau; TG Therapeautics: Consultancy; Abbvie: Consultancy; Prisma Health: Current Employment; Sanofi Aventis: Speakers Bureau. Kolibaba:Atara Biotech: Consultancy; Compass Oncology: Ended employment in the past 24 months; Verastem: Honoraria; Seattle Genetics: Research Funding; Pharmacyclics: Research Funding; Novartix: Research Funding; Janssen: Research Funding; Gilead: Research Funding; Genentech: Research Funding; Celgene: Research Funding; Acerta: Research Funding; AbbVie: Research Funding; Sumitomo Dainippon Pharma Oncology: Consultancy, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company; TG Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Lansigan:BMS: Consultancy; Seattle Genetics: Consultancy; BMS Steering Committee for MAGNIFY Program: Membership on an entity's Board of Directors or advisory committees; Spectrum Pharma: Consultancy, Research Funding. Reynolds:IHA Hematology/Oncology Consultants: Current Employment. Nowakowski:Kymera: Consultancy; Ryvu: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other; Curis: Consultancy; Kite: Consultancy; MorphoSys: Consultancy, Research Funding; Denovo: Consultancy; Seattle Genetics: Consultancy; Nanostrings: Research Funding; Celgene/BMS: Consultancy, Research Funding; Roche: Consultancy, Research Funding. Gharibo:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company; Bayer: Ended employment in the past 24 months. Ahn:BMS: Current Employment, Current equity holder in publicly-traded company. Li:BMS: Current Employment, Current equity holder in publicly-traded company. Rummel:Roche: Honoraria; Amgen GmbH: Honoraria; Celgene: Consultancy, Honoraria; Janssen: Honoraria; Novartis Pharma GmbH: Honoraria. Sharman:BeiGene: Research Funding; Bristol Meyers Squibb: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Pharmacyclics: Consultancy, Research Funding; AstraZeneca: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; AbbVie: Consultancy, Research Funding; TG Therapeutics: Consultancy, Research Funding; Acerta: Consultancy, Research Funding; Roche: Consultancy, Research Funding; Celgene: Consultancy, Research Funding.

8046 Background: Patients (pts) with relapsed iNHL have limited standard treatment options. The immunomodulatory agent lenalidomide shows enhanced activity with rituximab (ie, R2), which recently reported 39.4-mo median PFS in R/R iNHL pts (AUGMENT; J Clin Oncol. 2019;37:1188). Methods: MAGNIFY is a multicenter, phase IIIb trial in pts with R/R FL gr1-3a, MZL, or MCL (NCT01996865) exploring optimal lenalidomide duration. Lenalidomide 20 mg/d, d1-21/28 + rituximab 375 mg/m2/wk c1 and then q8wk c3+ (R2) are given for 12c followed by 1:1 randomization in pts with SD, PR, or CR to R2 vs rituximab maintenance for 18 mo. Data presented here focus on induction R2 in efficacy-evaluable FL and MZL pts (MCL not included) receiving ≥ 1 treatment with baseline/post-baseline assessments to analyze the primary end point of ORR by 1999 IWG criteria. Results: As of June 16, 2019, 393 pts (81% FL gr1-3a; 19% MZL) were enrolled with a median follow up of 23.7 mo (range, 0.6-57.8) for censored pts (n = 335). Median age was 66 y (range, 35-91), 83% had stage III/IV disease, with a median of 2 prior therapies (95% prior rituximab-containing). ORR was 69% with 40% CR/CRu (Table). Median DOR was 39.0 mo, and median PFS was 40.1 mo. 199 pts (51%) have completed 12c of R2, and 188 (48%) have been randomized and entered maintenance. 139 pts (35%) prematurely discontinued both lenalidomide and rituximab, primarily due to AEs (n = 52, 13%) or PD (n = 45, 11%). Most common all-grade AEs were 48% fatigue, 43% neutropenia, 36% diarrhea, 31% nausea, and 30% constipation. Grade 3/4 AE neutropenia was 36% (9 pts [2%] had febrile neutropenia); all other grade 3/4 AEs occurred in < 7% of pts. Conclusions: R2 is active with a tolerable safety profile in pts with R/R FL and MZL, including rituximab-refractory, double-refractory, and early relapse pts. Clinical trial information: NCT01996865 . [Table: see text]

e21006 Background: Induction with novel biological agents has significantly improved progression free survival (PFS) of MM pts. However, role and timing of ASCT is unclear and there remains a need for a practical means to predict post-ASCT outcome. Our goal was to determine the prognostic value of FDG PET/CT (PET) after induction therapy (IT) in comparison with other prognostic factors and International Myeloma Working Group (IMWG) response criteria. Methods: Prospective, multicenter study of 113 newly diagnosed MM pts undergoing IT+ASCT. IT was not controlled and consisted of 2 or 3 novel agent combinations. The tested variables to predict PFS are shown in table. Two PET scoring systems were used: Score1, positive>marrow uptake; Score2, positive>liver uptake. ROC analysis determined the SUV cut-off. Results: With a median follow-up of 29.5 mo 56 (49.6%) pts relapsed (median PFS: 24.3 mo). Results are displayed in table. Post-IT, when a "+" PET (Score2) was associated with less than a VGPR response, relapses occurred in 83% of pts vs. in only 30% when PET was "-" and pts were in CR or VGPR. Multivariate analysis revealed only ISS to be an independent predictor of PFS (p=0.014). Conclusions: Post-IT a "-" PET associated with CR+VGPR suggests a durable response. Qualitative PET evaluation using a more liberal threshold (liver) to define positivity can be used to accurately assess response in MM. These data failed to prove the post-IT IMWG and PET response to be independent prognosticators while ISS was a superior predictor. This may be attributed to inadequate sample size, nonuniform pre- and post-ASCT treatments, varying follow-up times. Further analyses with stratifying various prognostic indicators and therapy schemes in a larger population are underway to determine a definitive role for PET as a predictor of post-ASCT outcome. [Table: see text]

Abstract Background: Waldenstršms macroglobulinemia (WM) is an indolent B-lymphoplasmacytic lymphoma, which is highly sensitive to 20S proteasome inhibitors such as bortezomib. However, clinical resistance to the drug can be observed early at onset of therapy (primary or inherent resistance) or develop over time, through repeated exposure to the drug (acquired resistance). Although prior investigations into the biological mechanisms associated with bortezomib resistance (BR) have identified aberrations at the genomic (PSMB5 mutation) and transcriptional level (loss of XPB-1), there is limited data on the epigenetic abnormalities that support resistance to 20S proteasome inhibition. With this in mind, we conducted a comprehensive methylation and mRNA expression analysis in WM cells focusing on the molecular patterns that characterize inherent BR (iBR) as well as acquired BR (aBR). Materials and Methods: Bortezomib sensitive (BS) human WM cell lines, BCWM.1 and MWCL-1, the iBR WM cell line RPCI-WM1 (developed from a bortezomib-refractory WM patient) as well as aBR subclones (BCWM.1/BR, MWCL-1/BR) were used in the study. Methylation status of WM cells was profiled by Illumina Infinium 450k methylation array. Methylation IDAT files were background subtracted using GenomeStudio v1.9. Beta mixture quantile dilation (BMIQ) method in R watermelon package was used to adjust type II probes into distribution characteristic of type I probes. For each gene, probes were partitioned into 6 regions using R IMA package and the ones belonging to the same region were averaged, including transcription start sites (TSS; both 200 bp and 1500 bp upstream), 5' untranslated region (UTR), and 3'UTR, the first exon, and genebody. Gene regions showing a significant adjusted p-value and a beta difference of >0.1 or <-0.1 were selected for differential hypermethylation and hypomethylation, respectively. Correlation with gene expression was conducted only on genes showing >1.5 fold change in expression. Overview of methodology is shown in Figure 1. Results: We first assessed the differential methylation pattern (TSS, 200bp upstream of gene body) of bortezomib-sensitive (BS, BCWM.1, IC50 6nM) and iBR cells, (RPCI-WM1). A total of 3,801 hypermethylated and 1,865 hypomethylated DNA regions were observed in iBR cells relative to BS cells (Figure 2A). In iBR cells, a negative correlation between hypermethylated DNA and corresponding gene expression was found in 1,039 genes (Spearman r = -0.12) (Figure 2B). In parallel, we compared the methylation pattern (TSS 200bp) of BS WM cells (BCWM.1 and MWCL-1) with their aBR derivatives, which display ~20 – 50 fold resistance to bortezomib. aBR subclones showed differential hypermethylation of 1,521 DNA regions and hypomethylation of 651 genomic regions relative to BS WM cells. These findings were not unexpected as aBR cell lines, being derivatives of BS WM cells, are clonally related to the former, whereas iBR cells are derived from a different clone. Meta-analysis of iBR and aBR followed by pathway enrichment (NextBio, Illumina Inc), revealed a significant clustering of commonly hypermethylated genes within the Validated Transcriptional Targets of TP63 isoforms Canonical Pathway (p<1.9-E5, Figure 2C) and the CEBPA binding site Geneset 2 (p<8.2-E9, Figure 2D); pathways whose genes are actively involved in suppression of cell growth and differentiation. Further validation and functional relevance of candidate gene targets from this analysis, which are relevant to WM pathobiology, are currently being investigated. Conclusion: This is the first study to examine and correlate the global methylation and gene expression profiles in WM tumor cells that are inherently wired to resist 20S proteasome inhibition as well as tumor cells, which have acquired resistance through continuous exposure to bortezomib. Although considerable differences were observed in the methylation profiles of WM cells displaying inherent vs. acquired resistance, a number of common genes emerged and pointed towards transcriptional repressors, whose inactivation through methylation has been linked to other cancers. Altogether, these findings uncover cellular systems in WM cells, which are affected by DNA methylation, subsequent mRNA suppression and which may be associated as a whole with both inherent and acquired forms of bortezomib resistance. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Deubiquitinating enzyme (DUB) inhibitors are an emerging class of compounds, which are increasingly being regarded for their anti-cancer activity and therapeutic potential. The 19S regulatory particle of the proteasome contains two DUBs, USP14 and UCHL5, which are critical for the proper unfolding and deubiquitination of proteins prior to their entry into the 20S proteasome β-catalytic core. In B/plasma cell malignancies such as Waldenströms macroglobulinemia (WM) and multiple myeloma (MM), protein homeostasis and optimal proteasome functionality are paramount for tumor survival. This is evidenced by the success of 20S proteasome inhibition with bortezomib and carfilzomib, which have demonstrated remarkable clinical benefit in patients with WM or MM. As such, the proteasome degradation pathway represents a highly attractive and clinically validated, yet still largely unexplored therapeutic target. Here, we provide first evidence of the cytotoxic effects and molecular sequelae associated with a novel 19S proteasome DUB inhibitor, VLX1570, which selectively targets USP14 and UCHL5, in preclinical models of B/plasma cell cancers and their drug resistant tumor subclones. Materials: VLX1570 was obtained from Vivolux AB, Sweden. Bortezomib was purchased from Sellekchem, Houston TX. Human myeloma cell lines (OPM2, U266, KMS11), human WM cell lines (BCWM.1, MWCL-1 and RPCI-WM1), their respective bortezomib-resistant (BR) subclones as well as ibrutinib-resistant (IR) derivatives of BCWM.1 and RPCI-WM1 were used in experiments (total n=12). Peripheral blood mononuclear cells (PBMCs) from healthy donors were used to assess for cytotoxicity of VLX1570 in non-tumor cells. Results: A 72hr MTS assay first established sensitivity of plasma cell cancer models towards VLX1570, including drug resistant subclones (EC50 range, 20 – 90nM). Next we assessed whether loss of viability was due to apoptosis and observed dose-dependent annexin-V staining in ~50 – 70% of wild-type MM and WM cells, ~45 – 55% in corresponding BR models and ~50% in IR subclones when exposed to VLX1570 (100nm – 500nM) for 24hrs. VLX1570 was tested at similar concentrations in PBMCs and induced minimal cell death. To understand if VLX1570-induced apoptosis was mitochondrial mediated, we assessed mitochondrial outer membrane permeability (MOMP) in all plasma cell cancer models treated with the DUB inhibitor (100 – 500nM) and found a dose-dependent increase in MOMP (p<0.00025 – 0.000001). Activation of the mitochondrial/intrinsic apoptotic pathway was also evidenced by cleavage of caspase-9 and 3 on immunoblot analysis. As inhibition of protein deubiquitination results in accumulation of polyubiquitinated protein conjugates, we examined global ubiquitinated protein levels and found increasing amounts of high molecular weight poly-ubiquitinated protein in VLX1570 treated tumor cells in a dose-dependent manner. This prompted us to further delineate the potential cellular response mechanisms that relay the antitumor activity of VLX1570 in malignant plasma cells. Immunoblot analysis of drug sensitive and (bortezomib or ibrutinib) resistant MM and WM cell lines revealed several changes in ER stress response proteins, notably induction of HSP70 and splicing of XBP1; the latter event which was less prominent in BR cell lines treated with bortezomib. This suggested the ability of VLX1570 to overcome resistance through a rapid and potent proteotoxic effect, which overwhelmed the tumor cells stress response mechanisms beyond its capacity for survival. Finally, as abnormalities in the NFkB signaling pathway are implicated in malignant plasma cell survival, we found markedly decreased nuclear translocation of NFkB (p-P65) protein in tumor cells treated with VLX1570. Conclusions: The DUBs of the 19S proteasome cap offer an attractive target within the proteasome degradation system and whose inhibition by VLX1570 is able to circumvent mechanisms that support resistance to b-catalytic PI (bortezomib) or BTK inhibitor (ibrutinib) therapy. The studies undertaken thus far, coupled with more rigorous mechanistic and in vivo efficacy analyses currently underway, provides rational for the clinical development of DUB inhibitors for use in malignant B/plasma cell malignancies. Disclosures Martin: Janssen: Honoraria.