scholarly journals Loxo-305, a Highly Selective and Non-Covalent Next Generation BTK Inhibitor, Inhibits Diverse BTK C481 Substitution Mutations

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 4644-4644 ◽  
Author(s):  
Eliana B. Gomez ◽  
Lippincott Isabel ◽  
Mary S. Rosendahal ◽  
Stephen M. Rothenberg ◽  
Steven W. Andrews ◽  
...  
Keyword(s):  
Acquired Resistance ◽  
Binding Affinities ◽  
Next Generation ◽  
Wild Type ◽  
Employment Equity ◽  
Equilibrium Binding ◽  
Btk Inhibitor ◽  
Equity Ownership ◽  
Substitution Mutations ◽  
Btk Inhibitors

Introduction: Bruton's Tyrosine Kinase (BTK) is an essential component of normal and malignant B-cell receptor signaling. Covalent BTK inhibitors have transformed the treatment of B-cell malignancies but are limited by off-target toxicity and acquired resistance, leading to eventual treatment discontinuation and disease progression. Emerging evidence suggests that acquired resistance is mediated predominantly by BTK C481 substitution mutations at the covalent BTK inhibitors' binding site. There is significant unmet clinical need for new treatment approaches that overcome acquired resistance and minimize toxicity. LOXO-305 is a highly selective, non-covalent, next generation BTK inhibitor. We previously showed that LOXO-305 potently inhibited both wild-type (WT) BTK and BTK C481S -mediated kinase activity in enzyme and cell-based assays with nanomolar potency, caused regression of BTK-dependent lymphoma mouse xenograft models, and was more than 300-fold selective for BTK over 98% of 370 other kinases tested and showed no significant inhibition of non-kinase off targets at 1 mM (Brandhuber et al. SOHO 2018). In addition, ADME and pharmacokinetic experiments in two preclinical species predicted that LOXO-305 will have high human exposure and sustained BTK C481S target coverage in patients at clinically achievable doses. Here we describe the activity of LOXO-305 against additional BTK C481 substitution mutations, including mutations identified in patients with acquired resistance to covalent BTK inhibitors. We further determine equilibrium-binding affinities for LOXO-305 for diverse mutant BTK enzymes in comparison to other clinically available BTK inhibitors. Methods: To assess cellular BTK inhibitor potency, HEK293T cell lines transiently expressing wild-type BTK and BTK C481 substitution mutations were serum starved and incubated with LOXO-305 overnight. Cells were next incubated with serum and orthovanadate for 5 min and the phosphorylated Y223 BTK was analyzed by immunoblot. Bands were quantified and the IC50 values calculated with GraphPad Prism. The equilibrium-binding affinities for targeted BTK inhibitors to BTK enzyme variants were determined by surface plasmon resonance (SPR) using the Biacore T200. Biotinylated BTK variants were immobilized on a docked streptavidin coated sensor chip. Five concentrations of each inhibitor plus blank controls were analyzed. Association/dissociation rate constants were calculated by global fitting of the data to a 1:1 binding interaction model. Results: While BTK C481S possessed similar levels of basal Y223 autophosphorylation as wild-type BTK in cells, BTK C481T autophosphorylation was reduced by ~50%, C481R by ~90%, and mutants C481F, and C481Y were inactive in HEK293T cells. LOXO-305 inhibited Y223 phosphorylation of all active mutants with similar nanomolar potency. In contrast, autophosphorylation of all BTK C481 mutants were resistant to both Ibrutinib and acalabrutinib. Equilibrium-binding affinities of LOXO-305 for select BTK C481 substitution mutations confirmed LOXO-305's superior potency versus commercially available BTK inhibitors (ibrutinib and acalabrutinib). Conclusions: The next generation, non-covalent, highly selective BTK inhibitor LOXO-305 potently inhibited the cellular activity of BTK C481S, T and R mutations and displayed strong equilibrium binding to WT BTK and several BTK C481 substitution mutations. Together with high selectivity and significant BTK target coverage in vivo, these results indicate that LOXO-305 may overcome acquired resistance to covalent BTK inhibitors in patients without significant off-target toxicity. A phase 1 clinical trial of LOXO-305 is currently underway. Disclosures Gomez: LOXO Oncology Inc.: Employment, Equity Ownership. Isabel:Loxo Oncology: Employment. Rosendahal:Loxo Oncology: Employment. Rothenberg:LOXO Oncology Inc.: Employment. Andrews:Loxo Oncology: Employment. Brandhuber:LOXO Oncology Inc.: Employment, Equity Ownership.

LOXO-305, A Next Generation Reversible BTK Inhibitor, for Overcoming Acquired Resistance to Irreversible BTK Inhibitors

2018 ◽  
Vol 18 ◽  
pp. S216 ◽  
Author(s):  
Barbara Brandhuber ◽  
Eliana Gomez ◽  
Steven Smith ◽  
Todd Eary ◽  
Stacey Spencer ◽  
...  
Keyword(s):  
Acquired Resistance ◽  
Next Generation ◽  
Btk Inhibitor ◽  
Btk Inhibitors

scholarly journals LOXO-305: Targeting C481S Bruton Tyrosine Kinase in Patients with Ibrutinib-Resistant CLL

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 478-478
Author(s):  
Aishath S Naeem ◽  
Winnie I Nguy ◽  
Svitlana Tyekucheva ◽  
Stacey M. Fernandes ◽  
Vanessa Rai ◽  
...  
Keyword(s):  
Annexin V ◽  
Hek293 Cells ◽  
Wild Type ◽  
Employment Equity ◽  
Bcr Signaling ◽  
Treatment Naïve ◽  
Ic50 Values ◽  
Equity Ownership ◽  
Btk Inhibitors

Clinical success with the targeted Bruton Tyrosine Kinase (BTK) inhibitors ibrutinib and acalabrutinib has greatly improved the outcome of patients with relapsed chronic lymphocytic leukemia (CLL). However toxic side effects and acquired resistance due to C481S mutations in BTK remain an issue and the prognosis of those developing resistance is poor. Hence better therapeutic options are needed for these patients. Here we characterize a next generation highly selective reversible BTK inhibitor, LOXO-305, and describe its effectiveness in vitro in treatment naïve CLL patients and in those with C481S mutations. Unlike the irreversible BTK inhibitors ibrutinib and acalabrutinib, LOXO-305 does not require the C481 site for binding to the ATP binding domain of BTK. In addition, LOXO-305 is highly selective, with minimal activity against non-BTK kinase and non-kinase off targets, including ITK, TEC and EGFR. We evaluated the efficacy of LOXO-305 in BTK wild-type B cell lymphoma lines most similar to CLL, namely MEC1 and OSU-CLL, and in CLL patient samples, by determining its effect on cell viability, apoptosis and BCR signaling. In both cell lines LOXO-305 reduced cell viability and BCR mediated activation of BTK, PLCg2, ERK and AKT similar to ibrutinib. We measured cellular apoptosis in these cell lines with Annexin V APC and PI staining and showed that after 48 hours LOXO-305 treated cells had a significantly higher percentage of apoptotic cells in comparison with both DMSO (mean increase with LOXO-305: MEC1 21% (p = 0.0005) & OSU-CLL 35% (p = 0.0016)) and ibrutinib (mean increase with LOXO305: MEC1 19% (p=0.0006), OSU-CLL 22% (p=0.0013)). Since LOXO-305's mechanism of BTK inhibition does not involve covalent binding to the C481 site, we tested its efficacy in in vitro ibrutinib resistant models of stably transfected HEK293 cells expressing either wild-type (WT) or C481S BTK. In WT BTK HEK cells, both LOXO-305 and ibrutinib showed comparable inhibitory activity in vitro against wild-type BTK, with IC50 values for phospho-BTK inhibition equal to 5.69 nM and 3.33 nM, respectively. LOXO-305 also inhibited phospho-BTK in BTK-C481S-expressing HEK293 cells at an IC50 equal to 21.2 nM, while ibrutinib had no inhibitory effect at concentrations as high as 300nM. When we extended our analysis to treatment naïve CLL patient cells, we observed that both LOXO-305 and ibrutinib potently inhibited IgM-induced phospho-BTK with IC50 values equal to 1.34 ± 1.23 nM for LOXO-305 (n = 7, p < 0.0001) and 1.04 ± 1.26 nM for ibrutinib (n = 7, p < 0.0001). We also found a significant reduction in phosphorylation of PLCγ2 (Y1217), the immediate downstream effector of BTK (IC50 33 nM for each agent, n = 7, p = 0.02 for LOXO-305, p = 0.0017 for ibrutinib). When we compared the cellular cytotoxicity of LOXO-305 with ibrutinib and acalabrutinib, all three agents demonstrated significant induction of apoptosis (annexin V positive) in BTK wild-type cells compared to DMSO treatment: (LOXO-305: median 63.77% n=3, p = 0.0073, ibrutinib: median 57.76%, n=3, p < 0.0001, acalabrutinib: median 67.11%, n=3, p = 0.0397). In CLL patient cells harboring C481S mutations, we observed a decrease in BCR signaling with 0.6 μM LOXO-305 treatment, with 95% reduction in phospho-BTK (Y223) and 50% reduction in phospho-PLCγ2 vs DMSO (n = 3, phospho-BTK p < 0.0001, phospho-PLCγ2 p = 0.01). In comparison ibrutinib at 0.6 μM demonstrated 50% reduction in phospho-BTK (n = 3, p = 0.01) and no significant change in phospho-PLCγ2. We also observed a 73% reduction in phospho-ERK vs DMSO with 10 μM LOXO-305 treatment (n=3, p = 0.004) while ibrutinib and acalabrutinib showed no significant change. In CLL patient cells with C481S variant allele frequencies (VAF) of 87% and 89%, LOXO-305 was 40-fold more potent at inhibiting phospho-BTK than ibrutinib (IC50 for LOXO305 0.02 μM, for ibrutinib 0.9 μM). Even in patient cells with lower C481S VAF of 9%, LOXO-305 still demonstrated 30-fold higher potency than ibrutinib (IC50 LOXO-305 0.2 μM, ibrutinib 0.6 μM). Our findings show that LOXO-305 potently inhibits cell survival and BCR signaling in both treatment naïve and C481S CLL patient cells, and therefore may prove an effective treatment in both treatment naïve and ibrutinib-resistant CLL patients. A phase 1 clinical trial is ongoing. Disclosures Ebata: LOXO Oncology Inc.: Employment, Equity Ownership. Gomez:LOXO Oncology Inc.: Employment, Equity Ownership. Brandhuber:LOXO Oncology Inc.: Employment, Equity Ownership. Rothenberg:LOXO Oncology Inc.: Employment. Brown:Janssen, Teva Pharmaceuticals: Honoraria; Gilead, Loxo, Sun Pharmaceuticals, Verastem: Research Funding; Morphosys, Invectys (Data Safety Monitoring Board): Membership on an entity's Board of Directors or advisory committees; Abbvie, Acerta, Astra-Zeneca, Beigene, Catapult Therapeutics, Dynamo Therapeutics, Genentech/Roche, Gilead, Juno/Celgene, Kite, Loxo, Octapharma, Novartis, Pfizer, Pharmacyclics, Sunesis, TG Therapeutics, Verastem: Consultancy.

scholarly journals Potency and Selectivity of BTK Inhibitors in Clinical Development for B-Cell Malignancies

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 1871-1871 ◽  
Author(s):  
Allard Kaptein ◽  
Gerjan de Bruin ◽  
Maaike Emmelot-van Hoek ◽  
Bas van de Kar ◽  
Anouk de Jong ◽  
...  
Keyword(s):  
T Cells ◽  
B Cell ◽  
Fixed Time ◽  
Cell Receptor ◽  
B Cell Malignancies ◽  
Employment Equity ◽  
Cellular Assays ◽  
Btk Inhibitor ◽  
Equity Ownership ◽  
Btk Inhibitors

Abstract Background: Bruton tyrosine kinase (BTK) is a validated target for B-cell malignancies. The BTK inhibitor ibrutinib was approved in chronic lymphocytic leukemia, mantle cell lymphoma (MCL), and Waldenstrom macroglobulinemia. Acalabrutinib is a potent, highly selective, covalent BTK inhibitor with minimal off-target activity; it received accelerated FDA approval in October 2017 for the treatment of patients with MCL having ≥1 prior therapy. In addition to the approved covalent BTK inhibitors ibrutinib and acalabrutinib, clinical data in B-cell malignancies are available for spebrutinib (CC-292), tirabrutinib (ONO/GS-4059) and zanubrutinib (BGB-3111). We performed biochemical and cellular profiling of these 5 BTK inhibitors, investigating potency and selectivity. Methods: Two biochemical kinase assays assessed BTK inhibitor potency, with IC50 determination at a fixed time point (IMAP; Molecular Devices) or over time (LanthaScreen; Invitrogen); the latter was used to calculate binding kinetics. Kinome profiling was performed at a single dose (1 µM) using KINOMEscan (Eurofins DiscoverX). IC50 determinations were made using kinases with a Cys in the same position as the Cys481 residue in BTK, using assays developed in house (using IMAP and LanthaScreen) or at Thermo Fisher Scientific (Z'-LYTE) with IC50 determination at a fixed time point. On-target inhibition of BTK in cellular assays was evaluated using B-cell receptor-mediated activation of CD69 expression on peripheral B cells using human peripheral blood mononuclear cells (hPBMCs) or human whole blood (hWB). Off-target inhibition of epidermal growth factor receptor (EGFR) was evaluated in a cellular assay examining the effect of EGF-induced EGFR phosphorylation in A431 cells. Off-target inhibition of ITK and/or TXK was evaluated using T-cell receptor (TCR)-mediated activation of interleukin-2 expression in Jurkat T cells and CD25 cell surface expression using primary human peripheral T cells. Results: Based on biochemical binding kinetics, ibrutinib and zanubrutinib were the most potent BTK inhibitors (Table 1), followed by spebrutinib; acalabrutinib and tirabrutinib had comparable potency. Differences in potency were largely driven by differences in inactivation rates. However, differences in biochemical potency were lost (in part) in cellular assays using hPBMCs or hWB. EC50 values in hWB were <10 nM for ibrutinib, acalabrutinib and zanubrutinib. Spebrutinib had an EC50 of 140 nM in hWB, showing the greatest loss of potency versus biochemical assays and hPBMCs, going to the physiologically most relevant cellular experimental conditions (Table 2). Differences in overall kinase selectivity were observed among the BTK inhibitors (Figure 1; KINOMEscan). Acalabrutinib had the lowest hit rate; 1.5% of human wild-type kinases were inhibited >65% at 1 µM (excluding BTK). Kinase hit rate was also low for tirabrutinb (2.3%), whereas ibrutinib (9.4%), zanubrutinib (4.3%), and spebrutinib (8.3%) had higher hit rates. Acalabrutinib had a high selectivity for BTK over kinases with a Cys in the same position as the Cys481 residue in BTK (Table 2). Similar results were observed for tirabrutinib, whereas ibrutinib, spebrutinib and zanubrutinib were less selective in this panel of kinases with potential for off-target covalent binding by BTK inhibitors (Table 2). Acalabrutinib also had a higher selectivity for BTK over Src-family kinases than the other BTK inhibitors tested. Acalabrutinib and tirabrutinib had EC50 values >10 µM in the cellular assay of off-target inhibition of EGFR; ibrutinib, zanubrutinib, and spebrutinib had EC50 values of 0.07, 0.39, and 4.7 µM, respectively. No off-target inhibition was observed for acalabrutinib or tirabrutinib on TCR-mediated activation of T cells up to 10 µM. Ibrutinib, zanubrutinib, and spebrutinib had EC50 values <1 µM in Jurkat T cells. Similar results were observed in primary human peripheral T cells. Conclusion: BTK inhibitors in clinical development for B-cell malignancies had differing potency in biochemical assays, but these differences were lost (in part) in cellular assays, particularly in hWB. Among the BTK inhibitors tested, the greatest differentiation was observed in kinase selectivity profiles; acalabrutinib and tirabrutinib had the highest kinase selectivity. Disclosures Kaptein: Covaluation Pharma BV: Employment, Equity Ownership; Acerta Pharma BV: Consultancy, Equity Ownership; Apo-T BV: Consultancy. de Bruin:Acerta Pharma: Employment. Emmelot-van Hoek:Acerta Pharma: Employment. van de Kar:Acerta Pharma: Employment. de Jong:Acerta Pharma: Employment. Gulrajani:Acerta Pharma: Employment, Equity Ownership. Demont:Acerta Pharma: Employment. Covey:AstraZeneca: Equity Ownership; Acerta Pharma: Employment. Mittag:Acerta Pharma: Employment, Equity Ownership. Barf:Covaluation Holding BV: Employment, Equity Ownership; Acerta Pharma BV: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

scholarly journals FLX925 Is a Rationally Designed FLT3, CDK4/6 Inhibitor with a Desirable Resistance Profile

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 2323-2323 ◽  
Author(s):  
Sachie Marubayashi ◽  
Adam Park ◽  
Rajkumar Noubade ◽  
Huyen Phan ◽  
Gene Cutler ◽  
...  
Keyword(s):  
Cell Lines ◽  
Acquired Resistance ◽  
Wild Type ◽  
Resistance Mutations ◽  
Employment Equity ◽  
Secondary Resistance ◽  
Resistance Profile ◽  
Flt3 Inhibitor ◽  
Flt3 Inhibitors ◽  
Equity Ownership

Abstract Acquired secondary resistance mutations in FLT3 have been shown to limit the therapeutic benefit of FLT3 inhibitors in FLT3-ITD mutated AML. Multiple strategies have been pursued to address such resistance, including the development of kinase inhibitors that use alternate binding modes or by simultaneously targeting additional pathways. This latter approach may be focused on suppression of parallel oncogenic pathways to treat the acquired resistance, or on strategies to reduce or delay the acquisition of resistance. Here, we describe a rationally conceived next generation FLT3 inhibitor, FLX925, that was prospectively designed to address or avoid common resistance mechanisms with a unique binding mode and potent activity against CDK4/CDK6. We contextualize our findings by comparing FLX925 to other FLT3 inhibitors (quizartinib and gilteritinib) currently in late-stage clinical development and demonstrate that FLX925 has a superior resistance profile. FLX925 is a potent and selective type-1 inhibitor of FLT3 that retains its cellular potency against clinically relevant secondary resistance mutations in FLT3. This was evaluated in multiple experimental systems including isogenic Ba/F3 cells engineered to express FLT3-ITD with, or without, various known secondary FLT3 mutations. In addition, these data were extended to the human setting using both the MOLM13 and MOLM14 FLT3-ITD mutated AML cell lines and subclones of these lines harboring well-characterized resistance mutations described elsewhere. Data have been published previously demonstrating a superior resistance profile for FLX925 when compared to quizartinib and sorafenib. When compared to gilteritinib, FLX925 had a favorable profile of relative potencies against a range of FLT3-ITD resistance mutations. In addition to the isogenic murine and human models of FLT3 inhibitor resistance, with engineered known genetic alterations, we explored the activity of FLX925 and other FLT3 inhibitors in a model of in vitro acquired resistance. Using MOLM13 cells and standard protocols for the generation of drug resistance, we demonstrate that the magnitude of resistance to quizartinib and gilteritinib greatly exceeds that observed with FLX925 during the same timeframe. Pools of resistant cells from each compound treatment are being analyzed by next-generation sequencing in an effort to better understand the mechanism of resistance associated with each compound. We hypothesize that the CDK4/6 inhibitory activity, which is unique to FLX925, contributes to its superior resistance profile. Whether this is solely linked to an impact on the cell cycle or more recent findings of CDK6-driven transcription of FLT3 and PIM1 is an active area of investigation. Nonetheless, the CDK4/6 activity of FLX925 potentially broadens the utility of this compound to FLT3 wild-type AML. Here, we show FLX925, in contrast to other FLT3 inhibitors, potently suppresses the proliferation of a panel of AML cell lines. These data have been extended to FLT3 wild-type AML patient samples in which FLX925, but not gilteritnib, induced a desirable pharmacodynamic effects. The totality of the preclinical data suggest FLX925 may be a best-in-class inhibitor for the treatment of AML with, or without, FLT3-ITD mutations. FLX925 is currently being investigated in a Ph1/b dose-escalation study in subject with relapsed or refractory AML (NCT02335814). Disclosures Marubayashi: FLX Bio: Employment, Equity Ownership. Park:FLX Bio: Employment, Equity Ownership. Noubade:FLX Bio: Employment, Equity Ownership. Phan:FLX Bio: Employment. Cutler:FLX Bio: Employment, Equity Ownership; Amgen, Inc: Equity Ownership. Kassner:FLX Bio: Employment, Equity Ownership. Fridman:FLX Bio: Employment, Equity Ownership.

scholarly journals CC-92480 Is a Novel Cereblon E3 Ligase Modulator with Enhanced Tumoricidal and Immunomodulatory Activity Against Sensitive and Resistant Multiple Myeloma Cells

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 1812-1812 ◽  
Author(s):  
Antonia Lopez-Girona ◽  
Courtney G. Havens ◽  
Gang Lu ◽  
Emily Rychak ◽  
Derek Mendy ◽  
...  
Keyword(s):  
Cell Lines ◽  
Acquired Resistance ◽  
E3 Ligase ◽  
Immunomodulatory Activity ◽  
Employment Equity ◽  
Ic50 Value ◽  
Ic50 Values ◽  
Equity Ownership ◽  
Induction Of Apoptosis ◽  
Low Levels

Lenalidomide- and pomalidomide-based therapies are effective drugs in the treatment of patients with multiple myeloma (MM), however most patients with MM eventually relapse or become resistant. CC-92480, a novel cereblon (CRBN) E3 ligase modulator (CELMoD) with multiple activities including potent immunomodulation and single-agent antiproliferative effects, is being investigated in a phase 1 clinical trial (CC-92480-MM-001; NCT03374085) for patients with relapsed/refractory MM (RRMM). The present study investigates the preclinical data and mechanism of action of CC-92480 in MM models. CELMoD agents bound to CRBN confer differentiated substrate-degradation specificity on the CRL4CRBN E3 ubiquitin ligase. CRBN-modulator agents mediate destruction of Ikaros and Aiolos, transcription factors that contribute to myeloma cell survival. CC-92480 was found to produce rapid, deep, and sustained degradation of Ikaros and Aiolos, with superior antimyeloma activity. Accordingly, in a CRBN protein competitive binding assay, CC-92480 displaced a Cy-5-labeled CELMoD analog from CRBN with a 50% inhibitory concentration (IC50) value of 0.03 μM, whereas lenalidomide competed with an IC50 value of 1.27 μM in the same assay, demonstrating a higher binding affinity of CC-92480 for CRBN. Additionally, CC-92480 promoted the recruitment of Ikaros to the CRBN E3 ligase complex more effectively than pomalidomide in 2 orthogonal CRBN/Ikaros binding assays; it also triggered a more extensive cellular ubiquitination of Ikaros, and a faster, more efficient depletion of cellular Ikaros and Aiolos than pomalidomide. In various MM cell lines, including those with acquired resistance to lenalidomide or pomalidomide and low levels of CRBN, CC-92480 produced robust degradation of Ikaros and Aiolos followed by strong reduction of 2 additional and highly critical transcription factors, c-Myc and interferon regulatory factor 4, which are linked to the induction of apoptosis as measured by cleaved caspase-3. The tumoricidal activity of CC-92480 was shown to be CRBN dependent, since the effect was prevented by complete loss of CRBN or by the stabilization of Ikaros and Aiolos. CC-92480 displayed broad and potent antiproliferative activity across a panel of 20 MM cell lines that are either sensitive, have acquired resistance, or are refractory to lenalidomide or pomalidomide; the cell lines also contained diverse chromosomal translocations and oncogenic drivers typically found in MM patients. Approximately half of the MM cell lines evaluated were highly sensitive to CC-92480, with IC50 values for antiproliferative activity ranging from 0.04 to 5 nM; only 2 cell lines had IC50 values > 100 nM. CC-92480 inhibits cell proliferation and induces apoptosis in MM cell lines that are not sensitive to lenalidomide or pomalidomide. This panel of cell lines includes both refractory cell lines and resistant cell lines generated through continuous exposure to lenalidomide and pomalidomide that acquired low levels of CRBN protein or mutations in the CRBN gene. CC-92480 also induced deep destruction of Ikaros and Aiolos in cultures of peripheral blood mononuclear cells (PBMCs), which led to the activation of T cells and increased production of the cytokines interleukin-2 and interferon gamma. These responses occurred at the range of CC-92480 concentrations that show potent tumoricidal effect against MM cells. The T cell activation and enhanced cytokine production by CC-92480 led to the potent and effective immune-mediated killing of MM cells in co-cultures with PBMCs. CC-92480 is a potent antiproliferative and proapoptotic novel CELMoD with enhanced autonomous cell-killing activity in MM cells that are either sensitive, resistant, or have acquired resistance to lenalidomide and pomalidomide. CC-92480 has a unique and rapid degradation profile stemming from the enhanced efficiency to drive the formation of a protein-protein interaction between Ikaros and Aiolos and CRBN, inducing cytotoxic effects in a CRL4CRBN-dependent fashion that leads ultimately to the induction of apoptosis, even in the context of low or mutated CRBN protein. Additionally, similar to lenalidomide, CC-92480 conserves immunomodulatory activity against MM cells. These data support the clinical investigation of CC-92480 in patients with RRMM. Disclosures Lopez-Girona: Celgene Corporation: Employment. Havens:Pfizer: Employment, Equity Ownership; Celgene: Equity Ownership. Lu:Celgene Corporation: Employment, Equity Ownership. Rychak:Celgene Corporation: Employment, Equity Ownership. Mendy:Celgene Corporation: Employment. Gaffney:Celgene: Employment. Surka:Celgene: Employment, Equity Ownership. Lu:Celgene Corporation: Employment, Equity Ownership. Matyskiela:Celgene corporation: Employment. Khambatta:Celgene: Employment. Wong:Celgene Corporation: Employment, Equity Ownership. Hansen:Celgene Corporation: Employment. Pierce:Celgene Corporation: Employment, Equity Ownership. Cathers:Global Blood Therapeutics (GBT): Employment; Celgene Corporation: Equity Ownership. Carmichael:Celgene plc: Employment, Equity Ownership.

Analyses of 81 Chronic Myelomonocytic Leukemia (CMML) for EZH2, TET2, ASXL1, CBL, KRAS, NRAS, RUNX1, IDH1, IDH2, and NPM1 Revealed Mutations In 86.4% of All Patients with TET2 and EZH2 Being of High Prognostic Relevance

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 296-296 ◽  
Author(s):  
Vera Grossmann ◽  
Alexander Kohlmann ◽  
Christiane Eder ◽  
Nicholas C.P. Cross ◽  
Claudia Haferlach ◽  
...  
Keyword(s):  
Candidate Genes ◽  
Chronic Myelomonocytic Leukemia ◽  
Molecular Heterogeneity ◽  
Cell Renewal ◽  
Wild Type ◽  
Employment Equity ◽  
Ras Pathway ◽  
Equity Ownership ◽  
Exon 4 ◽  
Myelomonocytic Leukemia

Abstract Abstract 296 Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic malignancy that is characterized by features of both a myeloproliferative neoplasm and a myelodysplastic syndrome. Recently, we investigated 81 CMML cases (45 CMML-1, 36 CMML-2) diagnosed between 10/2005 - 9/2008, which had been characterized by chromosome banding analysis and mutation analysis in 6 candidate genes: Mutations were detected in TET2 (44.4%), CBL (22.2%), NRAS (22.2%), KRAS (12.3%), JAK2 (9.8%), RUNX1 (8.7%) (Kohlmann et al., J Clin Oncol. 2010 Jul 19). We now applied amplicon-based deep-sequencing using the small volume Titanium chemistry assay (454 Life Sciences, Branford, CT) to investigate additional 4 candidate genes: IDH1 (exon 4), IDH2 (exon 4) and NPM1 (exon 12) (at known mutational hotspot regions) and the complete coding region of EZH2. EZH2 encodes a catalytic subunit of the polycomb repressive complex 2, a highly conserved histone H3 lysine 27 methyltransferase that influences stem cell renewal. Mutations in EZH2 were recently described to play a role in MPN/MDS. The sequencing library preparation for IDH1, IDH2, NPM1, and EZH2, in total 22 amplicons, was performed using 48.48 Access Array technology (Fluidigm, South San Francisco, CA) to cope with the number of amplicons. In median, 498 reads per amplicon were obtained, thus yielding sufficient coverage for detection of mutations with high sensitivity. After excluding polymorphisms and silent mutations aberrations were detected in IDH1 (1/81; 1.2%), IDH2 (3/81; 3.7%), NPM1 (1/81; 1.2%), and EZH2 (10/81; 12.3%). Another gene recently described in hematological diseases is ASXL1 (additional sex combs like 1) on chromosome 20q11.1. Therefore, the hotspot region of ASXL1 exon 12 was additionally investigated by Sanger sequencing in those 20 cases, in which no mutation had been observed thus far. Nine of these 20 cases (45%) harbored a mutation in ASXL1, thus only 11 cases (13.6%) remained in this cohort in which no mutation was detected. Summarizing this data, 86.4% of these CMMLs harbored at least one molecular aberration with a median of two genes mutated (range 1–4). In more detail, we observed 11 novel distinct EZH2 mutations in ten patients: 7 missense, 3 frameshifts (2 deletions, 1 insertion), and one splice site mutation. EZH2 mutations were found to be heterogeneous and were spread over several exons, predominantly located in the four conserved regions (6/11 in the conserved SET domain; e.g. H680R, N659S). No case revealed a Tyr641 of EZH2 mutation as described for follicular and diffuse large B-cell lymphomas. In median, the burden of EZH2 mutations was 42.5% of sequencing reads per patient (range 1.4–98%). Similarly, a high mutation burden was detected in RUNX1 (median 46.7%), TET2 (median 44.6%), and CBL (median 42.5%) whereas the burden was low in RAS pathway alterations, i.e. NRAS (median 11.1%), KRAS (median 27%), or JAK2 V617F mutations (median 6.9%). With respect to associations of distinct mutations no specific pattern was observed, i.e. EZH2 mutations were concomitantly detected with TET2 (4/10), RUNX1 (3/10), CBL (3/10), JAK2 (3/10), NRAS (2/10), KRAS (1/10), and IDH2 (1/10), respectively. Further, EZH2 mutations were associated neither with morphologic CMML subtype or dysplastic or myeloproliferative characteristics nor with age, white blood cell count, thrombocytes count, or hemoglobin. However, with respect to clinical data a very poor outcome was observed for patients that carried EZH2 mutations compared to EZH2 wild-type cases (median OS 4.3 vs. 130.4 months; p<0.001). In contrast, a significantly better outcome was seen for patients who carried TET2 mutations compared to TET2 wild-type cases (median OS 130.4 vs. 53.6 months, p=0.013). Subsequently, we performed a survival analysis taking both EZH2 and TET2 mutations into account. Here, the cohort was significantly separated into three distinct prognostic groups, i.e. EZH2-mutated with a poor median OS of 4.3 months, EZH2/TET2 wild-type with a median OS of 90 months and TET2-mutated cases with a median OS of 130.4 months (p<0.001). In conclusion, our study revealed molecular mutations in 86.4% of 81 CMML patients providing new insights into the molecular heterogeneity of this disease. Besides alterations in TET2, CBL, ASXL1, and the RAS pathway, EZH2 is targeted by various types of frameshift and point mutations and is a novel biomarker with unfavorable prognosis and clinical utility. Disclosures: Grossmann: MLL Munich Leukemia Laboratory: Employment. Kohlmann:MLL Munich Leukemia Laboratory: Employment. Eder:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership, Research Funding. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Landmark Analyses of DNMT3A Mutations in Hematological Malignancies

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 407-407
Author(s):  
Vera Grossmann ◽  
Alexander Kohlmann ◽  
Claudia Haferlach ◽  
Tamara Alpermann ◽  
Melanie Wild ◽  
...  
Keyword(s):  
Overall Survival ◽  
Mutation Rate ◽  
Mutation Frequency ◽  
Cpg Methylation ◽  
Homozygous Mutation ◽  
Wild Type ◽  
Employment Equity ◽  
Acute Leukemias ◽  
Equity Ownership

Abstract Abstract 407 CpG methylation is an epigenetic modification that is important for cellular development. The DNMT3A gene, located on chromosome 2p23.3, encodes for a DNA methyltransferase and plays a central role in de novo CpG methylation. Recently, DNMT3A has been reported to be mutated in 22% of AML and 8% of MDS (Ley et al., N Engl J Med, 2010; Walter et al., Leukemia, 2011). Further, DNMT3A mutations were observed to be associated with a short overall survival in both diseases, respectively. In order to determine the role of DNMT3A mutations in leukemia we investigated two different entities by next-generation sequencing: 145 AML patients and 83 cases harboring a T-cell acute lymphoblastic leukemia (T-ALL). We applied an amplicon based deep-sequencing assay (454 Life Sciences, Branford, CT) in combination with the 48.48 Access Array technology (Fluidigm, South San Francisco, CA). The peripheral blood or bone marrow samples were obtained from untreated patients. The AML cohort was restricted to cases with normal karyotype (CN-AML). 87/145 (60%) cases were specifically selected to be wild-type for NPM1, FLT3-ITD, CEBPA, and MLL-PTD, whereas 58/145 (40%) samples were mutated in NPM1 (n=33) or double-mutated in NPM1 and FLT3-ITD (n=25). In our cohort of AML cases without mutations in NPM1, FLT3-ITD, CEBPA, and MLL-PTD, we observed a DNMT3A mutation frequency of 17.2% (15/87 cases). The DNMT3A mutation rate in the NPM1 mutated/FLT3 wild-type cases (16/33, 48.5%, P=0.001) and NPM1/FLT3-ITD mutated cases (19/25, 76%, P<0.001) was significantly higher, confirming the association of DNMT3A mutations with NPM1 and FLT3-ITD mutations that had been reported previously (Ley et al.). Interestingly, also in the cohort of T-ALL we detected patients that carried a DNMT3A mutation (16/83, 19.3%), which is very similar to the mutation frequency in AML, and has not been described yet. To further address the biology of DNMT3A mutations in acute leukemias we combined the AML and T-ALL cohorts and identified in total 31 distinct missense mutations in 65 patients (49 AML, 16 T-ALL). Most frequently, amino acid R882 located in exon 23 was mutated (n=29 cases). In addition, we identified 7 frame-shift alterations, 5 nonsense and 2 splice-site mutations. Moreover, 9 of the 65 mutated cases had two independent mutations. Focusing on AML, only three (6.1%) of the 49 DNMT3A-mutated cases were observed to harbor two different mutations concomitantly. In contrast, in the cohort of T-ALL we detected two different mutations in 6/16 (37.5%, P=0.003) cases. Further, in the cohort of AML, no homozygous mutation was detected, however, in the T-ALL group, two cases harbored a homozygous mutation. Therefore, only 3/49 AML (6.1%) cases, but 8/16 T-ALL (50%) cases showed biallelic mutation status (P<0.001). With respect to overall survival, no association was seen in the complete cohort of CN-AML cases (n=145). After limiting this cohort to the cases without mutations in NPM1, FLT3-ITD, CEBPA and MLL-PTD (n=87), an inferior survival was observed for DNMT3A-mutated patients as compared to DNMT3A wild-type patients (n=15 vs. n=72; alive at 2 years: 27.9% vs. 56.6%; P=0.048). Remarkably, also in the cohort of T-ALL a worse survival for patients with DNMT3A mutations was seen which has not been reported thus far (n=13 vs. n=64; alive at 1 years: 28.6% vs. 80.9%; P=0.001). Subsequently, we were interested whether gain-of-function mutations of the DNMT3A gene were associated with trisomy 2 and acquired uniparental disomy (aUPDs) of the short arm of chromosome 2 where DNMT3A is located. As such, we investigated 9 cases harboring a trisomy 2 (AML n=4, MDS n=4, and CMML n=1) and one MDS patient harboring an aUPD 2p, as confirmed by SNP microarray analyses (SNP Array 6.0, Affymetrix, Santa Clara, CA). Not all, but 3/9 cases with trisomy 2 harbored a DNMT3A mutation (one AML, MDS, and CMML case each), suggesting that duplication of DNMT3A mutations can enhance the effect of the mutation. Moreover, the single case with aUPD 2p also showed a mutation, further suggesting that LOH leading to loss of the wild-type DNMT3A may be another mechanism of disease leading to progression of leukemia. In conclusion, we here report on a high mutation rate of DNMT3A in both AML and T-ALL and independently confirmed an inferior overall survival in these two entities, respectively. This indicates a significant role of DNMT3A alterations in myeloid as well as in lymphoid neoplasms. Disclosures: Grossmann: MLL Munich Leukemia Laboratory: Employment. Kohlmann:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Alpermann:MLL Munich Leukemia Laboratory: Employment. Wild:MLL Munich Leukemia Laboratory: Employment. Weissmann:MLL Munich Leukemia Laboratory: Employment. Eder:MLL Munich Leukemia Laboratory: Employment. Dicker:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

A Novel Bruton′s Tyrosine Kinase Inhibitor CC-292 In Combination With The Proteasome Inhibitor Carfilzomib Iimpacts Multiple Myeloma Bone Microenviroment With Resultant Anti-Myeloma Activity

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 682-682 ◽  
Author(s):  
Homare Eda ◽  
Loredana Santo ◽  
Diana D Cirstea ◽  
Andrew J Yee ◽  
Tyler A Scullen ◽  
...  
Keyword(s):  
Bone Resorption ◽  
Tyrosine Kinase ◽  
Proteasome Inhibitor ◽  
Bone Volume ◽  
Employment Equity ◽  
Zone Formation ◽  
Sealing Zone ◽  
Btk Inhibitor ◽  
Equity Ownership ◽  
Rank Signaling

Abstract A member of the Tec family kinases, Bruton’s tyrosine kinase (Btk) modulates B-cell development and activation, and plays an important role in antibody production. Interestingly, Btk and Tec (the other Tec kinase family) regulate osteoclast (OC) differentiation via Receptor Activator of Nuclear Factor κ B (RANK) signaling. Moreover, OCs derived from X-linked agammaglobulinemia (XLA) patients who harbor Btk null mutations have impaired function. Here we show that a potent and specific Btk inhibitor, CC-292 inhibits OC function in multiple myeloma (MM) patients. CC-292 is a highly selective, covalent Btk inhibitor. OC derived from MM patient monocytes were assayed with or without CC-292. Interestingly, OC function was significantly inhibited in the presence of CC-292 (100 nM and 1000 nM) as demonstrated by pit formation assay. However, mRNA expression for TRAP and Cathepsin K, two OC differentiation markers were increased in the presence of CC-292 suggesting that CC-292 inhibits OC function without inhibiting OC differentiation. OC sealing zone contributes to OC bone resorption function. Given the role of c-Src and Proline-rich tyrosine Kinase 2 (Pyk2) signaling in sealing zone formation and OC function we next evaluated CC-292’s effect on Pyk2 and c-Src. Pyk2 plays a role in OC activation and localizes to the sealing zone in OC. RANK signaling activates c-Src, which phosphorylates Pyk2. Moreover c-Src controls OC bone resorption by regulating actin organization via cortactin. Interestingly, CC-292 (100 nM) inhibited c-Src total protein, c-Src phosphorylation and Pyk2 phosphorylation. Furthermore, CC-292 (100 nM) inhibited cortactin protein and mRNA expression, and upregulated c-Cbl protein (E3 ubiquitin ligase for c-Src) expression in OC derived from MM patient monocytes with resultant inhibition of OC sealing zone formation. However, at the same low doses (100 nM) CC-292 did not show any direct in vitro effect against MM cell viability. Because carfilzomib, a proteasome inhibitor that binds irreversibly to its target, has potent anti-MM activity and also inhibits OC resorptive activity, we studied CC-292 in combination with carfilzomib. Our data suggests that carfilzomib (1.25 nM) has no impact on OC sealing zone formation but inhibits OC differentiation. CC-292 (100 nM) in combination with carfilzomib (1.25 nM) inhibited not only sealing zone formation but also OC differentiation, resulting in stronger suppression of OC function than carfilzomib alone. The combination of CC-292 (30mg/kg p.o. for 5 days per week for 6 weeks) and carfilzomib (3 mg/kg i.v. x 2 days per week for 4 weeks and 2 mg/kg i.v. x 2 days per week for 2 weeks) significantly inhibited tumor burden and myeloma cell numbers in a diffuse NOD-SCID MM model. The calvarial cells derived from these mice treated with CC-292 alone, carfilzomib alone or the combination showed higher osteocalcin mRNA (osteoblast differentiation marker) expression. A specific bone resorption marker, carboxy-terminal telopeptide collagen crosslinks (CTX) in mouse serum was significantly inhibited in CC-292 and CC-292 in combination with carfilzomib treatment groups in comparison with control mice. Furthermore, 3D microCT reconstructions showed increase in cancellous bone volume in lumbar vertebrae in mice treated with CC-292 or carfilzomib, while the combination treatment resulted in an increase in cancellous bone volume in an additive manner. These data demonstrate that the novel BTK inhibitor CC-292 inhibits OC function through inhibition of OC sealing zone formation. Moreover, CC-292 in combination with carfilzomib augments effects against the bone microenvironment with resultant anti-MM activity. Disclosures: Arastu-Kapur: Onyx Pharmaceuticals, Inc.: Employment. Evans:Celgene Avilomics Research: Employment, Equity Ownership. Singh:Celgene Avilomics Research: Employment, Equity Ownership. Kirk:Onyx Pharmaceuticals, Inc.: Employment. Westlin:Celgene Avilomics Research: Employment, Equity Ownership. Raje:Celgene: Consultancy; Millenium: Consultancy; Onyx: Consultancy; Amgen: Consultancy; Acetylon: Research Funding; Eli Lilly: Research Funding.

Comprehensive Analysis Of U2AF1 Mutations In 843 Patients With Myeloid Neoplasms With Respect To Other Genetic Alterations

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 4973-4973
Author(s):  
Manja Meggendorfer ◽  
Christiane Eder ◽  
Sabine Jeromin ◽  
Claudia Haferlach ◽  
Wolfgang Kern ◽  
...  
Keyword(s):  
Next Generation Sequencing ◽  
Hot Spots ◽  
Melting Curve ◽  
Gene Mutations ◽  
Next Generation ◽  
Employment Equity ◽  
Total Cohort ◽  
Equity Ownership ◽  
Generation Sequencing ◽  
Splicing Machinery

Abstract Introduction Genes affecting the splicing machinery have been found to be frequently mutated in MDS patients. U2AF1 codes for one of these splicing components, showing two distinct mutational hot spots at amino acids Ser34 and Gln157. Mutations in U2AF1 induce global abnormalities in RNA splicing, producing intron containing unspliced RNAs. U2AF1 has been shown to be most frequently mutated in MDS cases (7-11%), but was so far investigated only in small subsets of AML and MPN and was found rarely mutated. Aim To determine the frequency of U2AF1 mutations (U2AF1mut) in different myeloid entities and to evaluate the correlation of U2AF1mut with other gene mutations, cytogenetics and clinical features. Patients and Methods The total cohort consisted of 843 patients, whereof 74 were diagnosed as AML, 201 as MDS, 243 as MPN, and 325 as MDS/MPN overlap. 331 patients were female, 512 male. Cytogenetics was available in 830 patients and these were grouped by the following karyotypes: normal karyotype (n=561), +8 (n=39), -7 (n=15), del(20q) (n=95), -Y (n=29), other aberrations (n=59), and complex karyotype (n=32). Based on the previously described association of U2AF1mut with del(20q) there was an intended selection bias to this abnormality. Mutational analyses for U2AF1 were performed by either melting curve analyses or next generation sequencing. In subcohorts we investigated mutations in ASXL1 (n=505), CBL (n=647), CEBPA (n=68), CSF3R (n=213), DNMT3A (n=260), ETV6 (n=129), EZH2 (n=355), FLT3-ITD (n=352), FLT3-TKD (n=239), IDH1/2 (n=367 and 286, respectively), JAK2 (n=681), KITD816 (n=244), KRAS (n=393), MLL-PTD (n=384), MPLW515 (n=612), NPM1 (n=477), NRAS (n=509), RUNX1 (n=516), SETBP1 (n=336), SF3B1 (n=839), SRSF2 (n=784), TET2 (n=428), and TP53 (n=239) by Sanger sequencing, next generation sequencing, gene scan, or melting curve analysis. Results In the total cohort we detected U2AF1 mutations in 55/843 (6.5%) patients, the two mutational hot spots were equally affected with 29 p.Ser34 and 26 p.Gln157 mutations, respectively. Mutation frequencies were 10.9% in MDS, 9.5% in AML, 7.1% in MDS/MPN overlap and 1.2% in MPN. U2AF1mut patients were older (median: 72.6 vs. 71.8 years; p=0.012), the mutation was more frequent in males (42/512 (8.2%) vs. 13/331 (3.9%) in females; p=0.015) and associated with lower hemoglobin levels (median: 9.5 vs. 11.0g/dL; p<0.001), and platelet counts (median: 78x109/L vs. 179x109/L; p=0.002). Regarding cytogenetics we found a high association of U2AF1mut to del(20q): in 18 of 95 cases (18.9%) with del(20q) a U2AF1 mutation was detected compared to 37 U2AF1mut in 735 cases (5.0%) with any other karyotype (p<0.001). This was true for AML (5/16 vs. 2/56; p=0.005), MDS (11/49 vs. 11/150; p=0.007) and MDS/MPN overlap cases (1/8 vs. 21/309; p=0.441). In contrast in MPN none of the 21 del(20q) patients showed a U2AF1 mutation compared to 18/74 in all other entities (p=0.01). Mutations in the two other genes of the splicing machinery, SF3B1 and SRSF2, occurred in 122/839 (14.5%) and 198/784 (25.3%) cases and were mutually exclusive with U2AF1mut. Only one case each showed an U2AF1mut and a SF3B1 (p=0.002) or SRSF2 (p<0.001) mutation. We furthermore analyzed a number of other gene mutations frequently mutated in myeloid entities and their association to U2AF1mut. There was no correlation to mutations in NPM1, FLT3-ITD and FLT3-TKD, MLL-PTD, and CEBPA in AML patients. In MDS patients there was also no correlation to mutations in ASXL1,ETV6, EZH2, TP53, RUNX1, NRAS, and KRAS. This was also true for JAK2, MPL, CBL, and TET2 mutations in MPN. However in MDS/MPN overlap patients U2AF1mut were more frequently found in cases with ASXL1mut (14/115 (12.2%) in ASXL1mut vs. 7/179 (3.9%) in ASXL1wt; p=0.01) and together with KITD816mut (3/10 (30%) in KITD816mut vs. 15/212 (7%) in KITD816wt; p=0.038). Conclusion 1) U2AF1 is most frequently mutated in MDS, followed by AML and MDS/MPN overlap and in contrast rarely mutated in MPN. 2) U2AF1mut highly correlates with del(20q) in MDS, AML and MDS/MPN overlap but not in MPN cases. 3) In MDS/MPN overlap U2AF1mut associates significantly with ASXL1mut and KITD816mut. Disclosures: Meggendorfer: MLL Munich Leukemia Laboratory: Employment. Eder:MLL Munich Leukemia Laboratory: Employment. Jeromin:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Degradation of Aiolos and Ikaros Followed By Downregulation of c-Myc and then IRF4 Leads to Programmed Cell Death in Myeloma Cells Sensitive to IMiDs® Immunomodulatory Compounds

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 4700-4700
Author(s):  
Chad C Bjorklund ◽  
Courtney G. Havens ◽  
Patrick R Hagner ◽  
Anita K. Gandhi ◽  
Maria Wang ◽  
...  
Keyword(s):  
Cell Death ◽  
Programmed Cell Death ◽  
Protein Expression ◽  
Cell Lines ◽  
Acquired Resistance ◽  
Clinical Samples ◽  
Employment Equity ◽  
Molecular Sequence ◽  
Sequence Of Events ◽  
Equity Ownership

Abstract Background: The zinc finger transcription factors, Aiolos (IKZF3) and Ikaros (IKZF1) were identified as lenalidomide (LEN) and pomalidomide (POM)-induced substrates of the cereblon (CRBN)-dependent Culin4 E3-ligase complex. While recent studies suggest that the anti-proliferative activity of LEN and POM in multiple myeloma (MM) cell lines in vitro is due in part to the targeted ubiquitination and subsequent proteasomal degradation of Aiolos and Ikaros, the downstream molecular mechanisms remain unknown. Using inducible shRNA-mediated knockdown combined with kinetic analyses, we systematically investigated the biological mechanisms associated with the degradation of Ikaros and Aiolos in MM cell lines that are sensitive to or have acquired resistance to LEN and POM. Results: In MM1.S and U266 MM cell lines stably engineered with doxycycline (DOXY)-inducible shRNAs, knockdown of either Ikaros or Aiolos showed a reduction in cell proliferation (80%-90%) as measured by 3H-thymidine incorporation after a 4 day treatment with DOXY. We demonstrated that this anti-proliferative effect is inherently tied to and precedes the induction of apoptosis, which was maximized (60%-80% AnnV+/ToPro3+) 5 days following Aiolos or Ikaros knockdown compared with a control shRNA. shRNA-mediated knockdown of Aiolos or Ikaros was furthermore associated with decreases in both c-Myc and IRF4 protein expression levels (70%-90% and 60%-80%, respectively) that were maximized by day 4. In turn, shRNA knockdown of either c-Myc or IRF4 elicited anti-proliferative (> 80% inhibition) and pro-apoptotic (50%-80%) responses as early as 48hrs after shRNA induction. These data suggest that the reduction of c-Myc and IRF4 protein levels downstream of Aiolos and Ikaros degradation account for the apoptotic effect and marks the onset of the cytotoxic response induced by LEN and POM in MM cells. To define the temporal order of events involving Aiolos, Ikaros, c-Myc and IRF4 in more detail, kinetic experiments following shRNA-mediated knockdown in parallel with drug treatments were performed. Data from these experiments showed that there is a distinct kinetic order of both LEN- and POM-mediated effects, initiated by immediate targeted degradation of Aiolos and Ikaros (within 90 min), followed by a decrease in c-Myc levels (24-48 hrs) with subsequent IRF4 downregulation (48-72 hrs), and finally, resulting in programmed cell death (3-5 days). Importantly, DOXY washout experiments, resulting in re-accumulation of Aiolos or Ikaros at early time points (24 hrs) partially overcame the antiproliferative effects of the shRNA-mediated knockdown of either target. Interestingly, upon the onset of c-Myc downregulation (24-48 hrs), the commitment to cell death could no longer be reversed in our experiments. Further, we generated MM1.S and U266 cells with acquired resistance to POM (10 µM; also cross-resistant to LEN) (MM1.S/PomR and U266/PomR , respectively), in which CRBN protein expression is substantially decreased (> 90%). Consequently, in these resistant cell lines, neither Aiolos nor Ikaros are degraded in the presence of LEN or POM. However, bypass of CRBN-dependent Aiolos degradation by DOXY-induced knockdown rescued c-Myc and IRF4 downregulation and concomitant inhibition of growth (90% and 60%, respectively), suggesting that resistant MM cells with acquired CRBN loss remain dependent on Aiolos and Ikaros. Conclusions: For the first time, our studies showed that degradation of Aiolos and Ikaros sets up a molecular sequence of events culminating in programmed cell death in MM cells. Our mechanistic studies showed that c-Myc is a key intermediate factor whose downregulation is a rate-limiting step for the transcriptional downregulation of IRF4 as well as for the commitment to cell death. Taken together, our results demonstrate a molecular sequence of events underlying the mechanism of action of cytotoxicity of LEN or POM in MM cells. Quantitative measurements of Aiolos and Ikaros degradation, and c-Myc and IRF4 downregulation in clinical samples would help validate these findings. Disclosures Bjorklund: Celgene Corp: Employment, Equity Ownership. Havens:Celgene Corporation: Employment, Equity Ownership. Hagner:Celgene Corp: Employment, Equity Ownership. Gandhi:Celgene Corp: Employment, Equity Ownership. Wang:Celgene Corp: Employment, Equity Ownership. Amatangelo:Celgene Corp: Employment, Equity Ownership. Lu:Celgene Corp: Employment. Wang:Celgene Corp: Consultancy. Breider:Celgene Corp: Employment. Ren:Celgene Corp: Employment. Lopez-Girona:Celgene Corp: Employment, Equity Ownership. Thakurta:Celgene Corp: Employment, Equity Ownership. Klippel:Celgene Corp: Employment. Chopra:Celgene Corp: Employment, Equity Ownership.

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