ALBERT

Description: Rapidly proliferating cells reprogram metabolism to support increased biosynthetic demands, a feature that can expose targetable vulnerabilities for therapeutic intervention. A chemical biology screen was performed in an effort to identify metabolic vulnerabilities in particular tumor subtypes, and revealed potent and selective activity of a novel dihydroorotate dehydrogenase (DHODH) inhibitor, AG-636, in cancer cell lines of hematologic origin. In contrast, cancer cell lines of solid tumor origin exhibited comparatively poor sensitivity. Evaluation of a lymphoma cell line panel demonstrated broad responsiveness to DHODH inhibition, independent of clinical subtype (e.g. ABC, GCB, double-hit). The on-target cellular activity of AG-636 was evaluated by examining the metabolic effects of AG-636 on cells and by evaluating the ability of extracellular uridine to rescue the effects of AG-636 on proliferation and viability. The metabolic changes incurred upon treatment of cells with AG-636 were consistent with a mechanism of action driven by inhibition of DHODH and de novo pyrimidine biosynthesis. Supraphysiologic concentrations of extracellular uridine rescued the effects of AG-636 on growth and viability as well as the effects on metabolism, further confirming on-target activity. The mechanistic basis for differential sensitivity to AG-636 was assessed by comparing the activity of the de novo pyrimidine biosynthesis and uridine salvage pathways in cancer cell lines of hematologic or solid tumor origin with similar proliferative rates. Differential response to AG-636 could not be attributed to varying abilities to utilize the de novo pyrimidine biosynthesis pathway or to salvage extracellular uridine. Real-time imaging of cells treated with AG-636, along with monitoring of extracellular uridine concentrations, demonstrated immediate effects on the viability of lymphoma cell lines in the setting of depleted extracellular uridine. In contrast, solid tumor cell lines were able to maintain growth for an additional period of time, suggestive of adaptive mechanisms to supply pyrimidine pools and/or to cope with nucleotide stress. The high in vitro activity of AG-636 in cancer cells of hematologic origin translated to xenograft models, including an aggressive, patient-derived xenograft model of triple-hit lymphoma and an ibrutinib-resistant model of mantle cell lymphoma in which complete tumor regression occurred. These studies support the development of AG-636 for the treatment of hematologic malignancies. A phase 1 study has been initiated in patients with relapsed/refractory lymphoma (NCT03834584). Disclosures Ulanet: Agios: Employment, Equity Ownership. Chubukov:Agios: Employment, Equity Ownership. Coco:Agios: Employment, Equity Ownership. McDonald:Agios: Employment, Equity Ownership. Steadman:Agios: Employment, Equity Ownership. Narayanaswamy:Agios: Employment, Equity Ownership. Ronseaux:Agios: Employment, Equity Ownership. Choe:Agios: Employment, Equity Ownership. Truskowski:Agios: Employment, Equity Ownership. Nellore:Aurigene Discovery Technologies: Employment. Rao:Firmus Laboratories: Employment, Equity Ownership. Lenz:Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Agios: Research Funding; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Gilead: Consultancy, Honoraria, Research Funding, Speakers Bureau; BMS: Consultancy; AstraZeneca: Consultancy, Honoraria, Research Funding; Bayer: Consultancy, Honoraria, Research Funding, Speakers Bureau; Roche: Employment, Honoraria, Research Funding, Speakers Bureau. Cooper:Agios: Employment, Equity Ownership. Murtie:Agios: Employment. Marks:Agios: Employment, Equity Ownership.

Description: MLN518 is a small molecule inhibitor of FLT3, PDGFR and c-Kit that is currently being evaluated as a therapy for AML. Previous phase I evaluation of MLN518 showed that it inhibits the phosphorylation of both wild-type and ITD-mutated FLT3 in patients’ leukemic blasts with an IC90 in the range of 100–175 ng/mL. Anti-leukemic activity was also observed, with decreases in both peripheral and bone marrow blasts. Dose-limiting toxicity, consisting of reversible general muscular weakness and/or fatigue was associated with trough plasma MLN518 concentrations 〉 1000 ng/mL. We are now conducting a phase II study of MLN518 in patients with relapsed or refractory AML and in untreated patients with AML considered unfit for standard AML therapies. Eligibility requires demonstration of the FLT3 ITD mutation in the patient’s blasts. All patients are treated with MLN518 at an initial dose of 525 mg po bid, with provision for dose reduction if MLN518-associated weakness occurs. Twenty patients have been treated with MLN518 in this study, eighteen of whom are currently evaluable (2 patients have recently started therapy). Toxicities associated with MLN518 therapy have included weakness/fatigue, QTc prolongation (relationship to MLN518 uncertain), and nausea and vomiting. MLN518 plasma concentration-time data for the first fourteen patients demonstrates that all patients achieved steady-state trough plasma concentrations 〉 150 ng/mL. Both inter- and intra-subject variability (%CV) in trough steady-state concentrations were 〈 30%. Assessment of total and phosphorylated FLT3 in leukemic blasts isolated from peripheral blood was possible in 4 patients. Western blots from blasts obtained before and after MLN518 dosing demonstrated either partial or complete inhibition of FLT3 phosphorylation with MLN518 plasma concentrations 〉 130 ng/mL. Of the eighteen evaluable patients, response could not be assessed in three because intercurrent illness and/or MLN518-associated toxicity precluded adequate treatment with MLN518 (≥ 14 days). Seven patients experienced progressive AML without evidence of any anti-leukemic effect. Two patients had stable disease for ≥ 50 days and subsequently underwent bone marrow transplantation. Although no complete or partial remissions have been observed, 6 patients have demonstrated evidence of an anti-leukemic effect with decreases in both peripheral and bone marrow blasts of 1-3 months duration. In these 6 patients the mean decrease in the absolute peripheral blast count was 92%, with a range of 85–100%. The mean decrease in the bone marrow blast percentage was 62%, with a range of 44–94%. We conclude that MLN518 has anti-leukemic activity in FLT3 ITD-mutated AML and should be further evaluated as a component of remission-induction and/or maintenance therapy in this disease.

Description: Tandutinib (MLN518/CT53518) is a novel quinazoline-based inhibitor of the type III receptor tyrosine kinases: FMS-like tyrosine kinase 3 (FLT3), platelet-derived growth factor receptor (PDGFR), and KIT. Because of the correlation between FLT3 internal tandem duplication (ITD) mutations and poor prognosis in acute myelogenous leukemia (AML), we conducted a phase 1 trial of tandutinib in 40 patients with either AML or high-risk myelodysplastic syndrome (MDS). Tandutinib was given orally in doses ranging from 50 mg to 700 mg twice daily The principal dose-limiting toxicity (DLT) of tandutinib was reversible generalized muscular weakness, fatigue, or both, occurring at doses of 525 mg and 700 mg twice daily. Tandutinib's pharmacokinetics were characterized by slow elimination, with achievement of steady-state plasma concentrations requiring greater than 1 week of dosing. Western blotting showed that tandutinib inhibited phosphorylation of FLT3 in circulating leukemic blasts. Eight patients had FLT3-ITD mutations; 5 of these were evaluable for assessment of tandutinib's antileukemic effect. Two of the 5 patients, treated at 525 mg and 700 mg twice daily, showed evidence of antileukemic activity, with decreases in both peripheral and bone marrow blasts. Tandutinib at the MTD (525 mg twice daily) should be evaluated more extensively in patients with AML with FLT3-ITD mutations to better define its antileukemic activity.

Description: The bromodomain and extraterminal (BET) proteins recognize acetylated lysine residues on histone tails and recruit transcriptional machinery to promote gene expression. The BET proteins are attractive drug targets because they regulate the expression of MYC, BCL2 and NF- κB target genes. We investigated the therapeutic potential of CPI-0610, an inhibitor of BET proteins, currently in Phase I testing in multiple myeloma (MM). Our preliminary data show that human MM cell lines are sensitive to BET inhibition, with IC50 values of 800-1000 nM being observed in MM.1S, MM.1R, RPMI-8226, LR5, H929 and U266 cell lines in 72h culture. We further show that CPI-0610 inhibits MM cell growth in the presence of cytokines and when co-cultured with bone marrow stromal cells. CPI-0610 induces apoptosis and G1 cell cycle arrest associated with MYC downregulation. However, protein levels of BCL2, NF- κ B and MCL1 remain unchanged in MM cells upon BET inhibition. The zinc finger transcriptional factor Ikaros (IKZF1) is highly expressed in MM (GEO dataset GSE36133). It is actively transcribed in the MM.1S cell line with an active transcription start site occupied by BRD4 and MED1 (Loven J et al. Cell 2013). Interestingly, we found that CPI-0610 suppresses Ikaros and IRF4 expression at the levels of both transcription and protein in MM cells. With the use of doxycycline-inducible shRNAs targeting IKZF1, IRF4 and MYC, we identified a positive feedback mechanism that is critical for MM cell survival. Individual knockdown of IRF4, IKZF1 or MYC all lead to induction of apoptosis in MM cells. Suppression of IRF4 decreases both Ikaros and MYC protein expression, suggesting that IRF4 is upstream of both Ikaros and MYC. Downregulation of MYC protein expression is observed following IKZF1 knockdown, suggesting that MYC is downstream of Ikaros. Finally, we observed a decrease in IRF4 protein level upon MYC downregulation, implicating a feedback mechanism from MYC to IRF4. Together, these data illustrate a molecular sequence of events going from IRF4 to IKZF1 to MYC and then back to IRF4, forming a positive feedback loop in MM cells. Based on the observation that shRNA-mediated knockdown of MYC and IKZF1 are toxic to MM, we combined CPI-0610 with lenalidomide, an immunomodulatory drug which stabilizes cereblon and facilitates Ikaros degradation in MM cells (Kronke J et al., and Lu G et al., Science 2014). We observed a synergistic cytotoxic effect in the cell lines tested (MM.1S and RPMI-8226). The enhanced cytotoxic effect of the combined treatment in MM cell lines is due in part to suppression of MYC, IKZF1 and IRF4. Ongoing studies will focus on understanding the molecular mechanism underlying this synergistic combination and validating its efficacy in vivo in order to provide a rationale for clinical protocols of BET inhibitors in MM. Disclosures Mertz: Constellation Pharmaceuticals: Employment, Equity Ownership. Sims:Constellation Pharmaceuticals: Employment, Equity Ownership. Cooper:Constellation Pharmaceuticals: Employment, Equity Ownership. Raje:Celgene Corporation: Consultancy; Eli Lilly: Research Funding; Takeda: Consultancy; Amgen: Consultancy; Onyx: Consultancy; AstraZeneca: Research Funding; Novartis: Consultancy; BMS: Consultancy; Acetylon: Research Funding; Millenium: Consultancy.

Description: Background: Tandutinib is an orally bioavailable small molecule inhibitor of FLT3, c-KIT, and PDGFR with a single-agent MTD of 525 mg b.i.d. Tandutinib demonstrated single agent anti-leukemic activity in patients with relapsed/refractory AML with FLT3 ITD mutations, with ≥50% decreases in bone marrow and peripheral blast counts in 12/25 patients and 1 CR without platelet normalization. Since tandutinib is synergistic with cytarabine and daunorubicin in vitro, we sought to determine the MTD of tandutinib in combination with standard induction chemotherapy in patients with newly diagnosed AML, with or without FLT3 ITD mutations. Methods: A starting dose of Tandutinib 200 mg b.i.d was administered during induction and consolidation therapy, and for an additional 6 months. Induction therapy consists of cytarabine 200mg/m2/day IVCI, days 1–7, plus daunorubicin 60mg/m2/day, days 1–3. Consolidation therapy is given as 2–4 cycles of standard (3000mg/m2 IV every 12h, days 1, 3, 5) or in older patients modified (2000mg/m2/day IV, days 1–5) high-dose cytarabine. DLT is defined as failure to recover marrow function (ANC ≥500/μL; platelets ≥20,000/μL), or grade 3/4 non-hematologic toxicity not resolved to grade 2 (except anorexia, alopecia, fatigue) by day 42 of induction therapy, or any unexpected grade 3/4 non-hematologic toxicities. Results: 29 patients have been enrolled: median age 60y (range 26–83); 13M, 16F; 23 de novo, 6 secondary AML; 9 with unfavorable cytogenetics; 5 with FLT3 ITD mutations. Cohort 1 consisted of 7 patients treated with continuous daily dosing of tandutinib 200 mg b.i.d. Due to GI intolerance, the protocol was amended so that tandutinib was administered only on days 1–14 of induction therapy and each cycle of consolidation. Under the amended schedule 8 patients were treated with tandutinib 200 mg b.i.d. (Cohort 2) and 14 patients have been treated with tandutinib 500 mg b.i.d. (Cohort 3). Full safety and efficacy data are available for the 15 patients in cohorts 1 and 2. Diarrhea, nausea and vomiting have been the most common drug-related AEs, and were more frequent with continuous daily dosing of tandutinib. GI tolerance in Cohort 2 has been acceptable, with no patients requiring termination or reduction in tandutinib for GI toxicity. Although continuous dosing was not feasible, no DLTs were seen in Cohorts 1 or 2; one DLT consisting of obtundation not clearly related to tandutinib during induction occurred in Cohort 3, One patient in Cohort 3 experienced non-dose limiting generalized muscle weakness, which reversed within 24 hours after discontinuation of tandutinib. Tandutinib was restarted at a reduced dose in this patient without recurrence. 5/7 patients in Cohort 1 and 6/8 patients in Cohort 2 achieved a CR. PK data have been collected for all 15 patients in Cohorts 1 and 2; median steady state tandutinib concentration was 195 ng/mL (range: 52–486). Conclusions: Tandutinib 200 and 500 mg b.i.d. in combination with standard therapy for newly diagnosed AML appears well tolerated using the amended dosing schedule (days 1–14). Updated results from Cohort 3 (tandutinib 500 mg b.i.d) will be presented.

Description: BACKGROUND: Ivosidenib (AG-120) and enasidenib (AG-221) are oral inhibitors of mutant IDH1 (mIDH1) and mutant IDH2 (mIDH2), respectively, approved for the treatment of relapsed/refractory IDH-mutant acute myeloid leukemia (AML). Here we report updated results from a phase 1 study on the safety and efficacy of each of these agents when combined with intensive chemotherapy in patients with newly diagnosed AML, as well as data regarding the rate of measurable residual disease (MRD)-negative complete remissions (CRs), mutation clearance and molecular profiling. METHODS: In this open-label, multicenter, phase 1 study (NCT02632708), eligible patients with newly diagnosed mIDH1 or mIDH2 AML are treated with induction therapy (daunorubicin 60 mg/m2/day or idarubicin 12 mg/m2/day x 3 days with cytarabine 200 mg/m2/day x 7 days) in combination with either ivosidenib 500 mg once daily (for mIDH1) or enasidenib 100 mg once daily (for mIDH2). After induction, patients may receive ≤4 cycles of consolidation therapy while continuing the mIDH inhibitor. Patients who complete or are ineligible for consolidation may continue on maintenance ivosidenib or enasidenib until the end of study. For patients who proceed to allogeneic hematopoietic stem cell transplant (HSCT), mIDH inhibitor treatment is discontinued prior to transplant and is not resumed post-transplant. mIDH1/2 variant allele frequency (VAF) is assessed in bone marrow mononuclear cells using Digital PCR Technology (Sysmex-Inostics Inc). IDH1/2 mutation clearance (IDH-MC) is defined as a reduction in the mIDH1/2 VAF to a level below the limit of detection of this assay (0.02-0.04%) for ≥1 on-treatment time point on or after Day 28 of induction. MRD in bone marrow aspirates is analyzed using multi-parameter flow cytometry. Baseline co-occurring mutations are identified with a 95-gene next generation sequencing panel targeted to hematologic malignancies. RESULTS: As of May 1, 2018, 134 patients had been treated: 47 with ivosidenib (median age 63 years, range 24-76) and 87 with enasidenib (median age 63 years, range 27-77; Table 1). Secondary AML (sAML; arising after myelodysplastic syndrome or another antecedent hematologic disorder, or after exposure to genotoxic injury) was present in 33/87 (38%) patients with mIDH2 and in 16/47 (34%) patients with mIDH1. The most frequent co-occurring baseline mutations were DNMT3A, NPM1 and NRAS for patients with IDH1 mutations; and DNMT3A, SRSF2 and ASXL1 for patients with IDH2 mutations. Ivosidenib or enasidenib combined with induction and consolidation was well tolerated, based on the frequency of grade ≥3 non-hematologic adverse events (Table 2) and hematologic recovery (Table 3). Times for ANC and platelet count recovery were nominally longer in patients with sAML. Among the 41 ivosidenib-treated patients evaluable for efficacy, a response of CR, CRi or CRp was achieved in 26/28 (93%) patients with de novo AML and 6/13 (46%) patients with sAML (Table 4). Twenty-one patients received ≥1 cycle of consolidation therapy and 11 patients received maintenance after consolidation. Seventeen patients proceeded to HSCT. Among the 77 enasidenib-treated patients evaluable for efficacy, a response of CR, CRi, or CRp was achieved in 33/45 (73%) patients with de novo AML and in 20/32 (63%) patients with sAML (Table 4). Thirty-seven patients received ≥1 cycle of consolidation therapy, 6 patients received maintenance directly after induction and 11 patients received maintenance after consolidation. Thirty-three patients proceeded to HSCT. Longitudinal VAF data are available for 31 ivosidenib-treated patients and 60 enasidenib-treated patients. In patients who achieved a CR, IDH-MC was observed in 41% (9/22) of those with mIDH1 (Table 5) and in 30% (11/37) of those with mIDH2 (Table 6). Flow cytometry assessments are available for 21 patients achieving a CR: MRD-negative CRs were observed in 89% (8/9) of those with mIDH1 and in 58% (7/12) of those with mIDH2. CONCLUSION: Ivosidenib or enasidenib in combination with induction and consolidation therapy has an acceptable safety profile with robust remission rates, MRD-negative CRs, and mutation clearance in a population of older, high-risk patients with mIDH AML. The clinical benefit of adding ivosidenib or enasidenib to induction, consolidation and maintenance therapy for patients with newly diagnosed mIDH AML will be further evaluated in a randomized phase 3 trial. Disclosures Stein: Celgene: Consultancy; Agios: Consultancy; Daiichi Sankyo: Consultancy; Bayer: Consultancy; Pfizer: Consultancy; Novartis: Consultancy. DiNardo:Karyopharm: Other: Advisory role; Medimmune: Other: Advisory role; Celgene: Other: Advisory role; Bayer: Other: Advisory role; Agios: Consultancy, Other: Advisory role; AbbVie: Consultancy, Other: Advisory role. Fathi:Jazz: Honoraria; Takeda: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Agios: Honoraria, Research Funding; Boston Biomedical: Consultancy, Honoraria; Astellas: Honoraria. Mims:Abbvie Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy. Pratz:Boston Scientific: Consultancy; AbbVie: Consultancy, Research Funding; Millenium/Takeda: Research Funding; Agios: Research Funding; Astellas: Consultancy, Research Funding. Savona:Boehringer Ingelheim: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding. Stein:Celgene: Speakers Bureau; Amgen: Speakers Bureau. Stone:AbbVie: Consultancy; Merck: Consultancy; Argenx: Other: Data and Safety Monitoring Board; Agios: Consultancy, Research Funding; Sumitomo: Consultancy; Pfizer: Consultancy; Amgen: Consultancy; Cornerstone: Consultancy; Astellas: Consultancy; Celgene: Consultancy, Other: Data and Safety Monitoring Board, Steering Committee; Otsuka: Consultancy; Jazz: Consultancy; Fujifilm: Consultancy; Arog: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Ono: Consultancy; Orsenix: Consultancy. Döhner:Astellas: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; AROG Pharmaceuticals: Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Jazz: Consultancy, Honoraria; AROG Pharmaceuticals: Research Funding; AbbVie: Consultancy, Honoraria; Agios: Consultancy, Honoraria; Astex Pharmaceuticals: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Celator: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Astex Pharmaceuticals: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Agios: Consultancy, Honoraria; Bristol Myers Squibb: Research Funding; Bristol Myers Squibb: Research Funding; Janssen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Seattle Genetics: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Jazz: Consultancy, Honoraria; Pfizer: Research Funding; Celator: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Pfizer: Research Funding. Pollyea:Celgene: Membership on an entity's Board of Directors or advisory committees; Argenx: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celyad: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Curis: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees. McCloskey:Amgen Pharmaceuticals: Speakers Bureau; Celgene Pharmaceuticals: Honoraria, Speakers Bureau; Pfizer: Consultancy; Takeda Pharmaceuticals: Consultancy, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Speakers Bureau; COTA: Equity Ownership. Odenike:ABBVIE: Honoraria, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; CTI/Baxalta: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Dava Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Oncotherapy Science: Research Funding; Agios: Research Funding; Celgene: Research Funding; NS Pharma: Research Funding; Janssen: Research Funding; Astex: Research Funding; Gilead Sciences: Research Funding. Lowenberg:Clear Creek Bio Ltd: Consultancy, Honoraria; Chairman Scientific Committee and Member Executive Committee, European School of Hematology (ESH, Paris, France): Membership on an entity's Board of Directors or advisory committees; Editorial Board "International Journal of Hematology": Membership on an entity's Board of Directors or advisory committees; Editorial Board "The Netherlands Journal of Medicine": Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Astex: Consultancy; "Up-to-Date", section editor leukemia: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Editorial Board "European Oncology & Haematology": Membership on an entity's Board of Directors or advisory committees; Elected member, Royal Academy of Sciences and Arts, The Netherlands: Membership on an entity's Board of Directors or advisory committees; Supervisory Board, National Comprehensive Cancer Center (IKNL), Netherlands: Membership on an entity's Board of Directors or advisory committees; Chairman, Leukemia Cooperative Trial Group HOVON (Netherlands): Membership on an entity's Board of Directors or advisory committees; international Scientific Advisory Board, Institute Gustave Roussy, Paris: Membership on an entity's Board of Directors or advisory committees; Royal Academy of Sciences and Arts, The Netherlands: Membership on an entity's Board of Directors or advisory committees. Ossenkoppele:Roche: Consultancy, Honoraria; Karyopharm: Consultancy, Research Funding; Genmab: Research Funding; Pfizer: Consultancy, Honoraria; Genentech: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Johnson & Johnson: Consultancy, Honoraria, Research Funding. Patel:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Dava Oncology: Honoraria; France Foundation: Honoraria. Lersch:Celgene: Employment. Nabhan:Agios: Employment. Choe:Agios: Employment, Equity Ownership. Wang:Agios: Employment, Equity Ownership. Hua:Agios: Employment, Equity Ownership. Almon:Agios: Employment, Equity Ownership. Cooper:Agios: Employment, Equity Ownership. Tallman:Cellerant: Research Funding; BioSight: Other: Advisory board; Daiichi-Sankyo: Other: Advisory board; ADC Therapeutics: Research Funding; Orsenix: Other: Advisory board; AbbVie: Research Funding; AROG: Research Funding.

Description: Inhibition of the bromodomain and extra-terminal (BET) proteins is a promising therapeutic strategy for various hematologic malignancies. Previous studies suggest that BET inhibitors constrain tumor cell proliferation and survival mainly through suppression of MYC transcription and activity. However, suppression of the transcription of additional genes also contributes to the anti-tumor activity of BET inhibitors but is less well understood. Here we investigated the therapeutic potential of CPI-0610, a novel BET inhibitor that is currently in a phase I clinical trial in relapsed multiple myeloma (MM) (ClinicalTrials.gov Identifier: NCT02157636). CPI-0610 displays potent in vitro cytotoxicity against MM cell lines and patient-derived MM cells by inducing G1 cell cycle arrest and caspase-dependent apoptosis. Furthermore, CPI-0610-mediated BET inhibition overcomes the protective effects conferred by cytokines and bone marrow stromal cells. We also confirmed the in vivo efficacy of CPI-0610 in a MM xenograft mouse model. CPI-0610 significantly delayed tumor growth and increased the survival of MM-bearing SCID mice. Our study found IKZF1 and IRF4 to be among the primary targets of CPI-0610, along with MYC. These findings indicate that BET inhibition not only results in a robust reduction of MYC transcription and activity but also suppresses the expression of IKZF1 and IRF4 in MM. Given that immunomodulatory drugs stabilize cereblon and facilitate Ikaros degradation in MM cells, we combined it with CPI-0610. Combination studies of CPI-0610 with lenalidomide or pomalidomide show in vitro synergism, in part due to concomitant suppression of IKZF1, IRF4, and MYC, providing a rationale for clinical testing of this drug combination in MM patients. Disclosures Mertz: Constellation Pharmaceuticals, Inc.: Employment, Equity Ownership. Sims:Constellation Pharmaceuticals, Inc.: Employment, Equity Ownership. Cooper:Constellation Pharmaceuticals, Inc.: Employment, Equity Ownership. Raje:Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Research Funding; Eli Lilly: Research Funding.

Description: Abstract 1331 BET (bromodomain and extra-terminal) proteins bind to acetylated lysine residues on histones and thereby directly and selectively regulate the expression of genes relevant to cancer. Small molecule inhibition of BET protein binding to chromatin suppresses the transcription of MYC, a subset of NF-κB-dependent genes, and BCL-2. Because of the clinical potential of this novel mechanism, we have discovered selective and potent small molecule inhibitors of BET bromodomains with physical and pharmacokinetic properties that are favorable for clinical development. CPI-267232 is representative of a series of small molecule BET inhibitors with these characteristics. In a biochemical binding assay it has an IC50 126 nM against BD1 of BRD4, and in the MV4-11 leukemia cell line it suppresses the transcription of MYC with an EC50 of 170 nM and inhibits its growth with a GI50of 120 nM. In a panel of more than 100 cancer cell lines CPI-267232 and other structurally dissimilar BET inhibitors demonstrate growth inhibitory activity most potently and consistently against cell lines of hematologic origin. Cells treated with CPI-267232 undergo a G1 arrest with the more sensitive lines undergoing apoptosis with longer periods of drug exposure (〉 48 hrs). CPI-267232 has high oral bioavailability in mice (∼80%) but is cleared rapidly, with an elimination half-life of approximately 3 hrs (in dogs, oral bioavailability is 94% with an elimination half-life of 9 hrs). PK-PD studies conducted in mice bearing subcutaneous xenografts of Raji Burkitt's lymphoma demonstrated that maximal (80%) suppression of MYC expression was achieved 4 hours following a single 30 mg/kg oral dose; MYC expression returned to baseline levels by 12 hours, consistent with the rapid elimination of the compound. Efficacy studies in nude mice bearing xenografts were subsequently conducted, with a 30 mg/kg PO bid regimen yielding a %T/C value of 23% (Raji) or regression (MV4-11) after 21 days of treatment. Evaluation of the relationships between various measurements of drug exposure and efficacy revealed that efficacy is primarily driven by maintaining drug concentration above a minimum value rather by total AUC or Cmax. This observation is consistent with the importance of exposure duration in effecting growth arrest and cell killing in tissue culture. Although the transcription of MYC is frequently suppressed, the overall effects of BET inhibition on gene transcription vary across cell lines of different origin. Genome-wide expression profiling of 2 myeloma and 3 leukemia cells lines at 4 and 24 hours after exposure to a small molecule BET inhibitor resulted in the identification of approximately 200 genes that were commonly either up- or down-regulated by at least 2-fold with statistical significance. In addition, a small set of BET inhibitor-sensitive genes has been identified in peripheral blood mononuclear cells. The discovery of novel BET inhibitors with optimized potency, selectivity, and pharmacokinetic properties, coupled with these insights into the pharmacokinetic and pharmacodynamic determinants of anti-tumor activity, provides an opportunity for the rational development of BET inhibition in the treatment of patients with hematologic malignancies. Disclosures: Sims: Constellation Pharmaceuticals: Employment. Normant:Constellation Pharmaceuticals: Employment. Sandy:Constellation Pharmaceuticals: Employment. Mertz:Constellation Pharmaceuticals: Employment. Bryant:Constellation Pharmaceuticals: Employment. O'Meara:Constellation Pharmaceuticals: Employment. Green:Constellation Pharmaceuticals: Employment. Cooper:Constellation Pharmaceuticals: Employment. Audia:Constellation Pharmaceuticals: Employment.

Description: The oncogenic tyrosine kinases, such as BCR-ABL, TEL-ABL, TEL-PDGFbR and FLT3-ITD, play a major role in the development of hematopoietic malignancy. They activate many of the same signal transduction pathways, including the RAS/MAPK pathway, STAT/JAK pathway and PI3-K/AKT pathway. Although activation of signal transduction pathway has been extensively studied, few bone fide target genes have been identified. To identify the critical target genes that are required for transformation in hematopoietic cells, specific tyrosine kinase inhibitors were applied to 32Dcl3 cells expressing various activated tyrosine kinases. Using Affymetrix oligonucleotide arrays, we have identified inhibitor of DNA binding 1 (Id1), which is involved in development, cell cycle and tumorigenesis, as a common target gene of oncogenic tyrosine kinases. To characterize the biological consequence of Id1 expression, we inhibited the expression of Id1 in two human leukemia cell lines (Molm-14 and K562) by an antisense Id1 construct. In both cell lines, we observed a growth inhibition associated with release of inhibition of p27Kip. In addition, inactivation of Id1 sensitized K562 cells to Trail-induced apoptosis. Our findings suggest that Id1 is an important target of constitutively activated tyrosine kinases, and may be a therapeutic target for leukemias involving oncogenic tyrosine kinases.

Description: Background: Dihydroorotate dehydrogenase (DHODH) is a mitochondrial enzyme involved in the de novo synthesis of pyrimidines, key building blocks for RNA and DNA biosynthesis. Inhibitors of DHODH are currently in clinical use for the treatment of rheumatoid arthritis (leflunomide) and multiple sclerosis (teriflunomide). Brequinar, a more specific and potent DHODH inhibitor, was evaluated in several phase 1 trials in patients with advanced solid tumors in the 1990s and demonstrated little evidence of antitumor activity; however, patients with hematologic malignancies were not evaluated in those studies. More recent preclinical studies show that cell lines and in vivo models derived from hematologic malignancies are highly sensitive to inhibition of DHODH. AG-636, a novel small molecule DHODH inhibitor, demonstrated strong in vitro and in vivo anti-tumor activity across diverse models of lymphoma and acute leukemia, supporting the evaluation of AG-636 as a treatment for patients with lymphoma and other hematologic malignancies. A phase 1, multicenter, open-label study investigating AG-636 for the treatment of patients with advanced lymphoma began enrollment on May 24, 2019 (NCT03834584). Methods: The primary objective of this study is to determine the maximum tolerated dose (MTD) of AG-636 and to characterize its dose-limiting toxicities (DLTs) when given to patients with advanced lymphoma. The study includes a dose escalation phase followed by an expansion phase. Approximately 54 adults (42 in the dose escalation phase and 12 in the expansion phase) with advanced lymphoma refractory to standard treatment, will be enrolled at up to 6 centers in the United States. Broad inclusion criteria enable patients with Hodgkin, Diffuse Large B-Cell (DLBCL), Follicular, Peripheral T-Cell, Cutaneous T-Cell, Mantle Cell, and less common subtypes of lymphoma as defined in 2017 by the World Health Organization to enroll. There are no limits on the number of prior lines of therapy and patients may have received prior stem cell transplant or chimeric antigen receptor T-cell therapy. Patients with active central nervous system disease are excluded. Patients must have an Eastern Cooperative Oncology Group performance status ≤2, an absolute neutrophil count ≥1.0×109/L, a platelet count ≥75×109/L, a serum total bilirubin level ≤1.5×upper limit of normal (ULN), alanine aminotransferase and aspartate aminotransferase levels ≤3.0×ULN, and a creatinine clearance ≥30 mL/min (Cockcroft-Gault formula). AG-636 is given as an oral capsule once daily for 2-5 days each week, with 1 cycle of therapy defined as 4 consecutive weeks of treatment. During the dose escalation phase of the study, successive cohorts of patients will be treated with increasing doses of AG-636 to estimate the MTD. The study employs a 2-parameter adaptive Bayesian logistic regression model using escalation with overdose control to guide dose escalation and to estimate the MTD. The MTD is the highest dose that is unlikely (