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Purpose: NF-κB, a transcription factor essential for inflammatory responses, is constitutively activated in many lymphomas. In preclinical studies, pelabresib (CPI-0610), an investigational (BET) bromodomain inhibitor, downregulated NF-κB signaling and demonstrated antitumor activity in vitro. Here we report the safety, pharmacokinetics, pharmacodynamics, and preliminary clinical activity from the first-in-human phase I study of pelabresib in patients with relapsed/refractory lymphomas (NCT01949883). Experimental Design: Sixty-four patients with relapsed/refractory lymphoma (median of 4 prior lines of therapy) were treated with either capsule (6, 12, 24, 48, 80, 120, 170, 230, 300 mg) or tablet (125, 225 mg) doses of pelabresib orally once daily on a 14 days on, 7 days off schedule. Results: The MTD was determined as the 225 mg tablet daily. The most frequent adverse events were fatigue, nausea, and decreased appetite. Thrombocytopenia, a class effect for all BET inhibitors, was dose-dependent, reversible, and noncumulative. Pelabresib exhibited dose-proportional increases in systemic exposure, rapid absorption, and a half-life of approximately 15 hours (supporting once daily dosing). The bioavailability of the tablet formulation was 60% greater than the capsules. Pelabresib suppressed IL8 and CCR1 mRNA at doses above 120 and 170 mg, respectively. Four patients (6.2%) had an objective response (2 complete response and 2 partial response) and 5 patients had prolonged stable disease. Conclusions/Discussion: Pelabresib is capable of BET target gene suppression in an exposure-dependent manner with an acceptable safety profile leading to the recommended phase II dose of the 125 mg tablet once daily. Significance: BET proteins inhibition can potentially modify the pathogenic pathways which contribute to many diseases including malignancies. Pelabresib (CPI-0610), a potent and selective small molecule BET proteins inhibitor, has a MTD of 225 mg once daily for 14 days with a 7-day break, clear pharmacokinetic/pharmacodynamic relationship, and manageable clinical safety profile. These findings are part of the foundation for the ongoing pivotal study of pelabresib in patients with myelofibrosis.

Supplemental tables with the number of patients treated with number of cycles and the incidence of DLTs.

Purpose:NF-κB, a transcription factor essential for inflammatory responses, is constitutively activated in many lymphomas. In preclinical studies, pelabresib (CPI-0610), an investigational (BET) bromodomain inhibitor, downregulated NF-κB signaling and demonstrated antitumor activity in vitro. Here we report the safety, pharmacokinetics, pharmacodynamics, and preliminary clinical activity from the first-in-human phase I study of pelabresib in patients with relapsed/refractory lymphomas (NCT01949883).Experimental Design:Sixty-four patients with relapsed/refractory lymphoma (median of 4 prior lines of therapy) were treated with either capsule (6, 12, 24, 48, 80, 120, 170, 230, 300 mg) or tablet (125, 225 mg) doses of pelabresib orally once daily on a 14 days on, 7 days off schedule.Results:The MTD was determined as the 225 mg tablet daily. The most frequent adverse events were fatigue, nausea, and decreased appetite. Thrombocytopenia, a class effect for all BET inhibitors, was dose-dependent, reversible, and noncumulative. Pelabresib exhibited dose-proportional increases in systemic exposure, rapid absorption, and a half-life of approximately 15 hours (supporting once daily dosing). The bioavailability of the tablet formulation was 60% greater than the capsules. Pelabresib suppressed IL8 and CCR1 mRNA at doses above 120 and 170 mg, respectively. Four patients (6.2%) had an objective response (2 complete response and 2 partial response) and 5 patients had prolonged stable disease.Conclusions/Discussion:Pelabresib is capable of BET target gene suppression in an exposure-dependent manner with an acceptable safety profile leading to the recommended phase II dose of the 125 mg tablet once daily.Significance:BET proteins inhibition can potentially modify the pathogenic pathways which contribute to many diseases including malignancies. Pelabresib (CPI-0610), a potent and selective small molecule BET proteins inhibitor, has a MTD of 225 mg once daily for 14 days with a 7-day break, clear pharmacokinetic/pharmacodynamic relationship, and manageable clinical safety profile. These findings are part of the foundation for the ongoing pivotal study of pelabresib in patients with myelofibrosis.

CONSORT diagram of patient disposition throughout study

Background OX40 (CD134) plays a role in the maintenance of late T-cell proliferation and survival. KHK4083 is a monoclonal antibody directed against OX40. We aimed to assess the safety and preliminary efficacy of KHK4083 in patients with moderately active ulcerative colitis (UC). Methods In this multicenter, double-blind, parallel-group, phase 2 study, patients with moderately active UC patients were randomized to ascending doses of intravenous KHK4083 (1, 3, or 10 mg/kg) or placebo every 2 weeks for 12 weeks. The primary endpoint was safety. The primary efficacy end point was the change from baseline in mean modified Mayo endoscopy subscore at week 12. Treatment with KHK4083 or placebo was continued every 4 weeks for up to 52 weeks in responders. Results Long-term treatment with KHK4083 was well tolerated, with treatment-related adverse events being predominantly transient mild-to-moderate infusion-related reactions. Exploratory analysis of biopsy samples showed the virtually complete elimination of OX40+ cells in colon mucosa after 12 weeks of KHK4083 treatment. There were no significant differences between any of the randomized KHK4083 dose groups and placebo for the mean change in Mayo endoscopy subscore from baseline to week 12. Conclusions KHK4083 can be safely administered intravenously at doses up to 10 mg/kg every 2 or 4 weeks for up to 52 weeks. Proof of pharmacodynamic action was confirmed by depletion of the elevated levels of the OX40+ cells associated with UC at all tested doses. Clinical response and mucosal healing (endoscopic improvement) in this population was not correlated with ablation of OX40+ T cells.

Background: Pelabresib (CPI-0610) is a potent, first-in-class, selective, oral small-molecule inhibitor of bromodomain and extraterminal domain (BET) proteins which is able to modify the expression of genes involved in nuclear factor kappa B (NFκB) signaling in patients with myelofibrosis (MF). Here we present results from MANIFEST (NCT02158858), an ongoing, global, open-label Phase 2 study investigating pelabresib monotherapy in patients with advanced MF who are intolerant/refractory to, or ineligible for ruxolitinib (RUX) and typically have very poor prognosis. Methods: Eligibility criteria are MF patients intolerant/refractory to or ineligible for JAKi, Dynamic International Prognostic Scoring System (DIPSS) risk category of ≥intermediate-2, platelets ≥75 × 10 9/L, and ≥2 symptoms measurable (score ≥1) per Myelofibrosis Symptom Assessment Form (MFSAF) v4.0. Additional criteria include red blood cell (RBC) transfusion dependent (TD) per Gale criteria in TD cohort or spleen volume of ≥450 cc by computed tomography/magnetic resonance imaging in non-TD cohort. Patients were enrolled as TD (defined as ≥2 U RBCs/month over 12 wks) and non-TD if TD criteria are not met. The primary endpoint in TD cohort is RBC transfusion independence (TI; defined as no transfusion for ≥12 wks), and ≥35% spleen volume reduction (SVR35) at wk 24 in the non-TD cohort. Secondary endpoints include number of patients with ≥50% total symptom score reduction (TSS50) per MFSAF v4.0 at wk 24, and safety. Additional exploratory endpoints include changes in plasma levels of proinflammatory cytokines and bone marrow (BM) morphology/fibrosis. Patients with assessment at wk ≥24 and those discontinuing after wk 12 are included in the analysis of the corresponding endpoint; these were the evaluable patients. Results: As of 29 September 2020, 27 pts were treated in the non-TD cohort for a median duration of 51 wks (2, 147 wks). At wk 24, 30% (7/23) evaluable pts achieved SVR35 (median change: -29%), and 48% (10/21) pts achieved TSS50 (median change: -56%). In the TD cohort, 19 pts were treated for a median duration of 32 wks (5, 78 wks). 21% (3/14) evaluable TD pts achieved RBC TI for ≥12 wks. Updated 24-wk data with a larger data set and new long-term data at 48 wks will be presented. Pt subgroup analyses revealed evidence of activity of pelabresib in a subset of pts who were ineligible to receive RUX, a patient population that generally has few therapeutic options. Clinical benefits observed with pelabresib included achievement of SVR35 and TSS50, improvements in bone marrow fibrosis, and increases in hemoglobin levels. A panel of 68 cytokines, including those known to be nuclear factor kappa B (NF-κB) targets linked to inflammation and elevated in MF pts, were evaluated in plasma samples obtained at baseline (BL) and during therapy. Cytokines were clustered to show different patterns of change during treatment with pelabresib. Overall, pelabresib significantly reduced plasma levels of several cytokines in RUX naïve or experienced pts (Figure). Cytokine changes with pelabresib in cluster 3 (which includes IL-6, CRP, RANTES, TNFa and IL-18, and is characterized by higher BL values and bigger decreases over time) and in cluster 5 (which includes EPO, TARC, ICAM-1 and IL-8, and is characterized by relatively lower BL values and less profound decreases over time) were more pronounced in RUX-naïve pts. 46 pts were evaluable for safety. The most common hematological treatment emergent adverse events (TEAEs) of any grade were thrombocytopenia (30%; ≥Grade 3: 15%) and anemia (15%; ≥Grade 3: 13%). The most common (≥20%) nonhematological TEAEs were nausea (39%; no ≥Grade 3), diarrhea (37%; ≥Grade 3: 4%), dysgeusia and asthenic conditions (30% each; no ≥Grade 3 for either), respiratory tract infections (28%; ≥Grade 3: 2%), cough (26%; no ≥Grade 3) and constipation and weight decrease (22% each; ≥Grade 3: 2% each). Conclusions: Preliminary data suggested pelabresib monotherapy was generally well tolerated and demonstrated signals of clinical activity in MF pts intolerant/refractory to or ineligible for JAKi, who have limited treatment options and poor outcomes. Figure 1 Figure 1. Disclosures Kremyanskaya: Astellas: Research Funding; Constellation: Research Funding; Incyte: Research Funding; Protagonist Therapeutics: Consultancy, Research Funding; Bristol Myers Squibb: Research Funding; Astex: Research Funding; Chimerix: Research Funding. Mascarenhas: Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; Galecto: Consultancy; Kartos: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy; Promedior: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech/Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Forbius: Research Funding; CTI Biopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Constellation: 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, Research Funding; Merus: Research Funding; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Geron: Consultancy, Research Funding; Prelude: Consultancy. Palandri: Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Membership on an entity's Board of Directors or advisory committees; AOP: Membership on an entity's Board of Directors or advisory committees; CTI: Consultancy. Vannucchi: Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees. Verstovsek: Celgene: Consultancy, Research Funding; NS Pharma: Research Funding; AstraZeneca: Research Funding; CTI BioPharma: Research Funding; Promedior: Research Funding; Protagonist Therapeutics: Research Funding; Roche: Research Funding; Ital Pharma: Research Funding; PharmaEssentia: Research Funding; Blueprint Medicines Corp: Research Funding; Sierra Oncology: Consultancy, Research Funding; Gilead: Research Funding; Genentech: Research Funding; Incyte Corporation: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Constellation: Consultancy; Pragmatist: Consultancy. Harrison: Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Promedior: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sierra Oncology: Honoraria; Incyte Corporation: Speakers Bureau; Constellation Pharmaceuticals: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Geron: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Galacteo: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Bose: CTI BioPharma: Honoraria, Research Funding; Blueprint Medicines: Honoraria, Research Funding; NS Pharma: Research Funding; Astellas: Research Funding; Promedior: Research Funding; Pfizer: Research Funding; Constellation Pharmaceuticals: Research Funding; Sierra Oncology: Honoraria; Kartos Therapeutics: Honoraria, Research Funding; Novartis: Honoraria; Celgene Corporation: Honoraria, Research Funding; Incyte Corporation: Honoraria, Research Funding; BMS: Honoraria, Research Funding. Schiller: Ono-UK: Consultancy, Research Funding; Daiichi-Sankyo: Research Funding; Deciphera: Research Funding; FujiFilm: Research Funding; Stemline Therapeutics, Inc.: Honoraria, Research Funding, Speakers Bureau; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sangamo: Research Funding; Actuate: Research Funding; BMS/Celgene: Consultancy, Current equity holder in publicly-traded company, Research Funding, Speakers Bureau; Constellation Pharmaceuticals: Research Funding; Amgen: Consultancy, Current equity holder in publicly-traded company, Honoraria, Research Funding, Speakers Bureau; Geron: Research Funding; Genentech-Roche: Research Funding; Tolero: Research Funding; Takeda: Research Funding; Forma: Research Funding; Astellas: Honoraria, Research Funding, Speakers Bureau; Jazz: Consultancy, Honoraria, Research Funding, Speakers Bureau; Gamida Cell Ltd.: Research Funding; Arog: Research Funding; Karyopharm: Research Funding; Onconova: Research Funding; Celator: Research Funding; Pfizer: Current equity holder in publicly-traded company, Research Funding; PrECOG: Research Funding; Regimmune: Research Funding; Mateon: Research Funding; Kite/Gilead: Honoraria, Research Funding, Speakers Bureau; Samus: Research Funding; Bio: Research Funding; Delta-Fly: Research Funding; Trovagene: Research Funding; Agios: Consultancy, Research Funding, Speakers Bureau; Elevate: Research Funding; Novartis: Consultancy, Research Funding; Abbvie: Research Funding; Actinium Pharmaceuticals, Inc: Research Funding; Sanofi: Honoraria, Research Funding, Speakers Bureau; Pharma: Consultancy; Johnson & Johnson: Current equity holder in publicly-traded company; Biomed Valley Discoveries: Research Funding; Eli Lilly: Research Funding; ASH foundation: Other: Chair-unpaid; Sellas: Research Funding; Ono: Consultancy; Incyte: Consultancy; Ariad: Research Funding; AstraZeneca: Consultancy; Kaiser Permanente: Consultancy; Cyclacel: Research Funding; MedImmune: Research Funding; Ambit: Research Funding; Leukemia & Lymphoma Society: Research Funding; Bluebird Bio: Research Funding; Boehringer-Ingleheim: Research Funding; Cellerant: Research Funding; CTI Biopharma: Research Funding; Janssen: Research Funding; Kura Oncology: Research Funding; Pharmacyclics: Honoraria, Speakers Bureau; Millennium: Research Funding; National Marrow Donor Program: Research Funding; NIH: Research Funding; Onyx: Research Funding; Pharmamar: Research Funding; UC Davis: Research Funding; UCSD: Research Funding; Evidera: Consultancy; NCI: Consultancy; Novartis: Speakers Bureau. Rampal: Jazz Pharmaceuticals: Consultancy; BMS/Celgene: Consultancy; Stemline: Consultancy, Research Funding; Sierra Oncology: Consultancy; Novartis: Consultancy; Pharmaessentia: Consultancy; CTI: Consultancy; Abbvie: Consultancy; Blueprint: Consultancy; Disc Medicine: Consultancy; Memorial Sloan Kettering: Current Employment; Incyte: Consultancy, Research Funding; Kartos: Consultancy; Constellation: Research Funding. Drummond: BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CTI: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Gupta: Sierra Oncology: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Honoraria; Pfizer: Consultancy; Constellation Pharma: Consultancy, Honoraria; Roche: Consultancy; Incyte: Honoraria, Research Funding; BMS-Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Patriarca: Novartis: Honoraria; Amgen: Honoraria; Takeda: Honoraria; Incyte: Honoraria; Pfizer: Honoraria; Argenix: Honoraria. Scandura: Constellation: Research Funding; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; MPN-RF (Foundation): Research Funding; CR&T (Foudation): Research Funding; European Leukemia net: Honoraria, Other: travel fees . Teichmann: Pfizer: Membership on an entity's Board of Directors or advisory committees. Hoffman: Novartis: Other: Data Safety Monitoring Board, Research Funding; Protagonist Therapeutics, Inc.: Consultancy; AbbVie Inc.: Other: Data Safety Monitoring Board, Research Funding; Kartos Therapeutics, Inc.: Research Funding. Colak: Constellation Pharmaceuticals: Current Employment. Ren: Constellation Pharmaceuticals: Current Employment. Bobba: Constellation Pharmaceuticals: Current Employment. Cui: Constellation Pharmaceuticals: Current Employment. Efuni: Constellation Pharmaceuticals: Current Employment. Talpaz: Imago: Consultancy; Constellation: Membership on an entity's Board of Directors or advisory committees; Takeda: Other: Grant/research support ; Celgene: Consultancy; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Background: Nuclear factor-κB (NF-κB), a transcription factor essential for inflammatory responses, is constitutively activated in many lymphomas. Pelabresib (CPI-0610) is a first-in-class, oral, small-molecule inhibitor of the tandem amino-terminal bromodomains (BD1 and BD2) of bromodomain and extraterminal domain (BET) proteins, which regulate gene expression pathways. In preclinical studies, pelabresib downregulated NF-κB signaling and demonstrated antitumor activity in vitro. Here we report the pharmacokinetics (PK), pharmacodynamics (PD), safety and tolerability, and preliminary efficacy results from the first-in-human Phase 1, multicenter, open-label, dose-escalation study of pelabresib in patients (pts) with relapsed or refractory lymphomas (NCT01949883). Methods: Adults with relapsed non-Hodgkin or Hodgkin lymphoma after at least one prior therapy or who were not eligible for high-dose chemotherapy and autologous stem cell transplant (HD-ASCT) or had refused HD-ASCT were enrolled. Pts were required to have platelet count ≥75 × 10 9/L, absolute neutrophil count ≥1.0 × 10 9/L and Eastern Cooperative Oncology Group (ECOG) performance status of ≤2. Pelabresib was administered under fasting conditions orally once daily (QD) for 14 days followed by a 7-day break in continuous 21-day cycles. Cohorts of three to six pts were sequentially enrolled with increasing doses of pelabresib (6, 12, 24, 48, 80, 120, 170, 230 and 300 mg with the capsule formulation, and 125 and 225 mg QD with the micronized tablet formulation) to assess maximum tolerated dose (MTD). Results: A total of 64 lymphoma pts, with a median of four prior therapies, were enrolled and treated with pelabresib, 47 pts with the capsule formulation and 17 pts with the tablet formulation. Pelabresib exhibited dose-proportional exposure with rapid absorption, with maximum plasma concentrations reached at 2.9 hours post dose. Plasma concentrations declined in a generally monophasic manner with a half-life of ~16 hours. Following 14 days of QD dosing, accumulation of pelabresib plasma concentrations was low (~40%), confirming the suitability of a QD dosing schedule. The tablet formulation displayed increased bioavailability compared with the capsule formulation (75 vs 60 %, respectively) and was selected for use in subsequent trials. PD analysis demonstrated appreciable suppression of interleukin-8 (IL8) and C-C motif chemokine receptor 1 (CCR1) mRNA in peripheral blood mononuclear cells at capsule doses greater than or equal to 120 and 170 mg, respectively, and for both tablet dose levels (125 and 225 mg) of pelabresib. Decreased expression of both IL8 and CCR1 were seen as early as 2 hours post dose, suggesting rapid transcriptional regulation following treatment. A total of 8 pts among all dosing groups had a dose limiting toxicity (DLT) during cycle 1 (hematologic changes [n = 5], gastrointestinal events [n = 2], and rash [n=1]). All 64 pts had ≥1 treatment emergent adverse event (TEAE) during the study; 44 (68.8%) pts had ≥1 TEAE of Grade 3 or higher. The most common TEAEs (>20%) were fatigue, nausea, vomiting, decreased appetite, thrombocytopenia, platelet count decreased, anemia, and lymphocyte count decreased. Gastrointestinal TEAEs were common but mostly low grade and easily manageable. Thrombocytopenia, frequently reported hematological TEAE and a class effect for all BET inhibitors, was dose dependent in both frequency and intensity, reversible, non-cumulative and not associated with bleeding events. There was a strong dose-dependent correlation of platelet count. There were no treatment related deaths. Four pts had an objective response (two complete responses in pts treated with 48 mg and 230 mg and two partial responses in pts treated with 230 mg and 300 mg), and five pts had prolonged (>6 months) stable disease, as per Revised Response Criteria for Malignant Lymphoma (2007). Conclusions: Pelabresib has a wide therapeutic index capable of BET target gene suppression with an acceptable safety profile. As previously reported, the MTD was 225 mg (Blum KA, et al. Ann Oncol 2018;29(Suppl 3):mdy048). Due to the dose dependent nature of the observed platelet count decrease, the 125 mg dose (with the ability to titrate up to 225 mg, if needed) was selected and is currently being studied in Phase 2 (MANIFEST; NCT02158858) and Phase 3 (MANIFEST-2; NCT04603495) trials of pts with myelofibrosis. Disclosures Flinn: Merck: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Teva: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Genentech: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Celgene: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Karyopharm Therapeutics: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Iksuda Therapeutics: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Calithera Biosciences: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; IGM Biosciences: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Agios: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Acerta Pharma: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Verastem: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Roche: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; TG Therapeutics: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; MorphoSys: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Infinity Pharmaceuticals: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Yingli Pharmaceuticals: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Nurix Therapeutics: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Trillium Therapeutics: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Takeda: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Portola Pharmaceuticals: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Unum Therapeutics: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Juno Therapeutics: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Constellation Pharmaceuticals: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Great Point Partners: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Curis: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Gilead Sciences: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Novartis: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Triphase Research & Development Corp.: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Pfizer: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Loxo: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Seagen: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Forty Seven: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Kite, a Gilead Company: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Incyte: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; ArQule: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Janssen: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; Rhizen Pharmaceuticals: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; Forma Therapeutics: Other: All research funding payments made to Sarah Cannon Research Institute, Research Funding; BeiGene: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; AstraZeneca: Consultancy, Other: All consultancy and research funding payments made to Sarah Cannon Research Institute, Research Funding; AbbVie: Consultancy, Other: All Consultancy and Research Funding payments made to Sarah Cannon Research Institute, Research Funding; Century Therapeutics: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Hutchison MediPharma: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Vincerx Pharma: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Sarah Cannon Research Institute: Current Employment; Servier Pharmaceuticals: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Yingli Pharmaceuticals: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Seagen: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Servier Pharmaceuticals: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute; Unum Therapeutics: Consultancy, Other: All consultancy payments made to Sarah Cannon Research Institute, Research Funding; Johnson & Johnson: Current holder of individual stocks in a privately-held company; Seattle Genetics: Research Funding. Goy: Bristol Meyers Squibb: Membership on an entity's Board of Directors or advisory committees; Constellation: Research Funding; Janssen: Research Funding; Xcenda: Consultancy; Medscape: Consultancy; Novartis: Consultancy, Honoraria; OncLive Peer Exchange: Honoraria; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; MorphoSys: Honoraria, Other; Incyte: Honoraria; AbbVie/Pharmacyclics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; COTA (Cancer Outcome Tracking Analysis): Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Leadership role; Bristol Meyers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie/Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Research Funding; Phamacyclics: Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Genentech/Hoffman la Roche: Research Funding; Acerta: Consultancy, Research Funding; Infinity/Verastem: Research Funding; Genomic Testing Cooperative: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Leadership role; Vincerx pharma: Membership on an entity's Board of Directors or advisory committees; Rosewell Park: Consultancy; LLC(Targeted Oncology): Consultancy; Elsevier's Practice Update Oncology, Intellisphere, LLC(Targeted Oncology): Consultancy; Michael J Hennessey Associates INC: Consultancy; Hoffman la Roche: Consultancy; Vincerx: Honoraria, Membership on an entity's Board of Directors or advisory committees; Physicians' Education Resource: Consultancy, Other: Meeting/travel support; AstraZeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Xcenda: Consultancy, Honoraria; Kite, a Gilead Company: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Elsevier PracticeUpdate: Oncology: Consultancy, Honoraria; Hackensack Meridian Health, Regional Cancer Care Associates/OMI: Current Employment. Younes: AZ: Current Employment, Other: Senior Vice President, Global Head of Haematology (Early and Late Stage) Oncology R&D at AstraZeneca. Bobba: Constellation Pharmaceuticals: Current Employment. Senderowicz: Constellation Pharmaceuticals: Current Employment. Efuni: Constellation Pharmaceuticals: Current Employment. Rippley: Constellation Pharmaceuticals: Current Employment. Abramson: EMD Serono: Consultancy; Genmab: Consultancy; Bristol-Myers Squibb Company: Consultancy, Research Funding; C4 Therapeutics: Consultancy; Morphosys: Consultancy; Kite Pharma: Consultancy; Novartis: Consultancy; Seagen Inc.: Research Funding; Allogene Therapeutics: Consultancy; Astra-Zeneca: Consultancy; Incyte Corporation: Consultancy; BeiGene: Consultancy; Kymera: Consultancy; Bluebird Bio: Consultancy; AbbVie: Consultancy; Karyopharm: Consultancy; Genentech: Consultancy.

Background: Myelofibrosis (MF) is characterized by progressive bone marrow (BM) fibrosis resulting from aberrant megakaryopoiesis and expression of pro-inflammatory cytokines. These processes, heavily influenced by bromodomain and extraterminal domain (BET) protein-mediated gene regulation, lead to myeloproliferation and cytopenias. There is a high unmet need for a treatment that can potentially delay or reverse BM fibrosis in patients (pts) with MF. Pelabresib (CPI-0610) is a potent, first-in-class, selective, oral small-molecule BET inhibitor, which is able to modify the expression of genes involved in nuclear factor kappa B (NFκB) signaling in pts with MF. Pelabresib is currently being investigated as a monotherapy and in combination with the JAK inhibitor (JAKi) ruxolitinib (RUX), in the ongoing MANIFEST Phase 2 study (NCT02158858). Methods: In arm 1 of MANIFEST, pelabresib is administered as monotherapy to pts with MF who are intolerant/refractory to, or ineligible for RUX; in arm 2, as an 'add-on' to RUX in pts with MF who have suboptimal/lost response; and in arm 3 as combination therapy with RUX in JAKi treatment-naïve pts with MF. To evaluate the effects of pelabresib on BM biology, analyses were conducted using BM biopsy samples obtained pre-treatment and at 24 weeks post-treatment during the MANIFEST trial. Central pathology review of reticulin staining was conducted to evaluate BM fibrosis (BMF) grading and immunohistochemistry staining for changes in erythroids (ERY) and megakaryocytes (MK), respectively. Independent digital images of stained BM slides were also evaluated with a semi-quantitative cell-specific detection algorithm for reticulin density, percentage CD71+ ERY, mean number of CD61+ MK and mean distance between nuclei for CD61+ MK. Results: Exploratory analyses across the three treatment arms showed BM improvements after 24 weeks of treatment. Paired comparison by digital analysis of baseline and 24-week treatment BM biopsies from 29 pts showed reduction (range 67%-15.5%) in reticulin intersections per field in 45% (13/29) pts. Furthermore, digital analysis of CD71+ ERY and CD61+ MK from paired biopsies showed increased ERY progenitors in 50% (16/32) pts, decreased MK density in 57% (15/26) pts and decreased MK clustering in 46% (12/26) pts at 24 weeks. Decreased MK clustering correlated with decreased density of CD61+ MK in 75% pts (9/12). Correlative analysis between observed clinical responses and bone marrow improvements are ongoing and will be available for presentation at the conference. We previously reported (Talpaz M, et al. ASH 2020; Abstract 2163) that in pts with MF, pelabresib can reduce spleen volume, improve symptoms, improve bone marrow fibrosis, demonstrate increase in hemoglobin levels, and reduce transfusion burden. Updated 24-week data reflecting a higher number of evaluable pts and new long-term data at 48 weeks across the MANIFEST trial, will be presented. Conclusions: Treatment with pelabresib as monotherapy or in combination with RUX, in both RUX treatment-naïve and -experienced pts with MF, resulted in increased ERY progenitors, decreased MK density and reduction of BM fibrosis, as assessed by digital pathology. These data suggest possible disease-modifying potential for pelabresib by improving BM histology and function, leading to potential clinical benefits. Disclosures Verstovsek: Roche: Research Funding; Promedior: Research Funding; Blueprint Medicines Corp: Research Funding; Incyte Corporation: Consultancy, Research Funding; Protagonist Therapeutics: Research Funding; Genentech: Research Funding; CTI BioPharma: Research Funding; Celgene: Consultancy, Research Funding; Gilead: Research Funding; Ital Pharma: Research Funding; PharmaEssentia: Research Funding; NS Pharma: Research Funding; AstraZeneca: Research Funding; Novartis: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; Constellation: Consultancy; Pragmatist: Consultancy. Salama: Mayo Clinic: Current Employment, Other: Mayo Clinic had the contractual work for the central pathology review for this study and I was one of the reviewing pathologists; Constellation Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Mascarenhas: AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kartos: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene/BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Constellation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy, Research Funding; Prelude: Consultancy; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; PharmaEssentia: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Galecto: Consultancy; Promedior: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merus: Research Funding; Forbius: Research Funding; CTI Biopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech/Roche: 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, Research Funding; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sierra Oncology: Consultancy, Membership on an entity's Board of Directors or advisory committees; Geron: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Talpaz: Celgene: Consultancy; Imago: Consultancy; Takeda: Other: Grant/research support ; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Constellation: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Mesa: La Jolla Pharma: Consultancy; Samus: Research Funding; Constellation Pharmaceuticals: Consultancy, Research Funding; Pharma: Consultancy; CTI: Research Funding; Abbvie: Research Funding; CTI: Research Funding; Genentech: Research Funding; Gilead: Research Funding; Promedior: Research Funding; Novartis: Consultancy; Celgene: Research Funding; Incyte Corporation: Consultancy, Research Funding; Sierra Oncology: Consultancy, Research Funding; AOP: Consultancy. Vannucchi: Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rampal: Incyte: Consultancy, Research Funding; Pharmaessentia: Consultancy; Blueprint: Consultancy; Disc Medicine: Consultancy; Stemline: Consultancy, Research Funding; BMS/Celgene: Consultancy; Novartis: Consultancy; Sierra Oncology: Consultancy; CTI: Consultancy; Abbvie: Consultancy; Jazz Pharmaceuticals: Consultancy; Constellation: Research Funding; Memorial Sloan Kettering: Current Employment; Kartos: Consultancy. Oh: Abbvie: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines: Membership on an entity's Board of Directors or advisory committees; Celgene Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Constellation: Membership on an entity's Board of Directors or advisory committees; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees; Disc Medicine: Membership on an entity's Board of Directors or advisory committees; Geron: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Kartos Therapeutics: Membership on an entity's Board of Directors or advisory committees; PharamaEssentia: Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Membership on an entity's Board of Directors or advisory committees. Taverna: Constellation Pharmaceuticals: Current Employment. Cui: Constellation Pharmaceuticals: Current Employment. Zavidij: Constellation Pharmaceuticals: Current Employment. Chen: Constellation Pharmaceuticals: Current Employment. Colak: Constellation Pharmaceuticals: Current Employment. Efuni: Constellation Pharmaceuticals: Current Employment. Keller: Constellation Pharmaceuticals: Current Employment. Trojer: Constellation Pharmaceuticals: Current Employment. Harrison: Galacteo: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte Corporation: Speakers Bureau; Constellation Pharmaceuticals: Research Funding; Sierra Oncology: Honoraria; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Geron: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keros: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Promedior: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Shire: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

BACKGROUND: KHK2455 is an oral selective inhibitor of Indoleamine 2,3-dioxygenase 1 (IDO1) and is being developed as an active immunotherapy to treat advanced or metastatic solid tumors. IDO1 is a rate-limiting enzyme that converts tryptophan (TRP) to kynurenine (KYN) and is linked to immunosuppression. IDO1 inhibition results in immune modulatory effects which may be important in boosting anti-cancer immune responses. The goal of this analysis was to develop a population pharmacokinetics (PK)-pharmacodynamics (PD) model to characterize KHK2455 exposure and its relationship to response in patients with locally advanced or metastatic solid tumors. METHOD: Plasma KHK2455 concentration, plasma KYN and TRP concentration were obtained from 36 subjects with locally advanced or metastatic solid tumors who received KHK2455 at 0.3, 1, 3, 10, 30, or 100 mg QD as a monotherapy run-in followed by combination therapy with anti-CCR4 antibody mogamulizumab in this first in human study of KHK2455. The nonlinear mixed effects modeling approach was used to develop a population PK-PD model using the data from both mono- and combination-therapy. The ratio of KYN to TRP (K:T ratio) was used as a PD marker. RESULTS: The population PK model included one-compartment model with transit compartment absorption, enterohepatic cycling, and linear elimination. The K:T ratio was well described by an indirect response model. Steady state simulations showed that, when compared to baseline, the K:T ratio decreased with increasing KHK2455 dose and reached to a constant nadir at 100 mg dose. CONCLUSIONS: A population PK-PD model was established to characterize the KHK2455 exposure and its relationship to response in patients with locally advanced or metastatic solid tumors. The PK-PD model will enable dose optimization simulations for the planned studies. ACKNOWLEDGEMENTS: We would like to express special appreciation to Dr. Solmaz Sahebjam, MD, for help in publishing this abstract. Citation Format: Krina Mehta, Shoko Koshiba, Maki Hasegawa, Tomonori Tayama, Douglas Marsteller, Floyd Fox, Yi Liu, Sergey Efuni, Denis Healy, Matthew Hruska. Population pharmacokinetic-pharmacodynamic analysis of KHK2455 in patients with locally advanced or metastatic solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1368.

Background: Indoleamine 2,3-dioxygenase 1 (IDO1) degrades tryptophan to kynurenine, suppressing T cell effector activity and increasing T regulatory cell activity. IDO1 expression is induced in some cancer cells and has been associated with suppression of effector T cell responses toward tumors. In nonclinical studies, IDO1 inhibition combined with other clinically established immune modulating agents (eg, anti-CTLA-4 or anti-PD-1 antibodies) showed a significant improvement in tumor growth suppression. KHK2455 is a long acting and selective IDO1 inhibitor under development as a new approach to enhance anti-tumor immunity. KHK2455 is being combined with different anti-cancer therapies to explore its ability to enhance anti-tumor immunity and overcome tumor immune evasion. Avelumab is a PD-L1 checkpoint inhibitor approved for treatment of urothelial carcinoma. This study represents an opportunity to assess the complementary action of KHK2455 IDO1 inhibition and avelumab checkpoint inhibition in the treatment of urothelial carcinoma. Methods: Study 2455-002 is a two-part, multicenter, open-label Phase 1 study of KHK2455 in combination with avelumab in adult subjects with locally advanced or metastatic urothelial carcinoma (including bladder, urethra, ureters, and renal pelvis), who are checkpoint inhibitor naїve and previously treated with platinum-based therapy. Part 1 (dose-escalation) has a 3+3 design to evaluate safety and tolerability and identify the maximum tolerated dose (MTD). Dose de-escalation based on dose limiting toxicities is permitted. Part 2 (cohort expansion) further explores the safety, pharmacokinetics, pharmacodynamics, and anti-tumor activity for the combination regimen at the MTD or highest tested dose. All subjects will receive oral KHK2455 at their assigned dose and avelumab IV. The primary study endpoints are safety and tolerability, and the secondary endpoints are efficacy (based on RECIST v1.1 criteria), pharmacokinetics, and immunogenicity. Exploratory endpoints include examination of pre and post treatment biopsies for intratumoral suppression of IDO1 activity to correlate peripheral and intratumoral suppression, along with pre and post treatment serum markers including, but not limited to, immune mediators and related cytokines. Descriptive statistics (n, mean, standard deviation, median, minimum, and maximum) for continuous variables and frequency distributions and percentages for discrete variables will be utilized. Approximately 44 subjects are planned for enrollment (12 subjects in Part 1 and 32 subjects in Part 2). Clinical trial information: NCT03915405 (sponsor: Kyowa Kirin Pharmaceutical Development, Inc.) Citation Format: Pratibha Desai, Santosh Rao, Yuta Ikawa, Barbara Kapelan, Sergey Efuni, Robert Latek, Takashi Sato, Denis Healy, Yousef Zakharia. An open-label, phase 1 study of IDO inhibitor KHK2455 in combination with avelumab in adult subjects with locally advanced or metastatic urothelial carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT238.

3040Background: IDO-1 inhibitors have shown antitumor activity in combination with immunotherapeutic agents in multiple cancers. KHK2455 is a novel and selective oral IDO-1 inhibitor. Unlike other ...