Abstract: 3015 Background: Bromodomain and extra-terminal (BET) proteins are epigenetic readers that control expression of genes involved in cell growth and oncogenesis. CC-90010 is an oral, potent and reversible BET inhibitor that showed promising activity in lymphoma and solid tumor cell lines and reduced tumor growth in xenograft models. Methods: CC-90010-ST-001 (NCT03220347; 2015-004371-79) is a phase I, first-in-human study of CC-90010 in patients (pts) with advanced solid tumors and R/R NHL. Three schedules and 11 dose levels were evaluated (Table). Primary objectives were to determine safety, maximum-tolerated dose and/or recommended phase II dose (RP2D). Secondary objectives were the identification of early activity signals, pharmacokinetics and pharmacodynamics (PD). Results: As of 10 Dec 2018, 69 pts were enrolled, 67 with solid tumors and 2 with R/R NHL. Data shown are from all pts (N = 69). The median age was 57 y (range, 21–80), 38 (55%) were male, and the median number of prior systemic anticancer regimens was 3 (range, 1–9). The RP2Ds were dose cohorts 3A and 4B. Dose-limiting toxicities (n = 6) occurred in dose cohorts 3A, 3C, and 4B. Grade 3/4 treatment-related adverse events (TRAEs) occurred in 17 pts (25%), most commonly (≥2 pts) thrombocytopenia (7%), platelet count decreased (4%), fatigue (3%), and increased alanine aminotransferase (3%). No deaths from toxicity occurred. Two pts (endometrial carcinoma and astrocytoma) had a partial response (PR); 1 occurred after the data cutoff. Seven pts had prolonged stable disease (SD) 〉 9 mo. Exposures and PD marker regulation increased with dose in each dosing schedule; terminal half-life was ~ 73 h. Conclusions: Most of the TRAEs observed were mild or moderate in severity, reversible, and manageable by dose adjustments and/or supportive care. Promising ongoing anticancer activity with prolonged SD and PRs were observed. The preliminary clinical data provide the rationale for dose expansion of CC-90010 in pts with selected advanced malignancies. Clinical trial information: NCT03220347. [Table: see text]

Abstract: The homeodomain transcription factor NKX2.2 is necessary for neuroendocrine (NE) differentiation in the central nervous system and pancreas. NE tumors derived from the gut are defined by their NE phenotype, which is used for diagnosis and contributes to tumorigenicity. We hypothesized that NKX2.2 is important for NE differentiation in normal and neoplastic gut. NKX2.2 and NE marker expression was investigated in the small intestine of embryonic and adult mice using immunofluorescence (IF). To determine the role of NKX2.2 in NE differentiation of the intestine, the phenotype of Nkx2.2 (−/−) mice was examined by IF and real-time (RT)-PCR. NKX2.2 and NE marker expression in human NE tumors of the gut and normal tissues were evaluated by immunohistochemistry and qRT-PCR. NKX2.2 expression was detected in the intervillus/crypt regions of embryonic and adult mouse intestine. Co-expression of Nkx2.2 with neurogenin3 (NEUROG3) and hormones was observed in the adult intestinal crypt compartment, suggesting NKX2.2 functions in NEUROG3-positive endocrine progenitors and newly differentiated endocrine cells. In the intestine of Nkx2.2 (−/−) mice, we found a dramatic reduction in the number of cells producing numerous hormones, such as serotonin, gastrin, cholecystokinin, somatostatin, glucagon-like peptide 1 (GLP-1), and secretin, but an increase in cells producing ghrelin. NKX2.2 was expressed in most (24 of 29) human NE tumors derived from diverse primary sites. We conclude NKX2.2 functions in immature endocrine cells to control NE differentiation in normal intestine and is expressed in most NE tumors of the gut, and is therefore a novel target of diagnosis for patients with gastrointestinal NE tumors.

Abstract: Purpose: The TP53 tumor suppressor is frequently mutated in colon cancer, but the influence of such mutations on survival remains controversial. We investigated whether mutations in the DNA-binding domain of TP53 are associated with survival in stage III colon cancer. Experimental Design: The impact of TP53 genotype was prospectively evaluated in Cancer and Leukemia Group B 89803, a trial that randomized stage III colon cancer patients to receive adjuvant 5-fluorouracil/leucovorin (5FU/LV) or 5FU/LV with irinotecan (IFL). Results: TP53 mutations were identified in 274 of 607 cases. The presence of any TP53 mutation did not predict disease-free survival (DFS) or overall survival with either adjuvant regimen when men and women were considered together or as separate groups. However, outcome differences among women became apparent when tumor TP53 genotype was stratified as wild-type versus zinc- or non-zinc-binding mutations in the TP53 DNA-binding domain. DFS at 5 years was 0.59, 0.52, and 0.78 for women with TP53 wild-type tumors, and tumors with zinc- or non-zinc-binding mutations, respectively. Survival at 5 years for these same women was 0.72, 0.59, and 0.90, respectively. No differences in survival by TP53 genotype were observed in men. Conclusions: The presence of any TP53 mutation within the DNA-binding domain did not predict survival in stage III colon cancer. However, TP53 genotype was predictive of survival in women following adjuvant therapy. Future colon cancer therapeutic trials, with inclusion of correlative molecular markers, should be designed to permit evaluation of survival and/or response to treatment in women separately from men. Clin Cancer Res; 19(20); 5777–87. ©2013 AACR.

Abstract: Neuroendocrine (NE) or carcinoid tumors of the small intestine (SI) frequently metastasize and produce the hormone serotonin, causing significant morbidity and mortality. A member of the ETS oncogene family of transcription factors, Fev, acts with the homeodomain transcription factor Nkx2.2 in the development of serotonin neurons in mice. In this study, we investigated the role of Fev in normal and neoplastic SI. In NE tumors (NETs) of the SI, serotonin stimulates tumor growth and causes debilitating symptoms, such as diarrhea, flushing, wheezing, and right-sided valvular heart disease (i.e. carcinoid syndrome). Compared with those in the matched normal human SI, FEV expression levels were significantly elevated in primary NETs (20-fold, P 〈 0.0001), lymph node metastases (35-fold, P =0.004), and NET liver metastases (22-fold, P 〈 0.0001) resected from patients with serotonin excess. Fev is expressed in the wild type but not in Nkx2.2 (−/−) mouse SI, in which cells producing serotonin are absent. Using recombination-based cell lineage tracing, we found that FEV-positive cells give rise to serotonin-producing cells in the SI. In Fev (−/−) mouse SI, we observed no difference in the number of cells producing serotonin or other hormones. We conclude that FEV expression identifies serotonin-producing cells in normal and neoplastic SI and is a novel target for diagnosis of patients with NETs of the SI.

Abstract: The bromodomain and extraterminal protein (BET) inhibitor trotabresib has demonstrated antitumor activity in patients with advanced solid tumors, including high-grade gliomas. CC-90010-GBM-001 (NCT04047303) is a phase I study investigating the pharmacokinetics, pharmacodynamics, and CNS penetration of trotabresib in patients with recurrent high-grade gliomas scheduled for salvage resection. Methods Patients received trotabresib 30 mg/day on days 1–4 before surgery, followed by maintenance trotabresib 45 mg/day 4 days on/24 days off after surgery. Primary endpoints were plasma pharmacokinetics and trotabresib concentrations in resected tissue. Secondary and exploratory endpoints included safety, pharmacodynamics, and antitumor activity. Results Twenty patients received preoperative trotabresib and underwent resection with no delays or cancelations of surgery; 16 patients received maintenance trotabresib after recovery from surgery. Trotabresib plasma pharmacokinetics were consistent with previous data. Mean trotabresib brain tumor tissue:plasma ratio was 0.84 (estimated unbound partition coefficient [KPUU] 0.37), and modulation of pharmacodynamic markers was observed in blood and brain tumor tissue. Trotabresib was well tolerated; the most frequent grade 3/4 treatment-related adverse event during maintenance treatment was thrombocytopenia (5/16 patients). Six-month progression-free survival was 12%. Two patients remain on treatment with stable disease at cycles 25 and 30. Conclusions Trotabresib penetrates the blood–brain-tumor barrier in patients with recurrent high-grade glioma and demonstrates target engagement in resected tumor tissue. Plasma pharmacokinetics, blood pharmacodynamics, and safety were comparable with previous results for trotabresib in patients with advanced solid tumors. Investigation of adjuvant trotabresib + temozolomide and concomitant trotabresib + temozolomide + radiotherapy in patients with newly diagnosed glioblastoma is ongoing (NCT04324840).

Abstract: Trotabresib, a novel bromodomain and extraterminal protein inhibitor, has demonstrated antitumor activity and blood–brain barrier penetration in patients with high-grade gliomas, and enhanced the antiproliferative effects of temozolomide in preclinical models. CC-90010-GBM-002 (NCT04324840) is a phase 1b/2 study investigating the addition of trotabresib to standard-of-care (SOC) concomitant temozolomide plus radiotherapy and adjuvant temozolomide, followed by maintenance trotabresib, in patients with newly diagnosed glioblastoma. The design of the dose escalation (part A) has been described previously (Vieito M, et al. SNO 2021. Abstract CTNI-51). Primary objectives of part A were to establish the safety, tolerability, and maximum tolerated dose/recommended phase 2 dose (RP2D) of trotabresib. In part A, addition of trotabresib to SOC was safe and well tolerated in the concomitant (N = 14) and adjuvant (N = 18) cohorts; the most frequent grade 3/4 treatment-related adverse event was thrombocytopenia (7/14 and 9/18 patients, respectively). The RP2D for trotabresib was 30 mg/day 4 days on/24 days off in both settings. At data cutoff (February 20, 2022), median duration of treatment was 34 weeks (concomitant cohort) and 33 weeks (adjuvant cohort); progression-free survival data are not yet mature. Trotabresib plasma pharmacokinetics and pharmacodynamics were consistent with monotherapy. At last follow-up, 6 and 5 patients remained on treatment in the concomitant and adjuvant dose-escalation cohorts, respectively, including 1 patient in cycle 20 with ongoing complete response. The ongoing randomized phase 2 dose expansion (part B; planned N = 162) is comparing concomitant trotabresib at the RP2D + SOC followed by adjuvant trotabresib at the RP2D + SOC, followed by maintenance trotabresib 45 mg/day 4 days on/24 days off, versus SOC alone in patients with newly diagnosed IDH–wild-type glioblastoma. Key objectives are to compare progression-free and overall survival, safety, and tolerability. Longer follow-up from part A and the first disclosure of data from part B will be presented.

Abstract: Background: Cluster of differentiation 47 (CD47), a widely expressed cell-surface ligand,is overexpressed in various malignancies and is correlated with worse outcomes in NHL. Interaction of CD47 and signal regulatory protein-α (SIRPα) delivers an antiphagocytic 'don't eat me' signal to promote tumor cell evasion from macrophages. CC-90002 is a humanized IgG4-PE CD47 antibody that inhibits CD47-SIRPα interaction and enabled phagocytosis across a panel of cancer cell lines (Narla et al. AACR.2017). In addition to high binding affinity, CC-90002 is potentially differentiated from other CD47 immunotherapies by its lack of ability to induce hemagglutination of red blood cells or hemolysis in nonclinical studies. CD47 antibodies can synergize with the CD20 antibody rituximab to induce phagocytosis of NHL cells in vitroand to eliminate lymphoma in mouse models (Chao et al. Cell.2010). We therefore examined CC-90002 plus rituximab for treatment of R/R NHL. Methods: This 2-part, phase I, multicenter study (CC-90002-ST-001; NCT02367196) is evaluating CC-90002 in subjects with advanced solid and hematologic malignancies. Part B of the study (reported here) is examining CC-90002 in combination with rituximab in subjects with CD20-positive R/R NHL. Dose escalation followed a modified 3+3 design. Subjects received escalating doses of CC-90002 intravenously at 4, 8, 15, 20, or 30 mg/kg every 2 weeks (Q2W) on days 1 and 15 plus rituximab 375 mg/m2 given on days −15, −8, and −1 and day 8 of cycles 1-6, 8, 10, and 12 in 28-day cycles. Primary endpoints are dose-limiting toxicities (DLTs), nontolerated dose (NTD), and maximimum tolerated dose. Secondary endpoints are pharmacokinetics, preliminary efficacy per International Working Group Response Criteria for NHL (Cheson et al. J Clin Oncol.2014), and frequency of antidrug antibodies. Results: Overall, 28 subjects have been enrolled and 24 were treated. As of July 5, 2019, 20 subjects had discontinued the study, most commonly for progressive disease (PD; n=9) or death (n=7). The median age at enrollment was 64 years (range, 27−81), and subjects had received a median of 3 prior systemic therapies (range, 2−9). Subjects received a median of 2 cycles of CC-90002 plus rituximab (range, 1−18). There were no CC-90002 dose reductions but 7 subjects had their dose interrupted, mostly because of thrombocytopenia and neutropenia. The NTD was established as 30 mg/kg Q2W.DLTs occurred in 3 subjects; 1 subject developed dyspnea attributed to an infusion-related reaction at 15 mg/kg Q2W CC-90002 and 2 subjects had grade 3 thrombocytopenia requiring platelet transfusion occurring at 30 mg/kg Q2W CC-90002. The most common adverse events (AEs) were hematologic (Table). Although anemia was common, there was no evidence of hemolysis. The most frequent grade 3/4 AEs were neutropenia (38%) and thrombocytoenia (21%). Seven deaths occurred on study or in follow-up, 6 from PD or complications related to NHL and 1 due to an AE (cytokine release syndrome in a subject who discontinued CC-90002 for PD and enrolled in another trial within the follow-up period). There were no treatment-related deaths. The overall response rate was 13% (95% CI, 2.7−32.4) and the disease control rate was 25% (95% CI, 9.8−46.7; Figure). One subject achieved a durable complete response (8 mg/kg; ongoing in cycle 18) and 2 had partial responses (15 mg/kg and 20 mg/kg); 3 subjects had stable disease. Among responders, the median duration of response was 3.9 months (95% CI, 1.9−3.9). CC-90002 exhibited linear pharmacokinetics at doses ≥15 mg/kg, suggesting target saturation at 15 mg/kg. In addition, a longer half-life was observed at higher (≥15 mg/kg) versus lower doses (t1/2≈ 3−7 days vs 1 day). Conclusions: The CD47-SIRPα checkpoint inhibitor, CC-90002,plus rituximab demonstrated tolerability and modest clinical activity in this early-phase study of heavily pretreated R/R NHL subjects. AEs were predominantly grade 1/2; cytopenias were the most common AEs with dose-limiting thrombocytopenia observed at 30 mg/kg Q2W. In contrast to other CD47-targeting immunotherapies and consistent with results of preclinical studies of CC-90002, hemolysis at a starting dose of up to 30 mg/kg CC-90002 was not observed. These preliminary data support further evaluation of targeting the CD47-SIRPα pathway in combination with rituximab in NHL. Disclosures Abrisqueta: Abbvie: Consultancy, Honoraria, Other: Travel, Accommodations, expenses, Speakers Bureau; Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, expenses, Speakers Bureau; Roche: Consultancy, Honoraria, Other: Travel, Accommodations, expenses, Speakers Bureau. Sancho:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Honoraria, Other: Advisory board; Novartis: Honoraria; Kern Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria; Celltrion: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squib: Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sandoz: Consultancy; F. Hoffmann-La Roche Ltd: Honoraria, Membership on an entity's Board of Directors or advisory committees. Cordoba:Janssen: Consultancy, Honoraria, Speakers Bureau; Servier: Consultancy, Honoraria, Speakers Bureau; Kyowa-Kirin: Consultancy, Honoraria, Speakers Bureau; Gilead: Consultancy, Research Funding, Speakers Bureau; Roche: Honoraria, Speakers Bureau; FUNDACION JIMENEZ DIAZ UNIVERSITY HOSPITAL: Employment; Celgene: Consultancy, Honoraria, Speakers Bureau; Pfizer: Consultancy. Persky:Sandoz: Consultancy; Morphosys: Other: Member, Independent Data Monitoring Committee; Debiopharm: Other: Member, Independent Data Monitoring Committee; Bayer: Consultancy. Andreadis:Juno: Research Funding; Pharmacyclics: Research Funding; Roche: Equity Ownership; Novartis: Research Funding; Jazz Pharmaceuticals: Consultancy; Celgene: Research Funding; Kite: Consultancy; Gilead: Consultancy; Merck: Research Funding; Genentech: Consultancy, Employment. Huntington:Pharmacyclics: Honoraria; Genentech: Consultancy; Bayer: Consultancy, Honoraria; DTRM Biopharm: Research Funding; AbbVie: Consultancy; Celgene: Consultancy, Research Funding. Carpio:University Hospital Vall D'Hebron: Employment. Morillo Giles:Hospital Universitario Fundacion Jimenez Diaz: Honoraria. Wei:Celgene Corp.: Employment, Equity Ownership. Li:Celgene Corp.: Employment, Equity Ownership. Zuraek:Celgene Corp.: Employment, Equity Ownership, Other: Travel, Accommodations, Expenses. Burgess:University of California: Other: Volunteer clinical faculty, without salary, Patents & Royalties: Patent - T315A and F317I mutations of BCR-ABL kinase domain; Celgene Corporation: Employment, Equity Ownership, Patents & Royalties: Patent - CD47 antibodies and methods of use thereof. Hege:Celgene Corporation: Employment, Equity Ownership, Patents & Royalties; Arcus Biosciences: Membership on an entity's Board of Directors or advisory committees; Mersana Therapuetics: Membership on an entity's Board of Directors or advisory committees; Society for Immunotherapy of Cancer: Membership on an entity's Board of Directors or advisory committees. Martín:iQone: Consultancy; Gilead: Consultancy, Honoraria; Roche: Consultancy, Honoraria, Other: Travel Expenses; Celgene: Consultancy, Honoraria, Other: Travel Expenses, Research Funding; Kiowa Kirin: Consultancy; Servier: Honoraria, Other: Travel Expenses; Teva: Research Funding; Janssen: Honoraria, Other: Travel Expenses, Research Funding.

Abstract: Background: CC-122, a pleiotropic pathway modifier, modulates the cullin 4 ring E3 ligase complex, which results in recruitment and degradation of Aiolos and Ikaros. This substrate degradation results in cell autonomous anti-lymphoma and immunomodulatory effects on T- and NK-cell function (Gandhi, ASH 2012). The anti-CD20 monoclonal antibody, obinutuzumab, improves direct cell killing and antibody-dependent cell-mediated cytotoxicity (ADCC) activity compared to rituximab (Mössner, 2010; Niederfellner, 2011). The combination of obinutuzumab with CC-122 revealed synergistic effects in follicular lymphoma (FL) and additive effects in diffuse large B-cell lymphoma (DLBCL) in in vivo models when compared to either as single agents (Hsiling Chiu, ASH 2015). CC-122 monotherapy has shown encouraging activity against DLBCL and FL in a Phase I clinical trial (Rasco, ASH 2013). Obinutuzumab has demonstrated efficacy in patients with relapsed/refractory indolent non-Hodgkin lymphoma (iNHL) (Salles, 2013) and DLBCL (Morschhauser, 2013) and has been approved by the FDA and the European Medicinal Agency for patients with previously treated FL. The current study was designed to evaluate the safety and efficacy of escalating doses of CC-122 in combination with obinutuzumab in patients with relapsed/refractory DLBCL and iNHL (NCT02417285). Methods: Subjects with relapsed/refractory DLBCL and iNHL (FL and marginal zone lymphoma [MZL]) were enrolled in this phase 1b study of CC-122 given orally on 5 out of 7 days per week (5/7 days) for 28 day cycles. Subjects were enrolled in cohorts of escalating dose levels of CC-122 (1.0 mg [n=4] , 2.0 mg [n = 4], 3.0 mg [n = 7] , 4.0 mg [n = 6]), with a fixed dose of obinutuzumab. Obinutuzumab is administered as an intravenous (IV) infusion at a dose of 1000 mg on Days 2, 8, and 15 of Cycle 1 and on Day 1 of Cycles 2 through 8. The initial 4 dose levels evaluated active ingredient in capsule (AIC) CC-122 formulation. In Cohort 5 (3.0 mg, [n = 5] ), subjects received CC-122 formulated capsules. Prophylaxis with granulocyte-colony stimulating factor (G-CSF) was not allowed during Cycle 1. As the study is ongoing, the CC-122 dose will be escalated until the maximum tolerated dose (MTD) is established on the CC-122 formulated capsule, using a modified 3+3 design. Subjects are evaluated for efficacy every 2 cycles(c) through c6 then every 3 cycles through c12, then every 6 cycles. Results: As of 1 June 2016, 26 subjects with relapsed/refractory DLBCL or iNHL were enrolled; all were evaluable for safety. The median age was 60 years and 84.6% were male. Thirteen subjects had DLBCL (50%), 13 (50%) had iNHL (12 FL [46.2%], 1 had MZL [3.8%] ). All subjects were ECOG 0-1. One subject experienced a dose-limiting toxicity (DLT) of Grade 4 neutropenia (Cohort 3) and no dose was considered a non-tolerated dose (NTD). The most common (≥ 10%) study drug-related treatment emergent adverse events (TEAEs) were neutropenia (50%), thrombocytopenia (30.8%), diarrhea, chills, and increased ALT (11.5% each). Seventeen subjects (65.4%) experienced at least one NCI CTCAE grade 3-4 TEAE related to study treatment (most common [≥ 10%] were neutropenia [42.3%] , thrombocytopenia [15.4%], and increased ALT [11.5%] ). Seven subjects experienced at least one serious AE suspected to be related to study treatment by the investigator (infusion related reaction [3 subjects], febrile neutropenia, neutropenia, thrombocytopenia, and pneumonia, [1 subject each] ). The overall response rate (ORR) for the 26 subjects enrolled, as of the efficacy cut off of 7 July 2016, was 53.8% (14/26); 8 of 12 (66.7%) FL, 5/13 (38.5%) DLBCL, and 1/1 MZL. Responses are ongoing in 12 of 14 of these subjects. ORR in the pooled higher dose cohorts of CC-122 (eg, a dose of 3 mg or higher, cohorts 3, 4, and 5) was 66.7% (12 of 18 subjects). Conclusion: The combination of CC-122 and obinutuzumab was well-tolerated in subjects with relapsed-refractory DLBCL and iNHL. AEs observed were consistent with the toxicity profile of CC-122 or obinutuzumab. Response rates observed were promising in this heavily pretreated population. Response rate appears higher in patients with FL however this warrants further investigation in a larger population. An NTD has not been reached and the MTD has not yet been established. Disclosures Michot: Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees. Vitolo:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria; Gilead: Honoraria; Takeda: Honoraria. Zinzani:Karyopharm: Membership on an entity's Board of Directors or advisory committees; Sandoz: Membership on an entity's Board of Directors or advisory committees; Millennium: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Infinity: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Bayer: Honoraria, Membership on an entity's Board of Directors or advisory committees; TG Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Kersten:Celgene: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding. Chiappella:Teva: Speakers Bureau; Janssen-Cilag: Speakers Bureau; Amgen: Speakers Bureau; Pfizer: Speakers Bureau; Roche: Speakers Bureau; Celgene: Speakers Bureau. Sarmiento:Celgene CITRE: Employment, Equity Ownership. Zuraek:Celgene Corporation: Employment, Equity Ownership. Pourdehnad:Celgene Corporation: Employment, Equity Ownership. Hege:Celgene Corporation: Employment, Equity Ownership. Nikolova:Celgene International: Employment, Equity Ownership. Ribrag:BMS: Membership on an entity's Board of Directors or advisory committees; ArgenX: Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Infinity: Membership on an entity's Board of Directors or advisory committees; Esai: Membership on an entity's Board of Directors or advisory committees; Pharmamar: Membership on an entity's Board of Directors or advisory committees; NanoString: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees.

Abstract: Standard-of-care treatment for newly diagnosed glioblastoma (ndGBM), consisting of surgery followed by radiotherapy (RT) and temozolomide (TMZ), has improved outcomes compared with RT alone; however, prognosis remains poor. Trotabresib, a novel bromodomain and extraterminal inhibitor, has demonstrated antitumor activity in patients with high-grade gliomas. Methods In this phase Ib, dose-escalation study (NCT04324840), we investigated trotabresib 15, 30, and 45 mg combined with TMZ in the adjuvant setting and trotabresib 15 and 30 mg combined with TMZ+RT in the concomitant setting in patients with ndGBM. Primary endpoints were to determine safety, tolerability, maximum tolerated dose, and/or recommended phase II dose (RP2D) of trotabresib. Secondary endpoints were assessment of preliminary efficacy and pharmacokinetics. Pharmacodynamics were investigated as an exploratory endpoint. Results The adjuvant and concomitant cohorts enrolled 18 and 14 patients, respectively. Trotabresib in combination with TMZ or TMZ+RT was well tolerated; most treatment-related adverse events were mild or moderate. Trotabresib pharmacokinetics and pharmacodynamics in both settings were consistent with previous data for trotabresib monotherapy. The RP2D of trotabresib was selected as 30 mg 4 days on/24 days off in both settings. At last follow-up, 5 (28%) and 6 (43%) patients remain on treatment in the adjuvant and concomitant settings, respectively, with 1 patient in the adjuvant cohort achieving complete response. Conclusions Trotabresib combined with TMZ in the adjuvant setting and with TMZ+RT in the concomitant setting was safe and well tolerated in patients with ndGBM, with encouraging treatment durations. Trotabresib 30 mg was established as the RP2D in both settings.