Johnson, Kathryn

Abstract Background/rationale Primary myelofibrosis (PMF) and post-polycythemia vera/essential thrombocythemia (Post-PV/ET MF) (collectively termed MF) are chronic hematopoietic malignancies with progressive bone marrow collagen fibrosis, peripheral cytopenias, extramedullary hematopoiesis, splenomegaly, debilitating constitutional symptoms and heightened risk of transformation to acute leukemia. The only currently approved therapies for MF are JAK inhibitors (JAKi) which can provide significant improvements in splenomegaly and systemic symptoms but do not fundamentally change the pathogenesis of the disease. As a result, additional non-JAKi therapies for patients with MF after JAKi failure represent an important translational focus. Reparixin is a novel, potent and specific inhibitor of the chemokine CXCL8 (IL)-8. IL-8 is a member of a class of cytokines involved in leukocyte recruitment and activation in tissues. There are two known types of CXCL8 receptors – CXCR1 and CXCR2, which are expressed in neutrophils (Baggiolini M, Adv Immunol 1994). IL-8/CXCR1/2 signaling has been shown to be a key mediator of inflammatory signaling in MF patients. Hematopoietic stem/progenitor cells from patients with MF are enriched for a CXCL8/CXCR2 gene signature and display enhanced proliferation and fitness in response to an exogenous CXCL8 ligand in vitro. Genetic deletion or a small molecule inhibitor of CXCR2 in MF mouse adoptive transfer models ameliorates fibrosis, extends overall survival and improves hematologic parameters (Dunbar A, Blood 2023). This pre-clinical data validates targeting this pathway in clinical investigations. Study design This is an open-label, phase II study assessing the efficacy, safety, and tolerability of reparixin in patients with Dynamic International Prognostic Scoring System (DIPSS) intermediate-2, or high-risk PMF, post ET/PV MF either after prior treatment with, or those who are ineligible for treatment with a JAKi. Patients will receive oral reparixin 1200 mg three times daily on a four-week cycle for a core study period of 24 weeks. Patients who achieve at least clinical improvement (CI) or stable disease (SD) with one grade improvement in bone marrow fibrosis by International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) criteria at the Cycle 7 response assessment may continue receiving reparixin until loss of response, disease progression, unacceptable toxicity, patients/physician withdrawal, or termination of study by sponsor. The study monitors both efficacy and toxicity using a Bayesian Optimal Phase 2 (BOP2) design. If response is observed in at least one patient out of 10 and safety is confirmed at the interim analysis, the trial will proceed to full enrollment of 26 patients. If more than three responses are observed in the total cohort, then a signal of activity is confirmed. Primary Objective: To estimate the efficacy of reparixin treatment in DIPSS intermediate-2 or high-risk subjects with PMF, post PV-MF, or post ET-MF. Secondary Objectives: To assess the efficacy of reparixin as determined by response assessment using IWG-MRT/ELN criteria at the end of Cycle 6 and Cycle 12. To assess the change in bone marrow fibrosis grade at the end of Cycle 6 and Cycle 12 with reparixin. To assess the safety of reparixin as measured by the adverse event profile of Common Terminology Criteria for Adverse Events v5.0. To assess spleen volume reduction by imaging after Cycle 6 and Cycle 12 as compared to baseline spleen volume. Key Exploratory Objectives: To evaluate changes in quality of life and patient-reported outcomes To conduct correlative studies to measure biomarkers of reparixin activity, such as Vascular Endothelial Growth Factor (VEGF) levels, bone marrow microvessel density, megakaryocyte number and peripheral blood CD34+ cell number, and patients with and without IL-8 secretion. Key inclusion criteria: Have a pathologically confirmed diagnosis of PMF, post-ET-MF, or post-PV-MF as per the WHO diagnostic criteria with intermediate-2 or higher risk disease by DIPSS Be refractory/resistant to or intolerant of/inappropriate for JAKi therapy Have adequate liver and kidney function Platelet count ≥ 25 x 109/L Bone marrow and peripheral blood blast count < 10% ANC ≥ 1000 mm3. MPN Research Consortium (MPN-RC) 120 is currently enrolling patients through the MPN-RC clinical sites throughout the United States. Clinical Trial Identifier NCT05835466

Abstract TGFβ plays a pivotal role in the pathobiology of myelofibrosis (MF) by not only promoting bone marrow fibrosis (BMF) but also by enhancing the dormancy of normal but not MF hematopoietic stem cells (HSCs). TGFβ has also previously been reported to inhibit normal megakaryocyte (MK) production (Bruno et al Blood 1998). TGFβ1 promotes the synthesis of collagen by normal human mesenchymal stromal cells (MSCs). Treatment of MSCs with AVID200, a potent TGFβ1/3 protein trap, significantly decreased MSC proliferation, phosphorylation of SMAD2, and collagen expression. Robust expression of pSMAD2 was observed in the absence of exogenous TGFβ in normal donor or MF-MKs, Addition of AVID200 to MKs decreased pSMAD2 without affecting total SMAD2/3 and led to increased numbers of MKs. Treatment of MF MNCs with AVID200 also led to increased numbers of progenitor cells with wild type JAK2 and a reduction of mutated colonies. A phase 1b trial of AVID200 (NCT03895112) was performed and completed in INT-2/high risk MF patients resistant/intolerant to ruxolitinib (rux); baseline platelet count of ≥ 25 x 10 9/L, and grade 2/3 BMF. Subjects received AVID200 intravenously on Day 1 of a 21 day cycle. Response was assessed by IWG/ELN criteria after 6 cycles of AVID200. Subjects attaining at least a CI or SD with a decrease in BMF by ≥1 grade, continued AVID200. We previously presented the results of the dose escalation study (Mascarenhas ASH 2020) demonstrating that AVID200 was well tolerated without dose limiting toxicities at 3 tested dose levels (Lots A and B) in dose cohorts of 180 mg (A), 550 mg (A)/70 mg (B), and 180 mg (B). Here we report updated safety and efficacy results of the phase 1b dose expansion stage at the two highest doses tested (70 mg (B) and 180 mg (B). Twenty-two subjects were enrolled (1 withdrew before receiving treatment) and 9 were treated with AVID200 in the dose escalation phase and 12 in the dose expansion phase [Table1]. Median time after rux discontinuation was 7.4 months (0.5-59.9). The most common mutations observed at baseline in this cohort included JAK2V617F (71%), TET2 (29%) ASXL1 (24%) and CALR (19%). (Fig 1) No DLTs were observed and Grade 3/4 AEs were observed in 16 (76.2%) subjects. Grade 3/4 non-hematologic AEs were observed in 8 (38.1%) subjects and included one subject in each case (epistaxis, mucositis, extraocular muscle paresis, fatigue, rash, duodenal hemorrhage, gastric hemorrhage, urinary tract infection, and syncope). Grade 3/4 hematologic AEs were anemia (6; 28.3%) and thrombocytopenia (2; 14.3%) [Table 2]. No fatal events were observed. The median number of cycles received was 5 (range 2 - 13) and 7 (33%) patients received more than 6 cycles. For dose levels 2-3 at cycle 7, a CI was attained in one subject at dose level 2 [anemia, spleen and TSS], 5 subjects had SD, 3 subjects had PD and two subjects with 10% and 15% blasts at screening developed MPN-BP while on study based on central review. Reasons for discontinuation by local PI included PD (n=8), lack of response (n=5), study completed (n=2), other (n=2), patient decision (n=1). Median % change in palpable spleen length was +10% (range -70% to +150%) and TSS change was -50% (-100% to +185.7%) The median platelet count at baseline was 114 x 10 9/L (range: 28-695) and 215 x 10 9/L (range: 66-263) after cycle 6 in 7 evaluable subjects (Fig 2A). Notably, 17 subjects had an increase in platelets from baseline during treatment and two subjects normalized their platelet counts. Maximum changes in platelets from baseline across all cycles was +63.8% [range -15.7%, +505.5%] (Fig 2B). Paired bone marrow biopsy pathology samples for 12 subjects were available for central review and showed no significant changes in BMF score or MK histo topography at end of treatment compared to baseline. All patients had elevated plasma levels of TGF β1, but not TGFβ2/β3 levels as detected by ELISA, which were dramatically reduced 21 days after the last dose of AVID200. AVID200 a TGFβ1/3 protein trap is well tolerated and clinical responses at cycle 7 of therapy in this advanced MF patient population were limited as judged by IWG/MRT response criteria. However, AVID200 therapy resulted in significant reduction in serum TGFβ levels and improvements in platelet counts indicating that TGF β1 plays a pivotal role in MF leading to thrombocytopenia which can be reversed with AVID200 therapy. We conclude that AVID200 may best be employed in combination therapy approaches in thrombocytopenic MF patients. Figure 1 Figure 1. Disclosures Mascarenhas: Constellation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Promedior: 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; Geron: Consultancy, Research Funding; Forbius: Research Funding; Genentech/Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; 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; 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; Galecto: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Prelude: Consultancy; Kartos: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; CTI Biopharm: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Geron: Consultancy; 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; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merus: Research Funding. Palmer: PharmaEssentia: Research Funding; Sierra Oncology: Consultancy, Research Funding; Incyte: Research Funding; CTI BioPharma: Consultancy, Research Funding; Protagonist: Consultancy, Research Funding. Kuykendall: Celgene/BMS: Honoraria; Pharmaessentia: Honoraria; Novartis: Honoraria, Speakers Bureau; Protagonist: Consultancy, Research Funding; Incyte: Consultancy; Abbvie: Honoraria; Blueprint: Honoraria. Mesa: Genentech: Research Funding; Promedior: Research Funding; Samus: Research Funding; Gilead: Research Funding; CTI: Research Funding; Abbvie: Research Funding; Sierra Oncology: Consultancy, Research Funding; Celgene: Research Funding; Novartis: Consultancy; Pharma: Consultancy; CTI: Research Funding; Constellation Pharmaceuticals: Consultancy, Research Funding; AOP: Consultancy; La Jolla Pharma: Consultancy; Incyte Corporation: Consultancy, Research Funding. Rampal: Stemline: Consultancy, Research Funding; Memorial Sloan Kettering: Current Employment; BMS/Celgene: Consultancy; Abbvie: Consultancy; CTI: Consultancy; Novartis: Consultancy; Disc Medicine: Consultancy; Blueprint: Consultancy; Pharmaessentia: Consultancy; Incyte: Consultancy, Research Funding; Jazz Pharmaceuticals: Consultancy; Constellation: Research Funding; Kartos: Consultancy; Sierra Oncology: Consultancy. Gerds: PharmaEssentia Corporation: Consultancy; Sierra Oncology: Consultancy; CTI BioPharma: Research Funding; Constellation: Consultancy; Celgene/Bristol Myers Squibb: Consultancy; AbbVie: Consultancy; Novartis: Consultancy. Yacoub: Novartis: Consultancy, 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; ACCELERON PHARMA: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Dynavex: Current equity holder in publicly-traded company; Cara: Current equity holder in publicly-traded company; Ardelyx: Current equity holder in publicly-traded company; Seattle Genetics: Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria, Speakers Bureau; Hylapharm: Current equity holder in publicly-traded company. Talpaz: Imago: Consultancy; Constellation: Membership on an entity's Board of Directors or advisory committees; 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; Takeda: Other: Grant/research support ; Celgene: Consultancy. Komrokji: Acceleron: Consultancy; Taiho Oncology: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; BMSCelgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; PharmaEssentia: 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; Geron: Consultancy; Jazz: Consultancy, Speakers Bureau. Kremyanskaya: Astellas: Research Funding; Astex: Research Funding; Chimerix: Research Funding; Bristol Myers Squibb: Research Funding; Constellation: Research Funding; Protagonist Therapeutics: Consultancy, Research Funding; Incyte: Research Funding. 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. Hoffman: Kartos Therapeutics, Inc.: Research Funding; Protagonist Therapeutics, Inc.: Consultancy; Novartis: Other: Data Safety Monitoring Board, Research Funding; AbbVie Inc.: Other: Data Safety Monitoring Board, Research Funding. OffLabel Disclosure: AVID200 is a TGFb trap and is in clinical testing for fibrotic diseases. It does not have an approved indication at this time.

Abstract Myelofibrosis (MF) is a clonal stem cell neoplasm characterized by abnormal JAK-STAT signaling, chronic inflammation, cytopenias, and risk of transformation to acute leukemia. Despite improvements in the therapeutic options for patients with MF, allogeneic hematopoietic stem cell transplantation remains the only curative treatment. We previously demonstrated multiple immunosuppressive mechanisms in patients with MF, including increased expression of programmed cell death protein 1 (PD-1) on T cells compared with healthy controls. Therefore, we conducted a multicenter, open-label, phase 2, single-arm study of pembrolizumab in patients with Dynamic International Prognostic Scoring System category of intermediate-2 or greater primary, post-essential thrombocythemia or post-polycythemia vera myelofibrosis that were ineligible for or were previously treated with ruxolitinib. The study followed a Simon 2-stage design and enrolled a total of 10 patients, 5 of whom had JAK2V617mutation, 2 had CALR mutation, and 6 had additional mutations. Most patients were previously treated with ruxolitinib. Pembrolizumab treatment was well tolerated, but there were no objective clinical responses, so the study closed after the first stage was completed. However, immune profiling by flow cytometry, T-cell receptor sequencing, and plasma proteomics demonstrated changes in the immune milieu of patients, which suggested improved T-cell responses that can potentially favor antitumor immunity. The fact that these changes were not reflected in a clinical response strongly suggests that combination immunotherapeutic approaches rather than monotherapy may be necessary to reverse the multifactorial mechanisms of immune suppression in myeloproliferative neoplasms. This trial was registered at www.clinicaltrials.gov as #NCT03065400.