Rowley, Scott D

PURPOSE Older patients with relapsed or refractory AML (RR AML) have dismal prognoses without allogeneic hematopoietic cell transplantation (alloHCT). SIERRA compared a targeted pretransplant regimen involving the anti-CD45 radioconjugate 131 I-apamistamab with conventional care. METHODS SIERRA (ClinicalTrials.gov identifier: NCT02665065 ) was a phase III open-label trial. Patients age ≥55 years with active RR AML were randomly assigned 1:1 to either an 131 I-apamistamab–led regimen before alloHCT or conventional care followed by alloHCT if initial complete remission (CR)/CR with incomplete platelet recovery (CRp) occurred. Initial response was assessed 28-56 days after alloHCT in the 131 I-apamistamab group and 28-42 days after salvage chemotherapy initiation; patients without CR/CRp or with AML progression could cross over to receive 131 I-apamistamab followed by alloHCT. The primary end point was durable complete remission (dCR) lasting 180 days after initial CR/CRp. Secondary end points were overall survival (OS) and event-free survival (EFS), assessed hierarchically in the intention-to-treat (ITT) population. RESULTS The ITT population included 153 patients ( 131 I-apamistamab [n = 76]; conventional care [n = 77]). In total, 44/77 conventional care arm patients crossed over and 40/77 (52%) received 131 I-apamistamab and alloHCT, with six patients (13.6%) experiencing a dCR. In the ITT population, the dCR rate was significantly higher with 131 I-apamistamab (17.1% [95% CI, 9.4 to 27.5]) than conventional care (0% [95% CI, 0 to 4.7]; P < .0001). The OS hazard ratio (HR) was 0.99 (95% CI, 0.70 to 1.41; P = .96), and the EFS HR was 0.23 (95% CI, 0.15 to 0.34), with HR <1 favoring 131 I-apamistamab. Grade ≥3 treatment-related adverse events occurred in 59.7% and 59.2% of the 131 I-apamistamab and conventional care groups, respectively. CONCLUSION The 131 I-apamistamab–led regimen was associated with a higher dCR rate than conventional care in older patients with RR AML. 131 I-apamistamab was well tolerated and could address an unmet need in this population.

Introduction: Failure to engraft donor cells is a devastating complication after allogeneic hematopoietic cell transplantation (HCT) while full engraftment remains a challenge in some recipients. Therapeutic approaches, such as recombinant hematopoietic growth factors, salvage only a minority of patients leaving affected patients at risk for recurrent infections and multiple blood products transfusions. PLX-R18 cells have been shown to mitigate bone marrow failure in rodent and non-human primate models. Further, these human placenta-derived mesenchymal-like adherent stromal cells secrete many cytokines after intramuscular (IM) injection that have been shown to stimulate growth and migration of bone marrow cells in vitro, e.g. MCP-1, IL-6, and IL-8. The initial results of the first cohort of this phase I trial were previously reported (ASH 2018 abstract 3379). Methods: Enrollment for this multi-center, open label, dose-escalation, phase I trial (ClinicalTrials.gov: NCT03002519) began in October 2017. Eligibility criteria included patients age ≥18 years who underwent either autologous (auto) or allogeneic (allo) HCT but suffered from incomplete hematopoietic recovery at least 3 months post-transplant, defined as failure to maintain either hemoglobin (Hb) &gt;8g/dL and/or neutrophil count (ANC) &gt;1,000/μL and/or platelet (PLT) count &gt;50,000/μL. Other eligibility criteria included no evidence of underlying malignancy at time of enrollment, no active infection and no evidence of grade 3-4 acute or severe chronic GvHD. Subjects were enrolled into 3 dose-escalating cohorts: low-dose at 1M cells/kg (n=3), intermediate-dose at 2M cells/kg (n=6), and high-dose at 4M cells/kg (n=10). The specified dose of PLX-R18 cells was injected IM in multiple locations and given twice, 1 week apart. Cohorts were recruited sequentially, and progression to the next cohort was based on the safety assessment of its predecessor. Adverse event grading used the NCI CTCAE criteria. As of July 2020, all patients in cohorts 1 and 2 (3 & 6 patients, respectively) and 10 patients in cohort 3 were treated. Data were analyzed using the lmerTest package (ver. 3.1.0) in R (ver. 3.6.1) to produce baseline-adjusted least square means. As study is in progress and data collection ongoing, not all subjects have data on all parameters for all time points. Results: Data on 19 subjects (29-75 yrs) with either allo (n=17) or auto (n=2) HCT are reported herein. Not all patients reached the 9 month time point. Four patients died while on study and 2 withdrew consent within the 1 year follow up period. All deaths and other severe adverse events (SAEs) occurred due to progression of primary disease and were assessed as not related by investigators and sponsor. Most frequent related AEs were injection-site reactions. The table summarizes number of patients who improved from below the critical level, as defined above, at day 0 to above the critical level for a sustained period. Only those patients that were below the critical blood levels at day 0 are shown. To date, the majority of such patients improved to above the critical level after treatment. For example, 9 patients had ANC &lt;1000/μL at day 0. Of the 4 patients for which data currently exists, all improved to ≥1000/μL at 9 months. The plots show changes in Hb, ANC and PLT up to 9 months following treatment. The dashed lines represent respective critical levels. Overall, there was improvement in the 3 parameters, with the greatest improvement observed in patients receiving the predicted optimal dose of 4M cells/kg. In this cohort, Hb levels increased from 9.29±0.5 to 13.19±1.2 (p=0.0019), ANC increased from 1.09±0.6 to 5.13±1.7 (p=0.018) and PLT increased from 45.7±10 to 175.9±28 (p=0.000012). Conclusions: Treatment with PLX-R18 is safe, well-tolerated and clearly effective in some patients. The most frequent AEs were reversible injection site reactions, all without sequelae. An overall improvement was observed in most patients, and among the high-dose cohort clinically impressive improvements in Hb, ANC and PLT were observed. The trial continues to follow up on patients. Upon completion, a large phase II trial, using the optimal dose, is considered for the same indication. Other attractive clinical areas for PLX-R18 therapy include acute radiation syndrome, bone marrow failure, aplastic anemia, myelofibrosis and with HCT as a "pan" cytokine to enhance rapid count recovery in all cells lines. Figure Disclosures Lazarus: Pluristem ltd: Consultancy. McGuirk:Astellas: Research Funding; Bellicum Pharmaceutical: Research Funding; Gamida Cell: Research Funding; Pluristem Ltd: Research Funding; Kite Pharmaceuticals: Consultancy, Honoraria, Research Funding, Speakers Bureau; Allo Vir: Consultancy, Honoraria, Research Funding; Juno Therapeutics: Consultancy, Honoraria, Research Funding; Novartis: Research Funding; Fresenius Biotech: Research Funding. Rowley:AbbVie: Current equity holder in publicly-traded company; FATE Therapeutics: Consultancy. Ofir:Pluristem: Current Employment. Shani:Pluristem ltd: Current Employment. Rowe:Pluristem ltd: Consultancy.

Abstract Introduction: Midostaurin, a multitargeted tyrosine kinase inhibitor (TKI), plus induction and consolidation chemotherapy followed by single-agent midostaurin maintenance therapy resulted in significant benefits in event-free and overall survival (OS) in adults with newly diagnosed FLT3-mutated acute myeloid leukemia (AML) compared with placebo (RATIFY study; Stone et al, N Engl J Med, 2017). In RATIFY, patients who received allogeneic hematopoietic stem cell transplant (alloSCT) did not receive midostaurin maintenance. Despite alloSCT providing the highest likelihood of sustained remission, relapse rates remain high (30%-59%; Schiller et al, Biol Blood Marrow Transplant, 2016), especially in patients with FLT3-internal tandem duplication-positive (ITD+) AML. Posttransplant maintenance therapy may improve this outcome. Here, we report the primary results from RADIUS, a randomized, open-label, phase 2 exploratory trial (NCT01883362) that investigated whether the addition of midostaurin to standard of care (SOC) after alloSCT could reduce the risk of relapse in patients with FLT3-ITD+ AML. Methods: Adults (aged 18-70 y) who had undergone myeloablative alloSCT in first complete remission (CR1), had achieved hematologic recovery, and were transfusion independent were eligible. Patients enrolled postengraftment and were randomized to receive SOC with or without midostaurin 50 mg twice daily continuously (4-week cycles) for up to 12 cycles. Study treatment started 28 to 60 days post-alloSCT and patients were followed for ≥24 months post-alloSCT. The primary endpoint was relapse-free survival (RFS) at 18 months post-alloSCT. Secondary endpoints included safety and disease-free survival (DFS), OS, and RFS at 24 months post-alloSCT. The study was not adequately powered to detect a statistical difference between the 2 arms; a sample size of 60 was calculated to detect a 50% reduction in the risk of relapse. Results: 60 patients were randomized (30 per arm). Baseline characteristics were generally balanced between the 2 arms. Overall, 30 patients completed 12 cycles of study treatment (14 with SOC; 16 with midostaurin). The median exposure to midostaurin was 10.5 months (range, 0.2 to 12.0 months) and the median dose intensity was 93 mg/day (range, 15-100 mg/day). Early treatment discontinuations were similar between arms (15 in the SOC arm; 13 in the midostaurin arm), frequently due to adverse events (AEs; 3% vs 23%) and consent withdrawal (20% vs 7%). Among 6 patients who withdrew consent in the SOC arm, 2 did so to pursue other TKI therapies. Midostaurin dose modifications occurred in 19 patients (63%), mostly due to AEs (84%); 1 instance was due to receiving a concomitant CYP3A4 inhibitor. With an estimated 18-month RFS (95% CI) of 76% (54%-88%) in the SOC arm and 89% (69%-96%) in the midostaurin arm, estimated relapse rates were 24% and 11%, respectively, which is a 46% relative reduction in the risk of relapse with the addition of midostaurin (Figure 1). At 18 months, the median RFS was not reached in either arm. Longer follow-up at 24 months (data not yet matured) will be presented, including RFS, OS, and DFS. In the SOC and midostaurin arms, AEs were reported in 87% and 100% of patients, respectively (the most common any-grade AE was vomiting: 23% vs 73%; Figure 2); serious AEs were reported in 57% and 30% of patients, respectively, with diarrhea (7% vs 13%), nausea (10% vs 3%), vomiting (10% vs 3%), and pyrexia (7% vs 7%) being the most common. Overall, 8 patients discontinued midostaurin therapy due to AEs (mostly gastrointestinal related) and 12 died on study (all during the follow-up phase; 8 in the SOC arm and 4 in the midostaurin arm [n=4 vs n=2 due to AML disease progression]). Rates of graft-vs-host disease (GVHD) were generally similar between the SOC and midostaurin arms (overall, 70% vs 73%; acute GVHD, 53% vs 57% [grade 2/3 events: 37% vs 30%; no grade 4 events]; chronic GVHD, 47% vs 37% [most events were mild or moderate; severe events: 1 with SOC and 2 with midostaurin]). Conclusions: Adding midostaurin to SOC reduced the risk of relapse at 18 months post-alloSCT by 46% (vs SOC). The safety profile of single-agent midostaurin was consistent with previous reports; no major safety concerns were identified when adding midostaurin to SOC following alloSCT. These data suggest that midostaurin monotherapy can be safely administered for ≤1 year and may improve outcomes in patients who undergo alloSCT in CR1. Disclosures Maziarz: Novartis Pharmaceuticals Corporation: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Consultancy, Honoraria; Juno Therapeutics: Consultancy, Honoraria; Kite Therapeutics: Honoraria; Athersys, Inc.: Patents & Royalties. Scott:Agios: Consultancy; Novartis: Research Funding; Celgene: Consultancy, Research Funding; Alexion: Consultancy. Deol:Kite Pharmaceuticals: Consultancy; Novartis: Consultancy. Kim:Novartis: Consultancy, Honoraria, Research Funding; Briston-Meyers Squibb: Consultancy, Honoraria, Research Funding; Paladin: Consultancy; Pfizer: Consultancy. Haines:Novartis: Employment. Bonifacio:Novartis: Employment. Rine:Novartis: Employment. Purkayastha:Novartis Pharmaceuticals Corporation: Employment.

Abstract Introduction Midostaurin is an orally available multikinase inhibitor that blocks FLT3 kinase activity. FLT3 mutations are associated with more frequent and earlier relapses and worse survival. The phase 3 RATIFY trial showed that midostaurin compared with placebo improved overall and event-free survival in newly diagnosed pts with FLT3-mutated AML when administered in combination with standard chemotherapy and as single-agent maintenance (Stone et al, ASH 2015). The ongoing RADIUS trial (NCT01883362) is investigating whether adding midostaurin to SOC after alloHSCT reduces the risk of relapse in pts with FLT3-ITD-mutated AML. Here we report safety data from the first 56 enrolled pts. Methods RADIUS is a randomized, open-label, phase 2 study comparing SOC vs midostaurin + SOC after alloHSCT in adult pts with AML with FLT3-ITD mutations (planned enrollment, N = 60). Study treatment started 28-60 days after alloHSCT. SOC was dictated by the treating physician. Pts were randomized to either SOC or midostaurin 50 mg twice daily + SOC (hereafter called the midostaurin arm) continuously for ≤ 12 months and will be followed up for ≥ 24 months. The study was designed to look for any safety or efficacy signals and not powered to find differences between study treatments. The primary endpoint is relapse-free survival at 18 months after alloHSCT. Adverse events (AEs) were followed up for 30 days after treatment. Key inclusion criteria are documented FLT3-ITD mutation, age 18-70 years, and first complete remission status. Pts could enroll after the date of engraftment and hematologic recovery to an absolute neutrophil count > 1000/μL and platelet count ≥ 20,000/μL without requiring transfusion. Results Pts were randomized from Feb 5, 2014, to Jun 13, 2016. The 2 arms (n = 28 each) were balanced regarding age, sex, and race. Most pts (93%) had de novo AML. At data cutoff (Jun 3, 2016), data were not mature enough to evaluate efficacy. Median (range) follow-up in the SOC and midostaurin arms was 240 (3-786) and 234 (3-656) days, respectively. Overall, 18 pts (64%) in the SOC arm and 19 pts (68%) in the midostaurin arm stopped treatment. Of these, 10 (36%) and 8 (29%) in the SOC and midostaurin arms, respectively, completed 12 months of treatment. Other reasons for stopping treatment were relapse (2 [7%] and 2 [7%]), death (2 [7%] and 0 [0%]), administrative problems (2 [7%] and 1 [4%]), withdrawn consent (1 [4%] and 3 [11%]), abnormal test results (1 [4%] and 0 [0%]), and AEs (0 [0%] and 4 [14%]). In the 24 pts who received ≥ 1 dose in the midostaurin arm, the median midostaurin dose was 76.2 (range, 25-100) mg daily. In the 15 pts (54%) who required a dose change, the reasons for dose changes were AEs (13 [46%]), dosing error (3 [11%]), re-escalation (3 [11%]), abnormal test results (2 [7%]), per protocol (2 [7%]), use of concomitant strong CYP3A4 inhibitors (1 [4%]), and other reasons (4 [14%]). The most common any-grade (Gr) AEs were fatigue (29%) and AST, headache, nausea and vomiting (all 25%) in the SOC arm and nausea and vomiting (both 64%) and diarrhea (43%) in the midostaurin arm (Figure 1). The most common Gr 3/4 AEs were nausea and hypertension in the SOC arm (all 3 [11%] each) and diarrhea, increased ALT, neutrophil count decreased (all 3 [11%] each) and platelet count decreased (5 [18%]) in the midostaurin arm. No on-treatment deaths occurred in the midostaurin arm. AEs led to discontinuation of midostaurin in 4 pts and included Gr 1 nausea, Gr 2 nausea and vomiting, Gr 3 lung infection, and Gr 2 elevated liver enzymes (n = 1 each). All of these except the lung infection were considered related to midostaurin. Graft-vs-host disease (GVHD) occurred in 16 pts (57%) in the SOC arm and 18 pts (64%) in the midostaurin arm (Figure 2). No stage ≥ 3 organ involvement occurred. Most cases of GVHD (11 [39%] in the SOC arm and 17 [61%] in the midostaurin arm) were acute. The most commonly affected organ was the skin (11 [39%] and 13 [46%], respectively, of which 5 [18%] and 4 [14%], respectively, were stage 2). Conclusions The preliminary safety data in the post-alloHSCT setting was consistent with data from other studies. Rates of Gr 1/2 nausea, vomiting, and diarrhea were higher in the midostaurin arm. Midostaurin did not change rates of GVHD. Because of the limited duration of follow-up, effects on chronic GVHD are unknown. Follow-up is ongoing, with efficacy data anticipated in 2017. Disclosures Maziarz: Athersys: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Scott:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Research Funding, Speakers Bureau; Alexion: Speakers Bureau; Agios: Membership on an entity's Board of Directors or advisory committees. Deol:Jazz Pharmaceuticals: Consultancy. Haines:Novartis: Employment. Bonifacio:Novartis: Employment. Rine:Novartis: Employment. Fernandez:Fate Pharmaceuticals: Honoraria; Chimerix: Honoraria; Sanofi: Speakers Bureau.