Smith, Catherine C.

Background: The FMS-like tyrosine kinase 3 (FLT3) inhibitor gilteritinib (Gilt) improves survival compared with standard salvage chemotherapy in relapsed/refractory (R/R) FLT3-mutated (FLT3mut+) acute myeloid leukemia (AML); however, relapses are common and long-term survival remains poor. Combination therapies of FLT3 tyrosine kinase inhibitors (TKIs) with agents that induce apoptosis have demonstrated preclinical synthetic lethality and enhanced cytotoxicity against FLT3mut+ clones. This may delay or prevent drug resistance. We present updated data from the dose-escalation and expansion cohorts of an ongoing, multicenter, open-label, Phase 1b trial (NCT03625505) of Gilt in combination with B-cell lymphoma 2 (BCL-2) inhibitor venetoclax (Ven) in patients (pts) with R/R FLT3mut+ AML. Methods: Pts with R/R AML with ≥1 prior line of therapy and Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 were eligible. The expansion cohort required FLT3mut+ R/R AML at enrollment. Pts received the recommended Phase 2 dose (RP2D) of Ven 400 mg in combination with Gilt 120 mg daily in 28-day cycles, following a 3-day ramp-up of Ven. Pts with prior Gilt were excluded from expansion, and none were enrolled in dose escalation; prior Ven or other FLT3 inhibitor was permitted. Concurrent use of moderate or strong CYP3A4 inhibitor was allowed. Interruptions of Ven or both drugs simultaneously were permitted for management of adverse events (AEs), and subsequent cycles could include dose adjustments to minimize myelosuppression or other drug-related AEs. The primary endpoint was modified composite complete remission (mCRc; complete response [CR] + CR with incomplete platelet recovery [CRp] + CR with incomplete blood count recovery [CRi]) + morphologic leukemia-free state (MLFS). Responses were graded by the International Working Group (IWG) for AML criteria (with adapted CRi criteria as presented in the ADMIRAL trial) for comparison with composite CR (CRc) used in Gilt development. All criteria for response used by IWG were maintained in these response definitions. Secondary endpoints included CR + CR with partial hematologic recovery (CRh) and duration of response (DOR) of mCRc. Results: At data cutoff, April 15, 2020, 39 R/R pts started therapy at the RP2D (internal tandem duplications [ITD] only [n=32]; tyrosine kinase domain [TKD] mutation only [n=5]; both TKD and ITD [n=2]). Median age was 63 years (range 23-85) and the majority had an ECOG status of 1-2 (87.2%). Most pts (n=29; 74.4%) had received ≥2 prior lines of therapy, including ≥1 FLT3 TKI (n=25, 64.1%; midostaurin, n=19; sorafenib, n=5; crenolanib, n=1). Twelve pts (30.8%) had prior stem-cell transplant (SCT); 3 (7.7%) had received prior Ven. Grade ≥3 treatment-emergent AEs (TEAEs) were reported in 37 pts (94.9%), and 28 (71.8%) reported serious AEs. The only Grade 3/4 nonhematologic TEAE reported in >20% of pts was febrile neutropenia (48.7%). Four pts (10.3%) experienced a fatal AE, including colitis, disease progression, multiple organ dysfunction syndrome, and bronchopulmonary aspergillosis (all n=1). AEs leading to Ven and Gilt interruptions occurred in 19 pts (48.7%) and 18 pts (46.2%), respectively, and AEs leading to dose reductions occurred in 2 pts (5.1%) for each treatment. Six pts (15.4 %) and 5 pts (12.8%) discontinued Ven and Gilt, respectively, owing to AEs. mCRc was achieved by 83.8% of pts (n=31/37; Table). With median duration of follow-up of 2.9 (range 0.8−11.0) months in all pts, median event-free survival was 5.1 (95% confidence interval: 2.8, 8.3) months but administrative censoring after short follow-up for a large number of recently enrolled patients limits interpretation; median DOR has not been reached. Eight pts (21.6%), all ITD only, proceeded to SCT. CR + CRh was achieved by 7 pts (18.9%). Conclusions: Ven plus Gilt achieved a very high overall rate of marrow and blood blast elimination and mCRc rate (84%) in this expansion cohort of heavily pretreated FLT3mut+ pts, the majority of whom had prior FLT3 TKI exposure. Using similar response assessment criteria, the high mCRc rate here suggests substantially greater antileukemic activity from Ven plus Gilt compared with single-agent Gilt. Cytopenias were prominent but manageable with dose interruption/modification on subsequent cycles. Nonhematologic toxicities were modest, and the combination was well tolerated. Disclosures Daver: Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Research Funding; Servier: Research Funding; Genentech: Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novimmune: Research Funding; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Trovagene: Research Funding; Fate Therapeutics: Research Funding; ImmunoGen: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Trillium: Consultancy, Membership on an entity's Board of Directors or advisory committees; Syndax: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Altman:AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Fujifilm: Research Funding; Astellas: Other: Advisory Board, Speaker (no payment), Steering Committee (no payment), Research Funding; Agios, Theradex, Abbvie: Other: Advisory Board; Astellas, Agios: Honoraria, Research Funding; Glycomimetics: Other: Data safety and monitoring committee; Daiichi Sankyo: Other: Advisory Board - no payment but was reimbursed for travel; Kura Oncology: Patents & Royalties: Scientific Advisory Board - no payment accepted; Biosight: Other: No payment but was reimbursed for travel . Levis:Menarini: Honoraria; Amgen: Honoraria; FujiFilm: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria; Astellas: Honoraria, Research Funding. Ritchie:Abbvie: Honoraria; Sierra Oncology: Honoraria; Incyte: Speakers Bureau; Novartis: Honoraria; Jazz pharmaceuticals: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding. McCloskey:Amgen: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Jazz: Consultancy, Honoraria. Smith:Abbvie: Other: Research Support, Research Funding; Sanofi: Honoraria; Astellas Pharma: Honoraria, Other: Research Support, Research Funding; FujiFilm: Other: Research support, Research Funding; Revolution Medicines: Other: Research Support, Research Funding; Daiichi Sanyko: Consultancy, Honoraria. Schiller:Johnson & Johnson: Current equity holder in publicly-traded company; Novartis: Consultancy, Research Funding; Sangamo: Research Funding; Tolero: Research Funding; Trovagene: Research Funding; Kaiser Permanente: Consultancy; Genentech-Roche: Research Funding; Geron: Research Funding; DeltaFly: Research Funding; Deciphera: Research Funding; Celator: Research Funding; FujiFilm: Research Funding; Ariad: Research Funding; Constellation: Research Funding; Cyclacel: Research Funding; Jazz Pharmaceuticals: Research Funding; Karyopharm: Research Funding; Kite Pharma: Research Funding; Mateon: Research Funding; MedImmune: Research Funding; Astellas Pharma: Honoraria, Research Funding; Actinium: Research Funding; Gamida: Research Funding; Bristol-Myers Squibb: Current equity holder in publicly-traded company, Research Funding; Daiichi Sankyo: Research Funding; Abbvie: Research Funding; Stemline: Speakers Bureau; Celgene: Research Funding, Speakers Bureau; Ono Pharma: Consultancy; Forma: Research Funding; Incyte: Consultancy, Research Funding, Speakers Bureau; Gilead: Speakers Bureau; Amgen: Consultancy, Current equity holder in publicly-traded company, Research Funding, Speakers Bureau; Onconova: Research Funding; Pfizer: Current equity holder in publicly-traded company, Research Funding; Regimmune: Research Funding; Samus: Research Funding; Agios: Consultancy, Research Funding, Speakers Bureau; AstraZeneca: Consultancy; Sanofi: Speakers Bureau. Bradley:AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Speakers Bureau. Tiu:Astellas Pharma Global Development: Current Employment; Eli Lilly & Company: Current equity holder in publicly-traded company, Ended employment in the past 24 months. Hong:F. Hoffmann-La Roche: Current equity holder in publicly-traded company; Genentech, Inc.: Current Employment. Tong:AbbVie, Inc.: Current Employment, Other: may hold stock or other options. Qin:AbbVie: Current Employment, Other: may hold stock or other options. Dilley:AbbVie Inc.: Current Employment, Other: may hold stock or stock options. Perl:Leukemia & Lymphoma Society.: Other; AbbVie Inc, Astellas, Actinium, Bayer HealthCare Pharmaceuticals, Daiichi Sankyo Inc, FUJIFILM Pharmaceuticals USA Inc: Research Funding; AbbVie Inc, Actinium Pharmaceuticals Inc, Astellas, Daiichi Sankyo Inc, FORMA Therapeutics, Loxo Oncology Inc, a wholly owned subsidiary of Eli Lilly & Company, NewLink Genetics: Other; AbbVie Inc, Arog Pharmaceuticals Inc, Astellas, Daiichi Sankyo Inc: Consultancy; Astellas, AbbVie Inc, Daiichi Sankyo, Actinium, Forma, Syndax, Loxo: Consultancy, Honoraria. OffLabel Disclosure: Venetoclax is a B-cell lymphoma 2 inhibitor approved in combination with azacitidine, or decitabine, or low-dose cytarabine for the treatment of newly-diagnosed acute myeloid leukemia (AML) in adults who are age 75 years or older, or who have comorbidities that preclude use of intensive induction chemotherapy. Gilteritinib is a kinase inhibitor indicated for the treatment of adult patients who have relapsed or refractory acute myeloid leukemia (AML) with an FLT3 mutation as detected by an FDA-approved test.

Abstract Introduction: ASP2215, a new tyrosine kinase inhibitor with activity against FMS-like receptor tyrosine kinase-3 (FLT3) and AXL receptor tyrosine kinase, is currently in development for the treatment of acute myeloid leukemia (AML). Methods: In an ongoing, first-in-human Phase 1/2, dose-escalation/dose-expansion study, the pharmacokinetic (PK) profile and pharmacodynamic (PD) effects of ASP2215 were evaluated under fasting conditions in patients with relapsed or refractory AML (R/R AML). Patients who met study criteria were assigned to treatment in the dose-escalation cohorts or were randomized to an open dose level in the dose-expansion cohorts. The dose-escalation cohort was a modified 3+3 with accelerated titration design that evaluated ascending oral doses of ASP2215 (20-450 mg), the dose-expansion cohort was a parallel, multi-dose-expansion cohort. Blood samples were collected and safety/tolerability assessments, including 12-lead electrocardiogram, were evaluated at protocol-specified time points for both cohorts. Effect of increasing ASP2215 exposure on inhibition of FLT3 phosphorylation, assessed via plasma inhibitory assay (PIA), was evaluated using an inhibitory PK/PD Emaxmodel. PK/PD analyses were performed to evaluate the relationship between ASP2215 exposure and changes from baseline in QTcF intervals (ΔQTcF) and changes from baseline in clinical laboratory values (e.g., creatinine kinase [ΔCK], aspartate aminotransferase [ΔAST]). Results: Data from an interim analysis of the dose-escalation/dose-expansion study were available from 215 subjects (n=23 [dose escalation], n=192 [dose expansion]). The ASP2215 PK parameters across the dose range (20-450 mg), evaluated after both single- and multiple-dose administration, are presented (Table); statistical analyses suggest the ASP2215 PK parameters are dose proportional from 20-450 mg. Median time to maximal concentration (Tmax) was observed between 2 hr and 6 hr after single and repeated oral dosing. The estimated median half-life (t1/2) ranged from approximately 45 hr to 159 hr based on the accumulation ratio; ASP2215 accumulation was extensive after multiple dose administration as reflected by the accumulation index (Rac) ranging from approximately 3.2-10. A strong correlation was shown for ASP2215 exposure-related inhibition of FLT3 phosphorylation, with >90% FLT3 inhibition observed by Day 8 at ASP2215 doses of ≥80 mg. Although a positive slope was observed between ΔQTcF and ASP2215 exposure, only 5% of the study population were reported as having a maximum post-baseline QTcF interval >500 msec. A similar trend was observed with ASP2215 concentration-related increases in ΔCK and ΔAST; however, <10% of all subjects experienced a Grade ≥3 shift from baseline in CK or AST concentrations. Conclusions: ASP2215 has demonstrated exposure-related FLT3 inhibition and a pharmacokinetic profile that support once-daily oral administration for the treatment of AML in subjects who relapsed after, or are refractory to, induction or salvage treatment. Table. ASP2215 Pharmacokinetic Parameters after Multiple-Dose Administration 20 mg (n=4) 40 mg (n=3) 80 mg (n=3) 120 mg (n=3) 200 mg (n=2) 300 mg (n=3) 450 mg (n=3) Cmax(ng/mL) 45.6 (30.5, 137) 106 (76.7, 140) 396 (217, 516) 282 (248, 593) 1460 (886, 2040) 1260 (1040, 2280) 1150 (776, 1530) Tmax(hr) 4.01 (4.00, 6.00) 3.87 (0.500, 6.00) 4.33 (4.00, 4.42) 2.02 (1.95, 5.75) 6.03 (6.00, 6.07) 6.05 (4.08, 6.07) 5.00 (4.07, 5.93) AUC0-24(ng·h/mL) 926 (543, 2480) 2460 (1750, 2800) 6280 (4160, 10600) 6190 (4200, 11300) 31500 (16500, 46600) 28700 (22300, 43300) 11500 (8070, 14900) t1/2 (hr) 52.8 (39.7, 83.1) 83.7 (68.5, 243) 91.5 (60.9, 108) 45.3 (30.5, 63.3) 143 (99.7, 186) 159 (83.3, 187) 56.9 (51.5, 62.3) Rac 3.70 (2.92, 5.51) 5.55 (4.64, 15.1) 6.02 (4.18, 7.02) 3.25 (2.38, 4.33) 9.08 (6.51, 11.7) 10.1 (5.53, 11.7) 3.94 (3.62, 4.27) Data are presented as median (minimum, maximum). AUC0-24, area under the concentration-time curve between 0-24 hr; Cmax, maximal concentration; t1/2, elimination half-life; Tmax, time to maximal concentration; Rac, accumulation ratio. Disclosures Smith: Astellas: Research Funding; Plexxikon: Research Funding. Off Label Use: ASP2215 is an investigational product for the treatment of AML. Perl:Astellas US Pharma Inc.: Consultancy; Ambit/Daichi Sankyo: Consultancy; Arog Pharmaceuticals: Consultancy; Asana Biosciences: Consultancy; Actinium Pharmaceuticals: Consultancy. Altman:Novartis: Other: Advisory board; BMS: Other: Advisory board; Seattle Genetics: Other: Advisory board; Spectrum: Other: Advisory board; Ariad: Other: Advisory board; Astellas: Other: Advisory board; assistance with abstract preparation. Gill:Astellas Pharma US, Inc: Employment. Kadokura:Astellas Pharma Global Development: Employment, Other: Personal fees. Yuen:Astellas Pharma, Inc.: Employment. Fisniku:Astellas: Employment. Liu:Astellas: Employment. Nagase:Astellas: Employment. Sargent:Astellas Pharma US, Inc: Employment. Bahceci:Astellas Pharma Global Development: Employment.

Abstract Background: Gilteritinib (ASP2215) is a novel, highly selective, potent oral FLT3/AXL inhibitor with preclinical activity against FLT3-ITD activating and FLT3-D835 resistance mutations. The objectives of this phase 1/2 study were to assess gilteritinib safety/tolerability, pharmacokinetic (PK) and pharmacodynamic (PD) profiles after single- and multiple-day dosing, and antileukemic effects in patients with R/R AML. Methods: This open-label study (NCT02014558) enrolled patients (≥18 yr) into 1 of 7 dose-escalation cohorts (20-450 mg once daily [QD]) or concomitant dose-expansion cohorts. While confirmed FLT3 mutation was not an inclusion criterion, each expanded dose level enrolled ≥10 patients with FLT3 mutations (FLT3mut+); 120 and 200 mg dose levels were further expanded with ≥40 FLT3mut+ patients. The choice to expand these dose cohorts was based upon FLT3 inhibition in correlative assays and clinical activity seen during dose escalation. Safety and tolerability were primary endpoints; blood samples were drawn from patients in the dose-escalation cohorts to evaluate gilteritinib PK parameters and PD effects. Antileukemic response rates (eg, complete remission [CR], CR with incomplete platelet recovery [CRp], CR with incomplete hematological recovery [CRi], overall response rate [ORR]) were secondary endpoints. Results: Patients (N=252; 129M:123F, median age 62 yr [range: 21-90]) enrolled between October 2013 and August 2015 received ≥1 dose of gilteritinib. The study population was heavily pretreated: 70% (n=177) had ≥2 prior AML therapies, 29% (n=73) had a prior stem cell transplant, and 25% (n=63) had prior TKI treatment with sorafenib most commonly used. Across the study, 194 patients had a locally confirmed FLT3 mutation (ITD, n=159; D835, n=13; ITD-D835, n=16; other, n=6). For all enrolled patients, progressive disease (n=75), lack of efficacy (n=44), adverse events (n=34), and death (n=29) were the most common reasons for treatment discontinuation. Seven deaths were considered possibly/probably related to treatment: pulmonary embolism, respiratory failure, hemoptysis, intracranial bleed, ventricular fibrillation, septic shock, and neutropenia (all n=1). Maximum tolerated dose was determined to be 300 mg when 2 of 3 patients in the 450 mg cohort experienced diarrhea and/or hepatic transaminase elevation as dose-limiting toxicities. Diarrhea (16%) and fatigue (15%) were the most commonly reported treatment-related adverse events of any grade. Less than 5% of patients (11/252) had a maximum post-baseline QTcF interval >500 msec. Gilteritinib concentrations were generally dose proportional and showed both a long-elimination half-life (45-159 h) and substantial accumulation (3.2-10 fold) by day 15. An exposure-related increase in the inhibition of FLT3 phosphorylation with increasing doses of gilteritinib was also observed. Gilteritinib showed strong antileukemic activity in FLT3mut+ patients (ORR=49%); response was observed less frequently in patients with wild-type FLT3 (ORR=12%). While CR, CRi, and CRp occurred at all doses, responses were enriched among FLT3mut+ patients with gilteritinib steady-state trough concentrations ≥100 ng/mL, which correlated with potent FLT3 inhibition in PD assays and corresponded to doses ≥80 mg. The ORR in 169 FLT3mut+ patients receiving ≥80 mg was 52% (Table); median overall survival in this patient population was ~31 wk (range: 1.7-61; Figure) and median duration of response was 20 wk (range: 1.1-55). Clinical responses occurred in FLT3mut+ patients with -ITD, -D835, and both mutations (ORR: 55%, 17%, and 62%, respectively) as well as in FLT3mut+ patients with or without prior TKI treatment (ORR: 42% vs 56%, respectively). Conclusions: This PD-driven, first-in-human study shows that gilteritinib was well tolerated and generated frequent, prolonged, clinically important responses in FLT3mut+ patients with R/R AML. Antileukemic responses were enriched in FLT3mut+ patients treated at doses that consistently and potently inhibited FLT3 phosphorylation. The survival of these patients appears better than expected for this patient population when treated with standard therapy. Our data suggest that FLT3 inhibition may improve survival in patients with FLT3mut+R/R AML; as such, phase 3 testing of oral gilteritinib 120 mg QD in patients with FLT3mut+R/R AML after first-line therapy is underway (NCT02421939). Disclosures Perl: Astellas US Pharma Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Daichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees; Asana Biosciences: Consultancy, Membership on an entity's Board of Directors or advisory committees; Arog Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Actinium Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees. Altman:Janssen: Other: advisory board; BMS: Membership on an entity's Board of Directors or advisory committees; Spectrum: Other: advisory board; Ariad: Other: advisory board; Seattle Genetics: Other: advisory board; Syros: Other: advisory board. Cortes:ARIAD: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Teva: Research Funding. Smith:Astellas: Research Funding. Erba:Jannsen: Consultancy, Research Funding; Millennium Pharmaceuticals, Inc.: Research Funding; Agios: Research Funding; Juno: Research Funding; Incyte: Consultancy, DSMB, Speakers Bureau; Daiichi Sankyo: Consultancy; Ariad: Consultancy; Amgen: Consultancy, Research Funding; Astellas: Research Funding; Gylcomimetics: Other: DSMB; Seattle Genetics: Consultancy, Research Funding; Sunesis: Consultancy; Novartis: Consultancy, Speakers Bureau; Celator: Research Funding; Celgene: Consultancy, Speakers Bureau; Pfizer: Consultancy. Gill:Astellas: Employment. Goldberg:Bristol Myers Squibb, Novartis: Speakers Bureau; Novartis: Consultancy; COTA Inc: Employment; Pfizer: Honoraria; Neostem: Equity Ownership. Jurcic:Astellas: Research Funding. Larson:Astellas: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy. Liu:Astellas: Employment. Ritchie:Celgene: Consultancy, Other: Travel, Accomodations, Expenses, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Novartis: Consultancy, Other: Travel, Accommodations, Expenses, Research Funding, Speakers Bureau; Ariad: Speakers Bureau; Pfizer: Consultancy, Research Funding; Astellas Pharma: Research Funding; Bristol-Meyers Squibb: Research Funding; NS Pharma: Research Funding. Schiller:Incyte Corporation: Research Funding. Strickland:Celator: Research Funding; Cyclacel: Research Funding; Karyopharm Therapeutica: Research Funding; GlaxoSmithKline: Research Funding; Baxalta: Consultancy; Boehringer Ingelheim: Consultancy, Research Funding; Ambit: Consultancy; Alexion Pharmaceuticals: Consultancy; Astellas Pharma: Research Funding; CTI Biopharma: Consultancy; Daiichi Sankyo: Consultancy; Sunesis Pharmaceuticals: Consultancy, Research Funding; Abbvie: Research Funding; Sanofi: Research Funding. Wang:Incyte: Speakers Bureau; Immunogen: Research Funding. Stuart:Sunesis: Consultancy, Honoraria, Other: Travel, Accomodations, Expenses, Research Funding; Agios: Research Funding; Incyte: Research Funding; Bayer: Research Funding; Celator: Research Funding; Astellas: Research Funding. Martinelli:Ariad: Consultancy, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; BMS: Speakers Bureau; Roche: Consultancy, Speakers Bureau; MSD: Consultancy; Genentech: Consultancy; Novartis: Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau. Bahceci:Astellas: Employment. Levis:Millennium: Consultancy, Research Funding; Astellas: Consultancy, Honoraria, Research Funding; Daiichi-Sankyo: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding.

Abstract Introduction: ASP2215 is a highly selective inhibitor of AXL and FMS-like tyrosine kinase-3 (FLT3) receptors. ASP2215 is active against both FLT3 internal tandem duplication [ITD] and D835 mutations. Prior analyses of an open-label, dose-escalation/dose-expansion study in subjects with relapsed or refractory acute myeloid leukemia (R/R AML) show ASP2215 was well tolerated from 20-300 mg and associated with antileukemic activity in FLT3 mutation-positive (FLT3+) patients at ≥80 mg with minimal activity observed in wild-type FLT3 subjects. Here we describe the tolerability and potent activity of ASP2215 in a large cohort of FLT3+ patients. Methods: Patients (≥18 years) with R/R AML were assigned to treatment in dose-escalation cohorts or were randomized to an open dose level in the dose-expansion cohorts. Although FLT3 mutation was not an inclusion criterion, each expanded dose level enrolled ≥10 FLT3+ subjects; 120 mg and 200 mg dose levels were further expanded with ≥40 FLT3+ subjects. Tolerability was assessed by adverse event (AE) monitoring. Response assessment was based on modified Cheson criteria and duration of response and overall survival were calculated using Kaplan-Meier estimates. Results: As of June 19, 2015,215 patients with a median age of 61 yr (range: 21-90) had received ≥1 dose of ASP2215 (safety population). Across the safety population, 65% of subjects received ≥2 prior lines of AML therapy, 29% had a hematopoietic stem cell transplant prior to ASP2215 treatment, and 23% had prior tyrosine kinase inhibitor (TKI) treatment. Approximately 73% of patients were FLT3+, of which 137 had FLT3-ITD mutation, 7 were FLT3-D835+, and 9 had both FLT3-ITD and D835. Treatment-related AEs of all Grades, reported in ≥10% of the safety population were diarrhea (16%), fatigue (13%), and increased AST (11%); <2% of subjects reported a Grade ≥3 QTc prolongation. Activity was assessed in the 133 FLT3+ patients treated with ASP2215 ≥80 mg. Overall response rate (ORR; composite complete [CRc] plus partial remission [PR]) for all FLT3+ subjects was 55% (Table). Median overall survival for FLT3+ patients receiving ASP2215 ≥80 mg was ~29 weeks (95% CI: 22-32) and was similar for patients who achieved CRc or PR (Figure). Treatment with ≥80 mg ASP2215 was associated with an ORR of 60% in FLT3-ITD subjects; ORR for the other FLT3 populations was 29% (Table). No difference was observed in median ORR of ASP2215 (≥80 mg) in TKI-naïve patients (55%) and patients with prior TKI treatment (55%). Conclusions: ASP2215, a novel AXL/FLT3 TKI, was well tolerated in subjects with R/R AML and demonstrated a strong antileukemic activity in FLT3+ subjects. Importantly, the ASP2215 response rate in these FLT3+ patients was independent of prior TKI treatment. Even in this heavily pretreated population, the survival of R/R FLT3+ AML patients who received ≥80 mg ASP2215 was longer than prior reports of cytotoxic chemotherapy or other FLT3 inhibitors. Table. ASP2215 Response Assessment 80 mg 120 mg 200 mg 300 mg 450 mg Total All FLT3+ Subjects Population, n 12 52 57 10 2 133 CRc, n (%) 5 (42) 25 (48) 28 (49) 3 (30) 0 61 (46) PR, n (%) 3 (25) 3 (6) 3 (5) 3 (30) 0 12 (9) ORR, n (%) 8 (67) 28 (54) 31 (54) 6 (60) 0 73 (55) Subjects with FLT3-ITD Only Population, n 10 46 50 8 0 114 CRc, n (%) 4 (40) 23 (50) 26 (52) 3 (38) 0 56 (49) PR, n (%) 3 (30) 3 (7) 3 (6) 3 (38) 0 12 (11) ORR, n (%) 7 (70) 26 (57) 29 (58) 6 (75) 0 68 (60) Subjects with FLT3-D835 and Subjects with FLT3-ITD and FLT3-D835 Population, n 2 5 5 1 1 14 CRc, n (%) 1 (50) 1 (20) 2 (40) 0 0 4 (29) PR, n (%) 0 0 0 0 0 0 ORR, n (%) 1 (50) 1 (20) 2 (40) 0 0 4 (29) CRc, composite complete remission (complete remission + complete remission with incomplete platelet recovery + complete remission with incomplete hematologic recovery); ORR, overall response rate; PR, partial response. NR, no response. Subjects with non-evaluable data (N=8) were not included in this curve. Figure 1. Overall Survival by Best Overall Response Achieved with ASP2215 ≥80 mg Across All FLT3+ Subjects Figure 1. Overall Survival by Best Overall Response Achieved with ASP2215 ≥80 mg Across All FLT3+ Subjects Disclosures Altman: BMS: Other: Advisory board; Novartis: Other: Advisory board; Spectrum: Other: Advisory board; Ariad: Other: Advisory board; Seattle Genetics: Other: Advisory board; Astellas: Other: Participation in an advisory board December 2013. Off Label Use: ASP2215 is currently under investigation for the treatment of AML and is not yet approved.. Perl:Arog Pharmaceuticals: Consultancy; Asana Biosciences: Consultancy; Actinium Pharmaceuticals: Consultancy; Ambit/Daichi Sankyo: Consultancy; Astellas US Pharma Inc.: Consultancy. Cortes:Pfizer: Consultancy, Research Funding; BerGenBio AS: Research Funding; Novartis: Consultancy, Research Funding; Teva: Research Funding; BMS: Consultancy, Research Funding; Ariad: Consultancy, Research Funding; Astellas: Consultancy, Research Funding; Ambit: Consultancy, Research Funding; Arog: Research Funding; Celator: Research Funding; Jenssen: Consultancy. Levis:Arog: Research Funding; Ambit: Research Funding; Takeda: Research Funding; Astellas: Consultancy. Smith:Plexxikon: Research Funding; Astellas: Research Funding. Claxton:NCI: Research Funding; Medimmune, Inc: Research Funding; Ambit Biosciences Corp: Research Funding; Incyte Corporation: Research Funding; Merck Sharp & Dohme Corp: Research Funding; Astellas Pharma: Research Funding. Erba:Seattle Genetics: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Ariad: Consultancy; Celgene: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; GlycoMimetics: Other: Data Safety and Monitoring Committees ; Jannsen (J&J): Other: Data Safety and Monitoring Committees ; Seattle Genetics: Consultancy, Research Funding; Millennium/Takeda: Research Funding; Amgen: Consultancy, Research Funding; Celator: Research Funding; Millennium/Takeda: Research Funding; Astellas: Research Funding; Sunesis: Consultancy; Celator: Research Funding; Pfizer: Consultancy; Astellas: Research Funding; Daiichi Sankyo: Consultancy; Sunesis: Consultancy; Ariad: Consultancy; Pfizer: Consultancy; GlycoMimetics: Other: Data Safety and Monitoring Committees ; Jannsen (J&J): Other: Data Safety and Monitoring Committees ; Daiichi Sankyo: Consultancy. Gill:Astellas Pharma US, Inc: Employment. Goldberg:Cyclacel: Research Funding; Celetor: Research Funding; Pfizer: Research Funding; Ambit: Research Funding; Astellas: Research Funding. Jurcic:Astellas Pharma: Research Funding. Larson:Astellas: Consultancy, Research Funding. Lui:Astellas Pharma US, Inc: Employment. Ritchie:Incyte: Speakers Bureau; Novartis: Speakers Bureau; Ariad: Other: Advisory Board; Celgene: Speakers Bureau; Onyx: Speakers Bureau. Sargent:Astellas Pharma US, Inc: Employment. Schiller:Sunesis: Honoraria, Research Funding. Strickland:Sunesis Pharmaceuticals: Other: Steering Committee and Advisory Board Participation; Alexion Pharmaceuticals: Other: Advisory Board Particpation; Amgen: Other: Advisory Board Particpation; Daiichi-Sankyo: Other: Advisory Board Particpation; Boehringer-Ingelheim: Other: Advisory Board Particpation. Wang:Immunogen: Research Funding. Stuart:Sunesis: Honoraria, Other: Advisory Board, Research Funding; Astellas Pharma, Inc: Research Funding. Baldus:Novartis: Research Funding. Martinelli:MSD: Consultancy; ARIAD: Consultancy; BMS: Speakers Bureau; Pfizer: Consultancy; Novartis: Speakers Bureau; Roche: Consultancy. Bahceci:Astellas Pharma Global Development: Employment.

7003 Background: Gilteritinib, a highly selective FLT3/AXL inhibitor, has displayed antileukemic activity in FLT3 mutation-positive (FLT3mut+) relapsed/refractory (R/R) AML in the CHRYSALIS Phase I/II study (NCT02014558), specifically at doses ≥80 mg/d. This exploratory analysis assessed molecular response to gilteritinib in a CHRYSALIS subpopulation. Methods: Molecular response was assessed from bone marrow aspirates obtained at baseline and at ≥1 additional time point from FLT3mut+ patients (≥18 y) treated with 120 or 200 mg/d gilteritinib. These doses were identified due to their ability to induce consistent, potent FLT3 inhibition and high clinical response rates. FLT3-ITD and total FLT3 were quantified by NGS to assess molecular response. A Cox regression model of overall survival (OS) by Kaplan-Meier estimation established a FLT3-ITD:total FLT3 ratio (ITD signal ratio) of 10−2as the threshold for improved survival. Results: Of 147 FLT3-ITDmut+ patients who received gilteritinib 120 or 200 mg/d, 80 were included in this analysis. Composite response rate for these 80 patients was 55%. During response, 20 patients (25%) had an ITD signal ratio of ≤10−2. Of these 20 patients, 18 had a ratio of ≤10−3 (major molecular response [MMR]) and 13 had a ratio of ≤10−4 (minimal residual disease [MRD] negative). Median time to achieve minimum signal ratio was 54 days. Elimination of morphologic leukemia was observed in 80% of patients with ITD signal ratios <10−2. Patients who had a signal ratio ≤10−2, MMR, or were MRD negative had significantly longer median OS than those who did not (Table). Conclusions: Molecular responses to gilteritinib in FLT3-ITDmut+ R/R AML correlated with clinical response and improved OS. This is the first demonstration of molecular response to a FLT3 inhibitor in AML. These data suggest ITD signal ratio may predict durable clinical benefit of gilteritinib. Clinical trial information: NCT02014558. [Table: see text]