FLT3 Wild-type Acute Myeloid Leukemia Research Articles

EP0042, a Dual FLT3 and Aurora Kinase Inhibitor: Results from an Ongoing Phase I/IIa Dose-Finding/Dose Optimization Study in Patients with Relapsed/Refractory Acute Myeloid Leukemia

Background: EP0042 was developed as an orally bioavailable potent inhibitor of FLT3 and Aurora kinases. Aurora kinases play an important role in acute myeloid leukemia (AML) and have been implicated in the development of resistance to FLT3 inhibitors (Joshi S et al. Cancer Cell 2021;39:999-1014, 8). Dual inhibition of FLT3 and Aurora kinase has been shown to overcome acquired resistance to selective FLT3 inhibition both in vitro and in vivo (Moore A et al. Leukemia 2012;26:1462-70; Tariq M et al. Br J Cancer 2021;125:966-74). Preliminary data from this ongoing Phase 1 study of EP0042 in relapsed/refractory AML were presented previously (Taussig et al. Blood 2022:140(Supplement 1): 6222-6223). Here we present further data from the dose finding and dose optimisation cohorts from the study. Methods The primary objective of this phase I/IIa, multi-centre study is to investigate safety/tolerability and to establish both the MTD and optimal dose of EP0042 when used as monotherapy, or in combination with established standard treatments in patients with AML, myelodysplastic syndrome (MDS) or chronic myelomonocytic leukemia (CMML) who have relapsed on or are refractory to previous therapy. Secondary objectives include PK characterisation and assessment of anti-tumour activity. Results As of July 13 th 2023, 38 patients (17 f/21 m) were enrolled across 9 different cohorts. Median age 72 years, range 25-84. Patients presented with relapsed/refractory AML (34), CMML (1) or MDS (3). 9 patients had FLT3 mutated AML at the point of entry (All FLT3 ITD). Patients were administered doses ranging from 40mg to 170mg, QD or BID, with different schedules, across 7 cohorts (Table 1). One Cycle = 28 days. 150mg BID 28/28 days was identified as the MTD with 2 DLTs identified, Grade 3 somnolence and ataxia, and Grade 3 encephalopathy. Two dose optimisation cohorts (Table 1) were subsequently initiated to further optimise the potential RP2D. These cohorts are currently ongoing. The median number of prior treatments was 2 (range 1-6). 12 patients received a prior FLT3 inhibitor including midostaurin, gilteritinib or sorafenib and 8/12 patients received ≥2 prior FLT3 inhibitors. 3 patients received prior ASCT. The most common treatment-emergent adverse events (TEAEs) ≥20% were: diarrhea (54.1%), fatigue (54.1%), febrile neutropenia (51.4%), decreased appetite (43.2%), dyspnea (35.1%), somnolence (29.7%), constipation (27.0%), ataxia (27.0%) and nausea (24.3%). 23.3% of TEAEs were > grade 3. The most common treatment related AEs (TRAEs, all grades ≥10%) were decreased appetite (29.7%), somnolence (29.7%), ataxia (27.0%), fatigue (24.3%), diarrhea (13.5%), nausea (13.5%) and dizziness (16.2%). No treatment-related death has been reported across all cohorts. Most events were manageable by temporary dose reductions and or/short interruptions. All events of ataxia and somnolence were reversible after a short treatment interruption. Across all cohorts, 18 patients achieved stable disease (SD) as best response (median no. of cycles = 3, range 1-11). 1 patient continued treatment for 11 cycles (100mg BID, FLT3wt) and another for 8 cycles (140 mg BID, FLT3-ITD) with clinical benefit. 1 patient achieved a best response of CR MRD- (150mg BID, FLT3wt) with aCRi first detected at C6D1 (2% blast, down from 38% at screening and 80% at C3D1) and confirmed with CR MRD- at C7D1 by flow cytometry. Treatment is still ongoing at C10 and patient remains transfusion independent for 4 months. Evidence of peripheral blast response was observed in 5 patients, with complete disappearance of peripheral blasts compared to baseline after a median time of 2 months on treatment. Data from the ongoing dose optimisation cohorts will be presented at the congress. Conclusions This extended data set confirms thatEP0042 has acceptable tolerability and safety. Two patient cohorts are ongoing to establish the optimum continuous dose regimen to take forward. Promising evidence of clinical benefit has been observed including a durable CR MRD-. This remission in a patient with FLT3 wild type AML indicates that EP0042 may have broader activity in AML, beyond FLT3 mutated disease. Dose optimisation cohorts are continuing to identify the RP2D. Further cohorts are planned for evaluation of EP0042 in combination with standard of care therapies.

The FLT3-like Gene Expression Signature Predicts Response to Quizartinib in Wild-Type FLT3 Acute Myeloid Leukemia: An Analysis of the Pethema Quiwi Trial

Background The identification of predictive biomarkers is crucial for guiding treatment decisions in acute myeloid leukemia (AML). Previously, we identified a FLT3-like gene expression signature in FLT3 wild-type AML patients, which clustered a variable proportion of FLT3 wild-type patients with FLT3-ITD and TKD mutated patients. The QUIWI trial was a randomized, placebo-controlled, phase II study preliminary showing a significant increase in overall survival (OS) in wild-type FLT3 AML patients treated with the FLT3 inhibitor quizartinib (Quiza) plus standard chemotherapy. This preplanned correlative study was designed to assess the value of the FLT3-like signature to predict responses to Quiza. Methods We performed RNA sequencing (RNAseq) analysis on a subset of patients from the clinical trial. RNA was extracted using standard methods, followed by assessment of nucleic acid integrity (TapeStation) and quantification (Qubit). Total mRNA sequencing was performed using polyA RNAseq with TruSeq technology. A total of 206 adequate samples from bone marrow and peripheral blood were sequenced (161 from FLT3-ITD negative enrolled in QUIWI; and 55 from FLT3-ITD positive patients who were screen failure of the QUIWI trial by this reason). The sequences were aligned to the GRCh37 reference genome using the Hisat algorithm. Gene expression quantification was performed using the Bioconductor workflow, and gene expression estimates (FPKM) were obtained. The gene expression estimates were log2 normalized. Finally, those genes mapping to the original FLT3-like signature (595 genes) were selected for downstream analysis. Clustering was based on the hierarchical method, using standard euclidean distance metrics. OS was defined as time from start of screening to death. Event-free survival (EFS) was defined as time from randomization to failure to achieve CR/CRi after 1 or 2 cycles, death in CR/CRi, or relapse (whichever occurred the first). Relapse-free survival was defined as time from randomization to disease relapse or death by any cause. Results Among the total 206 patients, a cluster of 54.37% (N=112) was enriched in FLT3-mutant cases (71.11% of cases, Figure 1A). This subgroup comprised 49.67% of wild-type FLT3 cases (N=80), hereafter FLT3-like patients. In the group of not FLT3-like patients, no differences were identified between the placebo and Quiza group in the total number of deaths (Fisher's p-value, 0.63), EFS (cox p-value, 0.83; HR 1.07 [0.56-2.06]), RFS (cox p-value 0.76; HR 0.88 [0.38-2.01]) and OS (cox p-value, 0.62; HR 1.22 [0.55-2.67]). Among FLT3-like patients, significant differences were identified in the total number of deaths (Fisher's p-value, 0.004), EFS (cox p-value, 0.009; HR 0.45 [0.25-0.82], RFS (cox p-value 0.01, HR 0.37 [0.18-0.79]) and OS (cox p-value 0.01, HR, 0.41 [0.20-0.84]) ( Figure 1B). No statistically significant association was observed between the FLT3-like pattern and the ELN-17 classification: 30.4% were low risk, 40.5% intermediate risk, 29.1% high risk. Conclusion The FLT3-like gene expression signature successfully identified a subset of patients who derived the most benefit from Quiz, while patients without the FLT3-like signature did not demonstrate a benefit compared with placebo. These findings support the use of the FLT3-like signature as a potential biomarker to identify those wild-type FLT3 AML patients who may benefit from Quiz, providing a valuable insight for personalized treatment in AML.

Evaluation of Emergent FLT3 Mutations (FLT3m) at Relapse in Patients (Pts) with Wild-Type FLT3 Acute Myeloid Leukemia (AML)

Background:FLT3 mutations (FLT3m) are detected in approximately 30% of newly diagnosed (ND) pts with AML and are associated with poor prognosis. FLT3m can also emerge in relapse in pts with previously wild-type FLT3 AML; however, their frequency and clinical implications are not well studied. Our objective was to identify pts who relapsed with emergent FLT3m and compare their clinical and pathological characteristics to those who relapse without FLT3m. Methods: We identified 686 pts with ND AML treated at our institution between 12/2005 and 01/2020, who achieved complete remission (CR) / CR with incomplete count recovery (CRi) and subsequent relapse of AML. Pts with available FLT3 status (ITD and TKD) at diagnosis and within 4 weeks of first relapse were included (N=300). A multiplex fluorescent-based PCR analysis followed by capillary electrophoresis for detection of FLT3 ITD and/or TKD was performed on DNA isolated from BM aspirate samples. Next-generation sequencing (NGS) at baseline was performed using the Illumina MiSeq platform with multigene panels (either 28-gene, 53-gene, or 81-gene) interrogating genes recurrently mutated in myeloid neoplasms. Results: Among 300 pts who achieved CR/CRi after induction and eventually relapsed, 216 (72%) had FLT3 wild-type (WT) AML and 84 (28%) had FLT3m AML at diagnosis. Baseline clinical features are shown in Table 1. 43 (14%) pts had a change of FLT3 status between baseline and relapse: 30 pts had FLT3m at baseline that wasn't detected at relapse, and 13 pts with FLT3 WT AML at baseline experienced relapse with FLT3m AML. The median remission duration (until 1st relapse) for the entire study cohort pts withFLT3 WT and pts with FLT3m AML was 7.8 months (range, 0.2-147.2), 9 months (0.2-147.2), and 6.1 months (range, 0.5-79.6), respectively. FLT3 wild-type at Diagnosis Among 216 pts with FLT3 WT AML at baseline, 203 (94%) and 13 (6%) experienced relapse with FLT3 wild-type and FLT3m AML, respectively. Comparison of baseline molecular features of FLT3 WT and FLT3m cohorts showed that pts who had relapsed AML with a positive FLT3m had more frequent concomitant NRAS mutations compared with pts who had FLT3 WT AML at relapse (60% vs 5%; p=0.003). No significant difference was seen in the frequency of TP53 (49% vs. 20%; p=0.36), NPM1 (15% vs. 40%; p=0.19), DNMT3A (16% vs. 40%; p=0.21), KRAS (5% vs. 0%; p=1), or PTPN11 (3% v. 0%; p=1) mutations between the two cohorts, respectively. Among 13 pts with AML with emergent FLT3m, 12 had diploid cytogenetics at diagnosis, but only 6 maintained the diploid status at relapse. The remaining 6 pts developed karyotypic clonal evolution at relapse (complex, n=1; KMT2A rearrangement, n=1; trisomy 8, n=1; other alterations, n=3). We had paired baseline and relapse NGS performed in 5 of 13 pts with relapsed AML, among these AMLs acquired new mutations. Nine newly acquired mutations were detected in the following genes: NPM1 (n=1), KRAS (n=1), RUNX1 (n=1), IDH2 (n=1), DNMT3A (n=1), ZRSR2 (n=1), WT1 (n=2), and STAG2 (n=1). Two of 5 pts had AML with no mutations at baseline, and 1 pt had AML with the same mutation profile at baseline and relapse. The median OS after relapse was 5.3 months and 5.5 months in pts with WT vs. FLT3m AML, respectively (P=0.29) (Figure 1). FLT3 mutant at diagnosis Among 84 pts with FLT3m AML at diagnosis, 52 (62%) and 32 (38%) pts experienced relapse with FLT3m and WT AML, respectively. Comparison of baseline molecular features of FLT3 WT and FLT3m AML showed a trend towards a higher frequency of NPM1 (77% vs. 47%; p=0.09) and DNMT3A mutations (55% vs. 21%; p=0.08) in patients who experienced relapse with FLT3m AML compared with FLT3 WT AML. No difference in the frequency TP53 (0% vs. 23%; p=0.13), KRAS (0% vs. 14%; p=0.27), NRAS (14% vs. 9%; p=0.63) and PTPN11 (7% vs. 14%; p=1) mutations was observed among both cohorts, respectively. The median OS after relapse was 8.1 months vs. 3.9 months in pts with FLT3 WT vs. FLT3m AML, respectively (p=0.005) (Figure 2). Conclusion: Our data suggest that FLT3m are more likely to emerge at AML relapse with concomitant NRAS mutations and indicate that FLT3m testing should be performed at relapse, irrespective of FLT3status at diagnosis. It is common for the FLT3 status to change, either from mutant to WT or vice versa. FLT3 status has immediate and clinically important implications for selection of appropriate therapeutic agents in the setting of salvage therapy. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

A Phase 1b Dose Escalation and Expansion Study of SNDX-5613, Azacitidine (AZA) and Venetoclax (VEN) in Newly Diagnosed, Patients ≥ 60 Years with Untreated NPM1-Mutated/ FLT3-Wild Type AML or KMT2A-Rearranged Acute Myeloid Leukemia (AML)

Background: SNDX-5613 is a potent, orally available, small molecule inhibitor of menin, which binds to MLL1, encoded by the KMT2A gene, and MLL1 fusion proteins. Menin expression leads to aberrant gene transcription through its activation of Homeobox-related genes, leading to maturation arrest and leukemogenesis in KMT2A-rearranged and NPM1-mutated leukemias. Inhibition of menin activity significantly blocks the transcriptional signature and subsequently the proliferative capacity of leukemia cells harboring NPM1 mutations or KMT2A rearrangements. SNDX-5613 and its analogs have demonstrated robust single-agent anti-proliferative activity in NPM1-mutated AML cells and AML patient-derived xenograft models. Currently, SNDX-5613 is being explored as a single agent in a phase 1/2 study in patients with NPM1-mutated or KMT2A-rearranged relapsed/refractory AML, mixed phenotypic acute leukemia and acute lymphoblastic leukemia. The primary objective of this study is to determine the safety and recommended dose of SNDX-5613 combined with AZA and VEN in untreated AML patients age ≥ 60 years who are not candidates for intensive chemotherapy. Study Design and Methods: This study is a sub-study of the BeatAML Master Trial (NCT03013998) in which untreated AML patients age ≥ 60 are assigned an investigational therapy based on cytogenetic and central genomic analysis. Patients must specifically harbor an identifiable NPM1 mutation without a concomitant FLT3 mutation or have a KMT2A rearrangement to be eligible. In this phase 1b study, the primary objective is to determine the safety and recommended dose using a standard 3+3 design based on dose-limiting toxicities with 3 dose levels (DL) of SNDX-5613 to be evaluated in combination with VEN/AZA and an anti-fungal (required during induction): 75mg (DL-1), 113mg (DL1), and 163mg (DL2). In continuation phase with anti-fungals not required, SNDX-5613 will be dosed at 113mg (DL-1), 163mg (DL1), or 226mg (DL2) with appropriate dose reductions added for both SNDX-5613 and VEN if continuing on anti-fungals. The secondary objectives are to assess the overall response rate, measurable residual disease (MRD) status, overall survival, transplant rate and duration of remission. During induction cycles, VEN (D1-28) and AZA (D1-7) are dosed per standard of care every cycle. SNDX-5613 is dosed continuously orally twice daily with dose levels listed above. In patients who achieve a morphologic remission (<5% blasts), SNDX-5613 will be held if absolute neutrophil count (ANC) is < 0.5x109/L and/or platelets (PLT) < 50x109/L. Patients can receive up to 3 induction cycles to achieve a composite complete remission (CRc: CR, CRi, CRh). Patients can receive continuation therapy with AZA, VEN and SNDX-5613 once they achieve CRc and after hematologic recovery. Following the determination of a safe and recommended dose in phase 1b, there will be a dose expansion cohort of 12-20 patients following the same schedule as described above (Figure 1) to further evaluate safety, tolerability and correlative biomarkers. Correlative objectives include assessment of SNDX-5613 pharmacokinetics and its correlation with response and toxicities. Additionally, the study will evaluate the impact of MRD, as measured by central flow cytometry and next-generation sequencing of NPM1 mutations. Additional evaluations and biomarkers of potential interest include menin- KMT2A-specific transcriptomic changes, myeloid differentiation/cell subset changes, mechanisms of resistance, and discovery of baseline features (methylation, mutations, etc.) that can impact outcomes. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Venetoclax synergizes with gilteritinib in FLT3 wild-type high-risk acute myeloid leukemia by suppressing MCL-1

AbstractBCL-2 inhibition has been shown to be effective in acute myeloid leukemia (AML) in combination with hypomethylating agents or low-dose cytarabine. However, resistance and relapse represent major clinical challenges. Therefore, there is an unmet need to overcome resistance to current venetoclax-based strategies. We performed high-throughput drug screening to identify effective combination partners for venetoclax in AML. Overall, 64 antileukemic drugs were screened in 31 primary high-risk AML samples with or without venetoclax. Gilteritinib exhibited the highest synergy with venetoclax in FLT3 wild-type AML. The combination of gilteritinib and venetoclax increased apoptosis, reduced viability, and was active in venetoclax-azacitidine–resistant cell lines and primary patient samples. Proteomics revealed increased FLT3 wild-type signaling in specimens with low in vitro response to the currently used venetoclax-azacitidine combination. Mechanistically, venetoclax with gilteritinib decreased phosphorylation of ERK and GSK3B via combined AXL and FLT3 inhibition with subsequent suppression of the antiapoptotic protein MCL-1. MCL-1 downregulation was associated with increased MCL-1 phosphorylation of serine 159, decreased phosphorylation of threonine 161, and proteasomal degradation. Gilteritinib and venetoclax were active in an FLT3 wild-type AML patient-derived xenograft model with TP53 mutation and reduced leukemic burden in 4 patients with FLT3 wild-type AML receiving venetoclax-gilteritinib off label after developing refractory disease under venetoclax-azacitidine. In summary, our results suggest that combined inhibition of FLT3/AXL potentiates venetoclax response in FLT3 wild-type AML by inducing MCL-1 degradation. Therefore, the venetoclax-gilteritinib combination merits testing as a potentially active regimen in patients with high-risk FLT3 wild-type AML.

Efficacy Analysis of Different FLT3 Inhibitors in Relapsed/Refractory Acute Myeloid Leukemia and High-Risk Myelodysplastic Syndrome Patients - a Systematic Review and Meta-Analysis

Background: Mutations in FMS like tyrosine kinase gene 3 (FLT3) are the most common genetic aberrations in acute myeloid leukemia (AML). Internal tandem duplications (ITD) are the most frequent FLT3 mutations, occurring in 20-30% of patients (pts) with newly diagnosed AML, and a minority are tyrosine kinase domain mutations. FLT3 mutation confers adverse prognosis in pts treated with standard chemotherapy (chemo) alone, and relapse risk is also higher compared to FLT3-wild type AML (HR-1.75). Studies of FLT3 inhibitors as monotherapy or in combination with chemo in the treatment of pts with FLT3-ITD relapsed/refractory (R/R) AML are associated with mixed results. No evidence synthesis has yet focused on the effect of FLT3 inhibitor alone in the treatment of R/R AML and high-risk myelodysplastic syndrome (HR-MDS). Hence, we analyzed the efficacy of various FLT3 inhibitors from different clinical trials used as monotherapy to treat pts with R/R AML and HR-MDS.Methods: We conducted a systematic review and meta-analysis of clinical trials of FLT3 inhibitors for pts with R/R AML and HR-MDS. We searched EMBASE and PubMed for clinical trials published between 1/1/2000 and 5/26/2021 using a combination of keywords and subject headings related to FLT3 inhibitors and AML. Titles/abstracts and full texts were screened by two independent reviewers, with conflicts arbitrated by a third reviewer. Studies were included if they were (1) full-length published journal articles that (2) reported the results of single-arm or double-arm phase I/II/III clinical R/R AML or HR-MDS. Outcomes of interest were composite response rate (CRc=complete response + complete response with incomplete count recovery) and overall response rate (ORR).Results: Thirty studies were included after the application of inclusion criteria (Figure 1). Two were excluded due to inadequate representation of pts with R/R AML and outcomes reported for stem cell transplant following FLT3 inhibitor use, respectively. Hence, 28 studies were included in the meta-analysis, with a total of 1927 pts. Quizartinib and sorafenib were the most frequently studied inhibitors (6 and 5 studies, respectively, Table 1). Heterogeneity testing was performed using Cochran's Q test and I 2 values. The Cochran's Q test p-value was less than 0.10 (p<0.01), and the I 2 value was more than 50% (I 2=87%), indicating the presence of heterogeneity. Thus, random-effects models were used. Asymmetry test was performed using Egger's linear regression test, which suggested the presence of publication bias (p=0.001; Figure 2). Thus, the trim-and-fill method was used to adjust for publication bias. Pooled ORR was 53% (95% CI, 43-63%) (Figure 2). Similarly, pooled CRc was 34% (95% CI, 26-44%, Figure 3). Pooled CRc and ORR were higher in studies involving quizartinib (40% and 61%, respectively) and gilteritinib (40% and 52%, respectively, Table 1). The CRc rates seen with FLT3 inhibitors are higher than the historical comparison of pts with FLT3-mutated-R/R AML treated with chemo only (CRc ~15%). This meta-analysis shows that FLT3 inhibitors as monotherapy leads to meaningful clinical responses in pts with FLT3-mutated-R/R AML.Conclusion: Most FLT3 inhibitors are effective as monotherapy for the treatment of pts with FLT3-mutated-R/R AML. Pooled response rates are notably higher in studies involving second-generation FLT3 inhibitors, particularly quizartinib and gilteritinib. Though not conclusive, the efficacy spectrum of various FLT3 inhibitors in the R/R setting could help design future studies and guide appropriate treatment selection; however, further validation is needed. Prospective clinical trials are required to compare the effectiveness of newer generation FLT3 inhibitors in pts with FLT3-mutated-R/R AML. [Display omitted] DisclosuresMaciejewski: Bristol Myers Squibb/Celgene: Consultancy; Novartis: Consultancy; Regeneron: Consultancy; Alexion: Consultancy. Balasubramanian: Servier Pharmaceuticals: Research Funding.

CG '806, a Highly Potent First-in-Class Pan-FLT3/BTK Inhibitor, Targets Multiple Clusters of Kinases Operative in Diverse Subtypes of Acute Myeloid Leukemia

CG'806 is a non-covalent pan-FMS like tyrosine kinase 3 (FLT3)/ Bruton's Tyrosine Kinase (BTK) multi-kinase inhibitor. This small molecule was designed to inhibit the wild type (WT) and C481S mutant forms of BTK, as well as the WT and mutant forms (including the internal tandem duplication, ITD) of the FLT3 receptor tyrosine kinase. Previously (2017 AACR Hematologic Malignancies abstract # 25 and #44), CG'806 was shown to have nM potency against FLT3 mutation-driven (including ITD and point mutations in tyrosine kinase domain) human acute myeloid leukemia (AML) primary patient cells, and in cultured human (eg. MV4-11 and MOLM-13) and mouse (Ba/F3) AML cell lines. CG'806 inhibited FLT3 signaling, induced apoptosis, and eradicated MV4-11 tumors with no observed toxicity in murine xenograft models. Because AML cells demonstrate extreme heterogeneity in gene expression and because FLT3 mutations account for no more than 30% of AML patients, the effect of CG'806 was further evaluated in AML cells without FLT3 mutations. Immunoblotting demonstrated that CG'806 potently decreased phospho-BTK, phospho-aurora kinases A/B/C and phospho-H3S10 without affecting FLT3 activity in AML cells having low/normal expression levels of homozygous WT FLT3 (eg. KG-1 and NOMO-1). Measurement of BrdU incorporation by flow cytometry demonstrated that CG'806 induced G2/M cell cycle arrest or polyploidy and subsequent apoptosis in FLT3 WT AML cell lines. Interestingly, CG'806 was found to induce G0/G1 cell cycle arrest but not polyploidy in FLT3-ITD driven MV4-11 and MOLM-13 cells with no effect on activity of BTK or aurora kinases at concentrations that completely inhibited FLT3 signaling (FLT3/STAT5/ERK). These findings indicate that the molecular mechanism of cell killing by CG'806 is context-dependent and varies in different AML subtypes. Evaluation of enzyme inhibitory activity (IC50) against 583 kinase enzymes, as well as binding affinities (Kd) with 483 kinase proteins, revealed pM to low nM IC50 and Kd values for CG'806 against the FLT3, BTK, AURK, c-Src, c-Met, c-Ret, DDR, TRK and STE/MAPK families of kinases. The ability of CG'806 to target multiple families or clusters of kinases is responsible for its broad efficacy in different AML subtypes driven by different genomic aberrations. Together, these findings illustrate the ability of CG'806 to inhibit entire FLT3 family of kinases, BTK and the AURK families and pathways that are operative in AML, thereby supporting the development of CG'806 for treatment of patients with FLT3-ITD and other subpopulations of patients with AML. DisclosuresZhang:Aptose Biosciences, Inc.: Employment. Local:Aptose Biosciences, Inc.: Employment. Benbatoul:Aptose Biosciences, Inc.: Employment. Folger:Aptose Biosciences, Inc.: Employment. Sheng:Aptose Biosciences, Inc.: Employment. Howell:Aptose Biosciences, Inc.: Membership on an entity's Board of Directors or advisory committees. Rice:Aptose Biosciences, Inc.: Employment, Equity Ownership, Patents & Royalties.

High-throughput proteomic profiling reveals mechanisms of action of AMG925, a dual FLT3-CDK4/6 kinase inhibitor targeting AML and AML stem/progenitor cells.

FLT3 mutations, which are found in a third of patients with acute myeloid leukemia (AML), are associated with poor prognosis. Responses to currently available FLT3 inhibitors in AML patients are typically transient and followed by disease recurrence. Thus, FLT3 inhibitors with new inhibitory mechanisms are needed to improve therapeutic outcomes. AMG925 is a novel, potent, small-molecule dual inhibitor of FLT3 and CDK4/6. In this study. we determined the antileukemic effects and mechanisms of action of AMG925 in AML cell lines and primary samples, in particular AML stem/progenitor cells. AMG925 inhibited cell growth and promoted apoptosis in AML cells with or without FLT3 mutations. Reverse-phase protein array profiling confirmed its on-target effects on FLT3-CDK4/6-regulated pathways and identified unrevealed signaling network alterations in AML blasts and stem/progenitor cells in response to AMG925. Mass cytometry identified pathways that may confer resistance to AMG925 in phenotypically defined AML stem/progenitor cells and demonstrated that combined blockade of FLT3-CDK4/6 and AKT/mTOR signaling facilitated stem cell death. Our findings provide a rationale for the mechanism-based inhibition of FLT3-CDK4/6 and for combinatorial approaches to improve the efficacy of FLT3 inhibition in both FLT3 wild-type and FLT3-mutated AML.

Combinatorial molecule screening identified a novel diterpene and the BET inhibitor CPI-203 as differentiation inducers of primary acute myeloid leukemia cells.

Combination treatment has proven effective for patients with acute promyelocytic leukemia, exemplifying the importance of therapy targeting multiple components of oncogenic regulation for a successful outcome. However, recent studies have shown that the mutational complexity of acute myeloid leukemia (AML) precludes the translation of molecular targeting into clinical success. Here, as a complement to genetic profiling, we used unbiased, combinatorial in vitro drug screening to identify pathways that drive AML and to develop personalized combinatorial treatments. First, we screened 513 natural compounds on primary AML cells and identified a novel diterpene (H4) that preferentially induced differentiation of FLT3 wild-type AML, while FLT3-ITD/mutations conferred resistance. The samples responding to H4, displayed increased expression of myeloid markers, a clear decrease in the nuclear-cytoplasmic ratio and the potential of re-activation of the monocytic transcriptional program reducing leukemia propagation in vivo. By combinatorial screening using H4 and molecules with defined targets, we demonstrated that H4 induces differentiation by the activation of the protein kinase C (PKC) signaling pathway, and in line with this, activates PKC phosphorylation and translocation of PKC to the cell membrane. Furthermore, the combinatorial screening identified a bromo- and extra-terminal domain (BET) inhibitor that could further improve H4-dependent leukemic differentiation in FLT3 wild-type monocytic AML. These findings illustrate the value of an unbiased, multiplex screening platform for developing combinatorial therapeutic approaches for AML.

Genomic markers of midostaurin drug sensitivity in FLT3 mutated and FLT3 wild-type acute myeloid leukemia patients.

Acute myeloid leukemia (AML) is a heterogeneous malignancy with the most common genomic alterations in NPM1, DNMT3A, and FLT3. Midostaurin was the first FLT3 inhibitor FDA approved for AML and is standard of care for FLT3 mutant patients undergoing induction chemotherapy [1, 2]. As there is a spectrum of response, we hypothesized that biological factors beyond FLT3 could play a role in drug sensitivity and that select FLT3-ITD negative samples may also demonstrate sensitivity. Thus, we aimed to identify features that would predict response to midostaurin in FLT3 mutant and wild-type samples.We performed an ex vivo drug sensitivity screen on primary and relapsed AML samples with corresponding targeted sequencing and RNA sequencing. We observed a correlation between FLT3-ITD mutations and midostaurin sensitivity as expected and observed KRAS and TP53 mutations correlating with midostaurin resistance in FLT3-ITD negative samples. Further, we identified genes differentially expressed in sensitive vs. resistant samples independent of FLT3-ITD status. Within FLT3-ITD mutant samples, over-expression of RGL4, oncogene and regulator of the Ras-Raf-MEK-ERK cascade, distinguished resistant from sensitive samples. Overall, this study highlights the complexity underlying midostaurin response. And, our results suggest that therapies that target both FLT3 and MAPK/ERK signaling may help circumvent some cases of resistance.

Venetoclax (Ven) added to intensive chemo with cladribine, idarubicin, and AraC (CLIA) achieves high rates of durable complete remission with low rates of measurable residual disease (MRD) in pts with newly diagnosed acute myeloid leukemia (AML).

7539 Background: Ven is a BCL2 inhibitor that is approved in combination with lower intensity therapy for pts with newly diagnosed AML who are ineligible for intensive chemo. We previously reported the safety and efficacy of cladribine and araC with idarubicin in young and fit pts with AML. Here, we studied the combination of ven with the intensive CLIA regimen in newly diagnosed AML. Methods: Pts &lt; 65 yrs with newly diagnosed FLT3-wildtype AML were enrolled. Induction was cladribine 5 mg/m2 IV on D 1-5, followed by ara-C 1.5 g/m2 IV on D 1-5, idarubicin 10 mg/m2 IV D 1-3, and ven at an effective dose of 400mg PO on D2-8. There was no ramp up for ven and dose modifications for CYP3A4 inhibitors were made. Consolidation consisted of up to 5 more cycles of CLIA+Ven. All pts underwent baseline next generation sequencing and MRD testing by multiparameter flow cytometry at the time of response. Results: 18 pts are enrolled, with a median age of 50 yrs (range, 18-64). Baseline pt characteristics are in Table. 16 pts were evaluable for response and 2 are too early. 14 of 16 pts (88%) achieved a remission, including 10 (63%) complete remission (CR) and 4 (25%) CR with incomplete count recovery (CRi). The median time to response was 1 cycle and the median number of cycles given was 2 (1-5). 10 of the 14 responders (71%) had undetectable MRD at the time of remission. Both nonresponding pts had a complex karyotype and 1 had a TP53 mutation. With a median follow up of 4.5 months (0.2 – 11.2), none of the responding pts have relapsed. 8 of the 14 responders (57%) have received allogeneic stem cell transplant. The median survival has not been reached; the 6-month OS and RFS are 90% and 100%, respectively. Treatment was well tolerated, with 0% 4-week mortality. The median days to ANC ≥ 1 and Platelets ≥ 100 were 30 (19-49) and 26 (18-39), respectively. Tumor lysis syndrome was not seen. The most common adverse events were neutropenic fever, pneumonia, nausea, and liver transaminitis. Conclusions: The addition of ven to CLIA was safe and effective in newly diagnosed pts with AML. The combination was not associated with early mortality or prolonged myelosuppression, but did result in high rates of durable MRD negative remissions. Clinical trial information: NCT02115295 . [Table: see text]

Loss of Heterozygosity of FLT3-ITD Is Common in Acute Myeloid Leukemia and May be a More Consistent Prognostic Marker Than FLT3-ITD Allele Frequency

Loss of Heterozygosity of FLT3-ITD Is Common in Acute Myeloid Leukemia and May be a More Consistent Prognostic Marker Than FLT3-ITD Allele Frequency

A Phase II Study of Midostaurin and 5-Azacitidine for Untreated Elderly and Unfit Patients With FLT3 Wild-type Acute Myelogenous Leukemia

BackgroundMidostaurin, a multikinase inhibitor, is approved for treatment of FLT3-mutant acute myeloid leukemia (AML). A phase I study established that midostaurin 75 mg orally twice daily for 14 days with standard dose azacitidine was safe and tolerable in elderly patients with AML. Herein, we report the phase II expansion cohort of previously untreated elderly or unfit patients with AML. Patients and MethodsPrimary objectives were to further describe the toxicity profile and determine the response rate in untreated patients with AML. Patients received midostaurin 75 mg orally twice daily on days 8 to 21 in combination with intravenous azacitidine at 75 mg/m2 on days 1 to 7. Plasma inhibitory activity assay for FLT3 was performed pretreatment and on day 8 and day 15 of each cycle. ResultsTwenty-six patients (median age, 74 years; range, 59-85 years) with FLT3 wild-type AML were accrued. Patients received a median of 2 cycles of therapy (range, 1-10 cycles). Seven (29%) of 24 evaluable patients achieved a clinical response (4 complete response; 1 complete response with incomplete count recovery; and 2 partial response). The median overall survival was 244 days (95% confidence interval, 203-467 days). Hematologic, infectious, and gastrointestinal toxicities were comparable to similar studies. Peripheral blood FLT3 wild-type phosphorylation declined to 8% to 55% of pretreatment by day 15 of cycle 1 (7 patients) and declined with subsequent cycles (< 10% baseline) in 2 patients who were analyzed after cycle 3. ConclusionMultiple cycles of azacitidine and midostaurin were not well-tolerated, but persistent inhibition of FLT3 wild-type phosphorylation suggest intermittent dosing of midostaurin should be considered in future low-intensity regimens for FLT3-mutant AML.

Treatment Patterns and Healthcare Resource Utilization (HRU) in Patients with Relapsed/Refractory (R/R) FLT3-Mutated (FLT3mut) and FLT3-Wild Type (FLT3wt) Acute Myeloid Leukemia (AML): A Multi-Country Medical Chart Study

Background: Salvage therapy for patients with R/R AML has long relied on chemotherapy as a bridge to hematopoietic stem cell transplantation (HSCT). With the advent of treatments targeted to biomarkers, such as fms-like tyrosine kinase 3 (FLT3), there is a need to understand current treatment patterns and HRU. This multi-country study utilized real-world evidence (RWE) collected from medical charts to evaluate treatment patterns and HRU among patients with R/R AML by FLT3 mutation status.Methods: Hematologists/oncologists were recruited from 10 countries (US, Canada, UK, France, Germany, Italy, Spain, Netherlands, Japan, and South Korea). Patients with AML who were classified as relapsed or refractory to initial treatment between January 1, 2013 and December 31, 2015 were eligible for inclusion. Eligible patients with R/R AML were randomly selected by physicians and were categorized into one of two cohorts: FLT3mut or FLT3wt patients. Stratified recruitment was used to ensure that an equal ratio of FLT3mut and FLT3wt patients were enrolled. The index dates were defined as the dates of R/R classification and data collection until the date of last follow-up or death.Results: The study included both FLT3mut (n=181) and FLT3wt (n=182) patients. Of the FLT3mut patients, 53.6% (n=97) had only an internal tandem duplication (ITD) mutation, 15.5% (n=28) had both ITD and tyrosine kinase domain (TKD) mutations, and 30.9% (n=56) only had a TKD mutation. Other mutations (eg, NPM1, IDH1/2, CEBPA, KIT, AXL) were seen in both cohorts; all other mutations were more common in FLT3mut patients. Compared with FLT3wt patients, FLT3mut patients were significantly younger at the event date (53.2 ± 15.2 vs 56.8 ± 14.6, P<.05) and more had an Eastern Cooperative Oncology Group score ≥2 (36.9% vs 33.0%; P<.01). FLT3mut patients were also more likely to have dysplasia-related AML (22.8% vs 12.6%; P<.01) and genetic abnormalities (38.9% vs 16.1%; P<.01) than FLT3wt patients.Despite treatment guidelines, which recommend specific chemotherapy-based regimens according to patient age and health status, nearly one-third of patients with R/R AML received only best supportive care (BSC) after being classified as R/R AML; more FLT3mut patients received BSC (39.8%) than FLT3wt patients (24.7%). While few patients received a FLT3 inhibitor (eg, midostaurin), this is most likely due to limited availability outside of a clinical trial. Overall, 20.8% of patients with R/R AML received some type of transplant; the rate of HSCT was similar between cohorts.Patients with R/R AML were high utilizers of healthcare resources. In the post-event period, patients averaged 0.52 hospital visits per month with a mean length of stay (LOS) of 16.6 days/visit and a mean LOS of 6.8 days/month; there was no significant difference between FLT3mut and FLT3wt cohorts. The mean number of pre-event intensive care unit (ICU) visits was 0.03 ± 0.15 with a mean LOS/visit of 10.8 ± 9.6. In the post-event period, the mean number of ICU visits was 0.16 ± 1.3 with a mean LOS of 7.5 ± 6.5 days/visit. In total, 30.1% of all patients with R/R AML had hospice care in the post-event period; the mean number of days in hospice was 4.1 ± 8.7 days (4.5 ± 9.7 days [FLT3mut] vs 3.8 ± 7.7 [FLT3wt]). In some instances in the pre-event period, patients with FLT3mut were higher users of healthcare resources. Compared with FLT3wt, patients with FLT3mut had a longer hospital LOS/visit (29.6 days vs 21.8 days; P<.05) and had significantly higher utilization of all types of outpatient visits, including: total outpatient, hematologist, nurse, and general practitioner (all P<.001).Conclusions: Utilizing RWE, these data reveal that patients with FLT3mut AML are diagnosed at an earlier age and utilize more healthcare resources than patients with FLT3wt AML. Further, for patients with R/R AML, regardless of mutation status and despite the availability of effective therapies, the most common treatment was BSC - a divergence from accepted treatment guidelines. Additionally, the breadth of treatments being used suggests that there is no real standard of care for patients with R/R AML. The availability of targeted agents (ie, FLT3 inhibitors) may provide treatment options for patients. DisclosuresGriffin:Novartis Pharma: Other: Grant, Patents & Royalties: Royalties ; Sun Pharmaceuticals: Consultancy; Lilly Pharmaceuticals: Other: Grant; Myeloproliferative Neoplasia Foundation: Other: Grant ; Analysis Group: Consultancy; RXi Pharmaceuticals: Consultancy; Astellas Pharma: Consultancy. Shah:Astellas Pharma: Employment. Song:Astellas Pharma: Consultancy. Yang:Astellas Pharma: Consultancy.

Expanding the Utility of Midostaurin in Acute Myeloid Leukemia - Predictive Mutational Signatures in Patient Samples without FLT3 mutations and Clinically Applicable Synergistic Drug Combinations

BackgroundFollowing the positive outcome of the RATIFY phase 3 clinical trial, the multi-kinase inhibitor midostaurin was approved for the treatment of adult patients with newly diagnosed FLT3-mutated acute myeloid leukemia (AML). However, we and others have observed that single agent midostaurin yields responses also in a substantial portion of patients not carrying FLT3 mutations. The molecular basis and the kinase targets mediating these responses are poorly understood and no biomarkers predictive of response in FLT3 wildtype (wt) AML patients exist. To identify markers distinguishing the FLT3 wt responding subset of patients, we trained machine learning multi-marker models using AML patient baseline transcriptomic and mutational data to predict ex vivo responders vs. non-responders. Further, to better understand the molecular basis of midostaurin responses and to explore the unique signaling networks modulated by midostaurin, we profiled the sensitivities of AML patient samples to midostaurin in comparison to, and in combination with, several clinically relevant oncological targeted agents of diverse mechanistic classes.ResultsMidostaurin target space is unique and it retains anti-leukemic potency under cytoprotective conditions. We have previously established that single agent midostaurin is effective ex vivo in about 25% of FLT3 wt AML patient samples and retains potency in a cytoprotective medium that masks the effects of more selective FLT3 inhibitors such as quizartinib, crenolanib and sorafenib (Karjalainen et al, Blood 2017). To further investigate the unique pathways that midostaurin, but not other FLT3 inhibitors targets, we correlated the response patterns of 87 AML patient samples in cytoprotective medium to midostaurin and 261 other kinase inhibitors in our oncology compound collection. In unsupervised cluster analysis, midostaurin showed highly similar response patterns to AZD7762, OTS167, milciclib, pacritinib, ENMD-2076 and fostamatinib. Publicly available in vitro kinase profiling (Tang et al, Cell Chem. Biol. 2018) suggested that midostaurin does not inhibit most of the primary targets of these other inhibitors, with only aurora kinases, JAK kinases and SYK appearing to be shared potent targets.Midostaurin anti-leukemic potency is determined by the mutational background. Several multi-marker, supervised machine learning models were compared to extract biomarker signatures from either baseline transcriptomic or mutational data, in the task of predicting ex vivo midostaurin response in samples cultured in cytoprotective medium. In the full cohort (N=81), the presence of FLT3 mutations (both internal tandem repeat and tyrosine kinase domain mutations) was the strongest predictor of response. In the FLT3 wt cases (N=49), our results revealed that other select mutations correlated well with either response or non-response upon Bayesian Linear Regression analysis with cross-validation (Ammad-Ud-Din et al, Bioinformatics, 2017). Mutations in PTPN11, U2AF1, SRSF2, RUNX1, JAK2 and BCOR predicted midostaurin responders, while mutations in GATA2, WT1, NPM1 and IDH2 were enriched in non-responders (Figure 1). Baseline transcriptomic profiles, however, did not provide added value for the predictive power.Midostaurin efficacy can be enhanced by combination with other targeted agents. Combinatorial drug screening of midostaurin in cytoprotective medium revealed several synergizing drug classes, including BCL-2 and MDM2-p53 inhibitors. Further analysis of synergizing agents in broader AML patient sample cohorts is ongoing.ConclusionsOur results show that midostaurin may reach its biological effects through inhibition of additional kinases than just FLT3. In both FLT3 mutant and wt cases, midostaurin responses are influenced by the overall mutational background. Furthermore, our data indicates that midostaurin efficacy can be enhanced through combination with other agents. Together, we have significantly expanded the understanding of molecular determinants of midostaurin response in primary AML cells, supporting predictive biomarker discovery efforts and development of synergistic drug combinations. The emerging hypotheses from this work will have to be tested in clinical studies. [Display omitted] DisclosuresPorkka:Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding. Marques Ramos:Novartis: Employment. Pallaud:Novartis: Employment. Aittokallio:Novartis: Research Funding. Wennerberg:Novartis: Research Funding.

Emerging Real-World Midostaurin Treatment Patterns and Outcomes in FLT3-Mutated Acute Myeloid Leukemia at a Comprehensive Cancer Center

Introduction: Fms-like tyrosine kinase 3 (FLT3) gene mutation occurs in approximately 25-30% of acute myeloid leukemia (AML) cases and is associated with poor prognosis. Decreased overall survival is reported in FLT3-mutated vs. FLT3-wildtype. Midostaurin, a pan-targeted kinase inhibitor that inhibits activated FLT3 received FDA approval in April 2017 for adult patients with newly diagnosed FLT3-mutated AML in combination with standard cytarabine and daunorubicin induction and cytarabine consolidation. We report descriptive US clinical treatment patterns and outcomes in FLT3-mutated early midostaurin-users, historical FLT3-mutated patients prior to midostaurin approval, and historical FLT3-wildtype AML patients all treated with 7+3 induction therapy at an academic cancer specialty hospital to support the development of a larger database across several comprehensive cancer centers.Methods: This retrospective, observational study utilized ICD codes, tumor registry data, and pharmacy records from the Huntsman Cancer Institute (HCI) to identify AML patients treated with 7+3 induction chemotherapy from 2007 to July 2018. FLT3-mutated midostaurin-users treated with 7+3 induction including midostaurin from May 2017 to July 2018 comprise Group 1. Historical FLT3-mutated patients prior to midostaurin approval (non-users) and FLT3-wildtype patients comprise Groups 2 and 3, respectively. Complete response (CR), relapse rates, overall survival and treatment patterns were described.Results: A total of 105 patients met eligibility for inclusion in the study. Groups 1, 2, and 3 included five, 39 and 61 patients, respectively. Off-label midostaurin use in Group 1 after induction therapy was observed in one patient with post-consolidation monotherapy and salvage therapy in combination with ATRA (tretinoin) and CLAG (cladribine, cytarabine, and filgrastim). Following midostaurin approval, two FLT3-mutated patients received induction therapy without midostaurin due to enrollment in clinical trials that excluded midostaurin use for induction and consolidation therapy. These two patients were excluded from the study. Descriptive results of the comparative groups are summarized in Table 1. CR rate from induction therapy was 100% for Group 1, 90% for Group 2, and 77% for Group 3. The proportion of patients who received consolidation therapy was 60%, 74%, and 67%, and patients who maintained CR during consolidation therapy was 100%, 83%, and 49% for Groups 1, 2, and 3, respectively. Sixty-six percent of eligible Group 1 patients, 74% of Group 2 patients, and 54% of Group 3 patients received transplant. Median time from diagnosis to transplant was 81, 99, and 145 days for Groups 1, 2, and 3, respectively. The proportion of patients who received salvage therapy in Groups 1, 2, and 3 was 20%, 38%, and 56% respectively. Median follow-up was 6 months for Group 1, 14 months for Group 2, and 24 months for Group 3. After CR, 20% of Group 1, 49% of Group 2, and 59% of Group 3 relapsed. All Group 1 patients were alive at time of analysis while four Group 2, and eight Group 3 patients died during the study period.Discussion: Similar CR and relapse rates were observed between the comparative groups, although early use observations indicate improved response rates of induction therapy and consolidation therapy in a limited Group 1 sample. Patients in Group 1 and Group 2 underwent transplant earlier and more frequently than patients in Group 3, which may explain the higher relapse rate in Group 3. As this data resource is expanded across similar institutions, statistical comparisons of FLT3-mutated AML patients treated with and without midostaurin can be made.Sponsorship: Funding for this study was provided by Novartis Pharmaceuticals. DisclosuresUnni:Novartis: Research Funding. Ndife:Novartis: Employment. Joseph:Novartis Pharmaceuticals Corporation: Employment; Amgen: Equity Ownership; Pfizer: Equity Ownership; Express Scripts: Equity Ownership. Bonifacio:Novartis: Employment. Stein:Novartis: Consultancy; Daiichi Sankyo: Consultancy; Agios: Consultancy; Bayer: Consultancy; Celgene: Consultancy; Pfizer: Consultancy. Shami:Lone Star Biotherapies: Equity Ownership; Pfizer: Consultancy; JSK Therapeutics: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Baston Biologics Company: Membership on an entity's Board of Directors or advisory committees. Kovacsovics:Amgen: Honoraria, Research Funding; Abbvie: Research Funding. Brixner:BD: Consultancy; Abbott: Consultancy; AbbVie: Consultancy; AstraZeneca: Consultancy; Gilead: Consultancy; Millcreek Outcomes Group: Equity Ownership; University of Utah: Research Funding. Stenehjem:Novartis: Research Funding.

Abstract 25: CG′806, a first-in-class FLT3/BTK inhibitor, exerts superior potency against AML cells harboring ITD, TKD and gatekeeper mutated FLT3 or wild-type FLT3

Abstract The receptor tyrosine kinase FLT3 can undergo a series of mutations, including the activating internal tandem duplication (ITD) in the juxtamembrane region and point mutations in the tyrosine kinase domain such as at the activation loop residue D835 (Thiede et al. 2002). FLT3 is widely accepted as a prime target for acute myeloid leukemia (AML) therapy, as the FLT3-ITD mutation is present in approximately 24% of AML patients and it is associated with very poor prognosis (Kottaridis et al. 2003). However, additional acquired mutations of FLT3, including D835 or “gatekeeper” F691 mutations that have been identified in clinical patients who showed resistance/relapse to FLT3 inhibitors sorafenib or quizartinib (Man et al. 2012; Smith et al. 2012), can render most FLT3 inhibitors ineffective. We also reported that aberrant upregulation of other parallel prosurvival signaling pathways may render AML resistant to FLT3-targeted therapy (Zhang et al. 2014). CG′806 is a small-molecule multi-kinase inhibitor against FLT3 and BTK kinases that is under development to treat FLT3-driven AML. A single test concentration of 25 nM in a 583-kinase panel, an IC50 analysis against 176 kinases, and a Kd analysis against 483 kinases illustrated the ability of CG′806 to target the entirety of FLT3-mutant enzymes and to inhibit additional kinases (e.g., BTK, AURK, STE group, and TRK/AXL/DDR group). CG′806 exerted potent picomolar IC50 antiproliferative activity against human AML cells and against Ba/F3 mouse AML cells with FLT3-ITD mutations (about 50 to 250-fold higher activity compared to quizartinib or gilteritinib). Specifically, compared to second-generation FLT3 inhibitors quizartinib or gilteritinib, CG′806 showed much more pronounced antiproliferative effects in leukemia cells with D835 mutations, the ITD plus F691I/Y842D/D835 mutations, or in FLT3 wild-type cells (IC50s were 0.17, 0.82, 9.49, 0.30, 8.26, 9.72, and 0.43 nM for human ITD-mutated AML cells MV4-11 (FLT3-ITD), MOLM13 (FLT3-ITD), murine ITD mutated leukemia cells Ba/F3 WT, Ba/F3-ITD, Ba/F3-D835Y, Ba/FLT3-ITD+D835Y, and “gatekeeper” mutation Ba/F3-ITD+F691L cells, respectively). Furthermore, CG′806 triggered profound apoptosis in cell lines and primary AML patient samples harboring FLT3-ITD mutations as well as WT. Mechanistically, CG′806 profoundly suppressed FLT3 and its downstream MAPK/AKT signaling, as well as phospho-Aurora, and/or phospho-BTK proteins, suggesting the ability of CG′806 to inhibit various kinases that function in AML signaling and appear to contribute to its effectiveness. Moreover, CG′806 demonstrated in vivo tumor eradication without toxicity when administered orally, once daily for 14 d as a single agent in the MV4:11 AML murine xenograft model, and demonstrated sustained micromolar plasma drug levels in mice after a single oral administration. CG′806 can be considered not only a pan-FLT3 inhibitor for targeting FLT3 wild-type and ITD-mutant AML, but also a one-of-a-kind agent killing leukemia cells with TKD or dual TKD plus ITD mutations, which are frequently associated with resistance/relapse in FLT3-mutant AML patients. CG′806 exerts a robust therapeutic window in animal xenograft studies and does not appear to elicit the adverse side effects seen with other multikinase inhibitors (i.e., weight loss, nausea, diarrhea, myelosuppression, and/or vomiting). CG′806 warrants further investigation for the treatment of newly diagnosed and relapsed/refractory patients with FLT3-mutated AML. Citation Format: Weiguo Zhang, Hongying Zhang, Andrea Local, William G. Rice, Charlie J. Ly, Guopan Yu, Stephen B. Howell, Michael Andreeff. CG′806, a first-in-class FLT3/BTK inhibitor, exerts superior potency against AML cells harboring ITD, TKD and gatekeeper mutated FLT3 or wild-type FLT3 [abstract]. In: Proceedings of the Second AACR Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; May 6-9, 2017; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(24_Suppl):Abstract nr 25.

MiR-155 promotes FLT3-ITD–induced myeloproliferative disease through inhibition of the interferon response

AbstractFLT3-ITD+ acute myeloid leukemia (AML) accounts for ∼25% of all AML cases and is a subtype that carries a poor prognosis. microRNA-155 (miR-155) is specifically overexpressed in FLT3-ITD+ AML compared with FLT3 wild-type (FLT3-WT) AML and is critical for the growth of FLT3-ITD+ AML cells in vitro. However, miR-155's role in regulating FLT3-ITD–mediated disease in vivo remains unclear. In this study, we used a genetic mouse model to determine whether miR-155 influences the development of FLT3-ITD–induced myeloproliferative disease. Results indicate that miR-155 promotes FLT3-ITD–induced myeloid expansion in the bone marrow, spleen, and peripheral blood. Mechanistically, miR-155 increases proliferation of the hematopoietic stem and progenitor cell compartments by reducing the growth-inhibitory effects of the interferon (IFN) response, and this involves targeting of Cebpb. Consistent with our observations in mice, primary FLT3-ITD+ AML clinical samples have significantly higher miR-155 levels and a lower IFN response compared with FLT3-WT AML samples. Further, inhibition of miR-155 in FLT3-ITD+ AML cell lines using CRISPR/Cas9, or primary FLT3-ITD+ AML samples using locked nucleic acid antisense inhibitors, results in an elevated IFN response and reduces colony formation. Altogether, our data reveal that miR-155 collaborates with FLT3-ITD to promote myeloid cell expansion in vivo and that this involves a multitarget mechanism that includes repression of IFN signaling.

Combined inhibition of GLI and FLT3 signaling leads to effective anti-leukemic effects in human acute myeloid leukemia.

Activation of the Hedgehog pathway has been implicated in the pathogenesis of several tumor types including myeloid leukemia. Previously we demonstrated that overexpression of Hedgehog downstream mediators GLI1/2 confers an adverse prognosis to patients with acute myeloid leukemia (AML) and is correlated with a FLT3 mutated status. To analyze a possible non-canonical activation of the Hedgehog pathway via FLT3 and PI3K, we performed blocking experiments utilizing inhibitors for FLT3 (sunitinib), PI3K (PF-04691502) and GLI1/2 (GANT61) in FLT3-mutated and FLT3 wildtype AML cell lines and primary blasts. Combination of all three compounds had stronger anti-leukemic effects in FLT3-mutated compared to FLT3 wildtype AML cells in vitro. Interestingly, the colony growth of normal CD34+ cells from healthy donors was not impeded by the triple inhibitor combination possibly opening a therapeutic window for the clinical use of inhibitor combinations. Besides, combined treatment with sunitinib, PF-04691502 and GANT61 significantly prolonged the survival of mice transplanted with FLT3-mutated MV4-11 cells compared to the single agent treatments. Furthermore, the inhibition of FLT3 and PI3K resulted in reduced GLI protein expression and promotor activity in FLT3-mutated but not in FLT3 wildtype AML cell lines in western blotting and GLI1/2 promoter assays supporting our hypothesis of non-canonical GLI activation via FLT3.In summary, FLT3-mutated in contrast to FLT3 wildtype cells or normal human hematopoietic progenitor cells are exquisitely sensitive to combined inhibition by FLT3, PI3K and GLI1/2 overcoming some of the limitations of current FLT3 directed therapy in AML. The development of GLI1/2 inhibitors is highly desirable.

Aggressive Aneuploid Acute Myeloid Leukemia Is Dependent on Alterations of P53, Gain of APC and PLK1 and Loss of RAD50

Abstract Chromosome number alterations, aneuploidy, is a hallmark of cancer. It occurs in about 15% of acute myeloid leukemia (AML) cases, is generally preserved throughout disease progression (Bochtler et al. Leukemia 2015) and correlates with adverse prognosis (Breems et al. JCO 2008, Papaemmanuil et al. NEJM 2016). This evidence highlights the need of understanding the molecular mechanisms that promote and sustain aneuploidy in AML, in order to define novel potential therapeutic targets. In the NGS-PTL project we profiled the genomic landscape of 536 hematological samples by whole exome sequencing (WES, Illumina). Among them, we analyzed 88 and 68 samples from aneuploid (A-) FLT3-wildtype AML (isolated trisomy and monosomy, complex and monosomal karyotype) and euploid (E-) AML (normal and complex karyotype, &lt;3 abnormalities), respectively (100 bp, paired-end). Variants were called by MuTect and Varscan 2.0. WES output was integrated with genotype data (CytoScan HD Array, Affymetrix and Nexus Copy Number analysis) and gene expression profiling (HTA 2.0 and TAC 3.0, Affymetrix). A-AML showed an increased genomic instability, as confirmed by a higher mutation load compared with E-AML (median number of variants: 22 (range: 2-95) and 11 (range: 3-45), respectively, p&lt;.001), which was associated with increased patients' age (median age of 62 for A-AML and 55 for E-AML, p&lt;.05). The increased age and mutation load correlated with a mutational signature with prominence of C&gt;A substitutions, compared with the C&gt;T transition-related signature, which is prevalent in AML. A-AML was associated with mutations and/or heterozygous deletion of TP53 (p&lt;.001), which co-occurred with copy number loss of both the tumor suppressor APC and the DNA repair gene RAD50 in 93% of cases (p&lt;.001). Moreover, A-AML was enriched for a gene expression signature of p53-deficiency, independently of TP53 structural defects (p&lt;.05, GSEA). Mutations and deregulated expression of genes involved in cell cycle contributed to the A-AML phenotype, with 68% A-AML vs. 32% E-AML patients (p&lt;.01) carrying at least one genomic lesion affecting the process. The alterations targeted the following pathways: DNA repair (i.e. reduced RAD50 expression, p&lt;.001), cell cycle checkpoints (i.e. mutated CHK2), regulation of PLK1 activity at G2/M transition (i.e. mutation and 2-fold upregulation of PLK1, p&lt;.01), mitotic metaphase and anaphase (i.e. increased CDC20 level, p&lt;.001) and separation of sister chromatids (i.e. mutated BUB1B, ESPL1, CENPO). Of note, a 3-gene signature composed of PLK1, CDC20 and RAD50, was able to discriminate 73% of patients between the A- and E-AML cohorts. This signature was confirmed at protein level. In parallel, E-AML showed a preferential dependency on epigenetic mechanisms, with recurrent genomic lesions of ASXL1/2, BCOR/L1, EZH2 and MLL, enrichment of FLT3 alterations and mutations activating RAS signal transduction (p&lt;.05). Of note, a HOX-related signature characterized by overexpression of the HOX family members HOXA7, HOXB3 and MEIS1 identified E-AML. We show here for the first time the molecular mechanisms promoting and maintaining aneuploidy in AML. Our results indicate that p53 deficiency, either caused by somatic mutations, copy number loss, impaired DNA damage response and enhanced PLK1 signaling synergize with APCgain, RAD50 structural or functional loss and forced progression through mitosis, to override cell cycle and mitotic checkpoints and allow the formation of daughter cells with an aberrant chromosome number. These mechanisms cooperate with recurrent mutations of genes involved in protein ubiquitination and proteasome-mediated protein catabolic process in A-AML, indicative of the attempt of aneuploid cells to override the proteotoxic stress due to the unbalanced protein load generated by the aneuploid condition. This evidence provides the rationale for exploiting proteasome inhibition (Velcade), p53 reactivation (MDM2/4 inhibitor) and targeting of the cell cycle (CHK1/2 inhibitor) downstream to p53 (WEE1 inhibitor) as strategies for novel combination therapies against aggressive aneuploid AML, which are under clinical investigation in our Institution and may serve as a model for aneuploid tumors. GS and AP: equal contribution. Supported by: FP7 NGS-PTL project, ELN, AIL, AIRC, PRIN, progetto Regione-Università 2010-12 (L. Bolondi). Disclosures Haferlach: MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Martinelli:Ariad: Consultancy, Speakers Bureau; MSD: Consultancy; Celgene: Consultancy, Speakers Bureau; Roche: Consultancy, Speakers Bureau; Genentech: Consultancy; Novartis: Speakers Bureau; BMS: Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau.