Mutant Acute Myeloid Leukemia Research Articles

FLT3 Inhibitors in Combination with FLAG-IDA in Relapsed or Refractory Acute Myeloid Leukemia

1. Introduction The addition of a FLT3 inhibitor improves overall survival in combination with front-line intensive chemotherapy in acute myeloid leukemia (AML). In the ADMIRAL trial, gilteritinib - a second-generation, type I FLT3 inhibitor - improved survival in relapsed or refractory AML compared to intensive chemotherapy. However, it is unknown whether the combination of a FLT3 inhibitor and intensive chemotherapy improves survival in the relapsed or refractory setting compared with intensive chemotherapy alone or intensive chemotherapy with venetoclax in FLT3 mut AML. 2. Methods We analyzed 27 patients with FLT3 mut AML treated with FLAG-IDA for relapsed or refractory disease from January 1, 2013 to April 18, 2023 at VCU Massey Comprehensive Cancer Center. Baseline disease characteristics were obtained, including molecular profiling either through PCR, NGS, or both, alongside cytogenetic risk, doses of induction regimens, response, and survival. We separated patients that underwent treatment with FLAG-IDA and a FLT3 inhibitor (gilteritinib, midostaurin, or sorafenib), venetoclax, or FLAG-IDA alone. Measurable residual disease (MRD) assays were PCR-based when available; otherwise, MRD was assessed through multiparameter flow cytometry. We used the D'Agostino & Pearson method for normality testing and the Kruskal-Wallis test for between-group comparisons. We applied the Bonferroni correction if multiple comparisons were made. We analyzed survival by the Kaplan-Meier method with significance determined by the log-rank test. The event for calculating the overall survival (OS) was the date of death. Patients were otherwise censored at the date of last contact. 3. Results All 27 patients treated with FLAG-IDA harbored mutations in FLT3-ITD (70.3%) or FLT3-TKD (29.6%). Twelve (44.4%) patients received FLT3 inhibitors with FLAG-IDA: eight (66.7%) with midostaurin, three (25.0%) with gilteritinib, and one (8.3%) with sorafenib. Five (41.6%) patients received a FLT3 inhibitor (FLT3i) for previously untreated disease, then subsequently received a FLT3i at disease progression. Ten (37.0%) patients received FLAG-IDA without a FLT3i, and five (18.5%) received FLAG-IDA and venetoclax. The median FLT3 variant allele frequency was 33.96% (95% CI, 5.1-63.9) in the FLT3i cohort, 18.0% (95% CI, 8.0-27.0) in the FLAG-IDA cohort, and 5.0% (95% CI, 3.0-29.0) in the venetoclax cohort. The median prior lines of therapy were as follows: three for the FLT3i cohort, two for the FLAG-IDA cohort, and three for the venetoclax cohort (p = 0.137). There was no difference in the achievement of CRc between the FLT3i and FLAG-IDA groups (27.3% vs 33.3%, p > 0.999) or between the FLT3i and venetoclax groups (27.3% vs 50.0%, p = 0.560). The proportion of responders that achieved MRD negativity was nonsignificantly higher in the FLT3i cohort (75.0% vs 20.0%, p = 0.206). The median overall survival nonsignificantly favored the FLT3i cohort compared to the FLAG-IDA cohort (7.7 months vs 4.1 months, p = 0.992) and the venetoclax cohort (7.7 months vs 6.3 months, p = 0.902). 4. Discussion The addition of a FLT3 inhibitor resulted in nonsignificantly higher rates of MRD negativity and prolonged overall survival when compared to FLAG-IDA alone or FLAG-IDA and venetoclax. The optimal combination regimen for relapsed or refractory FLT3 mut AML is unknown, but likely should include a FLT3 inhibitor. The limitations of our study include its retrospective nature; subsequent FLT3 inhibitor combinations or maintenance strategies may have provided a survival benefit the FLT3i cohort. Therefore, prospective clinical trial designs are needed to further confirm these findings.

TP53-Mutated Acute Myeloid Leukemia Patients Treated with Intensive Therapies Have Superior Outcomes: A Single Institution, Retrospective Study

Background: Mutations in TP53, found in 5-20% of acute myeloid leukemia (AML), confer poor prognosis and are associated with high rates of therapy resistance, high relapse rates, and dismal overall survival (OS). Recent advances have provided a variety of options for up-front AML therapy including a liposomal preparation of standard-of-care chemotherapy (CPX-351) and venetoclax-based combinations. Due to known poor outcomes with intensive chemotherapy, many providers are favoring less intense strategies for patients with TP53 mutant AML, but these approaches have not been directly compared for this patient subgroup. Strategies for treating TP53 mutant AML are highly heterogeneous and optimal treatment strategies have not been defined in this setting. We performed a retrospective study to compare the clinical outcomes of TP53 mutant AML patients treated at our center. Methods: The study was a single-center, retrospective cohort analysis conducted at the University of Minnesota. Adult patients (age ≥18 years) with the diagnosis of AML or myeloid sarcoma between January 1, 2014 and July 31, 2022 who have next-generation sequencing panel confirming a pathogenic TP53 mutation and received front-line therapy for AML at our center were included in this study. Kaplan-Meier analysis was used to estimate the probabilities of OS, defined as the date of treatment initiation to the date of death from any cause or last follow-up. Results: Our study includes 88 patients with TP53 mutant AML with available clinical data in an AML registry at our institution. Baseline demographic and clinical characteristics are summarized in Table 1. The median age at diagnosis was 67 years (range 28-87) with male predominance (65.9%). Among this, 15/88 patients (17.1%) had therapy-related AML and 40/88 patients (45.5%) had secondary AML. The median bone marrow blast percentage at diagnosis was 31% and peripheral blast percentage was 9%. The majority of patients have high variant allelic frequency (VAF, 71.9% with VAF > 0.4 for patients with available VAF data) and ASXL1 was the most frequent co-mutation identified followed by KRAS and NRAS. Treatment regimens were classified as intensive or nonintensive. Intensive treatment regimens included infusional cytarabine with either daunorubicin or idarubicin (7+3), liposomal cytarabine and daunorubicin (CPX-351), and mitoxantrone, etoposide and cytarabine (MEC). Nonintensive regimens included hypomethylating agents (decitabine or azacitidine) with or without venetoclax and clofarabine with low-dose subcutaneous cytarabine. A total of 66 patients were included in the survival analysis. There was no significant difference in OS between patients aged < 65 years and ≥ 65 years at diagnosis (2-year OS, 11% versus 5%, P=0.76). Superior 2-year OS was observed in patients who received front-line intensive (n = 31) versus nonintensive (n = 35) induction chemotherapy (2-year OS, 13% versus 3%, P=0.01, Figure 1). Patients who received intensive therapy for any line of treatment also demonstrated superior OS compared to those who never received intensive therapy (2-year OS, 12% versus 3%, P=0.02). The rate of achieving complete remission (CR) was higher in patients who received intensive treatment compared to non-intensive therapy in the first-line (51.6% versus 25.7%, P=0.03). Rate of CR at any time was also higher for patients who received intensive treatment for any line of treatment (50% versus 18.2%, P<0.01). Among the intensive first-line treatment group, 7+3 (n = 18) showed superior OS relative to CPX-351 (n = 12) (2-year OS, 22% versus 0%, P=0.03) although there was no significant difference in CR rate (55.6% versus 50%, P=0.77). Furthermore, significant survival benefit was shown in patients who underwent allogeneic hematopoietic cell transplantation compared to patients who had not (2-year OS, 21% versus 4%, P<0.01]). Conclusions: In our cohort, TP53 mutant AML patients treated with intensive chemotherapy and transplant have superior outcomes to those who do not. Since this was a retrospective study, we cannot rule out the possibility that these results are confounded by providers favoring more intensive therapies for fitter patients. However, these data imply that TP53 mutant patients may benefit from more intensive therapy and suggests that future work to define optimal therapy regimens in this patient population may incorporate intensive strategies.

Autophagy Induction Constitutes a Targetable Vulnerability in FLT3-Mutant Acute Myeloid Leukemia Cells Treated with FLT3-Inhibitors

Recently, we and others identified autophagy induction as a protective mechanism in FLT3-ITD mutant acute myeloid leukemia (AML) cells upon treatment with FLT3-inhibitors (FLT3i), constituting an increasing issue in clinical practice. Here, we investigated the molecular consequences of autophagy induction upon FLT3i treatment, exploring resistance mechanisms and interrogated whether autophagy inhibition can improve FLT3i antileukemic therapy. Drug response of primary FLT3-ITD AML samples ex vivo treated with FLT3i, quizartinib (AC220, n= 59) and midostaurin (PKC412, n=64), was associated with their transcriptional profile to unravel which molecular programs were enriched in poor responders. Both gene set enrichment analysis (GSEA) and single sample GSEA (ssGSEA) revealed enriched molecular signatures compatible with autophagy activation in poor responders to FLT3i, while sensitive samples enriched molecular signatures consonant with mitochondrial function. Enrichment scores for programs associated with “regulation of autophagy” and “autophagosome organization” were positively correlated to ex vivo response area under the curve values for AC220 and PKC412. To functionally address the molecular pathways associated with autophagy activation upon FLT3i treatment, MOLM-13 and MV4-11 AML cells ( FLT3-ITD) and primary AML samples, were treated with AC220 and PKC412 alone or in combination with the autophagy inhibitor chloroquine (CQ, 5-10μM). In FLT3-ITD AML models, treatment with FLT3i significantly induced the formation of acidic vesicular organelles, suggesting autophagy induction. We also observed a reduction of autophagy regulators in a dose- and time-dependent manner, evidenced by the conversion of LC3B-I to LC3B-II, with degradation of LC3B-II and p62. Furthermore, FLT3i treatment resulted in phosphorylation inhibition of AKT Ser473, mTOR Ser2448 and its downstream protein p70S6K Thr421/Ser424, and phosphorylation reduction of ULK1 Ser757. Combination of FLT3i with CQ (10 μM) significantly reduced cell viability and survival for both PKC412 and AC220 inhibitors. To rule out the off target effects associated with CQ treatment, we performed a knockdown (KD) on the key autophagy mediator ATG5 using shRNA-mediated inhibition in FLT3-ITD cells. In MOLM13 cells, FLT3i treatment in ATG5-KD cells significantly reduced the IC50 (control: 31nM vs. ATG5-KD: 17nM) and increased apoptosis induction (control: 41% vs. ATG5-KD: 58%). We validated these observations in ex vivo treated primary AML samples, where we observed that in FLT3-ITD but not in FLT3 wild-type samples, the combination of FLT3i (PKC412 and AC220) plus autophagy inhibitors (CQ) reduced cell proliferation and survival. In summary, we demonstrated that autophagy induction is a biological process intrinsically associated with drug resistance in FLT3-ITD mutant AMLs when treated with FLT3i. Hence, autophagy inhibition can be leveraged to increase the antileukemic effect of FLT3i and highlights the autophagy as a major acquired biological process associated with FLT3i therapy.

Integrated Methylation and Transcriptional Landscape and Evolution of Pediatric AML

Acute myeloid leukemia (AML) is an aggressive hematopoietic malignancy associated with poor outcomes despite intensive therapies. The genomic landscape of pediatric AML has been well characterized and has led to translational benefits, such as improved relapse predication and effective targeted therapies for a subset of individuals (e.g., FLT3-ITD AML). Despite these advances, the majority of patients continue to receive therapeutic interventions that have not changed in three decades. This underscores the need to advance our understanding of AML biology beyond genomic alterations (e.g., somatic mutations). Here, we present the largest (N = 858 patients) integrative analysis of pediatric AML paired transcriptomes and methylomes to date, performed at diagnosis for patients enrolled on Children's Oncology Group clinical trials AAML0531 (NCT00372593) or AAML1031 (NCT01371981). We also analyzed N = 400 and 253 corresponding transcriptomes and methylomes at relapse, respectively. Additionally, we performed comprehensive mutation and fusion calling from NGS data and integrated clinical covariates and outcomes. This robust dataset allowed us to uncover how pediatric AML epigenetics are perturbed from normal hematopoiesis, characterize the evolution of transcriptional and methylation changes from leukemia diagnosis to relapse, and identify more accurate relapse prediction models for pediatric AML. We initially performed unbiased hierarchical clustering on CpG sites that are differentially methylated between AML and normal bone marrow to identify distinct AML-restricted methylation (ARM) signatures. This analysis demonstrated that that these ARM clusters were enriched in specific cytomolecular subtypes of pediatric AML. Specifically, we identified methylation signatures that recapitulated their adult counterparts (e.g., IDH1/2, DNMT3A, WT1) and pediatric specific methylation signatures that clustered with RUNX1::RUNX1T1, CBFB::MYH11, KMT2A-rearrangement, NUP98::NSD1, NUP98::KDM5A, and CEBPA mutant AML. Next, we investigated the transcriptional and methylation signatures for the relapsed cases and compared them to diagnosis. We demonstrated that relapsed transcriptional and methylation signatures clustered within their cytomolecular subtype counterparts at diagnosis (i.e., AMLs at relapse more closely resemble AMLs at diagnosis with the same underlying gene fusion than other relapsed AMLs) ( Fig. 1A). However, analyzing our data in the context of these cytomolecular subtypes, we found that leukemias uniformly acquired a more stem-like state at relapse. We focused our biomarker discovery efforts on KMT2A-rearranged AMLs since (as a cohort) these patients have an intermediate risk of relapse and existing molecular biomarkers (e.g., KMT2A fusion partner and measurable residual disease detection) result in only modest improvements in relapse prediction. First, we found that CpG islands associated with CD34 and HOXA gene expression were frequently (but variably) hypermethylated, which was also associated with downregulation of CD34 and HOXA gene expression and favorable survival outcomes. Next, we performed non-negative matrix factorization on diagnosis and relapsed KMT2A-rearranged AMLs and identified a novel gene set associated with relapse and poor outcomes. These three distinct methylation-transcriptional findings (i.e., CD34, HOXA, and relapsed signatures) were subsequently transformed into a novel methylation-transcription biomarker score (MTBS) using machine learning algorithms (i.e., LASSO Cox regression). We used KMT2A-rearranged AML patients from AAML1031 as our training cohort (N = 129) to generate a MTBS that was able to distinguish KMT2A-rearranged cases with disparate outcomes. This algorithm was validated in an independent cohort from AAML0531 (N = 28) ( Fig. 1B). Additional methylation-transcriptional biomarker discovery efforts for pediatric AML are underway. Since pediatric AML is associated with a low mutational burden, understanding leukemia-specific transcriptional and epigenetic alterations is of utmost importance. Our study demonstrates the translational promise offered by deep functional genomic characterization of pediatric AML and we believe that further interrogation may provide additional novel insights into leukemia initiation, relapse prediction, and novel treatment approaches.

Synergistic Growth Inhibition of NPM1 Mutant AML PDX By Combined Therapy with BCL-2 Inhibitor Venetoclax (ABT-199) and Menin Inhibitor DS-1594b In Vivo

Introduction: Mixed-lineage-leukemia (MLL) translocations are prevalent in hematologic malignancies, resulting in aggressive leukemias resistant to standard therapies and low 5-year survival rates. These translocations lead to the production of MLL fusion proteins that promote leukemia development by enhancing proliferation, inhibiting hematopoietic differentiation, and driving leukemogenesis. Acute myeloid leukemia (AML), an aggressive blood cancer with a grim prognosis, particularly in elderly patients, frequently involves mutations in the nucleophosmin (NPM1) gene. Importantly, the interaction between Menin, MLL, and MLL fusion proteins play a crucial role in the pathogenesis of AML, both with MLL rearrangements (MLLr) and in leukemias carrying NPM1 mutations. Inhibition of the Menin-MLL interaction using novel Menin inhibitors has demonstrated efficacy in pre-clinical and clinical studies for both AML subsets. In this study, we investigate the effectiveness of the novel Menin-MLL inhibitor DS-1594b, developed by Daiichi Sankyo Co. Ltd., in combination with the BCL-2 antagonist venetoclax (ABT-199), in a patient-derived xenograft (PDX) model of NPM1-mutated acute leukemia. We have previously reported synergistic lethality and differentiation-inducing effects of this drug combination in both AML cell lines and primary leukemia samples in vitro (Ciaurro et al., Blood 2022). Our findings shed light on the potential of this therapeutic combination for the targeted treatment of AML with NPM1 mutations. Methods: NSG mice (female, 8-10 weeks old) were purchased from Jackson Laboratory. Mice were inoculated via the tail vein with NPM1m PDX/luc/GFP (3×10 6 cells). Once leukemia engraftment was confirmed by bioluminescent imaging mice were randomized in 4 groups: vehicle, ABT199, DS-1594b alone, and combination. After 12 days drugs were administered as follows: DS1594b at a dosage of 50 mg/kg by oral gavage for 4 weeks; ABT-199 at a dosage of 50 mg/kg by oral gavage for 2 weeks and 100mg/kg for the other 2 weeks. NSG mice were euthanized by CO 2 inhalation at the endpoint of the study in accordance with IACUC protocols. BM and spleens were harvested in a sterile environment and flushed in HBSS with 1% FBS. For CyTOF data spleen cells were initially barcoded and stained with metal-conjugated antibodies according to Fluidigm's protocols and samples were analyzed by CyTOF (Helios) Mass Cytometer. Results: New in vitro data confirmed synergistic lethality on additional AML cell lines and demonstrated upregulation of PARP-C and Caspase3-C apoptosis pathways using western blot analysis. Further, additional 3 primary AML patient samples showed additive or synergistic growth inhibition when treated with combination of drugs. In the in vivo experiment with NPM1m PDX/luc/GFP AML PDX model, we found that co-treatment with DS-1594b and venetoclax for four weeks resulted in a greater reduction in AML burden compared to treatment with either agent alone or a vehicle control as shown by Bioluminescence imaging. Moreover, weight of mice in the combo group was not significantly affected, while mice lost weight in vehicle and in single agent cohort due to rapid disease progression. The survival curve clearly demonstrated the benefits of the combination treatment, with the DS-1594b group having modest anti-tumor efficacy, and the combination group showing the greatest efficacy (Fig. 1A). To study the effects on cell differentiation, we used CyTOF technique, which allowed us to analyze a complete panel of 30 markers. We found two populations of cells, which we named populations (pop) 3 and pop 4, that were enriched in the group treated with the combination of drugs compared to the control group (Fig 1B). These populations of cells had higher levels of expression of CD33 and CD38, which are well-known markers of cellular differentiation. Conclusions: In this study, we present the in vivo effectiveness of DS-1594b in combination with venetoclax in a PDX model of NPM1-mutated AML. Moreover, the combination treatment exhibits differentiation-inducing effects, which contribute to its therapeutic effectiveness, and was safe. Overall, our findings strongly indicate that the combination of DS-1594b and venetoclax exhibits promising anti-leukemic activity in vivo and holds potential as a therapeutic strategy for AML patients with mtNPM1 mutations.

Practice Patterns of Transplant Centers Regarding Maintenance Treatment Post Allogeneic Hematopoietic Cell Transplantation in Acute Myeloid Leukemia: A Survey on Behalf of the EBMT Acute Leukemia Working Party

Introduction: Disease recurrence in acute myeloid leukemia (AML) remains the major reason of allogeneic hematopoietic cell transplantation (allo-HCT) failure. Strategies to reduce the risk of relapse such as prophylactic pharmacologic interventions post allo-HCT are more frequently applied by some transplant physicians, especially after the growing evidence of its efficacy and tolerability. Others are still being skeptical regarding its implementation due to difficulty proving efficacy by large randomized trials, or concerns of long-term toxicities. The aim of this study was to conduct a survey among the European Society for Blood and Marrow Transplantation (EBMT)-affiliated transplant centers to identify clinical practice patterns regarding maintenance treatment post-allo-HCT in AML. Methods: After the approval of the board of the Acute Leukemia Working Party (ALWP), EBMT-affiliated centers received by email a questionnaire-based survey between January and June 2023. The questionnaire consisted of 13 questions assessing clinical practices regarding maintenance treatment post allo-HCT in AML, specifically the indications of maintenance, the type, the drug used, and the duration of the treatment. Results: A total of 115 (out of 424) EBMT-affiliated centers from 31 countries responded to the survey with a response rate of 27.12%. Overall, 102 (88.8%) centers implement maintenance strategy whether pharmacological intervention or cellular therapy post allo-HCT in AML, most of the centers (N=67, 58.3%) use it based on a personalized decision, 17 (14.8%) use it routinely, and 18 (15.7%) use it exceptionally. Regarding the indication, the majority of the centers recommend maintenance treatment for AML patients in second remission or beyond (N=64, 62.7%) or in AML patients in first remission with high risk of relapse based on cytogenetic or molecular data (N=61, 59.8%), whereas 34 (33.3%) centers recommend it only for FLT3-mutant disease, and 11 (10.8%) centers in all patients regardless of the risk of disease. The majority of centers (N=77, 75.5%) use a combination of pharmacologic and cellular therapies, and 20 (19.6%) centers use only pharmacologic therapies. Among centers using pharmacologic therapies, 62 (63.9%) use hypomethylating agents (HMA) (azacitidine N=51 (82.3%), decitabine N=6 (9.6%), HMA with venetoclax N=23 (37%), HMA with donor lymphocyte infusion (DLI) N=38 (61%), or a combination of modalities in 42 (67.7%)). In general, most centers (N=35; 87.5%) do it pre-emptively either minimal residual disease (MRD) driven or chimerism driven, whereas 22 (55%) centers do it prophylactically. The majority of centers continue HMA for one-year duration (N=37, 59.7%), 15 (24.2%) for two years and only 10 (16.1%) continue until disease recurrence or toxicity. Out of 97 responding centers regarding the use of FLT3 inhibitors as maintenance, 93 (95.9%) are implementing this strategy. The most common choice was sorafenib in 82/93 (88.2%) centers, midostaurin in 28 (30%), and gilteritinib in 30 (32.2%). Among these, 56 (83.5%) centers use FLT3 inhibitors as prophylaxis whereas 28 (41.7%) use a pre-emptive approach. The preferred maintenance duration was for two years in 51 (54.8%) centers, followed by one-year duration in 30 (32.3%) centers, continuous until disease relapse or toxicity in 9 (9.7%) centers, and for five years in only 3 (3.2%) centers. Novel agents are used in 71 (70.2%) centers as maintenance either alone or in combination with HMA, of them 52 (73.2%) use venetoclax, and 13 (13.2%) use enasidenib. Finally, regarding practice patterns, 32 (29.6%) centers claim that maintenance treatment is part of their routine practice, 46 (42.6%) only for FLT3 mutant AML. Others are not routinely implementing maintenance because they are still skeptical and need more evidence by randomized clinical trials (N=8), whereas 5 centers are concerned regarding tolerability, and 16 (14.8%) cannot implement because of regulatory restrictions or lack of access. Conclusion: In this survey, the majority of responding EBMT-affiliated transplant centers is implementing post-transplant AML maintenance treatment, predominantly HMA and FLT3 inhibitors. Further studies are needed to clarify the appropriate strategy and duration of maintenance therapy. The study will help the EBMT to incorporate post-transplant strategies as a routine registry capture parameter.

Primary U2AF1 S34F Mutated Hematopoietic Cells Are Sensitive to Nonsense-Mediated RNA Decay Disruption In Vivo

Expression of mutant splicing factors alters RNA splicing in myeloid malignancies, including increased production of nonsense transcripts that rely on nonsense-mediated RNA decay (NMD) for clearance. Cell lines expressing spliceosome mutants are more sensitive to NMD inhibition than wild-type cells, and the differential sensitivity is partially dependent on R-loop formation. However, the impact of NMD disruption on the viability of primary hematopoietic cells with splicing factor mutations has not been tested in vivo. We engineered mouse MLL-AF9 acute myeloid leukemia (AML) cells to inducibly express a wild type ( U2AF1 WT) or mutant ( U2AF1 S34F) transgene of the U2AF1 splicing factor, and tested the effects of inhibiting the NMD pathway protein kinase, SMG1, in vivo. We injected U2AF1 WT and U2AF1 S34F mouse AML cells (B6, CD45.2) into congenic, irradiated secondary recipient mice (B6, CD45.1), induced transgene expression, and then treated the mice for 2 weeks with either a SMG1 inhibitor (SMG1i) at 60 mg/kg/day or vehicle. SMG1i treatment increased the overall survival (OS) of mice bearing U2AF1S34F AML cells (median OS of 53 days compared to 42 days for mice treated with vehicle; p =0.0003), but did not impact the OS of mice with U2AF1WT AML cells (median OS of 33 days for SMG1i-treated mice compared to median OS of 32 days for vehicle-treated mice, p=0.360). We extended these findings to a second cohort of mice, where we transplanted one primary U2AF1 S34F banked mouse AML sample into 48 secondary recipient mice. To allow direct comparison of isogenic cells with or without U2AF1 S34F expression, half the mice were treated with doxycycline to induce U2AF1 S34F expression, and half of the mice did not receive doxycycline. SMG1i treatment increased the OS of mice expressing the U2AF1S34F mutant allele (median OS of 66 days, compared to median OS of 54 days for mice treated with vehicle; p<0.0001), but had no impact on survival of mice bearing AML cells where U2AF1 S34F was not expressed (median OS of 50 days, compared to median OS of 52 days for mice treated with vehicle; p=0.95). To explore the underlying mechanism for the sensitivity of spliceosome mutant cells to NMD inhibition, we first examined the effects of SMG1i treatment on cell cycle progression and cell death in primary cells. We observed that primary U2AF1 S34F-expressing AML cells treated with SMG1i ex vivo (24 hours) had an increased fraction of cells in G2/M phase compared to U2AF1 WT-treated cells (mean 48% vs. 11% at 100nM, respectively, p<0.001). In addition, the fraction of Annexin V + cells was increased in U2AF1 S34F-expressing cells treated with SMG1i ex vivo compared to U2AF1 WT treated cells (mean fold-change at 500nM relative to DMSO 4.0 vs. 2.3, respectively, p=0.027). We then isolated primary mouse AML cells after 7 days of in vivo SMG1i treatment and analyzed R-loops (S9.6 antibody) and DNA damage (gH2AX) by immunofluorescence. SMG1i-treated U2AF1 S34F cells had a marked increase in R-loop levels compared to U2AF1 WT-treated cells (mean S9.6 nuclear intensity, 306.9 vs 182.6, respectively, p<0.0001). In addition, H2AX phosphorylation was increased in SMG1i-treated U2AF1 S34F compared to U2AF1 WT cells (mean gH2AX nuclear intensity, 136.7 vs 87.8, respectively p<0.0001).Thus, disrupting NMD in splicing factor mutant AML cells alters cell cycle progression and causes R-loop accumulation, DNA damage, and apoptotic cell death. The NMD pathway has been implicated in the regulation of the unfolded protein response (UPR) that controls protein homeostasis and impacts cell viability. We generated K562 cell lines expressing doxycycline-inducible U2AF1 S34F or U2AF1 WT constructs and confirmed increased sensitivity of U2AF1 S34F cells treated with SMG1i(IC50 128.1nM vs 578.5nM at 72 hours, respectively, p<0.0001). Next, we performed RNA-sequencing on U2AF1 WT and U2AF1 S34F cells that were treated with vehicle or SMG1i for 24 hours (n=3) and observed upregulation of endoplasmic reticulum and UPR pathway genes in SMG1i-treated U2AF1 S34F compared to U2AF1 WT cells (GSEA; FDR<0.01). Validation of these findings using primary mouse AML cells is ongoing, including the analysis of key regulators and protein biomarkers of the UPR pathway. The vulnerability of primary hematopoietic cancer cells with spliceosome mutations to NMD inhibition suggests the possibility for therapeutic targeting of NMD to treat myeloid malignancies with aberrant splicing.

Gilteritinib-Based Combination Therapy in Adult Relapsed/Refractory FLT3 Mutated Acute Myeloid Leukemia

Gilteritinib, a potent FMS-like tyrosine kinase 3 (FLT3) inhibitor, was approved for relapsed/refractory (R/R) FLT3 mutated acute myeloid leukemia (AML) patients but still showed limited efficacy. Here, the efficacy and safety of different gilteritinib-based combination therapy (gilteritinib plus hypomethylating agent [HMA] and venetoclax, G+HMA+VEN; gilteritinib plus HMA, G+HMA; gilteritinib plus venetoclax, G+VEN) in 33 R/R FLT3 mutated AML patients were retrospectively analyzed. Composite complete response (CRc) rate (complete response [CR]+CR with partial hematologic recovery [CRh]+CR with incomplete blood count recovery [CRi]), modified CRc rate (mCRc, CRc+morphologic leukemia-free state [MLFS]), overall survival (OS), duration of remission (DOR), and adverse events were analyzed and compared.The CRc and mCRc rate were 66.7% (12/18) and 88.9% (16/18) in patients who received G+HMA+VEN, which was higher compared with that in G+HMA (CRc: 18.2%, 2/11; mCRc: 45.5%, 5/11) or G+VEN (CRc: 50.0%, 2/4; mCRc: 50.0%, 2/4). The median OS for G+HMA+VEN, G+HMA, G+VEN treatment was not reached, 145.5 days, and 231.0 days, respectively (G+HMA+VEN vs G+HMA, p=0.011). The median DOR for G+HMA+VEN, G+HMA, G+VEN treatment was not reached, 82.0 days, and 77.0 days, respectively (G+HMA+VEN vs G+VEN, p=0.040). Four patients in G+HMA+VEN group received allogenic hematopoietic stem cell transplantation (alloHSCT) after remission exhibited prolonged OS and DOR. The most common grade 3/4 adverse events were cytopenia, febrile neutropenia and pulmonary infection, there were no difference among three groups.In conclusion, our data demonstrated promising response of G+HMA+VEN combination therapy in R/R FLT3 mutated AML patients, and it may consider as an effective bridge to transplantation.

A Phase I/II Study of Combination of ASTX727, Gilteritinib and Venetoclax in Patients with Relapsed/Refractory FLT3 Mutated Acute Myeloid Leukemia (AML)

Background Activating mutations in FLT3 occur in approximately 30% of patients (pts) with AML. Gilteritinib (GILT), a second-generation type I oral FLT3 inhibitor, has been approved in pts with relapsed/refractory (R/R) FLT3-mutated AML. We conducted a phase I/II study to evaluate the combination of decitabine/cedazuridine (ASTX727), venetoclax (VEN), and GILT in pts with FLT3-mutated R/R AML or intermediate-2/high risk MDS/CMML. Methods This phase I/II study included pts with 1) R/R FLT3-mutated AML or R/R intermediate-2/high risk MDS/CMML or 2) newly diagnosed FLT3-mutated AML unfit for intensive chemotherapy (eligible for phase II only). Here we report the initial data from the R/R cohort. In the phase I portion there was no restriction to the number of prior therapies received; however, in the phase II portion pts who had received ≥3 prior therapies were excluded. Pts with FLT3-ITD and/or TKD mutations were eligible. Pts were required to have a performance status ≤3, total bilirubin ≤2.5 x ULN, ALT/AST ≤3 x ULN, and creatinine clearance ≥30 mL/min. In cycle 1 (C1), pts received decitabine/cedazuridine (35mg/100mg) orally on days 1-5, VEN (ramp-up to 400mg with adjustment for concomitant azole) orally on days 1-28, and GILT orally continuously. The GILT dose ranged from 80mg to 120mg daily during the phase I dose escalation (3+3 design). A bone marrow biopsy was performed on day 14, and if blasts were <5% or the marrow was insufficient/aplastic, the VEN was held. For C2 and beyond, ASTX727 was given for 5 days, VEN was given for 14-21 days and GILT was given continuously. The primary endpoint for the phase I was the MTD; and for the phase II, the overall response (defined as CR, CRh, CRi, or MLFS within 2 cycles of therapy). Results The phase I portion is complete with 12 pts enrolled (11 AML, and 1 high-risk CMML). Nine pts received GILT 80mg and 3 received 120mg. No DLTs at either dose level were observed. However, 80mg of GILT was selected for the phase II portion of this study based on the more favorable safety/efficacy profile and better count recovery observed in a parallel study of azacitidine combined with VEN and GILT in AML. In the combined phase I/II cohort of pts with R/R AML or MDS/CMML, 15 pts have been treated. The median age was 65 years (range 38-83 years). Thirteen pts had a FLT3-ITD mutation (including 2 with a concomitant TKD mutation), and 1 pt had a FLT3-TKDmutation alone. Among pts with a FLT3-ITD, the median allelic ratio was 0.21 (range, 0.09 - 10.6). Among pts with a FLT3-TKD, the median allelic ratio was 0.05 (range, 0.02-0.09). Nine pts had diploid karyotype, 2 had adverse risk karyotype, and 4 had miscellaneous, intermediate-risk cytogenetic findings. The median number of prior therapies was 1 (range 1-9). Among the 15 pts treated, 8 (53%) responded: 1 (6%) with CRh, 3 (20%) with CRi, and 4 (27%) with MLFS. The pt with an isolated FLT3-TKD mutation (along with del7q) did not respond. The pt with high-risk CMML achieved a CRi. Six of 12 pts who received prior HMA + VEN responded (2 CRi and 4 MLFS), and 2 of 3 pts without prior HMA + VEN responded (1 CRh and 1 CRi). The median number of cycles received by pts was 2 (range 1-8). Best response was achieved by the end of C1 in 50% of responders, and by the end of C2 in the other 50% of responders. Of the 8 responders, 1 proceeded to alloSCT (with flow positive MRD at 0.3% but FLT3 negative by PCR), 1 is still receiving treatment on protocol with continued response, 5 relapsed without HSCT (median time to relapse 2 months [range, 0.5-7 months]), and 1 died in MLFS. The transplanted pt remains in MRD-negative remission 5 months after alloSCT and is receiving maintenance GILT off protocol. With a median follow-up of 3.8 months (range, 1-18 months), the median overall survival for the cohort was 6.1 months. There were 3 pts with grade 1-2 toxicities (1 with elevated liver enzymes, 2 with skin rash), 9 pts with grade 3 toxicities (9 with neutropenic fever, 4 of which became septic), no pts with grade 4 toxicities, and 2 patients with grade 5 toxicities (both had neutropenia and died from sepsis while on trial). Conclusion In this poor-risk population of pts with R/R FLT3-mutated AML or MDS/CMML, many of whom received prior HMA + VEN, the combination of ASTX727, VEN, and GILT was active, with an ORR of 53%. The trial continues to enroll to the R/R cohort, and is now open for patients with newly diagnosed FLT3-mutated AML who are unsuitable for intensive chemotherapy.

Comparable Survival of Treatment Naïve TP53 Mutated Acute Myeloid Leukemia Treated with Hypomethylating Agent Compared to Hypomethylating Agent Plus Venetoclax Based Therapy

Background TP53-mutated (m) acute myeloid leukemia (AML) is an adverse risk disease, which continues to have dismal outcome in the contemporary era of novel therapies. Venetoclax (VEN) in combination with hypomethylating agents (HMA; azacitidine or decitabine) have shown to improve complete remission (CR) rates compared to HMA alone, however no significant differences in overall survival (OS) have been observed. Methods We conducted a retrospective study through the COMMAND consortium (a collaboration of acute leukemia experts from 10 US academic institutions) to analyze the impact on survival outcomes of HMA plus (+) VEN compared to HMA-based therapies in adult (≥18 years) pts with TP53m AML. The AML Database of 381 pts with TP53m AML diagnosed between 2012-2022 was queried and 154 (40%) (HMA [n=50] and HMA +VEN [n=104]) pts were identified eligible for this analysis. Continuous variables were summarized as median (range) while categorical variables were reported as frequency (percentage). The Kaplan-Meier method was used to estimate OS, defined as time from diagnosis to death or last follow-up. Logistic regression models were used to determine the univariate and multivariate of OS. Multivariable models included all significant univariate predictors. All tests were two-sided with a p value <0.05 considered statistically significant. Results Baseline characteristics and responses The median age (years [yrs]) was 74 (range [R], 38-87) and 71 (R,29-88) yrs in the HMAand HMA + VEN groups (gps) (p= 0.23), respectively ( Table 1). Thirty-four (68%) and 57 (55%) patients (pts) were ≥ 70 yrs in the HMA and HMA + VEN gps, respectively (p= 0.16). Twenty-six percent vs 31% ( p=0.57), 86% vs 90% ( p=0.58) and 68% vs 73% ( p=0.56) of pts had secondary AML, had complex cytogenetics (CG), and had multi-hit TP53m in the HMA and HMA + VEN gps, respectively. The proportion of pts with most frequently occurring (> 5%) myeloid co-mutations ( RUNX1, ASXL1, TET2, DNMT3A, RAS, PTPN11 and JAK2) were not significantly (NS) different between the HMA and HMA + VEN gps, as shown in Table 1. The early treatment related mortality in first 30 days of induction was higher in the HMA+VEN gp (25%) when compared with the HMA gp (6%), p=0.004. The complete remission rates (CR/CRi) were higher in the HMA + VEN gp compared to the HMA gp (35% vs 18%, p=0.05). Similarly, the proportion of pts receiving allogeneic stem cell transplant (allo-HCT) after induction was higher in the HMA + VEN gp when compared with the HMA gp (13% vs 4%; p=0.14). Duration of response and overall survival The median follow up was 9.8 months (mo) (R, 1-56) and 5.80 mo (R, 1-30.4) in the HMA and HMA + VEN gps, respectively ( p=0.12). The median duration of response (DOR) was higher in the HMA +VEN gp (15.6 mo) when compared with the HMA gp (7.93 mo), but NS ( p=0.26). The median OS was NS different when comparing the HMA and HMA + VEN gps (9.23 vs 7.3 mo, p=0.80 [ Figure 1]). Multivariable analysis for duration of response and overall survival We did multivariable analysis (MVA) for DOR and OS using baseline variables ( Table 1) that showed significance/trend towards significance in univariate analysis ( p<0.1). Allo-HCT (HR; 0.11, 95% CI: 0.02-0.52, p=0.005) retained significance for better DOR, whereas age ≥ 70 yrs (HR; 1.7, 95% CI: 0.63-4.65, p=0.28) and complex CG (HR; 3.05, 95% CI: 0.79-11.73, p=0.10) did not retain significance in MVA. In MVA for OS, achievement of CR/CRi (HR; 0.35, 95% CI; 0.20-0.59, p=<0.001) and allo-HCT after induction (HR; 0.06, 95% CI; 0.09-0.46, p=0.007) retained favorable significance for OS, whereas complex CG (HR; 2.36, 95% CI: 1.11-4.99, p=0.02) retained significance for shorter OS. PTPN11m (HR; 1.57, 95%CI: 0.75-3.28, p=0.23) and TET2m (HR; 1.02, 95% CI: 0.56-1.87, p= 0.92) did not retain significance in MVA. Conclusion In this multi-center real-world study, while HMA+VEN led to improvement in CR rates and a higher proportion of pts were bridged to allo-HCT, it did not associate with an improvement in OS when compared with HMA monotherapy. More effective treatment strategies are warranted to improve outcome of pts with TP53m AML.

Plm-102, a Next Generation FLT3 Inhibitor, Shows Potent Anti-Leukemic Activity on Resistance to Gilteritinib in FLT3 Mutated Acute Myeloid Leukemia

Introduction: Mutations in the FMS-like tyrosine kinase 3 (FLT3) gene occur in approximately 25 ~ 30% of all acute myeloid leukemia (AML) cases, with FLT3-ITD mutations having a poor prognosis. In 2022, the FDA granted approval to Gilteritinib, a 2nd generation FLT3 inhibitor, for the treatment of relapsed or refractory AML. Although Gilteritinib has demonstrated efficacy in R/R AML patients, its response duration is limited due to the development of secondary resistance. Herein, we report a next-generation drug candidate, PLM-102, which has shown promising pre-clinical results to overcome the current unmet needs of Gilteritinib resistance, including FLT3-ITD-TKD and Ras mutations in FLT3-mutated AML. Aims: The main objective of this study is to investigate the effect of PLM-102 in in-vitro and in-vivo acquired Gilteritinib-resistant models and to elucidate the underlying signaling pathways. Methods: To establish Gilteritinib-resistant cell lines, we exposed the AML cells to FLT3 ligand at 10 ng/ml and Gilteritinib at concentrations ranging from 10 nM to 100 nM for four months. Subsequently, for the following four months, we treated the cells with Gilteritinib alone at 100 nM, omitting FLT3 ligand from the treatment. Whole Exome Sequencing (WES) and mRNA sequencing were performed on primary FLT3 mutated AML cells and Gilteritinib resistance FLT3 mutated AML cells. Subsequently, cell viability assays were carried out on both parent FLT3-mutated AML cells and Gilteritinib-resistant FLT3-mutated AML cells. To assess the activities of PLM-102 at the on-target and off-target resistant mechanisms, immunoblot studies were conducted. An in vivo study was performed using a Gilteritinib-resistant MOLM-14 AML xenograft mouse model. Results: We conducted Whole Exome Sequencing on the Gilteritinib-resistant MOLM-13 and MOLM-14 cell lines. The analysis revealed the presence of KRAS G13D and FLT3-ITD-C828G mutations in the Gilteritinib-resistant MOLM-13 cell line, and NRAS G13D and FLT3-ITD-G697R mutations in the Gilteritinib-resistant MOLM-14 cell line. In the evaluation of the efficacies of Gilteritinib and PLM-102 in Gilteritinib-resistant MOLM-14 cell lines. The GI 50 values for Gilteritinib and PLM-102 were determined to be 427 nM and 6.17 nM, respectively. In the studies with a xenograft model with Gilteritinib-resistant MOLM-14 cells (20 mg/kg, p.o.), the Tumor Growth Inhibition (TGI, %) values were determined as 71.9% vs 17.1% for PLM-102 vs Gilteritinib, respectively. These results demonstrated the superior in-vivo efficacies of PLM-102 in Gilteritinib-resistant cells. mRNA sequencing was performed on both MOLM-14 cells and Gilteritinib-resistance MOLM-14 cells, resulting in an upregulation of the cytokine-mediated signaling pathway, including chemokines, in the Gilteritinib-resistant MOLM-14 cells. Additionally, we conducted mRNA sequencing on Gilteritinib-resistant MOLM-14 cells treated with and without PLM-102 at a concentration of 10 nM. Interestingly, in the group treated with PLM-102 at 10 nM, we observed a notable decrease in the cytokine-mediated signaling pathway, including chemokines. These findings provide valuable insights into the potential mechanism by which PLM-102 exerts its anti-leukemic effect in Gilteritinib-resistant cells by modulating the cytokine-mediated signaling pathway. In Gilteritinib-resistant MOLM-14 cells harboring the NRAS G13D mutation, we confirmed hyperactivation of the MEK-ERK signaling pathway. The significantly improved effects in the combination of PLM-102 and Trametinib, a MEK inhibitor, were observed through cell viability assays and a xenograft model, further supporting their potential as a synergistic therapeutic approach. Currently, the GLP toxicological studies of PLM-102 has successfully completed, and the Investigational New Drug (IND) for human clinical studies will be submitted near future. Conclusions: Our results have confirmed that RAS-MEK-ERK signaling pathway and cytokine signaling pathway were activated by Gilteritinib resistance. Notably, PLM-102 exhibits exceptional anti-leukemic activity in Gilteritinib-resistant cell lines through the unique mechanism of inhibiting the RAS-MEK-ERK-cytokine signaling pathway. These results highlight the potential of PLM-102 as a third-generation inhibitor with favorable efficacies in patients with resistance to current FLT3 inhibitors.

Analysis of Post-Transplant Clinical Outcomes and Prognostic Factors in FLT3-ITD Mutated Acute Myeloid Leukemia Patients Under ELN 2022 Risk Stratification

Background In 2022 European LeukemiaNet (ELN) recommendations for diagnosis and management of acute myeloid leukemia (AML), one of the most important changes made to the genetic risk classification of AML is that the FLT3-ITD allelic ratio (AR) is no longer considered in the risk classification; consequently, AML with FLT3-ITD (without adverse-risk genetic lesions) are now categorized in the intermediate-risk group, irrespective of the allelic ratio or concurrent presence of NPM1 mutation. Aims To investigate the survival outcomes of FLT3-ITD mutated AML patients underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), based on prognostic stratification defined by the 2017 and 2022 ELN guidelines, and to analyze the risk factors affecting transplant prognosis. Methods A total of 163 FLT3-ITD mutated AML patients underwent allo-HSCT were enrolled in this study. Bone marrow aspirates were obtained, cytogenetic and molecular characteristics were collected at the time of diagnosis. Genetic risk category was classified according to the 2017 and 2022 edition of the European LeukemiaNet (ELN) recommendations. HLA-haploidentical donor transplants were performed if no HLA matched sibling or unrelated donor was available. Patients received myeloablative conditioning with a modified Bu/Cy/Flu/Ara-c (busulfan/cyclophosphamide/fludarabine/cytarabine) or MCBC (melphalan/cladribine/busulfan/cyclophosphamide) preparative regimen. The therapeutic process and clinical outcomes were retrospectively analyzed. Results We assessed 163 adults with FLT3-mutated AML (median age 37 years) allografted between 2017 and 2022 in our clinical center. The median follow-up of alive patients was 24.9 months. The 2-year relapse-free survival (RFS) and overall survival (OS) were 67.2% and 71.9%, respectively. The 2-year incidences of relapse and non-relapse mortality were 27.9% and 12.5%, respectively. There was no significant difference in survival outcomes between the intermediate and high-risk groups after transplantation, both defined by the 2017 and 2022 ELN guidelines. High FLT3-ITD allelic ratio (≥0.5) at initial diagnosis was associated with elevated WBC counts ( P<0.001), but did not affect the response ratefollowing induction chemotherapy ( P=0.059) . Patients with high allelic ratio were more likely to benefit from maintenance therapy after transplantation ( P=0.048 for OS). In univariate analysis, presence of NPM1 mutation and the allelic ratio of FLT3-ITD did not affect any of the transplant outcomes. In multivariate analysis, MRD-negative at transplantation, occurrence of chronic GVHD and posttransplant maintenance therapy improved OS and RFS. Conclusion Allo-HSCT can overcome the poor prognosis in patients with FLT3-ITD mutated AML. Neither the presence of NPM1 mutation nor the FLT3-ITD allelic ratio affected survival. Prevention of disease relapse after transplantation remains a challenge. The main prognostic factors affecting transplant outcomes included pre-transplant MRD status and the application of maintenance therapy. Thus, introduction of FLT3 inhibitors as post-transplant maintenance therapy and the development of highly sensitive MRD assays will further reduce disease recurrence and improve survival.

Real World Experience of FLT3-Inhibitor Post-Transplant Maintenance with Sorafenib Demonstrating Superior Overall- and Relapse Free Survival Following Allogeneic Hematopoietic Stem Cell Transplantation in FLT3-ITD Mutated Acute Myeloid Leukemia

Introduction Acute myeloid leukemia (AML) with FLT3-internal tandem duplication (ITD) is known to have a significantly high risk of relapse even with allogeneic stem cell transplantation (HCT), for which post-transplant maintenance therapy with FLT3 inhibitors (FLT3i) has been applied. Although there is a randomized trial comparing Sorafenib maintenance vs no treatment, real world experience is still limited. Despite the increased use of FTL3i maintenance in clinical practice, the optimal dose and duration of post-transplant Sorafenib maintenance remains uncertain. Accordingly, we performed a retrospective chart review to analyze the survival benefit with Sorafenib maintenance, dose tolerability and the impact of FLT3-ITD allele frequency (AF) at initial diagnosis of AML on treatment outcomes in the context of post-HCT Sorafenib maintenance. Patients and method We conducted a retrospective study including 69 patients who received an allogeneic HCT from 2019 to 2023 for AML with FLT3-ITD, of which 24 patients received Sorafenib as post-HCT maintenance therapy. Primary endpoint was relapse-free survival (RFS). The use of Sorafenib maintenance treatment was treated as a time-dependent covariate and Mantel-Byar test (MBT) was conducted to compare outcomes between Sorafenib maintenance group vs others, which will avoid immortal bias. FLT3-ITD allele frequency (AF) was assessed by molecular PCR test, and the cutoff was determined using a binary recursive partitioning method with AF of 54.6% as a cutoff. Results Out of 69 patients, 61 (88%) were in CR1 vs 8 (12%) in CR2 prior to HCT. Sorafenib was started in 24 patients (35%) at a median of 95 days post-HCT with a dose of 200mg every other day (n=2), 200mg once daily (n=17) or 200mg twice daily (n=5). The most common maintenance dose was 200mg once daily (n=9), followed by 200mg twice daily (n=6), 200mg every other day (n=5), and 400mg twice daily (n=1). The median Sorafenib maintenance duration was 15 months (1-53 months) at the last follow-up. There were no relapses in the patients who completed 2 years of Sorafenib maintenance. Sorafenib was discontinued in 6 patients, due to relapse (n=2), death of unrelated cause (n=1), GVHD (n=1), pneumonitis (n=1) and recurrent hypoglycemia (n=1). Adverse events requiring Sorafenib dose reduction included, GI intolerance (n=7), skin rash (n=7), thrombocytopenia (n=4), transaminitis (n=3), neuropathy (n=3), GVHD (n=2) and pneumonitis (n=2). The median follow-up duration for all the patients was 27 months (5-51) following HCT, or 13 months (1.3-48) following Sorafenib maintenance. Using Kaplan-Meier test, the 2-year RFS in patients on Sorafenib maintenance was 84.5% vs 40.5% for no Sorafenib (p=0.00049). The 2-year OS was 88.2% vs 53.9% (p=0.0043), respectively. The CIR was 9.8% vs 39.9% (p=0.00634), while the NRM was 5.6% vs 19.7% (p =0.122), respectively. In the MBT, Sorafenib maintenance was found to reduce the mortality risk by 62.5% (HR 0.375 (0.109-1.29], p=0.120) and reduced the relapse/mortality risk by 71.2% (HR 0.288 [0.084-0.984], p=0.047). With respect to FLT3-ITD AF, the group with higher AF showed extremely higher HR for RFS compared to those with lower FLT-ITD (HR 29.37 [3.007-286.8], p=0.0036). When evaluating RFS and OS with combined risk incorporating the use of Sorafenib and FLT3-ITD AF, we have 4 subgroups (figure 1). In patients with a lower AF, the RFS was 87.7% vs 56.8% in the Sorafenib (n=20), vs no Sorafenib group (n=31), respectively. In patients with a higher AF, the RFS was 66.7% vs 0.0% in the Sorafenib (n=3), vs no Sorafenib group (n=8; p=0.0009), respectively. In a multivariate analysis, we confirmed the 2-year RFS for patients who had a high FLT3-ITD and received Sorafenib maintenance was statistically significant when compared to no Sorafenib maintenance. Conclusion Sorafenib maintenance post-transplant in FLT3-ITD mutated AML patients significantly improves the OS and RFS. Sorafenib maintenance is tolerable with 200mg twice daily or lower in most patients. Reduced doses of Sorafenib improve tolerability, with no significant impact on increased risk of relapse. Higher AF group of FLT3-ITD at initial diagnosis defined by ≥54.6% using PCR, was associated with significantly increased risk of relapse even after HCT. Sorafenib maintenance seems to provide survival benefit in terms of RFS, particularly in the patients with higher AF FLT3-ITD.

Real-World Outcomes Using Front-Line Midostaurine in Combination with Intensive Chemotherapy for Patients Aged ≥ 60 Years Old with FLT3 Mutated Acute Myeloid Leukemia

BACKGROUND: The prognosis of patients with acute myeloid leukemia (AML) varies depending on the presence of mutations in the FLT3 tyrosine kinase. Internal tandem duplications (ITD) and mutations in the tyrosine kinase domain (TKD) result in continuous activation of FLT3, leading to uncontrolled blast proliferation. Since the publication of the clinical trial CALGB 10603 (RATIFY), it has been established that adding midostaurine to intensive chemotherapy improves the overall survival (OS) of patients with mutated FLT3. However, it is worth noting that this study only included patients 18-59 years old. Subsequently, a phase II clinical trial (AMLSG 16-10 trial) conducted a subgroup analysis suggesting that midostaurine may also benefit to patients between 60 and 70 years of age. Nevertheless, these findings have not been studied in real-world clinical practice. METHODS : This is multicentric non-interventional retrospective real-world study including patients ≥60 years of age with newly diagnosed FLT3-mutated AML treated with intensive chemotherapy and midostaurine (50 mg orally twice daily, d8-22) between 1st 2017 and July, 30 th 2021 from the French Innovate Leukemia Organization (FILO) and the Programa Español de Tratamientos en Hematología (PETHEMA). The primary objective was to evaluate the efficacy of midostaurine in combination with intensive chemotherapy in patients over 60 years old. We assessed the rate of complete remission (CR) or complete remission with incomplete hematologic recovery (CRi) after induction therapy, OS and event-free Survival (EFS). RESULTS: A total of 191 patients (FILO Group 122 (63.9%); PETHEMA Group 69 (36.1%)), aged between 60 and 77 years, were enrolled in the study. The patients had a median age of 67.8 years (range 60.1; 77.6). Among them, 134 (70.2%) were aged less than 70 years, while 57 (29.8%) were aged 70 years or older. 159 (83.3%) had a performance status (ECOG) of 1 or lower, while 24 (12.6%) had an ECOG of 2 or higher. 151 (79.1%) had de novo acute myeloid leukemia (AML), and 40 (20.9%) had secondary AML at diagnosis. The median white blood cell count at diagnosis was 26.5 x 10^9/L [5.99; 107]. The median percentage of blasts in the bone marrow at diagnosis was 76% [55; 88.5]. The frequency of FLT3-ITD mutation was 154 (80.6%), FLT3-TKD mutation was 44 (23%), and double mutations were observed in 7 (3.7%) patients. The median FLT3 ITD/wt ratio was 57% [22.5 - 78]. 119 (62.3%) were NPM1 muted. Regarding the intensive chemotherapy schedule in induction, 162 (84.8%) patients were treated with idarubicin-based regimens, 18 (9.4%) with daunorubicin-based regimens, and 8 (4.2%) with CPX-351. After induction, 150 (78.5%) of the patients achieved complete remission/complete remission with incomplete hematologic recovery (CR/CRi). Of those patients, 96 (64%) proceeded to intensive chemotherapy schedule in consolidation, with 83 (86.5%) of them receiving midostaurine. In contrast, 32 (21.3%) received non-intensive chemotherapy consolidation, with 27 (84.4%) receiving midostaurine. Additionally, 37 (24.7%) of the patients who achieved CR/CRi after induction underwent a hematopoietic-cell transplantation (HCT), with 33 (89.2%) undergoing allogeneic HCT and 4 (12.1%) undergoing autologous HCT. The median follow-up of the patients was 32 months. OS for the entire population was 23 months with a 2-years OS of 49.1% (95%CI: 41.5-56.7). Median EFS for the entire population was 11.1 months with a 2-years EFS of 37.1%. (95%CI: 29.6-44.5). For patients undergoing allogeneic HCT after achieving CR/CRi following induction, the median OS was not reached, with a 2-year OS of 69% (95% CI: 54.6-88.3). In contrast, for patients who achieved CR/CRi after induction but did not undergo allogeneic HCT, the OS was 32.6 months with a 2-year OS of 50.2% (95% CI: 48.4-68.2). CONCLUSIONS: This real-life study suggests that the addition of midostaurine to intensive chemotherapy regimens in elderly patients could result in acceptable CRc, OS and EFS. In order to establish the benefit of midostaurin, we will compare these results with a historical control cohort.

Immunosuppression in Isocitrate Dehydrogenase Mutated Acute Myeloid Leukemia

Introduction: Mutations in the isocitrate dehydrogenase (IDHmut) enzymes 1 and 2 are prevalent in a diverse array of human malignancies, including melanoma, glioma, acute immunoblastic T cell lymphoma (AITL) and acute myeloid leukemia (AML,15-20% of patients). IDHmut enzymes produce R-2-hydroxyglutarate (R-2-HG), an oncometabolite with immunomodulatory capability (Notarangelo et al, Science 2022). Immunotherapies in AML outside of allogeneic stem cell transplantation have proven to be largely ineffective, possibly due to immune evasion mechanisms intrinsic to myeloid malignancies. Herein, we aim to characterize the immune repertoire in IDHmut AML patients at the time of diagnosis, as well as the mechanisms by which R-2-HG may suppress immune cell function. Methods: The immune repertoire in cryopreserved peripheral blood mononuclear cells (PBMCs, n=10) and bone marrow mononuclear cells (BMMCs, n=8) of IDHmut AML patients were characterized using full spectrum flow cytometry to evaluate 30 different immune cell markers. T cell activation (CD25, CD69, CD40L, CD134), exhaustion (PD-1, CTLA-4, Lag-3, Tim-3), differentiation (Foxp3, CXCR3, CCR4, CCR6), and memory (CD45RA, CCR7, CD28, CD95) markers were assessed. IDH wild-type (IDHwt) AML PBMCs (n=4), BMMCs (n=12) and healthy volunteer PBMCs (n=6) and BMMCs (n=3) were used as controls. To investigate the effects of R-2-HG on CD4 + T cell activation, primary human naïve CD4 + T cells (CD4 +, CD45RA +) were isolated from healthy donors and activated (anti-CD3/CD28) in the presence of R-2-HG (20 mM) or PBS control. Activation, proliferation and cytokine production were assessed with flow cytometry, intracellular cytokine staining (ICS) and LEGENDplex at 4, 8, 24 and 72 hrs. The OT-II transgenic mouse model was used to assess antigen-specific T cell activation. T cell metabolism at rest and after activation in the presence of R-2-HG was evaluated using SCENITH (Argüello et al, Cell Metab 2021) and 13C 6-glucose isotope labeling coupled with mass spectrometry (MS) performed by the UCLA Metabolomics Center. Results: Full-spectrum flow cytometry analysis revealed a trend for higher CD4:CD8T cell ratio in AML BMMCs (fold=1.95, p=0.229) as well as increased CD4 + T cell activation and exhaustion markers compared to healthy donor BMMCs. No appreciable differences in CD4 + T cell markers were found between IDHwt AML and IDHmut AML, likely due to AML heterogeneity and small sample size. Nevertheless, our preliminary results suggest CD4 + T cell engagement in AML; thus, we chose to investigate how CD4 + T cells are affected by R-2-HG. Primary human naïve CD4 + T cells activated in the presence of R-2-HG exhibited a defect in early activation demonstrated by decreased CD69 expression (n=7, fold=0.773, p=0.001) and concomitant decreased production of IL-2 measured by ICS (n=7, fold=0.403, p=0.0001) and LEGENDplex (n=3, fold=0.557, p=0.046). Proliferation in the presence of R-2-HG was inhibited in a dose dependent manner (n=6, Division Index fold change=0.768, p=0.006 at 20mM). Antigen-specific OT-II CD4 + T cells showed a decrease in proliferation in response to OVA 323-339 (n=3, Division Index fold change=0.620, p=0.004). Given R-2-HG's structural similarity to α-ketoglutarate (αKG), we hypothesized that disruption in CD4 + T cell activation when cultured with R-2-HG may be due to metabolic dysfunction. Indeed, we found a decrease in global metabolism in CD4 + T cells cultured with R-2-HG (fold = 0.678, p = 0.009). MS revealed decreased levels of succinate and malate downstream and accumulation of αKG upstream of α-ketoglutarate dehydrogenase (KGDH) in the tricyclic acid (TCA) cycle, suggesting a defect in TCA flux (fold succinate / αKG ratio =0.134 unactivated, p = 0.029; 0.231 4h activation, p = 0.012; 0.328 24h activation, p = 0.004; Figure 1). Moreover, MS also showed increased amounts of essential amino acids (Ile, Leu, Met, Phe, Thr, Trp, Val, His; Figure 2), suggesting a compensatory reliance on amino acid import and metabolism. Conclusions: By characterizing primary AML samples at diagnosis, we found trending increases in CD4:CD8 ratio and expression of CD4 + T cell activation and exhaustion markers compared to healthy controls. We also demonstrate R-2-HG suppression of CD4 + T cells, potentially via inhibition of KGDH in the TCA cycle. Our studies show R-2-HG in IDHmut tumors can modulate CD4 + T cell function and contribute to immune escape in human AML.

Maintenance Therapy with Chidamide Decreases the Relapse in Fusion Gene-Positive AML Patients with MRD-Positive or ELN-High Risk

Purpose: Acute myeloid leukemia (AML) patients with fusion gene-positive including core binding factor (CBF), mixed-lineage leukemia (MLL) gene rearrangement have a high incidence of relapse if they are continious measurable residual disease (MRD)-positive or in ELN-high risk and could not be bridged to allogenetic heamatopoitic stem cell transplantation (allo-HSCT). As known histone deacetylase (HDAC) is abnormally recruited in these fusion gene-positive AML, also RUNX1 mutated AML, and could be a therapy target. Aim of this study is to assess the effect and safety of HDAC inhibitor chidamide as maintemance therapy in these AML patients. Methods: A multi-center retrospective study was performed. Patients with MRD-positive CBF-AML, MLL rearrangement or RUNX1 mutation AML, without being bridged to allo-HSCT were included. Maintemance with chidamide was started one to three months after consolidation for at least six months, at a dose of 10mg/day or 30mg twice a week. Results: Twelve patients were enrolled, included 8 with AML1-ETO-positive, 3 with RUNX1 mutation, 1 with MLL rearrangement. The median age was 33(16-62) years old. The ratio of male to female was 6 to 5. They previously experienced median 6(4-8) cycles of chemotherapy, included one with allo-HSCT, one with autologous-HSCT. They were all maintemanced with chidamide, except one with chidamide plus sorafenib. Eleven patients were available for outcome assessment. With a median follow-up of 14(2-67) months, among the 9 patients with MRD-positive, 6(66.7%) achieved MRD-negative, 1 stable disease, 2 relapsed and died. The median time to achieved MRD-negative was 2.5(1-12) months. The other 2 patients was contenious MRD-negative. The cumulative incidence of relapse was 2/11(18.2%). The rate of MRD-nagetive was 8/11(72.7%). The mortality rate was 2/11(18.2%). During the maintemance, 4 patients underwent bone marrow suppression, including 2 with grade 3, 2 with grade 1/2. One patients had an anorexia of grade 2. Conclusion: Maintenance therapy with chidamide might decrease the relapse in fusion gene-positive AML patients with MRD-positive or ELN-high risk, who could not take allo-HSCT, and prolong their survival, with a well toleration. Key words: chidamide, maintenance, fusion gene, acute myeloid leukemia

Single-Cell Proteomic Analysis Reveals Menin Inhibition-Induced Proteomic Alterations in AML Patients Treated with Revumenib

Menin inhibition is a promising therapeutic approach for acute myeloid leukemia (AML) with certain genetic alterations including KMT2A rearrangements or NPM1 mutations. The first-in-human Phase 1 clinical trial of revumenib (SNDX-5613) in patients with R/R AML showed promising results and induced complete remission in patients who refractory to multiple lines to therapy. These findings suggest that revumenib could provide a new therapeutic option for patients with AML with KMT2A and NPM1 genetic alterations. AML is characterized by the existence of distinct differentiation hierarchies, a phenomenon substantially contributing to disease heterogeneity. AML hierarchies exhibit distinct expressions of phenotypic profiles, apoptotic networks, signaling pathways, and metabolic profiles, leading to varying sensitivity towards targeted therapies, resulting in differential sensitivity to targeted therapies. Revumenib induces AML differentiation and thus shift the balance between AML hierarchies, resulting in drastic alterations in the overall AML proteomic profiles and enrichment of distinct leukemia phenotypes with differential sensitivity to targeted therapies. Detailed interrogation of revumenib-induced proteomic alterations could permit precise targeting of persistent cells and development of data-driven combinatorial approaches to achieve higher response rates. Moreover, the distinct combinations of genetic alterations can impact the efficacy of revumenib-induced differentiation and therapeutic outcomes. Thus, to better understand these complexities we performed multimodal single-cell (sc) analysis of AML landscape in R/R AML treated with revumenib (n=4) in Phase 1. We utilized two leukemia-focused 51-parameter CyTOF panels to analyze pre and post-treatment samples from R/R AML patients treated with revumenib. Sc proteogenomic profiling was performed using MissionBio platform using a panel covering 37 genes with recurrent AML-relevant mutations. UMAP and clustering analyses of CyTOF data identified AML blasts, unveiled quantitative changes in cell composition, and delineated proteomic shifts induced under revumenib therapy pressure. We observed enrichment of CD11b+/-CD68+, more differentiated monocytic cells situated at close proximity to AML blasts and depletion of immature AML blasts. Through unsupervised analysis, we discovered discrete AML differentiation hierarchies, delineated by a differentiation continuum that initiates with immature AML blasts (CD34+/-c-Kit+/-), progresses through intermediate AML blasts (CD68+/CD11b-/CD14-), and culminates with more differentiated monocytic cells (CD68++/CD11b+/CD14+/-). Notably, intermediate AML blasts and monocytic cells were enriched in post-treatment samples. Simultaneous ScDNA+protein analysis showed enrichment of differentiated AML blasts with monocytic/dendritic cell phenotype and harboring AML mutations. Differentiated AML blasts expressed higher levels of MCL1 and BCL-xL and upon differentiation we observed gradual downregulation of BCL2. Importantly, intermediate and more differentiated AML blasts under revumenib therapy expressed high levels of p53 protein, a feature that can partly attributed to NPM1 mutations. Sc proteomic analysis delineated proteomic shifts elicited by revumenib and identified potential therapeutic partners, by targeting MCL1, BCL-xL and MDM2, that could be used in combination with revumenib to improve therapeutic efficacy. We next performed differential expression analysis by comparing the proteomic profiles of pre- and post-therapy samples. We observed suppression of less differentiated AML phenotypic profiles (c-Kit, CD123, CD34) along with MEIS1 and PBX3. Importantly, we also observed significant alterations in immune landscape, suggesting that revumenib could rewire Myeloid-to-T and NK cell interaction/communication by inducing proteomic shifts and driving AML blast differentiation. Further analysis of an expanded cohort of R/R AML patients is currently underway. In conclusion, multimodal sc analysis revealed profound proteomic alterations induced by revumenib and identified potential therapeutic targets. These findings present new avenues for optimizing combinatorial treatment regimens, enhancing revumenib's efficacy, and illuminating survival mechanisms in persistent, differentiated AML blasts.

Real World Use of Azacitidine and Venetoclax in Acute Myeloid Leukemia in Frontline and Relapse/Refractory Settings: A Multicentric Study from French Auraml Group

Azacytidine and venetoclax combination regimen (AZA/VEN) is the standard of care in frontline acute myeloid leukemia (AML) settings for unfit to intensive chemotherapy patients. However, AZA/VEN is also associated with an increased hematological toxicity compared to azacytidine alone. In this context, alternative AZA/VEN regimens emerged progressively based on each physician experience and local procedures. Moreover, AZA/VEN is also recognized as a valuable therapeutic option in relapse/refractory settings. In this multicentric study, we aimed to evaluate the efficacy and safety of various AZA/VEN regimen in frontline and relapse/refractory (R/R) patients diagnosed with AML in real life setting. We retrospectively analyzed 331 patients from 11 different French centers (Saint-Etienne, Clermont-Ferrand, Lyon (Hopital Lyon Sud, Centre Léon Bérard), Vichy, Annecy, Chambery, Valence, Bourgoin-Jallieu, Grenoble, Roanne) in Auvergne Rhône Alpes (AURA) region, between January 2019 and February 2023. Composite complete remission was defined as in VIALE-A trial. Measurable residual disease (MRD) negativity was defined as ≤ 10 -3 by flow cytometry (on bone marrow) and/or ≤ 10 -4 for NPM1 by RT-qPCR. Overall, the entire cohort was composed of 186 and 146 patients in frontline and R/R settings respectively. In frontline setting, median age was 74.5 (19.1-86.1) and ELN 2022 risk groups were favorable, intermediate and unfavorable in 14.5, 16.7 and 68.8% respectively. De novo AML, MRC-AML, post-MPN/MDS AML and t-AML were 32.4%, 29.7%, 23.2% and 14.5% respectively. After 6 cycles, median CRc, morphologic leukemia free state (MLFS) and refractory rate were 66.4%, 5.4% and 28.2% respectively. Regarding probability of CRc, there was no significant difference between favorable and intermediate ELN 2022 risk group. Within unfavorable risk group, only complex karyotype was associated with lower CRc rate ( figure 1). Venetoclax dosage (400mg vs 100mg/d) and duration per cycle (28 days vs 21 days vs others) did not influence significantly CRc rate probability and OS. With a median follow-up of 7.3 months, median overall survival (OS) was 12.4 months (IC95%: 3.4-18.5). There was no significant difference in terms of OS according to ELN 2022 risk group classification ( figure 2). Among unfavorable risk group, only patients with unfavorable karyotype had a worst OS (median OS: 4.9 months), while patients with secondary AML mutations had similar OS than favorable/intermediate risk group (19.5 vs 20.2 vs 18.2 months, p=0.32). Reaching MRD negativity at any time during the first 6 cycles was associated with a better OS (26.1 vs 10.3 months, p<0.001). In responding patients, 22/122 withdrew VEN after a median of 5 cycles (range:1-17), while continuing AZA, mainly due to excessive hematological toxicity. Relapse free survival was similar between patients who stopped compared to those who continued up to progression. In multivariate analysis, only ECOG (continuous, HR= 1.52, p=0.04), IDH status (WT vs MUT: HR = 3.13, p=0.04, normal karyotype (yes vs no, HR=0.25, p=0.04) and CR type (CRMRD- vs other, HR= 0.21, p=0.001) significantly influence OS, whereas ELN 2022 did not In R/R settings, CRc rate was 43.8% and OS was 7.9 months. As in frontline setting, venetoclax dosage and duration per cycle did not influence CRs rate and OS. Febrile neutropenia (FN) occurred in 52.9%, 35.1% and 27.1% in cycle 1,2 and 3, respectively. Toxic death rates (TDR) range from 16.6% prior 2020 to 8.6% in 2021 and 6.25% from 2022 to 2023 (p=0.01). In or outpatient management for cycle 1 did not influence FN incidence. Azole prophylaxis did not significantly influence FN incidence. During cycle 1, shorter venetoclax duration regimens (<21 days/cycle) was associated with lower FN (41.5 vs 54.8%, p=0.042) compared to ≥21 days VEN cycle. In this real life settings study, our results suggest that outcome in frontline AZA/VEN treated patients is mainly driven by deep responses. Alternative AZA/VEN regimens were not associated with lower response rate and overall survival, while reducing venetoclax exposure during cycle 1 may reduce FN incidence without significant consequences on CR rate. TDR reduction through time suggest a learning curve and might be related to physician's skills improvement regarding AZA/VEN dosage schedules and supportive care management. An update with additional patients and longer follow-up will be presented at the meeting.

Molecular Measurable Residual Disease in Patients with Newly Diagnosed m IDH1 Acute Myeloid Leukemia Treated with Ivosidenib + Azacitidine

Background: Ivosidenib (IVO) + azacitidine (AZA) improved complete remission (CR) rates and overall survival (OS) relative to placebo (PBO) + AZA in patients (pts) with newly diagnosed mutant isocitrate dehydrogenase 1 (m IDH1) acute myeloid leukemia (AML) in the pivotal AGILE study (Montesinos et al. NEJM 2022). Prior analyses showed clinical responses to IVO+AZA were associated with deep clearance of m IDH1 (limit of detection [LOD]: 0.02-0.04% variant allele frequency [VAF]), as well as clearance of baseline co-mutations below the threshold of conventional next-generation sequencing (NGS) (LOD: 2.0% VAF) (Döhner et al. Blood 2022; Daigle et al. Blood 2021). Measurable residual disease (MRD), a negative prognostic marker, following chemotherapy is often detected via multiparametric flow cytometry or quantitative polymerase chain reaction although both techniques have their limitations. (Heuser et al. Blood 2021). NGS can detect a wide range of AML mutations and studies show that NGS-assessed MRD is highly predictive of both relapse and survival (Thol et al. Blood 2018; Tsai et al. Blood Adv 2021). However, a limitation of NGS is difficulty in distinguishing between somatic leukemia-associated mutations and clonal hematopoiesis of indeterminate potential (CHIP) (Bacher et al. Blood Cancer J 2018). We aimed to perform an NGS analysis of MRD responses in the AGILE study. Methods: All AGILE pts who had a best overall response (BOR) of CR, CR with incomplete count recovery, or CR with incomplete platelet recovery, and had ≥1 on-treatment bone marrow mononuclear cell (BMMC) sample available were included. Suggested timepoints for MRD testing included day 1 of treatment cycles 3, 5, 7, 9, 11, 14, 20, 26, and 32. Baseline and on-treatment BMMC DNA samples were analyzed using a diagnostic 51-gene myeloid NGS panel (LOD: 3% VAF) and a 26-gene AML MRD panel, respectively. For variants detected at baseline, the LOD was 0.1% VAF; for variants not detected at baseline (either emerging mutations or if baseline samples were unavailable), the LOD was 0.5% VAF. All variants above the applicable LOD with known or potential clinical significance were considered evidence of positive MRD, aside from DNMT3A, TET2 and ASXL1 (“DTA”) mutations to reduce the risk of false-positive MRD due to CHIP. Results: The analysis set comprised 173 samples from 33 IVO+AZA-treated pts and 10 PBO+AZA-treated pts (Fig. 1). Clinical response data were based on a March 18, 2021 primary analysis data cut; OS data were based on an updated June 30, 2022 data cut. The median number of baseline mutations was 4 (range: 1-10) per patient, median number of MRD assessments was 3 (range: 1-9) and median follow-up period was 189 days (range: 49-875). Ten (30.3%) IVO+AZA-treated pts became MRD-negative (MRD neg), compared with 2 (20.0%) PBO+AZA-treated pts. All pts attaining an MRD neg response had a BOR of CR (10 [34.5%] of 29 IVO+AZA-treated pts in CR; 2 [22.2%] of 9 PBO+AZA-treated pts in CR). Seven (70.0%) of the 10 MRD neg IVO+AZA-treated responding pts converted to an MRD neg response by day 1 of cycle 7 (C7D1). Fewer pts with an MRD neg response had an Adverse risk at baseline according to European LeukemiaNet 2022 genetic risk classification versus those pts with an MRD-positive (MRD pos) response (26.3% vs 73.7%) (Table 1). In the IVO+AZA arm, rates of event-free survival at 12 months and OS at 24 months were numerically higher in MRD neg vs MRD pos responders (80.0% vs 60.6% and 88.9% vs 72.3%, respectively) but did not reach statistical significance. All 5 (15.2%) IVO+AZA-treated pts with confirmed relapses had detectable MRD at the last completed assessment prior to relapse. One pt converted from an MRD neg to an MRD pos response (“MRD relapse”) 169 days prior to overt clinical relapse. Among the 23 IVO+AZA-treated pts without an MRD neg response, 16 were alive as of the updated data cut; OS duration ranged from 20.3-48.9 months. Conclusions: IVO+AZA induced molecular MRD negativity in approximately one third of responding pts with newly diagnosed m IDH1 AML; MRD neg responses were most often observed on or before C7D1. Interestingly, several pts had durable clinical responses and OS despite ongoing MRD positivity, potentially due to persistent CHIP rather than true MRD, illustrating the complexity of interpreting NGS MRD data. Additional analyses, including associations between specific molecular alterations, MRD response, and OS are ongoing and will be presented.

Shikonin Exerts an Antileukemia Effect against FLT3-ITD Mutated Acute Myeloid Leukemia Cells via Targeting FLT3 and Its Downstream Pathways

Introduction: Acute myeloid leukemia (AML) with internal tandem duplication (ITD) mutations in Fms-like tyrosine kinase 3 (FLT3) has an unfavorable prognosis. Recently, using newly emerging inhibitors of FLT3 has led to improved outcomes of patients with FLT3-ITD mutations. However, drug resistance and relapse continue to be significant challenges in the treatment of patients with FLT3-ITD mutations. This study aimed to evaluate the antileukemic effects of shikonin (SHK) and its mechanisms of action against AML cells with FLT3-ITD mutations in vitro and in vivo. Methods: The CCK-8 assay was used to analyze cell viability, and flow cytometry was used to detect cell apoptosis and differentiation. Western blotting and real-time polymerase chain reaction were used to examine the expression of certain proteins and genes. Leukemia mouse model was created to evaluate the antileukemia effect of SHK against FLT3-ITD mutated leukemia in vivo. Results: After screening a series of leukemia cell lines, those with FLT3-ITD mutations were found to be more sensitive to SHK in terms of proliferation inhibition and apoptosis induction than those without FLT3-ITD mutation. SHK suppresses the expression and phosphorylation of FLT3 receptors and their downstream molecules. Inhibition of the NF-κB/miR-155 pathway is an important mechanism through which SHK kills FLT3-AML cells. Moreover, a low concentration of SHK promotes the differentiation of AML cells with FLT3-ITD mutations. Finally, SHK could significantly inhibit the growth of MV4-11 cells in leukemia bearing mice. Conclusion: The findings of this study indicate that SHK may be a promising drug for the treatment of FLT3-ITD mutated AML.