High-risk Myelodysplastic Syndrome Research Articles

Fetal hemoglobin induction in azacytidine responders enlightens methylation patterns related to blast clearance in higher-risk MDS and CMML

BackgroundAs new treatment options for patients with higher-risk myelodysplastic syndromes are emerging, identification of prognostic markers for hypomethylating agent (HMA) treatment and understanding mechanisms of their delayed and short-term responses are essential. Early fetal hemoglobin (HbF) induction has been suggested as a prognostic indicator for decitabine-treated patients. Although epigenetic mechanisms are assumed, responding patients’ epigenomes have not been thoroughly examined. We aimed to clarify HbF kinetics and prognostic value for azacytidine treated patients, as well as the epigenetic landscape that might influence HbF re-expression and its clinical relevance.ResultsSerial HbF measurements by high-performance liquid chromatography (n = 20) showed induction of HbF only among responders (p = 0.030). Moreover, HbF increase immediately after the first azacytidine cycle demonstrated prognostic value for progression-free survival (PFS) (p = 0.032, HR = 0.19, CI 0.24–1.63). Changes in methylation patterns were revealed with methylated DNA genome-wide sequencing analysis (n = 7) for FOG-1, RCOR-1, ZBTB7A and genes of the NuRD-complex components. Targeted pyrosequencing methodology (n = 28) revealed a strong inverse correlation between the degree of γ-globin gene (HBG2) promoter methylation and baseline HbF levels (p = 0.003, rs = − 0.663). A potential epigenetic mechanism of HbF re-expression in azacytidine responders was enlightened by targeted methylation analysis, through hypomethylation of site -53 of HBG2 promoter (p = 0.039, rs = − 0.504), which corresponds to MBD2-NuRD binding site, and to hypermethylation of the CpG326 island of ZBTB7A (p = 0.05, rs = 0.482), a known HbF repressor. These changes were associated to blast cell clearance (pHBG2 = 0.011, rs = 0.480/pZBTB7A = 0.026, rs = 0.427) and showed prognostic value for PFS (pZBTB7A = 0.037, HR = 1.14, CI 0.34–3.8).ConclusionsEarly HbF induction is featured as an accessible prognostic indicator for HMA treatment and the proposed potential epigenetic mechanism of HbF re-expression in azacytidine responders includes hypomethylation of the γ-globin gene promoter region and hypermethylation of the CpG326 island of ZBTB7A. The association of these methylation patterns with blast clearance and their prognostic value for PFS paves the way to discuss in-depth azacytidine epigenetic mechanism of action.Graphical abstract

Multi-site randomized trial of a collaborative palliative and oncology care model for patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) receiving non-intensive therapy.

LBA6508 Background: Patients with AML and high-risk MDS receiving non-intensive chemotherapy have substantial quality of life (QOL) impairments and often do not engage in timely discussions with their clinicians about their end-of-life (EOL) care preferences. Yet interventions to optimize EOL care delivery and QOL for this population are lacking. Methods: We conducted a multi-site randomized clinical trial of a collaborative palliative and oncology care model compared to usual care in 115 adult patients with AML and high-risk MDS receiving non-intensive therapy at two tertiary care academic hospitals. Patients with a new diagnosis or relapse/ refractory disease were eligible to participate within 30 days of initiating therapy. Patients assigned to the intervention met with a palliative care clinician monthly in the outpatient setting and a minimum of twice weekly during every hospital admission. Patients assigned to usual care were seen by palliative care only upon request. We used Natural Language Processing methods to interrogate the Electronic Health Record (EHR) with a validated algorithm to collect documented EOL care preferences. The primary outcome was to compare time from documentation of EOL care preferences to death between the study arms. Secondary outcomes obtained from the EHR include rates of documentation of EOL care preferences, hospitalization, and hospice utilization at the EOL. Patient-reported secondary outcomes include discussions with clinicians about EOL care preferences, QOL (Functional Assessment of Cancer Therapy – Leukemia), and psychological distress (Hospital Anxiety and Depression Scale) at 3 months after enrollment. Results: We enrolled 51.8% (115/222) of eligible patients. The rate of documented EOL care discussions in the EHR was higher among intervention patients vs. usual care (96.5% vs. 68.4%, P<0.001). Overall, 61.7% (71/115) of patients died, and those receiving the intervention had a longer time from documentation of EOL care preferences to death (41 days vs. 1.5 days, P<0.001). Intervention patients were more likely to report discussing their EOL care preferences with their clinicians (56.9% vs. 14.0%, P<0.001), and less likely to be hospitalized in the last 30 days of life (70.6% vs. 91.9%, P=0.031). There was no difference in hospice utilization at the EOL. At 3 months, patients assigned to the intervention reported better QOL (138.6 vs. 125.5, P=0.010), but no difference in depression or anxiety symptoms compared to those assigned to usual care. Conclusions: Palliative care significantly improved rates of discussion and documentation of EOL care preferences, reduced hospitalization at the EOL, and improved QOL in patients with AML and high-risk MDS. Clinical trial information: NCT03310918 .

Latest results of a phase 2 study of IMM01 combined with azacitidine (AZA) as the first-line treatment in adults with higher risk myelodysplastic syndromes (MDS).

6510 Background: Patients diagnosed with higher-risk myelodysplastic syndrome (MDS) have poor prognosis. Azacitidine (Aza) has been shown to prolong survival in patients with treatment-naive, higher-risk MDS compared to a menu of standard of care options. IMM01 is a fusion protein comprising a recombinant signal regulatory protein α (SIRPα) and IgG1, exerting anti-tumor effects by inhibiting the "Don't eat me" signal and activating the "Eat me" signal, leading to robust antibody-dependent cellular phagocytosis (ADCP). Methods: This is an open-label, multi-center, phase 2 study (NCT05140811) that evaluated safety and efficacy of IMM01 in combination with AZA as the first-line treatment for patients with untreated higher-risk MDS. Enrolled patients were aged ≥18 years with intermediate to very high risk MDS, as defined by the Revised International Prognostic Scoring System (IPSS-R) score >3.5, and were not eligible for stem cell transplant or intensive chemotherapy. Patients were received intravenous IMM01 at a dosage of 2.0mg/kg/week and subcutaneous AZA at a dosage of 75 mg/m2 on days1-7 per 28-day cycle. Results: By the cutoff-day of Dec 22, 2023, 57 patients were enrolled in the study. The median age was 64 (30-83) years, with 41 (71.9%) being male, and 55 (96.5%) having an ECOG of ≥1. Based on risk classification per IPSS-R, 43.9% were high risk (HR) and 31.6% were very high risk (vHR). At baseline, the median levels of blood counts were 69 (35-136)g/L for hemoglobin, 43 (2-409)×109/L for platelets and 0.8 (0.1-8.6)×109/L for neutrophils. The median duration of follow-up was 12.8 months (95%CI:9.7-15.3). Among the 51 efficacy evaluable patients, overall response rate (ORR) was 64.7%, including 29.4% complete response (CR) rate, 15.7% marrow CR (mCR) with hematologic improvement (HI), 5.9% HI and 13.7% mCR alone. The median time to response (TTR) was 1.9 months (95%CI:1.8-2.8) and the median duration of response (DoR) was not reached(NR). The median of progression-free survival (PFS) was not reached, with an estimated 12-month PFS of 54.4% (95% CI, 31.4-72.6). NGS analysis identified common mutations in DNMT3A, ASXL1, U2AF1 and RUNX1. Notably, NPM1 mutations significantly correlate with treatment response, particularly achieving CR. The most common ≥G3 treatment related adverse events (TRAEs) (≥10%) included leukopenia (78.9%), thrombocytopenia (66.7%), neutropenia (66.7%), lymphopenia (56.1%), anemia (43.9%), infection (15.8%) and pneumonia (10.5%). Without using of a low priming dose, the Grade ≥3 hemolysis was rare (only 1.8%). Conclusions: IMM01 (without low-dose priming) combined with AZA were well tolerated and showed exciting efficacy results in patients with treatment-naive higher-risk MDS. Clinical trial information: NCT05140811 .

A phase II study of venetoclax (VEN) in combination with 10-day decitabine (DEC) in older/unfit pts with newly diagnosed (ND) or pts with relapsed/refractory (R/R) acute myeloid leukemia (AML), or high-risk myelodysplastic syndrome (HR-MDS).

6549 Background: We report long-term results of phase 2 study of 10-day DEC and VEN (DEC10-VEN) in AML/HR-MDS. Methods: This single-institution study (NCT03404193) included intensive chemotherapy-ineligible pts >60y with ND de novo AML or secondary AML (sAML), or R/R AML, or HR-MDS. Induction therapy: DAC 20 mg/m2 IV x 10d + VEN days 1-28. VEN was stopped on day 21 if bone marrow blasts ≤5%. Consolidation included DEC IV x 5 days + VEN days 1-21, every 4-8 weeks as previously described (DiNardo et al. Lancet Haem. 2020). Primary endpoint was ORR. Secondary endpoints are duration of response, OS, RFS, and safety. Here, we report an update with 232 pts and results of HR-MDS/CMML cohort. Results: 232 pts were enrolled thus far (ND AML-86; sAML-49; R/R AML-76; HR-MDS/CMML-21). Median follow up is 39 mo (36-46 mo). Median age was 73y in ND AML and 64y in R/R AML (Table). Three-fourths of pts inAML cohort were adverse risk by ELN 2022 risk. CR/CRi rates in ND AML, sAML, and R/R AML were 92%, 53%, and 40% and ORR was 88%, 69%, 58%, respectively. Median OS was 12.3 mo in frontline (FL, ND (16.7 mo) and sAML (10.4 mo)) and 7.6 mo in R/R. Similarly, median RFS was 9.1 (ND-10 mo and sAML-6.4 mo) and 7.5 mo, respectively. Median time to ANC ≥500 x 109/L in cycle 1 was 41 days and Plt ≥50 x 109/L was 31 days in FL pts. 30-day mortality was 2% in FL and 5% in R/R cohort. 18% in FL and 22% in R/R cohort proceeded to SCT. In HR-MDS cohort, the median age was 71y; 18/21 pts had prior treatment. ASXL1 was the most frequent mutation. ORR was 52% (CR+CRi-33%). Median OS-12.1, RFS-7.3 mo. Median time to ANC ≥500 x 109/L was 55 and plt ≥50 x 109/L was 51 days. Most common grade 3/4 AEs were infection with neutropenia (38%), febrile neutropenia (32%), thrombocytopenia (17%), and neutropenia (15%), consistent with HMA + VEN experience. Conclusions: DEC10-VEN demonstrated expected safety and efficacy in a particularly high-risk cohort of ND and R/R pts, with no evidence that 10-days of DEC provides improved responses over standard 5-days DEC. Clinical trial information: NCT03404193 . [Table: see text]

A first-in-human, phase 1, dose escalation study of SGR-2921 as monotherapy in patients with relapsed/refractory acute myeloid leukemia or myelodysplastic syndrome.

TPS6590 Background: Cell division cycle 7-related protein kinase (CDC7) is a cell cycle kinase that maintains DNA replication by phosphorylation and activation of the minichromosome maintenance protein 2 and 4 (MCMs), components of the replicative DNA helicase. Due to the CDC7's central role in maintaining replication fork integrity, chemical inhibition of CDC7 can ultimately lead to cancer cell death. SGR-2921 is an oral, small molecule inhibitor of CDC7. Preclinical studies demonstrate that SGR-2921 has potent anti-proliferative activity in AML cell lines representative of difficult to treat patient populations, agnostic of serious mutations (including those with p53 mutations), BTK resistance, and multiple prior lines of treatment. This anti-tumor activity has also been demonstrated in cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) AML models. Methods: This is a phase 1, FIH, open-label, single-agent, two-arm, dose escalation study (NCT#05961839) designed to evaluate safety and tolerability and identify the recommended phase 2 dose (RP2D) of SGR-2921 as monotherapy in subjects with relapsed or refractory (R/R) AML, high risk (HR) MDS, or very high risk (VHR) MDS. The study utilizes an accelerated titration design with single patient cohorts that transitions to a 3+3 design once a single Grade 2 event is observed. This is a multicenter global study (US, Spain and France). SGR-2921 will be administered orally, once daily, utilizing a 5-day on and 9-day off dosing schedule over a 28-day cycle. A maximum of 144 patients will be enrolled into dose escalation and exploratory cohorts. To evaluate the effect of CYP3A4 inhibition on SGR-2921 exposure, subjects will be enrolled into one of two staggered, parallel study treatment arms, according to concomitant administration with (Arm B) or without (Arm A) azole antifungals that are strong CYP3A4 inhibitors. A single dose PK run-in will be required for subjects enrolled into the first 3 cohorts of each treatment arm. Subjects will be treated at increasing doses of SGR-2921 until the maximum tolerated dose (MTD) is exceeded. A RP2D will be selected from one of the tolerable dose levels. Key study inclusion criteria include: Age ≥ 18 years of age; Life expectancy ≥ 8 weeks; Confirmed diagnosis of R/R AML or HR and VHR MDS; Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2. Key study exclusion criteria include: Active malignancies not related to AML or MDS within two years prior to the first dose or requiring ongoing treatment; active CNS leukemia; QTcF ≥470 msec. The primary objectives are to evaluate the safety and tolerability of SGR-2921 as monotherapy and to identify the RP2D. Secondary objectives include evaluating SGR-2921 pharmacokinetics and investigating preliminary antitumor activity. Clinical trial information: NCT05961839 .

Preliminary safety, efficacy and molecular characterization of emavusertib (CA-4948) in patients with relapsed/refractory (R/R) acute myeloid leukemia (AML) with FLT3 mutation (FLT3m).

6539 Background: AML is a heterogenous disease and exhibits a dynamic mutational landscape as the disease progresses. Internal tandem duplication (ITD) of FLT3 is considered an acquired late-event mutation and is associated with a poor prognosis in AML. Emavusertib is a potent oral inhibitor of both IRAK4 and FLT3, conferring potential dual efficacy advantages compared to other IRAK4 or FLT3 inhibitors as single agents. IRAK4 is upregulated during anti-FLT3- or other cytotoxic therapies, which drives a resistance pathway of early relapse and progression. Methods: The safety, clinical activity, and potential biomarkers of emavusertib in R/R AML and higher-risk myelodysplastic syndrome are being investigated in the ongoing open-label, Phase 1/2a TakeAim Leukemia trial (NCT04278768). Next generation sequencing (NGS) of 68 genes was performed on genomic DNA from bone marrow or peripheral blood mononuclear cells at baseline and on treatment. Here, we present preliminary safety, efficacy data and molecular characterization in a subset of enrolled AML patients who carried FLT3m at baseline and were treated with emavusertib monotherapy. Results: In this study, we treated 11 R/R AML patients with FLT3m at dose levels of 200-400 mg BID. The median number of prior anti-cancer therapies was 2 (range 1-6). 8 of 11 patients had prior exposure to FLT3 inhibitors. Treatment-related adverse events (TRAEs) Grade ≥ 3 were reported in 2 of 11 (18%) patients. All responders were dosed at the Recommended Phase 2 Dose (RP2D) of 300 mg BID and with < 3 lines of prior therapy. In addition, responders demonstrated more than 90% bone marrow blast reduction compared to baseline. The most common co-mutations in this subset of patients included RUNX1, NRAS, and TET2. Emavusertib treatment significantly decreased the variant allele frequency of these mutations. FLT3-ITD levels were decreased or became undetectable in responders. Additional corelative analysis between bone marrow blast counts and mutation status indicates that AML patients with FLT3m demonstrated increased bone marrow blast reductions (P≤0.05) on emavusertib treatment, when compared to FLT3 WT AML patients. Conclusions: Emavusertib has a favorable safety and tolerability profile in pretreated AML patients with FLT3m and demonstrated monotherapy anti-cancer activity in patients with FLT3m, including patients who have progressed on prior FLT3 inhibitors. Mutational profiles are suggestive of disease-modifying activity of emavusertib. We will present updated safety and efficacy data, including data for patients who proceeded to stem cell transplant. Enrollment in this ongoing trial is continuing at RP2D in patients with < 3 lines of prior anti-cancer therapies. Clinical trial information: NCT04278768 .

Preliminary safety and efficacy of oral azacitidine (Oral-AZA) in patients (pts) with low-/Intermediate (Int)-risk myelodysplastic syndromes (MDS): Phase 2 results from the ASTREON trial.

6509 Background: There is an unmet need for new treatment (tx) options in lower-risk MDS (LR-MDS) to address cytopenias and prevent progression to higher-risk MDS and acute myeloid leukemia. Here, we report safety and preliminary efficacy data from phase 2 of the ASTREON study, which evaluated 14-day Oral-AZA regimens in pts with Low-/Int-risk MDS. Methods: ASTREON is a phase 2/3, multicenter study evaluating safety and efficacy of Oral-AZA plus best supportive care (BSC) in pts with Low-/Int-risk MDS (NCT05469737). Phase 2 is an open-label, dose optimization study to determine the recommended phase 3 Oral-AZA dose. Eligible pts (≥ 18 years of age with Revised International Prognostic Scoring System [IPSS-R] Low-/Int-risk MDS and ≥ 1 cytopenia) were randomized 1:1 to receive Oral-AZA 200 mg or 300 mg QD for 14 d per 28-d cycle plus BSC. Primary endpoints are rates of adverse events (AEs) and complete remission (CR) within 6 cycles per International Working Group (IWG) 2006 criteria. Secondary endpoints include achievement of overall response (OR) (including CR, partial remission, marrow CR, hematologic improvement-erythroid response [HI-E], HI-platelet response, and HI-neutrophil response per IWG 2006 criteria); best OR; and OR duration. HI rates within 6 cycles were calculated by investigator assessment per IWG 2006 criteria for pts who received ≥ 75% of the cycle 1 dose and had ≥ 1 post-baseline (BL) efficacy assessment (modified intent-to-treat [mITT] population). Results: As of December 4, 2023, 47 pts were randomized and received ≥ 1 Oral-AZA dose (200 mg, n = 24; 300 mg, n = 23); 6 and 5 pts discontinued tx in the 200 mg and 300 mg arms. The median (range) tx durations were 24.1 (12.1–34.1) and 24.7 (7.7–39.1) wk for the 200 mg and 300 mg arms, respectively. IPSS-R scores and RBC transfusion burden at BL were balanced between tx arms. Most pts (42/47 [89.4%]) had prior MDS tx, including but not limited to erythropoiesis-stimulating agents, lenalidomide, luspatercept, and imetelstat. AE rates were similar between arms: 11/24 (45.8%) vs 12/23 (52.2%) pts in the 200 mg vs 300 mg arms reported ≥ 1 tx-related grade 3 or 4 tx-emergent AE. The most common tx-related AEs in both arms were hematologic and gastrointestinal. Tx-related serious AEs occurred in 1/24 and 3/23 pts in the 200 mg and 300 mg arms, respectively. One death occurred in the 300 mg arm and was considered tx-related. In the mITT population, 8/22 and 7/21 pts achieved any HI in the 200 mg and 300 mg arms, respectively. Six pts in each dose group achieved HI-E. Among mITT pts with anemia at BL, 6/19 (31.6%) pts in the 200 mg and 5/18 (27.8%) pts in the 300 mg arm achieved HI-E. Updated results will be presented. Conclusions: The safety of Oral-AZA 200 mg and 300 mg was consistent with the known Oral-AZA safety profile. Preliminary efficacy data support continued evaluation of Oral-AZA in LR-MDS. Clinical trial information: NCT05469737 .

Decades old communication training influences seen in patient-centric communication skills of transplant hematologists.

12099 Background: Competency in communication skills was added as a requirement for residencies in 1999. Numerous strategies have since been incorporated into all phases of medical education and beyond. “Ask-tell-ask” and “NURSE” are commonly taught strategies used to guide conversations between physicians and patients. “Ask-tell-ask” provides a structure for assessing and delivering medical knowledge to a patient. “NURSE” outlines methods for incorporating empathy into the medical provider’s statements. We evaluated for the presence of these communication strategies in a high-stakes discussion between a transplant hematologist and a simulated patient facing a new diagnosis of high-risk myelodysplastic syndrome (MDS). Methods: This is a sub-analysis from a mixed-methods, observational study. Our team recruited hematologists who routinely perform hematopoietic cell transplants and designed a patient scenario of a 67-year-old man with recently diagnosed high-risk MDS referred to hematology. Video-recorded virtual encounters simulated an initial hematology consultation appointment between the hematologist and an actor trained to portray the patient. We analyzed transcripts and coded for themes in the discussion content and structure. We evaluated for the use of known communication strategies “ask-tell-ask”, and “NURSE” empathic responses. Results: Of 37 hematologists from 25 academic centers who participated, 73% reported receiving at least some formal communication training. Hematologists ” when teaching patients about their disease and treatment options. For example, nearly all hematologists opened the encounter by asking the patient a perception question regarding their understanding of their disease; nearly all incorporated at least one "NURSE" empathic statement after telling the patient about their disease and its prognostic implications. Most explored the patient’s goals for treatment and described treatment options utilizing an “ask-tell-ask” approach. Nearly all concluded the encounter with a summary and strategy for next steps. Conclusions: While it is commonly held that teaching communication is difficult, these conversations between hematologists and patient actors show the impact of communication training delivered over the past twenty years through the routine incorporation of well-described strategies of “ask-tell-ask” and "NURSE". This observational study provides a window into how these teachings have permeated into medical practice and hematology/oncology specifically. The incorporation of commonly taught communication strategies into these physician-patient encounters provides evidence that teaching high-quality communication may change physician behavior in a sustained and diffuse way.

The E592K variant of SF3B1 creates unique RNA missplicing and associates with high-risk MDS without ring sideroblasts

AbstractAmong the most common genetic alterations in myelodysplastic syndromes (MDS) are mutations in the spliceosome gene SF3B1. Such mutations induce specific RNA missplicing events, directly promote ring sideroblast (RS) formation, and generally associate with a more favorable prognosis. However, not all SF3B1 mutations are the same, and little is known about how distinct hotspots influence disease. Here, we report that the E592K variant of SF3B1 associates with high-risk disease features in MDS, including a lack of RS, increased myeloblasts, a distinct comutation pattern, and a lack of favorable survival seen with other SF3B1 mutations. Moreover, compared with other hot spot SF3B1 mutations, E592K induces a unique RNA missplicing pattern, retains an interaction with the splicing factor SUGP1, and preserves normal RNA splicing of the sideroblastic anemia genes TMEM14C and ABCB7. These data have implications for our understanding of the functional diversity of spliceosome mutations, as well as the pathobiology, classification, prognosis, and management of SF3B1-mutant MDS.

Real-world study of the use of azacitidine in myelodysplasia in Australia.

Hypomethylating agents are the most widely used upfront therapy for patients with myelodysplastic syndrome (MDS) who are not suitable for hematopoietic stem cell transplantation. In Australia, azacitidine was, until recently, the only approved and subsidized treatment for patients with intermediate-2 and high-risk MDS, chronic myelomonocytic leukemia, and low blast acute myeloid leukemia. We analyzed prescription data to evaluate the real-world persistence and overall survival (OS) of patients prescribed azacitidine for the first time in Australia. A retrospective cohort analysis of patients who had been prescribed Pharmaceutical Benefits Scheme (PBS)-listed azacitidine for the first time, between January 2016 and April 2021, was conducted using the PBS 10% dataset. Treatment persistence and OS were estimated using Kaplan-Meier methods. The impact of the number of treatment cycles and treatment adherence on OS was also estimated. There were 351 patients in the PBS 10% dataset who initiated treatment with azacitidine. The average age (standard deviation [SD]) at azacitidine initiation was 71.9 (11.1) years and the average number (SD) of azacitidine prescriptions was 5.6 (0.2). The median persistence on azacitidine was 15.6 months, and the OS was 13.4 months. The median OS for patients who had six or more cycles of azacitidine treatment was greater compared to patients who had five or less cycles of treatment. The data from this real-world study illustrate the unmet medical needs of patients with MDS treated with azacitidine in Australia. The majority of patients are not treated with the optimal number of cycles of azacitidine, which is negatively correlated with patient outcomes.

Abstract PO4-14-01: Synergistic Activity of CDK8/19 Inhibitor RVU120 and MEK Inhibitors in Hormone-Negative Breast Cancer: Implications for Targeted Therapy

Abstract Breast cancer (BC) is a complex disease with distinct subtypes, including triple-negative breast cancer (TNBC), which lacks targeted therapies. CDK8 and CDK19, components of the mediator complex involved in transcriptional regulation, have emerged as potential therapeutic targets in BC. Transcriptomic analysis revealed that elevated CDK8 expression was associated with poor prognosis across all BC subtypes. Furthermore, previous studies demonstrated that sensitivity to CDK8/CDK19 inhibition correlated with high STAT3 phosphorylation and enrichment of TNF/NF-kB and STAT target genes in responder cells. In this study, we evaluated the responsiveness of TNBC cell lines to RVU120, a highly selective and potent CDK8/CDK19 inhibitor currently undergoing clinical trials for acute myeloid leukemia (AML), high-risk myelodysplastic syndrome (HR-MDS), and solid tumors. Notably, the sensitivity of TNBC cell lines to RVU120 varied depending on the culture conditions, with the presence of epidermal growth factor (EGF) identified as a major determinant of response variability. Considering the role of EGFR in activating downstream signaling pathways, including MAPK and STAT, and previous observations of synergy between small molecule CDK8 inhibitors and MEK inhibitors in neuroblastoma, we investigated MEK inhibitors as potential combination partners in hormone-negative BC. Among the 15 tested BC cell lines, a synergy between CDK8/CDK19 inhibitors and MEK inhibitors was observed in 5 cell lines, antagonism in another 5 cell lines, and no synergy in the remaining 5 cell lines, based on the analysis with Combenefit software (Loewe additivity model). Importantly, cell lines where synergy of the combination therapy has been observed, exhibited EGFR amplification and markers of activated RAS pathway. This pattern of response was consistent across different MEK and MEK/RAF inhibitors, including selumetinib, trametinib, and avutometinib. These findings highlight the synergistic potential of combining RVU120 with MEK inhibitors in hormone-negative BC, particularly in TNBC with EGFR amplification and an active RAS pathway. Ongoing studies involving RNAseq analysis and organoid screening aim to further elucidate the underlying mechanisms and confirm the efficacy of this combination therapy. Furthermore, in vivo efficacy experiments are necessary to validate in vitro activity of both compounds. Successful development of this therapeutic concept relies on the validation and implementation of selected partner drugs targeting RAS pathway, as well as the identification of suitable biomarkers such as EGFRamp or RAS-score. Promising findings of this study provide a rationale for exploring the combination of CDK8/CDK19 inhibitor RVU120 and MEK inhibitors as a potential targeted therapy strategy for hormone-negative BC. Citation Format: Urszula Pakulska, Adrianna Moszynska, Justyna Martyka, Jerzy Woznicki, Elzbieta Adamczyk, Marta Obacz, Kinga Keska Izworska, Katarzyna Wiklik, Agata Stachowicz, Hendrik Nogai, Milena Mazan, Tomasz Rzymski. Synergistic Activity of CDK8/19 Inhibitor RVU120 and MEK Inhibitors in Hormone-Negative Breast Cancer: Implications for Targeted Therapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-14-01.

Measurable residual disease monitoring by ddPCR in the early posttransplant period complements the traditional MFC method to predict relapse after HSCT in AML/MDS: a multicenter retrospective study

BackgroundDroplet digital PCR (ddPCR) is widely applied to monitor measurable residual disease (MRD). However, there are limited studies on the feasibility of ddPCR-MRD monitoring after allogeneic hematopoietic stem cell transplantation (allo-HSCT), especially targeting multiple molecular markers simultaneously.MethodsOur study collected samples from patients with acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS) in complete remission after allo-HSCT between January 2018 and August 2021 to evaluate whether posttransplant ddPCR-MRD monitoring can identify patients at high risk of relapse.ResultsOf 152 patients, 58 (38.2%) were MRD positive by ddPCR within 4 months posttransplant, with a median variant allele frequency of 0.198%. The detectable DTA mutations (DNMT3A, TET2, and ASXL1 mutations) after allo-HSCT were not associated with an increased risk of relapse. After excluding DTA mutations, patients with ddPCR-MRD positivity had a significantly higher cumulative incidence of relapse (CIR, 38.7% vs. 9.7%, P < 0.001) and lower rates of relapse-free survival (RFS, 55.5% vs. 83.7%, P < 0.001) and overall survival (OS, 60.5% vs. 90.5%, P < 0.001). In multivariate analysis, ddPCR-MRD positivity of non-DTA genes was an independent adverse predictor for CIR (hazard ratio [HR], 4.02; P < 0.001), RFS (HR, 2.92; P = 0.002) and OS (HR, 3.12; P = 0.007). Moreover, the combination of ddPCR with multiparameter flow cytometry (MFC) can further accurately identify patients at high risk of relapse (F+/M+, HR, 22.44; P < 0.001, F+/M-, HR, 12.46; P < 0.001 and F-/M+, HR, 4.51; P = 0.003).ConclusionddPCR-MRD is a feasible approach to predict relapse after allo-HSCT in AML/MDS patients with non-DTA genes and is more accurate when combined with MFC.Trial registrationClinicalTrials.gov identifier: NCT06000306. Registered 17 August 2023 –Retrospectively registered (https://clinicaltrials.gov/study/NCT06000306?term=NCT06000306&rank=1).

Gut Microbiota Composition Correlates with Disease Severity in Myelodysplastic Syndrome.

The myelodysplastic syndrome (MDS) is a heterogeneous group of clonal disorders of hematopoietic progenitor cells related to ineffective hematopoiesis and an increased risk of transformation to acute myelogenous leukemia. MDS is divided into categories, namely lineage dysplasia (MDS-SLD), MDS with ring sideroblasts (MDS-RS), MDS with multilineage dysplasia (MDS-MLD), MDS with excess blasts (MDS-EB). The International Prognostic Classification System (IPSS) ranks the patients as very low, low, intermediate, high, and very high based on disease evolution and survival rates. Evidence points to toll-like receptor (TLR) abnormal signaling as an underlying mechanism of this disease, providing a link between MDS and immune dysfunction. Microbial signals, such as lipopolysaccharides from gram-negative bacteria, can activate or suppress TLRs. Therefore, we hypothesized that MDS patients present gut microbiota alterations associated with disease subtypes and prognosis. To test this hypothesis, we sequenced the 16S rRNA gene from fecal samples of 30 MDS patients and 16 healthy elderly controls. We observed a negative correlation between Prevotella spp. and Akkermansia spp. in MDS patients compared with the control group. High-risk patients presented a significant increase in the genus Prevotella spp. compared to the other risk categories. There was a significant reduction in the abundance of the genus Akkermansia spp. in high-risk patients compared with low- and intermediate-risk. There was a significant decrease in the genus Ruminococcus spp. in MDS-EB patients compared with controls. Our findings show a new association between gut dysbiosis and higher-risk MDS, with a predominance of gram-negative bacteria.

Combining 5-azacitidine with the E-selectin antagonist uproleselan is an effective strategy to augment responses in myelodysplasia and acute myeloid leukaemia.

The interaction of acute myeloid leukaemic (AML) blasts with the bone marrow (BM) microenvironment is a major determinant governing disease progression and resistance to treatment. The constitutive expression of E-selectin in the vascular compartment of BM, a key endothelial cell factor, directly mediates chemoresistance via E-selectin ligand/receptors. Despite the success of hypomethylating agent (HMA)-containing regimens to induce remissions in older AML patients, the development of primary or secondary resistance is common. We report that following treatment with 5-azacitidine, promoter regions regulating the biosynthesis of the E-selectin ligands, sialyl Lewis X, become further hypomethylated. The resultant upregulation of these gene products, in particular α(1,3)-fucosyltransferase VII (FUT7) and α(2,3)-sialyltransferase IV (ST3GAL4), likely causes functional E-selectin binding. When combined with the E-selectin antagonist uproleselan, the adhesion to E-selectin is reversed and the survival of mice transplanted with AML cells is prolonged. Finally, we present clinical evidence showing that BM myeloid cells from higher risk MDS and AML patients have the potential to bind E-selectin, and these cells are more abundant in 5-azacitidine-non-responsive patients. The collective data provide a strong rationale to evaluate 5-azacitidine in combination with the E-selectin antagonist, uproleselan, in this patient population.

Abstract CT060: Phase 1 study of azacitidine in combination with evorpacept for higher-risk myelodysplastic syndrome (MDS)

Abstract Background:Evorpacept (EVO) is a high affinity CD47-blocking fusion protein with an inactive human immunoglobulin Fc region designed to enhance the activity of other anti-neoplastic therapies with minimal additional toxicity. Here, we present final phase 1 results from the ASPEN-02 study. Methods:ASPEN-02 is an open-label, multicenter phase 1/2 study designed to evaluate the safety and activity of EVO in combination with azacitidine (AZA) in subjects with newly diagnosed (ND) higher-risk (HR) or relapsed/refractory (R/R) MDS. Adult subjects with ND HR (IPSS-R &amp;gt; 3.5) or R/R MDS were enrolled into phase 1 cohorts receiving escalating doses of EVO (20 mg/kg Q2W, 30 mg/kg Q2W, and 60 mg/kg Q4W) combined with AZA (75 mg/m2 IV/SC x 7d) in a 28-day treatment cycle. A phase 1 dose expansion portion enrolled adults with ND HR MDS into two dosing cohorts determined to be safe at EVO 40 mg/kg Q4W and 60 mg/kg Q4W. This clinical trial is registered at clinicaltrials.gov: NCT04417517. Results: As of June 2, 2023, 65 subjects were treated in the phase 1 portion, including 13 subjects with R/R MDS [EVO doses of 20 mg/kg Q2W (n=1) or 60 mg/kg Q4W (n=12)], and 52 subjects with ND HR MDS [EVO doses of 40 mg/kg Q4W (n=23) and 60 mg/kg Q4W (n=29)]. Of 52 ND HRMDS subjects, 9 (17.3%) had therapy-related MDS. Multi-hit TP53 mutations were present at baseline in 2/13 (15.4%) R/R MDS and 3/52 (5.8%) ND HR MDS patients. 13/13 (100%) R/R MDS patients had received prior hypomethylating agents or cytotoxic chemotherapy. Median age was 70 (range 24 - 88) years, and baseline ECOG scores were 0 (n=27, 41.5%), 1 (n=31, 47.7%), or 2 (n=7, 10.8%). No dose-limiting toxicity was observed, and a maximum tolerated dose (MTD) was not reached. Treatment-emergent AEs and treatment-related AEs for EVO were reported in 65/65 (100%) and 35/65 (53.8%) subjects respectively; discontinuation, however, was infrequent. Seven (10.8%) subjects experienced a serious adverse event related to EVO. There were no EVO-related deaths on study. Preliminary PK indicated dose-proportional pharmacokinetics consistent with prior studies. Objective response [complete remission (CR), partial remission (PR), marrow CR (mCR), hematologic improvement (HI)], per modified International Working Group 2006 criteria, was observed in 19/52 (36.5%) ND HR [CR=8, mCR=9, HI=2] and 2/13 (15.4%) R/R [mCR=2] MDS subjects. Conclusion:The myeloid checkpoint inhibitor EVO was well tolerated in combination with AZA with an initial safety and activity profile comparable to that of historical AZA monotherapy. Additional updated data will be provided at the time of presentation. Citation Format: Guillermo Garcia-Manero, Bart L. Scott, Ashwin Kishtagari, Srinivasa R. Sanikommu, Aref Al-Kali, Je-Hwan Lee, Juan M. Bergua Burgues, Maria Diez-Campelo, Harry P. Erba, Carmen Garcia-Hernandez, Guillermo Sanz Santillana, Casey O'Connell, Jun-Ho Jang, Dong-Yeop Shin, Hamid Sayar, Mayank Rao, Richard S. Schwartz, Grace An, Feng Jin, Alison J. Forgie, Athanasios C. Tsiatis, Jessica K. Altman. Phase 1 study of azacitidine in combination with evorpacept for higher-risk myelodysplastic syndrome (MDS) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT060.

Abstract CT115: A first-in-human phase I study of CTX-712 in patients with advanced, relapsed or refractory malignant tumors (CTX-712-CL-01 study): Efficacy and safety in a hematologic malignancies cohort

Abstract Background: Mutations in genes encoding RNA splicing factors such as SF3B1, SRSF2, U2AF1, and ZRSR2, are common genetic aberrations in many forms of myeloid neoplasms. CTX-712 is a first-in-class, orally available, highly potent, and selective small molecule inhibitor of CDC2-like kinase (CLK), a key regulator of RNA splicing. Preclinical data show that CTX-712 demonstrated anti-proliferative activity in in-vitro and in-vivo models derived from hematologic malignancies. A phase I study of CTX-712 was conducted to evaluate the safety and the preliminary efficacy of CTX-712 in patients with relapsed or refractory acute myeloid leukemia (AML) and higher-risk myelodysplastic syndrome (MDS). Methods: The objectives of this cohort were to evaluate the dose-limiting toxicity (DLT), safety, pharmacokinetic (PK)/pharmacodynamic (PD) profiles, and preliminary efficacy of CTX-712 in patients with hematologic malignancies. A 3+3 design was used in two dose levels (70 mg and 105 mg twice a week (TW)) based on the safety data from the previous dose escalation cohort in patients with solid tumors. Results: As of data cutoff on November 20, 2023, a total of 14 patients (12 AML and 2 MDS) were enrolled in 70 mg TW (n=8) and 105 mg TW dose levels (n=6). DLT of Grade 4 pneumonia was observed in 1 of 3 DLT-evaluable patients in the 105 mg TW group. In the 70 mg TW group, no DLT was observed in 6 DLT-evaluable patients. Among the safety analysis population (n=14), median treatment duration was 76 days (Range 15-974 days). At data cutoff, treatment was ongoing in 1 patient and discontinued in 13 patients. The common any-grade adverse events (AEs) (≥30%) were diarrhea (57.1%) and nausea (42.9%). The most common Grade 3 or higher AE were white blood cell count decreased and tumor lysis syndrome (14.3%). In AML patients (n=12), complete remission (CR) was observed in 3 patients (25.0%), and CR with incomplete hematologic recovery (CRi) was observed in 1 patient (8.3%). The median time to remission was 67 days (Range 29-113 days), and the median duration of response was 281 days (Range 56-924 days). In MDS patients (n=2), CR was observed in 1 patient (50.0%). PK/PD profiles of the hematologic malignancies dose escalation cohort were comparable with those of the solid tumor cohort at the same dosage. Conclusions: CTX-712 demonstrated a manageable and tolerable safety profile and showed anti-tumor efficacy in patients with hematologic malignancies. Currently, a Phase I/II Study of CTX-712 in relapsed/refractory AML and higher risk MDS is ongoing using a new tablet formulation in the United States. Clinical trial information: jRCT2080224127 Citation Format: Hisayuki Yokoyama, Noriko Fukuhara, Koji Ando, Hiroatsu Iida, Takahiro Yamauchi, Suguru Fukuhara, Koji Izutsu, Yasushi Tanoue, Maki Yamamoto, Hirokazu Tozaki, Eiji Takahara, Shingo Shoji, Akio Mizutani, Daisuke Morishita, Robert W. Oda, Hiroshi Miyake, Noboru Yamamoto. A first-in-human phase I study of CTX-712 in patients with advanced, relapsed or refractory malignant tumors (CTX-712-CL-01 study): Efficacy and safety in a hematologic malignancies cohort [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT115.

Prospective performance of the IWG-2023 criteria and IPSS-M in a phase 2 trial of guadecitabine for higher-risk MDS or CMML

AbstractGuadecitabine (SGI-110) is a dinucleotide form of decitabine that has been studied in myelodysplastic syndrome (MDS) and acute myeloid leukemia. Here, we present the results of a single-center phase 2 trial of this agent for patients with higher-risk MDS or chronic myelomonocytic leukemia (CMML). Guadecitabine was administered at a dose of 60 mg/m2 subcutaneously for 5 days. Of 100 enrolled patients, 82% had MDS. The median age was 69 years, and International Prognostic Scoring System (IPSS) was intermediate-2 in 78% and high in 14%. Thirty-eight percent had complex cytogenetics, and 32% had TP53mut. By the International Working Group 2006 (IWG-2006) criteria, 25% achieved complete remission (CR), 30% marrow CR, and 33% no response (NR). Common grade 3 events were febrile neutropenia (32%) and infection (25%). Mortality rates at 4 and 8 weeks were 0% and 4%, respectively. The median overall survival (mOS) was 16.8 months. Patients who underwent transplantation (21%) had an mOS of 46.6 months. We then reanalyzed this data set using IPSS-Molecular (IPSS-M) and IWG-2023 response criteria. By IPSS-M, 60% of patients were classified as very high and 27% as high risk. By IWG-2023, overall response rate was 52%, with 30% CR, 14% CR with limited count recovery, and 42% NR. IPSS-M provided adequate risk stratification at enrollment. Patients classified as marrow CR had widely different outcomes when reclassified by IWG-2023. In conclusion, SGI-110 was active in high-risk MDS, but survival is unlikely to be superior to current hypomethylating agents. The study is registered at www.ClinicalTrials.gov as #NCT02131597.

Abstract 6744: Activating anti-MDS immunity with polarized dendritic cell vaccines

Abstract Less than 50% of patients with higher-risk myelodysplastic syndromes (MDS) show clinical response to standard-of-care hypomethylating (HMA) therapy. Significant enthusiasm existed for immunotherapy/HMA combinations for these patients, but studies have failed to deliver on the initial promise. We have demonstrated that patients with MDS have a deficiency in antigen-presenting cells, called CD141Hi dendritic cells (DC). DC-deficient MDS patients have reduced response to HMAs, worse overall survival, and show less response to cancer vaccination. We hypothesized that restoration of this population using a novel DC vaccination approach - alpha-type-1 polarized dendritic cells (αDC1) - might compensate for this deficiency and restore immunity. To generate αDC1s, we collected monocytes from MDS patients and healthy donors (HD) and cultured them for 6 days in vitro in the presence of recombinant human GM-CSF and IL-4 followed by an additional 18-24 hours in the presence of αDC1 maturation factors (poly-I:C/IFNα/IFNγ/TNFα/IL-1β). Overall, we attempted to generate αDC1s from 15 MDS samples; 13/15 exhibited intermediate to very high-risk disease and 10/15 are currently receiving HMA therapy. We successfully cultured cells from 8/15 samples (53%). Of the 8 MDS samples, 5 were collected from patients receiving HMA therapy (62.5%). We were unable to successfully culture αDC1s from the other 5 patients receiving HMA therapy, and thus the effect of HMA therapy on aDC1 generation remains unclear. To test the function of MDS αDC1s, we focused on two signals necessary to activate immune responses: 1) the expression of co-stimulatory molecules and 2) the production of IL-12p70. Flow cytometric analysis on αDC1s and immature DCs from MDS samples revealed intra-patient variation in the fold-change surface expression of CD40/80/83/86 and HLA-DR proteins. Additionally, there was a trend towards decreased up-regulation of CD80 and CD86 in MDS specimens compared to HD. To assess production of IL-12p70, we stimulated immature DCs and αDC1s with CD40L and performed ELISA analysis on the media supernatant. We found that 3 out of 4 samples could produce IL-12p70 (range 27 - 5,480 pg/ml). To date, our results suggest that generation of MDS patient-derived αDC1 cells is feasible and additional work is being performed to fully characterize their ability to activate anti-MDS immune responses. Since αDC1s have an established safety profile in patients with solid tumors, we anticipate that we will be able to rapidly translate our results to the clinic. Citation Format: Daniel Alvarado, Jennifer Peresie, Adam Brinkman, Cheryl Allen, Weijian Jiang, Pawel Kalinski, Tiffany Tanaka, Elizabeth Griffiths, Michael Nemeth. Activating anti-MDS immunity with polarized dendritic cell vaccines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6744.

Abstract 1484: 5-Aza-4'-thio-2'-deoxycytidine induces C to G transversions in a specific trinucleotide context and leads to acute lymphoid leukemia

Abstract Myelodysplastic syndromes (MDS) are a diverse group of blood cancers characterized by peripheral blood cytopenias and dysplastic blood cell morphology. Up to 40% of patients with high risk MDS will transform to acute myeloid leukemia (AML), an aggressive blood cancer with significant morbidity and an overall 5-year survival of less than 35%. Both MDS and AML have been linked to hypermethylation of cytosine residues. Hypermethylation in the 5’ regulatory region can result in epigenetic downregulation of gene expression, and it has been speculated that hypermethylation of tumor suppressor genes can contribute to malignant transformation. DNA methyltransferase inhibitors (DNMTi), most commonly cytidine analogs, are compounds that are used clinically to decrease 5’-cytosine methylation, with the aim of inducing the re-expression of tumor suppressor genes resulting in a halt of tumor progression. 5-Aza-4’-thio-2’-deoxycytidine (Aza-TdCyd or ATC) is a cytidine analog that incorporates an aza modification (nitrogen in place of carbon) of the cytosine base and a thioether modification of the deoxyribose sugar. ATC is a promising new DNMT1i that has demonstrated efficacy in preclinical studies of solid tumors. Based on these prior studies, we sought to characterize the potential therapeutic effect of ATC in MDS.Mice that express a NUP98::HOXD13 (NHD13) transgene develop an MDS that closely recapitulates all of the key features of human MDS, including pancytopenia, dysplastic morphology, and transformation to AML. We transplanted NHD13 and wild-type (WT) hematopoietic stem and progenitor cells into WT recipients, and used this model of MDS to investigate the therapeutic potential of ATC. We found that ATC treatment led to both T and B lineage lymphoid leukemia (ALL) originating from the NHD13 cells. Surprisingly, ATC treatment also led to T and B lineage ALL in the WT cells, and further experiments demonstrated that non-transplanted, healthy WT mice developed T and B cell ALL after treatment with ATC. In sum, all mice that received at least 8 cycles of ATC therapy at the 1.0 mg/kg dose developed leukemia. Whole exome sequencing of tumors revealed thousands of acquired mutations, almost all of which were C&amp;gt;G transversions in a previously unrecognized, specific 5’-NCG-3’ context. These mutations involved a number of genes well-known to be involved in human lymphoid leukemia, such as Notch1, Pten, Pax5, Trp53, and Nf1. Treatment of the human U937 and CEM cell lines in vitro showed thousands of acquired C&amp;gt;G transversions in a similar context. Taken together, these findings demonstrate that ATC can be a potent mutagen in human and mouse cells, both in vitro and in vivo. Citation Format: Ryan Matthew Bertoli, Yang Jo Chung, Michael Difilippantonio, Anthony Wokasch, Madison R. Marasco, Haley Klimaszewski, Susannah Garber, Yuelin Jack Zhu, Robert L. Walker, Dengchao Cao, James Doroshow, Paul Meltzer, Peter D. Aplan. 5-Aza-4'-thio-2'-deoxycytidine induces C to G transversions in a specific trinucleotide context and leads to acute lymphoid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1484.

Abstract 3129: BYON4413, an in vivo active CD123-targeting antibody-drug conjugate, combines effectively with azacitidine and venetoclax in acute myeloid leukemia cell lines

Abstract Background: CD123, the alpha chain of the interleukin-3 receptor (IL-3Rα), is overexpressed in multiple hematologic malignancies and found particularly highly expressed on the surface of acute myeloid leukemia (AML) cells. Furthermore, increased CD123 expression on leukemic stem cells relative to non-neoplastic hematopoietic stem cells makes CD123 an attractive tumor-associated target for an antibody-drug conjugate (ADC). BYON4413 is an ADC that consists of a novel humanized IgG1 anti-CD123 antibody site-specifically conjugated with Byondis' proprietary duocarmazine linker-drug technology, ByonZine® and ByonShieLD®. The efficacy of BYON4413 is studied as monotherapy and in combination with azacitidine and venetoclax (AZA/VEN), since the AZA/VEN regimen is the standard of care (SOC) for AML patients who are ineligible for intensive chemotherapy. Method: A panel of CD123+ and CD123- hematological cell lines and AML patient-derived bone marrow mononuclear cells (BMMCs)/peripheral blood mononuclear cells (PBMCs) were utilized in in vitro studies to determine the cytotoxic effects of BYON4413. The induction of apoptosis and cell killing by BYON4413 in a triple combination with AZA/VEN was studied in vitro using the CD123+ AML cell lines MOLM-13 and MV4-11. AML patient and cell line-derived xenograft models were used to investigate the in vivo efficacy of BYON4413. Results: In vitro studies with human AML cell lines show that BYON4413 is highly effective in eradicating CD123+ cells while having little impact on CD123- cells. These results were confirmed ex vivo with AML patient-derived BMMCs/PBMCs. BYON4413 effectively killed AML patient-derived blasts while largely sparing healthy hematopoietic cells. The triple combination of BYON4413 with AZA/VEN enhanced both apoptosis and cell killing of AML cell lines compared to the singular BYON4413 treatment. In vivo studies demonstrate that BYON4413 is remarkably efficient at reducing the tumor burden in AML patient- and cell line-derived xenograft models. Conclusions: Preclinical studies show that BYON4413 has potential to be an effective targeted therapy against CD123+ hematological malignancies such as AML. The enhanced efficacy of BYON4413 together with AZA/VEN suggests that a clinical benefit from the triple combination may be achievable and is worth further exploration. A first-in-human dose-escalation and expansion trial with BYON4413, designed to enroll R/R AML and high-risk MDS patients, is scheduled to start in Q2 2024. Citation Format: Miranda M.C. van der Lee, Tanja van Achterberg, Kaylee Hersmus, Annet Brouwers-Vos, Monique van der Vleuten, Maurien Pruis, Wendy Kappers, Gijs Verheijden, Gerwin Huls, Glenn van Wigcheren, Ruud Ubink, Aloys Sesink, Alyson MacInnes, Jan Jacob Schuringa, Wim Dokter. BYON4413, an in vivo active CD123-targeting antibody-drug conjugate, combines effectively with azacitidine and venetoclax in acute myeloid leukemia cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3129.