Burgess, Ashya

Abstract BACKGROUND: DNA methyltransferase inhibitors (DNMTi) are US FDA approved for the management of CMML. These agents are associated with an overall response rate (ORR) of 40-50%, with a true complete remission (CR) rate of <20%. TET2 mutations are seen in 60% of CMML, with TET2 being a ferrous and oxoglutarate dependent DNA-dioxygenase that oxidizes 5mC to generate 5hmC, 5fC and 5caC. Ascorbic acid (AA) is critical for TET activity and can enhance TET 1/2/3 dioxygenase function by binding to the catalytic domain and when given in high doses, can result in glutathione depletion and free radical induced cell death. In a pilot study (Xie et al. Blood 2024), we demonstrated that high dose IV AA can be clinically effective and induce changes in differentially methylated regions (DMR) involving hematopoietic enhancers and improve cytopenias in TET2-mutant (mt) patients [CCUS]. We expanded this study to combine high dose IV AA with DNMTi to enhance the demethylation effect and produce durable responses in new diagnosed, treatment requiring, TET2mt CMML patients. METHODS: At Mayo Clinic, the LS1781 (NCT03418038) clinical trial was amended to include Arm E, combing high dose IV AA with standard of care decitabine in newly diagnosed TET2mt CMML patients that needed therapy. IV AA was dosed at 1 g/kg on days 1, 3 and 5 (per 28-day cycle, max dose 100 gm) through a central line, based on demonstrated safety from phase 1 studies. Standard dosing was adopted for decitabine, and patients were then asked to take oral AA, 1 gm daily from days 6-28. Key inclusion criteria included a WHO-defined diagnosis of CMML with at least one detectable TET2 mutation requiring therapy with adequate performance status (ECOG PS <2) and organ function (creatinine clearance > 55 mL/min). Response was evaluated by the MDS/MPN International Working Group Criteria (Savona et al. Blood 2015). We measured pre- and post-therapy (4 cycles) bone marrow variant allele fractions (VAF) through next generation sequencing assays, transcriptomic changes through RNA seq, and DNA methylation changes using the Illumina Methylation EPIC array. RESULTS: Between February 2024 and July 2025, a total of six patients were enrolled. The median age at enrollment was 73 years (range: 65-80); all Caucasian with 3 (50%) males. All patients had a diagnosis of CMML-1 with a median bone marrow (BM) blast percentage of 3 (0-10), median hemoglobin 13 (9.5-14.5) g/dL, median WBC count of 5.7 (2.1-12.6) x 109/L, absolute monocyte count 1.4 (0.7-2.7) x 109/L, and platelet count of 92.5 (32-123) x 109/L. TET2 (100%, 4 patients > 1 TET2 mutation at mean VAF of 36%), SRSF2 (67%), and KRAS (33%) were the most frequent molecular abnormalities. Neutropenia (without infection/sepsis) was the only treatment-associated adverse effect seen in 3 (50%, all grade 3) patients. Response was assessed in patients who completed at least 4 cycles (n=5) of therapy, with all (100%) patients meeting criteria for either a complete response (n=2, 40%), optimal marrow response (n=1, 20%) or clinical benefit (platelet response, n=2, 40%). In five patients who had NGS assessment pre-and post-therapy, there was a >50% reduction in TET2mt VAF, with one patient loosing the KRAS G12D clone in its entirety. Furthermore, we identified significant changes in DNA methylation associated with treatment with >85% of the CpGs being hypomethylated post-treatment. RNA-sequencing on patients pre- and post-treatment, identified key transcriptomic changes, with a decrease in expression of leukemogenic genes. Integration of the differential methylation data with transcriptomic changes identified several genes in which changes in DNA methylation correlated with a change in gene expression. These genes include regulators of blood cell development and inflammatory response including GATA2, BCL2, and HLA-DPA. Several leukemia-associated genes were downregulated including MEIS1, TCL1A, and SETBP1. CONCLUSION: In TET2mt CMML, high dose IV AA acid enhances TET activity and synergizes with DNMTi with encouraging clinical responses in all patients and with no new safety signals. On completion of this study, we plan a randomized phase 2 trial comparing high dose IV AA with decitabine vs decitabine alone in newly diagnosed TET2/IDHmt CMML.

Abstract BACKGROUND: DNA methyltransferase inhibition offers palliative benefit but does not alter disease biology. in chronic myelomonocytic leukemia (CMML, Merlevede J et al. Nat Comm 2016). This was conclusively demonstrated in the phase 3 DACOTA study, where decitabine did not improve event-free survival in comparison to hydroxyurea (median 12.1 versus 10.3 months, P=0.27) in advanced myeloproliferative CMML (MP-CMML). Hence, there is in urgent need to develop disease modifying therapies for this dismal condition. We and others have demonstrated a role for RAS mutations in MP-CMML through the activation of the KMT2A-PLK1 axis. Targeting of this axis using onvansertib, an inhibitor of PLK1, has demonstrated its pre-clinical efficacy in MP-CMML patient-derived organoid and xenograft models. (Carr RM et al. Nat Comm 2021). METHODS: We conducted a single center phase 1 study to assess the safety and efficacy of onvansertib in relapsed/refractory MP-CMML (NCT05549661). We used a Bayesian Optimal Interval (BOIN) study design to determine the maximum tolerated dose (MTD). The three dose cohorts included 6, 9 and 12 mg/m2 given orally from days 1 to 21 of each 28-day cycle. Key inclusion criteria included a WHO-defined diagnosis of MP-CMML with a white blood cell (WBC) count > 13,000/mm3 and adequate organ function (estimated GFR > 50 mL/min/m2). Response was evaluated per the MDS/MPN International Working Group Criteria (Savona et al. Blood 2015). Targeting efficacy was assessed by measuring phosphorylation of TCTP (a PLK1 substrate), specifically pTCTP/TCTP ratios by immunoblotting in peripheral blood mononuclear cell (PBMC) samples pre and post cycle 1 (Days 1, 7, 21) and end of cycle 3. Pharmacokinetic studies and translational correlative studies were conducted per protocol. RESULTS: Between April 2023 and July 2025, a total of 9 patients were enrolled. The median age at enrollment was 68 years (range: 60-83); all caucasian with 4 (44%) males. All patients had a diagnosis of CMML-1 with a median bone marrow (BM) blast percentage of 4 (0-9), median hemoglobin 10 (7.1-13.2) g/dL, median WBC count of 11.1 (3.1-72.7) x 109/L (4 patients had a WBC count < 13 x 109/L at enrollment due to hydroxyurea use but were confirmed to be MP-CMML at diagnosis), absolute monocyte count 2.1 (1.9-19.6) x 109/L, and platelet count of 36 (20-494) x 109/L. TET2 (89%), SRSF2 (78%), ASXL1 (56%), NRAS, KRAS and CBL (22% each) were the most frequent molecular abnormalities. Previous therapies included hydroxyurea (n=8) and decitabine (n=1). Four patients were enrolled at the 6mg/m2dose level, 2 at the 9 mg/m2 dose level and we currently have one patient at the 12 mg/m2 dose level. While there were 2 planned patients at the 6 mg/m2 dose level, due to a case of pericardial effusion that was possibly drug related, an additional two patients were enrolled at the same dose level, without any dose limiting toxicity (DLT). Targeting efficacy was confirmed by pTCTP immunoblotting in PBMC samples from 4 patients (6 and 9 mg/m2 dose levels) showing suppressed pTCTP/TCTP ratios. No confirmed DLT has been identified thus far, and no grade 3 or 4 toxicities attributable to the study drug have been reported. Possible or unrelated grade 3 adverse effects included infections (sepsis/cellulitis, n=2, 22%), acute kidney injury (n=1, 11%), pericardial effusion (n=1, 11%), and atrial fibrillation with rapid ventricular response (n=1, 11%). Median duration on therapy was 124 (range: 15-654) days with most common cause of study discontinuation being disease progression (33%). Response was assessed as per the MDS/MPN IWG criteria in patients who received at least 1 cycle (n=8) with 3 (38%) patients meeting criteria for either hematological or optimal marrow response. Specifically, there was one (14%) patient with >100% platelet response, one (14%) with normalization of WBC count (baseline WBC count >50 x 109/L), one (14%) optimal marrow response with BM blast% reduction from 8 to 2, facilitating candidacy for an allogeneic hematopoietic stem cell transplantation, and three patients (38%) remained as stable disease. CONCLUSION: In MP-CMML, PLK1 inhibition with onvansertib is relatively well tolerated and shows preliminary efficacy in approximately 40% of patients, with one patient having an optimal marrow response at the 9 mg/m2 dose. Future directions include a dose expansion phase and studying upfront combination with DNA methyltransferase inhibitors.

TPS7089 Background: Chronic myelomonocytic leukemia (CMML) is a myelodysplastic/myeloproliferative overlap neoplasm (MDS/MPN) that can be further divided into MD (WBC < 13 x 109/L) and MP (≥13 x 109/L) subtypes. MP-CMML is enriched in RAS pathway mutations ( NRAS, CBL, KRAS, PTPN11 and NF1), has a shorter median survival (19 vs 36 months), has a higher rate of acute myeloid leukemia (AML) transformation (40% vs 10%) and has a unique transcriptomic and epigenetic composition. These RAS pathway mutations promote selective PLK1 overexpression, a mitotic checkpoint kinase. Given the relative inefficacy of hypomethylating agents (HMA) in MP-CMML and previously demonstrated in vitro and in vivo efficacy data for PLK1 inhibition on MP-CMML with RAS pathway mutations, we designed a phase 1 clinical trial testing the safety of onvansertib, a novel, orally bioavailable, PLK1 inhibitor in relapsed/refractory MP-CMML. Methods: This is an investigator-initiated, prospective, open-label, phase I study of onvansertib in MP-CMML relapsed/refractory (RR) or intolerant to existing therapies including HMA and hydroxyurea. The primary endpoint is characterization of safety. Secondary endpoints include efficacy as defined by the 2015 MDS/MPN International Working Group criteria, volumetric spleen response and symptom response via assessment with MPN-SAF-TSS. Inclusion criteria include MP-CMML RR following hydroxyurea or at least 4-cycles of HMA or intolerance of treatment with either, platelets ≥ 20,000/m3 and Cockcroft-Gault creatinine clearance ≥ 60 mL/min/m2. Hydroxyurea may continue for the first 28 days on study. Onvansertib will be given orally on days 1 through 21 of a 28-day cycle with a Bayesian optimal interval design to assess the safety and recommended phase II dose. Exploratory end points include targeting efficacy, impact of PLK1 and KMT2A expression and interactions with ASXL1 and TET2 mutations. Twenty-five patients will be enrolled at Mayo Clinic in Minnesota, with enrollment open since November 2022. Clinical trial information: NCT05549661 .