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Background: GSK3326595 is a potent, selective, reversible protein arginine methyltransferase 5 (PRMT5) inhibitor under investigation for treatment of myelodysplastic syndrome (MDS), chronic myelomonocytic leukemia (CMML), and acute myeloid leukemia (AML). In preclinical models of AML, PRMT5 inhibition decreased proliferation and increased cell death, supporting additional clinical research in myeloid neoplasms. Objectives: To determine the clinical activity, safety, tolerability, dosing, additional measures of clinical activity, pharmacokinetics, and pharmacodynamics of GSK3326595. Design: In part 1 of this open-label, multicenter, multipart, phase I/II study, adults with relapsed/refractory myeloid neoplasms (e.g., MDS, CMML, and AML) received monotherapy with 400 or 300 mg oral GSK3326595 once daily. Study termination occurred prior to part 2 enrollment. Methods: Clinical activity was determined by the clinical benefit rate (CBR; proportion of patients achieving complete remission (CR), complete marrow remission (mCR), partial remission, stable disease (SD) >8 weeks, or hematologic improvement). Adverse events (AEs) were assessed by incidence and severity. Exploratory examination of spliceosome mutations was performed to determine the relationship between genomic profiles and clinical response to GSK3326595. Results: Thirty patients with a median age of 73.5 years (range, 47–90) were enrolled; 13 (43%) and 17 (57%) received 400 and 300 mg of GSK3326595, respectively. Five (17%) patients met CBR criteria: 4 (13%) with SD >8 weeks and 1 (3%) achieving mCR. Of five patients with clinical benefit: three had SRSF2 mutation, one U2AF1, and one was splicing factor wild-type. Frequent GSK3326595-related AEs were decreased platelet count (27%), dysgeusia (23%), fatigue (20%), and nausea (20%). GSK3326595 had rapid absorption, with a T max of approximately 2 h and a terminal half-life of 4–6 h. Conclusion: GSK3326595 monotherapy had limited clinical activity in heavily pretreated patients despite robust target engagement. The safety profile was broadly consistent with other published PRMT5 inhibitor studies. Trial registration: ClinicalTrials.gov: NCT03614728.

Azacitidine/venetoclax is an active regimen in patients with newly diagnosed AML. However, primary or secondary resistance to azacitidine/venetoclax is an area of unmet need and overexpression of MCL-1 is suggested to be a potential resistance mechanism. Pevonedistat inhibits MCL-1 through activation of NOXA, and pevonedistat/azacitidine has previously shown activity in AML. To assess the tolerability and efficacy of adding pevonedistat to azacitidine/venetoclax in relapsed/refractory AML, we conducted a phase I multicenter openlabel study in 16 adults with relapsed/refractory AML. Patients were treated with azacitidine, venetoclax along with pevonedistat intravenously on days 1, 3 and 5 of each 28-day cycle at 10, 15 or 20 mg/m2 in successive cohorts in the dose escalation phase. The impact of treatment on protein neddylation as well as expression of pro-apoptotic BCL2 family members was assessed. The recommended phase II dose of pevonedistat was 20 mg/m2. Grade 3 or higher adverse events included neutropenia (31%), thrombocytopenia (13%), febrile neutropenia (19%), anemia (19%), hypertension (19%) and sepsis (19%). The overall response rate was 46.7% for the whole cohort including complete remission (CR) in 5 of 7 (71.4%) patients who were naïve to the hypomethylating agent/venetoclax. No measurable residual disease (MRD) was detected in 80.0% of the patients who achieved CR. The median time to best response was 50 (range: 23 – 77) days. Four patients were bridged to allogeneic stem cell transplantation. The combination of azacitidine, venetoclax and pevonedistat is safe and shows encouraging preliminary activity in patients with relapsed/refractory AML. (NCT04172844).

Haploidentical donors offer a potentially readily available donor, especially for non-White patients, for hematopoietic cell transplantation (HCT). In this North American collaboration, we retrospectively analyzed outcomes of first HCT using haploidentical donor and post-transplantation cyclophosphamide (PTCy) in myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) overlap neoplasms (MDS/MPN). We included 120 consecutive patients who underwent HCT using a haploidentical donor for MDS/MPN across 15 centers. Median age was 62.5 years and 38% were of non-White/Caucasian ethnicity. The median follow-up was 2.4 years. Graft failure was reported in seven of 120 (6%) patients. At 3 years, nonrelapse mortality (NRM) was 25% (95% confidence interval [CI]: 17-34), relapse 27% (95% CI: 18-36), grade 3-4 acute graftversus- host disease 12% (95% CI: 6-18), chronic graft-versus-host disease requiring systemic immunosuppression 14% (95% CI: 7-20), progression-free survival (PFS) 48% (95% CI: 39-59), and overall survival (OS) 56% (95% CI: 47-67). On multivariable analysis, NRM was statistically significantly associated with advancing age at HCT (per decade increment, subdistribution hazard ratio [sdHR] =3.28; 95% CI: 1.30-8.25); relapse with the presence of mutation in EZH2/RUNX1/SETBP1 (sdHR=2.61; 95% CI: 1.06-6.44); PFS with advancing age at HCT (per decade increment, HR=1.98, 95% CI: 1.13-3.45); and OS with advancing age at HCT (per decade increment, HR=2.01; 95% CI: 1.11-3.63) and splenomegaly at HCT/prior splenectomy (HR=2.20; 95% CI: 1.04-4.65). Haploidentical donors are a viable option for HCT in MDS/MPN, especially for those disproportionately represented in the unrelated donor registry. Hence, donor mismatch should not preclude HCT for patients with MDS/MPN, an otherwise incurable malignancy. In addition to patient age, disease-related factors including splenomegaly and high-risk mutations dominate outcomes following HCT.

Objective/background: Low risk myelodysplastic syndrome (MDS) is a marrow failure state eventually leading to transfusion dependence. Flow cytometry has previously been demonstrated as prognostic tool in MDS, however not thoroughly studied in lower risk MDS. In this study, we assessed whether assessment for immunophenotypic blast aberrancies by flow in low risk MDS patients has a prognostic role in these patients.Methods: A total of 63 consecutive patients diagnosed with low/intermediate risk MDS were included. We recorded initial flow results, and collected time to transfusion dependence, and AML progression.Results: On multivariate cox regression analysis, increasing IPSS-R score, an increase in the number of blast aberrancies on flow cytometry, and aberrant expression of CD7 on myeloid blasts increased likelihood of transfusion dependence.Conclusion:Low risk MDS patients with increasingly aberrant blast phenotypes by flow may be at risk for earlier transfusion dependence.