S197: NAVITOCLAX PLUS RUXOLITINIB IN JAK INHIBITOR-NAÏVE PATIENTS WITH MYELOFIBROSIS: PRELIMINARY SAFETY AND EFFICACY IN A MULTICENTER, OPEN-LABEL PHASE 2 STUDY

Abstract

Background: Ruxolitinib, a Janus kinase (JAK) 1/2 inhibitor, is the current standard of care for patients with myelofibrosis (MF) that improves disease symptoms in approximately 40% of patients with limited impact on disease biology. Many patients lose response over time, highlighting an unmet need for novel therapies. Navitoclax is a first-in-class, oral, small molecule that binds with high affinity to BCL-XL and BCL-2, key pro-survival proteins in the apoptotic pathway, and has a synergistic effect when used in combination with JAK inhibitors to enhance malignant cell death in MF. This ongoing, open-label, multicenter, phase II trial (NCT03222609) is evaluating the efficacy and safety of navitoclax with or without ruxolitinib in patients with MF and previously published data suggest clinically meaningful activity of the combination in patients with prior ruxolitinib failure (Pemmaraju et al., ASH 2020). Here, we report results from patients who were JAK inhibitor-naïve and treated with navitoclax and ruxolitinib combination therapy. Aims: N/A Methods: Enrolled patients had primary or secondary MF with splenomegaly (DIPSS ≥ Intermediate-1) and did not receive prior therapy with JAK-2 or bromodomain and extraterminal motif (BET) inhibitors. Patients initiated navitoclax at 100 mg once per day (QD) or 200 mg QD if baseline platelet count was ≤150 × 109/L or >150 × 109/L, respectively. Ruxolitinib was orally administered twice daily at a starting dose based on baseline platelet count as per the local ruxolitinib label. The primary endpoint was spleen volume reduction of ≥35% (SVR35) from baseline at week 24. SVR35 was assessed at weeks 12, 24, and once every 24 weeks thereafter. Key secondary endpoints were ≥50% reduction in total symptom score (TSS50), bone marrow fibrosis reduction, and anemia response (per International Working Group criteria). Adverse events (AEs) were monitored throughout the study. Results: As of Oct 04, 2021, 32 patients received navitoclax plus ruxolitinib. The median duration of follow-up was 6.1 (range, 1.9 to 18.6) months. Twenty-eight (88%) patients received a navitoclax dose of 200 mg, and 4 (13%) received 100 mg OD. The median age was 69 years (range, 44 to 83), median spleen volume was 1889.08 cm3 (range, 645.6 to 7339.6), and 38% had at least 1 prior line of therapy. The median navitoclax and ruxolitinib exposures were 24.1 (range, 5.1 to 80.9) and 24.1 (5.1 to 80.9) weeks, respectively. Thirty-one (97%) patients experienced ≥1 AE, 25 (78%) had Grade ≥3 AEs, and 6 (19%) had serious AEs. The most frequent Grade ≥3 AEs were anemia (34%), thrombocytopenia (31%), and neutropenia (19%). Three (9%) and 2 (6%) patients experienced an AE that led to navitoclax and ruxolitinib discontinuation, respectively, and 2 (6%; 1 progressive disease, 1 cardiac disorder unrelated to navitoclax) AEs led to death ≤30 days after the last dose of navitoclax. SVR35 was achieved by 52% of evaluable patients at week 24 (SVR35 in DIPSS Intermediate-2, 50%; High-risk, 33%) and by 76% at any time on the study (Table). The median time to first SVR35 was 12.1 (range, 11 to 47) weeks. Image:Summary/Conclusion: The combination of navitoclax and ruxolitinib was well tolerated and demonstrated early and robust reductions in spleen volume, anemia, and BM fibrosis in patients without prior JAK-2 inhibitor exposure. SVR35, anemia, and bone marrow fibrosis improved over time.