The Combination of Navitoclax and Ruxolitinib in JAK Inhibitor-Naïve Patients with Myelofibrosis Mediates Responses Suggestive of Disease Modification

Background: Myelofibrosis (MF) is a myeloproliferative neoplasm associated with splenomegaly, high symptom burden, bone marrow fibrosis (BMF), and poor prognosis. The Janus kinase inhibitor (JAKi) ruxolitinib is the current standard of care for patients with MF. It improves splenomegaly and disease symptoms with limited impact on disease biology, highlighting an unmet medical need in MF. Driver mutations of JAK2, CALR, and MPL are key to the pathogenesis of MF. Reduction in variant allele frequency (VAF) of driver mutations and reversal of BMF are suggestive of disease modification (Pemmaraju, Cancer, 2022). Additionally, mutations in ASXL1, EZH2, SRSF2, IDH1/2, and U2AF1 p.Q157 are classified as high molecular risk (HMR) mutations associated with a worse prognosis (Arber et al., Blood, 2016). We previously demonstrated evidence of disease modification independent of HMR mutations by adding navitoclax to ruxolitinib in patients with suboptimal responses to ruxolitinib monotherapy (Pemmaraju, Lancet Oncology, 2022). Herein, we investigated whether the type of MF and risk (e.g., age, Dynamic International Prognostic Scoring System [DIPSS], and HMR) correlated with clinical outcomes and responses suggestive of disease modification (e.g., VAF reduction and improvement in BMF) among JAKi treatment-naïve patients with MF treated with the combination of navitoclax and ruxolitinib.

Methods: Cohort-3 of the phase-2 multicenter REFINE study (NCT03222609) enrolled JAKi treatment-naïve patients with MF. Enrolled patients had primary or secondary MF with splenomegaly (DIPSS ≥ Intermediate-1) and did not receive prior JAK-2 therapy or bromodomain and extra terminal motif (BET) inhibitors. Patients initiated navitoclax at 100 mg QD or 200 mg QD if baseline platelet count was ≤ 150 × 10⁹/L or > 150 × 10⁹/L, respectively. Ruxolitinib was given BID with starting dose based on baseline platelet count per local label. The primary endpoint was spleen volume reduction of ≥ 35% (SVR₃₅) from baseline at week 24, assessed by MRI conducted by central review. Key secondary and exploratory endpoints evaluated in this analysis were a reduction in BMF obtained from BM biopsies by local evaluation and a reduction in VAF for the driver gene mutations (JAK2^V617, CALR, or MPL), respectively. Driver gene VAF and HMR mutations were determined in whole blood with the 50-gene Focus Myeloid next-generation sequencing panel (Interspace Pharma Solutions, Morrisville, NC, USA).

Results: As of Feb 07, 2022, all enrolled patients (N = 32) treated with navitoclax and ruxolitinib were evaluable for biomarker analysis. The median duration of follow-up was 6.1 months (range, 1.9 – 18.6); median age was 69 years (range, 44 – 83), and median spleen volume was 1889.08 cm³ (range, 645.6 – 7339.6). At baseline, 22 (69%) patients had JAK2, 6 (19%) had CALR, and 3 (9%) had MPL mutations. One (3%) patient was triple negative. Nineteen (59%) patients had HMR mutations.

SVR₃₅ at week 24 was observed in all subgroups known to confer poor prognosis, including age (≥75 years, 50% [n = 4/8]), high DIPSS score (Intermediate-2, 63% [n = 12/19]; high, 33% [n = 1/3]), and HMR mutations (47% [n = 9/19]; Figure).

BMF grade improvement was evaluable in 26/32 (81%) patients, of which 9/26 (35%) achieved ≥ 1-grade improvement at any time during treatment with a median time-to-improvement of 12.3 weeks (range, 12.1 – 24.1). Complete resolution of BMF was observed in 2/9 (22%) patients. The baseline BMF grades of these patients were 2 and 3. BMF ≥ 1-grade improvement was achieved by 7/13 (54%) patients with HMR mutations and 2/13 (15%) without HMR mutations.

Reduction in driver gene JAK2^V617 mutation VAF > 20% from baseline at week 12 or 24 was observed in 14/28 (50%) patients, and 5/14 (36%) patients achieved > 50% VAF reduction from baseline. There were no differences in > 20% VAF reductions from baseline to week 12 or 24 between those with or without HMR mutations (7/15 [47%] versus 7/13 [54%], respectively).

Conclusions: Among JAKi treatment-naïve patients with MF, the combination of navitoclax and ruxolitinib reduced splenomegaly in several high-risk groups known to confer poor prognosis. Reductions in BMF and VAF were independent of HMR mutations. The reduction in BMF and VAF for the driver mutation JAK2^V617 is encouraging and suggestive of evidence of disease modification with the combination of navitoclax and ruxolitinib.

Passamonti:Novartis: Honoraria; BMS: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria; Roche: Consultancy. Foran:Novartis, Servier, Pfizer, BMS, Taiho: Other: Formal Advisory Activities; AbbVie, Actinium, Aptose, Astex, H3Biosciences, Kura Oncology, Trillium, Xencor: Research Funding. Tandra:Alexion Pharmaceuticals: Honoraria; ADC Therapeutics: Honoraria. De Stefano:Amgen: Honoraria, Speakers Bureau; Bristol Myers Squibb/Celgene: Honoraria, Speakers Bureau; GlaxoSmithKline: Honoraria, Speakers Bureau; AbbVie: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees. Fox:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sierra Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees. Mattour:GSK: Consultancy; AbbVie, Amgen, BMS, KTRA, J&J: Current holder of stock options in a privately-held company. McMullin:Abbvie: Consultancy, Speakers Bureau; CTI: Consultancy; AOP: Research Funding, Speakers Bureau; BMS: Consultancy, Research Funding; Novartis: Consultancy, Speakers Bureau; Pfizer: Speakers Bureau; Sierra Oncology: Consultancy; Incyte: Consultancy, Speakers Bureau. Perkins:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria; Celgene: Other: Support for meetings and/or travel; Sierra Oncology: Honoraria, Other: Support for present manuscript. Rodríguez-Macias:BMS: Other: Advisory Role; Novartis: Other: Advisory Role; Jazz: Other: Advisory Role. Sibai:Novartis, BMS, Gilead, AbbVie, Jazz, Pfizer: Honoraria. Qin:AbbVie: Current Employment, Other: May own stock. Sun:AbbVie: Current Employment, Current equity holder in publicly-traded company. Potluri:AbbVie: Current Employment, Current equity holder in publicly-traded company. Harb:AbbVie: Current Employment, Other: May own stock. How:Novartis: Consultancy, Honoraria, Speakers Bureau; Teva: Honoraria; Astellas: Honoraria, Research Funding, Speakers Bureau; AbbVie: Research Funding; Sierra Oncology: Research Funding; Jazz: Other: Travel Expenses.

Navitoclax is a BCL-XL/BCL-2 inhibitor that is currently not approved for the treatment of myelofibrosis. Ruxolitinib is approved for the treatment of myelofibrosis