ArticlesAddition of navitoclax to ongoing ruxolitinib treatment in patients with myelofibrosis (REFINE): a post-hoc analysis of molecular biomarkers in a phase 2 study
Introduction
Myelofibrosis is a chronic myeloid neoplasm characterised by stem-cell-derived clonal proliferation, leading to cytokine release, myeloid hyperproliferation, and bone marrow fibrosis.1 Mutations in JAK2, CALR, and MPL have been identified as driver mutations in the pathogenesis of myelofibrosis, and result in constitutive JAK–STAT activation and subsequent expansion of myeloproliferative malignant cells.1, 2 Approximately 90% of patients with myelofibrosis harbour a mutation in at least one of these three driver genes.1 Additional somatic mutations of genes that affect DNA methylation (TET2 and IDH1/2), chromatin modification (ASXL1 and EZH2), RNA splicing (SF3B1, SRSF2, and U2AF1), and DNA repair (TP53) are frequently detected in myelofibrosis and are thought to contribute to disease progression or leukaemic transformation, or both.1, 3, 4 Mutations in ASXL1, EZH2, SRSF2, IDH1/IDH2, and U2AF1Q157 are classified as high molecular risk mutations that are associated with a worse prognosis.3 Treatment strategy in myelofibrosis is guided by risk stratifications according to clinical phenotypes and genetic mutations.4
Ruxolitinib is a selective JAK1/JAK2 inhibitor approved for the treatment of intermediate or high-risk myelofibrosis in the USA and in Europe, following the results of two phase 3, multicentre, randomised, double-blinded trials (COMFORT-I and COMFORT-II).5, 6 Although ruxolitinib treatment has been shown to improve inflammatory symptoms and splenomegaly, it does not clinically modify the disease. The definition of disease modification in myelofibrosis is yet to be established, but reversal of bone marrow fibrosis and reductions in driver gene variant allele frequency are generally thought to be suggestive of disease modification, and have been shown to be associated with improved patient outcomes.7 We have proposed that disease modification can be defined as therapy-induced survival benefit associated with a reduction in underlying bone marrow fibrosis and restoration of normal haematopoiesis.8 However, clinically meaningful disease modification, in the context of improved bone marrow fibrosis and reduced variant allele frequency, is infrequently achieved with ruxolitinib monotherapy.9, 10 Furthermore, more than half of patients discontinue treatment with ruxolitinib, and these patients have poor survival outcomes.11, 12 Taken together, these findings highlight crucial unmet needs in the treatment of myelofibrosis.
Several preclinical studies support a role for the BCL-XL/BCL-2 inhibitor navitoclax in therapeutic strategies targeting JAK/STAT-driven malignancies (eg, polycythaemia vera and myelofibrosis) and overcoming acquired resistance to JAK2 inhibition.13, 14 The REFINE trial evaluated the activity and safety of navitoclax in combination with ruxolitinib in patients with primary or secondary myelofibrosis who were no longer benefiting from ruxolitinib monotherapy (ie, patients who progressed or had a suboptimal response). In this study, the combination of navitoclax and ruxolitinib yielded a 35% or greater reduction in spleen volume (SVR35), improved bone marrow fibrosis, and alleviated anaemia in this difficult-to-treat patient population.15 Here, we report the results of the exploratory biomarker analyses of the REFINE trial that assessed whether navitoclax plus ruxolitinib could induce meaningful clinical responses in patients with adverse molecular risk, and mediate responses suggestive of disease modifications, including improvements in bone marrow fibrosis and reductions in driver gene variant allele frequency. The roles of anti-apoptotic BCL-2 family members BCL-XL, BCL-2, and MCL-1 in myelofibrosis-transformed peripheral blood mononuclear cells (PBMC) were explored.
Section snippets
Study design and participants
Full details of the study design, patient selection criteria, and endpoints have been previously reported.15 In brief, the ongoing REFINE trial is a phase 2, multicentre, open-label trial designed to assess the safety and activity of navitoclax alone or in combination with ruxolitinib in patients with primary or secondary myelofibrosis. Patients were enrolled into four cohorts (cohorts 1a, 1b, 2, and 3) according to previous JAK inhibitor treatment. Here, we report the post-hoc exploratory
Results
Between Nov 14, 2017, and April 10, 2019, 34 patients in cohort 1a received at least one dose of navitoclax in combination with ruxolitinib (figure 1; appendix p 8). As of May 6, 2021 (data cutoff), the median follow-up for the 34 survivors was 26·2 months (IQR 21·9–32·3). The median age was 68 years (IQR 61–75) and 68% of patients were male (table). At study entry, 33 patients were evaluable for biomarker analysis. Of them, 19 (58%) patients had one or more high molecular risk mutations;
Discussion
This study reports the post-hoc exploratory analyses of patients in cohort 1a of the open-label, phase 2 REFINE trial, which was designed to investigate the safety and activity of navitoclax in combination with ruxolitinib in patients with primary or secondary myelofibrosis who had received, but no longer benefited from, ruxolitinib. With the addition of navitoclax, a BCL-XL/BCL-2 inhibitor, splenomegaly and constitutional symptoms improved independently of high molecular risk mutations.
Data sharing
AbbVie is committed to responsible data sharing for the clinical trials it sponsors. This includes access to anonymised, individual, and trial-level data (analysis data sets), as well as other information (eg, clinical study reports), as long as the trials are not part of an ongoing or planned regulatory submission. These clinical trial data can be requested by any qualified researchers who engage in rigorous, independent scientific research, and will be provided following review and approval
Declaration of interests
NP reports a consulting or advisory role with Celgene, Stemline, Incyte, Novartis, Mustang Bio, Roche Diagnostics, and LFB; honoraria from Celgene, Stemline, Incyte, Novartis, Mustang Bio, Roche Diagnostics, and LFB; grants and funding from Affymetrix and Sager Strong Foundation; and board memberships (non-compensated) from Dan's House of Hope (board of directors) and HemOnc Times/Oncology Times (board member, editor-in-chief). JSG serves on the advisory board and steering committee for AbbVie
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