Phase 3 Trial of Selinexor and Ruxolitinib Starts in JAKi-Naive Myelofibrosis

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A phase 3 clinical trial (NCT04562389) has been initiated to assess the efficacy and safety of selinexor (Xpovio) given once a week at 60 mg in combination with ruxolitinib (Jakafi) in JAK inhibitor (JAKi)-naïve patients with myelofibrosis, according to Karyopharm Therapeutics, Inc.¹

The start of this phase 3 study is supported by phase 1 study results that showed rapid, deep, and sustained spleen responses and robust symptom improvement among patients at week 24 who were treated at the 60 mg dose level.

Findings revealed a 78.6% spleen volume response rate of ≥ 35% (SVR35) and 58.3% symptom improvement of ≥ 50% (TSS50) in the intent to treat patients, and SVR35 responses were observed in all 12 of the evaluable patients at any time. Additionally, rates were consistent regardless of subgroups, including patients treated with low dose ruxolitinib.

An improvement in major spleen and cytokine-related symptoms were observed and treatment with selinexor was generally well tolerated with a manageable adverse event (AE) profile. Most patients were able to remain on therapy for up to 74 weeks, and the most common treatment emergent AEs experienced with the 60 mg selinexor dose with ruxolitinib included nausea (78.6%), anemia (64.3%), thrombocytopenia (64.3%) and fatigue (57.1%).

The most common treatment-emergent grade ≥3 AEs with the combination with ruxolitinib were anemia (42.9%), thrombocytopenia (28.6%), and back pain (14.3%). Moreover, 75% of nausea events were grade 1 and did not lead to treatment-related discontinuations.

"The substantial degree of spleen volume reduction observed across all subgroups with selinexor 60 mg in combination with ruxolitinib is very encouraging. There is a significant unmet need in the treatment of patients with myelofibrosis, and these data demonstrate that the addition of XPO1 inhibition with selinexor with standard-of-care ruxolitinib has the potential to significantly improve outcomes for first-line myelofibrosis patients," said John Mascarenhas, MD, professor of medicine at the Icahn School of Medicine at Mount Sinai and director of the Center of Excellence for Blood Cancers and Myeloid Disorders, in a press release. "As the principal investigator for the phase 3 study, I look forward to defining a potential new standard of care for JAK-naïve patients [with myelofibrosis]."

In the randomized, double-blind, placebo-controlled phase 3 study, approximately 306 JAKi-naive patients with intermediate or high-risk myelofibrosis will be enrolled and randomized in a 2:1 fashion to receive ruxolitinib plus selinexor 60 mg or ruxolitinib plus placebo in 28-day cycles.²

Enrollment in the study is open to patients aged 18 years and older with a diagnosis of primary myelofibrosis, post-essential thrombocythemia, or post polycythemia vera myelofibrosis who have a measurable splenomegaly during the screening period, an international prognostic scoring system risk category of intermediate-1, or intermediate-2, or high-risk, an ECOG performance status of less than or equal to 2, and a life expectancy of greater than 6 months. Additionally, patients must have active symptoms of myelofibrosis, and provide bone marrow biopsy samples at screening and during the study.

The coprimary end points of the study include SVR35 and TSS50 at week 24. The key secondary end point of the study is anemia response at week 24 with other secondary end points for the phase 3 portion including overall survival, overall response rate, pharmacokinetics, and number of patients with AEs.

The study is currently recruiting patients in Virginia and is active at sites in California, Tennessee, and Utah. The estimated study completion date is December 2027.

Top-line data are expected to read out from this phase 3 study in 2025, and the company plans to further investigate selinexor in other frontline opportunities, including in combinations for the treatment of myelofibrosis.¹

"Selinexor and ruxolitinib appear to work synergistically, resulting in meaningful improvements in spleen response and total symptom score for patients with myelofibrosis," said Reshma Rangwala, MD, PhD, chief medical officer of Karyopharm, in a press release. "We believe that an opportunity exists to expand upon the initial response, depth, and duration of JAK inhibitors to ultimately improve patient outcomes. This combination has the potential to become a cornerstone treatment in frontline myelofibrosis and we are excited to start this pivotal trial to deliver on our goal of bringing forward an innovative new approach for the treatment of myelofibrosis that can benefit [patients with myelofibrosis]."

REFERENCES:

1. Karyopharm initiates pivotal phase 3 study of XPO1 inhibitor selinexor and ruxolitinib in JAK inhibitor (JAKi) naïve myelofibrosis. News release. Karyopharm Therapeutics, Inc. June 28, 2023. Accessed June 30, 2023. https://tinyurl.com/4phpud2y

2. Study of selinexor in combination with ruxolitinib in myelofibrosis. ClinicalTrials.gov. Updated June 29, 2023. Accessed June 30, 2023. https://classic.clinicaltrials.gov/ct2/show/NCT04562389