ORLANDO – Adding navitoclax to ruxolitinib improved responses in a phase 2 trial of patients with uncontrolled myelofibrosis (MF) and prolonged exposure to ruxolitinib.
Dr. Jacqueline S. Garcia
Navitoclax and ruxolitinib yielded “clinically meaningful” spleen responses, improved total symptom scores, and produced “encouraging” reductions in bone marrow fibrosis among patients with primary or secondary MF, according to Jacqueline S. Garcia, MD, of Dana-Farber Cancer Institute in Boston.
Dr. Garcia presented these results at the annual meeting of the American Society of Hematology.
Navitoclax binds with high affinity to BCL-XL, BCL-2, and BCL-W, Dr. Garcia noted. Preclinical research has shown that combining Janus kinase 2 (JAK2) inhibition with BCL-XL/BCL-2 inhibition has a synergistic cytotoxic effect on JAK2-mutated cells (Blood. 2009 Feb 12;113[7]:1522-5), and BCL-XL inhibition can overcome resistance to JAK2 inhibition (Cell Rep. 2013 Nov 27;5[4]:1047-59).
These findings led to the theory that combining navitoclax and ruxolitinib could overcome resistance to JAK2 inhibition in MF. The researchers tested this theory in a phase 2 trial (NCT03222609) of 34 MF patients.
The patients had primary MF (n = 16), post–polycythemia vera MF (n = 13), and post–essential thrombocythemia MF (n = 5). At baseline, their median age was 68 years (range 42-86 years), and 68% of them were men.
There were 33 patients with genetic testing results available. None of them were triple negative, 27 had JAK2 mutations, and 7 had CALR mutations. Roughly half of patients (n = 17) were classified as high molecular risk, with mutations in ASXL1, EZH2, IDH1/2, SRSF2, or U2AF1.
Treatment
All patients had received ruxolitinib for at least 12 weeks prior to their first dose of navitoclax. They had been receiving a stable dose of 10 mg or greater, twice daily, for at least 8 weeks. The median duration of prior ruxolitinib exposure was 21 months (range, 4-71 months).
On study, patients received navitoclax once daily plus the current stable dose of ruxolitinib (10 mg or greater twice daily). Navitoclax dosing started at 50 mg, but weekly dose escalation was allowed to a maximum daily dose of 300 mg. Treatment could continue until the loss of clinical benefit, unacceptable toxicity, or discontinuation.
There were 23 patients who received the maximum dose of navitoclax, and the median duration of navitoclax treatment was 330 days (range, 29-588 days). Of the 25 patients who started the study on a ruxolitinib dose higher than 10 mg twice daily, 22 had their dose reduced to 10 mg twice daily.
Nine patients discontinued study treatment – three due to adverse events, two due to progressive disease, and four for other reasons.
Efficacy
Navitoclax appears to overcome ruxolitinib resistance, Dr. Garcia said, citing improvements in spleen size, symptom scores, bone marrow fibrosis, white blood cell counts, and transfusion needs.
Thirty patients were evaluable for spleen response. At week 24, 30% had a spleen volume reduction of 35% or greater from baseline. At any time on study, 43% of patients had a spleen volume reduction of 35% or greater from baseline. More than half of patients (53%) had a resolution of palpable splenomegaly.
Eight of 32 patients (25%) had a reduction in bone marrow fibrosis, four with a one-grade reduction and four with a two-grade reduction.
Seventeen patients were evaluable for change in total symptom score. Eleven patients (65%) experienced a reduction in symptoms, and six (35%) had a 50% or greater reduction in symptoms. The median total symptom score was 12 (range, 0-30) at baseline and 7 (range, 0-23) at 24 weeks.
Patients had a significant reduction in white blood cells on study. The mean white blood cell reduction at week 24 was 25.8 x 109/L.
Patients’ hemoglobin levels remained stable over time, but a few patients had a decreased need for transfusions on study. Seven patients entered the study having received at least one unit of packed red blood cells in the prior 12 weeks. Four of them (57%) have had a transfusion-free period of at least 12 weeks on study.