Ruxolitinib/Pegylated Interferon Alpha 2a Reduces Spleen Length in Myelofibrosis

Jean-Jacques Kiladjian, MD, PhD

First-line ruxolitinib (Jakafi) plus pegylated interferon alpha 2a demonstrated durable spleen volume reduction in patients with myelofibrosis, according to findings from the phase 1/2 RUXOPeg trial (NCT02742324) that were presented at the 2022 ASH Annual Meeting.¹

The combination elicited a spleen reduction of at least 50% in 70% (95% CI, 53%-84%; n = 26/37) of patients from the combined phase 1 and 2 populations within the first 6 months of treatment. Specifically, 67% (95% CI, 41%-87%; n = 12) and 74% (95% CI, 49%-91%; n = 14) of patients experienced at least a 50% spleen reduction in phases 1 and 2, respectively.

“This treatment may also improve, after 12 months, the inflammatory cytokine profile and bone marrow histopathology that are probably important biomarkers of disease severity,” Jean-Jacques Kiladjian, MD, PhD, of Saint Louis Hospital in Paris, France, said in a presentation of the data.

The phase 1 portion of RUXOPeg was designed to test up to 9 different possible dose combinations of ruxolitinib plus pegylated interferon alpha 2a. Its primary end point was the occurrence of dose-limiting toxicities (DLTs) within 45 days of initiating treatment.

The phase 2 portion of this trial randomized patients to 1 of the 2 best dose combinations determined in the phase 1 portion. The primary end point of this portion was at least a 50% spleen length reduction, as measured by palpation, within the first 6 months of treatment.

Patients were eligible for this trial if they had intermediate- or high-risk myelofibrosis, needed active therapy, and had disease with a driver mutation. Patients were excluded if they had received prior treatment with ruxolitinib or pegylated interferon alpha 2a; had a contraindication for either drug; were eligible for stem cell transplantation; had inadequate liver, cardiac, or renal function; had autoimmune disease; or had a history of depression.

In the phase 1 portion, patients received ruxolitinib alone at 10 mg, 15 mg, or 20 mg twice daily for 2 weeks, then continued their ruxolitinib dose with the addition of pegylated interferon alpha 2a at 45 mcg, 90 mcg, or 135 mcg weekly. Patients were assessed for DLTs at 45 days and spleen response at 6 months and were followed for up to 12 months of study participation. At several time points throughout the study, the investigators also collected data on bone marrow biopsy, mutations, hematopoietic stem cell progenitors, cytokines, and immune effectors.

The phase 1 portion enrolled 18 patients. Three patients each received 10 mg ruxolitinib plus 45 mcg pegylated interferon alpha 2a, 15 mg ruxolitinib plus 45 mcg pegylated interferon alpha 2a, 15 mg ruxolitinib plus 135 mcg pegylated interferon alpha 2a, 20 mg ruxolitinib plus 45 mcg pegylated interferon alpha 2a, 20 mg ruxolitinib plus 90 mcg pegylated interferon alpha 2a, or 20 mg ruxolitinib plus 135 mcg pegylated interferon alpha 2a.

With no DLTs observed in the phase 1 portion, the phase 2 portion was opened to enroll 19 patients, who were randomized to receive 15 mg ruxolitinib twice daily plus 135 mcg pegylated interferon alpha 2a (n = 9) weekly or 20 mg ruxolitinib twice daily plus 135 mcg pegylated interferon alpha 2a (n = 10) weekly.

The median age of patients from both phases was 63.5 years (range, 37-71). In total, 57% (n = 21) of patients had primary myelofibrosis, and 43% (n = 16) had post–polycythemia vera (PV) and post­–essential thrombocythemia (ET). The median spleen length was 9 cm (range, 0-20) by palpation and was confirmed to be 19.5 cm (range, 10.6-30) by imaging.

Patients had a mean hemoglobin level of 12.2 g/dL (range, 7.8-16.2), a mean white blood cell count of 12.16 G/L (range, 3.5-36.1), and a mean platelet count of 372 G/L (range, 150-1304). In total, 20, 8, and 9 patients had intermediate 1-, intermediate 2-, and high-risk disease, respectively.

By month 12, the combination had elicited a spleen reduction of at least 50% in 76% (95% CI, 59%-88%; n = 28) of patients from the combined phase 1 and 2 populations. A total of 67% (95% CI, 41%-87%; n = 12) and 84% (95% CI, 60%-97%; n = 16) of patients experienced at least a 50% spleen reduction in phases 1 and 2, respectively.

The bone marrow biopsy analysis, conducted by centralized blinded review, investigated cellularity, megakaryocyte (MK) morphology, and fibrosis grade in 21, 24, and 20 patients, respectively. In total, 57% of patients experienced improved cellularity, and 25% of patients experienced improved MK morphology. Additionally, fibrosis grade improved in 5% of patients and worsened in 5% of patients.

The cytokine analysis showed that the inflammatory cytokine profile decreased with the combination in most patients.

Preliminary results of the immune effectors analysis showed that in general, by the end of treatment, the combination significantly increased patients’ proportion of B cells and significantly decreased their proportion of natural killer cells. No change in T lymphocytes was observed, although subgroup analyses are ongoing.

The molecular response analysis determined that at screening, 60% (n = 22), 30% (n = 11), and 10% (n = 4) of patients had JAK2 V617F, CALR, and MPL driver mutations, respectively. Additional mutations were found in 33 patients, for a total of 90 mutations in 17 genes and a mean of 3.4 mutations per patient. The combination elicited a significant decrease in JAK2 V617F–mutant allele burden, from 84% to 56% after 12 months of treatment.

“Such deep molecular responses, to our knowledge, have never been seen in patients with myelofibrosis before,” Kiladjian noted.

No significant difference was observed in the allele burdens for the other driver mutations after 12 months of treatment.

The molecular response for JAK2 V617F was heterogenous. From these data, the investigators determined 2 groups: a group of good responders, who had over a 50% decrease in their JAK2 V617F allele burden, and a group of poor responders, who had a lower decrease of their JAK2 V617F allele burden. The presence of additional mutations in ASXL1 was found to be an important factor for JAK2 V617F molecular response, as all patients with mutations in this gene were in the poor response group. Patients with JAK2 V617F mutations alone had a 70% decrease in their mutant allele burden, whereas those who had an additional mutation in ASXL1 had only a 10% decrease.

To determine whether the anti-JAK2 activity of ruxolitinib could interfere with the efficacy of pegylated interferon alpha 2a, the investigators studied the response on hematopoietic stem cell progenitors by clonal assays. This analysis confirmed a clear decrease in mutated hematopoietic stem cells at baseline and after 12 months of treatment, and a subpopulation analysis showed a decrease of both heterozygous and homozygous cells.

A previously developed mathematical model for predicting long-term responses in patients with PV and ET was found to be applicable to this study and predicted a long-term decrease and potential eradication of hematopoietic stem cells.

In total, 363 adverse effects (AEs) were associated with the combination, with 59%, 33%, 7.5%, and 0.5% being grades 1, 2, 3, and 4, respectively. The most frequent AEs were anemia (18.7%), thrombocytopenia (13.7%), gastrointestinal toxicities (7%), musculoskeletal toxicities (6.8%), and asthenia (6.6%). Serious AEs were observed in 6 patients, and included anemia (n = 2), skin cancer (n = 2), Raynaud’s phenomenon (n = 1), and urinary infection (n = 1). One patient died of acute myeloid leukemia transformation after 10.4 months.

“Of note, we saw a very low incidence of the AEs that are usually due to interferon alpha, suggesting that maybe the combination with ruxolitinib improves the tolerance to interferon alpha,” Kiladjian concluded.

Reference

Kiladjian J, Ianotto J, Soret J, et al. Final results of Ruxopeg, a phase 1/2 adaptive randomized trial of ruxolitinib (rux) and pegylated interferon alpha (IFNa) 2a in patients with myelofibrosis (MF). Blood. 2022;140(suppl 1):577-578. doi:10.1182/blood-2022-156389