December 5, 2023

Kyle Doherty

Although myeloproliferative neoplasms (MPNs), which are comprised of essential thrombocythemia, polycythemia vera (PV), and myelofibrosis, remain relatively rare— with estimated annual incidence rates of 1.03, 0.84, and 0.47 per 100,000 individuals, respectively—there remains an unmet need for effective treatment options for patients with these diseases who progress on standard of care therapies.¹ However, significant progress has been made in terms of understanding this group of disorders and developing treatment strategies to combat them, with Naveen Pemmaraju, MD, saying the medical field has entered a “golden era” of MPN treatment.

During a recent OncLive Peer Exchange^® video series titled “Expert Insights Into the Management of MPNs,” Jamile M. Shammo, MD, explained, “MPNs represent a heterogeneous group of hematopoietic stem cell neoplasms that share common features. Myeloid proliferation is certainly something that we see [in MPNs], as well as a propensity for thrombotic events, symptoms that are related either to constitutional symptoms or splenomegaly related. All 3 entities tend to progress to higher myeloid neoplasms; essential thrombocythemia [to] PV that goes to myelofibrosis and then myelofibrosis can evolve into acute leukemia. Of course, the rate of progression varies from one entity to the other, with essential thrombocythemia having the lowest risk [of progression].”

The development of MPNs is almost always associated with mutations in JAK2, making this family of genes an attractive treatment target. JAK2 mutations are observed in approximately 95% of patients with PV and approximately 50% of both patients with essential thrombocythemia and myelofibrosis. Notably, the emergence of additional treatment targets also has sparked the development of novel agents in recent years.¹

During the discussion, expert oncologists reviewed updated findings from ongoing and completed clinical trials in the field. They primarily focused on studies evaluating emerging agents in PV and myelofibrosis.

MANAGING PV

Abdulraheem Yacoub, MD, began the discussion on PV by noting that the JAK1/2 inhibitor ruxolitinib (Jakafi) has been the standard-of-care agent in PV since 2015. Prior to this, PV was historically managed with phlebotomy, hydroxyurea, and/or interferons. Ruxolitinib became the first FDA-approved drug for the treatment of patients with PV in December 2014 when it received an indication from the agency for patients who had an inadequate response to or were intolerant of hydroxyurea.²

“The introduction of ruxolitinib to the treatment landscape of patients with myelofibrosis has truly been transformative,” Shammo commented. “We all remember the patients we had in the clinic [in the past] and how we had simply nothing but supportive care to offer. Ruxolitinib was approved based on the results of 2 phase 3 studies. COMFORT-I [NCT00952289] randomly assigned patients [with myelofibrosis] to receive ruxolitinib or placebo and examined [spleen] volume reduction and reduction in total symptom score from baseline at 24 weeks. COMFORT-II [NCT00934544], which ran mostly in Europe, randomly assigned patients to be treated with ruxolitinib or best available therapy [as selected by the investigator]. This study [also evaluated] spleen volume reduction, but at week 48. In either trial, ruxolitinib was statistically significantly more active in attaining the primary end point and for that reason it was approved. Some might say that the evidence is perhaps less compelling than what you would [typically] find in a phase 3 study, but when you have multiple studies showing the same thing, that treatment with ruxolitinib improves [outcomes] compared with placebo or best available therapy, I tend to feel like it’s reasonable enough to believe that actually is the case.”

Long-term data from 2 phase 3 trials, RESPONSE (NCT01243944) and RESPONSE-2 (NCT02038036), comparing the safety and efficacy of ruxolitinib with best available therapy in different patient populations with PV recently were published in The Lancet Haematology. RESPONSE enrolled adult patients with PV who were resistant to or intolerant of hydroxyurea and randomly assigned them 1:1 to receive either ruxolitinib (n = 110) or best available therapy (n = 112; hydroxyurea, interferon or pegylated interferon, pipobroman, anagrelide (Agrylin), approved immunomodulators, or observation without pharmacological treatment). RESPONSE-2 enrolled a higher-risk patient population; eligible patients had inadequately controlled PV without splenomegaly and were intolerant of or resistant to hydroxyurea with an ECOG performance status of 2 or less. They were randomly assigned to receive ruxolitinib (n = 74) or best available therapy (n = 75).^3,4

Follow-up data from RESPONSE demonstrated that the 5-year overall survival (OS) rate was 91.9% (95% CI, 84.4%-95.9%) in the ruxolitinib group vs 91.0% (95% CI, 82.8%-95.4%) in the best available therapy arm. Most patients (88%) in the best available therapy arm crossed over to receive ruxolitinib, and no patients remained in this arm after week 80. There were 25 primary responders in the ruxolitinib arm, 6 of whom had progressed by the time of the final analysis. The 5-year probability of maintaining a primary composite response was 74% (95% CI, 51%-88%), the probability of maintaining complete hematological remission was 55% (95% CI, 32%-73%), and the probability of maintaining overall clinicohematological responses was 67% (range, 54%-77%).³

At a median follow-up of 67 months (IQR, 65-70), findings from RESPONSE-2 showed that the 5-year OS rate was 96% (95% CI, 87%-99%) in the ruxolitinib arm compared with 91% (95% CI, 80%-96%) in the best available therapy arm. In the ruxolitinib arm, 22% of patients (95% CI, 13%-33%) achieved durable hematocrit control with an estimated median duration of control not reached (NR) at week 260 (95% CI, 144-NR). Most patients in the best available therapy arm (77%) crossed over to ruxolitinib, no patients continued with best available therapy after week 80 per protocol, and the median duration of hematocrit control was not reported due to the small number of responders at week 80.⁴

In light of findings from RESPONSE and RESPONSE-2, investigators in both studies concluded that ruxolitinib is a safe and effective long-term treatment option for patients with PV for whom hydroxyurea proved ineffective.^3,4

“Both studies have ong-term follow-up and have published 5-year data showing very durable responses,” Yacoub said. “There were very few late failures on ruxolitinib and no unexpected adverse effects were observed with longterm follow up. This has built a strong case for ruxolitinib as a standard treatment for patients [with PV] after hydroxyurea failure.”

Ropeginterferon Takes Center Stage

A more recent breakthrough for patients with PV was the emergence of the interferon ropeginterferon alfa-2b-njft (Besremi). In November 2021, ropeginterferon became the first agent to receive FDA approval for patients with PV regardless of their treatment history.⁵

Ropeginterferon was compared with hydroxyurea in the phase 3 PROUD-PV trial (NCT01949805) and its extension continuation study, CONTI-PV (NCT02218047). Eligible patients were 18 years or older and had earlystage PV with no history of cytoreductive treatment or less than 3 years of previous hydroxyurea treatment. Patients could opt to enter CONTI-PV after 1 year of initial treatment in PROUD-PV.⁶

Findings from the studies revealed that at a median follow-up of 182.1 weeks (IQR, 166.3- 201.7) patients in PROUD-PV who received ropeginterferon (n = 122) achieved complete hematological response with normal spleen size at a rate of 21% compared with 28% of patients who received hydroxyurea (n = 123). However, in CONTI-PV, 53% of patients in the ropeginterferon arm (n = 95) had a complete hematological response with improved disease burden at 36 months vs 38% of patients in the hydroxyurea arm (n = 74; P = .044). Moreover, at 36 months in CONTI-PV, the complete hematological response rate regardless of spleen criterion was 71% vs 51% in the investigative and comparator arms, respectively (P = .012); at 12 months in PROUD-PV these rates were 43% vs 46%, respectively (P = .63).⁶

Study authors concluded that ropeginterferon was effective in inducing hematological responses. Although noninferiority to hydroxyurea in terms of hematological response and normal spleen size was not observed at 12 months, improved responses vs hydroxyurea were present at 36 months. Thus, the authors wrote that ropeginterferon offers an effective and “safe long-term avenue for treatment with distinct features from hydroxyurea.”⁶

“It’s wonderful to have options because we get patients with PV [who] could not be any more different,” Yacoub said. “They have different goals of care, and at the end of the day, we are treating individual patients, not diseases. For each patient, we have to define what we are trying to achieve. There are patients who are going to live with the disease a lot longer. They have more high-risk presentations and would benefit from the maximum data that we have with the application of the effective agents. There are patients who have relatively low-risk disease, and they’re likely going to live their natural lives with some medical management from our end. We have to individualize our choices.”

Looking ahead, the phase 3 VERIFY trial (NCT05210790) is underway with the aim of adding rusfertide (PTG-300), a novel and potent hepcidin mimetic, to the PV treatment landscape. Rusfertide previously demonstrated clinical activity in early-phase studies, characterized by good tolerability and consistent and durable hematocrit control, as well as improvements in iron deficiency among patients who required higher than normal amounts of phlebotomies even after standard-of-care therapy.⁷

VERIFY is enrolling patients with PV who have received at least 3 phlebotomies in the previous 6 months or at least 5 in the previous 12 months as a result of inadequate hematocrit control, with or without concurrent cytoreductive therapy. Eligible patients will be randomly assigned 1:1 to receive either placebo plus ongoing therapy or rusfertide plus ongoing therapy.

Part 1a of the trial is the double-blind, placebo- controlled, add-on phase that will enroll parallel groups and last 32 weeks. During part 1b, patients who complete part 1a will receive rusfertide for 20 weeks. Patients who successfully complete part 1b will enter the long term extension phase, part 2, and will continue to be treated with rusfertide for 104 weeks. The primary end point is the proportion of patients achieving a response in from week 20 to week 32 in part 1A. The study was initiated in January 2022 and has a target enrollment of 250 patients.⁷

Managing Myelofibrosis

Patients with myelofibrosis have more FDA-approved treatment options than those with PV. To date, 3 Janus kinase (JAK) inhibitors have been approved for the treatment of patients with myelofibrosis: ruxolitinib, fedratinib (Inrebic), and pacritinib (Vonjo).

Similar to PV, ruxolitinib became the first FDA-approved therapy for the treatment of patients with myelofibrosis, gaining an indication for patients with intermediate- and high-risk disease in November 2011. In August 2019, patients with intermediate- 2 or high-risk primary or secondary myelofibrosis gained fedratinib as an FDA-approved option. Finally, the FDA approved pacritinib in March 2022 for the treatment of adult patients with intermediate- or high-risk primary or secondary myelofibrosis with platelet levels below 50,000/μL.^8-10

“The current NCCN [National Comprehensive Cancer Network] guidelines are really agnostic of the second-line therapy, which is interesting,” Raajit K. Rampal, MD, PhD, said. “You can start a patient who [at that time] has over 50,000 platelets on ruxolitinib or fedratinib. And if there is a need to change therapy, you could use any of these 3 agents. That’s an important message for our audience to remember, that the second line is not platelet restricted. We have an abundance of options.”

After summarizing updated data from pivotal trials of the already approved agents, the panelists shifted their focus to new findings from trials evaluating investigational therapies beyond JAK inhibitors in myelofibrosis. Updates from the studies were presented during the 2023 American Society of Clinical Oncology Annual Meeting in June.

Novel Agents Seek to Augment the Armamentarium

In the phase 2 ACE-536-MF-001 trial (NCT03194542), investigators examined the erythroid maturation agent luspatercept-aamt (Reblozyl) for the management of anemia in patients with myelofibrosis; it occurs in approximately 40% of patients. Investigators noted that luspatercept demonstrated anemia improvement across all cohorts of in the study, regardless of transfusion dependency and use of ruxolitinib. For example, 26.3% (95% CI, 13.4%- 43.1%) of patients who were red blood cell transfusion dependent and received prior ruxolitinib (n = 38) achieved transfusion independence following treatment with luspatercept.¹¹

The phase 1/2 LIMBER study (NCT04455841) evaluated the safety and efficacy of the oral ALK2 inhibitor zilurgisertib alone and in combination with ruxolitinib in adult patients with intermediate 1 or 2 primary or secondary myelofibrosis. Among patients in the monotherapy group who were not transfusion dependent (n = 6), anemia improvement (hemoglobin increase of ≥ 1.5 g/ dL relative to baseline) occurred in 1 patient; this level of improvement was observed in 3 of 9 patients in the combination group. Zilurgisertib monotherapy or combination therapy with ruxolitinib was determined to be generally well tolerated and displayed the potential for therapeutic activity, the study authors concluded.¹²

Another phase 1/3 trial, XPORT-MF-034 (NCT04562389) evaluated a ruxolitinibcontaining combination, this time with the selective inhibitor of nuclear export selinexor (Xpovio) in patients with JAK inhibitor–naive myelofibrosis. At week 24, efficacy-evaluable patients (n = 22) achieved spleen volume reduction of at least 35% (SVR35) from baseline at a rate of 64%. Investigators noted that the combination displayed encouraging activity, and updated data will be made available at a future date.¹³

Finally, in a single-arm phase 2b study (NCT04217993) the oral, novel JAK/ACVR1 inhibitor jaktinib showed promising activity in patients with myelofibrosis who were intolerant to ruxolitinib. Efficacy-evaluable patients who received jaktinib (n = 44) achieved an SVR35 rate of 43% at 24 weeks, and the best spleen response rate was 55%. Notably, response was maintained for a minimum of 12 weeks in 80% of patients.¹⁴

“It’s exciting to have all these non-JAK inhibitors [in the pipeline],” Rampal said in conclusion. “Ultimately, hopefully, we can figure out what the best fit is for an individual patient. We’re not there yet, but with an abundance of data, we’ll get there. It’s also important to note that there are a number of agents that are earlier on [in development] that are moving along. Even beyond this next generation of non-JAK inhibitors already in the pipeline, there is a generation beyond that that is in clinical trial development.”

References

1. McMullin MF, Anderson LA. Aetiology of myeloproliferative neoplasms. Cancers (Basel). 2020;12(7):1810. doi:10.3390/cancers12071810
2. FDA approves ruxolitinib. News release. FDA. Updated February 22, 2016. Accessed October 18, 2023. bit.ly/3PVXObQ
3. Kiladjian JJ, Zachee P, Hino M, et al. Long-term efficacy and safety of ruxolitinib versus best available therapy in polycythaemia vera
   (RESPONSE): 5-year follow up of a phase 3 study. Lancet Haematol. 2020;7(3):e226-e237. doi:10.1016/S2352-3026(19)30207-8
4. Passamonti F, Palandri F, Saydam G, et al. Ruxolitinib versus bestavailable therapy in inadequately controlled polycythaemia vera without splenomegaly (RESPONSE-2): 5-year follow up of a randomised, phase 3b study. Lancet Haematol. 2022;9(7):e480-e492. doi:10.1016/ S2352-3026(22)00102-8
5. FDA approves treatment for rare blood disease. News release. FDA. November 12, 2021. Accessed October 18, 2023. bit.ly/3rXAt1u
6. Gisslinger H, Klade C, Georgiev P, et al; PROUD-PV Study Group. Ropeginterferon alfa-2b versus standard therapy for polycythaemia
   vera (PROUD-PV and CONTINUATION-PV): a randomised, non-inferiority, phase 3 trial and its extension study. Lancet Haematol.
   2020;7(3):e196-e208. doi:10.1016/S2352-3026(19)30236-4
7. Verstovsek S, Kuykendall A, Hoffman R, et al. Verify: a phase 3 study of the hepcidin mimetic rusfertide (PTG-300) in patients with polycythemia vera. Blood. 2022;140(suppl 1):3929-3931. doi:10.1182/ blood-2022-163755
8. Mascarenhas J, Hoffman R. Ruxolitinib: the first FDA approved therapy for the treatment of myelofibrosis. Clin Cancer Res. 2012;18(11):3008-3014. doi:10.1158/1078-0432.CCR-11-3145
9. FDA approves fedratinib for myelofibrosis. News release. FDA. August 16, 2019. Accessed October 18, 2023. bit.ly/3s30OuX
10. FDA approves drug for adults with rare form of bone marrow disorder. News release. FDA. March 1, 2022. Accessed October 18, 2023. bit.ly/3S0PVVj
11. Gerds AT, Harrison C, Kiladjian JJ, et al. Safety and efficacy of luspatercept for the treatment of anemia in patients with myelofibrosis: results from the ACE-536-MF-001 study. J Clin Oncol.2023;41(suppl 16):7016.doi:10.1200/JCO.2023.41.16_suppl.7016
12. Bose P, Mohan S, Oh S, et al. Phase 1/2 study of the activin receptor-like kinase (ALK)-2 inhibitor zilurgisertib (INCB000928,
    LIMBER-104) as monotherapy or with ruxolitinib (RUX) in patients (pts) with anemia due to myelofibrosis (MF). J Clin Oncol. 2023;41(suppl 16):7017. doi:10.1200/JCO.2023.41.16_suppl.7017
13. Ali H, Kishtagari A, Maher KR, et al. Selinexor (SEL) plus ruxolitinib (RUX) in JAK inhibitor (JAKi) treatment-naïve patients with
    myelofibrosis: updated results from XPORT-MF-034. J Clin Oncol. 2023;41(suppl 16):7063. doi:10.1200/JCO.2023.41.16_suppl.7063
14. Zhang Y, Zhou H, Xiao ZJ, et al. Jaktinib in patients (pts) with myelofibrosis (MF) who were intolerant to ruxolitinib (RUX): an open-label, single-arm phase 2b study. J Clin Oncol. 2023;41(suppl 16):7061.doi:10.1200/JCO.2023.41.16_suppl.7061

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