The addition of the MDM2 inhibitor navtemadlin (formerly KRT-232) to ruxolitinib (Jakafi) led to clinically meaningful improvements in spleen volume reduction (SVR) among patients with primary or secondary TP53 wild-type myelofibrosis who had a suboptimal response to ruxolitinib, according to findings from the phase 1/2 KRT-232-109 study (NCT04485260) presented during the 2023 European Hematology Association (EHA) Congress.

Results from the trial showed that at 24 weeks among efficacy-evaluable patients (n = 19) adding navtemadlin to ruxolitinib conferred a minimum SVR of 25% in 42% of patients and an SVR of at least 35% in 32%. Additionally, a minimum total symptom score (TSS) improvement of at least 50% was observed in 32% of patients.

“This therapeutic approach is clearly active,” John O. Mascarenhas, MD, said. “The combination of navtemadlin and ruxolitinib achieves two things: synergy in terms of cell kill directed at the CD34 myeloblasts population, which is really what we’re trying to accomplish, and an improved toxicity profile [compared with] monotherapy. This is a combination that could potentially even be used upfront in the JAL inhibitor-naïve patient population. MDM2 inhibition is here and likely is going to be a component in the future. Navtemadlin is poised to be at the forefront as a first-in-class agent to deliver that kind of clinical activity.”

In an interview with OncLive^®, Mascarenhas, professor of medicine at the Icahn School of Medicine at Mount Sinai, director of the Center of Excellence for Blood Cancers and Myeloid Disorders, and a member of Tisch Cancer Institute in New York, New York, discussed the design and rationale of KRT-232-109, more key findings from the trial, and potential future directions of the study.

OncLive: What is the mechanism of action of navtemadlin and what was the rationale for evaluating it in KRT-232-109?

Mascarenhas: Myelofibrosis is predominantly a TP53 wild-type disease. MDM2 negatively regulates TP53. [The] p53 pathway is important for regulating cell fate and balancing prosurvival and prodeath signals.

In myelofibrosis, MDM2 is overexpressed in CD34 cells, and this negatively regulates TP53 activity. It’s an alternative mechanism for cancer cells to increase the threshold for induction of apoptosis. Navtemadlin interrupts that interaction between MDM2 and wild-type TP53, thereby activating TP53 and inducing apoptosis.

What’s exciting about the phase 1b/2 study adding navtemadlin to patients receiving ruxolitinib with a suboptimal response is [the fact that] ruxolitinib works synergistically with navtemadlin in reducing p21. [This] essentially lowers the threshold to induce apoptosis in the setting of navtemadlin, so the two work well together to induce apoptosis in myelofibrosis CD34 cells—there’s great preclinical data that justify this concept.

What were the goals of the KRT-232-109 study?

The goal of the phase 1 was to determine the recommended phase 2 dose of navtemadlin in combination with ruxolitinib in these suboptimal ruxolitinib-[responding] myelofibrosis patients.

We evaluated 3 different dose levels and different dose schedules, and the recommended phase 2 dose based [not only] on the clinical results, but also on some of the pharmacokinetic results that were that were conducted is 240 mg of navtemadlin 7 days in a row of a 28-day cycle. [It’s a] 1-week-on-3-week-off [schedule of] 1-month cycles with the stable dose of ruxolitinib that the patient is on. So, you don’t adjust the dose of ruxolitinib, you simply add navtemadlin.

The ongoing purpose of the phase 2 [study] is to document the efficacy as measured by SVR and symptom improvement at 24 weeks.

What were some of the key inclusion criteria?

Patients had to have a platelet count greater than 100,000 because we often use platelet counts in these trials to determine eligibility. Patients had to have TP53 wild-type disease. Importantly, this approach is probably not effective in patients who have mutant disease because MBM2 doesn’t regulate mutant TP53. [Patients also needed to be] on ruxolitinib for at least 18 weeks, which is the minimal amount of time needed to determine whether someone has an optimal [response], suboptimal [response], or progressive disease, and at a stable dose of ruxolitinib for 8 weeks.

What were the key efficacy findings from KRT-232-109 presented during the 2023 EHA Congress?

We looked [what] we would normally look at in myelofibrosis, [such as] spleen response. The SVR [of] at least 35% at 24 weeks in evaluable patients was 32%. If you look at SVR [of at least] 25%, which is also considered by regulatory agencies a meaningful spleen response at 24 weeks, it was 42%. There was clear spleen reduction, and most patients [experienced] some degree of spleen response.

Symptom improvement was also seen; 32% of patients at week 24 had a 50% or greater TSS score and some of these patients had very significant spleen symptom burden at baseline. The drug was effective in addressing those 2 clinical end points.

What was really interesting was that patients, in some cases, had ruxolitinib doses of 5 mg twice daily going into the study, meaning they were coming in at low doses. And despite low doses of ruxolitinib, there was synergistic activity with navtemadlin[and] we were seeing very deep spleen and symptom responses. This speaks to the fact that biologically there is a priming almost of the diseased cells for TP53 induction of apoptosis with ruxolitinib. The preclinical data supported and translated very nicely into the clinical findings.

Are there any safety concerns clinicians should be aware of when using navtemadlin plus ruxolitinib?

[This was a] well-tolerated drug. We know that, as a class of agents, there is a degree of gastrointestinal [GI] toxicity with MDM2 inhibitors, [including] nausea, vomiting and diarrhea. [These events were] rarely grade 3/4 [in severity]; 70% of were grade 1. [Approximately] 60% of patients experienced some GI toxicity, usually in the first 2 cycles. Preemptively, we give antiemetic and an antidiarrheal. That is a very effective way of managing those nausea and diarrhea type toxicities.

The [inclusion] of ruxolitinib it seems to offset some of that toxicity. There may be some biologic reasons why there’s synergy with ruxolitinib, not just an efficacy, but also in improving the safety profile with navtemadlin. The deep responses that we see are also complemented by a well-tolerated combination.

What are the next steps for this research?

We want to finish the follow-up of patients enrolled in phase 2. We still have ongoing correlatives to look at. We presented correlatives that were very encouraging [showing] that we were having on-target stem cell–directed therapeutic effects, [such as] reduction of CD34 cell burden, reduction in bone marrow fibrosis, and reduction in driver RAF level in these patients that were treated.

We were clearly having disease-modifying effect, biologic response modification. We want to see that in a greater number of patients [and] I’d love to see some of the cytokine results. There’s still more to be done from a correlative science aspect and patient follow-up to be conducted.

Ultimately, where this will go is to a phase 3 study, which will be entitled BOREAS-2, where we’ll be [enrolling patients with] suboptimal ruxolitinib response and adding navtemadlin [and evaluating this treatment] vs placebo to improve responses.

Reference

Mascarenhas J, Jain T, Otoukesh S, et al. An open-label, global, phase (Ph) 1b/2 study adding navtemadlin (NVTM) to ruxolitinib (RUX) in patients (Pts) with primary or secondary myelofibrosis (MF) who have a suboptimal response to RUX. HemaSphere. 2023;7(suppl 3):S210.

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Spleen volume reduction (SVR) was associated with overall survival (OS) with pacritinib (Vonjo) in patients with myelofibrosis. Treatment with the JAK2 inhibitor also demonstrated comparable improvements in spleen and symptom response regardless of baseline platelet counts and hemoglobin levels, according to findings from the pivotal phase 3 PERSIST-1 (NCT01773187) and PERSIST-2 (NCT02055781) trials that were presented at the 2023 ASCO Annual Meeting.^1,2

Symptoms of myelofibrosis include marrow fibrosis, splenomegaly, and progressive cytopenia and prior approved agents include ruxolitinib (Jakafi) and fedratinib (Inrebic).

“The previous 2 JAK inhibitors ruxolitinib and fedratinib were for patients at a certain platelet cutoff, so that’s 50 [x 109/L] and above, and pacritinib ended up becoming approved for patients with myelofibrosis with platelets less than 50 [x 109/L], filling that urgent unmet medical need,” Naveen Pemmaraju, MD, associate professor in the Department of Leukemia, Division of Cancer Medicine at The University of Texas MD Anderson Cancer Center in Houston, said in an interview with OncLive^®.

Pacritinib is a JAK1-sparing inhibitor of JAK2/IRAK1/ACVR1 associated with improved SVR vs best available therapy (BAT), including ruxolitinib, in patients with myelofibrosis with platelets below 100 x 109/L in the PERSIST-2 trial. However, the relationship between SVR and OS in patients with thrombocytopenia is not well known. As such, investigators evaluated whether SVR with pacritinib or BAT is associated with improved survival in those with thrombocytopenia.

The analysis included patients from PERSIST-2 who were alive and on study who had received 200 mg of pacritinib twice daily or BAT at week 10 (week-12 SVR window).

In the pivotal PERSIST-2 trial, baseline characteristics in the pacritinib arm for responders (n = 65) and nonresponders (n = 24), respectively, were presented for age (median in years: 66 vs 67), Dynamic International Prognostic Scoring System (DIPSS) high risk (18.5% vs 46%), platelet count (median, 58 x 109/L vs 67 x 109/L), hemoglobin (median, 9.7 g/dL vs 9.3 g/dL), red blood cell transfusion requirement (38% vs 58%), prior JAK2 exposure (45% vs 50%), spleen volume (median, 2573 cm3 vs 2094.5 cm3), and palpable spleen length (median, 15.00 cm vs 12.75 cm).

Responders (n = 28) and nonresponders (n = 56) in the BAT arm had median ages of 66 years and 69 years, respectively. Moreover, 21% and 25% of patients, respectively, had DIPSS high-risk disease, median platelet counts of 68 x 109/L and 47 x 109/L, median hemoglobin of 10.0 g/dL and 9.6 g/dL, red blood cell transfusion requirement in 32% and 54%, prior JAK2 exposure in 64% and 45%, median spleen volume of 2907 cm3 and 2393 cm3, and median palpable spleen length of 12.00 cm and 14.50 cm.

Results showed that at least 10% SVR with pacritinib was prognostic for survival between responders and nonresponders (P <.0001). At least 20% and 35% or more SVRs were also prognostic for survival but to a lesser extent, with P values of .0199 and .3516, respectively. Authors also noted that any degree of SVR was associated with improved survival with pacritinib (HR, 0.08; 95% CI, 0.01-0.51; P = .0007).

Adjusting for baseline spleen volume and red blood cell transfusion requirement in univariate analysis did not affect the survival benefit with pacritinib at the 10% or greater SVR threshold.

Notably, SVR was not associated with survival with BAT at any threshold (SVR ≥10%, P =.4888; SVR ≥20%, P =.9821; SVR ≥35%, P =.8881).

“What is very encouraging is that we’re starting to see disease modification with these JAK inhibitors, not only showing spleen and symptom improvement, but also trying to show OS improvement and that the two can correlate,” Pemmaraju said. “Once we start to see spleen symptom improvement, as well as OS improvement, we can start to try to aim for and achieve disease modification, [which is] what matters to the patient. We’re starting to see that now, as we did with ruxolitinib and perhaps now with the newer JAK inhibitors.”

Additional findings from the analysis indicated that median dose intensity through week 12 was maintained with pacritinib at 200 mg twice daily in all patients who achieved SVR of at least 10%. Of the 28 patients who achieved SVR of at least 10% on BAT, the majority (n = 23) received ruxolitinib prior to the week-12 SVR evaluation. Of these patients, 78% were receiving no more than 10 mg of ruxolitinib twice daily and 43% were receiving no more than 5 mg of ruxolitinib twice daily. Other BATs included hydroxyurea (Hydrea) and prednisone.

Additionally, OS was associated with achieving at least 20% reduction in spleen length with pacritinib (HR, 0.14; 95% CI, 0.02-1.26; P =.0406; OS by spleen length reduction ≥35% and ≥50%, P =.0990 and P =.3008). However, separation of the curves was not as great for prognostication as SVR among responders and nonresponders.

“As pacritinib can be given at full dose regardless of platelet count, it is possible that pacritinib may offer a unique survival advantage for patients with myelofibrosis with moderate or severe thrombocytopenia who achieve ≥10% spleen reduction,” the authors wrote in the poster.

Although pacritinib is approved for use in patients with low platelet counts, clinical studies with the agent have included patients regardless of baseline anemia and thrombocytopenia. As such, another analysis was conducted, pooling the results of the PERSIST-1 and PERSIST-2 trials, to determine dosing patterns and efficacy outcomes by degree of baseline cytopenia.

Results showed that patients maintained median dose intensity of 100% regardless of whether they had baseline platelet counts below or above 100 x 109/L or baseline hemoglobin levels below 8 g/dL, between 8 g/dL and 10 g/dL, or 10 g/dL or above.

Additionally, between 21% and 28% of all patients, regardless of platelet and hemoglobin levels, achieved SVR of at least 35%; between 39% and 44% of patients achieved SVR of at least 25%; between 75.5% and 82% achieved SVR of at least 10%; and between 84% and 93% of patients achieved any spleen volume reduction. Moreover, the depth of the 24-week spleen reduction was similar across all platelet and hemoglobin strata.

Similarly, all patients achieved spleen reduction by week 12, and SVR remained consistent over time across all subgroups. Median hemoglobin also remained stable through week 24 across all hemoglobin thresholds, though some improvement was reported in patients with baseline levels below 8 g/dL.

Any improvement in total symptom score (TSS) was documented in between 80% and 87.5% of patients across all cytopenic groupings, although most patients with baseline hemoglobin below 8 g/dL (62.5%) derived the greatest magnitude in symptom improvement (TSS ≥50). Notably, 12-week TSS improvement occurred with deepening improvement through week 36, particularly in patients with baseline hemoglobin below 8 g/dL.

Regarding Patient Global Impression of Change response across all baseline blood count strata, approximately 80% of patients reported clinical improvement in disease symptoms and approximately 50% of patients classified their symptoms as “much” or “very much” improved at week 24.

“[This study] takes a look at the totality of the pacritinib data across doses across levels of cytopenias among patients and shows that while this drug is best known for its efficacy in cytopenic patients, it shows that the efficacy is about the same in those with higher blood counts as well, or at least it is certainly preserved in those patients as well,” Prithviraj Bose, MD, associate professor in the Department of Leukemia, Division of Cancer Medicine at The University of Texas MD Anderson Cancer Center, told OncLive^®.

References

1. Ajufo H, Bewersdorf JP, Harrison C, et al. Spleen volume reduction (SVR) predicts overall survival (OS) in myelofibrosis (MF) patients on pacritinib (PAC) but not best available therapy (BAT): PERSIST-2 landmark OS analysis. J Clin Oncol. 2023;41(suppl 16):7018. doi:10.1200/JCO.2023.41.16_suppl.7018
2. Bose P, Gagelmann N, Gupta V, et al. Consistency of pacritinib for spleen and symptom reduction in patients with myelofibrosis regardless of cytopenias. J Clin Oncol. 2023;41(suppl 16):7068. doi:10.1200/JCO.2023.41.16_suppl.7068

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The results were presented at the 2023 EHA Congress and met the primary end point of the trial.

At the April 28, 2022, data cutoff, findings from the interim analysis of the study showed that the 24-week independent review committee (IRC)-assessed SVR35 rate was 72.3% (95% CI, 57.4%-84.4%) in the jaktinib arm (n = 47) compared with 17.4% (95% CI, 5.0%-38.8%) in the hydroxyurea arm (n = 23; P ≤ .0001). Additionally, the best spleen response rates were 80.9% vs 26.1%, respectively (P ≤ .0001). The median maximum percentage change in spleen volume from baseline per IRC assessment were –46.6% vs –18.5%, respectively.

“Three small molecule JAK inhibitors have been approved for myelofibrosis by the FDA, including ruxolitinib [Jakafi], fedratinib [Inrebic], and pacrritinib [Vonjo],” Jie Jin, MD, PhD, a professor of medicine in the Department of Hematology, The First Affiliated Hospital, Zhejiang University School of Medicine, in Hangzhou, China, said during the presentation. “Currently in China, ruxolitinib is the only one that is available. Therefore, the treatment [options for] myelofibrosis in China is limited.”

ZGJAK016 was a double-blind, active-controlled, multicenter trial that enrolled adult patients with DIPSS intermediate-2 or high-risk myelofibrosis with an ECOG performance status of 1 or 0. Eligible patients also needed to have a palpable spleen of at least 5 cm below the left costal margin, a platelet count of at least 100 ´ 109/L, and no prior or a maximum of 10 days of treatment with a JAK inhibitor.

Following a 28-day screening period, enrolled patients were randomly assigned 2:1 to receive either jaktinib 100 mg twice daily plus a hydroxyurea placebo or hydroxyurea 0.5 g twice daily plus a jaktinib placebo for four 6-week cycles. At week 24, the extension period began, and patients who achieved SPV35 remained on their initially assigned treatment and those who did not received jaktinib 100 mg twice daily until criteria for termination. Patients were stratified by DIPSS risk status (intermediate-2 vs high-risk).

The primary end point of the study was SVR35 at week 24, measured by MRI or CT imaging and assessed by IRC. Key secondary end points included investigator-assessed SVR35 at week 24, best spleen response rate (defined as achieving SVR35 at any time), proportion of patients with reduction in MPN-SAF Total Symptom Score (TSS) of at least 50%, improvement in terms of anemia, and safety.

The baseline characteristics were well-balanced between the 2 arms; the median age was 63 years (range, 46-76) in the jaktinib arm compared with 62 years (range, 42-74) in the hydroxyurea arm. Most patients in both arms were women (61.7% vs 60.9%), had intermediate-2 DIPSS risk status (89.4% vs 87.0%), did not previously receive a JAK inhibitor (97.9% vs 91.3%), were JAK2 V617F positive (59.6% vs 69.6%), and had primary myelofibrosis (70.2% vs 73.9%). The median spleen volumes upon central review were 1389.7 cm3 (range, 433.6-5070.5) and 1249.1 cm3 (range, 579.6-3011.4), respectively. Additionally, the median platelet count and hemoglobin levels were similar between the 2 arms.

Most patients in the jaktinib arm completed 24 weeks of treatment (89.4%) and entered the extension period (83.0%). In the control arm, these rates were 69.6% and 69.6%, respectively. One patient in the hydroxyurea arm also received open-label jaktinib without unblinding. Four patients died on the jaktinib arm compared with 1 on the hydroxyurea arm; no death was determined to be treatment related.

Additional findings from the study showed that the SVR35 benefit was observed with jaktinib over hydroxyurea across all prespecified subgroups. The greatest differences in SVR35 rate in favor of jaktinib were observed among patients with a baseline MPN-SAF TSS greater than the median (72.0% [95% CI, 35.5%-85.9]), those with a DIPSS risk status of intermediate-2 (66.2% [95% CI, 42.2%-80.4%]), and those whose disease harbored a JAK2 V617F mutation (63.4% [95% CI, 35.0%-81.2%]).

More patients in the jaktinib arm experienced a reduction in MPN-SAF TSS from baseline compared with the hydroxyurea group at every time point examined in the interim analysis. This included week 6 (55.3% vs 34.8%), week 12 (59.6% vs 43.5%), week 18 (66.0% vs 39.1%), and week 24 (63.8% vs 43.5%).

Hemoglobin levels were increased from baseline in the jaktinib arm and decreased in the hydroxyurea arm. Among patients who received jaktinib who required a red blood cell transfusion (n = 7), 5 achieved a decreased in red blood cell transfusion unit of at least 50% by week 24 compared with 2 who received hydroxyurea and required a transfusion (n = 5).

Safety findings demonstrated that nearly all patients in the jaktinib and hydroxyurea arms experienced an any-grade treatment-emergent adverse effect (TEAE), at 97.9% and 100%, respectively. Most patients in both arms experienced a TEAE of grade 3 or higher severity (51.1% vs 60.9%).

Serious TEAEs were present in 27.7% of patients in the jaktinib arm compared with 47.8% in the hydroxyurea arm. TEAEs leading to dose reduction or interruption (23.4% vs 34.8%), as well as those leading to treatment discontinuation (8.5% vs 17.4%), were reported in both arms.

In the jaktinib arm, the most common any-grade TEAEs included thrombocytopenia (40.4%), anemia (38.3%), respiratory tract infections (21.3%), leukopenia (14.9%), fever (12.8%), and reduced blood bilirubin (12.8%). Common grade 3 or higher TEAEs consisted of anemia (25.5%), thrombocytopenia (17.0%), leukopenia (2.1%), neutropenia (2.1%), and decreased lymphocyte count (2.1%).

Comparatively in the hydroxyurea arm, the most common any-grade TEAEs included thrombocytopenia (52.2%), anemia (52.2%), leukopenia (30.4%), neutropenia (26.1%), decreased lymphocyte count (26.1%), and decreased blood bilirubin (26.1%). Grade 3 or higher TEAEs included anemia (43.5%), thrombocytopenia (39.1%), leukopenia (21.7%), neutropenia (21.7%), and decreased lymphocyte count (13.0%).

“At the time of this prespecified interim analysis, jaktinib has demonstrated an improved trend in symptom response vs hydroxyurea,” Jin said. “[Additionally], there were [fewer] cytopenias in the jaktinib group than the hydroxyurea [arm]. Our interim results demonstrate that jaktinib could be a new treatment option for patients with myelofibrosis [who are] DIPSS intermediate-2 or high-risk.”

_Reference

_{Zhang Yi, Zhhuan J, He A, et al. A randomized double-blind phase 3 study of jaktinib versus hydroxyurea in patients with intermediate-2 or high risk myelofibrosis. Hemasphere. 2023;7(suppl 3):S212.}

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