Improvement In Bone Marrow Fibrosis Research Articles

A Phase I Study of Ruxolitinib in Combination with Abemaciclib for Patients with Primary or Post-Polycythemia Vera/Essential Thrombocythemia Myelofibrosis

Background and Significance: Patients (pts) with primary or secondary myelofibrosis (MF) experience variable degrees of constitutional symptoms, cytopenias and risk of progression to acute myeloid leukemia leading to a reduced life-expectancy compared to age-matched controls. Although several oral Janus Kinase (JAK) inhibitors such as ruxolitinib (RUX) have been approved by the US FDA based on improvements in symptom burden and spleen volume compared to physician's choice of best available therapy, the duration of response to these agents is generally time-limited and treatment with JAK inhibitors is not considered to have disease-modifying potential. Furthermore, the median overall survival after RUX discontinuation is only 11-14 months highlighting the need for novel mechanism-based therapies for pts with disease progression on RUX. JAK2 V617F mutations promote transition from the G1 to S-phase of the cell cycle via increased expression of CDC25A, which is also upregulated in primary MPN patient samples. Additional cell cycle regulators such as CDK6 and Cyclin D have also been implicated in MF pathogenesis and contribute to myeloproliferation. Finally, we and others have shown synergistic effects of the combination of CDK4/6 inhibitors and RUX in murine models of MF (Rampal et al., CCR 2021) including improvement in bone marrow fibrosis suggesting the potential for disease-modifying activity. Several CDK4/6 inhibitors have been approved by the US FDA for the treatment of hormone receptor-positive metastatic breast cancer establishing a robust record of safety data. These preclinical data and known safety profile of CDK4/6 and RUX as single agents, provide rationale for combining CDK4/6 and JAK inhibition in pts with MF. Methods: This multicenter, phase I dose-escalation trial (NCT05714072) evaluates the safety of RUX + the CDK4/6 inhibitor abemaciclib in primary or secondary MF pts with intermediate-1/2 or high-risk disease by DIPSS who require treatment and had an inadequate response to RUX. Inadequate response to RUX is defined by (I) palpable splenomegaly ≥5 cm below the left costal margin at study entry AND/OR (II) active MPN symptoms, as defined by the presence of one symptom score ≥5 or two symptom scores ≥3 using the screening MPN-SAF TSS. Pts must have been on a stable dose of 10 mg or 15 mg BID of RUX for at least 4 weeks prior to enrollment with adequate platelet (≥75 x 10 9/L) and neutrophil counts (≥1.5 x 10 9/L). Key exclusion criteria include prior treatment with a CDK4/6 inhibitor, accelerated- or blast-phase MPN, platelet count <50 x 10 9/L in the 4 weeks before screening or platelet transfusion(s) within 8 weeks before screening, and absolute neutrophil count <0.5 x 10 9/L in the 4 weeks before screening. Among the currently FDA-approved CDK4/6 inhibitors, abemaciclib was chosen for combination therapy due to less myelosuppressive effects compared with other CDK4/6 inhibitors. This trial uses a conventional “3+3” dose-escalation design ( Figure), pts will be treated with increasing doses of abemaciclib added to a stable dose of RUX (10 mg or 15 mg BID). The pre-study dose of RUX will be maintained to determine the maximum tolerated dose of the combination of RUX and abemaciclib. The primary endpoint is to determine the maximum tolerated dose of RUX + abemaciclib. Secondary endpoints include measures of efficacy such as overall response rate, duration of response and survival endpoints. Exploratory endpoints include changes in allele fraction of driver mutations, gene expression profiling, and clonal architecture to identify biomarkers of response, mechanisms of resistance, and to assess for any disease-modifying effects of the combination therapy. At this time, 2 pts have been enrolled at dose level 0 without any dose-limiting toxicities observed. In line with the known adverse event profile of abemaciclib, grade 1 diarrhea occurred in one patient. One patient developed grade 3 neutropenia which promptly resolved with holding abemaciclib. No unexpected safety signal was noted and enrollment continues. This trial is open to enrollment at Memorial Sloan Kettering Cancer Center and will commence at MD Anderson Cancer Center later this year.

Bone Marrow Fibrosis Changes Do Not Correlate with Efficacy Outcomes in Myelofibrosis: Analysis of More Than 300 JAK Inhibitor-Naïve Patients Treated with Momelotinib or Ruxolitinib

Introduction: Bone marrow fibrosis (BMF) is a primary pathological and diagnostic feature of myelofibrosis (MF). BMF biopsies are evaluated and scored using updated WHO criteria, which consist of four escalating grades of severity: G0-G3 (Arber et al, 2016). Although BMF grade is not featured in the IPSS or DIPSS prognostic scoring systems, several studies have associated increasing degree of BMF with poor prognosis. Current clinical research efforts in MF often assess BMF, with the ultimate intent of demonstrating disease modification. To date, limited clinical data have compared efficacy outcomes in MF such as survival or symptom, splenic, and/or anemia responses with BMF changes. Here, we present BMF data from over 300 JAK inhibitor (JAKi)-naïve patients who participated in the double-blind, randomized, Phase 3 SIMPLIFY-1 (S1) study of momelotinib (MMB), an inhibitor of JAK1, JAK2 and ACVR1, vs ruxolitinib (RUX), a JAK1 and JAK2 inhibitor. Methods: BMF biopsies were collected pre-treatment (baseline), following 24 weeks of randomized treatment (RT) with either MMB or RUX, and at Week 96 during open-label treatment with MMB. Grading was performed by local hematopathologists and included assessments of reticulin and collagen. Other efficacy assessments included MFSAF symptom scoring, spleen volume imaging, transfusion independence (TI) status, and hemoglobin (Hgb) levels. Survival was estimated using KM analysis. Results: In S1, 128 sites in N. America, Europe & APAC enrolled patients; 211/215 patients randomized to MMB and 213/217 patients randomized to RUX had baseline BMF assessments with 59% in each arm registering as G3. Of these patients, 144 and 160 on MMB and RUX, respectively, had a paired biopsy at Week 24 (W24). Of patients with a W24 paired biopsy, the proportion with stable or improved BMF was similar between treatment arms: 22% who received MMB had a ≥1G improvement compared with 23% of patients who received RUX, and 85% of patients had stable or improved BMF on MMB compared to 81% on RUX (Table 1). In the MMB arm, 87% of the patients with BMF improvement of ≥1G were also W24 TI responders (TI-R), compared to 76% of those with stable or worsening BMF. In the RUX arm, 44% of those with ≥1G improvement in BMF and 56% with stable or worsening of BMF were also W24 TI-R. Furthermore, Hgb levels were noted to increase on MMB, regardless of BMF improvement or worsening, while Hgb levels were observed to decrease on RUX in patients with both improving and worsening BMF. No association between BMF outcome and spleen or symptom outcomes was noted for MMB or RUX. In both treatment arms, no improvement in overall survival (OS) was observed for those achieving ≥1G BMF improvement (MMB HR=0.78, p=0.5203; RUX→MMB HR=1.27, p=0.4789). Although not statistically significant, those registering worsening of BMF grade trended to have improved OS compared to those with no change (MMB HR=0.570; RUX HR=0.597) or improvement (MMB HR=0.818; RUX HR=0.523). Discussion: Improvement in BMF has been pursued as an endpoint in clinical trials and presumptively linked to disease modification. However, limited clinical data have been presented to date and the correlation of BMF changes with survival and other efficacy outcomes has not been well described. Data presented here show that with both MMB and RUX approximately 20% of patients had ≥1G BMF improvement, whilst BMF was stable in >60%. Interestingly, for patients treated with MMB, Hgb levels increased and TI-R was achieved regardless of BMF changes, suggesting the previously described anemia benefit of MMB is a feature of its JAK1, JAK2, and ACVR1-mediated mechanism of action which is not reciprocated by RUX. Patients treated with RUX - even those achieving ≥2G BMF improvement - did not have improved Hgb levels, nor symptom or splenic response. Furthermore, long-term follow up of patients achieving ≥1G BMF improvement did not demonstrate OS advantage. Conclusion: These data represent the most extensive analysis to date of the correlation of BMF changes with other outcome measures in JAKi-naïve patients with MF. Of particular note, anemia improvement was not linked with BMF changes. These findings bring into question the use of BMF assessment at W24 as a surrogate for clinical benefit. The clinical significance of BMF changes needs to be carefully evaluated to better understand its role in disease modification, the pathogenesis of MF, and clinically important patient outcomes. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

The Combination of Navitoclax and Ruxolitinib in JAK Inhibitor-Naïve Patients with Myelofibrosis Mediates Responses Suggestive of Disease Modification

Background: Myelofibrosis (MF) is a myeloproliferative neoplasm associated with splenomegaly, high symptom burden, bone marrow fibrosis (BMF), and poor prognosis. The Janus kinase inhibitor (JAKi) ruxolitinib is the current standard of care for patients with MF. It improves splenomegaly and disease symptoms with limited impact on disease biology, highlighting an unmet medical need in MF. Driver mutations of JAK2, CALR, and MPL are key to the pathogenesis of MF. Reduction in variant allele frequency (VAF) of driver mutations and reversal of BMF are suggestive of disease modification (Pemmaraju, Cancer, 2022). Additionally, mutations in ASXL1, EZH2, SRSF2, IDH1/2, and U2AF1 p.Q157 are classified as high molecular risk (HMR) mutations associated with a worse prognosis (Arber et al., Blood, 2016). We previously demonstrated evidence of disease modification independent of HMR mutations by adding navitoclax to ruxolitinib in patients with suboptimal responses to ruxolitinib monotherapy (Pemmaraju, Lancet Oncology, 2022). Herein, we investigated whether the type of MF and risk (e.g., age, Dynamic International Prognostic Scoring System [DIPSS], and HMR) correlated with clinical outcomes and responses suggestive of disease modification (e.g., VAF reduction and improvement in BMF) among JAKi treatment-naïve patients with MF treated with the combination of navitoclax and ruxolitinib. Methods: Cohort-3 of the phase-2 multicenter REFINE study (NCT03222609) enrolled JAKi treatment-naïve patients with MF. Enrolled patients had primary or secondary MF with splenomegaly (DIPSS ≥ Intermediate-1) and did not receive prior JAK-2 therapy or bromodomain and extra terminal motif (BET) inhibitors. Patients initiated navitoclax at 100 mg QD or 200 mg QD if baseline platelet count was ≤ 150 × 109/L or > 150 × 109/L, respectively. Ruxolitinib was given BID with starting dose based on baseline platelet count per local label. The primary endpoint was spleen volume reduction of ≥ 35% (SVR35) from baseline at week 24, assessed by MRI conducted by central review. Key secondary and exploratory endpoints evaluated in this analysis were a reduction in BMF obtained from BM biopsies by local evaluation and a reduction in VAF for the driver gene mutations (JAK2V617, CALR, or MPL), respectively. Driver gene VAF and HMR mutations were determined in whole blood with the 50-gene Focus Myeloid next-generation sequencing panel (Interspace Pharma Solutions, Morrisville, NC, USA). Results: As of Feb 07, 2022, all enrolled patients (N = 32) treated with navitoclax and ruxolitinib were evaluable for biomarker analysis. The median duration of follow-up was 6.1 months (range, 1.9 – 18.6); median age was 69 years (range, 44 – 83), and median spleen volume was 1889.08 cm3 (range, 645.6 – 7339.6). At baseline, 22 (69%) patients had JAK2, 6 (19%) had CALR, and 3 (9%) had MPL mutations. One (3%) patient was triple negative. Nineteen (59%) patients had HMR mutations. SVR35 at week 24 was observed in all subgroups known to confer poor prognosis, including age (≥75 years, 50% [n = 4/8]), high DIPSS score (Intermediate-2, 63% [n = 12/19]; high, 33% [n = 1/3]), and HMR mutations (47% [n = 9/19]; Figure). BMF grade improvement was evaluable in 26/32 (81%) patients, of which 9/26 (35%) achieved ≥ 1-grade improvement at any time during treatment with a median time-to-improvement of 12.3 weeks (range, 12.1 – 24.1). Complete resolution of BMF was observed in 2/9 (22%) patients. The baseline BMF grades of these patients were 2 and 3. BMF ≥ 1-grade improvement was achieved by 7/13 (54%) patients with HMR mutations and 2/13 (15%) without HMR mutations. Reduction in driver gene JAK2V617 mutation VAF > 20% from baseline at week 12 or 24 was observed in 14/28 (50%) patients, and 5/14 (36%) patients achieved > 50% VAF reduction from baseline. There were no differences in > 20% VAF reductions from baseline to week 12 or 24 between those with or without HMR mutations (7/15 [47%] versus 7/13 [54%], respectively). Conclusions: Among JAKi treatment-naïve patients with MF, the combination of navitoclax and ruxolitinib reduced splenomegaly in several high-risk groups known to confer poor prognosis. Reductions in BMF and VAF were independent of HMR mutations. The reduction in BMF and VAF for the driver mutation JAK2V617 is encouraging and suggestive of evidence of disease modification with the combination of navitoclax and ruxolitinib. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Pelabresib (CPI-0610) As Add-on to Ruxolitinib in Myelofibrosis: Durability of Response and Safety Beyond Week 24 in the Phase 2 MANIFEST Study

Background: Myelofibrosis (MF) is largely characterized by bone marrow (BM) fibrosis, splenomegaly and cytopenias. Progressive BM fibrosis results from aberrant megakaryopoiesis and proinflammatory cytokine expression, two processes that are tightly regulated by bromodomain and extraterminal domain (BET) protein-mediated expression of genes (eg NF-κB target genes, MYC and BCL-2) and often lead to myeloproliferation and cytopenias. Although the current standard of care for MF is treatment with the Janus kinase inhibitor (JAKi) ruxolitinib (RUX), many patients (pts) experience a suboptimal response to RUX monotherapy or must discontinue treatment due to cytopenias and therefore there is a significant unmet need for new therapies in this population. Pelabresib (CPI-0610; PELA) is an oral, small-molecule, investigational BET inhibitor that downregulates NF-κB signaling and other relevant genes involved in MF disease pathways (Mascarenhas J, et al. HemaSphere 2022;6:99-100). Aims: In the ongoing, open-label Phase 2 MANIFEST study (NCT02158858), PELA is under investigation as monotherapy and in combination with RUX in pts with MF. In Arm 2 of MANIFEST, pts with suboptimal/lost response to RUX are treated with PELA as 'add-on’ to RUX. In this abstract we will discuss results from the September 2021 data cut; updated data with longer follow-up on efficacy (≥35% reduction in spleen volume from baseline [BL; SVR35], ≥50% total symptom score reduction from BL [TSS50], duration of response and BM fibrosis improvement) and safety data from the planned July 2022 data cut will be presented. Methods: Pts in Arm 2 are stratified as transfusion dependent (TD; Arm 2A) and nontransfusion dependent (non-TD; Arm 2B). The primary endpoints are conversion from TD to transfusion independence (TI) in Arm 2A (TD cohort) and SVR35 at Week (Wk) 24 for Arm 2B (non-TD cohort). The secondary endpoints include TSS50 per MF Symptom Assessment Form v4.0 at Wk 24 and SVR35 at Wk 24 in Arm 2A (TD cohort). BM biopsies to assess BM fibrosis, durability of responses and safety data are evaluated. Data reported here are from the September 2021 data cut. Results: At Wk 24 in Arm 2 (N=86), 20% (16/81) of pts achieved SVR35 (Figures 1 and 2); 17% for Arm 2A (TD cohort) and 26% for Arm 2B (non-TD cohort). SVR35 at any time was achieved by 30% (24/81) of pts. At Wk 24, 27% (22/81) pts achieved ≥25% reduction in spleen volume from BL (SVR25); 26% (14/54) pts in Arm 2A (TD cohort) and 30% (8/27) pts in Arm 2B (non-TD cohort). Median spleen volume reduction for the full Arm 2 cohort was -18% at Wk 24. Durable (up to Wk 60) spleen volume reductions were observed as depicted in mean spleen volume change over time, and spleen volume reduction deepened over time (Figure 1). Twenty percent (16/80) pts had SVR35 response at Wk 48. In Arm 2A (TD cohort), the TD to TI rate was 16% (6/38). TSS50 at Wk 24 was 37% (30/81); 36% for Arm 2A (TD cohort) and 39% for Arm 2B (non-TD cohort). A total of 54% (46/86) of pts achieved TSS50 at any time. Median total symptom score reduction was -47% at Wk 24. As of data cut off, the median follow-up time was 24.4 (23.0-30.7) months and median treatment duration was 14.0 (8.4-20.6) months. After 24 wks of treatment, BM fibrosis improvement by ≥1 grade was achieved in 26% of evaluable pts by central pathology review; 50% of pts maintained the improvement at the next available assessment or longer. A total of 39% of pts achieved ≥1 grade improvement at any time (best response). The two most common hematologic treatment-emergent adverse events (TEAEs) of any grade were thrombocytopenia, reported in 52% (Grade ≥ 3: 33%) pts, and anemia, reported in 27% (Grade ≥ 3: 19%) pts. Low-grade gastrointestinal TEAEs and respiratory infections were observed but rarely a reason for treatment discontinuation. A total of 20 pts (23%) reported TEAEs that led to PELA discontinuation. Serious adverse events reported in ≥3 pts were anemia (6 pts), respiratory tract infections (4 pts) and urinary tract infections (3 pts). Conclusions: Based on these preliminary Phase 2 data, PELA as 'add-on’ to RUX in pts with a suboptimal/lost response to RUX monotherapy resulted in durable splenic and symptom responses, deepening of spleen responses over time, and was generally well tolerated. Additionally, improvement in BM fibrosis, as a marker of disease modification, was observed in 39% of treated pts. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Abstract LB108: Addition of navitoclax to ruxolitinib mediates responses suggestive of disease modification in patients with myelofibrosis previously treated with ruxolitinib monotherapy

Abstract Although ruxolitinib (RUX) is effective in alleviating splenomegaly and constitutional symptoms for patients with myelofibrosis (MF), it does not appear to modify underlying disease biology. RUX discontinuation rate within 5 years is approximately 40%, and patients have poor prognosis after discontinuing RUX [1]. The definition of disease modification in MF is evolving. Reversal of bone marrow fibrosis (BMF) and reduction in driver gene variant allele frequency (VAF) have been suggested as evidence of disease modification; however, clinical benefits derived from achieving these responses have not been fully elucidated. Ultimately, benefits in patient survival are requisite to claim true clinically meaningful disease modification. There is also an unmet need of effective therapies for patients with MF with high molecular risk (HMR) mutations (ASXL1, EZH2, IDH1/2, SRSF2, and U2AF1 Q157). REFINE (NCT03222609) is a phase 2 trial evaluating navitoclax (NAV), a BCL-XL/BCL-2 inhibitor, combined with RUX, in patients with MF who progressed on or had a suboptimal response to RUX monotherapy. Here, we report the exploratory analyses assessing BMF, VAF, and HMR with respect to outcomes. As BMF improvements were often observed in patients who achieved ≥35% reduction in spleen volume (SVR35), we explored if the survival benefit observed was due to this potentially disease modification-related response. All statistics were descriptive. As of May 6, 2021, 34 patients were enrolled in Cohort 1a and received ≥1 dose of NAV plus RUX. Of these, 32 were evaluable for BMF and 12 (38%) had ≥1 grade improvement during anytime on study, 4 of whom improved by 2 grades. For driver gene VAF reductions, 26 patients (JAK2, n=19; CALR, n=7) were evaluable and 6 (23%) achieved ≥20% reduction at Week 24. Five patients achieved both BMF and VAF responses. Median overall survival (OS) for patients who had ≥1 grade improvement in BMF was not reached compared with 28.5 months for those without improvement (P <0.01). Similarly, the median OS was also not reached for patients who achieved ≥20% VAF reduction versus 28.5 months for those who did not (P=0.05). Furthermore, no deaths were observed in patients with improvements in BMF or VAF. Within the patient group who had an SVR35 response at any time, median OS was not reached in those who had improved BMF (n=9), compared with an OS of 28.5 months for patients without BMF improvement (n=6; P <0.01). Of 34 patients, 33 were evaluable for molecular risk; 19 (58%) had HMR and 14 (42%) were without (non-HMR); at the time of analysis, median OS was not reached in either subgroup; there was no statistical significance in survival between HMR and non-HMR groups. Taken together, the results of these analyses demonstrate the ability of NAV, combined with RUX, to induce BMF improvement and VAF reduction. These responses are suggestive of disease modification as they were associated with improved OS for patients. In addition, the NAV plus RUX regimen potentially improved the outcome for patients with MF regardless of HMR status. Reference 1. Palandri F, Breccia M, Bonifacio M, et al. Life after ruxolitinib: Reasons for discontinuation, impact of disease phase, and outcomes in 218 patients with myelofibrosis. Cancer 2020; 126(6): 1243-52 Citation Format: Naveen Pemmaraju, Jacqueline Garcia, Jalaja Potluri, Yan Sun, Jason Harb, Srinivas K. Tantravahi, Srdan Verstovsek, Claire Harrison. Addition of navitoclax to ruxolitinib mediates responses suggestive of disease modification in patients with myelofibrosis previously treated with ruxolitinib monotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB108.

Defining disease modification in myelofibrosis in the era of targeted therapy.

The development of targeted therapies for the treatment of myelofibrosis highlights a unique issue in a field that has historically relied on symptom relief, rather than survival benefit or modification of disease course, as key response criteria. There is, therefore, a need to understand what constitutes disease modification of myelofibrosis to advance appropriate drug development and therapeutic pathways. Here, the authors discuss recent clinical trial data of agents in development and dissect the potential for novel end points to act as disease modifying parameters. Using the rationale garnered from latest clinical and scientific evidence, the authors propose a definition of disease modification in myelofibrosis. With improved overall survival a critical outcome, alongside the normalization of hematopoiesis and improvement in bone marrow fibrosis, there will be an increasing need for surrogate measures of survival for use in the early stages of trials. As such, the design of future clinical trials will require re‐evaluation and updating to incorporate informative parameters and end points with standardized definitions and methodologies.

Potential Disease-Modifying Activity of Navtemadlin (KRT-232), a First-in-Class MDM2 Inhibitor, Correlates with Clinical Benefits in Relapsed/Refractory Myelofibrosis (MF)

Potential Disease-Modifying Activity of Navtemadlin (KRT-232), a First-in-Class MDM2 Inhibitor, Correlates with Clinical Benefits in Relapsed/Refractory Myelofibrosis (MF)

Phase 1b Results of a Study to Assess the Efficacy and Safety of Vismodegib in Combination with Ruxolitinib in Patients with Intermediate- or High-Risk Myelofibrosis

Background: The JAK inhibitor (JAKi) ruxolitinib is approved for treatment of myelofibrosis (MF). Treatment for 5 years or more may be necessary to improve or stabilize bone marrow fibrosis, and a fraction of patients do not respond to ruxolitinib. The Hedgehog signaling pathway is involved in primitive and definitive bone marrow hematopoiesis, and maintenance of hematopoietic precursors, suggesting that addition of a Hedgehog pathway inhibitor (HPI) to ruxolitinib might improve responses. In a murine model of MF, a combination of a JAKi and HPI reduced fibrosis in the bone marrow and spleen and decreased splenomegaly. Vismodegib is a HPI approved for treatment of locally advanced and metastatic basal cell carcinoma. The MYLIE study aimed to assess the safety and efficacy of combined ruxolitinib and vismodegib for the treatment of MF. The pharmacokinetics (PK) of vismodegib were characterized in patients with intermediate or high-risk MF.Methods: In this phase 1b study, 10 patients with intermediate- or high-risk MF (per Dynamic International Prognostic Scoring System) received open-label vismodegib (150 mg/day orally) and ruxolitinib (15 or 20 mg orally twice daily, depending on baseline platelet count) for up to 48 weeks, or until withdrawal or discontinuation. PK samples were collected throughout the study. PK sampling was designed to characterize the PK of total and unbound vismodegib in this study for comparison with PK data collected in other patient populations. Efficacy outcomes assessed for phase 1b included spleen response (≥35% reduction in volume by computed tomography or magnetic resonance imaging) per central and investigator assessment, improvement in bone marrow fibrosis per central and investigator assessment (using European consensus grading system), symptom response (≥50% reduction in Myeloproliferative Neoplasm Symptom Assessment Form Total Symptom Score [MPN-SAF TSS]) and anemia response (per International Working Group for Myeloproliferative Neoplasms Research and Treatment [IWG-MRT] revised response criteria). We report results from the planned analysis of the phase 1b study for efficacy and safety at week 24.Results: Six patients with primary MF, 1 with post-polycythemia vera MF and 3 with post-essential thrombocythemia MF were treated with vismodegib and ruxolitinib for a median of 294.0 days. As of the interim analysis data cutoff (March 29, 2017), 4 patients had completed 48 weeks of study treatment with ruxolitinib and vismodegib, 5 patients were still receiving treatment, and 1 had discontinued treatment because of a vismodegib-related adverse event (AE) (dysgeusia). The most common AEs were muscle spasm (100% of patients), dysgeusia (50%), alopecia (50%), thrombocytopenia (50%), and nausea (40%). All were grade 1/2, except for 2 instances of grade 3 thrombocytopenia in 2 patients. Three patients experienced serious AEs: infection (3 patients), lung infiltration (1 patient), and vomiting (1 patient); none were considered by the investigators to be related to vismodegib. Because of AEs, 7 patients modified or interrupted their ruxolitinib dose, and 4 patients interrupted their vismodegib dose. At week 24, three patients achieved a ≥35% reduction in spleen volume (including the patient who discontinued early because the assessment occurred within the week 24 visit window) by central review (a spleen response occurred in 1 patient per the investigator assessment). According to the central reviews, no patients had improvement in bone marrow fibrosis (1 patient had improvement in bone marrow fibrosis per investigator assessment). Five patients experienced symptom response, and no patients experienced an anemia response. A further central review of bone marrow biopsy specimens from 5 patients at week 48 continued to show no improvement in fibrosis.Conclusions: There was no clear benefit of the addition of vismodegib to ruxolitinib in any of the phase 1b efficacy outcome measures assessed. Given the lack of evidence of a disease-modifying effect with addition of vismodegib to ruxolitinib, further evaluation of this combination will not be pursued.Source of funding: F. Hoffmann-La Roche DisclosuresKoschmieder:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Roche: Other: Clinical Trial participation; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support. Verstovsek:Incyte: Research Funding; NS Pharma: Research Funding; Blueprint Medicines Corp: Research Funding; Blueprint Medicines Corp: Research Funding; Galena BioPharma: Research Funding; Celgene: Research Funding; NS Pharma: Research Funding; Seattle Genetics: Research Funding; Genentech: Research Funding; Lilly Oncology: Research Funding; CTI BioPharma Corp: Research Funding; Astrazeneca: Research Funding; Promedior: Research Funding; Pfizer: Research Funding; Astrazeneca: Research Funding; Genentech: Research Funding; Gilead: Research Funding; Seattle Genetics: Research Funding; Bristol Myers Squibb: Research Funding; Bristol Myers Squibb: Research Funding; Gilead: Research Funding; Promedior: Research Funding; Celgene: Research Funding; CTI BioPharma Corp: Research Funding; Galena BioPharma: Research Funding; Roche: Research Funding; Pfizer: Research Funding; Lilly Oncology: Research Funding; Roche: Research Funding. Hooper:Roche Products Ltd: Employment. Tandon:F. Hoffmann-La Roche: Employment. Dimier:F. Hoffmann-La Roche: Employment, Other: Stock.

CDK6 Is a Therapeutic Target in Myelofibrosis.

Myelofibrosis (myelofibrosis) is a deadly blood neoplasia with the worst prognosis among myeloproliferative neoplasms (MPN). The JAK2 inhibitors ruxolitinib and fedratinib have been approved for treatment of myelofibrosis, but they do not offer significant improvement of bone marrow fibrosis. CDK6 expression is significantly elevated in MPN/myelofibrosis hematopoietic progenitor cells. In this study, we investigated the efficacy of CDK4/6 inhibitor palbociclib alone or in combination with ruxolitinib in Jak2V617F and MPLW515L murine models of myelofibrosis. Treatment with palbociclib alone significantly reduced leukocytosis and splenomegaly and inhibited bone marrow fibrosis in Jak2V617F and MPLW515L mouse models of myelofibrosis. Combined treatment of palbociclib and ruxolitinib resulted in normalization of peripheral blood leukocyte counts, marked reduction of spleen size, and abrogation of bone marrow fibrosis in murine models of myelofibrosis. Palbociclib treatment also preferentially inhibited Jak2V617F mutant hematopoietic progenitors in mice. Mechanistically, treatment with palbociclib or depletion of CDK6 inhibited Aurora kinase, NF-κB, and TGFβ signaling pathways in Jak2V617F mutant hematopoietic cells and attenuated expression of fibrotic markers in the bone marrow. Overall, these data suggest that palbociclib in combination with ruxolitinib may have therapeutic potential for treatment of myelofibrosis and support the clinical investigation of this drug combination in patients with myelofibrosis. SIGNIFICANCE: These findings demonstrate that CDK6 inhibitor palbociclib in combination with ruxolitinib ameliorates myelofibrosis, suggesting this drug combination could be an effective therapeutic strategy against this devastating blood disorder.

MO802DOES ETELCALCETIDE REVERSE MYELOFIBROTIC BONE CHANGES DUE TO HYPERPARATHYROIDISM? A CASE REPORT

Abstract Background and Aims A 21 year old boy with a diagnosis of Autosomal Recessive Polycystic Kidney Disease and Caroli disease reached a final stage of chronic kidney disease (CKD) and started haemodialysis. Method After 3 years in haemodialysis he underwent a kidney transplant from a cadaveric donor. His transplanted kidney worked fairly well until the patients was 31 year old when he developed graft dysfunction (serum creatinine from 2.7 to 5 mg/dL in a very short period). There was a concomitant increase in serum phosphate levels (8.3 mg/dl) and iPTH that progressively increased to 1032 pg/ml despite a traditional therapy. Results At age 32, the patient returned to haemodialysis treatment thrice weekly with a concomitant a progressive worsening of hyperparathyroidism with bone pain . Cinacalcet at a dosage of 30 mg daily treatment was initiated, then it was increased to 120 mg daily without any benefit. Two years later, being the clinical situation without any improvement and being the patient scarcely compliant to the therapy and because a further enlargement of parathyroid glands was observed, a Parathyroidectomy (PTX) was advised. Nevertheless, PTX was not performed because of patient’s refusal. Furthermore, despite Erythropoietic Stimulating Agent (ESA) therapy, he developed severe anemia that required regular and frequent blood transfusions. iPTH increased to 4500 pg/ml [Fig.1] with a parallel rise in alkaline phosphatase >600 UI/L [Fig.2]. A Computed Tomography scan showed multiple bone-thickening lesions. He thus initiated Etelcalcetide 5 mg e.v. 3 times a week, after the HD session but without any benefit. The dosage was then increased to 7.5 mg but the patient gradually became frail and developed pancytopenia and low-grade fever. Hematological evaluation with bone marrow biopsy was performed in December 2019. Bone marrow histology showed severe fibrosis [Myelofibrosis (MF) grade 3] with normal bone marrow cytogenetics. Blood samples for mutations in JAK-2, CALR, and MPL and BCR-ABL rearrangement were negative. There was no evidence for a myeloproliferative neoplasm (MPN) or metastatic lesions. During the following months, while on a 7,5 mg dose of etalcalcetide, there was a gradual reduction in iPTH [Fig.1] and serum alkaline phosphatase [Fig.2], up to 500 pg/dl and 200 IU/L respectively. The patient developed asymptomatic, often severe, hypocalcemia which was managed with therapy. The patient’s clinical conditions gradually improved, anemia responded to lower doses of ESAs. A bone marrow biopsy was repeated after one year (December 2020) and it showed a reduction in fibrosis (MF grade varying from 1-2). Then etelcalcetide dosage was reduced while serum calcium and phosphate levels were in the normal limit. Conclusion Myelofibrosis secondary to renal osteodystrophy is an uncommon complication. It has been rarely reported and usually is associated with primary hyperparathyroidism. Marrow fibrosis and pancytopenia is related to the excessive iPTH that upregulates production of cytokines and paracrine factors in the bone marrow (IL-1a, IL-6, FNF-a, TGF–b, and platelet-derived growth factor) and it has an important stimulatory effect on fibroblast proliferation. It is known that surgical parathyroidectomy is associated with a reduction of bone marrow fibrosis in primary hyperparathyroidism. To our knowledge, this is probably the first case of tertiary hyperparathyroidism in which the effect of etelcalcetide is comparable to parathyroidectomy as far as on calcium-phosphate balance, and a significant improvement in bone marrow fibrosis and hemoglobin. In conclusion, etelcalcetide at least in this patient seems as effective as PTX on bone balance, bone marrow and anemia.

The Addition of Navitoclax to Ruxolitinib Demonstrates Efficacy within Different High-Risk Populations in Patients with Relapsed/Refractory Myelofibrosis

The Addition of Navitoclax to Ruxolitinib Demonstrates Efficacy within Different High-Risk Populations in Patients with Relapsed/Refractory Myelofibrosis

MANIFEST, a Phase 2 Study of CPI-0610, a Bromodomain and Extraterminal Domain Inhibitor (BETi), As Monotherapy or “Add-on” to Ruxolitinib, in Patients with Refractory or Intolerant Advanced Myelofibrosis

MANIFEST, a Phase 2 Study of CPI-0610, a Bromodomain and Extraterminal Domain Inhibitor (BETi), As Monotherapy or “Add-on” to Ruxolitinib, in Patients with Refractory or Intolerant Advanced Myelofibrosis

Results from a Phase 2 Study of Navitoclax in Combination with Ruxolitinib in Patients with Primary or Secondary Myelofibrosis

Results from a Phase 2 Study of Navitoclax in Combination with Ruxolitinib in Patients with Primary or Secondary Myelofibrosis

Preliminary Report of MANIFEST, a Phase 2 Study of CPI-0610, a Bromodomain and Extraterminal Domain Inhibitor (BETi), in Combination with Ruxolitinib, in JAK Inhibitor (JAKi) Treatment Naïve Myelofibrosis Patients

Preliminary Report of MANIFEST, a Phase 2 Study of CPI-0610, a Bromodomain and Extraterminal Domain Inhibitor (BETi), in Combination with Ruxolitinib, in JAK Inhibitor (JAKi) Treatment Naïve Myelofibrosis Patients

S831 CPI‐0610, A BROMODOMAIN AND EXTRATERMINAL DOMAIN (BET) INHIBITOR, REDUCES PRO‐INFLAMMATORY CYTOKINES, BONE MARROW FIBROSIS AND THE NUMBER OF TRANSFUSIONS IN MYELOFIBROSIS PATIENTS

Background:Myelofibrosis (MF) is a myeloproliferative neoplasm associated with a cytokine (CK) milieu that leads to bone marrow (BM) fibrosis. Ruxolitinib (RUX) is the only approved therapy for MF, but patients (pts) can eventually relapse/have inadequate response. RUX can also worsen anemia and pts may require transfusions. BET proteins are transcriptional regulators that control key oncogenic pathways, including NF‐κB, MYC, and BCL2 and TGFβ signaling, an important driver of fibrosis. Preclinical studies suggest that a combination of a BET inhibitor (BETi) and RUX results in a synergistic reduction of the hallmarks of MF: splenomegaly, BM fibrosis and the mutant (MUT) allele burden (Kleppe 2018). CPI‐0610 is a selective and potent BETi that impacts megakaryocyte differentiation (unpublished data), cells responsible for pro‐inflammatory CK production and is currently being evaluated in MF, alone or in combination with RUX in a clinical trial with 3 arms: CPI‐0610 alone (Arm 1), CPI‐0610+RUX in pts exposed to RUX/with an inadequate response to RUX (Arm 2), or CPI‐0610+RUX in JAKi naïve pts with anemia (Arm 3). Arm 1 and 2 are stratified between transfusion dependence (TD) and splenomegaly at baseline.Aims:Phase 2 study to assess CPI‐0610 alone or “add‐on” to RUX in MF pts. Primary endpoints: conversion of TD to transfusion independence (TI), spleen volume response, patient reported outcomes, safety and PK. Additional endpoints include: changes in pro‐inflammatory CK levels, BM fibrosis and MUT profiling.Methods:Pt samples were used to analyze CK levels, MUT profiles and BM fibrosis. CK analyses utilized Myriad‐RBM InflammationMAP and CustomMAP and MUT analysis utilized the Rapid Heme Panel (Kluk, 2016).Results:23 pts were accrued to this multi‐center study, with 18 pts analyzed: MUT profiles which revealed the following MUT: 11 ASXL1(61%), 10 JAK2(56%), 6 CALR (33%) and 2 MPL(11%). 10 pts (56%) had at least 3 MUTs and 17 pts (94%) had at least one driver MUT (JAK2, CALR or MPL). 1 pt (6%) was triple negative and 12 pts (67%) had a high MUT profile (HMR). Baseline CK levels were elevated, in pts who failed/inadequate response to RUX. CPI‐0610 at a starting dose of 125 mg QD (days 1–14 of 21‐day cycle) reduced CK levels in both monotherapy and combination arms. Suppression of IL‐18 was observed in all pts analyzed (n = 8) with >50% decrease in 4/8 pts. Trends were also observed for a number of other CK, including IL‐8 and CRP. CK inhibition was sustained over multiple cycles of CPI‐0610 (combination/monotherapy). Best spleen volume reduction ranged from 6–44% in 10 pts. Out of the 4 pts with BM assessments (pre and at least 1 post), 2 were TD at baseline. Three pts had one grade improvement in BM fibrosis (1 at 6 mth, 2 at 1 yr) and had Hgb increases of ≥1.5 g/dL for ≥12 weeks without transfusions. The other pt had a 1 grade improvement in the BM reticulin score (at 6 mth). Moreover, both of the TD pts became TI. Hepcidin levels and PK will be presented. The most common adverse events were Grade 1/2 diarrhea, nausea/vomiting and reversible and non‐cumulative thrombocytopenia.Summary/Conclusion:CPI‐0610 alone or in combination with Rux demonstrates encouraging clinical activity (spleen responses, conversion to TI and improvement in BM fibrosis) with good tolerability. Assessment of CK levels suggest that CPI‐0610 therapy durably reduces pro‐inflammatory CK. Notably, levels of individual CK were reduced to levels observed in normal healthy donors and were maintained during treatment. Genomic profiling data shows that majority of pts had HMR MUT at baseline. Updated data will be presented.image

PS1449 DISSECTING THE THERAPEUTIC MECHANISM OF RUXOLITINIB IN JAK2V617F MEDIATED MPNS REVEALED AN INHIBITION OF BOTH ONCOGENIC AND NON-ONCOGENIC CELLS BY DOWN REGULATION OF INFLAMMATORY CYTOKINE LEVELS

Background: Ruxolitinib is a potent JAK2/JAK1 specific inhibitor approved by the FDA and EMA for the treatment of primary myelofibrosis (PMF). The primary clinical benefits of JAK2 inhibitors in PMF patients are reduction in spleen size, alleviation of constitutional symptoms and a significant improvement in the quality of life. However, no significant improvement of bone marrow fibrosis has been demonstrated so far, and the effect on the JAK2V617F allelic burden is modest. In addition, the beneficial clinical effects were also achieved in JAK2V617F negative PMF patients. Aims: It is unclear at the moment whether Ruxolitinib primarily blocks proliferation of the malignant clone or exerts its effects by inhibiting bystander normal hematopoietic cells or bone marrow niche cells. By clinical investigation it is not possible to dissect between these two modes of inhibitor action. However, JAK2V617F variants which are resistant towards clinically used inhibitors can be expressed in mice. Such a mouse model would allow investigation of the mode of action of the JAK2 inhibitors in PMF patients. Methods: So far no inhibitor resistant JAK2 mutations have been reported in patients. Therefore, a comprehensive cell based screening strategy was used to identify Ruxolitinib resistant JAK2V617F variants. Results: Using cell based screening method, we were able to identify seven specific mutations which confer resistance to Ruxolitinib while retaining the kinase activity. For this study, we used JAK2V617F+L902Q and JAK2V617F+L983F variants since these two variants were highly resistant towards the Ruxolitinib. In order to determine the disease phenotype of JAK2V617F+L902Q and JAK2V617F+L983F we transplanted retrovirally infected JAK2V617F and JAK2V617F+L902Q and JAK2V617F+L983F bone marrow into recipient mice. Similar to JAK2V617F recipients, JAK2V617F+L902Q and JAK2V617F+L983F transplanted mice showed an increase in WBC, HCT, RBC, HB and reticulocyte values. Histopathological analysis revealed that the myeloproliferative phenotype resembles PV with a proliferation of all three lineages albeit with only a moderate increase in megakaryopoeisis. Grade II bone marrow fibrosis was observed in JAK2V617F+L902Q and JAK2V617F+L983F after 2–3 months similar to JAK2V617F mice. Ruxolitinib treatment lead to a decrease in spleen size, length and WBC number in JAK2V617F mice however, surprisingly, JAK2V617F+L902Q and JAK2V617F+L983F mice also decreased the spleen size, length and WBC number after Ruxolitinib treatment. FACS analysis of different hematopoietic cell population from peripheral blood, spleen and bone marrow results suggested that Ruxolitinib mainly act on eGFP+ neutrophils and also on eGFP− neutrophils, B and T cells in JAK2V617F, JAK2V617F+L902Q and JAK2V617F+L983F MPN mouse models. Finally, analysis of pro inflammatory cytokines results from Ruxolitinib treated mice results showed significant down regulation of several cytokines including TNF-alpha, MCP-1, IL-6, INF-beta, IL-27 and IL-23 in both JAK2V617F and JAK2V617F+L902Q MPN mouse models suggesting that ruxolitinib mediated clinical benefits might also be due to the down regulation of inflammatory cytokines by inhibition of JAK1/2 signaling in both hematopoietic as well as non-hematopoietic cells. Summary/Conclusion: Taken together, our results clearly suggest that identification of novel inhibitors that specifically act on malignant cells and spare the non-malignant cells which play a major role in normal hematopoiesis will improve the clinical efficacy in PMF patients.

A phase 2 study of pracinostat combined with ruxolitinib in patients with myelofibrosis

Although ruxolitinib improves symptoms and splenomegaly in patients with advanced myelofibrosis, whether this agent is truly disease-modifying remains unclear. Histone deacetylase inhibitors (HDACi) downregulate JAK2 via interference with chaperone function. Pracinostat, a pan-HDACi, has modest single-agent activity in myelofibrosis. We conducted a single-institution, phase 2, investigator-initiated trial of ruxolitinib plus pracinostat (begun after 12 weeks of ruxolitinib) in 25 patients with myelofibrosis, of whom 20 received both agents. Sixteen (80%) patients had objective responses (all ‘clinical improvement’). The rate of spleen response (by palpation) was 74%, and that of symptom response 80%. Most responses occurred prior to pracinostat initiation. Three patients experienced improvement in bone marrow fibrosis, and one a near-complete molecular response after two years on study treatment. All patients discontinued pracinostat and are currently off-study. Pracinostat interruptions and dose reductions were frequent, often due to worsening anemia. These findings do not support continued development of pracinostat in myelofibrosis.

Updated Results of Phase 2 Study of Ruxolitinib in Combination with 5-Azacitidine in Patients with Myelofibrosis

Background:JAK1/2 inhibitor ruxolitinib (RUX) abrogates symptoms and organomegaly in patients with myelofibrosis (MF). Combination with azacitidine (AZA) may further improve its efficacy.Methods:We initiated a single institutional, single arm, prospective, phase 2 study of RUX AZA combination in adult patients with MF and < 20% blasts. Previous therapy with RUX or AZA was not allowed. RUX 5 - 20 mg orally twice daily was given continuously since cycle 1. AZA 25 - 75 mg/m2 on days 1 - 5 of each 28-day cycle was added starting cycle 4. Responses were assessed per International Working Group for Myelofibrosis Research and Treatment 2013 criteria (IWG-MRT). Enrollment cut-off for this analysis was December 31st, 2017 to allow > 6 months of follow-up for all enrolled patients. We plan to present updated results with additional 5 months of enrollment at the meeting.Results:Fifty two pts were enrolled on study between 03/2013-12/2017, and were evaluable for responses. Forty seven pts (84%) were treated with both agents (RUX and AZA), with a median of 25 cycles (range, 1-55). Median age was 66 years (range, 48-87). Thirty four pts (65%) had int-2/high DIPSS score, 40 pts (77%) had spleen ≥5 cm. Thirty pts (58%) were JAK2V617F positive. Among 36 pts tested for non-driver mutations (28-gene panel); 7 pts had ASXL1, 6 had TET2, 3 had IDH1/2 and 2 had EZH2 and TP53.After a median follow-up of 22+ months (range, 1-59+); 21 pts (40%) are on therapy with a median overall follow-up of 30+ months. The most common reasons for therapy discontinuation were elective stem cell transplantation (n=12), and uncontrolled disease (n=8), including progression to acute leukemia (n=4). Four pts (8%) primarily discontinued therapy due to drug related toxicity (cytopenias). Three treatment unrelated deaths occurred on study; one each due to sepsis, meningitis and metastatic melanoma.Thirty eight pts (73%) had objective response on a study (Table). Median time to response was 1.8 months (range, 0.7-19). Seven responses (21% of responders) occurred after the addition of AZA with a median time to response of 2 months. These responses included spleen and symptom clinical improvements in 26% and 16% of pts, respectively.In total, 26 (65%), and 23 (58%) pts had palpable spleen reduction by > 50% at any time on study, and at week 24, respectively. JAK2V617F allele reduction was noted in 13 (81%) of 16 evaluable pts.Thirty one pts (60%) had available bone marrow for sequential evaluation. Nineteen pts (61%) had a documented improvement in bone marrow fibrosis, collagen or osteosclerosis, with a median time to first response of 12 months (range, 6-18).The most common grade ≥3 non-hematologic toxicity on a study was infection (34%), constipation (21%), and nausea (14%). New onset of grade ≥3 anemia, thrombocytopenia and neutropenia occurred in 33%, 30% and 16% of pts, respectively.Conclusion:Concomitant RUX with AZA was feasible with overall IWG-MRT response rate of 73%, including >50% spleen reduction in 65% of pts. Moreover, 61% of pts achieved improvement in bone marrow fibrosis, collagen or osteosclerosis. ClinicalTrials.gov Identifier: NCT01787487.Table. [Display omitted] DisclosuresVerstovsek:Celgene: Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy; Italfarmaco: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Cortes:novartis: Research Funding. Pemmaraju:novartis: Research Funding; daiichi sankyo: Research Funding; Affymetrix: Research Funding; plexxikon: Research Funding; samus: Research Funding; celgene: Consultancy, Honoraria; abbvie: Research Funding; cellectis: Research Funding; stemline: Consultancy, Honoraria, Research Funding; SagerStrong Foundation: Research Funding. Bose:Blueprint Medicines Corporation: Research Funding; Incyte Corporation: Honoraria, Research Funding; Constellation Pharmaceuticals: Research Funding; Astellas Pharmaceuticals: Research Funding; Pfizer, Inc.: Research Funding; CTI BioPharma: Research Funding; Celgene Corporation: Honoraria, Research Funding. Daver:Pfizer: Consultancy; Novartis: Research Funding; ImmunoGen: Consultancy; Alexion: Consultancy; Incyte: Consultancy; Karyopharm: Research Funding; Sunesis: Research Funding; Otsuka: Consultancy; Novartis: Consultancy; Karyopharm: Consultancy; Sunesis: Consultancy; Daiichi-Sankyo: Research Funding; ARIAD: Research Funding; Incyte: Research Funding; Kiromic: Research Funding; Pfizer: Research Funding; BMS: Research Funding.

Myelofibrosis Drug Development through the Decade: Novel JAK Inhibitors

IntroductionMyelofibrosis (MF), a BCR-ABL negative myeloproliferative neoplasm (MPN), has an annual incidence of 1 in 100000 for the primary MF and 0.3-0.7 in 100000 for secondary MF in the USA. MF patients have a median survival of 6.5 years. The primary mutation, JAK2V617F, occurs in 40-60% of MF cases. Ruxolotinib, a JAK inhibitor, has been the mainstay in treating high risk, debilitating MF but largely clinical needs are unmet.MethodsA comprehensive literature research was performed using PubMed, Cochrane, EMBASE, Web of Science and Clinicaltrials.gov. We included all trials that were under development in phase I/II/III trials. Our search identified 1642 full-length manuscripts or abstracts with published results in the last decade ( Jan 2007 till Dec 2017) were screened for relevant studies. After screening by 2 independent reviewers, 212 articles were finalized for our final analyses. We have reviewed the mechanism of action, safety and efficacy of 2nd generation JAK inhibitors in this review.ResultsJAK1 inhibitor: Itacitinib reduced total symptom score (TSS) ≥ 50% in 15/42 (36%) patients. Mild gastrointestinal (GI) disturbances and some grade 3-4 myelosuppression (anemia: 33%, thrombocytopenia: 29%) were reported.JAK2 inhibitors: In PERSIST-1, pacritinib when compared to best available therapy (BAT) showed SVR ≥ 35% in 19.1% vs. 4.7% patients, with lower rates of myelosuppression (thrombocytopenia: 17%, anemia: 11%). In PERSIST-2, a phase III trial of pacritinb vs. BAT in patients with baseline cytopenias, similar efficacy was demonstrated (SVR ≥ 35%: 18% vs. 3%). Increasing rates of heart failure and intracranial hemorrhages led to a temporary hold which was lifted in August 2017. Lestaurtinib showed CI in 7 (44%) patients in a phase I trial (n=16) and 6 (27%) patients in a phase II trial (n=22). Most notable toxicities were G 1/2 GI disturbances, anemia occurred in 14% and thrombocytopenia in 23% of patients. In a phase III trial (n=193), fedratinib showed a SVR ≥ 35% and a TSS ≥ 50% in 40% and 36% patients, respectively. However, incidence of significant neurotoxicity and Wernicke's encephalopathy led to its suspension. Similarly, a trial of XL019 was terminated due to emergence of central and peripheral neurotoxicity. In a phase I trial (n=48), NS-018 exhibited a spleen length reduction (SLR) ≥ 50% in 20 (56%) patients along with prompt improvement in bone marrow fibrosis (37%). Anemia and thrombocytopenia were reported in 15% and 27% of patients, respectively. Dizziness (23%) and nausea (19%) were also reported. Gandotinib demonstrated SLR ≥50% in 62% patients, in a phase I trial (n=38). G1 diarrhea (55.3%) and nausea (42.1%) were the most common toxicities.JAK 1/2 inhibitors: SIMPLIFY-1 (S1), a phase III clinical trial (n=432) of momelotinib vs. ruxolotinib in JAK inhibitor-naïve patients, demonstrated non-inferiority for momelotinib, in spleen volume reduction (SVR) ≥ 35% (26.5% vs. 29%; p=0.01). However, SIMPLIFY-2 trial (S2), that compared these two drugs in JAK inhibitor exposed patients did not achieve similar responses with momelotinib (6.7% vs. 5.8%; p=0.90). Interestingly, momelotinib excelled at achieving transfusion independency in both trials (S1: 66.5% vs. 49.3%; p=0.001, S2: 43.3% vs 21.2%; p=0.001). Grade ≥ 3 infections and peripheral neuropathy were the major toxicities noted. These trials were suspended after 89% of patients failed to achieve the primary endpoint of SVR. AZD1480 demonstrated clinical improvement (CI) in four (11%) patients in a phase I trial (n=35). Most common adverse events included grade (G) 1-2 dizziness and anemia.ConclusionNovel JAK pathway inhibitors have shown promising efficacy in MF but safety concerns regarding the hematological (cytopenias) and non-hematological adverse effects needs to be addressed until their use in clinical practice is established. Momelotinib success in achieving anemia related endpoints is note-worthy and should be further explored in this regard. A phase II study [NCT03165734] evaluating pacritinib monotherapy as a second line treatment in patients with baseline thrombocytopenia is ongoing. DisclosuresNo relevant conflicts of interest to declare.

Beyond JAK2 Inhibitors: A Systematic Review of Management Strategies for Myelofibrosis

IntroductionDrugs that target activating mutations of Janus Kinase 2 (JAK2) have been the backbone of myelofibrosis (MF) management. With recent advancements in our understanding of the underlying molecular mechanisms involved in myelofibrosis (MF) pathogenesis, numerous novel agents have been developed in the last decade. We have systematically reviewed the mechanisms of actions, efficacy and safety of these drugs.MethodsA comprehensive literature research was performed using PubMed, Cochrane, EMBASE, Web of Science and Clinicaltrials.gov. We included all trials that were under development in phase I/II/III trials. Our search identified 1642 full-length manuscripts or abstracts with published results in the last decade were screened for relevant studies. Of these, 212 articles were finalized for our final analyses.ResultsHedgehog inhibitors (saridegib, glasdegib and sonidegib) targets signaling membrane protein, smoothened. The combination of sonidegib + ruxulotinib (RUX) elicited the best response. Spleen volume reduction (SVR) ≥35% and spleen length reduction (SLR) ≥50% was reported in 15 (55.6%) and 25 (92.6%) patients.Histone deacetylase inhibitors (panobinostat, pracinostat, vorinostat, givinostat) target JAK2-H3Y41-HP1 pathway involved in hematopoiesis and leukemogenesis. The combination of pracinostat + RUX demonstrated the best response in a phase II trial (n=22), with clinical improvement (IWG-MRT) in splenomegaly, symptoms and both were reported in four (18%), two (9%), and ten (45%) patients that were durable for a median of 7.5 months.Immunomodulators: Lenalidomide has shown anemia responses in 32% of patients in combination with prednisone, in a phase II trial (n=40). Improvement in bone marrow fibrosis (10/11 patients with G4 reduced to G2 or better) was also seen. Pomalidomide with or without prednisone has shown anemia responses varying from 17-24% across different trials. However, a recent phase III trial (n=32) comparing pomalidomide vs. placebo, found no difference in transfusion independence rates (16% vs. 16%, p=1.00).Azacytidine (AZA) and decitabine (DCB) are hypomethylating agents. An objective response rate (ORR) of 69% (n=39) with AZA+RUX was noted. DCB+RUX demonstrated an ORR of 57% with a median overall survival of 10.4 months, in a phase I trial (n=21).Imetelstat is a telomerase inhibitor that has shown an ORR of 21% among 33 MF patients. Responses were characterized by BMF improvement (n=4) and transfusion independence (3/7 responders).Anti Fibrotics: PRM 151, a recombinant pentraxin-2, has shown an ORR of 35% in a phase II trial (n=27). Anemia response was noted in 6/15 (40%) patients and BMF improvement in two patients, durable up to 72 weeks. Simtuzumab, an antibody lysysl oxidase like-2 (LOXL2) enzyme, failed to show any clinical benefit in a phase II study of 54 patients.Sotatercept and luspatercept are ligand “traps” that limit the activity of TGF-B superfamily ligands, involved in erythroid differentiation. Sotatercept monotherapy achieved transfusion independence (TI) in six (35%) of 17 evaluable patients. Luspatercept has recently been under investigation in patients with MF (NCT03194542).LCL-161 is a second mitochondrial activator of caspases (Smac)-mimetic, A phase II clinical trial (n=33) found an ORR of 30% (n=9). Five (56%) of the nine responders achieved anemia responses.Buparilisib and everolimus targets the PI3K/mTOR pathway. Buparilisib, a PI3K inhibitor, demonstrated a SLR ≥ 50% in 72% patients whereas everolimus, an mTOR inhibitor, showed an ORR of 23%.ConclusionThe combination of ruxolitinib with some of these novel agents such as hedgehog inhibitors and hypomethylating agents have shown promising efficacy with response rates of more than 40%. LCL-161 and sotatercept has been reassuring with respect to anemia management, achieving response rates of more than 30%. PRM-151 has shown durable responses and will be the first antifibrotic for MF, if approved. Even though initial results with some of these novel agents have been ground breaking, there is a need to further explore pathways that can be targeted to help prolong survival and modify the disease course in MF patients. DisclosuresNo relevant conflicts of interest to declare.