Citations

Abstract PAC203 is a randomized dose-finding study of pacritinib, an oral JAK2/IRAK1 inhibitor, in patients with advanced myelofibrosis who are intolerant of or resistant to ruxolitinib. Patients were randomized 1:1:1 to pacritinib 100 mg once per day, 100 mg twice per day, or 200 mg twice per day. Enhanced eligibility criteria, monitoring, and dose modifications were implemented to mitigate risk of cardiac and hemorrhagic events. Efficacy was based on ≥35% spleen volume response (SVR) and ≥50% reduction in the 7-component total symptom score (TSS) through week 24. Of 161 patients, 73% were intolerant of and 76% had become resistant to ruxolitinib; 50% met criteria for both. Severe thrombocytopenia (platelet count <50 × 103/μL) was present in 44%. SVR rates were highest with 200 mg twice per day (100 mg once per day, 0%; 100 mg twice per day, 1.8%; 200 mg twice per day, 9.3%), particularly among patients with baseline platelet counts <50 × 103/μL (17%; 4 of 24). Although TSS response rate was similar across doses (100 mg once per day, 7.7%; 100 mg twice per day, 7.3%; 200 mg twice per day, 7.4%), median percent reduction in TSS suggested a dose-response relationship (–3%, −16%, and −27%, respectively). Pharmacokinetic and pharmacodynamic modeling based on all available data showed greatest SVR and TSS reduction at 200 mg twice per day compared with lower doses. Common adverse events were gastrointestinal events, thrombocytopenia, and anemia. There was no excess of grade ≥3 hemorrhagic or cardiac events at 200 mg twice per day. Pacritinib 200 mg twice per day demonstrated clinical activity and an acceptable safety profile and was selected as the recommended dose for a pivotal phase 3 study in patients with myelofibrosis and severe thrombocytopenia. This trial was registered at www.clinicaltrials.gov as #NCT03165734.

Background: Myelofibrosis (MF) is a clonal bone marrow disorder characterized by a constitutional symptoms, splenomegaly, anemia, elevated WBC and bone marrow fibrosis. Ruxolitinib is a JAK2 inhibitor approved for patients with Intermediate-2 (INT-2) or high risk disease based on dynamic international prognostic scoring system (DIPSS), however, there are limited options for patients with early disease. Interferon alpha (IFNa) is a cytokine therapy that has been used in treatment of chronic myelogenous leukemia and polycythemia vera (PV). In these diseases, there can be a reduction in the clonal burden in addition to a hematologic response. Therefore, we sought to use this therapy in patients with MF. Methods: Patients who had MF were enrolled on an IRB approved clinical protocol in a single arm, single institution study. Patients were stratified to either an early disease arm (characterized by intermediate 1 (INT-1) risk or advanced disease (Int-2 or high-risk disease based on DIPSS). Patients were started on ropeginterferon (interferon-alpha 2b) at 50 ug every two weeks, and the dose was titrated up to either 300 ug every other week, or until unacceptable toxicity. Patients were monitored for response based on IWG criteria. Results: Ten patients with MF have been enrolled on the study to date (Early: 3, Int/High: 7). Median age was 69.5 (39 - 88), four patients were female. Five patients had primary MF (PMF), 4 had post-essential thrombocythemia and 1 post PV MF. Five patients had previous treatment for their disease. Four patients continue to receive active treatment (2 early disease, and 2 advanced disease). Reasons for stopping include disease progression (3), toxicity (1), alternate treatment (1) and lack of benefit (1). The median number of cycles for those who ended treatment was 7.5 (4-47), and for those who remain on treatment, they range from 16 - 46 cycles. Five patients achieved a clinical improvement, 3 had a spleen response, and 2 had a symptom response. A grade 3 adverse event (AE) potentially attributable to the treatment occurred in 6 patients (60%), 4 (40.0%) patients had anemia, and 2 (20.0%) patients had lymphopenia. Only one patient discontinued therapy due to AEs (dizziness, atrial fibrillation). One death has occurred to date, due to an unrelated cause. Discussion: Ropeginterferon is a well-tolerated therapy that results in clinical improvement in half the patients, and appears to be well tolerated. These results, along with historic data suggesting possible reduction in clonal burden, suggest that ongoing studies are warranted to further understand the clinical benefit of ropeginterferon. Disclosures Zimmerman: Pharmaessentia: Current Employment. Mesa:Incyte: Research Funding; AbbVie: Research Funding; Sierra Oncology: Consultancy; CTI BioPharma: Research Funding; Promedior: Research Funding; Genentech: Research Funding; Novartis: Consultancy; Samus Therapeutics: Research Funding; LaJolla Pharmaceutical Company: Consultancy; Bristol Myers Squibb: Research Funding. OffLabel Disclosure: Clinical trial

Introduction: Myeloproliferative neoplasms (MPN), including primary myelofibrosis (PMF), essential thrombocythemia (ET) and polycythemia vera (PV), have a propensity to evolve into blast phase myeloproliferative neoplasm (BP-MPN) with a 20-year incidence rate of 9.3 %, 3.9% and 2.6%, respectively. (Szuber et al., 2019)Treatment options for BP-MPN are limited and the prognosis of these patients is dismal with a median survival of only 3.6 months and 5-year survival rate of <5%.(Tefferi et al., 2018) Considering the recent reported data on the efficacy of venetoclax when combined with hypomethylating agents (HMA) in acute myeloid leukemia (AML) in both relapsed/refractory and newly diagnosed unfit patients, we have extended such combination therapy for patients with BP-MPN. Methods: We retrospectively analyzed 14 consecutive BP-MPN patients who received venetoclax plus HMA therapy between August 2018 and June 2020. We collected data regarding clinical characteristics of chronic phase MPN and BP-MPN, cytogenetic and leukemia mutation profile, efficacy and outcome. Oral venetoclax was administered in combination with azacitidine 75 mg/m2 days 1-7 (5 patients) or decitabine 20 mg/m2 days 1-5 (9 patients). Venetoclax dose was adjusted based on drug interactions particularly with azole antifungal prophylaxis. Diagnostic, risk and response assignments were according to the 2017 European LeukemiaNet (ELN) criteria.(Döhner et al., 2017) Minimal residual disease (MRD) assessment by flow cytometry, karyotype or next-generation sequencing (NGS) was performed in a subset of patients. Results: Patient characteristics at time of leukemic transformation, treatment details, response rates and overall outcome are shown in Table 1. Median age of patients was 67 years (range 48-81) with poor-risk cytogenetics in 69% of patients. JAK2 was mutated in 10 patients (71%) and CALR in 2 (14%); other mutations included TP53 in 5 patients (36%), TET2 in 4 (29%), KRAS in 3 (21%), IDH1/2 in 3 (21%), ASXL1 in 2 (14%) and U2AF1 in 2 (14%). Eight patients (57%) received venetoclax and HMA combination therapy upfront for their BP-MPN, 2 patients (14%) had failed HMA therapy previously and one patient had prior allogeneic hematopoietic stem cell transplant (AHSCT). Two patients (14%) presented with myeloid sarcoma; one of these two patients documented partial resolution of the extramedullary tumor by imaging studies, after treatment with venetoclax plus HMA. Among the remaining 12 patients, overall response rate (ORR) was 42% (n=5) and included complete remission (CR) in 3 patients (25%) and partial remission (PR) in another 2 (17%). The best response to therapy was seen after a median of 1 month (range, 1-2). Among 3 CR responders, 2 (66.6%) had minimal residual disease negative by NGS and not evidence of preceding MPN, then they successfully transitioned to AHSCT, while the third CR patient at the time of best response showed persistence of the TP53 mutation. Additionally, one PR patient subsequently relapsed and received salvage chemotherapy followed by AHSCT. (Table 2) Although data is limited by the small cohort and short follow up when the outcome of patients treated with venetoclax in combination with HMA were compared to Mayo Clinic's historical control of patients with BP-MPN treated with HMA alone (n=26) or intensive chemotherapy (n=69), there was higher CR rate in patients treated with venetoclax and HMA (25%) compared to those receiving HMA alone (4%; p=0.048) but not to those receiving intensive chemotherapy (35%; p<0.0001). Moreover, the intensive chemotherapy cohort showed 24% of CR with incomplete hematologic recovery (CRi) not seen in patients receiving HMA alone or HMA with venetoclax (Figure1). Conclusions: The relatively high rate of complete response observed in our patients with BP-MPN were similar to those reported in a pivotal study of elderly unfit AML patients treated upfront with venetoclax + HMA with overall response rates of 68%.(DiNardo et al., 2019) Furthermore, responders included patients with adverse molecular risk factors who usually respond poorly to conventional chemotherapy (i.e. TP53 mutated patients). Our observations provide preliminary evidence for the potential efficacy of venetoclax and HMA combination therapy in BP-MPN with the goal of achieving CR/CRi followed by consolidative AHSCT wherever possible to provide durable remission and meaningful survival benefit. Disclosures Foran: Agios: Honoraria, Research Funding; Trillium: Research Funding; Takeda: Research Funding; Kura Oncology: Research Funding; Aptose: Research Funding; Aprea: Research Funding; Actinium: Research Funding; Boehringer Ingelheim: Research Funding; Abbvie: Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Revolution Medicine: Consultancy; Xencor: Research Funding; H3Biosciences: Research Funding.

Background The COVID-19 pandemic continues to challenge effective treatment delivery to hematologically-compromised patients, including those with myeloproliferative neoplasms (MPNs). MPNs are characterized by clonal proliferation of hematopoietic cell lines in bone marrow. As such, increasing reports of COVID-19 related thrombotic events highlight how MPN patients are at an increased risk in navigating potential complications during this pandemic. Mitigation strategies to lesson MPN patient exposure to COVID-19 are vital. Though, such efforts come at an inherent cost to effective healthcare delivery. Restriction of regular in-clinic treatments and reported shortages of MPN pharmacotherapies present these patients with diminishing continued care. To understand how MPN patient care has been impacted by COVID-19, an internet-based questionnaire was deployed surveying a variety of disease and pandemic related items (reported elsewhere; Palmer J et al, ASH 2020 submitted). A single free-text response item instructed respondents to: "Please tell us anything else (bad or good) about how the COVID-19 outbreak has impacted your MPN care." This qualitative analysis evaluated first-hand comments directly from patients in order to form a richer understanding of how those with MPNs have been managing disease-related care amidst this pandemic. Methods This COVID-19 survey was hosted via Mayo Clinic's secured REDCap system for online surveys and posted on MPN organizational partner websites. Surveys were completely anonymous. The free-text responses describing impacts to MPN care were each independently reviewed by 2 individuals for overall sentiment (positive, negative, both, or neutral [no impact]) and categorized for themes. The 2 reviewers were assessed for agreement. Conflicting reviews were evaluated then adjudicated by an algorithm for cases meeting selected conditions or by lead author review for all remaining cases. Descriptive statistics are reported. Results Of the 1217 consenting adult patients participating in the overall COVID-19 study, 824 provided free-text responses. Of these, respondent MPN diagnoses included, essential thrombocythemia (n=324, 39%), polycythemia vera (n=251, 30%), myelofibrosis (n=153, 19%), and other/undisclosed (96, 12%); 69% (n=567) were female; median age was 63 (range 21-93); 38% (n=313) were from the US, 38% (n=313) UK, and 24% (n=198) other/unknown. There was 89% (n=734) sentiment agreement between reviewers. Free-text responses about the impact of COVID-19 on MPN care were 49% (n=400) negative, 21% (n=177) positive, 8% (n=65) both positive and negative, and 22% (n=182) neutral/no impact. Table 1 shows a selection of MPN patient free-text responses reflecting common negative and positive sentiment themes. Negative impact (n=400): The most common negative impact involved delays or cancellations of visits or perceived inaccessibility to regular providers (n=261, 65%). Primarily this sentiment was driven by lack of clinic availability and restrictions at treatment centers or by providers. However, some respondents reported delaying or canceling visits themselves due to fear of COVID-19 exposure. Perceived health consequences from this delay were also expressed. There were 129 (32%) respondents with concern regarding changes or access to medications, including explicit drug supply shortages. Some patients resorted to self-adjusting medications and reusing single-use supplies. General anxiety, stress, and isolation were also reported (n=98, 25%). Positive impact (n=177): Availability of telemedicine comprised the majority of positive impacts of the pandemic (n=95, 54%), with many noting the reduced travel time to visits. Routine local testing coupled with follow-up telemedicine was favorable. Despite general positivity towards telemedicine, some reported preferences for in-person visits; commenting that telemedicine was impersonal, difficult to schedule or receive virtual communication, and expressed concern for lack of spleen examinations during virtual visits. Conclusion Positive and negative aspects were reported including MPN-specific issues. Healthcare systems should use such data to emerge from the COVID-19 pandemic and retain the positive impacts such as telemedicine, while developing education materials and other resources to address the reported negative impacts where possible. Disclosures Mesa: CTI BioPharma: Research Funding; Promedior: Research Funding; Novartis: Consultancy; Sierra Oncology: Consultancy; Samus Therapeutics: Research Funding; Genentech: Research Funding; AbbVie: Research Funding; Incyte: Research Funding; LaJolla Pharmaceutical Company: Consultancy; Bristol Myers Squibb: Research Funding.

Preclinical Rationale: Myelofibrosis (MF) is a chronic myeloproliferative neoplasm for which there are limited therapies. TGFβ plays a pivotal role in the pathobiology of MF by not only promoting bone marrow fibrosis (BMF) and collagen deposition, but also by enhancing the dormancy of normal but not MF hematopoietic stem cells (HSCs). TGFβ has also previously been reported to inhibit normal megakaryocyte (MK) production (Bruno et al Blood 1998). TGFβ1 promotes the synthesis of collagen by normal human mesenchymal stromal cells (MSCs) and activates the TGFβ receptor I/SMAD pathway as well as non-canonical TGFβ pathways. We generated MKs from MF subject mononuclear cells (MNCs) and showed that they elaborated significantly greater levels of TGFβ1 than TGFβ2/3 TGFβ1 treatment reduced the numbers of hematopoietic colonies generated by normal but not MF MNCs. Treatment of MSCs with AVID200, a potent TGFβ1/3 protein trap, significantly decreased MSC proliferation, phosphorylation of SMAD2, and collagen expression. Robust expression of pSMAD2 was observed in the absence of exogenous TGFβ in normal donor or MF-MKs, Addition of AVID200 to -MKs decreased pSMAD2 without affecting total SMAD2/3, indicating that AVID200 blocks the effects of autocrine TGFβ produced by MKs and led to increased numbers of MKs. Moreover, treatment of primary MF MNCs with AVID200 led to increased numbers of progenitor cells with wild type JAK2 and a reduction of mutated colonies. AVID200 blocked TGFβ1-induced p57Kip2 expression and SMAD2 activation by MF MNCs allowing the normal progenitor cells to preferentially cycle, proliferate, and form hematopoietic colonies. Clinical Trial Design: Based on these findings, a phase 1 trial of AVID200 is ongoing in INT-2/high risk MF subjects resistant or intolerant to ruxolitinib; baseline platelet count of ≥ 25 x 109/L, and grade 2/3 BMF. Subjects received intravenous AVID200 (Lots A and B) in dose cohorts of 180 mg/m2 (A), 550 mg/m2 (A), 180 mg/m2 (B) on Day 1 of a 21 day cycle. Cohorts of 3 subjects with a target toxicity rate of 30% were enrolled to estimate the maximum tolerated dose (MTD). A modified toxicity probability interval design was used. Response was assessed by IWG/ELN criteria after 6 cycles of AVID200. Subjects attaining at least a CI or SD with a decrease in BMF by ≥1 grade, continued AVID200. Clinical Trial Results: 10 subjects were enrolled (1 withdrew before receiving treatment) and 9 were treated with AVID200 and were evaluable for DLT assessment [Table1]. Median time after ruxolitinib discontinuation was 3.5 months (0.5-12.2). No DLTs were observed. Grade 3/4 AEs (regardless of attribution) were observed in 6 (66.7%) subjects. Grade 3/4 non-hematologic AEs observed were epistaxis (1, 11.1%), extraocular muscle paresis (1, 11.1%), fatigue (1, 11.1%) and rash (1, 11.1%). Grade 3/4 hematologic AEs were anemia (3, 33.3%) and thrombocytopenia (2, 22.2%) [Table 2]. The median number of cycles received was 5.7 (range 0 - 12). 5 subjects received 6+ cycles and were evaluable. CI occurred in 2 subjects [anemia, spleen and TSS (n=1); TSS (n=1)] 1 of which is still being treated, 2 subjects had SD, 1 subject with 21% blasts prior to study treatment had progressive MPN-BP. 4 subjects failed to reach response evaluation after 6 cycles, 2 had PD due to increasing splenomegaly, 1 subject received an allogeneic transplant and 1 is still being treated [Cycle 2]. The median platelet count at baseline was 114 (range: 42-290) and 159 after cycle 6 [Figure 1]. Maximum changes in platelets from baseline was +64% [range -73%, 169%] in all subjects. 7 subjects had an increase in platelets from baseline during treatment. 2 subjects normalized their platelet count from thrombocytopenic levels. The effect of AVID200 on BMF is currently being examined. 2 subjects remain on treatment. Conclusions: AVID200 a TGFβ1/3 protein trap is well tolerated in advanced MF subjects. Clinical responses were observed at the 550 mg dose and the expansion efficacy cohorts at doses 2 and 3 are enrolling 12 additional subjects. Furthermore, AVID200 therapy improved thrombocytopenia in MF subjects which may be due to AVID200 inhibiting the effects of TGFβ1 on normal MKpoiesis. Updated subject safety and efficacy data along with correlative data will be presented. Disclosures Mascarenhas: Celgene, Prelude, Galecto, Promedior, Geron, Constellation, and Incyte: Consultancy; Incyte, Kartos, Roche, Promedior, Merck, Merus, Arog, CTI Biopharma, Janssen, and PharmaEssentia: Other: Research funding (institution). Kuykendall:Blueprint Medicines: Research Funding; BMS: Research Funding; Incyte: Research Funding; Novartis: Research Funding. Komrokji:Jazz: Honoraria, Speakers Bureau; Abbvie: Honoraria; Agios: Speakers Bureau; BMS: Honoraria, Speakers Bureau; Geron: Honoraria; Incyte: Honoraria; Acceleron: Honoraria; Novartis: Honoraria. Gerds:Gilead Sciences: Research Funding; Imago Biosciences: Research Funding; Sierra Oncology: Research Funding; Celgene: Consultancy, Research Funding; Roche/Genentech: Research Funding; CTI Biopharma: Consultancy, Research Funding; Apexx Oncology: Consultancy; AstraZeneca/MedImmune: Consultancy; Pfizer: Research Funding; Incyte Corporation: Consultancy, Research Funding. Migliaccio:Novartis: Research Funding. O'Connor-McCourt:Forbius: Current Employment. Tremblay:Forius: Current Employment. Nadler:Forbius: Consultancy; Nadler Pharma Associates: Current Employment; Symphogen: Consultancy; Iksuda Therapeutics: Consultancy; Tessa Therapeutics: Consultancy. Mesa:Celgene: Research Funding; Genetech: Research Funding; Samus: Research Funding; Promedior: Research Funding; CTI: Research Funding; LaJolla Pharma: Consultancy; Incyte: Research Funding; Sierra Onc: Consultancy; Abbvie: Research Funding; Novartis: Consultancy. Hoffman:Forbius: Consultancy; Abbvie: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Dompe: Research Funding; Protagonist: Consultancy.

Myelofibrosis (MF) is a chronic myeloid neoplasm characterized by either primary myelofibrosis, or secondary MF following essential thrombocythemia or polycythemia vera. Historically, therapy has been symptom directed; however, in 2011, the first janus kinase inhibitor (JAK-i) – ruxolitinib – was approved for treatment. This medication was found to be effective in reduction of symptom burden and spleen size; however, the median duration of response is about 3 years. In addition, many patients are intolerant or develop toxicities to ruxolitinib, including patients with anemia, as well as thrombocytopenia. Therefore, there is a critical need for alternate therapeutic options for patients with MF. Additional JAK-i have been developed over the last 8 years, including fedratinib, momelotinib, and pacritinib. Fedratinib recently received approval for treatment of MF both in the first-line and second-line setting. It has shown efficacy in the first-line setting, as well as in 30% of patients who are refractory/intolerant of ruxolitinib. This review covers the trials that have led to the approval of ruxolitinib as well as fedratinib, as well as reviews of two JAK inhibitors that are still under clinical investigation: momelotinib and pacritinib.