New developments in diagnosis, prognostication, and treatment of advanced systemic mastocytosis

Abstract Systemic mastocytosis (SM) has greatly benefited from the broad application of precision medicine techniques to hematolymphoid neoplasms. Sensitive detection of the recurrent KIT D816V mutation and use of next-generation sequencing (NGS) panels to profile the genetic landscape of SM variants have been critical adjuncts to the diagnosis and subclassification of SM, and development of clinical-molecular prognostic scoring systems. Multilineage KIT involvement and multimutated clones are characteristic of advanced SM (advSM), especially SM with an associated hematologic neoplasm (AHN). A major challenge is how to integrate conventional markers of mast cell disease burden (percentage of bone marrow mast cell infiltration and serum tryptase levels) with molecular data (serial monitoring of both KIT D816V variant allele frequency and NGS panels) to lend more diagnostic and prognostic clarity to the heterogeneous clinical presentations and natural histories of advSM. The approval of the multikinase/KIT inhibitor midostaurin has validated the paradigm of KIT inhibition in advSM, and the efficacy and safety of second-generation agents, such as the switch-control inhibitor ripretinib (DCC-2618) and the D816V-selective inhibitor avapritinib (BLU-285) are being further defined in ongoing clinical trials. Looking forward, perhaps the most fruitful marriage of the advances in molecular genetics and treatment will be the design of adaptive basket trials that combine histopathology and genetic profiling to individualize treatment approaches for patients with diverse AHNs and relapsed/refractory SM.

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Recent Advances in the Molecular Biology of Systemic Mastocytosis: Implications for Diagnosis, Prognosis, and Therapy

International Journal of Molecular Sciences ◽

10.3390/ijms21113987 ◽

2020 ◽

Vol 21 (11) ◽

pp. 3987 ◽

Cited By ~ 1

Author(s):

Margherita Martelli ◽

Cecilia Monaldi ◽

Sara De Santis ◽

Samantha Bruno ◽

Manuela Mancini ◽

...

Keyword(s):

Molecular Characterization ◽

Systemic Mastocytosis ◽

Gene Mutations ◽

Scoring Systems ◽

Molecular Data ◽

Loss Of Function ◽

Prognostic Information ◽

Genetic Profiling ◽

Kit D816v

In recent years, molecular characterization and management of patients with systemic mastocytosis (SM) have greatly benefited from the application of advanced technologies. Highly sensitive and accurate assays for KIT D816V mutation detection and quantification have allowed the switch to non-invasive peripheral blood testing for patient screening; allele burden has prognostic implications and may be used to monitor therapeutic efficacy. Progress in genetic profiling of KIT, together with the use of next-generation sequencing panels for the characterization of associated gene mutations, have allowed the stratification of patients into three subgroups differing in terms of pathogenesis and prognosis: (i) patients with mast cell-restricted KIT D816V; (ii) patients with multilineage KIT D816V-involvement; (iii) patients with “multi-mutated disease”. Thanks to these findings, new prognostic scoring systems combining clinical and molecular data have been developed. Finally, non-genetic SETD2 histone methyltransferase loss of function has recently been identified in advanced SM. Assessment of SETD2 protein levels and activity might provide prognostic information and has opened new research avenues exploring alternative targeted therapeutic strategies. This review discusses how progress in recent years has rapidly complemented previous knowledge improving the molecular characterization of SM, and how this has the potential to impact on patient diagnosis and management.

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Detection of Activated STAT5 in Neoplastic Mast Cells in Patients with Systemic Mastocytosis: Role of c-kit D816V.

Blood ◽

10.1182/blood.v106.11.3515.3515 ◽

2005 ◽

Vol 106 (11) ◽

pp. 3515-3515 ◽

Cited By ~ 1

Author(s):

Karoline Sonneck ◽

Matthias Mayerhofer ◽

Karoline V. Gleixner ◽

Marc Kerenyi ◽

Maria-Theresa Krauth ◽

...

Keyword(s):

Mast Cell ◽

Mast Cells ◽

Systemic Mastocytosis ◽

Cell Leukemia ◽

Oncogenic Signaling ◽

Kit Mutation ◽

Knock Out ◽

Mast Cell Leukemia ◽

Kit D816v

Abstract Recent data suggest that activated STAT5 contributes to growth and differentiation of mast cells (MC) and that STAT5-knock out mice are MC-deficient. We have recently shown that constitutively activated STAT5 acts as a potent oncogenic signaling molecule in hematopoietic progenitor cells (Cancer Cell2005;7:87–99). In the present study, we examined the expression of activated STAT5 in neoplastic MC in systemic mastocytosis (SM) and asked whether the SM-related oncogene c-kit D816V is involved in STAT5-activation. For the immunohistochemical detection of activated tyrosine phosphorylated STAT5 (P-Y-STAT5), we used the specific monoclonal antibody AX1 (Advantex) which does not react with inactive STAT5. In all patients with SM tested (indolent SM, n=11; smouldering SM, n=2; aggressive SM, n=1; mast cell leukemia, n=1; all exhibiting c-kit D816V), MC were found to display P-Y-STAT5. Expression of activated STAT5 was also demonstrable in the c-kit D816V-positive mast cell leukemia-derived cell line HMC-1. The reactivity of HMC-1 cells with AX1 antibody was abrogated by a STAT5-specific blocking-peptide. To define the role of c-kit D816V in STAT5-activation, Ba/F3 cells with doxycycline-inducible expression of c-kit D816V (Ton.kit) were employed. In these cells, induction of c-kit D816V was followed by a massive increase in phosphorylated STAT5 as determined by a specific DNA-binding assay, whereas the total amounts of STAT5-mRNA and of the STAT5-protein showed only a slight increase or remained unchanged. In summary, these data show that neoplastic MC in SM express activated STAT5 (P-Y-STAT5), and that the transforming c-kit mutation D816V leads to persistent activation of STAT5 in these cells.

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Kit Signaling Regulates Mitf Expression in Mastocytosis.

Blood ◽

10.1182/blood.v108.11.3601.3601 ◽

2006 ◽

Vol 108 (11) ◽

pp. 3601-3601

Author(s):

Youl-Nam Lee ◽

Pierre Noel ◽

Amir Shahlaee ◽

Melody Carter ◽

Reuben Kapur ◽

...

Keyword(s):

Bone Marrow ◽

Mast Cell ◽

Mast Cells ◽

Systemic Mastocytosis ◽

Tyrosine Kinase Receptor ◽

Bone Marrow Biopsies ◽

Activating Mutations ◽

Cell Assays ◽

Mast Cell Disease ◽

Mitf Expression

Abstract Mastocytosis is a heterogeneous disease arising from abnormal proliferation of mast cells. Activating mutations in codon D816 of the tyrosine kinase receptor, c-kit, are found in the majority of adult patients with systemic mastocytosis, an aggressive form of the disease. Constitutive activation of the Kit signaling pathway is critical to the transformed phenotype, and thus understanding how this pathway regulates downstream events is of great importance. A number of transcription factors are also essential to mast cell development, including the Microphthalmia-associated transcription factor (Mitf). We examined Mitf expression in bone marrow biopsies from nine patients with systemic mastocytosis by immunohistochemistry; we found that Mitf is highly expressed in all cases with the D816V mutation. In contrast, Mitf is not highly expressed in non-malignant mast cells in the bone marrow from patients with aplastic anemia and leukemia, suggesting thatMitf expression is regulated by Kit-dependent signalsMitf may play a role in the transformed phenotype of mastocytosis.We show that in normal mast cells, Kit signaling markedly upregulates Mitf expression. In both normal and malignant mast cells, pharmacologic inhibitors of Kit, and the downstream kinase, PI3K, block Mitf expression. To examine whether Mitf is required for transformed phenotype from constitutive Kit signaling in mast cells, we have used a shRNA-expressing lentivirus to knockdown Mitf expression in mastocytosis cell lines. We found that silencing of Mitf markedly impaired growth in proliferation and colony forming cell assays. This work demonstrates a link between two critical factors, Kit and Mitf, in the development of malignant mast cell disease.

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KIT Inhibitor Midostaurin in Patients with Advanced Systemic Mastocytosis: Results of a Planned Interim Analysis of the Global CPKC412D2201 Trial

Blood ◽

10.1182/blood.v120.21.799.799 ◽

2012 ◽

Vol 120 (21) ◽

pp. 799-799 ◽

Cited By ~ 15

Author(s):

Jason Gotlib ◽

Hanneke C. Kluin-Nelemans ◽

Tracy I. George ◽

Cem Akin ◽

Karl Sotlar ◽

...

Keyword(s):

Mast Cell ◽

Board Of Directors ◽

Null Hypothesis ◽

Systemic Mastocytosis ◽

Extension Phase ◽

Advisory Committees ◽

Grade 3 ◽

Stage 1 ◽

Median Change ◽

Kit D816v

Abstract Abstract 799 Background: Aggressive systemic mastocytosis (ASM) and mast cell leukemia (MCL) with or without an associated clonal hematologic non-mast cell lineage disease (AHNMD) are myeloproliferative neoplasms (MPN) with inadequate treatment options. The activating KIT D816V mutation occurs in ≈80% of patients (pts) with these advanced forms of SM and is central to disease pathogenesis. Midostaurin is an oral inhibitor of multiple tyrosine kinases, including wild-type and D816-mutated KIT. Promising results of an investigator-initiated trial (Gotlib et al. Blood. 2010;116:316) led to initiation of this multicenter phase 2 study (NCT00782067) of midostaurin in pts with advanced SM. Here, we report the efficacy and preliminary safety results of stage 1 of this trial. Methods: Midostaurin (100 mg BID) was administered continuously in 28-d cycles until progression or intolerable toxicity. Enrollment into an extension phase was permitted if the null hypothesis of an overall response rate (ORR) ≤ 30% was rejected per Fleming 2-stage design. Pts were required to have ≥ 1 measurable C-finding(s) (CF; eg, cytopenias, liver dysfunction) considered related to SM. The primary endpoint was ORR (major response [MR] + partial response [PR] according to Valent criteria) occurring in the first 6 cycles and maintained for ≥ 8 weeks (wk). International Working Group criteria for myelodysplastic syndrome (MDS; with slight modifications) were used to evaluate changes in transfusion dependence. Results: 62 pts were enrolled in stage 1, of whom 40 (65%) were eligible for efficacy evaluation. Reasons for ineligibility included absence of measurable CF (n = 11) or CF considered unrelated to SM (n = 11). Median age of eligible pts (25 males, 63%) was 64.5 y (range: 48–80 y). 33 (83%) pts had ASM (27 with an AHNMD) and 7 (18%) had MCL (3 with an AHNMD). AHNMDs (n=30) included 10 chronic myelomonocytic leukemia (CMML), 10 MDS/MPN-unclassified (MDS/MPN-u), 4 hypereosinophilic syndrome/chronic eosinophilic leukemia (HES/CEL), and 6 other subtypes. 22 (55%) pts received at least 1 prior therapy (median: 1.5; range: 1–4). 28 (70%) pts were KIT D816V/Y–positive, 3 (8%) were KIT D816V/Y–negative, and 9 (23%) were not evaluable for mutation status. The ORR was 60% (24/40), and most responses were MRs (21/24; Table). With a median follow-up of 27 months (mo), the median duration of response and median overall survival (OS) have not been reached. Of the 7 pts with MCL, 4 (57%) achieved an MR, including 3 ongoing incomplete remissions (IR) (19+ mo in 2 pts and 32+ mo in 1 pt). The OS in MCL pts was 22.6 mo. Additionally, 3 of 4 responding ASM/MCL-HES/CEL pts exhibited resolution of blood eosinophilia (mean baseline % and absolute eosinophils: 64% and 15.6 × 109/L). Median change in serum tryptase level among the 40 pts was −61% (range: −97% to 16%), with 16 (40%) pts exhibiting a ' 50% reduction lasting ≥ 8 wk. Median change in marrow mast cell (MC) burden in 32 evaluable pts was −41% (range: −92% to 83%), with 15/32 (47%) pts exhibiting a ≥ 50% reduction. All 62 pts received at least 1 dose of midostaurin and were included in the safety analysis. Grade 3/4 hematologic adverse events (AEs) considered drug-related were neutropenia (11%), anemia (3%), and thrombocytopenia (3%). The most common grade 3/4 drug-related non-hematologic AEs were fatigue (6%), nausea (6%), vomiting (5%), diarrhea (5%), and increased lipase (5%). As of March 15, 2012, therapy was discontinued in 26/40 pts: 7 for AEs (5 drug-related), 12 for disease progression, and 7 for other reasons. 3 of 30 pts with an AHNMD (2 CMML and 1 MDS/MPN-u) developed AML. Conclusion: In advanced SM pts, midostaurin was well tolerated and demonstrated a high rate of durable responses, including in MCL, which historically has a dire prognosis. The drug can produce significant reductions in MC burden, indicating the potential for disease modification. The stage 1 ORR was sufficient to reject the null hypothesis and permitted enrollment in the extension phase, where full accrual of 116 pts has been completed. Disclosures: Gotlib: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding. George:Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees. Akin:Novartis: Consultancy. Sotlar:Novartis: Consultancy. Awan:Allos Therapeutics: Speakers Bureau. Morariu:Novartis: Employment. Squier:Novartis: Employment. Villeneuve:Novartis: Employment. Emery-Salbert:Novartis: Employment. Horny:Novartis: Consultancy. Valent:Novartis: Consultancy, Honoraria. Reiter:Novartis: Consultancy, Honoraria.

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Mast cell leukemia

Blood ◽

10.1182/blood-2012-07-442400 ◽

2013 ◽

Vol 121 (8) ◽

pp. 1285-1295 ◽

Cited By ~ 96

Author(s):

Sophie Georgin-Lavialle ◽

Ludovic Lhermitte ◽

Patrice Dubreuil ◽

Marie-Olivia Chandesris ◽

Olivier Hermine ◽

...

Keyword(s):

Mast Cell ◽

Mast Cells ◽

Cell Activation ◽

De Novo ◽

Systemic Mastocytosis ◽

Mast Cell Activation ◽

Cell Leukemia ◽

Mast Cell Leukemia ◽

Kit D816v

Abstract Mast cell leukemia (MCL) is a very rare form of aggressive systemic mastocytosis accounting for < 1% of all mastocytosis. It may appear de novo or secondary to previous mastocytosis and shares more clinicopathologic aspects with systemic mastocytosis than with acute myeloid leukemia. Symptoms of mast cell activation—involvement of the liver, spleen, peritoneum, bones, and marrow—are frequent. Diagnosis is based on the presence of ≥ 20% atypical mast cells in the marrow or ≥ 10% in the blood; however, an aleukemic variant is frequently encountered in which the number of circulating mast cells is < 10%. The common phenotypic features of pathologic mast cells encountered in most forms of mastocytosis are unreliable in MCL. Unexpectedly, non-KIT D816V mutations are frequent and therefore, complete gene sequencing is necessary. Therapy usually fails and the median survival time is < 6 months. The role of combination therapies and bone marrow transplantation needs further investigation.

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A 3-Part, Phase 2 Study of Bezuclastinib (CGT9486), an Oral, Selective, and Potent KIT D816V Inhibitor, in Adult Patients with Nonadvanced Systemic Mastocytosis (NonAdvSM)

Blood ◽

10.1182/blood-2021-147072 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 3642-3642

Author(s):

Frank Siebenhaar ◽

Jason Gotlib ◽

Michael W. Deininger ◽

Daniel J. DeAngelo ◽

Francis Payumo ◽

...

Keyword(s):

Mast Cell ◽

Board Of Directors ◽

Research Funding ◽

Systemic Mastocytosis ◽

Symptom Burden ◽

Phase 2 ◽

Advisory Committees ◽

Management Committee ◽

Study Management ◽

Kit D816v

Abstract Systemic mastocytosis (SM) is characterized by mast cell infiltration of ≥ 1 extracutaneous organs and encompasses a spectrum of diagnoses that can range from a non-advanced to advanced disease (Shomali et al, 2018). There are two nonadvanced variants of SM: indolent systemic mastocytosis (ISM), which accounts for approximately 85% and smoldering systemic mastocytosis (SSM), which includes about 5% of the general SM population (Cohen et al, 2014, Jennings et al, 2014). ISM is characterized by 0 or 1 B-findings and SSM by 2 or more B findings and absence of organ damage or an associated hematologic neoplasm (Gotlib et al, 2018). There are currently no approved therapies to treat the underlying disease of ISM or SSM. Although anti-mediator therapies (e.g. anti-H1 and H2 antihistamines, leukotriene receptor antagonists, cromolyn sodium, corticosteroids) are used to control symptoms such as anaphylaxis, GI intolerance, and flushing to improve quality of life, their effectiveness and tolerability are variable. Many patients experience a persistently high symptom burden despite maximized anti-mediator therapies. Because the molecular pathogenesis of SM is driven by KIT D816V mutations in 95% of patients (Garcia-Montero et al, 2006, Jara-Acevedo et al, 2015, Vaes et al, 2017), other agents targeting this mutated kinase have been used to treat the spectrum of SM variants; however, toxicities such as cognitive impairment, GI effects, intracranial hemorrhage, and edema may limit dosing and thus efficacy. In addition to targeting KIT D816V, bezuclastinib was designed to avoid other closely related kinases with known liabilities, such as PDGFRα, PDGFRβ, wild-type KIT, VEGFR2 (KDR), and CSF1R (FMS). Furthermore, bezuclastinib has demonstrated minimal brain penetration and no CNS toxicities have been identified in preclinical studies. Preliminary clinical activity with bezuclastinib has been observed in patients with advanced solid tumors or locally advanced, unresectable, or metastatic gastrointestinal stromal tumor (GIST). A reduction in KIT exon 17 mutational burden was observed in patients treated with bezuclastinib. This reduction was temporally associated with a reduction in tumor burden supporting bezuclastinib as an active therapy in KIT-driven diseases (Wagner et al, 2018). This is a multi-center, Phase 2, double blind, placebo-controlled, 3-part clinical study to evaluate the safety, efficacy, and biomarker correlates (e.g. bone marrow mast cell percentage, serum tryptase level, and KIT D816V mutation burden) of the KIT inhibitor bezuclastinib in patients with ISM and SSM. This study will enroll patients with SSM and moderate-to-severe ISM who have inadequate control of their symptoms despite at least 2 anti-mediator treatments. Part 1 of the study is intended to determine the recommended dose of bezuclastinib in Part 2. Subjects will be randomized to placebo or 1 of 3 doses of bezuclastinib which will be administered in combination with a baseline regimen of best supportive care (BSC). Part 2 will evaluate the efficacy of bezuclastinib at the selected dose as compared with placebo. Efficacy will be measured by the reduction of symptom burden as assessed by the mastocytosis activity score (MAS), a disease specific patient reported outcome tool (Siebenhaar et al, 2018). In Part 3, patients who have completed treatment in Part 1 or Part 2 of the study, including those initially randomized to placebo, may participate in a long-term extension and receive open-label bezuclastinib in combination with BSC. The study will enroll approximately 138 subjects. Data from this study will support further development of bezuclastinib in SM. Disclosures Gotlib: Cogent Biosciences: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Chair for the Eligibility and Central Response Review Committee, Research Funding; PharmaEssentia: Honoraria, Membership on an entity's Board of Directors or advisory committees; Kartos: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Research Funding; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Deciphera: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Allakos: Consultancy; Incyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Blueprint Medicines: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Deininger: Novartis: Consultancy, Research Funding; SPARC, DisperSol, Leukemia & Lymphoma Society: Research Funding; Incyte: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Part of a Study Management Committee, Research Funding; Blueprint Medicines Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Part of a Study Management Committee, Research Funding; Fusion Pharma, Medscape, DisperSol: Consultancy; Sangamo: Consultancy, Membership on an entity's Board of Directors or advisory committees. DeAngelo: Incyte: Consultancy; Jazz: Consultancy; Novartis: Consultancy, Research Funding; Pfizer: Consultancy; Servier: Consultancy; Takeda: Consultancy; Abbvie: Research Funding; Forty-Seven: Consultancy; Autolus: Consultancy; Amgen: Consultancy; Agios: Consultancy; Blueprint: Research Funding; Glycomimetrics: Research Funding. Payumo: Cogent Biosciences, Inc: Current Employment. Mensing: Cogent Biosciences, Inc.: Current Employment. Jolin: Cogent Biosciences: Current Employment. Sachs: Cogent Biosciences: Current Employment. George: Bristol Meyers Squibb: Consultancy; Blueprint Medicines: Consultancy; Celgene: Consultancy; Incyte Corporation: Consultancy. OffLabel Disclosure: study of investigational agent

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Midostaurin (PKC412) Demonstrates a High Rate of Durable Responses in Patients with Advanced Systemic Mastocytosis: Results from the Fully Accrued Global Phase 2 CPKC412D2201 Trial

Blood ◽

10.1182/blood.v124.21.636.636 ◽

2014 ◽

Vol 124 (21) ◽

pp. 636-636 ◽

Cited By ~ 5

Author(s):

Jason Gotlib ◽

Hanneke C. Kluin-Nelemans ◽

Tracy I. George ◽

Cem Akin ◽

Karl Sotlar ◽

...

Keyword(s):

Mast Cell ◽

Research Funding ◽

Systemic Mastocytosis ◽

Organ Damage ◽

High Rate ◽

Advisory Committees ◽

Laboratory Services ◽

Grade 3 ◽

Stage 1 ◽

Kit D816v

Abstract Background: Patients (pts) with advanced systemic mastocytosis (SM), including aggressive SM (ASM) and mast cell leukemia (MCL) ± associated clonal hematologic non–mast cell lineage disease (AHNMD), have a poor prognosis with few effective treatment options. More than 80% of pts express the activating KIT D816V mutation. The oral multikinase inhibitor midostaurin inhibits wild-type and D816-mutated KIT. In this global phase 2 trial (NCT00782067), the largest prospective trial in advanced SM, a planned interim analysis of stage 1 pts demonstrated a high overall response rate (ORR) with reductions in marrow mast cell (MC) burden and a favorable safety profile (Gotlib et al, Blood 2012). Updated stage 1 results showed improvements in symptoms and quality of life (QOL) (Gotlib et al, Blood 2013). Here, we report primary results for the fully accrued trial. Methods: This single-arm trial consisted of an adapted Fleming 2-stage design. Midostaurin 100 mg twice daily was administered in continuous 28-day cycles until progression or unacceptable toxicity. Eligibility and responses (modified from Valent et al,Leuk Res 2003) were adjudicated by study steering committee (SSC). Histopathology was centrally assessed. Eligible pts had ≥ 1 measurable C-finding (CF) defined as SM-related organ damage. The primary endpoint was ORR (major response [MR] + partial response [PR]) occurring in the first 6 cycles and maintained for ≥ 8 weeks (wk). Results: Of 116 enrolled pts, 89 (77%) were eligible for efficacy evaluation; pts were considered ineligible by the SSC due to absence of measurable CF (n = 14) or organ damage considered unrelated to SM (n = 13). Median age was 64 years (range 25-82). Overall, 73 pts (82%) had ASM, including 57 (78%) with an AHNMD (ASM-AHNMD); 16 (18%) had MCL, including 6 (38%) with an AHNMD (MCL-AHNMD). AHNMDs included chronic myelomonocytic leukemia (n = 25), myelodysplastic/myeloproliferative neoplasm unclassifiable (n = 22), hypereosinophilic syndrome/chronic eosinophilic leukemia (HES/CEL; n = 5), and 11 other subtypes. A total of 37 pts (42%) had received ≥ 1 prior therapy (median 1; range 1-4). Seventy-seven pts (87%) were positive and 10 pts (11%) were negative for KIT D816V/Y/L mutation; 2 pts were not evaluable. The ORR was 60% (53/89); most responses were MRs (40/53, 75%), subtyped as incomplete remission (IR) in 36%, pure clinical response in 28%, and unspecified in 11%. PRs included good PR (GPR) in 21% and minor PR in 4% of pts. Overall, 12%, 11%, and 17% of pts had stable disease, progressive disease, or were not evaluable for response, respectively. After a median follow-up of 26 months (mo; range 12-54), the median duration of response (DOR) and median overall survival (OS) were 24.1 and 28.7 mo, respectively (Figure). Median OS in responders was 44.4 mo. Of 16 MCL pts, 8 responded, including 7 MRs (44%); median DOR was not reached (NR), with 3 IRs ongoing (49+, 33+, and 19+ mo). Median OS was 9.4 mo among all pts with MCL and NR among responders. Median change in MC burden in 72 evaluable pts was -59% (range -96% to 160%); 41 pts (57%) had ≥ 50% reduction. Median best change in serum tryptase level in 89 evaluable pts was -58% (range -99% to 185%); 32 pts (36%) had ≥ 50% reduction lasting ≥ 8 wk. Four of 5 responding ASM/MCL-HES/CEL pts (1 IR, 3 GPR) also had complete resolution of eosinophilia (mean % and absolute eosinophils at baseline: 57% and 12.4 × 109/L). Improvements in symptoms and QOL were consistent with those reported previously (Gotlib et al, Blood 2013). All 116 pts received ≥ 1 midostaurin dose and were evaluable for safety. Grade 3/4 drug-related hematologic adverse events (AEs) were neutropenia (5%), leukopenia (4%), febrile neutropenia (3%), anemia (3%), and thrombocytopenia (3%). Low-grade nausea was common but usually manageable with antiemetics. The most frequent grade 3/4 drug-related non-hematologic AEs included nausea (6%), vomiting (6%), fatigue (4%), and increased lipase/amylase (4%/3%). As of July 9, 2013, 65 pts had discontinued therapy, most commonly due to progression (n = 31) and AEs (n = 18; 11 were considered drug related [3 hematologic and 8 non-hematologic AEs]). Seven patients developed acute myeloid leukemia related to a prior AHNMD. Conclusions: Midostaurin exhibits a high rate of durable responses in pts with advanced SM, particularly in MCL, which has a dismal prognosis. The reductions in MC burden suggest that midostaurin may impact the natural history of the disease. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures Gotlib: Novartis Pharmaceuticals Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding, Travel Support Other. George:Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees. Akin:Novartis: Consultancy. Sotlar:Novartis Pharma: Laboratory Services, Laboratory Services Other; Nanostring Technologies: Consultancy. Hermine:Novartis: Research Funding. Awan:Boehringer Ingelheim: Consultancy; Lymphoma Research Foundation: Research Funding. Mauro:Ariad: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding; Novartis Oncology: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Speakers Bureau. Sternberg:Novartis Pharmaceuticals Corporation: Employment, Equity Ownership. Villeneuve:Novartis Pharma AG: Employment. Emery-Salbert:Novartis: Employment. Stanek:Novartis Pharmaceuticals Corporation: Employment. Hartmann:Novartis: Consultancy. Horny:Novartis: Consultancy. Valent:Novartis: Consultancy, Honoraria, Research Funding. Reiter:Novartis: Consultancy, Honoraria.

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Inhibitory Effects of Midostaurin and Blu-285 on Myeloid Progenitor Cells Derived from Patients with Multi-Mutated KIT D816V+ Advanced Systemic Mastocytosis

Blood ◽

10.1182/blood.v128.22.1964.1964 ◽

2016 ◽

Vol 128 (22) ◽

pp. 1964-1964 ◽

Cited By ~ 2

Author(s):

Mohamad Jawhar ◽

Nicole Naumann ◽

Sebastian Kluger ◽

Juliana Schwaab ◽

Georgia Metzgeroth ◽

...

Keyword(s):

Mast Cell ◽

Progenitor Cells ◽

Kinase Inhibitor ◽

Systemic Mastocytosis ◽

Relative Reduction ◽

Inhibitory Effects ◽

Dose Dependent ◽

Kit D816v

Abstract Recent data have highlighted that the molecular pathogenesis of advanced systemic mastocytosis (advSM) is complex. In addition to the phenotypically most important mutations in KIT, e.g. KIT D816V in 80-90% of patients, one or more additional mutations, e.g. in SRSF2, ASXL1, RUNX1, CBL, JAK2 and others, are present in 60-70% of patients (Jawhar et al., Leukemia 30, 2016). In individual patients, a complex mutational profile is detected not only in mature mast cells (MCs) but also in myeloid progenitors derived from granulocyte-macrophage colony-forming progenitor cells (CFU-GM), indicating multi-lineage involvement of all identified mutations in the vast majority of patients (Jawhar et al., Leukemia 29, 2015). Midostaurin, a multi-targeted kinase inhibitor, has demonstrated an overall response rate of 60% in advSM patients (Gotlib et al., NEJM 374, 2016). BLU-285 is a highly selective KIT D816V kinase inhibitor which has demonstrated biochemical activity on the mutated KIT enzyme (KIT D816V IC50 = 0.27 nM). In the current study, we sought to a) investigate the inhibitory effects of midostaurin and BLU-285 on single-cell-derived CFU-GM from bone marrow mononuclear cells derived from multi-mutated KIT D816V+ advSM patients and b) correlate the midostaurin CFU-GM data with clinical and various response parameters in midostaurin-treated advSM patients. The mutational status of CFU-GM colonies (median colonies per patient, n=20; range 10-30) was analyzed for KIT D816V and additional mutations by PCR followed by Sanger Sequencing. In 10 multi-mutated advSM patients (aggressive SM [n=8] or mast cell leukemia [n=2] with an associated hematological neoplasm), CFU-GM colonies were screened prior to midostaurin (month 0, n=10) and, if available, at month 6 on midostaurin (n=8). At month 0, a median of 90% (range, 40-100) CFU-GM colonies were KIT D816V+, while at month 6 a median of 70% (range, 5-100) CFU-GM colonies were KIT D816V+. A significant relative reduction (≥50%) in the proportion of KIT D816V+ colonies at month 6 was observed in 4/8 (50%) patients. Midostaurin-naïve CFU-GM were incubated with midostaurin at concentrations up to 1000 nM and showed a dose-dependent significant reduction (≥50%) of KIT D816V+ colonies in 1/7 (14%) patients. Overall, the in vitro effects correlated with the in vivo effects of midostaurin on CFU-GM and established IWG-MRT-ECNM response criteria (e.g. mast cell infiltration in BM, serum tryptase level) and KIT D816V allele burden in peripheral blood. Midostaurin-naïve CFU-GM from 7/10 (70%) patients were also incubated with different concentrations of BLU-285 ranging from 0 to 75 nM. A dose-dependent, significant relative reduction (≥50%) of KIT D816V+ CFU-GM colonies was observed at concentrations between 45 and 75nM in 5/7 (71%) patients. Of interest, 3/5 (60%) in vitro responders to BLU-285 were resistant to midostaurin (in vivo and in vitro) while CFU-GM colonies from 2 patients resistant to BLU-285 were also resistant to midostaurin. In addition to KIT D816V, recurrent molecular aberrations (median 2/patient, range 1-3) were identified in all patients, most frequently in SRSF2 (n=9), TET2 (n=7) and ASXL1 (n=4). Neither drug had an effect on the relative frequency of additional mutations in CFU-GM colonies. In summary, we conclude that a) the relative reduction of KIT D816V+ CFU-GM colonies between month 0 and month 6 on midostaurin correlates with clinical response, b) the CFU-GM colony assays may provide useful information for prediction of response to midostaurin, c) the highly selective KIT D816V inhibitor BLU-285 has significant activity against KIT D816V, even in cases which are resistant to midostaurin, and d) neither drug had an effect on the prognostically relevant additional mutations. Disclosures Evans: Blueprint Medicines: Employment, Equity Ownership. Gardino:Blueprint Medicines Corporation: Employment. Lengauer:Blueprint Medicines Corporation: Employment.

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Response Criteria in Advanced Systemic Mastocytosis: Evolution in the Era of KIT Inhibitors

International Journal of Molecular Sciences ◽

10.3390/ijms22062983 ◽

2021 ◽

Vol 22 (6) ◽

pp. 2983

Author(s):

William Shomali ◽

Jason Gotlib

Keyword(s):

Mast Cell ◽

Mast Cells ◽

Systemic Mastocytosis ◽

Myeloproliferative Neoplasms ◽

Organ Damage ◽

Response Criteria ◽

Molecular Response ◽

Tryptase Level ◽

Hematologic Neoplasm ◽

Kit D816v

Systemic mastocytosis (SM) is a rare clonal hematologic neoplasm, driven, in almost all cases, by the activating KIT D816V mutation that leads to the growth and accumulation of neoplastic mast cells. While patients with advanced forms of SM have a poor prognosis, the introduction of KIT inhibitors (e.g., midostaurin, and avapritinib) has changed their outlook. Because of the heterogenous nature of advanced SM (advSM), successive iterations of response criteria have tried to capture different dimensions of the disease, including measures of mast cell burden (percentage of bone marrow mast cells and serum tryptase level), and mast cell-related organ damage (referred to as C findings). Historically, response criteria have been anchored to reversion of one or more organ damage finding(s) as a minimal criterion for response. This is a central principle of the Valent criteria, Mayo criteria, and International Working Group-Myeloproliferative Neoplasms Research and Treatment and European Competence Network on Mastocytosis (IWG-MRT-ECNM) consensus criteria. Irrespective of the response criteria, an ever-present challenge is how to apply response criteria in patients with SM and an associated hematologic neoplasm, where the presence of both diseases complicates assignment of organ damage and adjudication of response. In the context of trials with the selective KIT D816V inhibitor avapritinib, pure pathologic response (PPR) criteria, which rely solely on measures of mast cell burden and exclude consideration of organ damage findings, are being explored as more robust surrogate of overall survival. In addition, the finding that avapritinib can elicit complete molecular responses of KIT D816V allele burden, establishes a new benchmark for advSM and motivates the inclusion of definitions for molecular response in future criteria. Herein, we also outline how the concept of PPR can inform a proposal for new response criteria which use a tiered evaluation of pathologic, molecular, and clinical responses.

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Nintedanib Targets KIT D816V Neoplastic Cells Derived from Induced Pluripotent Stem cells of Systemic Mastocytosis

10.1101/2020.05.06.080150 ◽

2020 ◽

Author(s):

Marcelo A. S. Toledo ◽

Malrun Gatz ◽

Stephanie Sontag ◽

Karoline V. Gleixner ◽

Gregor Eisenwort ◽

...

Keyword(s):

Stem Cells ◽

Mast Cell ◽

Progenitor Cells ◽

Pluripotent Stem Cells ◽

Systemic Mastocytosis ◽

Hematopoietic Progenitor Cells ◽

Patient Specific ◽

Hematopoietic Progenitor ◽

Induced Pluripotent ◽

Kit D816v

AbstractThe KIT D816V mutation is found in more than 80% of patients with systemic mastocytosis (SM) and is key to neoplastic mast cell (MC) expansion and accumulation in affected organs. KIT D816V therefore represents a prime therapeutic target for SM. Here we generated a panel of patient-specific KIT D816V induced pluripotent stem cells (iPSCs) from patients with aggressive SM (ASM) and mast cell leukemia (MCL) to develop a patient-specific SM disease model for mechanistic and drug discovery studies. KIT D816V iPSCs differentiated into neoplastic hematopoietic progenitor cells and MCs with patient-specific phenotypic features, thereby reflecting the heterogeneity of the disease. CRISPR/Cas9n-engineered KIT D816V human embryonic stem cells (ESCs), when differentiated into hematopoietic cells, recapitulated the phenotype observed for KIT D816V iPSC hematopoiesis. KIT D816V causes constitutive activation of the KIT tyrosine kinase receptor and we exploited our iPSCs and ESCs to investigate new tyrosine kinase inhibitors targeting KIT D816V. Our study identified nintedanib as a novel KIT D816V inhibitor. Nintedanib selectively reduced the viability of iPSC-derived KIT D816V hematopoietic progenitor cells and MCs in the nanomolar range. Nintedanib was also active on primary samples of KIT D816V SM patients. Molecular docking studies show that nintedanib binds to the ATP binding pocket of inactive KIT D816V. Our results suggest nintedanib as a new drug candidate for KIT D816V targeted therapy of advanced SM.

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