Pacritinib (SB1518)

Catalog No.S8057

Pacritinib (SB1518) Chemical Structure

Molecular Weight(MW): 472.58

Pacritinib (SB1518) is a potent and selective inhibitor of Janus Kinase 2 (JAK2) and Fms-Like Tyrosine Kinase-3 (FLT3) with IC50s of 23 and 22 nM in cell-free assays, respectively. Phase 3.

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2. For more details, such as half maximal inhibitory concentrations (IC50s) and working concentrations of each inhibitor, please click on the link of the inhibitor of interest.
3. "+" indicates inhibitory effect. Increased inhibition is marked by a higher "+" designation.
4. Orange "√" refers to compounds which do inhibitory effects on the related isoform, but without specific value.

Biological Activity

Description Pacritinib (SB1518) is a potent and selective inhibitor of Janus Kinase 2 (JAK2) and Fms-Like Tyrosine Kinase-3 (FLT3) with IC50s of 23 and 22 nM in cell-free assays, respectively. Phase 3.
Features Dual JAK2/FLT3 inhibitor that has progressed to Phase III clinical trials for treatment of Myelofibrosis.
FLT3 (D835Y) [1]
(Cell-free assay)
JAK2 (V617F) [1]
(Cell-free assay)
FLT3 [1]
(Cell-free assay)
JAK2 [1]
(Cell-free assay)
TYK2 [1]
(Cell-free assay)
6 nM 19 nM 22 nM 23 nM 50 nM
In vitro

Pacritinib is a potent inhibitor of both wild-type JAK2 and JAK2V617F mutant (IC50= 19 nM) that is present in high frequencies among patients with MPD. Relative to JAK2, Pacritinib is two-fold less potent against TYK2 (IC50= 50 nM), 23-fold less potent against JAK3 (IC50= 520 nM) and 56-fold less potent against JAK1 (IC50= 1280 nM). Pacritinib effectively permeates cells to modulate signaling pathways downstream of JAK2, whether agonist activated or mutationally activated. Pacritinib induces apoptosis, cell cycle arrest and antiproliferative effects in JAK2WT- and JAK2V617F-dependent cells. Pacritinib inhibits cell proliferation of Karpas 1106P and Ba/F3-JAK2V617F with IC50 of 348 and 160 nM, respectively. Pacritinib inhibits endogenous colony growth derived from erythroid and myeloid progenitors with IC50 of 63 and 53 nM , respectively. [1] SB1518 also inhibits FLT3 and its mutant FLT3-D835Y(IC50= 6 nM ). Pacritinib inhibits FLT3 phosphorylation and downstream STAT, MAPK and PI3K signaling in FLT3-internal-tandem duplication (ITD), FLT3-wt cells and primary AML blast cells. Pacritinib treatment leads to a dose-dependent decrease of pFLT3, pSTAT5, pERK1/2 and pAkt in FLT3-ITD harboring MV4-11 cells with IC50 of 80, 40, 33 and 29 nM , respectively. Treatment of the primary AML blast cells with Pacritinib for 3 h leads to a dose-dependent decrease of pFLT3, pSTAT3 and pSTAT5 with an IC50 below 0.5 μM. Pacritinib induces apoptosis, cell cycle arrest and anti-proliferative effects in FLT3-mutant and FLT3-wt cells. Pacritinib inhibits cell proliferation of FLT3-ITD-harboring cells MV4-11 and primary AML blast cells with IC50s of 47 nM and 0.19-1.3 μM, respectively. [2]

In vivo Pacritinib administrated at 150 mg/kg p.o. q.d. to JAK2V617F-dependent xenograft model, significantly ameliorates splenomegaly and hepatomegaly symptoms, with 60% normalization of spleen weight and 92% normalization of liver weight and is well tolerated without significant weight loss or any hematological toxicities, including thrombocytopenia and anemia. Pacritinib induces dose-dependent inhibition of tumor growth of JAK2V617F-dependent SET-2 xenograft model (40% for 75 mg/kg and 61% for 150 mg/kg). [1] Pacritinib is efficacious in FLT3-ITD-bearing MV4-11 xenograft models. Pacritinib treated once daily for 21 consecutive days, induces dose-dependent inhibition of tumor growth (38% for 25 mg/kg, 92% for 50 mg/kg and 121% for 100 mg/kg). Complete regression is observed in 3/10 and 8/8 mice for the 50 and 100 mg/kg/day groups, respectively. [2]


Kinase Assay:[1]
+ Expand

kinase activity assays:

All assays are carried out in 384-well white microtiter plates. Compounds are 4-fold serially diluted in 8 steps, starting from 10 μM. The reaction mixture consisted of 25 μL assay buffer (50 mM HEPES pH 7.5, 10 mM MgCl2, 5 mM MnCl2, 1 mM DTT, 0.1 mM Na3VO4, 5 mM β-glycerol phosphate). For FLT3 assays, the reaction contains 2.0 μg/mL FLT3 enzyme, 5 μM of poly(Glu,Tyr) substrate and 4 μM of ATP. For JAK1 assays, the reaction contains 2.5 μg/mL of JAK1 enzyme, 10 μM of poly(Glu,Ala,Tyr) substrate and 1.0 μM of ATP. For JAK2 assays, the reaction contained 0.35 μg/mL of JAK2 enzyme, 10 μM of poly (Glu,Ala,Tyr) substrate and 0.15 μM of ATP. For JAK3 assays, the reaction contained 3.5 μg/mL of JAK3 enzyme, 10 μM of poly (Glu,Ala,Tyr) substrate and 6.0 μM of ATP. For TYK2 assays, the reaction contained 2.5 μg/mL of TYK2 enzyme, 10 μM of poly (Glu,Ala,Tyr) substrate and 0.15 μM of ATP. The reaction is incubated at room temperature for 2 h prior to addition of 13 μL PKLight® detection reagent. After 10 min incubation luminescent signals are read on a multi-label plate reader.
Cell Research:[1]
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  • Cell lines: Karpas 1106P cells
  • Concentrations: ~10 μM
  • Incubation Time: 2 days
  • Method: Cells are seeded at 30-50% confluency in 96-well plates and are treated with different concentrations of compounds (in triplicate) for 48 h. Cell viability is monitored using the CellTiter-Glo assay.
    (Only for Reference)
Animal Research:[1]
+ Expand
  • Animal Models: Human megakaryoblastic leukemia xenografts SET-2
  • Formulation: 0.5% methylcellulose (w/v) and 0.1% Tween-80 in H2O
  • Dosages: 150 mg/kg
  • Administration: oral gavage
    (Only for Reference)

Solubility (25°C)

In vitro DMSO 11 mg/mL warmed (23.27 mM)
Water <1 mg/mL
Ethanol <1 mg/mL
In vivo

* 1 mg/ml means slightly soluble or insoluble.
* Please note that Selleck tests the solubility of all compounds in-house, and the actual solubility may differ slightly from published values. This is normal and is due to slight batch-to-batch variations.

Chemical Information

Molecular Weight 472.58


CAS No. 937272-79-2
Storage powder
in solvent
Synonyms N/A

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Clinical Trial Information

NCT Number Recruitment Conditions Sponsor/Collaborators Start Date Phases
NCT02891603 Not yet recruiting Graft Vs Host Disease|GVHD H. Lee Moffitt Cancer Center and Research Institute April 30, 2017 Phase 1|Phase 2
NCT02677948 Suspended Chronic Lymphocytic Leukemia|Lymphoma, Small Lymphocytic University of Michigan Cancer Center October 2016 Phase 1|Phase 2
NCT02564536 Not yet recruiting Chronic Myelomonocytic Leukemia|Juvenile Myelomonocytic Leukemia|Atypical Chronic Myeloid Leukemia|Myeloproliferative Neoplasm|Myelodysplastic Syndromes|Myelofibrosis Washington University School of Medicine|CTI BioPharma October 2016 Early Phase 1
NCT02323607 Recruiting Recurrent Adult Acute Myeloid Leukemia|Secondary Acute Myeloid Leukemia|Therapy-Related Acute Myeloid Leukemia|Untreated Adult Acute Myeloid Leukemia Bhavana Bhatnagar|CTI BioPharma|Ohio State University Comprehensive Cancer Center January 2016 Phase 1
NCT02342353 Recruiting Non-Small Cell Lung Cancer|Nonsmall Cell Lung Cancer|Carcinoma, Non-Small-Cell Lung Washington University School of Medicine December 2015 Phase 1|Phase 2
NCT02584777 Withdrawn Primary Myelofibrosis Baxalta US Inc.|CTI BioPharma November 2015 Phase 2

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JAK Signaling Pathway Map

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Cell Lines Assay Type Concentration Incubation Time Formulation Activity Description PMID