Drugs in Clinical Pipeline: Pacritinib | Dual Kinase Inhibitor | JAK2 Inhibitor | FLT3 Inhibitor

Pacritinib [11-(2-pyrrolidin-1-yl-ethoxy)-14,19-dioxa-5,7,26-triaza-tetracyclo(19.3.1.1(2,6).1(8,12))heptacosa-1(25),2(26),3,5,8,10,12(27),16,21,23-decaene] is a novel low-molecular weight pyrimidine-based macrocycle with potent inhibitory activities against Janus Kinase 2 (JAK2) and Fms-Like Tyrosine Kinase-3 (FLT3). 

Pacritinib shows a unique kinase profile with selective inhibition of Janus Kinase-2 with IC₅₀ values of 23 and 19 nM against JAK2^WT and JAK2^V617F respectively and an IC₅₀ value of 22 nM gainst FLT3. Within the JAK family, Pacritinib has IC₅₀ values of 50, 520 and 1280 nM for TYK, JAK3 and JAK2, respectively, showing high preference for JAK2. The rest of the evaluated kinases showed less than 30% inhibition when tested against 100 nM Pacritinib at ATP concentrations equivalent to its Michaelis constant (K_m) [1].

Pacritinib: 2D and 3D Structure

The activity of Pacritinib is as follows:

IC₅₀ (JAK1 enzyme assay) = 1280 ± 370 nM
IC₅₀ (JAK2 enzyme assay) = 23 ± 6 nM
IC₅₀ (JAK2^V617F enzyme assay) = 19 nM
IC₅₀ (JAK3 enzyme assay) = 520 ± 110 nM
IC₅₀ (TYK2 enzyme assay) = 50 ± 6 nM
IC₅₀ (FLT3 enzyme assay) = 22 ± 6 nM
IC₅₀ (FLT3^D835Y enzyme assay) = 6 nM

1H NMR (Estimated) for Pacritinib

References:

1. Hart, S.; et. al. SB1518, a novel macrocyclic pyrimidine-based JAK2 inhibitor for the treatment of myeloid and lymphoid malignancies. Leukemia 2011, 25(11), 1751-1759.

Drugs in Clinical Pipeline: AZD1480

AZD1480 [(S)-5-chloro-N2-(1-(5-fluoropyrimidin-2-yl)ethyl)-N4-(5-methyl-1H-pyrazol-3-yl)pyrimidine-2,4-diamine] is an oral, potent, ATP competitive, small molecule inhibitor of Janus Kinase 2 (JAK2) kinase, with an inhibition constant (K_i) of 0.26 nM. 

To evaluate Jak family selectivity of AZD1480, enzymatic assays were carried out Jak1, Jak2, and Jak3  at K_m levels of ATP and 5 mM ATP, which is the high end of ATP concentrations in cells. AZD1480 demonstrated significant Jak2 selectivity over Jak3, in particular at high ATP concentrations and marginal selectivity over Jak1 at K_m ATP [1].

The activity of AZD1480 is as follows:

IC₅₀ (JAK1 enzyme assay, K_m ATP) = 1.3 ± 0.1 nM

IC₅₀ (JAK2 enzyme assay, K_m ATP) = less than 0.4 nM

IC₅₀ (JAK3 enzyme assay, K_m ATP) = 3.9 ± 0.7 nM

IC₅₀ (JAK1 enzyme assay, 5 mM ATP) = 41 ± 1.0 nM

IC₅₀ (JAK2 enzyme assay, 5 mM ATP) = 58 ± 2.4 nM

IC₅₀ (JAK3 enzyme assay, 5 mM ATP) = 1363 ± 113 nM

References:

1. Zinda, M.; et. al. The JAK2 inhibitor AZD1480 potently blocks Stat3 signaling and oncogenesis in solid tumors. Cancer Cell 2009, 16(6), 487-497. 

Momelotinib | JAK1, JAK2 Inhibitor | Janus Kinase Inhibitor | Therapy for Myelofibrosis

Momelotinib [N-(cyanomethyl)-4-[2-[[4-(4-morpholinyl)phenyl]amino]-4-pyrimidinyl]-benzamide] is a small-molecule, ATP-competitive and highly selective inhibitor for Janus Kinase 1 (JAK1, IC₅₀ = 11 nM) and Janus Kinase 2 (JAK2, IC₅₀ = 18 nM). Momelotinib inhibited JAK1 and JAK2 equipotently, but had an IC₅₀ that was approximately ninefold higher for the closely related JAK3 (IC₅₀ = 155 nM) kinase as compared with JAK2.

Momelotinib: 2D and 3D Structure

In a ‘single-point’ screening assay that assesses the degree of enzyme inhibition at a specified Momelotinib concentration (100 nM or 1 uM), only eight kinases (JAK1, JAK2, CDK2/A, ROCK2, MAPK8, TBK1, PRKD1 and PRKCN) showed less than 50% at 100 nM [1].

Summary

Common name: CYT387; CYT 387; CYT-387; CYT 11387; CYT-11387; CYT11387

Trademarks:

Molecular Formula: C23H22N6O2

CAS Registry Number: 1056634-68-4

CAS Name: N-(Cyanomethyl)-4-[2-(4-morpholinoanilino)pyrimidin-4-yl]benzamide

Molecular Weight: 414.47

SMILES:O=C(NCC#N)C1=CC=C(C2=NC(NC3=CC=C(N4CCOCC4)C=C3)=NC=C2)C=C1

InChI Key: ZVHNDZWQTBEVRY-UHFFFAOYSA-N

InChI: InChI=1S/C23H22N6O2/c24-10-12-25-22(30)18-3-1-17(2-4-18)21-9-11-26-23(28-21)27-19-5-7-20(8-6-19)29-13-15-31-16-14-29/h1-9,11H,12-16H2,(H,25,30)(H,26,27,28)

Activity: Treatment of myelofibrosis; Anti-neoplastics Drug; Anti-inflammatory Agents

Status: Phase I/II

Originator: Gilead Sciences

Momelotinib Synthesis

US8486941B2: This is first disclosed synthesis for Momelotinib. It doesn't appear to be industrially optimized.

WO2015191846: The scheme is derived from the patent.

Identifications:

1H NMR (Estimated) for Momelotinib

13C NMR (Estimated) for Momelotinib

Experimental: ¹³C NMR (75.5 MHz, d₆-DMSO) δ 166.04, 162.34, 160.26, 159.14, 146.14, 139.87, 134.44, 132.73, 127.80, 126.84, 120.29, 117.49, 115.50, 107.51, 66.06, 49.16, 27.68.

References:
1. Pardanani, A.; et. al. CYT387, a selective JAK1/JAK2 inhibitor: in vitro assessment of kinase selectivity and preclinical studies using cell lines and primary cells from polycythemia vera patients. Leukemia 2009, 23(8), 1441-1445.
2. Brown, B. H.; et. al. N-(cyanomethyl)-4-(2-(4-morpholinophenylamino)pyrimidin-4-yl)benzamide hydrochloride salts. WO2015191846A1

3. Burns, C. J.; et. al. Phenyl amino pyrimidine compounds and uses thereof. US8486941B2

Drugs in Clinical Pipeline: AC410

AC410 [(S)-(4-fluorophenyl)(4-((5-methyl-1H-pyrazol-3-yl)amino)quinazolin-2-yl)methanol] is a potent, selective, orally-administered, small molecule inhibitor of Janus kinase 2 (JAK2, K_d = 0.18 nM) and has potential utility in autoimmune and inflammatory indications. JAK2 mediates the signaling of specific cytokines, including IL-5, IL-6, IL-12, IL-13, IL-23, and GM-CSF; each cytokine has a specific role for the immune system. The specific and potent inhibition of these cytokines could provide a more powerful impact on diseases than a bulk inhibition of JAK family members. The specificity of AC410 for JAK2 vis-a-vis JAK1 (K_d = 2.5 nM) and JAK3 (K_d = 5 nM) gives Ambit (Now Daichii Sankyo) an opportunity within the existing market landscape [1].

Ambit’s initial JAK2 candidate was AC430 [(4-fluorophenyl)(4-((5-methyl-1H-pyrazol-3-yl)amino)quinazolin-2-yl)methanol], a racemic mixture of two enantiomers, AC410 and AC409 [(R)-(4-fluorophenyl)(4-((5-methyl-1H-pyrazol-3-yl)amino)quinazolin-2-yl)methanol]. Ambit has chosen AC410 for further clinical development based on superior pharmacokinetics and potent anti-inflammatory properties in a preclinical model, and its inhibitory activity of JAK2 in cellular assays.

JAK2 is a member of the Janus kinase family, which includes JAK1, 2, 3, and Tyk2. Each member of the family mediates the signaling of a distinct set of cytokines that are involved in activation, proliferation, and survival of immune cells. Improper activation of cytokines can induce and exacerbate inflammation within the body and lead to inflammatory diseases.

The activity of AC410 is as follows:

K_d (JAK1 binding assay) = 2.5 nM

K_d (JAK2 binding assay) = 0.18 nM

K_d (JAK3 binding assay) = 5 nM

K_d (TYK2 binding assay) = 1.6 nM

The activity of AC430/AC409 is as follows:

K_d (JAK1 binding assay) = 6/15 nM

K_d (JAK2 binding assay) = 0.3/0.5 nM

K_d (JAK3 binding assay) = 10.5/21 nM

K_d (TYK2 binding assay) = 1.8/8.8 nM

Common Name: AC410

Synonyms: AC410; AC 410; AC-410

IUPAC Name: (S)-(4-fluorophenyl)(4-((5-methyl-1H-pyrazol-3-yl)amino)quinazolin-2-yl)methanol

CAS Number: 

SMILES:

Mechanism of Action: Kinase Inhibitor; JAK2 Inhibitor

Indication: Various Cancers; Anti-inflammatory Agents; Treatment of Autoimmune diseases

Development Stage: Phase I

Company: Ambit Biosciences: Daiichi Sankyo

The JAK kinase family is a cytoplasmic protein kinase family comprising the members JAK1, JAK2, JAK3, and TYK2. They all share a similar structure characterized by the presence of seven JAK homology (JH) domains. JAK1, JAK2 and TYK2 are expressed ubiquitously in mammals, whereas JAK3 expression is limited mainly to haematopoietically derived cells. As such, JAK3 is important for leucocyte activation and proliferation; namely, natural killer (NK), T and B cells.

Growth factor or cytokine receptors that recruit JAK kinases include the interferon receptors, interleukin receptors (receptors for the cytokines IL-2 to IL-7, IL-9 to IL-13, IL-15, IL-23), various hormone receptors (erythropoietin (Epo) receptor, the thrombopoietin (Tpo) receptor, the leptin receptor, the insulin receptor, the prolactin (PRL) receptor, the granulocyte colony-stimulating factor (G- CSF) receptor, the growth hormone receptor, receptor protein tyrosine kinases (such as EGFR and PDGFR), and receptors for other growth factors (leukemia inhibitory factor (LIF), oncostatin M (OSM), IFNα/ß/γ, granulocyte-macrophage colony-stimulating factor (GM-CSF), ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1)). JAK1 and JAK3 are responsible for the signal transduction of cytokine receptors containing the IL-2 receptor common γ chain, thus mediating signalling by IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21 cytokines that are essential for the development and maturation of T lymphocytes. Conversely, JAK2 is associated with haematopoietic growth factor receptors, as well as gp40-containing cytokine receptors. 

References:
1. Holladay, M. W.; et. al. An optically active pyrazolylaminoquinazoline, and pharmaceutical compositions and methods of use thereof. WO2012030917A1