Tyrosine Kinase 2 (TYK2) Allosteric Inhibitors To Treat Autoimmune Diseases
Yu Chang,† Shilin Xu,‡ and Ke Ding*,†
International Cooperative Laboratory of Traditional Chinese Medicine Modernization and Innovative Drug Development of Chinese Ministry of Education (MoE), The First Affiliated Hospital & School of Pharmacy, Jinan University, 601 Huangpu Avenue West, Guangzhou 510632, China
embers of the Janus family of kinase (JAK1, 2, 3, and TYK2) have been recognized as essential modulators of inflammation and immunity processes.1 A number of small molecule pan-JAK inhibitors have been approved by regulatory agencies or are in different stages of clinical investigation.2 However, almost all of these catalytically active site-directed JAK inhibitors display significant undesirable adverse effects that are being attributed to the low target specificity within the JAK family or across the kinome.2 TYK2 is a member of JAK family, regulating the signaling of a wide range of pro- inflammatory cytokines including IL12, IL23, and type 1 interferons (IFNα). Collective evidence supports that selective deactivation of TYK2 could be a novel promising therapeutic strategy with an optimal benefit-safety balance for the treatment of human autoimmune diseases including multiple sclerosis, Crohn’s disease, psoriasis, etc.3 Selective inhibition of TYK2 is a formidable challenge because of the high sequence homology within the catalytic domains of the JAK family kinases and the similarity of the ATP binding pocket of the human kinome. Encouragingly, the distinguishing catalytically inactive pseudokinase domain (JH2) in the JAK family could provide an ideal “allosteric” site for selective TYK2 inhibitory discovery. Wrobleski, Moslin, et al. from Bristol-Myers Squibb (BMS) have now disclosed the discovery of BMS-986165 (1) as the first JH2-targeting allosteric TYK2 inhibitor candidate
undergoing phase III clinical trial for psoriasis.4,5
The work published in this issue of the Journal of Medicinal Chemistry by Wrobleski, Moslin, et al. describes the detailed “hit-to-candidate” evolution of a series of N-methyl pyridazine- 3-carboXamide-based selective TYK2 allosteric inhibitors targeting the pseudokinase JH2 domain (Figure 1). Through screening a corporate compound collection specifically against the TYK2 JH2 domain with a scintillation proXimity assay (SPA), the BMS team identified a novel nicotinamide-based TYK2 JH2 inhibitor 2. The compound potently inhibited JH2 SYK2 with a single-digit nM IC50 value and suppressed IL-23 and IFNα signaling with IC50 values of 89 and 37 nM, respectively. However, compound 2 exhibited poor selectivity over the catalytic (JH1) domains of other JAK family members and displayed promiscuous activity in a kinome selectivity screen. Nevertheless, because of its good metabolic stability and high ligand efficiency, hit 2 was selected as a starting point for further multiparameter optimization of potency, selectivity, and drug-like properties.
A number of effective medicinal chemistry strategies were adopted to perform the “hit-to-candidate” optimization. (1) Structure-based drug design to confer target specificity. Structural feature analysis revealed the presence of a unique “alanine pocket” formed by a rare Ala671 residue in the TYK2 JH2 domain, which could potentially accommodate an N- methyl group in the C3- amide moiety. The methyl introduction indeed remarkably improved the target specificity over the JH1 domains of the JAK family members, as well as the kinome-selectivity of 265 known kinases, but the modification barely affected the inhibitory potency again the TYK2 JH2 domain. (2) Deuterium incorporation to attenuate metabolism of demethylation. I
n vivo N-demethylation of the C3 amides would generate a less selective primary amide metabolite. To minimize the potential side effect caused by the primary amide metabolite, a deuterium incorporation strategy was successfully applied to attenuate the metabolic liability of the methyl amide. (3) Isosteric replacement of the polar core to improve permeability. Through an isosteric replacement of the central polar pyridine core with a less basic but more hydrophobic pyridazine core, the BMS team increased the Caco-2 permeability of the compounds remarkably without sacrificing potency. (4) Reducing aromaticity to eliminate hERG activity. To decrease the hERG blocking activity to avoid potential cardiotoXicity of the molecules, the researchers replaced the peripheral 2-aminopyidine with a cyclopropyla- mide to disrupt the potential π-stacking interaction with the aromatic ring-rich hERG channel to achieve significantly reduced hERG channel inhibition. (5) A drug discovery approach, a methyl-1,2,4-triazole was identified to displace the structural water mediating the original hydrogen bond in the 3′ position, resulting in improvement of the potency in human whole blood. Through a combination of these effective lead optimization strategies, the BMS scientists successfully identified compound 1 as a highly promising clinical candidate, which represents a major breakthrough in the development of selective TYK2 inhibitors for the treatment of inflammation and autoimmune diseases. Compound 1 exhibited potent binding affinity to the TYK2 JH2 domain with an IC50 of 0.2 nM in the homogeneous time-resolved fluorescence (HTRF) assay and strongly suppressed IL-23/IFNα signaling in a cellular reporter assay (IC50 = 5 nM) and in human whole blood (hWB) assays (IC50 = 13 nM). In a Morrison titration assay, 1 displayed specific binding to TYK JH2, while no obvious activity to the JH1 domains of TYK2, JAK1, JAK2, and JAK (IC50 > 10 μM) was observed. The compound also exhibited high kinome selectivity against a panel of 249 kinases, demonstrating an extraordinary target specificity. Moreover, the compound also displayed excellent metabolic stability in liver microsomal stability tests of multiple species (T1/2> 120 min) and good
REFERENCES
(1) O’Shea, J. J.; Schwartz, D. M.; Villarino, A. V.; Gadina, M.; Mclnnes, I. B.; Laurence, A. The JAK-STAT pathway: impact on human disease and therapeutic intervention. Annu. Rev. Med. 2015, 66, 311−328.
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(3) Leitner, N. R.; Witalisz-Siepracka, A.; Strobl, B.; Muller, M.
Tyrosine kinase 2- surveillant of tumours and bona fide oncogene. passive permeability (Caco-2 Papp(A to B) = 73 nm/s). Further
in vivo pharmacokinetics evaluation revealed that the compound had outstanding PK properties in mouse, dog, and monkey. For example, following intravenous dosing and oral administration in the mouse (1 mg/kg and 10 mg/kg, respectively), compound 1 afforded a relatively low clearance (CL = 13 mL min−1 kg−1) and high oral exposure (Cmax = 7.5 μM, AUC = 36 μM h). Remarkably, the major issue of high hERG affinity encountered in this series of analogues was also successfully solved through medicinal chemistry efforts. Compound 1 showed low inhibition (26% at 10 μM) in the hERG potassium channel patch clamp assay. On the basis of itsstrong potency, high selectivity, minimal metabolic
liabilities, excellent PK parameters, and promising in vivo efficacy, compound 1 was nominated as a clinical candidate. In summary, as the first allosteric TYK2 inhibitor targeting the pseudokinase domain that has entered clinical trial, compound 1 is at the leading edge of selective TYK2 inhibitor development that avoids the safety issues of traditional JH1 pan-JAK inhibitors. The work provides an outstanding case of “hit-to-candidate” evolution of a first-in-class molecule by combining multiple medicinal chemistry strategies. Compound
1 is currently in late stage clinical development for the treatment of psoriasis. It is also noteworthy that recent studies suggested that TYK2 might be an oncogene that is avoiding Cytokine 2017, 89, 209−218.
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