7-Azaindole: A Versatile Scaffold for Developing Kinase Inhibitors

Abstract

The majority of kinase inhibitors have been developed as ATP competitors to interact with a hinge region in ATP binding sites of kinases. 7-Azaindole has been found as an excellent hinge binding motif by making two hydrogen bonds with the kinase hinge region. Vemurafenib, a B-RAF kinase (serine–threonine kinase [STK]) inhibitor approved by the U.S. Food and Drug Administration (FDA) for the treatment of melanoma, was created from this simple 7-azaindole fragment by successful use of structure-based drug design techniques. The huge potential of 7-azaindole as a hinge-binding motif has encouraged many researchers to employ it as a kinase privileged fragment. This paper will review recent examples of 7-azaindole-based kinase inhibitors, and discusses their binding interactions with the kinase hinge regions.

1. Introduction

Kinases constitute a large protein family comprising more than 500 members in humans. Each kinase plays important roles in signaling pathways that regulate crucial cellular processes, such as proliferation, differentiation, and survival.¹⁾ Accumulating pharmacology and pathology evidence strongly suggests that deregulation of kinase is associated with a variety of diseases including cancer, inflammation, neurodegenerative disorders, cardiovascular diseases, and complications of diabetes.²⁾ Recently, small-molecule kinase inhibitors have been aggressively explored to establish new therapeutic interventions in kinase-related diseases. As of March 2017, a total of 32 kinase inhibitors have been approved by the U.S. Food and Drug Administration (FDA), and more than 1000 clinical studies with kinase inhibitors are currently ongoing. Most kinase inhibitors reported to date are designed to bind to the ATP-binding site located in a deep cleft between N- and C-terminal lobes of the kinase catalytic domain, by forming hydrogen bond interactions with the hinge region that connects the two lobes.³⁾ The majority of kinase inhibitors bind to the active conformation of the kinase (known as type I inhibitors); however, some inhibitors bind to the inactive state of the kinase, which have a deep allosteric pocket generated by large conformational changes in kinase.⁴⁾ These inactive state binders include several types of inhibitors: the DFG (aspartic acid (Asp)-phenylalanine (Phe)-glycine (Gly))-out conformation binders (so-called “type II” inhibitors), the C-helix-out conformation binders (e.g., Lapatinib⁵⁾), and the “H3” pocket binders (e.g., CGI1746⁶⁾).

7-Azaindole is well known as a kinase privileged fragment,^7,8) and has been incorporated into many kinase inhibitors as a hinge-binding element. As shown in Fig. 1a, the pyridine N atom and the pyrrole NH in the 7-azaindole ring serve as a hydrogen bond acceptor and donor, respectively, to make bidentate hydrogen bonds with the hinge region of the kinase. In addition, 7-azaindole has five modification sites where various substituents can be readily attached. Therefore recent years have seen growing interest in this 7-azaindole scaffold; more than 100000 chemical structures having 7-azaindole framework have been registered in the CAS chemical database,⁹⁾ which is steadily increasing by the synthetic innovation and enrichment of commercially available derivatives.¹⁰⁾ Figure 1b shows representative kinase inhibitors having a number of substituents at various positions in the 7-azaindole ring.^11–16) Among them, vemurafenib (1), a B-RAF kinase (serine–threonine kinase [STK]) inhibitor, is the first FDA-approved 7-azaindole-based kinase drug for the treatment of melanoma.¹¹⁾ Vemurafenib was discovered through lead optimization starting from a small 7-azaindole fragment, and is recognized as the first successful example of “fragment-based” drug discovery approach.¹⁷⁾ Currently, several 7-azaindole-based kinase inhibitors (2–6) are under clinical evaluation as shown in Fig. 1b. Apart from PLX-8394 (6), a second-generation BRAF kinase inhibitor,¹⁶⁾ other compounds have been developed targeting various kinds of kinases including Janus kinase 3 (JAK3; a cytoplasmic tyrosine kinase [TK]),¹²⁾ colony stimulating factor 1 receptor (CSF1R; a receptor TK),¹³⁾ aurora kinases (STK),¹⁴⁾ and rho-associated, coiled-coil-containing protein kinase 1 (ROCK1; STK).¹⁵⁾ Comprehensive survey of a drug discovery database (substructure-search using Thomson Reuters Integrity^SM database¹⁸⁾ as of March 2017) revealed that more than 90 kinds of kinases have been shown sensitive to 7-azaindole-based kinase inhibitors—sufficient to cover the whole human kinome as shown in Fig. 2. These data suggest that 7-azaindole fragment can be useful as a starting point of medicinal chemistry targeting various kinases.

Fig. 1. (a) Hydrogen Bonds between 7-Azaindole Fragment and the Hinge Region of a Kinase Are Indicated by Dashed Line; (b) 7-Azaindole-Based Kinase Inhibitors in Clinic and Clinical Development

GK: gatekeeper amino acid residue.

Fig. 2. 7-Azaindole Scaffold Provides Broad Coverage of the Human Kinome

In this review, we will highlight recent attempts to develop 7-azaindole-based kinase inhibitors from the viewpoint of differences in binding modes in the ATP binding site elucidated by X-ray cocrysal structures.

2. Binding Mode of 7-Azaindole-Based Inhibitors

First, we investigated X-ray cocrystal structures of kinases complexed with small molecules having the 7-azaindole fragment available in the RCSB Protein Data Bank (PDB). We found a total of 70 structures registered in the PDB as shown in Table 1. These structural data include 37 kinds of kinases that belong to different kinase families.

Table 1. List of Cocrystal Structures of Kinases Complexed with 7-Azaindoles

Normal										Flipped		Non-hinge
PDB ID	Kinase	PDB ID	Kinase	PDB ID	Kinase	PDB ID	Kinase	PDB ID	Kinase	PDB ID	Kinase	PDB ID	Kinase
1ZYS	CHK1	3DK7	ABL	4AOI	MET	4RZV	BRAF	5JT2	BRAF/V600E	3CE3	MET	2QD9	p38a
2QHM	CHK1	3E87	AKT2	4BIC	MAP3K5	4WO5	BRAF	5KBR	PAK1	3CTJ	MET	3EN4	SRK
2QOH	ABL	3ETA	INSR	4BID	MAP3K5	4XP0	ERK2	5L4Q	AAK1	3DJ6	AurA	3VS7	HCK
2UVX	AKT2	3GFW	MPS1	4FK3	BRAF/V600E	4XV1	BRAF/V600E			3FQH	Syk	4JG7	RSK2
2Z60	ABL T315I	3GQL	FGFR	4FV9	ERK2	4XV9	BRAF			3LVP	IGF1R	4QMW	MST3
3BHT	CDK2	3HDM	SGK	4HVS	KIT	4Y85	COT			4AWI	JNK1	4WAF	ATR/PI3K
3BHU	CDK2	3HDN	SGK	4HW7	FMS	4YTH	JAK2			4BIE	ASK1	4YUQ	CDPK1
3C4C	BRAF	3JY9	JAK2	4IQ6	GSK3b	5HES	ZAK			4GU6	FAK
3C4E	PIM1	3OG7	BRAF/V600E	4JOA	ALK	5HKM	PDK1			4O91	TAK1-TAB1
3C4F	FGFR	3RCJ	PDK1	4K1B	PIM1	5HO8	PDK1			4YTF	JAK2
3DK3	ABL	3ZCL	MET	4P90	PAK1	5JRQ	BRAF/V600E			4YTI	JAK2
3DK6	ABL	3ZLS	MAP2K1	4R7H	FMS	5JSM	BRAF/V600E			5GJD	TAK1-TAB1

Note. Each crystal structure is classified into three binding modes: “normal,” “flipped,” and “non-hinge” based on the binding fashion of the azaindole ring.

Analysis of the captured cocrystal structures revealed that the 7-azaindole group binds to kinases with different binding modes, which can be classified into three groups such as “normal” (azaindole binds to the hinge as most frequently seen), “flipped” (azaindole moiety is flipped 180° with respect to “normal” binding mode), and “non-hinge” (azaindole binds at a different site from the hinge region; Fig. 3). As shown in Fig. 3, “normal” and “flipped” binding modes can form bidentate hydrogen bonds with the backbone amides of hinge amino acid residues, GK+1 (next to the gatekeeper residue) and GK+3 residues. Namely, the carbonyl oxygen of GK+1 interacts as a hydrogen bond acceptor and backbone N–H of GK+3 donates hydrogen bond in “normal” binding mode. On the other hand, in “flipped” binding mode, the GK+3 residue acts as both hydrogen bond donor and acceptor. In the case of inhibitors categorized into “non-hinge” binding mode, the 7-azaindole moiety binds at a different site from the hinge region, because such compounds have another hinge-binding motif in addition to 7-azaindole. The observation that both “normal” and “flipped” binding modes are possible in Janus kinase 2 (JAK2; TK), c-Met (Met; TK), and apoptosis signal-regulating kinase 1 (ASK1; STK) kinases suggests that the binding mode is not dependent on kinase structural features. Rather, it would depend on the ligand structure, because 2-substituted derivatives of the azaindole give only “flipped” binding mode (compounds 7–11^19–23) in Fig. 4). As illustrated in Fig. 3, the 2-position of the azaindole ring is directed to the GK residue in “normal” binding mode, and substitution at this position would result in steric hindrance. In contrast, there is open space facing the solvent-exposed space when compounds bind with the “flipped” binding mode, and this would bring a significant preference for binding orientation of 2-substituted azaindoles. Compounds 12–16 also bind to kinases with the “flipped” orientation^24–28); these compounds are type II kinase inhibitors, which can interact with a deep allosteric pocket created by conformational change in the activation loop that adopts the inactive-DFG-out conformation. Almost all 7-azaindoles with “normal” binding modes are type I kinase inhibitors except one ligand (PDB code, 3ETA), suggesting that there might be some relation between binding orientation of azaindole and type of kinase inhibitors.

Fig. 3. 7-Azaindole Group Can Bind to Kinases with Different Binding Modes

HP1: hydrophobic region 1; HP2: hydrophobic region 2; GK: gatekeeper amino acid residue.

Fig. 4. Azaindole-Based Inhibitors Showing “Flipped” Binding Modes

One example of a “flipped” binder was reported by researchers from Vertex. Decernotinib²⁹⁾ (VX-509; compound 18) is a selective JAK3 inhibitor developed for the treatment of rheumatoid arthritis (RA). The Janus kinases (JAKs) are a family of four cytoplasmic tyrosine kinases (JAK-1, 2, and 3 and TYK2) that regulate signaling of cytokine receptors, and thus inhibitors of JAKs are considered promising agents for novel immunosuppressive therapy.³⁰⁾ X-ray cocrystallographic study of VX-509 with JAK2, which was used as a surrogate of JAK3, revealed that the 7-azaindole moiety binds to the hinge region with the “flipped” orientation by making two hydrogen bonds with Leu932. Interestingly, a closely related compound 19 with a slightly different linker was found to adopt the “normal” binding mode (Fig. 5). Removal of the methyl group in the linker portion of compound 19 reversed the binding mode to “flipped” (compound 17, Figs. 4 and 5). Superposition of these structures suggested the terminal CF₃ group of three compounds binds to the same pocket (ribose binding site); however, the pyrimidine ring of compound 19 is flipped by nearly 180° compared with compounds 17 and 18. Flipping of binding modes has been observed for other ligands,³¹⁾ so it should be important to obtain X-ray cocrystal structures throughout the structure–activity relationship (SAR) study.

Fig. 5. “Normal” and “Flipped” Binding Modes of JAK3 Inhibitors

3. Interactions of 7-Azaindole-Based Inhibitors with Adjacent Binding Regions

Generally, kinase inhibitors are modified to enhance their interactions with binding pockets neighboring the hinge region during lead optimization study. Occasionally, improvement of target kinase selectivity may be observed in parallel with increasing potency when the new interactions are specific to the target kinase. As illustrated in Fig. 3, ATP competitive inhibitors bind to kinases by interacting with various regions: adenine binding region, ribose binding region, phosphate binding region, two hydrophobic regions located adjacent to adenine binding region, and latent back pocket only formed in an inactive conformation. Needless to say, azaindole-based kinase inhibitors reported so far have been designed to interact with these regions, and many cocrystal structures of them have been deposited in the PDB. Interactions of CDK2-meriolin 5 (PDB code: 3BHU) are illustrated in Fig. 6 as a typical “normal” binding mode of azaindole inhibitor.

Fig. 6. Azaindole-Based CDK Inhibitors (Meriolins)

Cyclin-dependent kinases (CDKs) are STKs, and play important roles in regulating the cell cycle; therefore CDKs may be attractive anti-cancer targets.³²⁾ Echalier et al.³³⁾ reported successful design of CDK inhibitors using interactions with the ribose binding region. Meriolins, structural hybrid of two natural kinase inhibitors (meridianins and variolins), are highly potent inhibitors of CDKs.³⁴⁾ The azaindole scaffold was substituted with 2-aminopyrimidine group at 3-position and alkoxy group at 4-position to interact with HP1 region and ribose binding region, respectively. CDKs have a large GK residue, Phe, which can interact with the pyrimidine ring via π–π interactions. This 2-aminopyrimidine group also interacts with the side chains of Glu51 and Lys33 in CDKs by making hydrogen bonds with them as shown in Fig. 6. The flexible Gly-rich loop of CDK2 undergoes rearrangement to cover the ribose binding region on ligand binding. Modification of the methoxy group of meriolin 3 with a larger propyl group (meriolin 5) resulted in significant improvement of the potencies for CDKs by occupying the ribose binding region, but further enlargement of R group dramatically diminished the inhibitory activities (meriolin 7).

7-Azaindole-based inhibitor 23, discovered by Genentech group, is an extremely potent inhibitor of Pim kinases (for Pim-1, -2, and -3, IC₅₀=3, 32, and 9 pM, respectively).³⁵⁾ Pim kinases are STKs and include three gene-encoded isoforms, Pim-1, -2, and -3. Pim kinases play key roles regulating cell cycle progression and apoptosis, and may be implicated in various diseases such as cancers.³⁶⁾ Pim kinases have a unique proline residue at GK+3 position of the hinge region, and thus there is no main chain N–H for donating a hydrogen bond. Nonetheless, 7-azaindole seems to make a bidentate hydrogen bond with the hinge region because replacement of the 7-azaindole ring with an indole ring resulted in a significant reduction of inhibitory potency (40-fold decrease; IC₅₀=1.3 nM for Pim-2). One hypothesis suggests that the N7 atom of the azaindole may make a non-canonical hydrogen bond with the α-hydrogen of Arg122 based on X-ray cocrystal structure data (PDB code: 4K1B) as depicted in Fig. 7. To increase potency, a pyrazolopyrimidine group was introduced at 3-position of the azaindole scaffold via amide linkage to occupy the HP1 hydrophobic region, where Lys67 provides an efficient hydrogen bond with N6 atom of the pyrazolopyrimidine ring. Incorporation of a basic piperidine moiety into the pyrazolopyrimidine to interact with the ribose binding region further increased potency. This piperidine forms a hydrogen bond with main chain CO of Glu171, and makes a salt bridge with Asp128, one of the acidic residues (termed acidic patch) at the bottom of the ribose binding pocket. Finally, substitution at 5-position of the azaindole with 2-fluorophenyl group to interact with the HP2 hydrophobic pocket flanked by the Gly-rich loop and the extended hinge region produced a highly potent pan-Pim kinases inhibitor with picomolar affinities.

Fig. 7. 7-Azaindole-Based Pim Kinases Inhibitor

Researchers at Bristol-Myers Squibb successfully used the azaindole scaffold for scaffold hopping approaches to improve poor pharmacokinetic properties of the parent compound.²⁷⁾ Met kinase is a receptor tyrosine kinase protein, and mediates various cellular signals such as epithelial cell dissociation (scattering), invasion, tubular morphogenesis, and angiogenesis.³⁷⁾ Aberrant Met signal activation has been reported in many cancers.³⁸⁾ The acylurea-substituted 7-azaindole 24 was designed to replace the pyrrolotriazine scaffold of the original Met inhibitor so as to improve pharmacokinetic properties. X-ray cocrystal structural analysis of compound 24 with Met kinase (PDB code: 3CTJ; Fig. 8) revealed that compound 24 binds to an inactive conformation of Met with the “flipped” binding mode. The central fluorophenyl ring is flanked by GK residue Leu1157 and Phe1223, and the acylurea linker makes hydrogen bonds with Asp1222 and Gly1127 as observed in other type II inhibitors.³⁾ The terminal 4-fluorophenyl ring makes hydrophobic interactions with aromatic side chains of Phe1134 and Phe1200 in the back pocket. The cocrystal structure suggests that substituents at 2- and 3-positions of the azaindole ring can be tolerated and would make further interactions with the HP2 hydrophobic region and the ribose binding region, respectively. Further optimization on 3-position of the azaindole ring of compound 24 produced compound 25 with a dramatic improvement in inhibitory activity for Met kinase (IC₅₀=2 nM). This compound showed good oral exposure in mice, and demonstrated excellent antitumor activity in an in vivo xenograft model.

Fig. 8. Azaindole-Based Met Kinase Inhibitors

Although crystallographic information is lacking, several 7-azaindole-based inhibitors for CDC7 kinase have been reported as shown in Fig. 9.^39–43) CDC7 is an STK that plays a conserved and important role in DNA replication, and has been recognized as a potential anticancer target.⁴⁴⁾ Unlike other kinases, CDC7 has large portions of kinase insert regions, and these regions would make crystallographic studies difficult,⁴⁵⁾ because CDC7 is a holo-enzyme and its activity is controlled by its activator, activator of S-phase kinase (ASK; also called DBF4). It is noteworthy that all azaindole-based CDC7 inhibitors have large substituents at the 3-postion of the azaindole ring. A computer modeling study of compound 30 complexed with CDC7 suggests that the azaindole group bound to CDC7 with the “normal” binding mode, and 3-position of the azaindole ring would direct to the HP2 hydrophobic region, where Lys90 could provide a hydrogen bond (Fig. 10).⁴³⁾ Interestingly, compound 30 is a reversible inhibitor but exhibited time-dependent inhibition with a slow-off rate kinetics only against CDC7 kinase. These effects might be elicited by a conformational change of the enzyme when compound 30 binds to the active site of CDC7. Generally, slow-off rate inhibitors show more potent effects in vivo because an increased residence time gives longer duration of action.

Fig. 9. 7-Azaindole-Based CDC7 Kinase Inhibitors

Fig. 10. Predicted Binding Mode of Compound 30 Complexed with CDC7 Kinase

4. Concluding Remarks

After the success of imatinib, protein kinases have become the most important class of drug target, especially in oncology. The majority of kinase inhibitors reported so far bind to the hinge region of kinases in a similar manner, and thus increased understanding the binding mode of the hinge binder moiety will provide new insights into the design of novel kinase inhibitors. Many hinge binding moieties have been reported and incorporated into kinase inhibitors as a hinge binding element. Among them, 7-azaindole has several useful features: possible bidentate hydrogen bond interactions; well-established chemistry for installing substituents into the ring structure; and good commercial availability of starting materials. We conducted a systematic analysis of the binding modes of 7-azaindole-based kinase inhibitors registered in the PDB, and found that those inhibitors are classified into three binding modes, such as “normal,” “flipped,” and “non-hinge,” based on the crystal structures complexed with the target kinases. It is noteworthy that these binding modes could be easily switched among each other by small modifications of the inhibitors, and this phenomenon could confuse medicinal chemists. Therefore it is important to confirm the binding mode by X-ray structural analysis throughout SAR studies.

Conflict of Interest

Takayuki Irie is an employee of Carna Biosciences, Inc. Masaaki Sawa is a member of the board of directors, Chief Scientific Officer at Carna Biosciences, Inc.

References

• 1) Manning G., Whyte D. B., Martinez R., Hunter T., Sudarsanam S., Science, 298, 1912–1934 (2002).
• 2) Cohen P., Nat. Rev. Drug Discov., 1, 309–315 (2002).
• 3) Liao J. J.-L., J. Med. Chem., 50, 409–424 (2007).
• 4) Müller S., Chaikuad A., Gray N. S., Knapp S., Nat. Chem. Biol., 11, 818–821 (2015).
• 5) Wood E. R., Truesdale A. T., McDonald O. B., Yuan D., Hassell A., Dickerson S. H., Ellis B., Pennisi C., Horne E., Lackey K., Alligood K. J., Rusnak D. W., Gilmer T. M., Shewchuk L., Cancer Res., 64, 6652–6659 (2004).
• 6) Di Paolo J. A., Huang T., Balazs M., Barbosa J., Barck K. H., Bravo B. J., Carano R. A. D., Darrow J., Davies D. R., DeForge L. E., Diehl L., Ferrando R., Gallion S. L., Giannetti A. M., Gribling P., Hurez V., Hymowitz S. G., Jones R., Kropf J. E., Lee W. P., Maciejewski P. M., Mitchell S. A., Rong H., Staker B. L., Whitney J. A., Yeh S., Young W. B., Yu C., Zhang J., Reif K., Currie K. S., Nat. Chem. Biol., 7, 41–50 (2011).
• 7) Ghose A. K., Herbertz T., Pippin D. A., Salvino J. M., Mallamo J. P., J. Med. Chem., 51, 5149–5171 (2008).
• 8) Tang J., Hamajima T., Nakano M., Sato H., Dickerson S. H., Lackey K. E., Bioorg. Med. Chem. Lett., 18, 4610–4614 (2008).
• 9) https://scifinder.cas.org/scifinder/
• 10) Mérour J.-Y., Buron F., Plé K., Bonnet P., Routier S., Molecules, 19, 19935–19979 (2014).
• 11) Bollag G., Tsai J., Zhang J., Zhang C., Ibrahim P., Nolop K., Hirth P., Nature (London), 11, 873–886 (2012).
• 12) Ito M., Yamazaki S., Yamagami K., Kuno M., Morita Y., Okuma K., Nakamura K., Chida N., Inami M., Inoue T., Shirakami S., Higashi Y., J. Pharmacol. Sci., 133, 25–33 (2017).
• 13) Tap W. D., Wainberg Z. A., Anthony S. P., Ibrahim P. N., Zhang C., Healey J. H., Chmielowski B., Staddon A. P., Cohn A. L., Shapiro G. I., Keedy V. L., Singh A. S., Puzanov I., Kwak E. L., Wagner A. J., von Hoff D. D., Weiss G. J., Ramanathan R. K., Zhang J., Habets G., Zhang Y., Burton E. A., Visor G., Sanftner L., Severson P., Nguyen H., Kim M. J., Marimuthu A., Tsang G., Shellooe R., Gee C., West B. L., Hirth P., Nolop K., van de Rijn M., Hsu H. H., Peterfy C., Lin P. S., Tong-Starksen S., Bollag G., N. Engl. J. Med., 373, 428–437 (2015).
• 14) Adams N. D., Adams J. L., Burgess J. L., Chaudhari A. M., Copeland R. A., Donatelli C. A., Drewry D. H., Fisher K. E., Hamajima T., Hardwicke M. A., Huffman W. F., Koretke-Brown K. K., Lai Z. V., McDonald O. B., Nakamura H., Newlander K. A., Oleykowski C. A., Parrish C. A., Patrick D. R., Plant R., Sarpong M. A., Sasaki K., Schmidt S. J., Silva D. J., Sutton D., Tang J., Thompson C. S., Tummino P. J., Wang J. C., Xiang H., Yang J., Dhanak D., J. Med. Chem., 53, 3973–4001 (2010).
• 15) Tokushige H., Inatani M., Nemoto S., Sakaki H., Katayama K., Uehata M., Tanihara H., Invest. Ophthalmol. Vis. Sci., 48, 3216–3222 (2007).
• 16) Zhang C., Spevak W., Zhang Y., Burton E. A., Ma Y., Habets G., Zhang J., Lin J., Ewing T., Matusow B., Tsang G., Marimuthu A., Cho H., Wu G., Wang W., Fong D., Nguyen H., Shi S., Womack P., Nespi M., Shellooe R., Carias H., Powell B., Light E., Sanftner L., Walters J., Tsai J., West B. L., Visor G., Rezaei H., Lin P. S., Nolop K., Ibrahim P. N., Hirth P., Bollag G., Nature (London), 526, 583–586 (2015).
• 17) Tsai J., Lee J. T., Wang W., Zhang J., Cho H., Mamo S., Bremer R., Gillette S., Kong J., Haass N. K., Sproesser K., Li L., Smalley K. S. M., Fong D., Zhu Y.-L., Marimuthu A., Nguyen H., Lam B., Liu J., Cheung I., Rice J., Suzuki Y., Luu C., Settachatgul C., Shellooe R., Cantwell J., Kim S.-H., Schlessinger J., Zhang K. Y. J., West B. L., Powell B., Habets G., Zhang C., Ibrahim P. N., Hirth P., Artis D. R., Herlyn M., Bollag G., Proc. Natl. Acad. Sci. U.S.A., 105, 3041–3046 (2008).
• 18) https://integrity.thomson-pharma.com/integrity/
• 19) Villaseñor A. G., Kondru R., Ho H., Wang S., Papp E., Shaw D., Barnett J. W., Browner M. F., Kuglstatter A., Chem. Biol. Drug Des., 73, 466–470 (2009).
• 20) Nemecek C., Metz W. A., Wentzler S., Ding F.-X., Venot C., Souaille C., Dagallier A., Maignan S., Guilloteau J.-P., Bernard F., Henry A., Grapinet S., Lesuisse D., Chem. Biol. Drug Des., 76, 100–106 (2010).
• 21) Liddle J., Bamborough P., Barker M. D., Campos S., Chung C.-W., Cousins R. P. C., Faulder P., Heathcote M. L., Hobbs H., Holmes D. S., Ioannou C., Ramirez-Molina C., Morse M. A., Osborn R., Payne J. J., Pritchard J. M., Rumsey W. L., Tape D. T., Vicentini G., Whitworth C., Williamson R. A., Bioorg. Med. Chem. Lett., 22, 5222–5226 (2012).
• 22) Singh O., Shillings A., Craggs P., Wall I., Rowland P., Skarzynski T., Hobbs C. I., Hardwick P., Tanner R., Blunt M., Witty D. R., Smith K. J., Protein Sci., 22, 1071–1077 (2013).
• 23) Heinrich T., Seenisamy J., Emmanuvel L., Kulkarni S. S., Bomke J., Rohdich F., Greiner H., Esdar C., Krier M., Grädler U., Musil D., J. Med. Chem., 56, 1160–1170 (2013).
• 24) Tan L., Nomanbhoy T., Gurbani D., Patricelli M., Hunter J., Geng J., Herhaus L., Zhang J., Pauls E., Ham Y., Choi H. G., Xie T., Deng X., Buhrlage S. J., Sim T., Cohen P., Sapkota G., Westover K. D., Gray N. S., J. Med. Chem., 58, 183–196 (2015).
• 25) Muraoka T., Ide M., Irie M., Morikami K., Miura T., Nishihara M., Kashiwagi H., Chem. Pharm. Bull., 64, 1622–1629 (2016).
• 26) Kim K. S., Zhang L., Schmidt R., Cai Z.-W., Wei D., Williams D. K., Lombardo L. J., Trainor G. L., Xie D., Zhang Y., An Y., Sack J. S., Tokarski J. S., D’Arienzo C., Kamath A., Marathe P., Zhang Y., Lippy J., Jeyaseelan R. Sr., Wautlet B., Henley B., Gullo-Brown J., Manne V., Hunt J. T., Fargnoli J., Borzilleri R. M., J. Med. Chem., 51, 5330–5341 (2008).
• 27) Cai Z.-W., Wei D., Schroeder G. M., Cornelius L. A. M., Kim K., Chen X.-T., Schmidt R. J., Williams D. K., Tokarski J. S., An Y., Sack J. S., Manne V., Kamath A., Zhang Y., Marathe P., Hunt J. T., Lombardo L. J., Fargnoli J., Borzilleri R. M., Bioorg. Med. Chem. Lett., 18, 3224–3229 (2008).
• 28) Elling R. A., Erlanson D. A., Yang W., Tangonan B. T., Hansen S. K., Romanowski M. J., ‹http://www.rcsb.org/pdb/explore/explore.do?structureId=3DJ6›
• 29) Farmer L. J., Ledeboer M. W., Hoock T., Arnost M. J., Bethiel R. S., Bennani Y. L., Black J. J., Brummel C. L., Chakilam A., Dorsch W. A., Fan B., Cochran J. E., Halas S., Harrington E. M., Hogan J. K., Howe D., Huang H., Jacobs D. H., Laitinen L. M., Liao S., Mahajan S., Marone V., Martinez-Botella G., McCarthy P., Messersmith D., Namchuk M., Oh L., Penney M. S., Pierce A. C., Raybuck S. A., Rugg A., Salituro F. G., Saxena K., Shannon D., Shlyakter D., Swenson L., Tian S.-K., Town C., Wang J., Wang T., Wannamaker M. W., Winquist R. J., Zuccola H. J., J. Med. Chem., 58, 7195–7216 (2015).
• 30) Ghoreschi K., Laurence A., O’Shea J. J., Immunol. Rev., 228, 273–287 (2009).
• 31) Aronov A. M., Tang Q., Martinez-Botella G., Bemis G. W., Cao J., Chen G., Ewing N. P., Ford P. J., Germann U. A., Green J., Hale M. R., Jacobs M., Janetka J. W., Maltais F., Markland W., Namchuk M. N., Nanthakumar S., Poondru S., Straub J., ter Haar E., Xie X., J. Med. Chem., 52, 6362–6368 (2009).
• 32) Shapiro G. I., J. Clin. Oncol., 24, 1770–1783 (2006).
• 33) Echalier A., Bettayeb K., Ferandin Y., Lozach O., Clément M., Valette A., Liger F., Marquet B., Morris J. C., Endicott J. A., Joseph B., Meijer L., J. Med. Chem., 51, 737–751 (2008).
• 34) Bettayeb K., Tirado O. M., Marionneau-Lambot S., Ferandin Y., Lozach O., Morris J. C., Mateo-Lozano S., Drueckes P., Schächtele C., Kubbutat M. H. G., Liger F., Marquet B., Joseph B., Echalier A., Endicott J. A., Notario V., Meijer L., Cancer Res., 67, 8325–8334 (2007).
• 35) Wang X., Magnuson S., Pastor R., Fan E., Hu H., Tsui V., Deng W., Murray J., Steffek M., Wallweber H., Moffat J., Drummond J., Chan G., Harstad E., Ebens A. J., Bioorg. Med. Chem. Lett., 23, 3149–3153 (2013).
• 36) Brault L., Gasser C., Bracher F., Huber K., Knapp S., Schwaller J., Haematologica, 95, 1004–1015 (2010).
• 37) Jiang W. G., Martin T. A., Parr C., Davies G., Matsumoto K., Nakamura T., Crit. Rev. Oncol. Hematol., 53, 35–69 (2005).
• 38) Peruzzi B., Bottaro D. P., Clin. Cancer Res., 12, 3657–3660 (2006).
• 39) Ermoli A., Bargiotti A., Brasca M. G., Ciavolella A., Colombo N., Fachin G., Isacchi A., Menichincheri M., Molinari A., Montagnoli A., Pillan A., Rainoldi S., Sirtori F. R., Sola F., Thieffine S., Tibolla M., Valsasina B., Volpi D., Santocanale C., Vanotti E., J. Med. Chem., 52, 4380–4390 (2009).
• 40) Woods K. W., Lai C., Miyashiro J. M., Tong Y., Florjancic A. S., Han E. K., Soni N., Shi Y., Lasko L., Leverson J. D., Johnson E. F., Shoemaker A. R., Penning T. D., Bioorg. Med. Chem. Lett., 22, 1940–1943 (2012).
• 41) Tong Y., Stewart K. D., Florjancic A. S., Harlan J. E., Merta P. J., Przytulinska M., Soni N., Swinger K. K., Zhu H., Johnson E. F., Shoemaker A. R., Penning T. D., ACS Med. Chem. Lett., 4, 211–215 (2013).
• 42) Harrington P. E., Bourbeau M. P., Fotsch C., Frohn M., Pickrell A. J., Reichelt A., Sham K., Siegmund A. C., Bailis J. M., Bush T., Escobar S., Hickman D., Heller S., Hsieh F., Orf J. N., Rong M., San Miguel T., Tan H., Zalameda L., Allen J. G., Bioorg. Med. Chem. Lett., 23, 6396–6400 (2013).
• 43) Irie T., Asami T., Sawa A., Uno Y., Hanada M., Taniyama C., Funakoshi Y., Masai H., Sawa M., Eur. J. Med. Chem., 130, 406–418 (2017).
• 44) Sawa M., Masai H., Drug Design, Development and Therapy, 2, 255–264 (2009).
• 45) Hughes S., Elustondo F., Di Fonzo A., Leroux F. G., Wong A. C., Snijders A. P., Matthews S. J., Cherepanov P., Nat. Struct. Mol. Biol., 19, 1101–1107 (2012).