Development of 2-(4-pyridyl)-benzimidazoles as PKN2 chemical tools to probe cancer

Article abstract of DOI:10.1016/j.bmcl.2020.127040

Kinases are signalling proteins which have proven to be successful targets for the treatment of a variety of diseases, predominantly in cancers. However, only a small proportion of kinases (<20%) have been investigated for their therapeutic viability, likely due to the lack of available chemical tools across the kinome. In this work we describe initial efforts in the development of a selective chemical tool for protein kinase N2 (PKN2), a relatively unexplored kinase of interest in several types of cancer. The most successful compound, 5, has a measured IC₅₀ of 0.064 μM against PKN2, with ca. 17-fold selectivity over close homologue, PKN1.

Full text of DOI:10.1016/j.bmcl.2020.127040

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Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Development of 2-(4-pyridyl)-benzimidazoles as PKN2 chemical tools to
probe cancer
⁎
Fiona Scotta, , Angela M. Falab,c, Lewis E. Pennicotta, Tristan D. Reuillona, Katlin B. Massirerb,c
,
Jonathan M. Elkinsd, Simon E. Warda,e
a Sussex Drug Discovery Centre, University of Sussex, Sussex House, Falmer, Brighton BN1 9RH, United Kingdom
b Centro de Química Medicinal (CQMED), Centro de Biologia Molecular e Engenharia Genética (CBMEG), Universidade Estadual de Campinas (UNICAMP), Campinas, SP
13083-875, Brazil
c Structural Genomics Consortium, Departamento de Genética e Evolução, Instituto de Biologia, UNICAMP, Campinas, SP 13083-886, Brazil
d Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7DQ, United Kingdom
e Medicines Discovery Institute, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
A R T I C L E I N F O
A B S T R A C T
Keywords:
Kinases are signalling proteins which have proven to be successful targets for the treatment of a variety of
diseases, predominantly in cancers. However, only a small proportion of kinases (< 20%) have been investigated
for their therapeutic viability, likely due to the lack of available chemical tools across the kinome. In this work
we describe initial efforts in the development of a selective chemical tool for protein kinase N2 (PKN2), a
relatively unexplored kinase of interest in several types of cancer. The most successful compound, 5, has a
measured IC50 of 0.064 μM against PKN2, with ca. 17-fold selectivity over close homologue, PKN1.
Kinases
Cancer
Heart failure
Inflammation
AGC kinase
PKN2
PRK2
Protein kinase N2
Benzimidazole
Chemical probe
Chemical tool
Chemical tools/probes are drug-like compounds used to answer
biological questions. They need not possess all the properties of a drug
candidate, which can be dialled in at a later point in the drug devel-
opment process. These compounds only need to be sufficiently stable,
potent and selective towards their particular target.1,2
kinome has been well-studied,5 and selective inhibitors are only
available for an even smaller fraction of those kinases.
Protein kinase N2 (PKN2) (Fig. 1) is one of these understudied ki-
nases. It is an AGC-type serine/threonine protein kinase. There are
more than 60 AGC protein kinases in the human genome with 14 fur-
ther classifications. PKN2 falls into the PKN sub-family, closely related
to the PKC sub-family, and is one of three homologues (PKN1/2/3). It
has a number of pseudonyms which include protein kinase C-related
kinase 2 (PRK2), PKNγ, PAK2, PRO2, and STK7.6
Historically, the approval of imatinib3 as an effective Abl kinase
inhibitor for treating chronic myeloid leukaemia stimulated efforts to
better understand the 518 human protein kinases and their role in
disease. Trends in research4 suggest that less than 20% of the human
Abbreviations: PKN, protein kinase N; Abl, Abelson murine leukemia viral oncogene; IC50, half maximal inhibitory concentration; AGC, protein kinase A/G/C
families; PKC, protein kinase C; PRK, protein kinase C-related kinase; PAK2, p21 activated kinase 2; PRO2, glutamate 5-kinase Pro2; STK, serine/threonine kinase;
PDB, protein databank; PARP, poly(ADP-ribose) polymerase; ChEMBL, European Molecular Biology Laboratory Chemical database; CLK, CDC2-like kinase; SAR,
structure activity relationship; CDI, 1,1′-carbonyldiimidazole; TR-FRET, time resolved fluorescence resonance energy transfer; THF, tetrahydrofuran; EtOH, ethanol;
HATU, hexafluorophosphate azabenzotriazole tetramethyl uronium; DIPEA, N,N-diisopropylethylamine; DCM, dichloromethane; AcOH, acetic acid; DMF, N,N-
dimethyl-formamide; KD, dissociation constant; Ki, inhibitor constant; NMR, nuclear magnetic resonance; DMSO, dimethyl sulfoxide; MeOH, methanol; GST, glu-
tathione S-transferase; DNA, deoxyribonucleic acid; SFM, scanning force microscopy; HEPES, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; TCEP, tris(2-
carboxyethyl)phosphine; EDTA, ethylenediaminetetraacetic acid; SDS, sodium dodecyl sulfate; PAGE, polyacrylamide gel electrophoresis; ATP, adenosine tripho-
sphate; EGTA, egtazic acid; CV, column volumes
⁎ Corresponding author.
E-mail addresses: f.scott@sussex.ac.uk (F. Scott), angelafala@gmail.com (A.M. Fala), l.e.pennicott@sussex.ac.uk (L.E. Pennicott),
treuillo@its.jnj.com (T.D. Reuillon), kmassire@unicamp.br (K.B. Massirer), jon.elkins@sgc.ox.ac.uk (J.M. Elkins), wards10@cardiff.ac.uk (S.E. Ward).
https://doi.org/10.1016/j.bmcl.2020.127040
Received 15 November 2019; Received in revised form 28 January 2020; Accepted 14 February 2020
0960-894X/©2020PublishedbyElsevierLtd.
Pleasecitethisarticleas:FionaScott,etal.,Bioorganic&MedicinalChemistryLetters,https://doi.org/10.1016/j.bmcl.2020.127040

F. Scott, et al.
Bioorganic&MedicinalChemistryLettersxxx(xxxx)xxxx
Fig. 1. PKN2 and its domain organisation. The structure organisation contains three repeats of ACC domain (anti-parallel coiled-coil) in the N-termini region (pink/
orange), a C2 calcium binding-like domain and in the C-terminal, the Ser/Thr kinase domain.
Fig. 2. Crystallographic structure of PKN2 bound to ATP-γS (PDB ID: 4CRS).
PKNs have a fairly conserved primary sequence and they share the
same architecture. The catalytic domain of PKN2 has 87% percent
identity with PKN1; 70% with PKN3; and 50% with PKC kinases, while
the N-termini regions are less conserved, sharing only 48% and 40%
between PKN1/2 and PKN2/3, respectively.7,8
PKNs have been linked to various cellular roles, including cytoske-
leton regulation,9 transport,10 cell adhesion,11 nutrient signalling,12
and cell cycle,13 as well as being a target of interest in colon,14 breast,15
renal,16 head,17 neck,17 and prostate cancers.18 They are also reportedly
involved in inflammation19,20 and heart failure.21 So far, there is one X-
ray crystal structure of PKN2 publicly available in the Protein Data
Bank (PDB ID: 4CRS) (Fig. 2).
Scheme 1. Preparation of Benzimidazoles 5 and 632–36
group was reduced to aniline 3 with sodium dithionate,33 followed by
the coupling of isonicotinic acid to the 3-position aniline to form amide
4,34 which was then heated in acetic acid to form benzimidazole 5.35
The scope of this chemistry enabled the synthesis of 14 analogues
using commercially available nitroanilines and di-anilines. Additional
alkylation conditions allowed the capping of the benzimidazole N-H36
(6) and alternative amide coupling conditions were used for preparing
compound 1137 and the penultimate amide intermediate used to make
compound 19.38
These previous studies have elucidated functions for PKN2 using
molecular and cell biology techniques, and the conclusions would be
greatly supported by validation through the use of small molecule in-
hibitors, especially to evaluate PKN2′s potential as a cancer drug target.
Potent inhibitors are known for several AGC kinase family members,
including ROCK22–25 and PKC,26 but currently there are no sufficiently
selective inhibitors for PKN2.12
The potencies and selectivities of these compounds were tested
using a TR-FRET binding-displacement assay in which the IC50 values
were measured (Table 1). Calculation of Ki values using the Cheng-
Prusoff equation and the KD of the tracer (previously determined) al-
lowed the affinity of the inhibitors for PKN2 and PKN1 to be compared
(Table 1).
This work describes an initial effort to develop such compounds
based around a benzimidazole core. Compound 5 was previously de-
veloped as a PARP inhibitor27–29 but exhibited higher potency towards
PKN2 than its desired target. Benzimidazoles are N-containing hetero-
cycles that are prevalent in medicinal chemistry.30 The compound was
found as part of a screen of the Abbott chemical library31 via the
ChEMBL database when searching for PKN2 inhibitors. It had a re-
ported Ki of 0.040 μM against PKN2 while only inhibiting two out of
137 other kinases (PKN1 and CLK4) with potencies lower than
0.100 μM.31 This was deemed a good starting point for repurposing the
compound as a PKN2 inhibitor. We report the synthesis of that com-
pound and subsequent SAR studies to determine its viability as a che-
mical tool for establishing the potential of PKN2 as a therapeutic target.
Compound 5 was successfully synthesised via a four step synthesis
(Scheme 1). 2-Amino-3-nitro-benzoic acid (1) was treated with am-
monia and CDI-coupling conditions32 to form amide 2. The 3-nitro
Compound 5 was validated as a PKN2 inhibitor (Ki = 0.032 μM)
with 17-fold selectivity over PKN1 (Ki = 0.500 μM) which was not
previously included in the Abbott library screen used in the Metz et al.
study.31
The benzimidazole NeH was capped using chemistry described by
Tsukamoto et al.36 While the alkylation conditions given were said to
be applicable to methylation of the benzimidazole using the corre-
sponding methyl halide, this proved unsuccessful; a dimethylated pro-
duct formed instead, thought to be due to the susceptibility for the 4′-
pyridyl to also alkylate after the benzimidazole NeH. Repeating the
specific reaction conditions used by the authors incorporated a methyl
acetate ester at the 1-position (6) which led to loss of binding to PKN2.
2

F. Scott, et al.
Bioorganic&MedicinalChemistryLettersxxx(xxxx)xxxx
Table 1
Structure activity relationships for benzimidazoles binding to PKN2 and PKN1. Measured IC50 values and corresponding calculated Ki values for PKN2 and PKN1 are
shown in μM. The assay Z’ factor was 0.7 < Z′ < 0.9.
#
R
R1
R2
X
Ar
PKN2
PKN1
IC50 (µM)
Standard Deviation (µM)
Ki (µM)
IC50 (µM)
Standard Deviation (µM)
Ki (µM)
5
6
7
CONH2
CONH2
CONH2
H
H
H
H
H
H
H
0.064
5.40
0.001
0.48
3.86
0.03
2.69
8.19
1.10
0.11
1.74
38.04
0.54
CH2COOMe
H
52.84
66.29
25.94
32.54
16.38
8
9
CONH2
CONH2
H
H
H
H
H
H
47.66
13.79
4.06
1.18
23.83
6.90
137.92
61.59
100.95
11.95
67.71
30.23
10
11
12
13
14
15
16
17
18
19
CONHMe
H
H
H
H
H
H
H
H
H
H
Br
H
H
H
H
H
H
H
H
H
H
2.12
0.27
9.57
3.79
0.21
0.06
5.20
23.86
0.79
0.58
0.01
1.06
10.59
56.66
99.41
45.54
58.94
38.81
56.69
38.54
109.30
4.45
1.70
5.20
CONMe2
H
38.84
16.23
7.71
19.42
8.11
25.96
34.63
17.58
8.33
27.81
48.80
22.36
28.93
19.05
27.83
18.92
53.66
2.19
H
CONH2
H
H
3.85
NO2
COOMe
H
H
2.50
1.25
H
31.29
42.09
5.02
15.64
21.05
2.51
13.48
1.61
COOEt
C^N
NO2
H
H
2.26
H
25.85
0.17
12.92
0.08
33.23
0.39
CONH2
that position using Suzuki coupling chemistry.39,40 This reaction was
attempted at multiple stages of the synthetic route but was un-
successful. Compound 19 was active against PKN2 but was nearly three
times less potent than compound 5. Despite this reduction in potency,
compound 19 is 26-fold selective over PKN1.
The SAR exploration around 5 confirms that the primary amide at
the 4-position, 4'-pyridyl and free NeH at the 1-position are necessary
for the compound’s activity against PKN2. Subsequent analogues pre-
pared for this series did not improve potency for the target within the
PKN family but did result in a slight improvement in selectivity over
PKN1 in compound 19.
Chemical tools are needed to facilitate the exploration of lesser
understood kinases such as PKN2 for its roles in healthy and cancerous
cells. Benzimidazole 5 was validated as an inhibitor of PKN2 with IC50
0.064 μM and with ca. 17-fold selectivity over PKN1 with reported high
selectivity across the wider kinome31. Our efforts to develop a new
compound to inhibit PKN2 resulted in compound 19 which was 26-fold
selective for PKN2 over PKN1 despite having a near three-fold reduc-
tion in potency compared to compound 5.
Scheme 2. Compounds 21 and 23 could not be synthesised from intermediates
20 and 22
Moving the 4′-pyridyl nitrogen in 7 and 8 resulted in loss of activity,
as did introducing an electron-donating methoxy group at the 3′-posi-
tion (9). This suggests the 4′-pyridyl ring acts as the hinge binder.
Attempts to make the 2′-pyridyl and 4′-pyrimidine analogues were
unsuccessful (Scheme 2).
Acknowledgements
Capping the amide with one (10) or two (11) methyl groups led to
increasing loss of activity respectively. Potency was lost when the
amide was moved to the 5-position of the benzimidazole ring (12),
Removing the amide completely (13) or exchanging the 4- or 5-position
for another functional group (14–18) also led to loss of activity.
Introduction of a bromine at the 6-position (19) was hoped to
provide a useful handle for incorporating various alkyl/aryl groups at
This work was supported by a Continuing Excellence Fund from the
Genome Damage and Stability Centre, University of Sussex. Thanks also
to additional funding from the Wellcome Trust for initial assay ex-
periments.
This work was also supported by the Brazilian agencies FAPESP
(Fundação de Amparo à Pesquisa do Estado de São Paulo) (2013/
3

F. Scott, et al.
Bioorganic&MedicinalChemistryLettersxxx(xxxx)xxxx
50724-5 and 2014/50897-0) and CNPq (Conselho Nacional de
Desenvolvimento Científico e Tecnológico) (465651/2014-3). The SGC
is a registered charity (number 1097737) that receives funds from
AbbVie, Bayer Pharma AG, Boehringer Ingelheim, Canada Foundation
for Innovation, Eshelman Institute for Innovation, Genome Canada,
Innovative Medicines Initiative (EU/EFPIA) [ULTRA-DD grant no.
115766], Janssen, Merck KGaA Darmstadt Germany, MSD, Novartis
Pharma AG, Ontario Ministry of Economic Development and
Innovation, Pfizer, Takeda, and Wellcome [106169/ZZ14/Z]. We thank
the staff of the Life Sciences Core Facility (LaCTAD) from State
University of Campinas (UNICAMP), for the proteomics analysis. AMF
received a CAPES fellowship (Coordenação de Aperfeiçoamento de
Pessoal de Nível Superior- 88887.136437/2017-00).
BAF180. DNA Repair (Amst). 2016;46:47–54. https://doi.org/10.1016/j.dnarep.
2016.05.030.
17. Rajagopalan P, Nanjappa V, Patel K, et al. Role of protein kinase N2 (PKN2) in ci-
garette smoke-mediated oncogenic transformation of oral cells. J Cell Commun Signal.
2018;12(4):709–721. https://doi.org/10.1007/s12079-017-0442-2.
18. O’Sullivan AG, Mulvaney EP, Hyland PB, Kinsella BT. Protein kinase C-related kinase
1 and 2 play an essential role in thromboxane-mediated neoplastic responses in
prostate cancer. Oncotarget. 2015;6(28):26437–26456. https://doi.org/10.18632/
oncotarget.4664.
19. Park YH, Wood G, Kastner DL, Chae JJ. Pyrin inflammasome activation and RhoA
signaling in the autoinflammatory diseases FMF and HIDS. Nat Immunol.
2016;17(8):914–921. https://doi.org/10.1038/ni.3457.
20. Schnappauf O, Chae JJ, Kastner DL, Aksentijevich I. The pyrin inflammasome in
health and disease. Front Immunol. 2019;10:1745. https://doi.org/10.3389/fimmu.
2019.01745.
21. Sakaguchi T, Takefuji M, Wettschureck N, et al. Protein kinase N promotes stress-
induced cardiac dysfunction through phosphorylation of myocardin-related tran-
scription factor A and disruption of its interaction with actin. Circulation. 2019.
https://doi.org/10.1161/CIRCULATIONAHA.119.041019.
To the best of our knowledge there are no competing interests with
involved parties.
22. Shaw D, Hollingworth G, Soldermann N, et al. Novel ROCK inhibitors for the
treatment of pulmonary arterial hypertension. Bioorg Med Chem Lett.
2014;24(20):4812–4817. https://doi.org/10.1016/j.bmcl.2014.09.002.
23. Pan J, Yin Y, Zhao L, Feng Y. Discovery of (S)-6-methoxy-chroman-3-carboxylic acid
(4-pyridin-4-yl-phenyl)-amide as potent and isoform selective ROCK2 inhibitors.
Bioorg Med Chem. 2019;27(7):1382–1390. https://doi.org/10.1016/J.BMC.2019.02.
047.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.bmcl.2020.127040.
24. Doe C, Bentley R, Behm DJ, et al. Novel Rho kinase inhibitors with anti-inflammatory
and vasodilatory activities. J Pharmacol Exp Ther. 2007;320(1):89–98. https://doi.
org/10.1124/jpet.106.110635.
References
25. Goodman KB, Cui H, Dowdell SE, et al. Development of dihydropyridone indazole
amides as selective Rho-kinase inhibitors. J Med Chem. 2007;50(1):6–9. https://doi.
org/10.1021/jm0609014.
1. Blagg J, Workman P. Choose and use your chemical probe wisely to explore cancer
biology. Cancer Cell. 2017;32(1):9–25. https://doi.org/10.1016/j.ccell.2017.06.005.
2. Arrowsmith CH, Audia JE, Austin C, et al. The promise and peril of chemical probes.
Nat Chem Biol. 2015;11(8):536–541. https://doi.org/10.1038/nchembio.1867.
3. Gleevec: the Breakthrough in Cancer Treatment. http://www.nature.com/scitable/
topicpage/gleevec-the-breakthrough-in-cancer-treatment-565. Accessed March 17,
2016.
26. Arencibia JM, Fröhner W, Krupa M, et al. An allosteric inhibitor scaffold targeting
the PIF-pocket of atypical protein kinase C isoforms. ACS Chem Biol.
2017;12(2):564–573. https://doi.org/10.1021/acschembio.6b00827.
27. Kock M, Lubisch W, Jentzsch A, Use of Parp Inhibitors in Cosmetic Preparations.
WO/2001/082877A2 2001.
28. Lubisch W, Kock M et al. Heterocyclically substituted benzimidazoles, the production
and application thereof. US6696437. 2004.
4. Fedorov O, Müller S, Knapp S. The (un)targeted cancer kinome. Nat Chem Biol.
2010;6(3):166–169. https://doi.org/10.1038/nchembio.297.
29. Takayama K, Koga Y et al. Benzimidazole Derivatives. WO/2001/021615. 2001.
5. Fabbro D, Cowan-Jacob SW, Moebitz H. Ten things you should know about protein
kinases: IUPHAR Review 14. Br J Pharmacol. 2015;172(11):2675–2700. https://doi.
org/10.1111/bph.13096.
́
30. Velık J, Baliharová V, Fink-Gremmels J, Bull S, Lamka J, Skálová L. Benzimidazole
drugs and modulation of biotransformation enzymes. Res Vet Sci.
2004;76(2):95–108. https://doi.org/10.1016/J.RVSC.2003.08.005.
31. Metz JT, Johnson EF, Soni NB, Merta PJ, Kifle L, Hajduk PJ. Navigating the kinome.
Nat Chem Biol. 2011;7(4):200–202. https://doi.org/10.1038/nchembio.530.
32. Francis C. Rix, Smita Kacker, Sudhin Datta, Rul Zhao VRE. Olefin polymerization
catalyst system and process for use thereof. US7601666. 2005.
6. Arencibia JM, Pastor-Flores D, Bauer AF, Schulze JO, Biondi RM. AGC protein ki-
nases: from structural mechanism of regulation to allosteric drug development for the
treatment of human diseases. Biochim Biophys Acta – Proteins Proteomics.
2013;1834(7):1302–1321. https://doi.org/10.1016/j.bbapap.2013.03.010.
7. Lim W, Tan B, Zhu Y, et al. The very C-terminus of PRK1/PKN is essential for its
activation by RhoA and downstream signaling. Cell Signal. 2006;18(9):1473–1481.
https://doi.org/10.1016/j.cellsig.2005.11.009.
33. Schmidt A, Shilabin AG, Nieger M, Mariand M, Levillain P, Sense JM. On benzo[b]
[1,4]diazepinium-olates, -thiolates and -carboxylates as anti-Hückel mesomeric be-
taines. Org Biomol Chem. 2003;1(23):4342–4350. https://doi.org/10.1039/
B308412D.
8. Bauer AF, Sonzogni S, Meyer L, et al. Regulation of protein kinase C-related protein
kinase 2 (PRK2) by an intermolecular PRK2-PRK2 interaction mediated by Its N-
terminal domain. J Biol Chem. 2012;287(24):20590–20602. https://doi.org/10.
1074/jbc.M111.327437.
34. Van Steijvoort BF, Kaval N, Kulago AA, Maes BUW. Remote functionalization: pal-
ladium-catalyzed C5(sp3)-H arylation of 1-Boc-3-aminopiperidine through the use of
a bidentate directing group. ACS Catal. 2016;6(7):4486–4490. https://doi.org/10.
1021/acscatal.6b00841.
9. Amano M, Nakayama M, Kaibuchi K. Rho-kinase/ROCK: a key regulator of the cy-
toskeleton and cell polarity. Cytoskeleton. 2010;67:545–554. https://doi.org/10.
1002/cm.20472.
35. White AW, Almassy R, Calvert AH, et al. Resistance-modifying agents. 9. 1 synthesis
and biological properties of benzimidazole inhibitors of the DNA repair enzyme poly
(ADP-ribose) polymerase. J Med Chem. 2000;43(22):4084–4097. https://doi.org/10.
1021/jm000950v.
10. Leroux AE, Schulze JO, Biondi RM. AGC kinases, mechanisms of regulation and in-
novative drug development. Semin Cancer Biol. 2018;48:1–17. https://doi.org/10.
1016/j.semcancer.2017.05.011.
36. Tsukamoto G, Yoshino K, Kohno T, Ohtaka H, Kagaya H, Ito K. Synthesis and anti-
inflammatory activity of some 2-(substituted-pyridinyl)benzimidazoles. J Med Chem.
1980;23(7):734–738. https://doi.org/10.1021/jm00181a007.
11. Calautti E, Grossi M, Mammucari C, et al. Fyn tyrosine kinase is a downstream
mediator of Rho/PRK2 function in keratinocyte cell–cell adhesion. J Cell Biol.
2002;156(1):137–148. https://doi.org/10.1083/jcb.200105140.
37. Tanaka H, Bohno A, et al. Azole-Substituted Pyridine Compound. WO/2019/031618.
2019.
12. Wallroth A, Koch PA, Marat AL, Krause E, Haucke V. Protein kinase N controls a
lysosomal lipid switch to facilitate nutrient signalling via mTORC1. Nat Cell Biol.
2019;21(9):1093–1101. https://doi.org/10.1038/s41556-019-0377-3.
13. Schmidt A, Durgan J, Magalhaes A, Hall A. Rho GTPases regulate PRK2/PKN2 to
control entry into mitosis and exit from cytokinesis. EMBO J. 2007;26(6):1624–1636.
https://doi.org/10.1038/sj.emboj.7601637.
38. Yoshikawa M, Motoshima K, Fujimoto K, Tai A, Kakuta H, Sasaki K. Pyridinium
cationic-dimer antimalarials, unlike chloroquine, act selectively between the schi-
zont stage and the ring stage of Plasmodium falciparum. Bioorg Med Chem.
2008;16(11):6027–6033. https://doi.org/10.1016/J.BMC.2008.04.051.
39. Hong S, Kim J, Yun S-M, et al. Discovery of new benzothiazole-based inhibitors of
breakpoint cluster region-abelson kinase including the T315I mutant. J Med Chem.
2013;56(9):3531–3545. https://doi.org/10.1021/jm301891t.
14. Cheng Y, Zhu Y, Xu J, et al. PKN2 in colon cancer cells inhibits M2 phenotype po-
larization of tumor-associated macrophages via regulating DUSP6-Erk1/2 pathway.
Mol Cancer. 2018;17:13. https://doi.org/10.1186/s12943-017-0747-z.
15. Lin W, Huang J, Yuan Z, Feng S, Xie Y, Ma W. Protein kinase C inhibitor cheler-
ythrine selectively inhibits proliferation of triple-negative breast cancer cells. Sci Rep.
2017;7(1):2022. https://doi.org/10.1038/s41598-017-02222-0.
40. Sutherlin DP, Sampath D, Berry M, et al. Discovery of (thienopyrimidin-2-yl)ami-
nopyrimidines as potent, selective, and orally available pan-pi3-kinase and dual pan-
PI3-kinase/mTOR inhibitors for the treatment of cancer. J Med Chem.
2010;53(3):1086–1097. https://doi.org/10.1021/jm901284w.
16. Hopkins SR, Mcgregor GA, Murray JM, Downs JA, Savic V. Novel synthetic lethality
screening method identifies TIP60-dependent radiation sensitivity in the absence of
4