Bioorganic & Medicinal Chemistry Letters
PB-10, a thiazolo[4,5-d] pyrimidine derivative, targets p21-activated kinase
4 in human colorectal cancer cells
Ruijuan Lia,b, Hanxun Wangb, Jian Wangb, , Maosheng Chengb,
a College of Pharmacy, Inner Mongolia Medical University, Huhhot 010110, PR China
b Key Laboratory of Structure-Based Drug Design & Discovery of Ministry of Education, School of Pharmaceutical Engineering, Shenyang Pharmaceutical University,
Shenyang 110016, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Targeting p21-activated kinase 4 (PAK4) is a potential therapeutic strategy against human colorectal cancer
(CRC). In this study, we synthesized a series of novel thiazolo[4,5-d]pyrimidine derivatives (PB-1–12) and
identified PB-10 (PAK4 IC50 = 15.12 μM) as a potential and potent PAK4 inhibitor. Our results showed that PB-
10 significantly suppressed the proliferation and colony formation of human CRC cells. PB-10 also arrested HCT-
116 CRC cells at sub G0/G1 phase while promoting the expression of proapoptotic proteins. In addition, PB-10
inhibited migration, invasion, and adhesion as well as the PAK4 downstream signaling pathway in HCT-116
cells. Molecular docking analysis showed possible binding modes between PB-10 and PAK4. Our study provides a
novel compound that may block the PAK4 signaling in CRC cells.
p21-Activated kinase 4
Inhibitor
Thiazolo[4,5-d]pyrimidine
Colorectal cancer
p21-Activated kinase 4 (PAK4) belongs to the PAK family of serine/
threonine kinases, playing impfortant roles in tumorigenesis and pro-
growth, cell cycle, survival, migration, and invasion in cancer cells.1–4
PAK4 overexpression has been detected in multiple cancer types, in-
cluding colorectal cancer (CRC).5 Elevated expression of PAK4 corre-
lates with advanced tumor stage and poor prognosis in CRC patients;
and PAK4 silencing can inhibit CRC cell proliferation while inducing
cell cycle arrest and apoptosis.4–6 Therefore, targeting PAK4 is a pro-
mising therapeutic strategy against CRC.
previous studies, using a structure-based virtual screening strategy, we
identified thiazolo[4,5-d]pyrimidine-derived compound
a
ZINC28569592 as a promising hit compound toward PAK4 with a half-
maximal inhibitory concentration (IC50) of 18.42 μM.18,19 In this study,
starting from the structure of ZINC28569592, we synthesized a series of
novel thiazolo[4,5-d]pyrimidine derivatives (PB-1–12) with various
structural modification (Fig. 1). In this new series, the chlorine atom at
portion, substituted by alkylic, cycloalkylic, arylalkylic residues. The
replacement of the chlorine by the amine function was not expected to
affect the potency of these compounds to bind the PAK4 active binding
site, and to establish hydrophobic-bond interactions with the amino
acid residues in the hydrophobic entrance of PAK4 active site. We
evaluated the inhibitory activity of these novel synthesized compounds
PB-1–12 toward PAK4, and PB-10 was identified as a novel and potent
lead compound targeting PAK4 in human CRC cells, providing a new
therapeutic approach against CRC.
As a p21-activated protein kinase that phosphorylates multiple
downstream genes, PAK4 is activated by p21 proteins via phosphor-
ments in its catalytic cleft to exchange nucleotide.7,8 Scientists have
developed various ATP-competitive compounds, such as Staurosporine,
LCH-7749944, PF-3758309, and KPT-9274, to inhibit phosphorylation
or conformational movements of PAK4.9–12 Although these compounds
are pan-PAK inhibitors due to the highly-conserved ATP-binding pocket
across the PAK family and did not progress beyond phase I clinical
trials, they provide helpful rationale and scaffolds for the development
of more selective and potent PAK4 inhibitors as anticancer ther-
Synthesis of the designed thiazolo[4,5-d]pyrimidine derivatives PB-
amine (6) as the key intermediate.20 This intermediate was obtained
from thiocarbamide (1) through the synthetic methodology. Treatment
of 1 with ethyl cyanoacetate and sodium ethoxide at 78 °C provided a
good yield of 2. Then, the resulting intermediate 2 was subjected to
nucleophilic substitution with benzyl bromide to produce 3. The C4-
position hydrogen of 3 was selectively substituted with bromine, and
Thiazolo[4,5-d]pyrimidines and their derivatives are purine analo-
gues that display diverse pharmacological properties, including anti-
tumor, antimicrobial, and antiinflammatory activities.15–17 In our
⁎ Corresponding authors.
Pleasecitethisarticleas:RuijuanLi,etal.,Bioorganic&MedicinalChemistryLetters,https://doi.org/10.1016/j.bmcl.2019.126807