I. Beria et al. / Bioorg. Med. Chem. Lett. 21 (2011) 2969–2974
2973
Table 6
in vivo activity on additional tumor models and for toxicological
studies that led to its selection as clinical candidate.
In vivo oral activity of compounds 2 and 7g on HCT116 tumor in nude micea,b
The 2.2 Å crystal structure of the PLK1 kinase domain (residues
36–345) in complex with NMS-P937 was solved to fully character-
ize the interactions between the enzyme and inhibitor and to bet-
ter understand the source of the PLK1 selectivity.16 As expected,
NMS-P937 binds in the ATP-pocket and most of the interactions
are similar to those found in the past with a close analog.10 Specif-
ically, NMS-P937 makes a series of donor–acceptor–donor hydro-
gen bonds with the PLK1 hinge residues (Glu131 & Cys133) and
the amide moiety hydrogen bonds with Lys82 and Asp194
(Fig. 3). The pyrazolo-quinazoline core of NMS-P937 is sandwiched
between Cys67 and Phe183 and the attached ethyl hydroxyl ex-
tends into the ribose pocket. The 20-trifluoromethoxy group binds
in a pocket formed by Arg57 and the hinge segment Leu132-
Cys133-Arg134 and multipolar interactions are present between
fluorine atoms and the guanidinium group of Arg57 and the back-
bone carbonyl of Arg134. Presumably, the ‘fit’ of the 20-trifluoro-
methoxy group in this pocket plays a crucial role in obtaining
PLK selectivity versus kinases bearing a residue bulkier in the posi-
tion corresponding to Leu132, such as those present in Aurora-A
and CDK2. In addition, the 50-methylpiperazine moiety contributes
to the PLK1 selectivity with respect to PLK 2–3 since it establishes a
polar interaction with the side chain of Glu140 and the same type
of interaction is hampered in both PLK2 and PLK3 where Glu140 is
replaced by histidine.10,17
Compound
Dose (mg/kg)
%TGImax (day)
%BWLmax (day)
Death
2
7g
90
90
120
59 (18)
71 (36)
84 (36)
14 (15)
10 (36)
18 (29)
3
0
0
a
n = 7 animals per study.
1–2 daily ꢁ 4 weekly cycles treatment.
b
Control
2.0
Compound 7g
Median tumor
weight (g)
1.0
0.0
10
15
20
25
30
35
Days
Figure 2. In vivo oral antitumor activity of 7g at 60 mg/kg, once a day, 1–10
consecutive days (blue line) on HCT116 xenograft model.
In summary, we report the identification of NMS-P937, a new
PLK1 specific inhibitor that was found to be highly potent on the
target and highly selective versus PLK2 and PLK3 isoforms, as well
as in a wide kinase panel. The compound showed good solubility
and PK properties suitable for either iv or oral administration.
When tested in vivo by oral administration, NMS-P937 showed
good activity and good tolerability also after prolonged treatment.
For its favorable characteristics, NMS-P937 was selected for clinical
development. NMS-P937 is the first selective PLK1 inhibitor given
orally to enter Phase I clinical studies.
Acknowledgments
We thank the group of Assay Development and Biochemical
Screening for the biochemical assay on kinase panel, Dario Ballinari
and the group of Cell Screening for cell proliferation assay, Paolo
Cappella for FACS analysis, Jay Bertrand for crystal structure and
discussion, Daniele Donati and Eduard R. Felder for their useful
comments on the manuscript.
Figure 3. Compound 7g bound to PLK1. Hydrogen bonds are shown as red dashed
lines.
Supplementary data
reversible body weight loss (BWLmax = 16%, day 15) (Table 5).
Higher activity and better tolerability was shown by compound
7g, with respect to 2, after oral administration (po) (Table 6). When
given orally at 90 mg/kg, once a day at days 1, 2, in a weekly sched-
uling ꢁ 4 cycles, compound 2 showed low activity (TGImax = 59%)
with 3/7 death. At the same dose and scheduling, compound 7g
exhibited good activity (TGImax = 71%, day 36) without any death.
In addition, the dose could be increased to 120 mg/kg, without
death and with an improvement of activity (TGImax = 84%, day
36). The better safety profile of 7g in comparison with 2 was
reaffirmed in the 1–10 daily oral scheduling treatment, where
partial regression on 6/7 animals was obtained at 60 mg/kg with
TGImax = 89% at day 23 (Fig. 2). At the same daily dose of 7g
(60 mg/kg), compound 2 showed toxicity with 5 out of 7 death at
five days after the end of the treatment. In view of its better selec-
tivity and safety profile, together with its suitability for a more
flexible scheduling, compound 7g (NMS-P937) was selected for
Supplementary data (mechanism of action by FACS analysis and
kinase profile of compound 7g) associated with this article can be
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