T. Wang et al. / Bioorg. Med. Chem. Lett. 23 (2013) 4790–4793
4791
NO2
NH2
NO2
b
a
NH
R
NH
R
F
1
3
2
NH2
NH2
NO2
NH2
NO2
NH2
b
c
R'
Br
R'
4
5
6
Scheme 1. Reagents and conditions: (a) RNH2, EtOH; (b) Pd/C, ammonium formate, reflux; (c) Pd(PPh3)4, K2CO3, R’B(OH)2.
NH2
O
R'
O
N
NH2
O
a
8
R
O
R'
+
O
Cl
+
NH
R
O
H
O
N
7
3, 6
R'
or commercially available
diamine
O
O
NH
R
9
R'
R'
N
N
OH
NH
c
b
O
N
R
N
R
O
O
10
11
Scheme 2. Reagents and conditions: (a) DCM, DIEA; (b) AcOH, toluene, heat; (c) NH2OH (50% in water), NaOH (1 M), THF/MeOH.
All of the compounds were first screened in the human ovarian
cancer SKOV3cell assay (Table 1). Compound 11a inhibited the cell
HDAC biochemical assays demonstrated that compound 11e
was a pan-HDAC inhibitor with single digit nano-molar IC50
against HDAC3, 5, 6, 9 and 10 (Table 2). In contrast to SAHA, 11e
potently inhibited HDAC4, 7 and 9.7 Additional cell based screening
revealed that compound 11e was a potent agent with broad anti-
proliferative activities and outperformed SAHA in most of the cell
lines we examined (Table 3).8,9 Notably, compound 11e potently
inhibited the pancreatic cancer MiaPaca line with an IC50 = 89
nM, and had an IC50 of 173 nM in the resistant lung cancer H69-
Gli1 line, a 25-fold improvement over standard cisplatin/etopside
proliferation with an IC50 of 2.7
lM, equally potent as SAHA
(IC50 = 2.3 M) in the same assay. Shortening the floppy carbon
l
chain appeared detrimental and compound 11b with a five carbon
linker was about four fold less potent than 11a. Substitutions on the
benzimidazole ring were explored next. Halogen substitution at the
6 position of the benzimidazole ring had beneficial effect and im-
proved the cell activity with 6-F (11c, IC50 = 1.9
remarkably, with 6-Cl (11d, IC50 = 0.32 M) and 6-Br(11e,
IC50 = 0.27 M). Further enhancement of the cell activity was
observed when a benzene ring (11f, IC50 = 0.1 M) was installed
lM) and more
l
l
(1:2) treatment (IC50 = 4.5 lM).
l
Finally, compound 11e was tested in the human pancreatic can-
cer MiaPaca xenograft mousemodel.10,11 Daily oral administration
of 11e at 100 mg/kg for 22 days resulted in 74% tumor growth inhi-
bition when compared to the vehicle control as measured on Day
22 (Fig. 2). It also showed comparable efficacy with Gemcitabine
(80 mg/kg) on Day 25 when the study ended. No gross toxicity of
11e was observed following daily oral dosing.
In conclusion, we have identified a series of benzimidazole
based HDAC inhibitors through cell screening and most of
these inhibitors exhibit potent cell activity. The lead compound
11e demonstrates broad anti-proliferative activity in a variety
of cell lines and is active in MiaPaca xenograft mouse model.
The potential of this novel class of HDAC inhibitors for treating
cancer and other HDAC related disorders in clinical is being
explored.
at 6-position. Attempts to improve the activity by manipulating
the terminal ring were not successful, and compounds 11g–l were
much less active than 11f. Shifting the substitutions from the
6- to the 5-position appeared unfavorable, and compound 11m
was about 30-fold less active than 11d. Electronic donating groups
such as 6-methoxy 11n and 6-dimethylamino 11o did not enhance
the activity and the imidazole[4,5-c]pyridine system 11p killed the
activity completely. Additional groups on the N-1 exemplified by
11q,11r, 11s and 11t proved mostly disadvantageous. While
compound 11q had similar activity as 11a, the other compounds,
11r–t, with bigger groups were all less active.
Compound 11e (a.k.a T009) and 11f emerged as the leads after
the cell based screening. Because compound 11e had better solu-
bility than 11f, it was chosen for further testing.