J.-F. Liu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 686–690
689
SF-268) and one primary cell culture (human mammary
cell, HMEC) in an MTS cell proliferation assay. The ac-
tive compounds with IC50 data are summarized in Table
1. The IC50 concentrations of active compounds were
less than 20 lM in most cancer cell lines tested. The
IC50 in HMEC cells was greater than 20 lM (data not
shown), indicating that compounds 5 target cancer cells
specifically. Interestingly, the highly oxygenated substi-
tution pattern of the pendant phenyl ring of 5 (4-hy-
droxy-3,5-dimethoxy) played an important role in the
activity. Conversely, the compounds with other func-
tional groups on R2 (5c–5e) or H (5b) (data not shown)
did not exhibit any cytotoxic activity. Regarding the
SAR of the R1 moiety, the compounds with substituents
on position 3, in general, are more active than those of
substituents on other positions (5a, 5h, 5j, and 5k vs
5l–5p, 5r). Given that compound 5b possesses the parent
structure found in 3, which was effective at inhibiting
gastric acid secretion and ulcer formation, and given
the identification of the cytotoxicity of compounds 5
in our hands, we believe that 2 may be a privileged sub-
structure in its own right.
tified that tetrahydropyrido[2,1-b]quinazolin-10(H)-one
(2) may be a privileged substructure. Screens with pH3
assay and tubulin assay suggested that this class of com-
pounds are antimitotic agents and exert their action
through the inhibition of tubulin polymerization. Re-
search on the design and synthesis of privileged struc-
ture-based quinazolinone natural product-templated
libraries and identification of novel antimitotic agents
is ongoing and the results will be reported in due course.
Acknowledgments
The authors thank Dr. Jeffrey Link, Mr. Ted Manley
for microwave technical support; Dr. Craig Thompson,
Mr. Bill Dahlberg, and Ms. Hannah Neumeier for assay
support.
References and notes
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The active compounds from cell-kill screens were pro-
gressed to the phosphohistone H3 (pH3) assay (Table
1) to evaluate whether they induce mitotic arrest.22
The results demonstrated that these compounds induced
mitotic arrest in a dose-dependent fashion with the EC50
of pH3 from 0.3 to 11 lM, suggesting that the mecha-
nism of the cell proliferation perturbation is very likely
caused by mitotic arrest.
Tubulin polymerization dynamics within the cell are
critical for completion of mitosis and are frequently tar-
geted by agents that induce mitotic arrest.23 The tubulin
polymerization assay was used to determine whether
these compounds perturbed tubulin dynamics. All of ac-
tive compounds in the MTS assay were selected for
screening in tubulin polymerization assay. They all
showed inhibitory activity to tubulin polymerization.
The representative data are shown in Figure 3. These
data strongly supports the notion that this class of com-
pounds interferes directly with tubulin polymerization
by binding to the tubulin and that this interaction is
the likely cause of mitotic arrest.
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Vehicle
(DMSO)
5f
10000
5g
5h
5a
Vinblastine
0
0
60
Time (Minutes)
Figure 3. The tubulin assay with selected compounds.