4990
J. Drewe et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4987–4990
Table 2. Comparison of caspase activation activity and growth inhibition activity of 5-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-7-phenyl-(E)-
2,3,6,7-tetrahydro-1,4-thiazepines
Entry
T47D
HCT116
a
b
a
b
EC50 (lM)
GI50 (lM)
GI50/EC50
EC50 (lM)
GI50 (lM)
GI50/EC50
2a
5b
5c
5d
5f
1.19 0.014
0.29 0.063
0.41 0.069
0.077 0.007
0.33 0.010
0.57 0.011
0.89 0.21
0.30 0.09
0.21 0.03
0.048 0.010
0.47 0.08
0.51 0.03
0.8
1.0
0.5
0.6
1.4
0.9
1.29 0.13
0.37 0.050
0.56 0.010
0.11 0.013
0.53 0.055
0.79 0.072
1.69 0.04
0.35 0.03
0.25 0.05
0.095 0.016
0.49 0.11
0.53 0.03
1.3
1.0
0.4
0.8
0.9
0.7
6a
a Data are means of three or more experiments and are reported as means standard error of the mean (SEM).
b Data are means of three experiments and are reported as means standard error of the mean (SEM).
Compounds 4c and 4d were both active, with potencies
in the 2 lM range, suggesting that a small substituent
such as OMe at the 2-position contributes positively to
the apoptosis inducing activity.
is not only useful for the identification of inducers of
apoptosis, but also is useful for subsequent optimization
and SAR study of screening hits.
In conclusion, we have identified a series of substituted
5-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-7-phenyl-
(E)-2,3,6,7-tetrahydro-1,4-thiazepines as potent apopto-
sis inducers. Compound 2a was found to arrest cancer
cells in G2/M and to inhibit tubulin polymerization,
which most probably is its mechanism of action for
induction of apoptosis. Through SAR studies, com-
pound 5d was identified as the most potent compound
in this series with an EC50 value of 0.08 lM in T47D
cells, which was >15-fold more potent than screening
hit 2a. Compound 5d also is highly active in the growth
inhibition assay with a GI50 value of 0.05 lM in T47D
cells and functions by inhibiting tubulin polymerization.
Since the SAR data show that a substituent at the 4-po-
sition is important for activity, and a small group at the
2-position contributes positively to activity, we explored
the combination of substituents at the 4-position with an
OMe group at the 2-position. Compounds 5a–5f were all
more active than the corresponding 4-substituted and 2-
OMe substituted analogs. Compound 5d was the most
potent analog, with an EC50 value of 0.08 lM. In com-
parison, the 3,4-diOMe analog 6a and 2,3-dimethoxy
analog 6b were less active than the 2,4-diOMe analog
5c. The 2,3,4-trimethoxy analog 7a was more potent
than 2,4- and 3,4-diOMe analogs 5c and 6a, confirming
that an OMe group at the 2- and 3-position contributes
positively to activity.
References and notes
Overall, the trend of apoptosis inducing activities of the
substituted thiazepines in human breast cancer T47D
cells was similar to that observed in human colon cancer
HCT116 cells (Table 1). All of the compounds that were
active in T47D cells were active in HCT116 cells, and all
of the compounds that were inactive in T47D cells up to
10 lM also were found to be inactive in HCT116 cells.
Compound 5d, the most active analog in T47D cells,
also was the most active one in HCT116 with an EC50
value of 0.1 lM.
1. Reed, J. C.; Tomaselli, K. J. Curr. Opin. Biotechnol. 2000,
11, 586.
2. Reed, J. C. Nat. Rev. Drug Discov. 2002, 1, 111.
3. Tolomeo, M.; Simoni, D. Curr. Med. Chem. AntiCancer
Agents 2002, 2, 387.
4. Fischer, U.; Schulze-Osthoff, K. Pharmacol. Rev 2005, 57,
187.
5. Cai, S. X.; Drewe, J.; Kasibhatla, S. Curr. Med. Chem.
2006, 13, 2627.
6. Kemnitzer, W.; Kasibhatla, S.; Jiang, S.; Zhang, H.;
Wang, Y.; Zhao, J.; Jia, S.; Herich, J.; Labreque, D.;
Storer, R.; Meerovitch, K.; Bouffard, D.; Rej, R.; Denis,
R.; Blais, C.; Lamothe, S.; Attardo, G.; Gourdeau, H.;
Tseng, B.; Drewe, J.; Cai, S. X. J. Med. Chem. 2004, 47,
6299.
7. Zhang, H.-Z.; Kasibhatla, S.; Wang, Y.; Herich, J.;
Guastella, J.; Tseng, B.; Drewe, J.; Cai, S. X. Bioorg.
Med. Chem. 2004, 12, 309.
8. Zhang, H.-Z.; Kasibhatla, S.; Kuemmerle, J.; Kemnitzer,
W.; Oliis-Mason, K.; Qui, L.; Crogran-Grundy, C.; Tseng,
B.; Drewe, J.; Cai, S. X. J. Med. Chem. 2005, 48, 5215.
9. Sirisoma, N.; Kasibhatla, S.; Nguyen, B.; Pervin, A.;
Wang, Y.; Claassen, G.; Tseng, B.; Drewe, J.; Cai, S. X.
Bioorg. Med. Chem. 2006, 14, 7761.
Selected thiazepines were assayed in a traditional growth
inhibition (GI50) assay to confirm that those active in
the caspase induction assay also inhibit tumor cell
growth. The growth inhibition assays in T47D and
HCT116 cells were run in a 96-well microtiter plate as
described previously9 and the data are summarized in
Table 2. Compound 5d had a GI50 value of 0.05 and
0.1 lM in T47D and HCT116 cells, respectively. In gen-
eral, the compounds more active in the apoptosis induc-
tion assay, as measured by caspase activation, also are
more potent in the growth inhibition assay, and the ratio
of GI50/EC50 is around 1 for all the tested compounds.
Compound 5d also was tested in the tubulin polymeriza-
tion assay and was found to be more active than hit 2a,
inhibiting tubulin polymerization completely at 5 lM.
Similar to what we reported earlier,6,11 these data con-
firm that the cell-based caspase activation HTS assay
10. Sucheta, K.; Prashant, A.; Rama Rao, N. Indian J. Chem.
Sect. B 1995, 34B, 893.
11. Cai, S. X.; Nguyen, B.; Jia, S.; Herich, J.; Guastella, J.;
Reddy, S.; Tseng, B.; Drewe, J.; Kasibhatla, S. J. Med.
Chem. 2003, 46, 2474.