Inhibition of Carboxylesterases by Benzil
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 17 5549
angle of ∼230° following the molecular dynamics simu-
lations (Figures 2, 3, and 4). Since we have previously
postulated that reactivity with the active site serine
residue within CEs is important for enzyme inhibition,21
it is likely that the conformation of the inhibitor when
at this particular angle allows nucleophilic attack of the
dione.
Supporting Information Available: Elemental com-
position analysis of compounds 5, 6, and 7 and the full details
of the crystal structure determinations for 6 and 7. This
material is available free of charge via the Internet at
http://pubs.acs.org.
References
(
1) Cashman, J.; Perroti, B.; Berkman, C.; Lin, J. Pharmacokinetics
and molecular detoxification. Environ. Health Perspect. 1996,
104, 23-40.
Similar results were observed with 2,2′-thenil (4) and
,3′-thenil (5), with the former compound demonstrating
3
(
2) Brzezinski, M. R.; Abraham, T. L.; Stone, C. L.; Dean, R. A.;
Bosron, W. F. Purification and characterization of a human liver
cocaine carboxylesterase that catalyzes the production of ben-
zoylecgonine and the formation of cocaethylene from alcohol and
cocaine. Biochem. Pharmacol. 1994, 48, 1747-1755.
3) Danks, M. K.; Morton, C. L.; Krull, E. J.; Cheshire, P. J.;
Richmond, L. B.; Naeve, C. W.; Pawlik, C. A.; Houghton, P. J.;
Potter, P. M. Comparison of activation of CPT-11 by rabbit and
human carboxylesterases for use in enzyme/prodrug therapy.
Clin. Cancer Res. 1999, 5, 917-924.
lower Ki values, reduced mobility around the dione
moiety, and a final dihedral angle close to 230° (Fig-
ure 4A). However, the mobility seen with bromine-
substituted thenils (Table 2 and Figure 4B) did not
correlate with enzyme inhibition. In these cases, in-
creased flexing was seen in the molecular dynamics
simulations that persisted for the entire 15 ps run
(
(
Figure 4B). Analysis of the contribution of halides to
(4) Danks, M. K.; Potter, P. M. Enzyme-prodrug systems: carboxyl-
esterase/CPT-11. Methods Mol. Med. 2004, 90, 247-262.
the aromaticity of the thiophene ring has been discussed
by Sargent et al.4 These authors reported that substi-
tution at the 5-position of the ring might influence the
distribution of the π electrons within the thiophene
moiety. These theoretical studies suggest that the
bromine atoms may disrupt the aromaticity of the rings
(
5) Khanna, R.; Morton, C. L.; Danks, M. K.; Potter, P. M. Proficient
metabolism of CPT-11 by a human intestinal carboxylesterase.
Cancer Res. 2000, 60, 4725-4728.
1
(
6) Pindel, E. V.; Kedishvili, N. Y.; Abraham, T. L.; Brzezinski, M.
R.; Zhang, J.; Dean, R. A.; Bosron, W. F. Purification and cloning
of a broad substrate specificity human liver carboxylesterase that
catalyzes the hydrolysis of cocaine and heroin. J. Biol. Chem.
1997, 272, 14769-14775.
4
1
due to π electron donation. Our studies indicate that
the halogen also influences the rotation around and the
dihedral angle of the dione bond within the thenils, and
hence both factors may contribute to the biological
activity of these compounds. However, substitution of
hydrogen atoms in the thiophene rings with bromine
increased the potency of the molecules toward CE
inhibition (Table 2). The most likely explanation for this
is that the halogen atoms significantly increase the
hydrophobicity of the molecules (log P values for the
bromo analogues are 4.06, as compared to 2.77 for 2,2′-
thenil, as calculated using ChemSilico Predict software
(
7) Potter, P. M.; Wolverton, J. S.; Morton, C. L.; Wierdl, M.; Danks,
M. K. Cellular localization domains of a rabbit and a human
carboxylesterase: Influence on irinotecan (CPT-11) metabolism
by the rabbit enzyme. Cancer Res. 1998, 58, 3627-3632.
(8) Satoh, T.; Hosokawa, M. The mammalian carboxylesterases:
from molecules to function. Annu. Rev. Pharmacol. Toxicol. 1998,
3
8, 257-288.
(
9) Satoh, T.; Hosokawa, M.; Atsumi, R.; Suzuki, W.; Hakusui, H.;
Nagai, E. Metabolic activation of CPT-11, 7-ethyl-10-[4-(1-
piperidino)-1-piperidino]carbonyloxycamptothecin, a novel anti-
tumor agent, by carboxylesterase. Biol. Pharm. Bull. 1994, 17,
6
62-664.
(10) Wadkins, R. M.; Morton, C. L.; Weeks, J. K.; Oliver, L.; Wierdl,
M.; Danks, M. K.; Potter, P. M. Structural constraints affect the
metabolism of 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyl-
oxycamptothecin (CPT-11) by carboxylesterases. Mol. Pharma-
col. 2001, 60, 355-362.
(ChemSilico LLC, Tewkesbury, MA)). Previous studies
(
11) Guemei, A. A.; Cottrell, J.; Band, R.; Hehman, H.; Prudhomme,
M.; Pavlov, M. V.; Grem, J. L.; Ismail, A. S.; Bowen, D.; Taylor,
R. E.; Takimoto, C. H. Human plasma carboxylesterase and
butyrylcholinesterase enzyme activity: correlations with SN-
with benzil analogues have indicated that substitution
of either chlorine or bromine atoms within the aromatic
rings, significantly reduces the Ki values for CE inhibi-
tion, likely due to enhanced affinity of the compound
3
8 pharmacokinetics during a prolonged infusion of irinotecan.
Cancer Chemother. Pharmacol. 2001, 47, 283-290.
10,21,25
for the highly hydrophobic enzyme active site.
The
(12) Morton, C. L.; Wierdl, M.; Oliver, L.; Ma, M.; Danks, M. K.;
Stewart, C. F.; Eiseman, J. L.; Potter, P. M. Activation of CPT-
results presented here with the 2,2′-thenil analogues are
consistent with these previous observations.
1
1 in mice: Identification and analysis of a highly effective
plasma esterase. Cancer Res. 2000, 60, 4206-4210.
(
(
(
13) Morton, C. L.; Taylor, K. R.; Iacono, L.; Cheshire, P.; Houghton,
P. J.; Danks, M. K.; Stewart, C. F.; Potter, P. M. Metabolism of
CPT-11 in esterase deficient mice. Proc. Am. Assoc. Cancer Res.
Overall, our data suggests that the inhibition of CEs
by aromatic diones is dependent upon the aromaticity
of the rings and the flexibility of the molecules around
the dione moiety. We are currently using these data to
predict the ability of novel compounds to inhibit these
enzymes, with the ultimate goal of designing and
synthesizing potent, water soluble CE inhibitors.
2002, 43, 248.
14) Potter, P. M.; Pawlik, C. A.; Morton, C. L.; Naeve, C. W.; Danks,
M. K. Isolation and partial characterization of a cDNA encoding
a rabbit liver carboxylesterase that activates the prodrug
Irinotecan (CPT-11). Cancer Res. 1998, 52, 2646-2651.
15) Bleiberg, H.; Cvitkovic, E. Characterisation and clinical manage-
ment of CPT-11 (irinotecan)-induced adverse events: the
European perspective. Eur. J. Cancer 1996, 32A Suppl 3, S18-
2
3.
Acknowledgment. This work was supported in part
by an NIH Cancer Center Core Grant P30 CA-21765
(
(
16) Rivory, L. P. Irinotecan (CPT-11): a brief overview. Clin. Exp.
Pharmacol. Physiol. 1996, 23, 1000-1004.
17) Saliba, F.; Hagipantelli, R.; Misset, J. L.; Bastian, G.; Vassal,
G.; Bonnay, M.; Herait, P.; Cote, C.; Mahjoubi, M.; Mignard, D.;
Cvitkovic, E. Pathophysiology and therapy of irinotecan-induced
delayed-onset diarrhea in patients with advanced colorectal
cancer: a prospective assessment. J. Clin. Oncol. 1998, 16,
(
J.L.H., K.J.P.Y., M.W., C.C.E., M.K.D., P.M.P.), the
American Lebanese Syrian Associated Charities (J.L.H.,
K.J.P.Y., M.W., C.C.E., M.K.D., P.M.P.), the Donors of
the American Chemical Society Petroleum Research
Fund (G.C.), Central Connecticut State University
Faculty-Research Grants (V.S., G.C.) Central Con-
necticut State University Research Grants (V.S., G.C.),
and NSF Grant 0111511 (M.Z., JU), and the diffrac-
tometer was funded by NSF grant 0087210, by Ohio
Board of Regents Grant CAP-491, and by Youngstown
State University.
2
745-2751.
(
(
(
18) Beroza, P.; Villar, H. O.; Wick, M. M.; Martin, G. R. Chemo-
proteomics as a basis for post-genomic drug discovery. Drug
Discovery Today 2002, 7, 807-814.
19) Dixon, S. L.; Villar, H. O. Bioactive diversity and screening
library selection via affinity fingerprinting. J. Chem. Inf. Com-
put. Sci. 1998, 38, 1192-1203.
20) Dixon, S. L.; Villar, H. O. Investigation of classification methods
for the prediction of activity in diverse chemical libraries.J.
Comput.-Aided Mol. Des. 1999, 13, 533-545.