2,4,5-Trisubstituted imidazoles: Novel nontoxic modulators of P-glycoprotein mediated multidrug resistance. Part 2

Article abstract of DOI:10.1016/S0960-894X(00)00521-7

Solution-phase combinatorial chemistry was applied to the optimization and development of clinical candidate OC144093 (22), a novel and nontoxic modulator of P-glycoprotein mediated multidrug resistance. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0960-894X(00)00521-7

Bioorganic & Medicinal Chemistry Letters 10 (2000) 2603±2605
2,4,5-Trisubstituted Imidazoles:
Novel Nontoxic Modulators of P-glycoprotein Mediated
Multidrug Resistance. Part 21
Chengzhi Zhang,y Sepehr Sarshar,* Edmund J. Moran,{ Sonja Krane,x
Jennifer C. Rodarte, Khalid D. Benbatoul,{ Ross Dixon and Adnan M. M. Mjallik
Ontogen Corporation, 6541 El Camino, Real Carlsbad, CA 92009, USA
Received 6 June 2000; accepted 7 September 2000
AbstractÐSolution-phase combinatorial chemistry was applied to the optimization and development of clinical candidate OC144-
093 (22), a novel and nontoxic modulator of P-glycoprotein mediated multidrug resistance. # 2000 Elsevier Science Ltd. All rights
reserved.
P-glycoprotein (Pgp) is a high molecular weight head-to-
tail dimeric protein that was originally isolated from
mutant Chinese hamster ovary cells in 1976.2 Each
monomer consists of multiple transmembrane domains
and an ATP binding site.3 Pgp is a normal constituent of
several tissues (e.g. intestinal, renal, and blood±brain
barrier) and plays a vital role in the clearance of structu-
rally unrelated toxic agents from the body via an active
e‚ux mechanism.4 Unfortunately, this critical property
of Pgp is a leading cause of fatality in cancer patients
whose tumor cells display intrinsic or acquired immunity
against a wide range of chemotherapies. Dubbed multi-
drug resistance or MDR, clinical oncologists were the
®rst to describe this syndrome which is often associated
with the over-expression of Pgp in cancer cells.5
In the preceding article, we described a novel class of
2,4,5-trisubstituted imidazoles (A) with potent Pgp
inhibitory pro®le.7 We now wish to report the successful
application of solution-phase combinatorial chemistry
to the development of the clinical candidate OC144-093
(22), a nontoxic modulator of Pgp mediated MDR.8
The structure±activity relationships (SARs) of the 1-
and 2-positions of the imidazole core were explored and
optimized using solid-phase combinatorial chemistry.7
In short, imidazoles with structures C and D showed the
highest potency. Although ester metabolism of imida-
zoles C was not very signi®cant, imidazoles D proved
more stable. However, pharmacokinetic measurements
indicated that the Me2N groups in both classes were
rapidly metabolized. N-Demethylation and N-oxide
formation are common metabolites of tertiary amines, a
problem that may be circumvented through the intro-
duction of bulky secondary amines. Our strategy for the
optimization of these amine functionalities is summar-
ized in Figure 1. Due to the limited availability of 1,2-
aryldiones, we decided to employ a solution-phase
approach in which various amine groups could be
introduced consecutively via nucleophilic displacement
on di¯uorobenzil.
Over the last decade, the development of in vitro MDR
modulators has been remarkably successful, yet to date no
agent has displayed signi®cant clinical ecacy.6 This is
largely due either to the inherent toxicity of these com-
pounds or to the heightened toxicity of the antineo-
plastic agents when co-administered with the modulator.
*Corresponding author. Present address: P®zer Global, San Diego, CA
92121, USA. Tel.: +1-858-622-7506; fax: +1-858-678-8277; e-mail:
sep.sarshar@agouron.com
This route proved most desirable since a large number
of symmetrical and unsymmetrical imidazoles could be
generated eciently. Tables 1 and 2 summarize the
activities of a number of these compounds.9 When the
nucleophile was Me2NH, a demethylated by-product B
formed in 10±15% during the cyclo-dehydration step.
This fortuitous result allowed us to explore the activity
yPresent address: Bayer Corporation, Pharmaceuticals Division, West
Haven, CT 06516, USA.
{Present address: Advanced Medicine, South San Francisco, CA
94080, USA.
xPresent address: Columbia University, Department of Chemistry,
New York, NY 10027, USA.
{Present address: Ligand Pharmaceuticals, La Jolla, CA 92121, USA.
kPresent address: TransTech Pharma, High Point, NC 27265, USA.
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00521-7

2604
C. Zhang et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2603±2605
of potential ®rst pass metabolites. To our delight, imi-
dazoles B showed both improved potency and meta-
bolic stability (Tables 1, 2, and 3). Subsequently, other
analogues of 5 were prepared using CH3NH2±HCl salt.
For imidazoles B increasing the bulk of the tertiary
amine substituent proved detrimental to the activity
(Table 1, entries 5 to 8). The best results were obtained
when both amine substituents were secondary (Table 1,
entries 11 and 12; Table 2 entries 19, 20, and 22).
Replacement of one of the amino substituents with a
¯uorine did not increase the metabolic stability of this
class (Table 3, entries 19, 21, and 22).
modulators. Figure 2 summarizes our strategy for the
synthesis of 2,5-disubstituted imidazoles E.
The 2,5-disubstituted imidazoles F show similar SAR
trends as the 2,4,5-trisubstituted imidazoles C and D but
have lower in vitro potency (Table 4). Hence, further
optimization was not pursued and compound 22 was
chosen as the initial clinical development candidate.
Pharmacokinetic studies in healthy male volunteers
(400 mg/oral gave) revealed 3±5 mM concentrations of
22 (OC144-093) in the plasma after 3±4 h. These plasma
levels are signi®cantly higher than the 1 mM concentra-
tion required for full reversal of Pgp mediated MDR in
preclinical models. Virtually no adverse side e€ects or
evidence of CNS toxicity was observed. When adminis-
tered with a fatty meal, a signi®cant increase in the oral
bioavailability of 22 was noted as compared to the fas-
ted state. Based on previous intravenous data, the oral
bioavailability of 22 in man is estimated to be greater
than 60% with food and its terminal half-life at around
22 h. The latter suggests that once- or twice-a-day oral
dosing may be sucient to maintain therapeutic levels
of the modulator. In a second placebo controlled study,
the tolerability and safety of three sequential escalating
doses of 200, 300, or 400 mg of 22 were evaluated.
Healthy male volunteers were dosed in parallel groups
Given the excellent potency and half-life of 22 (OC144-
093), we next turned our attention to improving the oral
bioavailability of these compounds. We initially focused
our e€orts on reducing the molecular weight of the
Table 2. Modulation of Pgp mediated multidrug resistance in CEM/
VLB 1000 cells
Figure 1. Solution-phase synthesis of tri-substituted imidazoles A and
B. (a) R1R2NH, K2CO3, DMSO, 90 ꢀC; (b) R3R4NH, K2CO3, DMSO,
90 ꢀC; (c) R5CHO, NH4OAc, AcOH, 100 ꢀC. A: X=R1R2N (80%); B:
X=R1NH (10±15%).
Table 1. Modulation of Pgp mediated multidrug resistance in CEM/
VLB 1000 cellsa
Compound
R1
R2
ED50, mMa
13
14
15
16
17
18
19
20
21
22
Me2N
Et2N
Me2N
Et2N
N-Morpholine
Me2N
Et2N
N-Pyrolidine
i-PrNH
i-PrNH
i-PrNH
i-PrNH
0.08
0.26
0.22
0.11
0.06
0.15
0.05
0.05
0.16
0.05
N-Morpholine
MeNH
MeNH
MeNH
MeNH
EtNH
Compound
R1
R2
ED50, mMb
F
i-PrNH
1
2
3
4
5
6
7
8
Me2N
Et2N
Pyrrolidine
(Allyl)2N
Me2N
Et2N
Pr2N
Bu2N
Me2N
Me2N
Et2N
0.30
0.57
0.37
5.50
0.13
0.07
0.18
2.10
0.59
0.31
0.20
0.12
Pyrrolidine
(Allyl)2N
MeNH
MeNH
MeNH
MeNH
NH2
NH2
MeNH
MeNH
aED50 is de®ned as the compound concentration that causes 50%
inhibition of cell growth.
Table 3. Dog pharmacokinetic parameters for selected imidazolesa
9
Compound
R1
R2
t1/2, h
F%
10
11
12
Et2N
MeNH
i-PrNH
13
19
21
22
Me2N
MeNH
F
Me2N
i-PrNH
i-PrNH
i-PrNH
0.5
35
36
45
41
1.35
1.27
2.79
aCEM/VLB1000 is a CEM (human lymphoma) derived cell line that
overexpresses Pgp and is selected for Vinblastine resistance.
bED50 is de®ned as the compound concentration that causes 50%
inhibition of cell growth.
i-PrNH
aDosage: 5 mg/kg, iv; 10 mg/kg, po

C. Zhang et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2603±2605
2605
for the enhancement of oral bioavailability of certain
therapeutic agents (e.g. paclitaxel and saquinavir) that
are substrates for Pgp in the gut.
References and Notes
1. Part 2 in the series. For additional data related to this work
see: (a) Mjalli, A. M. M.; Sarshar, S. U.S. Patent 5,700,826,
1997; Chem. Abstr. 1997, 126, 8263. (b) Mjalli, A. M. M.;
Sarshar, S. U.S. Patent 5,756,527, 1998; Chem. Abstr. 1998,
126, 352632. (c) Mjalli, A. M. M.; Zhang, C. U.S. Patent
5,840,721, 1998; Chem. Abstr. 1998, 126, 774230.
2. Juliano, R. L.; Ling, V. Biochim. Biophys. Acta 1978, 455,
152.
Figure 2. Synthesis of 2,5-disubstituted imidazoles E. (a) R1R2NH,
K2CO3, DMSO, 90 ꢀC (85±95%); (b) Hg(OAc)2 (50±60%); (c) NH3,
R3CHO, MeOH, 23 ꢀC (40±50%).
3. (a) Endicott, J. A.; Ling, V. Annu. Rev. Biochem. 1989, 58,
137. (b) Gottesman, M. M.; Pastan, I. Annu. Rev. Biochem.
1993, 62, 385.
Table 4. Modulation of Pgp mediated multidrug resistance in CEM/
VLB 1000 cells
4. (a) Thiebaut, F.; Tsuruo, T.; Hamada, H.; Gottesman, M.
M.; Pastan, I. Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 7735. (b)
Cordon-Cardo, C.; O'Brien, J. P.; Casals, D.; Rittman-
Grauer, L.; Biedler, J. L.; Melamed, M. R.; Bertino, J. R.
Proc. Natl. Acad. Sci. U.S.A. 1989, 86, 695.
5. Ambukar, S. V.; Dey, S.; Hrycyna, C. A.; Ramachandra,
M.; Pastan, I.; Gottesman, M. M. Annu. Rev. Pharmacol.
Toxicol. 1999, 39, 361.
6. Ford, J. M.; Hait, W. N. Pharmacol. Rev. 1990, 2, 155.
7. Sarshar, S.; Zhang, C. Z.; Moran, E. J.; Krane, S.; Rodarte,
J. C.; Benbatoul, K. D.; Dixon, R.; Mjalli, A. M. M. Bioorg.
Med. Chem. Lett. 2000, 10, 2599.
8. Details of the biological experiments have been published
separately, see: Newman, M. J.; Rodarte, J. C.; Benbatoul, K.
D.; Romano, S. J.; Zhang, C.; Krane, S.; Moran, E. J.; Uyeda,
R. T.; Dixon, R.; Guns, E. S.; Mayer, L. D. Cancer Res. 2000,
60, 2964.
9. MDR potentiation assays were carried out using CEM/
VLB1000 cells in the presence of Vinblastine (5 mg/mL) and
compound (0.01 to 50 mM). Verapamil was used as the refer-
ence standard. The compounds evaluated in Tables 1, 2, and 4
did not show inherent toxicity at the concentrations tested.
For detailed in vitro protocols see ref 8.
Compound
R1
ED50, mMa
23
24
25
26
27
Et2N
Pr2N
Morpholine
i-PrNH
i-BuNH
0.3
0.28
0.37
0.34
0.25
aED50 is de®ned as the compound concentration that causes 50%
inhibition of cell growth.
at 6, 12, and 24 h intervals, respectively. OC144-093 was
well tolerated at all dose levels and was free of any ser-
ious side e€ects. Currently, 22 is also being evaluated