Modulation of human mammary cell sensitivity to paclitaxel by new quinoline sulfonamides

Article abstract of DOI:10.1016/S0960-894X(01)00462-0

Sulfonamide derivatives of chloroquine and primaquine were synthesised and evaluated against both paclitaxel-sensitive and paclitaxel-resistant mammarian cancer cell lines. All derivatives exhibited at least 96% MDR reversal activity when co-administered with paclitaxel at 5 μM. The best compound, a chloroquine derivative, exhibited 99% MDR reversal activity when co-administered with paclitaxel at 1 μM. Molecular modelling studies reveal that these derivatives share a common pharmacophore with taxane MDR reversal agents.

Full text of DOI:10.1016/S0960-894X(01)00462-0

Bioorganic & Medicinal Chemistry Letters 11 (2001) 2457–2460
Modulation of Human Mammary Cell Sensitivity to Paclitaxel
by New Quinoline Sulfonamides
Kelly Chibale,a,* Iwao Ojima,b Hayley Haupt,a Xugong Geng,b Paula Perac
c
and Ralph J.Bernacki
aDepartment of Chemistry, University of Cape Town, Rondebosch 7701, South Africa
bDepartment of Chemistry, State University of New York at Stony Brook, NY 11794, USA
cDepartment of Pharmacology & Therapeutics, Grace Cancer Drug Centre, Roswell Park Cancer Institute,
Elm and Carlton Streets, Buffalo, NY14263, USA
Received 7 May 2001; accepted 28 June 2001
Abstract—Sulfonamide derivatives of chloroquine and primaquine were synthesised and evaluated against both paclitaxel-sensitive
and paclitaxel-resistant mammarian cancer cell lines.All derivatives exhibited at least 96% MDR reversal activity when co-
administered with paclitaxel at 5 mM.The best compound, a chloroquine derivative, exhibited 99% MDR reversal activity when co-
administered with paclitaxel at 1 mM.Molecular modelling studies reveal that these derivatives share a common pharmacophore
with taxane MDR reversal agents. # 2001 Elsevier Science Ltd.All rights reserved.
One major problem in cancer chemotherapy is cellular
resistance to structurally and functionally unrelated
chemotherapeutic agents.This multidrug resistance
(MDR) phenotype is often associated with an increase
in P-glycoprotein on the cell surface.1 P-glycoprotein, a
170-kDa plasma membrane protein, acts as an energy-
dependent drug efflux pump and its overexpression
results in reduced cellular drug accumulation.In the
absence of a 3-D structure, the design of MDR reversal
(MDRR) agents has relied on previous structure–activ-
ity relationship (SAR) studies.Although there has been
several of these, most have pointed to the importance of
a hydrophobic, conjugated planar ring as a key
structural requirement.2
resistance to paclitaxel has presented new challenges.
Thus restoring paclitaxel sensitivity to resistant tumours
is of vital importance.
The ability of the antimalarial drugs chloroquine 2 and
primaquine 3 as well as other quinolines to act as
MDRR agents for vinblastine-resistant (CEM/VLB100)
and vincristine-resistant (K562/ADM) cancer cell lines
has been previously reported.6À8 Within the context of
paclitaxel chemosensitising agents, some of the quini-
dine, quinine and quinacrine antimalarial drugs have
recently been reported to overcome in vitro and in vivo
paclitaxel resistance in vinblastine-resistant (CEM/
VLB100), non-Hodgkin’s lymphoma and hormone-
refractory prostate cancer cells.9À11 In this paper, we
report on the preliminary design, synthesis and biolo-
gical evaluation of new quinoline sulfonamides 4 and
5 with activity as paclitaxel chemosensitising agents
(Fig.1).
Paclitaxel (TaxolTM) 1 is one of the best anticancer
agents to be discovered in recent years.3 In 1992, pacli-
taxel was approved by the US FDA for the treatment of
advanced ovarian cancer and in 1994 for breast cancer.
Its clinical use has been expanded to the treatment of
lung, head, neck and gastrointestinal cancers.Paclitaxel
has a novel mode of action in promoting tubulin
assembly and stabilising the resulting microtubules.4,5
Unfortunately, like with many anticancer drugs,
Since the discovery of the chemosensitisation of MDR
cancer cell lines by 2 and 3 in the 1980s, little work has
been done to exploit these antimalarial agents as
MDRR agents in cancer.Among other things, we are
interested in exploring possible similarities in the
mechanisms of quinoline resistance in malaria and
mammalian MDR in cancer vis-a-vis the involvement of
P-glycoprotein in the former.Following on from the
*Corresponding author.Te:l. +27-21-650-2553; fax: +27-21-689-
7499; e-mail: chibale@science.uct.ac.za
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd.All rights reserved.
PII: S0960-894X(01)00462-0

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K. Chibale et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2457–2460
Figure 1. Structures of paclitaxel 1, chloroquine 2, primaquine 3, and sulfonamides 4 and 5.
previously described amide-based 5-alkoxyquinolines
with MDRR activity,8 we targeted some aromatic sul-
fonamide derivatives with varying methylene spacer
lengths for preliminary studies.This is in view of recent
observations that chloroquine derivatives with appro-
priate alkyl chain spacer lengths appear to evade the
mechanism(s) responsible for resistance to 2 in malarial
cells.12À14 Since hydrophobicity is an important feature
in MDRR agents, we reasoned that the presence of a
sulfonamide proton should provide us with a diversity
point for introducing various hydrophobic groups
during the exploration of SARs.
compounds generally showed no or very weak cyto-
toxicity at a test concentration of 10 mM in both cell
lines.The only exception was compound 4b, which was
found to be cytotoxic in both cell lines.
The compounds were then co-administered with pacli-
taxel at four different concentrations as shown in Table 2.
Paclitaxel recovered 96–99% of its efficacy against the
resistant human breast cancer cells when compounds 4
and 5 were co-administered at a concentration of 5 mM.
However, when co-administered with paclitaxel at a
concentration of 1 mM, only compound 4b exhibited
99% MDR reversal activity.Based on this, and the
result with compound 4a in comparison with the results
from compounds 5, it is apparent that the chloroquine
series 4 is superior to the primaquine series 5.It is
noteworthy that primaquine compounds 5a and 5b are
racemates and the biological activity may reside in one
enantiomer only.As such, higher potency may be
expected from the appropriate single enantiomer.
The synthesis of derivatives 4a and 5b was trivial and
straightforward and is exemplified in Scheme 1.Prima-
quine derivatives 5a and 5b were synthesised in a similar
manner from the free base 3.All new compounds gave
1H NMR, FABMS and, in relevant cases, microanalysis
data consistent with their structures.
In order to establish the intrinsic anticancer activity,
derivatives 4 and 5 were first tested against paclitaxel-
sensitive (LCC-WT-human breast carcinoma) and
paclitaxel-resistant (LCC6-MDR-MDR1 transfected)
cell lines, respectively.15 Cells were seeded at 2000 cells/
well in 96-well plates in complete medium-RPMI-1640
containing 5% FCS, 5% Nuserum IV, 2 mM l-gluta-
mine and 10 mM HEPES.Following overnight incuba-
tion, compounds were solubilized in 100% DMSO,
diluted in complete medium and added to cell plates.
After 72 h, cells were fixed, stained and total protein/well
was determined.Compound concentration that inhib-
ited growth by 50% was determined and reported as
IC50.The data are summarised in Table 1.The
Table 1. Cytotoxicity of quinolines 4 and 5 against sensitive and
resistant human breast cancer cellsa
Compound
IC50 (mM)ÆSD
% Growth inhibition
at 10 mM
LCC6-WT LCC6-MDR LCC6-WT LCC6-MDR
Paclitaxel 1 0.008Æ0.001 0.612Æ0.021
4a
4b
5a
5b
>10
1.7Æ0.09
>10
>10
2.0Æ0.24
>10
6
3
16
0
8
8
>10
>10
aLCC6-WT-human breast carcinoma; LCC-MDR-MDR1 transfected
line.
Scheme 1. Synthesis of target compounds 4a and 4b.

K. Chibale et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2457–2460
2459
Table 2. Modulation of human mammary cell sensitivity to pacli-
taxel by quinolines 4 and 5
obtained using SYBYL 6.4 by modifying the X-ray
structure of paclitaxel and minimising the resultant
conformers.The template forcing was performed using
the InsightII 2000/Discover Module (tRAs or the taxoid
as the template and 4a or 4b as the mover) using con-
stant valence force field (CVFF).The resultant con-
formers of 4a and 4b were energy-minimised so that the
energies of these conformers were within the 5 kcal/mol
range from that of the lowest energy conformation.
Then, these minimised conformers of 4a and 4b were
overlaid with the tRAs and the taxoid.The overlay
results are shown in Figure 3.
Compound
Concentration (mM)a IC50 (nM) % IC50 reduction
LCC6-MDR
Paclitaxel
490
13
19
0
97
96
99
nd
36
55
70
99
54
39
Paclitaxel+(5a)
Paclitaxel+(5b)
Paclitaxel+(4a)
Paclitaxel+(4b)
Paclitaxel+(5a)
Paclitaxel+(5b)
Paclitaxel+(4a)
Paclitaxel+(4b)
Paclitaxel+(4b)
Paclitaxel+(4b)
5
5
5
ndb
1
1
1
1
0.3
0.1
2.7
nd
353
249
164
6.2
254
338
As Figure 3a shows, the two naphthyl moieties of 4b
and the phenyl group of the C-2 benzoate as well as the
naphthalene group of the C-7 acyl moiety of SB-RA-
30001 have almost perfect fit.This is a rather surprising
finding.SB-RA-30001 possesses a high MDRR activity
with paclitaxel (97.5% at 1 mM against human breast
cancer cell line MCF7-ADR).16 As compared to 4b, the
aNo growth inhibition was seen at this concentration of reversal agent.
bNot determined due to cytotoxicity at 5 mM.
Since antimalarial drug analogues, 4 and 5, exhibited
substantial MDRR activity against LCC6-ADR when
co-administered with paclitaxel, we thought there might
be a common pharmacophore for these sulfonamide-
based compounds and taxane-based MDRR agents that
were developed earlier.Accordingly, we selected 4a and
4b as well as taxane MDRR agents (tRAs), SB-RA-
30001 and SB-RA-31012,16 and photoaffinity labelling
taxoid {3H}-SB-T-511117 for molecular modelling study
(Fig.2), and investigated common structural features
between these two totally different classes of compounds.
The molecular modelling was performed on a Silicon
Graphics O2 workstation using two programs: SYBYL
6.4 and InsightII 2000. The quinolinesulfonamides
structures, 4a and 4b, were constructed in SYBYL 6.4
and energy-minimised (Tripos force field, charges cal-
culated by the Gasteiger–Huckel method).The lowest
energy conformations of SB-RA-30001 and SB-RA-
31012, and photoaffinity taxoid {3H}-SB-T-5111 were
Figure 3. Molecular modelling graphics of quinolines overlaid with
tRAs and photoaffinity labelling taxoid.
Figure 2. Structures of taxane MDRR agents (tRAs) SB-RA-30001 and SB-RA-31012 and photoaffinity labelling taxoid {3H}-SB-T-5111.

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K. Chibale et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2457–2460
overlap of the naphthalene moiety of 4a with the naph-
thalene group of the C-7 acyl moiety of SB-RA-30001 is
only partial.This observation is consistent with the dif-
ference in activity of 4a and 4b.Figure 3b shows the
overlay of 4a, 4b and SB-RA-31012, that is a highly
potent MDRR agent for paclitaxel (99% reversal activ-
ity at 1 mM and 92% at 0.1 mM against LCC6-ADR).16
In this case, one of the aromatic rings of the naphthyl
moiety of 4b overlaps with one of the phenyl groups of
the benzophenone moiety of SB-RA-31012, but 4a does
not have overlap in this part of the molecule.As Table 2
shows, 4b exhibits high potency (99% reversal activity)
at 1 mM, but the potency drops to 33% at 0.1 mM.This
might be due to the fact that the methylene chain of 4b
is not long enough to reach a more preferable hydro-
phobic binding site to which the benzophenone moiety
of SB-RA-31012 binds.
Acknowledgements
Financial support through Grants 052075/Z/97 and
2039478 from the Wellcome Trust and National
Research Foundation (South Africa) respectively (KC),
as well as grants GM42798 (IO), CA73872 (RJB) and
CA16056 (RJB) from the National Institutes of Health,
is gratefully acknowledged.
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