Vol.2, No.8, 832-835 (2010) HEALTH
doi:10.4236/health.2010.28125
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Approaching intermolecular interactions and membrane
activity of taxol by FTIR Spectroscopy-implications for
anticancer therapeutics
Erhan Süleymanoglu
Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Gazi University, Ankara, Turkey;
Received 16 October 2009; revised 30 November 2009; accepted 2 December 2009.
ABSTRACT
We studied the incorporation of hydrophobic
drug Taxol into a solid lipid matrices by FTIR
spectroscopy. Lipid arrays containing different
molar fractions of the drug were made and
deposited on the spectrometer glass window
substrates for obtaining multilayer stacks. The
drug induced an alteration of lipid array spa-
cings, indicating the drug-lipid recognition.
Using excess amounts of Taxol provide infor-
mation on extrapolations on its cellular solubility
in biomembranes. The data obtained could be
used further for developing novel anticancer
drug formulations, as well as for elucidating its
novel cellular pharmacological targets.
Keywords: Antineoplastic Drugs; Taxol-Membrane
Interactions; Structural Changes; FTIR
Spectroscopy
1. INTRODUCTION
Taxanes are one of the most widely used antineoplastic
agents during the past 25 years. These drugs, which
cause cell cycle arrest and apoptosis following micro-
tubule stabilization are currently employed in treatment
of common cancers such as breast, lung and ovary [1,2].
Since most of the mechanims responsible for their
therapeutic action at the molecular level remain to be
determined, factors that affect tumour sensitivity, cellular
pharmacology and drug disposition have been intensely
investigated with the hope that their elucidation could
help the development of taxanes with improved efficacy,
boavailability and pharmacokinetics.
The various ways of administration of these lipophilic
drugs is often problematic due to their low aqueous
solubility. Use of solubilisers and other formulations with
a high dissolution rate therefore becomes a necessity in
order to achieve their therapeutic dose. Phospholipids
can be used to solubilise such drugs, with spontaneous
formation of complexes. Thus, encapsulation of hydro-
philic and binding of amphipathic as well as lipophilic
drugs is possible. Studying such drug-lipid recognitions
is important also in terms of aquiring detailed knowledge
of cellular functions of biomembranes and developing
novel models for better understanding of drug action [3].
Pharmaceutical and physicochemical analyses of drug-
membrane complexes have been studied by various
analytical methods employing a variety of drugs and
model membranes. Thermodynamic, spectroscopic and
microscopy approaches were used for structural chara-
cteization of these macromolecular associations. Among
these, vibrational spectroscopy (Infrared and Raman spe-
ctroscopy) provide useful information on dynamic
changes occuring after complex formation of various
biomolecules [4], making it a preferred method of
analysis which deserves to be employed also in drug-
membane studies. In its most popular mode of appli-
cation, the infrared (IR) measurements involve water
removal from samples, which often give rise to erra-
neous interpretations of the resulting spectra. Undou-
btedly, understanding the interactions of drugs with
biomembrane or with liposomal lipids following vesicle
encapsulation would help to develop improved therapeutic
formulations. Obviously, these are accompanied by
release or uptake of ions or water molecules. Deter-
mination of hydration/re-hydration effects on the physi-
cochemical characteristics of entrapped drugs depends
on the evaluation of the amount and structure of the
bound water. In addition, a variety of the existing poly-
morphs and their different efficiencies is worth studying
in more detail. The structural transitions of Taxol－a
widely used chemotherapeutic drug and phospholipids
following their recognition and complex formation is
briefly reported herein. The objective is to relate and use

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the obtained data further in pharmaceutical profiling and
design of lipid based anticancer drug delivery systems.
2. MATERIALS AND METHODS
Materials: L-α-phosphatidylcholine was purchased
from Avanti Polar Lipids (Alabaster, AL, USA). KBr and
Taxol were a product of Sigma Chem. Co., MI (USA).
FTIR Spectroscopy: Infrared spectra were recorded
on IFS 66/S FTIR spectrometer (Bruker Analytische
Messtechnik GmbH, Karlsruhe, Germany), equipped
with He-Ne laser detector and KBr beam splitter. KBr
pellet method was employed as FTIR sampling tech-
nique. The samples were prepared by mixing of lipid and
drug by mass in the desired ratios and pressing the
mixtures with a die press. Spectra were collected after
short incubation of lipid with Taxol. Interferograms were
accumulated over the spectral range 4000 cm-1 to 400 cm-1,
with a nominal resolution of 2 cm-1 and a minimum of
320 scans. The criterion for elimination of water effect
from the spectra was based on the stright baseline bet-
ween 1750 cm-1 and 2200 cm-1, where the water com-
bination mode is located.
3. RESULTS AND DISCUSSION
In the present work, Taxol-lipid mixtures in different
ratios were deposited on the FTIR slides to form oriented
stacks. The intention was to correlate solid-state stru-
ctural parameters, especially when higher drug ratios are
used and to make further deductions regarding the
application of FTIR spectroscopy in this mode for deter-
mination of Taxol organization in biomembranes of both
normal an malignant cells.
Such an information on the physical states of drugs
entrapped in lipidic surrounding simulating cellular
interfaces is very useful for predicting and designing
improved formulation properties. For better under-
standing of how Taxol recognizes and binds to cell
surface lipids and how it affects the packing and fluidity
of membranes, it is necessary to study its interactions
with phospholipid molecules emphasizing the engaged
functional groups. Since drugs exert their cellular effects
in a concentration dependent maner, it is useful to study
the effect of various Taxol concentrations on a simulated
membrane interface. This would give further insights
into the significance of surface activity of drug action.
Thus, in this study, the excess drug effects were followed
by varying drug concentration and keeping lipid con-
centration fixed. This would give further details con-
cerning the concentration dependent Taxol effects on
membranes and more interestingly would depict the
issue of possible mechanisms of drug-induced mem-
brane deformation. Such a design is based on the fact
that the addition of a drug induces certain perturbations
or leads to microdomain formation of phospholipid
moieties, which is detectable by FTIR spectroscopic
measurements.
Figure 1 shows the effect of increasing drug ratios on
the structure of the lipid. The IR spectra are highly
sensitive to existance of drug molecule in concentration
dependent fashion. In its lowest concentration Taxol
restricts the phospholipid flexibility. The highly ordered
all-trans hydrocarbon phospholipid chain predominated.
Gauche-(kinked) conformation, which leads to higher
rotational freedom was not depicted. Used in higher
amounts (Figure 1), the drug increases its affinity of
binding to phospholipid stacks. Thus, in higher amounts,
Taxol fluidized the phospholipid dispersion, as deduced
also from the subsequent thermal behaviour of the
relevant drug-lipid binary mixtures. These observations
are explained by the chemical structure of the employed
egg phosphatidylcholine and from the spatial features of
the drug molecule. As a bulky molecule, Taxol cannot
reach the inner parts of the hydrated phospholipid hy-
drocarbon chains. It only bound hydrophobic parts such
as their acyl chains. Under these conditions, the amor-
phous Taxol converted to anhydrous state, suggesting
that several solid-state structures of the drug coexist, in
agreement with [5]. In their elegant approach, J. H. Lee
et al. [6] emphasized the importance of studying the
various solid properties of Taxol. Major lipid specific
band frequencies were seen when equimolar ratios of
drug-lipid complexes were used. The most important of
these were those belonging to CH vibrations (2750-3100
cm-1) and CH2 wagging progression, as well as CH2
scissoring vibrations within the region 1150-1400 cm-1
and 1465-1475 cm-1. The former indicates the confor-
mational order while the later two provide information
about packing effects of the acyl chains, respectively.
PO2- vibrations are located at 1242 cm-1. On the other
hand, Taxol showed substantial bands at 1600-1750,
1180-1300 and 630-770 cm-1. Besides small shifts, all of
them were seen in the spectra of various drug-lipid
mixtures, depicting a drug dominated spectrum, indicating
their recognition and binding. Upon comparison with the
spectra of the unbound drug and lipid shifts of Taxol’s
carbonyls from 1736 cm-1 to 1732 cm-1 and from 1736
cm-1 to 1707 cm-1 were seen. These were retained also in
higher drug ratios. The strong bands at 3300-3500 cm-1
were due to OH-groups linked to the H-bonds. Following
drug-lipid recognition, the intensities were diminished and
additional band shifts occured. Apparently, this indicates
a conformational restriction of lipid due to bond for-
mation with the drug, depicting the decrease in drug
flexibility. In conclusion, FTIR spectroscopy clearly

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Wavenunber cm-1
Figure 1. Overall infrared spectra of various mixtures of Taxol with L-α-phosphatidylcholine. Samples were prepared as de-
scribed in Materials and Methods section. The effect of excess drug ratios are shown from bottom to top: 1:1; 1:3; 1:5; 1:7 and
1:10, lipid/drug fractions, respectively.
showed that Taxol-lipid recognition and binding was
governed by CH and CH2 groups, as well as H-bonded
surface OH-groups. PO2-, C=O, C=C and CH2 groups of
the drug were also engaged.
Thus, by following such a vibrational spectroscopic
approach, further insights into Taxol-membrane inter-
actions could be obtained and used for the under-
standing of the pharmacological activities of its many
formulations. In this respect, determining its recognition
with biomembranes employing dried cellular lipids
becomes crucial. Structural studies of Taxol-lipid arran-
gements, by FTIR spectroscopy, as presented, can give
valuable information about the orgnization of the drug in
cell membranes and can help to optimize lipid matrix
concerning its solubility potential. On the other hand, the
issue of how higher amounts of the drug lead to mem-
brane deformation could be clarified. For instance, a
novel hypothesis can be generated concerning the item
that rather than being driven only by the formation of
membrane-associated structural scaffolds, drug-induced
membrane deformation may require physical pertur-
bation of the lipid bilayer [7]. An emerging theme in this
process would be the importance of lipophilic drugs that
partially penetrate the lipid bilayer. In addition, such an
IR spectrosopic approach will define further important
issues, such as the particular mechanisms engaged in the
binding of lipophilic drugs with liposomal membranes;
the reversibility of this binding; the role played by other
factors in these recognitions with liposomal membranes
and release kinetics after entrappment, e.g. the signi-
ficance of the biological mileu or the involvement and
specificity of other lipid membranes.
Cell membranes have always been regarded as an
important subcellular organelle, both as a site of path-
ogenesis and as a therapeutic target. The issue of the use
of lipids as targets for overcoming antineoplastic drug
resistance is very interesting to study. How tumor cell
membrane alterations influence the response of cancer to
chemotherapy still remains to be defined. Exciting future
directions of studying Taxol-lipid interactions exist
regarding novel cancer treatment strategies. The moti-
vation for starting research in this field has come from
recent data on the role of lipid phase of cell membranes
in P-gp-mediated MDR activity, as well as in reversal of
tumor resistance to apoptotic stimuli. To prove the
possible Pgp-independent pathway of action causing
chemoresistance and increasing membrane permeability,
various Taxol-biomembrane systems involving molecules
leading to alterations in membrane fluidity and to
increase in chemosensitivity (chemosensitizers) could be

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employed in a dose-dependent manner. This could be
followed by applying fluorescence measurements in
isolated tumor biomembranes, in model membrane sys-
tems or in wild type or MDR animal and human cell
membranes. Thus, studying membrane dynamics in both
the outer hydrophobic region of the bilayer and in the
acyl chain region, respectively would be possible. Using
such chemosensitizers acting by increasing lipid bilayer
permeability would correlate with anticancer cytoto-
xicity. Thus, a new model can be build, based on the
action of chemosentisizers causing changes in membrane
structures and leading to membrane fluidity fluctuations
and increasing bilayer permeability, showing the signi-
ficant role of these events in Taxol cytotoxicity. Sub-
sequently, new therapeutic strategies can be designed.
Unfortunately, the conventional drug development
strategies suffer from high rates of design drawbacks due
to inability to predict tumor responce at an early stage of
the treatment. Thus, the employed therapy regimes can
not be individualized in terms of personalized medicine.
On the other hand, the currently used laboratory medicine
protocols often lead to high numbers of false-negative
results. Hence, there is a need for development of novel
methods both for detecting malignancy at an early stage,
as well as for predicting tumor responce to drug therapy.
Spectroscopy offers new possibilities in this respect. In
contrast to conventional histological techniques, vibra-
tional spectroscopic approaches, for instance, do not
require a special sample preparation. Undoubtedly, with
the current achievements of designs of light sources,
optical components, detectors and algorithms for data
processing, often employing artificial intelligence pro-
rammes such as neural network computing, the number of
their applications in disease recognition will increase in
the near future. The unappreciated yet biotherapeutic po-
tential of these methods in designing new cancer therapy
schemes should be emphasized. Vibrational spectra of
cells, tissues and biological fluids are a reflection of total
cellular chemistry and structure. Therefore, they provide
a measure for the entire chemical cellular status regarding
such metabolic events as cell cycle events, differentiation,
growth and cell death. Hence, vibrational spectroscopy
provide important information on vital cellular activities,
e.g. transcriptional and translational regulations, as well
as on post-translational modifi cations. Therefore, there
is increasing interest in the biomedical field in using
these methods as emerging biophotonic tools for diag-
nostic in situ and in vivo therapeutic applications. The
idea here, is to appreciate that human pathologies are
accompanied by alterations in the chemical compositions
of cells, tissues, organs, or body fluids. In this context,
vibrational spectroscopy, such as FTIR methods, appear
to be ideally suited for sensitive detection of such changes
of the secondary structures of the engaged biomacro-
molecules as a diagnostic technique. Biomedical IR
spectroscopy probes biological samples in a way that the
active vibrational modes of all constituents present in the
mixture are followed in a single experiment, resulting in
a very complex spectra though entire spectral range.
Thus, the obtained spectra provide spectral fingerprints
of the total chemical composition of the biosample under
study. Applied to cellular systems, such measurements
are useful for gaining further information on cellular
chemical structures, which are potential targets for novel
anticancer drug designs. Therefore, by following a tumor
specific biomolecular dynamics, new disease specific
drug designs can be suggested. For instance, proper
knowledge of the secondary structural changes of the
nucleic acid topologies and their role in cellular trans-
criptional and translational machinery of a tumor cell is
a pre-requisite for designing efficient sequence specific
DNA binding anticancer agents. In our opinion, espe-
cially when coupled to microscopic systems, IR and
Raman spectroscopic techniques will represent im-
portant tools improving the efficacy of the standard
laboratory methods for disease recognition and therapy.
4. ACKNOWLEDGEMENTS
This work was supported by Gazi University Research Foundation
(Project No: 02-2005/15). The technical assistance of Dr. N. Özkâr and
Dr. N. Özkan from The Central Laboratory of Middle East Technical
University (Ankara-Turkey) is greatly acknowledged.
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