Spectral studies on the molecular interaction of anticancer drug mitoxantrone with CTAB micelles

Spectral Studies on the Molecular Interaction of Anticancer DrugMitoxantrone with CTAB Micelles

MIRELA ENACHE,1 ELENA VOLANSCHI2

1“I. Murgulescu” Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, Bucharest 060021, Romania

2Department of Physical Chemistry, University of Bucharest, Blvd. Elisabeta 4-12, Bucharest 030018, Romania

Received 31 March 2010; revised 26 May 2010; accepted 09 June 2010

Published online 28 July 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jps.22289

ABSTRACT: The interaction of anticancer drug mitoxantrone with cationic surfactantcetyltrimethylammonium bromide (CTAB) has been investigated by absorption spectroscopyas a function of surfactant concentration ranging from the premicellar to postmicellar regionat pH 7.4 and 10. Interaction of mitoxantrone with CTAB micelles induces a bathochromicshift of both absorption maxima and spectral data showed that the micellization reduces thedimerization process and mitoxantrone is bound into micelles in the monomeric form. Bindingconstant and partition coefficient were estimated using the red shifts of the absorption maximain the presence of surfactant. From the resulting binding constants for mitoxantrone–surfac-tant interactions, it was concluded that the hydrophobic interactions have a great effect onthe binding of mitoxantrone to CTAB micelles. Also, by comparing the partition coefficientsobtained using pseudo-phase model, the hydrophobic interactions have a major role in thedistribution of mitoxantrone between micelle–water phases. Gibbs free energy of binding anddistribution of mitoxantrone between the bulk aqueous medium and surfactant micelles werecalculated. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci100:558–565, 2011Keywords: mitoxantrone; drug transport; surfactants; micelle

INTRODUCTION

The study of drug–surfactant interactions hasreceived an increased attention in the last periodof time because of widespread application of surfac-tants in pharmaceutical field, especially with respectto surfactant micelles ability to solubilize hydropho-bic drugs.1–4 Micellar systems (colloidal-sized clustersformed by surfactants in solution) have also been usedas model systems for biomembranes to investigatedifferent aspects of bilayer properties and functions.5

The physicochemical interactions of drugs with sur-factant micelles can be visualized as an approxima-tion for their interactions with biological membranes.This provides an insight into more complex biologi-cal processes like the passage of drugs through cellmembranes. An important and fundamental eventin the interaction of drugs with biological tissues at

Correspondence to: Mirela Enache (Telephone: +0213115831;Fax: +0213115831; E-mail: [email protected]; [email protected])Journal of Pharmaceutical Sciences, Vol. 100, 558–565 (2011)© 2010 Wiley-Liss, Inc. and the American Pharmacists Association

the molecular level is their binding to membranes,because it is related to the mechanism of drug ac-tion. As many biological processes occur at the ioniz-able surface of membranes or along their hydrophobicregion, a comparative study of the drug interactionwith cationic, zwiterionic, anionic and neutral surfac-tants may provide useful information on the natureof drug–membrane interaction.6–8

Micellar systems can solubilize poorly solubledrugs, increasing their bioavailability, and therefore,may be used as drug carriers by encapsulation ofthe drugs, in order to ensure the transport to spe-cific sites of action, to minimize drug degradation andloss, to prevent harmful side effects, thus improvingthe treatment efficacy.9

Drugs may be solubilized in the hydrophobic coreand/or on the interface of the micelles. The predom-inant location of the drug depends on its hydropho-bicity and interactions with the surfactant.10 The ex-tent of interaction between the drugs and the sur-factants can be best described by the hydrophobic ef-fect (primarily determined by the hydrophobic surfacearea of the drug molecule) and the electrostatic effect

558 JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 2, FEBRUARY 2011

MOLECULAR INTERACTION OF ANTICANCER DRUG MITOXANTRONE WITH CTAB MICELLES 559

Figure 1. Chemical structures of mitoxantrone andcetyltrimethylammonium bromide (CTAB).

(primarily determined by the charge associatedwith the drug molecule as well as the surfactantmolecules).11

The anthracenedione antitumor drug mitox-antrone (1,4-dihydroxy-5,8-bis[[2-[(2-hydroxyethyl)-amino]-ethyl]-amino]-9,10-anthracenedione) is asynthetic analogue of the anthracycline antibioticsdeveloped to eliminate the side effects of those,especially cardiotoxicity. Mitoxantrone has shownsignificant clinical effectiveness in the treatment ofadvanced breast and prostate cancers, lymphomaand acute leukemia.12–14 Its clinical usefulness islimited due to the chronic cardiotoxicity and by theoccurrence of multidrug resistance associated withthe overexpression of membrane transporters (e.g.,P-glycoprotein, MRP1, BCRP/MXR1).15

The present study aims to gain a better un-derstanding of the binding of charged and un-charged forms of antitumor drug mitoxantrone toa micellar system formed by a cationic surfactant[cetyltrimethylammonium bromide (CTAB)], com-monly accepted as model system for studying dif-ferent aspects of membrane interactions with drugmolecules, including their localization.1,8,9,16

The structures of the drug and cationic surfac-tant employed are shown in Figure 1. Mitoxantronehas a planar heterocyclic ring substituted with twopositively charged nitrogen-containing side chains atpH 7.4.

Binding constant and partition coefficient valuesfor the drug–surfactant interaction were determinedby absorption spectroscopy, based on the shift in ab-sorption spectra of the drug when going from anaqueous to a more hydrophobic environment.8 Theresults are discussed in comparison with anionicsurfactant, sodium dodecyl sulfate (SDS), previouslyinvestigated.17

MATERIALS AND METHODS

Mitoxantrone hydrochloride and CTAB were analyt-ical grade, supplied by Sigma (MO, USA) and usedwithout further purification. Mitoxantrone concen-tration in phosphate buffer solution (pH 7.4, ionicstrength 0.15 M) was determined spectrophotomet-

rically at 660 nm, using the molar absorption coeffi-cient ε = 19,500 M−1cm−1.18 Experiments were per-formed at room temperature and double distilled wa-ter was used for the preparation of solutions. Thespectrophotometric measurements were carried outin a Unicam Helios-" spectrophotometer (SpectronicUnicam, Cambridge, UK). Mitoxantrone–surfactantmicelles binding constant and micelle–water parti-tion coefficient were determined from the absorbancesat λ = 660 nm of series of solutions containing a fixeddrug concentration and increasing surfactant concen-tration, absorption measurements being made after 1to 2 min, time sufficient to ensure the attainment ofequilibrium. The spectral results are the average of3 to 5 different experiments. Even if CTAB does notabsorb at the analytical wavelength, the surfactantsolution was added also to the reference cell so thatthe sample and the reference would have the same re-fraction index. The determination of critical micellarconcentration (CMC) of CTAB in the presence of mi-toxantrone is based on the change in absorption spec-tra of drug, which indicates the beginning of micelleformation. At low CTAB concentrations, no variationin absorbance was observed and the onset of increasedabsorbance with further addition of CTAB was con-sidered as CMC.19–21 The mitoxantrone spectra fordifferent surfactant concentrations were decomposedin Gaussian bands using deconvolution procedure inPeakFit 4.11 software (Systat Software Inc., Chicago,IL) Linear and nonlinear fitting of the experimentaldata was performed using Origin 7.0 (MicroCal Soft-ware, Inc., Piscataway, NJ, USA) software.

RESULTS AND DISCUSSION

Interaction of mitoxantrone with cationic surfactantCTAB in phosphate buffer, pH 7.4, and carbonatebuffer, pH 10, has been investigated by UV-VIS ab-sorption spectroscopy in submicellar and micellar sur-factant concentrations.

The change in the absorption spectrum of mitox-antrone in phosphate buffer, pH 7.4, with increas-ing drug concentration (from 6.58 × 10−6 to 2.80 ×10−5) is shown in Figure 2. The visible spectrum ofmitoxantrone consists of three overlapping spectralcomponents: absorption maxima at 610 and 660 nm,corresponding, according to literature data22 to thedimer and monomer of the drug, and a shoulder atabout 580 nm more evident at higher drug concen-tration, corresponding to higher aggregates (HA) ofthe drug. The wavelengths of absorption maxima ofthe monomer and dimer remain unaltered when theconcentration of mitoxantrone increases. In the con-centration range 1 × 10−6 to 1 × 10−4 M the pH depen-dent dimerization process is predominant, the dimer-ization constant increasing with the increase of pH.23

DOI 10.1002/jps JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 2, FEBRUARY 2011

560 ENACHE AND VOLANSCHI

Figure 2. Absorption spectra of mitoxantrone in phos-phate buffer, pH 7.4, at several drug concentrations (from6.58 × 10−6 to 2.80 × 10−5 M). HA, higher aggregates; D,dimer; M, monomer.

The variation in the absorption spectra of mitox-antrone in phosphate buffer, pH 7.4, in the pres-ence of different CTAB concentrations is presented inFigure 3 and is characterized by two isosbestic pointsat 598 and 710 nm.

Unlike the previously investigated anionic surfac-tant SDS,17 on gradual addition of CTAB, the ab-sorption spectra of mitoxantrone are not changed(Fig. 3, spectra 1–4) up to a concentration of CTABof about 9.55 × 10−5 M (i.e., lower than CMC). Atthese low concentrations, the surfactant CTAB existsas cation monomers and the repulsive forces betweenthe positively charged nitrogen atoms from the lateralchains of the drug and the positively charged ammo-nium group of CTAB are expected to be significant,preventing formation of drug-monomer surfactantcomplexes. Therefore, the solution equilibria betweendifferent drug species (monomer, dimer, HA) are notinfluenced by the CTAB addition (curves 1–4 pass-ing by isosbestic point at 598 nm correspond to thesame ratio of monomer to dimer absorbances (AM/AD)as in a mitoxantrone solution of the same concentra-tion the spectrum of the drug is not modified, beingdetermined solely by the drug concentration.

In the case of anionic surfactant SDS, absorptionresults have outlined in premicellar range, a markeddecrease of absorbance of the drug and of the AM/ADratio with increasing surfactant concentration (pro-cess I, CSDS < CMC,). This process was assignedto the neutralization of the drug charges by elec-trostatic interaction between the positively chargedgroups of the drug and the negatively charged sur-factant group, allowing the formation of a drug–SDScomplex of defined stoichiometry (1:2) and favoringthe drug aggregation.17

Table 1. Spectral Parameters (Absorption Maxima of Dimer -8D, Monomer - 8M, and the Experimental Ratio of Monomer toDimer Absorbances - AM/AD) for Mitoxantrone in DifferentEnvironmental Conditions

Mitoxantrone 8D (nm) 8M (nm) AM/AD

Phosphate buffer, pH 7.4 610 660 0.76Carbonate buffer, pH 10 614 666 0.68CTAB pH 7.4 623 675 1.17

pH 10 624 678 1.28SDS17 pH 7.4 614 665 1.27

CTAB, cetyltrimethylammonium bromide; SDS, sodium dodecyl sulfate.

At CTAB concentrations higher than CMC, the in-tensity of both monomer and dimer bands increases,but the monomer absorbance at 660 nm becomes pre-dominant (Fig. 3). The intensity of the dimer bandincreases with decrease in intensity of the band at580 nm corresponding to HA of mitoxantrone, attest-ing the existence of multiple equilibria between dif-ferent species in solution (monomer, dimer, HA) andcharacterized by the isosbestic point at 598 nm. Tak-ing into account an increase in the AM/AD ratio from0.76 in the absence of surfactant to 1.17 at CTABconcentrations higher than CMC (Table 1), the dis-sociation of the dimers and HA triggered by the in-teraction of mitoxantrone with surfactant micellescan be assumed. In order to quantify the evolution ofthe three overlapping spectral components of mitox-antrone with CTAB concentration, the deconvolutionin elementary bands for the spectra in Figure 3a wasperformed.24 The results are presented in Figures 3band 3c and the calculated ratio of the areas of themonomer and dimer bands at pH 7.4 (0.73 for spec-trum 1 and 1.19 for spectrum 9 in Fig. 3a are consis-tent with the values in Table 1). Also, Figure 3d showsthe variation of monomer, dimer and HA componentswith CTAB concentration obtained from decomposi-tion spectra. It may be observed that the monomercomponent increases with the surfactant concentra-tion, on expense of the dimer and HA components,indicating the dissociation of these species caused bythe interaction of mitoxantrone with CTAB micelles.

The interaction of the drug with surfactant micellesis characterized by the isosbestic point at 710 nm,supporting the formation of a drug–micelle complexat CTAB concentrations above CMC. This process issimilar to process II observed in micellar range forSDS–mitoxantrone interaction, when the surfactantmicelles are formed and the drug is encapsulated inmicelles in monomer form.17

In presence of CTAB concentrations higher thanCMC, the visible spectra of mitoxantrone shift tohigher wavelengths as more drug molecules are takeninto the surfactant micelles (Table 1, Fig. 4). This redshift indicates that mitoxantrone molecules are lo-cated in micellar medium with smaller polarity thanthe bulk water environment.

JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 100, NO. 2, FEBRUARY 2011 DOI 10.1002/jps


Figure 3. The effect of cetyltrimethylammonium bromide (CTAB) concentrations on the ab-sorption spectra of 1.78 × 10−5 M mitoxantrone: (a) CTAB concentration in the range 0–9.55 ×10−5 M (spectra 1–4) and 1.21 × 10−4 M – 3.88 × 10−3 M (spectra 5–9); (b), (c) Deconvolution ofthe absorption spectra 1 and respectively 9 in Figure 3a; (d) Plot of the percent of componentband areas in deconvoluted spectra for monomer (•), dimer (�) and higher aggregates (�) withCTAB concentration. HA, higher aggregates.

The influence of pH on the mitoxantrone–CTAB in-teraction was also investigated and the results aresummarized in Table 1 and Figure 5. The reportedpKa values for mitoxantrone are 5.99 and 8.13, al-though they have not been attributed to any specificfunctionality in the molecule.25 Reported literaturedata indicate that at neutral pH mitoxantrone ex-ists as a dication with the two positive charges onthe aliphatic side chains.18 Therefore, we have stud-ied the interaction of mitoxantrone with CTAB only attwo pH values, where the literature data indicate thatmitoxantrone exists as dication (pH 7.4) with the twopositive charges on the aliphatic side chains,18 anduncharged species (pH 10), due to the deprotonationof amino groups of side chains at basic pH.26

At pH 10, both absorbance maxima of mitoxantroneare red shifted (666 and 614 nm, respectively) and the

AM/AD ratio decreases slightly from 0.76 for mitox-antrone (2.80 × 10−5 M) in phosphate buffer at 0.68,indicating that the dimerization process is favoredin basic environment. At basic pH, deprotonation ofNH3

+ groups of the side-chains reduces the repul-sion between monomers and favors the dimerizationprocess.26 In presence of CTAB, the spectral behaviorof mitoxantrone at pH 10 is quite similar to that atpH 7.4: the position of the monomer and dimer ab-sorption maxima is not significantly different but theAM/AD ratio increases from 0.68 to 1.27 (Table 1).

The variation of absorbance at 660 nm as a functionof surfactant concentration at pH 7.4 and 10 is pre-sented in Figure 5. The absorbance of the monomerpeak increases with CTAB concentration up to a sur-factant concentration of approximately 3 × 10−3 M atpH 7.4 and approximately 1 × 10−3 at pH 10; above



Figure 4. The effect of cetyltrimethylammonium bromide(CTAB) concentration on the two absorbance maxima ofmitoxantrone corresponding to the monomer (•) and thedimer (�).

these concentrations the absorbance seems to reach alimiting value.

The value of CMC for CTAB in presence of mi-toxantrone, determined from the change in the ab-sorption spectrum of mitoxantrone (the CTAB con-centration corresponding to the first point markingthe increase of absorbance in Fig. 5), is CMCCTAB= (1.21 ± 0.09) × 10−4 M and was used through-out the calculations. This value is smaller than theCMC value in pure water (9.10 × 10−4 M) and thatin 0.1 M phosphate buffer (8.00 × 10−4 M) reportedin literature,27,28 due to the well-known lowering of

Figure 5. Variation of the absorbance at 660 nm withcetyltrimethylammonium bromide (CTAB) concentrationfor pH 7.4 and pH 10. The symbols represent the experi-mental data and the full lines are the results of nonlinearfitting using Eq. (1).

the surfactant CMC, by the influence of different ionsand molecules present.29

Generally, a micellar structure is characterized bydifferent layers: (a) nonpolar core containing the hy-drocarbon tails of the surfactant; (b) Stern layer con-taining compact head groups of surfactant; and (c) rel-atively wider Gouy–Chapman region containing thecounterions followed by the aqueous bulk phase atan infinite distance from the core. Some counterionsand water molecules penetrate into the head groupsregion to different extent, giving it a dielectric con-stant that is intermediate between the hydrocarboncore and the aqueous bulk medium.30

Information about the position of the mitoxantronemolecule in the micelle can be obtained by comparingthe mitoxantrone spectra in the presence of CTAB mi-celles with the spectra in water and organic solventsof different polarities. The hydrocarbon core of anymicelles has a dielectric constant of 2 to 5,31 quitesimilar to that of 1,4-dioxane. As the spectrum of mi-toxantrone in the presence of CTAB micelles is verydifferent from the spectrum in 1,4-dioxane (spectrumnot shown), we may conclude that mitoxantrone is notlocalized in the core region of micelles, but probably atthe micelle–water interface with limited exposure tothe aqueous medium. The spectral red shift for mitox-antrone monomer band is about 15 nm in the presenceof CTAB micelles at pH 7.4 and about 18 nm at pH10 compared to its position in aqueous solution. Thisvalue is similar to the shifts in methanol (ε = 32.63)and ethanol (ε = 24.55), solvents with dielectric con-stants quite similar to the micellar–water interface.Micelle interface is an environment with dielectricconstant (ε = 36)32 intermediate between water (ε =80) and 1,4-dioxane (ε = 2). The octanol:water par-tition coefficient of mitoxantrone at pH 7.4 is log P= 0.79, which indicates that mitoxantrone is a fairlylipophilic drug,33 therefore it prefers to move frompolar aqueous medium in more hydrophobic mediumlike micelles. Taking into account all these results,we can conclude that mitoxantrone is encapsulatedin CTAB micelles as monomer, and most probablysituated in the micelle surface layer. This locationcan be explained by a cation–B interaction betweenthe uncharged ring systems of mitoxantrone and thecationic headgroups of CTAB, similar to pinacyanolcationic dye.34,35 The lower spectral shift (about 5 nm)observed for the SDS micelles indicates that the mi-cropolarity around mitoxantrone molecules in CTABmicelles is different from that in SDS micelle. In thecase of CTAB micelles the electrostatic interactionsare absent, the hydrophobic effect prevails, result-ing in a strong penetrating tendency of the drug andhigher spectral shift is observed. A similar conclusioncan be obtained considering the order of the aliphaticchain length for the surfactants, which follows theorder CTAB > SDS. The flexibility of longer chains



Table 2. Binding Constant (Kb), Partition Coefficient (Kx), theGibbs Free Energy of Binding (�G0

b) and the Standard FreeEnergy Change for the Transfer of Mitoxantrone From BulkWater to Micellar Phase (�G0

x) for the Interaction ofMitoxantrone with CTAB

CTAB

pH 7.4 pH 10

Kb, M−1 2933 ± 625 4365 ± 478�Gb

0, kJ/mol −19.78 −20.76Kx (1.72 ± 0.3) × 105 (2.65 ± 0.2) × 105

�Gx0, kJ/mol −29.86 −30.93

CTAB, cetyltrimethylammonium bromide.

of CTAB micelles may make the movement of mitox-antrone easier toward the core of micelles, resultingin higher spectral shift.36

Mitoxantrone–CTAB micelles interaction has beenevaluated at constant drug concentration and vary-ing concentration of surfactant, and the values of theabsorbance of monomer band have been utilized tocalculate the equilibrium constant by nonlinear re-gression (full lines in Fig. 5) assuming a 1:1 inter-action between the drug and the surfactant micelle,using Eq. (1).37 The results are presented in Table 2

A = A0 + AbKb[CTAB]1 + Kb[CTAB]

(1)

where A is the measured absorbance, A0 is the ab-sorbance of the drug in the absence of surfactant andAb is the absorbance of the drug bound to surfactantmicelles.

The Gibbs free energy of binding of mitoxantrone tosurfactant micelles can be obtained by the followingequation:

�G0b = −RT ln Kb. (2)

where R is the gas constant and T the absolute tem-perature. A Gibbs free energy of −19.78 kJ/mol corre-sponds to the binding constant obtained (Table 2).

The interaction between cationic drug mitox-antrone and anionic SDS micelles are expected to bestronger than that between cationic drug and cationicCTAB micelles because of the presence of the electro-static forces in addition to hydrophobic interaction.However, the binding constant for the interaction ofmitoxantrone with CTAB micelles (Kb = [2933 ± 625]M−1) is higher than that for the interaction with SDSmicelles (Kb = [1140 ± 50] M−1).17 Therefore, it fol-lows that the hydrophobic interactions have a greatcontribution to the binding of mitoxantrone to surfac-tant micelles. Similar values for the binding constantand Gibbs free energy were obtained for the interac-tion of cationic dye pinacyanol with cationic surfac-tant, n-dodecyl-trimethyl ammonium bromide, and

this attractive effect was explained by the cation–Binteraction between the uncharged ring system of thedrug mitoxantrone and the cationic headgroups ofsurfactant, which is sufficiently intense to overcomethe Coulombic repulsion between positively chargedspecies.34,35 Also, the binding constant for the inter-action of mitoxantrone with CTAB micelles at pH 10is higher than that for pH 7.4, probably because at ba-sic pH mitoxantrone is uncharged and the coulombicrepulsion between positively charged species at pH7.4 does not exist at pH 10, therefore the interactionof the drug molecule with CTAB micelles is stronger.

Drug–micelle interaction can be evaluated besidesthe binding constant (Kb), by the determination of thepartition coefficient (Kx), a thermodynamic parameterthat represents the affinity of a given solubilizate tothe micellar phase, relative the aqueous one. The par-tition coefficient is important not only in elucidatingthe mechanism of solubilization but also in under-standing of biological phenomena like interaction be-tween drugs and biological membranes. According tothe pseudo-phase model,38,39 the partition coefficientcan be determined from the following equation:

1�A

= 1�A∞

+ nw

Kx�A∞(CT+[CTAB] − CMC). (3)

where�A = A − A0 , �A∞ = Ab − A0 and nw = 55.5M is the molarity of water. The value of Kx is ob-tained from the slope of the plot of 1/�A versus 1/(CT+ [CTAB] − CMC) as shown in Figure 6 for pH 7.4and 10, and the results are summarized in Table 2.

The linear relation holds in a very high surfac-tant concentration region below which the curvetends to bend upwards with decreasing surfactant

Figure 6. Relation between 1/�A and 1/(CT + [CTAB] −CMC) (Eq. 3) for mitoxantrone (1.80 × 10−5 M) in CTABmicelles at two pH values. CMC, critical micellar concen-tration; CTAB, cetyltrimethylammonium bromide.



concentration. This deviation from linearity is con-sidered to be due to the approximation made in theevaluation of Eq. (3).39

From Eq. (4), the standard free energy change forthe transfer of mitoxantrone from bulk aqueous phaseto micellar phase is obtained. The results are pre-sented in Table 2:

�G0x= − RT ln Kx. (4)

By comparing the partition coefficients, obtainedfor the distribution of mitoxantrone molecules be-tween water and micellar phases, it can be observedthat the values of Kx are slightly higher for CTABthan SDS micelles. These results indicate that the hy-drophobic interactions have a major role in the distri-bution of mitoxantrone between micelle/water phasesbecause of the larger tail of CTAB molecules. Also,the results show that the uncharged mitoxantronemolecule (pH 10) exhibits larger partition coefficientthan that of positively charged mitoxantrone (pH 7.4).

CONCLUSIONS

The interaction of antitumor drug mitoxantrone withcationic CTAB surfactant has been investigated insubmicellar and micellar surfactant concentrationsat pH 7.4 and 10 by spectral (UV-VIS absorption)methods. At CTAB concentrations lower than CMC,no interaction of mitoxantrone with surfactant wasobserved because of electrostatic repulsion betweenthe positively charged nitrogen atoms from lateralchains of the drug and the positively charged am-monium group of CTAB. For micellar surfactant con-centrations, the change of spectra and enhancementof absorbance can be rationalized in terms of bind-ing of mitoxantrone to CTAB micelles. It was foundthat the binding constant for the interaction of mitox-antrone with CTAB micelles at pH 10 is higher thanthat for pH 7.4, probably because at basic pH mitox-antrone is uncharged and the repulsion between pos-itively charged species at pH 7.4 does not exist at pH10, and therefore the interaction of the drug moleculewith CTAB micelles is stronger. Also, the binding con-stant for the interaction of mitoxantrone with CTABmicelles is larger than for SDS micelles, attesting thatthe hydrophobic interactions play a major role in thebinding process. Moreover, the hydrophobic interac-tions have a major role in the distribution of mitox-antrone between micelle–water phases. Mitoxantroneis encapsulated in CTAB micelles as monomer, andmost probably situated in the micelle surface layer.This location can be explained by a cation–B inter-action between the uncharged ring systems of mi-toxantrone and the cationic headgroups of CTAB.These results can furnish useful information about

the character and properties of the interaction of mi-toxantrone with model and natural biological mem-branes.

ACKNOWLEDGMENTS

CNCSIS financial support (grant 486/2009) is grate-fully acknowledged.

REFERENCES

1. Xi J, Guo, R. 2007. Acid-base equilibrium of puerarin in CTABmicelles. J Pharm Biomed Anal 43:111–118.

2. Erdinc N, Gokturk S, Tuncay M. 2004. Interaction of epiru-bicin HCl with surfactants: Effect of NaCl and glucose.J Pharm Sci 93:1566–1575.

3. Sun W, Larive CK, Southard MZ. 2003. A mechanistic studyof danazol dissolution in ionic surfactant solutions. J PharmSci 92:424–435.

4. Santa E, Santa ZS. 1998. Solubilization experiments withsalicylic acid. Pharmazie 53:109–112.

5. Engberts JBFN, Hoekstra D. 1995. Vesicle-forming syntheticamphiphiles. Biochim Biophys Acta 1241:323–340.

6. Cudina O, Brboric J, Jankovic I, Karljikovic-Rajic K,Vladimirov S. 2008. Study of valsartan interaction with mi-celles as a model for biomembranes. Colloids Surf B Biointer-faces 65:80–84.

7. Caetano W, Tabak M. 1999. Interaction of chlorpromazineand trifluoroperazine with ionic micelles: Electronic absorp-tion spectroscopy studies. Spectrochim Acta A 55:2513–2528.

8. Caetano W, Tabak M. 2000. Interaction of chlorpromazine andtrifluoroperazine with anionic sodium dodecyl sulfate (SDS)micelles: Electronic absorption and fluorescence studies. J Col-loid Interface Sci 225:69–81.

9. Rangel-Yagui CO, Pessoa Jr A, Tavares LC. 2005. Micellarsolubilization of drugs. J Pharm Pharmaceut Sci 8:147–163.

10. Narang AS, Delmarre D, Gao D. 2007. Stable drug encapsu-lation in micelles and microemulsions. Int J Pharm 345:9–25.

11. Khossravi D. 1997. Drug-surfactant interactions: Effect ontransport properties. Int J Pharm 155:179–190.

12. Hagemeister F, Cabanillas F, Coleman M, Gregory SA,Zinzani PL. 2005. The role of mitoxantrone in the treatmentof indolent lymphomas. Oncologist 10:150–159.

13. Nowoselac AV, Reddy S, Sanmugarajah J. 2004. Acutepromyelocytic leukemia in a patient with multiple scle-rosis following treatment with mitoxantrone. Leukemia18:1561–1562.

14. Doughty JC, Kane E, Cooke TG, McArdle CS. 2002. Mitox-antrone and methotrexate chemotherapy with and withoutmitomycin C in the regional treatment of locally advancedbreast cancer. Breast 11:97–99.

15. Nieth C, Lage H. 2005. Induction of the ABC-TransportersMdr1/P-gp (Abcb1), Mrp1 (Abcc1), and Bcrp (Abcg2) duringestablishment of multidrug resistance following exposure tomitoxantrone. J Chemother 17:215–223.

16. Liu W, Guo R. 2005. The interaction between morin and CTABaggregates. J Colloid Interface Sci 290:564–573.

17. Enache M, Anghelache I, Volanschi E. 2010. Coupled spec-tral and electrochemical evaluation of the anticancer drug mi-toxantrone—sodium dodecyl sulfate interaction. Int J Pharm390:100–106.

18. Rosenberg LS, Carvlin MK, Krugh TR. 1986. The antitu-mor agent mitoxantrone binds cooperatively to DNA: Evi-dence for heterogeneity in DNA conformation. Biochemistry25:1002–1008.



19. Gokturk S, Tuncay M. 2003. Spectral studies of safranin-O in different surfactant solutions. Spectrochim Acta A59:1857–1866.

20. Patist A, Bhagwat SS, Penfield KW, Aikens P, Shah DO. 2000.On the measurement of critical micelle concentrations of pureand technical-grade nonionic surfactants. J Surfact Deterg3:53–58.

21. Samsonoff C, Daily J, Almog R, Berns DS. 1986. The use ofCoomassie brilliant blue for critical micelle concentration de-termination of detergents. J Colloid Interface Sci 109:325–329.

22. Lee BS, Dutta PK. 1989. Optical spectroscopic stud-ies of the antitumor drug 1,4-dihydroxy-5,8-bis[[2-[(2-hydroxyethyl)amino]ethyl]amino]-9,10-anthracenedione (mi-toxantrone). J Phys Chem 93:5665–5672.

23. Enache M, Volanschi E. 2010. Spectral characterization of self-association of antitumor drug mitoxantrone. Rev RoumaineChim 55:255–262.

24. Gonzales-Blanco C, Rodriguez LJ, Velazquez MM. 1997. Effectof the addition of water-soluble polymers on the structure ofaerosol OT water-in-oil microemulsions: A Fourier transforminfrared spectroscopy study. Langmuir 13:1938–1945.

25. Gennaro AR. 1995Remington: The science and practice ofpharmacy. Vol. II. 19th ed. Easton, PA: Mack Publishing,p 1257.

26. Feofanov A, Sharonov S, Kudelina I, Fleury F, Nabiev I.1997. Localization and molecular interactions of mitoxantronewithin living K562 cells as probed by confocal spectral imaginganalysis. Biophys J 73:3317–3327.

27. Awan MA, Shah SS. 1997. Hydrophobic interaction of am-phiphilic hemicyanine dyes with cationic and anionic sur-factant micelles. Colloids Surf A Physicochem Eng Aspects122:97–101.

28. Sarkar R, Ghosh M, Shaw AK, Pal SK. 2005. Ultrafastsurface salvation dynamics and functionality of an enzyme"-chymotrypsin upon interfacial binding to a cationic micelle.J Photochem Photobiol B Biol 79:67–78.

29. Sarkar M, Podar S. 2000. Studies of the interaction of surfac-tants with cationic dye by absorption spectroscopy. J ColloidInterface Sci 221:181–185.

30. Singh TS, Mitra S. 2007. Fluorescence behavior of intramolec-ular charge transfer probe in anionic, cationic, and nonionicmicelles. J Colloid Interface Sci 311:128–134.

31. Cevc G, Marsh D. 1987. Phospholipid bilayers: Physical prin-ciples and models. New York: John Wiley & Sons.

32. Mukerjee P, Ray A. 1966. Charge-transfer interactions andthe polarity at the surface of micelles of long-chain pyridiniumiodides. J Phys Chem 70:2144–2149.

33. Burns CP, Haugstad BN, Mossman CJ, North JA, IngrahamLM. 1988. Membrane lipid alteration: Effect on cellular up-take of mitoxantrone. Lipids 23:393–397.

34. Sabate R, Gallardo M, Estelrich J. 2001. Location ofpinacyanol in micellar solutions of N-alkyl trimethylammo-nium bromide surfactants. J Colloid Interface Sci 233:205–210.

35. Sabate R, Gallardo M, de la Maza A, Estelrich J. 2001.A spectroscopy study of the intearction of pinacyanol withn-dodecyltrimethylammonium bromide micelles. Langmuir17:6433–6437.

36. Sarpal RS, Belletete M, Durocher G. 1993. Fluorescence prob-ing and proton-transfer equilibrium reactions in water, SDS,and CTAB using 3,3-dimethyl-2-phenyl-3H-indole. J PhysChem 97:5007–5013.

37. Shen X, Belletete M, Durocher G. 1998. Study of the interac-tions between substituted 2,2′-bithiophenes and cyclodextrins.Chem Phys Lett 298:201–210.

38. Sepulveda L, Lissi E, Quina F. 1986. Interactions of neu-tral molecules with ionic micelles. Adv Colloid Int Sci 25:1–57.

39. Kawamura H, Manabe M, Miyamoto Y, Fujita Y, Tokunaga S.1989. Partititon coefficients of homologous T-phenylalkanolsbetween water and sodium dodecyl sulfate micelles. J PhysChem 93:5536–5540.


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Spectral studies on the molecular interaction of anticancer drug mitoxantrone with CTAB micelles