Pharmaceutical Research Vol 20 No 7 July 2003 © 2003
`
`Research Paper
`
`Hydrotropic Solubilization of
`Paclitaxel Analysis of Chemical
`Structures for Hydrotropic Property
`
`Jaehwi Lee Sang Cheon Lee
`Ghanashyam Acharya1 Chingjer Chang and
`Kinam Park12
`
`Received February 26 2003 accepted March 27 2003
`
`Purpose To identify hydrotropic agents that can increase aqueous
`paclitaxel PTX solubility and to study the chemical structures nec
`essary for hydrotropic properties so that polymeric hydrotropic
`agents can be synthesized
`Methods More than 60 candidate hydrotropic agents or hydro
`to increase the aqueous PTX
`tropes were tested for their ability
`solubility A number
`analogues were synthesized
`of nicotinamide
`showed a favorable hy
`based on the observation
`that nicotinamide
`for PTX were used to
`drotropic property The identified hydrotropes
`examine the structure activity relationship
`Results NADiethylnicotinamide NNDENA was found to be the
`most effective hydrotropic agent for PTX The aqueous PTX solubil
`ity was 39 mgml and 512 mgml at NNDENA concentrations
`of 35
`M and 595 M respectively These values are 56 orders of magnitude
`than the intrinsic solubility of 030 ± 002 Igml N
`greater
`Picolylnicotinamide Nallylnicotinamide and sodium salicylate were
`for PTX Solubility data showed that an
`also excellent hydrotropes
`effective hydrotropic agent should be highly water soluble while
`
`maintaining
`Conclusions
`
`segment
`a hydrophobic
`The present study identified several hydrotropic agents
`effective for increasing aqueous solubility of VD and analyzed the
`for this hydrotropic property This informa
`structural
`requirements
`tion can be used to find other hydrotropic compounds and to synthe
`for VD and other
`size polymeric hydrotropes
`that are effective
`poorly watersoluble drugs
`KEY WORDS hydrotropic agents solubilization poorly water
`soluble drug paclitaxel structure activity relationship
`
`INTRODUCTION
`
`Poor water solubility of many drugs and drug candidates
`causes significant problems in producing formulations with
`sufficiently high bioavailability 13 Paclitaxel PTX
`
`presents a good example of the importance of water solubil
`therapy has been hindered by its low
`ity Its use in cancer
`
`water solubility 4 which has required special formulations
`utilizing ethanol and Cremophore EL polyoxyethylated cas
`tor oil which has significant side effects such as hypersensi
`tivity reactions 5 Testing PTX in preclinical
`tumor model
`systems is also difficult 6 In addition the cosolvent mixture
`
`is diluted in isotonic saline solution before intravenous ad
`ministration and the diluted solution remains stable for only
`several hours 7 For hydrophobic
`drugs with poor water
`solubility including PTX several methods have been used to
`
`of Pharmaceutics and Biomedical Engineering Pur
`1 Departments
`due University West Lafayette Indiana 47907
`2 To whom correspondence
`should be addressed email kpark
`purdueedu
`
`increase their water solubility Poorly watersoluble drugs
`have been formulated into micron or submicronsize particu
`
`late preparations 3 liposomes and micelles 8 and solid
`dispersions 910 Cosolvent systems can increase the drug
`solubility significantly but
`the choices of clinically used sol
`vents are limited to ethylene glycol dimethylsulfoxide NN
`dimethylformamide Cremophore and ethanol 11
`In an attempt
`to find an alternative or supplementary
`method for
`increasing water solubility of poorly soluble
`drugs we have examined the possibility of using hydrotropes
`Hydrotropic agents hydrotropes have been used to increase
`the water solubility of poorly soluble drugs and in many in
`stances the water solubility has increased by orders of mag
`nitude 12 Hydrotropy is a collective molecular phenom
`enon describing an increase in the aqueous
`solubility of a
`poorly soluble compound by addition of a relatively large
`
`amount of a second solute ie a hydrotrope 1 Each hy
`
`is effective in increasing the water solubility
`drotropic agent
`hydrophobic drugs and no universal hydrotropic
`of selected
`agent has been found to be effective with all hydrophobic
`drugs Thus finding the right hydrotropic agents for a par
`drug requires the screening of a large
`ticular hydrophobic
`number of candidate hydrotropes In this study we examined
`various candidate agents for their abilities to solubilize PTX
`the structures of effective agents can be used for iden
`so that
`tification of other hydrotropic agents and for synthesis of hy
`drotropic polymers
`
`MATERIALS AND METHODS
`
`Materials
`
`PTX was obtained from Samyang Genex Corp Taejeon
`South Korea 6Hydroxynicotinic acid 11carbonyl
`diimidazole CDI diethylamine 3picolylamine nicotinoyl
`chloride hydrochloride allylamine acetic anhydride pyri
`dine and triethylamine were purchased from Aldrich Chemi
`cal Company Milwaukee WI and used without further pu
`chloride was dried and distilled over
`rification Methylene
`calcium hydride Tetrahydrofuran THF was distilled from
`sodium benzophenone before use n Hexane diethyl ether
`chloroform and methanol were of reagent grade All other
`chemicals were purchased from Fisher Scientific Pittsburgh
`PA Freshly prepared distilled water was used throughout
`
`Synthesis and Characterization of Nicotinatnide Analogues
`
`Instrumental Analysis
`111 and 13C NMR spectra were obtained using a Bruker
`ARX300 spectrometer at 300 MHz and 75 MHz respectively
`Elemental analysis was performed on a Perkin Elmer Series
`II CHNSO Analyzer 2400 UVVIS spectra were obtained by
`a Beckman DU® 640 spectrophotometer
`ion
`Electrospray
`ization mass spectrometry ESIMS assay was done using a
`FinniganMAT LCQ ThermoFinnigan Corp San Jose CA
`The electrospray needle voltage was set at 45 kV the heated
`to 10 V and the capillary tempera
`capillary voltage was set
`ture to 225°C Typical background source pressure was 12 x
`105 torr The sample flow rate was approximately 10 pimin
`Nitrogen gas was used for drying The LCQ was scanned to
`2000 amu for these experiments
`
`072487411030700102210
`
`© 2003 Plenum Publishing Corporation
`
`1022
`
`Abraxis EX2042
`Actavis LLC v Abraxis Bioscience LLC
`1PR201701101 1PR201701103 1PR201701104
`
`

`

`Hydrotropic Solubilization of Paclitaxel
`
`1023
`
`NPicolylnicotinamide
`
`To a solution of 3picolylamine 01 mol and pyridine
`02 mol in dry methylene chloride 600 ml was added nico
`tinoyl chloride hydrochloride 01 mol at 0°C The reaction
`mixture was stirred at room temperature for 24 h under ni
`trogen After 24 h the solvent was removed under
`reduced
`pressure and the crude product was dissolved in water neu
`tralized with sodium bicarbonate
`and extracted with chloro
`form 3 x 200 nil The solution was dried over anhydrous
`magnesium sulfate The solvent was removed at reduced pres
`sure and the product was isolated by column chromatogra
`phy on a silica gel using THFnhexane Yield was 80 mp
`105107°C XmaxTHF 256 nm 1H NMR DMSOd6 8 452
`d T = 58 Hz 2H 734 dd T = 48 77 Hz 1H 749 dd
`T = 48 81 Hz 1H 772775 m 1H 820823 m 1H
`846 dd T = 10 48 Hz 1H 858 d T = 24 Hz 1H 870
`dd T = 10 48 Hz 1H 906 d T = 20 Hz 1H 929 t T
`= 58 Hz 1H 13C NMR DMSOd6 8 404 1234 1296
`1347 1350 1351 1482 1483 1485 1489 1519 1649 ESI
`MS mz 214 14+H1 analysis calculated for Ci2HN30 C
`6759 H 520 N 1971 Found C 6773 H 510 N 1951
`
`NAllylnicotinamide
`
`To a stirred solution of allylamine 0168 mol in dry
`methylene chloride 500 ml nicotinoyl chloride hydrochlo
`ride 0112 mol and triethylamine 0225 mol were added at
`0°C The reaction mixture was stirred at room temperature
`for 24 h under nitrogen After 24 h the solvent was removed
`reduced pressure The brown liquid was dissolved in
`under
`distilled water and neutralized with sodium bicarbonate
`fol
`lowed by extraction with chloroform 3 x 200 nil The solvent
`was removed at reduced pressure and the crude product was
`column chromatographed with THFnhexane on a silica gel
`to produce a light yellow liquid Yield was 85 XmaxTHF
`260 nm 1H NMR DMSOd6 8 389394 m 2H 505520
`m 2H 582594 m 1H 747 dd T = 50 83 Hz 1H
`820 m 1H 868 dd T = 17 50 Hz 1H 887 t T = 56
`Hz 1H 904 d T = 17 Hz 1H 13C NMR DMSOd6 8
`415 1153 1233 1299 1349 1350 1485 1517 1646 ESI
`MS mz 163 M+Hr analysis calculated for C9110N20 C
`6665 H 621 N 1727 Found C 6653 H 607 N 1697
`
`6HydroxyNNDiethylnicotinamide
`
`To a stirred suspension of 6hydroxynicotinic acid 0108
`mol in THF 600 ml was added CDI 0108 mol in one
`portion The reaction mixture was stirred at reflux under ni
`trogen After 24 h diethylamine 0216 mol was added drop
`wise to the stirred suspension of N6hydroxynicotiny1
`imidazole in THF at reflux The reaction was further main
`tained for 24 h under nitrogen After cooling of the reaction
`mixture to room temperature 1N sodium hydroxide solution
`120 ml was added THF was evaporated
`and the aqueous
`solution of the crude product was washed with diethyl ether
`5 x 200 m1 The aqueous solution was then neutralized with
`1 N hydrochloric
`acid to pH 7 and extracted with chloroform
`3 x 200 m1 The solution was dried over anhydrous magne
`sium sulfate The solvent was removed at reduced pressure
`and the product was isolated by column chromatography
`on a
`Yield was 65 mp 113
`silica gel using THFnhexane
`115°C XmaxTHF 253 nm 1H NMR DMSOd6 8 109 t T
`
`= 72 Hz 6H 332 q T = 72 Hz 4H 634 d I = 91 Hz
`1H 745 dd I = 24 91 Hz 1H 750 d T = 24 Hz 1H
`13C NMR DMSOd6 8 133 410 1144 1193 1355 1397
`1619 1668 ESIMS mz 195 14+Hr analysis calculated
`for Ci0HN202 C 6184 H 727 N 1442 Found C 6173
`H 716 N 1447
`
`2HydroxyNNDiethylnicotinamide
`
`To a stirred suspension of 2hydroxynicotinic acid 0216
`in THF 700 ml was added CDI 0216 mol in one
`mol
`portion The reaction mixture was stirred at reflux under ni
`trogen After 24 h diethylamine 0323 mol was added drop
`wise to the stirred suspension of N2hydroxynicotiny1
`imidazole in THF at reflux The reaction was maintained for
`24 h under nitrogen After cooling of the reaction mixture to
`room temperature the solution was concentrated under re
`duced pressure The pale yellow precipitate was
`filtered
`washed with diethyl ether and dried in vacuo Yield was 70
`mp 9092°C XmaxTHF 313 nm 1H NMR DMSOd6 8
`100 t T = 72 Hz 3H 107 t T = 72 Hz 3H 312 q T =
`72 Hz 2H 335 q T = 72 Hz 2H 620 m 1H 738 dd
`T = 24 69 Hz 1H 741 dd T = 24 69 Hz 1H 13C NMR
`DMSOd6 8 128 141 384 422 1046 1293 1361 1384
`1592 1662 ESIMS mz 195 14+H1 analysis calculated
`for Ci0H4N202 C 6184 H 727 N 1442 Found C 6214
`H 718 N 1442
`
`NPicolylacetamide
`
`To a stirred solution of acetic anhydride 0069 mol in
`THF 50 ml a solution of 3picolylamine 0046 mol in THF
`20 ml was added dropwise at room temperature The reac
`tion mixture was stirred for 5 h under nitrogen After 5 h an
`excess of water was added and the aqueous solution was
`neutralized with 1 N sodium hydroxide The solvent was re
`moved at reduced pressure and the product was isolated by
`on a silica gel using THFnhexane
`column chromatography
`Yield was 85 XmaxTHF 257 nm 1H NMR CDC13 8 190
`s 3H 429 d T = 57 Hz 2H 716 dd T = 48 82 Hz
`1H 739 s 1H 754 m 1H 834 dd T = 14 48 Hz 1H
`835 d T = 14 1H 13C NMR CDC13 8 227 407 1234
`1342 1355 1481 1486 1704 ESIMS mz 151 14+Hr
`analysis calculated for C8fli0N20 C 6398 H 671 N 1865
`Found C 6385 H 661 N 1854
`
`NMR Measurement
`
`The 1H NMR spectra of NNDENA in D20 in the con
`centration range of 00025 to 136 M were obtained The ratios
`protons to the chemical
`shift of HDO protons 463 ppm were monitored with in
`creasing NNDENA concentrations
`
`of chemical shifts of nicotinamide
`
`Solubility Study
`
`Excess PTX was added to screw capped vials containing
`a fixed volume of the hydrotrope solution This mixture was
`for 24 h at 37°C An
`bar
`stirred using a magnetic stirring
`aliquot of the sample was collected
`and within 5 s it was
`filtered through a 02pm nylon membrane This immediate
`process prevented any possible formation of PTX
`
`filtering
`
`

`

`in the Presence of Various Hydrotropic Agents at 37°C
`used Mb
`
`PTX solubility mgml
`
`Concentration
`
`1024
`
`Table I Paclitaxel Solubilities
`
`Hydrotropic agent
`
`None PTX solubility in pure water
`NNDiethylnicotinamide
`NPicolylnicotinamide
`
`NAllylnicotinamide
`Sodium salicylate
`
`2Methacryloyloxyethyl phosphorylcholine
`
`Resorcinol
`
`N NDimethylnicotinamide
`NMethylnicotinamide
`
`Butylurea
`
`Pyrogallol
`
`NPicolylacetamide
`Procaine HC1
`Nicotinamide
`
`Pyridine
`
`3Picolylamine
`Sodium ibuprofen
`Sodium xylenesulfonate
`Ethyl carbamate
`
`6HydroxyNNdiethylnicotinamide
`Sodium ptoluenesulfonate
`
`Pyridoxal hydrochloride
`
`35
`
`35
`
`35
`
`35
`29
`35
`
`35
`
`35
`
`35
`
`35
`
`35
`25
`35
`35
`
`35
`15
`25
`
`00003
`39071
`
`29435
`
`14184
`
`5542
`
`3199
`
`2009
`
`1771
`
`1344
`
`1341
`
`1282
`
`1084
`
`0720
`
`0694
`0658
`
`0552
`0500
`
`0481
`
`0300
`0241
`
`0220
`
`0216
`
`Lee et al
`
`Standard deviation
`
`00000
`
`0600
`
`1205
`
`0385
`
`0514
`
`0037
`
`0012
`
`0026
`
`0006
`
`0071
`
`0008
`
`0003
`
`0005
`
`0031
`0080
`
`0063
`0070
`
`0080
`
`0028
`0004
`
`0002
`
`0008
`
`1Methy12pyrrolidone
`Sodium benzoate
`
`2Pyrrolidone
`
`Ethylurea
`
`N NDimethylacetamide
`NMethylacetamide
`Isoniazid
`
`35
`20
`25
`25
`35
`20
`35
`
`35
`
`35
`
`35
`10
`
`0071
`
`0050
`
`0038
`
`0030
`
`0015
`
`0012
`
`0009
`
`0002
`
`0006
`
`0002
`
`0003
`
`0002
`
`0001
`
`0002
`
`Mean ± SD n = 3 except for PTX solubility in pure water where n = 10
`less than 35 M represent
`the maximum solubilities of the hydrotropic agent
`b The concentrations
`b The aqueous PTX solubility is 030 ± 002 rigmi
`
`particles as a result of the temperature decrease
`The filtrate was diluted with acetonitrile 11 and the con
`centration of PTX was determined
`by an isocratic reverse
`phase HPLC Agilent 1100 series Agilent Technologies Wil
`mington DE using a Symmetry column Waters Corp
`
`to ambient
`
`Milford MA at 25°C The mobile phase consisted of aceto
`nitrilewater 4555 vv with a flow rate of 10 mlmin A
`diode array detector was set at 227 nm and linked to Chem
`Station software for data analysis The PTX concentrations in
`the samples were obtained from a calibration curve
`
`184
`
`H2 411104111
`
`182 I
`
`H6
`
`0
`
`0 0
`
`o
`
`o
`
`180 1
`
`165 1
`
`V Ir
`
`160 H5
`
`V V V
`
`Zvvv
`
`1
`
`0
`
`3
`2
`NNDiethylnicotinamide Log M
`Fig 2 The ratio of chemical shifts of nicotinamide
`protons to the
`chemical shift of HDO protons in D20 as a function of the concen
`115 and 116 indicate
`tration of NNdiethylnicotinamide
`the proton
`position of the nicotinamide
`ring of NNdiethylnico
`tinamide
`
`fChemicalShift
`
`Ratioso
`
`600
`
`500
`
`cr
`
`> 400
`
`2 300
`0
`co
`ITI 200
`
`00009
`
`E
`
`00006
`
`2 00003
`
`NNDiethylnicolinamide
`
`Log M
`
`T 100
`0
`0s
`
`0
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`0
`NNDiethylnicotinamide M
`Fig 1 Paclitaxel solubility as a function of the molar concentration
`The solubility of paclitaxel at 595 M of
`of NNdiethylnicotinamide
`NNdiethylnicotinamide is 5126 mgml The inserted plot shows the
`of NN
`paclitaxel solubility as a function of the log concentration
`
`diethylnicotinamide
`
`

`

`Hydrotropic Solubilization of Paclitaxel
`
`1025
`
`0
`CH380
`CNHCHCHO
`
`0
`
`U113
`
`0
`
`OH
`
`HO
`
`0
`OH
`II CH4
`
`0
`
`H
`
`C=0
`
`CH3
`
`=0
`
`Fig 3 Chemical structure of paclitaxel
`
`RESULTS AND DISCUSSION
`
`Paclitaxel Solubility by Hydrotropes
`
`lists
`
`and very low
`Because of its noted therapeutic potential
`water solubility PTX was
`chosen
`to examine hydrotropic
`properties of various agents in this study The exact mecha
`nisms involved in solubilization of PTX and other poorly
`are not clearly under
`soluble drugs by hydrotropic agents
`the structural
`stood so it
`is difficult
`to predict
`requirements of
`hydrotropes suitable for solubilizing PTX For this reason a
`large number of candidate agents were screened Table I
`the agents tested and the corresponding water solubilities of
`PTX measured in the presence of those agents Our prelimi
`that even good hydrotropes required a
`nary study suggested
`hydrotropic concentration of approximately 3 M For this rea
`son a concentration of 35 M was used for all agents to com
`the same condition
`pare their hydrotropic properties under
`The concentrations
`of some agents
`listed in Table I are
`smaller than 35 M because of their limited solubility Table I
`clearly identifies a number of hydrotropic agents effective for
`increasing the water solubility of PTX
`The aqueous solubility of PTX at 37°C was determined
`to be 030 ± 002 pLgml Thus a PTX concentration
`of 39
`mgml by NNdiethylnicotinamide NNDENA in Table I
`indicates more than 100000 fold increase in aqueous solu
`bility Equally effective was Npicolylnicotinamide N
`Allylnicotinamide sodium salicylate and 2methacryloyloxy
`increased the PTX solubility by four
`ethyl phosphorylcholine
`
`that
`
`orders of magnitude Other hydrotropes
`resulted in an
`aqueous PTX solubility more than 1 mgml were resorcinol
`NNdimethylnicotinamide Nmethylnicotinamide
`butyl
`urea pyrogallol and Npicolylacetamide The PTX solubility
`of 03 mgml by ethyl carbamate appears to be much smaller
`than that by NNDENA but still
`represents a 1000 fold in
`crease
`Another 35 agents not listed in Table I showed paclitaxel
`of 0005 mgml or 5 pigm1 or less They are
`solubilities
`in the descending order of solubilizing effect nipecotamide
`
`diamino2hydroxypropaneNNN Ntetramethylacetate
`
`35 M citric acid 20 M sodium gentisate 10 M N
`isopropylacrylamide 15 M methylurea 35 M 13
`30 M thiourea 25 M 1methylnicotinamide iodide 10
`M ticyclodextrin 015 M sodium thiocyanate 86 M
`urea 60 M caffeine 01 M glyceryl
`triacetate 02 M
`glycerin 35 M adenosine 0005 M ycyclodextrin 017
`M I3cyclodextrin 002 M diisopropylnicotinamide 005
`M pyridine3sulfonic acid 10 M o benzoic acid sulfimide
`001 M 26pyridinedicarboxamide 00025 M 34
`pyridinedicarboxamide 0025 M 4aminosalicylic
`0005 M Ltryptophan 005 M salicylaldoxime 01 M
`sucrose 20 M Llysine 20 M 4aminobenzoic
`salt 25 M Dsorbitol 30 M sodium Lascorbatc 30 M
`sodium propionate 35 M sodium acetate 40 M 2hy
`02 M 2hydroxyN
`00035 M and 6hydroxyN
`picolylnicotinamide 008 M
`Hydrotropic Property of NNDENA
`The hydrotropic property of NNDENA was examined in
`more detail Figure 1 shows the paclitaxel solubility as a func
`tion of the NNDENA concentration NNDENA at 595 M
`increased the PTX concentration to 512 mgml equivalent to
`06 M because the molecular weight of PTX is 854 gmol and
`this corresponds to 10 NNDENA molecules per paclitaxel
`molecule dissolved At the concentration
`of hydrotropes used
`in Table I however more than 100 hydrotropic agents
`are
`necessary for effective solubilization of PTX The inserted
`plot in Fig 1 shows the solubility increase of PTX as a func
`of NNDENA in the range of
`the log concentration
`tion of
`
`acid
`
`acid sodium
`
`droxyNNdiethylnicotinamide
`picolylnicotinamide
`
`Structure
`
`0
`
`CN
`
`CH2CH3
`
`L
`
`ai2uri3
`
`j
`
`N1
`
`CH2CH3
`
`CH2 CH3
`
`0 I
`
`I
`
`cnc
`
`CH2CH3
`
`CH2CH3
`
`Hydrotropic agent
`
`NNDiethylnicotinamide
`
`6HydroxyNNdiethylnicotinamide
`
`2HydroxyNNdiethylnicotinarnide
`
`Table II
`
`Conc used
`
`M
`
`PTX solubility
`mgml
`
`35
`
`20
`
`02
`
`20
`
`02
`
`3907
`
`098
`
`0001
`
`024
`
`000
`
`The maximum solubility of
`
`the hydrotropic agent
`
`

`

`1026
`
`Lee et al
`
`00028 to 05 M The water solubility of PTX begins to in
`crease at 011 M of NNDENA although the increase is small
`compared to higher concentrations of NNDENA
`Because the dissolution of PTX in NNDENA is expected
`through association of NNDENA molecules self
`to occur
`of NNDENA molecules was examined
`association
`using
`NMR Figure 2 shows
`the NNDENA concentration depen
`dence of the ratio of chemical shifts of nicotinamide protons
`to the chemical shift of HDO protons in D20 As the con
`centration of NNDENA increased to about 01 M the ratios
`the nicotinamide
`of chemical shifts of all protons of
`started to decrease The data indicate that NNDENA self
`via the vertical plane to plane interaction
`the
`associates
`of
`aromatic rings The crossover point in Fig 2 can be described
`as the minimum hydrotropic concentration MHC which is
`of selfaggregate formation The
`the threshold concentration
`MHC value of NNDENA in the aqueous media was esti
`mated to be 012 M Interestingly this MHC value is almost
`of 011 M where NNDENA
`the same as the concentration
`begins to exhibit the solubilizing ability for PTX in aqueous
`solutions
`
`ring
`
`Structural Analysis of Hydrotropic Property for PTX
`To gain insights into the structural
`requirements neces
`sary for hydrotropy chemical structures of various agents
`listed in Table I were analyzed for their ability to increase
`aqueous PTX solubility The structure of PTX is shown in Fig
`3 A few common features of good hydrotropes for PTX were
`identified
`
`High Water Solubility of Hydrotropic Agents
`The main criterion for effective hydrotropy is high water
`the water solubility is
`If
`solubility of the hydrotropic agent
`
`low eg less than 2 M the hydrotropic property is not ob
`served to be significant At 20 M PTX solubility was higher
`in NNDENA than in 6hydroxyNNdiethylnicotinamide
`The PTX solubility in NNDENA was greatly increased with
`the NNDENA concentration 2HydroxyNN
`increasing
`diethylnicotinamide with the maximum water solubility of
`only 02 M did not have any PTXsolubilizing effect The
`following example shows the importance of water solubility of
`aqueous PTX solubility
`on increasing
`
`hydrotropic agents
`Table II
`
`Table III
`
`Hydrotropic agent
`
`Conc
`
`used M PTX solubility
`
`mgml
`
`Sodium salicylate
`
`35
`
`554
`
`Pyrogallol 123
`trihydroxybenzene
`
`35
`
`128
`
`Nicotinamide
`
`3Picolylamine
`
`Nipecotamide
`
`NNDimethylacetamide
`
`NIsopropylacrylamide
`
`35
`
`35
`
`35
`
`35
`
`15
`
`069
`
`055
`
`0005
`
`0015
`
`0004
`
`Structure
`
`OH
`
`OH
`
`CN H2
`
`11
`
`0
`
`0
`
`CH a NG GH3
`
`CH3
`
`CH3
`H2C=HCCNHC11
`
`CH3
`
`13Diamino2hydoxypropane
`NNN Ntetramethylacetate
`
`0004
`
`HO
`
`The maximum solubility of
`
`the hydrotropic agent
`
``COOC H3
`0000 H
`N
`
`3
`
`H 3
`
`

`

`Hydrotropic Solubilization of Paclitaxel
`
`1027
`
`Structure
`
`cH2cH
`
`CN
`
`CH2CH3
`
`CH3
`
`CH3
`
`H
`
`CH3
`
`0 I
`
`I
`
`0
`
`II
`
`0 1
`
`1
`
`H2
`
`I
`
`N H2
`
`I
`
`IC
`
`CH3
`
`0
`
`Table IV
`
`Hydrotropic agent
`Conc used
`
`Conc used
`
`M
`
`FIX solubility
`mgml
`
`NNDiethylnicotinamide
`
`NNDimethylnicotinamide
`
`NMethylnicotinamide
`
`Nicotinamide
`
`35
`
`35
`
`35
`
`35
`
`3907
`
`177
`
`134
`
`069
`
`1Methylnicotinamide iodide
`
`10
`
`0003
`
`NNDiisopropylnicotinamide
`
`005
`
`0001
`
`The maximum solubility of
`
`the hydrotropic agent
`
`Hydrotropic agent
`Conc used
`
`Table V
`
`FIX solubility
`mgml
`
`Structure
`
`Sodium xylenesulfonate 25 Mr
`Sodium ptoluenesulfonate 25 Mr
`
`1Methy12pyrrolidone 35 M
`2Pyrrolidone 35 M
`
`NMethylnicotinamide 35 M
`Nicotinamide 35 M
`
`048
`
`022
`
`007
`
`004
`
`134
`
`069
`
`The maximum solubility of
`
`the hydrotropic agent
`
`CH3
`
`SO3N a
`
`SO3Na
`
`N
`
`1
`
`CH3
`
`H
`
`0
`
`IICN
`
`r t3
`
`ço
`
`CN H2
`
`

`

`1028
`
`Lee et al
`
`Table VI
`
`Conc
`used
`
`PTX
`
`M mgml
`
`solubility
`
`Hydrotropic agent
`
`Resorcinol
`
`13dihydroxybenzene
`
`35
`
`2009
`
`Pyrogallol
`
`123trihydroxybenzene
`
`35
`
`1282
`
`Structure
`
`OH
`
`OH
`
`OH
`
`OH
`
`The agents that did not show any appreciable hydrotro
`have low water solubilities as expected Ex
`triacetate 02 M caffeine 01 M sali
`pic properties
`cylaldoxime 01 M 34pyridinedicarboxamide 0025 M
`amples are glyceryl
`o benzoic acid sulfimide 001 M 4aminosalicylic acid 0005
`M adenosine 0005 M and 26pyridinedicarboxamide
`00025 M Those agents have low water solubility and thus
`
`showed almost no hydrotropic effect
`
`High Hydrophobicity of Hydrotropic Agents
`For those agents having high water solubilities the hy
`the
`drotropic property increases as
`the hydrophobicity of
`molecule increases Poorly soluble organic drugs are all hy
`drophobic ie nonpolar and do not interact with water mol
`ecules through hydrogen bonding Thus the presence or in
`drug molecules in water known as
`sertion of hydrophobic
`hydrophobic hydration causes a direct perturbation of water
`ie an alteration in the hydrogen bonding state of water mol
`ecules Water structure formers such as sucrose and sorbitol
`of poorly soluble drugs whereas water
`increase the solu
`structure disruptors such as nicotinamide
`bility by destroying clusters of associated water molecules and
`releasing water of solvation 13 Thus effective hydrotropic
`agents are expected to destabilize water structure and at the
`same time interact with poorly soluble drugs Hydrotropic
`
`inhibit dissolution
`
`component are not
`agents lacking a significant hydrophobic
`effective at all The following examples show the importance
`of hydrophobic groups in promoting hydrotropic properties
`
`Importance of Pyridine and Benzene Rings
`
`Almost all highly effective hydrotropic agents listed in
`Table I have either a pyridine or a benzene ring in their
`structures Molecules without such rings in their structures
`were not as effective as those containing the ring structures
`As shown in Table III nicotinamide
`and 3picolylamine dis
`the same hydrotropic property while nipecot
`played about
`
`amide which has a saturated ring structure is less than 1
`
`effective as nicotinamide Other agents without pyridine or
`benzene ring that had very small hydrotropic effect are urea
`and its alky derivatives methyl ethyl and butylurea glyc
`erin thiourea Nisopropylacrylamide Nmethylacetamide
`and 13
`NNdimethylacetamide
`sodium thiocyanate
`diamino2hydroxypropaneNNNNtetramethylacetate
`
`Maximum Hydrophobicity without Losing Water Solubility
`
`The hydrotropic properties
`of nicotinamide
`derivatives
`of mol
`show a positive correlation with the hydrophobicity
`ecules as long as water solubility is not lost As shown in Table
`IV NNDENA showed more than a 20 times higher hydro
`at the same
`tropic property than NNdimethylnicotinamide
`in turn was more
`concentration NNDimethylnicotinamide
`than Nmethylnicotinamide and Nmethylnic
`effective
`otinamide was twice as effective as nicotinamide 1Methyl
`iodide was too hydrophilic to be hydrotropic
`nicotinamide
`The poor hydrotropic property of NNdiisopropylnicotin
`amide results from its poor water solubility which is only
`005 M
`
`Increase in the Hydrotropic Property by a Factor of Two
`with a Methyl Group on the Ring
`
`At the same concentration
`
`sodium xylenesulfonate was
`
`more hydrotropic than sodium ptoluenesulfonate Table V
`A similar trend was seen with 1methyl2pyrrolidone and
`2pyrrolidone In both examples the presence of one methyl
`group increased the hydrotropic property of the molecule by
`
`Table VII
`
`Hydrotropic agent
`
`Conc usedM
`
`PTX solubility
`mgm1
`
`Structure
`
`NPicolylnicotinamide
`
`35
`
`2944
`
`NAllylnicotinamide
`
`NNDimethylnicotinamide
`
`35
`
`35
`
`1418
`
`177
`
`NH
`
`ifCH3CN
`
`UF13
`
`

`

`Hydrotropic Solubilization of Paclitaxel
`
`1029
`
`a factor of 2 The same result was observed for Nmethylni
`cotinamide and nicotinamide
`
`Decrease
`
`in Hydrotropic Property with a Hydroxyl Group
`The hydrophilicity of a molecule can be increased by
`attaching hydroxyl groups to the molecule Increase in hydro
`philicity comes with a reduction in the hydrotropic properties
`of the molecule For example pyrogallol which is more hy
`drophilic than resorcinol
`has lower hydrotropic property
`Table VI
`
`More Effective Hydrotropic Property by One Long
`Hydrophobic Chain Than by Two Shorter
`Hydrophobic Chains
`
`As shown in Table VII the high hydrotropic properties
`of Npicolylnicotinamide
`and Nallylnicotinamide
`suggest
`that one longer carbon chain is better than two shorter carbon
`chains eg one allyl group vs two methyl groups A signifi
`increase in PTX solubility by Npicolylnicotinamide may
`be partly related to the presence
`of another pyridine ring that
`
`cant
`
`Hydrotropic agent
`
`Conc used
`
`M
`
`PTX solubility
`mgm1
`
`Structure
`
`Table VIII
`
`Sodium salicylate
`
`35
`
`554
`
`2Methacryloyloxyethyl
`
`phosphorylcholine
`
`29
`
`320
`
`I13
`H2C=
`
`00 H 2CH2ONC H2CH2N CI199
`
`HCI
`
`I 0
`
`I
`
`C0C H2C H2NC2H52
`
`0
`
`H3C
`
`ON a
`
`Procaine HC1
`
`25
`
`072
`
`H2N
`
`Sodium ibuprofen
`
`15
`
`050
`
`Sodium xylenesulfonate
`
`25
`
`048
`
`Sodium ptoluenesulfonate
`
`25
`
`022
`
`Pyridoxal hydrochloride
`
`25
`
`022
`
`HO H2C
`
`Sodium benzoate
`
`005
`
`Isoniazid
`
`10
`
`001
`
`The maximum solubility of
`
`the hydrotropic agent
`
`SO3N a
`
`CH3
`
`OH
`
`HCI
`
`CHO
`COONa
`
`rN
`
`CON HN H2
`
`

`

`1030
`
`Lee et al
`
`is shown to be essential for hydrotropic property as discussed
`above
`
`Hydrophobic
`and Solute
`
`Interaction between Hydrotropic Agent
`
`Aliphatic derivatives of urea were studied for their ef
`fects on increasing the water solubility of PTX Butylurea
`shows
`the highest solubilizing effect among the analogues
`studied which suggests that as the hydrophobicity
`decreases
`the hydrotropic property also decreases Urea is known to
`break up the hydrogen bonded water molecule clusters sur
`solute molecules The poor hydrotropic
`rounding nonpolar
`property of urea suggests that disruption of water structure
`alone without substantial
`interaction with solute is not
`
`enough for effective hydrotropy
`
`Separation of Hydrophilic and Hydrophobic Domains
`A good hydrotropic agent appears to have hydrophilic
`domains on the same molecule Examples
`and hydrophobic
`are shown in Table VIII This is reasonable because hydro
`tropic agents are expected to have nonbonded hydrophobic
`solute molecules while main
`interactions with hydrophobic
`taining hydrophilic property for high water solubility It
`interesting to note that sodium salicylate is highly effective in
`dissolving PTX The carboxyl
`and hydroxyl groups are lo
`on the same side of
`the molecule resulting in clear
`cated
`separation of the hydrophilic domain from the hydrophobic
`domain The same may be true with 2methacryloyloxyethyl
`phosphorylcholine
`
`29 M ProcaineHC1 25 M sodium
`ibuprofen 15 M sodium xylenesulfonate 25 M and so
`p toluenesul
`dium
`fonate 25 M show easily identifiable separation of hydro
`
`is
`
`philic and hydrophobic parts
`
`Polymeric Hydrotropic Agents
`
`Although hydrotropic agents can increase the water solu
`bility of poorly soluble drugs by several orders of magnitude
`they have not been explored extensively in the pharmaceutics
`field The main reason for this may be the concern that
`the
`use of low molecular weight hydrotropic agents at high con
`in undesirable side effects including
`centrations may result
`however may be
`toxicity and cell damages This concern
`alleviated by preparing polymeric forms of hydrotropes For
`this reason we synthesized polymers of hydrotropic agents
`effective for PTX and hydrotropic polymers were as effective
`in increasing the wa
`as the low molecular weight counterpart
`ter solubility of PTX For example a polymeric form of N
`
`their hydrotropic properties
`
`picolylnicotinamide maintains
`14 Table I suggests several candidate hydrotropic agents
`into polymers NNDENA N
`that can be synthesized
`and sodium salicy
`picolylnicotinamide Nallylnicotinamide
`late appear to be good candidates for making polymeric hy
`drotropic agents for PTX
`ACKNOWLEDGMENTS
`
`This study was supported in part by National Institute of
`Health through grant GM 65284 Samyang Corporation and
`NSF IndustryUniversity Center for Pharmaceutical Process
`ing Research
`
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`2 R LObenberg G L Amidon and M Vierira Solubility as a
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`
`