Note: Descriptions are shown in the official language in which they were submitted.
1335819 2o208-l396
METAL CHELATE CONTAINING DIAGNOSTIC IMAGING CONTRAST MEDIA
This lnventlon relates to metal chelate composltlons,
ln partlcular contrast agent composltlons containlng chelates of
dlethylenetrlamlnepentaacetlc acld blsamldes (DTPA-blsamldes)
with calclum and wlth paramagnetlc metal lons, lanthanlde lons
or other heavy metal lons.
In dlagnostlc lmaglng, contrast agents are frequently
used to enhance the lmage contrast, for example between dlffer-
ent organs or between healthy and unhealthy tlssue wlthln the
same organ. The nature and manner of operatlon of the contrast
agents depend upon the nature of the lmaglng technique and the
organ or tlssue whlch ls to be lmaged.
Thus in magnetlc resonance lmaglng (MRI), lmage
contrast may be enhanced by lntroduclng lnto the body zone belng
lmaged a contrast agent which affects the nuclear spln reequi-
llbratlon characterlstlcs of the nuclel (generally water protons
ln body tlssues or flulds) which are responslble for the
magnetlc resonance (MR) slgnals from whlch the MR lmages are
generated.
In 1978 Lauterbur ~see Lauterbur et al., pages 752-759
in "Electrons to Tissues - Frontlers of Blologlcal Energetlcs",
Vol. 1, edlted by Dutton et al., Academlc Press, NY, 1978)
proposed the use of paramagnetlc metal lons, such as Mn~II), as
MRI contrast agents. More recently Scherlng AG ~ln EP-A-71564
and US-A-4647447) proposed the use of the dlmeglumlne salt of
the gadolinlum ~III) chelate of dlethylenetrlamlnepentaacetlc
acld (GdDTPA) as a MRI contrast agent. However, even though the
stablllty contrast of the GdDTPA chelate ls very hlgh, thls
compound, followlng lv admlnlstratlon, stlll releases hlghly
toxlc gadollnlum and thus lts dosage llmlt and range of lmaglng
.._
1335819
applications is limited by toxicity factors.
Various DTPA derivatives have been suggested in the
literature as the chelating agents for other
paramagnetic metal chelate MRI contrast agents and
several of these have been found to have lower
toxicities than the DTPA chelates. Thus for example
GdDTPA-bisamides, and in particular GdDTPA-
bisalkylamides, described by Salutar Inc in US-A-4687659
and Gd DTPA-bis(hydroxylated-alkylamides), such as those
described by Dean et al. in US-A-4826673 and by Schering
AG in EP-A-130934, have been found to be substantially
less toxic than GdDTPA-dimeglumine. Such chelates may
thus be used in substantially higher quantities than
GdDTPA and so are useful in a wider range of imaging
~5 applications. However from even such chelate compounds
as these there will be some in vivo release of the
paramagnetic metal and there is thus a continuing need
for the development of MRI contrast media of lower
toxicity.
Metal chelates have also been suggested as contrast
agents for X-ray imaging where contrast is achieved by
altering the attenuation of X-radiation passing through
the body being imaged. The X-ray attenuating effect
increases generally with atomic number and elements such
as lanthanides and heavy metals having atomic numbers
above 50 can provide the contrast required for clear
definition of body organs, body cavities, the vascular
system etc. Consequently, although iodinated organic
compounds are now widely used as X-ray contrast agents,
lanthanide and other heavy metal compounds have
attractive potential as X-ray contrast agents (see for
example US-A-4310507).
These metals include Ba, Bi, Cs and lanthanides
such as Ce, Dy, Lu, Yb and Gd for example. However
their toxicity limits the usefulness of these metals,
particularly for oral or parenteral administration.
They could not hitherto be used safely at the dosages or
3 133~819
concentrations required for effective contrast
enhancement. Moreover previously known lanthanide and
heavy metal chelates, while showing stability in vitro
show substantial and unacceptable toxicity after
administration.
The conventional iodinated X-ray contrast agents
however do have some limitations, particularly the
significant decrease in X-ray attenuation with the high
ke~r X-ray emissions required for computer tomography
(CT) Cc~nn;ng. Moreover commercial iodinated compound
formulations generally have high viscosities and are not
too easily administered. Moreover, while the toxicity
levels of the iodinated X-ray contrast agents are
generally acceptable such compounds can give rise to
physiochemitoxic dose-related reactions and to dose-
unrelated idiosyncratic reactions (see for example
Brasch, "Contrast media in paediatric radiology",
Workshop, Berlin, August 22-24, 1985, NY, Karger
(1987)).
Seltzer et al. have reported in Invest. Radiol.
14 400 (1979) that elements with atomic numbers between
58 and 68 attenuate a 120 kVp X-ray beam more than
elements with higher or lower atomic numbers and thus
compounds of such elements have potential as X-ray
contrast agents. The use of lanthanide series oxides,
e.g. cerium, gadolinium and dysprosium oxides, as
contrast agents in CT scAnn;ng of the liver using a 120
kVp polyenergetic X-ray beam was reported by Havron et
al. in J. Comput. Assist. Tomogr. 4:642-648 (1981).
Similar experiments were reported by Seltzer et al. in
J. Comput. Assist. Tomogr. 5:370-374 (1981).
US-A-4478816 describes methods of digital
radiography using as contrast agents rare earth chelates
of diethylenetriaminepentaacetic acid (DTPA),
ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid)
(EHPG) and N,N'-bis(2-hydroxybenzyl)ethylenediamine-
N,N'-diacetic acid (HBED). Lutetium and yttrium
133S819
chelates are said to be particularly useful in vascular
diagnostic studies by digital fluoroscopy because of
their K-edge mass attenuation coefficient
discontinuities at a high energy level near 60 keV. US-
A-4647447 supra also describes metal chelates as X-ray
contrast agents and US-A-4176173 describes tantalum and
hafnium chelates which can be used as contrast agents
with high energy X-ray sources, particularly in imaging
studies of the intestines.
The X-ray applications at high energy levels such
as CT sc~nn;ng would benefit from better contrast
agents. The greatest relative ratio of contrast
(contrast iodine/soft tissue) will be attained when the
energy of the X-ray beams straddles the large mass
attenuation coefficient discontinuity at the K-edge.
However, for all iodinated contrast agents,
consideration of excessi~e exposure to the patient and
insufficient X-ray tube output intensity at low energy
levels (near 33 k~p) negate utilization of the K-edge
subtraction approach. Unfortunately, iodine compounds
do not provide the necessary attenuation for high kVp
beams, and do not provide the level of image improvement
needed.
A safe and effective form for administering
lanthanides and heavy metals for X-ray contrast imaging
is thus a very important need in this field.
Thus although the use of paramagnetic metal
chelates and chelates of lanthanides and other heavy
metals as contrast agents in diagnostic imaging,
especially X-ray imaging, is known and widely described,
the major X-ray contrast agents continue to be the
iodinated compounds not least because of the toxicity
problems associated with the metals.
A summary of the pharmacology and toxicology of the
lanthanides is provided for example by Haley in J.
Pharm. Sci. 54:663-670 (1965).
While the toxicity of the metal species is
1335819
.
20208-1396
generally significantly reduced by fo~mulation as a
chelate compound and while many chelates have improved
solubilities relative to the free metal oxides, as
mentioned above the problem of metal toxicity remains
even with high stability constant chelates since
undesirable levels of the toxic metal ions are released
from the chelate complex into the body after
administration. The concentrations at which metal
chelates may be administered as contrast agents, and
hence the utility of such chelates as contrast agents
are thus limited by toxicity constraints. Indeed for X-
ray imaging the concentration of chelate considered safe
for general use with human subjects may be insufficient
for effective X-ray attenuation and for MR imaging the
usefulness of even high stability constant chelates such
a~ GdDTPA could be limited since the dosage required for
imaging certain organs may possibly be too toxic for
sa~e and ef~ective use.
It has therefore been an objective within the field
of diagnostic imaging, and especially X-ray and MR
imaging, to develop metal chelate containing contrast
media of reduced toxicity.
One approach, as mentioned above, has been to
investigate different chelating agents and in the MRI
field for example there are numerous publications
proposing the use of many different complexing agents
for chelating the paramagnetic metal ions. Examples of
such pulications include W089/00557 (Nycomed AS), EP-A-
292689 (Squibb), EP-A-232751 (Squibb), EP-A-230893
30 tBracco), EP-A-255471 (Schering), EP-A-277088
(Schering), EP-A-287465 (Guerbet), and the documents
cited therein.
An alternative approach has been to seek to enhance
the bioacceptability of the contrast media by
formulation of the contrast agent with other materials.
Thus in EP-A-270483, in which Schering acknowledge
6 1335819
the problem of in vivo gadolinium release from GdDTPA,
Schering have disclosed that they have found retention
in the body of the heavy metal (i.e. gadolinium) from
heavy metal complexes is reduced by formulating the
heavy metal complex together with one or more weaker
metal complexes and/or one or more free complexing
agents. Schering have stated in this publication that
the addition of free complexing agents or weak complexes
has an extraordinarily strong effect with reference to
the stability of the bonding of the heavy metal and thus
its detoxification and elimination but this statement is
qualified by a reference to the effect that a higher
toxicity may need to be accepted as the price for this
advantage~
In general the inclusion of excess chelating agents
in metal chelate containing contrast media is known from
the literature.
The present invention is based on our surprising
discovery that for metal chelate based contrast media,
by using a DTPA-bisamide as the chelating entity and by
including within the contrast media a calcium DTPA-
bisamide chelate an unpredictably large reduction in the
acute toxicity of the contrast medium can be obtained
thus enabling contrast media, e.g. MRI, X-ray
scintigraphic and ultrasound contrast media, of
significantly reduced toxicity to be produced and
thereby extending the potential field of use of metal
chelates as contrast media, especially in MRI and X-ray
imaging.
Viewed from one aspect therefore the present
invention provides a diagnostic imaging contrast medium
comprising a chelate of a 6-carboxymethyl-3,9-
bis(carbamoylmethyl)-3,6,9-triazaundecanedioic acid
(hereinafter a DTPA-bisamide) with a cation (hereinafter
the imaging cation) selected from paramagnetic metal
ions, lanthanide ions and heavy metal ions, and a
toxicity reducing amount of a calcium chelate of a DTPA-
1335813
bisamide.
Preferably, the chelates in the contrast media ofthe invention are chelates with compounds of formula I
HOOC ~ ~ COOH
N N N (I)
RlR3NOC ~ ~ COOH ~ CONR2R4
wherein Rl to R4 are each, independently, hydrogen, lower
(e.g. C16) alkyl, hydroxy lower alkyl, or polyhydroxy
Cll8 alkyl.
In the definition of substituents Rl to R4 above,
alkyl is deemed to include straight and branched as well
as unsaturated and, preferably, saturated groups.
Preferred DTPA-bisamides of formula I include those
of formula Ia
HOOC ~ ¦ ~ I \ r COOH
N N N (Ia)
RIR3NOC I ~ COOH ~ CONR2R~
wherein R3 and R4 are hydrogen and R1 and R2 are as
defined above, especially hydrogen or lower alkyl
(particularly methyl), as well as those of formula Ib
HOOC ~ I \ I \ r COOH
N N N (Ib)
RlR3NOC I ~--COOH ~ CONR2R4
wherein Rl and R2 are independently C16 mono- or poly-
hydroxyalkyl and R3 and R4 are independently hydrogen or
C16 alkyl, especially methyl. Particularly preferred
DTPA-bisamides of formula I include those of formula Ic
1~35819
HOOC ~ / \ I \ l - COOH
N N N (Ic)
RlR3NOC I ~--COOH \-- CONR2R4
wherein Rl and R2 both represent hydrogen or
dihydroxypropyl and R3 and R4 both represent hydrogen or
methyl. Especially preferred DTPA-bisamides of formula
I include
6-carboxymethyl-3,9-bis(methylcarbamoylmethyl)-3,6,9-
triazaundecanedioic acid (DTPA-BMA);
6-carboxymethyl-3,9-bis(N-methyl-N-2,3-dihydroxypropyl-
carbamoylmethyl)-3,6,9-triazaundecanedioic acid (DTPA-
BMPA); and
6-carboxymethyl-3,9-bis(2,3-dihydroxypropyl-carbamoyl-
methyl)-3,6,9-triazaundecanedioic acid (DTPA-APD).
Preferably the calcium chelate and the
paramagnetic/lanthanide/heavy metal chelate are both
chelates of DTPA-bisamides of formula Ia or are both
chelates of DTPA-bisamides of formula Ib or are both
chelates of DTPA-bisamides of formula Ic. Especially
preferably the calcium and paramagnetic/lanthanide/heavy
metal chelates are both chelates of the same DTPA
bisamide.
The contrast media of the invention may be used in
various different types of diagnostic imaging, for
example MR, X-ray, ultrasound and scintigraphic imaging,
but are especially suited for use as MRI or X-ray
contrast media. In this regard it will be realised that
the choice of the imaging cation will of course depend
upon the nature of the imaging technique in which the
contrast medium is intended to be used.
Thus for MRI contrast media the imaging cation will
be a paramagnetic metal ion, preferably a non-
9 1335819
radioactive species, and conveniently the metal will bea transition metal or a lanthanide, preferably having an
atomic number of 21-29, 42, 44 or 57-71. Metal chelates
in which the metal species is Eu, Gd, Dy, Ho, Cr or Fe
are especially preferred and Gd3+ and Dy3+ are
particularly preferred.
In the case of X-ray and ultrasound contrast media,
the imaging cation is preferably a cation of a
lanthanide or heavy metal species, e.g. a non-
radioactive metal, with an atomic number greater than37, preferably 50 or more, e.g. Ce, Dy, Er, Eu, Au, Ho,
La, Lu, Hg, Nd, Pr, Pm, Sm, Tb, Th, Yb, and the like.
Preferred metals include La, Yb, Dy and Gd, and Dy3+ and
Gd3+ are especially preferred.
I5 For scintigraphic contrast media, the imaging
~ation must of course be radioactive and any
conventional radioactive metal isotope complexable by a
DTPA-bisamide may be used~
It is especially preferred that the chelate
complexes, particular~y those of the imaging cations, be
neutral, that is the positive charge on the cation
should be matched by an equal negative charge on the
chelating moiety. Thus in the case of chelates of DTPA-
bisamides of formula I, the imaging cation is preferably
an M3+ cation, as is the case for example with gadolinium
(III) or dysprosium (III).
Without being limited to a particular theory of
interaction which might underlay the surprising
effectiveness of the contrast media of the invention,
the principle toxicity of the metal chelate contrast
agents is believed to derive from the displacement of
the imaging cation from the chelate by endogeneous metal
ions, especially Zn(II), normally present in the body.
It is believed that when contrast media according to the
invention are administered the Zn(II) available for
displacement preferentially displaces calcium from the
calcium DTPA-bisamide chelates, liberating non-toxic
1335819
calcium into the blood and leaving the imaging cation
secure in a stable chelate. The calcium DTPA-bisamide
chelates have been found to be uniquely suitable for
improving toxicity, apparently because they act in a
unique manner in this interaction. Administration of
calcium chelates of chelating agents other than DTPA-
bisamides (e.g~ CaDTPA) and administration of calcium
DTPA-bisamide chelates with chelates of imaging cations
with chelating agents other than DTPA-bisamides (e.g. Gd
DTPA) has not been found to produce the surprising
improvements in toxicity levels achieved with
compositions according to the inve~tion.
Wi~h the reduced toxicity provided by the contrast
media of the invention, image contrast can be increased
with greater safety and higher dosages of the contrast
agent, iOe. of the imaging cation, can safely be
administered, providing the ability to enhance image
contrast in a wider range of imaging applications, e.g.
for a wider range of organs.
As mentioned above, it is thought that the toxicity
r~duction is linked to Zn(II) displacement of imaging
cations a~d thus the imaging cations are conveniently
cations, e.g. lanthanide or heavy metal cations,
displaceable from a DTPA-bisamide chelate by Zn(II).
Examples of metal ions falling within this definition
include the ions of Ce, Dy, Er, Eu, Gd, Au, Ho, La, Lu,
Hg, Nd, Pr, Pm, Sm, Tb, Th, Yb and the like.
DTPA-bisamide chelating agents, such as those of
formula I above, are either known from the literature or
~ay be prepared in manners analogous to those described
in the literature. Thus for example DTPA-bisalkylamides
and methods for their preparation are disclosed in US-A-
4687659 and DTPA-bis(hydroxyalkyl-amides) and methods
for their preparation are disclosed in US-A-4826673 and
EP-A-130934.
The metal chelates of the DTPA-bisamides, i.e. the
chelates with the imaging cation and with calcium, can
3 5 8 19
be prepared in a conventional manner, e.g. by mixing in
aqueous solution stoichiometric quantities of a DTPA-
bisamide and a compound of the metal which dissolves to
liberate the metal species to be chelated, e.g. a metal
oxide or hydroxide (such as calcium hydroxide or
gadolinium oxide) or a soluble salt of calcium or of the
imaging cation.
- The calcium chelate in aqueous solution is
preferably a fully neutralized salt. The counterion for
the calcium chelate complex and indeed any necessary
counterion for the imaging cation chelate complex can be
any pharmaceutically acceptable non-toxic ion. Suitable
counterions include monovalent cations such as ions of
lithium, potassium and sodium and divalent cations such
as calcium and magnesium can also be used. Suitable
cations of organic bases include, for example,
ethanolamine, diethanolamine, morpholine, glucamine,
N,N-dimethylglucamlne, and N-methylglucamine. Ions of
amino acids such as lysine, arginine and ornithine and
other basic naturally occuring acids may also be
considered.
The contrast medium may be prepared by reacting a
DTPA-bisamide with soluble calcium and paramagnetic
metal, lanthanide or other heavy metal compounds in an
aqueous medium and such a process forms a further aspect
of the invention: preferably however the metal chelates
will be prepared separately and then admixed in the
desired ratio~
The contrast medium of the invention should contain
a sufficient amount of the calcium DTPA-bisamide chelate
to reduce the toxicity of the composition relative to
that of a composition from which the calcium chelate is
omitted but which is otherwise identical; however, any
amount of the calcium chelate will generally provide
some improvement. The amount of the calcium chelate
present should however be below toxic limits.
Conveniently compositions have a molar ratio of calcium
133581~
12
chelate to imaging ion chelate in the range from 1:200
to 1:5, preferably 1:200 to 1:10, especially 1:100 to
1:10, particuloarly 1:100 to 1:20, more particularly
1:30 to 1:15, especially about 1:20. The dosage amount
of the calcium chelate can conveniently be at a
physiologically tolerable level in the range of from
0.001 to 5 mmol/kg, preferably 0.001 to 1 mmol/kg,
especially preferably from 0.004 to 0.08 mmol/kg of
patient bodyweight~
As the calcium chelate may improve the
biotolerability of the imaging ion chelate by hindering
displacement of imaging ions from the chelate by zinc
ions it may therefore be desirable to match the
concentration or dosage of calcium chelate to the plasma
zinc concentration of the subject to which or to whom
the contrast medium is to be administered.
The concentration of the imaging ion chelate in the
compositions of the invention may be at conventional
levels or higher than conventional levels for the
imaging technique. Generally the contrast media of the
invention may contain from 0.001 to 5.0 moles per litre,
preferably 0.1 to 2 moles/litre, especially 0.1 to 1.2
moles/litre and particularly 0.5 to 1.2 moles/litre of
the imaging ion chelate. For MRI contrast media,
paramagnetic metal chelate concentrations are
conveniently 0.001 to 5, especially 0.1 to 1.2,
mole/litre while for X-ray contrast media lanthanide or
heavy metal chelate concentrations are conveniently 0.1
to 2, preferably 0.5 to 1.2, mole/litre.
The contrast media of the invention are
administered to patients for imaging in amounts
sufficient to yield the desired contrast with the
particular imaging technique. Generally dosages of from
0.001 to 5.0 mmoles of imaging ion chelate per kilogram
of patient bodyweight are effective to achieve adequate
contrast enhancement. For most MRI applications
preferred dosages of imaging ion chelate will be in the
13 1335819
range from 0.02 to 1.2 mmoles/kg bodyweight while for X-
ray applications dosages of from O.S to 1.5 mmoles/kg
are generally effective to achieve X-ray attenuation.
Preferred dosages for most X-ray applications are from
0.8 to 1.2 mmoles of the lanthanide or heavy metal
chelate/kg bodyweight.
For general use in X-ray radiography with a
lanthanide or heavy metal chelate, a dosage of at least
1 mmol/kg is required for optimum contrast. The ratio
LD50 to maximum effective dosage in rats considered to
provide an adequate margin of safety is about 15.
~dDTPA has an LD50 of 5~5 mmol/kg. GdDTPA-
bis(methylamide) (GdDTPA-BMA) has an LD50 of 15 mmol/kg.
The LD50 of a mixture of CaNaDTPA-BMA and GdDTPA-BMA is
34.4 mmol/kg, well above the level required for
effective X-ray image contrast.
The contrast media of the present invention may be
formulated with conventional pharmaceutical or
veterinary formulation aids, for example stabilizers,
~0 antioxidants, osmolality adjusting agents, buffers, pH
adjusting agents, etc., and may be in a form suitable
for parenteral or enteral administration, for example
injection or infusion or administration directly into a
body cavity having an external escape duct, for example
the gastrointestinal tract, the bladder or the uterus.
Thus the contrast media of the present invention may be
in conventional pharmaceutical administration forms such
as tablets, capsules, powders, solutions, suspensions,
dispersions, syrups, suppositories etc.; however,
solutions, suspensions and dispersions in
physiologically acceptable carrier media, for example
water for injections, will generally be preferred.
The contrast media according to the invention may
therefore be formulated for administration using
physiologically acceptable carriers or excipients in a
manner fully within the skill of the art. For example,
the chelate components, optionally with the addition of
1335819
14
pharmaceutically acceptable excipients, may be suspended
or dissolved in an aqueous medium, with the resulting
solution or suspension then being sterilized. As
mentioned above, suitable additives include, for
example, physiologically biocompatible buffers (as for
example, tromethamine hydrochloride), slight additions
of other chelating agents (as for example,
diethylenetriaminepentaacetic acid) or, optionally,
calcium or sodium salts (for example, calcium chloride,
calcium ascorbate, calcium gluconate or calcium
lac~ate)O
If the contrast media are to be formulated in
suspension form, e.g. in water or physiological saline
for oral administration, a small amount of soluble
chelate salt may be mixed with one or more of the
inactive ingredients traditionally present in or~l
solutions and/or surfactants and/or aromatics for
flavouring.
For-MRI and for X-ray imaging of some portions of
the body the most preferred mode for administering metal
chelates as contrast agents is parenteral, eOg.
intravenous, administration. Parenterally administrable
forms, e.g. intravenous solutions, should be sterile and
free from physiologically unacceptable agents, and
should have low osmolality to minimize irritation or
other adverse effects upon administration and thus the
contrast medium should preferably be isotonic or
slightly hypertonic. Suitable vehicles include aqueous
vehicles customarily used for administering parenteral
solutions such as Sodium Chloride Injection, Ringer's
Injection, Dextrose Injection, Dextrose and Sodium
Chloride Injection, Lactated Ringer's Injection and
other solutions such as are described in REMINGTON'S
PHARMACEUTICAL SCIENCES, 15th ed., Easton: Mack
Publishing Co, pp 1405-1412 and 1461-1487 (1975) and THE
NATIONAL FORMULARY XIV, 14th ed. Washington: American
Pharmaceutical Association (1975). The solutions can
1335819
contain preservatives, antimicrobial agents, buffers and
antioxidants conventionally used in parenteral
solutions, excipients and other additives which are
compatible with the chelates and which will not
S interfere with the manufacture, storage or use of
products.
The contrast media of the invention may also, of
course, be in concentrated or dried form for dilution
prior to administration.
Viewed from a yet further aspect the invention
provides the use of a calcium DTPA bisamide chelate for
the preparation of a contrast medium according to the
invention.
Viewed from a still further aspect the invention
provides the use of a DTPA-bisamide for the preparation
of a contrast medium according to the invention.
Viewed from another aspect the invention provides
the use of a chelate of a DTPA-bisamide with a cation
selected from paramagnetic metal cations, lanthanide
cations and other heavy metal cations, for the
preparation of a contrast medium according to the
invention .
Viewed from a further aspect the invention provides
a method of generating an image of a human or animal
body, said method comprising administering to said body
a contrast medium according to the invention and
generating an image, eOg. an MR, X-ray, ultrasound,
scintigraphic etc. image, of at least part of said body,
e.g. after permitting sufficient time to elapse for the
medium to distribute to the desired parts of said body.
Methods for applying MRI contrast media to improve
MR images, MRI equipment and MRI operating procedures
are described by Valk et al., BASIC PRINCIPLES OF
NUCLEAR MAGNETIC RESONANCE IMAGING, New York: Elsevier,
pp 109-114 (1985).
For X-ray imaging, the X-ray contrast media of the
invention can be used in standard conventional X-ray
1335819
16
procedures with conventional equipment in the same
manner as other contrast media. For other imaging
techniques, standard equipment and procedures may also
be used.
With the contrast media of this invention,
effective imaging contrast can be obtained with a wider
variety of organs such as kidney, urethra, bladder,
brain, spine, heart, liver, spleen, adrenal glands,
ovaries, skeletal muscle and the like.
The invention is further illustrated by the
following non-limiting examples and by the accompanying
drawings in which Figures 1, 2 and 3 are plots of CT
scans at 80 keV, 120 keV and 140 keV respectively of the
Intensity/Metal centre vs. Concentration for iohexol,
Gd DTPA-BMA and Dy DTPA-BMA.
Temperatures are given in degrees Celsius and
concentrations as weight percentages unless otherwise
specifiedc
- 17 1335819
EXAMPLE 1
DTPA-bismethYlamide Dihydrate
Methylamine (40% solution, 1.52 kg) in a 4 L beaker
was cooled in an ice bath. Solid DTPA-bisanhydride (1.0
kg) was added over 30-60 minutes with vigorous stirring.
The temperature was maintained below 35C during the
addition. Then the ice bath was removed, and the brown
solution stirred at room temperature for two hours. The
mixture was acidified to pH ca. 3 with concentrated HCl,
and the solution was filtered at 60-70C to remove traces
of insoluble material. To the hot solution was added
2.5 L ethanol and 2.5 L of isopropanol. After cooling
to room temperature for 6-24 hours, a colourless mass of
tan crystals was isolated by filtration. The filter
cake was washed with ethanol and then redissolved in 3 L
ethanol, 3 L isopropanol, and 3 L water. Active
charcoal was added to the hot solution, followed by
vacuum filtration. The solution was allowed to cool to
room temperature. After 6-24 hours, brilliant white
crystals were collected, washed with 2 L ethanol, and
dried for 12-24 hours. After drying, 838 g (67% yield)
of the title product were obtained, mp 110-113C.
EXAMPLE 2
Gd DTPA-bismethYlamide Trihydrate
DTPA-bismethylamide dihydrate (455.5 g, 1.0 mol),
Gd2O3 (181.2 g, 0.50 mol) and water (750 ml) are combined
and heated under reflux for 6-8 hours or until all solid
dissolves. The mixture is then checked for the presence
of free gadolinium with xylenol orange. If free
gadolinium is present, another 5 g of amide is added,
and the mixture heated under reflux for 2 hours. The
- 18 1335819
xylenol orange test is repeated, and more amide added if
neceCc~ry. Once the reaction mixture is clear with no
free gadolinium present, it is cooled to room
temperature, and the pH is checked. A small amount of 1
N NaOH can be added to adjust the pH of the mixture to
6.0-6.5. The solution is filtered, and an equal volume
of acetone is added with stirring. After 4-6 hours,
colorless crystals are collected, washed with 250 ml of
acetone, and dried for 12-24 hours in vacuo (1 mmHg, 60-
80C)
A yield of 540 g (86~) of product Gd DTPA-BMA was
obtained
Replacing Gd2O3 in the above procedure by Yb2O3 or
La203 the corresponding Yb or La chelates of DTPA-BMA are
produced~
EXAMPLE 3
NaCa DTPA-bismethylamide
Repeating the procedure of Example 2, replacing the
Gd2O3 oxide with a s~oichiometric molar equivalent amount
of CaO yields the corresponding NaCa DTPA-BMA.
NaCa DTPA-bisethylamide and NaCa DTPA-
bispropylamide are produced analogously using CaO and
DTPA-bisethylamide or DTPA-bispropylamide (see Examples
16 and 18).
EXAMPLE 4
Formulation of Gd DTPA-bismethylamide and NaCa DTPA-
bismethylamide
Solid gadolinium DTPA-bismethylamide trihydrate
(3.14 g, 5.0 mmol) was dissolved in ca. 6 mL of water
with stirring. Sodium calcium DTPA-bismethylamide
trihydrate (0.13 g, 0.25 mmol) was added, and the pH was
133~819
19
6Ø The addition of 10 microliters of 1 N NaOH (0.01
mmol, 0.2 mole%) increased the pH to 6.25. The
colorless mixture was diluted to 10 mL and sterile
filtered into a serum vial to yield a formulation that
was 500 mM gadolinium DTPA-bismethylamide and 25 mM
sodium calcium DTPA-bismethylamide.
Formulations containing Gd DTPA-bisethylamide and
NaCa DTPA-bisethylamide or Gd DTPA-bispropylamide and
NaCa DTPA-bispropylamide may be prepared analogously
using the gadolinium and calcium chelates of Examples
17, 19 and 3. Compositions containing NaCa DTPA-BMA or
NaCa DTPA-bisethylamide and the Yb or La chelates of
DTPA-BMA or DTPA-bisethylamide may similarly be prepared
using the chelates of Examples 2, 3 and 17.
EXAMPLE 5
DTPA-bis(2 3-dihydroxyProPYlamide) Dihydrate
A mixture of 54.8 g (600 mmol) of 3-amino-1,2-
propanediol, 84 mL (600 mmol) triethylamine, and 200 mL
dimethyl sulfoxide (DMSO) were combined with stirring at
room temr~rature. DTPA anhydride (71.5 g, 200 mmol) was
added in portions over 10 min. After stirring for 2 hrs
at room temperature, the amber reaction mixture was
concentrated under reduced pressure. The crude reaction
product was adjusted to pH 3.5 with 6 N HCl and then
chromatographed on a column of AGl-X4 anion exchange
resin (acetate form). The product was eluted with 1 N
acetic acid to provide 103 g (89%) of DTPA-bis-(2,3-
dihydroxypropylamide) dihydrate (DTPA-APD dihydrate) as
an oil. Lyophilization provided a colorless solid which
was determined to possess two waters of hydration.
EXAMPLE 6
Gd DTPA-APD
- 20 1335819
Gadolinium oxide (18.128 g, 50 mmol) and 54 g (94
mmol) DTPA-APD dihydrate were combined in 60 ml water
and heated under reflux. Additional DTPA-APD dihydrate
was added in small portions over 6 hours at reflux until
a xylenol orange test for ~Ycecc gadolinium ion was
negative. A total of 57.75 g (100 mmol) ligand was
necessary. After cooling, the reaction mixture was
diluted to 150 mL with water and filtered (0.2 micron
membrane filter). This 667 mM Gd DTPA-APD solution was
used for the formulations described in Examples 8 and 9.
EXAMPLE 7
NaCa DTPA-APD
DTPA-APD dihydrate (1.44 g, 2c5 mmol) and calcium
hydroxide ~186 mg, 2.S mmol) were combined in 3 mL water
and adjusted to pH 6~6 by the addition of ca. lo 5 mL 1 N
NaOH solution. This was used directly for a formulation
described in Example 9.
EXAMPLE 8
Preparation of 500 mM Gd DTPA-APD
A 67.5 mL (45 mmol) portion of the 667 mM Gd DTPA-
APD stock solution described in Example 6 was adjusted
to pH 6.0 with 1 N NaOH solution. After dilution to 90
mL, the resulting 500 mM Gd DTPA-APD solution was
sterile filtered into serum vials and autoclaved 30
minutes at 121C.
EXAMPLE 9
Formulation of 500 mM Gd DTPA-APD and 25 mM Na Ca DTPA-
APD solution
- 21 1 33S819
A 75 mL (50 mmol) portion of the 667 mM Gd DTPA-APD
stock solution described in Example 6 was combined with
the Na Ca DTPA-APD preparation (2.5 mmol) of Example 7.
The resulting solution was adjusted to pH S.9 with lN
NaOH and diluted to 100 mL. The solution was sterile-
filtered into serum vials and autoclaved 30 minutes at
121C.
EXAMPLE 10
DTPA-bis(N-methyl-2,3-dihYdroxypro~Ylamide)
N-methylaminopropanediol (50.0 g, 139.9 mmol) was
dissolved in DMSO t250 mL), and DTPA-bisanhydride was
added under a nitrogen atmosphere. After stirring
overnight (10 hours), the product was precipitated with
a 1:1 mixture of ether and chloroform. The crystals
were dissolved in water (150 mL) and precipitated once
more with ethanol (~400 mL). After 1 hour, the product
was separated from the solvent. Stirring with ethanol
(600 mL) produced a white powder which was dried in
vacuum. The yield of DTPA-bis-(N-methyl-2,3-
dihydroxypropylamide) (DTPA-BMPA) was 45.0 g (56%). Mp.
75-80C. FAB-MS: 568(M+l).
EXAMPLE 11
Gd DTPA-BMPA
DTPA-BMPA (39.0 g, 68.7 mmol) was dissolved in
water (50 mL). The water was distilled off to remove
ethanol; the oil was dissolved in water (250 mL); and
Gd2O3 (11.2 g, 31.0 mmol) was added. The mixture was
stirred for 16 hours at 100C and filtered, and the
solvent was removed. The product was dissolved in
methanol (110 mL) and precipitated with acetone (250
22 1335819
mL). The product was dissolved in water and dried.
This was repeated two times to remove traces of acetone.
Yield 40.4 g (81%). Mp. 280C. FAB-MS: 723(M+l) r
Anal. Calcd. for C22H38GdN5012: C, 35.60 H, 5.31; N, 9.70
Found: 36.125.25 10.39
EXAMPLE 12
NaCa DTPA-BMPA
DTPA-BMPA (5.0 g, 8.8 mmol) was dissolved in water
(50 ml), and Ca(OH)2 (0.65 g, 8.8 mmol) was added. The
mixture was stirred at room temperature for about 1.5
hours. The solution was neutralized with 2 M NaOH and
~5 then filtered. The filtrate was evaporated to dryness,
and the NaCa DTPA-BMPA compound was isolated as a white
powder. Yield 5.2 g t84%)~ Mp. 230 233C. FAB-MS:
628(~+1)
Anal. Calcd. for C2zH38CaN5NaOlz:C, 42.10; H, 6.10; N,11.16
Found: 41.48 5.96 10~96
EXAMPLE 13
Gd DTPA-BMPA and NaCa DTPA-BMPA Solution
Gd DTPA-BMPA (3.61 g, 5 mmol) and NaCa DTPA-BMPA
(0.157 g, 0.25 mmol) were dissolved in water (7 mL).
The pH was adjusted to between 5.5 and 6.5 and water (to
10 mL) was added. The solution was sterile filtered
into a 10 mL vial. The solution contained 0.5 mmol of
Gd per mL.
23 1 33S81 9
EXAMPLE 14
DY DTPA-bismethylamide Trihydrate
DTPA-bismethylamide dihydrate (DTPA-BMA) (22.77 g,
50.0 mmol) prepared according to the procedure of
Example 1, Dy2O3 (9.32 g, 25.0 mmol) and water (60 mL)
are combined and heated under reflux for 6-8 hours or
until all solids have dissolved. The mixture is tested
for free dysprosium with xylenol orange. If free
dysprosium is present, another 0.25 g of amide is added,
and the mixture is heated under reflux for 2 hours. The
xylenol orange test is repeated, and more amide added if
necessary. Once the absence of free dysprosium is
lS established by the xylenol orange test, the mixture is
cooled to 50-60C, and the pH is checked. If necessary,
warm (40-50C) 1 N NaOH may be used to adjust the pH of
the mixturs to 6O0-6O5~
The solution, colorless to bright yellow, is
filtered into an Erlenmeyer flask. To the stirred
solution, at room temperature, is added an equal volume
(ca. 75 mL) of acetone. Colorless crystals are
deposited over 4-24 hours. The crystals are collected,
washed with 15 mL acetone, and dried in vacuo (1 mmHg,
60-80C) for 12-24 hours. After cooling to room
temperature, 25.3 g (80%) Dy DTPA-bismethylamide
trihydrate (Dy DTPA-BMA) is obtained.
EXAMPLE 15
Formulation of Dy DTPA-bismethylamide and NaCa DTPA-
bismethylamide
To a 50 mL volumetric flask was added solid Dy
DTPA-BMA (25.3 g, 40 mmol) and 25 mL water. The mixture
was heated to 55-60C with stirring until all solids had
24 1335819
dissolved To the warm solution was added NaCa DTPA-
bismethylamide (1.0 g, 2 mmol) with stirring. After
all of the solids had dissolved, the pH 6.0 lemon-
colored solution was cooled to room temperature, diluted
to 50 mL with water, and sterile filtered into serum
vials to yield a 800 mM solution.
EXAMPLE 16
DTPA-bisethylamide Dihydrate
DTPA-bisanhydride (50.0 g 140 mmol) was added in
portions over 30 minutes to an ice-cold stirred solution
of 70% ethylamine (63.1 mL, 780 mmol). Water (30 mL)
was added and the mixture was stirred an additional 12
hours at ambient temperature. The mixture was
concentrated under reduced pressure to an oil, diluted
with water [100 mL), and adjusted to pH 2.5 with
concentrated HCl. The tan crystals which formed were
collected and recrystallized from ethanol to give
colorless crystals of DTPA-bisethylamide dihydrate.
Yield 44.2 g (71~), mp 105-109C. 1H NMR (250 MHz, D2O)
~ 3c68 (s, 4 H), 3.56 (s, 4 H), 3.49 (s, 2 H), 3.19 (m,
4 H), 3006 (m, 8 H), 0.91 (t, J = 7.0 Hz, 6 H).
Anal. Calcd. for C18H37N5Olo C, 44.71 H, 7.71 N, 14.48
Foundo 44.64 7.85 14.19
EXAMPLE 17
Gd DTPA-bisethylamide Trihydrate
The Gd DTPA-bisethylamide trihydrate was prepared
in situ in quantitative yield. A mixture of DTPA-bis-
ethylamide dihydrate (12.1 g, 25.0 mmol) and Gd2O3 (4.53
g, 12.5 mmol) in water (30 mL) was refluxed for 5 hours.
The solution was adjusted to pH 6.5 with 1 M NaOH.
Colorless crystals of Gd DTPA-bisethylamide trihydrate
,
~ 33S~9
soon formed, mp > 200C~ Positive ion FAB MS: 603
(M+H)~.
Anal. Calcd. for Cl8H36GdN50ll: C, 32.97 H, 5.S3 N, 10.68
Found: 33.39 5.58 10.55
Replacing Gd2O3 in the above procedure by Yb2O3 or La2O3,
the corresponding Yb or La chelates of DTPA-
bisethylamide are produced.
EXAMPLE 18
DTPA-bispropylamide Dihydrate
The tltle compound is synthesised analogously to
the bismethylamide and bisethylamide dihydrates of
Examples 1 and 16.
In addition, since propylamine and the higher
alkylamines are neat liquids at room temperature, it is
possible to prepare these DTPA-bisalkylamides by direct
reaction of the DTPA anhydride and the amine in an
appropriate neat organic solvent and the removal of
aqueous media should, in theory, increase the yield of
diamide through elimination of hydrolysis of the
dianhydride.
EXAMPLE 19
Gd DTPA-bispropylamide
The title compound is prepared analogously to the
Gd DTPA-bisamide chelates of Examples 2 and 17.
EXAMPLE 20
Acute Toxicity
Acute toxicity (LD50) values were determined for
26 1335819
compositions comprising 500 mM Gd DTPA-BM~ alone or
together with 25 mM of a zinc, magnesium, iron or
calcium chelate of DTPA-BMA, for compositions comprising
500 mM Gd DTPA-APD alone or together with 25 mM of the
calcium chelate of DTPA-APD, and, for further
comparison, for compositions comprising 500 mM Gd DTPA-
dimeglumine alone or together with 25 mM of a calcium
chelate of DTPA or DTPA-BMA. The acute toxicities were
determined by iv administration of the compositions to
Swiss Webster mice.
LD50 ( iV
Gd Chelate Added chelate mice,
mmol/kg)
Gd DTPA * None 5.5
Gd DTPA * Ca DTPA ++ 4.5
Gd DTPA * Ca DTPA-BMA+ 4.4
Gd DTPA-BMA None 15.0
Gd DTPA-BMA Ca DTPA-BMA + 34.4
Gd DTPA-BMA Mg DTPA-BM~ + 2.6
Gd DTPA-BMA Zn DTPA-BMA + 15.8
Gd DTPA-BMA Fe DTPA-BMA 12.8
Gd DTPA-APD None 13.8
Gd DTPA-APD Ca DTPA-APD + 44.0
* as the dimeglumine salt
+ as the sodium salt
++ as the trisodium salt
- 27 1335819
The results set forth above clearly show the
unpredicted and surprising reduction in contrast medium
toxicity achievable using the present invention.
By comparison with the above LD50 values, it may be
noted that the LD50 values for the iodinated X-ray
contrast agents meglumine diatrizoate and iopamidol are
respectively 18 and 25.4 (mice, rats).
EXAMPLE 21
Renal Fluoroscopy Study
After localization of the kidneys by portable
fluoroscopy with sodium diatrizoate in a mongrel dog,
the iodinated agent was allowed to clear. After renal
clearance was complete, a dose of 1.5 mmol/kg of Gd
DTPA-BMA yielded CT enhancement.
EXAMPLE 22
X-ra~ Attenuation Properties
The following data was obtained on a GE9800
clinical CT machine. Serial dilutions of iohexol, Gd
DTPA-BMA, and Dy DTPA-BMA were placed in test tubes and
imaged at the indicated energies. Region of interest
intensity values were determined. The results are shown
in Tables A, B and C and in the corresponding,
respective, plots of Figures 1, 2 and 3 of the
accompanying drawings.
TABLE A
Iohexol, Gd DTPA-BMA and Dy DTPA-BMA
CT Scans, 80 keV
Conc. mM Gd DTPA-BMA Dy DTPA-BMA Iohexol/I*
28 1335819
168
459 424 335
100 802 770 589
200 1485 1379 1023
300 2136 2003 1023
350 1023
400 2773 2591
500 3071 3071
* Concentration, mM of iodine
TABLE B
Iohexol, Gd DTPA-BMA and Dy DTPA-BMA
CT Scans, 120 keV
Conc. mMGd DTPA-BMA Dy DTPA-BMA Iohexol/I*
101
342 324 223
100 637 653 402
~00 1234 1221 744
300 1799 1791 1016
350 1024
400 2340 2334
500 2793 2781
* Concentration, mM of iodine
133~819
29
TABLE C
Iohexol, Gd DTPA-BMA and Dy DTPA-BMA
CT Scans, 140 keV
Conc. mMGd DTPA-8MA Dy DTPA-BMA Iohexol~I*
87
306 293 199
100 5~6 606 362
200 1156 1144 675
300 1672 1681 926
350 1008
400 2173 2185
500 2572 2605
* Concentration, mM of iodine
EXAMPLE 23
Viscosities
The viscosity of Gd DTPA-bismethylamide was
determined and is shown together with viscosities for
conventional iodinated X-ray contrast agents in Table D
below:
TABLE D
Viscositv, cps (mPa.s)
Compound Conc., mM20C 37C
Gd DTPA-BMA 6402 r O 1 o 4
Iohexol, 180 mgI/ml 473 3-1 2O0
240 mgI/ml 631 5.8 3.4
300 mgI/ml 788 11.8 6.3
350 mgI/ml 920 20.4 10~4
133S819
Diatrizoate, Sodium 394 (25%) lo 6 1~ 2
786 (50%) 3 O 3 2 . 3
Diatrizoate, Meglumine 371 (3096) 1. 9 1. 4
742 (60%) 6.2 4.,1
. .
