Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
` 1071834
This application is a division of copendin~ Canadian
application No. 239,651 filed November 1~, 1975.
BACKGROUND OF THE INVENTION
Recently, various organic phosphate and
phosphonate complexes of technetium-99m have been
suggested as gamma-emitting radionuclide agents for
skeletal imaging. The excellent physical characteristics
(half-life of six hours and monoenergetic gamma emission
of 140 KeV with an external photon yield of 90~o) of
the readily available radionuclide technetium-99m render
it an attractive substitute for the conventionally em-
ployed long-lived nuclide strontium ~5 (half-life
65 days) and the inconveniently short-lived fluorine
1~ (half-life 1.~3 hours). By virtue of its optimum
half-life characteristics and absence of beta emission,
technetium-99m can be administered in relatively large
doses (10-15 mCi) without exceeding reasonable radiation
levels.
Until fairly recently, technetium-99m has been
used almost exclusively in radioisotopic imaging pro-
cedures for almost every major organ in man with the
exception of the skeleton. Recently, however, various
organic phosphate and phosphonate complexes of technetium-
99m have been employed for skeletal imaging purposes.
(~erez et al, J. Nucl. Med. 13:7~g-7~9, 1972; Subramanian
et al, Radiolo~y, 9~:192-196, 1971; Subramanian et al,
Radiology, 102:701-704, 1972; Subramanian et al, J. Nucl.
Med., 13:947-950, 1972; Tofe et al, J. Nucl. Med.~ 15:69-74,
,~
- 2 _ ~
'~ ~
la7ls3~
1974; Yano, J. Nucl. Med. 14:73-7~, 1973; Castronova et al,
J. Nucl. Med. 13:~23-~27, 1972; and Subramanian et al,
J. Nucl. Med., August, 1975.
It was found that when solutions of these technetium-
99m phosphate and phosphonate complexes are given intra-
venously, the technetium-99m localizes to a great extent
in bone, particularly in diseased or abnormal areas of
the skeleton. Good visualization of both normal bone and
skeleton lesions is observed about 2 hours after adminis-
tration of the complexes. Normal and abnormal skeletal
tissues are readily delineated using conventional radio-
isotope imaging devices such as rectilinear scanners or
scintillation cameras.
There has been a continuing search in this area
for technetium-99m complexes having a higher bone uptake
than those currently employed in the art.
SUMMARY OF THE INVENTION
It has been found that a technetium-99m-tin-
imidodiphosphonate complex is a highly effective skeletal
imaging agent having a high uptake in bone.
The invention also relates to stannous imido-
diphosphonate complex employed as an intermediate for
preparing the technetium-99m-tin-imidodiphosphonate
complex.
~07~834
The invention includes a method for preparing
the technetium-99m-tin-imidodiphosphonate complex by
reducing a technetium-99m containing pertechnetate salt
with stannous ion in an aqueous medium in the presence
of imidodiphosphonic acid or a salt thereof.
The invention also relates to a bone-seeking
composition comprising a solution adapted for intravenous
administration containing the technetium-99m-tin-
imidodiphosphonate complex.
Moreover, the invention relates to a method of
skeletal imaging which includes the intravenous ad-
ministration of a solution adapted for intravenous
administration containing the technetium-99m-tin-
imidodiphosphonate complex.
DETAILED DESCRIPTDON OF THE INVENTION
The oomplexing agent for forming the composl-
tion of the invention is imidodiphosphonic acid having
the following structural formula:
O H O
Il 1 11 ,
HO - P - N - IP - OH
OH OH
This complexing agent is also referred to in the art
as "imidodiphosphate" (Reynolds et al, Calc. Tissue
1071834
Research, 10:302-313 (1~72); Larsen et al, Science,
166:1610, December 19, 1969; Robertson et al, Biochem.
Biophys. Acta, 222:677-6~0, 1970.) For example, the
tetrasodium salt of the free acid is marketed by
Boehringer-Mannheim Corporation, New York, as an
"imidodiphosphate". The free acid and its salts are
freely available or it may be prepared accordin~ to
the method of Neilsen et al, JACS, g3:99-102, 1961.
It is to be understood that the imidodiphosphonate
complexes of the invention may be formed from the free
imidodiphosphonic acid or suitable non-toxic, phar- -
maceutically acceptable salts thereof such as sodium,
etc.
Technetium-99m is commercially available either
from an isotope generator as a daughter product of
molybdenum-99 or as a direct product from a commercial
supplier. It is also available as a solvent extraction
product from molybdenum-99 solutions generally as alkaline
metal pertechnetate solutions at 5-100 mCi. A further
discussion of preparative methods appears in U.S. Patents
3,46~,~0~ and 3,3~2,152.
Commercially available stannous salts, both
hydrate and anhydrous, may be used as the tin source.
Most readily available are stannous chloride, sulfate
and acetate.
1071834
The composition of the invention is most
conveniently provided in sterile kit form consisting
of non-radioactive chemicals for mixing with a pertechnetate
prior to use. The kit may contain stannous salt solution,
imidodiphosphonate solution, alkaline and/or buffer
solution, or combinations thereof. Using sterile
pyrogen free water and reagents and using aseptic techniques,
these solutions can be mixed with each other and then with
the pertechnetate solution immediately prior to imaging.
The particular order of mixing is not critical. Thus,
the stannous salt could be added to the pertechnetate
solution and the mixture combined with the imidodiphosphonate
solution. Alternatively, the imidodiphosphonate could be
combined with the pertechnetate prior to the addition of
the stannous salt or combined with the stannous salt and
admixed with the pertechnetate. One particularly preferred
embodiment is a freeze-dried kit of stannous-imidodiphosphonate
complex formed from the tetrasodium salt of the imidodiphosphonic
acid and stannous chloride. The solution of the stannous
imidodiphosphonate complex is freeze-dried and may be ad-
mixed with the pertechnetate solution immediately prior to
skeletal imaging by the X-ray technician. The kits are
prepared under sterile conditions and the final pH of
the preparation is adjusted to 6.5 before freeze-drying.
To form the complçxj one simply adds to the kit vial the
desired activity of technetium-99m in 2-5 ml volume and
mixes well. The labeling yield is better than 9~ and
-- 6 --
1~71834
very little free pertechnetate is detectable.
The following is a non-limiting example of
a method of preparation of the composition of the invention.
~XAMPLE_l
125 mg of tetrasodium imidodiphosphonate and
2.5 mg of Sn C12-2H20 (HCl acid solution) were dissolved
in 30 ml of water. The pH was adjusted to 6.5 and the
volume brought up to 50 ml. 2 ml aliquots of the
stannous imidodiphosphonate complex solution (containing
, 10 5 mg tetrasodium imidodiphosphonate and 100 ug Sn C12-2H20)
were pipetted into 20 vials and lyophilized overnight.
The imaging agents employed in the following examples were
prepared by adding to each vial the desired activity of
technetium-99m in 2-5 ml volumes and mixing well. The
solutions were sterilized by passage through a 0.22 size
membrane filter. After labeling, the pH of the solutions
ranged from 6.2 to 6.5.
The above prepared complexes were utilized in
the examples set forth belowO
The organ distribution of the 99mTc imidodiphos-
phonate (IDP) was studied after I.V. injection of 50-200
uCi containing 0~1_0O2 mg of IDP per animal in New Zealand
adult albino rabbits weighing 3.5-5 kg and compared with
10-20 uCi of ~5Sr administered simultaneously as a biological
standard. The methods of tissue assay used were those
described in the Subramanian et al references, supra.
1~71834
These animals were sacrificed at various time intervals
from 15 min. to 24 hrs. after injection. Because of the
excellent skeletal uptake of 99mrrc IDP in rabbits, a dog
weighing 25 kgs was also imaged to evaluate the
biological behavior of this compound in a higher mammal
than the rabbit. A whole body image of the dog was ob-
tained in the right lateral projection 4 hours after in-
travenous injection of 5 mCi of 99mTc-IDP using the
Ohio Nuclear Model lOd~area scan camera fitted with
a 140 kev high sensitivity parallel hole collimator, with
the data density setting of 200.
A toxicological study was conducted in both mice
and rabbits by serial injection of graduated doses and
the acute toxicity of imidodiphosphonate (LD 50/30) was
determined to be 45-50 mg imidodiphosphonic acid per
kilogram body weight.
An imaging study was performed in an adult albino
rabbit weighing 4.2 kg after intravenous administration
of 5 mCi of 99mTc IDP using the Searle Radiographics HP~
gamma camera fitted with a 140 kev high resolution parallel
hole collimator. Images in the posterior projection were
obtained from one to twenty-four hours after injection in
three separate views collecting 300k counts for each.
No attempts were made to remove the urine from the bladder
during this study.
~071834
Because of the insignificant toxicological pro-
blems and high bone uptake of 99mTc-IDP a volunteer patient
was studied with this compound after informed consent was
obtained. Fifteen mCi of 99mTc-IDP containing 1.5 mg of
tetrasodium imidodiphosphonate (equivalent to 1 mg of the
acid) was intravenously injected in a 33-year-old female
with a recent modified left radical mastectomy and whole
body images of the patient in both anterior and posterior
projections were obtained 3 hours after injection using
an Ohio Nuclear Series 103 area scan scanning camera with a
high sensitivity, low energy parallel hole collimator.
The results of the above tests are discussed
below.
Table 1 contains biological distribution data
of 99mTc-IDP in rabbits with ~5Sr used simultaneously. The
numbers shown in parenthesis after the time of study is the
number of animals used per time interval. The values for - --
each organ shown are the averages for each group of animals.
The bone concentration shown as ~ dose / 1~ body weight is
the mean value of individual average of concentrations in
four types of bone; the femur, tibia, spine and pelvis. An
overall mean concentration of the four types of bone was
calculated for each animal and then the average of these mean
values were determined. Similarly the mean values for bone/
organ ratios were calculated for each group.
Table 2 contains comparative data from this and
1(~7183~
other studies on the distribution of a variety of 99mTc
labeled compounds in rabbits at 2 hours studied simul-
taneously with ~5Sr. The numbers in parenthesis under
each compound indicates the number of animals used for
each group. The values shown here have been derived
from the data in the Subramanian et al references, supra,
except for the IDP complex. Only the mean values of
the 99mTc-~5Sr ratios for each organ are shown.
Figure 1 consists of serial composite whole
body images of the ~.2 kg weight adult rabbit injected
with 5 mCi of 99mTc-IDP at the various times indicated
from 1 hour to 24 hours. Each whole body image is a com-
posite of three separate images for each of which 300k
counts were collected.
Figure 2 shows the whole body image of the dog
in the right lateral position at 4 hours after injection
of 5 mCi of 99mTc-IDP. The clear delineation of the
vertebral column and all the ribs are quite apparent.
The larger accumulation of the activity in the pelvic
area is the urine in the bladder. At ~ hours as much as
50~0 of injected activity could be in the urine.
Figure 3 illustrates comparative whole body images
in the 33-year-old female patient obtained with both
99mTc-MDP (methylene diphosphonate) and 99mTc-IDP performed
within a 10-day interval. These images were obtained with
15 mCi of each of the compounds and using an Ohio
Nuclear whole body imaging camera as previously
-- 10 --
!
071834
described~ The count rates obtained ~Yith 99n~Tc-IDP were
appro~imately twice that of the ~IDP compound. Due to higher
bone concentration and count rates the anterior image was
obtained in 8.6 minutes with IDP ~ersus 15.6 minutes l~ith
NDP using a data density of ~Q0 for both. Similarly the
posterior view took 8.2 minutes for IDP and 13.0 minutes
for ~lDP.
In order to compensate for biologic variation,
bone agents are best studied by comparing the quantitative
uptake of the new compound with simultaneously administered
55Sr as a means of normalization. In comparing several - --
99mTc labeled agents bet~een each other one should not
- only compare the whole organ uptake of individual compounds
but also the ratios of their concentrations with 85Sr, es-
pecially so in comparing bone uptakes. Table 1 illus-
trates the wide variation in concentrations in various
types of bone. Due to regional variation in bone uptake
with the skeleton it is difficult to correctly estimate
whole body bone uptake quantitatively. ~levertheless, the
data for single whole bones (femur and tibia) is useful.
By comparing the bone uptake (Table 1) one can see that
99mTc-IDP has approximately 25~ moreuptake than 55Sr at
earlier time intervals up to 2 hours and equivalent at
later times. This concentration change over serial time
intervals may be due to the metabolic breakdown of the
compound at the bone mineral surface with the 99mTc complex
~07183~
being more labile, while we know the biological half
life of ~5Sr is prolonged. Even at the later time in-
tervals than 2 hours, 99mTc-IDP concentration in bone
is at least 20-25~o higher than the other Tc complexes
(Table 2). The soft tissue concentrations of all these
complexes are lower, especially that of the muscle, than
~5Sr. The liver concentration is somewhat higher than
~5Sr for some 99mTc complexes. This should not be a pro-
blem because the total liver concentration is relatively
low. Overall, from the distribution studies in rabbits
it may be inferred that the 99mTc-IDP complex has the
highest bone uptake of all the compounds reported.
The rabbit images shown in Figure 1 clearly
demonstrate the high skeletal localization of 99mTc-IDP
at 1 hour to 2~ hours after injection of the compound.
The details of all skeletal structure is very clearly
delineated.
The dog image in Figure 2 is also included to
show the high quality of bone image that can be obtained
with 99mTc-IDP in a higher mammal than a rabbit.
After noting the increased bone uptake of 99mTc-
IDP in biodistribution studies and the safety of the com-
pound (as demonstrated by toxicity studies) a volunteer
patient was studied. Figure 3 illustrates the whole body
images both in the posterior and anterior projections of
of this patient studied with 99mTc-MDP and 99mTc-IDP on
- 12 -
1~7~834
separate days with the same dose and technique. The
count rate with the IDP complex was approximately
one and a half to two times bhat of the ~DP compound.
After the scans, individual images of selected areas
were obtained with a stationary gamma camera. In these
images, also done at similar time intervals, approxi-
mately gO percent higher count rates were obtained with
99mTc-IDP compared to the MDP complex. Much of this
increased count rate may be accounted for by the gO% higher
bGne uptake noted with IDP than MDP in the tissue assay
data. Part of this increased cound rate could be
attributed to the increased blood levels and soft tissue
concentrations of the IDP complex (compared to MDP).
Since identical conditions were used for both
the M~D and IDP complexes in this patient, a visual com-
parison of both the scans is possible. Clearly the 99mTc-
MDP images are superior.
-- 13 --
~07~3~
T~b1e ~ 99mTc Ldb~led St~nnous ImidodiphosphonD.te
- ` in Rabbi ts - ~~ ~
Simultaneous Study ~lith 85Sr
15 min (6) 1 hour (6) 2 hours (9) ~ hours (9) 24 hours (7)
ORGAN ~9 mTc 85Sr 99mTc 85Sr 99mTc 855r 99mTc 85Sr99mTc85Sr
X Dose in ~!hole Orq~n
BLOOD 15.4 16.1 5.90 8.17 2.925.19 1.69 2.720.7340.250LIYER 4.24 2.13 2.08 1.58 2.000.947 1.58 0.5760.6610.004
MUSCLE 9.32 15.6 4.47 9.55 3.017.96 1-53 4.800.5990.628
KID~IEY 5.52 1.27 4.75 0.938 4.390.638 2.90 0.2i57 2.19 0.022t~ARROll 1.07 0.903 0.646 0.817 0.643 0.499 Q.447 0.300 0.331 0.070
URINE 13.3 4.94 37.6 8.96 47.416.6 49.5 26.2 - -
WHOLE FEMUR 0.782 0.741 1.46 1.272.06 1.67 1.81 1.84 1.67 1.55
WHOLE TIBIA 0.561 0.540 1.12 1.031.63 1.34 1.57 1.57 1.09 1.38
% Dose/1% Body 11eight*
_ . ~
BLOOD2.20 2.29 0.843 l.li 0.420 0.742 0.242 0.388 0.105 0.331
LIYER1.40 0.692 0.674 0.489 0.734 0.357 0.491 0.168 0.225 0.016
t~lUSCLE -0.217 0.363 0.104 0.222 0.070 0.186 0.035 0.125 0.014 0.015
KID~lEY 11.8 2.68 8.14 1.54 8.02 1.14 5.41 0.488 4.63 0.067
~URROW 0.489 0.410 0.294 0.382 0.291 0.227 0.203 0.137 0.150 0.032
LG INT 1.03 1.79 0.491 0.961 0.331 0.762 0.142 0.421 0.0~3 0.088
SM INT 0.732 1.23 0.406 0.654 0.323 0.669 Q.245 0.300 0.069 0.042
FE~lUR 3.60 3.41 5.70 5.23 8.40 6.84 7.71 7.87 6.75 6.39
TIBIA3.14 3.02 5.26 4.67 7.94 6.60 7.59 7.64 6.64 6.58
PELVIS 6. 03 5.05 7.15 5.47 9.66 7.35 11 .0 9.83 8.97 8.13
SPINE3.63 3.76 6.23 5.82 9.25 8.05 8.97 9.57 6.96 6.96
AVC BONE 4.10 3.82 6.08 5.30 8.81 7.21 8.83 9.16 7.32 6.93
, _ _ _ _ RATIOS _ _
BON~/BLOOD 1.86 1.71 7.75 4.53 24.8 10.5 39.8 23.6 69.4 20.9
BONE/NUSCLE 18.7 10.6 68 23.9 177 44 288 73.3 528 462
BOJ~E/ltARROW 8~92 9.84 23 13.9 37 36 50 66.9 59 217
*" D~Se /-1/J Body l~leiyht
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