CA1071834A - Stannous imidodiphosphonate complex - Google Patents

Abstract

ABSTRACT

A stannous imidodiphosphonate complex suitable for admixture with a technetium - 99m containing pertechnetate salt to yield a complex suitable for use as a skeletal imaging agent is disclosed. The complex of the present invention is prepared by admixing a stannous halide with an alkali metal salt of imidodiphosphonic acid.

Description

` 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, ,~

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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 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.

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 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 !

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 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.

~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*
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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 = % Dosc in or~7~n or s2mole llt of ors2l~ or s2m~1e --~X 100 Body ~:ei~ht , :-- _ * ~ )718;~4 !Z: W ~; ~ H
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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of preparing a stannous imidodiphosphonate complex suitable for admixture with a technetium-99m containing pertechnetate salt to yield a complex suitable for use as a skeletal imaging agent, comprising admixing a stannous halide with an alkali metal salt of imidodiphosphonic acid.

2. A method according to Claim 1 wherein the stannous halide is stannous chloride and the alkali metal salt of imidodiphosphonic acid is the tetrasodium salt of imidodi-phosphonic acid.

3. A method according to Claim 1 including the additional step of freeze-drying the complex.

4. A stannous imidodiphosphonate complex suitable for admixture with a technetium-99m containing pertechnetate salt to yield a complex suitable for use as a skeletal imaging agent, whenever prepared according to the process of Claim 1, 2 or 3 or by an obvious chemical equivalent.