Tin-adsorbed resin for the preparation of 99mTc-radiopharmaceuticals: Stable complex of 99mTc-bleomycin

Tin-adsorbed Resin for the Preparation : Stable of 99”Tc-radiopharmaceuticals Complex of 99”Tc-bleomycin KAZUKO HORIUCHI’, AKIRA YOKOYAMA’*, YASUHISA FUJIBAYASHI’, HISASHI TANAKA’, TERUO ODORI’, HIDE0 SAJI’, RIKUSHI MORITA2 and KANJI TORIZUKA’ ‘Department

of Radiopharmaceutical Chemistry, Faculty of Pharmaceutical Science, Kyoto Shimoadachi-cho, Sakyo-ku, Kyoto 606, Japan *Department of Nuclear Medicine, Kyoto University Hospital, Shogoin, Kawaramachi, Sakyo-ku, Kyoto 606, Japan (Received 25 Junuary

University.

1980)

Stannous chloride has been the reducing agent of choice for the preparation of 99mTc-containing radiopharmaceuticals, whose effective chemical form is considered to be a complex. or complexes. of the reduced form of technetium. Labeling of ““Tc-BLM, a technetium complex of bleomycin. has been reported previously. but a stable complex for adequate clinical evaluation has been difficult to obtain. The main role of stannous chloride is as reducing agent but, depending upon the amount and the chemical state of the stannous ion, other phenomena have been detected and further implications for the tncorporation of 99mT~ into a ligand are discussed. However, the stannous ion adsorbed onto a cationtc exchange resin showed specific characteristics allowing the preparation of a stable complex of BLM, considered to be a mononuclear complex. The usefulness of this tin-adsorbed resin (Sn-resin) as an efficient device (kit) for the controlled delivery of Sn 2+ ion, permitting the simple preparation of a stable complex with good reproducibility in Nuclear Medicine facilities is presented.

Introduction radiopharmaceuticals involve MANY ““Tc-containing metal-complex formation between reduced forms of heptavalent technetium (TcO,) and a ligand carrying a chelating group to bind the technetium. Despite inherent problems, stannous chloride has been the most widely used reducing agent.“’ As otten menrionea, complex tormatton 01 thts reduced technetium with a ligand is complicated. Various complexes with different charges, molecular weights, stabilities, reactivities and consequently with different biological behavior are formed depending upon not only the complexing ability of the ligand group but also upon the labeling conditions under which they are prepared. (2-7) Lack of reproducibility, often deplored in the radiodiagnosis of a specific physiological state, is probably due to the instability of labeled complexes or to the presence of undesired complexes generated from some alteration in the preparation step or reagents, enhancing abnormal distribution in pathological cases. It has been found that in 99”Tc-labeling reactions with bleomycin (BLM), or penicillamine (Pen), several

* To whom

correspondence

should

be addressed. 47

complexes containing technetium in various chemical states were detected depending upon pH, and the concentrations of stannous chloride and ligand.(2,3’ Among them, a so-called mononuclear complex, postulated as a complex in which one atom of technetium in a tetravalent state coordinates with one molecule of BLM is regarded as a clinically valuable chemical form for effective tumor-imaging with 99”‘T~-BLM.‘2’ The search for a selective preparation method for that mononuclear complex has led us to propose the following reaction scheme: (a) Reduction of 99mTc0; from a 7+ state to 99mT~OZf, a 4+ state. (b) Complex formation of this reduced 99mTc species with a dissociated form (reactive form) of the ligand. In fact, in the labeling reaction of 99mTc-BLM under a very restricted condition where SnCl, concentration is minute, the optimal pH value and the concentration of the ligand required for the mononuclear complex formation agree with those theoretically derived from the step (b) reaction. Similar results have been also obtained in the labeling reaction of 99mTc-Pen and further confirmed by spectrophotometric studies carried out on the “Tc-Pen reaction, using a chemical concentration of 10-3-10-4 M of a

4x

K. Horiuchi

tetravalent Tc form, 99TcCI~~. in the absence of reducing agent.“) AS for the concentration of &Cl2 used for the reduction of 99mTcOb. (step a), a minute amount of SnC12 such as 10~7-10-9 mol was found to be necessary for the mononuclear 99mTc-BLM complex formation.(2) Preparation of St-i2+ solution with accuracy at this nanogram level has been a limiting factor in Nuclear Medicine facilities for labeling 99mTc-complexes with high efficiency and good reproducibility. Experimental results have shown that the labeling reaction was likely to yield unstable, hydrolytic, polynuclear complexes whenever a large amount of SnCl, was present. In the labeled solution, the presence of free pertechnetate has been often detected even at concentrations of Sn2’ higher than the equimolar amount needed for its reduction; probably this 99mTc0; was generated through reoxidation of hydrolyzed 99mTc species.‘2,3) These phenomena observed in the labeling reaction using SnC12 in solution led us to consider that stannous ion might be affecting both reaction steps (a) and (b), and that the so-called mononuclear complex might ideally be obtained if an equimolar concentration of Sn”, needed for the reduction of 99mTc0; to 99mT~02+, could be made available in a chemically pure state. This is a very difficult technical problem. In the 99mTc0; eluate, pertechnetate is present in extremely low but variable concentrations, so the addition of an exactly compatible amount of Sn2+ is difficult to achieve. The theory of cation exchange resins shows that the presence of large amounts of metal ion in the resin phase is apparently in constant equilibrium with a minute amount of free metal ion in the solution.“’ The formulation of Sn2’ adsorbed on cationic exchange resin was postulated as a means of supplying in the labeling system Sn2+ at a constant and lower concentration than that of the 99mT~0i in the medium. Thus, a labeling reaction carried out at a chosen pH and ligand concentration, optimal for the reaction of TcO’+ with the ligand, would promote the formation of mononuclear complexes; since under these circumstances, application of the Sn-adsorbed resin would possibly drive the reaction to form this complex, since only small quantities of Sn2+ would be released from the deposit existing in the solid phase, therefore preventing the undesirable effects of excess Sn2+ on the reaction step (b), even if the concentration of pertechnetate varied. This plausible rationale is presented and used to good advantage for the formulation of a Sn-resin kit system, for the labeling of 99mTc-BLM for clinical tumor imaging.

Materials and Methods Materials

99mTc0; a generator

and analytical

methods

saline solution (Mallinckrodt

was eluted regularly from Inc.) every morning, and

et al. 0.5-2.0 mCi ml-’ solution was used for the labeling reaction. Long-lived 99Tc0; and iL3SnC12 (2 N HCI) were obtained from New England Nuclear Corp. BLM was kindly supplied by Nihon Kayaku Co.. as a sterile lyophilized powder, in individual ampoules containing 15 mg. Its chemical form is a chloro or l/2 sulphate of BLM-A2 and BLM-B2 (2:l ratio). All chemicals and solvents were of reagent grade. The analytical systems employed in the analysis of the radiopharmaceuticals included thin-layer chromatography (TLC) and electrophoresis (EP). Merck silica gel strip and MeOH-10% NH,OAc (1: 1) as solvent was used for the chromatographic analysis. Toyo NO. 50 filter paper in a Toyo C electrophoresis apparatus at a constant voltage (5OOV, 1 h) with 0.2 M phosphate buffer (pH 7.0) was used in the electrophoretic analysis. A Fujitsu chromatoscanner was used for the analysis of the strip and a well-scintillation counter was used for resin adsorption studies with 1’3Sn. Preparation

of &-adsorbed

resin

Cationic exchange resin (Dowex 50 W X8, 100-200 mesh) was previously conditioned by washing it alternatively several times with large excess of saline and acid solution, according to the manufacturer’s instructions. Then, the resin was equilibrated with 2 N HCI and washed with distilled water until pH 5 to 6 was reached; the resin was dried in an oven at 80 C (3 h), then stored and used for the Sn2+ adsorption studies. (Some loss of Sn” activity was observed when the R-Na’ form was used.) In a 25 ml erlenmeyer, IO ml of 0.1 N HCI was purged with N2 gas for 15 min, and an accurately weighed crystal of SnC12’2H20 was dissolved. After 2 min. 200 mg of the conditioned resin was added and stirred under continuous N2 bubbling for another 5 min. Under an inert atmosphere, the stannous-ion exchange resin complex (Sn-resin) was carefully and rapidly separated from the aqueous phase by filtration and washed consecutively with 2 ml of buffer solution (acetate buffer 0.1 M, pH 6, purged with N2 gas for 15 min), followed by 2 ml of ethanol and 2 ml of methanol. After blotting with adsorbent paper, the Sn-resin was dried over silica gel and P205 under vacuum, in a small chamber (200 ml) for 48 h. The well-dried Sn-resin was carefully dispensed, in a dry atmosphere, into a 1 ml desiccated amber ampoule. sealed and sterilized by autoclaving for 30 min at 120’C (15 lb cmm3).

’ “.%I sorption studies Preliminary tin sorption studies with a cationic exchange resin was tested by adding an aliquot of i13SnC12 in 2N HCI to the solution of carrier SnC12 prepared in 0.1 N HCI as described in the previous section. About 0.1 nCi of the tracer was equilibrated for 20 min with the SnCl, present in each solution before the addition of the cationic exchange resin. Samples

49

Tin-adsorbedresin of the solution taken at different time intervals and/or the solid phase, were measured and their activity determined. Preparation ofreagent and ligand solutions Reagent solution: acetate buffer (0.1 M, pH 6) was prepared with commercial distilled water for injection and filtered through a Millipore membrane (0.22 pm), dispensed into ampoules, sealed and sterilized by autoclaving for 30 min at 120°C (15 lb cmm3). Ligand solution: BLM solution was prepared by dissolving one ampoule of lyophihzed product (15 mg) eluate and 2 ml of acetate with 2 ml of ““TcO; buffer (0.1 M, pH 6), just prior to the labeling reaction Labeling reaction For the labeling, the buffered BLM solution containing the gg”‘TcO; eluate was mixed with the corresponding amount of %-resin by inversion for 3 to 4min, and finally, the solid phase was separated by filtration through a 0.22 pm Millipore filter. Thin layer chromatography (TLC) and electrophoresis (EP) were carried out after the labeling reaction. Determination of optimal labeling parameters Since the effect of pH, BLM and SnCI, concentration has been reported already for the labeling reaction performed with the reducing agent in solution,(2) the optimal conditions derived from the use of the solid phase are presented. Cationic exchange resin containing different amounts of stannous ions over the range of 5 x lo-’ to 5 x 10-gmol mg-’ were evaluated. This Sn-resin prepared by equilibrating 200 mg of conditioned resin with 10 ml of 1O-2 M’ to 10d4 M SnClz solution, 0.1 N HCI as described in the previous section, were used for the studies of the labeling reaction carried out using a constant amount of the solid phase and also a variable amount while keeping the concentration constant. The variable pertechnetate concentration in ggMo-gg’“Tc generator eluates can affect the labeling reaction. So, the effect of varying pertechnetate concentration on the labeling yield of ““‘Tc-BLM was tested. A ““TcO; eluate from a generator with 48 h grow-in period, at an apparent concentration of 9.5 x lo-‘M was diluted 10-100 times with 0.9% saline solution. It was also compared with a solution prepared by the addition of carrier “TcO; up to a concentration of 1 x 1O-6 M to the generator eluate. Biodistribution of 99mTc-BLM Mice (ddy) bearing Ehrlich’s ascites carcinoma were used in the distribution studies. Tumor cells were transplanted subcutaneously to the left flank of the leg and were allowed to develop for at least 10 days before the injection of ““Tc-BLM labeled by the Snresin kit method. 50-1OOpCi in 0.1 ml of ““‘Tc-BLM were injected AR, 32 I -D

into the tail vein. The mice were killed by ether asphyxiation l-3 h or 24 h after injection. Samples of blood were withdrawn immediately by cardiac puncture. Samples of tumor, muscle, liver, kidney were removed from the mouse, weighed and counted in a well-type scintillation counter. Standards were prepared by transferring 0.1 ml to a volumetric flask and diluting to an activity level approximately equal to the sample. Standards were counted at the same time and the counting rates were corrected in the same manner as the samples. Data are expressed as percent per gram tissue. Description of BLM kit Kit components: -1 ampoule of BLM (15mg of potency) (Nihon Kayaku) -1 ampoule of acetate buffer 0.1 M, pH 6 (2 ml, sterile) -1 ampoule of Sn-resin, 1 x lo-’ mol Sn* +/mg (68 mg, sterile) -1 1Oml syringe 21G 1.5 in. and a needle of 18G 1 in. -1 10 ml vial (sterile) -1 Millipore filter, 0.22 pm (sterile) Preparation of Sn-resin (I x IO- 7 mol mg- ‘): Carefully and quickly 4.5 mg of SnC12.2H20 is weighed in a very dry atmosphere and dissolved in 10ml of 0.1 N HCl purged with N2 gas and mixed with 200mg of the conditioned cationic exchange resin as described under Methods. Labeling procedure: -Ligand solution preparation: one ampoule of BLM is dissolved in buffer acetate and 2 ml of gg”‘TcO; eluate (15-20 mCi for clinical use). The mixture is drawn into a lOm1 syringe and the 21G needle replaced by a 18G, 1 in., needle. -Labeling reaction: using the syringe containing the ligand solution, Sn-resin is drawn in and the mixture mixed by inversion for 34 min and filtered through the sterile Millipore filter into a sterile vial. The ““Tc-BLM is ready for injection. Shelf life: -The Sn-resin is stable for more than 6 months at 4°C. The crucial point for long storage is the formulation of an exhaustively dessicated Snresin dispensed in a well-dried ampoule under a very dry, inert atmosphere. The acetate buffer 0.1 M, pH 6 is stable for more than 6 months at 4°C. Note: Acetate buffer 1 M, pH 6 (0.2 ml) diluted with the ““TcO; saline eluate (3.8 ml) can be used whenever a higher specific activity is required.

Results Stannous ion sorption on a cationic exchange resin The studies of the exchange reaction resin and the SnCI, solution were

between the traced with

50

K. Horiuchi TABLE

Sn”

I.

Effect of stannous

total

%-resin

et al.

ion concentration

on ‘9mTc-bleomycin

labeling”

‘9mTc-BLM

(mol)

(mg)

(AZ + Bz)

5 x lo-’ 5 x lomx I x IO_’ I x IO__ 2 x IO_’ 2 x IO_’ 4 x IO_’ 8 x IO_’ I x lo-”

I I 2 4 4 8 8 I6 2

28.2”,, 91 .2”,, 91.8”,, 95.0”,, 9 I _4”,, 94.0” () 94.7” () 92.5”,, 84. I ” ,)

“‘“TcO~ I I Iv’,, 2.8”,,

_

2.2”,,

Orlgm

6.0”,, 8.5”,, 5.3”,, X.9”,, h-3”,, 5.2” 5.2”:: 10.8”,h

* Labeling reaction carried out with 2 ml of ligand solution (BLM: 7.5 mg) prepared as described under Methods. Labeling (“J obtained from TLC by integration of peak areas under 99mTc-BLM (A, + BZ) and/or 99”T~0; and at the origin. b Complex X (R, = 0.22-0.25) is detected at high concentration of Sn’ +.

l1 %nCl,. Progress of the reaction was tested at different time intervals. Since a rapid attainment of equilibrium was observed with this strong ion exchange resin, the time for equilibration was limited to 5 min. The exchange reaction was carried out first with different concentrations of SnC12. at a constant amount of resin and then this amount was varied while the concentration was kept constant. In the range of lo-’ to 10e4 M of SnCl, solution, the addition of more than 1OOmg of resin to 10ml of those solutions resulted in an almost complete sorption of tin. For example, 10ml of 10T3 M solution of SnCI, in 0.1 N HCI, showed uptakes of 84,96, 104 and 105”/, with 10, 40, 100 and 200 mg of resin respectively. Some loss of activity by adsorption on the wall of the erlenmeyer flask was observed at low concentrations of SnCl, (10e4 M). Higher acid strength (1 N HCI) improved the stability of the Snzi in solution but lowered the ion exchange capacity. Sn-resin

labeling reaction

of ““Tc-BLM

The optimal labeling parameters for g9”Tc-BLM preparation with this solid-phase system. Sn-resin, were tested. Namely, the amount of Sn”, the variability of TcO; concentration and the quality of the Sn-resin.

TABLE 2. Effect of pertechnetate

As a ligand solution containing 7.5 mg2 ml-’ of BLM is used, high 99mT~ activities in the “9mTc-BLM-A2 and B2 peaks (RI values. Az = 0.63-0.73. B2 = 0.27-0.40) are obtained with total amounts of 5 x lo-@ to 8 x lo-‘mol of Sn” adsorbed on the Sn-resin. Radioactivities at the origin (R, = 0.00) and at the R, value corresponding to TcO, (R, = 0.8W.90) increase at Sn’+ concentration higher than 8 x lo-’ mol and lower than 5 x lo-‘mol (Table 1). A new peak can be detected at R, 0.22-0.25 as the Sn*’ increases to 1 x 10m6 mol. An increase in the amount of resin slightly alters the acidity of the medium but no significant variation in the labeling efficiency is detected. For practical purposes, 4-8 mg of Sn-resin are chosen since this is a suitable amount for handling and preventing the obstruction of the Millipore filter used (0.22 pm. dia. 13 mm). The technetium carrier effect on the labeling yield was studied as shown in Table 2. The amount of stannous ion was maintained constant at 3-4 x lo-’ mol of Sn*+ adsorbed in &8 mg of resin. Insignificant effect on the labeling efficiency was detected over the TcO; concentration studied. The incorporation of g9mTc into BLM under the described conditions appeared to be greatly affected

concentration

on g”mTc-bleomycin Labeling

Pertechnetate concentration

g9mTc-BLM (AZ + W

l/lW ljlcr l/lb 100/l’

92.8”,,, 93.04; 95.004 93.70;

A99mTc0; b 99mTcO; c 99Tc0; d Labeling as described total (Sn” obtained on

labeling

yield”

yield (“,)

99mTcO;

Origin

1.4O” 1.8””

5.8”, 5.2”,, 5.0”” 5.3”,

l.O”,

eluate diluted with 0.9% NaCl solution. eluate used: 5 mCi ml-l (9.55 x 10d9 M). is added (1 x 10m6 M). reaction carried out with 2 ml of ligand solution (BLM: 7.5 mg) prepared under Methods, using 6-8 mg of %-resin containing 5 x lo-@ mol mg-‘. = 3-4 x lo-’ mol). Labeling (%) estimated by integration of peak areas TLC strips.

51

Tin-adsorbed resin

Sn-resin (10 mg) packed mini-column showed a low labeling yield, while a longer mixing time (10 min) did not improve the yield and other labeled products appeared instead. After the reaction is completed, separation of the St?+ containing solid phase was immediately carried out by filtration through a Millipore filter to stop further reaction.

(a)

Simple kit for labeling PPmTc-BLM Sn-resin could advantangeously be formulated in a kit form for clinical use as described, using standardized conditions of pH and the amount of ligand or Sn-resin. Sn-resin Ampoules containing 68mg of (1 x lo-’ mol mg-’ of Sn”) was the most suitable quantity for the labeling of 15 mg of BLM. This Snresin is prepared by equilibrating 200mg of conditioned resin with 2 x 10e3 M solutions of SnCI, (10 ml), as described under Methods. Good performance of this autoclaved Sn-resin dispensed in welldessicated small amber ampoule was observed over a 6 month period. The total amount of Snzf ion present in the solid phase ranges from 6 x lo-’ to 8 x lo-‘mol. higher than the reported amount of 2 x 10m9mol needed when Sn’+ was used in solution. Acetate buffer (pH 6) at a concentration of 0.1 M is employed but 1 M can also be formulated to satisfy a clinical need for high specific activity and diluted to 0.1 M with the pertechnetate eluate.

(b)

-Rf

FIG. I, Effect of Sn-resin gram

(TLC)

dessication. Thin-layer chromatoof 99mTc-Bleomycin labeled by the G-resin

kit method. Sn-resin dried 24 h over: (a) silica gel + PZ05 + vacuum, (b) silica gel + vacuum. R, of radioactivity peaks: ““Tc-BLM (AZ) = 0.6330.75; 99mTc-BLM (B2) = 0.274.40; 99”TcO; = 0.80-0.90; X = 0.22&0.25. Solvent; MeOH: 10% NH,OAc = 1:l. Developing time: 2h.

In vivo distribution

Bio-distribution studies in mice bearing Ehrhch carcinoma were performed with 9gmTc-BLM prepared with the kit as formulated and it has been shown to have a similar distribution to that already reported using the reducing agent in solution,“) as seen in Table 3. Tumor uptake of g9mTc-BLM by either method is comparable and good tumor-to-blood and tumor-to-muscle ratio is observed,

by the degree of dessication of the Sn-resin. The use of a strong dehydrating agent such as phosphorous pentoxide in the formulation of %-resin was important for a good performance (Fig. la). Lack of dessication induces formation of various g9mTc-complexes in addition to the g9mTc-BLM (A,) and 99mTc-BLM (BJ, as shown in Fig. lb; on the other hand the presence of the complexes serves as a quality control test for the St-r-resin states. The minimum necessary time for the labeling reaction to proceed was also tested. 2-3 min of inversion was the optimal mixing time for the labeling solution with the Sn-resin; a free flow of the mixture through a

TABLE3. Biodiostribution

o~‘~~~Tc-BLM

Discussion One approach to the search of radiopharmaceuticals of greater specificity and reproducibility is to investigate a better labeling mechanism to improve

of ““Tc-bleomycin

(Sn-resin Kit) in mice bearing

Ehrlich

ascites carcinoma,’

Tissue

Time after injection 3h

lh

n=9 Blood Muscle Tumor Kidney Stomach Liver ’ Values are percentages animals used.

0.53 0.14 0.46 3.14 0.68 0.51

f + + f + +

n=9

n=9 0.20 0.06 0.17 0.61 0.26 0.21

of injected

0.13 0.05 0.32 2.28 0.57 0.41 dose per gram

+ & & k + k

24 h

0.03 0.01 0.13 0.48 0.36 0.17

of tissue f

0.04 0.03 0.28 1.20 0.26 0.26

* 5 + k + f

0.01 0.01 0.18 0.27 0.26 0.03

I SD. n = number

of

52

K. Horiuchi

the chemical nature of the labeled species in the final preparation. As shown in Table 1 and Fig. 1, the stable complex of BLM can be prepared when 8 x lo-’ to 5 x lo-* mol of Sn’+ adsorbed on cationic exchange resin is used under optimal condition of pH and ligand concentration for the reaction of TcO’+ with the ligand to proceed to the formation of a complex having the characteristics of a mononuclear complex as postulated!” The chemically stable complex of BLM is formed with yield over 93% and insignificant effect from variable concentrations of TcO, are observed (Table 2). These results led us, as predicted, to demonstrate the need for an effective concentration of Sn2’ for the complete reduction of 99”Tc0; to 99mT~OZt to allow the mononuclear complex formation reaction to proceed. Some information about the effect of hydrolyzed Sn2+ species on the labeling reaction could be drawn also from the present work. In previous studies of 99”‘Tc-BLM labeling using SnClz in solution extreme care was required for the preparation and handling of nanogram amounts of SnC12; even at short-time intervals after the dissolution of the crystal in oxygenfree medium under continuous bubbling of N2 ageing phenomena were crucial factors for good labeling performances.(2) The effect of hydrolyzed Sn’+ species on the labeled product were suggested strongly by the great susceptibility of the reaction toward Sn-resin humidity (Fig. 1). Since the preparation of the Snresin is carried out carefully under a Nz atmosphere, that is, in the absence of oxygen, a factor affecting the oxidation of stannous ion,“‘) hydrolysis of Sn’+ rather than oxidation is the most likely phenomenon to consider. The presence of hydrolyzed species of stLnnous ion in the resin, besides limiting the reducing capacity, might induce the formation of hydrocomplex lyzed 99mTc species (Fig. lb). Mononuclear formation reaction (reaction step (b)) is considered to proceed in competition with the hydrolysis of the reduced 99mTc species. (3) So , it might be reasonable to suggest that due to weaker complexing ability of BLM its labeling may be markedly affected by the hydrolyzed Sn2+ species. It can be concluded that the effective concentration of Sn’+ in a pure chemical state, required for the mononuclear complex formation, without further hydrolysis of 99”Tc, is released from this Sn-resin according to the amount of metal present and any remaining excess of Sn ‘+ is easily removed with the resin by Millipore filtration, thus good control over the competing reaction can be obtained. Although solid phase systems have been cited previously!’ ‘,12) this new approach may help to explain the need for devices like Sn-resin for the preparation of a stable technetium complex of high purity. As an application of this new approach, a kit method using Sn-resin was formulated, and its suitability for preparing a stable 99mTc-BLM complex

et al.

with high efficiency and good reproducibility has been described. Organ distribution studies performed in mice bearing the Ehrlich tumor with this new formulation parallel the data previously reported using SnZc in solution prepared under very restricted conditions. So, the ability to control the preparation of a mononuclear complex is established. In the Sn-resin system, the amount of Sn2+ adsorbed on the resin could be easily and accurately dispensed in a chemically pure state with minimum care in handling, and moreover, its chemical state can be kept stable if the Sn-resin is stored under a dried atmosphere. In fact, the good stability of the Sn-resin reflected by good labeling performance over a 6 month period was observed. In addition, a very dry Sn-resin obviously resisted well the autoclaving process. These characteristics make Sn-resin suitable for the development of new kit systems. Kit preparation using Sn-resin can be further characterized. Careful handling is necessary only for the preliminary non-isotopic step such as the Sn-resin preparation under a nitrogen atmosphere and any pH adjustment of the ligand solution; then 99mTc labeling can be easily performed in the presence of air in a strikingly short time. The radiation exposure can be decreased if the reaction is performed in lead shielded vials or syringes. Also, technetium carrier effects are reduced and the potential effect of any Sn2+ excess can be avoided. A very stable 99mTc-BLM complex, with a labeling yield over 93”/, is made available and clinical re-evaluation of the complex has shown excellent results.” %14)

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15th

Int.

Ann.

Meet.

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of

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Medicine.

Groningen, Netherlands, September, 1977. Abstract. 12. CAMIN L. L., LITEPLO M. P. and PRATT F. R. J. lab. Comp. Radiopharm.

16, 24 (1979).

13. OWRI T. Jap. J. nucl. Med. 16, 721 (1979). 14. OLXJRI T. Jap. J. nucl. Med. 16, 829 (1979).