This invention relates the preparation of active ingredients and pharmaceutical compositions for decorporating radioactive isotopes from living organisms.

Nuclear fissions in the experimental, isotope-producing, or energy-supplying nuclear reac¬ tors and in nuclear weapon tests are accompanied by the ormation of a considerable amount of radio¬ active by-products. Majority of these hot materials

involves fission products and activated elements, including extremely hazardous radioactive isotopes such as iodine-131, strontium-89-90, cesium-134 and -137, cerium-141 and -14*4. Emitted into the environ¬ ment, they may result in a radioactive pollution to the kingdom of life.

There are three ways, three gates, these isotopes can get through entering the human body: the respiratory tract (breathing with air), the digestive tract (ingesting with foods and drinks), the epider (contacting with harmed or unharmed skin).

A good deal of possibilities are provided for reducing or even preventing injuries of health. Some isotopes, essentially radiostroncium, however, can only be protected from by hindering its gastro¬ intestinal resorption with peroral administration of suitable adsorbents. If the medical aid begins as late as several hours after the contamination, no efficient methods are available at the present state of the medical art for the resorbed proportion of the radioisotopes transported by the blood-stream and the lymph-flow to influence their deposition in bones, to prevent their hiatic binding .and to promote their decorporating.

This fact motivates the research on highly effective human and veterinary pharmaceuticals capable

of bonding radiostrontium in the blood-stream and in other extracellular regions in form of stable complexes. This would prevent the histic deposition of the isotope and permit ist natural excretion (faeces, urine) from the organism.

The following requirements are established to such a ph.a-_maceutic.al agent:

(a) the complex formation takes place in the biological system even in the presence of concurrent ions (such as Ca , Na , K , etc.) and ligands that are present in a great amount;

(b) it has an acceptably low level of toxicity (wide- range efficiency);

(c) it is water-soluble; and

(d) it can be administered parenterally as well.

In the early fifties when the rapid develop¬ ment of coordination chemistry commenced, predominantly the transition metal complexes were studied, over¬ shadowing the alkali and alkali earth metal ones that either do not form complexes with the readily accessible organic and inorganic ligands or these complexes have very low stability, only electrostatic inter-relations between the metal ions and the ligands keep them together. This concept was broken through by the dis¬ covery of "crown ether" and "cryptate" ligands in the late sixties.

Crown ethers contain mainly oxygen donor atoms while cryptates have both oxygen and nitrogen donors. Their construction holds the incorporated metal ions in cavities of well-defined size thus, only metals of certain sizes can form stable complexes with these types of ligands. Consequently, they are much more specific than ligands known before. Stability constants (10 g K) for some of these ligands with alkali earth metals in aqueous solution are presented in Table I (Coordination Chemistry of Macrocyclic Compounds, Ed. G.A. Melson, Plenum Press, 1979).

Table I

Ligand Ca ²⁺ Sr ²⁺ Ba ²⁺

15-crown-5 0.5 2.72 3.87 dicyclohexyl-18-crown-6 0.4 2.64 3.27 dibenzo-18-crown-6 - 1.00 1.95 l,10-diaza-4,7,13,16- -tetra- oxycyclo-octadecane - 2.56 2.97 cryptate-(2.1.1) 2.50 2.00 2.00 cryptate-(2.2.1) 6.95 7.35 6.30 cryptate-(2.2.2) 4.40 8.00 9.50 cryptate-(3.2.2) 2.00 3.40 6.00 cryptate-(3.3.2) 2.00 2.00 3.65

Date in Table I show a very considerable effect of the size of ligand "cavity" on the stability constants. In some cases, such as for cryptate-(2.2.2), the stability constant with Sr 2+ is higher by several orders of magnitude than with Ca 2+.

The above data motivated animal tests with the ligand cryptate-(2.2.2) (4,7,13,16,21,24-hexaoxa-l,10- -diazabicyclo-/8.8.8/-hexacosane) for removal of Sr-85, Ra-224, Pb-212, and Ba-140 as well as La-140 isotopes from the organisms ( .H. Miller, Naturwiss. 52, 248 /1970/; W.H. Muller and .A. Muller, Naturwiss. 61, 455 /1974/; W.H Muller et al., Naturwiss. 64, 96 /1977/; J. najfl et al. , 12th Ann. Meeting of ESR3, Budapest, 1976; J. Barsch, J. Geisler and Z. Szot, Nukleonika _< 23, 305 /1978/). The value of their result was vitiated by the concept that the metal complexes were formed in vitro then administered subcutaneously and their purging was studied. These experiments could prove only the fact that no dissociation of the complex formed externally from the radioactive metal and the ligand occured in an intricate biolog±al system instead of an in vivo co plexation of the radioactive isotope existing already in the animal with the ligand ad¬ ministered subsequently into a stable complex which coul be decorporated from the organism in the natural ways of excretion. It should be noted on the basis of real

experiences that ligand compounds are much less toxic in complex form than the ligands themselves.

In contrast to known complexes, stability constants of rare earth metal complexes of l,10-diaza-4,7,13,l6- -tetraoxacyclooctadecane-N,N'-diacetic acid, synthe¬ sized from the monocyclic cryptate decrease with the increasing atomic number (decreasing ionic size). Stability constants of C 2+ and 3r2+ complexes, how¬ ever, are identical within the experimental error (8.39 and 8.29, rsapectively) (CA. Chang, Inorg.Chem. 25, 355 /1986/) while complexes of non-cyclic ∑a ino- polycarboxylic acids (EDTA, ethylenediaminetetraacetic acid, DTPA, diethylenetria lnepentacetic acid, etc.) are considerably more stable with Ca 2+ than with Sr2+.

The purpose of this invention was the preparation of monocyclic cryptate ligands and their derivatives in order to influence in vivo stabilities of complexes avourably by linking functional groups to the macro- cycles. The final goal was to attain derivatives that would be suitable for the removal of radiostroncium, occasionally other radioactive metal isotopes, from the living organisms. It was proved by several experi¬ mental data that an active agent based on 1,4,10,13- -tetraoxa-7,16-diazacyclooctadecane-N,N'-dimalonic acid tetrasodium salt was capable of promoting the excretion of radiostroncium and radiocerium which had

been administered into various sites (peritoneal cavity, subcutaneous interstitial tissue, lung) of the .animal body.

The method of this invention comprises a new method to the preparation of compositions containing l,4,10,13-tetraoxa-7,10-diazacyclooctadecane dimalonic salts.

Preparation of such a compound was described by P. de Jong et al. (Reel. Trav. Chi . Pays-Has, 102, 164-173 /1983/). In this procedure, 1,4,10,13-tetra- oxa-7,10-diazacyclooctadecane was reacted with alpha- -halogenated methyl malonate ester for substituting hydrogen atoms on the nitrogen atoms and then ester was hydrolyzed into lithium salt.

We have found that alpha-brominated disodium ma¬ lonate is more preferable for substituting hydrogen atoms on the nitrogen atoms than alpha-halo enated methyl malonate. In this case, hydrolysis is omitted and the water-soluble salt is obtained directly. In addition, sodium salt is not hygroscopic in contrast to lithium salt thus, it is a more convenient active ingredient or the preparation of pharmaceutical com¬ positions or the like, .Another advantage of sodium salt to lithium one is its lower price.

In the procedure of this invention, the active agent containing l,4,10,13-tetraoxa-7,l6-diazacyclo-

octadecane-N,N'-dimalonic acid tetrasodium salt is prepared by reacting l,4,10,13-tetraoxy-7,16-diaza- cyclooctadecane with 2-bromomalonic acid disodium salt. Preferably, the reaction is carried out in a slightly alkalic aqueous medium at 70 to 80°C. Alkalicity of the reaction mixture is reasonably checked i h phenolphthalein indicator, adjusting and holding a pale pink colour of the mixture during the reaction.

The active agent containing 1,4,10,13-tetra- oxy-7,l6-diazacyclooctadecane-N,N'-dimalonic acid tetrasodium salt is capable of bonding radioactive metal isotopes, principally radiostroncium and radio¬ cerium, ingested into a living organism. The stable complex formed in vivo can be decorporated from the body in the natural ways in form of this complex.

The pharmaceutical composition of this invention comprises an active ingredient containing 1,4,10,13- tetraoxa-7,16-diazacyclooctadecane-N, '-dimalonic acid tetrasodium salt prepared by the procedure of this invention along with a pharmaceutically accepted carrier, such as normal saline solution or a 5-per cent by volume of glucose solution.

The composition comprises from 100 to 500 mg, preferably 250 mg of active ingredient mixed prefer¬ ably with a 5-per cent by volume of glucose solution.

Healing power of the composition has been evidenced by animal tests. In this way, the mini¬ mum .and average lethal doses (LD _Q , and LDJ- , respectively) have been established.

Por the determination of lethal doses, the active ingredient was administered intravenously at increasing concentrations to the animals. Mini¬ mum and average lethal doses were calculated from the mortality within 30 days. LD,- _Q - _>Q value of the active agent containing l,4,10,13-tetraoxa-7,l6- -diazacyclooctadecane-N,N'-dimalonic acid tetrasodium (DMCRYP) salt x NaBr (x = 2,5 - 8) as prepared accord¬ ing to Example I was 1.05 mmole/kg body weight. On every occasion, one tenth of this dose was intro¬ duced into each animal in this experiment.

Laboratory Small Animal Teat3 for the Effect of DMCRYP on the Enhanced Decorporation

The pharmaceutical composition containing DMCRYP active ingredient was denoted "PTR-23". The compo¬ sition contained a carrier, preferably sterilized normal saline solution or 5-per cent by weight of glucose solution. Preferable ratio of active agent to carrier was from 100 to 500 mg/cπr carrier.

In order to test the effect of DMCRYP on en¬ hancing the decorporation of radiostroncium a d the rare earth metal radiocerium from the body, male and female Swiss mice .and Wistar rats were selected. The experiments were generally conducted by ad- ministration of radiostroncium ) or radio¬ cerium of an activity from 37 to 54 kBq (1-2 iCi) into various sites of the animal body (peritoneal cavity, subcutaneous interstitial tissue, lung) followed by an intravenous injection of PTR-23 30 to 60 minutes later so that one injection intro¬ duced 100 umole/kg of active agent. In the comparative tests, a known polyaminopolycarboxylic acid-type decorporant (decorporating agent), calcium-trisodium salt of DTPA (diethylenetriamiTiopentacetic acid) (Heyl and Co., Berlin) was used at equimolar concentra¬ tion. The amount of residual isotopes in the animal organisms was determined by whole-body activity measurements in every 1 to 4 days and was expressed as per cent of activity introduced.

The effect of PTR-23 administered once (Day 0) intravenously on the enhanced excretion of Sr-85 isotope introduced into the peritoneal cavity is illustrated in Figure 1 where the percentage of re¬ sidual isotopes in the animal body (whole-body re-

tention) is plotted against the days of experiment. The efficiency of treatment with the compound of this invention 30 minutes after the administration of the isotope is indicated by the steep drop of the corresponding curve: on the Day 1, 35.8 per cent was attained which is less than a half of the Sr-85 content of control animals being 73.2 per cent. This ratio was consistent throughout the experiment, reach¬ ing 21.2 per cent after the treatment with PTR-23 in contrast to the 45.5 per cent of untreated controls. This series of experiments also illustrates that the decorporant DTPA is ineffective for removal of Sr isotope from the animal body (A. Catsch: Dekorporierung radioaktiver und stabiler Metallionen, . Thiemig Ver- lag, Munchen, 1968).

The present invention is more particularly illustrated by the following examples which are not intended to limit the scope of the invention.

Example 1 demonstrates the preparation of the active agent. Examples 2 through 6 illustrate the healing power of pharmaceutical compositions prepared therefrom.

Example 1

Preparation of l,4,10,13-tetraoxa-7,l6-diaza- cyclooctadecane-N,N'-dimalonic acid tetrasodium salt (DMCRYP) - containing active agent

2.80 g (15.3 mmole) of 2-bromomalonic acid was dissolved in 2 cπr of water and the solution was titrated with 1.5 to 2 M NaOH solution in the presence of 1 drop of phenolphthalein indicator to a pale pink colour. 1.00 g (3.81 mmole) of 1,4,10,13- -tetraoxy-7,l6-diazacyclooctadecane (Kryptofix 22, Merck) was added to the solution. The reaction mixture was kept at 75 to 80°C for 14 hours while 8.55 cm ³ of 1.873 M NaOH solution was dropped from a buret for maintaining the pink colour. The solution was then evaporated in vacuo and dehydrated still in vacuo on a water-bath at 80°C for 6 hours. The residue was taken up with 15 cur of dichlormethane, filtrated, extracted three times with dichlormethane and dried in nitrogen stream. The white solid product was ex¬ tracted with absolute ethanol until no considerable amount of material had been dissolved (15 to 17 times). A white deposit was precipitated from the extract during the extraction. The ethanolic extract was evaporated, taken up with dichlormethane, filtered, extracted three times with dichlormethane and dried in nitrogen stream. Yield of the product was 1.447 g.

The dichlormethane extract was evaporated in nitrogen stream and 0.357 g of highly hygroscopic yellowish crystals were obtained.

The residue from ethanolic extraction

(said white precipitate) was dissolved in 20 cwr of water and kept at 80°C for 20 minutes. The solution was evaporated in vacuo and dehydrated still in vacuo on a water-bath at 80°C for 5 hours. The further processing was the same as above. The ethanolic extract was evaporated in vacuo, taken up with dichlormethane, filtered, and dried in"nitrogen stream. 0.430 g solid was obtained.

Products from ethanolic extracts were com¬ bined, suspended in ethanol and stirred at 70°C for 30 minutes. The mixture was then evaporated, taken up with dichlormethane, filtered, and dried in nitrogen stream. Mass of the product was 1.830 g at a yield of 58 per cent. The product is a double salt of 1,4,10,13- -tetraoxa-7,l6-diazacyclooctadecane-N,N ¹ '-dimalonic acid tetrasodium salt with sodium bromide (containing 33 % by weight sodium bromide). Analysis

Characteristic IR bands (in KBr), cm ^"1 : 2950, 2868 ( , V ⁷ /C-H/) 1605 (vs, /C00/ _as ) 1430 (m, > /C00 _s )

Characteristic unidentified IR bands: 1350 (s), 1320 (s), 1095 (s) 928 (w) ^Η HMR data (in D ₂ 0), ppm:

2.92 (t , 8H, N-CH ₂ )

3.63 (t , 8H, 0-CH ₂ )

3.70 (sg, 8H, 0-CH ₂ -CH ₂ -0 )

4.00 (sg, 2H, N-CH) .

Water solubility: very soluble .

Example 2

The results with female Wistar rats are shown in Figure 2. The experimental arrangement and no¬ tations are identical to those in the general des¬ cription and in Figure 1. The only difference was in the delay between the introduction of the iso¬ tope into the peritoneal cavity and the intravenous administration of the active agent, being 60 days.The composition of this invention was even more efficient for rats. On the first day after the treatment, the amount of radiostroncium in the animal bodies dropped to 22.0 per cent by virtue of the new complexing agent as compared to the 69.6 per cent with the control which is more than three times higher. Like the results with mice, the ratio between the curves was consistent throughout the experiment reaching 13.5 and 36.8 per cent of residue at the end of test for the treated and the control animals, respectively. Retention values in the DTPA-treated group were lower than those in the control but the difference was not statistically significant.

It was clearly demonstrated by the experimen¬ tal data in Example 2 that the composition PTR-23 promoted the decorporation of Sr-85 administered into the • peritoneal cavity considerably , reducing thereby the radioactive load of the animal organism exposed to a single relatively low dose when the agent had been ingested into the blood-stream 60 minutes after the administration of the isotope.

Example 3

In this series of experiments, possibilities of decorporating radiostroncium got into the skin or the subcutaneous interstitial tissues were studied with a single intravenous treatment by PTR-23 (Fi¬ gure 3).

The results demonstrated that the amount of radiostroncium entered through the hurt epiderm (stabs, bruises, cuts) was markedly decreased by the composition PTR-23. Whole-body retention of the animals was 31.5 per cent in contrast to 56.9 per cent of the control (a gain of almost 50 per cent) on the Day 1 when the treatment was applied 30 minutes after the infection. Th-fe ratio was consistent throughout the experiment. Treatment with DTPA was ineffective again.

Example 4

Whole-body retention curves in Figure 4 refer to the elimination of radiostroncium ingested through

the trachea into the lungs of Wistar rats after the administration of the composition PTR-23 intra¬ venously or intraperitoneally. It was proved un¬ equivocally by.the experimental data that the efficiency of the agent was not influenced by the way of administration, i.e. identical effect was obtained both with intravenous and with intraperi- tonael treatment.

The effect of the composition of this inven¬ tion on the promotion of Sr decorporation is shown by the two lower curves in Figure 4. It can be seen again that the amount of Sr isotope ingested into the lungs decreased abruptly after the administra¬ tion of the said composition. On the Day 1, it dropped to 48.2 per cent while this level was 88.3 per cent in the control. The highest difference was obtained on the Day 18 when the retentions in the treated and control groups were 28.6 and 58.7 per cent, respectively.

Example 5

The dose effect of the decorporant of this inven¬ tion was measured on Swiss mice. Retention curves in Figure 5 represent an order of magnitude in the concentration of the agent (from 10 to lOO rUmole/kg) following the excretion of Sr isotope ingested

peritoneally. It was established from the experimen¬ tal data that, at a concentration of as low as 10^mole/k , the amount of isotope retained in the body was significantly lower than that in the control. The effect increased with the dose but above 50 umole/kg, the enhancement in the excretion was not proportional to the amount of the active agent as shown by retention values at the end of ex¬ periments (Day 30) being 40.6 per cent in .the control and 34.3, 28.3, 25.2, 23-9 and 21.8 per cent in the order of increasing dose. Consequently, it seemed to be reasonable to administer lower doses repeatedly for treating an internal infection of radiostroncium.

Example 6

The pharmaceutical composition of this invention was tested to other radioactive metals than radio¬ stroncium, mainly to the rare earth metal, cerium-144 for its removal from the animal body. Cerium-144 iso¬ tope was introduced peritoneally into female Swiss mice. 30 minutes after, the animals were treated intravenously with 100 umole/kg of PTR-23 or DTPA. Treatments were repeated twice, on the Days 2 and 4. The results are shown in Figure 6. Whole-body reten¬ tion curves characteristic to excretion of the iso¬ tope revealed that decorporating of the active iso-

tope from the animals was relatively slow in the control group. The first treatment with DTPA caused a slight decrease in the retention on the Day 2 (72.8 per cent as compared to 85.9 per cent) but the second and third treatments were ineffective, i.e. the further course of the two curves were identical. On the contrary, after the administration of the com¬ position of this invention, the activity retained in the body was only 56.2 per cent on the Day 2 (at the moment of the second treatment) in contrast to the above rate of 85.9 per cent. The difference was increas¬ ing due to the second and third treatments until the Day 7 when the level in the PTR-23 group was 33.4 per cent while the control level was 76.3 per cent (i.e. nearly two and a half-fold of the former). From this time, the rates of excretion (decorporation) were identical thus, the course of the curves was parallel. It was unequivocally demonstrated by the Examples that the composition containing 1,4,10,13-tetraoxa- -7,l6-diazacyclooctadecane-N,N'-dimalonic acid tetra¬ sodium salt (DMCRYP) (PTR-23) a favourably influenced the mobilization of radiostroncium and radiocerium. It is efficient in any case when the radioisotope enters the peritoneal cavity, subcutaneous interstitial tissues, or lungs. Studies on several hundreds of test animals have revealed no detrimental side-effect thus,

the composition of this invention is expected to be suitable for curing radioisotope-infected human patients as well.

As it. was concluded from the data in Table I, in the earlier studies with cryptate-(2.2.2) ligand for the removal of radiostroncium from living organisms, only the behaviour of metal/ligand complex formed in vitro was investigated when administered into the body (Muller, 1970; Miller et al. , 1974 and 1977; Knajfl et al. , 1976). Only J. Batsch et al. (Nukleoni- ka 2 , 305 /1978/) reported an experimental arrangement in which radiostroncium was ingested intravenously into rats followed by posterior treatment with cryp- tate-(2.2.2) peritoneally 0.5, 2, 4, 24, 48, 72, 192 and 216 hours later.In order to attain a considerable decorporation, a very high load of the active agent, 10 to 80 mg per animal, was necessary which was equal to or even higher than the saαilethal dose It should be mentioned that acute toxicity of cryp¬ tate-^.2.2) for rats in terra of ς ₀ is 292 umole/kg (I.C.R.P. Publication No. 20, p. 76 /1 72/). Even in these treatments, the reduction in the retention was never greater than 10 to 12 per cent. On the contrary, the composition of this invention reduced radioactivity in rats to 49•6 per cent at a load of 1/10 of the semi- lethal dose (cf. Example 2 and Figure 6) demonstrating the highly favourable efficiency of the composition of this invention.