INSOLUBLE SALTS OF LANTHANIDES FOR THE VISUAL DISPLAY, USING NUCLEAR MAGNETIC RESONANCE, OF THE GASTRO-INTESTINAL TRACT

Abstract: The present invention relates to diagnostic compositions which are particularly useful for the NMR imaging of the gastrointestinal tract, comprising physiologically acceptable aqueous suspensions of insoluble salts of lanthanides, buffered, if required, at a pH value which is variable between 6.0 and 8.5 and which are, if required, formulated with appropriate insoluble organic or inorganic additives and/or with dispersing agents, suspending agents or viscosity-enhancing agents, characterised in that they are able of increasing the value of the r2/r1 ratio, in which r1 and r2 are the longitudinal and transversal relaxivities of the protons of the surrounding water, thus permitting the production of clear images which have negative contrast and which lack artefacts of metallic type.

Description: INSOLUBLE SALTS OF LANTHANIDES FOR THE VISUAL DISPLAY, USING NUCLEAR MAGNETIC RESONANCE, OF THE GASTRO- INTE¬ STINAL TRACT The invention relates to suspensions of insoluble complexes or salts of lanthanide elements which are useful as contrast agents to produce NMR images of the gastrointestinal tract. Currently, the techniques which are preferably em¬ ployed for the diagnostic imaging of the abdomen in¬ clude the use of X-rays, using suspensions of BaSO, as contrast agents, computerised axial tomography and eco- graphy. However, nuclear magnetic resonance, although already capable of competing with axial tomography, especially as regards the assessment of focal lesions of liver, of tumors of suprarenal glands, of kidneys and of pelvic organs,, has not yet reached an adequate level of application in the gastrointestinal field. This is due to the fact that the visual display of the gastroenteric tract presents numerous problems which are associated, inter alia, with intestinal motility, with anatomical variations in different patients, and with the fact that the irregularities of the intestinal loops may be confused with anomalous structures asso¬ ciated with pathological feature. Further, the ob¬ servation of the principal abdominal organs, for exam¬ ple pancreas, is made difficult by the superposition of images from stomach and/or duodenum. Accordingly, it is necessary to obtain a contrast agent which permits the application of a safe diagno¬ stic technique such as NMR for the examination of these SUBSTITUTE SHEET organs as well. Till now, studies have been carried out on various classes of substances: and initial classifi¬ cation may subdivide them into positive contrast agents, i.e. those which are capable of simultaneously reducing both the longitudinal relaxation time T, and the transverse relaxation time T. of the protons of the surrounding water, and negative contrast agents which act selectively on T_. Actually, while the positive contrast agents permit improved observations of the or- gans in which they accumulate, the negative contrast agents have the function of eliminating the signal from the regions which contain them, thus permitting the de¬ limitation of the contours of said regions and the vi¬ sual display of the adjacent organs. In order to find positive contrast agents useful for the gastrointesti¬ nal tract, studies have been carried out on substances such as iron salts [Young et al. , Computerized Tomo¬ graphy 5 (1981) 543-547; esbey et al. , Magnetic Reso¬ nance Imaging 3 (1985) 57-64 and Radiology 149 (1983) 175-180; Clanton et al. , Radiology 153 (1984) 159], ga¬ dolinium complexes [Weinmann et al., Radiology 153 (P) (1984) 292] and chromium complexes [Kamisky et al. , Ma¬ gnetic Resonance in Medicine and Biology 1, (1988) 271]. On the other hand, with regard to negative con- trast agents, consideration has been given to di¬ spersions of diamagnetic substances such as kaolin or bentonite [Listinsky et al. , Magnetic Resonance in Me¬ dicine 8 (1989) 285-92], while as far as their strong selective effect on T 2 is concerned, suspensions of ap- propriately supported ferromagnetic or superparamagne- tiσ substances have been tested [Edelman et al. , Radio- SUBSTITUTE SHEET logy 161 (P) (1986) 314; Hahn et al. , Radiology 164 (1987) 37-41]. Moreover, it is then necessary to consi¬ der those substances which cancel the NMR signal due to lack of protons, such as perfluoro derivatives [Mattrey et al. , American Journal Roentgenology 148 (1987) 1259- 1263 and Radiology 161 (P) (1986) 314]. Possible contrast agents for NMR imaging of the gastroenteric tract are described in Patent documents US 4,719,098 (Gries) , EP-A-275,215 (Amersham) , US 4,615,879 (Runge) , EP-A-299,910 (Schering), WO 85/04330 (Nyegaard), WO 88/00060 (Adv. Magnetics). Such agents may be classified as positive contrast agents, in the light of what has been described in US 4,719,098, EP-A- 275,215, US 4,615,879 and EP-A-299,910. On the other hand WO 85/04330 and WO 88/00060 describe particles which act on the relaxation time T-,, and are therefore potential negative contrast agents. The contrast agents for gastrointestinal use which have been studied up to the present time have not yet obtained the desired go- als either as regards tolerability or as regards the possibility of obtaining images which are clear and which do not include artifacts of metallic type are due to a non-uniform distribution of the contrast agent in the tract to be examined. It is known that paramagnetic metal ions, in par¬ ticular those belonging to the transition metals or to the lanthanide elements, and their salts and/or com¬ plexes have the capacity to influence simultaneously and to a similar extent the relaxation times T, and ~ of the protons of the surrounding water, thus behaving as positive contrast agents. This property is well do- SUBSTITUTE SHEET cumented, inter alia, in the above cited US Patent 4,615,879, in which a description is given of insoluble derivatives of gadolinium (especially gadolinium oxa- late) for use in NMR diagnosis of the gastrointestinal tract. It has now unexpectedly been found that certain salts and/or complexes of paramagnetic metal ions of the lanthanides group have the unexpected ability to selectively influence the relaxation time T_ of the protons of the surrounding water, altering almost negligibly the time T.. of the same. In this way, such compounds make it possible to increase the r- > /r, ratio, which corresponds to the ratio of the transverse and longitudinal relaxivities (r, and r_ are inversely pro- portional to the relaxation times T. and T_, see "Contrast and Contrast Agents in Magnetic Resonance Imaging " (1989), P.A Rinck Ed., page 1, Recommenda¬ tions for the Nomenclature of Magnetic Resonance Con¬ trast Agent Terms). Therefore they are very promising negative contrast agents, particularly useful for the NMR examination of the gastrointestinal tract because they render it possible to obtain images clear and without those artefacts of metallic type which are cau¬ sed, for example, by the selective T. contrast agents based on ferromagnetic or superparamagnetic substances such as magnetite and iron oxides. Such artefacts are generally caused by a local accumulation of the con¬ trast agent, which generates a non-uniformity in the magnetic field, giving images which do not correspond to the actual pathological situation [see, in this con¬ nection, Lonne ark et al. , Acta Radiologica 30 (1989) 193-196 and Bach-Gansmo et al. , "Contrast and Contrast Agents in Magnetic Resonance Imaging" (1989), P.A. Rinck Ed., pages 94-104]. It has been found that particularly suitable sub- stances for the purpose of the invention are insoluble salts of lanthanides in which the metal ion is prefera¬ bly selected from terbium, dysprosium, holmium, erbium and thulium and the anion is a suitable inorganic or organic insolubility-promoting anion which is physiolo- gically compatible. Non-limiting examples of such anions may be selected from fluorides, oxalates and phosphates. Substances which have proved to be par¬ ticularly favourable according to the purpose of the present invention are the fluorides which combine a very low solubility, and thus a minimal absorption, with a marked selective reduction of the relaxation time T. of the protons of the surrounding water, thus permitting the achievement of high values of the ratio r 2 /r l' The influence of the paramagnetic material on the r./r, ratio is also dependent upon the particle size of the particulate material: it has been found that gene¬ rally a thinner particulate material is more effective in increasing the value of this ratio. To this aim, it is possible to make use of particles having a diameter in the range between 0.01 and 1,000 μ preferably bet¬ ween 0.05 and 500 μ. The concentration of the insoluble paramagnetic particulate material may range between 0.01 and 5% (weight/volume) and preferably between 0.1 and 3%. A further particularly significant aspect of the invention is also given by the completely unexpected finding that the addition of suitable insoluble parti¬ culate additives to the suspension of the salts and/or complexes of the lanthanides described above is capable of even further increasing the value of -C- j r-i resul¬ ting in a further benefit for the purposes of NMR ima¬ ging. Such additives may be selected from organic or inorganic substances which are insoluble and physiolo¬ gically compatible. As non-limiting examples from the point of view of a person skilled in the art, it is possible to mention cellulose derivatives such as hy- droxymethylcellulose and carboxymethylcellulose among organic substances, and insoluble salts such as BaSO. or silica among inorganic substances. In order to mantain the insolubility of the para¬ magnetic compounds of the invention during the passage in the district under examination, the suspensions of the same may be buffered at a suitable pH value using buffering agents which are physiologically compatible. Such a value is preferably neutral or slightly alka¬ line, i.e. in the range between 6.0 and 8.5. In crder to obtain satisfactory results from the diagnostic examination of the intestinal tract, it is also important that the contrast agent diffuse unifor- mly in the organ under examination and that the paramagnetic particulate material remain stable in su¬ spension during the analysis, without giving rise to local accumulations. In order to achieve this objec¬ tive, it is possible to use additives which are well known in the pharmacopoeia, like suspending agents, di¬ spersing agents or viscosity-enhancing agents. If re- quired, it is also possible to add excipients, edulco¬ rating agents, flavourings, preservatives and additives in accordance with well known pharmaceutical formula¬ tion techniques. " The following examples serve to further illustrate the invention, without nevertheless limiting its ap¬ plications, which are readily apparent to persons skil¬ led in the art. The products and reagents employed in the examples are commonly available commercially. Example 1 Preparation of insoluble salts of lanthanides: fluori¬ des - Preparation of HoF_ A few drops of concentrated HC1 are added to a 250 ml beaker containing 100 ml of bidistilled water under magnetic agitation, to adjust the pH value between 1 and 2. 1.7 g of HoCl,.6H 2 0 (0.0045 mol) are then added. 0.74 g of NaF (0.0176 mol) is then added to the solu- tion, and this is left under agitation for 30 minutes, maintaining the pH value between 1 and 2. The precipitate is then filtered under vacuum, wa¬ shed with 5 portions of 20 ml of bidistilled water, and dried at 100°C for 4 hours. 0.98 g of HoF, is obtained (Yield: 98%). The following salts are obtained using the same procedure: SUB Example 2 Preparation of insoluble salts of lanthanides: oxalates - Preparation of Dy_ (C- j O.)-. A few drops of dilute HCl (1:10) are added to a 250 ml beaker containing 100 ml of bidistilled water under magnetic agitation, to adjust the pH value bet¬ ween 3 and 4. 1.3 g of DyCl 3 .6H 2 0 (0.0034 mol) is then added. 0.6 g of oxalic acid (0.0067 mol) is added to the solution, and this is left under agitation for 40 minu¬ tes, maintaining the pH value between 3 and 4. The precipitate is then filtered under vacuum, wa¬ shed with 5 portions of 20 ml of bidistilled water, and dried at 100°C for 4 hours. 0.97 g of Dy 2 (^ 2 °^ 3 is obtained (Yield: 97%). The following are obtained using the same proce¬ dure: Gd 2 (C-,0 4 ) 3 (Yield: 98%) b 2 (C 2 0 4 ) 3 (Yield: 96%) Ho 2 (C 2 0 4 ) 3 (Yield: 96%) Er 2 (C 2 0 4 ) 3 (Yield: 97%) Example 3 Preparation of suspensions of insoluble salts of lanthanides for the determination of the ratio r- j /r, - - Preparation of a 0.3% (weight/volume) DyF, su¬ spension. 0.07 g of silicone SH and 0.3 g of DyF, are added, under agitation, to a 250 ml reactor equipped with a turbine-driven stirrer and containing 90 ml of distil- led water. After 5 minutes of stirring at ambient tempera¬ ture, the following are added in order: 0.91 g of diba- SUBSTITUTE SHEET sic sodium phosphate, 0.2 g of monobasic potassium pho¬ sphate, 0.33 g of Keltrol F (Xanthan gum). Stirring is continued for a further period of 10 minutes at such a speed as to prevent the inclusion of air. The volume is then made up to 100 ml with distil¬ led water, and the agitation continues until complete homogenisation is achieved. The dispersion obtained exhibits the following characteristics: pH = 7.3; viscosity = 250 mPas. 0.3% (weight/volume) suspensions of the following salts are prepared following the same procedure: HoF. GdF bFl ErF. Example 4 Determination of the ratio •£"--,/r, for the lantha- nide salt suspensions of the present invention. - Experimental protocol A) Apparatus MINISPEC. PC 120 (BRUKER) B) Observation frequency: 20 MHz (proton) C) Temperature: 39°C, with previous thermo- static temperature control of the NMR sample ube for 10 mi¬ nutes at working temperature. D) Concentrations (weight/volume) 0.01; 0.05; 0.25% E) Samples: Suspensions of the following salts (prepared in accordance with the procedure of Example 3) GdF. DyF- HoF. Gd 2 - (C 2 0 4 ) 3 , Dy 2 (C 2 0 4 ) 3 Ho '2. (c 2 o 4 ) 3 , GdP0„, DyPO, HOPO 4' SUBSTITUTE SHEET The longitudinal relaxivity of the protons of the surrounding water (r. ) was calculated using the "Inversion Recovery" sequences in accordance with the program supplied for the MINISPEC 120 BRUKER with which the measurements were made. The transverse relaxivity (r 2 ) was calculated using the Carr, Purcell, Meiboom and Gill sequences in accordance with the program supplied for the MINISPEC 120 BRUKER with which the measurements were made. Table 1 attached hereto shows the efficacy (E) of certain lanthanide salts, characterising the invention, in increasing the z~ !_ - ratio. The efficacy (E) was calculated by adopting as reference term gadolinium fluoride (GdF,) and was expressed as the ratio between the value of τ- ,'r, of the suspension of the lanthanide salt under examination and the corresponding value of r-,/r., found for the GdF, suspension. Table 1 shows the selective action on the reduction of the relaxation time T„ of the protons of the surrounding water, with the consequent increase of the -C-,/ -, ratio, by the pro¬ ducts object of the present invention with respect to the Gd salts adopted as reference terms. Example 5 Preparation of a DyF.. suspension in the presence of carboxymethylcellulose. A DyF, suspension is prepared in accordance with the procedure described in Example 3, using the fol¬ lowing quantities: SUBSTITUTE SHEET Bidistilled water 90 ml Silicone SH 0.07 g DyF 3 0.3 g Na 2 P0 4 0.91 g KHP0 4 0.2 g Keltrol F 0.33 g Before making up to volume, are added 5 g of inso¬ luble carboxymethylcellulose having a mean particle diameter of 10 μ, and agitation is maintained for 10 minutes. The volume of the suspension is then brought to 100 ml using bidistilled water, and the agitation con¬ tinues until complete homogenisation is achieved. Example 6 Determination of the ratio x 2 /x, for the suspen¬ sion described in Example 5. In accordance with the experimental conditions de¬ scribed in the protocol of Example , the value of the ratio x„ /x. was measured for the DyF, suspension with the addition of carboxymethyl cellulose (DyF,/CMC) and this was compared with that obtained for the suspen¬ sions of DyF, without carboxymethylcellulose (DyF,) prepared as described in Example 3. The results, which are reproduced in Table 1 attached hereto, show a large increase, almost two-fold, in the value of this ratio for the suspension of D Y F 3 with the addition of carboxymethylcellulose (DyF,/CMC) with respect to that without such addition. Example 7 Preparation of a suspension of DyF, with the addi¬ 98.64 g cf BaS0 4 , 0.6 g of sorbitol and 0.1 g of silicone SH are added to a twin-cone mixer and mixed for 30 minutes. 0.3 g of sodium carragenate and 0.36 g of DyF, are then added in small portions. After further mixing for 15 minutes , the mixture is poured into a 250 ml reactor and, under agitation, the volume is made up to 120 ml with distilled water. Example 8 Preparation of suspensions of insoluble salts of lanthanides of differing particle size. - Preparation of a DyF-, suspension (325 mesh). 0.7 g of silicone SH and 3 g of DyF-, (mean particle size 325 mesh) are added, under agitation, to a 1500 ml reactor equipped with a turbine-driven stirrer and con¬ taining 900 ml of distilled water. After 5 minutes of stirring at ambient temperature, 8 g of Keltrol F (xanthan gum) are added in small portions. After this, stirring is continued for a further period of 15 minutes at such a speed as to prevent the inclusion of air. The volume is then brought to 1000 ml using distilled water, and the agitation continues un¬ til complete homogenisation is achieved. The dispersion obtained has a viscosity of 2000 mPas. 0.3% (weight/volume) suspensions of the following were prepared in accordance with the same procedure: DyF, (particle size 60 mesh, mean diameter 250 μ) TbF, (particle size 325 mesh, mean diameter 44 μ) GdF, (particle size 325 mesh, mean diameter 44 μ) HoF, (particle size 325 mesh, mean diameter 44 μ) Example 9 . 2 /r, ratio for the suspen- SUBSTITUT sions of insoluble salts of lanthanides of differing particle size. The value of the -τ 2 /r, ratio was measured for the suspensions of lanthanides described in Example 8, in accordance with the experimental conditions described in the protocol of Example 4. Table 2 attached hereto shows the values of this ratio, from which it results that a thinner particle size is far more effective in increasing the value of x 2 /x ± . Example 10 Acquisition of "in vivo" NMR images using a DyF, suspension according to the invention. - Experimental protocol. The images were acquired on a 0.5 T "whole body imager" (Esaote-Genova) , using a coil having an inter¬ nal diameter of 8 cm. In order to reduce the artefacts due to movement (respiration, peristalsis), use was made of a spin-echo sequence 350/50/2 (TR/TE/NEX) with a field of view of 20 cm, 4 mm slicers, 256 x 256 matrix, and with "gradient moment nulling". A 3% (-weight/volume) DyF, suspension, prepared in accordance with the preparation described in Example 3, was administered "per os" to (male) Sprague Dawley rats, average weight 270 g, which were kept un¬ der fasting conditions for 18 hours, at a dosage of 30 ml/kg. The rat was observed using NMR for 1 hour after the administration. The contrast agent causes signal loss in the stomach and in the intestine. In the coro- nal sections observed at 30 minutes (Figure 1 attached hereto), the stomach is clearly defined, permitting good observation of liver and spleen. The loop formed by the duodenum can also be observed. SUBSTITUTE SHEET Table 1 - Efficacy (E) of the insoluble salts of lanthanides (LS) described in Examples 4 and 5 in increasing the r r. ratio of the transverse and longitudinal relaxi¬ vities of the protons of the surrounding water. CO c The efficacy (E) is expressed by the ratio CD CO r 2 / r]L (SL) H C r 2 r l (GdF 3 ) H **. m This is the suspension of DyF, with the addition of carboxymethylcellulose (CMC) described in Example 5 CO I m m H Table 2 - Values of the r_/r- ratio of the transverse and longitudinal relaxivities for the lanthanide salt suspensions described in Example 8. *: Mean particle size 325 mesh (corresponding to a mean diameter of 44 μ) **: Mean particle size 60 mesh (corresponding to a mean diameter of 250 μ)

Claims: CLAIMS 1. A composition for obtaining images of the gastro¬ intestinal tract using nuclear magnetic resonance, cha- racterised in that it is capable of increasing the va¬ lue of the r 2 /r-, ratio of the relaxivities of the pro¬ tons of the water of the region under examination and consisting in an aqueous suspension, which is physiolo¬ gically acceptable and can be administered by the oral or rectal route, comprising particles of an insoluble paramagnetic material and, if necessary, a buffering agent to maintain the pH value between 6.0 and 8.5 and/or physiologically acceptable additives which are useful as dispersing agents and/or agents influencing the viscosity of the suspension. 2. A composition according to Claim 1, characterised in that the insoluble particles of the paramagnetic ma¬ terial have a mean dimension which ranges between 0.01 and 1,000 μ. 3. A composition according to Claim 1, characterised in that the insoluble particles of the paramagnetic ma¬ terial have a mean dimension which ranges between 0.05 and 500 . 4. A composition according to Claim 1, characterised in that the paramagnetic material is an insoluble salt of a metal ion belonging to the lanthanide elements and the anion is a physiologically acceptable inorganic or organic insolubility-promoting anion. 5. A composition according to Claim 4, characterised in that the metal ion is selected from terbium, dyspro¬ sium, holmium and erbium, and the insolubility-promo- SUBSTITUTE SHEET ting anion is selected from fluoride, oxalate and pho¬ sphate ions. 6. A composition according to Claim 5 in which the paramagnetic insoluble salt is selected within the group consisting of DyF 3 , TbF 3 , HoF 3 and ErF 3 . 7. A diagnostic composition according to Claim 1 in which the particles of the insoluble paramagnetic mate¬ rial are present in a concentration which is variable between 0.01% and 5% (weight/volume) . 8. A composition according to Claim 1, characterised in that it further comprises physiologically acceptable organic or inorganic insoluble additives. 9. A composition according to Claim 8, characterised in that the insoluble paramagnetic material is selected within the group consisting of DyF,, TbF, , HoF, and ErF 3 . 10. A composition according to Claim 9, characterised in that the physiologically acceptable insoluble orga¬ nic additive is selected from cellulose derivatives such as hydroxymethylcellulose or carboxymethylcellu¬ lose. 11. A composition according to Claim 9, characterised in that the physiologically acceptable insoluble inor¬ ganic additive is BaSO.. 12. A diagnostic composition according to Claim 9, characterised in that the particles of the insoluble paramagnetic material are present in a concentration which ranges between 0.01% and 5% (weight/volume) . SUBSTITUTE SHEET

Inventors: AIME SILVIO, BOTTA MAURO, AIME, SILVIO, BOTTA, MAURO
Applicants: BRACCO IND CHIMICA SPA, BRACCO INDUSTRIA CHIMICA S.P.A.
Application year: 1991
Main classification: A61K49
IPC codes: A61K49