Drug – bio-affecting and body treating compositions – In vivo diagnosis or in vivo testing – Magnetic imaging agent
Reexamination Certificate
2000-09-11
2004-04-13
Raymond, Richard L. (Department: 1624)
Drug, bio-affecting and body treating compositions
In vivo diagnosis or in vivo testing
Magnetic imaging agent
C514S183000, C514S184000, C534S015000, C534S016000, C540S465000, C540S474000
Reexamination Certificate
active
06719958
ABSTRACT:
The present invention concerns a new class of polychelants, their chelates with metal ions and their physiologically acceptable salts, which can be used, either as they are or in association or formulation with other components, for diagnostic imaging as general or specific contrast agents for specific tissues, organs or body compartments.
The new class of contrast agents is constituted by molecules or macromolecules obtained by covalently linking chelants or chelates of metal ions to a “carrier” composed of an organic “backbone” which carries at least two primary amino groups, to which said chelants/chelates are attached through alkylene bridges. This class is characterized by the fact that at least one or, preferably, more primary amino groups of the “carrier” have been bifunctionalised, (through reductive dialkylation) with alkylene residues carrying said chelants or metal chelates or their salts, while the other primary amino groups can be present either as such (i.e., non-functionalized salified or not), or monofunctionalized with said chelant/chelate residues, the total number of chelants/chelates moieties attached to said amino groups being at least three. This class of contrast agents usually contains a high number of chelant/chelate residues per molecule, which are attached to the primary amino groups present in the carrier. In fact, depending on the structure of this carrier, the reactivity of the amino groups and the reaction conditions, up to two chelant/chelate residues can be attached to each primary amino group.
This invention concerns also a peculiar process for the preparation of these molecules, as well as their uses.
Complexes formed of chelating agents and suitable metal ions are in use both in nuclear medicine and in magnetic resonance imaging (MRI). In nuclear medicine, radioactive metal chelates are used as both diagnostics (scintigraphy, PET or positron emission tomography) and therapeutics. In nuclear medicine, macromolecules with high biospecificity such as, for example, antibodies and more recently, polypeptides are widely used. In this latter case they are analogues (both agonists and antagonists) of biologically active polypeptides. An example of this approach is Octreoscan, a derivative of somatostatin carrying a complex of
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, which was developed to visualize and localize tumors of neuroendocrin origin. A problem presented by these derivatives concerns the intrinsic biological activity of the carrier (also called address) macromolecules, the doses of which must be such as to provide improved visualization of the organ under investigation, without inducing appreciable pharmacological actions. The possibility of increasing the number of diagnostically efficacious sites for carrier molecule would permit a reduction of the dose required to obtain the same diagnostic effect and therefore also a reduction of the possibility of undesired effects connected to the pharmacological activity of the molecule. This problem becomes more important when it is necessary not to modify a number of the amino groups, particularly those required for receptor recognition or biological activity. For example, it is known that the s-amino group of lysine in position B29 of insulin can be modified without compromising the biological activity, while none of the &agr;-amino groups can be modified without altering the activity. The present invention, which enables the degree of substitution of the amino groups to be maximized, permits one to get around this problem and thus is highly advantageous for diagnostic techniques characterized by low sensitivity, such as, for example, MRI.
In the preparation of biospecific contrast agents for MRI, the most common approach has been first to react macromolecules, such as proteins and polylysine, with chelating agents having functional groups capable of conjugating the &egr;-amino group of lysine, preferably through formation of amide or analogous bonds, and then to complex the resulting compounds with gadolinium (for example, Ogan et al., Invest. Radiol., 1987, 22, 665-671). By this approach however it is not possible to link more than one chelant unit per amino group of the carrier. Indeed, the total number of chelant groups per protein is normally extremely low if compared with the total number of amino groups theoretically functionalizable on the molecule. For example, Lewis et al. (Bioconj. Chem., 1994, 5, 565-576) report the conjugation of the chelating agent DOTA (1,4,7,10-tetraazacyclododecan-N,N′,N″,N′″-tetraacetic acid) to cytochrome c through activation with N-hydroxysulphosuccinimide. Increasing the molar ratio between the active ester of DOTA and cytochrome c from 10:1 to 100:1 results in increasing from 2.64 to 8.79 the average number of chelating groups attached to the protein, out of a total of 19 available primary amino groups.
In addition, the subsequent formation of the complex with gadolinium does not ensure that the same happens quantitatively. The overall result is that not all the amino groups are functionalized with chelating groups and that not all the chelating groups introduced become saturated with gadolinium. Neither does the state of the art teach to link the free amino groups of the macromolecules of interest directly with performed chelates, or their salts, in such a way as to obtain the maximum chelation possible. In this respect see the following documents: U.S. Pat. No. 4,855,353, EP-A-481526, EP-A-243929, EP-A-255471, WO 9514491, GB 2169598 B, EP-A-038546, WO 9014881, and US 5,650,133. In particular, the last one seeks to obtain, and actually discloses, dichelants prepared by attaching two macrocyclic ligands to the two different extremities of a linker moiety. The preparation is carried out in a completely traditional manner, i.e., reacting an activated carboxy group with an amino group (either primary or secondary), thus giving final products that are amido derivatives. No possibility of preparing two macrocyclic dichelants moieties linked to the same amino group is suggested (the traditional synthetic pathway adopted cannot in any case give such result, as already explained above). The preferred compounds, disclosed in Example 12, comprise linkers that are terminal diamino derivatives, either primary or secondary, said amino groups being joined to the two macrocyclic chelant moieties through amido bonds, every amino group carrying just one chelating moiety.
As a consequence, diagnostically optimal doses of said contrast media contain high quantities of macromolecular carrier, with the result that undesired biological effects may arise. It would be highly desirable to be able to transport efficacious doses of metal chelate with substantially lower quantities of macromolecular carrier. So the technical need to be solved is the preparation of compounds that carry the maximum possible number of metal complexes per molecule, thus giving a positive answer to the above-mentioned problems.
The present invention solves this problem by allowing the linking of up to two units of chelants, or, even better, directly of their metal complexes, to each individual primary amino group present on the structure. This structure can for example be a macromolecule such as a protein, a polymer or a peptide, an amino acid or even a simple diamine or a polyamine. This aspect of the invention is particularly useful for those cases in which one or more primary amino groups of the address molecule must be maintained as such (for example after selective, easily removable protection) to preserve biological activity or tissue organ specificity (see the case cited above for insulin). Also in these cases the dialkylation of the other primary amino groups of the carrier with suitable chelant/chelate groups, according to the teaching of the present invention, yields a number of diagnostically or therapeutically active sites per molecule that is greater than that which is obtainable according to the current state of the art.
The same can be said for those polyamino carriers in which not all the
Gozzini Luigia
Maisano Federico
Murru Marcella
Dibra S.p.A.
Nixon & Vanderhye P.C.
Raymond Richard L.
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