Targeting multimeric imaging agents through multilocus binding

Abstract

The present invention relates to contrast agents for diagnostic imaging. In particular, this invention relates to novel multimeric compounds which exhibit improved relaxivity properties upon binding to endogenous proteins or other physiologically relevant sites. The compounds consist of: a) two or more Image Enhancing Moieties (IEMs) (or signal-generating moiety) comprising multiple subunits; b) two or more Target Binding Moieties (TBMs), providing for in vivo localization and multimer rigidification; and c) a scaffold framework for attachment of the above moieties. d) optional linkers for attachment of the IEMs to scaffold. This invention also relates to pharmaceutical compositions comprising these compounds and to methods of using the compounds and compositions for contrast enhancement of diagnostic imaging.

We claim:  
     
         1 . A method for increasing contrast using MRI or optical imaging wherein: 
 (a) a multilocus contrast agent binds to a target,    (b) contrast at the target is enhanced following binding of the contrast agent to the target,    (c) the contrast enhancement improves with either the number of IEMs, the rigidity of the molecule, or both.    
     
     
         2 . A method for increasing the relativity of a contrast agent wherein:(a) a multilocus contrast agent binds to a target, 
 (b) the relaxivity of the contrast agent increases upon binding to the target,    (c) the relaxivity per IEM of the contrast agent does not decrease upon binding, and wherein: 
 the contrast agent comprises 
 a) two or more Image Enhancing Moieties (IEMs);  
 b) two or more Target Binding Moieties (TBMs);  
 c) a scaffold to which the TBMs and IEMs are attached; and  
 d) optional linkers for attachment of the IEMs to the scaffold.  
 
   
     
     
         3 . A method for increasing the relativity according to  claim 2 , wherein the relativity is at least 10 mM −1 s −1  per IEM.  
     
     
         4 . A method for increasing the relaxivity according to  claim 2 , wherein the relaxivity is at least 15 mM −1 s −1  per IEM.  
     
     
         5 . A method for increasing the relaxivity according to  claim 2 , wherein the relaxivity is at least 20 mM −1 s −1  per IEM.  
     
     
         6 . A method for increasing the relaxivity according to  claim 2 , wherein the relaxivity is at least 25 mM −1 s −1  per IEM.  
     
     
         7 . A method for increasing the relativity according to  claim 2 , wherein the relaxivity is at least 30 mM −1 s −1  per IEM.  
     
     
         8 . A method for MR imaging of a target in an animal or human subject comprising the steps of administering an MRI contrast agent, allowing the contrast agent to bind to the target, and imaging a region of the subject's body in which the target is located wherein: 
 the MRI contrast agent comprises a scaffold, at least two IEMs each comprising a chelate of a paramagnetic metal ion and covalently bound to the scaffold either directly or by one or more intervening linkers, and at least two TBMs that have an affinity for the target and are covalently bound to atoms of the scaffold that are different from the atoms at which the IEMs are bound;    wherein the relaxivity of the contrast agent increases upon binding;    and wherein the target is a protein, polysaccharide, cell, fluid, glycoprotein, or a thrombus.    
     
     
         9 . A targeted MRI contrast agent comprising a scaffold, 2 to 4 TBMs covalently bound to said scaffold, 2 to 4 IEM's wherein said IEMs are either covalently bound to said scaffold or covalently bound to one or more linkers, wherein said linkers, if present, are covalently bound to said scaffold and wherein: 
 each IEM comprises a chelate of a paramagnetic metal ion,    each TBM is covalently bound to atoms of the scaffold not covalently bound to an IEM,    each TBM has an affiinity for a target, and    the relaxivity of the contrast agent when bound to said target is at least two-fold greater than the relaxivity in the unbound state.    
     
     
         10 . A method for increasing the affinity of a contrast: agent for its target comprising multilocus binding of the contrast agent to a target, wherein the contrast agent comprises 
 a) and two or more Image Enhancing Moieties (IEM);    b) two or more Target Binding Moieties(TBMs);    c) a scaffold to which the TBMs and IEMs are attached;    d) optional linkers for attachment of the IEMs to scaffold.    
     
     
         11 . A multilocus contrast agent having the structure VIII):  
       
         
           
           
               
               
           
         
       
       wherein m is an integer from 1 and 10 inclusive; 
 n is an integer from 2 to 10 inclusive;  
 o is 0 to 1;  
 p is 0 to 1;  
 each A is independently selected from the group consisting of O, CH 2 , C═O, C═NH, NH, NR, or CHR; and  
 B is selected from the group consisting of CH and N; and  
 R is C 1 -C 10  straight or branched chain alkyl, C 2 -C 10  straight or branched chain alkenyl or alkynyl, and wherein up to four carbon atoms are optionally substituted with halogen, O, N or S.  
 
     
     
         12 . A multilocus contrast agent having the structure (IX):  
       
         
           
           
               
               
           
         
       
       wherein each m is independently an integer from 1 and 8 inclusive; 
 each A is independently selected from the group consisting of O, CH 2 , C═O, C═NH, NH, NR, or CHR,  
 R is C 1 -C 10  straight or branched chain alkyl, C 2 -C 10  straight or branched chain alkenyl or alkynyl, and wherein up to four carbon atoms are optionally substituted with halogen, O, N or S; and  
 n is an integer from 2 to 10 inclusive.  
 
     
     
         13 . The contrast agent according to  claim 12  wherein A is C═O.  
     
     
         14 . The contrast agent according to  claim 12  wherein A is O.  
     
     
         15 . A multilocus contrast agent having the structure of Formula (X):  
       
         
           
           
               
               
           
         
       
       wherein m is an integer from 1 and 10 inclusive; 
 n is an integer from 2 to 10 inclusive;  
 o is 0 to 1;  
 p is 0 to 1;  
 each A is independently selected from the group consisting of O, CH 2 , C═O, C═NH, NH, NR, or CHR; and  
 B is selected from the group consisting of CH and N; and  
 R is C 1 -C 10  straight or branched chain alkyl, C 2 -C 10  straight or branched chain alkenyl or alkynyl, and wherein up to four carbon atoms are optionally substituted with halogen, O, N or S.  
 
     
     
         16 . A multilocus contrast agent having the structure (XI):  
       
         
           
           
               
               
           
         
       
     
     
         17 . The multilocus contrast agent according to claims  11 ,  12 ,  13 ,  14 ,  15  or  16  wherein the TBM comprises a substituted aryl group.  
     
     
         18 . The multilocus contrast agent according to  claim 17  wherein the IEM is selected from the group consisting of diethylenetriamine pentaacetic acid (DTPA) and derivatives thereof; 1,4,7-triazacyclononane; 1,4,7,10-tetraazacyclododecane (Cyclen) and derivatives thereof; 1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid tert-bu-ester) (DO2A-t-bu-ester); 1,4,7,10-tetraazacyclododecane-1,4,7-tris(acetic acid, t-bu-ester) (DO3A-t-bu-ester); 1,4,7-tris(tert-butoxycarbonyl)-1,4,7-tetraazacyclododecane (DO3-t-BOC); 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and derivatives thereof; 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonic acid) (DOTP).  
     
     
         19 . A contrast agent according to  claim 18  wherein the IEM is diethylenetriamine pentaacetic acid (DTPA).  
     
     
         20 . A contrast agent according to claims  11 ,  12 ,  13 ,  14 ,  15  or  16  wherein the TBM is a peptide.  
     
     
         21 . A contrast agent according to  claim 20  wherein the TBM is a fibrin binding peptide.  
     
     
         22 . A contrast agent according to the formula:  
       (TBM) q -S-[L m -IEM n ] p    
       wherein: 
 TBM is a target binding moiety, S is a scaffold, L is a linker, IEM is an image enhancing moiety, and  
 q, m, n, and p are all independent integers wherein: 
 q is an integer from 2 to 6 inclusive,  
 each m is independently 0 or 1,  
 each n is independently an integer from 2 to 4 inclusive,  
 p is an integer from 2 to 4 inclusive, and  
 
 wherein: 
 each TBM is covalently bound to S by a chemical bonds between two atoms,  
 each L, if present, is covalently bound to an IEM by a chemical bond between two atoms,  
 each L, if present, is covalently bound to S by a chemical bond between two atoms, and  
 the at least two TBMs are attached to different atoms of the scaffold.  
 
 
     
     
         23 . A contrast agent for optical or MR imaging comprising: 
 a) two or more Image Enhancing Moieties (IEMs);    b) two or more Target Binding Moieties (TBMs);    c) a scaffold to which the TBMs and IEMs are attached; and    d) optional linkers for attachment of the IEMs to the scaffold, 
 wherein the scaffold comprises a structure of formula (XII):  
                     
 and m and n are independent integers wherein:  
   m is an integer from 0 to 3 inclusive,    n is an integer from 0 to 2 inclusive,    each A is independently selected from the group consisting of NH, NR, O, S, CH 2 , C═O, C═NH, C═NR, and CHR,    wherein:    R is C 1 -C 10  straight or branched chain alkyl, C 2 -C 10  straight or branched chain alkenyl or alkynyl, and wherein up to four carbon atoms are optionally substituted with halogen, O, N or S.    
     
     
         24 . The compound M8-24.  
       
         
           
           
               
               
           
         
       
     
     
         25 . The compound M8-11.  
       
         
           
           
               
               
           
         
       
     
     
         26 . The compound M8-08.