Radiolabeled affibody molecules

Abstract

The invention provides a radiolabeled affibody molecule comprising a fragment of an IgG-binding domain of protein A from Staphylococcus aureus , a bifunctional linker, and a radiolabel comprising 18 F or 76 Br, wherein the bifunctional linker links the fragment and the radiolabel. The affibody molecule binds with high affinity to select receptors, which are over-expressed in certain cancers. Since the radionuclides emit a positron, the in vitro and in vivo binding characteristics of the radiolabeled affibody can be assessed using diagnostic imaging.

1 . A radiolabeled affibody molecule comprising a fragment of an IgG-binding domain of protein A from  Staphylococcus aureus , a bifunctional linker, and a radiolabel comprising  18 F or  76 Br, wherein the bifunctional linker links the fragment and the radiolabel, provided that when the radiolabel is  76 Br, then the bifunctional linker does not include a phenolic OH group. 
     
     
         2 . The radiolabeled affibody molecule of  claim 1 , wherein the fragment of an IgG-binding domain of protein A from  Staphylococcus aureus  is a specific affinity ligand selected against an extra cellular domain of HER2 or EGFR. 
     
     
         3 . The radiolabeled affibody molecule of  claim 1 , wherein the fragment of an IgG-binding domain of protein A from  Staphylococcus aureus  is Z HER2:4 , (Z HER2:4 ) 2 -Cys, His 6 -(Z HER2:4 ) 2 , Z HER2:342 , Z HER2:7 , Z HER2:342 , Z HER2:24 , Z HER2:79 , Z HER2:2 , Z HER2:8 , Z HER2:25 , Z LibHER2:mat , Z HER2:470 , Z HER2:382 , Z HER2:477 , Z HER2:492 , Z HER2:475 , Z HER2:473 , Z HER2:489 , Z HER2:487 , Z HER2:336 , His 6 -Z HER2:342 , or His 6 -Z HER2:7 . 
     
     
         4 . (canceled) 
     
     
         5 . The radiolabeled affibody molecule of  claim 1 , wherein the bifunctional linker comprises an imide group. 
     
     
         6 . The radiolabeled affibody molecule of  claim 1 , wherein the bifunctional linker has
 (i) a heterocyclic imide group linking a terminal thio group of the fragment and an aryl group linking the radiolabel,   (ii) a carboxy group linking an alpha amino group of the fragment and an aryl group linking the radiolabel, or   (iii) a carboxy group linking an epsilon amino group of the fragment and an aryl group linking the radiolabel.   
     
     
         7 . (canceled) 
     
     
         8 . (canceled) 
     
     
         9 . The radiolabeled affibody molecule of  claim 6 , wherein the bifunctional linker is 
       
         
           
           
               
               
           
         
       
     
     
         10 . (canceled) 
     
     
         11 . The radiolabeled affibody molecule of  claim 1 , wherein the radiolabel is  18 F. 
     
     
         12 . The radiolabeled affibody molecule of  claim 1 , wherein the radiolabel is  76 Br. 
     
     
         13 . The radiolabeled affibody molecule of  claim 1 , which is 
       
         
           
           
               
               
           
         
         or 
       
       
         
           
           
               
               
           
         
         wherein A-S is the His 6 -Z HER2:342  fragment of an IgG-binding domain of protein A from  Staphylococcus aureus.    
       
     
     
         14 . (canceled) 
     
     
         15 . A pharmaceutical composition comprising the radiolabeled affibody molecule of  claim 1  and a pharmaceutically acceptable carrier. 
     
     
         16 . A method of locating a receptor that is overexpressed in a tissue or organ of a subject comprising
 a) administering to the subject a radiolabeled affibody molecule comprising a fragment of an IgG-binding domain of protein A from  Staphylococcus aureus , a bifunctional linker, and radiolabel comprising  18 F or  76 Br, wherein the bifunctional linker links the fragment and the radiolabel, provided that when the radiolabel is  76 Br, then the bifunctional linker does not include a phenolic OH group,   b) obtaining a diagnostic image of the tissue or organ,   c) determining the location of radiolabeled affibody molecule bound to the tissue or organ, and   d) correlating the location of the bound radiolabeled affibody molecule with the location of the receptor in the subject.   
     
     
         17 . A method of measuring the quantity of a receptor that is overexpressed in a tissue or organ of a subject comprising
 a) administering to the subject a radiolabeled affibody molecule comprising a fragment of an IgG-binding domain of protein A from  Staphylococcus aureus , a bifunctional linker, and radiolabel comprising  18 F or  76 Br, wherein the bifunctional linker links the fragment and the radiolabel, provided that when the radiolabel is  76 Br, then the bifunctional linker does not include a phenolic OH group,   b) obtaining a positron emission tomography (PET) image of the tissue or organ,   c) determining the amount of radiolabeled affibody molecule bound to the tissue or organ, and   d) correlating the amount of the bound radiolabeled affibody molecule with the quantity of receptor in the subject.   
     
     
         18 .- 22 . (canceled) 
     
     
         23 . The method of  claim 16 , wherein the diagnostic image is a PET image, a magnetic resonance image (MRI), a computerized tomography (CT) scan, an x-ray contrast image, single photon emission computed spectroscopy (SPECT) image, or a combination thereof. 
     
     
         24 . The method of  claim 16 , wherein step b) comprises obtaining a PET image or SPECT image of the tissue or organ. 
     
     
         25 . (canceled) 
     
     
         26 . The method of  claim 16 , wherein the fragment of an IgG-binding domain of protein A from  Staphylococcus aureus  is Z HER2:4 , (Z HER2:4 ) 2 -Cys, His 6 -(Z HER2:4 ) 2 , Z HER2:342 , Z HER2:7 , Z HER2:342 , Z HER2:24 , Z HER2:79 , Z HER2:2 , Z HER2:8 , Z HER2:25 , Z LibHER2:mat , Z HER2:470 , Z HER2:382 , Z HER2:477 , Z HER2:492 , Z HER2:475 , Z HER2:473 , Z HER2:489 , Z HER2:487 , Z HER2:336 , His 6 -Z HER2:342 , or His 6 -Z HER2:7 . 
     
     
         27 . (canceled) 
     
     
         28 . The method of  claim 16 , wherein the bifunctional linker comprises an imide group. 
     
     
         29 . The method of  claim 16 , wherein the bifunctional linker has
 (i) a heterocyclic imide group linking a terminal thio group of the fragment and an aryl group linking the radiolabel,   (ii) a carboxy group linking an alpha amino group of the fragment and an aryl group linking the radiolabel, or   (iii) a carboxy group linking an epsilon amino group of the fragment and an aryl group linking the radiolabel.   
     
     
         30 . (canceled) 
     
     
         31 . (canceled) 
     
     
         32 . The method of  claim 29 , wherein the bifunctional linker is 
       
         
           
           
               
               
           
         
       
     
     
         33 . (canceled) 
     
     
         34 . The method of  claim 16 , wherein the radiolabel is  18 F. 
     
     
         35 .- 39 . (canceled)