Radiometal-binding analogues of luteinizing hormone releasing hormone

Abstract

Peptide, derivatives of leutenizing hormone releasing hormone that are capable of binding radionuclides are provided. The peptide derivatives are readily labeled with isotopes of rhenium or technetium, while retaining their ability to tightly bind LHRH receptors. Methods for preparing the labeled peptides and their use in methods of radiodiagnosis and radiotherapy are described.

What is claimed is:  
     
       1. A peptide comprising the amino acid sequence X 1 -X 2 -X 3 -ser-X 4 -X 5 -X 6 -X 7 -pro-X 8 -NH 2 , 
       wherein X 1  is pyroglutamic acid or D-acetylnaphthylalanine,  
       X 2  is histidine or D-4-chlorophenylalanine,  
       X 3  is D- or L-tryptophan or tyrosine,  
       X 4  is tyrosine, leucine, or arginine,  
       X 6  is leucine or tryptophan,  
       X 7  is arginine or lysine,  
       X 8 -NH 2  is glycine amide or D-alanine amide, and wherein X 5  is an amino acid derivative capable of stably chelating technetium-99m, rhenium-186, or rhenium-188, and has the structure:                    
       wherein R 1  is H, OH, peptide, a sugar, a targeting molecule, lower alkyl, substituted lower alkyl, or a protecting group that can be removed under the conditions of peptide synthesis;  
       R 2  is H, lower alkyl, or substituted lower alkyl; W is from 1-20 atoms long and is selected from the group consisting of cycloalkyl, aryl, or alkaryl groups, a substituted or unsubstituted alkylene chain, and a chain substituted with at least one heteroatom;  
       Z is an amino acid or a peptide containing 2-5 residues, or Z is COCH 2  or COCH(CH 2 SP 2 ), in which P 2  is H or a sulfur protecting group;  
       A and D are the same or different and each is selected from the group consisting of H, COCH 2 NR 3 NR 4 C(S)NHR 5 , COCH 2 NR 6 NR 7 C(S)NHR 8 , COCH 2 NR 9 NR 10 C(O)CH 2 SP 2 ,  CONR 11 NR 12 C(O)CH 2 SP 2 , NR 13 C(S)NHR 14 , or COCH 2 NR 15 COCH 2 SP 2 ;  
       R 3 , R 4 , R 6 , R 7 , R 9 , R 10 , R 11 , R 12 , R 13 , and R 15  are the same or different, and each represents H, lower alkyl, or substituted lower alkyl; and  
       R 5 , R 8 , and R 14  are the same or different and each is H, lower alkyl, substituted lower alkyl, aryl, or substituted aryl;  
       or X 5    is selected from the group consisting of:                      
       
         wherein said amino acid sequence contains at least one thiol or thiocarbonyl group.  
       
     
     
       2. A peptide according to  claim 1 , wherein X 5  is selected from the group consisting of:                  
                   
     
     
       3. A peptide according to claim  2   1 , wherein X 1  is pyro-glutamic acid, X 2  is histidine, and X 8  is glycine amide. 
     
     
       4. A peptide according to  claim 3 , wherein X 3  is tyrosine, X 4  is leucine, X 6  is tryptophan, and X 7  is lysine. 
     
     
       5. A peptide according to  claim 4 , wherein X 5  is                    
     
     
       6. A peptide according to claim  5   4 , wherein X 5  is                    
     
     
       7. A peptide according to  claim 4 , wherein X 5  is                    
     
     
       8. A peptide according to  claim 3 , wherein X 3  is tryptophan, X 4  is tyrosine, X 6  is leucine, and X 7  is arginine. 
     
     
       9. A peptide according to  claim 8 , wherein X 5  is                    
     
     
       10. A peptide according to  claim 8 , wherein X 5  is                    
     
     
       11. A peptide according to  claim 8 , wherein X 5  is                    
     
     
       12. A peptide according to  claim 2 , wherein X 1  is D-acetylnaphthylalanine, X 2  is D-4-chlorophenylalanine, X 3  is D-tryptophan, X 4  is arginine, X 6  is leucine, X 7  is arginine, and X 8 -NH 2  is D-alanine amide. 
     
     
       13. A peptide according to  claim 12 , wherein X 5  is                    
     
     
       14. A peptide according to claim  12   1 , wherein X 5  is                    
     
     
       15. A peptide according to claim  12   1 , wherein X 5  is                    
     
     
       16. A peptide according to  claim 12 , wherein X 5  is                    
     
     
       17. A peptide according to claim  2   1 , wherein X 1  is D-acetylnaphthylalanine, X 2  is D-4-chlorophenylalanine, X 3  is D-tryptophan, X 4  is arginine, X 6  is tryptophan, X 7  is lysine, and X 8 -NH 2  is glycine amide. 
     
     
       18. A method of preparing a metal-chelating composition, comprising contacting a solution of a peptide with stannous ions, wherein said peptide comprises the amino acid sequence X 1 -X 2 -X 3 -ser-X 4 -X 5 -X 6 -X 7 -pro-X 8 -NH 2 , 
       wherein X 1  is pyroglutamic acid or D-acetylnaphthylalanine,  
       X 2  is histidine or D-4-chlorophenylalanine,  
       X 3  is D- or L-tryptophan or tyrosine,  
       X 4  is tyrosine, leucine, or arginine,  
       X 6  is leucine or tryptophan,  
       X 7  is arginine or lysine,  
       X 8 -NH 2  is glycine amide or D-alanine amide,  
       X 5  is an amino acid derivative capable of stably chelating technetium-99m, rhenium-186, or rhenium-188, and has the structure:                    
       wherein R 1  is H, OH, a peptide, a sugar, a targeting molecule, lower alkyl, substituted lower alkyl, or a protecting group that can be removed under the conditions of peptide synthesis;  
       R 2  is H, lower alkyl, or substituted lower alkyl; W is from 1-20 atoms long and is selected from the group consisting of cycloalkyl, aryl, or alkaryl groups, a substituted or unsubstituted alkylene chain, and a chain substituted with at least one heteroatom;  
       Z is an amino acid or a peptide containing 2-5 residues, or Z is COCH 2  or COCH(CH 2 SP 2 ), in which P 2  is H or a sulfur protecting group;  
       A and D are the same or different, and each is selected from the group consisting of H, COCH 2 NR 3 NR 4 C(S)NHR 5 , COCH 2 NR 6 NR 7 C(S)NHR 8 , COCH 2 NR 9 NR 10 C(O)CH 2 SP 2 , CONR 11 NR 12 C(O)CH 2 SP 2 , NR 13 C(S)NHR 14 , or COCH 2 NR 15 COCH 2 SP 2 ;  
       R 3 , R 4 , R 6 , R 7 , R 9 , R 10 , R 11 , R 12 , R 13 , and R 15  are the same or different, and each represents H, lower alkyl, or substituted lower alkyl; and  
       R 5 , R 8 , and R 14  are the same or different and each is H, lower alkyl, substituted lower alkyl, aryl, or substituted aryl,  
       or X 5    is selected from the group consisting of:                      
       
         wherein said amino acid sequence contains at least one thiol or thiocarbonyl group; 
       
       and then contacting said solution with  99m pertechnetate,  186 perrhenate or  188 perrhenate and recovering the radiolabeled peptide.  
     
     
       19. The method of  claim 18 , wherein said peptide specifically binds cells or tissues that express LHRH receptors. 
     
     
       20. The method of  claim 18 , wherein said radionuclide is selected from  188 Re- or  186 Re-perrhenate and  99 Tc-pertechnetate. 
     
     
       21. A method of imaging a tumor, an infectious lesion, a myocardial infarction, a clot, artherosclerotic plaque, or a normal organ or tissue, comprising administering to a human patient a radiolabeled peptide that specifically binds to cells or tissues that express LHRH receptors, together with a pharmaceutically acceptable carrier, and, after a sufficient time for said radiolabeled peptide to localize and for non-target background to clear, the site or sites of accretion of said radiolabeled peptide detecting by an external imaging camera, 
       wherein said radiolabeled peptide is prepared by contacting a solution of a peptide with stannous ions, wherein said peptide comprises the amino acid sequence X 1 -X 2 -X 3 -ser-X 4 -X 5 -X 6 -X 7 -pro-X 8 -NH 2 ,  
       wherein X 1  is pyroglutamic acid or D-acetylnaphthylalanine,  
       X 2  is histidine or D-4-chlorophenylalanine,  
       X 3  is D- or L-tryptophan or tyrosine,  
       X 4  is tyrosine, leucine, or arginine,  
       X 6  is leucine or tryptophan,  
       X 7  is arginine or lysine, and  
       X 8 -NH 2  is glycine amide or D-alanine amide,  
       X 5  is an amino acid derivative capable of stably chelating technetium-99m, rhenium-186, or rhenium-188, and has the structure:                    
       wherein R 1  is H, OH, a peptide, a sugar, a targeting molecule, lower alkyl, substituted lower alkyl, or a protecting group that can be removed under the conditions of peptide synthesis; R 2  is H, lower alkyl, or substituted lower alkyl; W is from 1-20 atoms long and is selected from the group consisting of cycloalkyl, aryl, or alkaryl groups, a substituted or unsubstituted alkylene chain, and a chain substituted with at least one heteroatom;  
       Z is an amino acid or a peptide containing 2-5 residues, or Z is COCH 2  or COCH(CH 2 SP 2 ), in which P 2  is H or a sulfur protecting group;  
       A and D are the same or different, and each is selected from the group consisting of H, COCH 2 NR 3 NR 4 C(S)NHR 5 , COCH 2 NR 6 NR 7 C(S)NHR 8 , COCH 2 NR 9 NR 10 C(O)CH 2 SP 2 , CONR 11 NR 12 C(O)CH 2 SP 2 , NR 13 C(S)NHR 14 , or COCH 2 NR 15 COCH 2 SP 2 ,  
       R 3 , R 4 , R 6 , R 7 , R 9 , R 10 , R 11 , R 12 , R 13 , and R 15  are the same or different, and each represents H, lower alkyl, or substituted lower alkyl; and  
       R 5 , R 8 , and R 14  are the same or different and each is H, lower alkyl, substituted lower alkyl, aryl, or substituted aryl,  
       or X 5    is selected from the group consisting of:                      
       
         wherein said amino acid sequence contains at least one thiol or thiocarbonyl group; 
       
       and then contacting said solution with  99m pertechnetate,  186 perrhenate or  188 perrhenate and recovering the radiolabeled peptide.  
     
     
       22. A method of preparing peptides according to  claim 1 , comprising the  coupling of  amino acids and amino acid analogues by solid phase peptide synthesis.