Small Peptides Specifically Bind to Colorectal Cancers

Abstract

Cancers are extremely heterogeneous in terms of the frequency and types of mutations present in different malignant tumors. Thus, it is likely that uniform clinical treatment is not optimal for all patients, and that the development of individualized therapeutic regimens may be beneficial. Multiple, unique small peptides bind to cell lines derived from different colon adenocarcinomas. Within two hours of contact, the colorectal cancer cells are able to transfer a 32 P radioisotope from the small peptides to cellular proteins; the transfer occurs at a substantially higher rate than in the colorectal cancer cells than in cell lines derived from other cancers or from normal tissues.

1 . A method of delivering a radioactive isotope to a colon adenocarcinoma cell, comprising:
 administering to a colon adenocarcinoma cell a radioactive isotope-labeled peptide, wherein the peptide is a substrate for protein kinase A (PKA) comprising the motif R-X-S/T or R-R/K-X-S/T, whereby the peptide binds to the cell and the radioactive isotope is internalized and transferred to cellular proteins.   
     
     
         2 . The method of  claim 1  wherein the peptide comprises a sequence R-R-X-S. 
     
     
         3 . The method of  claim 1  wherein the peptide comprises a sequence R-R-A/G-S. 
     
     
         4 . The method of  claim 1  wherein the peptide comprises a sequence S-R-R-X-S. 
     
     
         5 . The method of  claim 1  wherein the peptide comprises a sequence R-R-X-S-G/A. 
     
     
         6 . The method of  claim 1  wherein the peptide comprises a sequence G-S-R-R-X-S. 
     
     
         7 . The method of  claim 1  wherein the peptide comprises a sequence R-R-X-S-V. 
     
     
         8 . The method of  claim 1  wherein the peptide comprises a sequence R-R-X-S-V-G/A. 
     
     
         9 . The method of  claim 1  wherein the peptide comprises a sequence R-R-X-S selected from the group consisting of SEQ ID NO: 1-28. 
     
     
         10 . The method of  claim 1  wherein the peptide comprises from 4-50 amino acid residues. 
     
     
         11 . The method of  claim 1  wherein the peptide comprises from 4-35 amino acid residues. 
     
     
         12 . The method of  claim 1  wherein the peptide comprises from 4-30 amino acid residues. 
     
     
         13 . The method of  claim 1  wherein the peptide comprises from 9-15 amino acid residues. 
     
     
         14 . The method of  claim 1  wherein the peptide comprises a sequence R-R-X-S and has at least 90% amino acid residue identity with a sequence selected from the group consisting of SEQ ID NO: 1-28. 
     
     
         15 . The method of  claim 1  wherein the radioactive isotope is  32 P or  33 P. 
     
     
         16 . The method of  claim 1  wherein the radioactive isotope is  125 I or  131 I. 
     
     
         17 . The method of  claim 1  wherein the adenocarcinoma cell is in a patient with a colon tumor or metastasis. 
     
     
         18 . The method of  claim 17  further comprising the step of:
 determining location of the radioactive isotope in the patient by an imaging technique. 
 
     
     
         19 . The method of  claim 17  further comprising the step of:
 monitoring size of the tumor. 
 
     
     
         20 . The method of  claim 1  wherein the adenocarcinoma cell is in a xenograft in an animal. 
     
     
         21 . The method of  claim 1  wherein the adenocarcinoma cell is in culture. 
     
     
         22 . A method to screen a protein kinase A (PKA) substrate peptide for its ability to deliver radioactive isotope to a colon adenocarcinoma cell, comprising:
 (a) contacting a radioactive isotope-labeled peptide with the colon adenocarcinoma cell of a patient; and   (b) measuring binding of the peptide to the colon adenocarcinoma cell; and/or   (c) measuring transfer of the radioactive isotope from the peptide to proteins of the adenocarcinoma cell of the patient.   
     
     
         23 . A peptide which has at least 90% homology to a sequence selected from the group consisting of SEQ ID NO: 1-28, said peptide able to bind to the surface of a colon adenocarcinoma cell at least 50-fold more than to a normal colon cell. 
     
     
         24 . The peptide of  claim 23  wherein the peptide comprises from 4-50 amino acid residues. 
     
     
         25 . The peptide of  claim 23  wherein the peptide comprises from 4-34 amino acid residues. 
     
     
         26 . The peptide of  claim 23  wherein the peptide comprises from 4-25 amino acid residues. 
     
     
         27 . The peptide of  claim 23  wherein the peptide comprises from 9-15 amino acid residues. 
     
     
         28 . The peptide of  claim 23  wherein the peptide comprises a sequence R-R-X-S. 
     
     
         29 . The peptide of  claim 23  wherein the peptide comprises a sequence R-X-S/T. 
     
     
         30 . The peptide of  claim 23  wherein the peptide comprises a sequence R-R/K-X/S/T. 
     
     
         31 . The peptide of  claim 23  which is radiolabeled with a radioisotope. 
     
     
         32 . The peptide of  claim 23  which is phosphorylated. 
     
     
         33 . The peptide of  claim 23  which is isolated and purified. 
     
     
         34 . The peptide of  claim 31  wherein the radioisotope is  32 P or  33 P. 
     
     
         35 . The peptide of  claim 31  wherein the radioisotope is  125 I or  131 I. 
     
     
         36 . The peptide of  claim 23  which comprises a sequence selected from the group consisting of SEQ ID NO: 1-28. 
     
     
         37 . The peptide of  claim 23  wherein the amino acid backbone of the peptide consists of a sequence selected from the group consisting of SEQ ID NO: 1-28.