Evaluation of an 111In-radiolabeled peptide as a targeting and imaging agent for ErbB-2 receptor expressing breast carcinomas.

Abstract

PURPOSE:

The cellular targeting and tumor imaging properties of a novel ErbB-2-avid peptide, discovered from bacteriophage display, were evaluated in human breast carcinoma cells and in breast carcinoma-xenografted mice.

EXPERIMENTAL DESIGN:

The affinity of the ErbB-2 targeting peptide KCCYSL and its alanine substituted counterparts for the extracellular domain (ECD) of purified recombinant ErbB-2 (ErbB-2-ECD) was assessed by fluorescence titration. Binding of the KCCYSL peptide to breast and prostate carcinoma cells was analyzed by confocal microscopy. A DOTA(GSG)-KCCYSL peptide conjugate was radiolabeled with 111In, and stability, target binding, and internalization were analyzed in vitro. In vivo biodistribution and single-photon emission computed tomography imaging studies were done with the radiolabeled peptide in MDA-MB-435 human breast tumor-bearing severe combined immunodeficient mice.

RESULTS:

KCCYSL peptide exhibited high affinity (295 +/- 56 nmol/L) to ErbB-2-ECD. Substitution of alanine for lysine, tryptophan, and cysteine reduced the peptide affinity approximately 1- to 2.4-fold, whereas replacing leucine completely abolished binding. Both biotin-KCCYSL and 111In-DOTA(GSG)-KCCYSL were capable of binding ErbB-2-expressing human breast carcinoma cells in vitro. Approximately 11% of the total bound radioactivity was internalized in the carcinoma cells. Competitive binding studies indicated that the radiolabeled peptide exhibited an IC(50) value of 42.5 +/- 2.76 nmol/L for the breast carcinoma cells. 111In-DOTA(GSG)-KCCYSL was stable in serum and exhibited rapid tumor uptake (2.12 +/- 0.32 %ID/g) at 15 min postinjection and extended retention coupled with rapid whole body disappearance, as observed by biodistribution and single-photon emission computed tomography imaging studies, respectively.

CONCLUSIONS:

The DOTA(GSG)-KCCYSL peptide has the potential to be used as a tumor-imaging agent and a vehicle for specific delivery of radionuclide or cytotoxic agents for tumors overexpressing ErbB-2.

• Authors: Senthil R Kumar, Thomas P Quinn, Susan L Deutscher
• Journal: Clinical cancer research : an official journal of the American Association for Cancer Research (Clin Cancer Res) Vol. 13 Issue 20 Pg. 6070-9 (Oct 15 2007) ISSN: 1078-0432 [Print] United States
• PMID: 17947470 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Contrast Media
• Indium Radioisotopes
• Peptides
• Recombinant Proteins
• Receptor, ErbB-2

Topics

• Animals
• Breast Neoplasms (diagnostic imaging, metabolism)
• Cell Line, Tumor
• Contrast Media (pharmacology)
• Diagnostic Imaging (methods)
• Gene Expression Regulation, Neoplastic
• Humans
• Indium Radioisotopes (pharmacology)
• Inhibitory Concentration 50
• Mice
• Mice, SCID
• Microscopy, Confocal
• Peptides (chemistry)
• Receptor, ErbB-2 (metabolism)
• Recombinant Proteins (chemistry)
• Tomography, Emission-Computed, Single-Photon (methods)
• Tomography, X-Ray Computed (methods)