Preclinical Evaluation of the Breast Cancer Cell-Binding Peptide, p160

Abstract

Purpose: Selective delivery of drugs into the target tissue is expected to result in high drug concentrations in the tissue of interest and therefore enhanced drug efficacy. To develop a peptidebased radiopharmaceutical, we investigated the properties of a peptide with affinity for human breast cancer, which has been selected through phage display. Experimental Design: The bioactivity of the p160 peptide (VPWMEPAYQRFL) was evaluated in vitro and in vivo. The specific binding to human breast cancer MDA-MB-435 cells was confirmed in competition experiments. Internalization of the peptide was investigated with confocal microscopy. Furthermore, the biodistribution of 131 I-labeled p160 was studied in tumor-bearing mice. In vivo stability was evaluated at different periods after tracer administration using highperformance liquid chromatography analysis. Results: The binding of 125 I-labeled p160 was inhibited up to 95% by the unlabeled peptide with an IC 50 value of 0.6 Amol/L. In addition, 40% of the total bound activity was found to be internalized into the human breast cancer cells. Although a rapid degradation was seen, biodistribution studies in nude mice showed a higher uptake in tumor than in most of the organs. Perfusion of the animals caused a reduction of the radioligand accumulation in the healthy tissues, whereas the tumor uptake remained constant. A comparison of [

Evaluation of an 111In-Radiolabeled Peptide as a Targeting and Imaging Agent for ErbB-2 Receptor–Expressing Breast Carcinomas

“…The observed instability of the radiolabeled peptide(s) in serum after 1 h is not uncommon or surprising because the chemically synthesized linear peptide contains only natural amino acids, which are susceptible to proteolysis (31). Peptides on filamentous phage are presented as fusion proteins to stable coat proteins and are therefore protected against proteolysis (33). The 111 In-DOTA(GSG)-KCCYSL peptide bound well to the ErbB-2 -positive MDA-MB-435 breast carcinoma cells whereas binding to nonreceptor expressing cells was negligible.…”

111In-Labeled Galectin-3–Targeting Peptide as a SPECT Agent for Imaging Breast Tumors

“…Because the chemically synthesized peptide contained only natural amino acids, some degree of proteolysis might be expected. However, the original peptide sequence was selected on filamentous bacteriophage as a fusion to a stable coat protein and therefore was likely protected against proteolysis (17,27 ).…”

Identification of Ligands and Translation to Clinical Applications

“…This approach has been used in various applications, such as in the mapping and mimicking of epitopes, the identification of new receptors and natural ligands, high-affinity antibodies and analogs, the isolation of specific antigens binding to bioactive compounds, the production of novel enzyme inhibitors and DNA-binding proteins, and the probing of cellular and tissue-specific processes. Phage display has been successfully applied for the identification of peptides with a high specificity for target tumor neovasculature or a variety of human tumor cells (16,(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33).…”

“…This degradation inevitably leads to a stability problem, with a plasma half-life in the range of several minutes (26)(27)(28)(29)(30). Stability may be increased by shortening the peptide after identification of the essential binding sequence using an alanine scan, exchange of single amino acids, introduction of D-amino acids, peptide cyclization, and coupling to chelators such as DOTA.…”