In vitro and in vivo analysis of [⁶⁴Cu-NO2A-8-Aoc-BBN(7–14)NH₂]: a site-directed radiopharmaceutical for positron-emission tomography imaging of T-47D human breast cancer tumors☆

Abstract 

Introduction

Human breast cancer, from which the T-47D cell line was derived, is known to overexpress the gastrin-releasing peptide receptor (GRPR) in some cases. Bombesin (BBN), an agonist for the GRPR, has been appended with a radionuclide capable of positron-emission tomography (PET) imaging and therapy. ⁶⁴Cu-NO2A-8-Aoc-BBN(7–14)NH₂ (NO2A=1,4,7-triazacyclononane-1,4-diacetate) has produced high-quality microPET images of GRPR-positive breast cancer xenografted tumors in mice.

Methods

The imaging probe was synthesized by solid-phase peptide synthesis followed by manual conjugation of the 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) bifunctional chelator and radiolabeling in aqueous solution. The radiolabeled conjugate was subjected to in vitro and in vivo studies to determine its specificity for the GRPR and its pharmacokinetic profile. A T-47D tumor-bearing mouse was imaged with microPET/CT and microMRI imaging.

Results

The ⁶⁴Cu-NO2A-8-Aoc-BBN(7–14)NH₂ targeting vector was determined to specifically localize in GRPR-positive tissue. Accumulation was observed in the tumor in sufficient quantities to allow for identification of tumors in microPET imaging procedures. For example, uptake and retention in T-47D xenografts at 1, 4 and 24 h were determined to be 2.27±0.08, 1.35±0.14 and 0.28±0.07 % ID/g, respectively.

Conclusions

The ⁶⁴Cu-NO2A-8-Aoc-BBN(7–14)NH₂ produced high-quality microPET images. The pharmacokinetic profile justifies investigation of this bioconjugate as a potentially useful diagnostic/therapeutic agent. Additionally, the bioconjugate would serve as a good starting point for modification and optimization of similar agents to maximize tumor uptake and minimize nontarget accumulation.

Keywords: T-47D, Copper-64, Bombesin, Gastrin-releasing peptide, Site-directed radiopharmaceutical, NOTA