In Vivo Fluorescence Lifetime Imaging Monitors Binding of Specific Probes to Cancer Biomarkers

Yasaman Ardeshirpour,Gary Griffiths,Jacek Capala,Samuel Achilefu,Ilya Lyakhov,Rafal Zielinski,Olga Vasalatiy,Moinuddin Hassan,Aleksandr V Smirnov,Jay R Knutson,Amir Gandjbakhche,Victor Chernomordik,Irina V Lebedeva

doi:10.1371/journal.pone.0031881

Abstract

One of the most important factors in choosing a treatment strategy for cancer is characterization of biomarkers in cancer cells. Particularly, recent advances in Monoclonal Antibodies (MAB) as primary-specific drugs targeting tumor receptors show that their efficacy depends strongly on characterization of tumor biomarkers. Assessment of their status in individual patients would facilitate selection of an optimal treatment strategy, and the continuous monitoring of those biomarkers and their binding process to the therapy would provide a means for early evaluation of the efficacy of therapeutic intervention. In this study we have demonstrated for the first time in live animals that the fluorescence lifetime can be used to detect the binding of targeted optical probes to the extracellular receptors on tumor cells in vivo. The rationale was that fluorescence lifetime of a specific probe is sensitive to local environment and/or affinity to other molecules. We attached Near-InfraRed (NIR) fluorescent probes to Human Epidermal Growth Factor 2 (HER2/neu)-specific Affibody molecules and used our time-resolved optical system to compare the fluorescence lifetime of the optical probes that were bound and unbound to tumor cells in live mice. Our results show that the fluorescence lifetime changes in our model system delineate HER2 receptor bound from the unbound probe in vivo. Thus, this method is useful as a specific marker of the receptor binding process, which can open a new paradigm in the “image and treat” concept, especially for early evaluation of the efficacy of the therapy.

Highlights

One of the most important factors in choosing a proper treatment strategy for cancer is characterization of biomarkers in cancer cells, and this can be rather challenging
One of the important factors that is frequently missing in cancer treatment is continuous monitoring the response of the tumor receptors to the therapy, especially at the early stages, to quantify the binding process, which is critical for evaluation of drug efficacy
In vivo Study To investigate the effect of binding the HER2-specific Affibody fluorescent probe to the HER2 receptor-positive tumor on fluorescence lifetime, three different cases were considered

Summary

Introduction

One of the most important factors in choosing a proper treatment strategy for cancer is characterization of biomarkers in cancer cells, and this can be rather challenging. Recent advances in Monoclonal AntiBodies (MAB) as primaryspecific drugs, targeting tumor receptors, show that their efficacy depends strongly on overexpression of specific receptors. One of the important factors that is frequently missing in cancer treatment (mainly using MAB) is continuous monitoring the response of the tumor receptors to the therapy, especially at the early stages, to quantify the binding process, which is critical for evaluation of drug efficacy. In vivo fluorescence imaging is an alternative noninvasive imaging technique, which can be used separately or in adjunction with other modalities for timely monitoring of the biomarker during the course of treatment.

Methods

Results

Discussion

Conclusion