Quantitative imaging of receptor-ligand engagement in intact live animals

Area of Science:

• Biomedical Imaging
• Preclinical Drug Development
• Molecular Imaging

Background:

• Accurate quantitation of receptor-ligand engagement is crucial for targeted drug development.
• In vivo, non-invasive measurement of this engagement in preclinical models remains a significant challenge.
• Existing ex vivo methods for receptor assessment may not reflect in vivo drug delivery dynamics.

Purpose of the Study:

• To establish a non-invasive, whole-body imaging method for quantifying intracellular receptor-ligand binding in vivo.
• To assess the utility of macroscopic lifetime-based Förster Resonance Energy Transfer (MFLI-FRET) imaging for preclinical drug development.
• To evaluate MFLI-FRET as a tool for guiding targeted drug therapy in heterogeneous tumors.

Main Methods:

• Utilized whole-body macroscopic lifetime-based Förster Resonance Energy Transfer (MFLI-FRET) imaging.
• Performed longitudinal imaging in intact, live animals bearing tumor xenografts.
• Measured FRET levels and correlated them with intracellular ligand binding and ex vivo receptor expression.

Main Results:

• MFLI-FRET successfully quantified intracellular receptor-ligand binding in vivo.
• FRET levels inversely correlated with raw fluorescence intensity, specifically reporting on transferrin receptor binding.
• Tumor FRET levels correlated with intracellular ligand binding but not with traditional ex vivo receptor expression assessments.

Conclusions:

• MFLI-FRET enables direct, non-invasive measurement of systemic delivery, target availability, and intracellular drug delivery in preclinical studies.
• This technique is well-suited for guiding targeted drug therapy development in heterogeneous tumors within live small animals.
• MFLI-FRET offers a valuable tool for advancing precision medicine through improved preclinical drug evaluation.