A paired-agent fluorescent molecular imaging strategy for quantifying antibody drug target engagement in in vivo window chamber xenograft models

Area of Science:

• Molecular imaging
• Pharmacodynamics
• Biomedical engineering

Background:

• Accurate measurement of drug target engagement is crucial for effective antibody therapy.
• Whole tumor imaging requires robust methods to assess drug distribution and binding dynamics.
• Existing imaging strategies may not fully capture the complexities of drug-target interactions in vivo.

Purpose of the Study:

• To develop and validate a paired-agent fluorescent molecular imaging strategy for quantifying drug target engagement in whole tumors.
• To assess the accuracy of the imaging method across diverse tumor physiologies and antibody characteristics.
• To demonstrate the in vivo detection of binding site barriers using this novel imaging approach.

Main Methods:

• A paired-agent imaging protocol using targeted and control fluorescent agents was designed.
• Dynamic imaging was performed before and after antibody therapy administration.
• Computational simulations were used to estimate drug target engagement error margins.
• Experimental validation was conducted to assess in vivo performance.

Main Results:

• Simulations predicted drug target engagement estimation within a 15% error margin under various conditions.
• The method demonstrated robustness across a range of tumor blood flow, vascular permeability, and target densities.
• Antibody affinity and binding rates were shown to be well-tolerated by the imaging strategy.
• The first in vivo detection of a binding site barrier was achieved.

Conclusions:

• The paired-agent fluorescent molecular imaging strategy provides a reliable method for measuring drug target engagement in whole tumors.
• This technique offers significant potential for advancing drug distribution and binding imaging.
• The ability to detect binding site barriers opens new avenues for understanding drug pharmacodynamics.