Development of pH Activatable SWIR Imaging Probes for Ratiometric pH Imaging and In Vivo Analysis of Antibody-Drug Conjugate Linkers

Authors

• P Shrestha
• MJ Schnermann

Abstract

Altered pH homeostasis is a hallmark of cancer. The ability to visualize changes in pH in complex organisms could enable new fluorescence-guided surgical strategies that will allow precise tumor margin delineation, facilitating thorough resection while sparing healthy tissue. Such approaches might also help track the fate and activation of targeted-drug delivery strategies, such as antibody drug conjugates. To realize this goal, we hypothesize that responsive, protein-targeted probes in the short-wave infrared (SWIR) region (1000 nm to 1400 nm) would be enabling technology. SWIR imaging enables improved resolution and tissue penetration, though existing probes are unsuitable for our goals. We designed Benz-NorCy7-pH, a cyanine with absorption maxima at 980 nm and an emission maxima of 1000 nm, which shows remarkable pH sensitivity. When conjugated with Panitumumab (an anti-EGFR antibody), Benz-NorCy7-pH revealed an excellent tumor-to-background ratio of approximately 23-fold. SWIR imaging also allows for the multiplexing abilities where two different dyes can be associated with two distinct biochemical processes. A mixture of two mAb probe dyes: FNIR-766 (785 nm excitation) representing antibody internalization and Benz-NorCy7-pH (890 nm excitation) as lysosomal degradation can be used to calculate their respective half-life. In addition, Benz-NorCy7-pH can compare activity of protease cleavable linker like Val-Cit with non-cleavable linkers. Conjugation of Benz-NorCy7-pH with albumin lead to rapid tumor accumulation, but also rapid clearance, providing insight in the biological fate of this common drug delivery vehicle. Overall, these novel probes provide a new strategy to visualize the fate and local molecular environment of biomolecules.

Scientific Focus Area: Chemical Biology

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