posted on 2021-12-20, 18:05authored bySyed Muhammad Usama, Sierra C. Marker, Donald R. Caldwell, Nimit L. Patel, Yang Feng, Joseph D. Kalen, Brad St. Croix, Martin J. Schnermann
Antibody–drug conjugates (ADCs)
are a rapidly emerging therapeutic
platform. The chemical linker between the antibody and the drug payload
plays an essential role in the efficacy and tolerability of these
agents. New methods that quantitatively assess the cleavage efficiency
in complex tissue settings could provide valuable insights into the
ADC design process. Here we report the development of a near-infrared
(NIR) optical imaging approach that measures the site and extent of
linker cleavage in mouse models. This approach is enabled by a superior
variant of our recently devised cyanine carbamate (CyBam) platform.
We identify a novel tertiary amine-containing norcyanine, the product
of CyBam cleavage, that exhibits a dramatically increased cellular
signal due to an improved cellular permeability and lysosomal accumulation.
The resulting cyanine lysosome-targeting carbamates (CyLBams) are
∼50× brighter in cells, and we find this strategy is essential
for high-contrast in vivo targeted imaging. Finally,
we compare a panel of several common ADC linkers across two antibodies
and tumor models. These studies indicate that cathepsin-cleavable
linkers provide dramatically higher tumor activation relative to hindered
or nonhindered disulfides, an observation that is only apparent with in vivo imaging. This strategy enables quantitative comparisons
of cleavable linker chemistries in complex tissue settings with implications
across the drug delivery landscape.